Our data suggest that APAP treatment leads to GSH depletion, protein adduct formation, mitochondrial dysfunction, and oxidant
stress and eventually oncotic www.selleckchem.com/products/BKM-120.html necrosis in HepaRG cells, similar to what has been observed in primary mouse hepatocytes but not in typical human hepatoma cells. The basis for this behavior is that HepaRG cells are capable of differentiating into two subpopulations: one with hepatocyte-like morphology and gene expression and one with the appearance of biliary epithelial cells.22, 24 The hepatocyte-like cells express a nearly complete complement of drug-metabolizing enzymes, including most of the cytochrome P450 enzymes.25, 26 HepaRG cells also possess many other characteristics unique to adult differentiated hepatocytes, including hepatocyte-specific transporter expression,25, 33 iron-loading capacity,34 and inducibility of CYPs and other proteins.33, 35 Thus, these cells have the potential to be a useful tool to study mechanisms of drug hepatotoxicity in a human system. The distinct advantage of the HepaRG cell line over primary human hepatocytes is the unlimited availability of identical cells. Nevertheless, they are hepatoma-derived selleck chemical and there is the
possibility that certain intracellular signaling mechanisms might be different. It is therefore important to study mechanisms of cell death induced by known hepatotoxicants in these cells. Acetaminophen hepatotoxicity in rodents depends on the formation of the reactive metabolite NAPQI, which can be detoxified by glutathione. However, after depletion of GSH in the cell, NAPQI binds to cellular proteins, which is considered the initiating event in the toxicity.2, 36 Our experiments with HepaRG cells identified depletion of cellular GSH and the formation of protein
adducts as the earliest detectable events. This is consistent with mouse studies of APAP hepatotoxicity.18, 37 Evidence for increased GSH turnover and detection of APAP-protein adducts in human plasma after APAP exposure suggests that these events also MCE公司 occur in humans.38, 39 Although our data agree with the general hypothesis of reactive metabolite formation, GSH depletion and protein adduct formation as early response to APAP exposure, the sequence of events is not as previously assumed. Our data clearly show that protein adduct formation occurs parallel to GSH consumption and does not require extensive GSH depletion. In fact, protein adducts were detected in HepaRG cells and in HepG2 cells before significant effects on GSH levels and well before any evidence of mitochondrial dysfunction and cell death. This suggests that small amounts of protein binding per se does not initiate toxicity and probably a certain level needs to be reached to trigger the early mitochondrial effects. More recently, mitochondrial dysfunction and the MPT have emerged as central to the mechanism of APAP-induced cell death in cultured rodent hepatocytes10-12 and in vivo.