The protective effect of losartan in the nephropathy of the diabetic rat includes the control of monoamine oxidase type A activity.

Monoamine oxidase activity (MAO-A and B) levels, as intracellular source of reactive oxygen species, might increase in diabetic nephropathy (DN) contributing to reduce dopamine levels and to unbalance kidney redox state. We explored the hypothesis that beneficial effects of losartan, an angiotensin-II type 1 receptor (AT1) blocker, in DN included the control of MAO activity levels. In kidneys of normoglycemic and diabetic, streptozotocin-injected (55 mg/kg) rats, treated or untreated with losartan, an AT1 antagonist (20 mg/kg/day in the drinking water), we investigated MAO activity radiochemically and antioxidant enzymes including catalase, aldehyde dehydrogenase and superoxide dysmuthase spectrophotometrically. In addition, we also evaluated malondialdehyde and carbonylated protein levels spectrophotometrically as indexes of oxidative attack to lipids and proteins. Diabetic rats showed signs of nephropathy, including renal hypertrophy, proteinuria, high acethylglucosaminidase and -glutamyltranspeptidase urinary levels. In diabetic kidneys, MAO-A and catalase activities as well as malondialdehyde levels, were found significantly higher than in normoglycemic ones. Interestingly, in diabetic kidneys, MAO-A activity correlated not only with catalase but also with gamma-glutamyltranspeptidase urinary levels. Our results indicate that the control of MAO-A activity is to be included amongst the mechanisms of protection afforded by losartan in DN. In fact, the prevention of MAO-A raise might increase dopamine availability and, as suggested by the correlation with gamma-GGT, reduce oxidative attack to tubular cells.