INCREASE IN BRAIN NITRIC-OXIDE SYNTHASE ACTIVITY IN DAUNORUBICIN-TREATED RATS

Anthracyclines such as daunorubicin are very effective anticancer agen ts. These drugs are known to cause side effects including cardiotoxici ty. Anthracyclines are neurotoxic to laboratory animals. Nitric oxide is a novel and very important chemical messenger in the brain. However , at higher levels, nitric oxide causes well defined neurotoxicity. Th erefore, we determined nitric oxide synthase activity in rat brain aft er daunorubicin treatment in an effort to explain the neurotoxicity pr oduced by anthracyclines. Male Sprague-Dawley rats were treated with d ifferent subcutaneous doses of daunorubicin (0.1-4.0 mg/kg/week for fi ve weeks) while control animals were injected with phosphate buffered saline. There was a significant increase (80%) of nitric oxide synthas e activity in daunorubicin-treated animals as compared to controls. Th is activity was inhibited by N-monomethyl-L-arginine (NMMA), nitroargi nine, N-6-aminohexyl-5-chloro-1-napthalene sulfonamide (W-7), a calmod ulin antagonist, suggesting that the nitric oxide synthase activity is calmodulin dependent. Further, our in vitro studies demonstrated that daunorubicin interacted with calmodulin as measured by N-phenyl-1-nap thylamine (NPN) fluorescence. These results indicate that daunorubicin increases nitric oxide synthase activity in rat brain which may incre ase the levels of nitric oxide. The increased levels of nitric oxide m ay cause neurotoxicity. Our results further indicate that daunorubicin interacts with calmodulin and enhances nitric oxide synthase activity which is dependent on calmodulin.