Joint effects of dietary cadmium and polychlorinated biphenyls on metallothionein induction, lipid peroxidation and histopathology in the kidneys and liver of bank voles

Free-living bank voles have been shown to be more sensitive to cadmium (Cd) toxicity than the rodents exposed to Cd under laboratory conditions. The present study was designed to find out whether polychlorinated biphenyls (PCBs), common environmental co-contaminants, increase susceptibility to Cd toxicity through inhibition of metallothionein (MT) synthesis-a low molecular weight protein that is considered to be a primary intracellular component of the protective mechanism. For 12 weeks, the male bank voles were provided with diets containing Cd (0.05 microg/g (control) and 10 microg/g dry wt) and PCBs (0, 10 and 50 microg/g dry wt) alone or in combination under long (16 h) and short (8 h) photoperiods. At the end of exposure period, histological examinations and analyses of MT, Cd, Fe and lipid peroxidation in the kidneys and liver were carried out. Dietary PCBs did not affect Cd inducibility of renal MT, but decreased it significantly in the liver; however, no signs of Cd toxicity (measured by histopathology) occurred in both organs. On the contrary, PCBs at the highest dose increased significantly lipid peroxidation in the kidneys and liver (4-fold) only in the bank voles raised under a long photoperiod; the PCB-induced hepatic lipid peroxidation was accompanied by extensive histopathological changes including hepatocyte enlargement, necrosis and steatosis. Co-treatment with dietary Cd significantly suppressed the increase in lipid peroxidation and apparently reduced hepatic damage. These data indicate that (1) dietary PCBs do not enhance Cd toxicity in the kidneys and liver of bank voles and (2) dietary Cd suppresses PCB-induced hepatotoxicity that appears to be photoperiod-dependent.