Rescue Treatment with L-Citrulline Inhibits Hypoxia-Induced Pulmonary Hypertension in Newborn Pigs

Abstract

Infants with cardiopulmonary disorders associated with hypoxia develop pulmonary hypertension. We previously showed that initiation of oral L-citrulline before and continued throughout hypoxic exposure improves nitric oxide (NO) production and ameliorates pulmonary hypertension in newborn piglets. Rescue treatments, initiated after the onset of pulmonary hypertension, better approximate clinical strategies. Mechanisms by which L-citrulline improves NO production merit elucidation. The objective of this study was to determine whether starting L-citrulline after the onset of pulmonary hypertension inhibits disease progression and improves NO production by recoupling endothelial NO synthase (eNOS). Hypoxic and normoxic (control) piglets were studied. Some hypoxic piglets received oral L-citrulline starting on Day 3 of hypoxia and continuing throughout the remaining 7 days of hypoxic exposure. Catheters were placed for hemodynamic measurements, and pulmonary arteries were dissected to assess NO production and eNOS dimer-to-monomer ratios (a measure of eNOS coupling). Pulmonary vascular resistance was lower in L-citrulline-treated hypoxic piglets than in untreated hypoxic piglets but was higher than in normoxic controls. NO production and eNOS dimer-to-monomer ratios were greater in pulmonary arteries from L-citrulline-treated than from untreated hypoxic animals but were lower than in normoxic controls. When started after disease onset, oral L-citrulline treatment improves NO production by recoupling eNOS and inhibits the further development of chronic hypoxia-induced pulmonary hypertension in newborn piglets. Oral L-citrulline may be a novel strategy to halt or reverse pulmonary hypertension in infants suffering from cardiopulmonary conditions associated with hypoxia.

Changes in the nitric oxide pathway of the pulmonary vasculature after exposure to hypoxia in swine model of neonatal pulmonary vascular disease

“…) or dysfunction/uncoupling of eNOS (Fike et al. , , ), the present study provides evidence that there are disruptions in the NO‐cGMP pathway more downstream to eNOS/NO. Thus, in our model for neonatal PH the impaired endothelium‐dependent vasodilatation was accompanied by a reduced responsiveness to NO in vivo, which may be caused by altered sensitivity and/or activity of sGC.…”

“…There is increasing evidence that alterations in the NO‐cGMP signaling pathway play an important role in the pathogenesis of neonatal pulmonary vascular disease, including PH (Fike et al. , , ; Berkenbosch et al. ).…”

“…() found an impaired production of NO, through reduced eNOS protein expression and/or activity or dysfunction/uncoupling of eNOS (Fike et al. , , ) in swine following exposure to hypoxia in the early postnatal period. Timing of hypoxia and/or the animal model used may influence the effect of hypoxia on the NO‐pathway.…”

Advances in Neonatal Pulmonary Hypertension

“…Oral citrulline has been reported as an effective method to increase serum L -arginine concentrations and may represent a strategy for improving endogenous NO signaling. In newborn piglets exposed to 3-10 days of hypoxia, L -citrulline increased NO production and reduced chronic hypoxia-induced PH even after the onset of disease [72]. Another in vivo study demonstrated that subcutaneous L -citrulline reduced vascular remodeling and alveolar growth arrest in an experimental neonatal rat model of oxygen-induced BPD [73].…”

Pharmacologic strategies in neonatal pulmonary hypertension other than nitric oxide

“…It is interesting that although L-arginine supplementation can improve NO signaling, oral citrulline is more effective than arginine in increasing serum L-arginine concentrations with fewer side effects. Rescue therapy with L-citrulline has been shown to ameliorate hypoxia-induced-pulmonary hypertension in newborn piglets 101 . In adult patients with idiopathic pulmonary hypertension or Eisenmenger syndrome, oral L-citrulline malate reduced pulmonary arterial pressure and improved six minute walking distance 102 .…”