Potential therapeutic uses of L-citrulline beyond genetic urea cycle disorders

L-citrulline (referred to hereafter as citrulline), a non-essential amino acid and an intermediate in the urea cycle, is widely recognized for its role in managing genetic urea cycle disorders (UCDs). Recent studies, however, suggest that citrulline's therapeutic potential extends beyond UCDs, particularly in conditions associated with nitric oxide (NO) deficiency, endothelial dysfunction, and oxidative stress. This review explores citrulline's emerging applications in sickle cell disease (SCD), post-operative pulmonary hypertension (PH), hepatic veno-occlusive disease (HVOD), and bronchopulmonary dysplasia (BPD), as well as its speculative use in asthma and acute respiratory distress syndrome (ARDS). In SCD, citrulline may restore NO bioavailability, potentially reducing the incidence and severity of vaso-occlusive crises and preventing complications like pulmonary hypertension. In the context of post-operative PH, citrulline's capacity to enhance NO production can improve pulmonary vascular resistance, decrease right ventricular strain, and reduce the need for mechanical ventilation. Citrulline's protective effects on endothelial function and its ability to mitigate oxidative stress offer promising adjunctive therapy for HVOD, particularly in patients undergoing bone marrow transplantation. In BPD, citrulline could promote alveolar development, reduce inflammation, and improve long-term respiratory outcomes. Despite these promising findings, further research is necessary to determine optimal dosing strategies and to evaluate long-term efficacy and safety. The potential role of citrulline in modulating NO production in conditions like asthma and ARDS also warrants further investigation. This review underscores the versatile therapeutic potential of citrulline and highlights the need for continued research into its applications across various conditions associated with NO deficiency and endothelial dysfunction.