As knowledge regarding mechanisms of pentachlorophenol (PCP) toxicity in neuronal cell lines is limited, the aim of the study was to evaluate the effects of PCP and its active metabolites, tetrachloro-1,4-benzoquinone (TCBQ) and tetrachlorohydroquinone (TCHQ) in human neuroblastoma SH-SY5Y cells. All compounds induced cytotoxic effects in time- and dose-dependent manners, and resulted in differential modes of cell death. Reduced mitochondrial membrane potential (ΔᴪM) and oxidative damage lead to apoptosis and necrosis following TCBQ and PCP exposure, respectively. Time-dependent investigations revealed transient ΔᴪM recovery in TCHQ exposed cells, and redox stress. Sufficient ΔᴪM recovery allowed apoptosis completion in TCHQ exposed cells, whereas overwhelming metabolic and oxidative stress saw a conversion from apoptotic to necrotic-like cell death. The onset of mitochondrial dysfunction preceded that of redox damage for all compounds, indicating that oxidative damage is secondary to ΔᴪM insult. Cytotoxic events were further linked to cell cycle. S phase and G2/M blocks were observed after 12 h exposure to TCBQ and TCHQ, respectively, while a G1 block occurred after 24 h exposure to PCP. This study provides new insight regarding time-dependant toxic effects of PCP and its metabolites in human neuronal cells.
Keywords: Cell death; Mitochondrial membrane potential; Oxidative stress; Pentachlorophenol; Tetrachloro-1,4-benzoquinone; Tetrachlorohydroquinone.
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