Certain factors have been found to decrease the risk of developing ulcerative colitis. Chief among them is the association of cigarette smoking with a decreased incidence of developing ulcerative colitis (Abraham et al., 2003; Odes, 2001). Some investigators have labeled ulcerative colitis a disease of non-smokers (Madretsma, 1996). The risk of developing ulcerative colitis is greatest among individuals who have recently quit smoking followed by non-smokers (Farrell and Peppercorn, 2002).
Tar products in tobacco smoke have been shown to inhibit the electron transport chain. Studies quantifying the effect of cigarette tar on mitochondrial electron transport activity report an 82% inhibition rate on whole chain respiration (Pryor et al., 1992). In this study nicotine had no effect on electron transport activity. ETC inhibition will reduce mitochondrial hydrogen peroxide generation. Cigarette smokers have also been reported to have reduced monoamine oxidase activity (Fowler et al., 2003). MAO, located on the mitochondrial outer membrane, is the main enzyme responsible for endogenous catecholamine metabolism. Inhibition of this enzyme decreases enzymatic oxidation of catecholamines and the generation of hydrogen peroxide which is a by-product of this reaction. Extracts of cigarette tar are reported to inhibit a number of P450 enzyme systems (Van Vleet et al., 2001). Hydrogen peroxide is a by-product of P450 metabolism and inhibition of these enzymes can lower H2O2generation.
Cigarette smoke extract has also been reported to inhibit the production of cytokines, including TNF-alpha, by greater than 90%. (Ouyang et al., 2000). Cytokines are an integral component of the inflammatory response in ulcerative colitis and their reduction may confer protection.
Thus, smoking may confer protection by inhibiting H2O2 production and preventing the induction phase of ulcerative colitis. However, during the time the ETC is inhibited by smoking, reducing equivalents, the substrate for H2O2 production, have been accumulating within mitochondria of all cells of the body including colonic epithelial cells. Inhibition of the electron transport chain also causes up-regulation of ETC associated enzymes in an attempt at overcoming the blockade. During the time of ETC inhibition glutathione production may also be down regulated since the cell does not have use for high levels of antioxidants when H2O2 production is low.
When an individual suddenly stops smoking this inhibition is abruptly removed resulting in greater ETC activity fueled by increased substrate and enzymatic activity. This also results in extra hydrogen peroxide being produced which, in susceptible individuals, may overwhelm the available glutathione within the colonic epithelial cells and increase the risk of induction.
Based on ETC inhibition, the risk of induction would be expected to be lowest in active smokers. Smokers that have recently quit smoking would be at highest risk since they are producing the most H2O2. Non-smokers would have the lowest risk. This mirrors the statistical risk of smoking as it relates to ulcerative colitis.
Smoking cessation during active ulcerative colitis would therefore be expected to exacerbate the condition. An increase in severity of ulcerative colitis has been reported in patients who stopped smoking during active ulcerative colitis (Beaugerie et al., 2001).
Nicotine is a parasympathomimetic and exerts its effect on the GI tract largely by stimulation of the parasympathetic ganglia. Its effect is to generally increase tone and contractility (National Academy of Sciences, 2001). The nicotine in cigarette smoke enhances intestinal peristaltic activity which tends to increase the fecal stream and prevent fecal stasis which can increase colonic bacterial and epithelial oxidant stress loads. Abrupt cessation of this adjuvant to colonic peristaltic activity would tend to favor stasis of colonic contents and promote constipation which is a risk factor for the development of ulcerative colitis (see constipation above). Thus, the methods of the invention contemplate regulated, progressive cessation of smoking in a patient.