l ‐citrulline prevents asymmetric dimethylarginine‐mediated reductions in nitric oxide and nitrosative stress in primary human airway epithelial cells

Summary Background Asthma is associated with reduced systemic levels of l ‐arginine and increased asymmetric dimethylarginine ( ADMA ). This imbalance leads to nitric oxide synthase ( NOS ) uncoupling with reduced nitric oxide ( NO ) formation and greater oxidative and nitrosative stress. Whether this imbalance also occurs in bronchial epitheliumof asthmatics is unknown. Objectives We used primary human bronchial epithelial cells ( HBEC s) from asthmatics and healthy controls to evaluate: (i) ADMA ‐mediated NOS uncoupling reduces epithelial production of NO and increases oxygen and nitrogen reactive species, and (ii) l ‐citrulline can reverse this mechanism by recoupling NOS , restoring NO production and reducing oxidative and nitrosative stress. Results In HBEC s IL ‐13 and INF γ stimulated NOS 2 and increased NO x levels. The addition of ADMA reduced NO x and increased H 2 O 2 levels (p<0.001). Treatment with l ‐citrulline (800, 1600 μ m ) rescued NO x when the l ‐arginine media concentration was 25 μ m but failed to do so with higher concentrations (100 μ m ). Under reduced l ‐arginine media conditions, HBEC s treated with l ‐citrulline increased the levels of argininosuccinate, an enzyme that metabolizes l ‐citrulline to l ‐arginine. l ‐citrulline prevented the ADMA ‐mediated increase in nitrotyrosine in HBEC s in cells from asthmatics and controls. Conclusions and Clinical Relevance Increasing ADMA reduces NO formation and increases oxidative and nitrosative stress in airway epithelial cells. l ‐citrulline supplementation restores NO formation, while preventing nitrosative stress. These results, suggest that l ‐citrulline supplementation may indeed be a powerful approach to restore airway NO production and may have a therapeutic potential in diseases in which there is a defective production of NO .