Effect of butylated hydroxyanisole added in vitro or administered to rats on N,N-dibutylnitrosamine and N-butyl-N-(4-hydroxybutyl)nitrosamine metabolism by post-mitochondrial supernatant of liver homogenates.

The effect of butylated hydroxyanisole (BHA) on P-450-dependent omega-hydroxylation of N,N-dibutylnitrosamine (NDBA) to N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN), and the further oxidation of BBN to N-butyl-N-(3-carboxypropyl)nitrosamine (BCPN) by the alcohol/aldehyde dehydrogenase system was investigated using the post-mitochondrial supernatant of liver homogenates (S9) from acutely and chronically BHA pretreated animals or S9 fractions from untreated rats with BHA added. Acute oral BHA (50 and 250 mg.kg-1) did not change NDBA omega-oxidation, which was reduced by 35% only when the compound was administered 0.5% in the diet for 3 weeks. BCPN formation from BBN was unaffected by acute and chronic BHA pretreatment. In order to verify whether BHA or its metabolite(s) had a direct effect on NDBA and BBN oxidation, the compound was added to S9 fractions from untreated rats at various concentrations. Only when BHA concentrations were equimolar or in a 10-fold molar excess to the substrate concentration, we observed 30-50% inhibition of BBN formation and a reduced BCPN formation (60-80% of control values), from BBN. Thus, only at very high BHA concentrations could we confirm the inhibition of P-450-dependent mixed function oxidase and alcohol dehydrogenase activities involved in the metabolism of NDBA and BBN.

Effect of acute and chronic butylated hydroxyanisole administration on in vivo glucuronidation of N-nitrosobutyl(4-hydroxybutyl)amine in rats.

The urinary metabolic pattern of N-nitrosobutyl(4-hydroxybutyl)amine (NB4HBA) administered ip at a dose of 5 mg/kg body weight was studied in animals either pretreated with butylated hydroxyanisole (BHA) as a single oral dose of 50 or 250 mg/kg, or fed a diet containing 0.1 or 0.5% BHA. The 24-hr urinary excretion of NB4HBA, its glucuronic acid-conjugate (NB4HBA-G) and N-nitrosobutyl(3-carboxypropyl)amine (NB3CPA) in control rats were 0.12, 0.75 and 30% of the administered dose, respectively, and were not changed after a single oral dose of 50 mg BHA/kg. NB4HBA-G was significantly reduced in the urine of rats given 250 mg BHA/kg. In vitro assays carried out using rat-hepatic microsomal preparations as the source of the enzyme UDP-glucuronyl transferases (GT) and NB4HBA as the substrate, suggest that a competition between NB4HBA and BHA for the same enzyme may be the cause of the decreased NB4HBA-G excretion observed in vivo. A fourfold increase in NB4HBA-G urinary excretion was observed after chronic 0.5% BHA feeding; moreover, the glucuronic acid-conjugate of NB3CPA (NB3CPA-G), which was not detected in the controls or after acute BHA treatment, appeared in the urine of rats given dietary BHA for 3 wk, accounting for about 10% of the administered NB4HBA. In vitro experiments indicate that the increased glucuronides excretion may be the result of an elevated hepatic GT activity.

Effect of butylated hydroxyanisole on the metabolism of N-nitrosodi-n-butylamine and N-nitrosobutyl(4-hydroxybutyl)amine by rat hepatic S9 preparations in vitro.

N-Nitrosodi-n-butylamine (NDBA), the NADPH generating system and various concentrations of butylated hydroxyanisole (BHA) added to rat hepatic S9 fractions resulted in a significant drop (30-50%) in N-nitrosobutyl(4-hydroxybutyl)amine (NBHBA) formation and a consequent rise in the amount of substrate recovered unchanged. When NBHBA and NAD+ were incubated with BHA and S9 fractions, the amount of N-nitrosobutyl(3-carboxypropyl)amine (NBCPA) was decreased by 20-40%, and the amount of unmetabolized NBHBA increased.