Antidiabetic and antihyperlipidemic activities of Phyllanthus emblica L. extract in vitro and the regulation of Akt phosphorylation, gluconeogenesis, and peroxisome proliferator-activated receptor α in streptozotocin-induced diabetic mice

Abstract

Background: The fruits of Phyllanthus emblica L. are high in nutrients and have excellent health care function and developmental value. There are many management strategies available for diabetes and hyperlipidemia. Nevertheless, there is a lack of an effective and nontoxic drug. Objective: The present study was designed to first screen four extracts of P. emblica L. on insulin signaling target gene expression levels, including glucose transporter 4 (GLUT4) and p-Akt/t-Akt. The ethyl acetate extract of P. emblica L. (EPE) exhibited the most efficient activity among the four extracts and was thus chosen to explore the antidiabetic and antihyperlipidemic activities in streptozotocin (STZ)-induced type 1 diabetic mice. Design: All mice (in addition to one control (CON) group) were administered STZ injections (intraperitoneal) for 5 consecutive days, and then STZ-induced mice were administered EPE (at 100, 200, or 400 mg/kg body weight), fenofibrate (Feno) (at 250 mg/kg body weight), glibenclamide (Glib) (at 10 mg/kg body weight), or vehicle by oral gavage once daily for 4 weeks. Finally, histological examination, blood biochemical parameters, and target gene mRNA expression levels were measured, and liver tissue was analyzed for the levels of malondialdehyde (MDA), a maker of lipid peroxidation. Results: EPE treatment resulted in decreased levels of blood glucose, HbA1C, triglycerides (TGs), and total cholesterol and increased levels of insulin compared with the vehicle-treated STZ group. EPE treatment decreased blood levels of HbA1C and MDA but increased glutathione levels in liver tissue, implying that EPE exerts antioxidant activity and could prevent oxidative stress and diabetes. The EPE-treated STZ mice displayed an improvement in the sizes and numbers of insulin-expressing β cells. EPE treatment increased the membrane expression levels of skeletal muscular GLUT4, and also reduced hepatic mRNA levels of glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase thereby inhibiting hepatic gluconeogenesis. This resulted in a net glucose lowering effect in EPE-treated STZ mice. Furthermore, EPE increased the expression levels of p-AMPK/t-AMPK in both the skeletal muscle and liver tissue compared with vehicle-treated STZ mice. EPE-treated STZ mice showed enhanced expression levels of fatty acid oxidation enzymes, including peroxisome proliferator-activated receptor α (PPARα), but reduced expression levels of lipogenic genes including fatty acid synthase, as well as decreased mRNA levels of sterol regulatory element binding protein 1c (SREBP1c), apolipoprotein-CIII (apo-CIII), and diacylglycerol acyltransferase-2 (DGAT2). This resulted in a reduction in plasma TG levels. EPE-treated STZ mice also showed reduced expression levels of PPAR γ. This resulted in decreased adipogenesis, fatty acid synthesis, and lipid accumulation within liver tissue, and consequently, lower TG levels in liver tissue and blood. Furthermore, EPE treatment not only displayed an increase in the Akt activation in liver tissue, but also in C2C12 myotube in the absence of insulin. These results implied that EPE acts as an activator of AMPK and /or as a regulator of the insulin (Akt) pathway. Conclusions: Taken together, EPE treatment exhibited amelioration of the diabetic and hyperlipidemic state in STZ-induced diabetic mice.

Keywords

• diabetes
• streptozotocin
• phyllanthus emblica l
• antihyperlipidemic
• gluconeogenesis
• insulin-expressing β cells