Measurement of urinary free and acylcarnitines: quantitative acylcarnitine profiling in normal humans and in several patients with metabolic errors

Do food and stress biomarkers work for wastewater-based epidemiology? A critical evaluation

Dietary characteristics and oxidative stress are closely linked to the wellbeing of individuals. In recent years, various urinary biomarkers of food and oxidative stress have been proposed for use in wastewater-based epidemiology (WBE), in efforts to objectively monitor the food consumed and the oxidative stress experienced by individuals in a wastewater catchment. However, it is not clear whether such biomarkers are suitable for wastewater-based epidemiology. This study presents a suite of 30 urinary food and oxidative stress biomarkers and evaluates their applicability for WBE studies. This includes 22 biomarkers which were not previously considered for WBE studies. Daily per capita loads of biomarkers were measured from 57 wastewater influent samples from nine Australian catchments. Stability of biomarkers were assessed using laboratory scale sewer reactors. Biomarkers of consumption of vitamin B2, vitamin B3 and fibre, as well as a component of citrus had per capita loads in line with reported literature values despite susceptibility of degradation in sewer reactors. Consumption biomarkers of red meat, fish, fruit, other vitamins and biomarkers of stress had per capita values inconsistent with literature findings, and/or degraded rapidly in sewer reactors, indicating that they are unsuitable for use as WBE biomarkers in the traditional quantitative sense. This study serves to communicate the suitability of food and oxidative stress biomarkers for future WBE research.

Potential grape-derived contributions to volatile ester concentrations in wine

Grape composition affects wine flavour and aroma not only through varietal compounds, but also by influencing the production of volatile compounds by yeast. C₉ and C₁₂ compounds that potentially influence ethyl ester synthesis during fermentation were studied using a model grape juice medium. It was shown that the addition of free fatty acids, their methyl esters or acyl-carnitine and acyl-amino acid conjugates can increase ethyl ester production in fermentations. The stimulation of ethyl ester production above that of the control was apparent when lower concentrations of the C₉ compounds were added to the model musts compared to the C₁₂ compounds. Four amino acids, which are involved in CoA biosynthesis, were also added to model grape juice medium in the absence of pantothenate to test their ability to influence ethyl and acetate ester production. β-Alanine was the only one shown to increase the production of ethyl esters, free fatty acids and acetate esters. The addition of 1 mg∙L⁻¹ β-alanine was enough to stimulate production of these compounds and addition of up to 100 mg∙L⁻¹ β-alanine had no greater effect. The endogenous concentrations of β-alanine in fifty Cabernet Sauvignon grape samples exceeded the 1 mg∙L⁻¹ required for the stimulatory effect on ethyl and acetate ester production observed in this study.

l-Carnitine transport in human placental brush-border membranes is mediated by the sodium-dependent organic cation transporter OCTN2

Maternofetal transport of l-carnitine, a molecule that shuttles long-chain fatty acids to the mitochondria for oxidation, is thought to be important in preparing the fetus for its lipid-rich postnatal milk diet. Using brush-border membrane (BBM) vesicles from human term placentas, we showed that l-carnitine uptake was sodium and temperature dependent, showed high affinity for carnitine (apparent Km= 11.09 ± 1.32 μM; Vmax= 41.75 ± 0.94 pmol·mg protein−1·min−1), and was unchanged over the pH range from 5.5 to 8.5. l-Carnitine uptake was inhibited in BBM vesicles by valproate, verapamil, tetraethylammonium, and pyrilamine and by structural analogs of l-carnitine, including d-carnitine, acetyl-d,l-carnitine, and propionyl-, butyryl-, octanoyl-, isovaleryl-, and palmitoyl-l-carnitine. Western blot analysis revealed that OCTN2, a high-affinity, Na+-dependent carnitine transporter, was present in placental BBM but not in isolated basal plasma membrane vesicles. The reported properties of OCTN2 resemble those observed for l-carnitine uptake in placental BBM vesicles, suggesting that OCTN2 may mediate most maternofetal carnitine transport in humans.

Analysis of amino acids as formamidene butyl esters by electrospray ionization tandem mass spectrometry

Amino acid formamidene butyl esters are optimally prepared by heating amino acids with dimethylformamide dimethylacetal (DMF-DMA) for 2 minutes at 65 degrees C and then with n-butanol/hydrogen chloride for 15 minutes at 65 degrees C. The formamidene butyl esters of simple alpha-amino acids and beta-amino acids afford between 1.1 and 20 times the signal intensity of the corresponding butyl esters during electrospray ionization tandem mass spectral analysis. Complex alpha-amino acids, such as ornithine, arginine and citrulline, and gamma-amino acids are better analyzed as butyl esters. Secondary alpha-amino acids, such as proline and sarcosine, give a mixture of two iminium salts with the DMF-DMA derivatization method. A derivative incorporating two molecules of the amino acid predominates at higher derivatization temperatures. Contrary to a previous report, N-formylamino acids were not detected. The presence of secondary amino acids in amino acid mixtures, derivatized as formamidene butyl esters, affords derivatives that incorporate two different amino acids. The new formamidene butylation method is unlikely to replace the butylation procedure used by neonatal blood spot screening programs for amino acid disorders, since a much poorer response was obtained with formamidene butyl esters of arginine and citrulline, important in the diagnosis of arginase deficiency and citrullinaemia.

Gas chromatographic profiling and determination of urinary acylcarnitines

A method is described for the routine profiling and determination in urine of most of the acylcarnitines clinically relevant for the diagnosis of organic acidurias. The procedure, which does not require expensive apparatus, involves extraction of the acylcarnitines on strong cation-exchange disposable columns, mild alkaline hydrolysis and gas chromatography of the liberated monocarboxylic acids. The different steps were optimized in order to increase the analytical performance. No significant interferences were encountered, the limit of detection (signal-to-noise ratio = 3:1) ranged from 0.1 to 4 mg/l and the between-day coefficient of variation from 3.6 to 17.7%, depending on the acyl species. The rapidity of the method results from the application of a single solid-phase extraction on disposable columns. The acyl moieties are chromatographed underivatized in order to permit the identification of short-, medium- and long-chain acylcarnitines. The method was assessed by analysing fourteen urine specimens from patients presenting an organic aciduria.

Enhancement of mass spectrometric detection of LTC4, LTD 4, and LTE 4 by derivatization

Several acylating reagents are synthesized and used to introduce quatemary phosphonium or ammonium or ternary sulfonium functions into a simple model of a peptido leukotriene (PLT). One of these reagents was selected for further study with LTE4, LTD4, and LTC4. We demonstrate that acylation of the free amine function of PLTs to produce the 5-triphenylphosphoniumvaleryl-amide (TPPV) derivatives enhances chemical stabilities and significantly increases responses in fast-atom bombardment and continuous-flow liquid secondary ion mass spectrometry (CF-LSIMS) relative to the native PLTs. With high-performance liquid chromatography inlet to CF-LSIMS, we demonstrate the facile detection in selected ion monitoring of the TPPV derivative of 3 pg of LTD4.

Enzyme reactor for urinary acylcarnitines assay by reversed-phase high-performance liquid chromatography

An immobilized enzyme reactor, made up acylcarnitine hydrolase, carnitine dehydrogenase and diaphorase in sequence, was developed for the sensitive and selective determination of urinary free and individual acylcarnitines by a reversed-phase high-performance liquid chromatography. A 100-microliter urine sample was directly injected onto the TSKgel ODS 80Ts column and eluted by a step-gradient procedure. The eluent was mixed with the substrate solution of beta-NAD+ (1.0 mmol/l), resazurin (25 mumol/l) and Tris acetate (0.2 mol/l, pH 9.0). The mixture was passed through the immobilized enzyme reactor at 40 degrees C. Acylcarnitines were hydrolyzed and the converted to rezorufin which was measured by monitoring the fluorescence intensity at lambda EX = 560 nm and lambda EM = 580 nm. Free, acetyl-, glutaryl-, propionyl-, butyryl-, isobutyryl-, valeryl- and isovalerylcarnitine were determined within 55 min with detection limits (< 1 mumol/l) and within-run and day-to-day imprecision (C.V. < 6%). Free, acetyl- and isobutyrylcarnitine were found in normal urine. On the other hand, propionylcarnitine was detected in the urine of children with propionic aciduria and methylmalonic aciduria and multiple acylcarnitines were found in the urine of children with glutaric aciduria (type II).

Quantification of carnitine and specific acylcarnitines by high-performance liquid chromatography: application to normal human urine and urine from patients with methylmalonic aciduria, isovaleric acidemia or medium-chain acyl-CoA dehydrogenase deficiency

This paper describes the development of a high-performance liquid chromatographic method for the quantitation of free carnitine, total carnitine, acetylcarnitine, propionylcarnitine, isovalerylcarnitine, hexanoylcarnitine and octanoylcarnitine in human urine. Carnitine and acylcarnitines were isolated from 10 or 25 microliters of urine using 0.5-ml columns of silica gel, derivatized with 4'-bromophenacyl trifluoromethanesulfonate and separated by high-performance liquid chromatography. Using 4-(N,N-dimethyl-N-ethylammonio)-3-hydroxybutanoate ("e-carnitine") as the internal standard, standard curves (10-300 nmol/ml) were generated. Carnitine and acylcarnitines were quantified (when they were present) in normal human urine and the urine of patients diagnosed with one of three different disorders of organic acid metabolism: methylmalonic aciduria, isovaleric aciduria, isovaleric acidemia, and medium-chain acyl-CoA dehydrogenase deficiency.

Isolation of acylcarnitines from urine: a comparison of methods and application to long-chain acyl-CoA dehydrogenase deficiency

Carnitine esters from acetylcarnitine (C2 acyl chain) to octadecanoylcarnitine (C18 acyl chain) can be extracted from urine with recoveries of greater than 80%. However, to obtain such recoveries, it is important to choose the method of extraction appropriate to the acylcarnitines of interest. For acylcarnitines with acyl chain length C2 to C8 (acetylcarnitine to octanoylcarnitine), an ion-exchange procedure is recommended. Acylcarnitines with acyl chain length C8 to C12 (octanoylcarnitine to dodecanoylcarnitine) are best isolated from carefully acidified urine by solvent extraction with butan-1-ol. For long-chain acylcarnitines, C10 to C18 (decanoylcarnitine to octadecanoylcarnitine), solvent extraction of unacidified urine with hexan-2-ol is particularly simple and effective.

Identification of urinary acylcarnitines using gas chromatography-mass spectrometry: preliminary clinical applications

Many disorders of organic acid metabolism are associated with abnormalities in the levels of acylcarnitines excreted in urine. Profiling of urinary acylcarnitines allows diagnosis and characterisation of many acidurias and acidemias, monitoring dietary treatment of such patients, and elucidation of the metabolism of some exogenous acidic compounds. Urine (ca. 0.5 ml) was subjected to a simple work-up by ion-exchange chromatography, and the isolated acylcarnitines were derivatized by cyclization in 35 min to give volatile lactones that are compatible with gas chromatography-mass spectrometry using electron or chemical ionization. The feasibility of this new and affordable procedure has been confirmed by identifying urinary acylcarnitines in cases of medium-chain acyl-coenzyme A dehydrogenase deficiency, propionic acidemia and isovaleric acidemia.

Direct gas chromatographic assay of urinary medium-chain fatty acylcarnitines by their thermal decomposition

We report a gas chromatographic assay for urinary medium-chain acylcarnitines which employs their property of thermal lability, and by circumventing the need for specialised mass spectroscopy is suitable for routine laboratory use. The method produces readily interpreted, uncomplicated chromatograms and has proved to be both sufficiently sensitive and specific to enable detection of octanoylcarnitine in a symptomatic individual with medium-chain CoA dehydrogenase deficiency and in two asymptomatic siblings following administration of a carnitine load.

Analysis of acylcarnitines as their N-demethylated ester derivatives by gas chromatography-chemical ionization mass spectrometry

A novel approach to the analysis of acylcarnitines has been developed. It involves a direct esterification using propyl chloroformate in aqueous propanol followed by ion-pair extraction with potassium iodide into chloroform and subsequent on-column N-demethylation of the resulting acylcarnitine propyl ester iodides. The products, acyl N-demethylcarnitine propyl esters, are volatile and are easily analyzed by gas chromatography-chemical ionization mass spectrometry. For medium-chain-length (C4-C12) acylcarnitine standards, detection limits are demonstrated to be well below 1 ng starting material using selected ion monitoring. Well-separated gas chromatographic peaks and structure-specific mass spectra are obtained with samples of synthetic and biological origin. Seven acylcarnitines have been characterized in the urine of a patient suffering from medium-chain acyl-CoA dehydrogenase deficiency.

Synthesis, characterisation and high-performance liquid chromatography of C6-C16 dicarboxylyl-mono-coenzyme A and -mono-carnitine esters

The synthesis and purification of the mono-coenzyme A and mono-carnitine esters of the homologous series of straight-chain even-numbered dicarboxylic acids (C6-C16) is described. The corresponding 3-hydroxyacyl- and 2-enoyl-CoA esters were prepared enzymatically. A reversed-phase high-performance liquid chromatographic (HPLC) system for the analysis of the intact CoA esters is described and their chromatographic behaviour documented. Reversed-phase HPLC systems for the analysis of the 4-bromophenacyl derivatives of the dicarboxylyl-mono-carnitines and the 4-nitrobenzyl derivatives of the free acids are also described. Some preliminary studies of the metabolism of [U-14C]hexadecanedionoyl-mono-CoA by rat liver peroxisomes and rat skeletal muscle mitochondria are described illustrating the application of these methods.

Detection of hereditary metabolic disorders involving amino acids and organic acids

Inherited disorders in the metabolism of amino acids and organic acids may cause neurological dysfunction and acute metabolic crises. For many of these disorders, early diagnosis and early treatment can greatly improve the outcome. A general description of the clinical manifestations and a discussion of selected techniques and approaches for the laboratory diagnosis are reviewed.

Alteration of urinary carnitine profile induced by benzoate administration

To study the effect of sodium benzoate on carnitine metabolism, the acylcarnitine profile in the urine of five normal volunteers and two patients with urea cycle disorders was examined with fast atom bombardment-mass spectrometry. The volunteer subjects were given 5 g of sodium benzoate orally and the two patients with urea cycle disorders (carbamyl phosphate synthetase deficiency type I and ornithine transcarbamylase deficiency) were already undergoing treatment with sodium benzoate and L-carnitine. The amount of benzoylcarnitine excretion depended on the dose of both sodium benzoate and L-carnitine in a reciprocal relation. Increased excretions of acetylcarnitine and propionylcarnitine were also noted after sodium benzoate administration. The alteration of the urinary aclycarnitine profile was consistent with the change of mitochondrial CoA profile predicted by in vitro studies of an animal model. It is suggested that urinary acylcarnitine analysis is important to assess the effect of benzoate administration on mitochondrial function in vivo. Supplementation with carnitine may be necessary to minimise the adverse effects of sodium benzoate treatment in hyperammonaemia.

High-performance liquid chromatographic separation of acylcarnitines following derivatization with 4'-bromophenacyl trifluoromethanesulfonate

A high-performance liquid chromatographic method for the separation of acylcarnitines after derivatization with 4'-bromophenacyl trifluoromethanesulfonate is presented. Derivatization of acylcarnitines was achieved at room temperature within 10 min. Separation of the acylcarnitine 4'-bromophenacyl esters was accomplished by high-performance liquid chromatography using as the analytical column a Resolve-PAK 5-microns C18 radially compressed cartridge eluted with a tertiary gradient containing varying proportions of water, acetonitrile, tetrahydrofuran, triethylamine, potassium phosphate, and phosphoric acid. Acylcarnitine 4'-bromophenacyl esters were detected spectrophotometrically at 254 nm. Baseline separation was obtained for a standard mixture (5 nmol of each injected) containing carnitine, acetyl-, propionyl-, butyryl-, valeryl-, hexanoyl-, heptanoyl-, octanoyl-, nonanoyl-, decanoyl-, lauroyl-, myristroyl-, palmitoyl-, and stearoylcarnitine. Nearly complete separation was obtained for a standard mixture containing butyryl-, isobutyryl-, isovaleryl-, and 2-methylbutyrylcarnitine. The method was applied to a normal human urine and then to this same urine spiked with the acylcarnitine standards. Urinary acylcarnitine profiles from patients having propionic acidemia, isovaleric acidemia, and medium-chain acyl-CoA dehydrogenase deficiency were performed. Urinary isovalerylcarnitine was quantified in the patient with isovaleric acidemia using heptanoylcarnitine as an internal standard.

Application of fast atom bombardment with tandem mass spectrometry and liquid chromatography/mass spectrometry to the analysis of acylcarnitines in human urine, blood, and tissue

Using a precursor-ion scan function on a triple quadrupole mass spectrometer, acylcarnitines were detected in the target matrices at or below concentrations of 1 nmol per gram by fast atom bombardment mass spectrometry. Acylcarnitine profiles from patients with known metabolic disorders were consistent with previously acquired data. Putative acylcarnitine signals were confirmed in one case by administration of stable isotope-labeled carnitine, which equilibrated rapidly with the endogenous pool. The addition of a continuous flow system enabled rapid sequential analysis without operator intervention, indicating the potential for automation of the analytical procedure. Incorporation of a micro-LC column enabled on-line liquid chromatographic/mass spectrometric analysis of selected patient samples. Large-scale screening and quantitative analysis of urine or blood for diagnostic acylcarnitines are now practicable.