Background: Smoking differentially influences susceptibility to the inflammatory bowel diseases (IBDs) Crohn's disease (CD) and ulcerative colitis (UC). We investigated the effects of nicotine on cytokine, cell cycle, and apoptotic responses in peripheral blood mononuclear cells (PBMCs) frorn IBD patients and healthy controls (HCs).
Methods: PBMCs from IBD patients and HC were stimulated with lipopolysaccharide (LPS; 1 mu g/mL) or phytohemagglutinin (PHA, 5 or 0.5 mu g/mL), +/- nicotine (1, 10, 100 mu g/mL). Cytokines (IL1 beta, IL2, IL10, IL12/IL23p40, TGF beta, TNF alpha) were measured in supernatants at 24 hours. After 72 hours cells were analyzed by flow cytometry for cell cycle and apoptosis. Statistical modeling was used to identify interactions between cytokines and cell cycle / apoptosis and minimize confounding effects.
Results: Stimulation by LPS and PHA (5 mu g/mL) increased IL12/IL23p40 production from CD and UC versus HC (P < 0.05); PHA (0.5 mu g/mL) increased IL1 beta in UC and decreased TGF beta from CD and UC (P < 0.01). In all groups, nicotine reduced LPS- and PHA (0.5 mu g/mL)-stimulated production of IL1 beta, IL10, TGF beta, and TNFa (P < 0.001). Cell cycle analysis showed that PHA, but not LPS, induced proliferation and decreased G(0)/G(1) resting cells in CD and UC versus HC (P < 0.001). Nicotine decreased PHA-stimulated S-phase proliferation and increased G, G, resting cells (P < 0.01). Modeling showed independent associations between IL12/IL23p40 and apoptosis (P = 0.01), IL1 beta and testing cells (P = 0.006), TNF alpha and proliferating cells (P < 0.001). Disease activity and smoking habit had no effect.
Conclusions: Dysregulated cytokine profiles in UC and CD are associated with specific alterations in cell cycle responses; these effects may be modified by nicotine, and potentially by anticytokine therapies.