Effect of silybin on high-fat-induced fatty liver in rats

Silybin, a natural antioxidant, has been traditionally used against a variety of liver ailments. To investigate its effect and the underlying mechanisms of action on non-alcoholic fatty liver in rats, we used 60 4-6-week-old male Sprague-Dawley rats to establish fatty liver models by feeding a high-fat diet for 6 weeks. Hepatic enzyme, serum lipid levels, oxidative production, mitochondrial membrane fluidity, homeostasis model assessment-insulin resistance index (HOMA-IR), gene and protein expression of adiponectin, and resistin were evaluated by biochemical, reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis. Compared with the model group, silybin treatment (26.25 mg·kg-1·day-1, started at the beginning of the protocol) significantly protected against high-fat-induced fatty liver by stabilizing mitochondrial membrane fluidity, reducing serum content of alanine aminotransferase (ALT) from 450 to 304 U/L, decreasing hepatic malondialdehyde (MDA) from 1.24 to 0.93 nmol/mg protein, but increasing superoxide dismutase (SOD) and glutathione (GSH) levels from 8.03 to 9.31 U/mg protein and from 3.65 to 4.52 nmol/mg protein, respectively. Moreover, silybin enhanced the gene and protein expression of adiponectin from 215.95 to 552.40, but inhibited that of resistin from 0.118 to 0.018. Compared to rosiglitazone (0.5 mg·kg-1·day-1, started at the beginning of the protocol), silybin was effective in stabilizing mitochondrial membrane fluidity, reducing SOD as well as ALT, and regulating gene and protein expression of adiponectin (P < 0.05). These results suggest that mitochondrial membrane stabilization, oxidative stress inhibition, as well as improved insulin resistance, may be the essential mechanisms for the hepatoprotective effect of silybin on non-alcoholic fatty liver disease in rats. Silybin was more effective than rosiglitazone in terms of maintaining mitochondrial membrane fluidity and reducing oxidative stress.

A link between sleep loss, glucose metabolism and adipokines

The present review evaluates the role of sleep and its alteration in triggering problems of glucose metabolism and the possible involvement of adipokines in this process. A reduction in the amount of time spent sleeping has become an endemic condition in modern society, and a search of the current literature has found important associations between sleep loss and alterations of nutritional and metabolic contexts. Studies suggest that sleep loss is associated with problems in glucose metabolism and a higher risk for the development of insulin resistance and type 2 diabetes mellitus. The mechanism involved may be associated with the decreased efficacy of regulation of the hypothalamus-pituitary-adrenal axis by negative feedback mechanisms in sleep-deprivation conditions. In addition, changes in the circadian pattern of growth hormone (GH) secretion might also contribute to the alterations in glucose regulation observed during sleep loss. On the other hand, sleep deprivation stress affects adipokines - increasing tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) and decreasing leptin and adiponectin -, thus establishing a possible association between sleep-debt, adipokines and glucose metabolism. Thus, a modified release of adipokines resulting from sleep deprivation could lead to a chronic sub-inflammatory state that could play a central role in the development of insulin resistance and type 2 diabetes mellitus. Further studies are necessary to investigate the role of sleep loss in adipokine release and its relationship with glucose metabolism.

Mechanisms of endothelial dysfunction in obesity-associated hypertension

Obesity is strongly associated with high blood pressure, dyslipidemia, and type 2 diabetes. These conditions synergistically increase the risk of cardiovascular events. A number of central and peripheral abnormalities can explain the development or maintenance of high blood pressure in obesity. Of great interest is endothelial dysfunction, considered to be a primary risk factor in the development of hypertension. Additional mechanisms also related to endothelial dysfunction have been proposed to mediate the development of hypertension in obese individuals. These include: increase in both peripheral vasoconstriction and renal tubular sodium reabsorption, increased sympathetic activity and overactivation of both the renin-angiotensin system and the endocannabinoid system and insulin resistance. The discovery of new mechanisms regulating metabolic and vascular function and a better understanding of how vascular function can be influenced by these systems would facilitate the development of new therapies for treatment of obesity-associated hypertension.

Association of postalimentary lipemia with atherosclerotic manifestations

We identified different lipemic and metabolic responses after the ingestion of a standardized meal by healthy adults and related them to atherosclerotic markers. Samples from 60 normolipidemic adults were collected before and after a liquid meal (40 g fat/m² body surface) at 0, 2, 4, 6, and 8 h for measurements of lipids, free fatty acids (FFA), insulin, cholesteryl ester transfer protein (CETP), autoantibodies to epitopes of oxidized LDL (oxLDL Ab), lipolytic activities, and apolipoprotein E polymorphism. Mean carotid intima-media thickness (cIMT) was determined by Doppler ultrasound. The volunteers were classified into early (N = 39) and late (N = 31) triacylglycerol (TAG) responders to the test meal. Late responders showed lower HDL cholesterol concentration at fasting and in the TAG peak, lower insulin and higher FFA concentrations compared to early responders. Multivariate regression analyses showed that mean cIMT was associated with gender (male) and age in early responders and by cholesterol levels at the 6th hour in late responders. oxLDL Ab were explained by lipoprotein lipase and negatively by hepatic lipase and oxLDL Ab (fasting period) by CETP (negative) and FFA (positive). This study is the first to identify a postalimentary insulin resistance state, combined with a reduced CETP response exclusively among late responders, and the identification of the regulators of postalimentary atherogenicity. Further research is required to determine the metabolic mechanisms described in the different postalimentary phenotypes observed in this study, as well as in different pathological states, as currently investigated in our laboratory.

Genetic analysis of the ELOVL6 gene polymorphism associated with type 2 diabetes mellitus

Recent animal studies have indicated that overexpression of the elongation of long-chain fatty acids family member 6 (Elovl6) gene can cause insulin resistance and β-cell dysfunction. These are the major factors involved in the development of type 2 diabetes mellitus (T2DM). To identify the relationship between single nucleotide polymorphisms (SNP) ofELOVL6 and T2DM pathogenesis, we conducted a case-control study of 610 Han Chinese individuals (328 newly diagnosed T2DM and 282 healthy subjects). Insulin resistance and islet first-phase secretion function were evaluated by assessment of insulin resistance in a homeostasis model (HOMA-IR) and an arginine stimulation test. Three SNPs of the ELOVL6 gene were genotyped with polymerase chain reaction-restriction fragment length polymorphism, with DNA sequencing used to confirm the results. Only genotypes TT and CT of the ELOVL6 SNP rs12504538 were detected in the samples. Genotype CC was not observed. The T2DM group had a higher frequency of the C allele and the CT genotype than the control group. Subjects with the CT genotype had higher HOMA-IR values than those with the TT genotype. In addition, no statistical significance was observed between the genotype and allele frequencies of the control and T2DM groups for SNPs rs17041272 and rs6824447. The study indicated that the ELOVL6 gene polymorphism rs12504538 is associated with an increased risk of T2DM, because it causes an increase in insulin resistance.

Association of adult weight gain and nonalcoholic fatty liver in a cross-sectional study in Wan Song Community, China

Our objective was to examine associations of adult weight gain and nonalcoholic fatty liver disease (NAFLD). Cross-sectional interview data from 844 residents in Wan Song Community from October 2009 to April 2010 were analyzed in multivariate logistic regression models to examine odds ratios (OR) and 95% confidence intervals (CI) between NAFLD and weight change from age 20. Questionnaires, physical examinations, laboratory examinations, and ultrasonographic examination of the liver were carried out. Maximum rate of weight gain, body mass index, waist circumference, waist-to-hip ratio, systolic blood pressure, diastolic blood pressure, fasting blood glucose, cholesterol, triglycerides, uric acid, and alanine transaminase were higher in the NAFLD group than in the control group. HDL-C in the NAFLD group was lower than in the control group. As weight gain increased (measured as the difference between current weight and weight at age 20 years), the OR of NAFLD increased in multivariate models. NAFLD OR rose with increasing weight gain as follows: OR (95%CI) for NAFLD associated with weight gain of 20+ kg compared to stable weight (change <5 kg) was 4.23 (2.49-7.09). Significantly increased NAFLD OR were observed even for weight gains of 5-9.9 kg. For the “age 20 to highest lifetime weight” metric, the OR of NAFLD also increased as weight gain increased. For the “age 20 to highest lifetime weight” metric and the “age 20 to current weight” metric, insulin resistance index (HOMA-IR) increased as weight gain increased (P<0.001). In a stepwise multivariate regression analysis, significant association was observed between adult weight gain and NAFLD (OR=1.027, 95%CI=1.002-1.055, P=0.025). We conclude that adult weight gain is strongly associated with NAFLD.

Effect of physical training on liver expression of activin A and follistatin in a nonalcoholic fatty liver disease model in rats

Nonalcoholic fatty liver disease (NAFLD) is characterized by fat accumulation in the liver and is associated with obesity and insulin resistance. Activin A is a member of the transforming growth factor beta (TGF)-β superfamily and inhibits hepatocyte growth. Follistatin antagonizes the biological actions of activin. Exercise is an important therapeutic strategy to reduce the metabolic effects of obesity. We evaluated the pattern of activin A and follistatin liver expression in obese rats subjected to swimming exercise. Control rats (C) and high-fat (HF) diet-fed rats were randomly assigned to a swimming training group (C-Swim and HF-Swim) or a sedentary group (C-Sed and HF-Sed). Activin βA subunit mRNA expression was significantly higher in HF-Swim than in HF-Sed rats. Follistatin mRNA expression was significantly lower in C-Swim and HF-Swim than in either C-Sed or HF-Sed animals. There was no evidence of steatosis or inflammation in C rats. In contrast, in HF animals the severity of steatosis ranged from grade 1 to grade 3. The extent of liver parenchyma damage was less in HF-Swim animals, with the severity of steatosis ranging from grade 0 to grade 1. These data showed that exercise may reduce the deleterious effects of a high-fat diet on the liver, suggesting that the local expression of activin-follistatin may be involved.

Plasma levels and placental expression of vaspin in pregnant women with diabetes mellitus

The present study aimed to investigate visceral adipose tissue-specific serpin (vaspin) concentrations in serum and term placentas and relate these values to insulin resistance and lipid parameters in women with gestational diabetes mellitus (GDM). A total of 30 GDM subjects and 27 age-matched pregnant women with normal glucose tolerance (NGT, control) were included. Serum glucose, glycated hemoglobin (HbA1c), lipid profile, insulin, and vaspin were measured at the end of pregnancy, and homeostasis model of assessment-insulin resistance (HOMA-IR) values were calculated. Vaspin mRNA and protein levels in placentas were measured by real-time fluorescence quantitative reverse transcription polymerase chain reaction (RT-qPCR) and Western blotting, respectively. Serum vaspin levels were significantly lower in the GDM group than in controls (0.49±0.24 vs 0.83±0.27 ng/mL, respectively; P<0.01). Three days after delivery, serum vaspin levels were significantly decreased in subjects with GDM (0.36±0.13 vs0.49±0.24 ng/mL, P<0.01). However, in the GDM group, serum vaspin levels were not correlated with the parameters evaluated. In contrast, in the control group, serum vaspin levels were positively correlated with triglycerides (TG; r=0.45, P=0.02) and very low-density lipoprotein cholesterol (VLDL-C; r=0.42, P=0.03). Placental mRNA vaspin (0.60±0.32 vs0.68±0.32, P=0.46) and protein (0.30±0.08 vs0.39±0.26; P=0.33) levels in the GDM group did not differ significantly from those in the control group, but were negatively correlated with neonatal birth weight in the GDM group (r=-0.48, P=0.03; r=-0.88; P<0.01). Our findings indicated that vaspin may be an important adipokine involved in carbohydrate and lipid metabolism and may also play a role in fetal development.

Vagotomy ameliorates islet morphofunction and body metabolic homeostasis in MSG-obese rats

The parasympathetic nervous system is important for β-cell secretion and mass regulation. Here, we characterized involvement of the vagus nerve in pancreatic β-cell morphofunctional regulation and body nutrient homeostasis in 90-day-old monosodium glutamate (MSG)-obese rats. Male newborn Wistar rats received MSG (4 g/kg body weight) or saline [control (CTL) group] during the first 5 days of life. At 30 days of age, both groups of rats were submitted to sham-surgery (CTL and MSG groups) or subdiaphragmatic vagotomy (Cvag and Mvag groups). The 90-day-old MSG rats presented obesity, hyperinsulinemia, insulin resistance, and hypertriglyceridemia. Their pancreatic islets hypersecreted insulin in response to glucose but did not increase insulin release upon carbachol (Cch) stimulus, despite a higher intracellular Ca2+ mobilization. Furthermore, while the pancreas weight was 34% lower in MSG rats, no alteration in islet and β-cell mass was observed. However, in the MSG pancreas, increases of 51% and 55% were observed in the total islet and β-cell area/pancreas section, respectively. Also, the β-cell number per β-cell area was 19% higher in MSG rat pancreas than in CTL pancreas. Vagotomy prevented obesity, reducing 25% of body fat stores and ameliorated glucose homeostasis in Mvag rats. Mvag islets demonstrated partially reduced insulin secretion in response to 11.1 mM glucose and presented normalization of Cch-induced Ca2+ mobilization and insulin release. All morphometric parameters were similar among Mvag and CTL rat pancreases. Therefore, the higher insulin release in MSG rats was associated with greater β-cell/islet numbers and not due to hypertrophy. Vagotomy improved whole body nutrient homeostasis and endocrine pancreatic morphofunction in Mvag rats.

IGF2, LEPR, POMC, PPARG, and PPARGC1 gene variants are associated with obesity-related risk phenotypes in Brazilian children and adolescents

Association studies of genetic variants and obesity and/or obesity-related risk factors have yielded contradictory results. The aim of the present study was to determine the possible association of five single-nucleotide polymorphisms (SNPs) located in the IGF2, LEPR, POMC, PPARG, and PPARGC1genes with obesity or obesity-related risk phenotypes. This case-control study assessed overweight (n=192) and normal-weight (n=211) children and adolescents. The SNPs were analyzed using minisequencing assays, and variables and genotype distributions between the groups were compared using one-way analysis of variance and Pearson's chi-square or Fisher's exact tests. Logistic regression analysis adjusted for age and gender was used to calculate the odds ratios (ORs) for selected phenotype risks in each group. No difference in SNP distribution was observed between groups. In children, POMC rs28932472(C) was associated with lower diastolic blood pressure (P=0.001), higher low-density lipoprotein (LDL) cholesterol (P=0.014), and higher risk in overweight children of altered total cholesterol (OR=7.35, P=0.006). In adolescents, IGF2 rs680(A) was associated with higher glucose (P=0.012) and higher risk in overweight adolescents for altered insulin (OR=10.08, P=0.005) and homeostasis model of insulin resistance (HOMA-IR) (OR=6.34, P=0.010). PPARGrs1801282(G) conferred a higher risk of altered insulin (OR=12.31, P=0.003), and HOMA-IR (OR=7.47, P=0.005) in overweight adolescents. PARGC1 rs8192678(A) was associated with higher triacylglycerols (P=0.005), and LEPR rs1137101(A) was marginally associated with higher LDL cholesterol (P=0.017). LEPR rs1137101(A) conferred higher risk for altered insulin, and HOMA-IR in overweight adolescents. The associations observed in this population suggested increased risk for cardiovascular diseases and/or type 2 diabetes later in life for individuals carrying these alleles.