Pituitary toxicity but lack of rat colon carcinogenicity of a DC-magnetic field in a medium-term bioassay.

The present study was designated to evaluate the effect of direct current induced permanent magnetic field (DC-MF) on chemically induced rat colon carcinogenesis. Five experimental groups of male S.D. rats were injected with 1,2-dimethylhydrazine (DMH) subcutaneously, 20 mg/kg b.wt., once a week for four weeks, with exposure to 1 mT DC-MF (12 hours/day) as follows: Before (pre) the carcinogen administration (group 1), simultaneously (group 2), after (post) the carcinogen administration (group 3) and daily from the beginning to the end of the experiment after 12 weeks (group 4). Rats of group 5 served as carcinogen-only treated controls while those of group 6 were non-treated controls. There were no differences in the incidences and multiplicities of colonic aberrant crypt foci (ACF), putative preneoplastic lesions, among all groups except that large foci in group 1 were significantly fewer in numbers than those found in group 5. Proliferating cell nuclear antigen labeling indexes (PCNA-LI) in the colon epithelium were essentially the same in MF-treated and control rats. Histopathological examination showed evident hemorrhage in the pituitary glands of some rats of groups 1-3, and in most rats of group 4. Transmission electron microscopy also revealed ultrastructural changes, but DNA ploidy analysis revealed no carcinogenicity to MF-exposed pituitary glands. Serum levels of AST, ALT, total protein, creatinine, albumin, albumin/globulin ratio and growth hormone levels did not change among the groups. The present study revealed that the action of an artificial MF on rats is not carcinogenic/or cancer-promoting, at least in the present protocol for colon carcinogenesis.

Effect of 2-(carboxyphenyl) retinamide and genistein on the formation of early lesions in 1,2-dimethylhydrazine-induced colon carcinogenesis in rats.

Aberrant crypt foci (ACF) are recognized as preneoplastic lesions for colon cancer, and ACF in rodents are widely used as an intermediate biomarker to predict tumorigenicity in the colon. However, a lack of correlations between the formation of ACF and the development of colonic tumors has been reported in several studies. For example, 2-(carboxyphenyl) retinamide (2-CPR) and genistein were reported to inhibit the carcinogen-induced formation of ACF, whereas both of them were later found to enhance colon tumorigenesis in rats treated with azoxymethane (AOM). Recently, we have identified b-catenin-accumulated crypts (BCAC) in the colon of rats shortly after administration of AOM, and provided evidence that these are independent early lesions of classical ACF, and BCAC might be direct precursors for colon cancers. In the present study, we performed a comparative analysis of the modifying effects of 2-CPR and genistein on 1,2-dimethylhydrazine (DMH)-induced BCAC and ACF in male F344 rats. Dietary administration of 2-CPR (315 ppm) significantly reduced the total number, multiplicity and size of ACF in DMH-exposed colonic mucosa, while genistein (250 ppm) had no significant effects on DMH-induced ACF formation. In contrast, both of 2-CPR and genistein significantly enhanced the multiplicity and size of DMH-induced BCAC when compared with DMH alone group. In addition, both 2-CPR and genistein significantly increased the proliferating cell nuclear antigen (PCNA) index preferentially in BCAC. Together with previous findings that 2-CPR and genistein are tumor promoters in the colon, our results support the concept that BCAC are precursors of colon tumors and suggest that these lesions are more reliable short-term biomarkers for colon carcinogenesis in rodents than ACF.

Overexpression of cyclin D1 and cyclin E in 1,2-dimethylhydrazine dihydrochloride-induced rat colon carcinogenesis

Deregulation of G1 cyclins has been reported in several human and rodent tumors including colon cancer. To investigate the expression pattern of G1 cyclins in 1,2- dimethyl-hydrazine dihydrochloride (DMH)-induced rat colon carcinogenesis, we studied the expression of cyclin D1 and cyclin E by quantitative reverse transcription-polymerase chain reaction (RT-PCR) analysis and immunohistochemistry (IHC). The mRNA level of cyclin D1 was increased 1.2-fold in adenocarcinomas but not significantly in adenomas, when compared with normal rat colonic mucosa (p<0.05). The cyclin E mRNA level was increased 2.7-fold in adenomas and 3.3-fold in adenocarcinomas (p<0.05). The PCNA mRNA level was also increased 1.9-fold in adenomas and 1.8-fold in adenocarcinomas (p<0.05). Immunohistochemical staining revealed exclusive nuclear staining of the neoplastic cells for cyclin D1, cyclin E and PCNA. Cyclin D1 expression was detected in 56.3% of the adenomas and in 61.5% of the adenocarcinomas examined, whereas cyclin E expression was detected in 87.5% of the adenomas and in 92.3% of the adenocarcinomas. Overall, cyclin D1, cyclin E and PCNA expression was significantly increased at both the mRNA and protein levels in normal colonic mucosa, adenomas and adenocarcinomas, but there was no significant difference in the degree of expression of these genes in adenomas and adenocarcinomas. Our results indicate that the overexpression of cyclin D1 and cyclin E may play an important role during the multistage process of rat colon carcinogenesis, at a relatively early stage, and may disturb cell-cycle control in benign adenomas, and thereafter, participate in tumor progression.

Localizaçäo de lesöes tumorais induzidas pela 1, 2-demetilhidrazina e seu grau de atipia no colon de ratos / Location and malignancy of tumoral lesions induced by 1, 2-dimethylhydrazine in the colon of rats

As diversas técnicas para o tratamento cirúrgico da Síndrome do Intestino Curto apresentam, ainda hoje, problemas de dificil resolução. De todas, as mais promissoras são o transplante de intestino delgado e o transplante de colo. Uma técnica intermediária que mostrou resultados controversos tanto clínicos como experimentais, é a interposição de segmentos de colo no trajeto do intestino delgado após extensas ressecções. Sua aplicação serve, todavia, como um meio de se estudar a adaptação do colo, inclusive visando os transplantes. Neste trabalho foi estudada a indução de tumores pela 1,2-dimetilhidrazina, sua localização e grau de atípia nos diferentes segmentos intestinais após ressecção de 80 por cento do jejuno-íleo. Foram encontradas 24 lesões ao exame macroscópico após a décima sexta se-mana de pós-operatório. O número de lesões por animal variou de 0 a 9. Das 24 lesões en-contradas, 20 estavam no colo (83,33 por cento), sendo que 11 estavam localizadas no cólon proximal, 3 no cólon distal e 6 anorretais. No estudo histológico, a maioria das lesões era de grau III. Este trabalho mostrou que o método de indução de tumores pela 1,2-dimetilhidrazina é apropriado para o estudo de tumores intestinais em ratos.