Next Article in Journal
Energy Balance and Risk of Mortality in Spanish Older Adults
Next Article in Special Issue
Leptin Improves Parameters of Brown Adipose Tissue Thermogenesis in Lipodystrophic Mice
Previous Article in Journal
Fermented Deer Blood Ameliorates Intense Exercise-Induced Fatigue via Modulating Small Intestine Microbiota and Metabolites in Mice
Previous Article in Special Issue
Fractalkine, sICAM-1 and Kynurenine Pathway in Restrictive Anorexia Nervosa–Exploratory Study
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Nutrients
Volume 13
Issue 5
10.3390/nu13051544
nutrients-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Communication

Leptin Receptors Are Not Required for Roux-en-Y Gastric Bypass Surgery to Normalize Energy and Glucose Homeostasis in Rats

by
Mohammed K. Hankir
1,*,
Laura Rotzinger
1,
Arno Nordbeck
1,
Caroline Corteville
1,
Ulrich Dischinger
2,
Juna-Lisa Knop
1,
Annett Hoffmann
1,
Christoph Otto
1 and
Florian Seyfried
1,*
1
Department of General, Visceral, Vascular and Pediatric Surgery, University Hospital Wuerzburg, 97080 Wuerzburg, Germany
2
Department of Endocrinology, University Hospital Wuerzburg, 97080 Wuerzburg, Germany
*
Authors to whom correspondence should be addressed.
Nutrients 2021, 13(5), 1544; https://0-doi-org.brum.beds.ac.uk/10.3390/nu13051544
Submission received: 17 April 2021 / Revised: 27 April 2021 / Accepted: 28 April 2021 / Published: 4 May 2021
(This article belongs to the Special Issue Periphery-Brain Interactions and Leptin in the Regulation of Whole-Body Energy Metabolism)
Browse Figures
Versions Notes

Abstract

:
Sensitization to the adipokine leptin is a promising therapeutic strategy against obesity and its comorbidities and has been proposed to contribute to the lasting metabolic benefits of Roux-en-Y gastric bypass (RYGB) surgery. We formally tested this idea using Zucker fatty fa/fa rats as an established genetic model of obesity, glucose intolerance, and fatty liver due to leptin receptor deficiency. We show that the changes in body weight in these rats following RYGB largely overlaps with that of diet-induced obese Wistar rats with intact leptin receptors. Further, food intake and oral glucose tolerance were normalized in RYGB-treated Zucker fatty fa/fa rats to the levels of lean Zucker fatty fa/+ controls, in association with increased glucagon-like peptide 1 (GLP-1) and insulin release. In contrast, while fatty liver was also normalized in RYGB-treated Zucker fatty fa/fa rats, their circulating levels of the liver enzyme alanine aminotransferase (ALT) remained elevated at the level of obese Zucker fatty fa/fa controls. These findings suggest that the leptin system is not required for the normalization of energy and glucose homeostasis associated with RYGB, but that its potential contribution to the improvements in liver health postoperatively merits further investigation.

Graphical Abstract

1. Introduction

Bariatric surgery is currently the most effective treatment option against morbid obesity, with numerous prospective clinical studies showing that Roux-en-Y gastric bypass (RYGB) is associated with marked and sustained weight loss as well as long-term remission of type 2 diabetes and fatty liver disease [1,2,3,4,5]. Because RYGB reduces stomach size and excludes the duodenum from contact with ingested food, physical restriction and malabsorption of nutrients, respectively, were originally thought to mainly account for its beneficial effects on energy and glucose homeostasis [6]. With the aid of rodent models of RYGB, however, it is becoming increasingly evident that complex changes in various molecular, cellular, and systems processes take place postoperatively [7,8,9,10], better understanding of which may guide the development of more effective, noninvasive treatments against metabolic disease.
Leptin is a 16-kDa endocrine protein mainly released from white adipocytes and circulates in proportion to fat mass, thereby serving as a negative feedback signal to the brain about long-term energy stores [11,12]. Beyond its centrally-mediated effects on suppressing appetite and increasing energy expenditure [11,12], leptin also lowers blood glucose [13] and limits hepatic lipid accumulation [14,15]. Accordingly, leptin-deficient ob/ob mice have severe hyperphagic obesity, hyperglycemia, and fatty liver [16,17]. On the other hand, diet-induced obesity is thought to arise from the development of central leptin resistance as a result of persistently elevated circulating leptin levels [18,19] as well as from complex pro-inflammatory processes that directly interfere with hypothalamic leptin receptor signaling [20,21,22,23]. For these reasons, leptin supplementation to ob/ob mice normalizes their metabolic status [24,25,26,27], whereas leptin sensitizers such as neutralizing leptin antibodies [19], hypothalamic ER stress relievers [28,29,30], and other molecules [31,32] have taken center stage in obesity drug development.
Because RYGB mainly reduces fat mass [33], it is associated with a marked reduction in circulating leptin levels [34,35,36]—even beyond chronic caloric restriction-induced weight loss alone [37,38,39,40,41,42]. Nevertheless, endogenous leptin action has been proposed to be enhanced postoperatively [43,44,45,46,47,48], thereby preventing the powerful counter-regulatory response to depletion of energy stores which normally leads to weight-regain [11,12]. Indeed, the disproportionately reduced circulating leptin levels associated with RYGB may in itself enhance endogenous leptin action by reversing central leptin resistance [46]. Further, the appetite suppressing effects of exogenous leptin are increased in RYGB-treated, diet-induced obese Wistar rats associated with an attenuation of hypothalamic inflammation and ER stress [45]. Studies using ob/ob mice directly aimed at assessing the requirement of the leptin system for the beneficial outcomes of RYGB on energy and glucose homeostasis, however, have yielded conflicting results [43,44]. Specifically, the sustained weight loss and food intake suppression following RYGB was found to be preserved in one study [44], but not in another [43], although in both studies RYGB failed to fully improve glycemic control [43,44]. In contrast, weight loss and enhanced insulin sensitivity [49] as well as improved fasting blood glucose levels and oral glucose tolerance [50] in leptin-unresponsive db/db mice [51], which lack the intracellular signaling domain unique to leptin b receptors due to an autosomal recessive point mutation in the leptin receptor gene [52], appear to be largely preserved following RYGB.
Zucker fatty fa/fa rats are another genetic model of leptin receptor deficiency since they harbor an autosomal recessive point mutation in the leptin receptor gene—distinct from the db/db point mutation—which causes an inhibitory amino acid substitution in the extracellular domain common to all leptin receptor subtypes (a–f) [53,54,55]. As a result, Zucker fatty fa/fa rats are obese and hyperlipidemic [56,57] and exhibit markedly impaired oral glucose tolerance [57,58] as well as fatty liver [57,59]. Numerous studies have been performed aimed at assessing the metabolic effects of RYGB on Zucker fatty fa/fa rats [60,61,62,63,64] and on the inbred [65] Zucker diabetic fatty fa/fa rat strain [38,62,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81], but their descriptions on food intake are generally either incomplete [60,61,62,63,64,66,67,68,71,78,79,81] or, in many studies, entirely missing [38,69,70,72,73,74,75,76,77,80]. Additionally, only a few of these studies incorporated a lean control group in the form of heterozygous Zucker fatty fa/+ rats [60,62,63,76], which is essential if any conclusions are to be drawn about whether RYGB normalizes metabolic status. Surprisingly, all of these studies overlooked the role of leptin receptors in the lasting metabolic benefits associated with RYGB. We therefore directly asked if leptin receptors are required for RYGB to normalize energy and glucose homeostasis as well as fatty liver by using Zucker fatty fa/fa rats.

2. Materials and Methods

2.1. Animals

Twenty-eight male Zucker fatty fa/fa and 12 Zucker fatty fa/+ rats were purchased from Charles River, France, aged 6 weeks. Data from part of these rats (16 Zucker fatty fa/fa and 5 Zucker fatty fa/+ rats) were previously reported [62] and were incorporated into the present study to increase statistical power. All rats were individually housed under ambient humidity and a temperature of 22 °C in a 12 h light/dark cycle with free access to tap water and Purina 5008 Lab diet (Purina Mills, St. Louis, MO, USA, 16.7% of calories from fat), unless otherwise stated. An additional group of 11 previously phenotyped male Wistar that received RYGB at 11 weeks of age [82] were also incorporated into the present study (Figure 1). These rats were placed under identical housing and surgical conditions as Zucker fatty rats, but were given an Altromin C1090-60 high-fat diet (Altromin, Lage, Germany, 60% calories from fat) for 5-weeks preoperatively to induce obesity (478.8 ± 6.8 g) and a choice between an Altromin C1090-60 high-fat diet and an Altromin C1090-10 low-fat diet (Altromin, Lage, Germany, 10% kcal from fat) postoperatively to assess changes in food preference [82]. All experiments were reviewed and approved by the Animal Care Committee of the local government of Unterfranken, Bavaria, Germany (License numbers 55.2-2531.01-72/12 and 55.2-2532-2-467).

2.2. Surgeries

At 12 weeks of age, when Zucker fatty fa/fa rats developed obesity (443.1 ± 3.6 g), they were randomly allocated to RYGB (n = 16) or sham (n = 12) surgeries (Figure 1). The remaining 12 Zucker fatty fa/+ rats were also scheduled for sham surgery (Figure 1). These group sizes are based on previous publications in which significant differences were observed [62,83]. All surgeries were performed under sterile conditions in 6 h fasted rats by an experienced bariatric surgeon after subcutaneous administration of 5 mg/kg carprofen as analgesia and intraperitoneal administration of 1.25 mg/kg amoxicillin as prophylactic antibiotic. Surgical anesthesia was induced with an isoflurane/oxygen mixture, and the abdomen was then opened using a midline laparotomy and closed following procedures using continuous suturing.
For the sham procedure, the gastro-esophageal junction and small intestine were first mobilized. A gastrostomy on the anterior wall of the stomach was next performed followed by a jejunostomy as previously described [62,83]. For the RYGB procedure, the jejunum was first transected 15 cm below the pylorus. The stomach was next transected 3 mm below the gastro-esophageal junction, and the stomach remnant was subsequently closed to create the ∼15 cm biliopancreatic limb. To create the ∼80 cm alimentary limb, the aboral jejunum was anastomosed in an end-to-side fashion to the small stomach pouch (which was ∼5% of the original gastric volume). Finally, a 7-mm side-to-side jejuno-jejunostomy between the biliopancreatic limb and the alimentary limb at the level of the lower jejunum was performed to create a∼25 cm common channel as previously described [62,83].

2.3. Perioperative Care

Upon recovery from surgeries, rats were placed on a liquid diet (vanilla-flavored Ensure, Abbott Laboratories, IL, USA, 22% calories from fat) for 6 days postoperatively and then returned to their previous solid diet (Figure 1). For analgesia, they were subcutaneously administered 5 mg/kg carprofen once daily for the first 2 postoperative days.

2.4. Metabolic Measurements

Food intake was measured daily from postoperative day 6, while body weight was measured daily throughout the 27-day monitoring period (Figure 1). An oral glucose tolerance test (OGTT) was performed at the beginning of the dark cycle on postoperative day 27 in Zucker fatty rats (Figure 1). For blood glucose measurements during the OGTT, a small tail vein incision was made in 8 h fasted rats, and a drop of blood was directly applied onto a glucometer (Breeze 2® glucometer, Bayer, Zurich, Switzerland) at baseline and 15, 30, 60 and 120 min after 10 mL/kg body weight ingestion of a 25% glucose solution. A further 100 µL of tail vein blood was collected at each time-point into tubes containing EDTA. Plasma was isolated by centrifugation at 8000 rpm for 10 min at 4 °C and stored at −20 °C. Homeostatic model of insulin resistance (HOMA-IR) was calculated by the dividing the product of fasting plasma insulin (in µU/L) and blood glucose (in nmol/L) levels by 22.5 [84]. Matsuda–DeFronzo insulin sensitivity index (ISI-M) was calculated based on the results of the OGTT as follows:
ISI-M = 10,000/(G0 × I0 × Gmean × Imean)1/2
where G and I represents blood glucose (in mmol/dL) and plasma insulin (in mU/L) levels, respectively, and ‘0’ and ‘mean’ indicates fasting value and mean value during the OGTT, respectively [85].

2.5. Tissue Harvesting

At the 28th postoperative day, overnight-fasted Zucker Fatty rats were euthanized by isoflurane overdose 45 min after a fixed meal of 3 g Purina 5008 diet. Cardiac blood was collected into tubes containing EDTA and plasma was isolated by centrifugation at 8000 rpm for 10 min at 4 °C and stored at −20 °C. Epididymal white adipose tissue (eWAT) and retroperitoneal white adipose tissue (rWAT) were dissected according to a standardized protocol, weighed and summed to provide a measure of visceral WAT (vWAT) [86].

2.6. ELISAs

Plasma insulin was measured using an Ultrasensitive Rat Insulin ELISA kit (Mercodia AB, Uppsala, Sweden, #10-1251-10), plasma GLP-1 using a Rat GLP-1 ELISA kit (EMD Millipore, MA, USA, #EZGLP1T-36 K), plasma leptin using a Rat Leptin ELISA kit (Abcam, Cambridge, UK, #ab100773), plasma alanine transaminase (ALT) using a Rat ALT Simplestep® ELISA kit (Abcam, Cambridge, UK #ab264579), and plasma aspartate transaminase (AST) using a Rat AST Simplestep® ELISA kit (Abcam, Cambridge, UK, #ab263883) according to the manufacturer’s instructions.

2.7. Bomb Calorimetry

Feces were collected from Zucker fatty rats on postoperative day 28, dried in an oven and weighed. Fecal energy content (kcal/g) was then measured using ballistic bomb calorimetry.

2.8. Liver Histology

Freshly harvested liver from Zucker fatty rats was fixed with 4% paraformaldehyde for 24 h at room temperature and then embedded in paraffin blocks, cut into 2 μm-thick sections and mounted on glass slides for hematoxylin and eosin (H&E) staining according to a standard protocol. Representative images from each group were taken on a Keyence BZ-1000 microscope at a magnification of 20×.

2.9. Statistics

Statistical analysis was performed using GraphPad PRISM Version 8®. Data are expressed as mean ± standard error of the mean (SEM). A one-way analysis of variance (ANOVA) with Sidak’s post hoc test or two-tailed, unpaired t-test was used to determine differences between groups.

3. Results

3.1. Leptin Receptors Are Not Required for RYGB to Normalize Energy Homeostasis

We first assessed body weight trajectories in lean, obese, and RYGB-treated Zucker fatty rats over the course of a 27-day monitoring period (Figure 1). Consistent with the leptin receptor-deficient state of Zucker fatty fa/fa rats, baseline body weights of RYGB-treated (443.7 ± 2.8 g) and obese (442.3 ± 6.7 g) rats were significantly higher than lean rats (348.8 ± 8.1 g; p < 0.0001 for both comparisons) (Figure 2a). From postoperative day 3 onwards, both obese and lean rats progressively gained body weight (Figure 2a). In contrast, RYGB-treated rats lost body weight until postoperative day 6, which then largely stabilized and eventually converged with lean rats by study close at postoperative day 27 (414.7 ± 12.5 g vs. 405.0 ± 10.7 g, respectively; p = 0.99) (Figure 2a).
To ascertain if the effect on body weight of our RYGB rat model is similar when leptin receptors are intact, we incorporated data previously obtained from RYGB-treated, diet-induced obese Wistar rats [82]. Because these rats weighed significantly more than RYGB-treated Zucker fatty fa/fa rats at baseline (p < 0.01), body weights for this comparison were expressed as percentage change (Figure 2b). This revealed similar percentage weight loss for both groups during postoperative days 0–6, but RYGB-treated Zucker fatty fa/fa rats then slightly regained body weight at postoperative day 9, whereas RYGB-treated Wistar rats did so later at postoperative day 18 (Figure 2b). As a result, percentage weight loss was significantly greater for RYGB-treated Wistar rats during postoperative days 9–15 (p < 0.05) (Figure 2b). However, percentage weight loss between groups was similar from postoperative days 18–27, such that RYGB-treated Wistar rats weighed 6.7 ± 2.8% less, whereas RYGB-treated Zucker fatty fa/fa rats weighed 5.6 ± 1.4% less compared with baseline by study close at postoperative day 27 (p = 0.78) (Figure 2b).
In accordance with the changes in body weights between Zucker fatty rat groups, average daily food intake of RYGB-treated rats was similar to lean rats (i.e., normalized) from postoperative days 16–18 onwards, whereas it was always significantly lower than obese rats (p < 0.0001) up until study close at postoperative days 25–27 (21.5 ± 1.8 kcal vs. 32.5 ± 0.9 kcal per day, respectively; p < 0.0001) (Figure 2c). Notably, average daily food intake of RYGB-treated rats was significantly lower than lean rats from postoperative days 7–9 (p < 0.0001) to postoperative days 13–15 (p < 0.01), which we attribute to the longer time it requires for the reconfigured gastrointestinal tract to fully heal.
To exclude malabsorption as a cause of changes in body weight in our RYGB rat model, we measured energy content in fecal samples collected from Zucker fatty rats at postoperative day 28 by bomb calorimetry. This revealed negligible differences between groups (Figure 2d).
To determine the effects of RYGB on adiposity, vWAT was dissected and weighed from Zucker fatty rats following euthanasia at postoperative day 28. This revealed that vWAT of obese rats weighed significantly more than lean and RYGB-treated rats (28.4 ± 1.2 g vs. 8.0 ± 0.6 g and 18.6 ± 1.0 g, respectively; p < 0.0001 for both comparisons) (Figure 2e). Sidak post hoc test also revealed that the vWAT of RYGB-treated rats weighed significantly more than lean rats (p < 0.0001) (Figure 2e). These group differences in vWAT weights were fully reflected in plasma leptin levels, which were the highest for obese rats (3.1 ± 0.11 µg/mL), followed by RYGB-treated rats (1.9 ± 0.10 µg/mL), and then by lean rats (0.8 ± 0.07 µg/mL) (Figure 2f).

3.2. Leptin Receptors Are Not Required for RYGB to Normalize Oral Glucose Tolerance

Next, to determine if leptin receptors are required for RYGB to normalize glycemic control, an OGTT was performed at postoperative day 27 (Figure 1). Fasting blood glucose levels at baseline were significantly higher for obese compared with lean rats (105.8 ± 8.6 mg/dL vs. 80.8 ± 3.3 mg/dL, respectively; p = 0.01), whereas they were similar for RYGB-treated rats (92.9 ± 3.7 mg/dL) compared with both lean (p = 0.23) and obese (p = 0.27) rats (Figure 3a). During the OGTT, blood glucose levels peaked for lean rats at 15 min and then steadily declined by 120 min (Figure 3a). In contrast, blood glucose levels peaked for obese rats at 30 min but remained elevated at 60 min before slowly declining by 120 min (Figure 3a). The blood glucose excursion curve for RYGB-treated rats during the OGTT was markedly different to both lean and obese rats peaking at 15 min, then steeply dropping to below baseline values at 60 min and then returning to near baseline values at 120 min (Figure 3a). This blood glucose dynamic is similar to that described for RYGB-treated, non-diabetic/diabetic patients during a mixed meal tolerance test and has been attributed to increased glucose absorption and clearance [87,88]. Further, area under the curve (AUC) analysis revealed a normalization of integrated blood glucose levels during the OGTT for RYGB-treated rats (Figure 3a).
Concerning plasma insulin levels, obese rats were hyperinsulinemic at baseline (1.2 ± 0.2 nmol/L), with significantly higher plasma insulin levels compared with both lean (0.14 ± 0.01 nmol/L) and RYGB-treated (0.39 ± 0.07 nmol/L) rats (p < 0.0001 for both comparisons) (Figure 3b). During the OGTT, plasma insulin levels only slightly rose for lean rats peaking at 15 min and then gradually declined by 120 min (Figure 3b). For obese rats, plasma insulin levels peaked at 30 min, but remained elevated at 60 min before gradually declining by 120 min (Figure 3b). Again, the plasma insulin curve for RYGB-treated rats during the OGTT was qualitatively different from both lean and obese rats with plasma insulin levels peaking at 15 min, but remaining elevated at 30 min, before steeply declining to near baseline levels by 120 min (Figure 3b). This could be explained by the increased release of the incretin GLP-1 in RYGB-treated rats, which also peaked 15 min into the OGTT (Figure 3c). Again, the plasma profile of insulin and GLP-1 during the OGTT in RYGB-treated rats is similar to that described for RYGB-treated, non-diabetic/diabetic patients during a mixed-meal tolerance test [87,88]. AUC analysis revealed similar integrated circulating insulin levels during the OGTT for RYGB-treated compared with obese rats, which were significantly higher than lean rats (p < 0.0001 for both comparisons) (Figure 3b). On the other hand, AUC analysis revealed the highest integrated circulating GLP-1 levels during the OGTT for RYGB-treated rats compared with both lean (p < 0.0001) and obese (p < 0.001) rats (Figure 3c).
Based on the OGTT data, we calculated HOMA-IR indices, as an indicator of insulin resistance [84], and found them to be normalized in RYGB-treated rats (Figure 3d). In contrast, ISI-M indices, as an indicator of insulin sensitivity [85], were significantly higher for lean rats compared with both obese and RYGB-treated rats (p < 0.0001 for both comparisons) (Figure 3e).

3.3. Leptin Receptors Might Be Required for RYGB to Normalize Liver Health

Finally, to determine if leptin receptors are required for RYGB to normalize liver health, we performed H&E staining on paraffin-embedded liver sections and also measured circulating levels of the liver enzymes ALT and AST as indicators of liver damage. This revealed that obese rats had markedly more hepatic lipid deposits than lean rats (Figure 4a), in line with previous studies [57,59], whereas RYGB-treated rats had similar hepatic lipid deposits compared with lean rats (Figure 4a). Interestingly, although circulating levels of ALT were higher in obese rats compared with lean rats (0.92 ± 0.03 mg/mL vs. 0.52 ± 0.05 mg/mL; p < 0.0001), again in line with previous studies [57,59], they remained elevated in RYGB-treated rats (0.91 ± 0.06 mg/mL) (Figure 4b). In contrast, circulating levels of AST were similar between groups (Figure 4c).

4. Discussion

Zucker fatty fa/fa rats harbor an autosomal recessive point mutation in the leptin receptor gene that negatively affects the extracellular domain common to all leptin receptor subtypes (a–f) [53,54,55], making them an established genetic model of leptin receptor deficiency. We obtained evidence using these rats that the leptin system is not required for RYGB to normalize energy and glucose homeostasis, whereas it might play an independent role in improving liver health.
The first studies aimed at assessing the requirement of the leptin system in the improvements in energy and glucose homeostasis associated with RYGB used leptin-deficient ob/ob mice [43,44]. Our findings do not align with those of Hao et al. [43] who showed that the changes in body weight of ob/ob and diet-induced obese mice following RYGB were markedly different. A potential reason for the discrepancy with our findings is that the RYGB mouse model of Hao et al. [43] is not associated with suppression of food intake and instead causes malabsorption, unlike the RYGB-treated Zucker fatty fa/fa rats described here. Our findings do, however, agree with those of Mokadem et al. [44] who showed that RYGB induced sustained weight loss in ob/ob mice up until the end of the 6-week monitoring period and reduced average food intake by 23%. In contrast, body weight and oral glucose tolerance in the RYGB-treated ob/ob mice of Mokadem et al. [44] were not normalized. The reasons for the discrepancies with our findings could be due to species differences or the degree of diminished leptin action between ob/ob mouse (absolute) and Zucker fatty fa/fa rat (severely diminished) models. In this regard, while Zucker fatty fa/fa rats reduce food intake upon central leptin administration at pharmacological doses [89,90], they fail to do so to peripherally administered leptin [90]. Therefore, it is unlikely that any residual circulating leptin action could contribute to the suppression of food intake in RYGB-treated Zucker fatty fa/fa rats.
Because RYGB is very technically demanding to execute in mice, more studies have been performed aimed at assessing its metabolic effects in Zucker fatty fa/fa [60,61,62,63,64] and Zucker diabetic fatty fa/fa [38,62,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80] rats. These studies, however, like those in db/db mice [49,50], were not directly aimed at assessing the requirement of the leptin system in the improvements in energy and glucose homeostasis associated with RYGB. This is most likely why their details of food intake are either generally incomplete [60,61,62,63,64,66,67,68,71,78,79,81], or missing [38,49,50,69,70,72,73,74,75,76,77,80], and their study conclusions are unrelated to leptin. Our findings differ from the studies showing a lack of sustained weight loss associated with RYGB [38,64,68,71,74,75,78,80], but are in line with the majority that do [61,62,63,66,67,69,72,76,79,81]. Further, our findings are consistent with the studies showing suppression of average food intake associated with RYGB over the postoperative monitoring period [62,66,67,71,78,79,81]. The reasons for the discrepancies between studies could be due to the age of rats when surgeries were performed, the postoperative maintenance diet, the duration of the postoperative monitoring period, as well as the RYGB model, which can vary significantly between laboratories [91]. Nevertheless, our study extends previous work by showing a clear normalization of food intake by RYGB that is sustained at a late postoperative time-point when body weight is also normalized by the procedure.
Importantly, we could demonstrate that the changes in body weight over the course of a 27-day monitoring period in RYGB-treated Zucker fatty fa/fa rats largely overlapped with diet-induced obese Wistar rats that have intact leptin receptors. This is in line with other studies showing similar 13% weight loss 11 days after RYGB in Zucker diabetic fatty fa/fa rats and Sprague-Dawley rats [67], as well as similar body weight trajectories over a lengthier 4-week postoperative monitoring period in these rats [68,78]. In contrast, the potent weight lowering and appetite suppressing effects of various small molecule leptin sensitizers in diet-induced obese mice are lost in both ob/ob and db/db mice [28,29,32]. These findings collectively argue against sensitization to endogenous leptin playing a causal role in the outcome of RYGB on energy homeostasis. A recent study using diet-induced obese Wistar rats, however, reached the opposite conclusion [45]. A major limitation of this study is that it focused only on the effects of exogenous leptin treatment [45]. Moreover, food intake in the RYGB-treated rats of Chen et al. [45] returned to the levels of sham-operated counterparts and was not affected when central leptin resistance was induced pharmacologically [45].
With regards to glucose homeostasis, previous studies have consistently shown lower fasting blood glucose and/or plasma insulin levels in RYGB-treated Zucker fatty fa/fa and Zucker diabetic fatty fa/fa rats compared with sham-operated counterparts [38,61,63,64,66,67,68,69,71,72,76,79,81]. Additionally, studies with a longitudinal design have shown that RYGB improves oral glucose tolerance at postoperative days 21 and 30 compared with baseline [74,79]. Because we included a lean control group in the form of sham-operated fa/+ Zucker fatty rats, we could show a normalization of fasting plasma insulin levels and HOMA-IR indices associated with RYGB, which is consistent with a previous study [63]. We further found normalized oral glucose tolerance, which differs from a previous study in Zucker diabetic fatty fa/fa rats [76]. This discrepancy can possibly be attributed to strain differences, since Zucker diabetic fatty fa/fa rats additionally harbor a point mutation that affects insulin transcription in pancreatic beta cells [92], rendering them genuinely diabetic unlike Zucker fatty fa/fa rats [65]. In contrast, we did not find significantly higher ISI values in RYGB-treated Zucker fa/fa rats compared with sham-operated counterparts, which differs from a previous study in which it was higher [61]. While we cannot offer an explanation for this discrepancy, the evidence from studies on Zucker fatty and Zucker diabetic fatty fa/fa rats generally suggests that leptin receptors are not required for the improvement/normalization of glucose homeostasis associated with RYGB [38,61,63,64,66,67,68,69,71,72,74,76,79,81].
The global prevalence of fatty liver disease has risen dramatically alongside that of obesity, and there currently exists no specific medical treatment [93]. Numerous prospective clinical studies have shown, however, that RYGB is associated with a marked improvement in liver health as determined histologically and reflected by a normalization of circulating ALT and AST levels [94]. Similarly, there is ample evidence that leptin protects against accumulation of liver fat [95], with rodent studies implicating leptin receptors in the hypothalamus [15] and the dorsal vagal complex [14]. Further, leptin sensitizers markedly improve fatty liver and lower circulating ALT/AST levels in diet-induced obese mice [19,28,29]. We, however, found lower liver fat in RYGB-treated Zucker fatty fa/fa rats compared with sham-operated counterparts, similar to a previous study [64] and also to RYGB-treated ob/ob mice [44], suggesting that the leptin system is not required for this metabolic benefit postoperatively. In contrast, circulating ALT levels between RYGB-treated and sham-operated Zucker fatty fa/fa rats were similar. While this might suggest that leptin receptors are required for the complete normalization of liver health associated with RYGB, a previous study documented lower circulating ALT levels in RYGB-treated Zucker diabetic fatty fa/fa rats compared with sham-operated counterparts [71]. Clearly, more in-depth preclinical studies are needed on the extent to which RYGB improves fatty liver disease, including its impact on inflammation and fibrosis, and the potential role played by the leptin system.
If leptin is not required for the improved energy and glucose homeostasis associated with RYGB, then this raises the obvious question as to which peripheral factors are required. We confirmed that circulating levels of the anorexigenic and incretin gut hormone GLP-1 are increased by RYGB in Zucker fatty/Zucker diabetic fatty fa/fa rats [61,62,68,75,78,79]. However, rodent studies have shown that like leptin receptors, GLP-1 receptors are not required for the effects of RYGB on body weight and glycemic control [96,97], although there is pharmacological evidence suggesting that GLP-1 receptor signaling is required for the postoperative improvement in oral glucose tolerance [98]. Similarly, the farnesoid X receptor (FXR), which is a target of bile acids, is required for the improvements in glycemic control associated with RYGB in mice [99]. Still, the peripheral factors required for the improvements in energy homeostasis associated with RYGB remain unknown, and their identification represents an important future line of investigation. Notably, Zucker fatty fa/fa or Zucker diabetic fatty fa/fa rats, with their sustained suppression of food intake following RYGB [66], may be the ideal model for such investigations. This is because food intake suppression in RYGB-treated, diet-induced obese mice and rats tends to diminish over time [9,45,67,82,97,99,100] or is even absent [43,78,96].
Strengths of the present study include the well-powered group sizes allowing for robust statistical comparisons to be performed, as well as the incorporation of a lean control group. Another study strength is the detailed reporting of body weight and food intake absent in previous studies with RYGB-treated Zucker fatty fa/fa or Zucker diabetic fatty fa/fa rats. We also directly compared body weight changes following RYGB in leptin receptor-deficient and replete states, revealing the non-essential role of the leptin system in the normalization of energy homeostasis postoperatively. A limitation of the present study is that despite achieving the degree of food intake suppression associated with RYGB in patients [101], the 30–40% weight loss characteristic of the procedure [3] was not reached. However, when factoring in the rapid weight gain of sham-operated Zucker fatty fa/fa rats, RYGB-treated rats weighed 25.5 ± 2.2% less, which resembles the clinical outcome. Additionally, we did not directly compare the effects of RYGB on glucose homeostasis and fatty liver with a diet-induced obese group in which endogenous leptin action could be restored or enhanced, which needs to be performed in future studies. Finally, we did not challenge RYGB-treated Zucker fatty fa/fa rats with a high-fat diet postoperatively, which could have uncovered a more prominent role for the leptin system in preventing weight regain [44].
In summary, we have presented evidence arguing against the requirement of the leptin system in the normalization of energy and glucose homeostasis associated with RYGB, which is consistent with the majority of previous studies in Zucker fatty fa/fa and Zucker diabetic fatty fa/fa rats as models of leptin receptor deficiency [61,62,63,66,67,69,72,76,79,81] and thus places them in a new light.

Author Contributions

Conceptualization, M.K.H.; methodology, C.C. and F.S.; software, M.K.H. and F.S.; validation, C.O.; formal analysis, M.K.H., A.H. and F.S.; investigation, L.R., A.N., M.K.H., U.D. and J.-L.K.; resources, F.S.; data curation, M.K.H. and F.S.; writing—original draft preparation, M.K.H.; writing—review and editing, M.K.H., A.H. and F.S.; visualization, M.K.H. and F.S.; supervision, F.S. and C.O.; project administration, F.S. and C.O.; funding acquisition, F.S. All authors have read and agreed to the published version of the manuscript.

Funding

This publication was funded by the Interdisciplinary Center for Clinical Research of Wuerzburg (IZKF) (grant number Z-3/44), the German Research Foundation (DFG) and the University of Wuerzburg in the funding programme Open Access Publishing.

Institutional Review Board Statement

All animals experiments described in this manuscript were reviewed and approved by the Animal Care Committee of the local government of Unterfranken, Bavaria, Germany (License numbers 55.2-2531.01-72/12 and 55.2-2532-2-467).

Informed Consent Statement

Not applicable.

Data Availability Statement

The data in this manuscript are available on request from the corresponding authors.

Acknowledgments

We thank Manuela Hofmann and Bettina Porsch for skilled technical assistance with the experiments described in this manuscript.

Conflicts of Interest

The authors declare no conflict of interest and that the funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.

References

  1. Lassailly, G.; Caiazzo, R.; Ntandja-Wandji, L.C.; Gnemmi, V.; Baud, G.; Verkindt, H.; Ningarhari, M.; Louvet, A.; Leteurtre, E.; Raverdy, V.; et al. Bariatric Surgery Provides Long-term Resolution of Nonalcoholic Steatohepatitis and Regression of Fibrosis. Gastroenterology 2020, 159, 1290–1301.e1295. [Google Scholar] [CrossRef]
  2. Mingrone, G.; Panunzi, S.; De Gaetano, A.; Guidone, C.; Iaconelli, A.; Capristo, E.; Chamseddine, G.; Bornstein, S.R.; Rubino, F. Metabolic surgery versus conventional medical therapy in patients with type 2 diabetes: 10-year follow-up of an open-label, single-centre, randomised controlled trial. Lancet 2021, 397, 293–304. [Google Scholar] [CrossRef]
  3. Adams, T.D.; Davidson, L.E.; Litwin, S.E.; Kim, J.; Kolotkin, R.L.; Nanjee, M.N.; Gutierrez, J.M.; Frogley, S.J.; Ibele, A.R.; Brinton, E.A.; et al. Weight and Metabolic Outcomes 12 Years after Gastric Bypass. N. Engl. J. Med. 2017, 377, 1143–1155. [Google Scholar] [CrossRef]
  4. Schauer, P.R.; Bhatt, D.L.; Kirwan, J.P.; Wolski, K.; Aminian, A.; Brethauer, S.A.; Navaneethan, S.D.; Singh, R.P.; Pothier, C.E.; Nissen, S.E.; et al. Bariatric Surgery versus Intensive Medical Therapy for Diabetes—5-Year Outcomes. N. Engl. J. Med. 2017, 376, 641–651. [Google Scholar] [CrossRef] [Green Version]
  5. Sjostrom, L.; Narbro, K.; Sjostrom, C.D.; Karason, K.; Larsson, B.; Wedel, H.; Lystig, T.; Sullivan, M.; Bouchard, C.; Carlsson, B.; et al. Effects of bariatric surgery on mortality in Swedish obese subjects. N. Engl. J. Med. 2007, 357, 741–752. [Google Scholar] [CrossRef] [Green Version]
  6. Evers, S.S.; Sandoval, D.A.; Seeley, R.J. The Physiology and Molecular Underpinnings of the Effects of Bariatric Surgery on Obesity and Diabetes. Annu. Rev. Physiol. 2017, 79, 313–334. [Google Scholar] [CrossRef]
  7. Kwon, I.G.; Kang, C.W.; Park, J.P.; Oh, J.H.; Wang, E.K.; Kim, T.Y.; Sung, J.S.; Park, N.; Lee, Y.J.; Sung, H.J.; et al. Serum glucose excretion after Roux-en-Y gastric bypass: A potential target for diabetes treatment. Gut 2020. [Google Scholar] [CrossRef]
  8. Wei, X.; Lu, Z.; Li, L.; Zhang, H.; Sun, F.; Ma, H.; Wang, L.; Hu, Y.; Yan, Z.; Zheng, H.; et al. Reducing NADPH Synthesis Counteracts Diabetic Nephropathy through Restoration of AMPK Activity in Type 1 Diabetic Rats. Cell Rep. 2020, 32, 108207. [Google Scholar] [CrossRef]
  9. Ye, Y.; Abu El Haija, M.; Morgan, D.A.; Guo, D.; Song, Y.; Frank, A.; Tian, L.; Riedl, R.A.; Burnett, C.M.L.; Gao, Z.; et al. Endocannabinoid Receptor-1 and Sympathetic Nervous System Mediate the Beneficial Metabolic Effects of Gastric Bypass. Cell Rep. 2020, 33, 108270. [Google Scholar] [CrossRef]
  10. Ben-Zvi, D.; Meoli, L.; Abidi, W.M.; Nestoridi, E.; Panciotti, C.; Castillo, E.; Pizarro, P.; Shirley, E.; Gourash, W.F.; Thompson, C.C.; et al. Time-Dependent Molecular Responses Differ between Gastric Bypass and Dieting but Are Conserved Across Species. Cell Metab. 2018, 28, 310–323.e316. [Google Scholar] [CrossRef] [Green Version]
  11. Friedman, J.M. Leptin and the endocrine control of energy balance. Nat. Metab. 2019, 1, 754–764. [Google Scholar] [CrossRef] [PubMed]
  12. Seoane-Collazo, P.; Martinez-Sanchez, N.; Milbank, E.; Contreras, C. Incendiary Leptin. Nutrients 2020, 12, 472. [Google Scholar] [CrossRef] [Green Version]
  13. D’Souza A, M.; Neumann, U.H.; Glavas, M.M.; Kieffer, T.J. The glucoregulatory actions of leptin. Mol. Metab. 2017, 6, 1052–1065. [Google Scholar] [CrossRef] [PubMed]
  14. Hackl, M.T.; Furnsinn, C.; Schuh, C.M.; Krssak, M.; Carli, F.; Guerra, S.; Freudenthaler, A.; Baumgartner-Parzer, S.; Helbich, T.H.; Luger, A.; et al. Brain leptin reduces liver lipids by increasing hepatic triglyceride secretion and lowering lipogenesis. Nat. Commun. 2019, 10, 2717. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  15. Jiang, L.; Su, H.; Wu, X.; Shen, H.; Kim, M.H.; Li, Y.; Myers, M.G., Jr.; Owyang, C.; Rui, L. Leptin receptor-expressing neuron Sh2b1 supports sympathetic nervous system and protects against obesity and metabolic disease. Nat. Commun. 2020, 11, 1517. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  16. Ingalls, A.M.; Dickie, M.M.; Snell, G.D. Obese, a new mutation in the house mouse. J. Hered. 1950, 41, 317–318. [Google Scholar] [CrossRef]
  17. Zhang, Y.; Proenca, R.; Maffei, M.; Barone, M.; Leopold, L.; Friedman, J.M. Positional cloning of the mouse obese gene and its human homologue. Nature 1994, 372, 425–432. [Google Scholar] [CrossRef]
  18. Knight, Z.A.; Hannan, K.S.; Greenberg, M.L.; Friedman, J.M. Hyperleptinemia is required for the development of leptin resistance. PLoS ONE 2010, 5, e11376. [Google Scholar] [CrossRef]
  19. Zhao, S.; Zhu, Y.; Schultz, R.D.; Li, N.; He, Z.; Zhang, Z.; Caron, A.; Zhu, Q.; Sun, K.; Xiong, W.; et al. Partial Leptin Reduction as an Insulin Sensitization and Weight Loss Strategy. Cell Metab. 2019, 30, 706–719.e706. [Google Scholar] [CrossRef]
  20. Loh, K.; Fukushima, A.; Zhang, X.; Galic, S.; Briggs, D.; Enriori, P.J.; Simonds, S.; Wiede, F.; Reichenbach, A.; Hauser, C.; et al. Elevated hypothalamic TCPTP in obesity contributes to cellular leptin resistance. Cell Metab. 2011, 14, 684–699. [Google Scholar] [CrossRef] [Green Version]
  21. Olofsson, L.E.; Unger, E.K.; Cheung, C.C.; Xu, A.W. Modulation of AgRP-neuronal function by SOCS3 as an initiating event in diet-induced hypothalamic leptin resistance. Proc. Natl. Acad. Sci. USA 2013, 110, E697–E706. [Google Scholar] [CrossRef] [Green Version]
  22. Valdearcos, M.; Robblee, M.M.; Benjamin, D.I.; Nomura, D.K.; Xu, A.W.; Koliwad, S.K. Microglia dictate the impact of saturated fat consumption on hypothalamic inflammation and neuronal function. Cell Rep. 2014, 9, 2124–2138. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  23. Zhang, X.; Zhang, G.; Zhang, H.; Karin, M.; Bai, H.; Cai, D. Hypothalamic IKKbeta/NF-kappaB and ER stress link overnutrition to energy imbalance and obesity. Cell 2008, 135, 61–73. [Google Scholar] [CrossRef] [Green Version]
  24. Halaas, J.L.; Gajiwala, K.S.; Maffei, M.; Cohen, S.L.; Chait, B.T.; Rabinowitz, D.; Lallone, R.L.; Burley, S.K.; Friedman, J.M. Weight-reducing effects of the plasma protein encoded by the obese gene. Science 1995, 269, 543–546. [Google Scholar] [CrossRef]
  25. Pelleymounter, M.A.; Cullen, M.J.; Baker, M.B.; Hecht, R.; Winters, D.; Boone, T.; Collins, F. Effects of the obese gene product on body weight regulation in ob/ob mice. Science 1995, 269, 540–543. [Google Scholar] [CrossRef]
  26. Singh, A.; Wirtz, M.; Parker, N.; Hogan, M.; Strahler, J.; Michailidis, G.; Schmidt, S.; Vidal-Puig, A.; Diano, S.; Andrews, P.; et al. Leptin-mediated changes in hepatic mitochondrial metabolism, structure, and protein levels. Proc. Natl. Acad. Sci. USA 2009, 106, 13100–13105. [Google Scholar] [CrossRef] [Green Version]
  27. Campfield, L.A.; Smith, F.J.; Guisez, Y.; Devos, R.; Burn, P. Recombinant mouse OB protein: Evidence for a peripheral signal linking adiposity and central neural networks. Science 1995, 269, 546–549. [Google Scholar] [CrossRef]
  28. Lee, J.; Liu, J.; Feng, X.; Salazar Hernandez, M.A.; Mucka, P.; Ibi, D.; Choi, J.W.; Ozcan, U. Withaferin A is a leptin sensitizer with strong antidiabetic properties in mice. Nat. Med. 2016, 22, 1023–1032. [Google Scholar] [CrossRef] [Green Version]
  29. Liu, J.; Lee, J.; Salazar Hernandez, M.A.; Mazitschek, R.; Ozcan, U. Treatment of obesity with celastrol. Cell 2015, 161, 999–1011. [Google Scholar] [CrossRef] [Green Version]
  30. Feng, X.; Guan, D.; Auen, T.; Choi, J.W.; Salazar Hernandez, M.A.; Lee, J.; Chun, H.; Faruk, F.; Kaplun, E.; Herbert, Z.; et al. IL1R1 is required for celastrol’s leptin-sensitization and antiobesity effects. Nat. Med. 2019, 25, 575–582. [Google Scholar] [CrossRef]
  31. Dodd, G.T.; Xirouchaki, C.E.; Eramo, M.; Mitchell, C.A.; Andrews, Z.B.; Henry, B.A.; Cowley, M.A.; Tiganis, T. Intranasal Targeting of Hypothalamic PTP1B and TCPTP Reinstates Leptin and Insulin Sensitivity and Promotes Weight Loss in Obesity. Cell Rep. 2019, 28, 2905–2922.e2905. [Google Scholar] [CrossRef]
  32. Tam, J.; Cinar, R.; Liu, J.; Godlewski, G.; Wesley, D.; Jourdan, T.; Szanda, G.; Mukhopadhyay, B.; Chedester, L.; Liow, J.S.; et al. Peripheral cannabinoid-1 receptor inverse agonism reduces obesity by reversing leptin resistance. Cell Metab. 2012, 16, 167–179. [Google Scholar] [CrossRef] [Green Version]
  33. Haghighat, N.; Kazemi, A.; Asbaghi, O.; Jafarian, F.; Moeinvaziri, N.; Hosseini, B.; Amini, M. Long-term effect of bariatric surgery on body composition in patients with morbid obesity: A systematic review and meta-analysis. Clin. Nutr. 2020, 40, 1755–1766. [Google Scholar] [CrossRef]
  34. Arakawa, R.; Febres, G.; Cheng, B.; Krikhely, A.; Bessler, M.; Korner, J. Prospective study of gut hormone and metabolic changes after laparoscopic sleeve gastrectomy and Roux-en-Y gastric bypass. PLoS ONE 2020, 15, e0236133. [Google Scholar] [CrossRef]
  35. Salman, M.A.; El-Ghobary, M.; Soliman, A.; El Sherbiny, M.; Abouelregal, T.E.; Albitar, A.; Abdallah, A.; Mikhail, H.M.S.; Nafea, M.A.; Sultan, A.; et al. Long-Term Changes in Leptin, Chemerin, and Ghrelin Levels Following Roux-en-Y Gastric Bypass and Laparoscopic Sleeve Gastrectomy. Obes. Surg. 2020, 30, 1052–1060. [Google Scholar] [CrossRef] [PubMed]
  36. Unamuno, X.; Izaguirre, M.; Gomez-Ambrosi, J.; Rodriguez, A.; Ramirez, B.; Becerril, S.; Valenti, V.; Moncada, R.; Silva, C.; Salvador, J.; et al. Increase of the Adiponectin/Leptin Ratio in Patients with Obesity and Type 2 Diabetes after Roux-en-Y Gastric Bypass. Nutrients 2019, 11, 2069. [Google Scholar] [CrossRef] [Green Version]
  37. Guijarro, A.; Osei-Hyiaman, D.; Harvey-White, J.; Kunos, G.; Suzuki, S.; Nadtochiy, S.; Brookes, P.S.; Meguid, M.M. Sustained weight loss after Roux-en-Y gastric bypass is characterized by down regulation of endocannabinoids and mitochondrial function. Ann. Surg. 2008, 247, 779–790. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  38. Lau, R.G.; Kumar, S.; Hall, C.E.; Palaia, T.; Rideout, D.A.; Hall, K.; Brathwaite, C.E.; Ragolia, L. Roux-en-Y gastric bypass attenuates the progression of cardiometabolic complications in obese diabetic rats via alteration in gastrointestinal hormones. Surg. Obes. Relat. Dis. 2015, 11, 1044–1053. [Google Scholar] [CrossRef]
  39. Lips, M.A.; Pijl, H.; van Klinken, J.B.; de Groot, G.H.; Janssen, I.M.; Van Ramshorst, B.; Van Wagensveld, B.A.; Swank, D.J.; Van Dielen, F.; Smit, J.W. Roux-en-Y gastric bypass and calorie restriction induce comparable time-dependent effects on thyroid hormone function tests in obese female subjects. Eur. J. Endocrinol. 2013, 169, 339–347. [Google Scholar] [CrossRef]
  40. Lips, M.A.; van Klinken, J.B.; Pijl, H.; Janssen, I.; van Dijk, K.W.; Koning, F.; van Harmelen, V. Weight loss induced by very low calorie diet is associated with a more beneficial systemic inflammatory profile than by Roux-en-Y gastric bypass. Metabolism 2016, 65, 1614–1620. [Google Scholar] [CrossRef]
  41. Neinast, M.D.; Frank, A.P.; Zechner, J.F.; Li, Q.; Vishvanath, L.; Palmer, B.F.; Aguirre, V.; Gupta, R.K.; Clegg, D.J. Activation of natriuretic peptides and the sympathetic nervous system following Roux-en-Y gastric bypass is associated with gonadal adipose tissues browning. Mol. Metab. 2015, 4, 427–436. [Google Scholar] [CrossRef] [PubMed]
  42. Olivan, B.; Teixeira, J.; Bose, M.; Bawa, B.; Chang, T.; Summe, H.; Lee, H.; Laferrere, B. Effect of weight loss by diet or gastric bypass surgery on peptide YY3-36 levels. Ann. Surg. 2009, 249, 948–953. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  43. Hao, Z.; Munzberg, H.; Rezai-Zadeh, K.; Keenan, M.; Coulon, D.; Lu, H.; Berthoud, H.R.; Ye, J. Leptin deficient ob/ob mice and diet-induced obese mice responded differently to Roux-en-Y bypass surgery. Int. J. Obes. 2015, 39, 798–805. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  44. Mokadem, M.; Zechner, J.F.; Uchida, A.; Aguirre, V. Leptin Is Required for Glucose Homeostasis after Roux-en-Y Gastric Bypass in Mice. PLoS ONE 2015, 10, e0139960. [Google Scholar] [CrossRef] [Green Version]
  45. Chen, J.; Haase, N.; Haange, S.B.; Sucher, R.; Munzker, J.; Jager, E.; Schischke, K.; Seyfried, F.; von Bergen, M.; Hankir, M.K.; et al. Roux-en-Y gastric bypass contributes to weight loss-independent improvement in hypothalamic inflammation and leptin sensitivity through gut-microglia-neuron-crosstalk. Mol. Metab. 2021, 48, 101214. [Google Scholar] [CrossRef]
  46. Hankir, M.K.; Seyfried, F. Partial Leptin Reduction: An Emerging Weight Loss Paradigm. Trends Endocrinol. Metab. 2020, 31, 395–397. [Google Scholar] [CrossRef]
  47. Natividad, J.M.; Agus, A.; Planchais, J.; Lamas, B.; Jarry, A.C.; Martin, R.; Michel, M.L.; Chong-Nguyen, C.; Roussel, R.; Straube, M.; et al. Impaired Aryl Hydrocarbon Receptor Ligand Production by the Gut Microbiota Is a Key Factor in Metabolic Syndrome. Cell Metab. 2018, 28, 737–749.e734. [Google Scholar] [CrossRef] [Green Version]
  48. Ceccarini, G.; Pelosini, C.; Ferrari, F.; Magno, S.; Vitti, J.; Salvetti, G.; Moretto, C.; Marioni, A.; Buccianti, P.; Piaggi, P.; et al. Serum IGF-binding protein 2 (IGFBP-2) concentrations change early after gastric bypass bariatric surgery revealing a possible marker of leptin sensitivity in obese subjects. Endocrine 2019, 65, 86–93. [Google Scholar] [CrossRef]
  49. Liu, B.; Kuang, L.; Liu, J. Bariatric surgery relieves type 2 diabetes and modulates inflammatory factors and coronary endothelium eNOS/iNOS expression in db/db mice. Can. J. Physiol. Pharmacol. 2014, 92, 70–77. [Google Scholar] [CrossRef]
  50. Huang, T.; Fu, J.; Zhang, Z.; Zhang, Y.; Liang, Y.; Ge, C.; Qin, X. Pancreatic islet regeneration through PDX-1/Notch-1/Ngn3 signaling after gastric bypass surgery in db/db mice. Exp. Ther. Med. 2017, 14, 2831–2838. [Google Scholar] [CrossRef] [Green Version]
  51. Hummel, K.P.; Dickie, M.M.; Coleman, D.L. Diabetes, a new mutation in the mouse. Science 1966, 153, 1127–1128. [Google Scholar] [CrossRef]
  52. Chen, H.; Charlat, O.; Tartaglia, L.A.; Woolf, E.A.; Weng, X.; Ellis, S.J.; Lakey, N.D.; Culpepper, J.; Moore, K.J.; Breitbart, R.E.; et al. Evidence that the diabetes gene encodes the leptin receptor: Identification of a mutation in the leptin receptor gene in db/db mice. Cell 1996, 84, 491–495. [Google Scholar] [CrossRef] [Green Version]
  53. Chua, S.C., Jr.; White, D.W.; Wu-Peng, X.S.; Liu, S.M.; Okada, N.; Kershaw, E.E.; Chung, W.K.; Power-Kehoe, L.; Chua, M.; Tartaglia, L.A.; et al. Phenotype of fatty due to Gln269Pro mutation in the leptin receptor (Lepr). Diabetes 1996, 45, 1141–1143. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  54. Iida, M.; Murakami, T.; Ishida, K.; Mizuno, A.; Kuwajima, M.; Shima, K. Substitution at codon 269 (glutamine→proline) of the leptin receptor (OB-R) cDNA is the only mutation found in the Zucker fatty (fa/fa) rat. Biochem. Biophys. Res. Commun. 1996, 224, 597–604. [Google Scholar] [CrossRef]
  55. Phillips, M.S.; Liu, Q.; Hammond, H.A.; Dugan, V.; Hey, P.J.; Caskey, C.J.; Hess, J.F. Leptin receptor missense mutation in the fatty Zucker rat. Nat. Genet. 1996, 13, 18–19. [Google Scholar] [CrossRef]
  56. Zucker, L.M.; Zucker, T.F. Fatty, a new mutation in the rat. J. Hered. 1961, 52, 275–278. [Google Scholar] [CrossRef]
  57. LaBranche, T.P.; Kopec, A.K.; Mantena, S.R.; Hollingshead, B.D.; Harrington, A.W.; Stewart, Z.S.; Zhan, Y.; Hayes, K.D.; Whiteley, L.O.; Burdick, A.D.; et al. Zucker Lean Rats with Hepatic Steatosis Recapitulate Asymptomatic Metabolic Syndrome and Exhibit Greater Sensitivity to Drug-Induced Liver Injury Compared with Standard Nonclinical Sprague-Dawley Rat Model. Toxicol. Pathol. 2020, 48, 994–1007. [Google Scholar] [CrossRef]
  58. Ionescu, E.; Sauter, J.F.; Jeanrenaud, B. Abnormal oral glucose tolerance in genetically obese (fa/fa) rats. Am. J. Physiol. 1985, 248, E500–E506. [Google Scholar] [CrossRef] [PubMed]
  59. Carmiel-Haggai, M.; Cederbaum, A.I.; Nieto, N. A high-fat diet leads to the progression of non-alcoholic fatty liver disease in obese rats. FASEB J. 2005, 19, 136–138. [Google Scholar] [CrossRef]
  60. Bankoglu, E.E.; Seyfried, F.; Rotzinger, L.; Nordbeck, A.; Corteville, C.; Jurowich, C.; Germer, C.T.; Otto, C.; Stopper, H. Impact of weight loss induced by gastric bypass or caloric restriction on oxidative stress and genomic damage in obese Zucker rats. Free Radic. Biol. Med. 2016, 94, 208–217. [Google Scholar] [CrossRef]
  61. Meirelles, K.; Ahmed, T.; Culnan, D.M.; Lynch, C.J.; Lang, C.H.; Cooney, R.N. Mechanisms of glucose homeostasis after Roux-en-Y gastric bypass surgery in the obese, insulin-resistant Zucker rat. Ann. Surg. 2009, 249, 277–285. [Google Scholar] [CrossRef] [Green Version]
  62. Seyfried, F.; Miras, A.D.; Rotzinger, L.; Nordbeck, A.; Corteville, C.; Li, J.V.; Schlegel, N.; Hankir, M.; Fenske, W.; Otto, C.; et al. Gastric Bypass-Related Effects on Glucose Control, beta Cell Function and Morphology in the Obese Zucker Rat. Obes. Surg. 2016, 26, 1228–1236. [Google Scholar] [CrossRef]
  63. Wolff, B.S.; Meirelles, K.; Meng, Q.; Pan, M.; Cooney, R.N. Roux-en-Y gastric bypass alters small intestine glutamine transport in the obese Zucker rat. Am. J. Physiol. Gastrointest. Liver Physiol. 2009, 297, G594–G601. [Google Scholar] [CrossRef] [Green Version]
  64. Xu, Y.; Ohinata, K.; Meguid, M.M.; Marx, W.; Tada, T.; Chen, C.; Quinn, R.; Inui, A. Gastric bypass model in the obese rat to study metabolic mechanisms of weight loss. J. Surg. Res. 2002, 107, 56–63. [Google Scholar] [CrossRef]
  65. Clark, J.B.; Palmer, C.J.; Shaw, W.N. The diabetic Zucker fatty rat. Proc. Soc. Exp. Biol. Med. 1983, 173, 68–75. [Google Scholar] [CrossRef]
  66. Abegg, K.; Corteville, C.; Docherty, N.G.; Boza, C.; Lutz, T.A.; Munoz, R.; le Roux, C.W. Effect of bariatric surgery combined with medical therapy versus intensive medical therapy or calorie restriction and weight loss on glycemic control in Zucker diabetic fatty rats. Am. J. Physiol. Regul. Integr. Comp. Physiol. 2015, 308, R321–R329. [Google Scholar] [CrossRef] [Green Version]
  67. Bhutta, H.Y.; Deelman, T.E.; le Roux, C.W.; Ashley, S.W.; Rhoads, D.B.; Tavakkoli, A. Intestinal sweet-sensing pathways and metabolic changes after Roux-en-Y gastric bypass surgery. Am. J. Physiol. Gastrointest. Liver Physiol. 2014, 307, G588–G593. [Google Scholar] [CrossRef] [Green Version]
  68. Bhutta, H.Y.; Rajpal, N.; White, W.; Freudenberg, J.M.; Liu, Y.; Way, J.; Rajpal, D.; Cooper, D.C.; Young, A.; Tavakkoli, A.; et al. Effect of Roux-en-Y gastric bypass surgery on bile acid metabolism in normal and obese diabetic rats. PLoS ONE 2015, 10, e0122273. [Google Scholar] [CrossRef]
  69. Canney, A.L.; Cohen, R.V.; Elliott, J.A.; Aboud, C.M.; Martin, W.P.; Docherty, N.G.; le Roux, C.W. Improvements in diabetic albuminuria and podocyte differentiation following Roux-en-Y gastric bypass surgery. Diabetes Vasc. Dis. Res. 2020, 17, 1479164119879039. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  70. Guo, Y.; Liu, C.Q.; Liu, G.P.; Huang, Z.P.; Zou, D.J. Roux-en-Y gastric bypass decreases endotoxemia and inflammatory stress in association with improvements in gut permeability in obese diabetic rats. J. Diabetes 2019, 11, 786–793. [Google Scholar] [CrossRef] [Green Version]
  71. Guo, Y.; Liu, C.Q.; Shan, C.X.; Chen, Y.; Li, H.H.; Huang, Z.P.; Zou, D.J. Gut microbiota after Roux-en-Y gastric bypass and sleeve gastrectomy in a diabetic rat model: Increased diversity and associations of discriminant genera with metabolic changes. Diabetes Metab. Res. Rev. 2017, 33. [Google Scholar] [CrossRef]
  72. Huang, H.; Aminian, A.; Hassan, M.; Dan, O.; Axelrod, C.L.; Schauer, P.R.; Brethauer, S.A.; Kirwan, J.P. Gastric Bypass Surgery Improves the Skeletal Muscle Ceramide/S1P Ratio and Upregulates the AMPK/ SIRT1/ PGC-1alpha Pathway in Zucker Diabetic Fatty Rats. Obes. Surg. 2019, 29, 2158–2165. [Google Scholar] [CrossRef] [PubMed]
  73. Kumar, S.; Lau, R.; Hall, C.; Palaia, T.; Brathwaite, C.E.; Ragolia, L. Bile acid elevation after Roux-en-Y gastric bypass is associated with cardio-protective effect in Zucker Diabetic Fatty rats. Int. J. Surg. 2015, 24, 70–74. [Google Scholar] [CrossRef] [PubMed]
  74. Mocanu, A.O.; Mulya, A.; Huang, H.; Dan, O.; Schauer, P.R.; Dinischiotu, A.; Brethauer, S.A.; Kirwan, J.P. Effect of Roux-en-Y Gastric Bypass on the NLRP3 Inflammasome in Pancreatic Islets from Zucker Diabetic Fatty Rats. Obes. Surg. 2016, 26, 3076–3081. [Google Scholar] [CrossRef] [Green Version]
  75. Mosinski, J.D.; Aminian, A.; Axelrod, C.L.; Batayyah, E.; Talamas, H.R.; Daigle, C.; Mulya, A.; Scelsi, A.R.; Schauer, P.R.; Brethauer, S.; et al. Roux-en-Y Gastric Bypass Restores Islet Function and Morphology Independent of Body Weight in ZDF Rats. Am. J. Physiol. Endocrinol. Metab. 2021. [Google Scholar] [CrossRef]
  76. Nair, M.; Martin, W.P.; Zhernovkov, V.; Elliott, J.A.; Fearon, N.; Eckhardt, H.; McCormack, J.; Godson, C.; Brennan, E.P.; Fandriks, L.; et al. Characterization of the renal cortical transcriptome following Roux-en-Y gastric bypass surgery in experimental diabetic kidney disease. BMJ Open Diabetes Res. Care 2020, 8, e001113. [Google Scholar] [CrossRef]
  77. Pal, A.; Rhoads, D.B.; Tavakkoli, A. Effect of Portal Glucose Sensing on Systemic Glucose Levels in SD and ZDF Rats. PLoS ONE 2016, 11, e0165592. [Google Scholar] [CrossRef]
  78. Pal, A.; Rhoads, D.B.; Tavakkoli, A. Portal milieu and the interplay of multiple antidiabetic effects after gastric bypass surgery. Am. J. Physiol. Gastrointest. Liver Physiol. 2019, 316, G668–G678. [Google Scholar] [CrossRef]
  79. Shimizu, H.; Eldar, S.; Heneghan, H.M.; Schauer, P.R.; Kirwan, J.P.; Brethauer, S.A. The effect of selective gut stimulation on glucose metabolism after gastric bypass in the Zucker diabetic fatty rat model. Surg. Obes. Relat. Dis. 2014, 10, 29–35. [Google Scholar] [CrossRef]
  80. Vangoitsenhoven, R.; Mulya, A.; Mosinski, J.D.; Brethauer, S.A.; Schauer, P.R.; Kirwan, J.P.; Aminian, A. Effects of gastric bypass surgery on expression of glucose transporters and fibrotic biomarkers in kidney of diabetic fatty rats. Surg. Obes. Relat. Dis. 2020, 16, 1242–1248. [Google Scholar] [CrossRef]
  81. Seyfried, F.; Bueter, M.; Spliethoff, K.; Miras, A.D.; Abegg, K.; Lutz, T.A.; le Roux, C.W. Roux-en Y gastric bypass is superior to duodeno-jejunal bypass in improving glycaemic control in Zucker diabetic fatty rats. Obes. Surg. 2014, 24, 1888–1895. [Google Scholar] [CrossRef] [PubMed]
  82. Dischinger, U.; Corteville, C.; Otto, C.; Fassnacht, M.; Seyfried, F.; Hankir, M.K. GLP-1 and PYY3-36 reduce high-fat food preference additively after Roux-en-Y gastric bypass in diet-induced obese rats. Surg. Obes. Relat. Dis. 2019, 15, 1483–1492. [Google Scholar] [CrossRef] [PubMed]
  83. Seyfried, F.; Miras, A.D.; Bueter, M.; Prechtl, C.G.; Spector, A.C.; le Roux, C.W. Effects of preoperative exposure to a high-fat versus a low-fat diet on ingestive behavior after gastric bypass surgery in rats. Surg. Endosc. 2013, 27, 4192–4201. [Google Scholar] [CrossRef] [Green Version]
  84. Matthews, D.R.; Hosker, J.P.; Rudenski, A.S.; Naylor, B.A.; Treacher, D.F.; Turner, R.C. Homeostasis model assessment: Insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 1985, 28, 412–419. [Google Scholar] [CrossRef] [Green Version]
  85. Matsuda, M.; DeFronzo, R.A. Insulin sensitivity indices obtained from oral glucose tolerance testing: Comparison with the euglycemic insulin clamp. Diabetes Care 1999, 22, 1462–1470. [Google Scholar] [CrossRef]
  86. Miras, A.D.; Seyfried, F.; Phinikaridou, A.; Andia, M.E.; Christakis, I.; Spector, A.C.; Botnar, R.M.; le Roux, C.W. Rats fed diets with different energy contribution from fat do not differ in adiposity. Obes. Facts 2014, 7, 302–310. [Google Scholar] [CrossRef]
  87. Camastra, S.; Muscelli, E.; Gastaldelli, A.; Holst, J.J.; Astiarraga, B.; Baldi, S.; Nannipieri, M.; Ciociaro, D.; Anselmino, M.; Mari, A.; et al. Long-term effects of bariatric surgery on meal disposal and beta-cell function in diabetic and nondiabetic patients. Diabetes 2013, 62, 3709–3717. [Google Scholar] [CrossRef] [Green Version]
  88. Jacobsen, S.H.; Bojsen-Moller, K.N.; Dirksen, C.; Jorgensen, N.B.; Clausen, T.R.; Wulff, B.S.; Kristiansen, V.B.; Worm, D.; Hansen, D.L.; Holst, J.J.; et al. Effects of gastric bypass surgery on glucose absorption and metabolism during a mixed meal in glucose-tolerant individuals. Diabetologia 2013, 56, 2250–2254. [Google Scholar] [CrossRef] [Green Version]
  89. Cusin, I.; Rohner-Jeanrenaud, F.; Stricker-Krongrad, A.; Jeanrenaud, B. The weight-reducing effect of an intracerebroventricular bolus injection of leptin in genetically obese fa/fa rats. Reduced sensitivity compared with lean animals. Diabetes 1996, 45, 1446–1450. [Google Scholar] [CrossRef] [Green Version]
  90. Dryden, S.; King, P.; Pickavance, L.; Doyle, P.; Williams, G. Divergent effects of intracerebroventricular and peripheral leptin administration on feeding and hypothalamic neuropeptide Y in lean and obese (fa/fa) Zucker rats. Clin. Sci. 1999, 96, 307–312. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  91. Seyfried, F.; le Roux, C.W.; Bueter, M. Lessons learned from gastric bypass operations in rats. Obes. Facts 2011, 4 (Suppl. S1), 3–12. [Google Scholar] [CrossRef] [Green Version]
  92. Griffen, S.C.; Wang, J.; German, M.S. A genetic defect in beta-cell gene expression segregates independently from the fa locus in the ZDF rat. Diabetes 2001, 50, 63–68. [Google Scholar] [CrossRef] [PubMed] [Green Version]
  93. Mantovani, A.; Dalbeni, A. Treatments for NAFLD: State of Art. Int. J. Mol. Sci. 2021, 22, 2350. [Google Scholar] [CrossRef]
  94. Fakhry, T.K.; Mhaskar, R.; Schwitalla, T.; Muradova, E.; Gonzalvo, J.P.; Murr, M.M. Bariatric surgery improves nonalcoholic fatty liver disease: A contemporary systematic review and meta-analysis. Surg. Obes. Relat. Dis. 2019, 15, 502–511. [Google Scholar] [CrossRef] [PubMed]
  95. Martinez-Una, M.; Lopez-Mancheno, Y.; Dieguez, C.; Fernandez-Rojo, M.A.; Novelle, M.G. Unraveling the Role of Leptin in Liver Function and Its Relationship with Liver Diseases. Int. J. Mol. Sci. 2020, 21, 9368. [Google Scholar] [CrossRef] [PubMed]
  96. Ye, J.; Hao, Z.; Mumphrey, M.B.; Townsend, R.L.; Patterson, L.M.; Stylopoulos, N.; Munzberg, H.; Morrison, C.D.; Drucker, D.J.; Berthoud, H.R. GLP-1 receptor signaling is not required for reduced body weight after RYGB in rodents. Am. J. Physiol. Regul. Integr. Comp. Physiol. 2014, 306, R352–R362. [Google Scholar] [CrossRef] [Green Version]
  97. Mokadem, M.; Zechner, J.F.; Margolskee, R.F.; Drucker, D.J.; Aguirre, V. Effects of Roux-en-Y gastric bypass on energy and glucose homeostasis are preserved in two mouse models of functional glucagon-like peptide-1 deficiency. Mol. Metab. 2014, 3, 191–201. [Google Scholar] [CrossRef]
  98. Carmody, J.S.; Munoz, R.; Yin, H.; Kaplan, L.M. Peripheral, but not central, GLP-1 receptor signaling is required for improvement in glucose tolerance after Roux-en-Y gastric bypass in mice. Am. J. Physiol. Endocrinol. Metab. 2016, 310, E855–E861. [Google Scholar] [CrossRef] [Green Version]
  99. Li, K.; Zou, J.; Li, S.; Guo, J.; Shi, W.; Wang, B.; Han, X.; Zhang, H.; Zhang, P.; Miao, Z.; et al. Farnesoid X receptor contributes to body weight-independent improvements in glycemic control after Roux-en-Y gastric bypass surgery in diet-induced obese mice. Mol. Metab. 2020, 37, 100980. [Google Scholar] [CrossRef]
  100. Shin, A.C.; Zheng, H.; Townsend, R.L.; Sigalet, D.L.; Berthoud, H.R. Meal-induced hormone responses in a rat model of Roux-en-Y gastric bypass surgery. Endocrinology 2010, 151, 1588–1597. [Google Scholar] [CrossRef] [Green Version]
  101. Svane, M.S.; Jorgensen, N.B.; Bojsen-Moller, K.N.; Dirksen, C.; Nielsen, S.; Kristiansen, V.B.; Torang, S.; Wewer Albrechtsen, N.J.; Rehfeld, J.F.; Hartmann, B.; et al. Peptide YY and glucagon-like peptide-1 contribute to decreased food intake after Roux-en-Y gastric bypass surgery. Int. J. Obes. 2016, 40, 1699–1706. [Google Scholar] [CrossRef]
Nutrients 13 01544 g001 550
Figure 1. Schematic of experimental design. RYGB: Roux-en-Y gastric bypass; POD: postoperative day; BW: body weight; FI: food intake; OGTT: oral glucose tolerance test; DIO: diet-induced obese.
Figure 1. Schematic of experimental design. RYGB: Roux-en-Y gastric bypass; POD: postoperative day; BW: body weight; FI: food intake; OGTT: oral glucose tolerance test; DIO: diet-induced obese.
Nutrients 13 01544 g001
Nutrients 13 01544 g002 550
Figure 2. Leptin receptors are not required for RYGB to normalize energy homeostasis. (a) Body weight in grams (g) of sham-operated fa/+ (lean) Zucker fatty rats (n = 12), sham-operated (obese) fa/fa Zucker fatty rats (n = 12), and RYGB-treated fa/fa Zucker fatty rats (n = 16) during the 27-day monitoring period. (b) Percentage (%) body weight change relative to baseline for RYGB-treated fa/fa rats (n = 16) in (a) and RYGB-treated Wistar rats (n = 11) from Dischinger et al. [82]. (c) Average daily food intake in kilocalories (kcal) in the rats from (a) during the 27-day monitoring period. (d) Fecal energy, (e) visceral white adipose tissue weight and (f) plasma leptin in the rats from (a) at postoperative day 28. Data are presented as mean ± SEM. Statistical significance was determined by one-way ANOVA with Sidak post hoc test in (a,c,e,f) and by two-tailed, unpaired t-test in (b). §§§§ p < 0.0001 for sham-operated fa/+ vs. sham-operated fa/fa Zucker fatty rats, ** p < 0.01 and **** p < 0.0001 for RYGB-treated fa/fa vs. sham-operated fa/fa Zucker fatty rats and #### p < 0.0001, ### p < 0.001 and ## p < 0.01 for RYGB-treated fa/fa vs. sham-operated fa/+ Zucker fatty rats, and + p < 0.05 for RYGB-treated fa/fa Zucker fatty vs. RYGB-treated Wistar rats.
Figure 2. Leptin receptors are not required for RYGB to normalize energy homeostasis. (a) Body weight in grams (g) of sham-operated fa/+ (lean) Zucker fatty rats (n = 12), sham-operated (obese) fa/fa Zucker fatty rats (n = 12), and RYGB-treated fa/fa Zucker fatty rats (n = 16) during the 27-day monitoring period. (b) Percentage (%) body weight change relative to baseline for RYGB-treated fa/fa rats (n = 16) in (a) and RYGB-treated Wistar rats (n = 11) from Dischinger et al. [82]. (c) Average daily food intake in kilocalories (kcal) in the rats from (a) during the 27-day monitoring period. (d) Fecal energy, (e) visceral white adipose tissue weight and (f) plasma leptin in the rats from (a) at postoperative day 28. Data are presented as mean ± SEM. Statistical significance was determined by one-way ANOVA with Sidak post hoc test in (a,c,e,f) and by two-tailed, unpaired t-test in (b). §§§§ p < 0.0001 for sham-operated fa/+ vs. sham-operated fa/fa Zucker fatty rats, ** p < 0.01 and **** p < 0.0001 for RYGB-treated fa/fa vs. sham-operated fa/fa Zucker fatty rats and #### p < 0.0001, ### p < 0.001 and ## p < 0.01 for RYGB-treated fa/fa vs. sham-operated fa/+ Zucker fatty rats, and + p < 0.05 for RYGB-treated fa/fa Zucker fatty vs. RYGB-treated Wistar rats.
Nutrients 13 01544 g002
Nutrients 13 01544 g003 550
Figure 3. Leptin receptors are not required for RYGB to normalize oral glucose tolerance. (a) Blood glucose and the associated area under the curve (AUC), (b) plasma insulin and the associated AUC and (c) plasma GLP-1 and the associated AUC during an oral glucose tolerance test in sham-operated (lean) fa/+ Zucker fatty rats (n = 12), sham-operated (obese) fa/fa Zucker fatty rats (n = 12), and RYGB-treated fa/fa Zucker fatty rats (n = 16) at postoperative day 27. (d) HOMA-IR and (e) ISI-M indices calculated from the rats in (a). Data are presented as mean ± SEM. Statistical significance was determined by one-way ANOVA with Sidak post hoc test. §§§§ p < 0.0001, §§§ p < 0.001, §§ p < 0.01 and § p < 0.05 for sham-operated fa/+ vs. sham-operated fa/fa Zucker fatty rats, **** p < 0.0001, ** p < 0.001 and * p < 0.05 for RYGB-treated fa/fa vs. sham-operated fa/fa Zucker fatty rats and #### p < 0.0001, ### p < 0.001, ## p < 0.01, # p < 0.05 for RYGB-treated fa/fa vs. sham-operated fa/+ Zucker fatty rats.
Figure 3. Leptin receptors are not required for RYGB to normalize oral glucose tolerance. (a) Blood glucose and the associated area under the curve (AUC), (b) plasma insulin and the associated AUC and (c) plasma GLP-1 and the associated AUC during an oral glucose tolerance test in sham-operated (lean) fa/+ Zucker fatty rats (n = 12), sham-operated (obese) fa/fa Zucker fatty rats (n = 12), and RYGB-treated fa/fa Zucker fatty rats (n = 16) at postoperative day 27. (d) HOMA-IR and (e) ISI-M indices calculated from the rats in (a). Data are presented as mean ± SEM. Statistical significance was determined by one-way ANOVA with Sidak post hoc test. §§§§ p < 0.0001, §§§ p < 0.001, §§ p < 0.01 and § p < 0.05 for sham-operated fa/+ vs. sham-operated fa/fa Zucker fatty rats, **** p < 0.0001, ** p < 0.001 and * p < 0.05 for RYGB-treated fa/fa vs. sham-operated fa/fa Zucker fatty rats and #### p < 0.0001, ### p < 0.001, ## p < 0.01, # p < 0.05 for RYGB-treated fa/fa vs. sham-operated fa/+ Zucker fatty rats.
Nutrients 13 01544 g003
Nutrients 13 01544 g004 550
Figure 4. Leptin receptors might be required for RYGB to normalize liver health. (a) Representative hematoxylin and eosin (H&E) staining of liver sections, (b) plasma alanine transferase (ALT), and (c) plasma aspartate transferase (AST) of sham-operated fa/+ (lean) Zucker fatty rats (n = 12), sham-operated (obese) fa/fa Zucker fatty rats (n = 12), and RYGB-treated fa/fa Zucker fatty rats (n = 16) at postoperative day 28. Data are presented as mean ± SEM. Scale bar: 50 µm. Statistical significance was determined by one-way ANOVA with Sidak post hoc test. §§§§ p < 0.0001 for sham-operated fa/+ vs. sham-operated fa/fa Zucker fatty rats and #### p < 0.0001 for RYGB-treated fa/fa vs. sham-operated fa/+ Zucker fatty rats.
Figure 4. Leptin receptors might be required for RYGB to normalize liver health. (a) Representative hematoxylin and eosin (H&E) staining of liver sections, (b) plasma alanine transferase (ALT), and (c) plasma aspartate transferase (AST) of sham-operated fa/+ (lean) Zucker fatty rats (n = 12), sham-operated (obese) fa/fa Zucker fatty rats (n = 12), and RYGB-treated fa/fa Zucker fatty rats (n = 16) at postoperative day 28. Data are presented as mean ± SEM. Scale bar: 50 µm. Statistical significance was determined by one-way ANOVA with Sidak post hoc test. §§§§ p < 0.0001 for sham-operated fa/+ vs. sham-operated fa/fa Zucker fatty rats and #### p < 0.0001 for RYGB-treated fa/fa vs. sham-operated fa/+ Zucker fatty rats.
Nutrients 13 01544 g004
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Share and Cite

MDPI and ACS Style

Hankir, M.K.; Rotzinger, L.; Nordbeck, A.; Corteville, C.; Dischinger, U.; Knop, J.-L.; Hoffmann, A.; Otto, C.; Seyfried, F. Leptin Receptors Are Not Required for Roux-en-Y Gastric Bypass Surgery to Normalize Energy and Glucose Homeostasis in Rats. Nutrients 2021, 13, 1544. https://0-doi-org.brum.beds.ac.uk/10.3390/nu13051544

AMA Style

Hankir MK, Rotzinger L, Nordbeck A, Corteville C, Dischinger U, Knop J-L, Hoffmann A, Otto C, Seyfried F. Leptin Receptors Are Not Required for Roux-en-Y Gastric Bypass Surgery to Normalize Energy and Glucose Homeostasis in Rats. Nutrients. 2021; 13(5):1544. https://0-doi-org.brum.beds.ac.uk/10.3390/nu13051544

Chicago/Turabian Style

Hankir, Mohammed K., Laura Rotzinger, Arno Nordbeck, Caroline Corteville, Ulrich Dischinger, Juna-Lisa Knop, Annett Hoffmann, Christoph Otto, and Florian Seyfried. 2021. "Leptin Receptors Are Not Required for Roux-en-Y Gastric Bypass Surgery to Normalize Energy and Glucose Homeostasis in Rats" Nutrients 13, no. 5: 1544. https://0-doi-org.brum.beds.ac.uk/10.3390/nu13051544

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop