Formation of catechols via removal of acid side chains from ibuprofen and related aromatic acids

Abstract

Although ibuprofen [2-(4-isobutylphenyl)-propionic acid] is one of the most widely consumed drugs in the world, little is known regarding its degradation by environmental bacteria. Sphingomonas sp. strain Ibu-2 was isolated from a wastewater treatment plant based on its ability to use ibuprofen as a sole carbon and energy source. A slight preference toward the R enantiomer was observed, though both ibuprofen enantiomers were metabolized. A yellow color, indicative of meta-cleavage, accumulated transiently in the culture supernatant when Ibu-2 was grown on ibuprofen. When and only when 3-flurocatechol was used to poison the meta-cleavage system, isobutylcatechol was identified in the culture supernatant via gas chromatography-mass spectrometry analysis. Ibuprofen-induced washed-cell suspensions also metabolized phenylacetic acid and 2-phenylpropionic acid to catechol, while 3- and 4-tolylacetic acids and 2-(4-tolyl)-propionic acid were metabolized to the corresponding methyl catechols before ring cleavage. These data suggest that, in contrast to the widely distributed coenzyme A ligase, homogentisate, or homoprotocatechuate pathway for metabolism of phenylacetic acid and similar compounds, Ibu-2 removes the acidic side chain of ibuprofen and related compounds prior to ring cleavage.

FIG. 1.

The enantiomeric fraction (EF) of R-ibuprofen (○) and overall ibuprofen concentration (⧫) in a growing Ibu-2 culture in which ibuprofen was the sole carbon and energy source. The concentrations of both ibuprofen enantiomers were determined by chiral CE analysis. The error bars represent standard deviations.

FIG. 2.

Proposed pathway for the metabolism of ibuprofen by Ibu-2. Metabolites b to d were all detected via GC-MS. b, isobutylcatechol; c, 5-formyl-2-hydroxy-7-methylocta-2,4-dienoic acid; d, 2-hydroxy-5-isobutylhexa-2,4-dienedioic acid.

FIG. 3.

Average final culture density (n = 3) as measured by optical density (OD) at 600 nm when Ibu-2 was inoculated in liquid MSM culture containing ibuprofen or its analogs [ipf, ibuprofen; paa, phenylacetic acid; 2ppa, 2-phenylpropionic acid; 3taa, 3-tolylacetic acid; 4taa, 4-tolylacetic acid; 2(4t)pa, 2-(4-tolyl)propionic acid]. The error bars represent standard deviations.