The disposition and metabolism of acrylic acid and ethyl acrylate in male Sprague-Dawley rats

Abstract

Following oral dosing of [2,3- 14C]acrylic acid (AA; 4, 40, or 400 mg/kg) and [2,3- 14C]ethyl acrylate (EA; 2, 20, or 200 mg/kg), the dosed radioactivity was rapidly excreted, with 50–75% of the dose for both compounds eliminated within 24 hr. The primary excretory metabolite for both compounds is carbon dioxide, accounting for 44–68% of the dose. HPLC analysis of the urine of AA- and EA-dosed animals indicated the presence of 3-hydroxypropionic acid. The detection of this metabolite suggests the incorporation of AA into propionic acid metabolism and may explain the rapid evolution of carbon dioxide from AA and EA. HPLC analysis of urine from EA-dosed rats revealed the presence of two metabolites derived from glutathione conjugation, N-acetyl- S-(carboxyethyl)cysteine and N-acetyl- S-(carboxyethyl)cysteine ethyl ester. The excretion of the N-acetyl cysteine derivatives of EA, expressed as a percentage of the dosed compound, decreased in a dose-dependent manner that may be attributed to the depletion of glutathione in organs primarily responsible for glutathione conjugation. No significant decrease in hepatic nonprotein sulfhydryl (NPSH) content was observed following oral dosing with EA at 2–200 mg/kg. However, the depletion of NPSH content at the dosing site, forestomach, and glandular stomach, decreased significantly between 0.02 and 0.2% EA in the dose solution (2 and 20 mg/kg). This observation would suggest that the dosing site represents a significant site of conjugation for relatively low doses of EA. Treatment with the carboxylesterase inhibitor, tri- o-cresyl phosphate (TOCP), 18 hr prior to acrylate dosing potentiated the depletion of hepatic nonprotein sulfhydryls, emphasizing the dominance of hydrolysis as a systemic detoxifying mode in this species. In contrast to EA, AA did not significantly decrease NPSH content in the liver, blood, or forestomach at oral doses of <8% AA in the dose solution (400 mg/kg), although a significant depletion of NPSH was observed in the glandular stomach at doses >0.08% (4 mg/kg). No conjugation involving the double bond of AA could be detected in in vitro reactions with glutathione or in the in vivo metabolites, suggesting a secondary effect of AA on NPSH content in these organs. The weights of the forestomach and glandular stomach increased with AA dose, reflecting gross edema and inflammation. With EA this effect on organ weight was only demonstrated in the forestomach, and the response was increased when hydrolysis of EA was inhibited with TOCP. The effect of AA or EA on stomach weight and NPSH content may be attributed to the concentration of these local irritants in the dose solution at the site of dosing.