Differential behaviour of cell membranes towards iron-induced oxidative damage and the effects of melatonin.

The ability of melatonin to protect iron-induced lipid peroxidation was studied in various rat cell membranes. The concentration of cellular membrane malondialdehyde (MDA) was used as an index of induced oxidative membrane damage. Cell membranes from the brain, heart, kidney and liver of the male Sprague-Dawley rat were incubated with ferric ammonium citrate (20 microg/ml iron) alone for 3 h and concomitant with varying concentrations of melatonin ranging from 125 to 2,000 microM. The basal MDA levels of all the cell membranes were 25.0+/-1.4 (brain), 21.2+/-0.2 (heart), 10.0+/-0.9 (kidney) and 20.7+/-0.4 (liver) microM/g membrane protein, and the highest lipid peroxidation after exposure to iron occurred in the kidney (314.4%), followed by the heart (151.3%), the liver (130.4%) and the brain (121.7%). This peroxidative effect was completely (ED50 846.7 microM for the heart) and partially suppressed by melatonin (ED50 462.1 microM for the brain, 178.3 microM for the kidney and 886.6 microM for the liver). This inhibition effect on MDA production by these cell membranes was also found - except for the liver - if melatonin was used alone. These results show that the direct effect of lipid peroxidation on cellular membrane following iron exposure is markedly reduced by melatonin.