Abstract
Paracetamol is very widely used as an analgesic drug. However at massive doses it causes liver failure. Liver damage develops in two stages. The first phase appears to be due directly to metabolites of paracetamol. The second phase is poorly understood and the present study is concerned to determine whether apoptosis plays a role. Initial investigations concentrated on whether and when apoptosis occurs in paracetamol intoxication. One hour after administration of 500mg/Kg bw of paracetamol to mice there was depletion of hepatic glutathione and cytoplasmic vacuolation in hepatocytes which became more severe at 2h. In addition to these changes, the nuclei in some sinusoidal endothelial cells appeared apoptotic. At 3h there was some necrosis and apoptosis of hepatocytes and red blood cells accumulated in the sinusoids. Congestion increased progressively as did serum transaminases but glutathione levels progressively recovered. . Apoptotic and necrotic hepatocytes disappeared at 4h but were observed again at 5h and 6h. Further experiments investigated the effect of anti-apoptotic agents. Treatment with gadolinium chloride, which inhibits Kupffer cell function, abolished apoptotic changes and reduced the damage whereas treatment with the caspase inhibitor Z-VAD-FMK completely abolished paracetamol-induced apoptosis and necrosis. The degree of protection was clearly greater than that afforded by the vehicle (DMSO) on its own. The development of changes in thioacetanide intoxication was also studied. The time course was similar to paracetamol although the changes developed slower and the early intoxication less pronounced. Even so, by 6h both apoptosis and necrosis were prominent in the centrilobular area. By 17 and 24h there was massive red blood cell congestion and all the hepatocytes in the centrilobular area showed TUNEL positive staining. Gadolinium chloride pre-treatment abolished completely the apoptosis in the earlier stage (6h) but failed to protect it at later stages (24h). The results of thioacetamide toxicity studies indicated that Kupffer cells are involved in the early phase of liver damage. These studies showed that apoptosis occurs at two points in the development of liver damage caused by paracetamol and thioacetamide. The first burst is associated with the first-phase damage and pro-apoptotic mediators released by Kupffer cells. The second burst of is associated with marked congestion in the centrilobular zone. The degree of apoptosis in the second phase of damage suggests that it may play an important role in the development of liver failure.