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Metabolite profiling in succinate semialdehyde dehydrogenase (SSADH; Aldh5a1-/-) deficient mice previously revealed elevated gamma-hydroxybutyrate (GHB) and total GABA in urine and total brain and liver extracts. In this study, we extend our metabolic characterization of these mutant mice by documenting elevated GHB and total GABA in homogenates of mutant kidney, pancreas and heart. We quantified beta-alanine (a GABA homolog and putative neurotransmitter) to address its potential role in pathophysiology. We found normal levels of beta-alanine in urine and total homogenates of mutant brain, heart and pancreas, but elevated concentrations in mutant kidney and liver extracts. Amino acid analysis in mutant total brain homogenates revealed no abnormalities except for significantly decreased glutamine, which was normal in mutant liver and kidney extracts. Regional amino acid analysis (frontal cortex, parietal cortex, hippocampus and cerebellum) in mutant mice confirmed glutamine results. Glutamine synthetase protein and mRNA levels in homogenates of mutant mouse brain were normal. We profiled organic acid patterns in mutant brain homogenates to assess brain oxidative metabolism and found normal concentrations of Kreb's cycle intermediates but increased 4,5-dihydroxyhexanoic acid (a postulated derivative of succinic semialdehyde) levels. We conclude that SSADH-deficient mice represent a valid metabolic model of human SSADH deficiency, manifesting focal neurometabolic abnormalities which could provide key insights into pathophysiologic mechanisms.

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The analysis of acylglycines is an important biochemical tool for the diagnosis of inherited disorders of mitochondrial fatty acid beta-oxidation. A stable isotope dilution gas chromatography negative chemical ionisation mass spectrometry method for the quantitative analysis of short- and medium-chain acylglycines as their bis(trifluoromethyl)benzyl (BTFMB) ester derivatives is described. The diagnostic usefulness of the method was demonstrated in nine patients with medium-chain acyl-coenzyme A (CoA) dehydrogenase (MCAD) deficiency, and seven patients with multiple acyl-CoA dehydrogenation defect (MAD). The urinary acylglycine profiles in these patients were compared to those in controls (n = 19), children on a medium-chain triglyceride (MCT) supplemented diet (n = 4), and patients with various other diseases (n = 5).

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Guanidinoacetate methyltransferase (GAMT) deficiency (creatine deficiency syndrome) is a recently discovered inborn error of creatine biosynthesis. Affected patients have elevated concentrations of guanidino-acetate, the metabolic precursor of creatine, in urine, plasma and cerebrospinal fluid. In addition, urinary creatinine excretion and plasma creatinine concentration are decreased. For biochemical evaluation of patients suspected to suffer from GAMT deficiency, correct quantification of creatinine in plasma is important. Here we report our experience with different quantification techniques. We found that creatinine in plasma from two GAMT-deficient patients appeared normal when measured by the Jaffé method but was decreased when measured enzymatically or by HPLC. The apparently normal levels of creatinine as measured by the Jaffé method were not caused by guanidinoacetate. In urine, the Jaffé method and the enzymatic method gave similar results, indicating that in urine no false elevations of creatinine can be expected. As the Jaffé method is still widely used for routine plasma creatinine measurements, it is important to realize it cannot be used to exclude GAMT deficiency.

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A previously described method for the determination of GABA in CSF has been expanded to include both GABA and beta-ALA, using a single GC-MS analysis. A stable isotope labelled internal standard for beta-ALA was synthesised to achieve accurate quantification. This new combined method expands the diagnostic power compared to an isolated GABA measurement. Control values for free and total GABA and free and total beta-ALA are described. Age <2 years: free GABA 0.017-0.067 microM, total GABA 4.2-13.4 microM; free beta-ALA 0.049-0.11 microM, total beta-ALA 2.1-4.6 microM. Age >2 years: free GABA 0.032-0.17 microM, total GABA 3.3-12.2 microM; free beta-ALA 0.021-0.058 microM, total beta-ALA 0.91-3.5 microM.

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N-l-Leucyldoxorubicin (Leu-Dox) was developed as a prodrug of doxorubicin (Dox) in order to diminish the cardiotoxic side-effect associated with repeated anthracycline treatment. To study the pharmacokinetics of Leu-Dox, Dox and other metabolites a sensitive and selective assay was needed. Leu-Dox and six of its known metabolites were extracted from plasma using an in-line reversed-phase precolumn (40-50 microns C8 particles). The trapped analytes were subsequently flushed to the analytical column (3 microns C18) using 0.5 ml of phosphate buffer (pH 3.5)-acetonitrile (2:1, v/v), which also served as the isocratic mobile phase. Within 12 min, a clean baseline-resolved chromatogram is obtained by fluorescence detection. Recoveries were almost quantitative and highly reproducible, with standard deviations less than or equal to 5.4% and less than or equal to 2.7% at spiked concentrations of 10 and 100 nM. Using 300 microliters of plasma, detection limits ranged from 0.3 to 0.8 nM at a signal-to-noise ratio of 3. The calibration curves were linear from 1 to 300 nM (r2 greater than or equal to 0.999) for each of the seven compounds. The between-day accuracy was in the range 91-99% and 99-105% at 10 and 100 nM, respectively, with standard deviations of 1-4%. Application of the assay to the analysis of plasma from patients after administration of Leu-Dox proved successful.

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Anthracyclines are very effective against soft tissue sarcomas, with cardiotoxicity being an important side effect after repeated administration. To estimate the relative cardiotoxicity of various anthracyclines and their metabolites, we developed an isolated mouse left atrium model. To relate an effect of doxorubicin, 4'-epidoxorubicin and their four main metabolites (doxorubicinol, epidoxorubicinol and the aglycons 7-deoxydoxorubicinon and 7-deoxydoxorubicinolon) to concentrations in the tissue instead of the incubation bath, a method of quantifying the anthracyclines in small tissue samples was developed. Atria were homogenized by sonication followed by extraction of the anthracyclines with methanol. The extract was directly analyzed by high-performance liquid chromatography with fluorescence detection. Recoveries for the six compounds tested ranged from 67.5% for 4'-epidoxorubicin to 100.6% for 7-deoxydoxorubinol aglycon with coefficients of variation of 2-3% at two spiked concentrations (0.1 and 1 nmol/mg of tissue). The calibration plots were linear (r2 greater than 0.996) over the concentration range tested (0.05-1 nmol/mg wet weight). The limits of detection (4-10 pmol/mg of tissue) were low enough to allow the determination of the anthracyclines at all relevant tissue concentrations.

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