Rapid quantification of underivatized alloisoleucine and argininosuccinate using mixed-mode chromatography with tandem mass spectrometry.

Plasma elevations of the amino acids alloisoleucine and argininosuccinic acid (ASA) are pathognomonic for maple syrup urine disease and argininosuccinate lyase deficiency, respectively. Reliable detection of these biomarkers is typically achieved using methods with tedious sample preparations or long chromatographic separations, and many published amino acid assays report poor specificity and/or sensitivity for one or both of these compounds. This report describes a novel liquid chromatography tandem mass spectrometry (LC-MS/MS) method that provides rapid quantification of alloisoleucine and ASA in human plasma. The basis of this method is a mixed-mode solid phase separation that achieves baseline resolution of alloisoleucine from isobaric interferents without the use of derivatization or ion pairing agents. The inject-to-inject time is 6 min including elution, column washing and re-equilibration. Validation studies demonstrate excellent limits of quantification (1 µmol/L), linearity (r = 0.999 from 1 to 250 µmol/L), accuracy (bias = -3.8% and -10.1%), and inter-assay imprecision (CV < 8.06%) for plasma analyses. Data from long-term clinical application confirms chromatographic consistency equivalent to more traditional reversed-phase or HILIC based columns. Additional matrix studies indicate low suppression (<10%) for a wide range of amino acids and compatibility with other matrixes such as blood spot analyses. Finally, analysis of our first 257 clinical specimens demonstrates high analytic specificity and sensitivity, allowing the detection of subtle but clinically relevant elevations of alloisoleucine and ASA that may be missed by other less sensitive methods. In conclusion, the novel LC-MS/MS method reported here overcomes a number of the challenges associated with alloisoleucine and ASA quantification. Combining this approach with published incomplete amino acid quantification methods allows, for the first time, a rapid and comprehensive LC-MS/MS analysis of underivatized amino acids without the use of ion pairing agents.

Expanding the phenotype in argininosuccinic aciduria: need for new therapies.

OBJECTIVES: This UK-wide study defines the natural history of argininosuccinic aciduria and compares long-term neurological outcomes in patients presenting clinically or treated prospectively from birth with ammonia-lowering drugs. METHODS: Retrospective analysis of medical records prior to March 2013, then prospective analysis until December 2015. Blinded review of brain MRIs. ASL genotyping. RESULTS: Fifty-six patients were defined as early-onset (n = 23) if symptomatic < 28 days of age, late-onset (n = 23) if symptomatic later, or selectively screened perinatally due to a familial proband (n = 10). The median follow-up was 12.4 years (range 0-53). Long-term outcomes in all groups showed a similar neurological phenotype including developmental delay (48/52), epilepsy (24/52), ataxia (9/52), myopathy-like symptoms (6/52) and abnormal neuroimaging (12/21). Neuroimaging findings included parenchymal infarcts (4/21), focal white matter hyperintensity (4/21), cortical or cerebral atrophy (4/21), nodular heterotopia (2/21) and reduced creatine levels in white matter (4/4). 4/21 adult patients went to mainstream school without the need of additional educational support and 1/21 lives independently. Early-onset patients had more severe involvement of visceral organs including liver, kidney and gut. All early-onset and half of late-onset patients presented with hyperammonaemia. Screened patients had normal ammonia at birth and received treatment preventing severe hyperammonaemia. ASL was sequenced (n = 19) and 20 mutations were found. Plasma argininosuccinate was higher in early-onset compared to late-onset patients. CONCLUSIONS: Our study further defines the natural history of argininosuccinic aciduria and genotype-phenotype correlations. The neurological phenotype does not correlate with the severity of hyperammonaemia and plasma argininosuccinic acid levels. The disturbance in nitric oxide synthesis may be a contributor to the neurological disease. Clinical trials providing nitric oxide to the brain merit consideration.

A randomized controlled trial to evaluate the effects of high-dose versus low-dose of arginine therapy on hepatic function tests in argininosuccinic aciduria.

OBJECTIVE: To compare the effects of combinatorial therapy with low-dose arginine and a nitrogen scavenging agent (sodium phenylbutyrate) vs. monotherapy with high-dose arginine on liver function tests in patients with argininosuccinic aciduria (ASA). STUDY DESIGN: Twelve patients with ASA were enrolled in a double-blind, placebo-controlled, cross-over study design. Subjects were randomized to receive either a low-dose of arginine therapy (100 mg · kg(-1) · d(-1)) combined with sodium phenylbutyrate (500 mg · kg(-1) · d(-1)) (LDA arm) or a high-dose of arginine alone (500 mg · kg(-1) · d(-1)) (HDA arm) for one week. At the end of one week of therapy, liver function tests were assessed and metabolite fluxes were measured using a multi-tracer stable isotope protocol. RESULTS: Plasma aspartate aminotransferase (AST), alanine aminotransferase (ALT), and measures of synthetic functions of the liver were the primary outcomes. Subjects had significantly increased levels of argininosuccinate (P<0.03) and AST levels (P<0.01) after treatment with high-dose arginine. In the subset of subjects with elevated AST or ALT, treatment with high-dose of arginine was associated with further increases in plasma levels of both aminotransferases. Whereas subjects had increased arginine and citrulline flux with high-dose arginine therapy, the glutamine flux was not different between the two treatment arms. The synthetic liver functions as assessed by prothrombin time, INR, and coagulation factor levels were not different between the HDA and LDA arms. CONCLUSIONS: Administering higher doses of arginine in subjects with ASA results in increases in AST and ALT levels, especially in the subset of patients with elevated baseline aminotransferases. Hence, low-dose arginine sufficient to normalize arginine levels in plasma combined with nitrogen scavenging therapy should be considered as a therapeutic option for treatment of ASA in patients with elevations of hepatic aminotransferases.

Argininosuccinate lyase deficiency.

The urea cycle consists of six consecutive enzymatic reactions that convert waste nitrogen into urea. Deficiencies of any of these enzymes of the cycle result in urea cycle disorders (UCDs), a group of inborn errors of hepatic metabolism that often result in life-threatening hyperammonemia. Argininosuccinate lyase (ASL) catalyzes the fourth reaction in this cycle, resulting in the breakdown of argininosuccinic acid to arginine and fumarate. ASL deficiency (ASLD) is the second most common UCD, with a prevalence of ~1 in 70,000 live births. ASLD can manifest as either a severe neonatal-onset form with hyperammonemia within the first few days after birth or as a late-onset form with episodic hyperammonemia and/or long-term complications that include liver dysfunction, neurocognitive deficits, and hypertension. These long-term complications can occur in the absence of hyperammonemic episodes, implying that ASL has functions outside of its role in ureagenesis and the tissue-specific lack of ASL may be responsible for these manifestations. The biochemical diagnosis of ASLD is typically established with elevation of plasma citrulline together with elevated argininosuccinic acid in the plasma or urine. Molecular genetic testing of ASL and assay of ASL enzyme activity are helpful when the biochemical findings are equivocal. However, there is no correlation between the genotype or enzyme activity and clinical outcome. Treatment of acute metabolic decompensations with hyperammonemia involves discontinuing oral protein intake, supplementing oral intake with intravenous lipids and/or glucose, and use of intravenous arginine and nitrogen-scavenging therapy. Dietary restriction of protein and dietary supplementation with arginine are the mainstays in long-term management. Orthotopic liver transplantation (OLT) is best considered only in patients with recurrent hyperammonemia or metabolic decompensations resistant to conventional medical therapy.

Argininosuccinic aciduria: clinical and biochemical phenotype findings in Malaysian children.

Argininosuccinic aciduria is an inborn error of the urea cycle caused by deficiency of argininosuccinate lyase (ASL). ASL-deficient patients present with progressive intoxication due to accumulation of ammonia in the body. Early diagnosis and treatment of hyperammonemia are necessary to improve survival and prevent long-term handicap. Two clinical phenotypes have been recognized--neonatal acute and milder late-onset form. We investigated patients with hyperammonemia by a stepwise approach in which quantitative amino acids analysis was the core diagnostic procedure. Here, we describe the clinical phenotypes and biochemical characteristics in diagnosing this group of patients. We have identified 13 patients with argininosuccinic aciduria from 2003 till 2009. Ten patients who presented with acute neonatal hyperammonemic encephalopathy had markedly elevated blood ammonia (> 430 micromol/L) within the first few days of life. Three patients with late-onset disease had more subtle clinical presentations and they developed hyperammonemia only during the acute catabolic state at two to twelve months of age. Their blood ammonia was mild to moderately elevated (> 75-265 micromol/L). The diagnosis was confirmed by detection of excessive levels of argininosuccinate in the urine and/or plasma. They also have moderately increased levels of citrulline and, low levels of arginine and ornithine in their plasma. Two patients succumbed to the disease. To date, eleven patients remained well on a dietary protein restriction, oral ammonia scavenging drugs and arginine supplementation. The majority of them have a reasonable good neurological outcome.

Argininosuccinic aciduria: clinical and biochemical phenotype findings in Malaysian children

Argininosuccinic aciduria is an inborn error of the urea cycle caused by deficiency of argininosuccinate lyase (ASL). ASL-deficient patients present with progressive intoxication due to accumulation of ammonia in the body. Early diagnosis and treatment of hyperammonemia are necessary to improve survival and prevent long-term handicap. Two clinical phenotypes have been recognized--neonatal acute and milder late-onset form. We investigated patients with hyperammonemia by a stepwise approach in which quantitative amino acids analysis was the core diagnostic procedure. Here, we describe the clinical phenotypes and biochemical characteristics in diagnosing this group of patients. We have identified 13 patients with argininosuccinic aciduria from 2003 till 2009. Ten patients who presented with acute neonatal hyperammonemic encephalopathy had markedly elevated blood ammonia (> 430 micromol/L) within the first few days of life. Three patients with late-onset disease had more subtle clinical presentations and they developed hyperammonemia only during the acute catabolic state at two to twelve months of age. Their blood ammonia was mild to moderately elevated (> 75-265 micromol/L). The diagnosis was confirmed by detection of excessive levels of argininosuccinate in the urine and/or plasma. They also have moderately increased levels of citrulline and, low levels of arginine and ornithine in their plasma. Two patients succumbed to the disease. To date, eleven patients remained well on a dietary protein restriction, oral ammonia scavenging drugs and arginine supplementation. The majority of them have a reasonable good neurological outcome.

Sustained engraftment and tissue enzyme activity after liver cell transplantation for argininosuccinate lyase deficiency.

BACKGROUND & AIMS: Donor cell engraftment with expression of enzyme activity is the goal of liver cell transplantation for inborn errors of liver metabolism with a view to achieving sustained metabolic control. METHODS: Sequential hepatic cell transplantations using male and female cells were performed in a 3.5-year-old girl with argininosuccinate lyase deficiency over a period of 5 months. Beside clinical, psychomotor, and metabolic follow-up, engraftment was analyzed in repeated liver biopsies (2.5, 5, 8, and 12 months after first infusion) by fluorescence in situ hybridization for the Y-chromosome and by measurement of tissue enzyme activity. RESULTS: Metabolic control was achieved together with psychomotor catch-up, changing the clinical phenotype from a severe neonatal one to a moderate late-onset type. The child was no longer hospitalized and was able to attend normal school. Sustained engraftment of male donor liver cells was shown in repeated biopsies, reaching 19% at 8 months and 12.5% at the 12-month follow-up. XXYY tetraploid donor cells were mainly detected during the infusion period (2.5- and 5-month biopsies), whereas in the follow-up 8-month and 1-year biopsies, diploid donor cell subpopulations had become dominant. Moreover, argininosuccinate lyase activity, originally absent, became measurable in 2 different biopsy samples at 8 months, reaching 3% of control activity, indicating in situ metabolic effect and supporting the clinical evolution to a moderate form of the disease. CONCLUSIONS: Liver cell transplantation can achieve donor cell engraftment in humans in a significant proportion, leading to sustained metabolic and clinical control with psychomotor catch-up.

Serial diffusion-weighted magnetic resonance imaging in adult-onset citrullinaemia.

A 25-year-old Chinese man presented with a 2-year history of recurrent coma. His plasma ammonia level was extremely elevated, with raised citrulline level and absence of argininosuccinic acid. Adult-onset citrullinaemia, a condition rarely reported outside the Japanese population, was diagnosed. Serial magnetic resonance (MR) imaging, including diffusion-weighted (DW) studies, showed initial involvement of the insula cortex and cingulate gyrus, changing to a pattern of multiple small lesions in the depths of the cortical sulci. This changing pattern of lesions over time on DW MR imaging has not previously been described in adult-onset citrullinaemia.

A mouse model of argininosuccinic aciduria: biochemical characterization.

Argininosuccinate lyase (AL) has several roles in intermediary metabolism. It is an essential component of the urea cycle, providing a pathway for the disposal of excess nitrogen in mammals. AL links the urea cycle to the tricarboxylic acid (TCA) cycle by generating fumarate. Finally, AL is required for the endogenous production of arginine. In this latter role it may function outside ureagenic organs to provide arginine as a substrate for nitric oxide synthases (NOS). Increasing evidence suggests that argininosuccinate synthetase (AS) and AL are more globally expressed, and the coordinate regulation of AS and AL gene expression with that of the inducible form of NOS (iNOS) provides evidence that this may facilitate the regulation of NOS activity. Deficiency of AL leads to the human urea cycle disorder argininosuccinic aciduria. We produced an AL deficient mouse by gene targeting in order to investigate the role of AL in endogenous arginine production. This mouse also provides a model of the human disorder to explore the pathogenesis of the disorder and possible new treatments. Metabolic studies of these mice demonstrated that they have the same biochemical phenotype as humans, with hyperammonemia, elevated plasma argininosuccinic acid and low plasma arginine. Plasma nitrites, derived from NO, were not reduced in AL deficient mice and there was no significant difference is the level of cyclic GMP, the second messenger induced by NO.

Detection of neonatal argininosuccinate lyase deficiency by serum tandem mass spectrometry.

Argininosuccinate lyase (ASL) deficiency (McKusick 207900) is an inborn error of the urea cycle. The leading symptom is progressive hyperammonaemia, which is a life-threatening condition, particularly in patients with a neonatal onset. Early diagnosis and treatment of the hyperammonaemia are necessary to improve survival and the long-term outcome of ASL-deficient patients. Currently, the diagnosis of ASL deficiency is based on the measurement of urea cycle intermediates and amino acids by automated quantitative ion exchange chromatography in plasma and urine. Here, we report a newborn presenting with coma and severe hyperammonaemia. ASL deficiency was suspected on the basis of an adapted tandem mass spectrometric (MS-MS) procedure which allows determination of argininosuccinate in addition to the amino acids in serum samples. MS-MS measurements revealed a characteristic increase of argininosuccinate, a moderate increase of citrulline, and lowered levels of arginine and ornithine in the serum of the patient. The diagnosis was confirmed by the detection of a novel homozygous frameshift mutation in exon 14 of the argininosuccinate lyase gene. We propose MS-MS as a diagnostic tool suitable for the rapid detection of specific alterations in the amino acid spectra caused by ASL deficiency.

Screening blood spots for argininosuccinase deficiency by electrospray tandem mass spectrometry.

Argininosuccinase deficiency is relatively more common in Saudi Arabia than other urea cycle detects (UCD) and its presentation is usually acute and virtually identical to the clinical presentation of other UCD. We developed a rapid, sensitive, and specific screening method for the diagnosis of argininosuccinase deficiency from blood spots. using electrospray tandem mass spectrometry. A 96-well microplate batch process is used for extraction of argininosuccinic acid (ASA), other amino acids and acylcarnitines (Rashed et al. 1995). ASA and other metabolites are derivatized to the corresponding butyl derivatives. The tris-butyl ester of ASA (MH = 459.3) yields two major fragments at m/z 70 and m/z 144 under mild collision induced collision. montitored in the product ion spectrum using a narrow mass range (65-150 kDa). A processing algorithm "CAMPA" is used to automatically calculate the height ratios of selected masses and flags data files as "abnormal" when certain threshold is exceeded. The method is integrated with our existing 2-minute MS/MS method for profiling amino acids and acylcarnitines (Rashed et al. 1997). Using this approach for two years we diagnosed 16 ALD cases from 14 hyperammonemic infants, one high-risk newborn, and one from a regular newborn screening blood spot.

Unknown syndrome in sibs: pili torti, growth delay, developmental delay, and mild neurological abnormalities.

We present male and female sibs of consanguineous parents with features including pili torti with unusual hair shaft electron microscopic (EM) findings, growth delay, developmental delay, and mild to moderate neurological abnormalities. The features of the cases presented here have not been noted in the previously reported clinical syndromes in which pili torti may be found.

Investigation of urea cycle enzyme disorders by 1H-NMR spectroscopy.

High resolution proton nuclear magnetic resonance spectroscopy (1H-NMR) has been used to study patients with inborn errors of the urea cycle to evaluate further the diagnostic potential of this technique. The 1H-NMR metabolic profile from the urine of patients with citrullinaemia and argininosuccinic aciduria consistently demonstrated the presence of the diagnostic metabolites citrulline, N-acetylcitrulline and argininosuccinate, respectively. The profile from the urine of patients with ornithine carbamoyl transferase deficiency, is potentially diagnostic, but orotate was only detected in samples from three out of four patients. The characteristic fingerprint that each of the metabolites produces is unlike that of any other we have seen, including analogues of the metabolites which are structurally very similar such as arginine, ornithine and aspartate. The level of excretion of the metabolites from the patients with citrullinaemia and argininosuccinic aciduria has been well within the range of NMR detection.

Dietary management reverses grooving and abnormal polarization of hair shafts in argininosuccinase deficiency.

We have observed that the fragile hair of two untreated patients with argininosuccinic aciduria showed abnormal alternating zones of bright and dark banding by polarizing microscopy. Scanning electron microscopy documented discontinuous grooves with a 50 to 100 microns periodicity. Results of amino acid analysis of the hair were essentially normal. After the patients were treated with a low-protein, arginine-supplemented diet, the hair assumed a normal appearance. Five patients already treated with diet showed no hair abnormalities. The pathogenesis of the hair changes in unknown, but our findings suggest that products generated in the disease can adversely affect metabolically active tissue such as hair.

[Argininosuccinic aciduria. Comparative studies and detection of carriers in 3 affected families]. / Aciduria argininsuccínica. Estudios comparativos y detección de portadores en tres familias afectas.

Three patients with argininosuccinic aciduria are described. One of them is a neonatal form, with typical acute course and severe hyperammonemia who died on the sixth day of life. Postmortem analysis showed a marked plasmatic accumulation of argininosuccinic acid. Later on, red blood cell ASA-lyase levels demonstrated the heterozygosity of her parents and sisters. The two other patients are late onset forms and were diagnosed after detection of ASA and its anhydrides in plasma and urine. Levels of these metabolites did not correlate with levels of residual ASA-lyase in erythrocytes. Treatment with a hypoproteic diet supplemented with arginine has improved their clinical state. Carriers have been detected in both families. Importance of rapid diagnosis and treatment of hyperammonemic patients in order to prevent neurologic damage is emphasised.