Immunohistochemical detection of ras and myc oncogene expression in regenerating rat liver

Farnesyltransferase inhibitors reduce Ras activation and ameliorate acetaminophen-induced liver injury in mice

Hepatotoxicity due to overdose of the analgesic and antipyretic acetaminophen (APAP) is a major cause of liver failure in adults. To better understand the contributions of different signaling pathways, the expression and role of Ras activation was evaluated after oral dosing of mice with APAP (400-500 mg/kg). Ras-guanosine triphosphate (GTP) is induced early and in an oxidative stress-dependent manner. The functional role of Ras activation was studied by a single intraperitoneal injection of the neutral sphingomyelinase and farnesyltransferase inhibitor (FTI) manumycin A (1 mg/kg), which lowers induction of Ras-GTP and serum amounts of alanine aminotransferase (ALT). APAP dosing decreases hepatic glutathione amounts, which are not affected by manumycin A treatment. However, APAP-induced activation of c-Jun N-terminal kinase, which plays an important role, is reduced by manumycin A. Also, APAP-induced mitochondrial reactive oxygen species are reduced by manumycin A at a later time point during liver injury. Importantly, the induction of genes involved in the inflammatory response (including iNos, gp91phox, and Fasl) and serum amounts of proinflammatory cytokines interferon-gamma (IFNgamma) and tumor necrosis factor alpha, which increase greatly with APAP challenge, are suppressed with manumycin A. The FTI activity of manumycin A is most likely involved in reducing APAP-induced liver injury, because a specific neutral sphingomyelinase inhibitor, GW4869 (1 mg/kg), did not show any hepatoprotective effect. Notably, a structurally distinct FTI, gliotoxin (1 mg/kg), also inhibits Ras activation and reduces serum amounts of ALT and IFN-gamma after APAP dosing. Finally, histological analysis confirmed the hepatoprotective effect of manumycin A and gliotoxin during APAP-induced liver damage.

CONCLUSION

This study identifies a key role for Ras activation and demonstrates the therapeutic efficacy of FTIs during APAP-induced liver injury.

Nutritional modulation of the final outcome of hepatotoxic injury by energy substrates: an hypothesis for the mechanism

Survival after hepatocellular injury and necrosis may depend on the ability of the remaining hepatocytes to divide and restore an adequate population of functioning cells. Although adequate nutritional support is necessary for liver regeneration after severe liver damage, much is yet to be discovered concerning which nutritional factors are critical for liver regeneration. Clinically, nutritional substances are administered only from the energy aspect, without regard to whether or how these substrates may facilitate or impede liver tissue repair processes. Glucose is used as principal source of energy in liver damage because of accompanying marked hypoglycemia. But the contribution of glucose to compensatory liver regeneration and/or survival is unclear. This paper advances the hypotheses that: (1) glucose increases the toxicity of centrilobular hepatotoxicants by inhibiting hepatic cell division and tissue repair allowing unrestrained progression of injury; (2) fatty acids facilitate hepatic-cell division permitting hepatolobular restoration to occur thus preventing death from even a lethal dose. If hepatic tissue repair can be stimulated by some therapeutically compatible mechanism, then it might be possible to prevent death from even massive hepatocellular injury. In addition to nutritional manipulation, it should be possible to exploit molecular mechanisms that regulate organized cell division (tissue repair) to increase survival rates of patients suffering from fulminant hepatic failure. These findings have significant impact on tissue repair in a variety of other organs and tissues, particularly in diabetes-like conditions.