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Oxidative DNA damage in humans could arise also from incorrect nutritional habit and life style. DNA strand breaks with apurinic/apyrimidinic sites, oxidized purines and oxidized pyrimidines were assessed in 24 subjectively healthy vegetarians (plant food, dairy products, eggs) and compared with 24 non-vegetarians (traditional diet, general population). DNA strand breaks + oxidized purines are significantly reduced in vegetarians (p<0.05), DNA strand breaks are nonsignificantly decreased. The sufficient antioxidative status (overthreshold values of natural essential antioxidants, which mean a reduced risk of free radical disease) is crucial in free radical defense. Intake of protective food commodities (fruit, vegetables, dark grain products, grain sprouts, oil seeds) is significantly higher in vegetarians. Alternative nutrition subjects have a significantly increased plasma levels of vitamin C, vitamin E, beta-carotene with high incidence of overthreshold values (92% vs. 42% - vitamin C, 67% vs. 33% - vitamin E, 67% vs. 17% - beta-carotene). There is recorded a significant inverse linear correlation between values of DNA strand breaks + oxidized purines and vitamin C or beta-carotene levels (p<0.01, p<0.05). Vegetarian diet is significantly more rich source of antioxidants. The results of reduced endogenous DNA damage and higher antioxidative status in vegetarians document that a correct vegetarian nutrition might represent an effective cancer prevention.

We describe an alternative assay to determine genotoxicity. Its main feature is that it combines two measures in a single experiment; the inhibition of replicative DNA synthesis together with the stimulation of DNA repair. We show that, in tests of four different genotoxic agents, the assay gives results that are entirely consistent with what is known about the mode of action of these agents. In addition, we have demonstrated that chemical carcinogens requiring metabolic activation can be examined using a standard procedure of incubation with a microsomal activating fraction. We consider the combined assay for DNA synthesis inhibition and repair synthesis to be a useful way for the rapid prescreening of chemicals suspected of genotoxic activity on the level of mammalian cells.

A series of experiments was conducted to determine the dose response relationship with respect to both cytotoxicity and morphological transformation in Syrian hamster embryo cells exposed to different chemicals. The effects of the following model chemical carcinogen/mutagens were investigated: 3-methyl cholanthrene (3-MC), benzo(a)pyrene (B(a)P), N-methyl-N-nitro-N-nitroso-guanidine (MNNG), N-methyl-N-nitrosourea (MNU), the noncarcinogenic weak mutagen methyl methanesulfonate (MMS) and nonmutagenic pesticides Supercypermethrin EC, VUCHT 524, and Dual. The results showed that all carcinogen/mutagens, i.e. 3-MC, B(a)P, MNNG, and MNU increased the number of morphological transformations on the maximum level at concentrations < TD50-TD70 (TD = toxic dose) and remained more or less on the same level at higher concentrations. Similar effect was observed in embryo cells treated with nonmutagenic Supercypermethrin EC. Very low concentrations of nonmutagenic pesticide VUCHT 524 stimulated proliferation of cells and at the same time induced the maximum level of morphological transformations. MMS and Dual did not induce morphological transformation of embryo cells at all. Induction of morphological transformation in embryo cells is evidently independent of the activity of a chemical to induce gene mutations and seems to be a valuable assay for studying the carcinogenic effects of lower doses of suspicious chemicals.

In study of the genotoxic effects of theophylline, this substance was subjected to a series of tests. Its potential mutagenicity was followed at the level of both bacteria and mammalian cells. The capacity of the substance to damage human DNA was determined by the so-called DNA inhibition test and by the method of alkaline elution of DNA. In the absence of the enzymatic microsomal S9 fraction, theophylline showed very weak mutagenic effects on bacteria and mammalian cells. However, in both cases this weak mutagenic effect was eliminated through a simultaneous application of theophylline and the S9 fraction. The results of the remaining tests proved negative regardless of whether the S9 fraction was present or absent. Our results lead us to infer that theophylline exerts no genotoxic action under in vivo conditions.

Induction of 6-thioguanine-resistant mutations was studied in Chinese hamster V79 cells treated with nitrofurylacrylic acid under aerobic and hypoxic conditions. The results obtained demonstrated that the mutagenic activity of this substance, less significant in aerobic conditions, was very high under hypoxic conditions. A gradual increase in mutation frequencies according to the applied concentrations of nitrofurylacrylic acid was observed, the maximal values being at 0.8 mg of the substance per 1 ml of growth medium. The mutagenic effects of nitrofurylacrylic acid were independent of its cytostatic effect that was higher in aerobic than hypoxic conditions. Mutagenic capacity of this substance found in vitro in mammalian V79 cells suggests its possible carcinogenic potential in vivo under conditions favorable for metabolic activation of this nitrofuran-derived compound.

The capacity of ftorafur to induce resistance to 6-thioguanine in V79 hamster cells was investigated. The treatment conditions were arranged in order to favor the induction of such gene mutations. The synchronous cells were treated in the beginning of S phase, i.e., when the replication of the genes responsible for the expression of resistance to 6-thioguanine took place. Part of the experiments was carried out in presence of the S9 microsomal fraction. The results showed that ftorafur was a weak mutagen after a short-term exposure in the presence of adequate amounts of the S9 fraction. In absence of the S9 fraction or when other than-optimal amounts were used, we repeatedly failed to detect any increase in the occurrence of mutated cells. Also the cytotoxic effects of this substance were investigated. We found that a short-term treatment of V79 hamster cells with lower concentrations of ftorafur resulted in decrease of growth rate, higher concentrations after a short-term treatment were in turn slightly toxic. Long-term treatments are, depending on the concentration and time of treatment used, considerably toxic.

The ability to induce gene mutations at the HGPRT locus in Chinese hamster V79 cells and to inhibit DNA synthesis in human EUE cells has been followed in eighteen chemical substances and ultraviolet light. The aim was to determine whether following of inhibition of DNA synthesis in impaired human cells may serve as an indicator of the mutagenicity of the relevant chemical substance. The results permit us to assume that following of DNA synthesis, the so-called DNA-inhibition test provides a preliminary information on the genotoxicity of the chemical substance, although the degree of inhibition of DNA synthesis need not necessarily denote the measure of the mutagenic effect of the substance. As certain further tests, utilising in vitro mammalian cells, so also the DNA-inhibition test yields a certain percentage of false positive results. Hence, it is important to combine this test with further express in vitro tests on the level of mammalian cells.