Objective: In experimental animals, elevated nitric oxide (NO) production has been implicated in the pathogenesis of a lupus-like syndrome. Abnormalities of lung function tests are reported in a high proportion of patients with systemic lupus erythematosus (SLE). We investigated whether NO output in exhaled air might be increased in patients with SLE and whether it is related to disease activity and to respiratory function abnormalities.
Methods: Lung volume, maximal expiratory flow at 50 and 25% of vital capacity (MEF50 and MEF25), diffusion coefficient for carbon monoxide (KCO), and NO in the exhaled air were measured in 27 outpatients with SLE (23 women, age 39.2 +/- 16.3). NO in exhaled air was also measured in 30 healthy control subjects. Disease activity was assessed by the European Consensus Lupus Activity Measurement (ECLAM) scoring system.
Results: Mean values of peak concentrations of NO exhaled air were 64.8 +/- 27.9 parts per billion (ppb) in patients and 31.6 +/- 7.7 ppb in controls, p < 0.001. Peak NO concentration was directly related to ECLAM activity score (p < 0.05) and inversely related to MEF25 (p < 0.05).
Conclusion: NO in exhaled air is significantly increased and correlated with disease activity in patients with SLE. Whether increased NO output depends on respiratory tract inflammation, as the relationship with MEF25 may suggest, or on circulating cytokines produced elsewhere remains to be investigated.