Lucy M. Anderson

Induction of dimethylnitrosamine demethylase activity in mouse liver by polychlorinated biphenyls and 3-methylcholanthrene

Abstract Hepatic dimethylnitrosamine (DMN) demethylase activity in male C57BL/6 mice, assayed with 1 or 5 mM DMN and expressed per g liver, increased after i.p. treatment with Aroclor 1254 [polychlorinated biphenyls (PCBS), 500 mg/kg, 96 hr before assay], compared with parallel oil-injected controls. This increase was of statistical significance when either the postmitochondrial supernatant fraction (sup) or isolated microsomes were assayed. The induction appeared larger with 5 mM DMN as substrate (about 180 per cent) than with 1 mM DMN (about 65 per cent). PCBs also induced sup DMN (5 mM) demethylase activity in (C57BL/6 × BALB/c)F 1 and Swiss-Webster mice. 3-Methyl-cholanthrene exposure (80 mg/kg, 48 hr) resulted in a small but significant increase in sup hepatic DMN (5 mM) demethylase activity in C57BL/6 and F 1 mice. Isolated microsomes from C57BL/6 livers exhibited only 40–60 per cent of the DMN (1 or 5 mM) demethylase activity present in the corresponding sup; such preparations may not give an accurate indication of in vivo activity. Inclusion of the lipid layer with the sup resulted in a significant increase in DMN (5 mM) demethylase activity in Aroclor-induced, but not in control, C57BL/6 mouse livers. The number of cells per unit area of liver, determined microscopically after treatment of C57BL/6 mice with PCBs, decreased slightly (15 per cent) but significantly compared with controls. Thus, enzyme activity per g liver represents a conservative approximation of activity per cell, which is the parameter that should be measured for demonstration of induction or repression and for evaluation of potential toxic or carcinogenic effects.

Two crops of primary lung tumors in BALB/c mice after a single transplacental exposure to urethane

Transplacental exposure of BALB/c mice to urethane on day 17 of gestation resulted in the appearance of 2 distinct crops of primary lung tumors (adenomas). The first, smaller crop occurred in 6--12% of the offspring by 12 weeks of age. The second crop, seen after 9 months of age, consisted of tumors in 45% of the offspring. This finding indicates a potentially useful model system for studying tumor latency. It also suggests caution in the choice of short endpoints in time carcinogenesis assays based on lung tumors in certain strains of mouse.

N6 (Methylnitroso)adenosine: A carcinogenic nitrosamine derived from a naturally-occurring nucleoside

N6(Methylnitroso) adenosine (M6(NO)Ado) is found readily under acidic conditions by the interaction of nitrite with 6-methyladenosine, a naturally-occurring nucleoside. Swiss mice were treated with M6(NO)Ado by injection (40 mg/kg each treatment) transplacentally and then as newborns and young adults. The incidences of lymphomas, primary lung tumors, and hepatic neoplasms were significantly greater in these treated animals than in controls. These results demonstrate the tumorigenicity of M6(NO)Ado.

Murine Colonic Mucosal Metabolism and Cytotoxicity of Benzo[α]pyrene

Homogenates of colonic mucosa from seven mouse strains metabolized 14C-benzo[α]pyrene (BP) to alkali-soluble and water-phase products. In those strains in which liver aryl hydrocarbon hydroxylase activity is inducible by β-naphthoflavone (β-NF), the C57BL/6, BALB/c, C3H and random-bred Swiss CD-1, colonic metabolism of BP was also induced by intraperitoneal treatment with 150 mg/kg β-NF 24 h before the assay. No increase in the colonic metabolism of BP was seen after β-NF treatment of the noninducible strains, AKR, DBA and SWR. A detailed study of the products formed was carried out with C57BL/6 male mice. High-performance liquid-chromatography analysis of the products of BP metabolism revealed that phenolic derivatives predominated, but that a small percentage of the BP was converted into the proximate carcinogen, the BP-7,8-diol. Addition of uridine 5′-diphosphoglucuronic acid to the incubation mixture caused an increase in total product formation and a shift from alkali-soluble to water-phase products. Of the water-phase products formed by β-NF-induced colonic mucosal homogenates, about 40% were nondialyzable and associated with precipitable material. In a study of the cellular effects of BP on the colonic mucosa, intrarectal administration of 1 mg BP had a significant cytotoxic effect, as indicated by the number of pyknotic cells and 3H-thymidine-labeling index, and prior treatment with β-NF afforded significant protection against this cytotoxicity.

Lack of carcinogenic effect of nitrosochlordiazepoxide and of nitrosomethylphenidate given orally to mice.

Abstract The nitroso derivatives of two widely used psychotropic drugs, chlordiazepoxide and methylphenidate, were each administered in the drinking-water of (C57BL/6 × BALB/c) F 1 mice at concentrations of 50 and 100 mg/litre, respectively. The mice were treated on the first 4 days of each week from weaning until they were 18 months old. They were autopsied when moribund or at 26 months of age. No increase in tumour incidence, compared to controls, occurred as a result of treatment with either nitrosamine. The mice exposed to nitrosochlordiazepoxide had a significantly lower overall incidence of spontaneous tumours than controls.

N6-(Methylnitroso)Adenosine: a Carcinogen of Environmental Significance

ABSTRACT The naturally occurring nucleoside N 6 -methyladenosine upon nitrosation, under conditions similar to those existing in the gastric contents, is converted into N 6 -(methylnitroso)adenosine (m 6 (NO)Ado), an effective multipotential carcinogen. This compound is also formed by tRNA nitrosation in vitro. We have studied several materials to determine the possibility that m 6 (NO)Ado occurs in the environment. The analytical procedures were those used for volatile and nonvolatile N-nitroso compounds: high pressure liquid chromatography, thermal energy analysis, and mutagenesis assays. We have found that western-type human food and animal feces of animals fed with it contained a fraction of a N-nitroso compound with the same retention time as m 6 (NO)Ado at concentrations ranging from 1.1-3.2 ppm. Therefore, m 6 (NO)Ado can be considered as a carcinogen of possible environmental significance. KEYWORDS : Carcinogenesis, mutagenesis, tRNA, nitrosation, N-nitrosaminopurines, food, feces analysis.