Polychlorinated biphenyls (PCB-153) and (PCB-77) absorption in human liver (HepG2) and kidney (HK2) cells in vitro: PCB levels and cell death.

An understanding of congener specific cellular absorption of PCBs is important to the study of the organ specific body burden of an individual and to their toxic effects. We have previously demonstrated that single PCB congeners induce cytotoxicity, as evidenced by decreased cellular viability and accelerated apoptotic death. There is very little, if any, information available on the differences in toxicity due to the nature of absorption of PCBs in different cells. To obtain such information human liver (HepG2) cells (in medium with 10% FBS) were exposed to 70 μM of both PCB-153 (non-coplanar hexachlorobiphenyl) and PCB-77 (coplanar tetrachlorobiphenyl), and human kidney (HK2) cells in serum free medium were exposed to 80 and 40 μM of PCB-153 and PCB-77 respectively, according to their LC(50) values in these cells. Medium and cells were collected separately at each time interval from 30 min to 48 h, and PCB concentrations were analyzed in both by GC-MS using biphenyl as an internal standard following hexane:acetone (50:50) extraction. We also performed trypan blue exclusion, DNA fragmentation and fluorescence microscopic studies in assessing cell viability and apoptotic cell death. About 40% of PCB-153 (35 μM, 50% of the maximum value) was detected in HepG2 cells within 30 min, and it reached its highest concentration at 6h (60 μM), concomitant with the PCB depletion in the medium (5 μM). For PCB-77, the highest concentrations within the cells were reached at 3h. However, the absorption levels of PCB-153 and PCB-77 in HK2 cells reached their peaks at 3 and 6h respectively. Exposure of human liver and kidney cells to PCB-153 and PCB-77 caused accelerated apoptotic cell death in a time-dependent manner. The studies demonstrated that (1) liver cells initiate the absorption of PCBs much faster than kidney cells; however, the concentration reaches its maximum level much earlier in kidney cells; (2) both PCB-153 and PCB-77 induced enhanced apoptotic death in liver and kidney cells; and (3) kidney cells are more vulnerable to PCBs based on the results of apoptosis and cellular viability, even with almost similar absorption or tissue burden of PCBs.