Obese Rodents Research Articles

Short- and Long-Term High-Fat Diet Exposure Differentially Alters Phasic and Tonic GABAergic Signaling onto Lateral Orbitofrontal Pyramidal Neurons.

The chronic consumption of caloric dense high-fat foods is a major contributor to increased body weight, obesity, and other chronic health conditions. The orbitofrontal cortex (OFC) is critical in guiding decisions about food intake and is altered with diet-induced obesity. Obese rodents have altered morphologic and synaptic electrophysiological properties in the lateral orbitofrontal cortex (lOFC). Yet the time course by which exposure to a high-fat diet (HFD) induces these changes is poorly understood. Here, male mice are exposed to either short-term (7 d) or long-term (90 d) HFD. Long-term HFD exposure increases body weight, and glucose signaling compared with short-term HFD or a standard control diet (SCD). Both short and long-term HFD exposure increased the excitability of lOFC pyramidal neurons. However, phasic and tonic GABAergic signaling was differentially altered depending on HFD exposure length, such that tonic GABAergic signaling was decreased with early exposure to the HFD and phasic signaling was changed with long-term diet exposure. Furthermore, alterations in the short-term diet exposure were transient, as removal of the diet restored electrophysiological characteristics similar to mice fed SCD, whereas long-term HFD electrophysiological changes were persistent and remained after HFD removal. Finally, we demonstrate that changes in reward devaluation occur early with diet exposure. Together, these results suggest that the duration of HFD exposure differentially alters lOFC function and provides mechanistic insights into the susceptibility of the OFC to impairments in outcome devaluation.SIGNIFICANCE STATEMENT This study provides mechanistic insight on the impact of short-term and long-term high-fat diet (HFD) exposure on GABAergic function in the lateral orbitofrontal cortex (lOFC), a region known to guide decision-making. We find short-term HFD exposure induces transient changes in firing and tonic GABA action on lOFC pyramidal neurons, whereas long-term HFD induces obesity and has lasting changes on firing, tonic GABA and inhibitory synaptic transmission onto lOFC neurons. Given that GABAergic signaling in the lOFC can influence decision-making around food, these results have important implications in present society as palatable energy dense foods are abundantly available.

Abstract 045: High Fat Diet Increases Blood Pressure In Sprague Dawley Rats And Induces Salt Sensitive Hypertension: Role Of NKCC2 In The Thick Ascending Limb (TAL)

The Western Diet is characterized by elevated added sugars, fat, and salt and is known to promote hypertension. Chronic high fat intake induces obesity in rodents but the effects on blood pressure are variable between rat/mouse strains. The early effects of a high fat diet, prior to the onset of obesity, in kidney function, signaling and NaCl reabsorption have been poorly studied. In the kidneys, the thick ascending limb (TAL) absorbs 25% of filtered NaCl through the apical Na/K/2Cl cotransporter NKCC2. NKCC2 is activated by phosphorylation at residues Thr 96,101 , or Ser 126 or by increasing its trafficking to the apical surface. The effects of a high fat diet on NKCC2 activity and blood pressure have been poorly studied in the Sprague Dawley (SD) rat, a widely used rodent model. We hypothesized that a high fat diet (60%kCal saturated fat, HF) activates NKCC2 and induces salt sensitive hypertension. We first tested the effects HF on blood pressure (BP). SD rats (Charles Rivers) were trained for tail cuff SBP and placed on HF or control diet for 4 weeks. After 2 weeks, HF diet increased SBP by 9±4 mmHg and at 4 weeks by 13±4 mmHg (p<0.05). We then added high salt diet (4% Na, HS, n=7) which further increased SBP by 19±5 mmHg in HF rats reaching 151±5 mmHg after 4 weeks. SBP did not change in rats fed HS or HF alone (HS: 121±4, HF: 132±4 mmHg, p<0.05 vs HF+HS). In isolated TALs, 2 weeks of HF did not change total NKCC2 expression or P-Thr 96,101 , but enhanced P-Ser 126 NKCC2 (78±26%, p<0.05) and increased surface/intracellular NKCC2 ratio by 22±8% (p<0.03). After 8 weeks of HF diet, surface to intracellular NKCC2 was higher in HF (+54±9% from HS, p<0.05) and HF+HS rats (+40±18% of HS) compared to those fed HS alone. Body weight gain was similar in groups after 2 weeks, but after 8 weeks, rats on HF or HF+HS gained more weight than HS alone (p<0.05). Blood glucose was not different between groups. Our data suggest that 2 weeks of a HF diet induces early signaling in TALs, prior to obesity, that may contribute to increase BP or induce salt sensitivity in normal rats.

Obesity-associated microglial inflammatory activation paradoxically improves glucose tolerance

Hypothalamic gliosis associated with high-fat diet (HFD) feeding increases susceptibility to hyperphagia and weight gain. However, the body-weight-independent contribution of microglia to glucose regulation has not been determined. Here, we show that reducing microglial nuclear factor κB (NF-κB) signaling via cell-specific IKKβ deletion exacerbates HFD-induced glucose intolerance despite reducing body weight and adiposity. Conversely, two genetic approaches to increase microglial pro-inflammatory signaling (deletion of an NF-κB pathway inhibitor and chemogenetic activation through a modified Gq-coupled muscarinic receptor) improved glucose tolerance independently of diet in both lean and obese rodents. Microglial regulation of glucose homeostasis involves a tumor necrosis factor alpha (TNF-α)-dependent mechanism that increases activation of pro-opiomelanocortin (POMC) and other hypothalamic glucose-sensing neurons, ultimately leading to a marked amplification of first-phase insulin secretion via a parasympathetic pathway. Overall, these data indicate that microglia regulate glucose homeostasis in a body-weight-independent manner, an unexpected mechanism that limits the deterioration of glucose tolerance associated with obesity.

GDF15 increases insulin action in the liver and adipose tissue via a β-adrenergic receptor-mediated mechanism

Growth differentiation factor 15 (GDF15) induces weight loss and increases insulin action in obese rodents. Whether and how GDF15 improves insulin action without weight loss is unknown. Obese rats were treated with GDF15 and displayed increased insulin tolerance 5h later. Lean and obese female and male mice were treated with GDF15 on days 1, 3, and 5 without weight loss and displayed increased insulin sensitivity during a euglycemic hyperinsulinemic clamp on day 6 due to enhanced suppression of endogenous glucose production and increased glucose uptake in WAT and BAT. GDF15 also reduced glucagon levels during clamp independently of the GFRAL receptor. The insulin-sensitizing effect of GDF15 was completely abrogated in GFRAL KO mice and also by treatment with the β-adrenergic antagonist propranolol and in β1,β2-adrenergic receptor KO mice. GDF15 activation of the GFRAL receptor increases β-adrenergic signaling, in turn, improving insulin action in the liver and white and brown adipose tissue.

Dietary pulses as a means to improve the gut microbiome, inflammation, and appetite control in obesity.

A dysbiotic intestinal microbiome has been linked to chronic diseases such as obesity, which may suggest that interventions that target the microbiome may be useful in treating obesity and its complications. Appetite dysregulation and chronic systemic low-grade inflammation, such as that observed in obesity, are possibly linked with the intestinal microbiome and are potential therapeutic targets for the treatment of obesity via the microbiome. Dietary pulses (e.g., common beans) are composed of nutrients and compounds that possess the potential to modulate the gut microbiota composition and function which can in turn improve appetite regulation and chronic inflammation in obesity. This narrative review summarizes the current state of knowledge regarding the connection between the gut microbiome and obesity, appetite regulation, and systemic and adipose tissue inflammation. More specifically, it highlights the efficacy of interventions employing dietary common beans as a means to improve gut microbiota composition and/or function, appetite regulation, and inflammation in both rodent obesity and in humans. Collectively, results presented and discussed herein provide insight on the gaps in knowledge necessary for a comprehensive understanding of the potential of beans as a treatment for obesity while highlighting what further research is required to gain this understanding.

Green Tea Induces the Browning of Adipose Tissue—Systematic Review

Several foods and nutrients are being studied extensively because they have a positive effect on thermogenesis and the browning of white adipose tissue. Therefore, this study aims to evaluate, through a systematic review, the effect of green tea for inducing browning of adipose tissue. The systematic review was built following the recommendations of the Preferred Reporting Items for Systematic Reviews and Meta-Analyze. We searched the following electronic databases: PubMed (Medline), Science Direct, Scopus, and Web of Science. We included ten experimental articles that used green tea to treat induced obesity in rodents. Green tea reduced the weight of white and brown adipose tissue, positively regulated gene expression and microRNA that regulate the metabolism of adipose tissue, and morphological changes were identified as beige tissue. According to the results found, the factors involved in this induction to browning are PPARγ, PGC-1α, UCP1, CPT, and PRDM16. Therefore, green tea promotes the browning of adipose tissue in rodents. It is important to emphasize the need for studies in obese humans to identify whether the same metabolic response occurs.

Exercise ameliorates chronic inflammatory response induced by high-fat diet via Sestrin2 in an Nrf2-dependent manner

Chronic inflammation is a major contributor to the development of metabolic disorders and is commonly seen in studies of diet-induced obesity in humans and rodents. Exercise has been shown to have anti-inflammatory properties, though the exact mechanisms are still not fully understood. Sestrins and Nrf2 are of interest to researchers as they are known to protect against inflammation and oxidative stress. In this study, we aim to explore the interconnection between Sestrin2 (SESN2) and Nrf2 and their roles in exercise benefits on chronic inflammation. Our data showed that SESN2 knockout aggravated the abnormalities of body weight, fat mass, and serum lipid that were induced by a high-fat diet (HFD), and a concomitant increase of TNF-α, IL-1β and IL-6 in both serum and skeletal muscle. Notably, exercise was found to reverse these changes, and SESN2 was found to be necessary for exercise to reduce the inflammatory response in skeletal muscles, though not in serum. Immunoprecipitation and bioinformatics prediction experiments further revealed that SESN2 directly binds to Nrf2, indicating a protein-protein interaction between the two. Furthermore, our data demonstrated that SESN2 protein is necessary for exercise-induced effects on Nrf2 pathway in HFD-fed mice, and Nrf2 protein is necessary to enable SESN2 to reduce the inflammation caused by palmitic acid (PA)+ oleic acid (OA) treatment in vitro. Our findings indicate that exercise mitigates chronic inflammation induced by HFD through SESN2 in an Nrf2-dependent manner. Our study reveals a novel molecular mechanism whereby the SESN2/Nrf2 pathway mediates the positive impact of exercise on chronic inflammation.

Sudachitin and Nobiletin Stimulate Lipolysis via Activation of the cAMP/PKA/HSL Pathway in 3T3-L1 Adipocytes.

Polymethoxyflavones are flavonoids that are abundant in citrus fruit peels and have beneficial effects on human health. Previous studies have demonstrated that the polymethoxyflavones, namely sudachitin and nobiletin, ameliorate obesity and diabetes in humans and rodents. Although nobiletin induces lipolysis in adipocytes, lipolytic pathway activation by sudachitin has not been clarified in adipocytes. In this study, the effect of sudachitin on lipolysis was elucidated in murine 3T3-L1 adipocytes. Glycerol release into the medium and activation of the cyclic AMP (cAMP)/protein kinase A (PKA)/hormone-sensitive lipase (HSL) pathway was evaluated in 3T3-L1-differentiated adipocytes. Treatment with sudachitin and nobiletin for 24 and 48 h did not induce cytotoxicity at concentrations of up to 50 μM. Sudachitin and nobiletin at concentrations of 30 and 50 μM increased intracellular cAMP and medium glycerol levels in 3T3-L1 adipocytes. Western blotting revealed that sudachitin and nobiletin dose-dependently increased protein levels of phosphorylated PKA substrates and phosphorylated HSL. Sudachitin- and nobiletin-induced glycerol release, phosphorylation of PKA substrates, and HSL phosphorylation were suppressed by pharmacological inhibition of adenylate cyclase and PKA. These findings indicated that sudachitin, similar to nobiletin, exerts anti-obesogenic effects, at least in part through the induction of lipolysis in adipocytes.

Childhood obesity is linked to putative neuroinflammation in brain white matter, hypothalamus, and striatum.

Neuroinflammation is both a consequence and driver of overfeeding and weight gain in rodent obesity models. Advances in magnetic resonance imaging (MRI) enable investigations of brain microstructure that suggests neuroinflammation in human obesity. To assess the convergent validity across MRI techniques and extend previous findings, we used diffusion basis spectrum imaging (DBSI) to characterize obesity-associated alterations in brain microstructure in 601 children (age 9-11years) from the Adolescent Brain Cognitive DevelopmentSM Study. Compared with children with normal-weight, greater DBSI restricted fraction (RF), reflecting neuroinflammation-related cellularity, was seen in widespread white matter in children with overweight and obesity. Greater DBSI-RF in hypothalamus, caudate nucleus, putamen, and, in particular, nucleus accumbens, correlated with higher baseline body mass index and related anthropometrics. Comparable findings were seen in the striatum with a previously reported restriction spectrum imaging (RSI) model. Gain in waist circumference over 1 and 2 years related, at nominal significance, to greater baseline RSI-assessed restricted diffusion in nucleus accumbens and caudate nucleus, and DBSI-RF in hypothalamus, respectively. Here we demonstrate that childhood obesity is associated with microstructural alterations in white matter, hypothalamus, and striatum. Our results also support the reproducibility, across MRI methods, of findings of obesity-related putative neuroinflammation in children.

Setmelanotide, a melanocortin-4-receptor agonist, increases the hypercapnic ventilatory response and relieves hypoventilation in obese mice

Introduction: Obesity leads to high cardiorespiratory morbidity and mortality. Obese individuals can develop obesity hypoventilation syndrome (OHS) characterized by daytime hypercapnia in the absence of alternative underlying causes. OHS leads to daytime sleepiness, cardiovascular complications, and cyanosis. There is no effective pharmacotherapy for OHS. Leptin, an adipose-produced hormone, improves breathing in OHS, but obese individuals and rodents are resistant to the beneficial effects of leptin. The melanocortin axis is a downstream target of leptin but effects of this axis on control of breathing are poorly studied. Setmelanotide is an FDA-approved drug for weight loss that specifically binds to the melanocortin 4 receptor (MC4R). We have previously demonstrated that C57BL/6J mice with diet induced obesity (DIO) hypoventilate during sleep and exhibit all features of OHS. We hypothesized that the activation of MC4R by setmelanotide augments the control of breathing during sleep in DIO mice. Methods: We performed a proof-of-concept single dose randomized trial of intraperitoneal setmelanotide (1.0 mg/kg) vs vehicle in DIO C57BL/6J mice using a cross-over design. The injections were followed by sleep studies, and measurements of the hypercapnic ventilatory response, oxygen consumption (VO2), and carbon dioxide production (VCO2). Results: Activation of MC4R by setmelanotide increased inspiratory flow, respiratory rate, and minute ventilation during NREM and REM sleep compared to vehicle. Activation of MC4R by setmelanotide increased the hypercapnic ventilatory response. Setmelanotide also increased VCO2, and VO2, but the ventilation was increased out of proportion to the upregulation of metabolism, which was evident from increases in the VE/VO2 and VE/VCO2 ratios. Conclusion: Activation of MC4R by setmelanotide relieved hypoventilation during sleep and increased the hypercapnic ventilatory response in obese mice. Our study identified MC4 as a promising therapeutic target in OHS. NIH (R01 HL128970, R01 HL133100, and R01 HL138932), AHA (#915167). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

The catabolism of bilirubin to urobilin might be a leading factor in obesity-induced insulin resistance: New findings in human studies

For unknown reasons, plasma bilirubin levels are lower in obese humans and rodents. One possible explanation is that the hepatic expression of enzymes that regulate its half-life, such as the UGT1A1 UDP-glucuronosyltransferase, is higher in the obese compared to lean persons. Bilirubin is marked for excretion within the liver by the conjugation of two glucuronyl groups by UGT1A1, where it is then transported to the intestines by the biliary system. Once in the intestines, the gut microbiota containing bilirubin reductase remove the glucornyl groups and modify the structure to produce urobilin which can be absorbed via the hepatic portal vein and enter the systemic circulation. Previous correlation studies indicate that urobilin might be a factor that induces visceral obesity and cardiovascular disease. However, the physiological function of urobilin is unknown. The purpose of our study was to determine if there is a correlation between bilirubin and urobilin compared to adiposity and insulin resistance in lean and obese women and men. We hypothesized that bilirubin would be lower and urobilin higher in the plasma of obese humans compared to lean. We found that the plasma levels of urobilin and bilirubin are inversely correlated in women and men. Urobilin levels were positively associated with adiposity (BMI R 2 =0.29 and body fat percentage R 2 =0.25) and insulin resistance (blood glucose R 2 =0.05, insulin R 2 =0.22, and HOMA IR R 2 =0.18) in obese women. Urobilin was only correlated with adiposity in males (BMI R 2 =0.025 and body fat percentage R 2 =0.03). However, the males were not insulin resistant and had no significant difference in HOMA IR compared to lean men. In both women (BMI R 2 =0.065 and body fat percentage R 2 =0.05) and men (BMI R 2 =0.24 and body fat percentage R 2 =0.13), plasma bilirubin levels were negatively associated with adiposity. We observed that plasma bilirubin levels are negatively associated with adiposity, which has been previously reported. The new findings in our study indicate that urobilin is positively associated with adiposity and insulin resistance. Based on these data, we propose that bilirubin and urobilin are maintained at inverse levels in humans via the UGT1A1 axis and that activity is higher in the obese, reducing plasma bilirubin and providing more substrates to produce urobilin in the gut. These events cause an elevation in plasma urobilin levels that commence obesity-associated comorbidities. Future work to determine the role of urobilin in obesity-associated comorbidities such as insulin-resistant diabetes is warranted and may provide a biomarker for the early This work was supported by the National Institutes of Health R01DK121797 (T.D.H.J.). The sample collection was supported by the Center for Clinical and Translational Science (CCTS) grant UL1TR001998 at the University of Kentucky. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

High Fat Diet Suppresses Energy Expenditure Via Neurons in the Brainstem

Oxidation of fat by brown adipose tissue (BAT) contributes to energy balance and heat production. During cold exposure, BAT thermogenesis produces heat to warm the body. Obese subjects and rodents, however, show impaired BAT thermogenesis to the cold. Our previous studies suggest that vagal afferents synapsing in the nucleus tractus solitarius (NTS), tonically inhibit BAT thermogenesis to the cold in obese rats. NTS neurons send projections to the dorsal aspect of the lateral parabrachial nucleus (LPBd), which is a major integrative center that receives warm afferent inputs from the periphery and promotes inhibition of BAT thermogenesis. This study investigated the contribution of LPBd neurons in the impairment of BAT thermogenesis in rats fed a high-fat diet (HFD). By using a targeted dual viral vector approach, we found that chemogenetic activation of an NTS-LPB pathway inhibited BAT thermogenesis to the cold. We also found that the number of Fos-labelled neurons in the LPBd was higher in rats fed a HFD than in chow diet-fed rats after exposure to a cold ambient temperature. Nanoinjections of a GABAA receptor agonist into the LPBd area rescued BAT thermogenesis to the cold in HFD rats. These data reveal the LPBd as a critical brain area that tonically suppresses energy expenditure in obesity during skin cooling. These findings reveal novel effects of high-fat diets in the brain and in the control of metabolism and can contribute to the development of therapeutic approaches to regulate fat metabolism.

Ascorbic acid reduces insulin resistance and pancreatic steatosis by regulating adipocyte hypertrophy in obese ovariectomized mice.

Ascorbic acid has been suggested to regulate obesity in obese male rodents.Moreover, increased adipocyte size has been associated with metabolic disease. Thus, we investigated the effects of ascorbic acid on adipocyte hypertrophy and insulin resistance in high-fat diet (HFD)-induced obese ovariectomized (OVX) C57BL/6J mice, an animal model of obese postmenopausal women. Administration of ascorbic acid (5%w/w in diet for 18 weeks) reduced the size of visceral adipocytes without changes in body weight and adipose tissue mass in HFD-fed obese OVX mice compared with obese OVX mice that did not receive ascorbic acid. Ascorbic acid inhibited adipose tissue inflammation, as shown by the decreased number of crown-like structures and CD68-positive macrophages in visceral adipose tissues. Ascorbic acid-treated mice exhibited improved hyperglycemia, hyperinsulinemia, and glucose and insulin tolerance compared with nontreated obese mice. Pancreatic islet size and insulin-positive β-cell area in ascorbic acid-treated obese OVX mice decreased to the levels observed in low-fat diet-fed lean mice. Ascorbic acid also suppressed pancreatic triglyceride accumulation in obese mice. These results suggest that ascorbic acid may reduce insulin resistance and pancreatic steatosis partly by suppressing visceral adipocyte hypertrophy and adipose tissue inflammation in obese OVX mice.

Leptin deficiency-caused behavioral change - A comparative analysis using EthoVision and DeepLabCut.

Obese rodents e.g., the leptin-deficient (ob/ob) mouse exhibit remarkable behavioral changes and are therefore ideal models for evaluating mental disorders resulting from obesity. In doing so, female as well as male ob/ob mice at 8, 24, and 40 weeks of age underwent two common behavioral tests, namely the Open Field test and Elevated Plus Maze, to investigate behavioral alteration in a sex- and age dependent manner. The accuracy of these tests is often dependent on the observer that can subjectively influence the data. To avoid this bias, mice were tracked with a video system. Video files were further analyzed by the compared use of two software, namely EthoVision (EV) and DeepLabCut (DLC). In DLC a Deep Learning application forms the basis for using artificial intelligence in behavioral research in the future, also with regard to the reduction of animal numbers. After no sex and partly also no age-related differences were found, comparison revealed that both software lead to almost identical results and are therefore similar in their basic outcomes, especially in the determination of velocity and total distance movement. Moreover, we observed additional benefits of DLC compared to EV as it enabled the interpretation of more complex behavior, such as rearing and leaning, in an automated manner. Based on the comparable results from both software, our study can serve as a starting point for investigating behavioral alterations in preclinical studies of obesity by using DLC to optimize and probably to predict behavioral observations in the future.

Which housekeeping gene is the best choice for RT-qPCR analysis in mice fed with a high-fat diet? Studies in the liver, kidney, pancreas, and intestines

High-fat diet (HFD)-induced obesity in rodents in association with Reverse Transcription and real-time Polymerase Chain Reaction (RT-qPCR) analysis have been extensively used to investigate the gene expression regulation in metabolic syndrome. qPCR requires careful standardization, and the commonly chosen housekeeping genes (HKGs) are involved in basal metabolic pathways, which makes the choice of HKG more difficult in obesity-related studies. In this study, we investigated the expression and stability of putative HKGs, such as Ppia, Tubb2a, Tfrc, Tbp, Mrpl32, Gusb, Rn18s, Rplp0, Hprt-1, B2m, Gapdh and Actb in the liver, kidney, endocrine and exocrine pancreas, small and large intestines of HFD-treated mice. The Ct values were used to determine the stability of HKG expression by RefFinder, comparing the GeNorm, NormFinder, BestKeeper, and comparative delta-Ct method algorithms. The influence of the diet on putative HKGs expression was also evaluated by 2-ΔΔCt analysis. The most stable HKGs were: Tbp and Mrpl32 in the liver, Mrpl32 and Tubb2a in the kidney, Hrpt-1 and Gapdh in the pancreatic islets and cecum, Tbp and Ppia for the exocrine pancreas, and Rn18s, Hrpt-1, and Actb for jejunum. On the contrary, Tubb2a|Trfc must be avoided to normalize the qPCR data from the HFD liver, B2m from the kidney, Trfc|Ppia and Tubb2a|B2m from the endocrine and exocrine pancreas, respectively, B2m from the jejunum, and Rn18s and Actb from the cecum portion of the large intestine. We provided the best and worse HKGs to use in the RT-qPCR analysis of tissues involved in the regulation of energy metabolism in the HFD mice model.

Sleeve Gastrectomy-Induced Weight Loss Increases Insulin Clearance in Obese Mice.

Sleeve gastrectomy (SG) successfully recovers metabolic homeostasis in obese humans and rodents while also resulting in the normalization of insulin sensitivity and insulinemia. Reduced insulin levels have been attributed to lower insulin secretion and increased insulin clearance in individuals submitted to SG. Insulin degradation mainly occurs in the liver in a process controlled, at least in part, by the insulin-degrading enzyme (IDE). However, research has yet to explore whether liver IDE expression or activity is altered after SG surgery. In this study, C57BL/6 mice were fed a chow (CTL) or high-fat diet (HFD) for 10 weeks. Afterward, the HFD mice were randomly assigned to two groups: sham-surgical (HFD-SHAM) and SG-surgical (HFD-SG). Here, we confirmed that SG improves glucose-insulin homeostasis in obese mice. Additionally, SG reduced insulinemia by reducing insulin secretion, assessed by the analysis of plasmatic C-peptide content, and increasing insulin clearance, which was evaluated through the calculation of the plasmatic C-peptide:insulin ratio. Although no changes in hepatic IDE activity were observed, IDE expression was higher in the liver of HFD-SG compared with HFD-SHAM mice. These results indicate that SG may be helpful to counteract obesity-induced hyperinsulinemia by increasing insulin clearance, likely through enhanced liver IDE expression.

Bilirubin Levels Are Negatively Correlated with Adiposity in Obese Men and Women, and Its Catabolized Product, Urobilin, Is Positively Associated with Insulin Resistance.

Bilirubin levels in obese humans and rodents have been shown to be lower than in their lean counterparts. Some studies have proposed that the glucuronyl UGT1A1 enzyme that clears bilirubin from the blood increases in the liver with obesity. UGT1A1 clearance of bilirubin allows more conjugated bilirubin to enter the intestine, where it is catabolized into urobilin, which can be then absorbed via the hepatic portal vein. We hypothesized that when bilirubin levels are decreased, the urobilin increases in the plasma of obese humans, as compared to lean humans. To test this, we measured plasma levels of bilirubin and urobilin, body mass index (BMI), adiposity, blood glucose and insulin, and HOMA IR in a small cohort of obese and lean men and women. We found that bilirubin levels negatively correlated with BMI and adiposity in obese men and women, as compared to their lean counterparts. Contrarily, urobilin levels were positively associated with adiposity and BMI. Only obese women were found to be insulin resistant based on significantly higher HOMA IR, as compared to lean women. The urobilin levels were positively associated with HOMA IR in both groups, but women had a stronger linear correlation. These studies indicate that plasma urobilin levels are associated with obesity and its comorbidities, such as insulin resistance.

Finding balance: understanding the energetics of time-restricted feeding in mice.

Over the course of mammalian evolution, the ability to store energy likely conferred a survival advantage when food became scarce. A long-term increase in energy storage results from an imbalance between energy intake and energy expenditure, two tightly regulated parameters that generally balance out to maintain a fairly stable body weight. Understanding the molecular determinants of this feat likely holds the key to new therapeutic development to manage obesity and associated metabolic dysfunctions. Time-restricted feeding (TRF), a dietary intervention that limits feeding to the active phase, can prevent and treat obesity and metabolic dysfunction in rodents fed a high-fat diet, likely by exerting effects on energetic balance. Even when body weight is lower in mice on active-phase TRF, food intake is generally isocaloric as compared with ad libitum fed controls. This discrepancy between body weight and energy intake led to the hypothesis that energy expenditure is increased during TRF. However, at present, there is no consensus in the literature as to how TRF affects energy expenditure and energy balance as a whole, and the mechanisms behind metabolic adaptation under TRF are unknown. This review examines our current understanding of energy balance on TRF in rodents and provides a framework for future studies to evaluate the energetics of TRF and its molecular determinants.

Impaired rate-dependent depression of the H-reflex in type-2 diabetes, prediabetes, overweight and obesity: A cross-sectional study.

Type-2 diabetes is a chronic metabolic disorder characterized by hyperglycemia, resulting from deficits in insulin secretion or insulin resistance. According to the International Diabetes Federation, approximately 463 million people suffered from this condition in 2019, with a rapidly increasing impact in low-and middle-income countries. Obesity is a well-known risk factor for diabetes, and current data project a continuous increase in diabetes prevalence worldwide in obese individuals. Among the common complications, diabetic peripheral neuropathy (DPN) causes sensory symptoms, including pain that contributes to foot ulceration, and if not controlled, limb amputation may occur. The diagnosis of DPN is a clinical problem. Rate-dependent depression (RDD) of the Hoffmann reflex in the lower limbs has been proposed as a test to determine the presence of neuropathic pain in subjects with type-1 and type-2 diabetes. Recently, impaired RDD has been described in obese and diabetic rodent models. In this study, we characterized the RDD by evaluating the H-reflex at 0.2, 1, 2, 5, and 10 Hz in 39 patients with type-2 Diabetes mellitus (T2DM) and 42 controls without diabetes, subsequently classified as overweight/obese and prediabetic. A significant decrease in the RDD of the H-reflex was found in T2DM subjects at 1, 2, 5, and 10 Hz (P < .001) stimulation frequencies compared to controls, but not at 0.2 Hz (P = .48). A major finding of this study is that impaired RDD was also found in 11/25 overweight and obese subjects in at least 2 stimulation frequencies, being 10 of those classified in prediabetic levels according to their HbA1C values. The RDD of the H-reflex could be used as a quantitative and sensitive tool to study T2DM subpopulations with peripheral neuropathy. RDD could be used as a screening tool in combination with clinical tests to diagnose DPN and evaluate the progression of this condition.

The aldolase inhibitor aldometanib mimics glucose starvation to activate lysosomal AMPK

The activity of 5′-adenosine monophosphate-activated protein kinase (AMPK) is inversely correlated with the cellular availability of glucose. When glucose levels are low, the glycolytic enzyme aldolase is not bound to fructose-1,6-bisphosphate (FBP) and, instead, signals to activate lysosomal AMPK. Here, we show that blocking FBP binding to aldolase with the small molecule aldometanib selectively activates the lysosomal pool of AMPK and has beneficial metabolic effects in rodents. We identify aldometanib in a screen for aldolase inhibitors and show that it prevents FBP from binding to v-ATPase-associated aldolase and activates lysosomal AMPK, thereby mimicking a cellular state of glucose starvation. In male mice, aldometanib elicits an insulin-independent glucose-lowering effect, without causing hypoglycaemia. Aldometanib also alleviates fatty liver and nonalcoholic steatohepatitis in obese male rodents. Moreover, aldometanib extends lifespan and healthspan in both Caenorhabditis elegans and mice. Taken together, aldometanib mimics and adopts the lysosomal AMPK activation pathway associated with glucose starvation to exert physiological roles, and might have potential as a therapeutic for metabolic disorders in humans.