Biomedical subjects

N Castagnoli

Publications and source records attributed to N Castagnoli.

At least 181 records · Page 10Linked to original sources

PubMedDate not supplied

Metabolic studies on phencyclidine: characterization of a phencyclidine iminium ion metabolite.

Studies on the metabolic bioactivation of the psychotomimetic amine phencyclidine have been pursued through the characterization of a new metabolite which is formed via initial cytochrome P-450 catalyzed oxidation of the parent drug to the corresponding iminium species. CI mass spectrometric and diode array UV and 1H NMR spectral analyses provided evidence for the conjugated amino enone compound, 1-(1-phenylcyclohexyl)-2,3-dihydro-4-pyridone. Confirmation of the proposed structure was achieved by comparing the 1H NMR and high-resolution EI mass spectral properties of the metabolic isolate with the corresponding spectra of an authentic synthetic sample. Possible intermediates involved in the formation of the dihydropyridone metabolite from the phencyclidine iminium ion are discussed in terms of structural analogies to reactive intermediates formed in the bioactivation of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

Animals↗

PubMedDate not supplied

Metabolic studies on the nigrostriatal toxin MPTP and its MAO B generated dihydropyridinium metabolite MPDP+.

The metabolic fates of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and its two-electron oxidation product, the 1-methyl-4-phenyl-2,3-dihydropyridinium species (MPDP+), have been examined in mouse brain and liver tissue fractions. Incubations of MPTP (50 microM and 1 mM) with mouse brain preparations result in the expected MAO B catalyzed formation of MPDP+. The four-electron oxidation product, the 1-methyl-4-phenyl-pyridinium species (MPP+), was the only other metabolite detected. The oxidation of 50 microM MPDP+ to MPP+ in the same preparations appears to be mediated by unidentified components present in membrane containing structures. The behavior of MPTP in mouse liver subcellular fractions is considerably more complex. NADPH-supplemented liver microsomes convert MPTP to the desmethyl and N-oxide metabolites. At high (1 mM) initial concentrations of MPTP there is evidence that NADPH-dependent, pargyline-insensitive liver microsomal enzymes also catalyze the oxidation of MPTP to MPDP+. Incubations of MPDP+ with mouse liver preparations containing the cytosolic fraction led to the rapid disappearance of the substrate and the quantitative formation of a metabolic product with mass spectral and diode array UV characteristics expected for a lactam structure. Menadione, an inhibitor of the cytosolic enzyme aldehyde oxidase, inhibits the formation of this product. Unambiguous characterization of this metabolite as 1-methyl-4-phenyl-5,6-dihydro-2-pyridone was achieved by comparison of its high-resolution 1H NMR and high-resolution EI mass spectra with the corresponding spectra of a synthetic standard.(ABSTRACT TRUNCATED AT 250 WORDS)

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Liver and lung microsomal metabolism of the tobacco alkaloid beta-nicotyrine.

The in vitro metabolic fate of beta-nicotyrine has been examined in rabbit lung and liver microsomal preparations as part of an effort to characterize the formation of potentially reactive metabolic species that may contribute to the toxic properties of tobacco products. HPLC analysis revealed the formation of an unstable metabolite which displayed HPLC-MS/MS characteristics consistent with the structure 1-methyl-5-(3-pyridyl)-3-pyrrolin-2-one. Attempted synthesis of this pyrrolinone, however, resulted in the isolation of the isomeric 1-methyl-5-(3-pyridyl)-2-pyrrolin-2-one. The HPLC, diode array UV, and mass spectral characteristics of this delta 4,5-isomer proved to be identical with those of the metabolite derived from beta-nicotyrine. Studies in D2O suggest that the 2- and 3-pyrrolinones are in equilibrium in aqueous solution. The metabolite undergoes autoxidation, possibly via radical intermediates, to yield 1-methyl-5-(3-pyridyl)-5-hydroxy-3-pyrrolin-2-one.

Animals↗

PubMedDate not supplied

Studies on 4-benzyl-1-methyl-1,2,3,6-tetrahydropyridine, a nonneurotoxic analogue of the parkinsonian inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

Previous reports indicate that 4-benzyl-1-methyl-1,2,3,6-tetrahydropyridine (BMTP), the benzyl analogue of the Parkinsonian inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), is not neurotoxic in the C-57 black mouse even when administered at a dose 10 times greater than the dose of MPTP required to cause an 85% depletion of neostriatal dopamine. Intrastriatal microdialysis in the rat with the corresponding 4-benzyl-1-methylpyridinium ion BMP+ for 60 min, however, causes nerve terminal destruction similar to that observed following a 15-min perfusion with the 1-methyl-4-phenylpyridinium ion MPP+, the monoamine oxidase B (MAO-B) generated metabolite derived from MPTP. With the aid of purified beef liver MAO-B and synthetic standards, we observed the efficient and quantitative conversion of BMTP to the corresponding 2,3-dihydropyridinium intermediate BMDP+, which underwent further, but incomplete, oxidation to BMP+. These MPTP-type properties point to in vivo effects, such as pharmacokinetic parameters and/or alternative metabolic pathways, to account for BMTP's lack of neurotoxicity.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Studies on the cytochrome P-450 catalyzed ring alpha-carbon oxidation of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP).

In vitro metabolic studies have established that rat liver cytochromes P-450IIB1 and P-450IA1 but not rabbit liver cytochrome P-450IIB4 catalyze the oxidation of the Parkinsonian inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to the corresponding dihydropyridinium (MPDP+) and pyridinium (MPP+) species. Kinetic experiments with the most effective isozyme, cytochrome P-450IA1, indicate that the reaction proceeds at a moderate velocity [Vmax = 20.1 nmol/(min.nmol of P-450IA1)] and high Km (0.87 mM). Furthermore, kinetic deuterium isotope effect measurements provided DV and D(V/K) values of 2.99 and 1.04, respectively. A comparison with the corresponding values for the monoamine oxidase B (MAO-B) catalyzed reaction (4.37 and 9.35, respectively) suggests that either these enzymes catalyze the ring alpha-carbon oxidation of MPTP by different pathways or that the initial one-electron transfer to generate an aminium radical intermediate previously proposed for both enzyme systems is reversible in the case of MAO-B and irreversible in the case of cytochrome P-450IA1.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Studies on the in vitro conversion of haloperidol to a potentially neurotoxic pyridinium metabolite.

Evidence that partially oxidized piperidine derivatives such as the Parkinsonian inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) are biotransformed in a reaction catalyzed by monoamine oxidase B (MAO-B) to neurotoxic pyridinium metabolites led to studies resulting in the identification of the haloperidol-derived pyridinium metabolite in the urine of drug-treated rats. The present in vitro studies examine the metabolic pathway governing this overall four-electron oxidation. Although haloperidol and its 1,2,3,6-tetrahydropyridine dehydration product were not substrates for purified bovine liver MAO-B, both compounds were biotransformed to the pyridinium product by rat liver microsomal preparations. The dependence on NADPH and the inhibition by SKF-525A argue that one or more liver cytochrome P-450 isozymes may catalyze this transformation. Attempts to detect possible metabolic intermediates were not successful. Chemical model studies, however, suggest that the expected intermediary amino enol and dihydropyridinium species may be too unstable to isolate. The possible significance of this pathway with respect to haloperidol-induced central nervous system dysfunction is considered.

Animals↗

PubMedDate not supplied

C-formylation in the presence of rat brain mitochondria of the 2,3,4,5-tetrahydropyridinium metabolite derived from the psychotomimetic drug phencyclidine.

The 1-(1-phenylcyclohexyl)-2,3,4,5-tetrahydropyridinium metabolite derived from the psychotomimetic agent phencyclidine [1-(1-phenylcyclohexyl)piperidine] is converted to 1-(phenylcyclohexyl)-1,2,3,4-tetrahydropyridine-5-carboxaldehyde in the presence of rat brain and liver mitochondria. The C-5 formylation of synthetic 1-(1-phenylcyclohexyl)-2,3,4,5-tetrahydropyridinium perchlorate by N5-formyltetrahydrofolic acid (folinic acid) suggests that this biotransformation is mediated by a transformylation process involving this N5- or the corresponding N10-formyltetrahydrofolic acid.

Animals↗

PubMedDate not supplied

Synthesis and neurotoxicological evaluation of putative metabolites of the serotonergic neurotoxin 2-(methylamino)-1-[3,4-(methylenedioxy)phenyl] propane [(methylenedioxy)methamphetamine].

Theoretical considerations and recent experimental data have prompted an investigation of the neurotoxicological properties of the 6-hydroxydopamine analogue 2-(methylamino)-1-(2,4,5-trihydroxyphenyl)propane (5) and its possible precursor 1-[2-hydroxy-4,5-(methylenedioxy)phenyl]-2- (methylamino)propane (4), potential metabolites of the serotonergic neurotoxin MDMA. Systemic, intracerebroventricular, and intraparenchymal (intrastriatal and intracortical) administration of 4 led to no detectable alterations of hippocampal or cortical serotonin or striatal dopamine levels in the rat under conditions that caused significant biogenic amine depletions by established neurotoxins. By contrast, intraparenchymal administration of 5 caused profound depletions of dopamine and serotonin, with the former being more severely depleted than the latter. Although not conclusive, these data suggest a possible role for 5 in the mediation of MDMA's neurotoxic actions.

3,4-Methylenedioxyamphetamine↗

PubMedDate not supplied

Studies on 1,2,3,6-tetrahydropyridine derivatives as potential monoamine oxidase inactivators.

The Parkinsonian-inducing neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and close structural analogs are the only known cyclic tertiary amines with good monoamine oxidase substrate properties. In addition to its excellent substrate properties, MPTP is a mechanism-based inactivator of monoamine oxidase B (MAO-B). In an attempt to exploit the special interactions between this cyclic tertiary allylamine and MAO-B, we have initiated studies to evaluate the enzymatic and biological properties of MPTP analogs bearing functional groups which are known to mediate the metabolism-dependent inactivation of this enzyme. This paper describes the synthesis, enzyme substrate/inhibitor properties, and neurotoxic/neuroprotective properties of 1-cyclopropyl-4-phenyl-1,2,3,6-tetrahydropyridine, the corresponding acyclic secondary amine (E)-4-cyclopropyl-2-phenyl-2-butene, and 4-cyclopropyl-1-methyl-1,2,3,6-tetrahydropyridine.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Metabolic studies on haloperidol and its tetrahydropyridine analog in C57BL/6 mice.

The neuroleptic agent haloperidol (HP) is biotransformed in humans to a pyridinium metabolite, HPP+, that displays neurotoxic properties resembling those of the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-derived neurotoxic pyridinium metabolite MPP+. We report here that HP and its tetrahydropyridine dehydration product 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1,2,3,6- tetrahydropyridine (HPTP) are metabolized in vivo by the MPTP-susceptible C57BL/6 mouse to several pyridinium metabolites including HPP+ and the 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-hydroxybutyl]pyridinium species RHPP+, the pyridinium species corresponding to reduced haloperidol (RHP), a major circulating metabolite of HP. Atmospheric pressure ion-spray (API) mass spectral data also suggest the formation of fluorophenyl ring-hydroxylated derivatives of these two pyridinium metabolites. Furthermore, HPLC tracings reveal the presence of HPP+, RHPP+, and two phenolic pyridinium metabolites in brain tissue extracts of HPTP, but not HP, treated mice. The neurotoxic potential of MPTP-type pyridinium species suggests that these metabolites may contribute to some of the neurological disorders observed in humans undergoing chronic HP treatment.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Mechanistic studies on the monoamine oxidase B catalyzed oxidation of 1,4-disubstituted tetrahydropyridines.

Previous studies have established that 1-cyclopropyl-4-phenyl-1,2,3,6- tetrahydropyridine (6) is an efficient time and concentration dependent inhibitor of the flavin containing enzyme monoamine oxidase B (MAO-B). This behavior is consistent with a proposed mechanism based inactivation pathway initiated by transfer of one of the nitrogen nonbonding pairs of electrons to the oxidized flavin cofactor to generate an amine radical cation intermediate. Subsequent opening of the strained cyclopropylamine ring is thought to lead to a primary carbon centered radical that inactivates the enzyme by covalent modification of the flavin or an essential active site functionality. We now have examined the MAO-B inactivator and substrate properties of 4-benzyl-1-cyclopropyl-1,2,3,6-tetrahydropyridine (11). This compound also is a time and concentration dependent inhibitor of MAO-B. Unexpectedly, however, compound 11 proved to be an excellent MAO-B substrate. These results are discussed in terms of possible catalytic pathways for the MAO-B catalyzed oxidation of 1,4-disubstituted-1,2,3,6- tetrahydropyridines.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Probing the mechanism of bioactivation of MPTP type analogs by monoamine oxidase B: structure-activity studies on substituted 4-phenoxy-, 4-phenyl-, and 4-thiophenoxy-1-cyclopropyl-1,2,3,6-tetrahydropyridines.

Previous studies have shown that 4-benzyl-1-cyclopropyl-1,2,3,6-tetrahydropyridine is an excellent monoamine oxidase B (MAO-B) substrate (kappa cat/KM = 1538 min-1 mM-1) although the corresponding 4-phenyl analog displays MAO-B inactivating properties only. This behavior led us to speculate that the pathway for the MAO-B catalyzed oxidation of these tetrahydropyridines may not necessarily proceed via an initial single electron transfer step as proposed by others but rather through an initial alpha-carbon hydrogen atom abstraction step. In the present studies we have examined the interactions of various 4-phenoxy-, 4-phenyl-, and 4-thiophenoxy-1-cyclopropyl-1,2,3,6-tetrahydropyridine derivatives, some of which bear substituents on the phenyl ring. The 4-thiophenoxy- and all of the 4-phenoxytetrahydropyridine derivatives proved to be substrates but not inactivators of MAO-B, while several of the 4-phenyltetrahydropyridine derivatives were inactivators but not substrates. A case of particular interest was 1-cyclopropyl-4-(2-methylphenyl)-1,2,3,6-tetrahydropyridine, which displayed only substrate properties. The results are discussed in terms of two catalytic pathways, one of which involves partitioning of the proposed cyclopropylaminyl radical cation intermediate between cyclopropyl ring opening and proton loss while the second involves partitioning of the parent amine between an initial single electron transfer step, leading to cyclopropylaminyl radical cation formation and enzyme inactivation, and an initial alpha-carbon hydrogen atom abstraction step, leading to an allylic radical and dihydropyridinium product formation.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

Enzyme-catalyzed bioactivation of cyclic tertiary amines to form potential neurotoxins.

The pyridinium metabolites formed in the MAO-B catalyzed oxidation of 1-methyl-4-substituted-1,2,3,6-tetrahydropyridinyl derivatives, such as the parkinsonian inducing agent 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), cause the selective degeneration of nigrostriatal neurons, presumably by inhibition of mitochondrial respiration and depletion of ATP stores. The possibility that other partially oxidized piperidinyl derivatives also may be biotransformed to toxic pyridinium metabolites has led us to examine the metabolic fate of the neuroleptic agent haloperidol (HP) and its tetrahydropyridinyl dehydration product 4-(4-chlorophenyl)-1[4-(4-fluorophenyl)-4-oxobutyl]- 1,2,3,6-tetrahydropyridine (HPTP). In vitro metabolic studies employing tissue preparations isolated from rodents, baboons and humans have documented that cytochrome P4503A enzymes catalyze the biotransformation of both HP and HPTP to yield the corresponding pyridinium metabolite HPP+. An analogous biotransformation profile has been observed with "reduced haloperidol" (RHP), an abundant, circulating metabolite of HP formed by the stereospecific reduction of the benzoyl carbonyl group of HP. In vivo studies also have documented these pathways in humans, baboons and rodents. Although both HPP+ and RHPP+ are found in the urine and plasma of HP treated patients and HP or HPTP treated baboons, attempts to identify an MPTP-type lesion in baboons following long-term treatment with HPTP have failed. On the other hand, evidence for a lesion of the nucleus basalis of Meynert has been obtained. Additionally, the urinary excretion of abnormal organic acids and acylcarnitine conjugates suggests that HP and/or metabolites derived from HP interfere with energy production pathways.

Amines↗

PubMedDate not supplied

The role of cytochromes P-450 and flavin-containing monooxygenase in the metabolism of (S)-nicotine by rabbit lung.

Rabbit lung microsomes metabolize (S)-nicotine primarily to (S)-nicotine delta 1',5'-iminium ion, which is the precursor of (S)-cotinine, the major urinary metabolite of (S)-nicotine in mammals. (S)-Nicotine-N'-oxide and normicotine are also produced as minor metabolites. alpha-Methylbenzylaminobenzotriazole, a mechanism-based suicide inhibitor of rabbit lung cytochromes P-450 2 and 6, inhibited (S)-nicotine oxidation in parallel with inhibition of benzphetamine N-demethylation and ethoxyresorufin O-deethylation. Pretreatment of rabbits with TCDD or Aroclor 1260 had no effect and markedly inhibited (S)-nicotine oxidation, respectively, strongly suggesting that alpha-methylbenzylaminobenzotriazole inhibition was due to inactivation of rabbit lung P-450 2. Reconstitution with cytochromes P-450 2 and 5 demonstrated that only P-450 2 was active toward (S)-nicotine, yielding predominantly the iminium ion, with smaller amounts of nornicotine, (S)-nicotine N'-oxide, and an unknown metabolite also detected. The purified rabbit lung P-450 2-catalyzed oxidation of (S)-nicotine to (S)-nicotine delta 1',5'-iminium ion exhibited a Km of 70 microM and a Vmax of 1.5 min. Covalent binding of (S)-5-3H-nicotine to rabbit lung macromolecules was dependent upon rabbit lung P-450 2-catalyzed formation of the iminium ion. Antibodies raised against P-450 2 inhibited the rabbit lung microsomal metabolism of (S)-nicotine to (S)-nicotine delta 1',5'-iminium ion by almost 95%. Titration of reconstituted P-450 2 with cytochrome b5 produced a concentration-dependent inhibition of nicotine oxidase activity. Increasing the ratio of NADH to NADPH in incubations containing lung microsomes and (S)-nicotine decreased the yield of the iminium ion, confirming the inhibitory effect of cytochrome b5 on the P-450 2-catalyzed alpha-carbon oxidation reaction. NADH alone did not support the lung microsomal metabolism of (S)-nicotine. N'-oxidation of (S]-nicotine is catalyzed by purified pig liver flavin-containing monooxygenase. A number of experiments involving the use of P-450 inhibitors, titration with NADPH-cytochrome P-450 reductase antibodies, and determination of the pH-enzyme activity profile suggested that rabbit lung flavin-containing monooxygenase contributes to a small amount of the N'-oxide produced by rabbit lung microsomes. Further examination with purified flavin-containing monooxygenase isolated from rabbit lung microsomes demonstrated that (S)-nicotine is a poor substrate for this enzyme. The low yield of N'-oxide, relative to other metabolites, in rabbit lung is uncharacteristic for most mammalian tissues and presumably reflects the unusual substrate specificity of rabbit lung flavin-containing monooxygenase.

Animals↗

PubMedDate not supplied

Studies on the molecular mechanism of bioactivation of the selective nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine.

Detailed studies have been carried out on the monoamine oxidase B-catalyzed bioactivation of the nigrostriatal toxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) by rat brain mitochondrial preparations. Isolates of incubation mixtures run in H2O and D2O displayed chemical ionization mass spectral characteristics expected for the 1-methyl-4-phenyl-2,3-dihydropyridinium species MPDP+, a proposed intermediate in the biotransformation of MPTP to the 1-methyl-4-phenylpyridinium metabolite (MPP+) previously characterized in both in vitro and in vivo experiments. Further characterization of MPDP+ was achieved by comparison of the diode array UV spectral tracings of the metabolite with synthetic MPDP+ perchlorate (CIO4-) and by the isolation of a cyano adduct from mitochondrial coincubation mixtures of MPTP and sodium cyanide. MPDP+ CIO4- was shown to undergo disproportionation to MPP+ and MPTP, a reaction which suggests that this molecule may participate in redox reactions with dopamine that could lead to neurotoxic oxidation products.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗

PubMedDate not supplied

The metabolic disposition of laudanosine in dog, rabbit, and man.

This paper summarizes the results of studies of the metabolic fate of laudanosine, a major degradation product of atracurium. Intravenous bolus doses of laudanosine (1-3 mg/kg) were administered to eight dogs and two rabbits anesthetized with halothane, and urine and bile samples were collected for up to 6 hr. Urine samples also were collected from two surgical patients given repetitive doses of atracurium. Metabolites were isolated from all samples using C18-Sep Paks. Treatment of the isolates with beta-glucuronidase followed by purification of the hydrolysate by preparative liquid chromatography provided metabolite fractions which were characterized by analytical liquid chromatography and capillary gas chromatography combined with nitrogen-phosphorus and/or electron ionization-mass spectrometric detection. Reference compounds were employed as chromatographic retention time markers. O-Trimethylsilyl, O-tert-butyldimethylsilyl, and N-trifluoroacetyl derivatives of the metabolites and reference compounds were used for gas chromatographic and mass spectrometric analysis. In all three species, the following metabolites of laudanosine were identified: pseudocodamine (4'-desmethyllaudanosine), pseudolaudanine (6-desmethyllaudanosine), laudanine (3'-desmethyllaudanosine), codamine (7-desmethyllaudanosine), N-norlaudanosine, N-norpseudocodamine, and N-norpseudolaudanine.

Animals↗

PubMedDate not supplied

Phencyclidine iminium ion. NADPH-dependent metabolism, covalent binding to macromolecules, and inactivation of cytochrome(s) P-450.

The phencyclidine iminium ion (PCP-Im+), a potentially reactive 2,3,4,5-tetrahydropyridinium species, is formed by the cytochrome(s) P-450-catalyzed alpha-carbon oxidation of phencyclidine (PCP), a commonly abused psychotomimetic agent. Incubation of PCP-Im+ with liver microsomes obtained from phenobarbital-induced rabbits resulted in over 50% loss of microsomal N-demethylase activity and 30% reduction in cytochrome(s) P-450 content. These effects were concentration-dependent, irreversible, and exhibited pseudo-first order kinetics, characteristics of a mechanism-based enzyme inactivation process. Incubation of 3H-PCP-Im+ with liver microsomes resulted in covalent binding of radioactive material to macromolecules by a process that also was NADPH-dependent. PCP-Im+ was metabolized by liver microsomes in the presence of NADPH and this metabolism was inhibited by SKF 525A and carbon monoxide. HPLC analysis has led to the preliminary characterization of an oxidized metabolite of PCP-Im+ which also is formed from PCP. These results support the proposal that this tetrahydropyridinium metabolite of PCP is biotransformed in a cytochrome(s) P-450-catalyzed reaction to form reactive species capable of covalent interactions with biomacromolecules.

Animals↗

PubMedDate not supplied

Stereoselectivity of naphthalene epoxidation by mouse, rat, and hamster pulmonary, hepatic, and renal microsomal enzymes.

Previous studies have demonstrated the formation of three glutathione conjugates during the hepatic and pulmonary microsomal metabolism of naphthalene in the presence of reduced glutathione and cytosolic enzymes containing the glutathione transferases. These glutathione conjugates now have been identified by negative ion fast atom bombardment mass spectrometry, by proton NMR spectroscopy, and by chemical synthesis from the (1S,2R)- and (1R, 2S)-naphthalene 1,2-oxide enantiomers as isomeric hydroxyglutathionyldihydronaphthalene derivatives. All three glutathione adducts yielded prominent mass spectral ions at m/z 450 (M-H)-, 432 (dehydration product), and 306 (glutathionyl moiety) which were consistent with the monoglutathionyl derivatives of hydroxydihydronaphthalene. Signals in the proton NMR spectra at 3.60 and 4.95 ppm (adduct 1) and 3.60 and 4.95 ppm (adduct 2) indicated that these conjugates were diastereomers of 1-hydroxy-2-glutathionyl-1,2-dihydronaphthalene. Corresponding signals for H1 and H2 at 4.22 and 4.45 ppm for adduct 3 showed that this isomer was generated from attack of glutathione at the 1 position of the naphthalene 1,2-oxide. Incubation of synthetic (1S, 2R)-naphthalene 1,2-oxide with glutathione in the presence of glutathione transferases resulted in the formation of adducts 1 and 3 in approximately equal proportions; under identical conditions, glutathione conjugate 2 was formed from (1R, 2S)-naphthalene 1,2-oxide. Incubation of naphthalene, glutathione, and glutathione transferases with pulmonary, hepatic, or renal microsomal preparations from mouse, rat, and hamster resulted in the formation of all three glutathione conjugates. Substantial differences in the rates of formation of the individual conjugates were observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗