L-Citrulline Attenuates Arrested Alveolar Growth and Pulmonary Hypertension in Oxygen-Induced Lung Injury in Newborn Rats

Bronchopulmonary dysplasia (BPD) is characterized by arrested alveolar development and complicated by pulmonary hypertension (PH). NO promotes alveolar growth. Inhaled NO (iNO) ameliorates the BPD phenotype in experimental models and in some premature infants. Arginosuccinate synthetase (ASS) and arginosuccinate lyase (ASL) convert l-citrulline to l-arginine; l-citrulline is regenerated during NO synthesis from l-arginine. Plasma levels of these NO precursors are low in PH. We hypothesized that l-citrulline prevents experimental O2-induced BPD in newborn rats. Rat pups were assigned from birth through postnatal day (P) 14 to room air (RA), RA + l-citrulline, 95% hyperoxia (BPD model), and 95%O2 + l-citrulline. Rat pups exposed to hyperoxia had fewer and enlarged air spaces and decreased capillary density, mimicking human BPD. This was associated with decreased plasma l-arginine and l-citrulline concentrations on P7. l-Citrulline treatment significantly increased plasma l-arginine and l-citrulline concentrations and increased ASL protein expression in hyperoxia. l-Citrulline preserved alveolar and vascular growth in O2-exposed pups and decreased pulmonary arterial medial wall thickness (MWT) and right ventricular hypertrophy (RVH). Increased lung arginase (ARG) activity in O2-exposed pups was reversed by l-citrulline treatment. l-Citrulline supplementation prevents hyperoxia-induced lung injury and PH in newborn rats. l-Citrulline may represent a novel therapeutic alternative to iNO for prevention of BPD.