Melatonin reduces UV-induced reactive oxygen species in a dose-dependent manner in IL-3-stimulated leukocytes

Reactive oxygen species (ROS) are presumed to be involved in inflammatory U V reactions of the skin. This in vitro study was performed to investigate t he suppressive effect of melatonin in interleukin-3 (IL-3) stimulated leuko cytes. Neutrophilic granulocytes were isolated from EDTA-treated whole bloo d and placed in a phosphate-buffered saline (PBS) containing IL-3. Cell sus pensions were either treated with PBS (control) or with increasing doses of melatonin (0.1, 0.5, 1. 2, 3, 5, 7.5, 10 mmol). One PBS solution was left unirradiated and the other nine solutions (PBS and melatonin) were irradiat ed with 750 mJ/cm(2) UVB light (280-360 nm, max: 310 nm). Radical formation was measured by the chemiluminescence technique. UV-irradiated leukocytes showed a 5-fold higher radical Formation than unirradiated leukocytes. Mela tonin, in increasing doses in powers of ten, led to a maximum suppression o f free radicals at 10 nmol (P = 0.01) and 1 mmol melatonin (P = 0.001), sho wing a biphasic. non-linear, dose-response relationship. Melatonin, given i n amounts of 0.1-10 mmol, led to a direct dose-dependent suppression of ROS . Radical formation was suppressed significantly in a range from 0.5 to 10 mmol (P = 0.001). Melatonin is known to function as a radical scavenger and antioxidant; some of these melatonin effects may be receptor independent, while others may be receptor dependent.