The Department of Biomedicine

BBB seminar: George E.N. Kass

Protein kinases and paracetamol-induced hepatic injury

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George E.N. Kass
School of Biomedical and Molecular Sciences, University of Surrey, Guildford, UK

The mild analgesic drug paracetamol (acetaminophen, AAP) induces severe hepatic injury when taken in excessive doses. Recent evidence from our laboratory shows that the initial form of damage is through apoptosis but this process fails to go to completion and degenerates into necrosis (1). The activation of apoptosis involves the translocation of the pro-apoptotic Bcl-2 family members Bax and Bid (as truncated Bid) to mitochondria and the subsequent release of cytochrome c. Bid cleavage and translocation but not Bax translocation are dependent on caspase activity. Further studies into the mechanism through which AAP initiates apoptosis were conducted in vitro using human HuH7 hepatoma cells. AAP-induced apoptosis in HuH7 cells as evidenced by chromatin condensation was preceded by the translocation of Bax to mitochondria and the cytoplasmic release of the pro-apoptotic factors cytochrome c and Smac/DIABLO. A concomitant loss of mitochondrial membrane potential occurred. Activation of the mitochondrial pathway of apoptosis led to the activation of execution caspases-3 and 7. AAP-induced apoptosis and cell death was blocked by inhibitors of caspases but not by inhibitors of calpains, cathepsins and serine proteases. Apoptosis was unaffected by inhibitors of the mitochondrial permeability transition pore and by inhibitors of Jun N-terminal kinases, p38 MAP kinase or MEK1/2. However, pharmacological inhibition of glycogen synthase kinase-3 (GSK-3) decreased AAP-induced apoptosis. In comparison, endoplasmic reticulum stress-induced but not prooxidant-induced apoptosis of HuH7 cells was sensitive to GSK-3 inhibition. It is concluded that AAP-induced apoptosis involves the mitochondrial pathway of apoptosis that is mediated by GSK-3 and most likely initiated through an endoplasmic reticulum stress response.

1. El-Hassan, H. Anwar, K., Macanas-Pirard, P., Crabtree, M., Chow, S.C. Price, S.C., Lee, P.C., Hinton, R.H., Kass, G.E.N. 2003 Toxicol Appl Pharmacol, 191:118-129.