Tumor necrosis factor alpha reduces butyrate oxidation in vitro in human colonic mucosa: a link from inflammatory process to mucosal damage?
BACKGROUND
Butyrate produced by colonic bacterial fermentation is the main fuel for colonocytes, glucose being an alternative fuel. During inflammatory bowel disease, butyrate oxidation by colonocytes is impaired, and increased production of proinflammatory cytokines is detected in the colonic mucosa. We hypothesized that proinflammatory cytokines might reduce butyrate oxidation, and we assessed the in vitro effects of 3 proinflammatory cytokines on butyrate and glucose oxidation in colonic mucosa.


METHODS
Colonic biopsies were obtained from normal mucosa in 42 patients who underwent a colonoscopy. Biopsies were incubated in RPMI 1640 with [1-14C]-butyrate or [U-14C]-glucose with or without 1 of the 3 following proinflammatory cytokines: tumor necrosis factor alpha (TNFalpha), interleukin (IL)-1beta, and IL-6. For each cytokine, 4 different concentrations were tested in 8 subjects. Concentrations overlapped those commonly found in inflamed mucosa and had no cytotoxicity as assessed in preliminary experiments using both the trypan blue exclusion test and lactate dehydrogenase release. Production of 14CO2 (picomoles per microgram dry weight per hour) was measured after a 2-hour incubation and expressed as a percentage of the control [14C]-substrate oxidation without cytokines.


RESULTS
Whereas glucose oxidation was not affected, butyrate oxidation was reduced significantly (P < 0.05) by TNFalpha at concentrations of 100 (-26 +/- 6%), 1000 (-32 +/- 7%), and 5000 pg/mL (-34 +/- 5%). IL-1beta (0, 500, 5000, and 25,000 pg/mL) and IL-6 (0, 100, 1000, and 5000 pg/mL) did not affect either substrate oxidation.


CONCLUSIONS
TNFalpha at concentrations found in inflamed mucosa reduces butyrate oxidation in vitro in mucosa from healthy controls. This result is not caused by a cytotoxic effect of TNFalpha and is not balanced by an increased oxidation of glucose. Reduced butyrate oxidation results in a decreased energy supply to colonocytes and may explain, in part, mucosal damage occurring during attacks of inflammatory bowel disease.
Nancey
Stéphane
S
Department of Gastroenterology, Institut National de la Santé et de la Recherche Médicale, Centre Hospitalier Lyon-Sud, Pierre-Bénite, France.
Moussata
Driffa
D
Graber
Ivan
I
Claudel
Sylvette
S
Saurin
Jean-Christophe
JC
Flourié
Bernard
B
D000368:Aged; D001419:Bacteria; D001706:Biopsy; D002087:Butyrates / Q000378:metabolism*; D016022:Case-Control Studies; D003106:Colon / Q000166:cytology / Q000276:immunology* / Q000502:physiology*; D003113:Colonoscopy; D016207:Cytokines / Q000378:metabolism / Q000502:physiology; D005260:Female; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D006801:Humans; D007249:Inflammation; D007413:Intestinal Mucosa / Q000276:immunology* / Q000502:physiology*; D008297:Male; D008875:Middle Aged; D010084:Oxidation-Reduction; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
D002087:Butyrates; D016207:Cytokines; D014409:Tumor Necrosis Factor-alpha; D005947:Glucose