MELATONIN PROTECTS NEURONS FROM SINGLET OXYGEN-INDUCED APOPTOSIS

Singlet oxygen (O-2[(1) Delta g]) is a very reactive molecule that can be produced by living cells and may contribute to cytotoxicity. The p ineal hormone melatonin has been reported to possess potent antioxidan t activity, and to be capable of scavenging O-2((1) Delta g). We inves tigated whether melatonin might reduce the neurotoxic action of O-2((1 ) Delta g). The cytotoxic effect of singlet oxygen was studied in prim ary cultures of cerebellar granule neurons pretreated with a photosens itive dye, rose bengal, and exposed to light-a procedure that generate s O-2((1) Delta g). We found that this procedure triggers neuronal dea th, which is preceded by mitochondrial impairment (assayed by the rate of the reduction of MTT, 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl te trazolium bromide, into formazan), and by DNA fragmentation-a marker o f apoptosis. DNA fragmentation was determined in situ by terminal deox ynucleotidyl transferase assay; cell death was assayed with 0.4% trypa n blue solution-viable cells with an intact membrane are not permeable to trypan blue; dead cells are, and thus, they are stained blue. Neur oprotection was obtained with the pineal hormone melatonin. In a cell- free system, melatonin also protected the enzyme creatine kinase (EC 2 .7.3.2) from the rose bengal-induced injury. The results suggest that melatonin might counteract the cytotoxic action of singlet oxygen. Fur ther studies are needed to clarify the exact role singlet oxygen and m elatonin might play in neurodegenerative diseases.