Oyster metallothionein as an oxyradical scavenger: implications for hemocyte defense responses

In order to better understand the interplay between metallothionein (MT) and reactive oxygen species (ROS) in oyster hemocytes, studies of the hydrogen peroxide (H2O2) scavenging properties of MT were carried out in a cell-free system. Mammalian MT is involved in protection against oxidative stress by virtue of its ability to scavenge free radicals; therefore, the H2O2 scavenging potentials of Crassostrea virginica and rabbit MTS were compared. Oyster and rabbit MTs showed similar dose-dependent suppression of H2O2-stimulated, luminol-augmented chemiluminescence (CL); the EC50 for CL (25 microM H2O2) was approximately 1.0 microM MT for both species. The interaction of ROS with MT in hemocytes could play a role in protection of the cells and surrounding tissues from oxidants associated with antimicrobial responses. Mobilization of bound zinc from MT by hemocyte-derived ROS may produce aberrant regulatory effects on various cellular processes. The data suggest that MT may be involved in immunoregulatory pathways in oyster hemocytes as a result of its ability to scavenge antimicrobial ROS.