Biotransformation of aryl alkylamines by Cunninghamella bainieri

Microbial models for drug metabolism

This review describes microbial transformation studies of drugs, comparing them with the corresponding metabolism in animal systems, and providing technical methods for developing microbial models. Emphasis is laid on the potential for selected microorganisms to mimic all patterns of mammalian biotransformations and to provide preparative methods for structural identification and toxicological and pharmacological studies of drug metabolites.

Microbial transformation of 3,4-methylenedioxy-N-methylamphetamine and 3,4-methylenedioxyamphetamine

The biotransformation of 3,4-methylenedioxy-N-methylarnphetamine (MDMA) and 3,4-methylenedioxyamphetamine (MDA) was examined in the fungus Cunninghamella echinulata. In addition to the reported mammalian metabolites (MDA, 3,4-methylenedioxybenzyl methyl ketoxime, 3,4-methylenedioxybenzyl methyl ketone) and the parent substrate, there were six novel metabolites detected. N-Acetyl-3,4-methylenedioxyamphetamine (NAcMDA) was unequivocally identified and three unidentified metabolites related to NAcMDA were also detected. N-Acetyl-3,4-methylenedioxy-1-phenyl-1-hydroxy-2-aminopropane was tentatively identified as a metabolite of MDMA. The only metabolite of MDA identified was NAcMDA. Two metabolites related to MDA remain unidentified.Key words: Cunninghamella, amphetamine, biotransformation, 3,4-methylenedioxy-N-methylamphetamine, 3,4-methylenedioxyamphetamine.

Fungal transformations of antihistamines: metabolism of brompheniramine, chlorpheniramine, and pheniramine to N-oxide and N-demethylated metabolites by the fungus Cunninghamella elegans

1. Two strains of the filamentous fungus Cunninghamella elegans (ATCC 9245 and ATCC 36112) were screened for their ability to metabolize three alkylamine-type antihistamines; brompheniramine, chlorpheniramine and pheniramine. 2. Based on the amount of parent drug recovered after 168 h of incubation, C. elegans ATCC 9245 metabolized 60, 45 and 29% of brompheniramine, chlorpheniramine and pheniramine added respectively. The results from strain ATCC 36112 were essentially identical to those of strain ATCC 9245. 3. The metabolic products of N-oxidation and N-demethylation were isolated by reversed-phase hplc and identified by analysing their mass and proton nmr spectra. For all three antihistamines, the mono-N-demethylated metabolite was produced in the greatest amounts. The chloro- and bromo-substituents appeared not to affect the route of metabolism but did influence the relative amounts of metabolites produced. 4. Circular dichroism spectra of the metabolites and the unmetabolized parent antihistamines showed each to be a racemic mixture of the (+) and (-) optical isomers. In addition, comparison of the metabolism of racemic chlorpheniramine to that of optically pure (+) chlorpheniramine showed no significant differences in the ratios of metabolites produced. There was therefore no metabolic stereoselectivity observed by the fungal enzymes.

Microbial metabolism of 2-arylpropionic acids: chiral inversion of ibuprofen and 2-phenylpropionic acid

The metabolism of (R,S)-ibuprofen has been investigated in 24 microbial cultures. Of these Cunninghamella elegans, Mucor hiemalis, and Verticillium lecanii catalyzed the oxidation of the drug to 2-[4-(2-hydroxy-2-methylpropyl)phenyl]propionic acid, a known mammalian metabolite. The extent of metabolism was greatest with V. lecanii, with some 47% of the substrate being consumed over a 7-day incubation period. Enantiomeric analysis indicated stereoselective metabolism of (R)-ibuprofen, the enantiomeric composition of the residual substrate being R/S = 0.25. Following a preparative scale incubation of (R,S)-ibuprofen with V. lecanii, in which the reaction was allowed to go to completion, the metabolite was found to be predominantly of the S-configuration (S/R = 2.1), suggesting that chiral inversion of either the drug and/or the metabolite had taken place. Analysis of extracts following incubation of (R,S)-, (R)-, and (S)-2-phenylpropionic acid with V. lecanii, for 21 days, indicated that chiral inversion of the (R)-enantiomer to its optical antipode had taken place. The results of these investigations indicate that microorganisms, in addition to mammals, are able to mediate the chiral inversion of 2-arylpropionic acids. This observation may have implications for the preparation of optically pure 2-arylpropionic acids.

Biotransformation of tri-substituted methoxyamphetamines by Cunninghamella echinulata

1. Four trimethoxyamphetamine analogues were incubated with the filamentous fungus Cunninghamella echinulata. 2. 2,4,5-Trimethoxyamphetamine and 2,5-dimethoxy-4-ethoxyamphetamine were poorly metabolized by C. echinulata ATCC 9244 and C. echinulata var. elegans ATCC 9245. 2,5-Dimethoxy-4-(n)-propoxyamphetamine was mainly metabolized through N-acetylation and O-dealkylation with minor amounts of several aliphatic hydroxylation metabolites formed. 2,5-Dimethoxy-4-methylthioamphetamine was extensively metabolized to the corresponding sulphoxide. 3. 2,5-Dimethoxy-4-methylthioamphetamine metabolism was inhibited by ethanol and quinidine. Sparteine did not inhibit the formation of the sulphoxide and may have shunted the substrate through alternate metabolic pathways. 4. Incubation conditions can affect the rate and extent of fungal biotransformation of 2,5-dimethoxy-4-methylthioamphetamine, and influence dextrose utilization, ammonia formation and pH.

In vitro assessment of cytotoxicity and biotransformation of propranolol in Cunninghamella echinulata

1. Biotransformation studies with five concentrations of racemic propranolol were conducted using the filamentous fungus Cunninghamella echinulata ATCC 9244. 2. The rate of formation and subsequent disappearance of a new major metabolite, 8-hydroxypropranolol, was dose-dependent. Desisopropylpropranolol and 4-hydroxypropranolol were also formed. 4-Hydroxypropranolol was the major fungal metabolite in earlier studies. 3. Propranolol exerted a dose-dependent response on biotransformation, fungal growth, dextrose utilization, ammonia formation and incubation broth pH. Determination of dextrose utilization and incubation broth pH would provide reliable, cost-effective and convenient alternative methods for cytotoxicological evaluation.

Use of a microbial model for the determination of drug effects on cell metabolism and energetics: study of citrulline-malate

Euglena gracilis can be used as a microbial model to study the effect of drugs on lactate metabolism and gluconeogenetic synthesis. The cell growth and metabolism have been characterized in a 33 mM lactate medium, non-supplemented or supplemented by dl-malate or by l-citrulline alone or by the compound formed by the stoichiometric combination of the two components: the citrulline-malate (Stimol). The malate of the complex accelerated the ammonium disappearance, while the citrulline facilitated the lactate consumption. A synergistic action of the complex, by comparison with the additive effects of the individual components, on most of the parameters studied was detected. A remarkable resistance to anoxia, and a quicker recovery under aeration of the cells supplemented with CM, were evident: after carbonation for 2 min the total nucleotides in the medium were increased by 44 per cent with an unchanged energy charge; and after a prolonged (20 min) anoxia followed by an aeration, the capacities of the cells to synthesize ATP in the presence of excesses of both ADP and phosphate were two-fold higher in Stimol treated cells than in control.

Biotransformation of 2-, 3-, and 4-methoxy-amphetamines by Cunninghamella echinulata

1. Three methoxyamphetamine analogues have been incubated with Cunninghamella echinulata under different environmental and nutrient conditions. 2. The biotransformation of 4-methoxyamphetamine was inhibited by cobalt; the carbon source and other trace metals had no effect. The rate of biotransformation of 4-methoxyamphetamine and formation of 4-hydroxyamphetamine was greater in cultures incubated on 30 degrees angle brackets rather than flat. 3. Carbon monoxide, ethanol and quinidine had a significant effect on methoxyamphetamine metabolism. 4. Metabolism was influenced by the position of the methoxy side-chain and substrate concentration. In day 7 samples the relative order for biotransformation was 3- greater than 4- greater than 2-methoxyamphetamine. 5. O-Demethylation was the major metabolic route in the biotransformation of 4-methoxyamphetamine but occurred to a lesser extent with 3-methoxyamphetamine, and was only a trace pathway with 2-methoxyamphetamine. N-acetylation was a trace pathway.

Use of microorganisms for the study of drug metabolism: an update

The use of microorganisms as tools in the study of drug metabolism appears to be gaining popularity. The selected examples cited here provide additional evidence of the utility of these systems as alternative in vitro models for studying drug metabolism in humans. However, as was noted earlier, this model, nor any other in vitro model system could ever replace animals in biomedical research. However, it is apparent from the numerous examples cited here and in the previous review of this area that microorganisms are a reliable, reproducible alternative to small animals as predictive models in drug metabolism studies. The continuing development of techniques that reduce the use of animals in research is encouraged and this procedure appears to be gaining more widespread acceptance for such use.

Microbial models of mammalian metabolism: biotransformations of phenacetin and its O-alkyl homologues with Cunninghamella species

1. The analgesic compound phenacetin and its O-alkyl homologues were metabolized by Cunninghamella elegans to yield the O-dealkylation product paracetamol (acetaminophen), and metabolites resulting from omega-1 hydroxylation and further oxidations. 2. Structural identification was based upon physical, spectral and chromatographic comparisons of isolated metabolites with synthetic standards generated by alkylation of paracetamol with the appropriate alkyl halide, epoxide, or alpha,beta-unsaturated ketone. 3. The rank order of O-dealkylation within the homologous series based upon either substrate disappearance or phenol formation was found to be ethyl greater than isopropyl greater than n-propyl greater than n-butyl greater than methyl.

Fungal metabolism of 4-substituted amphetamines

1. rac.-4-Ethoxyamphetamine was incubated with 14 different yeast and fungal microorganisms. 4-Hydroxyamphetamine was the major metabolite; traces of N-acetyl-4-ethoxyamphetamine were also detected. 2. The major fungal (Cunninghamella) metabolite of 4-propoxyamphetamine and 4-benzyloxyamphetamine was 4-hydroxyamphetamine. The major metabolites of 4-methoxyamphetamine were N-acetyl-4-methoxyamphetamine and 4-hydroxyamphetamine. 3. Acetoin derivatives were formed when alkoxyamphetamine substrates were incubated in the presence of various fungi and yeasts. 4. The findings indicate that Cunninghamella echinulata may be a useful microbial model for drug disposition and interaction studies.