Sleeve Gastrectomy Reduces Hepatic Steatosis by Improving the Coordinated Regulation of Aquaglyceroporins in Adipose Tissue and Liver in Obese Rats.

BACKGROUND: Glycerol constitutes an important metabolite for the control of lipid accumulation and glucose homeostasis. Our aim was to investigate the potential role of aquaglyceroporins, which are glycerol channels mediating glycerol efflux in adipocytes (AQP3 and AQP7) and glycerol influx (AQP9) in hepatocytes, in the improvement of adiposity and hepatic steatosis after sleeve gastrectomy in an experimental model of diet-induced obesity (DIO). METHODS: Male Wistar DIO rats (n = 161) were subjected to surgical (sham operation and sleeve gastrectomy) or dietary interventions [fed ad libitum a normal diet (ND) or a high-fat diet (HFD) or pair-fed to the amount of food eaten by sleeve-gastrectomized animals]. The tissue distribution and expression of AQPs in biopsies of epididymal (EWAT) and subcutaneous (SCWAT) white adipose tissue and liver were analyzed by real-time PCR, Western blot, and immunohistochemistry. RESULTS: Four weeks after surgery, DIO rats undergoing sleeve gastrectomy showed a reduction in body weight, whole-body adiposity, and hepatic steatosis. DIO was associated with a tendency towards an increase in EWAT AQP3 and SCWAT AQP7 and a decrease in hepatic AQP9. Sleeve gastrectomy downregulated AQP7 in both fat depots and upregulated AQP3 in EWAT, without changing hepatic AQP9. Aqp7 transcript levels in EWAT and SCWAT were positively associated with adiposity and glycemia, while Aqp9 mRNA was negatively correlated with markers of hepatic steatosis and insulin resistance. CONCLUSION: Our results show, for the first time, that sleeve gastrectomy, a widely applied bariatric surgery procedure, restores the coordinated regulation of fat-specific AQP7 and liver-specific AQP9, thereby improving whole-body adiposity and hepatic steatosis.

Expression of syntaxin 8 in visceral adipose tissue is increased in obese patients with type 2 diabetes and related to markers of insulin resistance and inflammation.

BACKGROUND AND AIMS: Obesity is associated with increased adipose tissue inflammation as well as with the development of type 2 diabetes (T2D). Syntaxin 8 (STX8) is a protein required for the transport of endosomes. In this study we analyzed the relationship of STX8 with the presence of T2D in the context of obesity. METHODS: With this purpose, 21 subjects (seven lean [LN], eight obese normoglycemic [OB-NG] and six obese with type 2 diabetes [OB-T2D]) were included in the study. Gene and protein expression levels of STX8 and GLUT4 were analyzed in visceral adipose tissue (VAT). RESULTS: mRNA (p = 0.008) and protein (p <0.001) expression levels of STX8 were significantly increased in VAT of OB-T2D patients. Moreover, gene expression levels of SLC2A4 (GLUT4) were downregulated (p = 0.002) in VAT of obese patients. We found that STX8 was positively correlated (p <0.05) with fasting glucose concentrations, plasma glucose 2 h after an OGTT and C-reactive protein. Interestingly, the expression of STX8 was negatively correlated (p <0.05) with the expression of SLC2A4 in VAT. CONCLUSIONS: Increased STX8 expression in VAT appears to be associated with the presence of T2D in obese patients through a mechanism that may involve GLUT4.

Osteopontin deletion prevents the development of obesity and hepatic steatosis via impaired adipose tissue matrix remodeling and reduced inflammation and fibrosis in adipose tissue and liver in mice.

Osteopontin (OPN) is a multifunctional extracellular matrix (ECM) protein involved in multiple physiological processes. OPN expression is dramatically increased in visceral adipose tissue in obesity and the lack of OPN protects against the development of insulin resistance and inflammation in mice. We sought to unravel the potential mechanisms involved in the beneficial effects of the absence of OPN. We analyzed the effect of the lack of OPN in the development of obesity and hepatic steatosis induced by a high-fat diet (HFD) using OPN-KO mice. OPN expression was upregulated in epididymal white adipose tissue (EWAT) and liver in wild type (WT) mice with HFD. OPN-KO mice had higher insulin sensitivity, lower body weight and fat mass with reduced adipose tissue ECM remodeling and reduced adipocyte size than WT mice under a HFD. Reduced MMP2 and MMP9 activity was involved in the decreased ECM remodeling. Crown-like structure number in EWAT as well as F4/80-positive cells and Emr1 expression in EWAT and liver increased with HFD, while OPN-deficiency blunted the increase. Moreover, our data show for the first time that OPN-KO under a HFD mice display reduced fibrosis in adipose tissue and liver, as well as reduced oxidative stress in adipose tissue. Gene expression of collagens Col1a1, Col6a1 and Col6a3 in EWAT and liver, as well as the profibrotic cytokine Tgfb1 in EWAT were increased with HFD, while OPN-deficiency prevented this increase. OPN deficiency prevented hepatic steatosis via reduction in the expression of molecules involved in the onset of fat accumulation such as Pparg, Srebf1, Fasn, Mogat1, Dgat2 and Cidec. Furthermore, OPN-KO mice exhibited higher body temperature and improved BAT function. The present data reveal novel mechanisms of OPN in the development of obesity, pointing out the inhibition of OPN as a promising target for the treatment of obesity and fatty liver.

Effect of sleeve gastrectomy on osteopontin circulating levels and expression in adipose tissue and liver in rats.

BACKGROUND: Sleeve gastrectomy (SG) constitutes an effective procedure for the treatment of morbid obesity. The aim of the present study was to establish in rats the effects of surgically induced weight loss on circulating concentrations and mRNA expression in adipose tissue and liver of osteopontin (OPN), a proinflammatory protein involved in the development of obesity. METHODS: Eighty male diet-induced obese Wistar rats were subjected to surgical interventions [sham operation (SH), SG, or pair-fed to the amount of food eaten by SG animals] and dietary interventions [fed ad libitum with a normal chow diet (ND) or a high-fat diet (HFD)]. Body, epididymal adipose tissue (EWAT), and liver weights were determined. Circulating OPN concentrations and the transcript levels of Spp1 (OPN) in EWAT and liver were analyzed. RESULTS: Rats undergoing SG showed decreased body weight (P < 0.001) and fat mass (P < 0.001) and greater excess weight loss (P < 0.001). The HFD significantly decreased serum OPN levels (P < 0.001). However, SG did not change serum OPN concentrations. OPN expression was dramatically increased in animals fed HFD (P < 0.001) in EWAT, but was unaffected by SG. The expression of OPN in the liver was not affected by HFD or SG. CONCLUSIONS: Circulating OPN levels decreased with HFD feeding remaining unaltered after SG. The expression of Spp1 in EWAT and liver was not modified by SG. The global improvement of metabolism after SG appears not to involve changes in serum OPN concentrations as well as in EWAT and liver expression in rats.

Comparative effects of gastric bypass and sleeve gastrectomy on plasma osteopontin concentrations in humans.

BACKGROUND: Bariatric surgery (BS) has proven to be an effective treatment for morbid obesity. Osteopontin (OPN) is a proinflammatory cytokine involved in the development of obesity. The aim of our study was to determine the effect of weight loss following BS on circulating levels of OPN in humans. METHODS: Body composition and circulating concentrations of OPN and markers of bone metabolism were determined in obese patients who underwent Roux-en-Y gastric bypass (RYGB; n = 40) or sleeve gastrectomy (SG; n = 11). RESULTS: Patients who underwent RYGB or SG showed decreased body weight (P < 0.001) and body fat percentage (P < 0.001) as well as lower insulin resistance. However, plasma OPN levels were significantly increased after RYGB (P < 0.001) but remained unchanged following SG (P = 0.152). Patients who underwent RYGB also showed significantly increased C-terminal telopeptide of type-I collagen (ICTP) (P < 0.01) and osteocalcin (P < 0.001) while bone mineral density tended to decrease (P = 0.086). Moreover, OPN concentrations were positively correlated with the bone resorption marker ICTP after surgery. On the other hand, patients who underwent SG showed significantly increased ICTP levels (P < 0.05), and the change in OPN was positively correlated with the change in ICTP and negatively with the change in vitamin D after surgery (P < 0.05). CONCLUSIONS: RYGB increased circulating OPN levels, while they remained unaltered after SG. The increase in OPN levels after RYGB could be related to the increased bone resorption in relation to its well-known effects on bone of this malabsorptive procedure in comparison to the merely restrictive SG.

Peripheral signalling involved in energy homeostasis control.

The alarming prevalence of obesity has led to a better understanding of the molecular mechanisms controlling energy homeostasis. Regulation of energy intake and expenditure is more complex than previously thought, being influenced by signals from many peripheral tissues. In this sense, a wide variety of peripheral signals derived from different organs contributes to the regulation of body weight and energy expenditure. Besides the well-known role of insulin and adipokines, such as leptin and adiponectin, in the regulation of energy homeostasis, signals from other tissues not previously thought to play a role in body weight regulation have emerged in recent years. The role of fibroblast growth factor 21 (FGF21), insulin-like growth factor 1 (IGF-I), and sex hormone-binding globulin (SHBG) produced by the liver in the regulation of body weight and insulin sensitivity has been recently described. Moreover, molecules expressed by skeletal muscle such as myostatin have also been involved in adipose tissue regulation. Better known is the involvement of ghrelin, cholecystokinin, glucagon-like peptide 1 (GLP-1) and PYY(3-36), produced by the gut, in energy homeostasis. Even the kidney, through the production of renin, appears to regulate body weight, with mice lacking this hormone exhibiting resistance to diet-induced obesity. In addition, the skeleton has recently emerged as an endocrine organ, with effects on body weight control and glucose homeostasis through the actions of bone-derived factors such as osteocalcin and osteopontin. The comprehension of these signals will help in a better understanding of the aetiopathology of obesity, contributing to the potential development of new therapeutic targets aimed at tackling excess body fat accumulation.

Short-term effects of sleeve gastrectomy and caloric restriction on blood pressure in diet-induced obese rats.

BACKGROUND: Sleeve gastrectomy constitutes an effective surgical procedure for the treatment of morbid obesity. The aim of the present study was to establish the effects of sleeve gastrectomy and caloric restriction on weight loss and cardiovascular parameters in diet-induced obese (DIO) rats. METHODS: Male Wistar DIO rats were subjected to surgical interventions (n = 30) (sham operation, sleeve gastrectomy, or pair-fed to the amount of food eaten by sleeve-gastrectomized animals and compared to lean control rats) or dietary interventions (n = 40) (fed ad libitum a normal diet (ND) or a high-fat diet or an ND with a caloric restriction of 25 %). Systolic blood pressure (SBP), diastolic blood pressure, and mean blood pressure values and heart rate (HR) were recorded in conscious, resting animals by noninvasive tail-cuff plethysmography before and 3 weeks after surgical or dietary interventions. RESULTS: Both sleeve gastrectomy and caloric restriction induced a reduction in body weight, whole-body adiposity, and serum leptin together with an increased excess weight loss in DIO rats. Sleeve gastrectomy was further associated with an improvement in insulin resistance and the lipid profile, as well as with a reduction in serum ghrelin levels. A decrease in HR and heart weight was observed in caloric-restricted groups. Sleeve-gastrectomized rats not only exhibited a reduction in HR (∆HR = -45 ± 19 bpm) but also in SBP values (∆SBP = -22 ± 10 mmHg) compared to the DIO rats (∆SBP = 14 ± 8 mmHg). CONCLUSION: Our findings provide evidence that the beneficial effects of sleeve gastrectomy on blood pressure values are beyond weight loss in rats with diet-induced obesity.

Leptin reduces the expression and increases the phosphorylation of the negative regulators of GLUT4 traffic TBC1D1 and TBC1D4 in muscle of ob/ob mice.

Leptin improves insulin sensitivity in skeletal muscle. Our goal was to determine whether proteins controlling GLUT4 traffic are altered by leptin deficiency and in vivo leptin administration in skeletal muscle of wild type and ob/ob mice. Leptin-deficient ob/ob mice were divided in three groups: control, leptin-treated (1 mg/kg/d) and leptin pair-fed ob/ob mice. Microarray analysis revealed that 1,546 and 1,127 genes were regulated by leptin deficiency and leptin treatment, respectively. Among these, we identified 24 genes involved in intracellular vesicle-mediated transport in ob/ob mice. TBC1 domain family, member 1 (Tbc1d1), a negative regulator of GLUT4 translocation, was up-regulated (P = 0.001) in ob/ob mice as compared to wild types. Importantly, leptin treatment reduced the transcript levels of Tbc1d1 (P<0.001) and Tbc1d4 (P = 0.004) in the leptin-treated ob/ob as compared to pair-fed ob/ob animals. In addition, phosphorylation levels of TBC1D1 and TBC1D4 were enhanced in leptin-treated ob/ob as compared to control ob/ob (P = 0.015 and P = 0.023, respectively) and pair-fed ob/ob (P = 0.036 and P = 0.034, respectively) mice. Despite similar GLUT4 protein expression in wild type and ob/ob groups a different immunolocalization of this protein was evidenced in muscle sections. Leptin treatment increased GLUT4 immunoreactivity in gastrocnemius and extensor digitorum longus sections of leptin-treated ob/ob mice. Moreover, GLUT4 protein detected in immunoprecipitates from TBC1D4 was reduced by leptin replacement compared to control ob/ob (P = 0.013) and pair-fed ob/ob (P = 0.037) mice. Our findings suggest that leptin enhances the intracellular GLUT4 transport in skeletal muscle of ob/ob animals by reducing the expression and activity of the negative regulators of GLUT4 traffic TBC1D1 and TBC1D4.

Sleeve gastrectomy reduces blood pressure in obese (fa/fa) Zucker rats.

BACKGROUND: Sleeve gastrectomy constitutes an effective surgical procedure for the treatment of morbid obesity in humans and rodents with diet-induced obesity. The aim of the present study was to establish the effects of sleeve gastrectomy on weight loss and cardiovascular parameters in genetically obese (fa/fa) Zucker rats. METHODS: Eleven-week-old male obese (fa/fa) (n = 20) Zucker rats were assigned to three alternative procedures (sham operation, sleeve gastrectomy, or pair-fed to the amount of food eaten by sleeve-gastrectomized animals) and compared with lean Zucker (Fa/Fa) rats (n = 9). Systolic (SBP), diastolic (DBP), and mean (MBP) blood pressure values as well as heart rate (HR) were recorded in conscious, resting animals by non-invasive tail-cuff plethysmography before and 3 weeks after the surgical interventions. RESULTS: Sleeve-gastrectomized rats experienced a reduction in body weight (P < 0.01), total adiposity amounts (P < 0.001), together with an increased excess weight loss (%EWL) (P < 0.05) compared with sham-operated and pair-fed animals 3 weeks after the surgical interventions. Rats with sleeve gastrectomy exhibited reduced (P < 0.01) blood pressure values (ΔSBP = -11 ± 8 mmHg; ΔDBP = -6 ± 4 mmHg; ΔMBP = -8 ± 6 mmHg) compared with the control group, but no changes were observed in HR (P = 0.560). Sham-operated and pair-fed groups did not alter their cardiovascular variables. CONCLUSIONS: Our findings provide evidence of the beneficial effects of sleeve gastrectomy on blood pressure values in addition to the weight loss in obese (fa/fa) Zucker rats independently of surgical trauma and food intake reduction.

Sleeve gastrectomy induces weight loss in diet-induced obese rats even if high-fat feeding is continued.

BACKGROUND: Sleeve gastrectomy (SG) has been used for the surgical treatment of morbid obesity as a first or definitive procedure with satisfactory results. The objective of this study in rats was to establish the effects of SG on weight loss depending on the post-surgical type of diet followed. METHODS: Thirty male Wistar rats were fed ad libitum during 3 months on a high-fat diet (HFD) to induce obesity. After this first phase, rats were subdivided in three groups of ten rats each and underwent a sham intervention, an SG, or no surgery but were pair-fed to the amount of food eaten by the animals of the SG group. At this time point, half of the animals in each group continued to be fed on the HFD, while the other half was switched to a normal chow diet (ND). Thus, the following subgroups were established: sham-ND, sleeve-ND, pair-fed-ND as well as sham-HFD, sleeve-HFD, and pair-fed-HFD. Body weight and food intake were recorded daily for 4 weeks. The feed efficiency rate (FER) was determined from weekly weight gains and caloric consumption during this period. RESULTS: Statistically significant (P < 0.05) differences in body weight were observed between the six experimental groups after 4 weeks of the interventions with rats in the sleeve-ND group experimenting the highest weight loss (-78.2 ± 10.3 g) and animals in the pair-fed-HFD group exhibiting the lowest weight reduction (-4.0 ± 0.1 g). Interestingly, the FER value of rats that underwent the SG and continued to be fed on a HFD was significantly (P < 0.05) lower than that of sham operated and pair-fed animals on the same diet. CONCLUSION: The positive effects of SG on weight reduction are observed in obese rats submitted to the intervention and subsequently following an ND or even an HFD.