Inhibitory action of melatonin on H2O2- and cyclophosphamide-induced DNA damage

Melatonin, the pineal gland hormone known for its ability to modulate circa dian rhythm, has recently been studied in its several functions. It is beli eved to inhibit cancer growth, to stimulate the immune system and to act as an antioxidant. In particular, this latter activity is ascribed to two dif ferent mechanisms: stimulation of radical detoxifying enzymes and scavengin g of free radicals. We used this compound in mammalian cells in vitro to in vestigate its mechanism of action in modulating DNA damage, Cytogenetic and cytofluorimetric analyses were performed. We show that melatonin is able t o modulate chromosome damage (chromosomal aberrations and sister chromatid exchanges) induced by cyclophosphamide. Conversely its involvment in modula ting oxidative processes, thereby reducing DNA damage, is less clear. In pa rticular, melatonin is able to decrease H2O2-induced chromosomal aberration s but not sister chromatid exchanges and has been found to induce oxygen sp ecies in a cytofluorimetric test (DCFH assay).