RECOVERY POTENTIAL OF HEPATOCYTES FROM INHIBITION OF ALBUMIN SECRETION BY CADMIUM

The aim of this study was to examine albumin production, a typical liv er-specific function, in hepatocytes treated with Cd and to examine th e reversibility of the perturbations induced by the toxic metal. Cultu res of freshly isolated rat hepatocytes were exposed to increasing amo unts of Cd in modified Leibowitz L-15 medium for 20 h; the cells were then allowed to recover by further incubation in Cd-free medium for an additional period of 20 h. The levels of albumin secreted into the ex tracellular medium were determined by enzyme-linked immunosorbent assa y and were found to be reduced by Cd in a concentration-dependent fash ion over the first 20 h. Inhibition was seen at Cd concentrations that did not cause any loss of cellular viability (up to 0.5 muM Cd), as j udged from the release of lactate dehydrogenase by the cells. After re placement of the exposure medium by Cd-free medium, the same pattern o f diminished albumin secretion was obtained, revealing the persistence of the cytotoxic effects when recovery conditions were applied. Moreo ver, hepatocytes exposed to 0.5 muM Cd for 20 h and processed for visu alization of albumin immunoreactive sites using protein A-gold and ele ctron microscopy exhibited very low albumin-specific labeling as compa red to the controls (0.6 +/- 0.05 vs. 20.0 +/- 2.6 gold particles/mum2 ). Intracellular glutathione levels were not significantly changed by Cd either after the initial exposure or after the incubation that foll owed in control medium. The accumulation of Cd by the cells, as measur ed by graphite furnace atomic absorption spectrophotometry, was concen tration dependent. It remained stable after medium change, indicating that Cd efflux was negligible upon reestablishment of normal condition s. The present data show that the perturbations in albumin metabolism caused by Cd are not readily alleviated after the cells are returned t o Cd-free medium, suggesting a limited short-term recovery potential a gainst cytotoxic damage. The data also demonstrate that hepatocyte-spe cific functions can be used as sensitive indicators for the detection of cellular disturbances by hepatotoxins.