Ectopic Lipid Deposition Research Articles

Regulation of adipocyte thermogenesis: mechanisms controlling obesity.

Adipocyte biology has been intensely researched in recent years due to the emergence of obesity as a serious global health concern and because of the realization that adipose tissue is more than simply a cell type that stores and releases lipids. The plasticity of adipose tissues, to rapidly adapt to altered physiological states of energy demand, is under neuronal and endocrine control. The capacity for white adipocytes to store chemical energy in lipid droplets is key for protecting other organs from the toxic effects of ectopic lipid deposition. In contrast, thermogenic (brown and beige) adipocytes combust macronutrients to generate heat. The thermogenic activity of adipocytes allows them to protect themselves and other tissues from lipid overaccumulation. Advances in brown fat biology have uncovered key molecular players involved in adipocyte determination, differentiation, and thermogenic activation. It is now, well appreciated that three distinct adipocyte types exist: white, beige, and brown. Moreover, functional differences are present within adipocyte subtypes located in anatomically distinct locations. Adding to this complexity is the recent realization from single-cell sequencing studies that adipocyte progenitors are also heterogeneous. Understanding the molecular details of how to increase the number of thermogenic fat cells and their activation may delineate some of the pathophysiological basis of obesity and obesity-related diseases. Here, we review recent advances that have extended our understanding of the central role that adipose tissue plays in energy balance and the mechanisms that control their amount and function.

Liraglutide attenuates renal tubular ectopic lipid deposition in rats with diabetic nephropathy by inhibiting lipid synthesis and promoting lipolysis

Liraglutide is a new hypoglycemic drug. The previous studies have shown that liraglutide can improve the renal outcomes of patients with type 2 diabetes. Recently, it was approved by the U.S. FDA for used as a weight-loss drugs. However, the mechanism of its improvements of renal function in diabetic nephropathy patients is unclear. In addition, the effect of liraglutide on lipid metabolism is also not clear. The purpose of this study was to investigate the effects and mechanisms of liraglutide in alleviating ectopic lipid deposition (ELD) in rats with diabetic nephropathy (DN). Male Sprague-Dawley (SD) rats were treated with high-fat diet + unilateral nephrectomy + low-dose STZ combined to establish a DN rat model to evaluate the lipid-lowering effect of liraglutide. Liraglutide at 0.4 mg/kg/d were subcutaneous injected into for 12 weeks (DN + liraglutide group). After the DN rat model was established, body weight loss, 24-h urine volume increasing, serum triglycerides (TG) and serum total cholesterol (TCh) increasing, ectopic lipid droplet deposition in renal tubular increasing, mesangial proliferation in renal tissue were observed in DN rats. The treatment with liraglutide could reduce the body weight and the average daily food intake of the rats, as well as TG, TCh, and ectopic lipid droplet deposition in renal tubular. Metabolomics result showed that serum differential metabolites between the DN - vehicle control group and the DN + liraglutide group mainly included serine, threonine, phenylalanine, oxyproline, threonine, sorbitol, glyceryl monostearate, glycerol monostearate, and β-d-glucuronic acid. Moreover, liraglutide can reduce plasma lipid levels in DN rats by increasing the products of lipolysis including 1-monopalmitin and 1-monoostearin. Immunohistochemistry and Western blot showed that the expression levels of lipid synthesis-related sterol regulatory element binding protein 1 (SREBP-1) and fatty acid synthase (FAS) were significantly increased, and lipolysis-related adipose triglyceride lipase (ATGL) and hormone-sensitive lipase (HSL) were significantly decreased both in the renal tissue of DN rats and PA-induced HK-2 cells (lipid droplet accumulation model). However, liraglutide can attenuate renal tubular ectopic lipid deposition in DN rats by inhibiting SREBP-1, FAS and increasing ATGL, HSL protein expression level, and also ameliorated PA-induced lipid accumulation in renal tubular epithelial cells. These lipid metabolism changes were attributed to liraglutide by upregulating AMP-activated protein kinase (AMPK) phosphorylation in the kidney of DN rats. Collectively, these findings confirm that liraglutide inhibits lipid synthesis and promotes lipolysis to attenuate renal ectopic lipid deposition in DN rats by promoting AMPK phosphorylation.

Mechanisms of Myosteatosis in Obesity and the Effects of Muscle Hypertrophy

ObjectiveTo determine the mechanism of ectopic lipid deposition in skeletal muscle in obesity and if any impact is conferred by increasing muscle mass.MethodsSkeletal muscles from db/db mice, a well characterized model of human obesity, were isolated and myosteatosis assessed for lipid content via NMR, chemical assay and transmission electron microscopy. Genes involved in lipogenesis, lipid storage and oxidation were assessed by qPCR. To determine the effects of hypermuscularity, db/db mice were crossed with mice lacking myostatin, a myokine that inhibits muscle growth, to generate lean, obese, and hypermuscular obese mice.ResultsObese mice exhibited a 3‐fold increase in muscle triglyceride content, which appeared on electron microscopy as diffuse and heterogeneous lipid droplet accumulation in individual muscle fibers. Lipogenic pathways, assessed by expression of sterol regulatory element binding protein (SREBP) and its downstream targets stearyl CoA desaturase‐1 (SCD1), acetyl‐CoA carboxylase (ACC) and fatty acid synthase (FAS), were increased in obesity as was expression of perilipins. Muscle from obese mice was characterized by accumulation of mitochondria and increased expression of carnitine palmitoyltransferase I (CPT1). Deletion of myostatin produced a 40% increase in skeletal muscle mass and reversed the observed change in lipid content and gene expression.ConclusionObesity increases both lipogenesis and lipid oxidation in the skeletal musculature of obese mice. The balance of these processes favors lipid accumulation as evidenced by droplet formation and enhanced expression of droplet‐related proteins. Deletion of myostatin produced muscle hypertrophy and clearance of ectopic lipids. Specific links between muscle hypertrophy and excess muscle lipids remain to be defined.Support or Funding InformationTitle: Circadian Origins of Vascular Disease in Obesity | Investigator(s): Stepp, David W. and Fulton, David J., Augusta University, Augusta, GA | Agency: National Institute of Health (NIH) | Institute: National Heart, Lung and Blood Institute (NHLBI) | Type: Research Project (RO1) | Project #: 1RO1HL147159‐01

CRTC1 Maintains Metabolic Homeostasis and Protects Against Partial Lipodystrophy & Insulin Resistance by Regulating Diet‐Responsive White Adipose Tissue Remodeling

Humans evolved the ability to store lipid in specialized tissue called adipose to support survival. Adipose provides an energy depot that can be quickly mobilized in response to acute stress (fight‐or‐flight), for reproduction and during extended fasting. Defects in white adipose tissue (WAT) function, and inability of the WAT depots to expand in the context of overnutrition, will lead to ectopic lipid accumulation in the muscle and liver triggering serious metabolic diseases such as type 2 diabetes (T2D).Our data demonstrate that CREB Regulated Transcription Coactivator 1 (CRTC1) gene function is important in maintaining metabolic fitness. CRTC1 is expressed primarily in the hypothalamus where it controls satiety in response to cAMP and Ca2+ signals. Recent studies identified small nucleotide polymorphisms (SNPs) in the human gene locus CRTC1 that correlate with decreased adiposity in the context of obesity, indicating that CRTC1 may play an important role in adipose function. Here, we describe a previously unknown role of CRTC1 in the regulation of epididymal WAT (eWAT) expansion in response to high fat diet (HFD).Basal CRTC1 protein expression in eWAT is low compared to that in the brain, yet specifically increased in eWAT in response to HFD. Loss of CRTC1 by whole‐body germline knockout (CRTC1 KO mice), acute antisense oligonucleotide knockdown in WAT (CRTC1 ASO mice), and tissue‐specific germline knockout in adipose tissue (CRTC1 AKO mice) results in impaired HFD‐responsive eWAT expansion, observed as a ~50% decrease in eWAT size. Diminished capacity for eWAT expansion coincides with elevated lipid accumulation in liver and muscle, hyperglycemia, hyperinsulinemia and glucose intolerance in these animals relative to wildtype or control.CRTC1 knockdown by adenoviral shRNA decreased glucose uptake, increased lipolysis and impeded expression of the key adipogenesis marker PPARγ in differentiated 3T3‐L1 adipocytes. Animal models with decreased CRTC1 expression (CRTC1 KO, ASO and AKO) also exhibited decreased PPARγ expression in eWAT but only on HFD, suggesting that CRTC1 is required for diet‐responsive eWAT remodeling and for maintaining a differentiated state in adipocytes. Supportive of this hypothesis, we observed significantly decreased eWAT FGF1 mRNA expression, plasma FGF1 and WAT FGF1 levels in HFD‐fed animal models of CRTC1 loss relative to control. FGF1 plays a major role in eWAT remodeling and expansion in response to diet: our data indicate that CRTC1 is required for HFD‐mediated upregulation of FGF1. Together, our findings reveal a regulatory axis that is essential for eWAT remodeling and expansion, and that leads to ectopic lipid deposition and insulin resistance when perturbed. Understanding how CRTC1 regulates FGF1 and impacts the PPARγ pathway in eWAT will provide important insights into adipocyte function and into how eWAT expansion is modulated to maintain metabolic homeostasis, allowing identification of new potential targets to treat diseases such as T2D.Support or Funding InformationLife Science Research Foundation Fellowship, Sponsor: Gilead Sciences Inc.; R01 DK083834, PI: Marc Montminy

The NLRP3 inflammasome regulates adipose tissue metabolism.

Adipose tissue regulates metabolic homeostasis by participating in endocrine and immune responses in addition to storing and releasing lipids from adipocytes. Obesity skews adipose tissue adipokine responses and degrades the coordination of adipocyte lipogenesis and lipolysis. These defects in adipose tissue metabolism can promote ectopic lipid deposition and inflammation in insulin-sensitive tissues such as skeletal muscle and liver. Sustained caloric excess can expand white adipose tissue to a point of maladaptation exacerbating both local and systemic inflammation. Multiple sources, instigators and propagators of adipose tissue inflammation occur during obesity. Cross-talk between professional immune cells (i.e. macrophages) and metabolic cells (i.e. adipocytes) promote adipose tissue inflammation during metabolic stress (i.e. metaflammation). Metabolic stress and endogenous danger signals can engage pathogen recognition receptors (PRRs) of the innate immune system thereby activating pro-inflammatory and stress pathways in adipose tissue. The Nod-like receptor protein 3 (NLRP3) inflammasome can act as a metabolic danger sensor to a wide range of pathogen- and damage-associated molecular patterns (PAMPs and DAMPs). Activation of the NLRP3 inflammasome facilitates caspase-1 dependent production of the pro-inflammatory cytokines IL-1β and IL-18. Activation of the NLRP3 inflammasome can promote inflammation and pyroptotic cell death, but caspase-1 is also involved in adipogenesis. This review discusses the role of the NLRP3 inflammasome in adipose tissue immunometabolism responses relevant to metabolic disease. Understanding the potential sources of NLRP3 activation and consequences of NLRP3 effectors may reveal therapeutic opportunities to break or fine-tune the connection between metabolism and inflammation in adipose tissue during obesity.

Exercise training results in depot-specific adaptations to adipose tissue mitochondrial function

We assessed differences in mitochondrial function in gluteal (gSAT) and abdominal subcutaneous adipose tissue (aSAT) at baseline and in response to 12-weeks of exercise training; and examined depot-specific associations with body fat distribution and insulin sensitivity (SI). Obese, black South African women (n = 45) were randomized into exercise (n = 23) or control (n = 22) groups. Exercise group completed 12-weeks of aerobic and resistance training (n = 20), while the control group (n = 15) continued usual behaviours. Mitochondrial function (high-resolution respirometry and fluorometry) in gSAT and aSAT, SI (frequently sampled intravenous glucose tolerance test), body composition (dual-energy X-ray absorptiometry), and ectopic fat (MRI) were assessed pre- and post-intervention. At baseline, gSAT had higher mitochondrial respiratory capacity and hydrogen peroxide (H2O2) production than aSAT (p < 0.05). Higher gSAT respiration was associated with higher gynoid fat (p < 0.05). Higher gSAT H2O2 production and lower aSAT mitochondrial respiration were independently associated with lower SI (p < 0.05). In response to training, SI improved and gynoid fat decreased (p < 0.05), while H2O2 production reduced in both depots, and mtDNA decreased in gSAT (p < 0.05). Mitochondrial respiration increased in aSAT and correlated with a decrease in body fat and an increase in soleus and hepatic fat content (p < 0.05). This study highlights the importance of understanding the differences in mitochondrial function in multiple SAT depots when investigating the pathophysiology of insulin resistance and associated risk factors such as body fat distribution and ectopic lipid deposition. Furthermore, we highlight the benefits of exercise training in stimulating positive adaptations in mitochondrial function in gluteal and abdominal SAT depots.

Mitochondrial Dysfunction, Insulin Resistance, and Potential Genetic Implications.

Insulin resistance (IR) is fundamental to the development of type 2 diabetes (T2D) and is present in most prediabetic (preDM) individuals. Insulin resistance has both heritable and environmental determinants centered on energy storage and metabolism. Recent insights from human genetic studies, coupled with comprehensive in vivo and ex vivo metabolic studies in humans and rodents, have highlighted the critical role of reduced mitochondrial function as a predisposing condition for ectopic lipid deposition and IR. These studies support the hypothesis that reduced mitochondrial function, particularly in insulin-responsive tissues such as skeletal muscle, white adipose tissue, and the liver, is inextricably linked to tissue and whole body IR through the effects on cellular energy balance. Here we discuss these findings as well as address potential mechanisms that serve as the nexus between mitochondrial malfunction and IR.

Metabolic effects of a prolonged, very-high-dose dietary fructose challenge in healthy subjects

Increased fructose intake has been associated with metabolic consequences such as impaired hepatic lipid metabolism and development of nonalcoholic fatty liver disease (NAFLD). The aim of this study was to investigate the role of fructose in glucose and lipid metabolism in the liver, heart, skeletal muscle, and adipose tissue. Ten healthy subjects (age: 28±19 y; BMI: 22.2±0.7 kg/m2) underwent comprehensive metabolic phenotyping prior to and 8 wk following a high-fructose diet (150 g daily). Eleven patients with NAFLD (age: 39.4±3.95 y; BMI: 28.4±1.25) were characterized as "positive controls." Insulin sensitivity was analyzed by a 2-step hyperinsulinemic euglycemic clamp, and postprandial interorgan crosstalk of lipid and glucose metabolism was evaluated, by determining postprandial hepatic and intra-myocellular lipid and glycogen accumulation, employing magnetic resonance spectroscopy (MRS) at 7 T. Myocardial lipid content and myocardial function were assessed by 1H MRS imaging and MRI at 3 T. High fructose intake resulted in lower intake of other dietary sugars and did not increase total daily energy intake. Ectopic lipid deposition and postprandial glycogen storage in the liver and skeletal muscle were not altered. Postprandial changes in hepatic lipids were measured [Δhepatocellular lipid (HCL)_healthy_baseline: -15.9±10.7 compared with ± ΔHCL_healthy_follow-up: -6.9±4.6; P=0.17] and hepatic glycogen (Δglycogen_baseline: 64.4±14.1 compared with Δglycogen_follow-up: 51.1±9.8; P=0.42). Myocardial function and myocardial mass remained stable. As expected, impaired hepatic glycogen storage and increased ectopic lipid storage in the liver and skeletal muscle were observed in insulin-resistant patients with NAFLD. Ingestion of a high dose of fructose for 8 wk was not associated with relevant metabolic consequences in the presence of a stable energy intake, slightly lower body weight, and potentially incomplete absorption of the orally administered fructose load. This indicated that young, metabolically healthy subjects can at least temporarily compensate for increased fructose intake. This trial was registered at www.clinicaltrials.gov as NCT02075164.

Short-term GLP-1 receptor agonist exenatide ameliorates intramyocellular lipid deposition without weight loss in ob/ob mice.

Ectopic lipid deposition is closely associated with type 2 diabetes (T2D). Accumulating evidence shows that GLP-1 receptor agonists (GLP-1 RAs) improve obesity and liver steatosis. However, it remains unknown whether and how they ameliorate lipid deposition in skeletal muscle. This study aimed to investigate the effect of exenatide (a GLP-1 RA) on intramyocellular lipid deposition in the skeletal muscle of T2D models and its dependence on weight loss. Ob/ob mice and diet-induced obese (DIO) mice were treated with exenatide (24 nmol/kg), leptin (1 mg/kg), or saline control intraperitoneally once daily for 4 weeks. Phenotypic evaluations were performed during and after the intervention. PA-induced myoblast C2C12 cells were used as an in vitro model. The expression of key enzymes involved in lipid metabolism was assessed in the skeletal muscle of ob/ob mice and DIO mice. In ob/ob mice, 4-week exenatide treatment did not improve the body weight and fat mass, but modestly ameliorated intramyocellular lipid deposition and lipid profiles. In DIO mice, it remarkably alleviated the body weight, lipid profiles, and intramyocellular lipid deposition. In the skeletal muscle of these two models, exenatide treatment activated the AMP-activated protein kinase (AMPK) signaling pathway, stimulated lipid oxidation enzymes, and upregulated the insulin signaling pathway. In vitro, exendin-4 activated the AMPK signaling pathway and stimulated lipid metabolism to improve lipid accumulation in palmitate-induced myoblast C2C12 cells. Exenatide ameliorated intramyocellular lipid deposition without body weight reduction in ob/ob mice, but alleviated body weight and intramyocellular lipid deposition in DIO mice. The underlying mechanism included the activation of AMPK signaling pathway and improvement in insulin sensitivity, independent of weight loss in ob/ob mice.

Ipragliflozin Ameliorates Endoplasmic Reticulum Stress and Apoptosis through Preventing Ectopic Lipid Deposition in Renal Tubules.

Background: Chronic kidney disease (CKD) and non-alcoholic steatohepatitis (NASH) are major health burdens closely related to metabolic syndrome. A link between CKD and NASH has been assumed; however, the underlying mechanism is still unknown. Ectopic lipid deposition (ELD) in the hepatocyte results in endoplasmic reticulum (ER) stress, which plays an important role in the development of steatohepatitis. ELD is also assumed to play a role in the development of kidney injury. We aimed to investigate the role of ELD and ER stress in the development of CKD, and evaluate the efficacy of a sodium glucose cotransporter-2 inhibitor, ipragliflozin. Methods: Male FLS-ob/ob mice that closely imitate the pathophysiology of NASH were treated with vehicle or ipragliflozin. Metabolic characteristics, histology of the kidney, ER stress, and apoptotic signals were evaluated. Results: The serum triglyceride was significantly lower in mice treated with ipragliflozin. Ipragliflozin reduced ELD in renal tubules. Ipragliflozin also reduced the expression levels of GRP78 and CHOP, apoptotic cells, and interstitial fibrosis. Conclusions: ELD induced kidney injury through ER stress. Ipragliflozin improved the pathogenesis of CKD by reducing ELD and ER stress in NASH-model mice. Our results suggest ipragliflozin has therapeutic effect on CKD in NASH.

The Effect of Lipotoxicity on Renal Dysfunction in a Nonobese Rat Model of Metabolic Syndrome: A Urinary Proteomic Approach.

Introduction The development of metabolic syndrome-associated renal dysfunction is exacerbated by a number of factors including dyslipidemia, ectopic deposition of lipids and their toxic metabolites, impairment of lipid metabolism, and insulin resistance. Renal dysfunction is also affected by the production of proinflammatory and profibrotic factors secreted from adipose tissue, which can in turn directly impair kidney cells and potentiate insulin resistance. In this study, we investigated the manifestation of renal lipid accumulation and its effect on renal dysfunction in a model of metabolic syndrome—the hereditary hypertriglyceridemic rat (HHTg)—by assessing microalbuminuria and targeted urinary proteomics. Male Wistar control rats and HHTg rats were fed a standard diet and observed over the course of ageing at 3, 12, and 20 months of age. Results Chronically elevated levels of triglycerides in HHTg rats were associated with increased levels of NEFA during OGTT and over a period of 24 hours (+80%, P < 0.01). HHTg animals exhibited qualitative changes in NEFA fatty acid composition, represented by an increased proportion of saturated fatty acids (P < 0.05) and a decreased proportion of n-3 PUFA (P < 0.01). Ectopic lipid deposition in the kidneys of HHTg rats—triglycerides (+30%) and cholesterol (+10%)—was associated with markedly elevated microalbuminuria as ageing increased, despite the absence of microalbuminuria at the young age of 3 months in these animals. According to targeted proteomic analysis, 3-month-old HHTg rats (in comparison to age-matched controls) exhibited increased urinary secretion of proinflammatory parameters (MCP-1, IL-6, IL-8, P < 0.01) and decreased urinary secretion of epidermal growth factor (EGF, P < 0.01) before manifestation of microalbuminuria. Elevation in the urinary secretion of inflammatory cytokines can be affected by increased relative expression of MCP-1 in the renal cortex (P < 0.05). Conclusions Our results confirm dyslipidemia and ectopic lipid accumulation to be key contributors in the development of metabolic syndrome-associated renal dysfunction. Assessing urinary secretion of proinflammatory cytokines and epidermal growth factor can help in detecting early development of metabolic syndrome-associated renal dysfunction.

The PPARδ Agonist GW501516 Improves Lipolytic/Lipogenic Balance through CPT1 and PEPCK during the Development of Pre-Implantation Bovine Embryos.

The PPARs (peroxisome proliferator-activated receptors) play critical roles in the regulation of lipid and glucose metabolism. PPARδ, a member of the PPARs family, is associated with decreased susceptibility to ectopic lipid deposition and is implicated in the regulation of mitochondrial processes. The current study aimed to determine the role of PPARδ in fatty acid β-oxidation and its influence on PEPCK for the lipogenic/lipolytic balance during in vitro bovine oocyte maturation and embryo development. Activation of PPARδ by GW501516, but not 2-BP, was indicated by intact embryonic PEPCK (cytosolic) and CPT1 expression and the balance between free fatty acids and mitochondrial β-oxidation that reduced ROS and inhibited p-NF-κB nuclear localization. Genes involved in lipolysis, fatty acid oxidation, and apoptosis showed significant differences after the GW501516 treatment relative to the control- and 2-BP-treated embryos. GSK3787 reversed the PPARδ-induced effects by reducing PEPCK and CPT1 expression and the mitochondrial membrane potential, revealing the importance of PPARδ/PEPCK and PPARδ/CPT1 for controlling lipolysis during embryo development. In conclusion, GW501516-activated PPARδ maintained the correlation between lipolysis and lipogenesis by enhancing PEPCK and CPT1 to improve bovine embryo quality.

Pigment Epithelial-Derived Factor Deficiency Accelerates Atherosclerosis Development via Promoting Endothelial Fatty Acid Uptake in Mice With Hyperlipidemia.

BackgroundEndothelial cell injury, induced by dyslipidemia, is the initiation of atherosclerosis, resulting in an imbalance in endothelial fatty acid (FA) transport. Pigment epithelial‐derived factor (PEDF) is an important regulator in lipid metabolism. We hypothesized that PEDF is involved in endothelium‐mediated FA uptake under hyperlipidemic conditions.Methods and ResultsCirculating PEDF levels were higher in patients with atherosclerotic cardiovascular disease than in normal individuals. However, decreasing trends of serum PEDF levels were confirmed in both wild‐type and apolipoprotein E–deficient mice fed a long‐term high‐fat diet. Apolipoprotein E–deficient/PEDF‐deficient mice were generated by crossing PEDF‐deficient mice with apolipoprotein E–deficient mice, and then mice were fed with 24, 36, or 48 weeks of high‐fat diet. Greater increases in body fat and plasma lipids were displayed in PEDF‐deficient mice. In addition, PEDF deficiency in mice accelerated atherosclerosis, as evidenced by increased atherosclerotic plaques, pronounced vascular dysfunction, and increased lipid accumulation in peripheral tissues, whereas injection of adeno‐associated virus encoding PEDF exerted opposite effects. Mechanistically, PEDF inhibited the vascular endothelial growth factor B paracrine signaling by reducing secretion of protein vascular endothelial growth factor B in peripheral tissue cells and decreasing expression of its downstream targets in endothelial cells, including its receptors (namely, vascular endothelial growth factor receptor‐1 and neuropilin‐1), and FA transport proteins 3 and 4, to suppress endothelial FA uptake, whereas PEDF deletion in mice activated the vascular endothelial growth factor B signaling pathway, thus causing markedly increased lipid accumulation.ConclusionsDecreasing expression of PEDF aggravates atherosclerosis by significantly impaired vascular function and enhanced endothelial FA uptake, thus exacerbating ectopic lipid deposition in peripheral tissues.

Metformin Improves Fertility in Obese Males by Alleviating Oxidative Stress-Induced Blood-Testis Barrier Damage.

Background/Aims Obesity, which is related to increased oxidative stress in various tissues, is a risk factor for male infertility. Metformin is reported to have an antioxidant effect; however, the precise role of metformin in obesity-induced male infertility remains unknown. The current study is aimed at exploring the effects of metformin and characterizing its underlying mechanism in the fertility of obese males. Methods An obese male mouse model was generated by feeding mice with a high-fat diet; then, the mice were administered metformin in water for 8 weeks. Reproductive ability, metabolic parameters, and follicle-stimulating hormone (FSH) were assessed by cohabitation, enzymatic methods, and ELISA, respectively. Damage to the integrity of the blood-testis barrier (BTB), which ensures spermatogenesis, was assessed by transmission electron microscopy and immunofluorescence with a biotin tracer. Malondialdehyde (MDA), superoxide dismutase (SOD), and reactive oxygen species (ROS) were employed for the assessments of oxidative stress. BTB-related proteins were measured by immunoblotting. Nuclear factor κB (NF-κB) was assessed by immunofluorescence. Results High-fat-diet-fed mice presented evident lipid metabolic disturbances, disrupted BTB integrity, and decreased reproductive function. Metformin alleviated the decrease in male fertility, decreased ectopic lipid deposition in the testis, and increased serum FSH levels. A further mechanistic analysis revealed that metformin ameliorated the high-fat-diet-induced injury to the BTB structure and permeability and restored the disordered BTB-related proteins, which might be associated with an improvement in oxidative stress and a recovery of NF-κB activity in Sertoli cells (SCs). Conclusion Metformin improves obese male fertility by alleviating oxidative stress-induced BTB damage. These findings provide new insights into the effect of metformin on various diseases and suggest future possibilities in the treatment of male infertility.

Beneficial effects of troxerutin on metabolic disorders in non-obese model of metabolic syndrome.

BackgroundTroxerutin (TRX) has a beneficial effect on blood viscosity and platelet aggregation, and is currently used for the treatment of chronic varicosity. Recently, TRX can improve lipid abnormalities, glucose intolerance and oxidative stress in high-fat diet-induced metabolic disorders. In this study, we tested the effect of TRX on metabolic syndrome-associated disorders using a non-obese model of metabolic syndrome–the Hereditary Hypertriglyceridaemic rats (HHTg).MethodsAdult male HHTg rats were fed standard diet without or with TRX (150 mg/kg bwt/day for 4 weeks).ResultsCompared to untreated rats, TRX supplementation in HHTg rats decreased serum glucose (p<0.05) and insulin (p<0.05). Although blood lipids were not affected, TRX decreased hepatic cholesterol concentrations (p<0.01) and reduced gene expression of HMGCR, SREBP2 and SCD1 (p<0.01), involved in cholesterol synthesis and lipid homeostasis. TRX-treated rats exhibited decreased lipoperoxidation and increased activity of antioxidant enzymes SOD and GPx (p<0.05) in the liver. In addition, TRX supplementation increased insulin sensitivity in muscles and epididymal adipose tissue (p<0.05). Elevated serum adiponectin (p<0.05) and decreased muscle triglyceride (p<0.05) helped improve insulin sensitivity. Among the beneficial effects of TRX were changes to cytochrome P450 family enzymes. Hepatic gene expression of CYP4A1, CYP4A3 and CYP5A1 (p<0.01) decreased, while there was a marked elevation in gene expression of CYP1A1 (p<0.01).ConclusionOur results indicate that TRX improves hepatic lipid metabolism and insulin sensitivity in peripheral tissues. As well as ameliorating oxidative stress, TRX can reduce ectopic lipid deposition, affect genes involved in lipid metabolism, and influence the activity of CYP family enzymes.

Higher dietary protein intake preserves lean body mass, lowers liver lipid deposition, and maintains metabolic control in participants with long-chain fatty acid oxidation disorders.

Medical nutrition therapy for long-chain fatty acid oxidation disorders (LC-FAODs) currently emphasizes fasting avoidance, restricted dietary long-chain fatty acid intake, supplementation with medium chain triglycerides, and increased carbohydrate intake. We hypothesize that increasing dietary protein intake relative to carbohydrate intake would preserve metabolic control yet induce physical benefits including reduced hepatic lipogenesis. Therefore, we compared two dietary approaches with similar fat intake but different carbohydrate to protein ratios in participants diagnosed with LC-FAODs. Thirteen participants were enrolled and randomized into either a high-protein (PRO) or a high-carbohydrate (CHO) diet for 4 months. Baseline and 4-month assessments included body composition, ectopic lipid deposition, and resting energy expenditure. End of study assessments also included total energy expenditure, metabolic responses to oral feedings, and whole-body fatty acid oxidation capacity. At the end of the dietary intervention, both groups had similar energy expenditure, fat and glucose oxidation rates, and glucolipid responses to mixed meal and oral glucose loads. Neither dietary group experienced worsening symptoms related to their LC-FAOD. Compared to the CHO group, the PRO group exhibited increased blood levels of short-chain acylcarnitines, reduced intrahepatic lipid content, and maintained lean body mass while the CHO group lost lean mass. In patients with LC-FAODs, increasing protein intake maintained metabolic control, reduced liver fat without risk of metabolic decompensation, and helped preserve lean body mass. We propose that a modest increase in dietary protein along with fasting avoidance and fat restriction may improve body composition and energy expenditure in patients with LC-FAODs.

Gestational Diabetes Mellitus a Dysfunctional Metabolic State-A Perspective

Pregnancy is considered as a test for beta cell reserve. If there is a good function, insulin resistance will overcome. If not, gestational diabetes will occur. Insulin resistance (IR) present in normal pregnancy is required to provide nutrients to the growing fetus. There is a rapid increase of insulin in such an insulin resistant state. The possibility of lipid deposition in muscle fibers (intramyocellular) could be one of the possible mechanism of IR in gestational diabetes mellitus (GDM). The poor response of insulin release, possible fat deposition in the skeletal muscle or ectopic fat deposition may cause dysfunctional homeostasis in GDM. This will definitely influence the fine tuning of metabolic machinery of a growing fetus. Children born with such subtle metabolic state will probably be more prone to glucose intolerance and ectopic lipid deposition. The finding that children born to GDM mothers are prone to glucose intolerance may be an eye-opener to monitor such children for beta cell function.

Maternal betaine protects rat offspring from glucocorticoid-induced activation of lipolytic genes in adipose tissue through modification of DNA methylation.

Excessive exposure of glucocorticoids activates adipose lipolysis, increases circulating free fatty acids, and contributes to ectopic lipid deposition in liver and skeletal muscle. Our previous study demonstrated that maternal betaine supplementation attenuates glucocorticoid-induced hepatic lipid accumulation in rat offspring. However, it is unclear whether maternal betaine supplementation is effective in preventing glucocorticoid-induced lipolysis in the adipose tissue of offspring. In this study, 20 pregnant rats were fed with basal or betaine-supplemented (10g/kg) diets throughout gestation and lactation, and the offspring rats were raised on the basal diet from weaning till 3months of age followed by daily intraperitoneal injection of saline or 0.1mg/kg dexamethasone (DEX) for 3weeks. Chronic DEX treatment significantly (P < 0.05) decreased serum corticosterone level and increased proinflammatory cytokines, such as TNFα, IL-1β, and IL-6. Meanwhile, GR protein content in adipose tissue was increased in response to DEX treatment, which was associated with a significant (P < 0.05) up-regulation of ATGL and HSL expression at both mRNA and protein levels. All these DEX-induced changes were significantly (P < 0.05) attenuated in progeny rats derived from betaine-supplemented dams. Furthermore, DEX-induced hypomethylation of ATGL and HSL gene promoters was reversed by maternal betaine supplementation. Taken together, these results suggest that maternal betaine supplementation is effective in alleviating glucocorticoid-induced lipolysis in adipose tissue with modification of DNA methylation on the promoter of lipolytic genes.

1938-P: GLP-1 Receptor Agonist Ameliorates Intramyocellular Lipid Deposition without Weight Loss by Activating AMPK

Objective: Ectopic deposition of lipids is closely related with type 2 diabetes (T2D). Whether and how GLP-1 receptor agonists (GLP-1 RAs) ameliorate lipid deposition in skeletal muscle remain unknown. Here, we investigate the effect of GLP-1 RA exenatide on intramyocellular lipid deposition of skeletal muscle in T2D models and whether this process depends on weight loss. Methods: ob/ob mice and diet-induced obese (DIO) mice were treated with exenatide, leptin or saline control i.p. for four weeks. Systemic phenotypic evaluations were carried out during and after the intervention. An in vitro model used palmitate-treated myoblast C2C12 cells. The expression of key enzymes involved in lipid metabolism was assessed in skeletal muscle of ob/ob mice and DIO mice. Results: In ob/ob mice, body weight and fat mass were not improved by four-week exenatide treatment. However, intramyocellular lipid deposition and lipid profiles were still modestly ameliorated by exenatide. In DIO mice, body weight, lipid profiles and intramyocellular lipid were all remarkably alleviated by exenatide but not by leptin. In skeletal muscle of these two models, activated AMPK signaling pathway, stimulated lipid oxidative enzymes and improved insulin signaling pathway were observed by exenatide treatment. In vitro, exendin-4 activated AMPK signaling pathway and promoted lipid metabolism to improve lipid accumulation in palmitate-treated myoblast C2C12 cells, and inhibiting AMPK abolished this effect. Conclusion: Exenatide ameliorates intramyocellular lipid deposition before the weight loss effect appears in ob/ob mice. While both body weight and intramyocellular lipid are alleviated remarkably at the same time by exenatide in DIO mice. Thus, the effect of exenatide on ameliorating intramyocellular lipid deposition could be independent on weight loss by activating AMPK signaling pathway. Disclosure F. Xu: None. H. Cao: None. Z. Chen: None. H. Gu: None. W. Guo: None. B. Lin: None. J. Weng: None.

2036-P: Gut Microbes Regulate Insulin Clearance in Mice

Obesity and insulin resistance are associated with hyperinsulinemia, which is caused by increased insulin secretion and/or reduced insulin clearance. Impaired insulin clearance may be caused by ectopic lipid deposition in liver and skeletal muscle, the key sites of insulin clearance and degradation. Insulin is the key hormone regulating blood glucose. The composition of the intestinal microbiota can regulate aspects of diet-induced obesity and glucose metabolism. Here we found that the microbiota also regulates insulin clearance during prolonged diet-induced obesity. Male C57Bl/6J mice fed 45% high fat diet (HFD) for a prolonged period had impaired insulin clearance relative to chow fed mice as measured by insulin/C-peptide ratio during an oral glucose tolerance test. High fat fed mice also showed impaired insulin clearance measured after injection of insulin - mice fed chow or 45% HFD had plasma insulin concentration measured at 0, 5, 30, and 60 minutes following injection of human insulin and area under the curve calculated. Treatment of 45% HFD-fed mice with an antibiotic cocktail of Neomycin/Ampicillin for 2 weeks improved insulin clearance after insulin injection. Next, we colonized previously germ-free mice with the microbiota from chow or 45% HFD-fed “donor” mice for 6 weeks. The previously germ-free “recipient” mice colonized with feces-resident microbes from chow or HFD fed donors did not differ in insulin clearance when recipient mice were fed a chow diet. However, when colonized recipient mice were switched from chow to 45% HFD for 2 weeks the recipient mice colonized with microbes from 45% HFD fed donors showed impaired insulin clearance relative to recipient mice colonized with microbes from chow fed donors. Our results demonstrate that diet-induced changes in fecal microbes are an independent factor regulating insulin clearance. Diet-induced changes in the gut microbiota and consequent impaired insulin clearance may participate in hyperinsulinemia leading to exacerbated insulin resistance and obesity. Disclosure K.P. Foley: None. S. Zlitni: None. B.M. Duggan: None. B.D. Henriksbo: None. N.G. Barra: None. J.F. Cavallari: None. F. Forato Anhê: None. T. Lau: None. Y. Chen: None. J.D. Schertzer: None. Funding Canadian Institutes of Health Research