Simultaneous effects of lead and cadmium on primary cultures of rat proximal tubular cells: interaction of apoptosis and oxidative stress.

The combined effects of lead (Pb) and cadmium (Cd) on primary cultures of rat proximal tubular (rPT) cells were studied. These cells were either treated with Pb acetate (0.5 and 1 μM) alone, Cd acetate (2.5 and 5 μM) alone, or a combination of Pb and Cd acetate, and then joint cytotoxicity was evaluated. The results showed that the combination of these two metals decreased cell viability and increased the number of apoptotic and necrotic cells and lactate dehydrogenase release synergistically. Simultaneously, increased intracellular reactive oxygen species, malondialdehyde, and calcium levels and decreased mitochondrial membrane potential, intracellular acidification, and inhibition of Na(+), K(+)-, and Ca(2+)-ATPase activities were shown during the exposure. In addition, apoptotic morphological changes induced by these treatments in rPT cells were demonstrated by Hoechst 33258 staining. The apoptosis was markedly prevented by N-acetyl-L-cysteine, whereas necrosis was not affected. In summary, there was a synergistic cytototic effect of Pb combined with Cd on rPT cells. Cell death induced by Pb-Cd mixture was mediated by an apoptotic and a necrotic mechanism. Apoptotic death was the chief mechanism. Changes of intracellular events were intimately correlated with both oxidative stress and mitochondrial dysfunction, which promoted the development of apoptosis.