Citrulline in health and disease. Review on human studies.

The amino acid L-citrulline (CIT) is safely used from the neonatal period onwards in those with urea cycle defects and carbamyl phosphate synthetase or ornithine transcarbamylase deficiencies, but several lines of enquiry indicate that it might have a much wider therapeutic role. When protein intake is low and there is a catabolic state, endogenous arginine (ARG) synthesis cannot fully be met and its supplementation can prove challenging, particularly in patients with critical and multisystem illness. Supplementary CIT could constitute a safer but still focused means of delivering ARG to endothelial and immune cells as CIT is efficiently recycled into these cells and as kidneys can convert CIT into ARG. Unlike ARG, CIT is efficiently transported into enterocytes and bypasses liver uptake. It also appears to prevent excessive and uncontrolled nitric oxide (NO) production. Animal studies and early human data indicate positive effects of CIT on protein synthesis, in which its contribution is thought mediated through the mTOR pathway. It appears that CIT is an anabolic pharmaconutrient that can be safely administered even in critically ill patients. Promising results in cardiovascular diseases and in disease-related malnutrition can now be considered sufficient to justify formal clinical exploration in these areas and in sarcopenia in general.

Precision medicine in rare disease: Mechanisms of disparate effects of N-carbamyl-l-glutamate on mutant CPS1 enzymes.

This study documents the disparate therapeutic effect of N-carbamyl-l-glutamate (NCG) in the activation of two different disease-causing mutants of carbamyl phosphate synthetase 1 (CPS1). We investigated the effects of NCG on purified recombinant wild-type (WT) mouse CPS1 and its human corresponding E1034G (increased ureagenesis on NCG) and M792I (decreased ureagenesis on NCG) mutants. NCG activates WT CPS1 sub-optimally compared to NAG. Similar to NAG, NCG, in combination with MgATP, stabilizes the enzyme, but competes with NAG binding to the enzyme. NCG supplementation activates available E1034G mutant CPS1 molecules not bound to NAG enhancing ureagenesis. Conversely, NCG competes with NAG binding to the scarce M792I mutant enzyme further decreasing residual ureagenesis. These results correlate with the respective patient's response to NCG. Particular caution should be taken in the administration of NCG to patients with hyperammonemia before their molecular bases of their urea cycle disorders is known.

Augmenting ureagenesis in patients with partial carbamyl phosphate synthetase 1 deficiency with N-carbamyl-L-glutamate.

Identical studies using stable isotopes were performed before and after a 3-day trial of oral N-carbamyl-l-glutamate (NCG) in 5 subjects with late-onset carbamyl phosphate synthetase deficiency. NCG augmented ureagenesis and decreased plasma ammonia in 4 of 5 subjects. There was marked improvement in nitrogen metabolism with long-term NCG administration in 1 subject.

A case of carbamoyl phosphate synthetase 1 deficiency presenting symptoms at one month of age.

Carbamoyl phosphate synthetase 1 deficiency (CPS1D) is an autosomal recessive disorder of the urea cycle which causes hyperammonemia. Two forms of CPS1D are recognized: a lethal neonatal type and a less severe, delayed onset type. Neonatal CPS1D cases often present their symptoms within the first days of life. Delayed onset type were adolescents or adults, and infantile cases were rare. We report a case of CPS1D in a boy who developed symptoms at one month of age. He showed excellent response to treatments including continuous hemodialysis, drugs and a low-protein diet. His development and weight gain were good at the last follow-up at 1 year and three months of age. Molecular assay of the CPS1 gene demonstrated that the patient was heterozygous for c.2407C>G (R803G: maternal) in exon 20 and c.3784C>T (R1262X: paternal) in exon 32. Our clinical experience suggests that CPS1D could be one of the causes of hyperammonemia in early infantile cases.

Survival after treatment with phenylacetate and benzoate for urea-cycle disorders.

BACKGROUND: The combination of intravenous sodium phenylacetate and sodium benzoate has been shown to lower plasma ammonium levels and improve survival in small cohorts of patients with historically lethal urea-cycle enzyme defects. METHODS: We report the results of a 25-year, open-label, uncontrolled study of sodium phenylacetate and sodium benzoate therapy (Ammonul, Ucyclyd Pharma) in 299 patients with urea-cycle disorders in whom there were 1181 episodes of acute hyperammonemia. RESULTS: Overall survival was 84% (250 of 299 patients). Ninety-six percent of the patients survived episodes of hyperammonemia (1132 of 1181 episodes). Patients over 30 days of age were more likely than neonates to survive an episode (98% vs. 73%, P<0.001). Patients 12 or more years of age (93 patients), who had 437 episodes, were more likely than all younger patients to survive (99%, P<0.001). Eighty-one percent of patients who were comatose at admission survived. Patients less than 30 days of age with a peak ammonium level above 1000 micromol per liter (1804 microg per deciliter) were least likely to survive a hyperammonemic episode (38%, P<0.001). Dialysis was also used in 56 neonates during 60% of episodes and in 80 patients 30 days of age or older during 7% of episodes. CONCLUSIONS: Prompt recognition of a urea-cycle disorder and treatment with both sodium phenylacetate and sodium benzoate, in conjunction with other therapies, such as intravenous arginine hydrochloride and the provision of adequate calories to prevent catabolism, effectively lower plasma ammonium levels and result in survival in the majority of patients. Hemodialysis may also be needed to control hyperammonemia, especially in neonates and older patients who do not have a response to intravenous sodium phenylacetate and sodium benzoate.