L-citrulline supplementation reverses the impaired airway relaxation in neonatal rats exposed to hyperoxia

Abstract

BackgroundHyperoxia is shown to impair airway relaxation via limiting L-arginine bioavailability to nitric oxide synthase (NOS) and reducing NO production as a consequence. L-arginine can also be synthesized by L-citrulline recycling. The role of L-citrulline supplementation was investigated in the reversing of hyperoxia-induced impaired relaxation of rat tracheal smooth muscle (TSM).MethodsElectrical field stimulation (EFS, 2–20 V)-induced relaxation was measured under in vitro conditions in preconstricted tracheal preparations obtained from 12 day old rat pups exposed to room air or hyperoxia (>95% oxygen) for 7 days supplemented with L-citrulline or saline (in vitro or in vivo). The role of the L-citrulline/L-arginine cycle under basal conditions was studied by incubation of preparations in the presence of argininosuccinate synthase (ASS) inhibitor [α-methyl-D, L-aspartate, 1 mM] or argininosuccinate lyase inhibitor (ASL) succinate (1 mM) and/or NOS inhibitor [Nω-nitro-L-arginine methyl ester; 100 μM] with respect to the presence or absence of L-citrulline (2 mM).ResultsHyperoxia impaired the EFS-induced relaxation of TSM as compared to room air control (p < 0.001; 0.5 ± 0.1% at 2 V to 50.6 ± 5.7% at 20 V in hyperoxic group: 0.7 ± 0.2 at 2 V to 80.0 ± 5.6% at 20 V in room air group). Inhibition of ASS or ASL, and L-citrulline supplementation did not affect relaxation responses under basal conditions. However, inhibition of NOS significantly reduced relaxation responses (p < 0.001), which were restored to control level by L-citrulline. L-citrulline supplementation in vivo and in vitro also reversed the hyperoxia-impaired relaxation. The differences were significant (p <0.001; 0.8 ± 0.3% at 2 V to 47.1 ± 4.1% at 20 V without L-citrulline; 0.9 ± 0.3% at 2 V to 68.2 ± 4.8% at 20 V with L-citrulline). Inhibition of ASS or ASL prevented this effect of L-citrulline.ConclusionThe results indicate the presence of an L-citrulline/L-arginine cycle in the airways of rat pups. L-citrulline recycling does not play a major role under basal conditions in airways, but it has an important role under conditions of substrate limitations to NOS as a source of L-arginine, and L-citrulline supplementation reverses the impaired relaxation of airways under hyperoxic conditions.

L-citrulline for protection of endothelial function from ADMA–induced injury in porcine coronary artery

“…− overproduction. Ramadan and co-workers demonstrated that the presence of an L-citrulline/L-arginine cycle in the airways of rat pups and L-citrulline supplementation reversed the impaired relaxation of airways under hyperoxic conditions 24 . Ananthakrishnan and associates indicated that L-citrulline supplementation ameliorated the development of pulmonary hypertension and increased NO production in piglets exposed to chronic hypoxia 25 .…”

Arginine Therapy for Lung Diseases

“…Supplemental inhaled NO (iNO) also ameliorates the BPD phenotype in experimental models and in some premature infants. Lung parenchymal NO-mediated relaxation is impaired in rat neonates exposed to hyperoxia ( Sopi et al, 2007 ), which could be restored by inhibition of the increased arginase activity ( Ali et al, 2012 ), or with supplementation with L -arginine ( Ali et al, 2012 ) or L -citrulline ( Sopi et al, 2012 ). L -Citrulline supplementation prevents hyperoxia-induced lung injury and PH in newborn rats ( Vadivel et al, 2010 ).…”

Curcumin analogs (B2BrBC and C66) supplementation attenuates airway hyperreactivity and promote airway relaxation in neonatal rats exposed to hyperoxia

“…Pups were exposed to neonatal hyperoxia starting at age P5 which represent the transition day from saccular to alveolar phase of lung development in rats (O'Reilly & Thebaud, 2014). The 5th day of life, as starting point for exposure to oxygen might not be critical to induce strong structural changes in the airways and interstitial parenchyma of lungs to represent remodeling, but it is critical day to induce functional changes in respiratory system, particularly to trigger airway hyperreactivity that was proven in our previous publications (Sopi et al, 2007(Sopi et al, , 2012. Lungs at this age are immature, which is one of the risk factors of BPD (Speer, 2006).…”

“…The trachea was removed and prepared free of serosal connective tissue in an ice-cold oxygenated Krebs-Henseleit (KH) buffer (concentration in mM: 118.2 NaCl, 25 NaHCO 3 , 4.6 KCl, 1.2 KH 2 PO 4 , 1.2 MgSO 4 , 2.5 CaCl 2, and 10% D-glucose, pH = 7.4; all obtained from Sigma-Aldrich). Two cylindrical airway segments of 3-mm length were isolated from the midportions of the tracheas for each animal, and transferred into a tissue-organ bath containing KH buffer (10 ml) at 37°C, as previously described (Sopi et al, 2012).…”