Beneficial effects of silibinin against the progression of metabolic syndrome, increased oxidative stress, and liver steatosis in Psammomys obesus, a relevant animal model of human obesity and diabetes.

BACKGROUND: Insulin resistance and oxidative stress are major pathogenic mechanisms leading to chronic liver diseases in diabetic subjects. The gerbil Psammomys obesus is a unique model of nutritional diabetes resembling the disease in humans. This study investigated whether the natural ingredient silibinin, known as hepatoprotective, could decrease oxidative stress and reduce liver damage in obese gerbils. METHODS: Control animals were fed their vegetable-based low caloric diet while two other rat groups ingested a high calorie diet for 14 weeks. Silibinin, or its vehicle, was administrated by gastric intubation (100 mg/kg per day) from the 7th week of treatment, which corresponds to an established insulin resistance state. At the end of the experiments, the hepatic biochemical profile, markers of oxidative stress in either plasma or liver tissue, and histological alterations were examined. RESULTS: Diabetic P. obesus displayed many metabolic disturbances (hyperinsulinemia, hyperglycemia, dyslipidemia), which were aggravated for the last 8 weeks. These events were coupled with greater oxidative stress (decline in glutathione, rise in lipoperoxidation). In addition, glutathione peroxidase activity was reduced while the level of superoxide dismutase was elevated. Interestingly, treatment with silibinin alleviated most of the metabolic defects, especially high triglyceride levels, reduced insulin resistance and largely restored antioxidant status. Also, Masson's trichrome staining revealed distinct steatosis, yet silibinin partially reversed this manifestation. CONCLUSION: Silibinin affords substantial protection against the progression of insulin resistance in Type 2 diabetes mellitus for P. obesus by hampering the oxidative process and improving hepatic metabolism.

Hepatic mitochondrial alterations and increased oxidative stress in nutritional diabetes-prone Psammomys obesus model.

Mitochondrial dysfunction is considered to be a pivotal component of insulin resistance and associated metabolic diseases. Psammomys obesus is a relevant model of nutritional diabetes since these adult animals exhibit a state of insulin resistance when fed a standard laboratory chow, hypercaloric for them as compared to their natural food. In this context, alterations in bioenergetics were studied. Using liver mitochondria isolated from these rats fed such a diet for 18 weeks, oxygen consumption rates, activities of respiratory complexes, and content in cytochromes were examined. Levels of malondialdehyde (MDA) and gluthatione (GSH) were measured in tissue homogenates. Diabetic Psammomys showed a serious liver deterioration (hepatic mass accretion, lipids accumulation), accompanied by an enhanced oxidative stress (MDA increased, GSH depleted). On the other hand, both ADP-dependent and uncoupled respirations greatly diminished below control values, and the respiratory flux to cytochrome oxydase was mildly lowered. Furthermore, an inhibition of complexes I and III together with an activation of complex II were found. With emergence of oxidative stress, possibly related to a defect in oxidative phosphorylation, some molecular adjustments could contribute to alleviate, at least in part, the deleterious outcomes of insulin resistance in this gerbil species.

The flavonoid silibinin decreases glucose-6-phosphate hydrolysis in perfused rat hepatocytes by an inhibitory effect on glucose-6-phosphatase.

BACKGROUND/AIMS: The flavonoid silibinin has been reported to be beneficial in several hepatic disorders. Recent evidence also suggests that silibinin could be beneficial in the treatment of type 2 diabetes, owing to its anti-hyperglycemic properties. However, the mechanism(s) underlying these metabolic effects remains unknown. METHODS: The effects of silibinin on liver gluconeogenesis were studied by titrating hepatocytes from starved rats with sub-saturating concentrations of various exogenous substrates in a perifusion system. Hepatocytes from fed rats were also used to investigate glycogenolysis from endogenous glycogen. The effect of silibinin on glucose-6-phosphatase kinetics was determined in intact and permeabilized rat liver microsomes. RESULTS: Silibinin induced a dose-dependent inhibition of gluconeogenesis associated with a potent decrease in glucose-6-phosphate hydrolysis. This effect was demonstrated whatever the gluconeogenic substrates used, i.e. dihydroxyacetone, lactate/pyruvate, glycerol and fructose. In addition, silibinin decreased the glucagon-induced stimulation of both gluconeogenesis and glycogenolysis, this being associated with a reduction of glucose-6-phosphate hydrolysis. Silibinin inhibits glucose-6-phosphatase in rat liver microsomes in a concentration-dependent manner that could explain the decrease in glucose-6-phosphate hydrolysis seen in intact cells. CONCLUSION: The inhibitory effect of silibinin on both hepatic glucose-6-phosphatase and gluconeogenesis suggests that its use may be interesting in treatment of type 2 diabetes.

Effect of maternal obstructive cholestasis during pregnancy on the biliary transport of horseradish peroxidase in the rat offspring.

MOCP (maternal obstructive cholestasis during pregnancy) induces a reversible impairment in bile formation in young rats born to these mothers. The aim of the present study was to gain information on the effects of MOCP on the maturation of pathways involved in protein secretion into bile in young (4-week-old) rats. The amount of hepatic alpha-tubulin and the structure of the microtubular network were apparently not affected by MOCP. HRP (horseradish peroxidase) was used as a model protein, and its secretion into bile after administration through the jugular vein was measured. In adult (8-week-old) rats, two peaks of HRP output into bile were observed following administration: an early peak presumably due to paracellular transfer, and a late peak presumably due to transcytosis. In young rats (4 weeks old), the early peak was similar to that of adult animals, and was not affected by MOCP. However, the late peak was markedly smaller in young control rats, and was further reduced by MOCP. Brefeldin A decreased, whereas taurocholate did not change, the early peak, whereas both affected the transcytotic transport of HRP. Brefeldin A delayed HRP secretion (similarly in control and MOCP groups), without affecting cumulative output, whereas taurocholate accelerated the transcytotic transport of HRP in the control group, but not in the MOCP group. These results suggest that MOCP affects the maturation of hepatocyte mechanisms involved in the transcytotic secretion of HRP into bile.