Identification and comparison of the urinary metabolites of [1,2,3-13C3]acrylic acid and [1,2,3-13C3]propionic acid in the rat by homonuclear 13C nuclear magnetic resonance spectroscopy.

Acrylic acid (AA) and its esters are used extensively for the production of a variety of polymers. Despite their ubiquitous nature, little has been reported on the metabolism of the parent acid. The metabolites of AA may be volatile, unstable, polar, and thus difficult to isolate. Therefore, 13C NMR was used to help identify and compare directly the urinary metabolites of both 99% 13C-enriched AA and propionic acid (PA). Male Sprague-Dawley rats received [1,2,3-13C]AA (400 mg/kg in water p.o.) or an equimolar dose of [1,2,3-13C]propionate together with a radioactive tracer, [2,3-14C]AA, or [1-14C]propionate, respectively, and excreta were collected for 72 hr. For both acids, expiration of 14CO2 was the major route of elimination of radiolabel (approximately 80%). Approximately 6% of the dose was excreted in the urine. Urine was analyzed directly using proton-decoupled 13C and two-dimensional 13C homonuclear correlated NMR spectroscopy. The urine from AA-treated rats revealed major signals, the intensity of which was time-dependent, from at least five 13C-enriched metabolites of AA. Signals have been assigned to 3-hydroxypropionic acid, N-acetyl-S-(2-carboxyethyl)cysteine, and N-acetyl-S-(2-carboxyethyl)cysteine-S-oxide by comparison with spectra of authentic standards. No unchanged AA was detected. In contrast, the spectra of urine from a propionate-treated rat revealed only a few minor 13C-enriched signals that were assigned to methylmalonic acid. No unchanged PA was detected.(ABSTRACT TRUNCATED AT 250 WORDS)