isosafrole and Necrosis

Previously it was shown that methylenedioxybenzenes (MDBs), particularly isosafrole, were highly effective at preventing CCl4-induced liver necrosis in vivo (Z.S. Zhao, P.J. O'Brien, The prevention of CCl4-induced liver necrosis in mice by naturally occurring methylenedioxybenzenes, Toxicol. Appl. Pharmacol., 140 (1996) 411-421), probably as a result of forming metabolic intermediate complexes with cytochrome P450. In the following it was shown that pretreatment of mice with isosafrole also completely prevented ferric nitrilotriacetate (FeNTA)-induced renal necrosis and lipid peroxidation, even though metabolic activation by cytochrome P450 is not involved. The naturally occurring or synthetic MDBs that prevented CCl4 hepatotoxicity also prevented hepatocyte lipid peroxidation. induced by FeNTA, but other cytochrome P450 inhibitors were ineffective. These compounds, in decreasing order of antioxidant effectiveness, were sesamol, 4-t-butyl-methylenedioxybenzene, isosafrole, piperonyl butoxide and 4-bromo-methylenedioxybenzene and safrole, whereas, benzodioxole, 3,4-(methylenedioxy)-toluene and 1,2-(methylenedioxy)-4-nitrobenzene were ineffective. Pre-incubating the hepatocytes with P450 inhibitors decreased the protective effects of isosafrole, suggesting that the catecholic metabolites of MDBs were responsible for the antioxidant activity. A greater inhibition of FeNTA-induced lipid peroxidation by catecholic metabolites was observed. Since cytochrome P450 did not participate in FeNTA-induced hepatocyte or microsomal lipid peroxidation, it is likely that the antioxidant properties of MDBs or their catecholic metabolites also contribute to their in vivo protection against CCl4 or FeNTA-induced hepato- or nephrotoxicity.

Topics: Animals; Antioxidants; Carcinogens; Chemical and Drug Induced Liver Injury; Cytochrome P-450 Enzyme System; Dioxoles; Ferric Compounds; Kidney; Kidney Diseases; Lipid Peroxidation; Liver; Liver Diseases; Male; Mice; Microsomes, Liver; Necrosis; Nitrilotriacetic Acid; Rats; Rats, Sprague-Dawley; Safrole

Methylenedioxybenzenes (MDBs) and structurally related alkenylbenzenes were compared for their effectiveness in preventing carbon tetrachloride (CCl4)-induced liver necrosis in mice. Pretreatment with isosafrole, safrole, dihydrosafrole, and benzodioxole at dosages as low as 10 mg/kg significantly prevented the increase in plasma transaminase levels and histochemical changes associated with CCl4-induced liver necrosis, whereas piperonyl butoxide (PBO), eugenol, isoeugenol, sesamol, and curcumin did not prevent CCl4 hepatotoxicity even at 200 mg/kg. However, isosafrole was only partly hepatoprotective if administered 10 min after the toxicant. Liver microsomes isolated 1 hr after isosafrole but not after PBO administration had a markedly decreased CYP2E1 activity. Isosafrole, safrole, dihydrosafrole, and benzodioxole in vitro also inhibited CYP2E1-dependent metabolism more effectively than eugenol and isoeugenol, whereas PBO did not inhibit CYP2E1 activity. The protective effects of isosafrole, safrole, and benzodioxole were therefore predominantly attributed to their ability to inactivate CYP2E1, the major isozyme involved in CCl4 bioactivation. The marked potentiation of CCl4 hepatotoxicity in CYP2E1-induced mice was also completely prevented by isosafrole but not PBO pretreatment, supporting the hypothesis that CYP2E1 inhibition by isosafrole contributes to its hepatoprotective effect against CCl4. Isosafrole and safrole also prevented bromotrichloromethane (BrCCl3)-induced hepatocyte cytotoxicity, whereas PBO was ineffective.

Topics: Animals; Carbon Tetrachloride; Cytochrome P-450 Enzyme Inhibitors; Dioxoles; Liver; Male; Mice; Mice, Inbred Strains; Microsomes, Liver; Necrosis; Plants; Safrole