Unraveling the Cyclization of l-Argininosuccinic Acid in Biological Samples: A Study via Mass Spectrometry and NMR Spectroscopy.

Since l-argininosuccinic acid (ASA) is the characteristic biomarker for the diagnosis of certain diseases, its reliable detection in complex biological samples is necessary to obtain a complete evaluation with greater specificity and accuracy. ASA can undergo intramolecular cyclization, yielding an equilibrium with the resulting cyclic forms, which can predominate under different analytical conditions. In this work, the appearance and transformation of the different forms of ASA have been studied and a strategy for targeted screening analysis of ASA and its cyclic forms using capillary electrophoresis-electrospray ionization-time-of-flight mass spectrometry (CE-ESI-TOF-MS) has been developed. The data and spectra obtained allowed us to gain further insight into accurate identification, concluding that there is a dynamic equilibrium depending on the pH. Moreover, one- and two-dimensional NMR spectroscopy experiments have allowed us to determine the predominant tautomeric structure for the major cyclic ASA derivative, confirming the importance of intramolecular hydrogen bonds.

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.

Liver transplantation for argininosuccinic aciduria: clinical, biochemical, and metabolic outcome.

We report successful liver transplantation in a young adult with argininosuccinic aciduria but without cirrhosis. Plasma amino acid profile normalized and brain magnetic resonance spectroscopy indicated improved metabolism after transplantation. The general well-being of the patient and his quality of life improved. We suggest that orthotopic liver transplantation should be considered for patients with argininosuccinic aciduria even in the absence of cirrhosis, with the aim of correcting (at least in part) central nervous system metabolism, thereby preventing further neurological deterioration.

Class selection of amino acid metabolites in body fluids using chemical derivatization and their enhanced 13C NMR.

We report a chemical derivatization method that selects a class of metabolites from a complex mixture and enhances their detection by 13C NMR. Acetylation of amines directly in aqueous medium with 1,1'-13C(2) acetic anhydride is a simple method that creates a high sensitivity and quantitative label in complex biofluids with minimal sample pretreatment. Detection using either 1D or 2D 13C NMR experiments produces highly resolved spectra with improved sensitivity. Experiments to identify and compare amino acids and related metabolites in normal human urine and serum samples as well as in urine from patients with the inborn errors of metabolism tyrosinemia type II, argininosuccinic aciduria, homocystinuria, and phenylketonuria demonstrate the method. The use of metabolite derivatization and 13C NMR spectroscopy produces data suitable for metabolite profiling analysis of biofluids on a time scale that allows routine use. Extension of this approach to enhance the NMR detection of other classes of metabolites has also been accomplished. The improved detection of low-concentration metabolites shown here creates opportunities to improve the understanding of the biological processes and develop improved disease detection methodologies.

Trichorrhexis nodosa secondary to argininosuccinicaciduria.

Argininosuccinicaciduria is a rare metabolic disorder of the urea cycle associated with the inability to excrete nitrogenous waste in the form of urea. Along with low serum arginine, hepatomegaly, and mental retardation, congenital trichorrhexis nodosa is a distinguishing feature of the disorder. We present a 3.5-year-old girl diagnosed with argininosuccinicaciduria who presented to the dermatology clinic with hair thinning and loss since birth. Microscopic evaluation revealed nodular swellings on the hair shafts and frayed cortical fibers consistent with the diagnosis of trichorrhexis nodosa occurring in the setting of argininosuccinicaciduria.

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.

Prenatal diagnosis of citrullinemia and argininosuccinic aciduria: evidence for a transmission ratio distortion in citrullinemia.

BACKGROUND: In the course of 25 years, we have experienced a high rate of affected fetuses in the prenatal diagnosis of citrullinemia. METHODS AND RESULTS: Ninety-one pregnancies at 1 in 4 risk were tested; 36 were diagnosed as affected (39.5%; P = 0.0015). The high rate of positive diagnoses was found both after chorionic villus sampling (24/68 = 35.3%) and amniocentesis (12/23 = 52.2%) despite the completely different and independent techniques used. Using exactly the same (indirect) enzyme assay for argininosuccinic aciduria on chorionic villi and a similar method on amniotic fluid, the expected rate of affected fetuses was found: 13/53 = 24.5%. Technical and genetic causes for the unexpected results were excluded by confirmatory studies performed on independent fetal material, which was available for 27 of the 36 fetuses affected with citrullinemia. Biochemical confirmation was obtained in the 27 cases, whereas in 18 fetuses homozygosity or compound heterozygosity for disease-causing mutations were retrospectively demonstrated in the stored fetal cells. CONCLUSION: The results suggest the occurrence of preferential transmission of the mutant allele. An explanation for this phenomenon may be found in a protective role of argininosuccinic acid synthetase deficiency in mutant sperm cells against the possibly detrimental or apoptotic effect of nitric oxide produced normally from arginine by nitric oxide synthase.

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.

Clinical, enzymatic, and molecular genetic characterization of a biochemical variant type of argininosuccinic aciduria: prenatal and postnatal diagnosis in five unrelated families.

A biochemical variant of argininosuccinate lyase deficiency, found in five individuals, is introduced. In comparison to classical patients, the variant cases of argininosuccinate lyase deficiency were characterized by residual enzyme activity as measured by the incorporation of [14C]citrulline into proteins. The five patients of different ethnic backgrounds presented with relatively mild clinical symptoms, variable age of onset, marked argininosuccinic aciduria and severe, but not complete, deficiency of argininosuccinate lyase. [14C]Citrulline incorporation into proteins, which is completely blocked in classical argininosuccinic aciduria, was only partially reduced in fibroblasts of these patients. Further investigation showed that previous standard conditions of the assay were not optimal. Higher concentrations of citrulline in the incubation medium strongly stimulated 14C incorporation in normal cells, but not in the patients; as a result, the relative incorporation level in the patients dropped to 6-28% compared to 18-75% of normal in the original procedure. Prenatal diagnosis was successfully performed in three of the families. Affected pregnancies were indicated by (partial) deficiency of [14C]citrulline incorporation in chorionic villi and/or increased levels of argininosuccinate in amniotic fluid. Analysis of the ASL gene in the five patients revealed a considerable allelic heterogeneity. Three novel mutations--R385C (2 patients), V178M and R379C--were detected in homozygous states, whereas one patient was compound heterozygous for the known mutations R193Q and Q286R. In conclusion, there are patients of different ethnic backgrounds who are characterized by residual activity of argininosuccinate lyase and who present with less severe clinical courses. In addition, we present an improved biochemical assay for accurate prenatal and postnatal diagnosis.

A novel stop codon mutation (X465Y) in the argininosuccinate lyase gene in a patient with argininosuccinic aciduria.

Argininosuccinate lyase (ASL) deficiency (McKusick 207900) is a rare autosomal recessive disorder affecting the urea cycle. The cardinal symptom in the neonatal form is progressive hyperammonemia, which is often life-threatening. However, clinical symptoms in the late onset form are quite heterogeneous. As well as measurement of ASL activity, analysis of the ASL gene is necessary to clarify the genetic basis of various phenotypes. We report a patient with late onset argininosuccinate lyase deficiency (ASLD) who had hepatomegaly and mildly increased level of ammonia. By mutation analysis of the mRNA and genomic DNA from the patient's leukocytes, we identified a novel missense mutation 1395G>C in the homozygous state, which results in the exchange of a stop codon to tyrosine at amino acid position 465 (X465Y). This unique mutation causes an elongation of fifty amino acids in the C-terminal region of the ASL protein, and is likely related to a milder phenotype compared with previously reported mutations. In addition, this is the first report on mutation analysis in a Japanese ASLD patient.

13C NMR spectroscopy: a convenient tool for detection of argininosuccinic aciduria.

Proton decoupled high resolution 13C NMR spectra of argininosuccinic acid have been measured in a series of dilute water solutions of various acidity. These data have provided a basis for unequivocal determination of the presence of this metabolite in the investigated sample. The method additionally enables simultaneous rough estimation of the metabolite concentration. In order to check the practicability of the usage of this spectroscopy for diagnostic purposes, the spectra of several unprocessed urine samples have been recorded including three from patients with argininosuccinic aciduria. It has been concluded that 13C NMR spectroscopy can be a convenient method of recognising the above syndrome and probably many other inborn metabolic errors which manifest themselves with the excretion of the marker metabolite in amounts comparable to (or larger than) creatinine.

Intragenic complementation and the structure and function of argininosuccinate lyase.

Argininosuccinate lyase (ASL) catalyzes the reversible hydrolysis of argininosuccinate to arginine and fumarate, a reaction important for the detoxification of ammonia via the urea cycle and for arginine biosynthesis. ASL belongs to a superfamily of structurally related enzymes, all of which function as tetramers and catalyze similar reactions in which fumarate is one of the products. Genetic defects in the ASL gene result in the autosomal recessive disorder argininosuccinic aciduria. This disorder has considerable clinical and genetic heterogeneity and also exhibits extensive intragenic complementation. Intragenic complementation is a phenomenon that occurs when a multimeric protein is formed from subunits produced by different mutant alleles of a gene. The resulting hybrid protein exhibits greater enzymatic activity than is found in either of the homomeric mutant proteins. This review describes the structure and function of ASL and its homologue delta crystallin, the genetic defects associated with argininosuccinic aciduria and current theories regarding complementation in this protein.

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.

Pregnancy and argininosuccinic aciduria.

We present the outcome of a pregnancy in a woman with mild argininosuccinic lyase deficiency to add to the collective experience of the maternal and fetal effects of urea cycle defects. In females affected with argininosuccinic lyase deficiency, careful clinical and biochemical monitoring of pregnancy will minimize the risk of metabolic decompensation in the perinatal period. Furthermore, it would appear that argininosuccinate is not teratogenic to the development of the human fetus.