Interactions between melatonin, reactive oxygen species, and nitric oxide.

Accumulation of reactive oxygen species is critical for the neuropathology of Alzheimer's disease. Melatonin hormone, an antioxidant, could play a key role in aging and senescence. Nitric oxide, a biologically active unstable radical, is synthesized by nitric oxide synthase when converting L-arginine to L-citrulline. We have investigated whether the treatment of cultured cells with melatonin could possibly reduce the release of free radicals and other ROS. We assayed NO indirectly by measuring the level of its stable end products, nitrite/nitrate (NOx), using the Griess reagent. When the neuroblastoma cells such as N1E-115 were treated with a NO donor such as sodium nitroprusside (SNP), a significant level of NOx was detected in a time- and dose-dependent manner in the conditioned medium compared to the untreated cells or SNP-containing media. In neuroblastoma cells, the release of NOx as mediated by SNP was significantly inhibited by treatment with (i) carboxy-PTIO, a NO scavenger; (ii) SOD-1, superoxide dismutase; and (iii) melatonin. In these cells SNP-mediated NOx release was mediated by superoxide ions and/or free radicals that can be inhibited by melatonin. The ROS-scavenging function of melatonin along with its neuroprotective and neurodifferentiating role can be utilized for the prevention of neurodegenerative disorders such as AD.