Cultures of Human Colonic Epithelial Cells Isolated from Endoscopical Biopsies from Patients with Inflammatory Bowel Disease. Effect of IFNγ, TNFα and IL-1β on Viability, Butyrate Oxidation and IL-8 Secretion

Abstract

Cytokjne-mediated impairment of viability and metabolic function of epithelial cells has been suggested as a possible early pathogenic event in the development of inflammatory bowel disease (IBD). It is currently unknown whether pro-inflammatory cytokines have a direct effect on human nontransformed colonic epithelial cells. We investigated the effects of TNFα, IFNγ and IL-1β on viability, short chain fatty acid (butyrate) oxidation and IL-8 secretion in human colonic epithelial cell cultures in vitro obtained from macroscopically normal mucosa from IBD patients and controls. Colonic crypts were isolated from endoscopical biopsies by ultra-short (10 min) EDTA/EGTA treatment, and exposed to TNFα, IFNγ and IL-1β for 24 hours. The combination of TNFoc+IFNγ induced a significant decrease in cell viability as judged by methyltetrazoleum (MTT) metabolism which decreased to median 68 % of unexposed cultures (P<0.01). This effect was more pronounced than that observed after addition of TNFα (median 88 %) (P<0.05), but not IFNγ alone (median 78 %), whereas IL-1(3 had no significant effect. Cells from IBD patients were significantly less sensitive to TNFα + IFNγ exposure (median 74 %) compared to cells from controls (median 58 %) (P < 0.05). Butyrate oxidation, as measured by entrapment of CO₂, was not inhibited in cells exposed to TNFα + IFNγ, neither from controls (median 112%) nor from IBD patients (median 108%), suggesting a relative increase of this specific metabolic function in living cells in response to immunoinflammatory stress. IL-8 levels in cell supernatants were increased by TNFα + IFNγ, supporting the role of the epithelium in signalling between luminal factors and mucosal immune cells. In conclusion, we report that TNFα and IFNγ damage and influence human colonic epithelial cell function in vitro and that such mechanisms, if operative in vivo, also may be involved in the pathogenesis of IBD

Key Words:

• Butyrate oxidation
• Crohn's disease
• Cytokines
• Inflammatory Bowel Disease
• Ulcerative colitis