Mechanism of Cordyceps militaris polysaccharide hypoglycemic
|School||Shandong Normal University|
|Keywords||polysaccharide type 1 diabetes Th1/Th2 polarization macrophage|
Type 1 diabetes or insulin-dependent diabetes mellius (IDDM)is an autoimmune disease that causes the selective destruction of insulin-secreting βcells in the pancreatic islets and the absolute deficiency in the production of insulin. Recently, it is considered that proper treatment of diabetes requires much more than insulin and dietary modification. Herbal medicine, as an effective aid in the treatment of diabetes, has been used to improve the hyperglycemic condition in diabetic patients. Cordycpes militaris, another species of Cordyceps, has also been used as a traditional medicine in china for hundreds of years. It possesses similar components and bioactivities to those of C. sinensis, and great effort has been invested to produce C. militaris biological compounds using liquid culture mycelium, which could be provided easily by industrialized mass-production system. However, there has been little study to examine the hypoglycemic action of the polysaccharides from either the cultured mycelia or the culture supernatant of C. militaris. In this study, for the first time, we examined the hypoglycemic effect of the polysaccharides extracted from the fruiting body, the cultured mycelia and culture medium of C. militaris, on diabetic mice induced by multiple low-dose strepozotocin (MLD-STZ). Furthermore, the possible immunological mechanisms by which the extracellular polysaccharide ameliorate hyperglycemia was investigated. Diabetes could be induced by the method of MLD-STZ. Here male BALB/c mice were induced diabetes and the immunological analysis was made to investigate the cytokines profile in the thymus and spleen, as well as the macrophages (Mps) during the development of MLD-STZ induced autoimmune diabetes. During the development of diabetes, Mp showed a “incomplete”oxidative Mp phenotype due to the significantly decreased intracellular glutathione with the reduced release of TNF-αand IL-12 production upon in vitro LPS stimulation, however, without the elevated release of IL-6. In addition, the phagocytosis activity was also declined compared to the control mice. On the other hand, the splenocytes and the thymocytes in both diabetic groups showed augmented secretion of IFN-γor IL-4 on in vitro ConA stimulation, however, the mean ratio of IFN-γto IL-4 levels in the early diabetes group were higher than the control group, but became lower several weeks later after the occurrence of diabetes, suggesting a pathogenetic Th1 phenotype gradually to a tendency of Th2 during the development of diabetes. Our results implied that likely OMp may be relevant in the development of type 1 diabetes,and the cytokines profile of Mps is not likely the only factor regulating the Th1/Th2 balance in MLD-STZ induced diabetic mice. To investigate the hypoglycemic activity of the polysaccharides, extracted from fruiting body (BP), cultured mycelia (MP) and exopolysaccaride (EP), the polysaccharides were injected intraperitoneal indiabetic mice induced by MLD-STZ. Only EP showed potent hypoglycemic activity in diabetic mice during the observing period, and this effective group were examined in immunological base. The IL-4 and IFN-γlevels of the supernatant in stimulated splenocytes, and the IL-6 and TNF-αlevels secreted from the splenic APC stimulated with LPS were compared among the control group, the EP group and the untreated diabetic group. Meanwhile, the related cytokines levels of the lymphocytes were also investigated with different concentrations of EP in vitro. Our results showed that the cytokines levels (IL-4 and IFN-γ) production of splenocytes stimulated by ConA were decreased in EP group, meanwhile the ratio of IFN-γ/IL-4 was moderately inhibited. IL-6 secretion of the splenic APC of the EP group was also significantly enhanced leading to a lower ratio of TNFα/IL-6 than that of the diabetic mice. These data suggest that treatment of EP could reduce the blood glucose in MLD-STZ induced diabetic mice. The immunological base of the hypoglycemic activity was probably associated with inducing the differentiation of Th cells into Th2 cells through enhancement of IL-6 production by the splenic APC. As it mentioned above that at the early stage of diabetes, Mps in diabetic mice showed a OMp phenotype and deficient function, we next examined if the EP could improve the OMp phenotype. In vivo and in vitro the IL-6 secreted by Mps was enhanced significantly by the EP, which would prompt a Th2 bias. In addition, the amount of nitro oxide released byLPS-stimulation of and the phagocytosis activity in diabetic mice were also increased by EP. The failure of protection in islet damages induced by STZ in vitro also imply that the protection from diabetes by EP may be mediated by the immunological mechanisms. In conclusion, the EP could regulate the cytokines profile released by the lymphocytes to a Th2 bias, which could correct the pathogenetic Th1 phenotype in spleen at the early stage of diabetes induced by MLD –STZ to some extent. The regulation is more likely made by the increase of IL–6 levels secreted by the APCs, such as Mps. The hypoglycemic activity of the EP may be mediated mainly by the immunological mechanisms.