In this study, we investigated the carcinogenic response of transgenic mice carrying the human prototype c-Ha-ras gene, namely Tg rasH2/CB6F1 mice, to various genotoxic carcinogens and compared it with that of control non-transgenic CB6F1 mice (non-Tg mice). The present studies were conducted as the first step in the evaluation of the Tg rasH2/CB6F1 mouse as a model for the rapid carcinogenicity testing system. Short-term (< or = 6 months) rapid carcinogenicity tests of various genotoxic carcinogens, 4-nitroquinoline-1-oxide, cyclophosphamide, N,N-diethylnitrosamine, N-methyl-N-nitrosourea, N-methyl-N'-nitro-N-nitrosoguanidine and methylazoxymethanol, revealed that Tg rasH2/CB6F1 mice are more susceptible to these genotoxic carcinogens than control non-Tg mice. Tg rasH2/CB6F1 mice developed tumors more rapidly compared with non-Tg mice. Malignant tumors were observed only in the carcinogen-treated Tg rasH2/CB6F1 mice, but not in non-Tg mice treated with the same carcinogens. Each carcinogen induced tumors in corresponding target tissues of the Tg rasH2/CB6F1 mice. Only a very few lung adenomas but no other tumors were seen as spontaneous tumors during the 6 months of carcinogenicity tests. These results demonstrate that more rapid onset and higher incidence of more malignant tumors can be expected with high probability after treatment with various genotoxic carcinogens in the Tg rasH2/CB6F1 mice than in control non-Tg mice. The Tg rasH2/CB6F1 mouse seems to be a promising candidate as an animal model for the development of a rapid carcinogenicity testing system.

Glyoxal and methylglyoxal were tested for tumor-promoting potential in a two-stage stomach carcinogenesis model. Male outbred Wistar rats were initially given N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) in the drinking water (100 mg/l) along with a 10% sodium chloride dietary supplement for 8 weeks. Thereafter, they were returned to basal diet and maintained on drinking water containing no addition or either 0.5% glyoxal or 0.25% methylglyoxal for 32 weeks and then killed for necropsy and histological examination at week 40. Glyoxal treatment significantly increased the incidence of adenocarcinomas in the pylorus of the glandular stomach of rats pretreated with MNNG and sodium chloride. Furthermore, although methylglyoxal did not enhance the development of adenocarcinomas, the incidence of hyperplasias in the pylorus was significantly increased. The results indicate that glyoxal exerts tumor promoting activity on rat glandular stomach carcinogenesis and that methylglyoxal might also have promoting potential.

The aims of this study were to investigate the effect of aminoguanidine (AG) on slowing of motor nerve conduction velocity (MNCV) of the sciatic nerve in streptozocin-induced diabetic rats and to assess its mechanism of action. The MNCV of the sciatic nerve was measured electrophysiologically in diabetic rats treated with and without AG for 16 weeks. To elucidate the action of AG, morphological lesion and abnormality of polyol pathway metabolism in the nerve were examined and tissue levels of advanced glycosylation end-products (AGE) were determined as an indicator of AGE accumulation in tissue. Diabetic rats were treated with AG at three doses of 10, 25 and 50 mg/kg for 16 weeks. Myelinated fiber morphometry and nerve Na+,K(-)-ATPase activity were determined. The AGE levels in renal cortex were measured by a specific ELISA. Aminoguanidine dose-dependently ameliorated slowing of MNCV 16 weeks after the treatment without changing body weight or blood glucose levels. No difference in myelinated fiber morphometry or Na+,K(+)-ATPase activity with or without AG treatment was detected in diabetic rats. Diabetes increased the AGE level in the renal cortex by six times compared to non-diabetic rats, and AG reduced the rise in the AGE level by 40%. The MNCV was inversely correlated with the AGE levels. We conclude that improvement of conduction slowing by AG in experimental diabetes may be through decreasing the AGE level in the peripheral tissues. Aminoguanidine may have a therapeutic potential in controlling diabetic peripheral neuropathy.

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