ROLE OF METALLOTHIONEIN AND OTHER ANTIOXIDANTS IN SCAVENGING SUPEROXIDE RADICALS AND THEIR POSSIBLE ROLE IN NEUROPROTECTION

Based on the inhibition of nitrite formation by generating superoxide from xanthine/xanthine oxidase (X/XO) reaction system, metallothionein (MT) and other sulfhydryl containing amino acids have been selected t o test their abilities to scavenge superoxide radicals. Different conc entrations of metallothionein and other sulfhydryl containing molecule s e.g. cysteine, N-acetyl-cysteine and glutathione, were used to asses s superoxide scavenging properties. Metallothionein scavenges superoxi de radical in a dose-dependent manner with increasing concentrations a s evidenced by the inhibition of nitrite formation. Similar abilities to scavenge superoxide radicals were shown by cysteine, N-acetyl-cyste ine. Glutathione also scavenges superoxide radical in a dose-dependent manner. In vitro experiments demonstrated that metallothionein is sup erior in scavenging superoxide radicals compared to other sulfhydryl m olecules such as cysteine, N-acetyl-cysteine and even glutathione. The data, further, suggest that metallothionein-II has a 6-fold higher ca pacity to scavenge superoxide radical than metallothionein-I. In addit ion, metallothionein-like protein was isolated from different regions of mouse brain treated with zinc. Brain metallothionein-like protein i nhibits nitrite formation as demonstrated by other scavengers; however , the extent of inhibition is different by this protein isolated from different brain regions. The present study suggests that metallothione ins and metallothionein-like proteins isolated from mouse brain act as neuroprotective agents by scavenging superoxide radicals. Published b y Elsevier Science Ltd.