Detection of neonatal argininosuccinate lyase deficiency by serum tandem mass spectrometry

Underlying antihypertensive mechanism of egg white-derived peptide QIGLF using renal metabolomics analysis

The kidney is an important target organ in the treatment of hypertension, but the effect of peptide QIGLF with antihypertensive activity on kidneys remains unknown. In the work, we aimed to further understand the hypotensive effects of QIGLF in spontaneously hypertensive rats (SHRs) using widely targeted metabolomics technology to investigate the kidney metabolic profiling variations. After four weeks of oral administration, the results showed different renal metabolomics profiles between QIGLF and model groups. Besides, a total of 10 potential biomarkers were identified, that is, 3-hydroxybutanoate, 20-hydroxyeicosatetraenoic acid, 19(S)-hydroxyeicosatetraenoic acid, 15-oxoETE, L-ornithine, malonate, uridine, uridine 5'-monophosphate, argininosuccinic acid, and N-carbamoyl-L-aspartate. These metabolites might exhibit antihypertensive activity of QIGLF by regulating synthesis and degradation of ketone bodies, arachidonic acid metabolism, pyrimidine metabolism, and arginine biosynthesis. These findings suggest that QIGLF might alleviate hypertension by inhibiting renal inflammation, promoting natriuresis, and regulating renal nitric oxide production.

Treatment of periscapular tendinopathy with radiofrequency coblation: A case report

Overuse injuries of the tendon – ‘tendinopathy’ – account for 30%–50% of all sporting injuries and a high proportion of orthopaedic referrals from primary care physicians. Tendinopathies often have a multifactorial aetiology and injury can be due to a combination of both acute and chronic trauma which contributes to loss of tissue integrity and eventual rupture. Our incomplete understanding of the mechanisms surrounding tendon pathophysiology continues to cause difficulties in treatments beyond loading regimes which can be unsuccessful in up to 30% of cases. We describe an uncommon case of tendinopathy affecting the periscapular muscle/tendon unit in a 35-year-old female with persistent pain around the inferior posterior pole of her right scapula. Magnetic resonance imaging findings confirmed oedema of the muscles around the inferior scapular margin in keeping with enthesopathy/tendinopathy and she was treated with radiofrequency coblation to the area. This case highlights radiofrequency ablation as a surgical option should non-operative treatments fail in the rare diagnosis of periscapular tendinopathy.

Argininosuccinate synthetase gene is silenced by CpG methylation in children with phenylketonuria

OBJECTIVES

The concentration of tyrosine and the ratio of branch-amino acid to the aromatic amino acid in phenylketonuria (PKU) patients are much lower than that of normal people, which reveal that PKU patients have amino acid metabolism disorder. The aim of the present study was to investigate the arginine level in blood, the expression of argininosuccinate synthetase (ASS), the rate-limiting enzyme in arginine synthesis pathway, and the methylation of ASS in patients with PKU.

DESIGN AND METHODS

Twenty-five children with PKU and 65 healthy controls were investigated in this study. Blood concentration of arginine was analyzed by automatic amino acid analyzer. The methylation of ASS gene promoter was evaluated by using methylation-specific polymerase chain reaction (MSP) and bisulfite sequencing PCR (BSP) methods, and the mRNA level of ASS was evaluated by semi-quantitative RT-PCR.

RESULTS

Blood concentration of arginine in PKU patients without dietary control was 0.017±0.009mmol/L while in normal persons was 0.129±0.007mmol/L, which is statistically significant (P<0.001). The promoter of ASS was methylated in PKU (15/15, 100%) but not in normal persons (0/15). The mRNA level of ASS in PKU patients was lower than that of normal people, which was well correlated with its methylation status.

CONCLUSIONS

The silencing of ASS due to aberrant promoter CpG methylation may be an important mechanism for arginine biosynthesis disorders in PKU. High levels of phenylalanine and low levels of arginine are common characteristics in PKU patients. These findings would extend the current understanding of arginine, ASS in the development of PKU disease.

Study of the fragmentation of arginine isobutyl ester applied to arginine quantification in Aedes aegypti mosquito excreta

It has been demonstrated that argininolysis and uricolysis are involved in the synthesis and excretion of urea in Aedes aegypti female mosquitoes. To further investigate the metabolic regulation of urea in female mosquitoes, it is desirable to have a rapid and efficient method to monitor arginine (Arg) concentration in mosquito excreta. Thus, a procedure currently used for the identification of Arg in urea cycle disorders in newborn babies was adapted to analyze Arg in A. aegypti excreta. The fragmentation patterns of the isobutyl esters of Arg and (15)N(2)-Arg (labeled at the guanidino group) were explored by electrospray ionization (ESI)-tandem mass spectrometry and fragmentation pathways not described before were characterized. In addition, Arg, (18)O(2)-Arg, (15)N(2)-Arg and (15)N(2)-(18)O(2)-Arg were also analyzed to elucidate some of the minor fragments in greater detail. Mosquito excreta from individual females were collected before and at different times after feeding a blood meal, mixed with (15)N(2)-Arg, an internal standard, and then derivatized as isobutyl esters. Based on the fragmentation mechanisms of Arg standards, studied by MS(2) and MS(3), Arg in the mosquito excreta was successfully analyzed by ESI-multiple reaction monitoring in a triple-quadrupole mass spectrometer. Arg excretion was monitored over a 120 h window before and after feeding female mosquitoes with a blood meal, with the maximum level of Arg excretion observed at 36-48 h post blood feeding. This method provides an efficient and rapid tool to quantify Arg in individual blood-fed mosquitoes, and can be applied to other organisms, whose small size severally limits the use of conventional biochemical analysis.

Novel mutations underlying argininosuccinic aciduria in Saudi Arabia

Background

Argininosuccinic aciduria (ASAuria) is an autosomal recessive disorder of the urea cycle relatively common in Saudi Arabia as a consequence of extensive consanguinity. It is the most common urea cycle disorder identified in the Saudi population, which therefore prioritizes the need to delineate the underlying molecular defects leading to disease.

Findings

We utilized Whole Genome Amplification (WGA), PCR and direct sequencing to identify mutations underlying ASAuria cases diagnosed by our institution. A missense mutation that accounts for 50% of Saudi ASAuria patients was recently reported by our laboratory. In this study we report a further six novel mutations (and one previously reported) found in Saudi patients with ASAuria. The novel four missense, one nonsense and one splice-site mutation were confirmed by their absence in >300 chromosomes from the normal population. Pathogenicity of the novel splice-site mutation was also confirmed using reverse transcriptase-PCR analysis. Cross species amino acid conservation at the substituted residues described were observed in some but not all instances.

Conclusions

Together, the eight mutations described by our laboratory, encompass >90% of ASAuria patients in Saudi Arabia and add to about 45 other ASAuria mutations reported worldwide.

Investigation of citrullinemia type I variants by in vitro expression studies

Mild citrullinemia is an allelic variant of classical citrullinemia type I also caused by deficiency of the urea cycle enzyme argininosuccinate synthetase (ASS). Affected patients comprise a biochemical but no clinical phenotype. However, there is no reliable parameter allowing conclusions regarding the course of the disorder or its type of manifestation. The aim of this study was to test the importance of varying levels of ASS residual activities for the severity at diagnosis. Bacterial in vitro expression studies allowed the enzymatic analysis of purified wild-type and the mutant ASS proteins p.Ala118Thr (c.352G>A), p.Trp179Arg (c.535T>C), p.Val263Met (c.787G>A), p.Arg265Cys (c.793C>T), p.Met302Val (c.904A>G), p.Gly324Ser (c.970G>A), p.Gly362Val (c.1085G>T), and p.Gly390Arg (c.1168G>A). In the chosen system, classical mutations do not show any significant enzymatic activity, whereas mutations associated with a mild course yield significant ASS activity levels. The mutation p.Ala118Thr (c.352G>A) impresses by a high residual activity (62%) but a severe reduction of affinity toward the substrates citrulline and aspartate. This mutation was identified in a hitherto healthy female adult with no history of known citrullinemia who had died during the postpartum period from hyperammonemic coma. The results of this study suggest that even a high level of residual ASS activity is not a reliable prognostic marker for an uneventful clinical course. Determination of ASS residual activities, therefore, cannot help in anticipating the risk of metabolic derangement. This study should guide clinicians as well as patients with mild citrullinemia toward a lifelong awareness of the disorder.

Automated GC-MS analysis of free amino acids in biological fluids

A gas chromatography-mass spectrometry (GC-MS) method was developed for the quantitative analysis of free amino acids as their propyl chloroformate derivatives in biological fluids. Derivatization with propyl chloroformate is carried out directly in the biological samples without prior protein precipitation or solid-phase extraction of the amino acids, thereby allowing automation of the entire procedure, including addition of reagents, extraction and injection into the GC-MS. The total analysis time was 30 min and 30 amino acids could be reliably quantified using 19 stable isotope-labeled amino acids as internal standards. Limits of detection (LOD) and lower limits of quantification (LLOQ) were in the range of 0.03-12 microM and 0.3-30 microM, respectively. The method was validated using a certified amino acid standard and reference plasma, and its applicability to different biological fluids was shown. Intra-day precision for the analysis of human urine, blood plasma, and cell culture medium was 2.0-8.8%, 0.9-8.3%, and 2.0-14.3%, respectively, while the inter-day precision for human urine was 1.5-14.1%.

Determination of ornithine in human plasma by hydrophilic interaction chromatography–tandem mass spectrometry

The amino acid ornithine (Orn) acts as a vital part in the physiologically fundamental urea cycle. As such, it is a main intermediate in the catabolic breakdown as well as in the synthesis of arginine and is involved in many other metabolic pathways with potential clinical implications. We here describe a LC-MS-MS method for the detection of Orn in human plasma which is fast, easy and precise. The sample preparation comprises only protein precipitation and the addition of the isotopic labeled I.S. The analytes are separated by hydrophilic interaction chromatography (HILIC) in less than 4min on a silica column with an isocratic mobile phase consisting of 0.1% trifluoroacetic acid in water and acetonitrile in the ratio of 25:75. Orn and its I.S. are detected and quantified by APCI tandem mass spectrometry. The calibration function is linear from 7.5 to 205 micromol/l and covers the range of concentrations found in patients undergoing different clinical interventions. The quantification results are independent with regard to the biological matrix analyzed. The intra-day and inter-day relative standard deviations are 1.1% and 3.5%, respectively. As an application of the described method in clinical investigations, we report arginine and ornithine plasma concentration results from an arginine supplementation study enrolling healthy volunteers and patients suffering from hypercholesterolemia. After oral dosing of 110 mg/kg arginine, ornithine plasma concentrations rose from 54 to 148 micromol/l after 2h and were back to baseline after 24h. However, arginine to ornithine ratios kept constant during the complete observation time.

Use of tandem mass spectrometry for multianalyte screening of dried blood specimens from newborns

BACKGROUND

Over the past decade laboratories that test for metabolic disorders have introduced tandem mass spectrometry (MS/MS), which is more sensitive, specific, reliable, and comprehensive than traditional assays, into their newborn-screening programs. MS/MS is rapidly replacing these one-analysis, one-metabolite, one-disease classic screening techniques with a one-analysis, many-metabolites, many-diseases approach that also facilitates the ability to add new disorders to existing newborn-screening panels.

METHODS

During the past few years experts have authored many valuable articles describing various approaches to newborn metabolic screening by MS/MS. We attempted to document key developments in the introduction and validation of MS/MS screening for metabolic disorders. Our approach used the perspective of the metabolite and which diseases may be present from its detection rather than a more traditional approach of describing a disease and noting which metabolites are increased when it is present.

CONTENT

This review cites important historical developments in the introduction and validation of MS/MS screening for metabolic disorders. It also offers a basic technical understanding of MS/MS as it is applied to multianalyte metabolic screening and explains why MS/MS is well suited for analysis of amino acids and acylcarnitines in dried filter-paper blood specimens. It also describes amino acids and acylcarnitines as they are detected and measured by MS/MS and their significance to the identification of specific amino acid, fatty acid, and organic acid disorders.

CONCLUSIONS

Multianalyte technologies such as MS/MS are suitable for newborn screening and other mass screening programs because they improve the detection of many diseases in the current screening panel while enabling expansion to disorders that are now recognized as important and need to be identified in pediatric medicine.

ESI-MS/MS analysis of underivatised amino acids: a new tool for the diagnosis of inherited disorders of amino acid metabolism. Fragmentation study of 79 molecules of biological interest in positive and negative ionisation mode

The diagnosis of inherited disorders of amino acids (AA) metabolism is usually performed on automated analysers by ion-exchange chromatography and quantification after ninhydrin derivatisation of about 50 different AA. A single run liquid chromatography/tandem mass spectrometry (LC/MS/MS) method for these molecules can be an alternative to this time-consuming technique. The first step of this development is the infusion study of the fragmentation of 79 molecules of biological interest in electrospray ionisation tandem mass spectrometry (ESI-MS/MS), in positive and in negative ionisation mode. Among them, three molecules can be detected only in negative ionisation mode, 38 only in positive mode and 38 in the two modes. All the most abundant fragmentations are presented, with optimisation of the MS/MS parameters. The positive ionisation mode was retained for the simultaneous analysis of 76 molecules. One sensitive and/or specific transition is proposed for the monitoring of each molecule. Improvement in sensitivity of detection was obtained with the use of an acidic mobile phase. Flow injection analysis studies led us to highlight a number of interferences-due to isobaric molecules, to in-source collision-induced dissociation, or to natural isotopic distribution of the elements-which are listed. For a reliable quantification method, these molecules have to be separated by LC before analysis in the tandem mass spectrometer. Ion-pairing reversed-phase liquid chromatography (RPLC) using perfluorinated carboxylic acids as ion-pairing agents has already been found suitable for analysis of AA in MS/MS positive ionisation mode and is under development.