Moving towards a novel therapeutic strategy for hyperammonemia that targets glutamine metabolism.

Patients with urea cycle disorders intermittently develop episodes of decompensation with hyperammonemia. Although such an episode is often associated with starvation and catabolism, its molecular basis is not fully understood. First, we attempted to elucidate the mechanism of such starvation-associated hyperammonemia. Using a mouse embryonic fibroblast (MEF) culture system, we found that glucose starvation increases ammonia production, and that this increase is associated with enhanced glutaminolysis. These results led us to focus on α-ketoglutarate (AKG), a glutamate dehydrogenase inhibitor, and a major anaplerotic metabolite. Hence, we sought to determine the effect of dimethyl α-ketoglutarate (DKG), a cell-permeable AKG analog, on MEFs and found that DKG mitigates ammonia production primarily by reducing flux through glutamate dehydrogenase. We also verified that DKG reduces ammonia in an NH4 Cl-challenged hyperammonemia mouse model and observed that DKG administration reduces plasma ammonia concentration to 22.8% of the mean value for control mice that received only NH4 Cl. In addition, we detected increases in ornithine concentration and in the ratio of ornithine to arginine following DKG treatment. We subsequently administered DKG intravenously to a newborn pig with hyperammonemia due to ornithine transcarbamylase deficiency and found that blood ammonia concentration declined significantly over time. We determined that this effect is associated with facilitated reductive amination and glutamine synthesis. Our present data indicate that energy starvation triggers hyperammonemia through enhanced glutaminolysis and that DKG reduces ammonia accumulation via pleiotropic mechanisms both in vitro and in vivo. Thus, cell-permeable forms of AKG are feasible candidates for a novel hyperammonemia treatment.

Physical, cognitive, and social status of patients with urea cycle disorders in Japan.

Urea cycle disorders (UCDs) are inherited metabolic diseases that lead to hyperammonemia. Severe hyperammonemia adversely affects the brain. Therefore, we conducted a nationwide study between January 2000 and March 2018 to understand the present status of UCD patients in Japan regarding diagnosis, treatments, and outcomes. A total of 229 patients with UCDs (126 patients: ornithine transcarbamylase deficiency [OTCD]; 33: carbamoyl phosphate synthetase 1 deficiency [CPS1D]; 48: argininosuccinate synthetase deficiency [ASSD]; 14: argininosuccinate lyase deficiency [ASLD]; and 8: arginase 1 deficiency [ARG1D]) were enrolled in the present study. Although growth impairment is common in patients with UCDs, we discovered that Japanese patients with UCDs were only slightly shorter than the mean height of the general adult population in Japan. Patients with neonatal-onset UCDs are more likely to experience difficulty finding employment and a spouse; however, some patients with late-onset UCDs were employed and married. Additionally, intellectual and developmental disabilities, such as attention deficit hyperactivity disorder (ADHD) and autism, hinder patients with UCDs from achieving a healthy social life. Moreover, we identified that it is vital for patients with UCDs presenting with mild to moderate intellectual disabilities to receive social support. Therefore, we believe the more robust social support system for patients with UCDs may enable them to actively participate in society.

Diabetes mellitus exacerbates citrin deficiency via glucose toxicity.

AIMS: Citrin is an aspartate/glutamate carrier that composes the malate-aspartate reduced nicotinamide adenine dinucleotide (NADH) shuttle in the liver. Citrin deficiency causes neonatal intrahepatic cholestasis (NICCD), failure to thrive and dyslipidemia (FTTDCD) and adult-onset type II citrullinemia (CTLN2). Hepatic glycolysis is essentially impaired in citrin deficiency and a low-carbohydrate diet was recommended. The lethal effect of infusion of glycerol- and fructose-containing osmotic agents was reported in these patients. Hyperalimentation was also reported to exacerbate CTLN2; however, glucose toxicity was unclear in citrin deficiency. METHODS: We studied two CTLN2 patients complicated with type 2 diabetes mellitus (DM), Case 1 presented with hyperammonemic encephalopathy accompanied with DM, while Case 2 presented with hyperammonemic encephalopathy relapse upon the onset of DM after several years' remission following supplementation with medium-chain triglycerides (MCT) and adherence to a low-carbohydrate diet. RESULTS: Insulin therapy with MCT supplementation and a low-carbohydrate diet improved hyperammonemia and liver function in Case 1. Additional insulin therapy improved hyperammonemia in Case 2. CONCLUSION: Glucose is not toxic for citrin deficiency in normoglycemia because glucose uptake and metabolism by hepatocytes are limited in normoglycemia. However, glucose becomes toxic during persistent hyperglycemia and antidiabetic therapy is indispensable for CTLN2 patients with DM.

Sodium phenylbutyrate improved the clinical state in an adult patient with arginase 1 deficiency.

An adult female patient was diagnosed with arginase 1 deficiency (ARG1-D) at 4 years of age, and had been managed with protein restriction combined with sodium benzoate therapy. Though the treatment was successful in ameliorating hyperammonemia, hyperargininemia persisted. After being under control with a strict restriction of dietary protein, severe fall of serum albumin levels appeared and her condition became strikingly worsened. However, after sodium phenylbutyrate (NaPB) therapy was initiated, the clinical condition and metabolic stability was greatly improved. Current management of ARG1-D is aimed at lowering plasma arginine levels. The nitrogen scavengers, such as NaPB can excrete the waste nitrogen not through the urea cycle but via the alternative pathway. The removal of nitrogen via alternative pathway lowers the flux of arginine in the urea cycle. Thereby, the clinical complications due to insufficient amount of protein intake can be prevented. Thus, NaPB therapy can be expected as a useful therapeutic option, particularly in patients with ARG1-D.

Japanese patients with mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase deficiency: In vitro functional analysis of five novel HMGCS2 mutations.

Mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase (HMGCS2) deficiency is a metabolic disorder caused by mutations in the HMGCS2 gene. The present study describes the identification of four cases of HMGCS2 deficiency in Japan. Hepatomegaly and severe metabolic acidosis were observed in all cases. Fatty liver was identified in three cases, which suggested the unavailability of fatty acids. All patients presented with a high C2/C0 ratio, suggesting that the fatty acid oxidation pathway was normal during metabolic crisis. Genetic analyses revealed five rare, novel variants (p.G219E, p.M235T, p.V253A, p.S392L and p.R500C) in HMGCS2. To confirm their pathogenicity, a eukaryotic expression system and a bacterial expression system was adopted that was successfully used to obtain affinity-purified HMGCS2 protein with measurable activity. Purified M235T, S392L and R500C proteins did not retain any residual activity, whilst the V253A variant showed some residual enzymatic activity. Judging from the transient expression experiment in 293T cells, the G219E variant appeared to be unstable. In conclusion, the present study identified five novel variants of HMGCS2 that were indicated to be pathogenic in four patients affected by HMGCS2 deficiency.

Cystic biliary atresia with paucity of bile ducts and gene mutation in KDM6A: a case report.

BACKGROUND: Biliary atresia (BA) cases are generally not associated with congenital abnormalities. However, accurate diagnosis of BA is often challenging because the histopathological features of BA overlap with those of other pediatric liver diseases and rarely overlap with those of other genetic disorders. We experienced a rare case of BA with the histopathological finding of bile duct paucity, a gene mutation in KDM6A, and KS-like phenotypes. CASE PRESENTATION: A male baby was diagnosed with biliary atresia by intraoperative cholangiography at 4 days of age, and histological examination following a liver biopsy revealed a paucity of bile ducts and several typical clinical findings of Alagille syndrome. However, Alagille syndrome was ruled out after neither JAG1 nor NOTCH2 gene mutations were identified. Whole-exome sequencing on DNA from his parents was additionally performed to examine other possible syndromic disorders, and a mutation was identified in KDM6A. However, Kabuki syndrome was not diagnosed as a result. The histological finding of interlobular bile duct paucity and the genetic mutation in KDM6A, as well as several clinical findings consistent with Alagille syndrome or Kabuki syndrome, made it difficult to confirm the diagnosis of BA. CONCLUSIONS: Based on the interesting findings of the present case, we hypothesized that KDM6A is associated with hepatic malformations via a connection with the Notch signaling pathway.