Background: The flavonoid luteolin has anti-inflammatory properties both in vivo and in vitro. However, the impact of luteolin on experimental models of colitis is unknown.
Methodology/principal findings: To address the therapeutic impact of luteolin, NF-kappaB(EGFP) transgenic mice were fed a chow diet containing 2% luteolin- or isoflavone-free control chow (AIN-76), and acute colitis was induced using 3% dextran sodium sulfate (DSS). Additionally, development of spontaneous colitis was evaluated in IL-10(-/-);NF-kappaB(EGFP) transgenic mice fed 2% luteolin chow diet or control chow diet. Interestingly, NF-kappaB(EGFP) transgenic mice exposed to luteolin showed worse DSS-induced colitis (weight loss, histological scores) compared to control-fed mice, whereas spontaneous colitis in IL-10(-/-);NF-kappaB(EGFP) mice was significantly attenuated. Macroscopic imaging of live resected colon showed enhanced EGFP expression (NF-kappaB activity) in luteolin-fed mice as compared to control-fed animals after DSS exposure, while cecal EGFP expression was attenuated in luteolin-fed IL-10(-/-) mice. Interestingly, confocal microscopy showed that EGFP positive cells were mostly located in the lamina propria and not in the epithelium. Caspase 3 activation was significantly enhanced whereas COX-2 gene expression was reduced in luteolin-fed, DSS-exposed NF-kappaB(EGFP) transgenic mice as assessed by Western blot and immunohistochemical analysis. In vitro, luteolin sensitized colonic epithelial HT29 cells to TNFalpha-induced apoptosis, caspase 3 activation, DNA fragmentation and reduced TNFalpha-induced C-IAP1, C-IAP2 and COX-2 gene expression.
Conclusions/significance: We conclude that while luteolin shows beneficial effects on spontaneous colitis, it aggravates DSS-induced experimental colitis by blocking NF-kappaB-dependent protective molecules in enterocytes.