Published online Apr 15, 1998. doi: 10.3748/wjg.v4.i2.112
Revised: February 20, 1998
Accepted: March 20, 1998
Published online: April 15, 1998
AIMS: 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 β-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 (350 mg/kg) 48 h after BNF (200 mg/kg) and either of DADS (200 mg/kg), or NAC (500 mg/kg) or both DADS and NAC. DADS was given 2 h 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 h. A sharp depletion of GSH (approximately 62% of its initial content at 2 h and 67% at 4 h) and a linear elevation of ALT levels (536.8 ± 29.5 Sigma units at 2 h and 1302.5 ± 74.9 at 4 h) 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 h, and ALT was 126 ± 18 and 157.5 ± 36.6 Sigma units at 2 and 4 h. 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 (IC50 = 4.6 μM).
CONCLUSIONS: 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.