Pharmacokinetics and biological fate of 3-(2,2, 2-trimethylhydrazinium)propionate dihydrate (MET-88), a novel cardioprotective agent, in rats

In this study, we examined the disposition, metabolism, and excretion of a novel cardioprotective agent, 3-(2,2, 2-trimethylhydrazinium)propionate dihydrate (MET-88), in rats. The disposition of MET-88 after oral and i.v. administration of 2, 20, and 60 mg/kg indicated that the pharmacokinetics of MET-88 were nonlinear. The profiles of radioactive MET-88 and total radioactivity in plasma were consistent at doses of 20 and 60 mg/kg. However, at 2 mg/kg, the plasma MET-88 levels were obviously lower than the total. The excretion of radioactivity after oral administration of MET-88 indicated that increasing doses led to a shift from exhaled CO(2) to urinary excretion as the major excretion route. Major metabolites in plasma after oral administration of MET-88 were glucose, succinic acid, and 3-hydroxypropionic acid, and in vitro studies revealed that MET-88 was converted to 3-hydroxypropionic acid by gamma-butyrobetaine hydroxylase (EC 1.14. 11.1). An isolated liver perfusion system modified to trap CO(2) gas was used to examine the excretion pathway of MET-88. [(14)C]CO(2) gas was decreased by the addition of iodoacetic acid, DL-fluorocitric acid, or gamma-butyrobetaine to this system, and subsequent thin-layer chromatography analyses of perfusates revealed that MET-88 was first converted to 3-hydroxypropionic acid by gamma-butyrobetaine hydroxylase and then was biosynthesized to glucose and metabolized to CO(2) gas via the glycolytic pathway and tricarboxylic acid cycle.

Batch culture biodegradation of methylhydrazine contaminated NASA wastewater

The batch culture degradation of NASA wastewater containing mixtures of citric acid, methylhydrazine, and their reaction product was studied. The organic contaminants present in the NASA wastewater were degraded by Achromobacter sp., Rhodococcus B30 and Rhodococcus J10. While the Achromobacter sp. showed a preference for the degradation of the citric acid, the Rhodococcus species were most effective in reducing the methylhydrazine and the reaction product. Removals of more than 50% were observed for citric acid, methylhydrazine and the reaction product when the NASA wastewater was inoculated with the microbes in batch cultures. Simulation and chemical characterization of citric acid and hydrazine mixtures show that the interaction is partly of a chemical nature and leads to the formation of a conjugated UV/Visible absorbing compound. An 'azo' carbonyl derivative of the citric acid, consistent with the spectral data obtained from the investigation, has been proposed as the possible product.

Purification and characterization of the rat liver gamma-butyrobetaine hydroxylase

The biosynthesis of carnitine from lysine and methionine involves five enzymatic reactions. Gamma-butyrobetaine hydroxylase (BBH; EC 1.14.11.1) is the last enzyme of this pathway. It catalyzes the reaction of hydroxylation of gamma-butyrobetaine to carnitine. This enzyme had never been purified to homogeneity from rat tissue. This paper describes the purification and characterization of the rat liver BBH. This protein has been purified some 413 fold by ion exchange, affinity and gel-filtration chromatographies and appears as a dimere of 43,000 Daltons subunits by PAGE. The affinity chromatography column used in the purification process utilizes 3-(2,2,2-trimethylhydrazinium)propionate (THP), a BBH inhibitor, as the ligand. Polyclonal antibodies were raised against the liver enzyme. They were able to precipitate BBH activity in either a crude liver extract or a purified fraction of the enzyme. Furthermore, it crossreacts with a 43 kDa protein in the liver. No evidence for extra hepatic enzyme was found.

[Comparative study of the antioxidant activity of gamma-butyrobetaine and its natural and synthetic derivatives in vitro]

Experiments in vitro with the use of a rat brain homogenate demonstrated antioxidant activity of methyl ether (3(2,2,2-trimethylhydrazinium) propionate possessing a positive charge at the quaternary nitrogen atom. The antioxidant activity was due to intensified neutralization of superoxide anion radicals and, correspondingly, inhibited peroxidation of endogenous brain lipids. The other compounds under study, namely, gamma-butyrobetaine, its methyl ether, and 3(2,2,2-trimethylhydrazine) propionate did not exhibit antioxidant properties.

Magnetic polyethyleneimine (PEI) microcapsules as retrievable traps for carcinogen electrophiles formed in the gastrointestinal tract

Semi-permeable magnetic microcapsules containing polyethyleneimine (PEI) have been developed as retrievable carcinogen traps. In vitro, the soluble core PEI and membrane both bound reactive substances of limited aqueous stability, such as from [14C]N-methyl-N-nitrosourea ([14C]NMU), and aqueous stable dyes of molecular weight up to 1000. The core/membrane location ratio of binding was dependent upon membrane characteristics of the microcapsule batch used. Microcapsules administered intragastrically to rats bound up to 0.006% of [14C]dimethylhydrazine ([14C]DMH) and 1.4% of [14C]NMU administered i.p. or intrarectally, respectively. Time-dependency of [14C]DMH binding was consistent with labelling of microcapsules within the small intestine. There were no detectable metabolites from [14C]DMH trapped within the colon, whereas binding of [14C]NMU indicated that microcapsules could bind transient species present within the colon in competition with the faecal bulk. These results indicate that this approach could be used to detect highly unstable and possibly genotoxic substances in situ, hitherto unknown, formed within the intestinal lumen.

Organ-specific effects of 1,2-dimethylhydrazine in hamster

Uptake and metabolism of the carcinogen 1,2-dimethylhydrazine (DMH) were compared in isolated epithelial cells from the colon and the small intestine. A new method was developed to separate colonic epithelial cells into surface columnar cells and crypt cells without the use of any proteolytic enzymes. Colonic columnar cell-enriched fraction exhibited DMH metabolism two to three times higher than that of crypt cells. The carcinogen binding was much lower in the small intestine as compared to the colon. In the small intestine, the crypt cell-enriched fraction showed higher carcinogen binding as compared to villus cells. Pyrazole was found to inhibit DMH binding by isolated small intestinal and colonic epithelial cells. The extent of inhibition was maximum in cells showing the greatest ability to incorporate DMH.

In vivo formation of sigma-methyl- and sigma-phenyl-ferric complexes of hemoglobin and liver-cytochrome P-450 upon treatment of rats with methyl- and phenylhydrazine

Ferric sigma-phenyl complexes of hemoglobin and liver cytochrome P-450 are formed in vivo upon administration of C6H5NHNH2 to rats. Small amounts of the sigma-methyl complex of hemoglobin were also detected in vivo upon treatment of rats with CH3NHNH2. At the doses used for CH3NHNH2 (25 and 50 mg/kg) the states and levels of hemoglobin in the blood and spleen, and of cytochrome P-450 in the liver were almost unchanged. On the contrary, C6H5NHNH2 (25-100 mg/kg) led to a decrease of the HbO2 blood level (10-50%), together with an increase in the HbFe(III) level and the appearance of the HbFe(III)-C6H5 complex. The concentration of this complex reaches its maximum value (2 mM) 1 h after C6H5NHNH2 administration (20% of total hemoglobin). At the same time large amounts of HbO2, HbFe(III) and HbFe(III)-C6H5 appeared in the spleen, and remained high up to 24 h after treatment. Treatment of rats with C6H5NHNH2 (25-100 mg/kg) led to a significant decrease in the level of liver cytochrome P-450 (a 70% decrease 2 h after treatment with 100 mg/kg C6H5NHNH2). About 15% of the remaining cytochrome P-450 existed as a cyt.-P-450-Fe(III)-C6H5 complex, a new example of cytochrome P-450-Fe-metabolite complex which is stable in vivo.

Activation of the colon carcinogen 1,2-dimethylhydrazine in a rat colon cell-mediated mutagenesis assay

Suspensions of rat colon epithelial cells metabolized the potent colon carcinogen, 1,2-[14C]dimethylhydrazine (DMH), into 14C-labeled, alkali-soluble volatile products, presumably CO2. The colon cell suspensions, however, were less effective than rat hepatocyte suspensions. In addition, we used a cell-mediated mutagenesis assay to test rat colon epithelial cells grown from tissue explants for their ability to metabolize DMH into products mutagenic for human P3 teratoma cells. Mutagenesis in the P3 cells was indicated by an acquired resistance to 6-thioguanine. Cocultivation of the colon cells with the P3 cells in the cell-mediated assay resulted in mutagenesis, whereas in the absence of the colon cells, no mutagenesis by DMH was observed. Similar results were obtained in a hepatocyte-mediated mutagenesis assay. Colon cells were also able to activate another carcinogen, benzo(a)pyrene, into products mutagenic for the P3 cells. Individual epithelial clonal populations isolated from the colon cultures grown from tissue explants, however, expressed different capacities to activate DMH and benzo(a)pyrene into mutagens, and a high degree of DMH activation by cells from a colon clone was not necessarily associated with a similar degree of benzo(a)pyrene activation. Our results indicate that the colon itself contains epithelial cell types capable of effectively converting DMH into mutagenic (and presumably carcinogenic) products without necessarily involving intermediary metabolism by hepatocytes as previously thought.

The effect of mixed-function oxidase and amine oxidase inhibitors on the activation of dialkylnitrosamines and 1,2-dimethylhydrazine to bacterial mutagens in mice

The effect of the mixed-function oxidase inhibitor phenylimidazole (PI) and the amine oxidase inhibitors iproniazid (IPRO) and aminoacetonitrile (AAN) on the mutagenic activity of various carcinogens was determined in intrasanguineous host-mediated assays, using mice as hosts and E. coli 343/113 as an indicator of mutagenic activity. The carcinogenic compounds dimethyl-, diethyl-, methylethyl-, and diethanolnitrosamine (DMNA, DENA, MENA, and DELNA respectively) and 1,2-dimethylhydrazine (SDMH) were administered i.p. to mice pretreated or not with one of the inhibitors. After 4 h exposure to each of the carcinogens, E. coli cells recovered from the liver of non-pretreated mice showed considerable induction of VALr mutations; after pretreatment of the hosts with the three inhibitors, significant reduction of the amounts of induced mutants in vivo was observed. Particularly, PI proved a very efficient inhibitor of DENA, MENA, DELNA, and SDMH mutagenicity (93%-97% reduction), suggesting that these carcinogens are mainly activated by cytochrome P-450-dependent enzymes. However, since PI might also inhibit the NAD-mediated activation of DELNA by alcohol dehydrogenase (ADH), the present experiments do not rule out an additional role of ADH in the in vivo mutagenic activation of DELNA. AAN and IPRO were less and much less effective, respectively, in reducing the mutagenic activity of all compounds. Surprisingly, PI showed less inhibition of the mutagenic activity of DMNA (60% reduction), as compared to the other carcinogens; this indicates that metabolic routes other than the cytochrome P-450-dependent enzyme system may be important for the activation of DMNA.

Effect of inhibitors of the FAD-containing monooxygenase system from rat liver microsomes on monomethylhydrazine metabolism and activation to reactive metabolites

Several inhibitors of the FAD-containing monooxygenase (FAD-MO) system from rat liver microsomes (imipramine, chlorpromazine, mercaptoethylamine, dithiothreitol, naphthylthiourea, phenylthiocarbamide) and one inhibitor of the liver microsomal cytochrome P-450 (P-450)-mediated biotransformations (SKF 525 A), were tested as possible inhibitors of monomethylhydrazine (MMH) biotransformation to CO2 and to reactive metabolites that bind covalently to nucleic acids and proteins. Results confirm previous suggestions that both FAD-MO and P-450 are involved in MMH metabolism to CO2 and suggest a similar participation of both systems for production of reactive metabolites interacting with macromolecules.

In vitro DNA and nuclear proteins alkylation by 1,2-dimethylhydrazine

The methylating carcinogen 1,2-dimethylhydrazine (DMH) CAS 540.73.8 is highly organ-specific and, under certain experimental conditions, produces a high incidence of adenocarcinoma in the colon of rodents. We have tried to assess the possibility that part of the organ-specifity in the carcinogenic effect of DMH could be attributed to its metabolism by specific microsomal enzymes. In particular, we compared the in vitro effects of DMH in the presence of either colon or liver microsomes from animals that had been treated with microsomal enzyme inducers. V79 Chinese hamster cells were used as the target to evaluate the damage to the genetic material, as judged by (1) formation of adducts of DNA bases and (2) amino acid modifications in nuclear proteins using [Me-14C]DMH and appropriate analytical detection systems. Our results tend to support the above postulated hypothesis.

[Effect of sex hormones on the 1,2-dimethylhydrazine metabolic activity in the kidneys of CBA-strain mice]

1,2-dimethylhydrazine (DMH) metabolizing activity of kidney microsomes was shown to be two times higher in male, than in female CBA mice. Castration decreased DMH metabolizing activity of male kidney microsomes to the females' level. DMH metabolizing activity of castrated males treated with testosterone propionate was identical to that of intact males. The incorporation of 14C-DMH into kidney DNA was also higher in male, than in female CBA mice.

The effect of diets high in fat and/or fiber on colonic absorption of DMH in the rat

The possibility that long-term feeding of diets high in fat or fiber could alter the colonic mucosa and subsequent colonic absorption of 1,2-dimethylhydrazine (DMH) in situ was examined in the rat model. Male Sprague-Dawley rats were fed one of four experimental diets for six weeks prior to studies of DMH absorption and bile acid excretion; dietary treatments consisted of two levels of fat (12 and 47% of calories from corn oil) fed at each of two levels of fiber (plus or minus 15% wheat bran). Two sets of DMH absorption studies (Studies 1 and 2) were performed; the first used a 10- and the second a 20-minute test period. In Study 1, DMH absorption was greater in those animals that had been fed the high level of corn oil when additional fiber was not present in the diet. When a longer absorption period was used (Study 2), this effect of diet on DMH absorption was not apparent. The level of fiber, not the fat intake, altered bile acid excretion. Bile acid concentration (mg/g dry wt) decreased with added fiber, whereas total bile acid excretion (mg/day) increased. These results indicate that high levels of dietary fat may result in small increases in DMH absorption which are unrelated to changes in bile acid concentration.

Fatty acid stimulated N-demethylation of 1,2-dimethylhydrazine and tetramethylhydrazine by rat colonic mucosa

A fatty acid stimulated, NADPH-independent pathway for the N-demethylation of 1,1-dimethylhydrazine (1,1-DMH) with the generation of HCHO was demonstrated in 10,000 g soluble fractions of colonic mucosal homogenates. Tetramethylhydrazine and, to a lesser extent, aminopyrine, but not 1,2-DMH or methylhydrazine, were also substrates for this reaction. Isolated superficial colonic epithelial cells metabolized 1,1-DMH at a faster rate than proliferative epithelial cells. Indomethacin, an inhibitor of cyclooxygenase activity, and 5,8,11,14-eicosatetraynoic acid (ETYA), an inhibitor of both cyclooxygenase and lipoxygenase activities, suppressed HCHO production from 1,1-DMH by 50 and 80%. However, in the presence of indomethacin or ETYA, arachidonate hydroperoxide stimulated HCHO formation. This suggested a peroxidative mechanism for 1,1-DMH metabolism, related in part to prostaglandin synthesis. A possible role for lipoxygenase activity in mediating 1,1-DMH metabolism was suggested by the ability of linoleate, which did not increase prostaglandin synthesis, to stimulate 1,1-DMH metabolism and by the fact that ETYA was more effective than indomethacin as an inhibitor of 1,1-DMH metabolism. The fatty acid stimulated pathway for N-demethylation was clearly distinct from the mixed function oxidase activities. NADPH did not stimulate 1,1-DMH metabolism to HCHO. 7,8-Benzoflavone or SKF-525A, inhibitors of cytochrome P-450, and methimazole, an inhibitor of N-demethylation catalyzed by the hepatic microsomal FAD-containing monooxygenase, did not suppress HCHO formation. To the extent that 1,1-DMH and tetramethylhydrazine reach the colon unchanged, the results suggest that fatty acid stimulated cooxidation pathways in colonic mucosa may contribute to the metabolism of these agents. Metabolism by superficial cells which are destined to slough may be an important defense mechanism against the toxic and carcinogenic actions of these hydrazines in colon.

Colonic absorption of 1,2-dimethyl hydrazine (DMH) in the rat

1,2-Dimethyl hydrazine (DMH) is absorbed in the colon by passive diffusion in the 0.1-5.0 mM concentration range. Absorption of DMH is enhanced by both conjugated and unconjugated bile acids. The presence of hydroxy-fatty acids in the colon markedly increased DMH absorption while fatty acids of different chain length did not influence absorption.

Influence of diet on 1,2-dimethylhydrazine metabolism in rat liver

The metabolism of 1,2-dimethylhydrazine (DMH) was investigated in isolated perfused livers excised from Sprague-Dawley rats fed four semisynthetic diets over two generations. The diets were varied within normal physiological limits, without producing specific deficiencies. Diet was shown to have an influence on the growth of animals and on the cholesterol content and beta-glucuronidase activity in the blood serum. However, diet did not influence the rate of metabolism of DMH or the concentration of metabolites.

The mitochondrial metabolism of 1,2-disubstituted hydrazines, procarbazine and 1,2-dimethylhydrazine

Sonication of isolated rat hepatocytes caused a pronounced decrease in the metabolism of biphenyl due to dilution of the cytosolic pool of NADPH, but did not greatly reduce the rate of procarbazine oxidation to its azo derivative. This result suggested the existence of two enzyme systems which can oxidize 1,2-disubstituted hydrazines: an NADPH-dependent (cytochrome P-450) and an NADPH-independent hydrazine oxidase. Upon assaying the various cell fractions of the hepatocyte, it was noted that the NADPH-independent hydrazine oxidase activity was localized in the mitochondria. The reaction was not linked to mitochondrial electron transport, but preincubation of isolated mitochondria with N,N-dimethylpropargylamine markedly inhibited both monoamine oxidase activity (benzylamine and kynuramine deamination) and procarbazine oxidation. During a 15-fold purification of the enzyme, benzylamine oxidase and procarbazine oxidase activity copurified, demonstrating that the rat liver mitochondrial monoamine oxidase can convert procarbazine to its respective azo derivative. 1,2-Dimethyl- and monomethylhydrazine were also metabolized by monoamine oxidase. Procarbazine did not inactivate monoamine oxidase like other hydrazines; this most likely reflects the fact that the oxidation product of the 1,2-disubstituted hydrazines is a stable azo derivative. However, procarbazine is a competitive substrate for the enzyme and may exert some of its toxic neurological effects by altering the metabolism of biogenic amines.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and activation of 1,1-dimethylhydrazine and methylhydrazine, two products of nitrosodimethylamine reductive biotransformation, in rats

Nitrosodimethylamine (DMN) and two of its metabolites, methylhydrazine (MH) and 1,1-dimethylhydrazine (UDMH), were metabolized to CO2 by liver slices obtained from Sprague-Dawley rats. Under the conditions used, DMN and MH produced reactive metabolites that bound covalently to nucleic acids, but UDMH did not. Rat liver microsomes or 9,000 X g supernatants were able to transform DMN, MH, and UDMH to CH2O. In the cases of MH and UDMH, enzymatic and nonenzymatic pathways of CH2O formation were observed in both liver microsomes and 9,000 X g supernatants. DMN, MH, and UDMH led to covalent binding (CB) to proteins in incubation mixtures containing either microsomes or 9,000 X g supernatants. In the case of DMN, the process was enzymatic and required NADPH in both cellular fractions. In the case of MH, the process was enzymatic in microsomes and required NADPH and O2. With UDMH or MH and 9,000 X g supernatants, nonenzymatic interactions resulting in CB to proteins dominated. All these results suggest that part of the CO2 produced during DMN metabolism might be derived from UDMH and MH. Similarly, a significant part of the CB of DMN metabolites to proteins in incubation mixtures containing microsomes or 9,000 X g supernatants might be derived from enzymatic and nonenzymatic reactions of UDMH or MH. Also, a minor part of the CB of DMN-reactive metabolites to nucleic acids might have resulted from MH's further biotransformation to reactive metabolites. Overall, biotransformation of DMN and MH might not be a detoxication process, as previously thought, but one related to some of the DMN toxic effects.

Induction of colon mucosal beta-glucuronidase production as a mechanism for 1,2-dimethylhydrazine colon carcinogenesis

Although early studies in germ-free rats showed almost complete dependence on dimethylhydrazine (DMH) colon carcinogenesis upon the presence of colon bacteria, no adequate explanation was given for the 20% tumor incidence observed in germ-free animals. Bacterial activation of liver microsomal products releasing active proximate carcinogens has been the accepted reason for the exquisite specificity DMH has for the colon. Recent work, including the present study, show the colon mucosa is capable of metabolizing carcinogens and activating conjugating forms metabolized in the liver independent of the intestinal microflora. Mucosal beta-glucuronidase production was assayed in coded, scraped mucosa samples from the duodenum/jejunum, ileum, right colon, and left colon of normal and DMH-treated rats. Normal mucosal beta-glucuronidase production was highest in the left colon followed by the right colon, duodenum, and ileum, respectively. Enzyme production in the left colon was significantly increased 24 hours after injection of 25 mg/kg body weight DMH. No elevation was seen in other mucosal samples. Metabolism of DMH to oxidated forms conjugated to glucuronic acid is well established. Thus, this study offers a possible role for carcinogen, induction of a metabolic enzyme in its target tissue.

A free radical mediated cooxidation of tetramethylhydrazine by prostaglandin hydroperoxidase

Prostaglandin endoperoxide synthase catalyzed the oxidation of tetramethylhydrazine to the tetramethylhydrazine radical cation, as detected by electron spin resonance spectroscopy. Oxidation of tetramethylhydrazine by prostaglandin endoperoxide synthase also resulted in the N-demethylation of tetramethylhydrazine leading to the formation of formaldehyde. Both the radical and formaldehyde formation were dependent on arachidonic acid, inhibited by indomethacin, and supported by 15-hydroperoxyarachidonic acid, indicating that the metabolism was peroxidative. We propose that tetramethylhydrazine undergoes two sequential one-electron oxidations yielding an iminium cation, which is then hydrolyzed to yield formaldehyde. Metabolism of hydrazines by prostaglandin endoperoxide synthase may be of importance in tissue containing low mixed-function oxidase activity.

Metabolism of the carcinogen 1,2-dimethylhydrazine by isolated human colon microsomes and human colon tumor cells in culture

Human colon microsomes catalyze the metabolism of the model colon carcinogen 1,2-dimethylhydrazine. Activity appears to be distributed in a gradient towards the lower end of the colon. Highest activities were observed for microsomes prepared from the descending segment of the colon with the transverse segment exhibiting lower activities, while the ascending segment showed the lowest rate of metabolism. Dimethylhydrazine metabolism in each segment is inhibited significantly by inhibitors of the cytochrome P-450-dependent mixed function oxidase system. Microsomes prepared from a human colon tumor cell also catalyze the metabolism of 1,2-dimethylhydrazine. Metabolic activity in the cell line can be induced two-fold by treatment of cells with phenobarbital and three-fold by treatment of the cells with phenobarbital plus hydrocortisone. These results show that human colon activates 1,2-dimethylhydrazine and suggest that the human colon may be capable of activating other carcinogens in situ.

Effect of dietary protein concentration on yield of mutagenic metabolites from 1,2-dimethylhydrazine in mice

The effects of varying dietary protein concentrations on the metabolism of 1,2-dimethylhydrazine (DMH) to mutagenic products by male C57BL/6 X C3H F mice were assayed by in vivo and in vitro methods. DMH and its metabolite, azoxymethane (AOM), did not increase the mutation frequency of Salmonella typhimurium (strain G-46) in vitro alone or in the presence of mouse liver homogenates capable of activating the promutagen dimethylnitrosamine. Methylazoxymethanol (MAM), another metabolite of DMH, was mutagenic in vitro without activation. S.c. administration of DMH, AOM, or MAM at dosages ranging from 0.2 to 0.8 mmol/kg of body weight caused dose-dependent increases in mutations of S. typhimurium in the host-mediated assay, and molar potencies increased progressively from DMH to AOM to MAM. S.c. or i.p. injections of AOM increased host-mediated mutagenesis within 20 min, while increases in mutagenesis by DMH required at least 1 hr. When [14C]DMH was administered, [14C]azomethane was expired immediately, while 14CO2 began to appear 1 hr after DMH administration. The percentage of administered [14C]DMH expired as azomethane varied inversely with dietary protein concentration, while AOM-induced host-mediated mutagenesis was directly proportional to dietary protein (p less than 0.01). The percentage of DMH converted to mutagenic end products was limited by losses of the volatile metabolite azomethane, especially in protein-deficient mice. Greater expiration of azomethane and decreased conversion of AOM to MAM, both seen with restriction of dietary protein, were associated with a smaller body burden of DMH metabolites.

Metabolism of 1,2-dimethylhydrazine by cultured rat colon epithelial cells

The colon carcinogen 1,2-dimethylhydrazine (DMH) was cultured with rat colon epithelial cells to determine if these cells have the ability to metabolize DMH. Colon epithelial cells isolated from conventional and germfree Sprague-Dawley rats were incubated in CMRL 1066 supplemented medium containing 14C-DMH. Cells from both groups of rats metabolized DMH to gaseous metabolites, to metabolites in the medium that were putatively identified as azoxymethane and methylazoxymethanol, and to products that bound to DNA. Cells from germfree rats metabolized DMH at an equal or greater rate than cells from conventional rats for the criteria examined. This report demonstrates that rat colon epithelial cells can metabolize DMH without previous metabolism by other tissues or colon bacteria.

Metabolism of 1,2-dimethylhydrazine in isolated perfused rat liver

The metabolism of 1,2-dimethylhydrazine (DMH) was investigated in isolated perfused rat liver. The separation of [14C]DMH and its metabolites azomethane (AM), azoxymethane (AOM) and methylazoxymethanol (MAM) was performed by high pressure liquid chromatography (HPLC). The fractions were quantitatively detected by liquid scintillation counting of the radioactivity. It was demonstrated that DMH is highly metabolized by the liver. After 1 h of perfusion, the median amounts of DMH and its metabolites in the medium were: DMH, 16%; AM, 3%; AOM, 42%; MAM, 30% of the given dose. During this time 9.9% and 0.7% of the total radioactivity were eliminated as AM and CO2 in the oxygen stream of the perfusion apparatus; 0.6% were excreted by bile and 12.3% stored in hepatic tissue. The reaction rate (t1/2) of each individual metabolic step was estimated by means of a mathematical kinetic model as follows: DMH leads to AM, 21.8 min; AM leads to AOM, 1.5 min; AOM leads to MAM, 41.5 min; MAM leads to, 611 min. The results are discussed in comparison to in vivo experiments.

Cell specificity in hepatocarcinogenesis: preferential accumulation of O6-methylguanine in target cell DNA during continuous exposure to rats to 1,2-dimethylhydrazine

Concentrations of the major methylated DNA purines were determined in two liver cell cell populations of Fischer 344 rats during administration of 30 ppm 1,2-dimethylhydrazine (SDMH) in the drinking water for periods of up to 4 weeks. Quantitation of 7-methylguanine and O6-methylguanine (O6MG) was achieved by highly sensitive optical methods following separation of DNA bases by high-performance liquid chromatography. Overall alkylation as indicated by the concentration of 7-methylguanine was near maximum in both hepatocytes and liver nonparenchymal cells by the third day of SDMH administration. Similar amounts of 7-methylguanine were present in the two liver cell populations at seven of nine time points during 4 weeks of exposure. In contrast, dramatic differences in the cumulative concentrations of O6MG were seen in the two cell populations. Nonparenchymal cells accumulated O6MG during the first 8 days of exposure and had up to a 30-fold greater concentration of this product than did the corresponding hepatocytes. In the hepatocytes, a rapid decline in O6MG concentration was observed between 1 and 3 days of exposure to SDMH. Thereafter, only low levels of this promutagenic lesion were present in hepatocytes. Exposure of rats to the same regimen of SDMH for up to 10 months caused angiosarcomas in the livers of over 90% of the animals, while hepatocellular carcinomas occurred in only 40%. Thus, a strong correlation exists between the inability to repair O6MG and cell specificity for carcinogenesis.

Bile acids: effects on absorption of 1,2-dimethylhydrazine and 7,12-dimethylbenz[a]anthracene in the colon of the rat and guinea pig

The specific effects of bile acids as cocarcinogens were investigated. Absorptions of [14C]7,12-dimethylbenz[a]anthracene, [14C]dimethylhydrazine ([14C]DMH), and [3H]inulin from loops of colons from outbred Sprague-Dawley rats and Hartley guinea pigs were determined. In each animal absorption of one carcinogen and inulin was studied in one control loop and in an experimental loop containing either deoxycholic acid (DOC) or chenodeoxycholic acid (CDOC). DOC had a more pronounced effect on increasing loss of carcinogen from the intestinal lumen than did CDOC. This role of bile acids was consistent with their known effect of increasing intestinal permeability. Less carcinogen remained in the colon mucosa when DOC was present in the intestinal lumen. Although [14C]DMH was absorbed more rapidly from the intestinal lumina of guinea pigs than from those of rats, the rat accumulated more of the carcinogen in the intestinal mucosa and liver.

Aberrant and nonrandom methylation of chromosomal DNA-binding proteins of colonic epithelial cells by 1,2-dimethylhydrazine

The alkylating carcinogen 1,2-dimethylhydrazine (DMH) induces colonic tumors with high incidence. The sites of in vivo modification of target macromolecules were studied using [methyl-3H]DMH. Carcinogen binding to subcellular fractions of colonic epithelial cells was analyzed at time intervals ranging from 10 min to 36 hr, with particular emphasis on the alkylation of nuclear constituents. DMH modifies not only nucleic acids but also histones and other DNA-binding proteins in the target cells. Separation of the 3H-methylated amino acids showed aberrant methylation patterns after exposure to [3H]DMH, as compared with methylations observed with [methyl-3H]methionine as a natural methyl group donor. DMH-modified histone H1 contained methylated lysin, arginine, and histidine residues not normally found, and other histones had abnormal methylarginine contents. High-mobility-group proteins and other nuclear proteins contained methyllysine residues not normally detected. Proteins known to be associated with template-active and more accessible DNA sequences, such as the high-mobility group proteins and the multiacetylated forms of histones H3 and H4, were preferentially damaged after exposure to [3H]DmH. The result suggests that carcinogen-induced chromosomal damage is not random and may selectively affect proteins in the actively transcribing or replicating genes in the target cells. That damage affects the amino acids most likely to be involved in DNA binding.

Metabolic activation of DMH by colonic microsomes: a process influenced by type of dietary fat

A study was conducted to determine whether 1,2-dimethylhydrazine (DMH), a potent colon carcinogen, is activated to a more potent mutagen by the drug-metabolizing system of the colonic mucosa and to determine the extent to which this metabolism is modified by lipids in the diet. DMH-treated rats fed a diet enriched with 10% corn oil exhibited markedly elevated colonic enzyme levels for mutagen production. This diet also produced the greatest number of animals with colon tumors, when compared with diets containing other levels and sources of lipid. The potential risk of a diet in which unsaturated fat is the sole source of lipid is underlined.

Considerations on the carcinogenicity of the mushroom poison gyromitrin and its metabolites

Monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH), but not N-methyl-N-formylhydrazine (MFH), a mushroom poison, can be oxidized by the weak oxidant 2,6-dichlorophenolindophenol. Hydrogen peroxide is formed by this oxidation, and has been found to cause decay of DNA in aqueous solution as measured by the decreased viscosity of a DNA solution in the presence of the hydrazines. Furthermore, MMH and UDMH but not MFH inhibit the incorporation of [3H]thymidine and [3H]uridine into DNA and RNA of Ehrlich ascites carcinoma (EAC) cells. These experiments show that MFH is an inactive compound in contrast to MMH and UDMH. Since the hydrolysis rate of MFH, to produce MMH, is low, it is concluded that MFH must be activated in vivo into toxic metabolites which are ultimately responsible for the known high carcinogenicity of MFH.

In vivo kinetics of O6-methylguanine and 7-methylguanine formation and persistence in DNA of rats treated with symmetrical dimethylhydrazine

The rates of appearance and removal of 7-methylguanine and O6-methylguanine in DNA from rat liver, kidney, and colon were determined at various intervals up to 120 hr after i.p. administration of 10.2, 40.7, 81.5, or 163 mg 1,2-dimethylhydrazine (SDMH) per kg body weight (one-sixteenth, one-fourth, one-half, or one 50% lethal dose) using high-pressure liquid chromatography and fluorescence spectrophotometry. In most cases, increasing doses of SDMH slowed the rate of methylation of DNA, especially of the liver; colon DNA was methylated at a faster rate than was liver DNA, and kidney DNA was methylated at the slowest rate following SDMH administration. Removal of O6-methylguanine was slow (half-life, 37 to 50 hr) when this base was present in liver DNA at concentrations above 400 mumol/mol guanine; as the concentration fell below 300 mumol O6-methylguanine per mol guanine, the removal rate more than doubled (half-life, 16 to 19 hr). Some evidence was obtained to suggest that in the first 12 hr after maximum DNA methylation following SDMH administration, a rapid time-dependent removal of 7-methylguanine from liver and kidney but not colon DNA occurred. In these instances, then, the rates of formation and removal of aberrant methylated bases did not follow first-order kinetics.

Metabolism of aflatoxin B1, benzo[a]pyrene, and 1,2-dimethylhydrazine by cultured rat and human colon

A model system for comparing carcinogen metabolism between human and rat colon has been developed. Tissue explants maintained under chemically defined conditions were treated with radioactively labeled carcinogens. After incubation for 24 hours, the binding of radioactive carcinogen to DNA was quantitated. Further, the carcinogen-DNA adducts and carcinogen metabolites released into the culture media were identified. Both human and rat colon activate benzo[a]pyrene (BP), aflatoxin B1 (AFB), and 1,2-dimethylhydrazine (DMH) into chemical species that reacted with cellular macromolecules. When human and rat colons were compared, the metabolism of AFB and DMH was qualitatively similar - the same major carcinogen-DNA adducts and metabolic profile. However, the mean binding levels of DMH and AFB to colonic DNA were higher in rats than in humans. BP-guanine adducts were the major adducts formed by both rat and human colonic DNA. However, BP-adenine adducts were observed in rat colonic DNA but not in human colonic DNA. A positive correlation for the binding of BP and DMH to human DNA of different individuals was observed, but no correlation was found between BP and AFB. The data suggest that similar enzyme systems may be involved in the metabolism of BP and DMH, whereas different enzymes might be involved in the metabolic activation of AFB.

Effects of selenium on 1,2-dimethylhydrazine metabolism and DNA alkylation

Sodium selenite (Se) decreases the incidence of colon tumors induced in rats by 1,2-dimethylhydrazine (DMH). In order to determine the basis for this inhibition, we studied the effects of Se on DMH metabolism, DNA alkylation and the rate of cell turnover of the target tissue. The effects of Se pretreatment (4 p.p.m. in the drinking water, for 2, 4 or 6 weeks) on DMH metabolism were monitored in male Sprague-Dawley rats by measuring expired 14CO2 and azo[14C]methane over a 12 h period after a.c. injection of [14C]DMH (20 mg/kg body weight). Compared to control rats, which received only [14C]DMH, Se pretreatment caused an increase in exhaled azomethane (31--69%) and a corresponding decrease in 14CO2 (4--33%) as the length of treatment increased from 2 to 6 weeks. The extent of DNA alkylation (measured as N-7 and O6-methylguanine formation) after Se pretreatment was reduced 20--27% in liver and was increased 40--43% in colon. Metabolic incorporation of [14C] from [14C]DMH into adenine and guanine (presumably via C1 pathways) was reduced 69--72% in colon DNA of Se-treated rats and [3H]thymidine incorporation was reduced 61--65%. This may have been due to decreased cell turnover. A similar response was not observed in the liver. The data suggest that Se decreases hepatic DMH metabolism, and that this may be compensated by an increase in extrahepatic metabolism and alkylation. Although colon alkylation is increased by Se pretreatment, fewer tumors result. This may be due to a decrease in DNA synthesis in this tissue.

Metabolism of 1,2-dimethylhydrazine by cultured human colon

The overall metabolism of 1,2-dimethylhydrazine, and organotropic colon carcinogen in rodents, has been studied using human colon explant cultures. The binding level of 1,2-dimethylhydrazine to DNA which in this study includes both reaction of metabolites with DNA and incorporation of radioactive metabolites into DNA, showed a 100-fold variation among the 120 people studied. When different anatomical colonic sites were compared, the highest mean binding levels were found in the ascending and sigmoid colon. No significant difference in the median and mean binding levels were observed in nontumorous colon obtained surgically from patients with colon cancer and colon obtained from immediate autopsy, but decreased mean binding levels were seen in tissues obtained by surgery from patients with non-cancerous colonic disorders. Several exogenous chemicals were found to modify the metabolism. When the colon explants were co-incubated with 1,2-dimethylhydrazine and these chemicals, the binding level of 1,2-dimethylhydrazine to DNA was (a) increased by either indole 3-carbinol or phenobarbital, (b) decreased with disulfiram, butylated hydroxytoluene, or taurodeoxycholic acid, and (c) unaltered by lithocholic acid.

Inhibition of the alkylation of nucleic acids and of the metabolism of 1,2-dimethylhydrazine by aminoacetonitrile

Pretreatment of rats with aminoacetonitrile inhibited the metabolism of [14C]1,2-dimethylhydrazine to 14CO2 and increased the expiration of [14C]-azomethane. Alkylation of nucleic acids following administration of 1,2-dimethylhydrazine was reduced by aminoacetonitrile to 5% of control levels in liver, 11% of control levels in kidney and 43% of control levels in colon.

Investigations into the metabolism and mode of action of the colon carcinogens 1,2-dimethylhydrazine and azoxymethane

Colon cancer can be induced reliably in rodents with 1,2-dimethylhydrazine and azoxymethane (AOM). Our studies deal with the mode of action of these compounds and their organotropism. A partial summary of our previous work on the metabolism of 1,2-dimethylhydrazine and its inhibition by disulfiram, carbon disulfide and other thiono-sulfur compounds is presented. On-going studies with AOM-14C indicate that in male F-344 rats, this carcinogen is rapidly metabolized to 14CO2 (37%, 48 hours), and to methylazoxymethanol-14C (MAM) (0.6--1%), which, along with other metabolites, appears in the urine. Pretreatment of rats with phenobarbital or chyrsene increased exhaled 14CO2 to 53% and 65%, respectively. Pretreatment with disulfiram or CS2 causes a complete, although transient, inhibition of exhaled 14CO2, decreases urinary MAM, and increases significantly the levels of unmetabolized AOM in the exhaled air and in urine. Thus, phenobarbital and chrysene appear to stimulate, while disulfiram and CS2 appear to inhibit, the metabolism of AOM. In vitro hydroxylation of AOM to MAM was demonstrated with rat liver homogenates and microsomal fractions. A hypothetical scheme for the endogenous formation of AOM is presented.

Investigations into the metabolism and mode of action of the colon carcinogens 1,2-dimethylhydrazine and azoxymethane

Colon cancer can be induced reliably in rodents with 1,2-dimethylhydrazine and azoxymethane (AOM). Our studies deal with the mode of action of these compounds and their organotropism. A partial summary of our previous work on the metabolism of 1,2-dimethylhydrazine and its inhibition by disulfiram, carbon disulfide and other thiono-sulfur compounds is presented. On-going studies with AOM-14C indicate that in male F-344 rats, this carcinogen is rapidly metabolized to 14CO2 (37%, 48 hours), and to methylazoxymethanol-14C (MAM) (0.6--1%), which, along with other metabolites, appears in the urine. Pretreatment of rats with phenobarbital or chyrsene increased exhaled 14CO2 to 53% and 65%, respectively. Pretreatment with disulfiram or CS2 causes a complete, although transient, inhibition of exhaled 14CO2, decreases urinary MAM, and increases significantly the levels of unmetabolized AOM in the exhaled air and in urine. Thus, phenobarbital and chrysene appear to stimulate, while disulfiram and CS2 appear to inhibit, the metabolism of AOM. In vitro hydroxylation of AOM to MAM was demonstrated with rat liver homogenates and microsomal fractions. A hypothetical scheme for the endogenous formation of AOM is presented.