[Clinical characteristics and analysis of mass spectrometric data in 33 patients with maple syrup urine disease]

OBJECTIVE

To explore the clinical characteristics and the diagnostic method of maple syrup urine disease (MSUD).

METHODS

From January 2003 to December 2011, a total of 14 000 patients with suspected inherited metabolism diseases were tested. The blood levels of leucine and valine of these patients were detected by tandem mass spectrometry. The urinary level of branched-chain α-ketoacids was tested by gas chromatography-mass spectrometry. And the diagnosis was based on the elevated levels of leucine and valine in blood and branched-chain α-ketoacids in urine.

RESULTS

Thirty-three MSUD patients were confirmed. Their median age of initial visit was 0.17 years old (range: 7 days to 30 years old). The peak onset age of them was 2-30 days old, including 28 cases of neonatal onset (84.8%). The presenting symptoms of 28 cases were feeding difficulties (n=14), poor response, lethargy and seizures. Their median blood levels of leucine and valine (1901 (458-5804) and 600 (315-1617) µmol/L) were significantly higher than their normal levels ((50-300) and (60-250) µmol/L, both P<0.01). Their urinary levels of 2-OH-isovaleric acid, 2-keto-isovaleric acid, 2-keto-3-methylvaleric acid, 2-keto-isocaproic and acetylglycine (262.5 (5.4-624.3), 35.8 (1.9-156.0), 133.8 (7.4-611.5), 518.7 (17.2-2121.2) and 280.5 (11.0-1087.9) respectively) significantly higher than their normal levels (0, <0.1, 0, 0, <0.1 respectively, all P<0.01). In 5 intermittent MSUD patients, their blood levels of leucine and valine (402 (348-958) and 556 (322-808) µmol/L) were significantly higher than their normal levels (both P<0.01). The urinary level of 2-OH-isovaleric acid was significantly higher than its normal levels (P<0.01) while the urinary levels of other α-ketoacids were normal.

CONCLUSIONS

The confirmation of MSUD remains difficult because of a lack of specific clinical features. The detections of tandem mass spectrometry and gas chromatography-mass spectrometry may aid its early diagnosis.

Organic acidurias: approach, results and clinical relevance

More than twenty-five inherited organic acidurias have been identified during the last fifteen years. This remarkable development is due mainly to the introduction of gas chromatography, and gas chromatography combined with mass spectrometry, in paediatric laboratories for metabolic disease. The chemical approach is determined mainly by physical properties of the acid, such as their extractability and volatility. Most progress has been made with extractable acids. The techniques used for derivatization are mentioned, such as trimethylsilylation, methylation and the preparation of asymmetric derivatives for the separation of optical enantiomers. Metabolite patterns may be so characteristic that the underlying enzyme defect can be deduced. Examples are the leucine degradation defects, all encountered in the authors' laboratory: branched-chain ketoaciduria; isovaleric acidaemia; 3-methylcrotonylglycinuria; 3-methylglutaconic aciduria; and 3-hydroxy-3-methylglutaric aciduria. These abnormalities are discussed. D-glyceric aciduria is shown as an example of a not yet fully understood organic aciduria. The clinical approach varies. Metabolic acidosis is an indication for organic acid analysis in urine and plasma, but in many defects there is no acidosis, or only a transient one caused by secondary metabolites, such as lactic and 3-hydroxybutyric acids. Gas chromatography is an obligatory routine investigation in screening programmes for inborn errors of metabolism, especially for the examination of acutely ill neonates and premature babies.

Metabolism of myosmine in Wistar rats

The alkaloid myosmine is present not only in tobacco products but also in various foods. Myosmine is easily nitrosated, yielding 4-hydroxy-1-(3-pyridyl)-1-butanone (HPB) and the esophageal tobacco carcinogen N'-nitrosonornicotine. Due to its widespread occurrence, investigations on the metabolism and activation of myosmine are needed for risk assessment. Therefore, the metabolism of myosmine has been studied in Wistar rats treated with single oral doses of [pyridine-5-3H]myosmine at 0.001, 0.005, 0.5, and 50 micromol/kg body weight. Oral administration was achieved by feeding a labeled apple bite. Radioactivity was completely recovered in urine and feces within 48 h. At the two lower doses, 0.001 and 0.005 micromol/kg, a higher percentage of the radioactivity was excreted in urine (86.2 +/- 4.9% and 88.9 +/- 1.7%) as compared with the higher doses, 0.5 and 50 micromol/kg, where only 77.8 +/- 7.3% and 75.4 +/- 6.6% of the dose was found in urine. Within 24 h, urinary excretion of radioactivity was nearly complete with less than 4% of the total urinary output appearing between 24 and 48 h. The two major metabolites accounting for >70% of total radioactivity in urine were identified as 3-pyridylacetic acid (20-26%) and 4-oxo-4-(3-pyridyl)butyric acid (keto acid, 50-63%) using UV-diode array detection and gas chromatography-mass spectrometry measurements. 3-Pyridylmethanol (3-5%), 3'-hydroxymyosmine (2%) and HPB (1-3%) were detected as minor metabolites. 3'-Hydroxymyosmine is exclusively formed from myosmine and therefore might be used as a urinary biomarker for myosmine exposure in the future.

Effect of minimal enteral feeding on splanchnic uptake of leucine in the postabsorptive state in preterm infants

We conducted a controlled, randomized trial to study the effect of minimal enteral feeding on leucine uptake by splanchnic tissues, as an indicator of maturation of these tissues, in preterm infants in the first week of life. Within a few hours after birth, while receiving only glucose, a primed constant infusion of [1-(13)C]-leucine was started and continued for 5 h via the nasogastric tube, whereas 5,5,5 D3-leucine was infused intravenously (for both tracers, priming dose 2 mg/kg, continuous infusion 2 mg/kg/h). Patients were thereafter randomized to receive solely parenteral nutrition (C), parenteral nutrition and 20 mL breast milk/kg/d (BM), or parenteral nutrition and 20 mL formula/kg/d (F). On d 7, the measurements were repeated, after discontinuing the oral intake for 5 h. Fourteen infants were included in group C, 12 in group BM, and 12 in group F. There was no difference in energy intake or nitrogen balance at any time. On d 1, plasma enrichment for the nasogastric tracer was lower than for the intravenous tracer for all three groups, both for leucine and for alpha-keto-isocaproic acid. On d 7, the enrichment for leucine and alpha-keto-isocaproic acid for the nasogastric tracer was lower than for the intravenous tracer for the groups BM and F (BM: 3.65 +/- 1.20 nasogastric versus 4.64 +/- 0.64 i.v.; F: 4.37 +/- 1.14 nasogastric versus 5.21 +/- 0.9 i.v.). In the control group, there was no difference between tracers. The lower plasma enrichment for the nasogastric tracer compared with the intravenous tracer suggests uptake of leucine by the splanchnic tissues. We conclude that minimal enteral feeding--even in low volumes of 20 mL/kg/d--increases the leucine uptake by the splanchnic tissue. We speculate that this reflects a higher protein synthesis of splanchnic tissues in the groups receiving enteral nutrition.

Renal clearance of branched-chain L-amino and 2-oxo acids in maple syrup urine disease

In maple syrup urine disease (MSUD), branched-chain L-amino (BCAA) and 2-oxo acids (BCOA) accumulate in body fluids owing to an inherited deficiency of branched-chain 2-oxo acid dehydrogenase complex activity. In MSUD, little information is available on the significance of urinary disposal of branched-chain compounds. We examined the renal clearance of leucine, valine, isoleucine and alloisoleucine, and their corresponding 2-oxo acids 4-methyl-2-oxopentanoate (KIC), 3-methyl-2-oxobutanoate (KIV), (S)-(S-KMV), and (R)-3-methyl-2-oxopentanoate (R-KMV), using pairs of plasma and urine samples (n = 63) from 10 patients with classical MSUD. The fractional renal excretion of free BCAA was in the normal range (< 0.5%) and independent of the plasma concentrations. The excretion of bound (N-acylated) BCAA was normal and not significantly dependent on the BCAA plasma concentrations. The fractional renal excretion of BCOA was in the order KIC << KIV < R-KMV < or = S-KMV (range (%): KIC 0.1-25; KIV 0.14-21.3; S-KMV 0.26-24.6; R-KMV 0.1-35.9), significantly correlated with the KIC plasma concentrations, and generally higher than that of the related BCAA. The results show that the renal excretion of free BCAA as well as of the acylated derivatives is negligible. The renal excretion of BCOA, however, to some extent counteracts increases in BCAA concentrations and thus contributes to the lowering of total BCAA pools in MSUD.

A GC/MS/MS screening method for multiple organic acidemias from urine specimens

A gas chromatography tandem mass spectrometry method using an ion trap GC/MS system was developed to quickly screen urine samples for 14 organic acids associated with multiple organic acidemias. The following organic acids are used as diagnostic markers: methylmalonic acid, glutaric acid, 2-ketoisocaproic acid, succinylacetone, 3-methylcrotonylglycine, tiglylglycine, isovalerylglycine, fumaric acid, butyrylglycine, propionylglycine, hexanoylglycine, adipic acid, suberic acid, and sebacic acid. 2-ketocaproic acid is used as an internal standard. The samples are prepared using a solid-phase extraction and converted to trimethylsilyl derivatives. The extraction efficiency for the 14 compounds is between 57 and 106%. A derivatized standard mixture of the 14 markers is run prior to the patient samples to determine the accurate absolute and relative retention times. The samples are then injected and the product ion spectra monitored. For data analysis, one characteristic product ion plot is extracted for each of the 14 marker compounds, and the presence of a peak with the expected retention time is determined. The areas of the product ion peaks are compared with the reference range determined from 30 normal controls. Ten samples of patients with known organic acidemias were measured. For all patients, diagnostic peaks at the expected retention times of at least five times the upper limit of the reference range were detected. The method, with its relatively fast sample preparation, short 10.0 min run time and simple data analysis, is suitable for use as a quick metabolic screen of very sick patients in whom there is concern regarding the possibility of a treatable inborn error.

Quantitation of 4-oxo-4-(3-pyridyl)butanoic acid and enantiomers of 4-hydroxy-4-(3-pyridyl)butanoic acid in human urine: A substantial pathway of nicotine metabolism

A liquid chromatography-atmospheric pressure chemical ionization-tandem mass spectrometry (LC-APCI-MS/MS) method was developed to analyze human urine for 4-oxo-4-(3-pyridyl)butanoic acid (keto acid) and the enantiomers of 4-hydroxy-4-(3-pyridyl)butanoic acid (hydroxy acid) to test our hypothesis that (S)-hydroxy acid could be a biomarker of metabolic activation of the tobacco-specific carcinogens 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) while (R)-hydroxy acid would be formed predominantly from nicotine, as indicated by studies with rats. Urine was collected from smokers, and from the same individuals after they had stopped smoking and used a nicotine transdermal system (nicotine patch) for 3 weeks. If (S)-hydroxy acid were a biomarker of NNK and NNN metabolic activation, its levels should be higher in the urine of smokers than in nicotine patch users because tobacco smoke, but not the nicotine patch, contains NNK and NNN. Internal standard, [2,2,3,3,4-D5]hydroxy acid, was added to an aliquot of urine, which was then subjected to solid phase extraction. The eluant containing hydroxy acid was esterified with acidic methanol, followed by treatment with (S)-(-)-alpha-methylbenzyl isocyanate, producing methyl-4(S)- or methyl-4(R)-[(S)-alpha-methylbenzylcarbamoyl]-4-(3-pyridyl)buta noate [(S,S)- or (R,S)-MMPB, respectively]. After HPLC purification, the MMPB diastereomers were separated and quantified by LC-APCI-MS/MS. Mean levels of (S)- and (R)-hydroxy acid were 14.1 +/- 8.0 and 1120 +/- 600 ng/mL, respectively, in smokers during ad lib smoking (n = 18), while the corresponding levels during nicotine patch use (n = 18) were 4.1 +/- 3.3 and 363 +/- 228 ng/mL. The amounts of (S)-hydroxy acid were far higher than could be formed from NNK and NNN, and the total amount of hydroxy acid indicated that it was a substantial urinary metabolite of nicotine, in contrast to results with rats. Therefore, the study was extended to quantify keto acid. This was accomplished by NaBH4 treatment of urine, which converted keto acid to hydroxy acid quantitatively, which was in turn analyzed as described above. Levels of keto acid while subjects were smoking and using the nicotine patch were 228 +/- 129 (n = 8) and 97.5 +/- 80.6 ng/mL (n = 8), respectively. These results indicate that conversion of nicotine to keto acid and hydroxy acid is a substantial metabolic pathway in humans, accounting for an estimated 14% of the nicotine dose. Apparently, keto acid is extensively converted to hydroxy acid in humans, in contrast to the results with rats. (S)-Hydroxy acid in human urine cannot be used as a biomarker of NNK and NNN metabolic activation because it is overwhelmed by the (S)-hydroxy acid formed from nicotine, despite the fact that >98% of the urinary hydroxy acid has the (R)-configuration. These results provide new insights about nicotine metabolism in humans.

Identification of new cystathionine mono-oxo acids, S-(3-oxo-3-carboxy-n-propyl) cysteine and S-(2-oxo-2-carboxyethyl) homocysteine, in the urine of a patient with cystathioninuria

Novel cystathionine mono-oxo acids, S-(3-oxo-3-carboxy-n-propyl) cysteine and S-(2-oxo-2-carboxyethyl) homocysteine, and cyclic amino acid, cystathionine ketimine, have been detected in the urine of a patient with cystathioninuria using liquid chromatography-mass spectrometry with an atmospheric pressure ionization interface system and an amino acid analyzer. To determine these cystathionine mono-oxo acids and cystathionine ketimine we took advantage of the selective absorbance at 380 nm of the phenylisothiocyanate-ketimine interaction product. The total concentrations of these compounds found in the urine samples of a cystathioninuric patient and six healthy subjects were respectively 3611.3 and 148.4 micrograms +/- 35.9/g of creatinine. The cystathioninuric patient excreted 20 times more cystathionine mono-oxo acids in the urine than healthy subjects.

Effects of birth asphyxia on urinary organic acid excretion

Using capillary gas chromatography-mass spectrometry, the effects of birth asphyxia on the urinary organic acid profile of term babies was investigated. Random urine samples were collected on days 1 and 8 from 19 babies with fetal distress, 19 with moderate birth asphyxia and 12 with severe asphyxia causing encephalopathy. Controls were 27 well neonates. Statistically significant abnormalities were found only for the severely asphyxiated group: increased concentrations of lactic, pyruvic, 3-hydroxybutyric, 4-hydroxyphenyllactic and 4-hydroxy-3-methoxymandelic acids, and excretion of four abnormal metabolites, 2-hydroxybutyric, 2-oxoisocaproic, 2-hydroxyisovaleric and 2-oxo-3-methylvaleric acids. Six other babies had increased lactic acid excretion, associated in four with transient 'jitterness' or hypotonia. Organic acid studies may help to grade the severity of perinatal asphyxia in the outcome or intervention studies.

[Richards-Rundle syndrome]

Among 43 female patients aged 17-46 years with almost severe oligophrenia there were four with primary hypogonadism, one of them a case of Richards Rundle syndrome, now aged 20 years with absence of secondary sex characters, hypoplastic genitals, deafness, ataxia, wasting of muscles and reduced jerks. In cases of hypogonadism and hypogenitalism should be searched for mental and neurologic disorders, also for genetic counseling of the siblings.

Identification of 3-oxodicarboxylic acids in human urine

Gas chromatography-mass spectrometry has been used to detect a series of 3-oxodicarboxylic acids in human urine as their corresponding dimethyl ester trimethylsilyl enol ethers. 3-Oxohexanedioic acid, 3-oxooctanedioic acid and 3-oxodecanedioic acid were demonstrated to be normal urine constituents. Increased amounts of these acids were excreted after ingestion of decanedioic acid. These findings support the hypothesis that dicarboxylic acids are degraded by ordinary beta-oxidation.

High-performance liquid chromatographic determination of alpha-keto acids in human serum and urine using 1,2-diamino-4,5-methylenedioxybenzene as a precolumn fluorescence derivatization reagent

A simple and highly sensitive high-performance liquid chromatographic (HPLC) method for the determination of alpha-keto acids in human serum and urine is described. In an acidic solution, twelve species of alpha-keto acids examined were converted by reaction with 1,2-diamino-4,5-methylenedioxy-benzene into highly fluorescent derivatives. The derivatives were separated isocratically by reversed-phase HPLC on a TSK gel ODS-80TM column and detected fluorimetrically. Eight alpha-keto acids in human serum and eleven alpha-keto acids in human urine can be determined simultaneously. The detection limits (signal-to-noise ratio = 5) are 6-44 fmol in an injection volume of 5 microliters. The intra-assay relative standard deviations for both serum and urine sample analyses are usually ca. 5%.

High-performance liquid chromatographic determination of glyoxylic acid and other carbonyl compounds in urine

A high-performance liquid chromatographic method for the determination of carbonyl compounds, namely aldehydes, ketones and keto acids in urine, has been developed. Pre-column derivatization with 2,4-dinitrophenylhydrazine offers sufficient sensitivity for the determination of glyoxylic acid in urine with a detection limit of 0.5 mg/l. The separation is performed on a C18 10-micron column and with an acetonitrile-aqueous buffer mobile phase, which also allows the resolution of the syn and anti geometric isomers. Matrix effects, precision, accuracy, limits of detection and structural selectivity of the method are discussed.

Determination of alpha-keto acids in serum and urine by high-performance liquid chromatography with fluorescence detection

A simple, rapid and highly sensitive high-performance liquid chromatographic method for the determination of alpha-keto acids in serum and urine is described. In dilute hydrochloric acid, alpha-keto acids are converted by 1,2-diamino-4,5-dimethoxybenzene into highly fluorescent quinoxalinone derivatives. The derivatives are isocratically separated simultaneously within 14 min by reversed-phase chromatography on a Radial-Pak cartridge C18 and detected fluorimetrically. The limits of detection are 10-300 fmol in an injection volume of 10 microliters (40-1200 pmol/ml of serum or urine). This sensitivity permits precise determination of several alpha-keto acids in 5 microliter of serum or urine from healthy persons, and also the determination of phenylpyruvic acid in normal urine which cannot be simultaneously determined by other methods.

Thiamine response in maple syrup urine disease

We measured the biochemical response for four patients with maple syrup disease to pharmacologic doses of thiamine, and correlated their response to their branched chain alpha-ketoacid dehydrogenase activity. We observed a linear correlation between the concentrations of each plasma branched-chain amino acid and its corresponding ketoacid analogue. In addition, the renal tubular reabsorption of branched-chain amino and ketoacids was nearly complete within these physiologic concentrations. Three children responded to thiamine therapy with a reduction in concentration of plasma and urinary branched-chain amino and ketoacids. Each responder had at least 5% activity for branched chain alpha-ketoacid dehydrogenase in their mononuclear blood cells and in whole cell fibroblasts from cultured skin when compared to the activity in normal control cells. We propose that each child with maple syrup urine disease be assessed for their response to thiamine by quantifying the concentration of branched-chain amino acids in plasma before and after vitamin supplementation.

pH regulation of endogenous acid production in subjects with chronic ketoacidosis

In a previous study of starvation-induced acute ketoacidosis, net ketoacid production was inhibited by acid and facilitated by base ingestion. To determine whether hydrogen ion modifies net ketoacid production during chronic ketoacidosis, six over-weight volunteers ingested NaHCO3, NaCl, or NH4Cl (2 mmol X kg-1 X day-1), each for 7 days, during weeks 6-8 of ketogenic dieting. During days 4-7 of each phase, blood bicarbonate was stable but lower in the NH4Cl (19.6 +/- 0.7 mM) than the NaHCO3 (23.7 +/- 0.7 mM) phases. Throughout these periods, acid intake differed by 216 mmol/day, whereas acid output differed by 129 mmol/day between the NaHCO3 and the NH4Cl phases. The major contribution to this difference in acid balance was a difference in net organic acid (ketoacid) production. Although blood ketones were stable, ketoacid excretion, reflecting net ketoacid production, was decreased by 59% with acid and increased by 66% with base compared with NaCl (control) ingestion. Thus, in this state of chronic ketoacidosis, challenges to acid-base balance were countered by a rapidly occurring, sustained, reversible, and quantitatively significant modification of net acid production which acted as an effective mechanism for acid-base regulation.

Nutrition support of inborn errors of amino acid metabolism

Programs for nutrition support of patients with phenylketonuria, maternal phenylketonuria, branched chain ketoaciduria and vitamin B-6 non-responsive homocystinuria were written in BASIC. These programs plan diets to fill diet prescriptions using natural foods, available amino acid-free or restricted elemental products, milk or infant proprietary formulae and protein-free fat and carbohydrate sources. Emphasis is placed on satisfying the amino acid and protein prescriptions simultaneously. The final semisynthetic formula is evaluated for vitamins, minerals, renal solute load and renal net acid excretion. Fluid requirement is estimated. The paper describes how the conventional protocols are enhanced by computerization and details the requisite calculations.

Fluorescent analysis of alpha-keto acids in serum and urine by high-performance liquid chromatography

A procedure for rapid separation and microquantitative determination of various alpha-keto acids in serum and urine was developed. The procedure used reverse-phase high-performance liquid chromatography of the alpha-keto acids after derivatization into fluorescent quinoxalines by reaction with o-phenylenediamine. Deproteinization of serum with tungstic acid or methanol facilitated a constant recovery of alpha-keto acids. The useful range of analysis of seven alpha-keto acids by isocratic chromatography was from 10 to 250 pmol. The fluorescence emission was measured at 410 nm with excitation at 350 nm. The data obtained from samples of patients with chronic pyruvic acidemia and maple syrup urine disease, confirmed the usefulness of the method in clinical applications. A slightly modified procedure was needed for the analysis of oxaloacetic acid and phenylpyruvic acid.

Characterization of artefacts produced by treatment of organic acids with diazomethane

When alpha, beta-unsaturated acids and alpha-keto acids react with diazomethane not only are the corresponding methylates produced, but also diazomethane is added to the C = C double bond or to the oxo group. The gas chromatographic and mass spectral behaviour of these undesired products and some further artefacts produced in the hot inlet lines of a gas chromatograph are described. The mass spectra and retention indices allowed the structural assignment of several "unknown" compounds found previously in the methylated acid fraction of urine. A detailed analysis of the reaction of alpha-oxo acids with diazomethane revealed that, besides the already known oxirane methyl esters, homologous esters are also produced by an insertion reaction.

Pyruvate dehydrogenase subcomplex with lipoamide dehydrogenase deficiency in a patient with lactic acidosis and branched chain ketoaciduria

The overall and three component activities of pyruvate dehydrogenase complex were measured in the liver and muscle from a patient who died at 1.9 years with increased concentrations of serum lactate, alpha-ketoglutarate and branched chain amino acids. The component activities of both lipoate acetyltransferase and pyruvate dehydrogenase were similar to those of normal controls, but the overall pyruvate dehydrogenase complex activity was 11 to 30% of controls and lipoamide dehydrogenase activity was not detected. The overall activity was significantly increased by the addition of lipoamide dehydrogenase purified from human liver. Immunochemical studies carried out with antibody prepared against lipoamide dehydrogenase from rat liver, could detect no immunoreactive material in liver and muscle homogenates from the patient, suggesting that the deficiency of lipoamide dehydrogenase activity was due to the lack of enzyme protein.

Studies of urinary organic acid profiles of a patient with dihydrolipoyl dehydrogenase deficiency

Using gas chromatography-mass spectrometry (GC/MS), urinary organic acid profile studies were carried out on a patient with dihydrolipoyl dehydrogenase (E3) deficiency. Elevated levels of 2-hydroxyglutaric acid, 2-hydroxyisocaproic acid and 2-oxoisocaproic acid were observed in addition to lactic acid, 2-oxoglutaric acid, 2-hydroxyisovaleric acid and 2-hydroxybutyric acid previously described in patients with E3 deficiency. The 2-oxoglutaric acid levels were significantly lowered after branched-chain amino acid restriction. In an acute period, the patient was slightly ketoacidotic and excreted larger amounts of 2-oxoglutaric acid and lactic acid than in a static period. It was shown that, prior to confirmatory enzyme studies, patients with E3 deficiency who were suspected to have atypical maple syrup urine disease or chronic lactic acidosis can be rapidly identified by GC/MS analysis of urinary acids.

Episodic hypoglycemia with psi-hydroxy fatty acid excretion

We present case histories of two young children with episodes of hypoglycemia, elevation of SGOT, low insulin levels, increased urinary excretion of psi-hydroxy fatty acids (5-hydroxyhexanoic, 7-hydroxyoctanoic and 9-hydroxydecanoic), traces of the corresponding psi-ketoacids and elevations of urinary adipic, suberic, and sebacic acids. The ratio of psi-hydroxy fatty acids to 3-hydroxybutyric in the urine of these patients is higher than in patients of similar ages with similar illnesses. These acids persisted while the patients were well. Increased urinary psi-hydroxy fatty acids could be reproduced by a load of medium chain triglycerides without precipitating other clinical symptoms. Three children with hypoglycemia were found not to excrete measurable amounts of these unusual acids while ill. A medium chain triglyceride load in one of these children after recovery failed to elicit psi-hydroxy acid excretion. Small amounts of urinary 5-hydroxyhexanoic acid only were found in two patients with acute Reye's syndrome and in three of five severely ill children with starvation ketonuria. In this last group, no urinary psi-hydroxyacids could be detected after recovery. Normal children do not excrete measurable amounts (less than 1 mg/g creatinine) of these psi-hydroxyacids.

3-Hydroxy- and 3-keto-3-phenylpropionic acids: novel metabolites of benzoic acid in horse urine

The metabolism of benzoic acid has been examined in the horse, using 14C- and deuterium-labelled compounds. Chromatographic analysis of the urine showed the presence of hippuric acid, benzoyl glucuronide and benzoic acid and a discrete band which accounted for 2% of the dose administered. This material was isolated by solvent extraction and HPLC and, following treatment with diazomethane, examined by GC/MS. The major component of this fraction was 3-hydroxy-3-phenylpropionic acid methyl ester, which was accompanied by very much smaller amounts of cinnamic acid methyl ester and acetophenone. The two latter minor components have been shown to be artefacts produced during workup and analysis. Cinnamic acid methyl ester arises by the thermal decomposition of 3-hydroxy-3-phenylpropionic acid methyl ester on the GC column. It is proposed that acetophenone has formed, during workup, by decarboxylation of 3-keto-3-phenylpropionic acid. It is suggested that 3-hydroxy and 3-keto-3-phenylpropionic acids, which are also endogenous in horse urine, have arisen by an addition of a 2 carbon fragment to benzoyl CoA, in a sequence analogous to the reactions of fatty acid biosynthesis. Some implications of the metabolic interrelationships between xenobiotic acids and fatty acids are discussed.

Glucagon stimulation of phenylalanine metabolism. The effects of acute and chronic glucagon treatment

The effects of acute and chronic glucagon treatment on phenylalanine metabolism in vivo in the rat have been investigated. A single, large dose of glucagon (2 mg/kg, i.p.) increased metabolism of a large load of phenylalanine (1.27 g/kg) via hydroxylation and transamination. The increased metabolism was associated with increased activities of hepatic phenylalanine:pyruvate aminotransferase, tyrosine aminotransferase and phenylalanine hydroxylase. In rats administered this amount of phenylalanine, the p-hydroxyphenylpyruvate dioxygenase reaction was apparently rate limiting, as indicated by increased urinary excretion of p-hydroxyphenylpyruvate and p-hydroxyphenyllactate, in addition to urinary excretion of phenylpyruvate and phenyllactate. Chronic glucagon treatment (1.25 mg/kg every 12 hr for 8 days) increased oxidation of the large phenylalanine load and urinary excretion of phenylpyruvate and phenyllactate but not p-hydroxyphenylpyruvate or p-hydroxyphenyllactate. The increased excretion of phenylpyruvate and phenyllactate was associated with an increase in hepatic phenylalanine: pyruvate aminotransferase activity. The absence of p-hydroxyphenylpyruvate in the urine and the increased oxidation of phenylalanine imply that, in rats administered glucagon chronically, flux of p-hydroxyphenylpyruvate through the p-hydroxyphenylpyruvate dioxygenase reaction was increased. A kinetic assay for phenylalanine hydroxylase based on measurement of oxygen consumption in described.

Urinary excretion of 3-hydroxy-3-methylglutaric acid in the diabetic condition

Urinary levels of 3-hydroxy-3-methylglutaric acid (HMG) were measured by gas-liquid chromatography (GLC) after an extraction with tetrahydrofuran in normal rats, streptozotocin-diabetic rats and starved rats. The analysis was also carried out in the urine of three diabetic patients after suspending the insulin treatment. Detectable amounts of HMG are excreted in urine by normal humans and rats and such an excretion increases in the diabetic condition. Starved rats present only traces of HMG in the urine.

Urinary excretion of succinylacetone and delta-aminolevulinic acid in patients with hereditary tyrosinemia

Succinylacetone was excreted in the urine from four patients, with hereditary tyrosinemia i.e., two patients with the severe infantile type with fatal outcome and two patients with less severe juvenile form. In the urine from two patients with neonatal transient tyrosinemia and from normal individuals succinylacetone was not detectable. The urinary excretion of delta-aminolevulinic acid was also increased in all patients with hereditary tyrosinemia compared to patients with neonatal transient tyrosinemia and to normal individuals. The results presented support the hypothesis of a deficiency of fumarylacetoacetase in hereditary tyrosinemia. Furthermore an analytical method for the quantitative determination of succinylacetone in urine using GC-MS is described.

Analysis of the oxocarboxylic acid fraction in serum and urine as O-methyloximes by thermionic specific detection

After O-methyloximation of the carbonyl functions, the organic acids in serum and urine are extracted by anion-exchange chromatography, transformed into the methyl esters and pre-fractionated by thin-layer chromatography. In one of the four fractions and on the basis of the nitrogen in the O-methyloxime esters, the profiles of the oxocarboxylic acids are analyzed by gas chromatography with thermionic specific detection. The method has good specificity for the oxocarboxylic acids and is suitable for comparative studies. During diabetic or fasting ketoacidosis the serum concentrations of 3-oxobutyric acid and of the amino acid metabolites 2-oxobutyric, 2-oxoisovaleric and especially 2-oxo-3-methylvaleric and 2-oxoisocaproic acid are increased. In urine mainly 3-oxobutyric acid and only small amounts of the 2-oxocarboxylic acids are excreted.

Deficiency of fumarylacetoacetase in a patient with hereditary tyrosinemia

A patient is described with type I tyrosinemia characterized by urinary excretion of succinylacetone together with increased excretion of tyrosine, p-hydroxyphenyllactic, p-hydroxyphenylpyruvic and p-hydroxyphenylacetic acids. Fumarylacetoacetase was measured in a liver biopsy and found to be very low compared to control liver. Furthermore the mass spectra of succinylacetone and fumarylacetoacetate (methoxime-TMS derivatives) are reported. Control jejunal mucosa, leucocytes and fibroblasts showed no enzyme activity; hence the prenatal diagnosis of this disease by measuring the fumarylacetoacetase activity in cultured amniotic fluid cells is not possible at present.

Propionyl-CoA carboxylase deficiency: case report, effect of low-protein diet and identification of 3-oxo-2-methylvaleric acid 3-hydroxy-2-methylvaleric acid, and maleic acid in urine

Vomiting, lethargy and metabolic acidosis were the main initial symptoms of metabolic disease in a 1 month old girl. Her older sister had died from a similar disease, considered to be Reye's syndrome, at an age of 15 months. The urine of the present case contained 2-methylcitric acid, 3-hydroxypropionic acid, N-propionylglycine, 2-hydroxy-3-methylbutyric acid, N-tiglylglycine, 3-hydroxyvaleric acid and glutaric acid. These metabolites are all known to be associated with propionyl-CoA accumulation. Free propionic acid was not detected in the urine. In addition, the urine contained 3-oxo-2-methylvaleric acid and 3-hydroxy-2-methylvaleric acid, probably formed by condensation of two molecules of propionyl-CoA. The identity of these metabolites was confirmed by synthesis. An elevated urinary concentration of maleic acid and fumaric acid was another constant abnormality. The activity of propionyl-CoA carboxylase in leucocytes was about 20% of the normal activity. The girl was teated with a low-protein diet since the diagnosis was made at an age of 1 month, and her psychomotor development was satisfactory at an age of 2 1/2 years. She had a few episodes of acidosis during infections.

Isolation and identification of 2-oxo-5-guanidinovaleric acid in urine of patients with hyperargininaemia by chromatography and gas chromatography/mass spectrometry

An unknown guanidino-positive peak has been identified in urines of three sisters affected with hyperargininaemia. Identification was made on the basis of its similarity with the liquid and thin-layer chromatographic characteristics of enzymatically synthesized 2-oxo-5-guanidinovaleric acid. Identification was also made by combined gas chromatography-mass spectrometry of the unknown compound peak. The synthesis of enzymatically formed 2-oxo-5-guanidinovaleric acid was controlled by nuclear magnetic resonance and combined gas chromatography-mass spectrometry.

[2-Methyl-3-oxovaleric acid: a characteristic metabolite in propionic acidemia]

Urine samples from 9 patients with propionic acidemis were analyzed with respect to secondary propionyl-CoA metabolites by means of gas chromatography-mass spectrometry. A wide range of variation was observed. The presence of methylcitric and 2-methyl-3-oxovaleric acids, however, was demonstrable in all urines investigated in considerable amounts. For laboratories analyzing urinary organic acids as their methyl esters, 2-methyl-3-oxovaleric acid is considered to be of diagnostic value. In addition to the usual metabolites, the excretion of N-2-methylbutyrylglycine has been demonstrated in the urine of one patient with propionic acidemia.

Excretion of alpha-keto-delta-guanidinovaleric acid and its cyclic form in patients with hyperargininemia

alpha-Keto-delta-guanidinovaleric acid, in equilibrium with its cyclic form, has been identified in the urines of three sisters affected with hyperargininemia. Identification was achieved on the basis of its similarity with the enzymatically synthesized compounds.

Prostacyclin overproduction in Bartter's syndrome

Urinary excretion of 6-keto-prostaglandin F1alpha and thromboxane B2, the major metabolites of prostacyclin and of thromboxane A2, respectively, was measured by specific radioimmunoassays in five female patients with Bartter's syndrome and in five normal female controls. The patients with Bartter's syndrome excreted about four times as much 6-keto-PGF1alpha as the controls; their excretion of thromboxane B2 was no different from that of the controls. These data suggest that overproduction of prostacyclin mediates both the hyper-reninaemia and the hyporesponsiveness of blood-pressure to pressor agents in Bartter's syndrome.

The identification of 3-keto-2-methylvaleric acid and 3-hydroxy-2-methylvaleric acid in a patient with propionic acidemia

Two abnormal metabolites, 3-keto-2-methylvaleric acid and 3-hydroxy-2-methylvaleric acid, have been identified and quantitated in the urine of a child with propionic acidemia. These metabolites may be produced as a result of the self-condensation of propionyl-CoA. Data are presented to show that the unusual ketone, 3-pentanone, which has been observed previously in the urine of patients with propionic acidemia, is produced as a result of the decarboxylation of 3-keto-2-methylvaleric acid.