Protective effects of a G. lucidum proteoglycan on INS-1 cells against IAPP-induced apoptosis via attenuating endoplasmic reticulum stress and modulating CHOP/JNK pathways.

Fudan-Yueyang-G. lucidum (FYGL) is a water-soluble macromolecular proteoglycan extracted from Ganoderma lucidum which has been used for health promotion for a long time in China. The aim of this study was to investigate the protective effects of FYGL on INS-1 rat insulinoma beta cells against IAPP-induced cell apoptosis, as well as the underlying mechanisms. The results showed that apoptotic cells were significantly increased when incubated with islet amyloid polypeptide (IAPP). However, cytotoxicity of IAPP was significantly attenuated by co-incubation of the cells with FYGL. The results of RT-PCR showed that mRNA expression of caspase-3, caspase-12 and C/EBP homologous protein (CHOP) in IAPP-treated cells were inhibited by FYGL. Moreover, FYGL significantly prevented the IAPP-induced abnormal expression of inositol-requiring protein-1α (IRE1α), protein kinase RNA (PKR)-like ER kinase (PERK), activating transcription factor 6 (ATF6), as well as suppressed the activation of CHOP and c-Jun N-terminal kinase (JNK). Taken together, our results suggest that FYGL protects INS-1 pancreatic beta cells against IAPP-induced apoptosis through attenuating endoplasmic reticulum stress (ERS) and modulating CHOP/JNK pathways.

Effect of a novel proteoglycan PTP1B inhibitor from Ganoderma lucidum on the amelioration of hyperglycaemia and dyslipidaemia in db/db mice.

Protein tyrosine phosphatase 1B (PTP1B) is implicated in the negative regulation of the insulin signalling pathway by dephosphorylating the insulin receptor (IR) and IR substrates. Ganoderma lucidum has traditionally been used for the treatment of diabetes in Chinese medicine; however, its anti-diabetic potency and mechanism in vivo is still unclear. Our previously published study reported a novel proteoglycan PTP1B inhibitor, named Fudan-Yueyang-Ganoderma lucidum (FYGL) from G. lucidum, with a half-maximal inhibitory concentration (IC50) value of 5·12 (sem 0·05) µg/ml, a protein:polyglycan ratio of 17:77 and 78 % glucose in polysaccharide, and dominant amino acid residues of aspartic acid, glycine, glutamic acid, alanine, serine and threonine in protein. FYGL is capable of decreasing plasma glucose in streptozotocin-induced diabetic mice with a high safety of median lethal dose (LD50) of 6 g/kg. In the present study, C57BL/6 db/db diabetic mice were trialed further using FYGL as well as metformin for comparison. Oral treatment with FYGL in db/db diabetic mice for 4 weeks significantly (P < 0·01 or 0·05) decreased the fasting plasma glucose level, serum insulin concentration and the homeostasis model assessment of insulin resistance. FYGL also controlled the biochemistry indices relative to type 2 diabetes-accompanied lipidaemic disorders. Pharmacology research suggests that FYGL decreases the plasma glucose level by the mechanism of inhibiting PTP1B expression and activity, consequently, regulating the tyrosine phosphorylation level of the IR ß-subunit and the level of hepatic glycogen, thus resulting in the improvement of insulin sensitivity. Therefore, FYGL is promising as an insulin sensitiser for the therapy of type 2 diabetes and accompanied dyslipidaemia.

A protein tyrosine phosphatase 1B activity inhibitor from the fruiting bodies of Ganoderma lucidum (Fr.) Karst and its hypoglycemic potency on streptozotocin-induced type 2 diabetic mice.

Inhibition of protein tyrosine phosphatase 1B (PTP1B) activity has been considered to be a promising therapy approach to treat type 2 diabetes. In this work, a novel PTP1B activity inhibitor, named FYGL (Fudan-Yueyang-G. lucidum), was screened from the fruiting bodies of Ganoderma lucidum and showed an efficient PTP1B inhibitory potency with IC50 = 5.12 ± 0.05 µg/mL. FYGL is a water-soluble macromolecular proteoglycan with a protein to polysaccharide ratio of 17:77 and a viscosity-average molecular weight (M(η)) of 2.6 × 105. The type 2 diabetic mice treated orally by FYGL showed an obvious decrease in plasma glucose level compared with the diabetic controls without drug treatment, comparable with that of diabetic mice treated with metformin, a clinical drug. The toxicity of FYGL is very low. The results indicate that FYGL may serve as a drug candidate or a health-care food for diabetic therapy or protection.