Distribution and metabolism of the retinoid, N-(4-methoxyphenyl)-all-trans-retinamide, the major metabolite of N-(4-hydroxyphenyl)-all-trans-retinamide, in female mice.

The metabolism and disposition of N-(4-methoxyphenyl)-all-trans-retinamide (MPR), the major metabolite of N-(4-hydroxyphenyl)-all-trans-retinamide (4-HPR), were investigated in female B6D2F1 (BDF) mice. Following a single oral dose of 10 mg/kg, MPR distributed to the serum, liver, mammary gland, urinary bladder, and skin. The highest levels of MPR were detected in the liver and mammary gland, and the largest values for AUC were in the mammary gland followed by the skin and liver. The t1/2 for MPR was 5.1 hr in liver, 5.6 hr in serum, 18.7 hr in urinary bladder, 23.1 hr in skin, and 26.6 hr in mammary gland. MPR and five metabolites were detected; levels varied between tissues. One metabolite was 4-HPR; the other four, which eluted at 7, 12, 13, and 18 min, remain unidentified. The major metabolite of MPR was the 18-min metabolite and comprised 17% of total retinoid in skin and 14% in mammary gland. 4-HPR was only a minor metabolite of MPR; 4-HPR was not detectable in serum or urinary bladder and accounted for less than 4% of total retinoid in the other tissues. In mice dosed with 10 mg/kg 4-HPR, the parent compound, MPR, a putative 4-HPR ester, and three of the MPR metabolites (7, 13, and 18 min) were found. These data suggest that the interconversion of 4-HPR and MPR greatly favors formation of MPR.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of the chemopreventive retinoid N-(4-hydroxyphenyl)retinamide by mammary gland in organ culture.

N-(4-Hydroxyphenyl)retinamide (4-HPR) is considered to be the most effective chemopreventive retinoid for chemically induced mammary carcinogenesis in rats. However, the mechanism of 4-HPR action in mammary cells is poorly understood. In the present study we examined the metabolism of 4-HPR in the mouse mammary gland in organ culture. Mammary glands excised from BALB/c mice were incubated with 4-HPR in the presence of insulin, prolactin and steroid hormones for 6 days. The glands were extracted with chloroform/methanol (2:1, v/v), and the metabolites were separated on a reversed-phase h.p.l.c. column. Three metabolites were separated in addition to 4-HPR; one of the metabolites, M2, was co-eluted with 13-cis-4-HPR, M3 was co-eluted with N-(4-methoxyphenyl)retinamide (4-MPR) and M1 remains unidentified. There appeared to be some hormonal regulation in the distribution of metabolites in the glands. Increased levels of 4-MPR and M1 were observed in insulin-plus-prolactin-treated glands as compared with the glands incubated with steroid hormones. Furthermore, it was observed that M1 isolated from the livers of 4-HPR-treated rats competed for the cellular retinoic acid-binding protein (CRABP) sites; however, 4-HPR did not bind to CRABP. These results indicate that mouse mammary gland can metabolize 4-HPR and that the metabolites which compete for CRABP sites may have physiological significance in the retinoid inhibition of mammary carcinogenesis.

Effects of pretreatment with the retinoid N-(4-hydroxyphenyl)-all-trans-retinamide and phenobarbital on the disposition and metabolism of N-(4-hydroxyphenyl)-all-trans-retinamide in mice.

The effects of pretreatment with N-(4-hydroxyphenyl)-all-trans-retinamide (4-HPR) and phenobarbital (PB) on the distribution and metabolism of 4-HPR, and on the levels of hepatic cytochromes, were investigated in female BDF mice. Pretreatment of mice for 3 days with 10 mg/kg 4-HPR had no effect on the disposition of 4-HPR in the serum, liver, mammary gland, or urinary bladder. 4-HPR pretreatment also had no effect on the pharmacokinetics of any of its metabolites in the liver, or on the levels of hepatic cytochromes P450 or b5. By contrast, pretreatment of mice for 3 days with 80 mg/kg PB had a significant effect on the disposition of 4-HPR in all the tissues examined; the areas under the concentration-time curves for PB-pretreated mice were half those for vehicle-pretreated mice. PB pretreatment also significantly reduced the levels of four metabolites of 4-HPR in the liver and increased the levels of hepatic cytochromes P450 and b5. These data suggest that prior or concomitant administration of drugs that induce the mixed function oxidase system could result in changes in retinoid disposition and metabolism; such changes may alter retinoid chemopreventive activity.

Genetic variability in deacetylation of 2-acetylaminofluorene and N-hydroxy-2-acetylaminofluorene in inbred strains of mice.

Genetic variability in 2-acetylaminofluorene (AAF) and N-hydroxy-2-acetylaminofluorene (N-OH-AAF) deacetylase activities was examined in 19 inbred strains of mice. AAF deacetylase activities ranged from 0.60 to 1.33 nmol/min/mg protein, and there was an approximately 2.5-fold difference in AAF deacetylase activity between the fastest (C57BL/6J) and slowest (RIIIS/J) mouse strains. N-OH-AAF deacetylase activities ranged from 3.28 to 13.24 nmol/min/mg protein, and the difference between the fastest (AU/SsJ) and slowest (RIIIS/J) strains was 4-fold. N-OH-AAF deacetylase activity was higher (5-13 times) than AAF deacetylase activity in all strains examined. Thus, there are genetic differences in AAF and N-OH-AAF deacetylase activities; these differences may play an important role in individual susceptibility to the mutagenic and carcinogenic effects of the aromatic amides.

Comparative activity of dietary or topical exposure to three retinoids in the promotion of skin tumor induction in mice.

The activity of dietary and topical administration of three retinoids, all-trans-retinoic acid, 13-cis-retinoic acid, and N-(4-hydroxyphenyl)retinamide (4-HPR), as promoters of skin tumor induction in SENCAR mice was studied. When administered as dietary supplements at their maximum tolerated dose levels, all three retinoids promoted tumorigenesis in mice initiated with a single topical dose of 5 micrograms 7,12-dimethylbenz(a)anthracene. Maximal promoting activity was observed with dietary 13-cis-retinoic acid; dietary 4-HPR was significantly less active than was either isomer of retinoic acid. When administered via topical application, all-trans- and 13-cis-retinoic acids both promoted skin tumor induction; 4-HPR did not. HPLC analysis of skin samples from mice receiving dietary 4-HPR showed the parent compound and six metabolites; these metabolites were not found in the skin of mice receiving topical 4-HPR exposure, although 4-HPR itself was present. These data indicate that skin tumor promotion can be induced by systemic administration as well as topical application of the all-trans- and 13-cis-retinoic acids. Substitution of a 4-hydroxyphenylamide terminal group results in a significant reduction in promoting activity. 4-HPR appears to require metabolic activation for tumor promoting activity; this metabolism does not occur in the skin following topical application, but is observed following systemic exposure.

Potentiation of vitamin A hepatotoxicity by butylated hydroxytoluene.

The interaction between the natural vitamin A ester retinyl acetate (RA) and the phenolic antioxidant butylated hydroxytoluene (BHT) in the induction of biliary hyperplasia and hepatic fibrosis in female Sprague-Dawley rats was characterized. Using a 3 X 3 matrix design, rats were fed diets supplemented with (per kilogram diet) 0, 125, or 250 mg RA and/or 0, 2500, or 5000 mg BHT. The 125-mg dose of RA induced no gross hepatotoxicity, while the 250-mg dose of RA induced a low incidence of hepatic fibrosis in rats examined after 120 and 180 days of exposure. Exposure to BHT alone induced hepatocellular hypertrophy and dose-related increases in liver weight, but no hepatocellular pathology. Simultaneous administration of RA plus BHT resulted in significant increases in the incidence of biliary hyperplasia and hepatic fibrosis compared to that induced by RA alone. BHT reduced total hepatic vitamin A content at all RA dose levels. Thus, mechanisms other than increases in liver vitamin A levels must underlie the potentiation by BHT of RA hepatotoxicity.

N-(4-hydroxyphenyl)-all-trans-retinamide pharmacokinetics in female rats and mice.

The distribution of N-(4-hydroxyphenyl)-all-trans-retinamide (4-HPR) and its metabolites was investigated in the liver, serum, mammary gland, and urinary bladder of female rats and mice. Following an iv dose of 5 mg/kg to rats, 4-HPR distributed to all tissues examined with the highest levels reached in the liver. The distribution period was completed in about 4 hr and was followed by first order elimination kinetics. The t1/2 for 4-HPR elimination from the liver was 9.4 hr, from the serum was 12.0 hr (not significantly different from liver), from the mammary gland was 43.6 hr, and from the urinary bladder was 9.3 hr. A 5-day ip dosing study (5 mg/kg/day of 4-HPR) in both rats and mice revealed that 4-HPR distributed to all tissues examined with the highest levels reached in the urinary bladder. 4-HPR and four metabolites were detected in the tissues. One coeluted with a cis isomer of 4-HPR (M2), another with N-(4-methoxyphenyl)-all-trans-retinamide (4-MPR) (M3), a third appeared to be a 4-HPR-ester (M4), and the fourth remains unidentified (M1). However, the amount of each metabolite varied between tissues and between species. The concentration of 4-HPR was significantly 2-4 times lower and the percentage of M3 (4-MPR) was 3 times higher in the mouse tissues than in the corresponding tissues of the rat. M2 (cis-4-HPR) and M4 (4-HPR-ester) were present in rat liver but not in mouse liver.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic differences in 2-aminofluorene pharmacokinetics between intact C57BL/6J and A/J mice.

Studies of genetically determined differences in arylamine acetylation with the model carcinogen 2-aminofluorene in C57BL/6J and A/J inbred mouse strains showed that individual differences in the pharmacokinetics of 2-aminofluorene were dependent on differences in 2-aminofluorene N-acetyltransferase activity in liver and blood. Elimination rates of 2-aminofluorene from blood of mice administered a single ip dose of 30, 50, or 100 mg/kg of 2-aminofluorene were dose-dependent in both strains. At a dose of 100 mg/kg, the average rate of 2-aminofluorene elimination was approximately three times faster in rapid acetylator (C57BL/6J) mice than in slow acetylator (A/J) mice (0.36 +/- 0.02 hr-1 vs. 0.12 +/- 0.02 hr-1), and that in B6AF1 mice was intermediate (0.24 +/- 0.02 hr-1) to the parental lines. These results support previous observations that acetylation of arylamines is controlled by intermediate dominant inheritance of two major alleles at a single locus. Comparison of the average rate of elimination of 2-aminofluorene from blood of the congenic mouse line, A.B6-NATr, (0.27 +/- 0.05 hr-1) which has the rapid acetylator allele placed on the A/J background provided evidence that modifying genes of the A/J mouse significantly reduced the effect of the rapid acetylator allele on the rate of 2-aminofluorene elimination. A trend was observed toward a greater apparent volume of distribution for 2-aminofluorene in A/J than in C57BL/6J mice.