Effects of dietary compounds on alpha-hydroxylation of N-nitrosopyrrolidine and N'-nitrosonornicotine in rat target tissues.

Male F344 rats were pretreated with various dietary compounds, and the effects of pretreatment on the in vitro alpha-hydroxylation of N-nitrosopyrrolidine or N'-nitrosonornicotine were determined in assays with liver microsomes or cultured esophagus, respectively. Dietary compounds included phenols, cinnamic acids, coumarins, indoles, and isothiocyanates. Pretreatments were carried out either by administering the compound by gavage 2 hr prior to sacrifice (acute protocol) or by adding the compound to the diet for 2 weeks (chronic protocol). Acute pretreatment with benzyl isothiocyanate, allyl isothiocyanate, phenethyl isothiocyanate, phenyl isocyanate, and benzyl thiocyanate but not sodium thiocyanate inhibited formation of alpha-hydroxylation products of both nitrosamines. When the chronic pretreatment protocol was used, only phenyl isothiocyanate and sodium thiocyanate inhibited formation of alpha-hydroxylation products of both nitrosamines. Pretreatments with butylated hydroxyanisole, p-methoxyphenol, or N-acetylcysteine had little, if any, effect on the alpha-hydroxylation of N-nitrosopyrrolidine or N'-nitrosonornicotine. Chronic pretreatment with p-hydroxycinnamic acid, 4-hydroxy-3- methoxycinnamic acid, coumarin, umbelliferone, limetine , indole, indole-3-carbinol, indole-3-acetonitrile, and L-tryptophan induced activity for the alpha-hydroxylation of N-nitrosopyrrolidine. The results of this study indicate that isothiocyanates are possible candidates for further study as potential inhibitors of carcinogenesis by N-nitrosopyrrolidine and N'-nitrosonornicotine.

Inhibition of target tissue activation of N'-nitrosonornicotine and N-nitrosopyrrolidine by dietary components.

Twenty-one dietary and related chemicals have been evaluated for their potential inhibitory activities against the tumorigenic effects of N-nitrosopyrrolidine and N'-nitrosonornicotine using in-vitro metabolic assays in the target tissues, namely, rat liver microsomes and cultured rat oesophagus, respectively. Compounds studied include phenols, cinnamic acids, coumarins, isothiocyanates and indoles. Isothiocyanates were the most potent inhibitors of both nitrosamines in the acute studies, but were less active in chronic studies. This difference may be explained by the pharmacokinetic properties of these compounds. Phenols, cinnamic acids, coumarins and indoles were primarily inducers of N-nitrosopyrrolidine metabolism. The results suggest that isothiocyanates, in general, are the most promising chemicals for future study as protective agents against the carcinogenic effects of these nitrosamines.

Effects of route of administration and dose on the carcinogenicity of N-nitrosodiethanolamine in the Syrian golden hamster.

N-Nitrosodiethanolamine was assayed for carcinogenicity in Syrian golden hamsters by s.c. injection, topical application, and oral cavity swabbing. Three groups of 30 hamsters each received 27 weekly s.c. injections of either 500, 170, or 58 mg of N-nitrosodiethanolamine per kg in 0.9% NaCl solution. In the group treated with 500 mg/kg, 19 of 30 animals developed nasal cavity tumors, 7 of 30 had tracheal tumors, and 2 of 30 had tumors of the larynx. Among the animals treated with 170 mg/kg, 7 of 29 presented with nasal cavity tumors and 4 of 29 presented with tracheal tumors. In the group treated with 58 mg/kg, only two tracheal tumors were observed. Acetone solutions of N-nitrosodiethanolamine were applied to the shaved backs of three groups of 30 hamsters, each three times weekly for 36 weeks, at doses of 25, 8, or 2.5 mg; the total doses were the same as in the groups treated by s.c. injection. At the 25-mg dose level, 5 of 30 animals developed nasal cavity tumors and 4 of 30 animals had tumors of the trachea. No skin tumors were observed. The incidence of respiratory tract tumors in the groups treated with 8 or 2.5 mg was not significant compared to controls. The oral cavities of 40 hamsters were swabbed three times weekly for 45 weeks with 20 mg of N-nitrosodiethanolamine; the total dose was the same as the highest doses given by s.c. or topical administration. Seventeen of 38 hamsters had nasal cavity tumors, 6 of 38 developed tracheal tumors, and 1 of 38 presented with a tumor of the larynx. No tumors were observed in the oral cavity. The results of this study demonstrate that N-nitrosodiethanolamine is organospecific for the Syrian golden hamster nasal cavity and trachea and that it induces tumors in these sites at doses lower than previously reported.

Effects of fluorine substitution on the tumor initiating activity and metabolism of 5-hydroxymethylchrysene, a tumorigenic metabolite of 5-methylchrysene.

The tumor initiating activity on mouse skin of 5-hydroxymethylchrysene (5-HOMeC), a major metabolite of the carcinogen, 5-methylchrysene (5-MeC), was investigated. After an initiating dose of 30 microgram, with promotion by tetradecanoylphorbol acetate, 5-HOMeC induced skin tumors in 90% of the animals, with 9.5 tumors/mouse, 5-MeC gave a 75% incidence of skin tumors with 6.2 tumors/mouse. The tumorigenic activities after a 10 microgram initiating dose were; 5-HOMeC, 45% skin tumor-bearing animals and 2.6 tumors/-mouse; 5-MeC, 55% skin tumor-bearing animals and 5.6 tumors/mouse. In contrast, 6-hydroxy-methylchrysene was inactive. To investigate the mechanism of activation of 5-HOMeC, 3-fluoro-5-hydroxymethylchrysene (3-F-5-HOMeC) and 7-fluoro-5-hydroxymethylchrysene (7-F-5-HOMeC) were prepared and assayed for tumor initiating activity at a dose of 30 microgram. 7-F-5-HOMeC gave 95% tumor-bearing animals and 7.9 tumors/animal whereas 3-F-5-HOMeC gave only 5% tumor-bearing animals and 0.1 s/animal. The inhibition of tumorigenicity by substitution of fluorine at the 3-position, but not the 7-position of 5-HOMeC is strictly analogous to results obtained previously with 5-MeC and suggests a similar mechanism of activation for both compounds. The metabolites formed upon incubation of 5-HOMeC with cofactors and the 9000 x g supernatant from Aroclor pretreated rats were separated by h.p.l.c. The 1,2-dihydrodiol and 7,8-dihydrodiol of 5-HOMeC were identified. The major phenolic metabolite was identified as 1-hydroxy-5-hydroxymethylchrysene. In the in vitro metabolism of 7-F-5-HOMeC under the same conditions, we identified the 1,2-dihydrodiol but not the 7,8-dihydrodiol. In the metabolism of 3-F-5-HOMeC, oxidation in the 1-4 ring was inhibited relative to that observed in the metabolism of 5-HOMeC. These results suggest that 5-HOMeC is activated primarily through formation of its 1,2-dihydrodiol.