Evolution of metabolic disorder in rats fed high sucrose or high fat diet: Focus on redox state and mitochondrial function.

Glucotoxicity and lipotoxicity are major hallmarks of metabolic disorder. High consumption of fat or carbohydrate rich food is a major risk of metabolic disorder. However, the evolution of high fat or high carbohydrate diet-induced metabolic disorder is not clear. In the study, we tried to find distinguished and common ways involved in the pathogenesis of insulin resistance induced by high fat (HF) and high sucrose (HS) diet. We found that HS diet induced mild glucose intolerance (2month), followed by a "temporary non-symptom phase" (3month), and then induced significant metabolic abnormality (4month). HF diet induced an early "responsive enhancement phase" (2month), and then gradually caused severe metabolic dysfunction (3-4month). After a mild induction of mitochondrial ROS generation (2month), HS diet resulted in a "temporary non-symptom phase" (3month), and then induced a more significant mitochondrial ROS production (4month). The impairment of mitochondrial function induced by HS diet was progressive (2-4month). HF diet induced gradual mitochondrial ROS generation and hyperpolarization. HF diet induced an early "responsive enhancement" of mitochondrial function (2month), and then gradually resulted in severe decrease of mitochondrial function (3-4month). Despite the patterns of HS and HF diet-induced insulin resistance were differential, final mitochondrial ROS generation combined with mitochondrial dysfunction may be the common pathway. These findings demonstrate a novel understanding of the mechanism of insulin resistance and highlight the pivotal role of mitochondrial ROS generation and mitochondrial dysfunction in the pathogenesis of metabolic disorder.

Differential effect of Se on insulin resistance: regulation of adipogenesis and lipolysis.

Insulin resistance is the characteristic of type 2 diabetes mellitus and metabolic disorder. The biological effect of selenium (Se) on insulin sensitivity and metabolic function was contradictory. In this study, we designed two animal protocols to investigate the effect of physiological Se on high-fat (HF) diet-induced insulin resistance in mice and examined the influence of Se on adipocyte differentiation and lipolysis in isolated bone marrow stromal stem cells. The results showed that pre-treatment with Se, mimicking thiazolidinediones, increased adipocyte differentiation and fat deposit in adipose tissue and reduced ectopic lipid content and consequent ROS generation and mitochondrial dysfunction in livers, protecting against HF diet-induced insulin resistance. Post-treatment with Se promoted lipolysis in adipose tissue and ectopic lipid accumulation in livers and aggravated subsequent ROS generation and mitochondrial dysfunction, exacerbating insulin resistance induced by HF diet. Activation of GPx1 and Sepp1 was responsible for Se-exhibited bi-directional significance, which was at the crossroad of the biological effect of Se, leading to differential directions: one way is to accelerate mitotic clonal expansion and increase key regulators of adipocyte differentiation, such as PPARγ and C/EBPα/ß, leading to enhancement of adipogenic differentiation; the other way is to activate PKA/HSL pathway, reinforcing lipolysis. Further studies are needed to elucidate the mechanism underlying GPx1 and Sepp1-exerted differential effects under different conditions. Anyhow, these findings may partly explain the contradiction of the biological significance of Se and demonstrate a novel understanding of the mechanism of Se-exerted benefit or harmful effects in the context of high consumption of fat.

Effect of diosgenin on metabolic dysfunction: Role of ERß in the regulation of PPARγ.

The present study was designed to investigate the effect of diosgenin (DSG) on metabolic dysfunction and to elucidate the possible molecular mechanisms. High fat (HF) diet-fed mice and 3T3-L1 preadipocytes was used to evaluate the effect of DSG. We showed that DSG attenuated metabolic dysfunction in HF diet-fed mice, as evidenced by reduction of blood glucose level and improvement of glucose and insulin intolerance. DSG ameliorated oxidative stress, reduced body weight, fat pads, and systematic lipid profiles and attenuated lipid accumulation. DSG inhibited 3T3-L1 adipocyte differentiation and reduced adipocyte size through regulating key factors. DSG inhibited PPARγ and its target gene expression both in differentiated 3T3-L1 adipocytes and fat tissues in HF diet-fed mice. Overexpression of PPARγ suppressed DSG-inhibited adipocyte differentiation. DSG significantly increased nuclear expression of ERß. Inhibition of ERß significantly suppressed DSG-exerted suppression of adipocyte differentiation and PPARγ expression. In response to DSG stimulation, ERß bound with RXRα and dissociated RXRα from PPARγ, leading to the reduction of transcriptional activity of PPARγ. These data provide new insight into the mechanisms underlying the inhibitory effect of DSG on adipocyte differentiation and demonstrate that ERß-exerted regulation of PPARγ expression and activity is critical for DSG-inhibited adipocyte differentiation.

Effect of alcohol on diethylnitrosamine-induced hepatic toxicity: Critical role of ROS, lipid accumulation, and mitochondrial dysfunction.

Hepatocellular carcinoma (HCC) is the fifth most common cancer in men and the seventh in women worldwide. Chronic heavy alcohol consumption is a major risk factor for the development of HCC. However, the mechanism underlying the direct association between alcohol consumption and HCC is far from completely understood. In the present study, we investigated the effect of chronic consumption of alcohol on diethylnitrosamine (DEN)-induced cytotoxicity, which was essential for the malignant transformation. We showed that alcohol deceased survival of mice treated by DEN and promoted DEN-induced toxicity and hepatic injury. In addition, alcohol promoted DEN-induced increase of proinflammatory factors, collagen content and fibrosis-related genes, including collagen1, 3 and 4, TMIP1, TIMP2 and TGFß1, and compensatory proliferation. Alcohol may increase alcohol dehydrogenase (ADH) and cytochrome P4502E1 (CYP2E1) expression, enhanced reactive oxygen species (ROS) generation, and resulted in a vicious circle between ROS generation, lipid accumulation, and mitochondrial dysfunction, aggravating liver injury and toxicity in DEN-treated mice. These results demonstrated that the combination of alcohol and carcinogens could aggravate carcinogen-induced cytotoxicity in the early phase of rumourigenesis through ADH and CYP2E1-generated ROS and the resultant cytotoxic process. The present study provided direct experimental evidence for alcohol-promoted toxicity and hepatic injury in carcinogen (DEN)-treated mice.