Routine gas chromatographic/mass spectrometric analysis of urinary organic acids. Results over a three-year period

Advances in the metabolic profiling of acidic compounds in children's urines achieved by comprehensive two-dimensional gas chromatography

The main objective of this work was to evaluate a comprehensive two-dimensional gas chromatographic (GCxGC) coupled to quadrupole mass spectrometry (qMS) method in the field of biomarker candidates' discovery. To this purpose we developed a GCxGC-qMS method suitable for the separation of organic acids and other classes of compounds with silylable polar hydrogen such as sugars, amino-acids, and vitamins. As compared to those obtained by a widely used 1D-GC method, the urinary chromatographic profiles performed by the proposed 2D-GC method exhibit higher resolution and sensitivity, leading to the detection of up to 92 additional compounds in some urine samples including some well-known biomarkers. In order to validate the proposed method we focused on three metabolites of interest with various functional groups and polarities including CH3-malonic acid (MMA: biomarker of methylmalonic acidemia), 3-hydroxy-3-methyl-glutaric acid (3-OHMGA: biomarker of 3-hydroxy-3-methylglutaric acidemia), and phenylpiruvic acid (PhPA: marker of phenylketonuria). While these three metabolites can be considered as representative of organic acids classically determined by 1D-GC, they cannot be representative of new detected metabolites. Thus, we also focused on quinolic acid (QUIN), taken as an example of biomarker not detected at basal levels with the classical 1D GC-qMS method. In order to obtain sufficient recoveries for all tested compounds, we developed a sample preparation protocol including a step of urea removal followed by two extraction steps using two solvents of different polarity and selectivity. Recoveries with the proposed method reached more than 80% for all targeted compounds and the linearity was satisfactory up to 50μmol/L. The CVs of the within-run and within-laboratory precisions were less than 8% for all tested compounds. The limits of quantification (LOQs) were 0.6μmol/L for MMA, 0.4μmol/L for 3-OHMGA, 0.7μmol/L for PhPA, and 1μmol/L for QUIN. The LOQs of these metabolites obtained by a classical GC-MS method under the same chromatographic conditions were 5μmol/L for MMA, 4μmol/L for 3-OHMGA, 6μmol/L for PhPA while QUIN was below the limit of detection. As compared to 1D-GC, these results highlight the enhanced detectability of urine metabolites by the 2D-GC technique. Our results also show that for each new detected compound it is necessary to develop and validate an appropriate sample preparation procedure.

Biosynthesis, degradation and pharmacological importance of the fatty acid amides

The identification of two biologically active fatty acid amides, N-arachidonoylethanolamine (anandamide) and oleamide, has generated a great deal of excitement and stimulated considerable research. However, anandamide and oleamide are merely the best-known and best-understood members of a much larger family of biologically occurring fatty acid amides. In this review, we will outline which fatty acid amides have been isolated from mammalian sources, detail what is known about how these molecules are made and degraded in vivo, and highlight their potential for the development of novel therapeutics.

Derivatization in mass spectrometry-3. Alkylation (arylation)

The review is devoted to alkylation (arylation) as a widely employed derivatization procedure for the protection of OH (carboxylic acids, phosphoric acids, sulfonic acids, alcohols, polyols, phenols, enols), SH (thiols) and NH (amines, amides) groups in order to increase volatility, to improve the chromatographic properties and, if possible, mass spectral properties of derivatives. Chemical aspects of derivatization and various alkylation (arylation) reagents and reaction procedures are described. Specific mass spectral (electron ionization, chemical ionization) features of derivatives helpful in identification, structure elucidation, profiling and quantitative determination of the above-mentioned polar compounds by coupled gas chromatography or high-performance liquid chromatography are discussed. Some common analytical applications of the procedures in organic chemistry, clinical chemistry, environmental chemistry etc. are briefly summarized.

Point mutations in the murine fumarylacetoacetate hydrolase gene: Animal models for the human genetic disorder hereditary tyrosinemia type 1

Hereditary tyrosinemia type 1 (HT1) is a severe autosomal recessive metabolic disease associated with point mutations in the human fumarylacetoacetate hydrolase (FAH) gene that disrupt tyrosine catabolism. An acute form of HT1 results in death during the first months of life because of hepatic failure, whereas a chronic form leads to gradual development of liver disease often accompanied by renal dysfunction, childhood rickets, neurological crisis, and hepatocellular carcinoma. Mice homozygous for certain chromosome 7 deletions of the albino Tyr; c locus that also include Fah die perinatally as a result of liver dysfunction and exhibit a complex syndrome characterized by structural abnormalities and alterations in gene expression in the liver and kidney. Here we report that two independent, postnatally lethal mutations induced by N-ethyl-N-nitrosourea and mapped near Tyr are alleles of Fah. The Fah(6287SB) allele is a missense mutation in exon 6, and Fah(5961SB) is a splice mutation causing loss of exon 7, a subsequent frameshift in the resulting mRNA, and a severe reduction of Fah mRNA levels. Increased levels of the diagnostic metabolite succinylacetone in the urine of the Fah(6287SB) and Fah(5961SB) mutants indicate that these mutations cause a decrease in Fah enzymatic activity. Thus, the neonatal phenotype present in both mutants is due to a deficiency in Fah caused by a point mutation, and we propose Fah(5961SB) and Fah(6287SB) as mouse models for acute and chronic forms of human HT1, respectively.

Capillary electrophoresis for rapid profiling of organic acidurias

Organic acids analysis is a powerful technique in the diagnosis of inborn errors of metabolism. Clinically, patients present with severe symptoms, and early detection and appropriate treatment are often lifesaving. Most of the existing methods are based on gas chromatography in combination with mass spectrometry and require sophisticated equipment and complex sample pretreatment and derivatization. We propose a rapid, simple, and automated capillary electrophoretic method for routine analysis of urine to detect 27 organic acids related to metabolic diseases. With this method, direct measurements are performed on samples after initial centrifugation and dilution, if needed. Separation is performed in pH 6.0 phosphate buffer with methanol added as an organic modifier, −10 kV applied potential, and ultraviolet detection at 200 nm. The assay is completed in <15 min, and alternative separation conditions are proposed in case of overlapping peaks. The developed method allows the identification and quantitation of methylmalonic, pyroglutamic, and glutaric acids in samples of patients with diseases related to these acids.

Stable-isotope selected-ion monitoring quantification of methylmalonic acid in dried filter-paper urine samples

Urea and creatinine were measured by Kodak Ektachem methods and methylmalonic acid by stable-isotope gas chromatography-mass spectrometry in 24 urine samples from patients with methylmalonic acidaemia. For each sample analyses were performed both directly on the liquid urine and on an aliquot which had been blotted onto filter paper and dried. There was good correlation between the methylmalonate/creatinine ratios in liquid and dried urine (r2 = 0.983). Urine dried on filter paper can be used advantageously for monitoring treatment in patients with this disorder.

A new neonatal case of N-acetylglutamate synthase deficiency treated by carbamylglutamate

N-Acetylglutamate synthase (NAGS) deficiency is a rare, autosomal recessive urea-cycle disease. Its clinical presentation is not different from the other hereditary hyperammonaemias. We report a new neonatal case with hyperammonaemic coma. A test by carbamylglutamate was performed at 25 days of life. Since then, the child was treated by carbamylglutamate three or four times a day with a total dose of 80-100 mg/kg per day. Today, the boy is 1 year old. He receives carbamylglutamate 200 mg four times a day. He has normal somatic and neurological development and good metabolic balance.

Propionic acidaemia: clinical, biochemical and therapeutic aspects. Experience in 30 patients

Comprehensive data on 30 patients with propionic acidaemia, diagnosed by selective screening for inborn errors of metabolism, are presented. The most valuable diagnostic metabolites found were methylcitric-, 3-hydroxypropionic-, and 2-methyl-3-oxovaleric acids. Hyperlysinaemia and hyperlysinuria are also characteristic findings in this disease. The metabolic pattern found in propionic acidaemia is discussed extensively as are enzymatic findings. Residual activity of propionyl-CoA carboxylase is neither a predictive marker for severity nor for outcome of the disease. Propionate fixation assays were less reliable for confirmation of propionic acidaemia and of no prognostic value. Clinical presentation of the disease is discussed in detail. Besides the well-known unspecific findings (poor appetite, feeding difficulties, vomiting, dehydration, weight loss, muscular hypotonia, dyspnoea, somnolence, apathy, convulsion, coma, severe metabolic acidosis, hyperammonaemia) various skin abnormalities have been detected in about 50% of all patients. In 27% "dermatitis acidemica" was found.

Mevalonic aciduria in 3 siblings: a new recognizable metabolic encephalopathy

Mevalonic aciduria, due to mevalonate kinase deficiency, is the first recognized defect in the biosynthesis of cholesterol and isoprenoids. Very few patients with this disorder have been reported. Three siblings born from consanguineous parents are reported. Several clinical signs were present in all 3 children, including failure-to-thrive, susceptibility to infections, hepatosplenomegaly, cataract, and psychomotor retardation. Dysmorphic features were more apparent in the two older siblings. Urinary organic acid analysis by gas chromatography/mass spectrometry invariably revealed a high urinary excretion rate of mevalonic acid. Mevalonate kinase activity assayed in fibroblasts was very low. Diagnosis of this very rare disease may be suspected simply on clinical evidence; it is confirmed by abnormal excretion of mevalonic acid.

Carnitine palmitoyl transferase I deficiency presenting as a Reye-like syndrome without hypoglycaemia

An apparently healthy girl aged 2 years 9 months developed a coma with hepatomegaly within 24 h after an influenza-like infection. Plasma glucose and urinary organic acid profile were normal but plasma and urinary carnitine concentrations were increased. Despite symptomatic therapy, she died 11 days later. Oxidation of [1-14C] palmitic acid in the patient's fibroblasts was severely decreased (13% of controls). Further investigations revealed a deficiency of carnitine palmitoyl transferase I (CPT I) in the patient's fibroblasts (15% of controls) whereas CPT II activity was normal. Only four patients with CPT I deficiency have been reported so far. The subtle clinical and biochemical presentation of this disorder, which may account for the small number of cases diagnosed, is discussed.

Purification of electron transfer flavoprotein from pig liver mitochondria and its application to the diagnosis of deficiencies of acyl-CoA dehydrogenases in human fibroblasts

Medium chain acyl-CoA dehydrogenase (MCAD) and long chain acyl-CoA dehydrogenase (LCAD) deficiency are defects of mitochondrial beta-oxidation. The method of choice to measure specifically acyl-CoA dehydrogenase activity in human tissues uses purified electron transfer flavoprotein (ETF). We describe a simple and optimized method of purification allowing isolation of ETF with a degree of purity never reported so far. An assay for acyl-CoA dehydrogenase activity in cultured skin fibroblasts was developed using microquantities of electron transfer flavoprotein and substrate. MCAD deficiency was demonstrated in fibroblasts from nine patients and LCAD deficiency in fibroblasts from two patients.

Organic acids in aqueous humour and plasma: post mortem study in infants and diagnosis of enzymopathies

Organic acids have been determined in aqueous humour and plasma by gas chromatography-mass spectrometry in 38 cases of infant death and 4 cases of inherited metabolic disease: one had a complex fatty-acid oxidation disorder with a large urinary excretion of adipic acid, the others had a disorder of propionate catabolism with a large urinary excretion of methylmalonic acid. In each case we found in aqueous humour the abnormal metabolite present in urine. Thus aqueous humour could be a suitable material for retrospective diagnosis of inherited metabolic diseases at autopsy in sudden infant death syndrome.