OXIDANT RESISTANCE OF CADMIUM-ADAPTED HUMAN LUNG FIBROBLASTS

Metallothionein (MT) is a metal and thiol-rich protein readily induced by cadmium (Cd) exposure, In vitro experiments have demonstrated that MT is able to serve as a scavenger of hydroxyl radicals as well as su peroxide anions, albeit to a lesser extent, The role of MT as a mediat or in Cd induced oxidant resistance was investigated in a non-transfor med human lung fibroblast cell line (IMR-90). Cells were passaged thre e times either in a Cd-containing medium (8.9 mu M CdCl2) or in a medi um which lacked Cd. Cellular MT content, as quantitated by a modificat ion of the heme/Cd-109 binding assay, increased significantly with eac h passage in Cd. Immunocytochemistry studies revealed that all Cd-pret reated cells contained MT and that MT was localized in both cytoplasmi c and nuclear compartments. Immunolabeling was more intense in some ce lls compared to others. Very slight immunolabeling was observed in phy siological control cells, grown in the absence of Cd, and virtually no staining was observed in Cd-adapted or non-adapted cells when primary antibody was omitted. Using the xanthine/xanthine oxidase system as a generating system for active oxygen species, we found that the magnit ude of cell injury for Cd-adapted and non-adapted fibroblasts was depe ndent upon oxidant concentration and duration of oxidant exposure. Cd- adapted fibroblasts, which were characterized by over-expression of MT , were significantly more resistant to injury by active oxygen species and also exhibited a greater ability to scavenge extracellular hydrog en peroxide compared to cells with no previous history of Cd exposure, Experiments with aminotriazole demonstrated that catalase was not a m ajor contributor to the additional hydrogen peroxide scavenging capaci ty of Cd-adapted cells. The data presented in this report are consiste nt with involvement of MT in protecting critical cellular targets from reactive oxygen species.