Glucose uptake of the muscle and adipose tissues in diabetes and obesity disease models: evaluation of insulin and β3-adrenergic receptor agonist effects by 18F-FDG

Alterations in skeletal muscle morphology and mechanics in juvenile male Sprague Dawley rats exposed to a high-fat high-sucrose diet

Although once a health concern largely considered in adults, the obesity epidemic is now prevalent in pediatric populations. While detrimental effects on skeletal muscle function have been seen in adulthood, the effects of obesity on skeletal muscle function in childhood is not clearly understood. The purpose of this study was to determine if the consumption of a high-fat high-sucrose (HFS) diet, starting in the post-weaning period, leads to changes in skeletal muscle morphology and mechanics after 14 weeks on the HFS diet. Eighteen 3-week-old male CD-Sprague Dawley rats were randomly assigned to a HFS (C-HFS, n = 10) or standard chow diet (C-CHOW, n = 8). Outcome measures included: weekly energy intake, activity levels, oxygen consumption, body mass, body composition, metabolic profile, serum protein levels, and medial gastrocnemius gene expression, morphology, and mechanics. The main findings from this study were that C-HFS rats: (1) had a greater body mass and percent body fat than control rats; (2) showed early signs of metabolic syndrome; (3) demonstrated potential impairment in muscle remodeling; (4) produced lower relative muscle force; and (5) had a shift in the force-length relationship, indicating that the medial gastrocnemius had shorter muscle fiber lengths compared to those of C-CHOW rats. Based on the results of this study, we conclude that exposure to a HFS diet led to increased body mass, body fat percentage, and early signs of metabolic syndrome, resulting in functional deficits in MG of childhood rats.

Association of an ADRB3 Variant with Coronary Artery Disease Within the Chinese Han Population: Construction of a Predictive Nomogram Model

Objective: Coronary artery disease (CAD) is a the most common type of heart disease, and is associated with the highest mortality rate. The role of the β₃-adrenergic receptor gene (ADRB3) in energy homeostasis and lipolysis suggests that it may be associated with obesity, insulin resistance, diabetes, and hypertension. Herein, we sought to examine the relationship between CAD and variants of the ADRB3 gene in individuals with Han and Uygur ethnicities in China. Methods: All 1022 participants were genotyped for two ADRB3 single nucleotide polymorphisms (SNPs; rs1892818 and rs9693898) using real-time polymerase chain reaction (TaqMan). Uygur (259 CAD patients, 161 control group) and Han (308 CAD patients, 294 control group) were included in two case-control studies. We subsequently developed a predictive model using ADRB3 genetic variation and clinical variables to predict risk of CAD. Results: The rs1892818 CT genotype (8.5% vs 3.9%, p = 0.019) and T allele (4.3% vs 1.9%, p = 0.021) were more frequently detected in the control subjects compared to CAD patients of the Han population but not in the Uygur population. The rs9693898 was not associated with CAD in either ethnic population. Logistic regression analysis further demonstrated that carriers of the rs1892818 CT genotype had a lower risk of CAD than did those with the CC genotype (CT vs CC, p = 0.044, odds ratio [OR] = 0.441, 95% confidence interval [CI]: 0.199-0.976). Using this data, we constructed a predictive nomogram model for CAD with an area under the curve (95% CI) of 0.722 (0.682, 0.761). Conclusions: Our results suggest that rs1892818 is associated with CAD in the Han population and that the CT genotype of rs1892818 may serve as a protective factor for CAD in Han individuals. The proposed nomograms can be used for the prediction of CAD in this population.

An obesogenic diet impairs uncoupled substrate oxidation and promotes whitening of the brown adipose tissue in rats

Brown adipose tissue (BAT) is rich in mitochondria containing uncoupling protein 1 (UCP1), and dissipates energy through thermogenesis. However, even though BAT mass and its UCP1 content increase in rodents chronically fed a high-fat sucrose-enriched (HFS) diet, marked expansion of adiposity still occurs in these animals, suggesting insufficient BAT-mediated HFS diet-induced thermogenesis. Thus, the objective of this study was to investigate the metabolic and molecular mechanisms that regulate BAT thermogenesis in HFS-induced obesity. To accomplish this, rats were fed either a standard chow or HFS diet for 8 weeks. Subsequently, glucose and fatty acid metabolism and the molecular mechanisms underlying these processes were assessed in freshly isolated primary BAT adipocytes. Despite increasing BAT mass and its UCP1 content, the HFS diet reduced uncoupled glucose and palmitate oxidation in BAT adipocytes. It also markedly diminished tyrosine hydroxylase content and lipolysis in these cells. Conversely, glucose uptake, lactate production, glycerol incorporation into lipids, palmitate incorporation into triacylglycerol (TAG), phosphoenolpyruvate carboxykinase and glycerol kinase levels, and lipoprotein lipase and cluster of differentiation 36 gene expression were increased. In summary, a HFS diet enhanced glyceroneogenesis and shifted BAT metabolism toward TAG synthesis by impairing UCP1-mediated substrate oxidation and by enhancing fatty acid esterification in intact brown adipocytes. These adaptive metabolic responses to chronic HFS feeding attenuated BAT thermogenic capacity and favoured the development of obesity. KEY POINTS: Despite increasing brown adipose tissue (BAT) mass and levels of thermogenic proteins such as peroxisome proliferator-activated receptor γ coactivator 1α, carnitine palmitoyltransferase 1B and uncoupling protein 1 (UCP1), an obesogenic high-fat sucrose-enriched (HFS) diet attenuated uncoupled glucose and fatty acid oxidation in brown adipocytes. Brown adipocytes diverted glycerol and fatty acids toward triacylglycerol (TAG) synthesis by elevating the cellular machinery that promotes fatty acid uptake along with phosphoenolpyruvate carboxykinase and glycerol kinase levels. The HFS diet increased glucose uptake that supported lactate production and provided substrate for glyceroneogenesis and TAG synthesis in brown adipocytes. Impaired UCP-1-mediated thermogenic capacity and enhanced TAG storage in BAT adipocytes were consistent with reduced adipose triglyceride lipase and tyrosine hydroxylase levels in HFS diet-fed animals.

Remodeling on adipocytic physiology of organophosphorus esters in mature adipocytes

The emerging endocrine disruption chemicals organophosphate esters (OPEs) pose high risk of metabolic disruption. However, limited information is available on physiological disturbance of OPEs on adipose, a major endocrine and metabolic organ. In this study, physiological change was investigated after exposing 3T3-L1fully differentiated adipocytes to six OPEs at non-cytotoxic concentrations. We found two chlorinated-OPEs (tris-(2-chloro-1-(chloromethyl) ethyl) phosphate (TDCPP) and tris(2-chloroisopropyl) phosphate (TCPP)) and two alkyl-OPEs (tributyl phosphate (TBP) and tris (2-butoxyethyl) phosphate (TBEP)) induced inflammation-like adipokines (chemoattractant protein 1 and interleukin-6), respectively. Increment of insulin-resistance-related hormones (resistin and leptin) were observed under TDCPP, TCPP, and TBP exposure. Functional and mechanistic investigation revealed that all of the compounds inhibited lipolysis at basal level through dephosphorylated HSL^ser563, the rate limiting enzyme of lipolysis. Triphenyl phosphate (TPhP), tricresyl phosphate (TCP), TDCPP, TBP and TBEP enhanced glucose uptake at both basal and insulin-stimulated status. We evidenced that impact was independent of the classical pIRS^ser639/pAKT^ser473 nor the insulin-independent AMPK pathway. The elevated mRNA of slc2a4 and its transcriptional factor LXRα may, at least partially, explain for the increase of glucose uptake. Given the focus within the endocrine disruption on glands, it would be prudent not to ignore endocrinal impact on adipocytes.

Interleukin-6 mimics insulin-dependent cellular distribution of some cytoskeletal proteins and Glut4 transporter without effect on glucose uptake in 3T3-L1 adipocytes

Interleukin (IL)-6, a known proinflammatory cytokine, is released in both visceral adipose tissue and contracting skeletal muscle. In this study, we used microRNA profiling as a screening method to identify miRNA species modified by IL-6 treatment in mouse 3T3-L1 adipocytes. miRNA microarray analysis and qRT-PCR revealed increased expression of miR-146b-3p in adipocytes exposed to IL-6 (1 ng/ml) during 8-day differentiation. On the basis of ontological analysis of potential targets, selected proteins associated with cytoskeleton and transport were examined in the context of adipocyte response to insulin, using immunofluorescence and confocal microscopy. We concluded that IL-6: (i) does not affect insulin action on actin cellular distribution; (ii) modulates the effect of insulin on myosin light chain kinase (Mylk) distribution by preventing its shift toward cytoplasm; (iii) mimics the effect of insulin on dynein distribution by increasing its near-nuclear accumulation; (iv) mimics the effect of insulin on glucose transporter Glut4 distribution, especially by increasing its near-nuclear accumulation; (v) supports insulin action on early endosome marker Rab4A near-nuclear accumulation. Moreover, as IL-6 did not disturb insulin-dependent glucose uptake, our results do not confirm the IL-6-induced impairment of insulin action observed in some in vitro studies, suggesting that the effect of IL-6 is dose dependent.

The difference between steroid diabetes mellitus and type 2 diabetes mellitus: a whole-body 18F-FDG PET/CT study

AIMS

Steroid diabetes mellitus (SDM) is a metabolic syndrome caused by an increase in glucocorticoids, and its pathogenesis is unclear. ¹⁸F-FDG PET/CT can reflect the glucose metabolism of tissues and organs under living conditions. Here, PET/CT imaging of SDM and type 2 diabetes mellitus (T2DM) rats was used to visualize changes in glucose metabolism in the main glucose metabolizing organs and investigate the pathogenesis of SDM.

METHODS

SDM and T2DM rat models were established. During this time, PET/CT imaging was used to measure the %ID/g value of skeletal muscle and liver to evaluate glucose uptake. The pancreatic, skeletal muscle and liver were analyzed by immunohistochemistry.

RESULTS

SDM rats showed increased fasting blood glucose and insulin levels, hyperplasia of islet α and β cells, increased FDG uptake in skeletal muscle accompanied by an up-regulation of PI3Kp85α, IRS-1, and GLUT4, no significant changes in liver uptake, and that glycogen storage in the liver and skeletal muscle increased. T2DM rats showed atrophy of pancreatic islet β cells and decreased insulin levels, significantly reduced FDG uptake and glycogen storage in skeletal muscle and liver.

CONCLUSIONS

The pathogenesis of SDM is different from that of T2DM. The increased glucose metabolism of skeletal muscle may be related to the increased compensatory secretion of insulin. Glucocorticoids promote the proliferation of islet α cells and cause an increase in gluconeogenesis in the liver, which may cause increased blood glucose.

Beneficial Effects of an Aged Black Garlic Extract in the Metabolic and Vascular Alterations Induced by a High Fat/Sucrose Diet in Male Rats

Aged black garlic (ABG) is a functional food with antioxidant and anti-inflammatory properties. Recent studies also report its beneficial metabolic effects in a context of obesity or diabetes, although the mechanisms involved are poorly understood. The aim of this work was to analyze the effects of an ABG extract in the vascular and metabolic alterations induced by a high-fat/sucrose diet in rats. For this purpose, male Sprague–Dawley rats were fed either a standard chow (controls; n = 12) or a high-fat/sucrose diet (HFD; n = 24) for 16 weeks. From week 8 on, half of the HFD rats were treated with a commercial ABG extract concentrated in S-allyl cysteine and melanoidins (ABG10+®; 250 mg/kg daily by gavage; 5 mL/kg). ABG10+®-treated rats showed lower mean caloric intake, body weight, triglycerides, low density lipoprotein cholesterol (LDL-c), insulin and leptin serum concentrations and higher high density lipoprotein cholesterol (HDL-c) and adiponectin serum concentrations than non-treated rats. In the hypothalamus, ABG10+® treatment induced an increase in the gene expression of proopiomelanocortin (POMC) and a decrease in leptin receptor (ObR) mRNA levels. No significant changes were found in visceral adipose tissue except for an overexpression of β3-adrenergic receptor (β3-ADR) in ABG-treated rats. In subcutaneous adipose tissue, ABG10+® treatment decreased adipose weight and downregulated the gene expression of PPAR-γ, LPL, ObR and HSL. In brown adipose tissue, an overexpression of InsR, GLUT-4, UCP-1 and β3-ADR in ABG10+®-treated rats was found, whereas PPAR-γ mRNA levels were significantly decreased. Regarding vascular function, ABG10+® treatment attenuated the obesity-induced vasoconstriction in response to potassium chloride both in presence/absence of perivascular adipose tissue (PVAT). On the contrary, aorta segments from ABG-treated rats showed and improved relaxation in response to acetylcholine only when PVAT was present, with this fact possible being related to the decreased gene expression of proinflammatory cytokines in this tissue. In conclusion, ABG10+® administration partially improves the metabolic and vascular alterations induced by a high-fat/high-sucrose diet in rats through modifications in the gene expression of proteins and neuropeptides involved in inflammation, fat metabolism and food intake regulation. Further studies are required to assess the bioavailability of ABG between rats and humans.

Differential effects of high-fat diet and exercise training on bone and energy metabolism

Bone microarchitecture and strength are impaired by obesity and physical inactivity, but the underlying molecular regulation of bone metabolism in response to these factors is not well understood. Therefore, we analyzed bone and energy metabolism in male mice fed a high-fat or standard chow diet for 12 weeks with or without free access to running wheels. High-fat diet (HFD) mimicked the human condition of obesity and insulin resistance, including symptoms such as elevated serum glucose and insulin levels and reduced insulin-stimulated glucose uptake into muscle and adipose tissue. Interestingly, HFD also decreased (-44%) glucose uptake into bone marrow. Bone mass was reduced (-45%) by HFD due to a diminished (-45%) bone remodeling rate. Bone matrix quality aspects, such as biomechanical stability, were additionally decreased. Concurrently, the bone marrow adiposity increased (+63%) in response to a HFD. Further, we detected elevated expression of the Wnt signaling inhibitor dickkopf-1 (Dkk-1, +42%) in mice fed a HFD, but this was not reflected in serum samples obtained from obese humans. In mice, exercise attenuated the adverse effects of HFD by reversing the glucose uptake into bone marrow, improving the bone mass and bone matrix quality while decreasing the bone marrow adiposity. This data shows that exercise prevents some, but not all of the negative effects of HFD on bone health and suggests that insulin signaling in bone marrow and Dkk-1 signaling may be involved in the pathogenesis of bone loss induced by HFD.