Green tea attenuates diabetes induced Maillard-type fluorescence and collagen cross-linking in the heart of streptozotocin diabetic rats

The enhanced myocardial collagen content, collagen glycation and the resulting advanced glycation end products (AGE) which exhibit the characteristics of increased cross-linking are proposed for the stiffness of myocardium in diabetes. To explore the cardioprotective effect of green tea in diabetes, we study the effect of green tea extract on myocardial collagen characteristics in streptozotocin diabetic rats. The effect of green tea on marker enzymes in serum and cardiac tissues were also assayed to understand the extent of protection. Six weeks after the diabetes induction, diabetic rats were treated with green tea extract [300 mg (kg body weight)(-1) day(-1)] for 4 weeks. AGE were determined by fluorescence assay and cross-linking of collagen by solubility measurement while collagen content was measured by biochemical assay. The activities of aspartate transaminase (AST), lactate dehydrogenase (LDH) and creatine kinase (CPK) were measured by biochemical assay. The increase in blood glucose, glycated hemoglobin and systolic blood pressure in diabetic rats were reduced upon green tea treatment. The activities of AST, LDH and CPK were significantly increased in serum whereas decreased in cardiac tissues in diabetic rats representing the cardiac damage. Administration of green tea to diabetic rats significantly ameliorates these enzyme activities. There was no significant difference in the myocardial collagen content among the experimental rats. A significant (P < 0.05) increase in collagen linked Maillard-type fluorescence and decrease in collagen solubility in the myocardium of diabetic rats as compared to control rats (0.955 +/- 0.02 versus 0.683 +/- 0.04 and 30 +/- 1.41 versus 45.17 +/- 1.17, respectively) indicates the increase in advanced glycation end products formation and degree of collagen cross-linking. Green tea administration to diabetic rats significantly (P < 0.05) decreased the fluorescence (0.73 +/- 0.02) whereas increased the solubility of collagen (41.5 +/- 1.04) indicating the reduction in advanced glycation end products and collagen cross-linking. The present study reveals that green tea by ameliorating myocardial collagen characteristics may provide a therapeutic option in the treatment of cardiovascular complications of diabetes. (C) 2007 Elsevier Ltd. All rights reserved.