MANGANESE INHIBITS SUPEROXIDE-DISMUTASE ACTIVITY

Manganese is an essential trace element, which in excess causes neurotoxic Parkinsonian syndrome. Many toxic processes are mediated by oxygen free radicals (OFR), and these are destroyed by several defense mechanisms including superoxide dismutase (SOD). SOD converts superoxide radical to hydrogen peroxide. Manganese ion at a concentration of 0.83 mu g/ml, a little higher than that found in normal human brain tissue, inhibited SOD activity in an in vitro assay using 6-hydroxydopamine as substrate. Mg had no effect at 0.33 mu g/ml, somewhat less than the normal brain manganese level. Mn had no effect on autoxidation of 6-hydroxydopamine in the absence of SOD in concentrations up to 1.67 mu g/ml. It is concluded that Mn can inhibit SOD in vitro, and it is therefore possible that in vivo manganese neurotoxicity may be mediated by excess OFR due to inhibition of intracellular cerebral SOD by manganese.