Allergic rhinitis (AR) is the most common ailment caused by allergies in children and is associated with high cardiovascular risk. Passive smoke can exacerbate the clinical course of AR and atherosclerosis. Yet, the mechanisms accounting for AR-driven vascular dysfunction and for the worsening effect imparted by passive smoke (PS) on patients with AR remains partially understood. Nor is it known if passive smoking-induced oxidative stress is involved in arterial dysfunction in children with persistent AR. One-hundred and thirty children, including 65 children with persistent AR and 65 healthy controls (HC), will be recruited in this project. Aim of this research project will be to compare endothelial function assessed by flow-mediated dilation (FMD), oxidative stress assessed by blood levels of isoprostanes, serum activity of soluble NOX2-dp (sNOX2-dp) and nitric oxide (NO) bioavailability in these two groups of children. Serum cotinine levels will also be assessed to measure exposition to passive smoking and a subgroup analysis will be performed in the two groups to evaluate sNOX2-dp levels, serum isoprostanes, NO and FMD in children exposed to passive smoking compared to children not exposed.
Until now, no studies have assessed whether NADPH oxidase-2 has a role in oxidative stress that characterize children with persistent AR. Previous studies have shown, in fact, that other isoforms of NADPH oxidase, such as Nox1, Nox4, DOX1 and DOX2, are over-expressed in the airway epithelium and mucosa. Our study will provide the first report attesting that serum NADPH-2 oxidase activation levels are elevated in children with persistent AR and implicated in the endothelial dysfunction in these subjects.
Previous studies have explored the presence of elevated oxidative stress in patients with AR. For instance, isoprostane and NO levels were tested and found increased in the exhaled air and in nasal lavage of AR subjects. Environmental sources as allergens, air pollution and cigarette smoke could represent a trigger to produce excessive ROS in patients with persistent AR. A chronic exposition to allergens stimulates inflammatory cells, such as eosinophils and neutrophils in the airway mucosa to produce OS by NADPH oxidase. Of interest, we will evaluate in this project if an association between cotinine levels and serum sNox2-dp levels does exist in AR patients. Previously, we found that NOX-2 activation is higher in active smokers and studies on animal exposed to passive smoking have documented NADPH oxidase activation in blood, lung and bronchiolar epithelialcells. All this evidence together supports the notion that NADPH oxidase generated-OS is a key player in the physiopathology of rhinitis. Accordingly, a recent study demonstrated a positive association of tobacco smoke exposure with rhinitis. Previous studies in animal models reported the effect of passive smoking on NADPH oxidase. Mukherejee et al found that guinea pigs exposed to side stream smoke had an increased activity of NADPH oxidase and a decreased activity of glutathione peroxidase. Meng et al. found in mice exposed to smoke an upregulation of NADPH oxidase isoform NOX-1. Furthermore, an in vitro study in human keratinocytes showed after cigarette smoke exposure a higher activation of cellular NADPH oxidase. Another experimental study in Human Umbilical Vein Endothelial Cells exposed to smoke showed a reduction of eNOS activity and stimulation of NADPH oxidase activity. Previously we found in human that NOX-2 activation is higher in active smokers and in children exposed to passive smoking but no-data were available on the effect of passive smoking on NADPH oxidase in AR. NADPH oxidase plays a pivotal role in modulating endothelial function. Children at risk of atherosclerosis, such as those with obesity, obstructive sleep apnoea and hypercholesterolemia,have endothelial dysfunction and increased NADPH oxidase derived OS. On the other hand, when NADPH oxidase is down-regulated, as in children with hereditary deficiency of gp-91 phox, the endothelial function is improved and the oxidative burden is lower than in controls.
Another novel aspect of our project will be the evaluation of endothelial dysfunction in children with persistent AR. Elcioglu and colleagues showed reduced FMD values in adults with chronic rhinitis. In the Bruneck and ARMY studies enhanced atherosclerosis was found in subjects with persistent AR, so we will also evaluate IMT values in subjects with persistent AR. Future studies must validate the association between surrogate markers of atherosclerosis, such as IMT and FMD, and cardiovascular events in subjects with persistent AR. In conclusion, our study could demonstrate the effect of passive smoking on Nox-2 induced OS and endothelial dysfunction in children with persistent AR.