Influence of disulfiram on the metabolism of the urinary bladder carcinogen N-butyl-N-(4-hydroxybutyl)nitrosamine in the rat

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Abstract
The effect of feeding disulfiram (DSF) to rats on the metabolism of N-butyl-N-(4-hydroxybutyl)nitrosamine (BHBN) was examined in order to study the mechanism by which DSF inhibits bladder cancer induction by BHBN. After 2 weeks of feeding 0.5% DSF in the diet, animals were given [14C]BHBN (25 mg/kg) and the urine and expired CO2 were collected for 8 h. Radioactivity in expired air was very low, but DSF caused a significant reduction in expired 14CO2 (control 1.0% of dose; DSF 0.6%), presumably by inhibition of .alpha.-hydroxylation pathways. There was no difference in the excretion of total urinary radioactivity (control 84%; DSF 85%). Urine was analyzed by h.p.l.c. for BHBN, N-butyl-N-(3-carboxypropyl)nitrosamine (BCPN), N-butyl-N-2-hydroxy-(3-carboxypropyl)nitrosamine (BHCPN) and N-butyl-N-carboxymethylnitrosamine (BCMN). DSF did not alter the urinary excretion of BCPN (control 64% of dose; DSF 61%), whereas BHCPN excretion was increased (control 11% of dose; DSF 22%) and urinary levels of BCMN were decreased (control 10% of dose; DSF 4%). The metabolism of BHBN was also studied in isolated hepatocytes from control and DSF-fed rats. Hepatocytes were incubated in Liebovitz''s L-15 medium containing 0.5 mM [14C]BHBN and aliquots of the medium were removed for h.p.l.c. analysis at 0.5, 1,2 and 4 h. Metabolic rates are expressed as .mu.mol/h/5 million cells. There was no difference in the overall rate of metabolism of BHBN in control and DSF-fed rats. BHBN was very rapidly oxidized to BCPN and the rate was not affected by DSF treatment (control 1.82; DSF 1.76). The rate of accumulation of BHCPN was increased 3.5-fold in the DSF-fed rats (control 0.06; DSF 0.21) and BCMN could not be detected. Taken together, these data show that (i) DSF may inhibit the low extent of .alpha.-hydroxylation of BHBN or BCPN; (ii) DSF does not inhibit the rapid oxidation of BHBN to BCPN and (iii) DSF appears to inhibit the metabolism of BHCPN.