MODULATION OF MITOCHONDRIAL-MEDIATED APOPTOSIS IN THE HEART AND LIVER OF STREPTOZOTOCIN-INDUCED DIABETIC RATS BY QUERCETIN AND VITAMIN E

Abstract

A major feature of Type 2 Diabetes Mellitus (T2DM) is tissue wastage, arising from excessive apoptosis. Excessive apoptosis could be a function of mitochondrial disorders in T2DM. Antioxidants, such as quercetin and Vitamin E, have been shown to be useful in the delay of progression of diabetes-induced complications. However, their effect on the apoptotic process in T2DM is unknown. This study was designed to investigate the effects of quercetin and vitamin E on mitochondrial Permeability Transition (mPT) pore, an event preceding apoptosis, in streptozotocin-induced diabetic rats. Diabetes was induced in male Wistar rats with a single intraperitoneal administration of 40 mg/kg streptozotocin (STZ). Animals which had consistent 72 hours fasting blood glucose concentrations of ≥250 mg/dL were considered diabetic. Thirty-six diabetic rats (100-120 g) were equally divided into six groups, treated orally and daily for 28 days with water (diabetic control; DC), 10 mg/kg quercetin (Q10), 30 mg/kg quercetin (Q30), 10 mg/kg Vitamin E, 10 mg/kg each of quercetin and Vitamin E (Q10 &VitE) and 0.6 mg/kg glibenclamide separately. Additional 6 normal male rats were used as non-diabetic control. Animals were sacrificed, liver and heart mitochondria were isolated by differential centrifugation. Mitochondrial lipid peroxidation (mLPO), mPT and mitochondrial ATPase (mATPase) were determined by standard methods using a spectrophotometer. Levels of Cytochrome C Release (CCR), activities of caspase 9 (C9) and caspase 3 (C3) were determined immunohistochemically in heart, and liver. Insulin level was determined using ELISA. Formalin-fixed heart and liver tissues were examined microscopically after Haematoxylin and Eosin staining. Data were analysed using descriptive statistics and ANOVA at α0.05.

The percentage reduction in mLPO in the liver and heart were 11.2, 22.0 (Q10 & V); 13.4, 13.1(Q10); 22.4, 27.2 (Q30); 13.1, 38.0 (Vitamin E) and 15.4, 41.3 (glibenclamide) respectively relative to DC (liver 61.3; heart 78.0). Similarly, the percentage inhibition of mPT pore in the liver and heart were 89.2, 87.3, 64.0, 85.2, 70.1 and 50.3, 45.4, 82.0, 50.2 and 43.4, respectively in the Q10 & V, Q10, Q30, Vitamin E and glibenclamide compared with DC (liver 14.3; heart 20.0). Liver and heart mATPase were reduced when treated with Q10 & V, Q10, Q30, and Vitamin E relative to DC. Significant decreases in CCR were observed in the liver (41.0, 23.3 and 58.1%) and heart (33.2, 20.3 and 17.1%) after treatment with Q10 &V, Q30 and Vitamin E compared with DC (liver 90.4%; heart 98.0%). The STZ-induced CCR was associated with reduction in liver C9 by 12.0% in Q10 & V and in the heart by 28.2% in Vitamin E. Activation of C3 in T2DM rats were reduced in the liver by 10.2% in glibenclamide and in the heart by 16.1% in Vitamin E relative to DC (liver 73.4%; heart 65.2%). Insulin was increased significantly in all the treatment groups relative to DC. Histological examinations revealed congestion of vessels in the heart and liver.

Co-administration of quercetin and Vitamin E synergistically protected the heart and liver of rats with Type 2 Diabetes Mellitus via down regulation of mitochondrial-mediated apoptosis.