Blood ammonia and glutamine as predictors of hyperammonemic crises in patients with urea cycle disorder

Quo vadis ureagenesis disorders? A journey from 90 years ago into the future

The pathway of ammonia disposal in the mammalian organism has been described in 1932 as a metabolic cycle present in the liver in different compartments. In 1958, the first human disorder affecting this pathway was described as a genetic condition leading to cognitive impairment and constant abnormalities of amino acid metabolism. Since then, defects in all enzymes and transporters of the urea cycle have been described, referring to them as primary urea cycle disorders causing primary hyperammonemia. In addition, there is a still increasing list of conditions that impact on the function of the urea cycle by various mechanisms, hereby leading to secondary hyperammonemia. Despite great advances in understanding the molecular background and the biochemical specificities of both primary and secondary hyperammonemias, there remain many open questions: we do not fully understand the pathophysiology in many of the conditions; we do not always understand the highly variable clinical course of affected patients; we clearly appreciate the need for novel and improved diagnostic and therapeutic approaches. This study does look back to the beginning of the urea cycle (hi)story, briefly describes the journey through past decades, hereby illustrating advancements and knowledge gaps, and gives examples for the extremely broad perspective imminent to some of the defects of ureagenesis and allied conditions.

Intellectual disability and autism in propionic acidemia: a biomarker-behavioral investigation implicating dysregulated mitochondrial biology

Propionic acidemia (PA) is an autosomal recessive condition (OMIM #606054), wherein pathogenic variants in PCCA and PCCB impair the activity of propionyl-CoA carboxylase. PA is associated with neurodevelopmental disorders, including intellectual disability (ID) and autism spectrum disorder (ASD); however, the correlates and mechanisms of these outcomes remain unknown. Using data from a subset of participants with PA enrolled in a dedicated natural history study (n = 33), we explored associations between neurodevelopmental phenotypes and laboratory parameters. Twenty (61%) participants received an ID diagnosis, and 12 of the 31 (39%) who were fully evaluated received the diagnosis of ASD. A diagnosis of ID, lower full-scale IQ (sample mean = 65 ± 26), and lower adaptive behavior composite scores (sample mean = 67 ± 23) were associated with several biomarkers. Higher concentrations of plasma propionylcarnitine, plasma total 2-methylcitrate, serum erythropoietin, and mitochondrial biomarkers plasma FGF21 and GDF15 were associated with a more severe ID profile. Reduced 1-13C-propionate oxidative capacity and decreased levels of plasma and urinary glutamine were also associated with a more severe ID profile. Only two parameters, increased serum erythropoietin and decreased plasma glutamine, were associated with ASD. Plasma glycine, one of the defining features of PA, was not meaningfully associated with either ID or ASD. Thus, while both ID and ASD were commonly observed in our PA cohort, only ID was robustly associated with metabolic parameters. Our results suggest that disease severity and associated mitochondrial dysfunction may play a role in CNS complications of PA and identify potential biomarkers and candidate surrogate endpoints.

[Expert consensus on the diagnosis and treatment of neonatal hyperammonemia]

Neonatal hyperammonemia is a disorder of ammonia metabolism that occurs in the neonatal period. It is a clinical syndrome characterized by abnormal accumulation of ammonia in the blood and dysfunction of the central nervous system. Due to its low incidence and lack of specificity in clinical manifestations, it is easy to cause misdiagnosis and missed diagnosis. In order to further standardize the diagnosis and treatment of neonatal hyperammonemia, the Youth Commission, Subspecialty Group of Neonatology, Society of Pediatrics, Chinese Medical Association formulated the expert consensus based on clinical evidence in China and overseas and combined with clinical practice experience,and put forward 18 recommendations for the diagnosis and treatment of neonatal hyperaminemia.

Clearance and production of ammonia quantified in humans by constant ammonia infusion - the effects of cirrhosis and ammonia targeting treatments

BACKGROUND & AIMS

Hyperammonaemia is a key pathological feature of liver disease and the primary driver of hepatic encephalopathy (HE). However, the relative roles of increased ammonia production and reduced clearance are poorly understood as is the action of ammonia-targeting HE drugs. We aimed to quantify whole-body ammonia metabolism in healthy persons and patients with cirrhosis and to validate our method by examining the effects of glycerol phenylbutyrate and lactulose + rifaximin treatment.

METHODS

Ten healthy men and ten male patients with cirrhosis were investigated by 90-minute constant ammonia infusion to achieve steady-state plasma ammonia. Whole-body ammonia clearance was calculated as infusion rate divided by steady-state concentration increase and ammonia production as clearance times baseline ammonia concentration. Participants were re-investigated after the ammonia targeting interventions.

RESULTS

In healthy persons, ammonia clearance was 3.5 (3.1-3.9) L/min and production 49 (35-63) μmol/min. Phenylbutyrate increased clearance by 11% (4-19%, p=0.009). Patients with cirrhosis had a 20% decreased ammonia clearance of 2.7 (2.1-3.3) L/min (p = 0.02) and a nearly tripled production to 131 (102-159) μmol/min (p<0.0001). Lactulose + rifaximin reduced production by 20% (2-37%, p=0.03). The infusion was generally well-tolerated save one hyperammonaemic patient with cirrhosis with possible bleeding unrelated to the infusion who developed clinical HE that reverted when infusion was discontinued.

CONCLUSIONS

Whole-body ammonia clearance and production may be measured separately by the technique used. The method identified a lower clearance and a higher production in patients with cirrhosis, and showed that phenylbutyrate increases clearance, whereas lactulose + rifaximin reduces production. The method may be used to examine a range of questions related to normo-/pathophysiology and ammonia-targeting treatment mechanisms.

IMPACT AND IMPLICATIONS

High blood ammonia plays a key role in liver cirrhosis related brain dysfunction. However, the relative roles of increased ammonia production and reduced ammonia clearance are poorly understood as is the action of ammonia-targeting treatments. This study presents a relatively simple test to measure ammonia metabolism. By use of this test, it was possible to show that patients with liver cirrhosis have decreased ammonia clearance and increased ammonia production compared with healthy persons and to quantify distinctively different ammonia-targeting treatment effects. The test presented holds several perspectives for future studies of normal physiology and pathophysiology, not least in regard to elucidating effects of ammonia-targeting therapies.

CLINICAL TRIAL NUMBER

ClinicalTrials.gov (1-16-02-297-20).

Blood ammonia in patients with chronic liver diseases: A better defined role in clinical practice

Ammonia is one of the main players in the pathogenesis of hepatic encephalopathy (HE) in patients with chronic liver diseases. The usefulness of measuring ammonemia has been debated since many years. New data reveal that besides helping in the differential diagnosis of HE, ammonemia could be a prognostic marker not only in patients with HE, but also in patients without any neurological symptoms, suggesting a potential toxic role of ammonia beyond the brain. Finally, targeting ammonemia while monitoring therapeutic response could be a way to improve outcomes in patients with HE.

Switching to Glycerol Phenylbutyrate in 48 Patients with Urea Cycle Disorders: Clinical Experience in Spain

Background and objectives: Glycerol phenylbutyrate (GPB) has demonstrated safety and efficacy in patients with urea cycle disorders (UCDs) by means of its clinical trial program, but there are limited data in clinical practice. In order to analyze the efficacy and safety of GPB in clinical practice, here we present a national Spanish experience after direct switching from another nitrogen scavenger to GPB. Methods: This observational, retrospective, multicenter study was performed in 48 UCD patients (age 11.7 ± 8.2 years) switching to GPB in 13 centers from nine Spanish regions. Clinical, biochemical, and nutritional data were collected at three different times: prior to GPB introduction, at first follow-up assessment, and after one year of GPB treatment. Number of related adverse effects and hyperammonemic crisis 12 months before and after GPB introduction were recorded. Results: GPB was administered at a 247.8 ± 102.1 mg/kg/day dose, compared to 262.6 ± 126.1 mg/kg/day of previous scavenger (46/48 Na-phenylbutyrate). At first follow-up (79 ± 59 days), a statistically significant reduction in ammonia (from 40.2 ± 17.3 to 32.6 ± 13.9 μmol/L, p < 0.001) and glutamine levels (from 791.4 ± 289.8 to 648.6 ± 247.41 μmol/L, p < 0.001) was observed. After one year of GPB treatment (411 ± 92 days), we observed an improved metabolic control (maintenance of ammonia and glutamine reduction, with improved branched chain amino acids profile), and a reduction in hyperammonemic crisis rate (from 0.3 ± 0.7 to less than 0.1 ± 0.3 crisis/patients/year, p = 0.02) and related adverse effects (RAE, from 0.5 to less than 0.1 RAEs/patients/year p < 0.001). Conclusions: This study demonstrates the safety of direct switching from other nitrogen scavengers to GPB in clinical practice, which improves efficacy, metabolic control, and RAE compared to previous treatments.

Variable disease manifestations and metabolic management within a single family affected by ornithine transcarbamylase deficiency

We report on a family with ornithine transcarbamylase (OTC) deficiency, an X-linked urea cycle disorder, with variable disease severity and tailored management strategies based on each family member's biochemical profile and clinical presentation. Our primary patient is a female monozygotic twin who presented to medical care at 10 months of age with acute liver failure, gastrointestinal symptoms, altered mental status, hypoglycemia, and hyperammonemia. The patient's older brother, known to have hemizygous OTC deficiency, died at 8 months of age from cardiac arrest after complications secondary to his diagnosis. Despite her family history, manifestation of symptoms of heterozygous (partial) OTC deficiency went unrecognized by multiple providers based on misconceptions regarding a female's risk for X-linked disease. Despite barriers related to the family's low socioeconomic status, follow-up care by a multidisciplinary metabolic care team, including moderate protein restriction and nitrogen scavenger therapy, led to positive outcomes for the patient. Her twin sister and mother are also heterozygous for variants in OTC and remain controlled on moderate protein restriction. This case illustrates the importance of genotyping all individuals with genetic risk factors for OTC deficiency and the variability in disease manifestation that necessitates tailored treatment approaches for individuals with partial OTC deficiency.

MicroRNA-1297 participates in the repair of intestinal barrier injury in patients with HIV/AIDS via negative regulation of PLCβ1

To explore the role of the miRNA-1297/phospholipase Cβ1 (PLCβ1) axis in intestinal barrier injury. Abnormally expressed miR-1297 and its target gene PLCβ1 as well as their transcriptome sequencing were confirmed by bioinformatics analysis. Next, the intestinal barrier injury was induced by lipopolysaccharide (LPS) in the CCCHIE-2 cells. Subsequently, the impacts of miR-1297 and PLCβ1 on the transcriptome were estimated. QRT-PCR and Western blotting were conducted to detect the relative mRNA and protein expressions, respectively. The cell viability and permeability were analyzed by MTT assay and fluorescent yellow detection. miR-1297 was significantly upregulated in patients with human immunodeficiency virus/acquired immunodeficiency syndrome and targeted PLCβ1. Moreover, overexpressed PLCβ1 was mainly enriched in the transforming growth factor-beta signaling pathway, while the knockdown of miR-1297 was focused on the arginine biosynthesis pathway. The overexpression of miR-1297 could reduce the PLCβ1 expression and inhibit the viability of CCCHIE-2 cells injured by LPS, while the effect of the downregulation of miR-1297 was on the opposite. Western blotting and cell fluorescence localization experiments revealed that the inhibition of miR-1297 increased the expressions of PLCβ1 and ZO-1. In addition, the upregulation of miR-1297 strengthened the permeability in cells injured by LPS, as did the knockdown of PLCβ1. miR-1297 could restrain the repair of intestinal barrier injury via negatively regulating PLCβ1 and its tight junction downstream protein ZO-1 in CCC-HIE-2 cells injured by LPS, which indicated that PLCβ1 and miR-1297 might be important targets for the repair of intestinal barrier injury.

Perceptions and use of phenylbutyrate metabolite testing in urea cycle disorders: Results of a clinician survey and analysis of a centralized testing database

The nitrogen scavengers sodium and glycerol phenylbutyrate (PB), approved for chronic treatment of urea cycle disorders (UCDs), undergo hepatic conversion to phenylacetate (PAA), which conjugates glutamine to form phenylacetylglutamine for urinary nitrogen excretion. Elevated PAA has been associated with reversible neurological toxicity, with symptoms similar to hyperammonemia. Plasma PB metabolite analysis can assess for toxicity and therapeutic drug levels. An online survey was undertaken to assess US clinician perceptions and use of the test in addition to an analysis of centralized US laboratory records. Survey responses from 52 clinicians were analyzed, including 58% who reported using plasma PB metabolite testing. Test users reported managing more UCD patients than nonusers. Users rated the test as "often helpful" for ruling out PAA toxicity (44%), informing PB dosing decisions (42%), and assessing adherence (28%). Test results were reported as most often unremarkable (61%) or suggestive of poor adherence (13%); 46% of users had never encountered results indicative of PAA toxicity. Analyses of laboratory records for 1668 plasma metabolite tests determined that only 5% of samples had plasma PAA-to-phenylacetylglutamine ratios associated with increased risk of PAA toxicity. Nearly half of surveyed clinicians were unsure of metabolite targets; those conducting ad hoc (versus regular) testing were significantly more likely to be unsure of targets. One-fifth of test users identified uncertainties, including questions about test validation, timing, and interpretation. Increased awareness of published PB metabolite data and further clinician education on test interpretation may help to inform the use of metabolite testing to optimize UCD care.

Unfavorable clinical outcomes in patients with carbamoyl phosphate synthetase 1 deficiency

PURPOSE

Carbamoyl phosphate synthetase 1 (CPS1) deficiency affects the first step of urea cycle and is a severe form of urea cycle disorder (UCD). The severity of hyperammonemic encephalopathy determines the clinical course of UCDs. Here, we describe the genetic and clinical characteristics of CPS1 deficiency in Korea.

PATIENT AND METHODS

This study included seven patients with CPS1 deficiency genetically confirmed from January 1992 to September 2020. The peak ammonia level during the first crisis, the half time of peak ammonia level, the initial plasma amino acid levels, and neurological outcomes were compared between CPS1 deficiency and two common UCDs (i.e., 17 patients with argininosuccinate synthetase 1 deficiency and 24 patients with ornithine transcarbamylase deficiency).

RESULT

Eleven CPS1 mutations were identified, including 10 novel mutations. Eight mutations were missense. Six patients with CPS1 deficiency had neonatal type. The peak ammonia level, initial glutamate level, and accompanying rate of irreversible neurological damages were highest in patients with CPS1 deficiency. The patient with late-onset CPS1 deficiency responded dramatically to N-carbamylglutamate treatment.

CONCLUSION

The clinical manifestations of CPS1 deficiency were the most severe among UCDs. Considering the high proportion of missense mutations, responsiveness to N-carbamylglutamate would be evaluated in a future study.

A randomized trial to examine the impact of food on pharmacokinetics of 4-phenylbutyrate and change in amino acid availability after a single oral administration of sodium 4-phenylbutyrarte in healthy volunteers

Urea cycle disorders (UCDs), inborn errors of hepatocyte metabolism, result in the systemic accumulation of ammonia to toxic levels. Sodium 4-phenylbutyrate (NaPB), a standard therapy for UCDs for over 20 years, generates an alternative pathway of nitrogen deposition through glutamine consumption. Administration during or immediately after a meal is the accepted use of NaPB. However, this regimen is not based on clinical evidence. Here, an open-label, single-dose, five-period crossover study was conducted in healthy adults to investigate the effect of food on the pharmacokinetics of NaPB and determine any subsequent change in amino acid availability. Twenty subjects were randomized to one of four treatment groups. Following an overnight fast, NaPB was administered orally at 4.3 g/m² (high dose, HD) or 1.4 g/m² (low dose, LD) either 30 min before or just after breakfast. At both doses, compared with post-breakfast administration, pre-breakfast administration significantly increased systemic exposure of PB and decreased plasma glutamine availability. Pre-breakfast LD administration attenuated plasma glutamine availability to the same extent as post-breakfast HD administration. Regardless of the regimen, plasma levels of branched-chain amino acids (BCAA) were decreased below baseline in a dose-dependent manner. In conclusion, preprandial oral administration of NaPB maximized systemic exposure of the drug and thereby its potency to consume plasma glutamine. This finding may improve poor medication compliance because of the issues with odor, taste, and pill burden of NaPB and reduce the risk of BCAA deficiency in NaPB therapy.

A second Warburg-like effect in cancer metabolism: The metabolic shift of glutamine-derived nitrogen: A shift in glutamine-derived nitrogen metabolism from glutaminolysis to de novo nucleotide biosynthesis contributes to malignant evolution of cancer

Carbon and nitrogen are essential elements for life. Glucose as a carbon source and glutamine as a nitrogen source are important nutrients for cell proliferation. About 100 years ago, it was discovered that cancer cells that have acquired unlimited proliferative capacity and undergone malignant evolution in their host manifest a cancer-specific remodeling of glucose metabolism (the Warburg effect). Only recently, however, was it shown that the metabolism of glutamine-derived nitrogen is substantially shifted from glutaminolysis to nucleotide biosynthesis during malignant progression of cancer-which might be referred to as a "second" Warburg effect. In this review, address the mechanism and relevance of this metabolic shift of glutamine-derived nitrogen in human cancer. We also examine the clinical potential of anticancer therapies that modulate the metabolic pathways of glutamine-derived nitrogen. This shift may be as important as the shift in carbon metabolism, which has long been known as the Warburg effect.

Neonatal factors related to survival and intellectual and developmental outcome of patients with early-onset urea cycle disorders

PURPOSE

We aimed to identify prognostic factors for survival and long-term intellectual and developmental outcome in neonatal patients with early-onset urea cycle disorders (UCD) experiencing hyperammonaemic coma.

METHODS

We retrospectively analysed ammonia (NH3) and glutamine levels, electroencephalogram and brain images obtained during neonatal coma of UCD patients born between 1995 and 2011 and managed at a single centre and correlated them to survival and intellectual and developmental outcome.

RESULTS

We included 38 neonates suffering from deficiencies of argininosuccinate synthetase (ASSD, N = 12), ornithine transcarbamylase (OTCD, N = 10), carbamoylphosphate synthetase 1 (CPSD, N = 7), argininosuccinate lyase (ASLD, N = 7), N-acetylglutamate synthase (NAGS, N = 1) or arginase (ARGD, N = 1). Symptoms occurred earlier in mitochondrial than in cytosolic UCD. Sixty-eight percent of patients survived, with a mean (standard deviation-SD) follow-up of 10.4 (5.3) years. Mortality was mostly observed in OTCD (N = 7/10) and CPSD (N = 4/7) patients. Plasma NH3 level during the neonatal period, expressed as area under the curve, but not glutamine level was associated with mortality (p = .044 and p = .610). 62.1% of the patients had normal intellectual and developmental outcome. Intellectual and developmental outcome tended to correlate with UCD subtype (p = .052). No difference in plasma NH3 or glutamine level during the neonatal period among developmental outcomes was identified. EEG severity was linked to UCD subtypes (p = .004), ammonia levels (p = .037), duration of coma (p = .043), and mortality during the neonatal period (p = .020). Status epilepticus was recorded in 6 patients, 3 of whom died neonatally, 1 developed a severe intellectual disability while the 2 last patients had a normal development.

CONCLUSION

UCD subtypes differed by survival rate, intellectual and developmental outcome and EEG features in the neonatal period. Hyperammonaemia expressed as area under the curve was associated with survival but not with intellectual and developmental outcome whereas glutamine was not associated with one of these outcomes. Prognostic value of video-EEG monitoring and the association between status epilepticus and mortality should be assessed in neonatal hyperammonaemic coma in further studies.

A mutation-independent CRISPR-Cas9-mediated gene targeting approach to treat a murine model of ornithine transcarbamylase deficiency

Ornithine transcarbamylase (OTC) deficiency is an X-linked urea cycle disorder associated with high mortality. Although a promising treatment for late-onset OTC deficiency, adeno-associated virus (AAV) neonatal gene therapy would only provide short-term therapeutic effects as the non-integrated genome gets lost during hepatocyte proliferation. CRISPR-Cas9-mediated homology-directed repair can correct a G-to-A mutation in 10% of OTC alleles in the livers of newborn OTC spfash mice. However, an editing vector able to correct one mutation would not be applicable for patients carrying different OTC mutations, plus expression would not be fast enough to treat a hyperammonemia crisis. Here, we describe a dual-AAV vector system that accomplishes rapid short-term expression from a non-integrated minigene and long-term expression from the site-specific integration of this minigene without any selective growth advantage for OTC-positive cells in newborns. This CRISPR-Cas9 gene-targeting approach may be applicable to all patients with OTC deficiency, irrespective of mutation and/or clinical state.

Quantification of urinary derivatives of Phenylbutyric and Benzoic acids by LC-MS/MS as treatment compliance biomarkers in Urea Cycle disorders

PURPOSE

Salts of phenylacetic acid (PAA) and phenylbutyric acid (PBA) have been used for nitrogen elimination as a treatment for hyperammonaemia caused by urea cycle disorders (UCD). A new analytical method for PBA measurement in urine which helps to evaluate the drug adherence has been implemented.

METHODS

Urine specimens from UCD patients receiving PBA were analysed by tandem mass spectrometry to measure urine phenylacetylglutamine (PAGln). Some clinical and biochemical data for each patient were collected.

RESULTS

Our study included 87 samples from 40 UCD patients. The PAGln levels did not correlate with height, weight or age. However, the PAGln values showed correlation with PBA dose (r = 0.383, P = 0.015). Plasma glutamine and ammonia levels presented a positive correlation (r = 0.537, P < 0.001). The stability for PAGln in urine was determined at different storage temperatures.

CONCLUSIONS

We have developed a simple method for the determination of PAGln in urine, which acts as useful biomarker of effective drug delivery. PAGln in urine is stable at room temperature at least for 15 days, and for several months when frozen at -20 °C. This procedure is useful for the optimization and monitorization of the drug dose allowing the use of spot urine samples.

Urea Cycle Related Amino Acids Measured in Dried Bloodspots Enable Long-Term In Vivo Monitoring and Therapeutic Adjustment

BACKGROUND

Dried bloodspots are easy to collect and to transport to assess various metabolites, such as amino acids. Dried bloodspots are routinely used for diagnosis and monitoring of some inherited metabolic diseases.

METHODS

Measurement of amino acids from dried blood spots by liquid chromatography-tandem mass spectrometry.

RESULTS

We describe a novel rapid method to measure underivatised urea cycle related amino acids. Application of this method enabled accurate monitoring of these amino acids to assess the efficacy of therapies in argininosuccinate lyase deficient mice and monitoring of these metabolites in patients with urea cycle defects.

CONCLUSION

Measuring urea cycle related amino acids in urea cycle defects from dried blood spots is a reliable tool in animal research and will be of benefit in the clinic, facilitating optimisation of protein-restricted diet and preventing amino acid deprivation.

Suggested guidelines for the diagnosis and management of urea cycle disorders: First revision

In 2012, we published guidelines summarizing and evaluating late 2011 evidence for diagnosis and therapy of urea cycle disorders (UCDs). With 1:35 000 estimated incidence, UCDs cause hyperammonemia of neonatal (~50%) or late onset that can lead to intellectual disability or death, even while effective therapies do exist. In the 7 years that have elapsed since the first guideline was published, abundant novel information has accumulated, experience on newborn screening for some UCDs has widened, a novel hyperammonemia-causing genetic disorder has been reported, glycerol phenylbutyrate has been introduced as a treatment, and novel promising therapeutic avenues (including gene therapy) have been opened. Several factors including the impact of the first edition of these guidelines (frequently read and quoted) may have increased awareness among health professionals and patient families. However, under-recognition and delayed diagnosis of UCDs still appear widespread. It was therefore necessary to revise the original guidelines to ensure an up-to-date frame of reference for professionals and patients as well as for awareness campaigns. This was accomplished by keeping the original spirit of providing a trans-European consensus based on robust evidence (scored with GRADE methodology), involving professionals on UCDs from nine countries in preparing this consensus. We believe this revised guideline, which has been reviewed by several societies that are involved in the management of UCDs, will have a positive impact on the outcomes of patients by establishing common standards, and spreading and harmonizing good practices. It may also promote the identification of knowledge voids to be filled by future research.

Perspectives on urea cycle disorder management: Results of a clinician survey

BACKGROUND/AIMS

Urea cycle disorders (UCDs) are rare inborn errors of urea synthesis. US and European consensus statements on the diagnosis and treatment of UCDs were last published in 2001 and 2019, respectively. Recommendations are based primarily on case reports and expert opinion and there is limited agreement or consistency related to long-term management approaches. A clinician survey was conducted to assess current real-world practices and perspectives on challenges and unmet needs.

METHODS

A 14-item multiple-choice survey was administered to physicians in 2017. Clinicians who reported actively managing at least 1 patient with UCD were eligible to participate. Descriptive statistics were calculated for each survey item (frequencies for categorical variables; means, standard deviations, medians, and ranges for continuous variables).

RESULTS

Sixty-six US clinicians completed the survey (65 geneticists; 1 pediatric neurologist). Over 90% of responders agreed or strongly agreed that even modest elevations in ammonia could cause physiological and functional brain damage; >80% of respondents agreed that asymptomatic UCD patients are at risk of brain damage over time due to mild/subclinical elevations in ammonia. Eighty-six percent of clinicians agreed or strongly agreed with recommending genetic testing for female relatives when a patient is diagnosed with ornithine transcarbamylase deficiency. Ninety-four percent of respondents agreed that patients have better disease control when they are more adherent to their UCD therapy. Nearly 90% indicated that clinicians and patients would benefit from updated UCD management guidance. More than half (53%) of respondents rated the symptoms of UCDs as extremely or very burdensome to the everyday lives of patients and their families; only 8% rated UCD symptoms as slightly or not at all burdensome. The majority of clinicians agreed (48%) or strongly agreed (32%) that caring for a child or family member with a UCD has a negative impact on the quality of life and/or health of family members/guardians (e.g. stress, relationships, ability to work).

CONCLUSIONS

This self-reported survey suggests a need for updated and expanded clinical guidance on the long-term treatment and management of UCD patients.

Comparative Hepatotoxicity of Novel PFOA Alternatives (Perfluoropolyether Carboxylic Acids) on Male Mice

As novel alternatives to perfluorooctanoic acid (PFOA), perfluoropolyether carboxylic acids (multiether PFECAs, CF₃(OCF₂) _nCOO^-, n = 2-4) have been detected in various environmental matrices; however, public information regarding their toxicities remains unavailable. To compare the hepatotoxicity of multiether PFECAs (e.g., PFO2HxA, PFO3OA, and PFO4DA) with PFOA, male mice were exposed to 0.4, 2, or 10 mg/kg/d of each chemical for 28 d, respectively. Results demonstrated that PFO2HxA and PFO3OA exposure did not induce marked increases in relative liver weight; whereas 2 and 10 mg/kg/d of PFO4DA significantly increased relative liver weight. Furthermore, PFO2HxA and PFO3OA demonstrated almost no accumulation in the liver or serum; whereas PFO4DA was accumulated but with weaker potential than PFOA. Exposure to 10 mg/kg/d of PFO4DA led to 198 differentially expressed liver genes (56 down-regulated, 142 up-regulated), with bioinformatics analysis highlighting the urea cycle disorder. Like PFOA, 10 mg/kg/d of PFO4DA decreased the urea cycle-related enzyme protein levels (e.g., carbamoyl phosphate synthetase 1) and serum ammonia content in a dose-dependent manner. Both PFOA and PFO4DA treatment (highest concentration) caused a decrease in glutamate content and increase in both glutamine synthetase activity and aquaporin protein levels in the brain. Thus, we concluded that PFO4DA caused hepatotoxicity, as indicated by hepatomegaly and karyolysis, though to a lesser degree than PFOA, and induced urea cycle disorder, which may contribute to the observed toxic effects.

Transatlantic combined and comparative data analysis of 1095 patients with urea cycle disorders-A successful strategy for clinical research of rare diseases

BACKGROUND

To improve our understanding of urea cycle disorders (UCDs) prospectively followed by two North American (NA) and European (EU) patient cohorts.

AIMS

Description of the NA and EU patient samples and investigation of the prospects of combined and comparative analyses for individuals with UCDs.

METHODS

Retrieval and comparison of the data from 1095 individuals (NA: 620, EU: 475) from two electronic databases.

RESULTS

The proportion of females with ornithine transcarbamylase deficiency (fOTC-D), particularly those being asymptomatic (asfOTC-D), was higher in the NA than in the EU sample. Exclusion of asfOTC-D resulted in similar distributions in both samples. The mean age at first symptoms was higher in NA than in EU patients with late onset (LO), but similar for those with early (≤ 28 days) onset (EO) of symptoms. Also, the mean age at diagnosis and diagnostic delay for EO and LO patients were similar in the NA and EU cohorts. In most patients (including fOTC-D), diagnosis was made after the onset of symptoms (59.9%) or by high-risk family screening (24.7%), and less often by newborn screening (8.9%) and prenatal testing (3.7%). Analysis of clinical phenotypes revealed that EO patients presented with more symptoms than LO individuals, but that numbers of symptoms correlated with plasma ammonium concentrations in EO patients only. Liver transplantation was reported for 90 NA and 25 EU patients.

CONCLUSIONS

Combined analysis of databases drawn from distinct populations opens the possibility to increase sample sizes for natural history questions, while comparative analysis utilizing differences in approach to treatment can evaluate therapeutic options and enhance long-term outcome studies.

A Handheld, Colorimetric Optoelectronic Dynamics Analyzer for Measuring Total Ammonia of Biological Samples

This paper introduces a wireless, solid-state, portable, and automated device capable of measuring the total ammonia [ammonia (NH₃) and ammonium (NH₄⁺)] levels of fluids, including biological samples. This device reliably measures the total ammonia of biological samples (e.g., urine) faster than the current ammonia quantification techniques. Medical professionals typically estimate NH4⁺ levels using error-prone indirect measurement techniques (i.e., urine anion gap), which are time-consuming and are seldom suitable for periodic measurements. Several instantaneous measurements of total ammonia levels in a patient urine could be utilized as an early warning for both acid-base and/or potassium disturbances. Given the device’s operation mechanism, it is able to quantify the total ammonia concentration within a biological sample in only 5 s and can simultaneously transmit data to other devices via Bluetooth. The analytical operation demonstrated high sensitivity, high specificity, fast reversibility, rapid response time, and has enabled the accurate determination of total ammonia concentration in urine samples produced by subjects who had consumed diets of variable protein compositions.

Safety and efficacy of glycerol phenylbutyrate for management of urea cycle disorders in patients aged 2months to 2years

INTRODUCTION

Glycerol phenylbutyrate (GPB) is approved in the US for the management of patients 2months of age and older with urea cycle disorders (UCDs) that cannot be managed with protein restriction and/or amino acid supplementation alone. Limited data exist on the use of nitrogen conjugation agents in very young patients.

METHODS

Seventeen patients (15 previously on other nitrogen scavengers) with all types of UCDs aged 2months to 2years were switched to, or started, GPB. Retrospective data up to 12months pre-switch and prospective data during initiation of therapy were used as baseline measures. The primary efficacy endpoint of the integrated analysis was the successful transition to GPB with controlled ammonia (<100μmol/L and no clinical symptoms). Secondary endpoints included glutamine and levels of other amino acids. Safety endpoints included adverse events, hyperammonemic crises (HACs), and growth and development.

RESULTS

82% and 53% of patients completed 3 and 6months of therapy, respectively (mean 8.85months, range 6days-18.4months). Patients transitioned to GPB maintained excellent control of ammonia and glutamine levels. There were 36 HACs in 11 patients before GPB and 11 in 7 patients while on GPB, with a reduction from 2.98 to 0.88 episodes per year. Adverse events occurring in at least 10% of patients while on GPB were neutropenia, vomiting, diarrhea, pyrexia, hypophagia, cough, nasal congestion, rhinorrhea, rash/papule.

CONCLUSION

GPB was safe and effective in UCD patients aged 2months to 2years. GPB use was associated with good short- and long-term control of ammonia and glutamine levels, and the annualized frequency of hyperammonemic crises was lower during the study than before the study. There was no evidence for any previously unknown toxicity of GPB.

Quantitation of phenylbutyrate metabolites by UPLC-MS/MS demonstrates inverse correlation of phenylacetate:phenylacetylglutamine ratio with plasma glutamine levels

Urea cycle disorders (UCDs) are genetic conditions characterized by nitrogen accumulation in the form of ammonia and caused by defects in the enzymes required to convert ammonia to urea for excretion. UCDs include a spectrum of enzyme deficiencies, namely n-acetylglutamate synthase deficiency (NAGS), carbamoyl phosphate synthetase I deficiency (CPS1), ornithine transcarbamylase deficiency (OTC), argininosuccinate lyase deficiency (ASL), citrullinemia type I (ASS1), and argininemia (ARG). Currently, sodium phenylbutyrate and glycerol phenylbutyrate are primary medications used to treat patients with UCDs, and long-term monitoring of these compounds is critical for preventing drug toxic levels. Therefore, a fast and simple ultra-performance liquid chromatography (UPLC-MS/MS) method was developed and validated for quantification of phenylbutyrate (PB), phenylacetate (PA), and phenylacetylglutamine (PAG) in plasma and urine. The separation of all three analytes was achieved in 2min, and the limits of detection were <0.04μg/ml. Intra-precision and inter-precision were <8.5% and 4% at two quality control concentrations, respectively. Average recoveries for all compounds ranged from 100% to 106%. With the developed assay, a strong correlation between PA and the PA/PAG ratio and an inverse correlation between PA/PAG ratio and plasma glutamine were observed in 35 patients with confirmed UCDs. Moreover, all individuals with a ratio ≥0.6 had plasma glutamine levels<1000μmol/l. Our data suggest that a PA/PAG ratio in the range of 0.6-1.5 will result in a plasma glutamine level<1000μmol/l without reaching toxic levels of PA.

Targeting CPS1 in the treatment of Carbamoyl phosphate synthetase 1 (CPS1) deficiency, a urea cycle disorder

INTRODUCTION

Carbamoyl phosphate synthetase 1 (CPS1) deficiency (CPS1D) is a rare autosomal recessive urea cycle disorder (UCD), which can lead to life-threatening hyperammonemia. Unless promptly treated, it can result in encephalopathy, coma and death, or intellectual disability in surviving patients. Over recent decades, therapies for CPS1D have barely improved leaving the management of these patients largely unchanged. Additionally, in many cases, current management (protein-restriction and supplementation with citrulline and/or arginine and ammonia scavengers) is insufficient for achieving metabolic stability, highlighting the importance of developing alternative therapeutic approaches. Areas covered: After describing UCDs and CPS1D, we give an overview of the structure- function of CPS1. We then describe current management and potential novel treatments including N-carbamoyl-L-glutamate (NCG), pharmacological chaperones, and gene therapy to treat hyperammonemia. Expert opinion: Probably, the first novel CPS1D therapies to reach the clinics will be the already commercial substance NCG, which is the standard treatment for N-acetylglutamate synthase deficiency and has been proven to rescue specific CPS1D mutations. Pharmacological chaperones and gene therapy are under development too, but these two technologies still have key challenges to be overcome. In addition, current experimental therapies will hopefully add further treatment options.

Clinical course of 63 patients with neonatal onset urea cycle disorders in the years 2001-2013

BACKGROUND

Urea cycle disorders (UCDs) are rare inherited metabolic defects of ammonia detoxification. In about half of patients presenting with a UCD, the first symptoms appear within a few days after birth. These neonatal onset patients generally have a severe defect of urea cycle function and their survival and outcome prognoses are often limited. To understand better the current situation of neonatal onset in UCDs, we have performed a multicentre, retrospective, non-interventional case series study focussing on the most severe UCDs, namely defects of carbamoyl phosphate synthetase 1 (CPS1), ornithine transcarbamylase (OTC), and argininosuccinate synthetase (ASS).

METHODS AND RESULTS

Data of 63 patients were collected (27 patients with ASS deficiency, 23 patients with OTC deficiency, and 12 patients with CPS1 deficiency, one patient definite diagnosis not documented). The majority of patients (43/63, 68 %) had an initial ammonia concentration exceeding 500 μmol/L (normal < 100), of which most (26/43, 60.5 %) were also encephalopathic and were treated with hemodialysis. In patients surviving the initial crisis, recurrence of hyperammonemic events within the first 1.5 years of life occurred frequently (mean 3.6 events, range 0-20). Of all patients, 16 (25.4 %) died during or immediately after the neonatal period.

CONCLUSION

We observed in this cohort of neonatal onset UCD patients a high rate of initial life-threatening hyperammonemia and a high risk of recurrence of severe hyperammonemic crises. These corresponded to a high mortality rate during the entire study period (30.2 %) despite the fact that patients were treated in leading European metabolic centers. This underlines the need to critically re-evaluate the current treatment strategies in these patients.

Fasting Blood Ammonia Predicts Risk and Frequency of Hepatic Encephalopathy Episodes in Patients With Cirrhosis

BACKGROUND & AIMS

There is controversy over the use of measuring blood levels of ammonia (NH3) in the management of patients with overt hepatic encephalopathy (HE).

METHODS

We performed a retrospective analysis of data from a randomized, double-blind study of 178 patients with cirrhosis given glycerol phenylbutyrate (an NH3-lowering agent) or placebo for 16 weeks. Blood samples were collected at baseline and on study days 7 and 14 and NH3 levels were measured. The probabilities of having an HE episode, based on ammonia values, were modeled using binary logistic regression. A Cox proportional model was used to determine the risk of HE episodes in patients with baseline fasting NH3 levels ≤1.5-fold the upper limit of normal (ULN) versus patients with fasting NH3 levels >1.5-fold the ULN.

RESULTS

The risk and frequency of HE episodes and HE-related hospitalizations correlated with baseline (mean, 51 ± 6 μmol/L; ULN, 35 μmol/L) and on-study fasting levels of NH3, and increased sharply at levels >1.5-fold the ULN. Regardless of baseline level, NH3 exposure and the relative risk of HE episodes were decreased by glycerol phenylbutyrate.

CONCLUSIONS

In analysis of data from a phase 2 study of the effects of glycerol phenylbutyrate in patients with cirrhosis, we found that fasting levels of NH3 in blood can identify patients at risk for HE-related morbidity. Patients with HE might benefit from NH3-lowering therapy. ClinicalTrials.gov no: NCT 00999167.

Glutamine and hyperammonemic crises in patients with urea cycle disorders

Blood ammonia and glutamine levels are used as biomarkers of control in patients with urea cycle disorders (UCDs). This study was undertaken to evaluate glutamine variability and utility as a predictor of hyperammonemic crises (HACs) in UCD patients.

METHODS

The relationships between glutamine and ammonia levels and the incidence and timing of HACs were evaluated in over 100 adult and pediatric UCD patients who participated in clinical trials of glycerol phenylbutyrate.

RESULTS

The median (range) intra-subject 24-hour coefficient of variation for glutamine was 15% (8-29%) as compared with 56% (28%-154%) for ammonia, and the correlation coefficient between glutamine and concurrent ammonia levels varied from 0.17 to 0.29. Patients with baseline (fasting) glutamine values >900 μmol/L had higher baseline ammonia levels (mean [SD]: 39.6 [26.2]μmol/L) than patients with baseline glutamine ≤ 900 μmol/L (26.6 [18.0]μmol/L). Glutamine values >900 μmol/L during the study were associated with an approximately 2-fold higher HAC risk (odds ratio [OR]=1.98; p=0.173). However, glutamine lost predictive significance (OR=1.47; p=0.439) when concomitant ammonia was taken into account, whereas the predictive value of baseline ammonia ≥ 1.0 upper limit of normal (ULN) was highly statistically significant (OR=4.96; p=0.013). There was no significant effect of glutamine >900 μmol/L on time to first HAC crisis (hazard ratio [HR]=1.14; p=0.813), but there was a significant effect of baseline ammonia ≥ 1.0 ULN (HR=4.62; p=0.0011).

CONCLUSIONS

The findings in this UCD population suggest that glutamine is a weaker predictor of HACs than ammonia and that the utility of the predictive value of glutamine will need to take into account concurrent ammonia levels.