[Ascorbic acid hinderance of the prenatal carcinogenic effect of ethylurea and nitrite]

Comparative study of the effects of vitamin C and bleomycin on smokers' and non-smokers' lymphocytes in clastogenicity assays

Free radicals are products of metabolic reactions and of external factors that can injure different biological molecules. However, different antioxidant agents can prevent the action of these reactive species and the damage they cause. Vitamin C (VC) is an important micronutrient found in the diet, which presents defense mechanisms against the free radicals that challenge the cells of the organism. The objective of the present study was to investigate the effect of VC as a modulator of the damage induced in DNA by bleomycin (BLM) in lymphocytes from smokers and non-smokers. The difference in response to the mutagenic potential of BLM between smokers and non-smokers was also investigated. Peripheral blood lymphocyte cultures were treated simultaneously with BLM (20 microg/ml) and/or VC (100, 200, and 400 microg/ml) in the G2 phase of the cell cycle. The results obtained did not demonstrate a statistically significant difference in the response to the antitumor agent BLM between smokers and non-smokers. The data also showed that VC had no significant modulating effect on the frequency of chromosome aberrations induced by BLM in the cells of smokers and non-smokers under the experimental conditions used.

[Vitamin C in a long-term trial is without effect on experimental carcinogenesis]

This long-term study deals with the effect of ascorbic acid on chemically induced carcinogenesis of the small intestine in rats. Carcinoma was induced in 27 animals by application of N-Ethyl-N'-nitro-N-nitrosoguanidine (ENNG) alone in the drinking water (120 mg/1). The average survival time was 238 ( 40) days. The addition of large amounts of ascorbic acid to the food (3 g/100 g food) did not suppress the development of tumors. On the contrary, a significant reduction in the survival time was seen. All animals receiving ENNG and ascorbic acid only lived 207 ( 45) days on average. Neither histological type of tumor spread was influenced by the use of ascorbic acid. Giving ascorbic acid alone had no effect on the survival time and did not lead to changes in the tissue of the small intestine.

[Ascorbic acid and cancer of the duodenum. An experimental study (author's transl)]

This study applies to the agency of vitamin C on chemical carcinogenesis in the small intestine of rats. Administration of N-Ethyl-N'-nitro-N-nitrosoguanidine (ENNG) in drinking water produced tumors of the small intestine after 18 weeks in more than 90%. The induction of tumors could not be suppressed by a large amount (2-3%) of sodium ascorbate in food, but the depth of tumor infiltration was restricted. Cancer developed in 29 of 36 rats receiving ENNG only. In 25 animals of this group growth of tumor corresponded to a P4 stage. In 24 of 35 animals, additionally receiving vitamin C, P4 stage was observed in only 13 cases. Pathological changes in the small intestine could not be observed after the sole administration of vitamin C.

The use of short-term tests to measure the preventive action of reducing agents on formation and activation of carcinogenic nitroso compounds

The effect of reducing agents on the nitrosation of methylguanidine (MG) and on the in vitro activation of dimethylnitrosamine (DMN) was examined by measuring DNA-repair synthesis (unscheduled incorporation of [3h]TdR), shifts in alkaline sucrose gradients, frequency of chromosome aberrations, and clone-forming capacity of cultured human fibroblasts. The reducing agents examined were sodium ascorbate, cysteine, cysteamine, and propyl gallate. Since the short-term bioassays used can be quantitated, it has become relatively easy to detect the inhibitory action of reducing compounds on the nitrosation reaction of MG and metabolic activation (with S-9 preparation) of the precarcinogen DMN, to measure their effective dose range, and to establish the most effective ratios between inhibitory agent and reactant. The results indicate that DNA-repair synthesis is a suitable short-term test for studying the numerous combinations and premutations between several carcinogenic or non-carcinogenic agents, and for estimating the capacity of inhibitory agents to affect formation and activation of chemical carcinogens.

The effect of antioxidants on the production of volatile nitrosamines during the frying of bacon

In model system studies simulating the frying of bacon a considerable variation in the production of N-nitrosopyrrolidine (NOPyr) has been observed, as occurs in sliced bacon fried conventionally. The inclusion of ascorbate or erythorbate (isoacorbate) has led consistently to a fall in or an elimination of NOPyr production up to an addition of 300 ppm (1,5 mM). Above this concentration of ascorbate, the elimination of NOPyr formation persisted in some instances but in others an increased production of the nitrosamine occurred. Using alpha-tocopherol, a fall of NOPyr production during the simulated frying of bacon was obtained with increase of concentration of the antioxidant, there being a consistent elimination of the volatile nitrosamine following an additionof 500 ppm (1.16 mM). Whilst ascorbyl palmitate had a similar action in reducing or eliminating NOPyr production, no synergistic effect between it and alpha-tocopherol was noted in an experiment combining the two antioxidants. When bacon was fried in fat containing 400 or 800 ppm alpha-tocopherol, the total production of NOPyr and DMN in the fried bacon, cooked out fat and condensate was markedly reduced but not completely eliminated as in the model system studies. Similarly, the curing of bacon with a brine containing a mixture of alpha-tocopherol, ascorbyl palmitate and citric acid has led to considerable reductions in NOPyr and DMN output on frying when the combined concentrations of the two anti-oxidants were calculated to be 800 ppm.

Effect of sodium ascorbate on tumor induction in rats treated with morpholine and sodium nitrite, and with nitrosomorpholine

Groups of male MRC Wistar rats were treated for 2 years either with morpholine (10 g/kg food) together with sodium nitrite (3 g/l drinking water) or with N-nitrosomorpholine (NM, 0.15g/l drinking water). In both cases, a group of rats was given sodium ascorbate (22.7 g/kg food) in addition to these treatments. When ascorbate was present, the liver tumors induced by morpholine and nitrite showed a 1.7-fold longer induction period, a slightly lower incidence, and an absence of metastases in the lungs, indicating that ascorbate had inhibited the in vivo formation of NM. Ascorbate did not affect liver tumor induction by the performed NM. The group treated with morpholine, nitrite, and ascorbate had a 54% incidence of forestomach tumors, including an 18% incidence of squamous cell carcinomas, possibly because ascorbate promoted NM action in this organ.

[Practical tasks in cancer research (author's transl)]

Particularly urgent tasks for practical cancer research are pointed out: (1) recognition of the multidisciplinary character of oncology, (2) placement of the cancer patient more than before in the focus of research, (3) the use of modern methods of genetics to specify the definition of a "disposition", (4) the intensification of investigations into the field of chemical carcinogenesis, since prevention of cancer diseases seems most likely in this sector, and (5) elaboration of practical experimental models for the study of chemotherapeutic possibilities