Nephrotoxicity of CdCl2 and Cd-metallothionein in cultured rat kidney proximal tubules and LLC-PK1 cells.

Nephrotoxicity is the major adverse effect produced by chronic exposure to cadmium (Cd). This injury is thought to be caused by the Cd-metallothionein complex (CdMT). In intact animals, CdMT is more efficiently taken up by the proximal tubules than CdCl2 and results in more renal damage. However, the mechanism(s) by which CdMT produces renal injury is not yet understood completely. Therefore, we used cultured renal proximal tubular cells to study the nephrotoxicity of CdMT and CdCl2. Rat kidney proximal tubules were isolated by collagenase perfusion, followed by percoll isopycnic centrifugation. 14C-alpha-methylglucose uptake and lactate dehydrogenase leakage were used as indices of nephrotoxicity. Surprisingly, CdMT was less toxic than CdCl2 to the cultured rat proximal tubule cells, as well as to cultured LLC-PK1 cells (a pig kidney proximal tubular cell line). Consistent with these observations on nephrotoxicity, 109CdMT uptake into these cultured renal cells was much less than that of 109CdCl2. Transwell cultures of LLC-PK1 cells were also used to examine the toxicity and uptake of CdCl2 and CdMT following basolateral and apical exposure. Uptake of both CdCl2 and CdMT from basolateral exposure was higher than that from apical exposure. Again, more 109CdCl2 was taken up and more cytotoxicity was observed in the CdCl2- than CdMT-exposed cells. In summary, CdCl2 is more toxic than CdMT to cultured rat kidney proximal tubules as well as LLC-PK1 cells. This is in contradiction to the greater in vivo nephrotoxic effects of CdMT than CdCl2. Therefore, cultured renal cells do not appear to be an appropriate model to study the nephrotoxicity of CdMT; transport of CdMT into proximal tubular cells in vivo does not appear to be maintained in vitro.