Effects of combined use of diallyl disulfide and Nacetyl-cysteine on acetaminophen hepatotoxicity in beta-naphthoflavone pretreated mice.

AIM:To assess the protective effect of diallyl disulfide (DADS) and its combined use with N-acetyl-cysteine (NAC) on acetaminophen (APAP) hepatotoxicity in C57BL/6N (B6) mice pretreated with beta-naphthoflavone (BNF).METHODS:B6 mice were divided into six groups and all compounds used were injected intraperitoneally. Except for control and APAP group (receiving APAP only), the other groups received an injection of APAP (350mg/kg) 48 hours after BNF (200mg/kg) and either of DADS (200mg/kg), or NAC (500mg/kg) or both DADS and NAC.DADS was given 2 hours before APAP and NAC was injected with APAP.The mean survival time was recorded and livers were examined histologically.Hepatic glutathione (GSH) levels and plasma ALT were also determined at different time points.To evaluate the effect of DADS or NAC on hepatic P450 induction by BNF,liver microsomes were prepared and 7-ethoxyresorufin O-dealkylase (ERD) activity was determined using spectrofluorometrical methods. In vitro effect of DADS or NAC on ERD activity was assayed by directly incubating microsomal suspension with DADS or NAC of different concentrations.RESULTS:APAP was not toxic to mice without BNF pretreatment, but caused severe liver necrosis and death of all BNF-treated mice in 4 hours. A sharp depletion of GSH (approximately 62% of its initial content at 2 hours and 67% at 4 hours) and a linear elevation of ALT levels (536.8 plus minus 29.5 Sigma units at 2 hours and 1302.5 plus minus74.9 at 4 hours) were observed.DADS and NAC given individually produced mild protection,resulting in prolonged survival,a slower decline of GSH level and a less steeper elevation of ALT level.All mice died eventually. Co-administration of DADS and NAC completely protected mice.GSH level in this group lowered by about 35% and 30% at 2 and 4 hours, and ALT was 126 plus minus 18 and 157.5 plus minus 36.6 Sigma units at 2 and 4 hours. ERD activity in BNF-treated mice was about 5 times that of the constitutive level determined in normal mice. Neither DADS nor NAC inhibited P450 1A1/1A2 induction as determined by their effect on the induction of ERD activity.In vitro assay indicates that DADS,but not NAC,was a potent inhibitor of ERD activity(IC(50) = 4.6&mgr;m).CONCLUSION:A combined use of both DADS and NAC produced full protection in BNF treated mice against APAP hepatotoxicity.The mechanism is that DADS inhibits P450 1A1/1A2 activity, but not induction, which substantially reduces production of NAPQI, while NAC enhances liver detoxifying capability via serving as a precursor of GSH and stimulating GSH synthesis.