Characterization of chromium-induced apoptosis in cultured mammalian cells:: A differential scanning calorimetry study

The present study examined the cytotoxic effect of increasing Cr(VI) concentrations on cultured cells by a combination of biochemical methods and DSC, a novel use of DSC in the study of cell death. The characteristics of apoptotic cells are compared with normal cells. Chromatin in human epithelial-like L-41 cells has two thermal transitions at 100 and 105 °C. The heat from these endotherms is 90.5 ± 11.0 J/g DNA. The total heat of denaturation (Qd) is 27.5 ± 3.5 J/g dry biomass. The heat evolved (−Q) is 15.6 ± 3.0 J/g dry biomass. The treatment of cells with 20 μM Cr(VI) for 2 and 4 h has not revealed any changes in heat of denaturation and heat evolution (−Q). However increased treatment time with Cr(VI) at 20 μM resulted in significant changes to the thermal profile and a sharp linear decrease of (−Q) and Qd values. The Qd and (−Q) values of cells treated with 20 μM Cr(VI) for 48 h are equal to 15.5 ± 2.0 and 2.1 ± 0.4 J/g dry biomass, respectively. The changes in chromatin conformation, Bax expression and the collapse of the mitochondrial membrane permeability coincide with the time point from which the action of chromium is irreversible.