Cadmium-induced apoptosis in human normal liver L-02 cells by acting on mitochondria and regulating Ca2+ signals

Cadmium is a well-known toxic compound for the liver. It has been demonstrated to induce hepatotoxicity partly via apoptosis, but no uniform mechanism of apoptosis has so far been proposed. This study was first to determine whether cadmium-induced apoptosis in L-02 cells, second to observe the mechanism of cadmium-induced apoptosis. Studies of morphology, DNA fragmentation and apoptotic rate demonstrated that 60 μM cadmium induced apoptosis with strong effects on cell viability. A concomitant time-dependent decrease of Bcl-2 and mitochondrial transmembrane potential (ΔΨm) was observed. Subsequently, increase of caspase-3 activity and release of mitochondrial AIF were detected. However, cell pretreatment with a broad-specificity caspase inhibitor (Z-Asp) did not abolish apoptosis. These data demonstrated that the apoptotic events involved a mitochondria-mediated apoptotic pathway but not necessarily caspase-dependent signaling. On the other hand, intracellular free Ca2+ concentration ([Ca2+]i) of cadmium-exposed cells had significant increases and the Bapta-AM, a well-known calcium chelator, pretreatment partially blocked cadmium-induced apoptosis, indicating that the elevation of [Ca2+]i may play an important role in the apoptosis. Together, these results support the notion that cadmium-induced hepatotoxicity is comparable to effects in L-02 by inducing apoptotic pathways on the basis of acting on mitochondria and regulating Ca2+ signals.