Minireview: weapons of lean body mass destruction: the role of ectopic lipids in the metabolic syndrome

Limitation of adipose tissue by the number of embryonic progenitor cells

Adipogenesis in adulthood replaces fat cells that turn over and can contribute to the development of obesity. However, the proliferative potential of adipocyte progenitors in vivo is unknown (Faust et al., 1976; Faust et al., 1977; Hirsch and Han, 1969; Johnson and Hirsch, 1972). We addressed this by injecting labeled wild-type embryonic stem cells into blastocysts derived from lipodystrophic A-ZIP transgenic mice, which have a genetic block in adipogenesis. In the resulting chimeric animals, wild-type ES cells are the only source of mature adipocytes. We found that when chimeric animals were fed a high-fat-diet, animals with low levels of chimerism showed a significantly lower adipose tissue mass than animals with high levels of chimerism. The difference in adipose tissue mass was attributed to variability in the amount of subcutaneous adipose tissue as the amount of visceral fat was independent of the level of chimerism. Our findings thus suggest that proliferative potential of adipocyte precursors is limited and can restrain the development of obesity.

The herbal extract ALS-L1023 from Melissa officinalis alleviates visceral obesity and insulin resistance in obese female C57BL/6J mice

ETHNOPHARMACOLOGICAL RELEVANCE

Melissa officinalis L. (Labiatae; lemon balm) has traditionally been used as a medicinal herb to treat stress, anxiety, and insomnia. Current reports suggest that not only chronic stress stimulates angiogenesis, but angiogenesis also regulates adipogenesis and obesity. Because the herbal extract ALS-L1023 from Melissa officinalis inhibits angiogenesis, we hypothesized that ALS-L1023 could suppress visceral obesity and insulin resistance in obese female C57BL/6J mice, a mouse model of obese premenopausal women.

MATERIALS AND METHODS

The mice were grouped and fed for 16 weeks as follows: 1) low-fat diet (LFD), 2) high-fat diet (HFD), or 3) HFD supplemented with 0.4 or 0.8% ALS-L1023. Variables and determinants of visceral obesity, insulin resistance, and pancreatic dysfunction were then assessed via blood analysis, histology, immunohistochemistry, and real-time polymerase chain reaction.

RESULTS

ALS-L1023 decreased weight gain, visceral adipocyte size, and serum lipid levels in HFD-fed obese mice. ALS-L1023 also normalized hyperglycemia and hyperinsulinemia and concomitantly reduced blood glucose levels during oral glucose tolerance tests. The pancreatic islet size and insulin-positive β-cell area were significantly reduced in ALS-L1023-treated mice compared with untreated obese controls, reaching a level similar to that of LFD-fed lean mice. ALS-L1023 suppressed pancreatic lipid accumulation, infiltration of inflammatory cells, and collagen levels. ALS-L1023 treatment altered the pancreatic expression of genes involved in steatosis, inflammation, and fibrosis.

CONCLUSIONS

Our findings indicate that the herbal extract ALS-L1023 from Melissa officinalis not only inhibits visceral obesity, but also attenuates the increased fasting blood glucose, impaired glucose tolerance, and pancreatic dysfunction seen in female obese mice. These results suggest that ALS-L1023 may be effective in the prevention of visceral obesity and insulin resistance in obese premenopausal women.

Chinese olive (Canarium album L.) fruit regulates glucose utilization by activating AMP-activated protein kinase

A growing body of evidence demonstrates obesity-induced insulin resistance is associated with the development of metabolic diseases. This study was designed to investigate ethyl acetate fraction of Chinese olive fruit extract (CO-EtOAc)-mediated attenuation of obesity and hyperglycemia in a mouse model. About 60% HFD-fed mice were treated intragastrically with CO-EtOAc for last 6 weeks, and body weight, blood biochemical parameters as well as hepatic inflammation response were investigated. Our results showed that CO-EtOAc treatment significantly reduced the formation of hepatic lipid droplets, body weight gain, blood glucose, and improved serum biochemical parameters in HFD-induced obese and insulin resistant mice. We further explored the molecular mechanism underlying the blood glucose modulating effect of CO-EtOAc using L6 myotubes model. We conclude that CO-EtOAc effectively increases the glycogen content and glucose uptake by stimulating the membrane translocation of glucose transporter 4. In addition, CO-EtOAc depolarizes the mitochondrial membrane and decreases the mitochondrial oxygen consumption, which may result in AMPK activation and the consequent mitochondrial fission. This study shows that CO-EtOAc prevents the development of obesity in mice fed with HFD and is also capable of stimulating glucose uptake. The possible mechanism might be due to the effects of CO-EtOAc on activation of AMPK and promotion of mitochondrial fission.

Multiple Biomarkers Improved Prediction for the Risk of Type 2 Diabetes Mellitus in Singapore Chinese Men and Women

BACKGROUND

Multiple biomarkers have performed well in predicting type 2 diabetes mellitus (T2DM) risk in Western populations. However, evidence is scarce among Asian populations.

METHODS

Plasma triglyceride-to-high density lipoprotein (TG-to-HDL) ratio, alanine transaminase (ALT), high-sensitivity C-reactive protein (hs-CRP), ferritin, adiponectin, fetuin-A, and retinol-binding protein 4 were measured in 485 T2DM cases and 485 age-and-sex matched controls nested within the prospective Singapore Chinese Health Study cohort. Participants were free of T2DM at blood collection (1999 to 2004), and T2DM cases were identified at the subsequent follow-up interviews (2006 to 2010). A weighted biomarker score was created based on the strengths of associations between these biomarkers and T2DM risks. The predictive utility of the biomarker score was assessed by the area under receiver operating characteristics curve (AUC).

RESULTS

The biomarker score that comprised of four biomarkers (TG-to-HDL ratio, ALT, ferritin, and adiponectin) was positively associated with T2DM risk (P trend <0.001). Compared to the lowest quartile of the score, the odds ratio was 12.0 (95% confidence interval [CI], 5.43 to 26.6) for those in the highest quartile. Adding the biomarker score to a base model that included smoking, history of hypertension, body mass index, and levels of random glucose and insulin improved AUC significantly from 0.81 (95% CI, 0.78 to 0.83) to 0.83 (95% CI, 0.81 to 0.86; P=0.002). When substituting the random glucose levels with glycosylated hemoglobin in the base model, adding the biomarker score improved AUC from 0.85 (95% CI, 0.83 to 0.88) to 0.86 (95% CI, 0.84 to 0.89; P=0.032).

CONCLUSION

A composite score of blood biomarkers improved T2DM risk prediction among Chinese.

Bifidobacterium animalis subsp. lactis 420 for Metabolic Health: Review of the Research

The growing worldwide epidemic of obesity and associated metabolic health comorbidities has resulted in an urgent need for safe and efficient nutritional solutions. The research linking obesity with gut microbiota dysbiosis has led to a hypothesis that certain bacterial strains could serve as probiotics helping in weight management and metabolic health. In the search for such strains, the effect of Bifidobacterium animalis subsp. lactis 420 (B420) on gut microbiota and metabolic health, and the mechanisms of actions, has been investigated in a variety of in vitro, pre-clinical, and clinical studies. In this review, we aim to highlight the research on B420 related to obesity, metabolic health, and the microbiota. Current research supports the hypothesis that gut dysbiosis leads to an imbalance in the inflammatory processes and loss of epithelial integrity. Bacterial components, like endotoxins, that leak out of the gut can invoke low-grade, chronic, and systemic inflammation. This imbalanced state is often referred to as metabolic endotoxemia. Scientific evidence indicates that B420 can slow down many of these detrimental processes via multiple signaling pathways, as supported by mechanistic in vitro and in vivo studies. We discuss the connection of these mechanisms to clinical evidence on the effect of B420 in controlling weight gain in overweight and obese subjects. The research further indicates that B420 may improve the epithelial integrity by rebalancing a dysbiotic state induced by an obesogenic diet, for example by increasing the prevalence of lean phenotype microbes such as Akkermansia muciniphila. We further discuss, in the context of delivering the health benefits of B420: the safety and technological aspects of the strain including genomic characterization, antibiotic resistance profiling, stability in the product, and survival of the live probiotic in the intestine. In summary, we conclude that the clinical and preclinical studies on metabolic health suggest that B420 may be a potential candidate in combating obesity; however, further clinical studies are needed.

Obesity and Mechanisms of its Negative Impact on the Cardiovascular System

Currently, the number of obese people in the world is constantly increasing. Obesity has a direct negative impact on the heart and blood vessels, which can be considered not only as an appropriate response to an increase in the volume of circulating blood due to an increase in body weight, but also as a side tissue reaction of the myocardium to hormonal and metabolic changes inherent in obesity. Our review is devoted to the description of the mechanisms of influence of obesity on the structural and functional parameters of the heart, which create prerequisites for the development of cardiovascular diseases, as well as the existing contradictions. Currently, the accumulated data suggest that an excessive amount of adipose tissue, in addition to metabolic disorders, including insulin resistance, imbalance of adipokines and inflammation markers, leading to the development of lipotoxicity, can directly penetrate the myocardium and cause violations of its contractile properties, as well as affect the conduction of excitation pulses and provoke the development of rhythm and conduction disorders. The development of endothelial dysfunction in obesity ultimately leads to the development of atherosclerosis and coronary heart disease. In addition, obesity contributes to the emergence of risk factors for hypertension, diabetes, atrial fibrillation, chronic heart failure, obstructive sleep apnea syndrome. Given the differences in the literature on the effect of obesity on long-term outcomes in patients with cardiovascular diseases, it is important to conduct prospective studies on the role of individual factors and their combinations that affect the mortality of patients with cardiovascular diseases.

Triglyceride metabolism and angiopoietin-like proteins in lipoprotein lipase regulation

Hypertriglyceridemia is a risk factor for a series of diseases, such as cardiovascular disease (CVD), diabetes and nonalcoholic fatty liver disease (NAFLD). Angiopoietin-like proteins (ANGPTLs) family, especially ANGPTL3, ANGPTL4 and ANGPTL8, which regulate lipoprotein lipase (LPL) activity, play pivotal roles in triglyceride (TG) metabolism and related diseases/complications. There are many transcriptional and post-transcriptional factors that participate in physiological and pathological regulation of ANGPTLs to affect triglyceride metabolism. This review is intended to focus on the similarity and difference in the expression, structural features, regulation profile of the three ANGPTLs and inhibitory models for LPL. Description of the regulatory factors of ANGPTLs and the properties in regulating the lipid metabolism involved in the underlying mechanisms in pathological effects on diseases will provide potential therapeutic approaches for the treatment of dyslipidemia related diseases.

Resveratrol Treatment Enhances the Cellular Response to Leptin by Increasing OBRb Content in Palmitate-Induced Steatotic HepG2 Cells

The interaction of leptin with its hepatic longest receptor (OBRb) promotes the phosphorylation of signal transducer and activator of transcription-3 (STAT3), protecting the liver from lipid accumulation. However, leptin signalling is disrupted in hepatic steatosis, causing leptin resistance. One promising strategy to combat this problem is the use of bioactive compounds such as polyphenols. Since resveratrol (RSV) is a modulator of lipid homeostasis in the liver, we investigated whether treatment with different doses of RSV restores appropriate leptin action and fat accumulation in palmitate-induced steatotic human hepatoma (HepG2) cells. Both RSV metabolism and the expression of molecules implicated in leptin signalling were analysed. RSV at a 10 μM concentration was entirely metabolized to resveratrol-3-sulfate after 24 and counteracted leptin resistance by increasing the protein levels of OBRb. In addition, RSV downregulated the expression of lipogenic genes including fatty acid synthase (Fas) and stearoyl-CoA desaturase-1 (Scd1) without any significant change in Sirtuin-1 (SIRT1) enzymatic activity. These results demonstrate that RSV restored leptin sensitivity in a cellular model of hepatic steatosis in a SIRT1-independent manner.

Muscle metabolic reprogramming underlies the resistance of liver fatty acid-binding protein (LFABP)-null mice to high-fat feeding-induced decline in exercise capacity

Liver fatty acid-binding protein (LFABP) binds long-chain fatty acids with high affinity and is abundantly expressed in the liver and small intestine. Although LFABP is thought to function in intracellular lipid trafficking, studies of LFABP-null (LFABP^-/-) mice have also indicated a role in regulating systemic energy homeostasis. We and others have reported that LFABP^-/- mice become more obese than wildtype (WT) mice upon high-fat feeding. Here, we show that despite increased body weight and fat mass, LFABP^-/- mice are protected from a high-fat feeding-induced decline in exercise capacity, displaying an approximate doubling of running distance compared with WT mice. To understand this surprising exercise phenotype, we focused on metabolic alterations in the skeletal muscle due to LFABP ablation. Compared with WT mice, resting skeletal muscle of LFABP^-/- mice had higher glycogen and intramuscular triglyceride levels as well as an increased fatty acid oxidation rate and greater mitochondrial enzyme activities, suggesting higher substrate availability and substrate utilization capacity. Dynamic changes in the respiratory exchange ratio during exercise indicated that LFABP^-/- mice use more carbohydrate in the beginning of an exercise period and then switch to using lipids preferentially in the later stage. Consistently, LFABP^-/- mice exhibited a greater decrease in muscle glycogen stores during exercise and elevated circulating free fatty acid levels postexercise. We conclude that, because LFABP is not expressed in muscle, its ablation appears to promote interorgan signaling that alters muscle substrate levels and metabolism, thereby contributing to the prevention of high-fat feeding-induced skeletal muscle impairment.

A computational model of postprandial adipose tissue lipid metabolism derived using human arteriovenous stable isotope tracer data

Given the association of disturbances in non-esterified fatty acid (NEFA) metabolism with the development of Type 2 Diabetes and Non-Alcoholic Fatty Liver Disease, computational models of glucose-insulin dynamics have been extended to account for the interplay with NEFA. In this study, we use arteriovenous measurement across the subcutaneous adipose tissue during a mixed meal challenge test to evaluate the performance and underlying assumptions of three existing models of adipose tissue metabolism and construct a new, refined model of adipose tissue metabolism. Our model introduces new terms, explicitly accounting for the conversion of glucose to glyceraldehye-3-phosphate, the postprandial influx of glycerol into the adipose tissue, and several physiologically relevant delays in insulin signalling in order to better describe the measured adipose tissues fluxes. We then applied our refined model to human adipose tissue flux data collected before and after a diet intervention as part of the Yoyo study, to quantify the effects of caloric restriction on postprandial adipose tissue metabolism. Significant increases were observed in the model parameters describing the rate of uptake and release of both glycerol and NEFA. Additionally, decreases in the model's delay in insulin signalling parameters indicates there is an improvement in adipose tissue insulin sensitivity following caloric restriction.

Perilipin5 protects against lipotoxicity and alleviates endoplasmic reticulum stress in pancreatic β-cells

Background

Chronic exposure of pancreatic β-cells to excess free fatty acids is thought to contribute to type 2 diabetes pathogenesis in obesity by impairing β-cell function and even leading to apoptosis. In β-cells, lipid droplet-associated protein perilipin 5 (PLIN5) has been shown to enhance insulin secretion by regulating intracellular lipid metabolism; the roles of PLIN5 in response to lipotoxicity remain poorly understood.

Methods

INS-1 β-cells were transfected with PLIN5-overexpression adenovirus (Ad-PLIN5) and treated with palmitate. C57BL/6 J male mice were fed with high fat diet and tail intravenous injected with adeno-associated virus overexpressing PLIN5 (AAV-PLIN5) in β-cells.

Results

Our data showed that palmitate and PPAR agonists including WY14643 (PPARα), GW501516 (PPARβ/δ), rosiglitazone (PPARγ) in vitro all induced PLIN5 expression in INS-1 cells. Under palmitate overload, although upregulating PLIN5 promoted lipid droplet storage, it alleviated lipotoxicity in INS-1 β-cells with improved cell viability, cell apoptosis and β-cell function. The protection role of PLIN5 in β-cell function observed in cell experiments were further verified in in vivo study indicated by mitigated glucose intolerance in high fat diet fed mice with β-cell-specific overexpression of PLIN5. Mechanistic experiments revealed that enhanced FAO induced by elevation of PLIN5, followed by decreased ER stress may be a major mechanism responsible for alleviation of lipotoxicity observed in the present study.

Conclusions

Our finding substantiated the important role of PLIN5 in protection against lipotoxicity in β-cells.

Electronic supplementary material

The online version of this article (10.1186/s12986-019-0375-2) contains supplementary material, which is available to authorized users.

Potential Role of Leptin in Cardiac Steatosis Induced by Highly Saturated Fat Intake during Adolescence

SCOPE

To identify the age-dependent effect of diets containing elevated amounts of either saturated or unsaturated fatty acids on cardiac steatosis in mice.

METHODS AND RESULTS

Five- and eight-week-old C57BL/6J mice cohorts are given free access to either a saturated or an unsaturated fatty-acid-enriched diet during 8 weeks. Body weight (BW) and food intake are monitored during this period. Cardiac lipid content, carnitine palmitoyltransferase-I (CPT-I) activity, and the amount of uncoupling proteins 2 and 3 (UCP2 and UCP3) are analyzed and correlated with blood leptin concentration. Leptin and PPARγ gene expression is quantified in white adipose tissue (WAT). Both diets have a similar effect on food intake, BW, and adiposity, independently of the age. Nevertheless, cardiac steatosis is specifically identified in adolescent mice consuming the saturated diet. These animals also display lower activity of cardiac CPT-I, a down-regulation of cardiac UCP2, together with lower concentration of plasma leptin. Accordingly, leptin gene expression is reduced in the visceral WAT.

CONCLUSION

Consumption of diets containing elevated amounts of saturated fat during adolescence and early adult life promotes cardiac steatosis in mice. An insufficient endocrine activity of WAT, in terms of leptin production, may account for such an effect.

Ethnic distinctions in the pathophysiology of type 2 diabetes: a focus on black African-Caribbean populations

Type 2 diabetes (T2D) is a global public health priority, particularly for populations of black African-Caribbean ethnicity, who suffer disproportionately high rates of the disease. While the mechanisms underlying the development of T2D are well documented, there is growing evidence describing distinctions among black African-Caribbean populations. In the present paper, we review the evidence describing the impact of black African-Caribbean ethnicity on T2D pathophysiology. Ethnic differences were first recognised through evidence that metabolic syndrome diagnostic criteria fail to detect T2D risk in black populations due to less central obesity and dyslipidaemia. Subsequently more detailed investigations have recognised other mechanistic differences, particularly lower visceral and hepatic fat accumulation and a distinctly hyperinsulinaemic response to glucose stimulation. While epidemiological studies have reported exaggerated insulin resistance in black populations, more detailed and direct measures of insulin sensitivity have provided evidence that insulin sensitivity is not markedly different to other ethnic groups and does not explain the hyperinsulinaemia that is exhibited. These findings lead us to hypothesise that ectopic fat does not play a pivotal role in driving insulin resistance in black populations. Furthermore, we hypothesise that hyperinsulinaemia is driven by lower rates of hepatic insulin clearance rather than heightened insulin resistance and is a primary defect rather than occurring in compensation for insulin resistance. These hypotheses are being investigated in our ongoing South London Diabetes and Ethnicity Phenotyping study, which will enable a more detailed understanding of ethnic distinctions in the pathophysiology of T2D between men of black African and white European ethnicity.

Association of intracellular lipid accumulation in subcutaneous adipocyte precursors and plasma adipokines in bariatric surgery candidates

BACKGROUND

The adipocyte expansion is a critical process with implications in the pathogenesis of obesity associated metabolic syndrome. Impaired adipogenesis leads to dysfunctional, hypertrophic adipocytes, local inflammation and peripheric insulin resistance.

METHODS

We assessed the relationship between the adipogenic differentiation capacity of the subcutaneous adipose derived stem cells (ASCs), evaluated by total lipid accumulation, and the metabolic and hormonal profile in a group of obese female patients proposed for bariatric surgery (N = 20) versus normal weight female controls (N = 7).

RESULTS

The lipid accumulation (measured as optical density at 492 nm) of ASCs during their differentiation to adipocytes was significantly lower in ASCs isolated from obese patients as compared to ASCs isolated from normal weight patients (0.49 ± 0.1 vs. 0.71 ± 0.1, p < 0.001). Significant negative correlations between lipid accumulation in adipogenic differentiated ASCs and plasma concentrations of triglycerides (p < 0.01), insulin (p < 0.001), HOMA-IR (p < 0.01), adiponectin (p < 0.05) and leptin/adiponectin ratio (p < 0.05) were found in obese group.

CONCLUSIONS

In severely obese female patients, the abnormal adipogenesis is related to insulin resistance and leptin/adiponectin ratio. The abnormal lipid accumulation in the mature adipocyte derived from obese ASCs could possible predict the further development of type 2 diabetes mellitus in severely obese patients and influence the selection of patients for bariatric surgery.

Glucagon Receptor Antagonism Improves Glucose Metabolism and Cardiac Function by Promoting AMP-Mediated Protein Kinase in Diabetic Mice

The antidiabetic potential of glucagon receptor antagonism presents an opportunity for use in an insulin-centric clinical environment. To investigate the metabolic effects of glucagon receptor antagonism in type 2 diabetes, we treated Lepr^db/db and Lep^ob/ob mice with REMD 2.59, a human monoclonal antibody and competitive antagonist of the glucagon receptor. As expected, REMD 2.59 suppresses hepatic glucose production and improves glycemia. Surprisingly, it also enhances insulin action in both liver and skeletal muscle, coinciding with an increase in AMP-activated protein kinase (AMPK)-mediated lipid oxidation. Furthermore, weekly REMD 2.59 treatment over a period of months protects against diabetic cardiomyopathy. These functional improvements are not derived simply from correcting the systemic milieu; nondiabetic mice with cardiac-specific overexpression of lipoprotein lipase also show improvements in contractile function after REMD 2.59 treatment. These observations suggest that hyperglucagonemia enables lipotoxic conditions, allowing the development of insulin resistance and cardiac dysfunction during disease progression.

Connecting pancreatic islet lipid metabolism with insulin secretion and the development of type 2 diabetes

Obesity is the major contributing factor for the increased prevalence of type 2 diabetes (T2D) in recent years. Sustained positive influx of lipids is considered to be a precipitating factor for beta cell dysfunction and serves as a connection between obesity and T2D. Importantly, fatty acids (FA), a key building block of lipids, are a double-edged sword for beta cells. FA acutely increase glucose-stimulated insulin secretion through cell-surface receptor and intracellular pathways. However, chronic exposure to FA, combined with elevated glucose, impair the viability and function of beta cells in vitro and in animal models of obesity (glucolipotoxicity), providing an experimental basis for the propensity of beta cell demise under obesity in humans. To better understand the two-sided relationship between lipids and beta cells, we present a current view of acute and chronic handling of lipids by beta cells and implications for beta cell function and health. We also discuss an emerging role for lipid droplets (LD) in the dynamic regulation of lipid metabolism in beta cells and insulin secretion, along with a potential role for LD under nutritional stress in beta cells, and incorporate recent advancement in the field of lipid droplet biology.

The effects of green tea on lipid metabolism and its potential applications for obesity and related metabolic disorders - An existing update

Obesity is one of the top global issues, which induces several serious health consequences both physically and mentally, such as type 2 diabetes, cardiovascular diseases, dyslipidemia, eating disorders, depression and stress. However, the effective therapy to prevent and treat obesity and overweight, up to now, cannot be found nowadays. Several methods/medicines namely diet control, energy balance, environmental changes, genetic and stem cell therapies, new drugs/chemicals have been extensively studied to enhance the ability to control bodyweight and prevent obesity. Of all the aforementioned methods, green tea, used as a daily beverage, has shown beneficial impacts for the health, especially its anti-obesity effects. Available evidence shows that green tea can interrupt lipid emulsification, reduce adipocyte differentiation, increase thermogenesis, and reduce food intake, thus green tea improves the systemic metabolism and decreases fat mass. Here, we highlight and sum up the update investigations of anti-obesity effect of green tea as well as discuss the potential application of them for preventing obesity and its related metabolic disorders.

Targeting mitochondria to oppose the progression of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is a condition characterized by the excessive accumulation of triglycerides in hepatocytes. NAFLD is the most frequent chronic liver disease in developed countries, and is often associated with metabolic disorders such as obesity and type 2 diabetes. NAFLD definition encompasses a spectrum of chronic liver abnormalities, ranging from simple steatosis (NAFL), to steatohepatitis (NASH), significant liver fibrosis, cirrhosis, and hepatocellular carcinoma. NAFLD, therefore, represents a global public health issue. Mitochondrial dysfunction occurs in NAFLD, and contributes to the progression to the necro-inflammatory and fibrotic form (NASH). Disrupted mitochondrial function is associated with a decrease in the energy levels and impaired redox balance, and negatively affects cell survival by altering overall metabolism and subcellular trafficking. Such events reduce the tolerance of hepatocytes towards damaging hits, and favour the injurious effects of extra-cellular factors. Here, we discuss the role of mitochondria in NAFLD and focus on potential therapeutic approaches aimed at preserving mitochondrial function.

Circadian clocks and insulin resistance

Insulin resistance is a main determinant in the development of type 2 diabetes mellitus and a major cause of morbidity and mortality. The circadian timing system consists of a central brain clock in the hypothalamic suprachiasmatic nucleus and various peripheral tissue clocks. The circadian timing system is responsible for the coordination of many daily processes, including the daily rhythm in human glucose metabolism. The central clock regulates food intake, energy expenditure and whole-body insulin sensitivity, and these actions are further fine-tuned by local peripheral clocks. For instance, the peripheral clock in the gut regulates glucose absorption, peripheral clocks in muscle, adipose tissue and liver regulate local insulin sensitivity, and the peripheral clock in the pancreas regulates insulin secretion. Misalignment between different components of the circadian timing system and daily rhythms of sleep-wake behaviour or food intake as a result of genetic, environmental or behavioural factors might be an important contributor to the development of insulin resistance. Specifically, clock gene mutations, exposure to artificial light-dark cycles, disturbed sleep, shift work and social jet lag are factors that might contribute to circadian disruption. Here, we review the physiological links between circadian clocks, glucose metabolism and insulin sensitivity, and present current evidence for a relationship between circadian disruption and insulin resistance. We conclude by proposing several strategies that aim to use chronobiological knowledge to improve human metabolic health.

Anthocyanins in the Management of Metabolic Syndrome: A Pharmacological and Biopharmaceutical Review

The term "metabolic syndrome" (MetS) refers to a combination of diabetes, high blood pressure, and obesity. The origin of MetS includes a combination of multiple factors, such as sedentary lifestyle, unhealthy diet choice, and genetic factors. MetS is highly prevalent and adversely affects the general population by elevating risk of cardiovascular complications, organ failure, and much other pathology associated with late-stage diabetes. Anthocyanins (ANTs) are health-promoting bioactive compounds belonging to the flavonoids subclass of polyphenols. Numerous studies have reported the potential therapeutic benefits on MetS syndrome and diabetes from fruits rich in ANTs. This review summarizes the role of several dietary ANTs on preventing and managing MetS as well as the pharmacological mechanisms and biopharmaceutical features of their action. We also discuss potential nanoformulation and encapsulation approaches that may enhance the bioefficacy of ANTs in MetS. Experiments have demonstrated that ANTs may attenuate the symptoms of MetS via improving insulin resistance, impaired glucose tolerance, dyslipidaemia, cholesterol levels, hypertension, blood glucose, protecting β cells, and preventing free radical production. In brief, the intake of ANT-rich supplements should be considered due to their plausible ability for prevention and management of MetS. Additionally, randomized double-blind clinical trials are obligatory for evaluating the bioefficacy and pharmacological mechanisms of ANTs and their pharmaceutical formulations in patients with MetS.

Dysregulation of Sqstm1, mitophagy, and apoptotic genes in chronic exposure to arsenic and high-fat diet (HFD)

Arsenic (As) is a toxic and hazardous metalloid. Unfortunately, its presence in drinking water together with wrong nutritional patterns is associated with an increase in the occurrence of metabolic disorders in young people. Degradation of mitochondria is presented by a specific form of autophagy called mitophagy which is an important landmark leading to apoptosis during lipotoxicity. Lipotoxicity and cellular toxicity due to arsenic intake can lead to changes in mitophagy and apoptosis. The protein derived from SQSTM1 gene, also called p62, plays an important role in energy homeostasis in the liver, and it can contribute to the regulation of autophagic responses given its effect on signaling of mTOR, MAPK, and NF-KB. Consequently, changes in Sqstm1, mitophagy (BNIP3), and apoptotic (caspase 3) genes in the livers of NMRI mice were examined with the use of real-time RT-PCR Array followed by exposure to an environmentally relevant and negligible cytotoxic concentration of arsenite (50 ppm) in drinking water while being fed with a high-fat diet (HFD) or low-fat diet (LFD) for 20 weeks (LFD-As and HFD-As groups). While LFD-As and HFD groups showed a decrease in BNIP3 expression, a significant increase was observed in the HFD-As group. P62 gene showed downregulation in LFD-As and HFD groups, and upregeneration was observed in the HFD-As group. Caspase 3 showed increased expression as the key factor associated with apoptotic liver cell death in the three groups, with the highest value in HFD-As group. Overall, the changes observed in the expression of Sqstm1, BNIP3, and caspase 3 in this study can be related to the level of liver damage caused by exposure to arsenic and HFD and probably, BNIP3 pro-apoptotic protein is associated with an increased cell death due to HFD and As.

Insights into leptin signaling and male reproductive health: the missing link between overweight and subfertility?

Obesity stands as one of the greatest healthcare challenges of the 21st century. Obesity in reproductive-age men is ever more frequent and is reaching upsetting levels. At the same time, fertility has taken an inverse direction and is decreasing, leading to an increased demand for fertility treatments. In half of infertile couples, there is a male factor alone or combined with a female factor. Furthermore, male fertility parameters such as sperm count and concentration went on a downward spiral during the last few decades and are now approaching the minimum levels established to achieve successful fertilization. Hence, the hypothesis that obesity and deleterious effects in male reproductive health, as reflected in deterioration of sperm parameters, are somehow related is tempting. Most often, overweight and obese individuals present leptin levels directly proportional to the increased fat mass. Leptin, besides the well-described central hypothalamic effects, also acts in several peripheral organs, including the testes, thus highlighting a possible regulatory role in male reproductive function. In the last years, research focusing on leptin effects in male reproductive function has unveiled additional roles and molecular mechanisms of action for this hormone at the testicular level. Herein, we summarize the novel molecular signals linking metabolism and male reproductive function with a focus on leptin signaling, mitochondria and relevant pathways for the nutritional support of spermatogenesis.

Lipidomic analysis reveals significant lipogenesis and accumulation of lipotoxic components in ob/ob mouse organs

To further understand the role of lipogenesis and lipotoxicity in the development of obesity and diabetes, lipidomes of various organs from ob/ob mice and their wild type controls were analyzed by shotgun lipidomics at 10, 12, and 16 weeks of age. We observed that the amounts of fatty acyl (FA) chains corresponding to those from de novo synthesis (e.g., 16:0, 16:1, and 18:1 FA) were substantially elevated in ob/ob mice, consistent with increased expression of genes and proteins involved in biosynthesis. Polyunsaturated fatty acid species were moderately increased in the examined tissues of ob/ob mice, since they can only be absorbed from diets or elongated from the ingested n-3 or n-6 FA. Different profiles of FA chains between ob/ob mouse liver and skeletal muscle reflect diverging lipogenesis pathways in these organs. Amounts of vaccenic acids (i.e., 18:1(n-7) FA) in 12- and 16-week ob/ob mouse liver were significantly increased compared to their controls, indicating enhanced de novo synthesis of this acid through 16:1(n-7) FA in the liver starting at 12 weeks of age. Coincidentally, synthesis of triacylglycerol from monoacylglycerol in the liver was also increased in ob/ob mice starting at 12 weeks of age, as revealed by simulation of triacylglycerol synthesis. Moreover, levels of lipotoxic lipid classes were significantly higher in ob/ob mice than their age-matched controls, supporting the notion that elevated lipotoxic components are tightly associated with insulin resistance in ob/ob mice. Taken together, the current study revealed that lipogenesis and lipotoxicity in ob/ob mice likely contribute to insulin resistance and provides great insights into the underlying mechanisms of diabetes and obesity.

The role of obesity and adipose tissue dysfunction in gestational diabetes mellitus

Gestational diabetes mellitus is defined as diabetes diagnosed in the second or third trimester of pregnancy in patients with no history of diabetes prior to gestation. It is the most common complication of pregnancy. The underlying pathophysiology shares some common features with type 2 diabetes mellitus (T2DM) combining relatively insufficient insulin secretion with increased peripheral insulin resistance. While a certain degree of insulin resistance is the physiological characteristics of the second half of pregnancy, it is significantly more pronounced in patients with gestational diabetes. Adipose tissue dysfunction and subclinical inflammation in obesity are well-described causes of increased insulin resistance in non-pregnant subjects and are often observed in individuals with T2DM. Emerging evidence of altered adipokine expression and local inflammation in adipose tissue in patients with gestational diabetes suggests an important involvement of adipose tissue in its etiopathogenesis. This review aims to summarize current knowledge of adipose tissue dysfunction and its role in the development of gestational diabetes. We specifically focus on the significance of alterations of adipokines and immunocompetent cells number and phenotype in fat. Detailed understanding of the role of adipose tissue in gestational diabetes may provide new insights into its pathophysiology and open new possibilities of its prevention and treatment.

Expression analysis of a cholecystokinin system in human and rat white adipose tissue

AIM

Cholecystokinin (CCK) participates in the storage of dietary triglycerides in white adipose tissue (WAT). Our goal was to characterize, both in subcutaneous (Sc-WAT) and visceral WAT (Vis-WAT), the functional expression of the two known CCK receptors, CCK-1 (CCK-1R) and CCK-2 (CCK-2R), as well as of CCK.

MAIN METHODS

Gene and protein expression was assessed in different cell types of rat and human WAT by means of RT-PCR and western-blot, respectively. The functionality of CCK-Rs was tested by quantifying protein kinase B (Akt) phosphorylation after treatment of pre-adipocytes with the bioactive fragment of CCK, CCK-8. The CCK receptor subtype involved in Akt phosphorylation was investigated by using selective CCK-1R (SR-27,897) and CCK-2R antagonists (L-365,260).

KEY FINDINGS

In rats, CCK-1R (Cckar) and CCK-2R (Cckbr) gene expression was detected in the two types of WAT analyzed as well as in isolated adipocytes, mesenchymal stem cells and pre-adipocytes. CCK-1R and CCK-2R proteins were identified in adipocytes and, to a minor extent, in pre-adipocytes. In addition, CCK-2R were detected in subcutaneous mesenchymal stem cells. Gene expression of the CCK precursor preproCCK as well as CCK immunoreactivity were also found in Sc-WAT and Vis-WAT. In human WAT, CCK gene expression as well as CCK-2Rs and CCK were also identified. CCK-8 evoked Akt phosphorylation in rat pre-adipocytes, and this effect was antagonized by SR-27,897 and L-365,260.

SIGNIFICANCE

Our data show that both human and rat WAT express a complete CCK system, and suggest that CCK may have an autocrine/paracrine role in regulating adipose tissue biology.

Palmitic acid triggers inflammatory responses in N42 cultured hypothalamic cells partially via ceramide synthesis but not via TLR4

A high-fat diet induces hypothalamic inflammation in rodents which, in turn, contributes to the development of obesity by eliciting both insulin and leptin resistance. However, the mechanism by which long-chain saturated fatty acids trigger inflammation is still contentious. To elucidate this mechanism, the effect of fatty acids on the expression of the pro-inflammatory cytokines IL-6 and TNFα was investigated in the mHypoE-N42 hypothalamic cell line (N42). N42 cells were treated with lauric acid (LA) and palmitic acid (PA). PA challenge was carried out in the presence of either a TLR4 inhibitor, a ceramide synthesis inhibitor (L-cycloserine), oleic acid (OA) or eicosapentaenoic acid (EPA). Intracellular ceramide accumulation was quantified using LC-ESI-MS/MS. PA but not LA upregulated IL-6 and TNFα. L-cycloserine, OA and EPA all counteracted PA-induced intracellular ceramide accumulation leading to a downregulation of IL-6 and TNFα. However, a TLR4 inhibitor failed to inhibit PA-induced upregulation of pro-inflammatory cytokines.In conclusion, PA induced the expression of IL-6 and TNFα in N42 neuronal cells independently of TLR4 but, partially, via ceramide synthesis with OA and EPA being anti-inflammatory by decreasing PA-induced intracellular ceramide build-up. Thus, ceramide accumulation represents one on the mechanisms by which PA induces inflammation in neurons.

Perilipin 5 Deletion Unmasks an Endoplasmic Reticulum Stress-Fibroblast Growth Factor 21 Axis in Skeletal Muscle

Lipid droplets (LDs) are critical for the regulation of lipid metabolism, and dysregulated lipid metabolism contributes to the pathogenesis of several diseases, including type 2 diabetes. We generated mice with muscle-specific deletion of the LD-associated protein perilipin 5 (PLIN5, Plin5^MKO ) and investigated PLIN5's role in regulating skeletal muscle lipid metabolism, intracellular signaling, and whole-body metabolic homeostasis. High-fat feeding induced changes in muscle lipid metabolism of Plin5^MKO mice, which included increased fatty acid oxidation and oxidative stress but, surprisingly, a reduction in inflammation and endoplasmic reticulum (ER) stress. These muscle-specific effects were accompanied by whole-body glucose intolerance, adipose tissue insulin resistance, and reduced circulating insulin and C-peptide levels in Plin5^MKO mice. This coincided with reduced secretion of fibroblast growth factor 21 (FGF21) from skeletal muscle and liver, resulting in reduced circulating FGF21. Intriguingly, muscle-secreted factors from Plin5^MKO , but not wild-type mice, reduced hepatocyte FGF21 secretion. Exogenous correction of FGF21 levels restored glycemic control and insulin secretion in Plin5^MKO mice. These results show that changes in lipid metabolism resulting from PLIN5 deletion reduce ER stress in muscle, decrease FGF21 production by muscle and liver, and impair glycemic control. Further, these studies highlight the importance for muscle-liver cross talk in metabolic regulation.

Obesity does not promote tumorigenesis of localized patient-derived prostate cancer xenografts

There are established epidemiological links between obesity and the severity of prostate cancer. We directly tested this relationship by assessing tumorigenicity of patient-derived xenografts (PDXs) of moderate-grade localized prostate cancer in lean and obese severe combined immunodeficiency (SCID) mice. Mice were rendered obese and insulin resistant by high-fat feeding for 6 weeks prior to transplantation, and PDXs were assessed 10 weeks thereafter. Histological analysis of PDX grafts showed no differences in tumor pathology, prostate-specific antigen, androgen receptor and homeobox protein Nkx-3.1 expression, or proliferation index in lean versus obese mice. Whilst systemic obesity per se did not promote prostate tumorigenicity, we next asked whether the peri-prostatic adipose tissue (PPAT), which covers the prostate anteriorly, plays a role in prostate tumorigenesis. In vitro studies in a cellularized co-culture model of stromal and epithelial cells demonstrated that factors secreted from human PPAT are pro-tumorigenic. Accordingly, we recapitulated the prostate-PPAT spatial relationship by co-grafting human PPAT with prostate cancer in PDX grafts. PDX tissues were harvested 10 weeks after grafting, and histological analysis revealed no evidence of enhanced tumorigenesis with PPAT compared to prostate cancer grafts alone. Altogether, these data demonstrate that prostate cancer tumorigenicity is not accelerated in the setting of diet-induced obesity or in the presence of human PPAT, prompting the need for further work to define the at-risk populations of obesity-driven tumorigenesis and the biological factors linking obesity, adipose tissue and prostate cancer pathogenesis.

Dihydroceramide-desaturase-1-mediated caspase 9 activation through ceramide plays a pivotal role in palmitic acid-induced HepG2 cell apoptosis

In this study, results showed that the inhibition of PA-induced HepG2 cell growth takes place in a time- and concentration-dependent manner, that activation of caspase 9 is necessary for PA-induced HepG2 cell apoptosis, that dihydroceramide desaturase 1 (DES1) plays a key role in PA-mediated caspase 9 and caspase 3 activation, and that palmitoleic acid (POA), an omega-7 monounsaturated fatty acid, reverses PA-induced apoptosis through DES1 → Ceramide → Caspase 9 → Caspase 3 signaling.

Role of MicroRNAs in Obesity-Induced Metabolic Disorder and Immune Response

In all living organisms, metabolic homeostasis and the immune system are the most fundamental requirements for survival. Recently, obesity has become a global public health issue, which is the cardinal risk factor for metabolic disorder. Many diseases emanating from obesity-induced metabolic dysfunction are responsible for the activated immune system, including innate and adaptive responses. Of note, inflammation is the manifest accountant signal. Deeply studied microRNAs (miRNAs) have participated in many pathways involved in metabolism and immune responses to protect cells from multiple harmful stimulants, and they play an important role in determining the progress through targeting different inflammatory pathways. Thus, immune response and metabolic regulation are highly integrated with miRNAs. Collectively, miRNAs are the new targets for therapy in immune dysfunction.

Metabolic Disorders in Chronic Lung Diseases

Chronic lung diseases represent complex diseases with gradually increasing incidence, characterized by significant medical and financial burden for both patients and relatives. Their increasing incidence and complexity render a comprehensive, multidisciplinary, and personalized approach critically important. This approach includes the assessment of comorbid conditions including metabolic dysfunctions. Several lines of evidence show that metabolic comorbidities, including diabetes mellitus, dyslipidemia, osteoporosis, vitamin D deficiency, and thyroid dysfunction have a significant impact on symptoms, quality of life, management, economic burden, and disease mortality. Most recently, novel pathogenetic pathways and potential therapeutic targets have been identified through large-scale studies of metabolites, called metabolomics. This review article aims to summarize the current state of knowledge on the prevalence of metabolic comorbidities in chronic lung diseases, highlight their impact on disease clinical course, delineate mechanistic links, and report future perspectives on the role of metabolites as disease modifiers and therapeutic targets.

Linking Cancer Cachexia-Induced Anabolic Resistance to Skeletal Muscle Oxidative Metabolism

Cancer cachexia, a wasting syndrome characterized by skeletal muscle depletion, contributes to increased patient morbidity and mortality. While the intricate balance between protein synthesis and breakdown regulates skeletal muscle mass, the suppression of basal protein synthesis may not account for the severe wasting induced by cancer. Therefore, recent research has shifted to the regulation of “anabolic resistance,” which is the impaired ability of nutrition and exercise to stimulate protein synthesis. Emerging evidence suggests that oxidative metabolism can regulate both basal and induced muscle protein synthesis. While disrupted protein turnover and oxidative metabolism in cachectic muscle have been examined independently, evidence suggests a linkage between these processes for the regulation of cancer-induced wasting. The primary objective of this review is to highlight the connection between dysfunctional oxidative metabolism and cancer-induced anabolic resistance in skeletal muscle. First, we review oxidative metabolism regulation of muscle protein synthesis. Second, we describe cancer-induced alterations in the response to an anabolic stimulus. Finally, we review a role for exercise to inhibit cancer-induced anabolic suppression and mitochondrial dysfunction.

Sex-specific association between fibroblast growth factor 21 and type 2 diabetes: a nested case-control study in Singapore Chinese men and women

Background

Fibroblast growth factor 21 (FGF-21) is mainly secreted by liver and has been reported to be involved in the pathogenesis of type 2 diabetes. Some prospective studies have shown a positive association between FGF-21 and diabetes risk. However, no study has examined whether the association differed by sex, which has been reported between FGF-21 and atherosclerosis. Therefore, we prospectively evaluated the sex-specific association between FGF-21 and diabetes in a Chinese population.

Methods

Serum FGF-21 concentration was measured in a case-control study comprising of 251 incident diabetes cases and 251 age-sex-matched controls nested within a prospective population-based cohort, the Singapore Chinese Health Study. At blood collection between 1999 and 2004, participants were free of diagnosed diabetes, cardiovascular disease, and cancer. Incident self-reported diabetes cases were identified at follow-up II interview (2006–2010). Odds ratio (OR) and 95% confidence interval (CI) were calculated using multivariable logistic regression models.

Results

After adjustment for risk biomarkers of diabetes including lipids, liver enzymes and inflammatory marker, the OR of type 2 diabetes with per one unit increment in log FGF-21 concentration was 1.16 (95% CI 0.90–1.50). Significant interaction was found with sex (P-interaction = 0.029): the OR (95% CI) was 1.50 (1.00-2.25) in women and 0.89 (0.52–1.53) in men.

Conclusions

Higher serum FGF-21 level was associated with an increased risk of diabetes in Chinese women but not in men. The sex difference in the association between FGF-21 and diabetes risk deserves further investigation and replication in other populations.

Electronic supplementary material

The online version of this article (10.1186/s12986-017-0216-0) contains supplementary material, which is available to authorized users.

Anti-diabetic Effects of Ethanol Extract from Bitter Melon in Mice Fed a High-fat Diet

Present study aimed to determine the effect of ‘bitter melon’, a popularly used fruit in Bangladesh and several other Asian countries, on high-fat-diet-induced type 2 diabetes. To investigate the effect, ethanol extract from bitter melon (BME) as a dietary supplement with mouse chow was used. BME was found to significantly attenuate the high-fat diet (HFD) -induced body weight and total fat mass. BME also effectively reduced the insulin resistance induced by the HFD. Furthermore, dietary supplementation of BME was highly effective in increasing insulin sensitivity and reducing hepatic fat and obesity. These results indicate that BME could be effective in attenuating type 2 diabetes and could therefore be a preventive measure against type 2 diabetes.

Postprandial lipemia: factoring in lipemic response for ranking foods for their healthiness

One of the limitations for ranking foods and meals for healthiness on the basis of the glycaemic index (GI) is that the GI is subject to manipulation by addition of fat. Postprandial lipemia, defined as a rise in circulating triglyceride containing lipoproteins following consumption of a meal, has been recognised as a risk factor for the development of cardiovascular disease and other chronic diseases. Many non-modifiable factors (pathological conditions, genetic background, age, sex and menopausal status) and life-style factors (physical activity, smoking, alcohol and medication use, dietary choices) may modulate postprandial lipemia. The structure and the composition of a food or a meal consumed also plays an important role in the rate of postprandial appearance and clearance of triglycerides in the blood. However, a major difficulty in grading foods, meals and diets according to their potential to elevate postprandial triglyceride levels has been the lack of a standardised marker that takes into consideration both the general characteristics of the food and the food’s fat composition and quantity. The release rate of lipids from the food matrix during digestion also has an important role in determining the postprandial lipemic effects of a food product. This article reviews the factors that have been shown to influence postprandial lipemia with a view to develop a novel index for ranking foods according to their healthiness. This index should take into consideration not only the glycaemic but also lipemic responses.

What Is Lipotoxicity?

Enlarged fat cells in obese adipose tissue diminish capacity to store fat and are resistant to the anti-lipolytic effect of insulin. Insulin resistance (IR)-associated S-nitrosylation of insulin-signaling proteins increases in obesity. In accordance with the inhibition of insulin-mediated anti-lipolytic action, plasma free fatty acid (FFA) levels increase. Additionally, endoplasmic reticulum stress stimuli induce lipolysis by activating cyclic adenosine monophosphate/Protein kinase A (cAMP/PKA) and extracellular signal-regulated kinase ½ (ERK1/2) signaling in adipocytes. Failure of packaging of excess lipid into lipid droplets causes chronic elevation of circulating fatty acids, which can reach to toxic levels within non-adipose tissues. Deleterious effects of lipid accumulation in non-adipose tissues are known as lipotoxicity. In fact, triglycerides may also serve a storage function for long-chain non-esterified fatty acids and their products such as ceramides and diacylglycerols (DAGs). Thus, excess DAG, ceramide and saturated fatty acids in obesity can induce chronic inflammation and have harmful effect on multiple organs and systems. In this context, chronic adipose tissue inflammation, mitochondrial dysfunction and IR have been discussed within the scope of lipotoxicity.

Hepatokines: linking nonalcoholic fatty liver disease and insulin resistance

Hepatic steatosis is an underlying feature of nonalcoholic fatty liver disease (NAFLD), which is the most common form of liver disease and is present in up to ∼70% of individuals who are overweight. NAFLD is also associated with hypertriglyceridaemia and low levels of HDL, glucose intolerance, insulin resistance and type 2 diabetes mellitus. Hepatic steatosis is a strong predictor of the development of insulin resistance and often precedes the onset of other known mediators of insulin resistance. This sequence of events suggests that hepatic steatosis has a causal role in the development of insulin resistance in other tissues, such as skeletal muscle. Hepatokines are proteins that are secreted by hepatocytes, and many hepatokines have been linked to the induction of metabolic dysfunction, including fetuin A, fetuin B, retinol-binding protein 4 (RBP4) and selenoprotein P. In this Review, we describe the factors that influence the development of hepatic steatosis, provide evidence of strong links between hepatic steatosis and insulin resistance in non-hepatic tissues, and discuss recent advances in our understanding of how steatosis alters hepatokine secretion to influence metabolic phenotypes through inter-organ communication.

Myriocin treatment affects lipid metabolism in skeletal muscles of rats with streptozotocin-induced type 1 diabetes

PURPOSE

The aim of this work was to assess the effect(s) of de novo ceramide synthesis inhibition on lipid metabolism in skeletal muscle tissue of type 1 diabetic rats. The latter seems to be of vital importance, since previous works have shown its positive influence on lipid metabolism and glucose homeostasis in the case of its counterpart - type 2 diabetes.

MATERIALS/METHODS

The animals were randomly assigned to one of the following groups: C - control, M - myriocin (ceramide de novo synthesis inhibitor), D - diabetes (induced by streptozotocin injections); D+M - diabetes+myriocin. We have evaluated intracellular concentration of key sphingolipid species, via chromatography (GC and HPLC), and the activity of their most important enzymes, using radiometric approach. The aforementioned assessments were evaluated in respect to the three different types of muscle tissue representing different spectra of muscle metabolism (soleus - oxidative, red gastrocnemious - oxidative-glycolytic, white gastrocnemious - glycolytic).

RESULTS

Interestingly, our therapeutic intervention not only lowered the level of ceramide, its precursors (sphinganine) and derivatives (sphingosine and sphingosine-1-phosphate), but also reduced other lipid species (triacylglycerols, diacylglycerols and free fatty acids) content, thus improving glucose homeostasis in type 1 diabetic animals.

CONCLUSIONS

In the light of the results ensuing from this study, it seems conceivable that the reduction of intramuscular ceramide production and accumulation could bestow an insulin-sensitizing effect. If so, then SPT inhibition could find potential future applications as a therapeutic intervention aimed to mitigate the effects of insulin resistance.

Cellular models for the evaluation of the antiobesity effect of selected phytochemicals from food and herbs

Dietary phytochemicals from food and herbs have been studied for their health benefits for a long time. The incidence of obesity has seen an incredible increase worldwide. Although dieting, along with increased physical activity, seems an easy method in theory to manage obesity, it is hard to apply in real life. Obesity treatment drugs and surgery are not successful or targeted for everyone and can have significant side effects. This low rate of success is the major reason that the overweight as well as the pharmaceutical industry seek alternative methods, including phytochemicals. Therefore, more and more research has focused on the role of phytochemicals to alleviate lipid accumulation or enhance energy expenditure in adipocytes. This review discusses selected phytochemicals from food and herbs and their effects on adipogenesis, lipogenesis, lipolysis, oxidation of fatty acids, and browning in 3T3-L1 preadipocytes.

Sphingolipids in obesity and related complications

Sphingolipids are biologically active lipids ubiquitously produced in all vertebrate cells. Asides from structural components of cell membrane, sphingolipids also function as intracellular and extracellular mediators that regulate many important physiological cellular processes including cell survival, proliferation, apoptosis, differentiation, migration and immune processes. Recent studies have also indicated that disruption of sphingolipid metabolism is strongly associated with different diseases that exhibit diverse neurological and metabolic consequences. Here, we briefly summarize current evidence for understanding of sphingolipid pathways in obesity and associated complications. The regulation of sphingolipids and their enzymes may have a great impact in the development of novel therapeutic modalities for a variety of metabolic diseases.

Microvesicles Correlated with Components of Metabolic Syndrome in Men with Type 2 Diabetes Mellitus and Lowered Testosterone Levels But Were Unaltered by Testosterone Therapy

Aims. To investigate how circulating microvesicle phenotypes correlate with insulin sensitivity, body composition, plasma lipids, and hepatic fat accumulation. We hypothesized that changes elicited by testosterone replacement therapy are reflected in levels of microvesicles. Methods. Thirty-nine type 2 diabetic males with lowered testosterone levels were assigned to either testosterone replacement therapy or placebo and evaluated at baseline and after 24 weeks. Microvesicles were analysed by flow cytometry and defined as lactadherin-binding particles within the 0.1-1.0 μm gate. Microvesicles of platelet, monocyte, and endothelial cell origin were identified by cell-specific markers and their expression of CD36 was investigated. Results. Triglycerides correlated positively with all investigated microvesicle phenotypes in this study (p < 0.05), and indicators of hepatic fat accumulation, alanine aminotransferase, and gamma glutamyltransferase correlated with platelet and endothelial microvesicles and CD36-expressing microvesicles from platelets and monocytes (p < 0.05). BMI, waist circumference, and fat percentage correlated with CD36-expressing monocyte microvesicles (p < 0.05), while insulin sensitivity did not correlate with any microvesicle phenotypes. Microvesicle levels were unaffected by testosterone therapy. Conclusions. Metabolic syndrome components and hepatic fat accumulation correlated with microvesicle phenotypes, supporting the involvement of especially CD36 on monocytes in metabolic syndrome pathogenesis. Although testosterone therapy improved body composition measures, microvesicle phenotype levels were unaffected. This trial was registered at ClinicalTrials.gov (NCT01560546).

Therapeutic silencing of fat-specific protein 27 improves glycemic control in mouse models of obesity and insulin resistance

Obesity is a component of the metabolic syndrome, mechanistically linked to diabetes, fatty liver disease, and cardiovascular disease. Proteins that regulate the metabolic fate of intracellular lipid droplets are potential therapeutic candidates to treat obesity and its related consequences. CIDEC (cell death-inducing DFFA-like effector C), also known in mice as Fsp27 (fat-specific protein 27), is a lipid droplet-associated protein that prevents lipid mobilization and promotes intracellular lipid storage. The consequences of complete loss of FSP27 on hepatic metabolism and on insulin resistance are controversial, as both healthy and deleterious lipodystrophic phenotypes have been reported in Fsp27^−/− mice. To test whether therapeutic silencing of Fsp27 might be useful to improve obesity, fatty liver, and glycemic control, we used antisense oligonucleotides (ASOs) in both nutritional (high-fat diet) and genetic (leptin-deficient ob/ob) mouse models of obesity, hyperglycemia, and hepatosteatosis. We show that partial silencing Fsp27 in either model results in the robust decrease in visceral fat, improved insulin sensitivity and whole-body glycemic control, and tissue-specific changes in transcripts controlling lipid oxidation and synthesis. These data suggest that partial reduction of FSP27 activity (e.g., using ASOs) might be exploited therapeutically in insulin-resistant obese or overweight patients.

A Review of Potential Marine-derived Hypotensive and Anti-obesity Peptides

Bioactive peptides are food derived components, usually consisting of 3-20 amino acids, which are inactive when incorporated within their parent protein. Once liberated by enzymatic or chemical hydrolysis, during food processing and gastrointestinal transit, they can potentially provide an array of health benefits to the human body. Owing to an unprecedented increase in the worldwide incidence of obesity and hypertension, medical researchers are focusing on the hypotensive and anti-obesity properties of nutritionally derived bioactive peptides. The role of the renin-angiotensin system has long been established in the aetiology of metabolic diseases and hypertension. Targeting the renin-angiotensin system by inhibiting the activity of angiotensin-converting enzyme (ACE) and preventing the formation of angiotensin II can be a potential therapeutic approach to the treatment of hypertension and obesity. Fish-derived proteins and peptides can potentially be excellent sources of bioactive components, mainly as a source of ACE inhibitors. However, increased use of marine sources, poses an unsustainable burden on particular fish stocks, so, the underutilized fish species and by-products can be exploited for this purpose. This paper provides an overview of the techniques involved in the production, isolation, purification, and characterization of bioactive peptides from marine sources, as well as the evaluation of the ACE inhibitory (ACE-I) activity and bioavailability.