Abstract

Background and aims: Butyrate oxidation by colonocytes is impaired in ulcerative colitis. This study examined the activity of enzymes involved in butyrate oxidation in ulcerative colitis.

Methods: Activities of mitochondrial acetoacetyl coenzyme A (CoA) thiolase, crotonase and β-hydroxy butyryl CoA dehydrogenase were estimated spectrophotometrically in rectosigmoid mucosal biopsies from patients with ulcerative colitis and Crohn’s colitis, and control subjects undergoing colonoscopy for colon cancer or rectal bleeding.

Results: The activity of mitochondrial acetoacetyl CoA thiolase was decreased by 80% in ulcerative colitis (3.4 (0.58) μmol/min/g wet weight, n = 30) compared with control (16.9 (3.5), n = 18) and with Crohn’s colitis (17.6 (3.1), n = 12) (p<0.0001). The activity of two other mitochondrial butyrate oxidation enzymes—crotonase and β-hydroxy butyryl CoA dehydrogenase—as well as of cytoplasmic thiolase was normal in ulcerative colitis. Mitochondrial thiolase activity in ulcerative colitis did not correlate with clinical, endoscopic or histological indices of disease severity. Mitochondrial thiolase activity was reduced in the normal right colon mucosa of patients with left-sided ulcerative colitis. Enzyme kinetic studies revealed a lowered V_max, suggesting inhibition at a site distinct from the catalytic site. Reduced thiolase activity in ulcerative colitis was returned to normal by exposure to 0.3 mM β-mercaptoethanol, a reductant. Using normal colon mucosal biopsies, redox modulation of thiolase activity by hydrogen peroxide, a mitochondrial oxidant, could be shown. A significant increase in hydrogen peroxide formation was observed in ulcerative colitis biopsies.

Conclusion: A defect of mitochondrial acetoacetyl CoA thiolase occurs in ulcerative colitis. Increased reactive oxygen species generation in mitochondria of epithelial cells in ulcerative colitis may underlie this defect.