Modulation of inflammation in IBD: Alpha7nAChR expression and role of nicotine

Objective: The divergent effects of nicotine on natural history of inflammatory bowel diseases (IBD) are wellknown: while it’s beneficial in ulcerative colitis (UC) it increases risk of surgery and relapse in Crohn’s disease (CD). It has been shown that in animal models the modulatory effect of nicotine in intestinal inflammation involves the alpha7 nicotinic acetylcholine receptor (a7nAChR), activating a cholinergic counterinflammatory mechanism. Thus, aims of the study were to evaluate a7nAChmRNA levels on macrophages from patients with MC, UC and controls (HV) and nicotine effects on LPS-induced TNFa and IL10 production. Methods: Macrophages obtained from peripheral blood monocytes of UC and CD patients and HV were supplemented with M-CSF (7 days). a7nAchR-mRNA and protein levels were evaluated by qRT-PCR and FACS analysis using aBgt-FICS specific binding, respectively. Macrophages were pre-incubated with nicotine (1 mg ml-1 30 min) and then stimulated with LPS (1 lg ml-1 24 h). TNFa and IL10 levels were measured on supernatant using ELISA. Results: Macrophages from UC showed greater a7nAchR mRNA levels then cells from CD (0.00092 copies in UC Vs 0.000212 copies in CD, P = 0,006), while no differences were found with HV. FACS analysis confirmed greater a7AChR expression in UC patients (90.75 Gmean in UC Vs 15.62 Gmean in MC, P 0.031). Higher a7nAchR mRNA levels were observed in macrophages from IBD with colonic disease compared with small bowel involvement (P = 0.007). Nicotine significantly decreased LPS-stimulated TNFa release in macrophages from HV (from 13122.7 pg ml-1 to 9790.2 pg ml-1; P = 0.03), CD (14291.7 pg ml-1 to 10613.2 pg ml-1; P = 0.003) and UC (from 13723.9 pg ml-1 to 10238.5 pg ml-1; P = 0.000). This effect was more pronounced in macrophages from UC patients (-22.9%) compared with CD (-6.1%) and in IBD with colonic disease (-17.4%) compared to CD with small bowel involvement (+3.8%), although it did not reach statistical significance. Pretreatment with nicotine inhibited LPS-stimulated IL10 production by macrophages in HV, UC and CD, but not differences were observed among groups. Conclusion: Nicotine has a suppressive effect on TNFa and IL10 production by macrophages: diseaserelated or site-related differences in a7nAChR levels may justify the divergent effects of nicotine in IBD patients.