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.

L-Citrulline increases nitric oxide and improves control in obese asthmatics

“…Ultimately, this process may explain why some obese asthmatics have reduced NO airway bioavailability, with greater airway oxidative stress. Based on our previous findings showing that L-citrulline recouples airway epithelial NOS2, preventing these downstream events from occurring, we developed this pilot proof-of-concept study (5). majority of subjects were on maintenance therapy with ICS/long-acting β agonist (ICS/LABA) controllers.…”

“…This phenomenon may explain why lower L-arginine/ADMA ratios are associated with reduced lung function, more frequent respiratory symptoms, and lower asthma-related quality of life (8). In airway epithelial cells of obese asthmatics L-citrulline prevents many of the downstream effects associated with NOS2 uncoupling (5). Therefore, we hypothesized that in obese asthmatics with low or normal FeNO levels L-citrulline restores NO airway bioavailability, improving lung function and asthma control.…”

“…This can potentially occur via a metabolic imbalance characterized by lower L-arginine levels and higher concentrations of asymmetric dimethyl arginine (ADMA) (Figure 1 and ref. 5). Lower L-arginine/ADMA ratios favor airway epithelial inducible NO synthase (NOS2) uncoupling, promoting ROS formation at the expense of NO production.…”

Developments in the field of allergy in 2017 through the eyes of Clinical and Experimental Allergy

“…One of the key components of asthma pathophysiology, in addition to airway inflammation, 5 7 This was restored towards normal NO formation following L-citrulline supplementation. This shows mechanistic differences in epithelial cell function and also proposes the utility of Lcitrulline as a potential therapeutic to restore function.…”

Dietary L-Citrulline supplementation modulates nitric oxide synthesis and anti-oxidant status of laying hens during summer season

“…L-Cit directly attenuated ROS production by downregulating the protein expression levels of p67 phox , a critical component for NADH/NADPH superoxide generation (90). In vitro studies using asymmetric dimethylarginine (ADMA), a non-selective NOS inhibitor, demonstrated L-Cit effectiveness to restore NO production and attenuate nitrosative stress (91). Also, in atherosclerotic rabbits fed orally with L-arginine + L-Citrulline alone or with antioxidants, there was a reduction in superoxide production, downregulation of oxidation-sensitive (Elk-1 and p-CREB) genes with associated increments in NO synthase (eNOS) expressions and NOx plasma concentrations (71).…”