The atropisomers of 2,2',3,4,6-pentachlorobiphenyl (PeCB), 2,2',3,4,4',6-hexachlorobiphenyl (HeCB), and 2,2',3,3',4,4',6,6'-octachlorobiphenyl (OCB) were studied in the chick embryo hepatocyte culture to determine if chirality plays a role in the recognition events associated with the induction of cytochromes P450 and the accumulation of uroporphyrin (URO). Concentration-related induction of cytochrome P450 content, ethoxyresorufin-O-deethylase (EROD) and benzphetamine N-demethylase (BPDM) activities were measured. The rank order of potency for total cytochrome P450 induction was HeCB greater than OCB greater than or equal to PeCB. The (+)- and (-)-enantiomers of PeCB and OCB were of equal potencies as inducers of cytochromes P450, whereas the (+)-HeCB was greater than the (-)-HeCB. HeCB was a much more potent inducer of EROD activity than was either PeCB or OCB. EROD activity was induced to a much greater extent by the (+)-enantiomers of all compounds, with the (-)-enantiomers of PeCB and OCB being inactive. BPDM activity was induced by all three compounds in the order of OCB greater than or equal to HeCB greater than PeCB. The (-)-enantiomers were more potent inducers of BPDM activities than were the (+)-enantiomers, except for HeCB, in which the (+)- was more potent than the (-)-enantiomer. Analysis of porphyrin accumulation in cultures treated with delta-aminolevulinic acid revealed that (+)-HeCB caused the greatest percent URO accumulation, which also correlated with the greatest increase in EROD activity. All other enantiomers caused up to 47% URO accumulation, which did not correlate with an increase in EROD activity.

Animals↗

PubMedDate not supplied

Biotransformation of olivetol by Syncephalastrum racemosum.

A study of the biotransformation of olivetol by Syncephalastrum racemosum ATCC 18192 has led to the isolation of three metabolites, which were identified as 4'-hydroxy-olivetol, 3-(3,5-dihydroxyphenyl)-1-propanol, and 3-(3,5-dihydroxyphenyl)-1-propanoic acid. The structures of the isolated metabolites were deduced by comparison of their spectral properties (pmr, cmr, ms) with those of olivetol. The absolute configuration of 4'-hydroxy-olivetol was determined to be R by the Horeau partial resolution method. Biotransformation of olivetol therefore appears to occur by a subterminal oxidation process.

Biotransformation↗

PubMedDate not supplied

Models of retinoid metabolism: microbial biotransformation of alpha-ionone and beta-ionone.

Retinoic acid [1] and its analogues (retinoids) have recently generated interest as possible chemopreventive agents, but 1 is rapidly metabolized to many known as well as unknown products. Recently, microbial models have been employed for the study of mammalian metabolism. In this study two fungi, Aspergillus niger ATCC 16888 and Cunninghamella blakesleeana ATCC 8688a, were found to biotransform beta-ionone [2] and alpha-ionone [8] and may serve as models for the mammalian metabolism of retinoic acids. A. niger yielded oxidized metabolites, whereas C. blakesleeana gave products most of which were both oxidized and reduced. Methods developed here should prove amenable to studies utilizing 1 as the substrate for biotransformation.

Aspergillus niger↗

PubMedDate not supplied

A new strategy for the synthesis of polychlorinated biphenyl metabolites.

A general and high-yielding synthetic route is presented by which a variety of chlorinated dihydroxybiphenyl metabolites may be synthesized. These synthetic standards will permit the investigation of novel pathways of polychlorinated biphenyl activation. The biphenyldiols were synthesized via palladium-catalyzed cross-coupling of dimethoxyphenylboronic acids with aryl bromides in the presence of a base. The formed dimethoxybiphenyls were demethylated using boron tribromide to yield the chlorinated dihydroxybiphenyls. These compounds were characterized by IR, NMR, and GC/MS.

Polychlorinated Biphenyls↗

PubMedDate not supplied

Identification of catechol and hydroquinone metabolites of 4-monochlorobiphenyl.

Polychlorinated biphenyls (PCBs) may be metabolically activated to electrophiles, which bind to proteins and nucleic acids. One activation scheme involves the formation of reactive arene oxide intermediates during cytochrome P450-catalyzed hydroxylation. We propose a second activation pathway whereby PCB catechol and hydroquinone metabolites may be oxidized to reactive semiquinones and/or quinones. By employing 4-monochlorobiphenyl (4-MCB) as a model substrate and liver microsomes from rats treated with phenobarbital and 3-methyl-cholanthrene, five monol and three diol metabolites were identified. The major metabolite was 4-chloro-4'-monohydroxybiphenyl, followed by, in decreasing order, 4-chloro-3',4'-dihydroxybiphenyl, unknown B (a monol), 4-chloro-2',3'-dihydroxybiphenyl, 4-chloro-3'-hydroxybiphenyl, 4-chloro-2',5'-dihydroxybiphenyl, unknown A (a monol), and 4-chloro-2'-monohydroxybiphenyl. A trace of a dihydrodiol was detected by GC/MS. To elucidate the source of the diols, 4-MCB and the synthetic monol metabolites 4-chloro-2'-/-3'-/-4'-monohydroxybiphenyls were each employed as substrates in incubations with microsomes from rats treated with phenobarbital, 3-methylcholanthrene, or both inducers. The three diol metabolites were all produced from 4-MCB in incubations with microsomes from 3-methylcholanthrene-treated rats, but incubations with microsomes from phenobarbital-treated rats did not yield detectable amounts of 4-chloro-2',3'-dihydroxybiphenyl. 4-Chloro-2',3'-dihydroxybiphenyl was only found as a product of 4-chloro-2'-monohydroxybiphenyl. The 4-chloro-2',5'-dihydroxybiphenyl was found in extracts of incubations with 4-chloro-2'- and -3'-monohydroxybiphenyls, while the 4-chloro-3',4'-dihydroxybiphenyl was the only product found from 4-chloro-3'- and -4'-monohydroxybiphenyls. No other chlorinated diols were detected by GC/MS. These data suggest that the major route of biosynthesis of the diols was via a second hydroxylation step and not aromatization of dihydrodiols derived from primary arene oxides. We propose a scheme for the in vitro synthesis of the catechol and hydroquinone metabolites, which may be precursors for electrophilic semiquinone or quinone products with the potential for cytotoxic and genotoxic effects.

Animals↗

PubMedDate not supplied

Detection of PCB adducts by the 32P-postlabeling technique.

The purpose of this study was to determine whether lower chlorinated biphenyls would be bioactivated to electrophilic metabolites by microsomes alone or in combination with peroxidase. Monochloro- and dichlorobiphenyls were incubated with liver microsomes of rats treated with phenobarbital and beta-naphthoflavone, an NADPH-regenerating system, and deoxyguanosine 3'-monophosphate (dGp). The resultant adducts were analyzed by 32P-postlabeling either following microsomal incubation alone ("preoxidized") or coupled with subsequent oxidation with horseradish peroxidase/H2O ("oxidized"). The incubation of 4-monochlorobiphenyl (4-MCB) resulted in the formation of two minor adducts by microsomal activation alone. However, the oxidized sample showed two additional major adducts. Formation of the latter adducts was almost completely (> 80%) inhibited when the oxidation reaction was performed in the presence of ascorbic acid. The other test mono- and dichlorobiphenyls also formed 1-3 major adducts. Compared with microsomal activation alone, these adducts were enhanced after the oxidation reaction or detected only in the oxidized samples. These data suggest that (1) some adducts of the lower chlorinated biphenyls are derived from arene oxides and (2) many adducts may be formed by metabolism of the parent compounds to catechol and p-hydroquinone species, which are oxidized to semiquinones and/or quinones. The involvement of quinones and/or semiquinones was supported by UV/vis spectroscopic measurements, which showed that metabolites of 4-MCB can be oxidized to products with spectra characteristic of quinones. These data raise the possibility that lower chlorinated biphenyls may be genotoxic and may explain the fact that commercial polychlorinated biphenyl mixtures are complete rodent carcinogens.

Animals↗

PubMedDate not supplied

Metabolic activation of PCBs to quinones: reactivity toward nitrogen and sulfur nucleophiles and influence of superoxide dismutase.

Polychlorinated biphenyls (PCBs) may undergo cytochrome P-450-catalyzed hydroxylations to form chlorinated dihydroxybiphenyl metabolites. When the hydroxyl groups are ortho or para to each other, oxidation to a quinone may be catalyzed by peroxidases present within the cell. In order to study the reactivity of PCB-derived quinones, selected chlorophenyl 1,2- and 1,4-benzoquinones were synthesized and characterized, including their reduction potentials against a saturated calomel electrode. Two quinones, 4-(4'-chlorophenyl)-1,2-, and 4-(3',4'-dichlorophenyl)-1,2-benzoquinone, were obtained via the oxidation of the corresponding dihydroxybiphenyls with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone. Six 1,4-benzoquinones were synthesized via the Meerwein arylation: 2-(2'-chlorophenyl)-1,4-, 2-(3'-chlorophenyl)-1,4-, 2-(4'-chlorophenyl)-1,4-, 2-(2',5'-dichlorophenyl)-1,4-, 2-(3',4'-dichlorophenyl)-1,4-, and 2-(3',5'-dichlorophenyl)-1,4-benzoquinone. As a model study, the rate of reactivity of 2-(4'-chlorophenyl)-1,4-benzoquinone toward the nitrogen nucleophiles glycine, L-arginine, L-histidine- and L-lysine was determined under pseudo-first-order conditions at pH 7.4. The rate constants ranged from 0.45 to 0.75 min-1 M-1. Higher rates were obtained under conditions of higher pH. Two reaction products were identified as the 5- and 6-ring addition products in the ratio of 1:4. In contrast, the reaction of 2-(4'-chlorophenyl)-1,4-benzoquinone with the sulfur nucleophiles glutathione or N-acetyl-L-cysteine was instantaneous. The major product of the reaction of glutathione with 2-(4'-chlorophenyl)-1,4-benzoquinone was also the 6-ring addition product. The hydroquinone thioether could be enzymatically reoxidized to the quinone thioether. Also, the influence of atmospheric oxygen and superoxide dismutase on the rates of the following horseradish peroxidase/H2O2-catalyzed oxidations was investigated: 3,4-dichloro-2',5'-dihydroxybiphenyl to 2-(3',4'-dichlorophenyl)-1,4-benzoquinone and 3,4-dichloro-3',4'-dihydroxybiphenyl to 4-(3',4'-dichlorophenyl)-1,2-benzoquinone. While the presence or absence of atmospheric oxygen did not alter the rates of the oxidation reactions, the presence of superoxide dismutase significantly increased the rates of both oxidation reactions, having the greater effect on the oxidation of the 1,4-hydroquinone. These data show that PCB-derived quinones react with both nitrogen and sulfur nucleophiles of the cell and may explain, in part, the toxic effects of individual PCBs and PCB formulations, such as glutathione depletion, oxidative stress, and cell death.

Amino Acids↗

PubMedDate not supplied

Effect of nutritional obesity on the induction of CYP2B enzymes following phenobarbital treatment.

Human obesity is associated with a number of pathophysiologic processes, such as fatty infiltration and fibrosis of the liver. Although obesity has been shown to alter the metabolism of various xenobiotics, its effect on hepatic cytochromes P-450 is not known. In this study, the overfed rat was used as a model for examining the influence of obesity on the expression and regulation of hepatic cytochrome P-450 2B1/2B2. Sprague-Dawley rats were fed either a standard diet or an energy-dense diet for 32 weeks. The energy-dense diet resulted in a significant increase in body weight, serum triglyceride levels, and liver lipid content. Obesity did not influence baseline levels of spectral cytochrome P-450 content. Similar baseline activities of CYP2B1/2B2 (16 beta-testosterone hydroxylase and pentoxyresorufin O-dealkylation)--comparative protein levels of CYP2B1/2B2 (Western blot), and mRNA (slot blot)--were found in rats fed either diet. Half of the animals in each group were given 20 mg phenobarbital (intraperitoneal injection)/animal every 12 hr for three consecutive days. This resulted in similar phenobarbital plasma concentrations in both groups. Phenobarbital treatment increased the concentrations of cytochrome P-450 in both groups to the same extent. However, greater CYP2B1/2B2 activity was found in control rats following phenobarbital administration, whereas the amount of protein and mRNA was similar in each treated group. In conclusion, obesity did not affect the regulation of CYP2B1/2B2 enzymes. However, changes in the lipid environment associated with obesity may have affected the activity of these proteins.

Animals↗

PubMedDate not supplied

Disposition of tablet and capsule formulations of digoxin in the elderly.

STUDY OBJECTIVE: To compare digoxin tablets and liquid-filled capsules with respect to excretion of the drug and its metabolites in urine and feces at steady state. DESIGN: A randomized, crossover trial, each period lasting 3 weeks, with no washout period. SETTING: A university hospital. PATIENTS: Six patients, five of whom were elderly, with histories of gastrointestinal disorders, such as hypochlorhydria, intestinal bacterial overgrowth, and inflammatory bowel disease. INTERVENTIONS: The patients received digoxin once/day in either tablet or capsule form for 3 weeks, and then were switched to the other formulation. Total urinary and fecal excretion from the last 3 days of each regimen were analyzed for the drug and metabolites. MEASUREMENTS AND MAIN RESULTS: No statistically significant differences were found between tablets and capsules in recovery of digoxin or its metabolites in urine or feces (p = 0.05). One subject had a 4-fold increase in urinary drug excretion and 50% decrease in fecal excretion after taking the capsules compared with tablets. Intersubject variability in extent and type of metabolite excretion was greater than intrasubject variability. CONCLUSIONS: Fecal analyses may be an accurate way to classify patients as formers of digoxin reduction products.

Aged↗

PubMedDate not supplied

Two metabolites from Aspergillus flavipes.

Two novel fungal metabolites, N-benzoyl-L-phenylalaninol (1a) and asperphenamate (2) were isolated from the culture filtrate and mycelium of Aspergillus flavipes ATCC 11013. N-benzoyl-L-phenylalaninol was identified by direct comparison with an authentic sample. The structure of asperphenamate is proposed as (S)-N-benzoyl-phenylalanine-(S)-2-benzamido-3-phenyl propyl ester, based on chemical and spectroscopic evidence.

Aspergillus↗