Distribution and carcinogenic action of 1,2-dimethylhydrazine (SDMH) in rats

Markedly enhanced micronucleus induction by 1,2-dimethylhydrazine dihydrochloride in colonic cells of rats with bacterial colonization in the intestine

To investigate how intestinal bacteria affect host cytogenetic alterations in the early initiation step of colon carcinogenesis, we conducted a comet assay and micronucleus (MN) test using germ-free (GF) and conventionalized (Cvd) rats after a single subcutaneous injection of the carcinogen, 1,2-dimethylhydrazine dihydrochloride (DMH). DNA damage was also determined in the liver in comet assays, as DMH is metabolized and activated in this organ. The time-response patterns of DNA damage in the liver and colon were similar in both rats, and maximum values were observed at 3 h after the treatment. In contrast, the maximum frequency of micronucleated (MNed) colonic cells was markedly higher in the Cvd rats than in the GF rats and was observed after 72 h and 120 h, respectively. The frequency of MNed cells in non-treated animals was similar in the GF and Cvd rats. In addition, we determined time-responses in the incidence of apoptosis and cell proliferation indices, i.e., the numbers of BrdU-labeled cells, mitotic cells in the crypts, and crypt column heights, using histological sections of the colons in these rats. Maximal incidence of apoptosis was observed at 6 and 24 h in the Cvd and GF rats, respectively. The value in the Cvd rats tended to be higher than that in the GF rats. Cell proliferation was suppressed until 24 and 48 h in the Cvd and GF rats, respectively, and increased subsequently. The rebound response of cell proliferation was more pronounced and occurred earlier in the Cvd rats than that in the GF rats. We demonstrated that cytogenetic alterations other than DNA damage, particularly the MNed colonic cell induction by DMH, were markedly enhanced in rats with bacterial colonization in the intestine compared to those in GF rats.

Increased paracellular permeability of tumor-adjacent areas in 1,2-dimethylhydrazine-induced colon carcinogenesis in rats

Objective:

The morphology and functions of the proximal and distal large intestine are not the same. The incidence of colorectal cancer in these regions is also different, as tumors more often appear in the descending colon than in the ascending colon. Inflammatory bowel disease and colorectal cancer can increase transepithelial permeability, which is a sign of reduced intestinal barrier function. However, there is not enough evidence to establish a connection between the difference in colorectal cancer incidence in the proximal and distal colon and intestinal permeability or the effects of carcinogenesis on the barrier properties in various areas of the colon. The aim of the study was to assess the permeability of different segments of the large intestine according to a developed mapping methodology in healthy rats and rats with 1,2-dimethylhydrazine (DMH)-induced colon adenocarcinoma.

Methods:

The short circuit current, the transepithelial electrical resistance and the paracellular permeability to fluorescein of large intestine wall of male Wistar rats were examined in the Ussing chambers. The optical density of the solution from the serosa side to assess the concentration of the diffused fluorescein from mucosa to serosa was analyzed by spectrophotometry. The morphometric and histological studies were performed by optical microscopy.

Results:

Rats with DMH-induced colon adenocarcinomas showed elevated transepithelial electrical resistance in the areas of neoplasm development. In contrast, there was no change in the electrophysiological properties of tumor adjacent areas, however, the paracellular permeability of these areas to fluorescein was increased compared to the control rats and was characterized by sharply reduced barrier function.

Conclusions:

The barrier properties of the colon vary depending on tumor location. The tumors were less permeable than the intact intestinal wall and probably have a negative influence on tumor-adjacent tissues by disrupting their barrier function.

Carcinogenesis induced by a single administration of 1,2-diethylhydrazine in female rats of various ages

Three- or fourteen-month-old female L10 rats were exposed to a single intravenous injection of 1,2-diethylhydrazine (SDEH) at 150 mg/kg of body weight. At the 95th week after carcinogen treatment when the experiment was stopped, 30.7% and 4.5% of rats from the younger and older groups survived, respectively. Total tumor incidences were 68.8% and 84.6%, respectively, in rats treated with SDEH at the age of 3 or 14 months vs. 18.2% and 34.5% in corresponding young and old controls (P < 0.01). Leukemias, thyroid adenomas, uterine tumors and mammary malignancies developed more frequently in animals exposed to carcinogens than in control groups. No age-related differences in tumor incidence or localization between rats exposed to SDEH at various ages were observed, but tumors developed earlier in older groups than in younger groups. The results supported the suggestion that the accumulation of initiated cells in some tissues during natural aging is a cause of the age-related increase in cancer incidence.

Detection of carcinogenic exposures by urinalysis: induction of cell-mediated immunity

Studies were undertaken to determine whether urine collected from rats during the 24 h following exposure to the colon carcinogen 1,2-dimethylhydrazine (DMH) contained substances which would induce specific antitumor immunity. The evaluation for such components was carried out by administering the test and control urine to young male adult Fisher F344 inbred rats and then establishing the animals' antitumor cell-mediated immunity (CMI) at a 14-day post-exposure interval. The CMI was measured by determining the injury and destruction inflicted upon cultured X-ray-induced rat small bowel adenocarcinoma target cells by peripheral blood lymphoid cells obtained from the animals exposed to the urine. A significantly increased CMI was found to be induced by the urine collected from the chemically exposed rats, thus suggesting the presence of mutagenic/carcinogenic components. In addition, exposure through the levels of CMI that were induced, with an approximate threshold detection limit of 100 microgram (1.7 mumol)/kg body weight (100 ppb) to the chemical. These preliminary findings suggest that such immune measurements might serve as a basis for the development of a rapid and inexpensive bioassay for monitoring population exposures to carcinogenic substances.

Bile as a source of potential reactive metabolites

Many toxic substances are excreted via the bile as chemically inert metabolites. In some cases, however, highly toxic, mutagenic and carcinogenic products can be derived from bile, either directly or after further metabolism by intestinal microflora or intestinal cells. Potential reactive substances may thus reach biliary tract and intestinal cells via this route and may undergo subsequent enterohepatic circulation. The possible role of biliary reactants in carcinogenesis of the biliary tract and intestine is discussed.

Dependence of 1,2-dimethylhydrazine metabolism on its treatment schedule

The content of cytochromes P-450 and b5 in rat liver microsomes, as well as the extent of labeling of nucleic acids and proteins of the liver and kidneys and of mucosa from different intestinal segments, was studied in rats injected daily or once a week subcutaneously with similar total doses of 1,2-dimethyl-hydrazine (SDMH) and in untreated rats. Daily SDMH administrations led to a decrease in cytochrome P-450 activity. Pretreatment of rats with unlabelled SDMH resulted in decreased labeling of DNA, RNA, proteins, and acid-soluble fractions after [3H]SDMH injection. A more pronounced effect was found after the daily treatment.