Inhibition of cytochrome P450 2E1 expression by 2-(allylthio)pyrazine, a potential chemoprotective agent: hepatoprotective effects.
Cytochrome P450 2E1 (P450 2E1) is active in both the detoxification and activation of small organic molecules. The effects of 2-(allylthio)pyrazine (2-AP) on P450 2E1-catalytic activity and the expression of rat hepatic P450 2E1 were examined. 2-AP competitively inhibited 4-nitrophenol hydroxylase activity in vitro (Ki, 12 microM). 2-AP treatment of rats (200 mg/kg/day, p.o., 1-3 days old) resulted in 20-30% decreases in the rates of P450 2E1-specific metabolic activities. Immunoblot analysis also revealed that hepatic microsomes isolated from 2-AP-treated rats showed substantial decreases in P450 2E1 level. 2-AP-suppressed isoniazid (INH)-inducible hepatic P450 2E1 levels, as shown by both metabolic activities and immunoblot analyses. Thus, 2-AP was effective in suppressing both constitutive and inducible P450 2E1 expression. Northern blot analysis showed that 2-AP transiently suppressed the hepatic P450 2E1 mRNA level, suggesting that suppression in P450 2E1 expression by 2-AP may be mediated in part by transcriptional inactivation. Hepatoprotective effects of 2-AP against toxicants were monitored in mice. 2-AP pretreatment prior to the administration of lethal doses of acetaminophen (AAP) or INH substantially reduced toxicant-induced mortality. Whereas serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were markedly elevated after AAP administration (i.e. 9-20-fold), 2-AP pretreatment of animals before AAP administration resulted in >95% decreases in elevated serum aminotransferase activities. 2-AP was also effective against CCl4-induced hepatotoxicity. Whereas CCl4 treatment caused 35-70-fold increases in aminotransferase activities, treatment of mice with 2-AP (>10 mg/kg) resulted in the blocking of CCl4-induced liver toxicity. The hepatoprotective effect of 2-AP was in part due to 2-AP-induced elevation of hepatic GSH levels. Whereas AAP or CCl4 treatment resulted in 70-80% reduction in hepatic GSH levels, pretreatment of mice with 2-AP caused a 40-210% elevation in hepatic GSH levels, as compared with either AAP or CCl4 alone. 2-AP pretreatment also reduced AAP- or CCl4-induced increases in lipid peroxidation in a dose-dependent manner. The results of these metabolic activities and of immunoblot and RNA blot analyses demonstrate that 2-AP is efficacious in suppressing constitutive and inducible P450 2E1 expression and effective in protecting against toxicant-induced liver toxicity.
Kim
N D
ND
College of Pharmacy, Seoul National University, Korea.
Kwak
M K
MK
Kim
S G
SG
D000818:Animals; D002251:Carbon Tetrachloride / Q000633:toxicity; D019392:Cytochrome P-450 CYP2E1 / Q000235:genetics; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D005978:Glutathione / Q000032:analysis; D008099:Liver / Q000187:drug effects*; D008297:Male; D051379:Mice; D008813:Mice, Inbred ICR; D011719:Pyrazines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D017207:Rats, Sprague-Dawley
C104935:2-(allylthio)pyrazine; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D004791:Enzyme Inhibitors; D011719:Pyrazines; D012333:RNA, Messenger; D002251:Carbon Tetrachloride; D019392:Cytochrome P-450 CYP2E1; D005978:Glutathione