L-citrulline prevents Asymmetric Dimethylarginine-Mediated reductions in Nitric Oxide and Nitrosative Stress In Primary Human Airway Epithelial Cells

Abstract

Introduction

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 the bronchial epithelium of asthmatics is unknown.

Methods

Subjects with asthma and healthy controls underwent bronchoscopy to obtain human bronchial epithelial cells (HBECs), which were cultured and stimulated with IL-13 and IFNγ (both 10ng/ml) to determine the effects of ADMA and varying concentrations of L-arginine, on NO- metabolites (nitrites + nitrates or NOx), hydrogen peroxide and nitrotyrosine levels. HBECs were also treated with L-citrulline to prevent ADMA-mediated effects in NO bioavailability and nitrosative stress.

Results

In HBECsIL-13 and IFNγ stimulated NOS2 and increased NOx levels. The addition of ADMA reduced NOx and increased H₂0₂ levels (p<0.001). Treatment with L-citrulline (800μM, 1600μM) rescued NOx when the L-arginine media concentration was 25 μM but failed to do so with higher concentrations (100μM). Under reduced L-arginine media conditions, HBECs 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 HBECs in cells from asthmatics and controls.

Conclusion

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.

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