Protective effect of melatonin and catalase in bovine neutrophil-induced model of mammary cell damage

The effect of several antioxidants and a proteinase inhibitor on bovine neutrophil-induced mammary epithelial cell damage was investigated using an in vitro model of co-culturing bovine neutrophils and MAC-T cells, a mammary epithelial cell line. Epithelial cell damages were evaluated by measuring lactate dehydrogenase activity in culture media and by morphological observations of cells after acridine orange staining. Activation of neutrophils with Escherichia coli lipopolysaccharide and phorbol 12-myristate 13-acetate caused superoxide and gelatinase release in media. Activated neutrophils damaged the epithelial cells, as demonstrated by an increase in lactate dehydrogenase release and the observation of morphological changes. The addition of melatonin or catalase reduced neutrophil-induced cytotoxicity in a dose-dependent manner, whereas superoxide dismutase and aprotinin had no effect on cytotoxicity. Melatonin has been reported to scavenge hydroxyl radical and peroxynitrite, whereas catalase and superoxide dismutase scavenge hydrogen peroxide and superoxide, respectively. Our results suggest that hydroxyl radicals released by activated bovine neutrophils cause damage to mammary epithelial cells and that antioxidants may be useful to protect the mammary tissue during bovine mastitis.