Chronic nicotine intake increases the responses to muscarinic receptor stimulation

Nicotine Exerts a Stronger Immunosuppressive Effect than Its Structural Analogs and Regulates Experimental Colitis in Rats

Ulcerative colitis (UC) is an intractable disease that causes persistent colonic inflammation. Numerous studies have reported that smoking can afford clinical benefits in UC. This study aimed to elucidate whether nicotine, the main component in cigarettes, can exert pharmacological effects against experimental UC. To achieve this objective, we compared the effects of nicotine with those of structural nicotine analogs in a UC rodent model (Slc: Wistar rats, male, 9-week-old, and 220–250 g/rat). Nicotine, or a respective structural analog (nornicotine, cotinine, anabasine, myosmine, and anatabine), was administered intraperitoneally daily to rats (n = 6/group) exhibiting dextran sulfate sodium-induced experimental colitis. Examining the colon tissues of model rats, we compared disease severity, cytokine secretion, and α7 nicotine acetylcholine receptor (nAChR7) expression. We observed that nicotine administration induced weight loss at 2.35% in 10 days. Notably, the reduction in histological severity (score) of UC was more pronounced in rats treated with nicotine (score = 4.83, p = 0.042) than in untreated rats (score = 8.17). Nicotine administration increased nAChR7 expression 6.88-fold (p = 0.022) in inflammatory sites of the colon, mainly by suppressing the production of interleukin (IL)-1β and IL-6. Moreover, the secretion of these cytokines was suppressed in lipopolysaccharide-stimulated rat macrophages (MΦ) treated with nicotine. In conclusion, nicotine better alleviates experimental UC than the examined structural analogs by activating nAChR7 expression and suppressing proinflammatory cytokines in MΦ.

Evidence for the involvement of matrix metalloproteinases in the cardiovascular effects produced by nicotine

Nicotine plays a role in smoking-associated cardiovascular diseases, and may upregulate matrix metalloproteinase (MMP)-2 and MMP-9. We examined whether nicotine induces the release of MMP-2 and MMP-9 by rat smooth muscle cells (SMC), and whether doxycycline (non-selective MMP inhibitor) inhibits the vascular effects produced by nicotine. SMC were incubated with nicotine 0, 50, and 150 nM for 48 h. MMP-2 and MMP-9 levels in the cell supernatants were determined by gelatin zymography. The acute changes in mean arterial pressure caused by nicotine 2 micromol/kg (or saline) were assessed in rats pretreated with doxycycline (or saline). We also examined whether doxcycline (30 mg/Kg, i.p., daily) modifies the effects of nicotine (10mg/kg/day; 4 weeks) on the endothelium-dependent relaxations of rat aortic rings. Aortic MMP-2 levels were assessed by gelatin zymography. Aortic gelatinolytic activity was assessed using a gelatinolytic activity kit. MMP-2 and MMP-9 levels increased in the supernatant of SMC cells incubated with nicotine 150 nM (P<0.05) but not with 50 nM. Nicotine (2 micromol/kg) produced lower increases in the mean arterial pressure in rats pretreated with doxycycline than those found in rats pretreated with saline (26+/-4 vs. 37+/-4 mm Hg, respectively; P<0.05). Nicotine impaired of the endothelium-dependent responses to acetylcholine, and treatment with doxycycline increased the potency (pD2) by approximately 25% (P<0.05). While we found no significant differences in aortic MMP-2 levels, nicotine significantly increased gelatinolytic activity (P<0.05). These findings suggest that nicotine produces cardiovascular effects involving MMPs. It is possible that MMPs inhibition may counteract the effects produced by nicotine.

Dysregulation of gastric H,K-ATPase by cigarette smoke extract

AIM

To test whether the expression and activity of H,K-ATPase in parietal cells would be affected by cigarette smoke extract.

METHODS

Extracts of cigarette smoke were administered into mice by gastric gavage (5 mg/kg body weight/day) for 3 d or in drinking water for 7 or 14 d. For the latter, each day a mouse consumed 5 mL water containing extracts of two cigarettes, on average. Control littermate mice received only vehicle. To compare the amount of H,K-ATPase in control and smoke-treated mice, the stomach was processed for Western blotting and immunohistochemical analysis using monoclonal antibodies specific for alpha- or beta-subunits of H,K-ATPase. The p-nitrophenylphosphatase activity assay was used as a measurement for K-dependent H,K-ATPase activity.

RESULTS

Probed transblots showed an increase in the amount of H,K-ATPase in smoke-treated mice which was confirmed by immunohistochemistry and was found to be due to increased amounts of protein per parietal cell rather than an increased parietal cell number. The increase in the amount of H,K-ATPase was associated with an enhancement of its enzymatic activity. K-dependent activity in control and smoke-treated mice was significantly different (respectively, 0.12 micromol/mg vs 0.27 micromol/mg per minute, P < 0.05).

CONCLUSION

Administration of cigarette smoke extract is associated with an increase in the amount and activity of H,K-ATPase and hence, smokers are susceptible to development of peptic ulcer.