Effets de l’extrait au chlorure de méthylène/méthanol des feuilles de Terminalia glaucescens Planch ex Benth (Combretaceae) sur des paramètres métaboliques et du stress oxydant chez des souris traitées à la streptozotocine

Abstract

Diabetes is a serious disease that occurs in a human when his blood sugar level is high because either his body cannot produce enough insulin, or it does not produce it, or if it cannot use insulin it produces. It has been shown that high glucose level in extra or intracellular environments induce oxidative stress, considered as the motor mobilizing various pathological factors towards the complications of diabetes and associated organs. For a long time, insulin was the most used substance in the treatment of type 1 diabetes and in some type 2 diabetes. Nowadays, despite the effectiveness of insulin, medicinal plants are widely used in traditional medicine; especially in developing countries where the high cost and availability of insulin hinders its use by populations. A great interest was given to plants which are huge source of antioxidants compounds and studies reveal their anti-diabetic effects along with the high antioxidant power, which gives more hope to prevent and or limit the progression of diabetes and its complications. The present study was undertaken with Terminalia glaucescens use in cameroonian traditional medicine to manage diabetes. Therefore, the aim of this study was to evaluate the anti-hyperglycemic and antioxidant effects of the methylene chloride/methanol leaves extract of T. glaucescens on a mice treated with streptozotocin. During this study, the extract used was a macerate of the leaves of T. glaucescens prepared in a mixture of methylene chloride/methanol (v/v) for 7 days at room temperature. The pharmacological dose (200 mg/kg b.w) was obtained from traditional use and two other doses were generated (100 and 300 mg/kg b.w). The in vitro lipolytic activity of the methylene chloride/methanol extract of T. glaucescens was evaluated on differentiated 3T3-L1 adipocytes cells. The dosage of glycerol was used to evaluate this lipolytic activity in vitro. The anti hyperglycemic and antioxidant effects of the methylene chloride/methanol leaves extract of T. glaucescens were evaluated on a mice treated with a single administration of streptozotocin (STZ, 45 mg/kg, i.p.) for 5 consecutive days. The experiment was carried out with male albino mice of the Mus musculus strain housed in individual cages. Fasting blood glucose was assessed on days 0, 3, 6, and 12. At the end of the 15 days of the experiment, the animals were anesthetized with pentobarbital then sacrificed. Blood was collected into test tubes containing EDTA by intracardiac puncture and was centrifuged. The plasma was collected for the determination of some plasma biomolecules: lipids (triglyceride, total cholesterol, HDL-cholesterol, LDL-cholesterol, NEFA) and hormones (insulin and leptin). The antioxidant capacity of the extract in vivo, through the dosage of antioxidant enzymes (Catalase, superoxide dismutase and glutathione peroxidase) was determined in the liver homogenate. The results obtained from these experiments showed that, in the in vitro study on 3T3-L1 adipocytes cells, the extract of T. glaucescens induced a lypolitic activity marked by the significant increase in the release of glycerol (p < 0.01) compared to the control (receiving norepinephrine). In vivo, the extract at a dose of 300 mg/kg significantly reduced the plasmatic concentration of Leptin (p < 0.05), plasma lipids as TG (p < 0.05), TC (p < 0.05), NEFA (p < 0.05), total adipose tissue mass (p < 0.05) and weight gain (p < 0.05). This study revealed that compared to the negative control treated with STZ ( 45 mg/kg b.w, i.p.) the extract of T. glaucescens at a dose of 300 mg/kg significantly decreases blood sugar (p < 0.05) and significantly increases plasma insulin ( p < 0.01), food intake ( p < 0.01), water intake ( p < 0.01), MDA ( p < 0.01) for bringing them back to values close to the normal control, however, increased the activity of antioxidant enzymes , as SOD ( p < 0.01) , CAT ( p < 0.01), and GPx ( p < 0.01), and also significantly decreased plasma lipids, as TG (p < 0.05), CT (p < 0.05), LDL-c (p < 0.05), and NEFA (p < 0.05). In conclusion, the effects induced by the extract of T. glaucescens could justify the traditional use of this plant in the treatment of diabetes. The extract could be a powerful antioxidant that protects β cells against the destructive action of free radicals in diabetes case