Protective effect of melatonin on naphthalene‐induced oxidative stress and DNA damage in cultured macrophage J774A.1 cells

Naphthalene is a bicyclic aromatic compound that is widely used in various domestic and commercial applications. Previous studies in our laboratory have demonstrated enhanced production of reactive oxygen species, lipid peroxidation and DNA fragmentation in both in vitro and in vivo models following treatment with naphthalene. Melatonin (N‐acetyl‐5‐methoxytryptamine), an indole hormone, is the chief secretory product of the pineal gland and is an efficient free radical scavenger and antioxidant, both in vitro and in vivo. In this study, we have investigated the ability of 1 mM melatonin to protect against naphthalene-induced oxidative stress and DNA damage in cultured macrophage J774A.1 cells. No significant changes were observed when these macrophage cells were treated with 100 μM naphthalene. Approximately 2.0‐, 4.2‐ and 4.4‐fold increases in cytochrome c reduction were observed at 200, 400 and 500 mM concentrations of naphthalene, demonstrating the increased production of superoxide anion. At 24 h, lipid peroxidation increased by approximately 1.4‐, 2.1‐ and 2.2‐fold following treatment of these cells with 200, 400 and 500 mM concentrations of naphthalene, respectively, while 1.6‐, 2.8‐ and 2.8‐fold increases in DNA fragmentation were observed at these same concentrations. Two hour pretreatment of these cultured cells with 1 mM melatonin provided approximately 26–44% decreases in lipid peroxidation, superoxide anion production and DNA fragmentation in cells treated with 400 and 500 μM naphthalene. Cellular viability decreased significantly when cells were incubated with concentrations of naphthalene greater than 100 μM, while preincubation with melatonin significantly increased the cellular viability. These results demonstrate that naphthalene may induce toxic manifestations by enhanced production of reactive oxygen free radicals, resulting in lipid peroxidation and DNA damage, while preincubation with melatonin significantly suppressed cytoxicity in J774A.1 macrophage cells.