Effects Of Hydrogen Sulfide On Insulin Resistance And Its Mechanism

Hydrogen sulfide (H2S) is a poisonous gas with an offensive odor described as a rotten egg smell. But it is becoming increasingly clear that mammalian cells also produce H2S, Endogenous H2S is synthesized naturally in the body from L-cysteine mainly by the activity of two enzymes, cystathionine β-synthase (CBS) and cystathionine y-lyase (CSE). Endogenous H2S is now recognized as a novel gastrotransmitter and takes part in the pathogenesis of cardiovascular diseases, nervous system diseases, gastric ulceration, and infection.More over, H2S has been implicated to be associated with diabetes. An increase in H2S generation in pancreas and liver is observed in a rat model of streptozotocin-induced diabetes. H2S biosynthesis is decreased in a murine model of type1diabetes.These results imply the correlation of endogenous H2S and the pathogenesis of diabetes.However, the mentioned studies are not sufficient to demonstrate whether H2S play a role in glucose metabolism or pathogenesis of diabetes.Insulin resistance is characterized by impaired glucose uptake and reduced sensitivity to insulin in major insulin target tissues such as the skeletal muscles, adipose tissue and liver. Insulin resistance is the most important mechanism of the pathogenesis of type II diabetes.However, to date, there is no imformation about the potential role of H2S on insulin resistance and glucose uptake in insulin target tissues. The purpose of the present study is to assess the physiological role of H2S in the regulation of insulin sensitivity.First,the Effect of H2S on glucose metabolism was explored.L6myotubes and3T3-L1adipocytes were studied in our experiment. Treatment with high concentrations (500-1000μmol/L) of NaHS (H2S donor) resulted in a significant reduction in cell viability and relatively low concentrations (10-200μmol/L) didn’t affect cell viability as assessed using the MTT method, which indicates high concentrations of H2S may have cellular toxicity. So we treat cells with low concentrations of NaHSin glucose consumption test and glucose uptake assay.For glucose consumption test, We measured the concentration of glucose remaining in the medium of the cells with and without exposure to various concentrations of NaHS for24h. we found that NaHS at relatively low concentrations (10-100μmol/L) promoted glucose consumption in myotubes and adipocytes,with the Stimulation of100nM insulin for30min. For the study of glucose uptake in pathological state, we established and identified the insulin resistance cellular model according to the literature. Incubationof L6myotubes and3T3-L1adipocytes with NaHS (10-100μmol/L) for24h increased insulin-stimulated glucose transport activity in both the control and insulin-resistant cells. These data implicated H2S can regulate insulin sensitivity.To elucidate the signaling cascades that contribute to H2S-induced glucose uptake, metabolism and glucose uptake, the effects of H2S on intermediates of the insulin signaling pathway were investigated. NaHS treatment induced a dose and time dependent increase in InsR,PI3K and Akt phosphorylation in the presence of insulin in both cells. We added PI3K inhibitors LY294002to L6and3T3-L1cells, the effects of H2S on glucose uptake was blocked. These data suggest that H2S promotes glucose uptake by activating InsR/PI3K/Akt signaling.The phosphorylation of cbl and all the three MAP kinases(ERK,p38and JNK) was unaffected by the treatment of H2S in the presence of insulin. GLUT4is very important in insulin stimulated glucose transport.So we explored the effects of H2S on the translocation and expression of GLUT4,and found that H2S can enhance its translocation to the membrane.But H2S did not increase the expression of GLUT4.We further investigated the effect of H2S on insulin resistance in vivo. We used GK spontaneous type2diabetic rat as the disease model. The therapeutic effect of NaHS (30,60and120μmol/kg/d) was assessed by fasting blood glucose, fasting serum insulin, glucose tolerance test and insulin tolerance test, etc.The result showed that H2S at lower concentrations(30μmol·kg-1·d-1) decreased fasting blood glucose and improved glucose tolerance. But120μmol/kg/d NaHS deteriorated the pathological state in GK rats. NaHS has no effect on insulin secretion of diabetic GK rats. These data suggested that H2S at lower concentration can improve in vivo insulin resistance.In summary, the present study provides that H2S can increase insulin sensitivity both in vitro and in vivo, which probably relates to the activation of IR/PI3k/Akt.