1-Methyl-1H-1,2,4-triazole as the main marker of 1,1-dimethylhydrazine exposure in plants

With their wide application in chemical industry, human health and environmental toxic effects of hydrazines arise extensive concerns. Although hydrazine exposure is known to lead to inhibition of seed germination and seedling growth in plants, there are few reports about the mechanism of oxidation or transformation ways of hydrazines in plant tissue. In this research, garden cress (Lepidium sativum L.) and zucchini (Cucurbita pepo L.) were used as model plant objects to study 1,1-dimethylhydrazine exposure in vitro using the GC-MS system. The seed germination and plant growth experiments were carried out in Petri dishes using an aqueous media. Among the detected 1,1-dimethylhydrazine transformation products in plant tissues, 1-methyl-1H-1,2,4-triazole had the highest intensity and reproducibility. In our research, 1-methyl-1H-1,2,4-triazole formed at all contaminant concentrations in an extremely short period. This preliminary study determined 1,1-dimethylhydrazine environment contamination by detecting 1-methyl-1H-1,2,4-triazole in combination with other transformation products.

Styrax camporum, a typical species of the Brazilian cerrado, attenuates DNA damage, preneoplastic lesions and oxidative stress in experimental rat colon carcinogenesis

Styrax camporum Pohl, a typical species from the Brazilian cerrado, commonly known as "benjoeiro", is used to treat gastroduodenal diseases. In previous studies carried out by our research group, hydroalcoholic extract of S. camporum stems (SCHE) exhibited antigenotoxic and antiproliferative effects. For a comparative analysis of the chemopreventive effect of SCHE, the aim of this study was to investigate the influence of SCHE against carcinogen 1,2-dimethylhydrazine (DMH)-induced DNA damage and pre-neoplastic lesions in Wistar rat colon. Animals were treated orally with SCHE at 250, 500 or 1000 mg/kg body weight in conjunction with a subcutaneous injection of DMH. DNA damage was assessed using the comet assay while tpre-neoplastic lesions by aberrant crypt foci (ACF) assay. The following hepatic oxidative stress markers were determined including activities of catalase (CAT) and glutathione S-transferase (GST) as well as levels of reduced glutathione (GSH) and malondialdehyde (MDA). Treatment with SCHE was not genotoxic or carcinogenic at the highest dose tested (1000 mg/kg b.w.). The extract effectively inhibited DNA damage and pre-neoplastic lesions induced by DMH administration at all concentrations tested. Measurement of CAT, and GST activities and levels of GSH showed that SCHE did not reduce oxidative processes. In contrast, treatment with SCHE (1000 mg/kg b.w.) decreased liver MDA levels. Taken together, these findings suggested the chemopreventive effect attributed to SCHE in colon carcinogenesis, may be related to its capacity to inhibit DNA damage as well as an antioxidant action associated with its chemical constituents egonol and homoegonol.

The rat gut micronucleus assay: a good choice for alternative in vivo genetic toxicology testing strategies

The in vivo bone marrow (BM) micronucleus assay is one of the three tests in the standard test battery to assess the genotoxic potential of a pharmaceutical candidate. In some cases, depending on results of in vitro studies, the route of administration or the degree of systemic exposure, in vivo assessment of genotoxicity in the BM alone may not be sufficient. Based on the potential for high gut exposures to orally administered compounds with low systemic exposures as well as the potential susceptibility of rapidly dividing cells of the intestinal tissues, we have developed a modified technique for evaluating micronuclei formation in both the duodenum and colon of rats based on earlier publications. Adult male Sprague Dawley rats were treated once daily for 2 days with either vehicle control or with the test articles acetyl salicylic acid (ASA), carbendazim (CAR), cyclophosphamide (CP), dimethylhydrazine (DMH), mitomycin C (MMC) or vinblastine sulfate (VIN). The duodenum, colon, and BM were harvested, processed, and analyzed for micronucleus induction. Results from these studies demonstrated differences in the susceptibility for different test compounds in the three tissues tested. When MMC and VIN were dosed by different routes at the same dose levels both compounds produced positive results in all three tissues by intraperitoneal injection but not oral administration. These studies suggest that overall the GI micronucleus assay might be a useful tool for clastogenic and aneugenic compounds that are expected to produce high sustained concentrations in the gastrointestinal tract with little systemic exposure.

[Effect of jinfu kang to experimental precancerous colon lesions and urinary metabolites in rat]

OBJECTIVE

: To profile urinary metabolite variations from 1, 2-dimethylhydrazine (DMH)-induced precancerous colon rats, Jinfu Kang treated rats and healthy controls.

METHOD

We used ethyl chloroformate derivatization and gas chromatography-mass spectrometry (GC-MS) based metabonomic method to analyze rat urines.

RESULT

The time-dependent variations of metabolite profile showed a progressive deviation of the metabolism in the model group from the initial pattern over time and a systemic recovery of the metabolism in the treatment group, which is consistent with the histological results. The in-depth analysis indicated that the disorder of tricarboxylic acid cycle (TCA), tryptophan metabolism, polyamine metabolism and gut flora structure were associated with DMH intervention.

CONCLUSION

Metabolic study revealed that Jinfu Kang can effectively reverse metabolic departures in DMH-induced precancerous colon rat, which is consistent with pathological results.

[Effects of asymmetric dimethyl hydrazine on physical and chemical properties of blood plasma if experimental animals]

Asymmetric dimethyl hydrazine (ADH), a highly toxic propellant component, is known to cause metabolic disturbances in humans and laboratory animals. Focus of this investigation was placed on crystal-forming properties of blood serum, and types of plasma protein destructions in ADH-intoxicated rats. Object of investigation was blood plasma collected from rats exposed to 100 mg/kg of per oral ADH total (5 mg/kg per a day, 5 days a wk, 4 wks.). The crystal-forming ability of plasma was assessed with the teziographic technique. Severity of proteins destruction was determined by the content of carbonyl products of oxidative protein modification in plasma. Chronic exposure to low ADH doses caused oxidative destruction of proteins in blood plasma and, consequently, significant degradation of the plasma ability to form crystals reflected in an altered zonal phase structure and phase bursting on teziograms. Symmetry gave way to pathological structures, e.g. petals and loops. Amorphous areas grew in size, bursting lines thinned out. Concretions became less numerous. These data suggest a close relationship between the impairments in physical and chemical properties of blood plasma of experimental animals by highly toxic asymmetric dimethyl hydrazine.

Dietary arsenic affects dimethylhydrazine-induced aberrant crypt formation and hepatic global DNA methylation and DNA methyltransferase activity in rats

Cell culture studies have suggested that arsenic exposure results in decreased S-adenosylmethionine (SAM), causing DNA hypomethylation. Previously, we have shown that hepatic SAM is decreased and/or S-adenosylhomocysteine increased in arsenic-deprived rats; these rats tended to have hypomethylated DNA. To determine the effect of dietary arsenic on dimethylhydrazine (DMH)-induced aberrant crypt formation in the colon, Fisher 344 weanling male rats were fed diets containing 0, 0.5, or 50 microg As (as NaAsO2)/g. After 12 wk, dietary arsenic affected the number of aberrant crypts (p<0.02) and aberrant crypt foci (p<0.007) in the colon and the amount of global DNA methylation (p<0.04) and activity of DNA methyltransferase (DNMT) (p<0.003) in the liver. In each case, there were more aberrant crypts and aberrant crypt foci, a relative DNA hypomethylation, and increased activity of DNMT in the rats fed 50 microg As/g compared to those fed 0.5 microg As/g. The same phenomenon, an increased number of aberrant crypts and aberrant crypt foci, DNA hypomethylation, and increased DNMT tended to hold when comparing rats fed the diet containing no supplemental arsenic compared to rats fed 0.5 microg As/g. The data suggest that there is a threshold for As toxicity and that possibly too little dietary As could also be detrimental.

Effect of amaranth leaves on dimethylhydrazine-induced changes in multicomponent antioxidant system of rat liver

Effect of prefeeding dehydrated amaranth (A. gangeticus) leaves at 10 and 20% levels on a chemical toxicant, dimethylhydrazine (DMH)-induced free radical stress in rat liver was evaluated. DMH-induced rise in hepatic malondialdehyde (MDA), was diminished by AL. AL intake resulted in a significant increase in hepatic glutathione (GSH). The feeding of AL at 10% level increased the hepatic glucose-6-phosphate dehydrogenase (G-6-PDH) activity, while that at 20% level increased the hepatic glutathione reductase (GSSGR) as well, in addition to G-6-PDH. Amaranth leaves at 10 and 20% levels of feeding diminished the hepatic superoxide dismutase and glutathione peroxidase (GSH-Px) activities. DMH influenced adversely the hepatic antioxidant enzyme activities. Simultaneous administration of DMH and feeding of AL enhanced the DMH-induced decrease in hepatic GSH-Px. DMH enhanced formation of micronuclei was reverted significantly by AL intake. Hence, it was concluded that the consumption of AL at 20% level reduced DMH-induced impaired antioxidant status in rat liver.

Dietary copper and dimethylhydrazine affect protein kinase C isozyme protein and mRNA expression and the formation of aberrant crypts in colon of rats

Low dietary copper has been shown to decrease the expression of various protein kinase C (PKC) isozymes and increase the risk of colon cancer development in experimental animals. The purpose of this study was to investigate the relationship between dietary copper and carcinogen administration on PKC isozyme accumulation and aberrant crypt foci (ACF) formation in rats fed 0.9 and 7.7 microg Cu/g diet. After 24 and 31 d on the diets, the rats were injected with either dimethylhydrazine (DMH) (25 mg/kg i.p.) or saline and killed at two time points (2 wk and 8 wk after DMH). Rats fed low dietary copper had significantly lower (p<0.0001) hematocrits, hemoglobin, ceruloplasmin activity and plasma and liver copper concentrations than rats fed adequate dietary copper. Ingestion of low dietary copper significantly (p<0.005) increased the formation of DMH-induced ACF (116.8 vs 59.6). Low dietary copper significantly (p<0.05) decreased the concentration of PKC alpha, delta, and zeta in the colon at 2 wk but not at 8 wk. Thus, changes in PKC isoform protein concentration may be related to increased susceptibility of copper-deficient animals to colon cancer.

Tissue-specific expression of the p53 tumor-suppressor gene in the intestine of transgenic mice exposed to DMH and p53 antibodies

We studied the tissue-specific expression of the p53 gene in different parts of the intestine of mice treated with low doses of a carcinogen and exposed to different p53 antibodies. The human p53 promoter-CAT transgenic mice were immunized with different p53 antibodies (monoclonal - PAb 421 and DO1, and polyclonal - H-p53 and anti-soluble p53 IgG) and then exposed to low doses of dimethylhydrazine (DMH). Enzymatic CAT activity was determined in the ileum and colon 8 weeks later after the final injection of DMH. Expression of the p53 transgene in the normal ileum was twice as high as in the colon. Treatment with DMH significantly decreased the expression of the p53 transgene both in the ileum (from 18% to 100%) and in the colon (from 10% to 52%). Vaccination of mice protected at least in part such a decrease. The most effective results were found after exposure of mice to polyclonal H-p53 and to a lesser extent to anti-p53 IgG. No difference was found in the effects of antibodies on the small and large intestines. We concluded that polyclonal antibodies were more effective than monoclonal ones in protection against anti-p53 action of DMH. The observation of these effects may make it possible to explain the higher antitumor activity of polyclonal antibodies.

Effects of epidermal growth factor and dimethylhydrazine on crypt size, cell proliferation, and crypt fission in the rat colon. Cell proliferation and crypt fission are controlled independently

Crypt fission is now established as an important mechanism of intestinal growth and regeneration. It has been proposed that increased crypt size is the stimulus for crypt fission, because crypts preparing for fission are generally larger. Consequently, we investigated the effects of epidermal growth factor (EGF) and dimethylhydrazine, which are both known to stimulate crypt cell proliferation, on crypt fission in the rat intestine. We also examined whether the effects of EGF on both proliferation and crypt fission are modified by the pretreatment with dimethylhydrazine for 16 weeks, dimethylhydrazine was then discontinued for 8 weeks, followed by intravenous infusion of EGF for 1 week. There were four groups: vehicle alone, EGF alone, dimethylhydrazine alone, and dimethylhydrazine followed by EGF infusion. The rats were killed at 25 weeks and rates of intestinal crypt cell production, crypt size, and crypt fission were determined. Intravenously infused EGF significantly increased crypt cell production rate, but the magnitude of the effect decreased from the proximal to the distal colon. EGF caused an increase in crypt area, possibly reflecting an increase in crypt size. Importantly dimethylhydrazine had no significant effect on crypt cell production rate nor on crypt area in the distal colon, but it did cause an increase in crypt area in the mid-colon. The crypt fission index was significantly decreased by EGF and increased by dimethylhydrazine. There was no qualitative interaction between EGF and dimethylhydrazine. These results demonstrate the marked proliferative effect of intravenously infused EGF in the colon of orally fed rats, with significant site effects (P = 0.0007); the effect was greatest in the proximal colon and disappeared in the distal colon. The observation that EGF reduced crypt fission indicates that increased cell proliferation, per se, is not a stimulus for crypt fission. This is further supported by the observation that dimethylhydrazine increases crypt fission in crypts of normal size in the distal colon without significantly increasing cell proliferation. These results suggest that increasing crypt cellularity by proliferation is not sufficient to induce crypt fission, and factors other than increased crypt size by proliferation can control crypt fission. It is also probable that cell proliferation and crypt fission are independently regulated. Crypt fission appears to play a considerable role in the intestinal response to carcinogens.

Proliferation of mouse fibroblasts induced by 1,2-dimethylhydrazine auto-oxidation: role of iron and free radicals

Activation of 1,2-dimethylhydrazine (DMH) by prolonged auto-oxidation (24-h) induced proliferation of mouse fibroblasts at low hydrazine concentrations (0.1-1.0 mM) as determined by [3H-methyl]-thymidine uptake of confluent quiescent cells. Incubations were performed under conditions in which alkyl radicals are slowly formed by DMH auto-oxidation. The proliferative stimulus induced by DMH auto-oxidation complements that induced by insulin, PMA, and EGF. Inhibition by the iron chelators, o-phenanthroline and desferrioxamine, demonstrates that the induction of the proliferative effect is dependent on simple iron complexes. Proliferation was also inhibited by superoxide dismutase, catalase, and mannitol, implicating reactive oxygen species, although superoxide dismutase and catalase also inhibited alkyl radical formation, as determined by spin-trapping. These results suggest that cell proliferation induced by DMH auto-oxidation is mediated by reactive oxygen species, mainly the hydroxyl radical, and is dependent on simple iron complexes, possibly involving the Fenton reaction.

Dissimilar activation patterns of the carcinogen dimethylhydrazine (DMH) on intracellular polyamine metabolism in various organs

Weekly administrations of the potent carcinogen 1,2-dimethylhydrazine (DMH) predominantly induce carcinoma of the colon by nearly 100% after six months' treatment in rats. Polyamines, and especially the key enzyme of polyamine de novo synthesis ornithine decarboxylase (ODC) are well-known to play an important role in cell growth and tumor carcinogenesis. Male Wistar rats were s. c.-injected with a single dose of 20 mg DMH/kg b. wt. and five to eight animals were sacrificed 4, 8, 12, 24, 72, 120, 168, and 240 hours after injection of DMH or the basic solution, respectively. Additionally, seven animals were simultaneously treated with the ODC inhibitor alpha-difluoromethylornithine (DFMO) and sacrificed seven days after a single DMH injection. A single s. c.-dosage of the colon carcinogen DMH resulted in dissimilar activation patterns of polyamine metabolism in the various organs studied: in distal and less pronounced in proximal colonic mucosa ODC and putrescine are significantly increased seven days after application of DMH and DNA polymerase after ten days; in small intestinal mucosa ODC activity is significantly elevated after seven days and especially S-adenosylmethionine decarboxylase activity is significantly and prolonged increased between twelve and 72 hours after DMH injection; while spermidine/spermine N1-acetyltransferase activity is significantly elevated in liver after 168 and 240 hours, no changes compared to controls are found in the pancreas. DFMO treatment completely prevents DMH-induced activation of polyamine de novo synthesis and DNA polymerase in colon and small intestine. These data prove completely different and -interestingly-late appearing activation patterns of DMH on intracellular polyamine metabolism in various organ systems and further elucidate the complex metabolic changes following carcinogen treatment.

Development of aberrant crypt foci involves a fission mechanism as revealed by isolation of aberrant crypts

Morphological analysis of isolated colonic crypts in rats, postnatally, indicated that the crypts reproduce themselves by a fission mechanism, the division beginning at the crypt base and proceeding upwards until there are two separate crypts. Occasionally, before the separation is complete, a second fission process starts on one or both sides of a bifurcating crypt and a triple-branched or quadruple-branched crypt results. Analysis of isolated aberrant crypt foci (ACF) in rats treated with 1,2-dimethylhydrazine revealed that the development of ACF consisting of multiple crypts is also due to a fission mechanism. Initially, an indentation appears at the base of a single ACF crypt, with subsequent formation of a bifurcation and eventual crypt division.

Aspirin suppresses 1,2-dimethylhydrazine-induced alteration of proliferative parameters in rat colonic crypts

Human epidemiological reports and rodent experimental research data indicate a possible chemopreventive effect of regular aspirin use for decreasing risk of colon and rectum cancer incidence and mortality. We have previously demonstrated that aspirin can significantly suppress proliferative parameters in normal rat colonic epithelium when examined 24 h following an acute or chronic course of aspirin administration. To investigate whether aspirin would effectively suppress known carcinogen-induced changes in colonic epithelium, rats were given single s.c. injections of either aspirin (50 mg/kg bw) or saline on days 1-3 and either 1,2-dimethylhydrazine (DMH; 12 mg base/kg bw) or DMH vehicle on day 4 of each week for eight consecutive weeks. Rats were sacrificed 4 days after the last aspirin dose and 3 days after the last DMH or DMH vehicle dose. Using the proliferative biomarkers of proliferating cell nuclear antigen positive cells per midaxial crypt section (SCC), crypt proliferative zone height (PZ), crypt differentiated zone height (DZ), and total crypt height (CH), it was found that aspirin does suppress DMH-induced increases in SCC, PZ and CH. The findings demonstrate that aspirin has a long term (i.e. several days) protective effect against early carcinogen-induced proliferative changes in rat colonic crypts which may help account for aspirin's chemopreventive action against colon cancer.

Probiotics, cecal microflora, and aberrant crypts in the rat colon

Our hypothesis was that administration of bifidobacteria, Lactobacillus acidophilus or both to rats will minimize the numbers of aberrant crypts in the distal colon that develop in response to the carcinogen 1,2-dimethylhydrazine (DMH). A series of experiments was designed to test this hypothesis where the treatments used were as follows: skim milk controls (Skim-Basal), skim milk + bifidobacteria (Bifido-Basal), skim milk + fructooligosaccharide (Skim-FOS), and skim milk + bifidobacteria + fructooligosaccharide (Bifido-FOS). In two experiments, bifido-bacteria + FOS administration significantly decreased the number of aberrant crypts that developed, but there was no clear relationship of aberrant crypts to numbers of bifidobacteria or Clostridium perfringens. In the third experiment, the Bifido-FOS treatment led to significantly fewer aberrant crypts and aberrant crypt foci than the Bifido-Basal treatment. The Skim-FOS group had significantly more cecal bifidobacteria than the Skim-Basal group and significantly fewer C. perfringens than the Skim-Basal and Bifido-Basal. In a fourth experiment, L. acidophilus was added as an additional treatment. The number of aberrant crypts was not significantly different among the groups. However, the number of C. perfringens was significantly decreased by the addition of bifidobacteria, L. acidophilus or the combination of the two, whereas the numbers of bifidobacteria and L. acidophilus were not affected by treatment. A significant correlation (R2 = 0.84, P < 0.01) was noted between the body weight of rats at DMH administration and the magnitude of the difference in aberrant crypts between the Skim-Basal rats and the Bifido-FOS rats. The results suggest that there is variability in the effects of bifidobacteria and L. acidophilus administration on both aberrant crypt formation and C. perfringens.

The effect of lactulose on DNA damage induced by DMH in the colon of human flora-associated rats

Germ-free rats were fed purified diets containing sucrose (0.3%, wt/wt) as control or the synthetic disaccharide lactulose (0.3% wt/wt) and were then dosed orally with a human fecal suspension. After five weeks on the diets, these "human flora-associated" rats were transferred to diets in which the sucrose or lactulose level was raised to 3% (wt/wt). Four weeks later, the rats from each dietary group were dosed orally with saline (controls) or 1,2-dimethylhydrazine dihydrochloride (DMH, 15 mg/kg). Sixteen hours after the carcinogen dose, the rats were killed, colon cells were isolated, and the degree of DNA damage in the cells was assessed using the single cell microgel electrophoresis (Comet) assay. Samples of cecal contents were also removed from the saline-treated rats to determine changes in composition of the gut microflora. No significant diet-related differences in cecal bacterial numbers were observed, although there was a trend for the numbers of lactobacilli to be higher in the lactulose-fed animals. DNA damage in colon cells was quantified by measurement of the length of the cellular DNA image after electrophoresis, and the evaluated cells were assigned to classes according to the degree of damage: undamaged (< 40 microns), moderately damaged (40-80 microns), or severely damaged (> 80 microns). There were no significant diet-related differences in DNA damage in colon cells from rats treated with saline. Treatment with DMH induced a highly significant increase in DNA damage in sucrose- and lactulose-fed rats. However, in the rats treated with DMH, the degree of DNA damage was significantly (p < 0.05) less in the lactulose-fed animals than in those given the sucrose diet, as evidenced by a decrease in the percentage of cells with severe damage. In the sucrose-fed rats, severely damaged cells accounted for 33% of the total compared with only 12.6% in the lactulose-fed DMH-treated animals. The results of this study, which was performed in human flora-associated rats to provide data of relevance to humans, indicate that lactulose consumption offered a degree of protection from the genotoxic effects in the colonic mucosa of a known colon carcinogen.

Effects of dietary fibre on dimethylhydrazine-induced changes in prostanoid concentrations in rat colonic mucosa

1. This study was designed to elucidate the effects of guar gum, a dietary fibre, on changes in prostanoid contents induced by 1,2-dimethylhydrazine, a carcinogenic agent, in rat colonic mucosa. 2. Prostanoid contents were determined using high performance liquid chromatography; five prostanoids, namely 6-keto-prostaglandin F1 alpha, prostaglandin F2 alpha, prostaglandin E2, prostaglandin D2 and thromboxane B2, were detected. 3. Four subcutaneous injections of dimethylhydrazine, 60 mg/kg every 6 days, increased the mucosal concentrations of prostaglandin E2 and thromboxane B2 by approximately 50%. Other prostanoids did not change significantly throughout the experiments. 4. In rats treated with dimethylhydrazine and a fibre diet a significant increase in thromboxane B2 content was not observed, although a significant increase in prostaglandin E2 content was observed. These effects were observed in rats fed with fibre diet over 20 days but not observed in rats fed with fibre diet over 10 days. 5. From these results and the report that aspirin use at low doses is effective in the reduction of the risk of fatal colonic cancer, inhibiting thromboxane B2 synthesis by fibre diet might be involved in the protective effect against the occurrence of colonic cancer.

Elevation in diacylglycerol level and activation of protein kinase C in liver of mice administered with carcinogenic dose of 1,2-dimethylhydrazine

Five weeks treatment of male mice with 1,2-dimethylhydrazine leads to elevation in the level of diacylglycerol in liver. Increase in diacylglycerol content is accompanied by an increase in particulate activity of protein kinase C with a fall in its activity in cytosolic fraction. Quantitative analysis of neutral lipids of different subcellular fractions from liver reveals that diacylglycerol levels increases highly significantly in liver microsomal membranes of carcinogen treated mice. Separation of neutral lipids by thin layer chromatography indicates that also there is an increase in cholesterol esters in nuclei, mitochondria and microsomes of mice liver whereas monoacylglycerol almost disappeared in mitochondria and microsomes after DMH administration in comparison to their respective controls.

Cruciferous vegetables and glutathione: their effects on colon mucosal glutathione level and colon tumor development in rats induced by DMH

The effect of a diet containing 10-40% lyophilized cabbage or broccoli as cruciferous vegetable or 10-40% lyophilized potato as noncruciferous vegetable fed for 14 days on the colon mucosal glutathione (GSH) level was studied in male rats. The GSH levels of the duodenum mucosa and the liver were also measured. Cabbage and broccoli enhanced the colon and duodenum mucosal GSH levels in a dose-related manner; potato had no effect. All three vegetables had no effect on the liver GSH level. The effect of GSH on colon tumorigenesis induced by 1,2-dimethylhydrazine (DMH) was also examined in rats. Male Sprague-Dawley rats were injected with DMH (20 mg/kg body wt) weekly for 20 weeks. DMH lowered the colon mucosal GSH level. GSH (100 mg/day/rat) dissolved in the drinking water and given to rats during and after DMH injections had little or no effect on tumor incidence and total number of colon tumors. Tumors were larger in rats that received GSH than in those that received water. This study shows that the colon mucosal GSH level can be enhanced by feeding rats a diet high in cabbage or broccoli and that GSH added to the drinking water did not affect DMH-induced colon tumorigenesis under the experimental conditions used.

Oxidation of 1,1-dimethylhydrazine (UDMH) in aqueous solution with air and hydrogen peroxide

The degradation of 1,1-dimethylhydrazine (UDMH), a component of some rocket fuels, was investigated using atmospheric oxygen and hydrogen peroxide. The reactions were carried out in the presence and absence of copper catalysis and at varying pH. Reactions were also carried out in the presence of hydrazine, a constituent, along with UDMH, of the rocket fuel Aerozine-50. In the presence of copper, UDMH was degraded by air passed through the solution; the efficiency of degradation increased as the pH increased but the carcinogen N-nitrosodimethylamine (NDMA) was formed at neutral and alkaline pH. Oxidation was not seen in the absence of copper. Production of NDMA occurred even at copper concentrations of < 1 ppm. Oxidation of UDMH with hydrogen peroxide also gave rise to NDMA. When copper was absent degradation of UDMH did not occur at acid pH but when copper was present some degradation occurred at all pH levels investigated. The production of NDMA occurred mostly at neutral and alkaline pH. In general, higher concentrations of hydrogen peroxide and copper favored the production of NDMA. Dimethylamine, methanol, formaldehyde dimethylhydrazone, formaldehyde hydrazone, and tetramethyltetrazene were also produced. The last three compounds were tested and found to be mutagenic.

Similar patterns of hypomethylation in the beta-hydroxy-beta-methylglutaryl coenzyme A reductase gene in hepatic nodules induced by different carcinogens

Our earlier studies demonstrated that the beta-hydroxy-beta-methylglutaryl coenzyme A (HMG CoA) reductase gene is hypomethylated and overexpressed in hepatic nodules initiated by 1,2-dimethylhydrazine (1,2-DMH). The study presented here examined whether the pattern of DNA methylation of the HMG CoA reductase gene in hepatic nodules reflected carcinogen-DNA interaction during initiation. Accordingly, hepatic nodules were generated in male Fischer 344 rats with either 1,2-DMH or aristolochic acid (AA), which interact predominantly with the guanine and adenine bases in DNA, respectively. DNA from individual nodules was restricted with HpaII, MspI, and HhaI, and the fragments obtained were hybridized to a cDNA probe for HMG CoA reductase. The results indicated that the hypomethylation pattern in the reductase gene in the nodules initiated with these two carcinogens was similar, although they interacted with different bases in the DNA. The question still remained whether the DNA fragments obtained by digesting the two sets of nodules with the restriction endonucleases were from the same domains in the genome of HMG CoA reductase. To examine this, probes for the different domains of the HMG CoA reductase gene were generated from the cDNA using the restriction enzyme Accl. Three probes were obtained: (i) a 5'-end fragment corresponding to the membrane-spanning region, (ii) a second fragment corresponding to the 3'-end of the protein, and (iii) a third fragment spanning the region between (i) and (ii). Each of these probes was radiolabeled and hybridized to the HpaII- and HhaI-generated fragments from the DNA of hepatic nodules initiated with 1,2-DMH and AA. Irrespective of the carcinogen used for initiation, hypomethylation occurred in all three domains of the gene. More important, the pattern of hypomethylation was similar in the nodules initiated by the two carcinogens. Furthermore, an overall similarity was seen in the hypomethylation patterns in the c-myc and c-Ha-ras genes in the DNA of nodules initiated with either 1,2-DMH or AA. These results raise the possibility that the pattern of hypomethylation established in the hepatic nodules may not directly reflect the interaction between the initiating carcinogen and DNA but may represent a unique phenotype of hepatic nodules.

Target organ specificity of cell proliferation induced by various carcinogens

The target organ specificities of cell proliferation and histopathological lesion induction by 5 carcinogens having different target organs were evaluated using a multiorgan carcinogenesis bioassay. In Group 1, male F-344 rats aged 6 wk were sequentially treated with N-diethylnitrosamine (DEN, single 100-mg/kg ip injection, week 0), N-methyl-N-nitrosourea (MNU, 4 20-mg/kg ip injections, weeks 0-2), N-butyl-N-(4-hydroxybutyl)nitrosamine (BBN, 0.05% in drinking water, weeks 0-2), N,N'-dimethylhydrazine (DMH, 4 40-mg/kg sc injections, weeks 2-4), and dihydroxy-di-N-propylnitrosamine (DHPN, 0.1% in drinking water, weeks 2-4) during the first 4 wk. In Groups 2-6, rats were treated with only one of the above initiators, applied as in Group 1. Group 7 served as the no-treatment control. Bromouracil deoxyriboside (BUdR) labeling indices (LI) were counted in various organs at weeks 2 and 4. Numbers and areas of glutathione S-transferase placental form positive (GST-P+) liver foci were measured at weeks 2, 4, and 28. Preneoplastic or neoplastic lesion development was assessed at week 28. With regard to specific elevation of cell proliferation in target organs, BUdR LIs in the urinary bladder, liver, and colon were, respectively, increased in the BBN alone, DEN alone, and DMH alone treated groups as well as in Group 1. However, LIs of thyroid, lung, and kidney were also elevated by several carcinogens not including these organs in their carcinogenic target specificity. On the other hand, morphological lesions and GST-P+ foci were limited to Group 1 and the target organs of the corresponding carcinogen-treated groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Repair of O6-methylguanine and O4-methylthymidine in F344 rat liver following treatment with 1,2-dimethylhydrazine and O6-benzylguanine

Concentrations of O6-methylguanine, O4-methylthymidine, and N-7-methylguanine were measured in the livers of Fischer 344 rats following treatment with 1,2-dimethylhydrazine (20 mg/kg, s.c.) alone or in combination with the O6-alkylguanine transferase inhibitor O6-benzylguanine (100 mg/kg, i.p., daily). Animals were sacrificed at 12, 24, 36, or 48 h following 1,2-dimethylhydrazine exposure. Direct measurement of alkyltransferase demonstrated that daily treatment with O6-benzylguanine completely eliminated detectable alkyltransferase activity in the livers of treated rats. Adducts in liver DNA were quantitated by high performance liquid chromatography separation followed by fluorescence detection, UV absorbance, and/or specific radioimmunological assays. In animals exposed to 1,2-dimethylhydrazine alone O6-methylguanine concentrations declined rapidly, whereas animals exposed to both O6-benzylguanine and 1,2-dimethylhydrazine showed less removal of O6-methylguanine, with significant differences between the two populations appearing at 36 and 48 h. O4-Methylthymidine removal also differed significantly between the two groups, with O6-benzylguanine-treated animals exhibiting higher concentrations of adducts at 36 and 48 h. O6-Benzylguanine treatment had no effect on the removal of N-7-methylguanine. These results show that the rate of disappearance of both O6-methylguanine and O4-methylthymidine is slower following alkyltransferase depletion, suggesting that mammalian alkyltransferase is involved in the removal of O4-methylthymidine lesions as well as O6-methylguanine lesions.

Supplemental dietary calcium fails to alter the acute effects of 1,2-dimethylhydrazine on O6-methylguanine, O6-alkylguanine-DNA alkyltransferase and cellular proliferation in the rat colon

Prior studies from our laboratory have demonstrated that K-ras G to A mutations were detectable in a high percentage of carcinomas which developed in the colons of animals treated with the known colonic procarcinogen, 1,2-dimethyl-hydrazine (DMH). Moreover, in this model, the incidence of these mutations was decreased by a supplemental dietary calcium regimen which concomitantly decreased the frequency of rats with multiple tumors as well as tumor size. In an attempt to clarify the possible mechanism(s) involved in this antimutagenic effect of supplemental calcium, two groups of Sprague-Dawley rats were fed semisynthetic diets containing either 0.87 or 1.80% calcium by weight for 3 weeks, s.c. injected with 100 mg/kg of DMH and killed prior to and at various time periods (16-144 h) after injection. The colons of animals were analyzed and compared with respect to O6-methylguanine content in DNA, O6-alkylguanine-DNA alkyltransferase levels as well as cellular proliferation, as assessed by immunohistochemical staining of colonic crypts by bromodeoxyuridine. In certain experiments, these parameters were also analyzed in the proximal and distal colon before and at various times after administration of DMH. The results of these experiments demonstrated that supplemental dietary calcium was not found to influence significantly O6-methylguanine levels, alkyltransferase levels or cellular proliferation in the entire colon or in either colonic segment before or after the acute administration of DMH. DMH did, however, differentially alter all three of these biochemical parameters in the colonic segments (distal > proximal), possibly due to a greater degree of metabolic activation in the distal colon.

Proliferating cell nuclear antigen expression in normal, preneoplastic, and neoplastic colonic epithelium of the rat

Expression of the proliferating cell nuclear antigen (PCNA) was examined in normal rat intestinal tissues and in carcinogen-treated nonneoplastic and neoplastic colonic mucosa. In the normal intestine, PCNA expression was confined to the expected region of the proliferative compartment. A strong correlation was observed between PCNA labeling index and both [3H]thymidine labeling index (R = 0.993, P = 0.007) and percent of cells in S phase as determined by flow cytometry (R = 0.982, P = 0.018) and between the location of the maximal staining for PCNA and [3H]thymidine (R = 0.997, P less than 0.05). In animals treated with dimethylhydrazine (DMH), crypt hyperplasia, an increased PCNA labeling index, and shifts in both the region of maximal and the upper extent of PCNA expression were observed during DMH exposure; significant crypt hyperplasia and expansion of the PCNA-positive compartment persisted after completion of DMH injections. The patterns of PCNA expression and bromodeoxyuridine incorporation were similar in DMH-induced tumors. It is concluded that PCNA immunohistochemistry can be used as a reliable marker of the proliferative compartment in both normal and neoplastic colonic mucosa.

Evaluation of murine lymphocyte membrane potential, intracellular free calcium, and interleukin-2 receptor expression upon exposure to 1,1-dimethylhydrazine

The effects of 1,1-dimethylhydrazine (UDMH) on several early events associated with lymphocyte activation were examined. The concentration of intracellular calcium ([Ca2+]i) and membrane potential of murine lymphocytes were found to be altered upon exposure to UDMH; [Ca2+]i was increased in murine thymocytes, while splenocytes exhibited membrane hyperpolarization. In addition, interleukin-2 receptor expression induced by in-vitro concanavalin A stimulation of murine splenocytes at 24 and 48 h in the presence of UDMH was not affected. UDMH may interfere with the ability of these two distinct lymphocyte populations to regulate normal ionic fluctuations, thus contributing to altered immune responsiveness.

Profile of short-chain fatty acids and rectal proliferation in rats fed sucrose or cornstarch diets

Rats were fed high fat (231 g/kg diet), low calcium (1.3 g/kg diet), low cellulose (20 g/kg diet) diets in which carbohydrates were represented by sucrose or starch (460 g/kg diet). A subgroup of animals was treated with 1,2-dimethylhydrazine (DMH) twice, 4 and 8 d before the beginning of the dietary treatments. Animals fed the starch diet, compared with those fed the sucrose diet, had higher concentrations of cecal and fecal short-chain fatty acids and a significantly lower acetic acid:butyric acid ratio in the cecal contents at d 105. Ratios were 14.7 +/- 1.7 and 6.8 +/- 0.4 for rats fed the sucrose and starch diets, respectively (P less than 0.01). Cecal pH was significantly lower in animals fed the starch diet for 105 d. At d 105, rectal proliferation was lower in rats fed the starch diet (labeled cells/crypt were 7.89 +/- 0.56 and 3.57 +/- 0.40 for rats fed the sucrose and starch diets, respectively, P less than 0.01); at d 30 the effect of starch on proliferation was evident in controls but not in DMH-treated rats. Rectal proliferation data were negatively correlated with the concentration and percentage of butyric acid and positively correlated with the percentage of acetic acid, the acetic acid:butyric acid ratio and cecal pH. These results suggest that low rectal proliferation in animals fed a high fat, high starch diet might be associated with a lower relative concentration of butyric acid in the cecal contents.

Effect of 1,1-dimethylhydrazine (UDMH) on Corynebacterium parvum-associated immunosuppression in mice

These studies further investigate the immunoenhancement properties of UDMH by utilizing Corynebacterium parvum-induced immunosuppressed mice as well as evaluating activated macrophage production of reactive oxygen intermediates or their effects. Forty-eight hour Con A-induced lymphoblastogenic responses from splenocytes isolated from C. parvum and UDMH-treated Balb/C mice were significantly increased compared with C. parvum alone, although less than normal control mice (no treatment). In vitro bioassay of IL-2 production in cell culture supernatant isolated from these same treatment groups exhibited a pattern of stimulation similar to that of lymphocyte blastogenesis. In addition, UDMH did not interfere with H2O2-mediated suppression of either Con A- or LPS-induced lymphocyte blastogenesis and actually enhanced suppression of Con A-induced lymphocyte cultures at 25 micrograms/ml. We also report that production of superoxide anion from TPA-activated peritoneal macrophages exposed to various concentrations of UDMH in vitro was not affected. Although in vivo exposure to UDMH partially reversed C. parvum-induced immunosuppression in mice, the exact mechanism by which UDMH acts to reverse this immune suppression is not clear. UDMH does not appear to interfere with either activated peritoneal macrophage production of superoxide anion or H2O2-induced suppression of lymphocyte blastogenesis to elicit immune enhancement.

[Bioelectrical mechanism of the anti-arrhythmia effect of a synthetic acetylcholine analog EDIHYP]

The synthetic acetylcholine analogue ethyl-3-(2,2-dimethyl-2-ethyl-hydrazinium) propionic iodide (EDIHYP) exerts a powerful antiarrhythmic action in cardiac ischemic, reperfusion, and adrenergic lesions, as well as in infarction and postinfarction cardiosclerosis, as evidenced by animal experiments. The study was undertaken to examine the electrophysiological mechanism of EDIHYP s action on isolated rat heart cardiomyocytes. It was shown that the agent substantially reduced the resting potential, as well as action potential amplitude and duration in total ischemia and resultant reperfusion. The antiarrhythmic changes provided a multiple decrease in the duration of ventricular tachycardia and cardiac fibrillation in reperfusion. Thus, the fact that EDIHYP has a direct action on the bioelectrical activity of cardiomyocytes may play an important role in its antiarrhythmic effect in the whole body.

Expression of two cytochromes P450 involved in carcinogen activation in a human colon cell line

Cytochrome P450 is known to cause carcinogen activation and correspondingly increased cancer risk in animal models. In order to determine whether P450 in the colon may be involved in cancer development in the human, the human colon cell line LS174T was examined for the presence of various cytochromes P450. Two isozymes of P450 were identified in the human cell line. Expression of P450IA1 or IA2 was increased by treatment of the cell line with benzanthracene; the induction was demonstrated by an increase in RNA hybridizing to a probe for P450IA1 and by ethoxyresorufin deethylation activity. Western analysis of microsomes isolated from human colon tissue also demonstrated the presence of P450IA1, as well as a form which cross-reacted to an antibody to human P450IIC9. Another isozyme, P450IIE1, was identified by polymerase chain reaction amplification of RNA from LS174T cells. These results underscore the presence of cytochromes P450 in colonic tissue and provide a basis for the involvement of isozyme-specific P450 mediated reactions in carcinogenesis of the colon.

Induction of aberrant crypt foci in the large intestine of F344 rats by oral administration of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine

Carcinogenicity of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) to rat colon was investigated using the appearance of colonic aberrant crypt (AC), a preneoplastic lesion, as a marker. The number of AC foci per colon at experimental week 4 was 1.3 +/- 0.8; almost half the level of AC foci induced by 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-1), which is a known colon carcinogen. No ACs were observed in rats of the control group. A repeat experiment showed that induction of AC foci by PhIP administration was reproducible and a significant increase in the number of AC foci, 3.0 +/- 0.0, was observed after 12 weeks of PhIP administration. The majority of ACs induced by PhIP were localized in the distal part of the colon. The distribution was similar to those induced by Glu-P-1 and 1,2-dimethylhydrazine. Those data suggested that PhIP is possibly carcinogenic to rat colon.

Alterations in lectin binding in the proximal and distal colon of Sprague-Dawley rats with 1,2 dimethylhydrazine administration

Sequential changes in rhodamine or fluorescein isothiocyanate-conjugated lectin binding of proximal and distal colonic crypts were studied during and after the administration of the 1,2 dimethylhydrazine (DMH). Five adult its unexposed to DMH or vehicle served as baseline controls. Tissue from normal appearing colon and tumor tissue was incubated with Ulex europaeus agglutinin 1 (UEA), Arachis hypogaea (PNA), Dolichos biflorus (DBA) and Griffonia simplicafolia 1 (GSA1). Distinct regional differences were noted in the baseline controls. UEA, PNA and DBA binding were absent in the distal colonic crypt cells. In the proximal colon minimal UEA and PNA binding was noted in the lower crypt whereas DBA binding was intense. GSA1 binding was diffuse in the upper and lower crypt of both regions. During carcinogenesis a progressive increase in PNA binding was noted in normal appearing colonic crypts from both regions. A progressive increase in PNA binding in proximal and distal colonic tumors was noted over time. Similar to normal tissue, DBA bound markedly to proximal colon tumors but was absent in most distal colonic tumors. UEA stained all proximal tumors intensely at all time points. In distal colonic tumors, UEA staining was diminished at 30 weeks compared to tumors analyzed at 16, 22 and 26 weeks. Mucin depletion was also a feature of tumor tissue compared to adjacent normal and hyperplastic glands. This study documents the region specific changes in lectin binding in normal and neoplastic colonic crypts induced by DMH.

Long-term explant culture of human colon and a 3-step transformation model for rat colonic epithelium

Our previous studies have suggested that colonic epithelium from rodents pretreated in vivo with suboptimal doses of carcinogen could be more easily maintained in explant culture. Transformation of colonic epithelium from these explants may be induced by subsequent exposure to additional genotropic agents. Therefore, we describe the development of a 3-step transformation model which uses (1) in vivo pretreatment with a suboptimal dose of 1,2-dimethylhydrazine (DMH) followed by (2) in vitro organ culture and exposure to xenotropic murine sarcoma virus (X-MSV), and finally (3) xenograft maintenance in nude mice to allow sufficient time for transformation. Male Wistar rats were injected intramuscularly with 20 mg DMH/kg 10 times per week followed by the removal and explant culture of the colon, which was then treated in vitro with X-MSV, and transplanted into nude mice after 1 week of culture. All the nude mice (n = 6) transplanted with rat colon explants contained viable xenograft explant epithelium and 1 of the 6 showed transformation. Our results demonstrate that the epithelium from animals pretreated with suboptimal doses of carcinogens can be easily transformed. We also demonstrate that human colonic epithelium is viable for an extended period of time in this model. Based on these results, we hypothesize that such a 3-step transformation model is applicable for carcinogenesis studies of various organs from different species, including human if one uses dysplastic or 'pre-neoplastic initiated' tissues obtained at surgery (e.g., ulcerative colitis; Barret's esophagus, etc.).

Modifying effect of ascorbic acid and sodium ascorbate on the promoting stage of uterine sarcomogenesis induced in CBA mice by 1,2-dimethylhydrazine and estradiol-dipropionate

Administration of estradiol-dipropionate (EP) after the cessation of 1,2-dimethylhydrazine (DMH) treatment increased the incidence of uterine sarcomas in CBA mice from 32.5 (DMH alone) to 62.5%. Ascorbic acid (AA) (0.3% in drinking water) given simultaneously with EP decreased the tumour incidence to 35%. Sodium ascorbate did not exert an inhibiting effect. AA inhibited the increase of uterine weight produced in mice by EP and did not influence the growth of mouse transplantable uterine sarcomas. The mechanisms of the antiestrogenic effects of AA are discussed.

Effects of dietary fish oil and corn oil on protein kinase C distribution in the rat colon with and without 1,2 dimethylhydrazine treatment and in rat colonic adenocarcinoma

The activity and subcellular distribution of Protein Kinase C (PKC) was determined in the colons of Sprague-Dawley rats that were fed either a low fat rat chow or rat chow supplemented with 17% corn oil (40% ingested calories as fat). Rats given the high fat diets were either given no carcinogen or treated prior to or subsequent to the initiation of the test diets with 1,2 dimethylhydrazine (DMH). Rats were sacrificed and PKC activity determined in the soluble and particulate fractions of the colonic tissue 13 weeks after the initiation of the diets or DMH treatment, which was before tumor induction. In addition several rats were maintained on their diets until colon tumor formation occurred and PKC activity determined in the colonic tumor and compared to age matched control colonic tissue. In the absence of DMH, fish oil and corn oil equally augmented PKC activity and decreased the ratio of soluble/particulate PKC. With DMH treatment, corn oil augmented PKC as above, but fish oil supplementation resulted in a pattern of PKC activity and distribution more typical of a low fat diet, particularly when fish oil supplementation preceded DMH treatment. PKC activity in DMH induced colonic carcinomas was markedly depressed regardless of the fat source in the diet, when compared to colonic tissue from a non-DMH treated age matched low fat control.

Effect of polyamine oxidase inhibition on the colonic malignant transformation process induced by 1,2-dimethylhydrazine

Recent studies of colon adenocarcinomas in humans and experimentally induced colonic tumors in rodents have demonstrated selective elevations in the level of N1-acetylspermidine in these malignant tissues. The exact relationship of these alterations in acetylated polyamine levels to the malignant transformation process, however, remains unclear. In order to clarify this issue, rats were given s.c. injections of 1,2-dimethylhydrazine (DMH; 20 mg/kg body wt/week) or diluent for up to 26 weeks. After 10 weeks of carcinogen treatment, one-half of the animals in each group were also concomitantly given i.p. injections of MDL 72527 (20 mg/kg body wt/week), a specific inhibitor of polyamine oxidase, until they were killed. Animals were killed after 15 weeks of DMH treatment and polyamine levels as well as the activities of polyamine oxidase, ornithine decarboxylase and spermidine-N1-acetyltransferase were measured and compared in rat proximal and distal colonic mucosa of each group. Polyamine levels were also assessed in each of these groups after 26 weeks of treatment with this carcinogen +/- MDL 72527. In addition, in view of recent studies that have indicated that polyamines may influence certain oncogenes in human colonic carcinoma cells, tumors from DMH +/- MDL 72527 were analyzed for K-ras mutations. The results of these experiments demonstrated for the first time that: (i) MDL 72527 was a specific inhibitor of polyamine oxidase in normal and malignant colonic tissue; (ii) concomitant administration of this agent with DMH enhanced the elevation of colonic N1-acetylspermidine and significantly reduced the mean colonic tumor burden, as assessed by total tumor area per rat, produced by this carcinogen alone; (iii) analysis of K-ras mutations revealed a similar incidence (62-69%) in adenocarcinomas for both groups (+/- MDL 72527); (iv) however, analysis of the K-ras-mutated and non-mutated tumors revealed that in both carcinogen-treated groups (+/- MDL 72527), tumors with such mutations were smaller than their counterparts without such genetic alterations. Moreover, MDL 72527 reduced the average size of tumors, with and without such mutations, to a similar extent.

Hyperplasia of mouse duodenal crypts and its control by NK cells during the initial phase of DMH carcinogenesis

The possible regulatory role of NK cells on early events in chemical carcinogenesis remains undefined. The present study examined whether NK cells control 1,2-dimethylhydrazine (DMH)-induced hyperplasia of the duodenal crypt in CD1 mice. Mice receiving chronic DMH treatment showed a dose-dependent hyperplasia confined to the proliferative zone, with a parallel increase in mitotic and 3H-TdR-labelled cells and significant suppression of splenic NK activity. Complete ablation of splenic NK activity with anti-asialo GM-I antibody (alpha AGM-I) treatment slightly enhanced hyperplasia. Halving of the DMH dose for 2 weeks led to regression of hyperplasia, which was totally prevented by alpha AGM-I treatment. The alpha AGM-I treatment alone did not influence crypt size in normal mice. Finally, a stimulation of NK activity with Poly I:C treatment in DMH-treated mice caused regression of the DMH-induced hyperplasia. Our results suggest that hyperplastic cells with possible genetic alterations induced by the carcinogen express target structures for NK cells, but that simultaneous carcinogen-induced suppression of NK activity hampers their containment, allowing progression of hyperplasia to neoplasia, possibly owing to additional genetic changes.

1,2-Dimethylhydrazine-induced alterations in protein kinase C activity in the rat preneoplastic colon

Recently, a number of studies in experimental animals and humans have suggested that alterations in the activity of protein kinase C (PKC) may be involved in the malignant transformation process. To determine whether such alterations in this kinase were present before the development of 1,2-dimethylhydrazine (DMH)-induced colon cancers, rats were given s.c. injections of this procarcinogen (20 mg/kg body weight/week) or diluent for 10 or 15 weeks. Animals were sacrificed after these time periods and colonic epithelium was harvested from each group. The activity and distribution of PKC in the cytosolic and membrane fractions of these preparations as well as 1,2-diacylglycerol mass and phosphoinositide turnover were then examined and compared in the presence and absence of 10 nM 1,25-dihydroxycholecalciferol, an agent which has previously been found to influence these biochemical parameters in the normal rat colonic epithelium. The results of these studies demonstrate that: (a) the percentage of PKC activity in the membrane fraction was significantly greater in DMH-treated animals compared to their control counterparts at 10 and 15 weeks; (b) the total PKC activity was similar at 10 weeks, but markedly reduced in the colonic mucosa of the DMH-treated group at 15 weeks; (c) 1,2-diacylglycerol mass and phosphoinositide turnover were increased in the colonic mucosa of rats administered this carcinogen at both time points; and (d) in control, but not in DMH-treated animals, in vitro addition of 1,25-dihydroxycholecalciferol increased PKC activity, 1,2-diacylglycerol mass and phosphoinositide turnover at each of the times studied. Based on these findings, it would appear that alterations in PKC activity may play a role in the malignant transformation process of the colon in animals administered DMH.

Activity of 1,2-dimethylhydrazine in the mouse bone marrow micronucleus assay using a triple- and a single-dosing protocol

In the present study the ability of 1,2-dimethylhydrazine (DMH) to induce micronuclei in mouse bone marrow erythrocytes was investigated using 2 different dosing regimens. DMH caused an increase in micronuclei in both male and female mice following single administration and sampling after 24 h. The effect was more pronounced in female than in male animals. Triple administration of DMH at concentrations corresponding to 80, 40 and 20% of the median lethal dose (MLD) did not increase the incidence of micronuclei in either sex. Small increases in micronucleus incidence were observed after triple dosing at 100% of the MLD value. These results suggest that a future micronucleus protocol should include animals of both sexes and single and repeated administration of the test substance.

Activity of DMBA, DMH and CP in triple- and single-dose rodent bone-marrow micronucleus assays

1,2-Dimethylhydrazine, 7,12-dimethylbenzanthracene and cyclophosphamide were detected as positive using the triple-dose test protocol described by MacGregor (1989). Determination of the 3 day MLD may complicate the use of this test protocol.

Quantitative contribution of factors regulating rat colonic crypt epithelium: role of parenteral and enteral feeding, caloric intake, dietary cellulose level and the colon carcinogen DMH

To elucidate the role and quantitative contribution of several exogenous factors which may regulate colon crypt mitotic activity, proliferative zone height (PZH) and crypt height, groups of rats were subjected to various feeding regimens both with and without treatment with the colon carcinogen, 1,2-dimethylhydrazine (DMH). The rats were divided into two major groups and one group was given eight weekly injections of DMH base at 9.5 mg kg-1 body weight. Throughout this period and for two additional weeks the rats were isocalorically fed either a defined nutritionally complete diet with different levels of dietary cellulose or they were parenterally (i.v.) fed a nutritionally complete liquid formula with different caloric levels. The rats were then injected with colchicine 3 h prior to sacrifice to arrest and to collect dividing cells at metaphase. The results of multiple regression analysis of all data were interpreted to indicate that parenteral feeding caused dramatic suppression of the colon crypt height (CH) and of the number of metaphase figures per crypt (MC). Increased cellulose intake stimulated CH but suppressed MC. The CH was also stimulated by DMH. CH was positively correlated to PZH and MC. The MC was suppressed by cellulose intake and negatively correlated to PZH but was positively correlated to CH. The PZH was positively correlated to CH. These findings were related to the role of luminal food, functional workload, kcal intake and treatment with DMH on the measured colon crypt parameters. A quantitative assessment of factors that regulate the measured colonic crypt parameters was accomplished.

Reversible mitochondrial swelling in cultured rat hepatocytes exposed to 1,2-dimethylhydrazine

The early structural changes of F344 rat hepatocytes exposed to the hepatocarcinogen 1,2-dimethylhydrazine (DMH) were characterized in short-term monolayer cultures. Continuous exposure of monolayers to DMH (2-16 mM) caused cytoplasmic vacuoles visible by phase-contrast microscopy in all hepatocytes within 6 hr of exposure. These changes preceded maximal release of lactate dehydrogenase (LDH) which occurred after 48 hr of continuous exposure to cytocidal concentrations of DMH (8-16 mM). Ultrastructurally, hepatocytes exposed to DMH (4 mM, 6 hr) showed a twofold increase in mitochondrial diameter from 340 +/- 70 nm in control hepatocytes to 800 +/- 140 nm in DMH-exposed cells. Hepatocyte monolayers exposed to DMH (4 mM, 6 hr) with subsequent removal of DMH attained normal phase-contrast appearance within 6 hr. Ultrastructural studies showed no significant differences when compared with control hepatocytes and mitochondrial diameters (330 +/- 70 nm) were comparable with control hepatocytes. Pretreatment of hepatocytes with depletors of cellular reduced glutathione concentration, including 1,3-bis(2-chloroethyl)-1-nitrosourea (40 microM) and diethyl maleate (160 microM), did not potentiate hepatocellular vacuolation nor release of LDH from hepatocytes exposed to DMH (0-16 mM, 48 hr). These studies demonstrate a distinctive form of reversible high-amplitude mitochondrial swelling that can be monitored by phase-contrast microscopy of cultured hepatocytes in monolayers. Since DMH-induced mitochondrial swelling and its progression to irreversible injury are not potentiated by depletors of reduced thiols, this response appears distinct from prelethal mitochondrial swelling in hepatocytes subjected to oxyradical-mediated mechanisms of injury.

Calcium and magnesium utilization in rats: effect of dietary butterfat and calcium and of age

This factorial study was designed to examine the effect of short- and long-term ingestion of dietary calcium (0.25% and 1.0%) and butterfat (5% and 20%) and treatment with dimethylhydrazine (DMH) in rats. Calcium, magnesium and phosphorus absorption and, to a lesser extent, total diet digestibility decreased as the rats aged from 2 to 8 mo. Increased ingestion of butterfat had no effect on apparent absorption of calcium among young rats but tended to decrease calcium absorption in mature rats. The weak effect (P less than 0.05) of butterfat on calcium absorption reflected the small amount of calcium (less than 2% of fecal calcium) associated with lipids in feces. Ingestion of 10 vs. 2.5 mg Ca/g diet reduced the efficiency of apparent absorption of calcium, magnesium and phosphorus of young and mature rats and resulted in slightly, but significantly, greater retention of calcium in bone after 27 wk. The total amounts of calcium retained in tibias were correlated with the amounts of calcium absorbed by rats after 4, but not after 27, wk of dietary treatments. Rats dosed with DMH exhibited improved efficiency of calcium absorption, but the incidence of intestinal tumors did not affect mineral utilization.

Lectin-binding sites in neoplastic and non-neoplastic colonic mucosa of 1,2-dimethylhydrazine-treated rats

Qualitative changes of glycoconjugates in luminal surface and goblet cell mucin from colon mucosa of 1,2-dimethylhydrazine (DMH)-treated rats were studied. Eight fluoresceinated lectins were used: Dolichos biflorus (DBA), Glycine max (SBA), Triticum vulgare (WGA), Limax flavus (LFA), Arachis hypogaea (PNA), Griffonia simplicifolia-I (GS-I), Ulex europaeus-I (UEA-I) and Canavalia ensiformis (Con A). The lectin-binding patterns were studied in tumors arising in proximal and distal portions of the colon, in transitional mucosa (TM) and in mucosa distant from tumors. Lectin reactivity observed in mucosa of DMH-treated rats was compared with that obtained in colon mucosa of control rats. In tumors and non-neoplastic mucosa of DMH-treated rats the reactivity of DBA, SBA, WGA, LFA, GS-I and Con A were similar to that in the mucosa of control rats. In contrast, important changes were observed in the reactivity of UEA-I and PNA. Contrary to the staining in the control mucosa, UEA-I bound intensely to all carcinomas and PNA to 50% and 60% of carcinomas arising in proximal and distal colon, respectively. Moreover, in TM and mucosa distant from tumors, UEA-I and PNA also differed in their binding patterns to that obtained in the colonic mucosa of the control rats. UEA-I- and PNA-binding to luminal surface and UEA-I-binding to the mucin of distal colonic mucosa from DMH-treated rats was similar to that observed in rat fetal colon suggesting a reappearance of a fetal-type pattern. Contrarily, PNA-reactivity in goblet cell and carcinoma mucin is a unique feature of colonic carcinogenesis not present during fetal development.

Effect of dietary cellulose on cell proliferation and progression of 1,2-dimethylhydrazine-induced colon carcinogenesis in rats

The effects of different levels of dietary cellulose on colonic crypt mitotic activity and colon carcinogenesis were studied in 190 male Sprague-Dawley rats. Rats were divided into groups and fed a basal fiber-free diet supplemented with either 0, 5, or 15% pure cellulose (w/w), for periods of 10 weeks (initiation stage) or 32 weeks (promotional stage). Half of the rats in each group were given weekly s.c. injections of 9.5 mg 1,2-dimethylhydrazine (the base) (DMH) for 8 weeks. Some of the rats were killed at 10 weeks while most were killed 22 weeks later. In some groups the dietary cellulose level was changed to a different level at 10 weeks. Food intake and body weight data showed that the rats within each experiment were isocalorically fed. There was a direct correlation between crypt height and the percentage of cellulose in the diet. Addition of 5 or 15% dietary cellulose during the initiation stage of carcinogenesis resulted in a significant increase in crypt height. Increasing dietary cellulose after the initiation stage (0 to 5% and 5 to 15%) or maintaining a high dietary cellulose level throughout both the initiation and promotional stages (15%) resulted in a significant increase in crypt height. A DMH-induced increase in mitotic activity that was observed during the initiation stage was no longer evident after the 22-week promotional stage. The significant DMH-induced increases in proliferative zone height and crypt height that were initially observed during the initiation stage were also observed after the 22-week promotional stage. These data indicate that the initial DMH-induced increases observed in proliferative zone height and crypt height are irreversible. Addition of 5 or 15% cellulose was found to suppress DMH-enhanced mitotic activity in the crypts of the descending colon during the initiation stage of carcinogenesis. This finding was correlated with a significantly lower incidence of adenocarcinomas in rats maintained on 5 or 15% cellulose throughout both the initiation and promotional stages.

[The role of bile in the development of colon cancer induced by 1,2-dimethyl hydrazine in rats]

Experimental operative models were created in order to investigate the role of the bile acids in the development of colon cancer in rats. These techniques changed the concentration of bile acids in different parts of the colon, and the daily fecal total bile acid levels. The relationship between these changes and the development of 1,2-dimethylhydrazin-induced colon cancer was studied. Significantly more tumors than in the control group were found if the daily total bile acid level and the concentration of bile acids in the left subsite of the large bowel was increased. Our results suggest that bile acids, as promoting factors, may play a role in the development of colon cancer in rats.

Inositol-phosphate-induced enhancement of natural killer cell activity correlates with tumor suppression

In recent studies, we have demonstrated that inositol hexaphosphate (InsP6) inhibits experimental colon carcinogenesis. Since natural killer (NK) cells are involved in tumor cell destruction, we investigated the effect of InsP6 on murine NK cell activity. We show that; (i) 1,2-dimethylhydrazine (DMH), a colon carcinogen, depresses NK activity; (ii) in vivo treatment of mice with InsP6 enhances baseline NK activity and reverses DMH-induced depressed NK activity with an inverse correlation (r = -0.9811) with tumor incidence, (iii) short-term in vitro treatment of spleen cells and NK-enriched fraction with InsP6 also enhances NK cytotoxicity in a dose-dependent manner, (iv) inositol potentiates the action of InsP6. Our data suggest yet another important role of inositol phosphates in the regulation of cellular activity.

1,2-Dimethylhydrazine-induced alterations in N1-acetylspermidine levels and spermidine N1-acetyltransferase activity in rat colonic mucosa

To determine whether alterations in the "reverse" or "conversion" pathway for putrescine formation were involved in the induction of colonic tumors by 1,2-dimethylhydrazine, male albino rats of the Sherman strain were given injections s.c. of this agent (20 mg/kg body weight/week) or diluent for 5, 10, 15, and/or 26 weeks. Animals were sacrificed at each of these time periods and polyamine levels, including N1- and N8-acetylspermidine, as well as the activities of ornithine decarboxylase, spermidine N1-acetyltransferase and polyamine oxidase were measured and compared in rat proximal and distal colonic mucosa of each group. The results of these studies demonstrated that: (a) N1- and N8-acetylspermidine levels were similar in the control and treated proximal colonic segments at all time periods examined; (b) N1- and N8-acetylspermidine levels were also similar in the control and treated distal colonic segments at 5 and 10 weeks; (c) at 15 weeks the level of N1-acetylspermidine, but not N8-acetylspermidine, however, was increased in the treated distal colonic segment secondary to increases in the activity of spermidine N1-acetyltransferase; and (d) at 26 weeks, the level of N1-acetylspermidine remained higher in treated distal "uninvolved" colonic tissue and were markedly elevated in colonic tumors in both segments. Based on these findings, it would appear that the reverse pathway for putrescine formation may be involved in the 1,2-dimethylhydrazine-induced malignant transformation process of the rat colon.

An endogenous colon mitosis inhibitor reduces the increased cell proliferation in colonic epithelium induced by dietary cholic acid and treatment with 1,2-dimethylhydrazine

We have recently purified and identified a tripeptide (pGlu-His-GlyOH) in mouse intestinal extracts which reversibly inhibits normal colonic epithelial cell renewal in mice. We also found a similar response to a single injection of the peptide during bile-acid-induced hyperproliferation in the colonic epithelium. To investigate the effect of repeated injections of the same dose of the inhibitor under various pathological conditions of the colonic mucosa we either fed mice low-calcium cholic acid diet, treated the animals with a single injection of the colon carcinogen 1,2-dimethylhydrazine (DMH), or gave both treatments. The peptide reduced the mitotic rate and the labelling indices in the colonic epithelium during the first 5 days of feeding the low-calcium cholic acid diet, and the size of the proliferative compartment was reduced. Proliferating cells were found significantly closer to the base of the crypts in the peptide-treated animals. The mitotic rate was also reduced by each of repeated peptide injections during the first 72 h in the DMH-treated animals; the labelling indices at 48 and 72 h only. By feeding DMH-treated animals low-calcium cholic acid diet, similar results were obtained. However, in all carcinogen-treated animals the tripeptide had no effect on the size and localization of the proliferating cells in the colonic crypts.