The utility of EEG monitoring in neonates with hyperammonemia due to inborn errors of metabolism.

BACKGROUND: Continuous EEG studies demonstrate that neonates with seizures due to cerebral pathology, such as hypoxia ischemia, exhibit predominantly electrographic seizures (i.e. those only detected with EEG because they lack clinical features). Previous small case series demonstrate EEG changes and seizures during hyperammonemia associated with inborn errors of metabolism (IEM) but there are no reports utilizing continuous EEG in these conditions. OBJECTIVE: To characterize seizures and evaluate the utility of continuous EEG recording during hyperammonemia due to inborn errors of metabolism. METHODS: We retrospectively reviewed medical records and EEG tracings of neonates who presented with hyperammonemia due to inborn errors of metabolism who had continuous EEG and full medical records available for review, including follow up. RESULTS: Eight neonates with hyperammonemia were studied, 7 had urea cycle defects: Argininosuccinate lyase deficiency [3], (ornithine transcarbamylase deficiency [3], carbomyl phosphate synthase deficiency [1] and one had an organic acidemia: Methylmalonic acidemia [1]. Most common presentations were lethargy and poor feeding at 12-72 h of life. The highest blood ammonia level was 874 µmol/L (median); range 823-1647 µmol/L (normal value <50 µmol/L in term neonates). Seven were treated with hemodialysis in addition to nitrogen scavengers. Seven neonates had seizures; six had only electrographic seizures. Seizures initially occurred within 24-36 h of clinical presentation, sometimes with normal ammonia and glutamine levels. Neonates with seizures all lacked state changes on EEG. Inter burst interval duration correlated with degree of hyperammonemia. Two cases with normal plasma ammonia but increasing interburst interval duration were proven to have stroke by MRI. CONCLUSIONS: Seizures occur frequently in neonates with hyperammonemia; most can be detected only with continuous EEG. Seizures may occur when ammonia and glutamine levels are normal. Interburst interval duration is associated with ammonia levels or cerebral dysfunction from other brain pathology. Continuous EEG can be a useful tool for managing infants with hyperammonemia and may be essential for seizure management especially for infants in deep metabolic coma.

Identification of three novel mutations in fourteen patients with citrullinemia type 1.

OBJECTIVES: Citrullinemia type 1 (CTLN1) is an autosomal recessive genetic disorder caused by mutations in the argininosuccinate synthetase 1 (ASS1) gene, which encodes for the argininosuccinate synthetase enzyme. Here, we report genetic and clinical characterizations of 14 patients with citrullinemia type 1. DESIGN & METHODS: The study group consisted of 14 patients (4 females, 10 males) diagnosed with citrullinemia type 1 from three centers in Turkey. Age of onset, clinical presentation, initial citrulline and ammonia levels, family history and molecular genetic analysis were retrospectively evaluated. RESULTS: The mean age of the cohort and the mean age at the time of diagnosis were 48.3±36.5months (min: 12days, max: 10years) and 11.6±26.2months (min: 3days, max: 8years), respectively. In four patients, a homozygous p.Gly390Arg pathogenic variant was detected. All patients homozygous for p.Gly390Arg were diagnosed during the newborn period with the clinical presentation of classical citrullinemia. In each two patients, homozygous p.Arg86His, c.773+49C>T and p.Gly362Val pathogenic variants were detected. Clinical presentation was compatible with the mild form of the disease in patients homozygous for c.773+49C>T and for Gly362Val. Novel compound heterozygous genotypes (p.Ala164Pro/p.Gly390Arg; p.Leu290Pro/p.Gly390Arg; p.Thr389Pro/p.Gly390Arg) were identified in five patients. Of these, three siblings with CTLN1 were diagnosed with the compound heterozygous genotype p.Ala164Pro/p.Gly390Arg at the age of 4days, 5days and 2years, respectively. The other two patients with novel compound heterozygous genotypes (p.Leu290Pro/p.Gly390Arg; p.Thr389Pro/p.Gly390Arg) were identified in the first month of life as neonatal onset form and were born to non-consanguineous parents. CONCLUSION: In our study, consistent with the literature, a correlation was found between homozygous p.Gly390Arg mutation and the classic neonatal onset form. Mild citrullinemia was detected in patients with c.773+49C>T or p.Gly362Val pathogenic variants. This study adds to our understanding of the molecular genetic background of patients with CTLN1, and allows to infer on the correlation between the genotype and phenotype of the disease.

Arginine Deprivation With Pegylated Arginine Deiminase in Patients With Argininosuccinate Synthetase 1-Deficient Malignant Pleural Mesothelioma: A Randomized Clinical Trial.

IMPORTANCE: Preclinical studies show that arginine deprivation is synthetically lethal in argininosuccinate synthetase 1 (ASS1)-negative cancers, including mesothelioma. The role of the arginine-lowering agent pegylated arginine deiminase (ADI-PEG20) has not been evaluated in a randomized and biomarker-driven study among patients with cancer. OBJECTIVE: To assess the clinical impact of arginine depletion in patients with ASS1-deficient malignant pleural mesothelioma. DESIGN, SETTING, AND PARTICIPANTS: A multicenter phase 2 randomized clinical trial, the Arginine Deiminase and Mesothelioma (ADAM) study, was conducted between March 2, 2011, and May 21, 2013, at 8 academic cancer centers. Immunohistochemical screening of 201 patients (2011-2013) identified 68 with advanced ASS1-deficient malignant pleural mesothelioma. INTERVENTIONS: Randomization 2:1 to arginine deprivation (ADI-PEG20, 36.8 mg/m2, weekly intramuscular) plus best supportive care (BSC) or BSC alone. MAIN OUTCOMES AND MEASURES: The primary end point was progression-free survival (PFS) assessed by modified Response Evaluation Criteria in Solid Tumors (RECIST) (target hazard ratio, 0.60). Secondary end points were overall survival (OS), tumor response rate, safety, and quality of life, analyzed by intention to treat. We measured plasma arginine and citrulline levels, anti-ADI-PEG20 antibody titer, ASS1 methylation status, and metabolic response by 18F-fluorodeoxyglucose positron-emission tomography. RESULTS: Median (range) follow-up in 68 adults (median [range] age, 66 [48-83] years; 19% female) was 38 (2.5-39) months. The PFS hazard ratio was 0.56 (95% CI, 0.33-0.96), with a median of 3.2 months in the ADI-PEG20 group vs 2.0 months in the BSC group (P = .03) (absolute risk, 18% vs 0% at 6 months). Best response at 4 months (modified RECIST) was stable disease: 12 of 23 (52%) in the ADI-PEG20 group vs 2 of 9 (22%) in the BSC group (P = .23). The OS curves crossed, so life expectancy was used: 15.7 months in the ADI-PEG20 group vs 12.1 months in the BSC group (difference of 3.6 [95% CI, -1.0 to 8.1] months; P = .13). The incidence of symptomatic adverse events of grade at least 3 was 11 of 44 (25%) in the ADI-PEG20 group vs 4 of 24 (17%) in the BSC group (P = .43), the most common being immune related, nonfebrile neutropenia, gastrointestinal events, and fatigue. Differential ASS1 gene-body methylation correlated with ASS1 immunohistochemistry, and longer arginine deprivation correlated with improved PFS. CONCLUSIONS AND RELEVANCE: In this trial, arginine deprivation with ADI-PEG20 improved PFS in patients with ASS1-deficient mesothelioma. Targeting arginine is safe and warrants further clinical investigation in arginine-dependent cancers. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT01279967.

Argininosuccinate synthetase as a plasma biomarker of liver injury after acetaminophen overdose in rodents and humans.

CONTEXT: New biomarkers are needed in acetaminophen (APAP) hepatotoxicity. Plasma argininosuccinate synthetase (ASS) is a promising candidate. OBJECTIVE: Characterize ASS in APAP hepatotoxicity. METHODS: ASS was measured in plasma from rodents and humans with APAP hepatotoxicity. RESULTS: In mice, ASS increased before injury, peaked before alanine aminotransferase (ALT) and decreased rapidly. Fischer rats had a greater increase in ASS relative to ALT. Patients with abnormal liver test results had very high ASS compared to controls. ASS appeared to increase early in some patients, and declined rapidly in all. CONCLUSIONS: ASS may be a useful biomarker of acute cell death in APAP hepatotoxicity.

Inhibition of LPS toxicity by hepatic argininosuccinate synthase (ASS): novel roles for ASS in innate immune responses to bacterial infection.

Lipopolysaccharide (LPS), a structural component of Gram-negative bacteria, is implicated in the pathogenesis of endotoxemia/sepsis and multi-organ injury, including liver damage. We have shown that argininosuccinate synthase (ASS), a hepatic enzyme of the urea cycle, accumulates in circulation within 1h after treatment with both LPS alone and hepatotoxic combination of LPS and D-Galactosamine. These findings indicate ASS as a sensitive biomarker of liver responses to bacterial endotoxin. Furthermore, we suggest that the ASS release represents a potential counteracting liver reaction to LPS, and demonstrates anti-LPS activity of recombinant ASS (rASS) in vitro and in rodent models of endotoxemia in vivo. rASS physically bound to LPS, as indicated by a gel shift assay, and suppressed Escherichia coli growth in cultures consistent with direct antimicrobial properties of ASS. rASS reduced LPS cytotoxicity, TNF-α production, and increased cell viability in cultured mouse macrophages, even when added one hour following LPS challenge. Intraperitoneal injection of rASS (5 mg/kg) after treatment with a high dose of LPS remarkably increased survival of rodents, with a concomitant decrease of sepsis markers TNF-α, C-reactive protein (CRP), and lactate dehydrogenase (LDH) levels in blood. These results suggest that the endogenous ASS constitutes a novel liver-derived component of the innate immune response to bacterial LPS, and that recombinant ASS could mitigate the lethal effects of bacterial endotoxins during sepsis.

The role of molecular testing and enzyme analysis in the management of hypomorphic citrullinemia.

Expanded newborn screening detects patients with modest elevations in citrulline; however it is currently unclear how to treat these patients and how to counsel their parents. In order to begin to address these issues, we compared the clinical, biochemical, and molecular features of 10 patients with mildly elevated citrulline levels. Three patients presented with clinical illness whereas seven came to attention as a result of expanded newborn screening. One patient presented during pregnancy and responded promptly to IV sodium phenylacetate/sodium benzoate and arginine therapy with no long-term adverse effects on mother or fetus. Two children presented with neurocognitive dysfunction, one of these responded dramatically to dietary protein reduction. ASS enzyme activity was not deficient in all patients with biallelic mutations suggesting this test cannot exclude the ASS1 locus in patients with mildly elevated plasma citrulline. Conversely, all symptomatic patients who were tested had deficient activity. We describe four unreported mutations (p.Y291S, p.R272H, p.F72L, and p.L88I), as well as the common p.W179R mutation. In silico algorithms were inconsistent in predicting the pathogenicity of mutations. The cognitive benefit in one patient of protein restriction and the lack of adverse outcome in seven others restricted from birth, suggest a role for protein restriction and continued monitoring to prevent neurocognitive dysfunction.

Long-term survival of patients with argininosuccinate synthetase deficiency.

OBJECTIVE: To monitor long-term survival and outcome of patients with neonatal-onset argininosuccinate synthetase deficiency (ASD) who were treated with specific therapeutic protocols designed to activate alternative pathways of waste nitrogen excretion. DESIGN: Patients for this study included 24 infants born before 1990 and rescued from hyperammonemic coma caused by neonatal-onset ASD; they were referred to this center for enrollment in ongoing clinical studies of sodium benzoate, sodium phenylacetate, and sodium phenylbutyrate. Collaborating physicians throughout the United States and Canada provided information on survival, intellectual development, intercurrent hyperammonemic episodes, and anthropometric and biochemical measurements. RESULTS: The cumulative survival rate was 87.5% at 5 years and 72% at 10 years of age. Survivors include 15 patients currently treated with high doses of sodium phenylbutyrate; two patients have withdrawn. Among the treated group, 11 are classified as severely to profoundly mentally retarded. The remaining four patients have IQ measurements in the borderline to mentally retarded range. All patients have had intercurrent hyperammonemic episodes; our data indicate that the frequency of the episodes has decreased with implementation of the current protocol. These patients are growth retarded, but most have height-for-weight z scores within 2 SD of the mean. Laboratory studies of plasma amino acids and of hematopoietic, renal, and hepatic function are within normal limits with the exception of slightly elevated serum aminotransferase values. CONCLUSION: Our results indicate that these drugs are safe and that the current protocol improves survival rates. However, survival is accompanied by mental retardation, growth retardation, risk of hyperammonemic episodes, and the necessity of lifetime adherence to strict medication and dietary management.

[Serum argininosuccinate synthetase (ASS) in patients with chronic hepatitis C treated with interferon].

Serum ASS and serum GPT levels were determined in 16 patients with chronic hepatitis C treated with interferon. In all the patients, the serum ASS level decreased earlier than the serum GPT level, and this tendency was remarkable in patients who excellently responded to the treatment. Furthermore, the serum ASS level was fluctuated when the serum GPT levels being continuously flat in the course of the treatment, probably because of the shorter half life of ASS in the serum. In conclusion, the serum ASS level may catch the effect of interferon on inflammation in the liver more sensitively than the GPT.

Long-term expression of human argininosuccinate synthetase in mice following bone marrow transplantation with retrovirus-transduced hematopoietic stem cells.

Amphotropic and ecotropic packaging cell lines were used to obtain high titers (greater than 10(6) colony forming units/ml) of retroviruses encoding human argininosuccinate synthetase, and these viruses were used to transduce murine bone marrow cells using cocultivation in vitro. The bone marrow cells were transplanted into lethally irradiated recipient mice, and argininosuccinate synthetase activity was measured in peripheral blood. Transduction with amphotropic retrovirus resulted in short-term expression for a period of 1-8 weeks, and no animals expressed the human gene after 25 weeks. Over 60% of the animals transplanted with cells transduced with ecotropic retrovirus expressed the human gene 44 weeks post-transplant, although the level of expression varied over a wide range. Analysis of the DNA from transplanted animals demonstrated the presence of the human sequence in expressing animals, and S1 nuclease analysis of RNA confirmed the presence of the human RNA transcripts. Analysis of granulocyte/macrophage (GM) colonies derived from the bone marrow of transplanted, expressing animals revealed a correlation between the level of expression of the transduced gene with the percentage of GM colonies carrying the human gene sequence. These data demonstrate the feasibility of obtaining long-term expression of genes introduced into bone marrow cells using retroviral vectors and the feasibility of obtaining expression of a gene not normally expressed in bone marrow.

Expression of human argininosuccinate synthetase in murine hematopoietic cells in vivo.

As part of an effort to develop a model system for somatic gene therapy, a human argininosuccinate synthetase (AS) cDNA has been introduced into two gag+ retroviral vectors, and high titer clones were obtained for both constructs. The presence of proviral DNA sequences was detected in individual spleen colonies after infection of primary murine marrow cells with each virus. Mice were reconstituted for long-term survival with marrow infected with one virus, and they demonstrated elevated levels of AS expression in peripheral blood for up to eight weeks posttransplantation.

Urea cycle and protein content in leucocytes from normal persons and uraemics.

It was found experimentally that the activity of the urea-cycle enzymes in the leucocytes of uraemic rats was parallel to that in their liver. Conclusions as to the activity of the urea-cycle enzymes in the liver can thus be drawn from the urea-cycle enzyme activity in the leucocytes. Investigation of the urea-cycle enzyme in the leucocytes of patients with renal insufficiency, in the pre-dialytic and dialytic states, showed that in both groups the ornithine carbamoyl transferase and the argininosuccinate lyase activity was lower in both groups of patients than in normal persons. The dialysis patients show higher argininosuccinate synthetase activity. In both groups of patients the protein content of the leucocytes is markedly lowered.

Leukocyte urea cycle enzymes in hyperammonemia.

All enzymes of the urea cycle are demonstrable in circulating leukocytes. They show the same relative activities as those in liver except for argininosuccinate synthetase + lyase (combined) which seems to be disproportionately active. To see whether leukocytes reflect liver activity, blood from patients with three hepatic urea cycle disorders was tested. In each case, the leukocytes showed the same enzyme deficiency as was apparent from a liver biopsy (Table 4). Leukocyte assays appear to be reliable indicators of the enzyme lesions in inherited urea cycle enzyme defects and therefore may obviate the need for liver biopsy.