Exhaled nitric oxide in endotoxin-exposed adults: effect modification by smoking and atopy

Abstract

Objectives: Occupational exposure to endotoxin is associated with non-allergic asthma and other airway inflammatory reactions. Little is known about the role of mucosal nitric oxide (NO) production in endotoxin-induced airway inflammation. The objective was to explore exposure–response relationships between occupational endotoxin exposure and fractional concentrations of exhaled NO (FE_NO) and study the role of FE_NO as an intermediate factor in the relationship between endotoxin exposure and asthma-like symptoms.

Methods: FE_NO was measured online in 425 farmers and agricultural processing workers. For each participant (cumulative) endotoxin level was modelled on the basis of 249 personal measurements and job history. Atopy was assessed as specific serum IgE to common inhalant allergens, and other health data and personal characteristics by standardised questionnaires.

Results: A significant positive exposure–response relationship was found between endotoxin and FE_NO, but only in non-atopic, non-smoking subjects (p = 0.001). FE_NO was significantly associated with current wheeze and other asthma-like symptoms irrespective of atopy and current smoking. Associations between endotoxin exposure and symptoms changed slightly after adjusting for FE_NO.

Conclusions: A positive association was found between occupational endotoxin exposure and exhaled nitric oxide in non-smoking, non-atopic adults. Increased FE_NO was associated with asthma-like symptoms, but the role of FE_NO as an intermediate factor between endotoxin exposure and airway symptoms appears to be limited.