Increase in brain nitric oxide synthase activity in daunorubicin-treated rats

Anthracyclines such as daunorubicin are very effective anticancer agents. These drugs are known to cause side effects including cardiotoxicity. 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. Therefore, we determined nitric oxide synthase activity in rat brain after daunorubicin treatment in an effort to explain the neurotoxicity produced by anthracyclines. Male Sprague-Dawley rats were treated with different subcutaneous doses of daunorubicin (0.1-4.0 mg/kg/week for five weeks) while control animals were injected with phosphate buffered saline. There was a significant increase (80%) of nitric oxide synthase activity in daunorubicin-treated animals as compared to controls. This activity was inhibited by N-monomethyl-L-arginine (NMMA), nitroarginine, N-6-aminohexyl-5-chloro-1-napthalene sulfonamide (W-7), a calmodulin 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-napthylamine (NPN) fluorescence. These results indicate that daunorubicin increases nitric oxide synthase activity in rat brain which may increase the levels of nitric oxide. The increased levels of nitric oxide may cause neurotoxicity. Our results further indicate that daunorubicin interacts with calmodulin and enhances nitric oxide synthase activity which is dependent on calmodulin.