Detection and characterization of DNA adducts of 3-methylindole.

The pneumotoxin 3-methylindole is metabolized to the reactive intermediate 3-methyleneindolenine which has been shown to form adducts with glutathione and proteins. Reported here is the synthesis, detection, and characterization of nucleoside adducts of 3-methylindole. Adducted nucleoside standards were synthesized by the reaction of indole-3-carbinol with each of the four nucleosides under slightly acidic conditions, which catalyze the dehydration of indole-3-carbinol to 3-methyleneindolenine. Following solid phase extraction, the individual adducts were infused via an electrospray source into an ion trap mass spectrometer for molecular weight determination and characterization of the fragmentation patterns. The molecular ions and fragmentation of the dGuo, dAdo, and dCyd adducts were consistent with nucleophilic addition of the exocyclic primary amine of the nucleosides to the methylene carbon of 3-methyleneindolenine. The apparent chemical preference of this addition lead primarily to dAdo and dGuo adducts, with substantially less of the dCyd adduct formed. No adduct with dThd was detected. The adducts were purified by HPLC and subsequent NMR analysis of the dGuo and dCyd adducts confirmed the proposed structures. Mass spectral fragmentation of the three adducts produced primarily two ions which were the result of the loss of either the 3-methylindole moiety or the sugar. On a triple quadrupole electrospray mass spectrometer, the neutral loss of the sugar, [M + H - 116](+), was utilized for selected reaction monitoring of the calf thymus DNA adducts, formed by incubations of 3-methylindole with various microsomes (rat liver, goat lung, and human liver). All three adducts were detected from each of the microsomal incubations, following extraction and cleavage of the DNA to the nucleoside level. The dGuo adduct was the primary adduct formed, with smaller amounts of the dAdo and dCyd adducts. Rat hepatocytes incubated with 3-methylindole produced the same three adducts, in approximately the same proportions, while no adducts were detected in untreated hepatocytes. Microsomal incubations in the presence of ([3-(2)H(3)]-methyl)indole confirmed the formation and identification of the adducts as well as the fragmentation patterns. These results demonstrate that bioactivated 3-methylindole forms specific adducts with exogenous or intact cellular DNA, and indicates that 3-methylindole may be a potential mutagenic and/or carcinogenic chemical.

Quantitative analysis of capsaicinoids in fresh peppers, oleoresin capsicum and pepper spray products.

Liquid chromatography-mass spectrometry was used to identify and quantify the predominant capsaicinoid analogues in extracts of fresh peppers, in oleoresin capsicum, and pepper sprays. The concentration of capsaicinoids in fresh peppers was variable. Variability was dependent upon the relative pungency of the pepper type and geographical origin of the pepper. Nonivamide was conclusively identified in the extracts of fresh peppers, despite numerous reports that nonivamide was not a natural product. In the oleoresin capsicum samples, the pungency was proportional to the total concentration of capsaicinoids and was related by a factor of approximately 15,000 Scoville Heat Units (SHU)/microg of total capsaicinoids. The principle analogues detected in oleoresin capsicum were capsaicin and dihydrocapsaicin and appeared to be the analogues primarily responsible for the pungency of the sample. The analysis of selected samples of commercially available pepper spray products also demonstrated variability in the capsaicinoid concentrations. Variability was observed among products obtained from different manufacturers as well as from different product lots from the same manufacturer. These data indicate that commercial pepper products are not standardized for capsaicinoid content even though they are classified by SHU. Variability in the capsaicinoid concentrations in oleoresin capsicum-based self-defense weapons could alter potency and ultimately jeopardize the safety and health of users and assailants.

Specific dehydrogenation of 3-methylindole and epoxidation of naphthalene by recombinant human CYP2F1 expressed in lymphoblastoid cells.

3-Methylindole (3MI) is a naturally occurring pulmonary toxin that requires metabolic activation. Previous studies have shown that 3MI-induced pneumotoxicity resulted from cytochrome P-450-catalyzed dehydrogenation of 3MI to an electrophilic methylene imine (3-methyleneindolenine), which covalently bound to cellular macromolecules. Multiple cytochrome P-450s are capable of metabolizing 3MI to several different metabolites, including oxygenated products. In the present study, the role of human CYP2F1 in the metabolism of 3MI was examined to determine whether it catalyzes dehydrogenation rather than hydroxylation or ring oxidation. Metabolism was examined using microsomal fractions from human lymphoblastoid cells that expressed the recombinant human CYP2F1 P-450 enzyme. Expression of CYP2F1 in the lymphoblastoid cells proved to be an appropriate expression system for this enzyme. Products were analyzed using HPLC and the mercapturate, 3-[(N-acetylcystein-S-yl)methyl]indole, of the reactive intermediate was identified and quantified. Product analysis showed that human CYP2F1 efficiently catalyzed the dehydrogenation of 3MI to the methylene imine without detectable formation of indole-3-carbinol or 3-methyloxindole. High substrate concentrations of 3MI strongly inhibited production of the dehydrogenated product, a result that may indicate the existence of mechanism-based inhibition of CYP2F1 by 3MI. Recombinant CYP2F1 demonstrated remarkable selectivity for the bioactivation of 3MI to the putative dehydrogenated reactive electrophile. Bioactivation of naphthalene to its pneumotoxic epoxide by CYP2F1 was also demonstrated.

Oxidation at C-1 controls the cytotoxicity of 1,1-dichloro-2,2- bis(p-chlorophenyl)ethane by rabbit and human lung cells.

Isolated rabbit Clara cells and a transformed human bronchial epithelial cell line, BEAS-2B, were used to investigate the mechanism of cytotoxicity of 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD), a persistent insecticide and stable metabolite of 1,1,1-trichloro-2,2- bis(p-chlorophenyl)ethane. Both BEAS-2B cells and rabbit Clara cells were highly susceptible to DDD toxicity and were partially protected by 1-aminobenzotriazole, a suicide substrate inhibitor of cytochrome P450 enzymes. DDD (0.05 mM) killed 47 +/- 1.8% of rabbit Clara cells and 42 +/- 7.9% of BEAS-2B cells after 3 hr and 84 +/- 3.0% of rabbit Clara cells and 80 +/- 14% of BEAS-2B cells after 6 hr. Consequently, DDD is the most potent Clara cell toxicant recognized to date. The cytotoxicity of DDD to these cells was decreased by deuterium substitution at the C-1 position. Rabbit Clara cells and pulmonary microsomes incubated with 14C-DDD produced the fully oxidized acetic acid metabolite 2,2'-bis(p- chlorophenyl)acetic acid (DDA), but DDA was not formed by Clara cells when DDD was coincubated with 1-aminobenzotriazole. These results support the hypothesis that the cytotoxicity of DDD to susceptible subpopulations of rabbit and human lung cells is, at least in part, caused by cytochrome P450-mediated oxidation of DDD at C-1. A required step for the production of the cytotoxic intermediate is proposed to be the formation of a highly reactive acyl halide intermediate that is readily hydrolyzed to a stable, nontoxic metabolite, DDA.

Correlation between pulmonary cytochrome P450 transcripts and the organ-selective pneumotoxicity of 3-methylindole.

3-Methylindole (3MI) is a species- and organ-selective pneumotoxin; goats are the most susceptible species, mice are intermediate in susceptibility, and rabbits are the least susceptible species to its toxicity. Four different cDNA probes representative of human cytochrome P450 genes CYP2F1, CYP4B1, CYP2A6, and CYP2B6 were hybridized against RNA from lung and liver tissues of goat, mouse and rabbit. Transcripts representative of pulmonary P450s CYP2F1, CYP4B1 and CYP2B6 were present in goat lung. Transcripts for the CYP2F1 and CYP4B1 genes were observed in rabbit and mouse lung. In general, the probes selectively hybridized to pulmonary but not hepatic transcripts of all three species. The differences in susceptibilities among the three species could not be explained by the lack of 4B1 and 2F1 transcripts in the lungs of mice or rabbits that are less susceptible than goats, but the selective expression in the lung tissues of all three species may participate in the organ-selective bioactivation and pulmonary toxicity of 3MI in these species.

Metabolism and bioactivation of 3-methylindole by Clara cells, alveolar macrophages, and subcellular fractions from rabbit lungs.

3-Methylindole (3MI), a fermentation product of tryptophan produced by intestinal and ruminal microflora, has been shown to cause pneumotoxicity in several species subsequent to cytochrome P450-mediated biotransformation. Among several species studied, rabbits are comparatively resistant to 3MI-induced pneumotoxicity, especially when compared to goats or mice. In this study, rabbit pulmonary cells and subcellular fractions were used to examine the metabolism and bioactivation of 3MI. A covalent-binding metabolite was produced in 3MI incubations by both Clara cells and macrophages. The addition of the cytochrome P450 inhibitor, 1-aminobenzotriazole, to these incubations inhibited the production of covalent-binding metabolite(s) by 94% in Clara cells and only 24% in macrophages. In incubations of Clara cells or macrophages with 3MI and N-acetylcysteine (NAC), a polar conjugate was detected and tentatively identified as an adduct of 3-hydroxy-3-methylindolenine (3H3MIN). Also identified were 3[(N-glutathione-S-yl)-methyl]-indole (3MI-GSH) and 3-methyloxindole (3MOI). In rabbit lung microsomal incubations with 3MI and glutathione (GSH), 3MI-GSH, 3MOI, indole-3-carbinol, and a GSH adduct of 3H3MIN were identified. The addition of cytosol to the microsomal incubations with GSH did not increase the rate of formation of the GSH adducts, indicating that cytosolic GSH-S-transferases are not essential in the formation of these metabolites. GSH significantly decreased the covalent binding of an electrophilic metabolite in microsomal incubations. These data suggest that GSH may be important in the mitigation of 3MI toxicity. Furthermore, the comparison of 3MI bioactivation to electrophilic intermediates in Clara cells and alveolar macrophages suggests that 3MI is metabolized by different oxidative pathways in the two different cell types, although the same metabolites were produced by the two cell types. This study shows that rabbit pulmonary enzymes are capable of bioactivating 3MI to reactive intermediates which become covalently bound to cellular macromolecules. This indicates that the relative resistance of rabbits to 3MI-induced pneumotoxicity is probably not due to differences in metabolic enzymes which convert 3MI to reactive intermediates.

Identification of goat and mouse urinary metabolites of the pneumotoxin, 3-methylindole.

1. Urine from goats dosed i.v. with 3-methylindole (3MI; 15 mg/kg) or [methyl-14C] 3MI (15 mg/kg, 0.5 microCi/kg) contained at least 11 metabolites of 3MI. 2. Goat metabolized 3MI to sulfate conjugates of 4- or 7-hydroxy-3-methyloxindole, 5- or 6-hydroxy-3-methyloxindole, and 3,5- or 6-dihydroxy-3-methyloxindole; glucuronic acid conjugates of indole-3-carboxylic acid and 4- or 7-hydroxy-3-methyloxindole; and unconjugated 3-hydroxy-3-methyloxindole. Diastereoisomeric glucuronic acid conjugates of 3-hydroxy-3-methyloxindole were also identified in goat urine. 3. Urine from mice dosed i.p. with 3MI (400 mg/kg) or [ring-UL-14C] 3MI (400 mg/kg, 125 microCi/kg) contained at least six metabolites of 3MI. 4. Mice metabolized 3MI to glucuronic acid conjugates of 3,5- or 6-dihydroxy-3-methyloxindole, 5- or 6-hydroxy-3-methyloxindole, and indole-3-carboxylic acid; and unconjugated indole-3-carboxylic acid. Unconjugated 3-hydroxy-3-methyloxindole was identified in mouse urine in a previous report. 5. Both goats and mice metabolized 3MI to a mercapturate, 3-[(N-acetyl-L-cystine-S-yl)methyl]indole, which has been previously identified and was confirmed in this study. 6. 3-Methyloxindole was not identified in the urine of either goats or mice. 7. The major pathways of 3MI biotransformation in goats and mice is the formation of mono- and dihydroxy-3-methyloxindoles and their subsequent conjugation with glucuronic acid or sulfate. 8. There are no apparent qualitative differences in the biotransformation of 3MI between goats and mice that can account for their different sensitivities to 3MI-induced lung injury.

Identification of a cysteinyl adduct of oxidized 3-methylindole from goat lung and human liver microsomal proteins.

3-Methylindole is a selective pneumotoxin that is oxidized by cytochrome P-450 enzymes to a reactive intermediate. 3-Methyleneidolenine, a methylene imine electrophile, is the postulated reactive intermediate, and it binds to proteins, a reaction that probably initiates the pneumotoxicity of 3-methylindole. Thioether adducts of this electrophile are formed with glutathione in vitro, but the identity of the adducted electrophile with amino acid residues of microsomal proteins had not previously been determined. 3-Methylindole was incubated with NADPH and goat lung or human liver microsomal proteins, and the proteins were hydrolyzed. 3-(Cystein-S-ylmethyl)indole was isolated and identified as the major amino acid adduct of 3-methyleneindolenine, demonstrating that cysteine thiols preferentially attack the exocyclic methylene position and result in a covalently (thioether) attached 3-methylindole residue to these pulmonary and hepatic proteins. These results demonstrate that the putative methylene imine intermediate is indeed the active electrophile that binds to proteins and presumably initiates the toxic events.

Isolation, purification, and characterization of two new chemical decomposition products of methylazoxyprocarbazine.

We have previously reported that the antineoplastic agent, procarbazine, in aqueous solutions was chemically oxidized to its azoxy metabolites (methylazoxy and benzylazoxy). To determine if there was additional metabolism of the most active metabolite, methylazoxyprocarbazine, it was incubated in the presence and absence of CCRF-CEM human leukemia cells. Incubations were extracted, and potential metabolites were detected by HPLC with UV detection and by combined HPLC and thermospray mass spectrometric analysis. The major metabolite identified by HPLC with UV detection of the extracts was N-isopropyl-p-formylbenzamide; this was identified by comparison of its retention time with that of a synthesized standard. This identification was further corroborated by HPLC/thermospray mass spectrometry (LC/MS). Analysis of the extracts by LC/MS also showed the presence of a closely eluting peak that had a protonated molecular ion at m/z 207. This new metabolite was identified as N-isopropyl-(benzene-1,4-bis-carboxamide) by 1H NMR and gas chromatography/ion trap mass spectrometry. This metabolite is postulated to arise from breakage of the N-N bond in the hydrazine portion of the molecule. Reconstructed ion (m/z 236) current profiles from the analysis of the cell extracts indicated that there was only a trace amount of methylazoxyprocarbazine left after a 72-hr incubation. Interestingly, a peak with the same molecular weight as the parent compound (methylazoxyprocarbazine) was observed in the cellular incubations and also in extracts of control incubations in which methylazoxyprocarbazine was incubated in medium without cells. This unknown was silylated and identified as a hydroxyazo compound by an ion trap mass spectrometer operated under both single and multiple-stage mass analysis. Formation of this decomposition product appears to involve a novel intramolecular rearrangement of methylazoxyprocarbazine in solution. This pathway may be responsible for the formation of the ultimate cytotoxic species by chemical decomposition of procarbazine.

Non-enzymatic activation of procarbazine to active cytotoxic species.

The cellular cytotoxicity of procarbazine is thought to result from bioactivation of the parent compound through reactive intermediates to an ultimate alkylating species. Procarbazine is converted initially to azoprocarbazine, which is then N-oxidized through a cytochrome P-450-mediated process to a mixture of the positional isomers, benzylazoxyprocarbazine and methylazoxyprocarbazine. In order to define the bioactivation events that lead to the cytotoxic species, the in vitro cytotoxicities of the purified azoxy isomers as well as of the parent compound, procarbazine, were evaluated with the human leukemia cell line, CCRF-CEM. The methylazoxy isomer was found to be the most active species. Procarbazine inhibited the growth of CCRF-CEM cells but at a concentration much higher than that required for the methylazoxy isomer. Since procarbazine must be metabolized to form the cytotoxic species, we sought to determine if the active metabolite, methylazoxyprocarbazine, was being formed in the incubations. Solutions of procarbazine incubated with and without cells at 37 degrees C were analyzed by combined liquid chromatography-mass spectrometry with a thermospray interface. The azoxy metabolites of procarbazine appeared rapidly in cellular incubations and in the aqueous solutions without cells. More of the methylazoxy isomer was formed initially, but by 72 hr the benzylazoxy isomer was the predominant species. Thus, in these studies it appears that procarbazine was benzylazoxy isomer was the predominant species. Thus, in these studies it appears that procarbazine was non-enzymatically oxidized to the two azoxyprocarbazine isomers and that the methylazoxy compound was the most cytotoxic to CCRF-CEM cells.

Isolation of a mercapturate adduct produced subsequent to glutathione conjugation of bioactivated 3-methylindole.

Bioactivation of the pneumotoxin 3-methylindole (3MI) to a methylene imine intermediate has been demonstrated previously by trapping the electrophile with glutathione in goat lung microsomal incubations. To determine whether the same bioactivation process occurs in whole animals, 3MI was administered to goats, mice, and rats, and the urinary metabolites from these three species were analyzed by HPLC for the presence of the mercapturate that would be expected as the processed and excreted form of the 3MI-glutathione adduct. The mercapturate, 3-[(N-acetylcysteine-S-yl)-methyl]indole (3MI-NAC), was identified in the urine from all three species and was isolated from rat urine for structural identification by uv, NMR, and mass spectrometry. Synthetic 3MI-NAC had uv, NMR, and chromatographic characteristics identical to the isolated metabolite. The presence of this mercapturate in the urine of treated animals unequivocally demonstrates that 3MI is bioactivated to the methylene imine in vivo and that the glutathione adduct is also formed, presumably to detoxify the methylene imine.

Bioactivation of 3-methylindole by isolated rabbit lung cells.

3-Methylindole (3MI) is a pneumotoxin that causes selective lung lesions indicative of Clara cell and alveolar epithelial cell damage in ruminants and rodents. The present study examined the cytotoxicity of 3MI to isolated rabbit Clara cells, type II alveolar epithelial cells, and alveolar macrophages. 3MI produced a dose-dependent cytotoxicity to Clara cells detectable within 1 hr of incubation at 37 degrees C which reached a maximum at 3 hr. Concentrations of 0.25 and 0.5 mM 3MI were cytotoxic to Clara cells, while type II and alveolar macrophages required 1 mM 3MI before cytotoxicity was observed. The cytochrome P450 suicide substrate inhibitor, 1-aminobenzotriazole, inhibited 3MI-induced cytotoxicity in Clara cells, type II cells, and alveolar macrophages. These observations were consistent with a cytochrome P450-mediated bioactivation of 3MI to a toxic intermediate. Studies with a trideuteromethyl analog of 3MI demonstrated a much reduced cytotoxicity to Clara cells as well as to type II cells, and macrophages. The deuterium isotope effect suggested that C-H bond breakage at the 3-methyl group is a requisite oxidative transformation in the bioactivation of 3MI to a selective lung cell cytotoxin. The selectivity of cellular cytotoxicity is probably associated with higher rates of bioactivation by Clara cell cytochrome P450 monooxygenases compared to those of type II cells and macrophages. These studies demonstrate that 3MI is bioactivated in isolated pulmonary cells without the intervention of other organs and that bioactivation requires functional cytochrome P450 enzymes.

Organ-selective switching of 3-methylindole toxicity by glutathione depletion.

A high dose (550 mg/kg) of 3-methylindole (3MI) specifically damaged pulmonary tissue in Swiss-Webster mice without causing any hepatic or renal necrosis. When a glutathione depleter, L-buthionine-(S,R)-sulfoximine (BSO, 1.0 mmol/kg), was administered to mice 3 hr before a low dose of 3-methylindole (75 mg/kg), significant renal damage was observed by histopathological examination after 4 hr. The nephrotoxicity occurred without any observable pathological damage to lung tissues. Increased doses of BSO caused dose-dependent increases in renal toxicity. A low dose of BSO (1.0 mmol/kg) caused no depletion of renal glutathione levels, a large depletion of hepatic glutathione levels (60% of control values), and much larger increases in covalent binding of [methyl-14C]3-methylindole to renal tissues (3.4-fold) than to hepatic tissues (1.5-fold) or pulmonary tissues (2.1-fold). No evidence of hepatic or pulmonary histopathological damage was observed at any dose of BSO with 75 mg/kg 3MI. These results indicate that a shift in organ selectivity of 3MI-induced toxicity from pulmonary to renal sites occurs as a result of glutathione depletion in hepatic tissues. The production of a toxic metabolite in the livers of glutathione-depleted mice that is circulated to susceptible renal cells may be the mechanism of this interesting organ-selective shift in toxicity of 3MI.

Methylazoxyprocarbazine, the active metabolite responsible for the anticancer activity of procarbazine against L1210 leukemia.

Procarbazine is a 1,2-disubstituted hydrazine derivative that is used to treat human leukemias. The anticancer activity of procarbazine results from bioactivation to reactive intermediates. It is first oxidized to azoprocarbazine and further N-oxidized to a mixture of methylazoxyprocarbazine and benzylazoxyprocarbazine isomers. In this study the azoxyprocarbazine isomers were synthesized and purified. The cytotoxic effect of the metabolites on the L1210 murine leukemia cell line were then evaluated in vitro by use of a colorimetric assay using 3-(4,5-dimethyl-thiazol-2-yl)-2,5-diphenyl-tetrazolium bromide. The results of this study showed that the methylazoxyprocarbazine isomer was the most cytotoxic metabolite (IC50, 0.2 mM). The benzylazoxy isomer had an insignificant cytotoxic effect, and a mixture of the two isomers was intermediate in effectiveness. This assay, however, could not be used to determine the cytotoxicity of procarbazine since the drug itself (not the live cells) reduced the dye. A soft-agar clonogenic assay demonstrated that procarbazine was cytotoxic only at higher concentrations (IC50, 1.5 mM) than methylazoxyprocarbazine (IC50, 0.15 mM). The effect of procarbazine and its metabolites on the survival of L1210 tumor-bearing mice was determined, and methylazoxyprocarbazine was again the most effective compound. These studies demonstrate that the methylazoxyprocarbazine metabolite is probably the major cytotoxic intermediate involved in the mechanism of anticancer action of procarbazine.

Pathology and glutathione status in 3-methylindole-treated rodents.

Light and electron microscopic studies were performed to assess the pathology induced by 3-methylindole (3MI) in Sprague-Dawley rats and Swiss-Webster mice. Rats have not been established as a susceptible species to 3MI-induced pulmonary damage, whereas mice are known to be a good model for this pneumotoxicity. Therefore, mice were used as a comparison species for pneumotoxicity studies in the rat. Rats were as susceptible to 3MI-mediated toxicity as mice. The loss of Clara cells in the bronchiolar epithelium was the major pulmonary lesion in both species. Alveolar cells in the lungs of either species were not damaged. The only other lesion in the rat was that the nasal epithelium was totally eroded in caudal areas of the sinuses. Glutathione was depleted by 3MI in pulmonary tissues of mice and rats. Maximal depletion (53% of control values) occurred in rat lung. This work demonstrates that both rodent species are susceptible to 3MI-induced pulmonary damage.

Decreased pneumotoxicity of deuterated 3-methylindole: bioactivation requires methyl C-H bond breakage.

The bioactivation of the pulmonary toxin 3-methylindole has been postulated to proceed via the formation of an imine methide. To test this hypothesis, the toxicity in mice of 3-methylindole has been compared to the toxicity of its perdeuteromethyl analog. Deuteration of the methyl group should slow the rate of production of the corresponding imine methide and diminish the toxicity of deutero-3-methylindole, if C-H bond breakage occurs prior to or during the rate-determining step. In agreement with this hypothesis, deutero-3-methylindole was synthesized and was shown to be significantly less toxic (LD50 735 mg/kg) than 3-methylindole (LD50 578 mg/kg). Both compounds produced the same lesion at the LD50 dose, bronchiolar damage and mild alveolar edema, indicating that deuteration of 3-methylindole did not change the pathologic process. However, at a much lower dose (25 mg/kg), 3-methylindole produced a mild bronchiolar lesion whereas deutero-3-methylindole did not damage lung tissue. Additionally, administration of deutero-3-methylindole caused less pulmonary edema compared to 3-methylindole, as assessed by increased wet lung weights. Finally, the depletion of pulmonary glutathione by deutero-3-methylindole was considerably slower than depletion by 3-methylindole. The electrophilic imine methide has been postulated to be the intermediate which binds with and depletes glutathione. Therefore, the evidence presented here supports the involvement of an imine methide as the primary reactive intermediate in 3-methylindole-mediated pneumotoxicity.

Separate mechanisms for procarbazine spermatotoxicity and anticancer activity.

Procarbazine causes dose-dependent decreases in sperm count after a single i.p. injection in (C57BL/6 X DBA/2)F1 male mice. Two antioxidants, N-acetylcysteine and sodium ascorbate, administered with equimolar doses of procarbazine decreased the spermatotoxicity of procarbazine. At the highest doses of procarbazine (400 mg/kg) that caused a 56% decrease in sperm count, equimolar doses of N-acetylcysteine coadministered with procarbazine caused only a 17% decrease in sperm count, and equimolar doses of ascorbate coadministered with procarbazine caused only a 13% decrease in sperm count. Thus, protection against the spermatotoxic effects of procarbazine was demonstrated with either antioxidant. The effect of the antioxidants on the chemotherapeutic efficacy of procarbazine against murine L1210 leukemia was also assessed. Procarbazine at the highest dose (600 mg/kg) increased mean survival time of mice inoculated i.p. with 1 X 10(5) L1210 leukemia cells by 31%. Simultaneous administration of equimolar doses of either N-acetylcysteine or ascorbate given with procarbazine caused no change in the increased mean survival time of tumor-bearing mice. These results indicate a decrease in the toxicity of procarbazine when coadministered with antioxidants, via decreased spermatotoxicity without changing anticancer efficacy. The results also indicate that different mechanisms are involved in the spermatotoxicity and anticancer activity of procarbazine.

Structure of the glutathione adduct of activated 3-methylindole indicates that an imine methide is the electrophilic intermediate.

Goat lung microsomes were incubated with glutathione (GSH) and 3-methylindole (3MI) to produce an adduct between GSH and an electrophilic metabolite of 3MI. The GSH-3MI adduct was purified by reverse-phase HPLC, and its structure elucidated by UV and NMR spectrometry and by thermospray LC/MS. The adduct was shown to be 3-[(glutathion-S-yl)-methyl]indole. Since nucleophilic GSH adds to the methyl position of 3MI without the incorporation of oxygen into the molecule, an epoxide metabolite is probably not the electrophilic intermediate. More likely, an imine methide intermediate, resulting from nitrogen oxidation and hydrogen abstraction from the methyl group by cytochrome P-450 monooxygenases, is the electrophilic intermediate. The imine methide electrophile is therefore proposed to be the toxic intermediate in 3MI-mediated pulmonary toxicity.

Adducts of 3-methylindole and glutathione: species differences in organ-selective bioactivation.

Lung and liver microsomes of several species were evaluated for potential to form activated metabolites of 3-methylindole (3MI). Microsomes were incubated with [14C]3MI and glutathione (GSH). Electrophilic 3MI metabolites were trapped and quantitated as GSH adducts by HPLC, and by determining the amounts of activated intermediates which became covalently bound to microsomal protein. The highest rates of 3MI-GSH adduct formation by the lung were detected in microsomes of the goat, followed in decreasing order by pulmonary microsomes from the horse, monkey, mouse, and rat, respectively. In contrast, hepatic 3MI-GSH adduct production was highest in microsomes from the rat, followed by mouse, monkey, goat, and horse microsomes, respectively. These results suggest that the species and organ-selective toxicity of 3MI are primarily caused by differences in rates of oxidative metabolism of 3MI to an electrophilic intermediate.