Head-to-head trial of pegunigalsidase alfa versus agalsidase beta in patients with Fabry disease and deteriorating renal function: results from the 2-year randomised phase III BALANCE study

BACKGROUND

Pegunigalsidase alfa is a PEGylated α-galactosidase A enzyme replacement therapy. BALANCE (NCT02795676) assessed non-inferiority of pegunigalsidase alfa versus agalsidase beta in adults with Fabry disease with an annualised estimated glomerular filtration rate (eGFR) slope more negative than -2 mL/min/1.73 m2/year who had received agalsidase beta for ≥1 year.

METHODS

Patients were randomly assigned 2:1 to receive 1 mg/kg pegunigalsidase alfa or agalsidase beta every 2 weeks for 2 years. The primary efficacy analysis assessed non-inferiority based on median annualised eGFR slope differences between treatment arms.

RESULTS

Seventy-seven patients received either pegunigalsidase alfa (n=52) or agalsidase beta (n=25). At baseline, mean (range) age was 44 (18-60) years, 47 (61%) patients were male, median eGFR was 74.5 mL/min/1.73 m2 and median (range) eGFR slope was -7.3 (-30.5, 6.3) mL/min/1.73 m2/year. At 2 years, the difference between median eGFR slopes was -0.36 mL/min/1.73 m2/year, meeting the prespecified non-inferiority margin. Minimal changes were observed in lyso-Gb3 concentrations in both treatment arms at 2 years. Proportions of patients experiencing treatment-related adverse events and mild or moderate infusion-related reactions were similar in both groups, yet exposure-adjusted rates were 3.6-fold and 7.8-fold higher, respectively, with agalsidase beta than pegunigalsidase alfa. At the end of the study, neutralising antibodies were detected in 7 out of 47 (15%) pegunigalsidase alfa-treated patients and 6 out of 23 (26%) agalsidase beta-treated patients. There were no deaths.

CONCLUSIONS

Based on rate of eGFR decline over 2 years, pegunigalsidase alfa was non-inferior to agalsidase beta. Pegunigalsidase alfa had lower rates of treatment-emergent adverse events and mild or moderate infusion-related reactions.

TRIAL REGISTRATION NUMBER

NCT02795676.

Dairy Fat Intake, Plasma Pentadecanoic Acid, and Plasma Iso-heptadecanoic Acid Are Inversely Associated With Liver Fat in Children

OBJECTIVES

We sought to evaluate the relevance of pediatric dairy fat recommendations for children at risk for nonalcoholic fatty liver disease (NAFLD) by studying the association between dairy fat intake and the amount of liver fat. The effects of dairy fat may be mediated by odd chain fatty acids (OCFA), such as pentadecanoic acid (C15:0), and monomethyl branched chain fatty acids (BCFA), such as iso-heptadecanoic acid (iso-C17:0). Therefore, we also evaluated the association between plasma levels of OCFA and BCFA with the amount of liver fat.

METHODS

Observational, cross-sectional, community-based sample of 237 children ages 8 to 17. Dairy fat intake was assessed by 3 24-hour dietary recalls. Plasma fatty acids were measured by gas chromatography-mass spectrometry. Main outcome was hepatic steatosis measured by whole liver magnetic resonance imaging proton density fat fraction (MRI-PDFF).

RESULTS

Median dairy fat intake was 10.6 grams/day (range 0.0--44.5 g/day). Median liver MRI-PDFF was 4.5% (range 0.9%-45.1%). Dairy fat intake was inversely correlated with liver MRI-PDFF (r = -0.162; P = .012). In multivariable log linear regression, plasma C15:0 and iso-C17:0 were inverse predictors of liver MRI-PDFF (B = -0.247, P = 0.048; and B = -0.234, P = 0.009).

CONCLUSIONS

Dairy fat intake, plasma C15:0, and plasma iso-C17:0 were inversely correlated with hepatic steatosis in children. These hypothesis-generating findings should be tested through clinical trials to better inform dietary guidelines.

Tumor Metabolism and Neurocognition in CNS Lymphoma

BACKGROUND

The mechanistic basis for neurocognitive deficits in CNS lymphoma and other brain tumors is incompletely understood. We tested the hypothesis that tumor metabolism impairs neurotransmitter pathways and neurocognitive function.

METHODS

We performed serial cerebrospinal fluid (CSF) metabolomic analyses using liquid chromatography-electrospray tandem mass spectrometry to evaluate changes in the tumor microenvironment in 14 patients with recurrent CNS lymphoma, focusing on 18 metabolites involved in neurotransmission and bioenergetics. These were paired with serial mini-mental state examinations (MMSE) and MRI studies for tumor volumetric analyses. Patients were analyzed in the setting of the phase I trial of lenalidomide/rituximab. Associations were assessed by Pearson and Spearman correlation coefficient. Generalized estimating equation (gee) models were also established, adjusting for within-subject repeated measures.

RESULTS

Of 18 metabolites, elevated CSF lactate correlated most strongly with lower MMSE score (p<8E-8, rho=-0.67). High lactate was associated with lower GABA, higher glutamate/GABA ratio and dopamine. Conversely, high succinate correlated with higher MMSE score. Serial analysis demonstrated a reproducible, time-dependent, reciprocal correlation between changes in lactate and GABA concentrations. While high lactate and low GABA correlated with tumor contrast enhancing volume, they correlated more significantly with lower MMSE scores than tumor volumes.

CONCLUSIONS

We provide evidence that lactate production and Warburg metabolism may impact neurotransmitter dysregulation and neurocognition in CNS lymphomas. We identify novel metabolomic biomarkers that may be applied in future studies of neurocognition in CNS lymphomas. Elucidation of mechanistic interactions between lymphoma metabolism, neurotransmitter imbalance and neurocognition may promote interventions that preserve cognitive function.

Person Ability Scores as an Alternative to Norm-Referenced Scores as Outcome Measures in Studies of Neurodevelopmental Disorders

Although norm-referenced scores are essential to the identification of disability, they possess several features which affect their sensitivity to change. Norm-referenced scores often decrease over time among people with neurodevelopmental disorders who exhibit slower-than-average increases in ability. Further, the reliability of norm-referenced scores is lower at the tails of the distribution, resulting in floor effects and increased measurement error for people with neurodevelopmental disorders. In contrast, the person ability scores generated during the process of constructing a standardized test with item response theory are designed to assess change. We illustrate these limitations of norm-referenced scores, and relative advantages of ability scores, using data from studies of autism spectrum disorder and creatine transporter deficiency.

Cardiac tissue citric acid cycle intermediates in exercised very long-chain acyl-CoA dehydrogenase-deficient mice fed triheptanoin or medium-chain triglyceride

Anaplerotic odd-chain fatty acid supplementation has been suggested as an approach to replenish citric acid cycle intermediate (CACi) pools and facilitate adenosine triphosphate (ATP) production in subjects with long-chain fatty acid oxidation disorders, but the evidence that cellular CACi depletion exists and that repletion occurs following anaplerotic substrate supplementation is limited. We exercised very long-chain acyl-CoA dehydrogenase-deficient (VLCAD-/-) and wild-type (WT) mice to exhaustion and collected cardiac tissue for measurement of CACi by targeted metabolomics. In a second experimental group, VLCAD-/- and WT mice that had been fed chow prepared with either medium-chain triglyceride (MCT) oil or triheptanoin for 4 weeks were exercised for 60 minutes. VLCAD-/- mice exhibited lower succinate in cardiac muscle at exhaustion than WT mice suggesting lower CACi in VLCAD-/- with prolonged exercise. In mice fed either MCT or triheptanoin, succinate and malate were greater in VLCAD-/- mice fed triheptanoin compared to VLCAD-/- animals fed MCT but lower than WT mice fed triheptanoin. Long-chain odd acylcarnitines such as C19 were elevated in VLCAD-/- and WT mice fed triheptanoin suggesting some elongation of the heptanoate, but it is unknown what proportion of heptanoate was oxidized vs elongated. Prolonged exercise was associated with decreased cardiac muscle succinate in VLCAD-/- mice in comparison to WT mice. VLCAD-/- fed triheptanoin had increased succinate compared to VLCAD-/- mice fed MCT but lower than WT mice fed triheptanoin. Cardiac CACi were higher following dietary ingestion of an anaplerotic substrate, triheptanoin, in comparison to MCT.

Identification of pathognomonic purine synthesis biomarkers by metabolomic profiling of adolescents with obesity and type 2 diabetes

The incidence of type 2 diabetes is increasing more rapidly in adolescents than in any other age group. We identified and compared metabolite signatures in obese children with type 2 diabetes (T2D), obese children without diabetes (OB), and healthy, age- and gender-matched normal weight controls (NW) by measuring 273 analytes in fasting plasma and 24-hour urine samples from 90 subjects by targeted LC-MS/MS. Diabetic subjects were within 2 years of diagnosis in an attempt to capture early-stage disease prior to declining renal function. We found 22 urine metabolites that were uniquely associated with T2D when compared to OB and NW groups. The metabolites most significantly elevated in T2D youth included members of the betaine pathway, nucleic acid metabolism, and branched-chain amino acids (BCAAs) and their catabolites. Notably, the metabolite pattern in OB and T2D groups differed between urine and plasma, suggesting that urinary BCAAs and their intermediates behaved as a more specific biomarker for T2D, while plasma BCAAs associated with the obese, insulin resistant state independent of diabetes status. Correlative analysis of metabolites in the T2D signature indicated that betaine metabolites, BCAAs, and aromatic amino acids were associated with hyperglycemia, but BCAA acylglycine derivatives and nucleic acid metabolites were linked to insulin resistance. Of major interest, we found that urine levels of succinylaminoimidazole carboxamide riboside (SAICA-riboside) were increased in diabetic youth, identifying urine SAICA-riboside as a potential biomarker for T2D.

Cystathionine beta synthase deficiency and brain edema associated with methionine excess under betaine supplementation: Four new cases and a review of the evidence

CBS deficient individuals undergoing betaine supplementation without sufficient dietary methionine restriction can develop severe hypermethioninemia and brain edema. Brain edema has also been observed in individuals with severe hypermethioninemia without concomitant betaine supplementation. We systematically evaluated reports from 11 published and 4 unpublished patients with CBS deficiency and from additional four cases of encephalopathy in association with elevated methionine. We conclude that, while betaine supplementation does greatly exacerbate methionine accumulation, the primary agent causing brain edema is methionine rather than betaine. Clinical signs of increased intracranial pressure have not been seen in patients with plasma methionine levels below 559 μmol/L but occurred in one patient whose levels did not knowingly exceed 972 μmol/L at the time of manifestation. While levels below 500 μmol/L can be deemed safe it appears that brain edema can develop with plasma methionine levels close to 1000 μmol/L. Patients with CBS deficiency on betaine supplementation need to be regularly monitored for concordance with their dietary plan and for plasma methionine concentrations. Recurrent methionine levels above 500 μmol/L should alert clinicians to check for clinical signs and symptoms of brain edema and review dietary methionine intake. Levels approaching 1000 μmol/L do increase the risk of complications and levels exceeding 1000 μmol/L, despite best dietetic efforts, should be acutely addressed by reducing the prescribed betaine dose.

A post glycosylphosphatidylinositol (GPI) attachment to proteins, type 2 (PGAP2) variant identified in Mabry syndrome index cases: Molecular genetics of the prototypical inherited GPI disorder

We report that recessive inheritance of a post-GPI attachment to proteins 2 (PGAP2) gene variant results in the hyperphosphatasia with neurologic deficit (HPMRS) phenotype described by Mabry et al., in 1970. HPMRS, or Mabry syndrome, is now known to be one of 21 inherited glycosylphosphatidylinositol (GPI) deficiencies (IGDs), or GPI biosynthesis defects (GPIBDs). Bi-allelic mutations in at least six genes result in HPMRS phenotypes. Disruption of four phosphatidylinositol glycan (PIG) biosynthesis genes, PIGV, PIGO, PIGW and PIGY, expressed in the endoplasmic reticulum, result in HPMRS 1, 2, 5 and 6; disruption of the PGAP2 and PGAP3 genes, necessary for stabilizing the association of GPI anchored proteins (AP) with the Golgi membrane, result in HPMRS 3 and 4. We used exome sequencing to identify a novel homozygous missense PGAP2 variant NM_014489.3:c.881C > T, p.Thr294Met in two index patients and targeted sequencing to identify this variant in an unrelated patient. Rescue assays were conducted in two PGAP2 deficient cell lines, PGAP2 KO cells generated by CRISPR/Cas9 and PGAP2 deficient CHO cells, in order to examine the pathogenicity of the PGAP2 variant. First, we used the CHO rescue assay to establish that the wild type PGAP2 isoform 1, translated from transcript 1, is less active than the wild type PGAP2 isoform 8, translated from transcript 12 (alternatively spliced to omit exon 3). As a result, in our variant rescue assays, we used the more active NM_001256240.2:c.698C > T, p.Thr233Met isoform 8 instead of NM_014489.3:c.881C > T, p.Thr294Met isoform 1. Flow cytometric analysis showed that restoration of cell surface CD59 and CD55 with variant PGAP2 isoform 8, driven by the weak (pTA FLAG) promoter, was less efficient than wild type isoform 8. Therefore, we conclude that recessive inheritance of c.881C > T PGAP2, expressed as the hypomorphic PGAP2 c.698C > T, p.Thr233Met isoform 8, results in prototypical Mabry phenotype, HPMRS3 (GPIBD 8 [MIM: 614207]). This study highlights the need for long-term follow up of individuals with rare diseases in order to ensure that they benefit from innovations in diagnosis and treatment.

Promises and pitfalls of untargeted metabolomics

Metabolomics is one of the newer omics fields, and has enabled researchers to complement genomic and protein level analysis of disease with both semi-quantitative and quantitative metabolite levels, which are the chemical mediators that constitute a given phenotype. Over more than a decade, methodologies have advanced for both targeted (quantification of specific analytes) as well as untargeted metabolomics (biomarker discovery and global metabolite profiling). Untargeted metabolomics is especially useful when there is no a priori metabolic hypothesis. Liquid chromatography coupled to mass spectrometry (LC-MS) has been the preferred choice for untargeted metabolomics, given the versatility in metabolite coverage and sensitivity of these instruments. Resolving and profiling many hundreds to thousands of metabolites with varying chemical properties in a biological sample presents unique challenges, or pitfalls. In this review, we address the various obstacles and corrective measures available in four major aspects associated with an untargeted metabolomics experiment: (1) experimental design, (2) pre-analytical (sample collection and preparation), (3) analytical (chromatography and detection), and (4) post-analytical (data processing).

Brain Magnetic Resonance Imaging Findings in Poorly Controlled Homocystinuria

Homocystinuria is an inherited metabolic disorder most commonly caused by cystathionine β-synthase deficiency. Severe cases can cause white matter abnormalities that can mimic other vascular, toxic and metabolic disorders on computed tomography and magnetic resonance imaging. We present such a case which demonstrates not only extensive white matter abnormalities on magnetic resonance imaging, but also previously unreported basal ganglia signal abnormalities and imaging manifestations of increased intracranial pressure, likely caused by elevated methionine and betaine therapy. We also review the literature and discuss the potential underlying biologic mechanisms of these imaging findings.

A study on the safety and efficacy of reveglucosidase alfa in patients with late-onset Pompe disease

BACKGROUND

Late-onset Pompe disease is a rare genetic neuromuscular disorder caused by lysosomal acid alpha-glucosidase (GAA) deficiency that ultimately results in mobility loss and respiratory failure. Current enzyme replacement therapy with recombinant human (rh)GAA has demonstrated efficacy in subjects with late-onset Pompe disease. However, long-term effects of rhGAA on pulmonary function have not been observed, likely related to inefficient delivery of rhGAA to skeletal muscle lysosomes and associated deficits in the central nervous system. To address this limitation, reveglucosidase alfa, a novel insulin-like growth factor 2 (IGF2)-tagged GAA analogue with improved lysosomal uptake, was developed. This study evaluated the pharmacokinetics, safety, and exploratory efficacy of reveglucosidase alfa in 22 subjects with late-onset Pompe disease who were previously untreated with rhGAA.

RESULTS

Reveglucosidase alfa plasma concentrations increased linearly with dose, and the elimination half-life was <1.2 h. Eighteen of 22 subjects completed 72 weeks of treatment. The most common adverse events were hypoglycemia (63%), dizziness, fall, headache, and nausea (55% for each). Serious adverse events included hypersensitivity (n = 1), symptomatic hypoglycemia (n = 2), presyncope (n = 1), and acute cardiac failure (n = 1). In the dose-escalation study, all treated subjects tested positive for anti-reveglucosidase alfa, anti-rhGAA, anti-IGF1, and anti-IGF2 antibodies at least once. Subjects receiving 20 mg/kg of reveglucosidase alfa demonstrated increases in predicted maximum inspiratory pressure (13.9%), predicted maximum expiratory pressure (8.0%), forced vital capacity (-0.4%), maximum voluntary ventilation (7.4 L/min), and mean absolute walking distance (22.3 m on the 6-min walk test) at 72 weeks.

CONCLUSIONS

Additional studies are needed to further assess the safety and efficacy of this approach. Improvements in respiratory muscle strength, lung function, and walking endurance in subjects with LOPD may make up for the risk of hypersensitivity reactions and hypoglycemia. Reveglucosidase alfa may provide a new treatment option for patients with late-onset Pompe disease.

TRIAL REGISTRATION

ISRCTN01435772 and ISRCTN01230801 , registered 27 October 2011.

The mPEG-PCL Copolymer for Selective Fermentation of Staphylococcus lugdunensis Against Candida parapsilosis in the Human Microbiome

Many human skin diseases, such as seborrheic dermatitis, potentially occur due to the over-growth of fungi. It remains a challenge to develop fungicides with a lower risk of generating resistant fungi and non-specifically killing commensal microbes. Our probiotic approaches using a selective fermentation initiator of skin commensal bacteria, fermentation metabolites or their derivatives provide novel therapeutics to rein in the over-growth of fungi. Staphylococcus lugdunensis (S. lugdunensis) bacteria and Candida parapsilosis (C. parapsilosis) fungi coexist in the scalp microbiome. S. lugdunensis interfered with the growth of C. parapsilosis via fermentation. A methoxy poly(ethylene glycol)-b-poly(ε-caprolactone) (mPEG-PCL) copolymer functioned as a selective fermentation initiator of S. lugdunensis, selectively triggering the S. lugdunensis fermentation to produce acetic and isovaleric acids. The acetic acid and its pro-drug diethyleneglycol diacetate (Ac-DEG-Ac) effectively suppressed the growth of C. parapsilosis in vitro and impeded the fungal expansion in the human dandruff. We demonstrate for the first time that S. lugdunensis is a skin probiotic bacterium that can exploit mPEG-PCL to yield fungicidal short-chain fatty acids (SCFAs). The concept of bacterial fermentation as a part of skin immunity to re-balance the dysbiotic microbiome warrants a novel avenue for studying the probiotic function of the skin microbiome in promoting health.

Diagnosis and Monitoring of Cystinosis Using Immunomagnetically Purified Granulocytes

BACKGROUND

Cystine determination is a critical biochemical test for the diagnosis and therapeutic monitoring of the lysosomal storage disease cystinosis. The classical mixed-leukocyte cystine assay requires prompt specialized recovery/isolation following blood drawing, providing cystine concentrations normalized to total protein from assorted types of white blood cells, each with varying cystine content.

METHODS

We present a new workflow for cystine determination using immunomagnetic granulocyte purification, and new reference ranges established from 47 patient and 27 obligate heterozygote samples assayed. Samples were collected in acid-citrate dextrose tubes and their stability was proven to allow for overnight shipping before analysis. Cystine was quantified by LC-MS/MS.

RESULTS

The new method was reproducible (<15% root mean square error) and specific, assaying purified granulocytes from blood samples that no longer required immediate preparation and therefore allowing for up to 30 h before processing. There was a nearly a 2-fold increase in the therapeutic target (1.9 nmol half-cystine/mg protein) range, established using distributions of patient, obligate heterozygote, and control samples. The 2.5-97.5 percentile ranges (-2 SD to +2 SD around mean) for these cohorts were 0.67-6.05 nmol/mg protein for patients, 0.33-1.35 nmol/mg protein for obligate heterozygotes, and 0.09-0.35 nmol/mg protein for controls.

CONCLUSIONS

The intracellular cystine determination method using immunopurified granulocytes followed by LC-MS/MS analysis improves the inherent variability of mixed leukocyte analysis and eliminates the need for immediate sample preparation following blood draw.

In vivo monitoring of urea cycle activity with (13)C-acetate as a tracer of ureagenesis

BACKGROUND

The hepatic urea cycle is the main metabolic pathway for detoxification of ammonia. Inborn errors of urea cycle function present with severe hyperammonemia and a high case fatality rate. Long-term prognosis depends on the residual activity of the defective enzyme. A reliable method to estimate urea cycle activity in-vivo does not exist yet. The aim of this study was to evaluate a practical method to quantify (13)C-urea production as a marker for urea cycle function in healthy subjects, patients with confirmed urea cycle defect (UCD) and asymptomatic carriers of UCD mutations.

METHODS

(13)C-labeled sodium acetate was applied orally in a single dose to 47 subjects (10 healthy subjects, 28 symptomatic patients, 9 asymptomatic carriers).

RESULTS

The oral (13)C-ureagenesis assay is a safe method. While healthy subjects and asymptomatic carriers did not differ with regards to kinetic variables for urea cycle flux, symptomatic patients had lower (13)C-plasma urea levels. Although the (13)C-ureagenesis assay revealed no significant differences between individual urea cycle enzyme defects, it reflected the heterogeneity between different clinical subgroups, including male neonatal onset ornithine carbamoyltransferase deficiency. Applying the (13)C-urea area under the curve can differentiate between severe from more mildly affected neonates. Late onset patients differ significantly from neonates, carriers and healthy subjects.

CONCLUSION

This study evaluated the oral (13)C-ureagenesis assay as a sensitive in-vivo measure for ureagenesis capacity. The assay has the potential to become a reliable tool to differentiate UCD patient subgroups, follow changes in ureagenesis capacity and could be helpful in monitoring novel therapies of UCD.

p300 is not required for metabolic adaptation to endurance exercise training

The acetyltransferase, E1a-binding protein (p300), is proposed to regulate various aspects of skeletal muscle development, metabolism, and mitochondrial function,viaits interaction with numerous transcriptional regulators and other proteins. Remarkably, however, the contribution of p300 to skeletal muscle function and metabolism,in vivo, is poorly understood. To address this, we used Cre-LoxP methodology to generate mice with skeletal muscle-specific knockout of E1a-binding protein (mKO). mKO mice were indistinguishable from their wild-type/floxed littermates, with no differences in lean mass, skeletal muscle structure, fiber type, respirometry flux, or metabolites of fatty acid and amino acid metabolism.Ex vivomuscle function in extensor digitorum longus and soleus muscles, including peak stress and time to fatigue, as well asin vivorunning capacity were also comparable. Moreover, expected adaptations to a 20 d voluntary wheel running regime were not compromised in mKO mice. Taken together, these findings demonstrate that p300 is not required for the normal development or functioning of adult skeletal muscle, nor is it required for endurance exercise-mediated mitochondrial adaptations.-LaBarge, S. A., Migdal, C. W., Buckner, E. H., Okuno, H., Gertsman, I., Stocks, B., Barshop, B. A., Nalbandian, S. R., Philp, A., McCurdy, C. E., Schenk, S. p300 is not required for metabolic adaptation to endurance exercise training.

Successful Domino Liver Transplantation from a Patient with Methylmalonic Acidemia

Liver transplantation has been reported in patients with methylmalonic acidemia (MMA), but long-term outcome is controversial. Many patients with other approved indications for liver transplantation die before donor grafts are available. A 28-year-old man with MMA underwent cadaveric liver transplantation. His liver was used as a domino graft for a 61-year-old man with primary sclerosing cholangitis, who had low priority on the transplant waiting list. Surgical outcome was successful, and after transplantation both patients have excellent graft function. The patient with MMA showed substantial decrease in methylmalonate in urine (from 5,277 ± 1,968 preoperatively to 1,068 ± 384 mmol/mol creatinine) and plasma (from 445.9 ± 257.0 to 333.3 ± 117.7 μmol/l) over >1-year follow-up, while dietary protein intake increased from 0.6 to 1.36 ± 0.33 g/kg/day. The domino recipient maintained near-normal levels of plasma amino acids but did develop elevated methylmalonate in blood and urine while receiving an unrestricted diet (peak plasma methylmalonate 119 μmol/l and urine methylmalonate 84-209 mmol/mol creatinine, with 1.0-1.9 g/kg/day protein). Neither patient demonstrated any apparent symptoms of MMA or metabolic decompensation during the postoperative period or following discharge.

CONCLUSION

Liver transplantation substantially corrects methylmalonate metabolism in MMA and greatly attenuates the disease. In this single patient experience, a liver from a patient with MMA functioned well as domino graft although it did result in subclinical methylmalonic acidemia and aciduria in the recipient. Patients with MMA can be considered as domino liver donors for patients who might otherwise spend long times waiting for liver transplantation.

Perturbations of tyrosine metabolism promote the indolepyruvate pathway via tryptophan in host and microbiome

The drug nitisinone (NTBC) is used to treat tyrosinemia type I, and more recently has been also used for the treatment of another disorder of tyrosine metabolism, alkaptonuria. While studying the dose effects of NTBC treatment on alkaptonuria, untargeted metabolomics revealed perturbations in a completely separate pathway, that of tryptophan metabolism. Significant elevations in several indolic compounds associated with the indolepyruvate pathway of tryptophan metabolism were present in NTBC-treated patient sera and correlated with elevations of an intermediate of tyrosine metabolism. Indolic compounds of this pathway have long been associated with commensal bacterial and plant metabolism. These exogenous sources of indoles have been more recently implicated in affecting mammalian cell function and disease. We studied the correlation of these indolic compounds in other disorders of tyrosine metabolism including tyrosinemia types I and II as well as transient tyrosinemia, and demonstrated that 4-hydroxyphenylpyruvate (4-HPP) was directly responsible for the promotion of this pathway. We then investigated the regulation of the indolepyruvate pathway and the role of 4-HPP further in both mammalian cells and intestinal microbial cultures. We demonstrated that several of the indolic products, including indolepyruvate and indolelactate, were in fact generated by human cell metabolism, while the downstream indole metabolite, indolecarboxaldehyde, was produced exclusively by microbial cultures of human gut flora. This study describes a symbiotic perturbation in host and microbiome tryptophan metabolism in response to elevations related to defects of tyrosine metabolism and concomitant drug treatment.

Metabolic Effects of Increasing Doses of Nitisinone in the Treatment of Alkaptonuria

Alkaptonuria is an autosomal recessive disease involving a deficiency of the enzyme homogentisate dioxygenase, which is involved in the tyrosine degradation pathway. The enzymatic deficiency results in high concentrations of homogentisic acid (HGA), which results in orthopedic and cardiac complications, among other symptoms. Nitisinone (NTBC) has been shown to effectively treat alkaptonuria by blocking the conversion of 4-hydroxyphenylpyruvate to HGA, but there have been concerns that using doses higher than about 2 mg/day could cause excessively high levels of tyrosine, resulting in crystal deposition and corneal pathology. We have enrolled seven patients in a study to determine whether higher doses of NTBC were effective at further reducing HGA levels while maintaining tyrosine at acceptable levels. Patients were given varying doses of NTBC (ranging from 2 to 8 mg/day) over the course of between 0.5 and 3.5 years. Urine HGA, plasma tyrosine levels, and plasma NTBC were then measured longitudinally at various doses. We found that tyrosine concentrations plateaued and did not reach significantly higher levels as NTBC doses were increased above 2 mg/day, while a significant drop in HGA continued from 2 to 4 mg/day, with no significant changes at higher doses. We also demonstrated using untargeted metabolomics that elevations in tyrosine from treatment resulted in proportional elevations in alternative tyrosine metabolic products, that of N-acetyltyrosine and γ-glutamyltyrosine.

Validation of a dual LC-HRMS platform for clinical metabolic diagnosis in serum, bridging quantitative analysis and untargeted metabolomics

Mass spectrometry-based metabolomics is a rapidly growing field in both research and diagnosis. Generally, the methodologies and types of instruments used for clinical and other absolute quantification experiments are different from those used for biomarkers discovery and untargeted analysis, as the former requires optimal sensitivity and dynamic range, while the latter requires high resolution and high mass accuracy. We used a Q-TOF mass spectrometer with two different types of pentafluorophenyl (PFP) stationary phases, employing both positive and negative ionization, to develop and validate a hybrid quantification and discovery platform using LC-HRMS. This dual-PFP LC-MS platform quantifies over 50 clinically relevant metabolites in serum (using both MS and MS/MS acquisitions) while simultaneously collecting high resolution and high mass accuracy full scans to monitor all other co-eluting non-targeted analytes. We demonstrate that the linearity, accuracy, and precision results for the quantification of a number of metabolites, including amino acids, organic acids, acylcarnitines and purines/pyrimidines, meets or exceeds normal bioanalytical standards over their respective physiological ranges. The chromatography resolved highly polar as well as hydrophobic analytes under reverse-phase conditions, enabling analysis of a wide range of chemicals, necessary for untargeted metabolomics experiments. Though previous LC-HRMS methods have demonstrated quantification capabilities for various drug and small molecule compounds, the present study provides an HRMS quant/qual platform tailored to metabolic disease; and covers a multitude of different metabolites including compounds normally quantified by a combination of separate instrumentation.

Infants suspected to have very-long chain acyl-CoA dehydrogenase deficiency from newborn screening

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is a fatty acid oxidation disorder with widely varying presentations that has presented a significant challenge to newborn screening (NBS). The Western States Regional Genetics Services Collaborative developed a workgroup to study infants with NBS positive for VLCADD. We performed retrospective analysis of newborns with elevated C14:1-acylcarnitine on NBS in California, Oregon, Washington, and Hawai'i including available confirmatory testing and clinical information. Overall, from 2,802,504 children screened, there were 242 cases screen-positive for VLCADD. There were 34 symptomatic true positive cases, 18 asymptomatic true positives, 112 false positives, 55 heterozygotes, 11 lost to follow-up, and 12 other disorders. One in 11,581 newborns had an abnormal NBS for suspected VLCADD. Comparison of analytes and analyte ratios from the NBS demonstrated statistically significant differences between true positive and false positive groups for C14:1, C14, C14:1/C2, and C14:1/C16. The positive predictive value for all true positive cases was 94%, 54%, and 23% when C14:1 was ≥2.0 μM, ≥1.0 μM, and ≥0.7 μM, respectively. Sequential post-analytical analysis could reduce the referral rate in 25.8% of cases. This study is the largest reported follow-up of infants with NBS screen-positive results for suspected VLCADD and demonstrates the necessity of developing comprehensive and consistent long-term follow-up NBS systems. Application of clinical information revealed differences between symptomatic and asymptomatic children with VLCADD. Comparison of NBS analytes and analyte ratios may be valuable in developing more effective diagnostic algorithms.

A model-driven quantitative metabolomics analysis of aerobic and anaerobic metabolism in E. coli K-12 MG1655 that is biochemically and thermodynamically consistent

The advent of model-enabled workflows in systems biology allows for the integration of experimental data types with genome-scale models to discover new features of biology. This work demonstrates such a workflow, aimed at establishing a metabolomics platform applied to study the differences in metabolomes between anaerobic and aerobic growth of Escherichia coli. Constraint-based modeling was utilized to deduce a target list of compounds for downstream method development. An analytical and experimental methodology was developed and tailored to the compound chemistry and growth conditions of interest. This included the construction of a rapid sampling apparatus for use with anaerobic cultures. The resulting genome-scale data sets for anaerobic and aerobic growth were validated by comparison to previous small-scale studies comparing growth of E. coli under the same conditions. The metabolomics data were then integrated with the E. coli genome-scale metabolic model (GEM) via a sensitivity analysis that utilized reaction thermodynamics to reconcile simulated growth rates and reaction directionalities. This analysis highlighted several optimal network usage inconsistencies, including the incorrect use of the beta-oxidation pathway for synthesis of fatty acids. This analysis also identified enzyme promiscuity for the pykA gene, that is critical for anaerobic growth, and which has not been previously incorporated into metabolic models of E coli.

Metabolomics reveals signature of mitochondrial dysfunction in diabetic kidney disease

Diabetic kidney disease is the leading cause of ESRD, but few biomarkers of diabetic kidney disease are available. This study used gas chromatography-mass spectrometry to quantify 94 urine metabolites in screening and validation cohorts of patients with diabetes mellitus (DM) and CKD(DM+CKD), in patients with DM without CKD (DM-CKD), and in healthy controls. Compared with levels in healthy controls, 13 metabolites were significantly reduced in the DM+CKD cohorts (P≤0.001), and 12 of the 13 remained significant when compared with the DM-CKD cohort. Many of the differentially expressed metabolites were water-soluble organic anions. Notably, organic anion transporter-1 (OAT1) knockout mice expressed a similar pattern of reduced levels of urinary organic acids, and human kidney tissue from patients with diabetic nephropathy demonstrated lower gene expression of OAT1 and OAT3. Analysis of bioinformatics data indicated that 12 of the 13 differentially expressed metabolites are linked to mitochondrial metabolism and suggested global suppression of mitochondrial activity in diabetic kidney disease. Supporting this analysis, human diabetic kidney sections expressed less mitochondrial protein, urine exosomes from patients with diabetes and CKD had less mitochondrial DNA, and kidney tissues from patients with diabetic kidney disease had lower gene expression of PGC1α (a master regulator of mitochondrial biogenesis). We conclude that urine metabolomics is a reliable source for biomarkers of diabetic complications, and our data suggest that renal organic ion transport and mitochondrial function are dysregulated in diabetic kidney disease.

Cysteamine modulates oxidative stress and blocks myofibroblast activity in CKD

Therapy to slow the relentless expansion of interstitial extracellular matrix that leads to renal functional decline in patients with CKD is currently lacking. Because chronic kidney injury increases tissue oxidative stress, we evaluated the antifibrotic efficacy of cysteamine bitartrate, an antioxidant therapy for patients with nephropathic cystinosis, in a mouse model of unilateral ureteral obstruction. Fresh cysteamine (600 mg/kg) was added to drinking water daily beginning on the day of surgery, and outcomes were assessed on days 7, 14, and 21 after surgery. Plasma cysteamine levels showed diurnal variation, with peak levels similar to those observed in patients with cystinosis. In cysteamine-treated mice, fibrosis severity decreased significantly at 14 and 21 days after unilateral ureteral obstruction, and renal oxidized protein levels decreased at each time point, suggesting reduced oxidative stress. Consistent with these results, treatment of cultured macrophages with cysteamine reduced cellular generation of reactive oxygen species. Furthermore, treatment with cysteamine reduced α-smooth muscle actin-positive interstitial myofibroblast proliferation and mRNA levels of extracellular matrix proteins in mice and attenuated myofibroblast differentiation and proliferation in vitro, but did not augment TGF-β signaling. In a study of renal ischemia reperfusion, cysteamine therapy initiated 10 days after injury and continued for 14 days decreased renal fibrosis by 40%. Taken together, these data suggest previously unrecognized antifibrotic actions of cysteamine via TGF-β-independent mechanisms that include oxidative stress reduction and attenuation of the myofibroblast response to kidney injury and support further investigation into the potential benefit of cysteamine therapy in the treatment of CKD.

Elevation of guanidinoacetate in newborn dried blood spots and impact of early treatment in GAMT deficiency

Guanidinoacetate methyltransferase (GAMT) deficiency is a good candidate disorder for newborn screening because early treatment appears to improve outcomes. We report elevation of guanidinoacetate in archived newborn dried blood spots for 3 cases (2 families) of GAMT deficiency compared with an unaffected carrier and controls. We also report a new case of a patient treated from birth with normal developmental outcome at the age of 42 months.

Pharmacokinetics of cysteamine bitartrate following intraduodenal delivery

Cysteamine is approved for the treatment of cystinosis and is being evaluated for Huntington's disease and non-alcoholic fatty liver disease. Little is known about the bioavailability and biodistribution of the drug. The aim was to determine plasma, cerebrospinal fluid (CSF), and tissue (liver, kidney, muscle) cysteamine levels following intraduodenal delivery of the drug in rats pretreated and naïve to cysteamine and to estimate the hepatic first-pass effect on cysteamine. Healthy male rats (n = 66) underwent intraduodenal and portal (PV) or jugular (JVC) venous catheterization. Half were pretreated with cysteamine, and half were naïve. Following intraduodenal cysteamine (20 mg/kg), serial blood samples were collected from the PV or the JVC. Animals were sacrificed at specific time points, and CSF and tissue were collected. Cysteamine levels were determined in plasma, CSF, and tissue. The Cmax was achieved in 5-10 min from PV and 5-22.5 min from JVC. The PV-Cmax (P = 0.08), PV-AUC0-t (P = 0.16), JVC-Cmax (P = 0.02) and JVC-AUC0-t (P = 0.03) were higher in naive than in pretreated animals. Plasma cysteamine levels returned to baseline in ≤120 min. The hepatic first-pass effect was estimated at 40%. Peak tissue and CSF cysteamine levels occurred ≤22.5 min, but returned to baseline levels ≤180 min. There was no difference in CSF and tissue cysteamine levels between naïve and pretreated groups, although cysteamine was more rapidly cleared in the pretreated group. Cysteamine is rapidly absorbed from the small intestine, undergoes significant hepatic first-pass metabolism, crosses the blood brain barrier, and is almost undetectable in plasma, CSF, and body tissues 2 h after ingestion. Sustained-release cysteamine may provide prolonged tissue exposure.

Biochemical, molecular, and clinical characteristics of children with short chain acyl-CoA dehydrogenase deficiency detected by newborn screening in California

BACKGROUND

Short-chain acyl-CoA dehydrogenase deficiency (SCADD) is an autosomal recessive inborn error of mitochondrial fatty acid oxidation with highly variable biochemical, genetic, and clinical characteristics. SCADD has been associated with accumulation of butyryl-CoA byproducts, including butyrylcarnitine (C4), butyrylglycine, ethylmalonic acid (EMA), and methylsuccinic acid (MS) in body fluid and tissues. Differences in genotype frequencies have been shown between patients diagnosed clinically versus those diagnosed by newborn screening. Moreover, while patients diagnosed clinically have a variable clinical presentation including developmental delay, ketotic hypoglycemia, epilepsy and behavioral disorders, studies suggest patients diagnosed by newborn screening are largely asymptomatic. Scant information is published about the biochemical, genetic and clinical outcome of SCADD patients diagnosed by newborn screening.

METHODS

We collected California newborn screening, follow-up biochemical levels, and ACADS mutation data from September, 2005 through April, 2010. We retrospectively reviewed available data on SCADD cases diagnosed by newborn screening for clinical outcomes.

RESULTS

During the study period, 2,632,058 newborns were screened and 76 confirmed SCADD cases were identified. No correlations between initial C4 value and follow-up biochemical markers (C4, EMA or MS levels) were found in the 76 cases studied. We found significant correlation between urine EMA versus MS, and correlation between follow-up C4 versus urine EMA. Of 22 cases where ACADS gene sequencing was performed: 7 had two or more deleterious mutations; 8 were compound heterozygotes for a deleterious mutation and common variant; 7 were homozygous for the common variant c.625G>A; and 1 was heterozygous for c.625G>A. Significant increases in mean urine EMA and MS levels were noted in patients with two or more deleterious mutations versus mutation heterozygotes or common polymorphism homozygotes. Clinical outcome data was available in 31 patients with follow-up extending from 0.5 to 60 months. None developed epilepsy or behavioral disorders, and three patients had isolated speech delay. Hypoglycemia occurred in two patients, both in the neonatal period. The first patient had concomitant meconium aspiration; the other presented with central apnea, poor feeding, and hypotonia. The latter, a c.625G>A homozygote, has had persistent elevations in both short- and medium-chain acylcarnitines; diagnostic workup in this case is extensive and ongoing.

CONCLUSIONS

This study examines the largest series to date of SCADD patients identified by newborn screening. Our results suggest that confirmatory tests may be useful to differentiate patients with common variants from those with deleterious mutations. This study also provides evidence to suggest that, even when associated with deleterious mutations, SCADD diagnosed by newborn screening presents largely as a benign condition.

45-Year-old female with propionic acidemia, renal failure, and premature ovarian failure; late complications of propionic acidemia?

We describe a 45-year-old patient who was diagnosed with propionic acidemia in infancy, who experienced an unstable first two years of life but who eventually had a good developmental outcome. She developed severe renal failure requiring renal transplantation in her forties and premature ovarian failure. Renal failure and premature ovarian failure have not previously been associated with propionic acidemia. We hypothesize that propionic acidemia may have contributed to these complications, and discuss several possible mechanisms for this, emphasizing mainly the electron transport chain/mitochondrial energy deficiency hypothesis.

Pharmacokinetics of enteric-coated cysteamine bitartrate in healthy adults: a pilot study

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Cysteamine bitartrate is taken lifelong, every 6 h and for the treatment of cystinosis. Recent studies using cysteamine for for other diseases such as neurodegenerative disorders adopt the same dosing regimen for cysteamine. Regular cysteamine bitartrate (Cystagon) may cause upper gastrointestinal symptoms in some patients.

WHAT THIS STUDY ADDS

This is the only study that provides pharmacokinetic data for cysteamine delivered in an enteric-release preparation in normal subjects. EC-cysteamine is very well tolerated and does not cause increased gastrin concentrations, even at relatively high doses. EC-cysteamine at the higher dose results in better drug uptake as measured by Cmax and AUC and is more likely to be effective.

AIMS

Cysteamine bitartrate (Cystagon) is the approved treatment for cystinosis. Poor compliance and patient outcome may occur because the drug needs to be taken every 6 h and in some patients causes gastrointestinal symptoms due to hypergastrinaemia. A formulation of cysteamine requiring twice daily ingestion would improve the quality of life for these patients. This study compares the pharmacokinetics and gastrin production following cysteamine bitartrate non-enteric-coated and cysteamine bitartrate enteric-coated in normal healthy subjects.

METHODS

Enteric-coated cysteamine was prepared. Following single doses of cysteamine bitartrate non-enteric-coated 450 mg and cysteamine bitartrate enteric-coated 450 mg and 900 mg, serial plasma cysteamine and gastrin concentrations were measured. Two subjects also received cysteamine bitartrate non-enteric-coated 900 mg. Gastrointestinal (GI) symptoms were recorded.

RESULTS

Six healthy adults (mean age 20.7 years, range 18-24 years; mean weight 59.3 kg) received drug. All post-dose gastrin concentrations were within the normal range (<100 pg ml(-1)). The tmax following cysteamine bitartrate non-enteric-coated (mean and SD is 75+/-19 min) was shorter than cysteamine bitartrate enteric-coated (220+/-74 min) (P=0.001), but only the Cmax and AUC estimates following 900 mg cysteamine bitartrate enteric-coated were significantly greater than any of the other preparations or doses (P<0.05). One patient had GI symptoms following both 900 mg cysteamine bitartrate non-enteric-coated and cysteamine bitartrate enteric-coated.

CONCLUSION

Although patient numbers were low, single high doses of cysteamine bitartrate enteric-coated were better tolerated than similar doses of cysteamine bitartrate non-enteric-coated in the healthy subjects and all had normal gastrin concentrations. The delayed tmax following cysteamine bitartrate enteric-coated suggested that the cysteamine was released enterically.

Novel mutations in the human MCCA and MCCB gene causing methylcrotonylglycinuria

Methylcrotonylglycinuria (MCG) is an inborn error of leucine catabolism and has a recessive pattern of inheritance that results from the deficiency of 3-methylcrotonyl-CoA carboxylase (MCC). The clinical phenotypes are highly variable ranging from neonatal onset with severe neurological involvement to asymptomatic adults. Here we identified two novel MCCA (exon 3: c.137G>A; p.46G>E), (IVS7-1G>A splice site mutation), and four novel MCCB (exon 11: c.1065A>T; p.355L>F), (exon 15: c.1430A>G; p.477Q>R), (exon 16: c.1549G>A; p.517G>R), (exon 16: c.1559A>C; p.520Y>S) mutant alleles from five MCC-deficient patients.

Long-term treatment of cystinosis in children with twice-daily cysteamine

OBJECTIVE

Cystinosis causes renal and other organ failure. Treatment with 6-hourly cysteamine bitartrate (Cystagon, Mylan, Morgantown, West Virginia) reduces intracellular cystine and the rate of organ deterioration. A recent study showed that an enteric-release cysteamine required less frequent daily dosing. This report describes the long-term use of enteric-coated (EC) cysteamine bitartrate (Cystagon) in children with cystinosis.

STUDY DESIGN

After a pharmacokinetic and pharmacodynamic study of EC-cysteamine in children with cystinosis, 5 patients remained on twice-daily treatment. White blood cell cystine levels were measured 12 hours after ingestion every 4 to 8 weeks. These levels were then compared with the patient's previous 6-h post-dose levels taken while on regular cysteamine bitartrate before entering the study. Blood chemistry was also measured.

RESULTS

Five children with cystinosis (mean age, 9 years; range, 8 to 17 years) who previously took cysteamine bitartrate (mean dose, 47 mg/kg body wt), received EC-cysteamine for 10 to 27 months (mean dose, 25 mg/kg body wt) and had mean white blood cell cystine levels of 0.77 and 0.71 nmol half-cystine/mg protein, respectively. During the study period, patients maintained adequate growth and there was no significant deterioration in renal or thyroid function. Two children were required to restart acid suppression after 6 months on EC-cysteamine therapy.

CONCLUSIONS

Long-term, twice-daily EC-cysteamine, given at approximately 60% of the previous daily dose of cysteamine bitartrate, was effective at maintaining white blood cell cystine levels within a satisfactory range. There was no significant deterioration in renal or thyroid function.

Positive newborn screen in the biochemically normal infant of a mother with treated holocarboxylase synthetase deficiency

Expanded programmes of newborn screening permit early diagnosis in time to prevent serious complications. These programmes have begun to detect patients who might otherwise remain asymptomatic. An additional confounding variable is the positive screen that results from maternal rather than neonatal disease. This was the case in an infant in whom elevated hydroxyisovalerylcarnitine (C(5)OH) in his newborn screen was the result of placental transfer from his mother, whose holocarboxylase synthetase deficiency was being successfully treated with biotin. The mother had been diagnosed and treated with biotin prenatally. She had no phenotypic feature of holocarboxylase synthetase deficiency, most importantly no episodes ever of acute metabolic acidosis. In the infant a repeat screen was also positive. On day 28 the infant's plasma C(5)OH carnitine was 0.05 mumol/L (normal) and urinary organic acids on day 39 were normal. The mother's excretion of 3-hydroxyisovaleric acid was 109 mmol/mol creatinine. These observations indicate that holocarboxylase synthetase deficiency is one more maternal metabolic disease which may lead to a positive screen in her unaffected newborn infant. They also make the point that holocarboxylase synthetase deficiency in an infant should be detectable in programmes of neonatal screening, which was not clear previously.

Agalsidase alfa and kidney dysfunction in Fabry disease

In male patients with Fabry disease, an X-linked disorder of glycosphingolipid metabolism caused by deficient activity of the lysosomal enzyme alpha-galactosidase A, kidney dysfunction becomes apparent by the third decade of life and invariably progresses to ESRD without treatment. Here, we summarize the effects of agalsidase alfa on kidney function from three prospective, randomized, placebo-controlled trials and their open-label extension studies involving 108 adult male patients. The mean baseline GFR among 54 nonhyperfiltrating patients (measured GFR <135 ml/min per 1.73 m(2)) treated with placebo was 85.4 +/- 29.6 ml/min per 1.73 m(2); during 6 mo of placebo, the mean annualized rate of change in GFR was -7.0 +/- 32.9 ml/min per 1.73 m(2). Among 85 nonhyperfiltrating patients treated with agalsidase alfa, the annualized rate of change was -2.9 +/- 8.7 ml/min per 1.73 m(2). Treatment with agalsidase alfa did not affect proteinuria. Multivariate analysis revealed that GFR and proteinuria category (< 1 or > or = 1 g/d) at baseline significantly predicted the rate of decline of GFR during treatment. This summary represents the largest group of male patients who had Fabry disease and for whom the effects of enzyme replacement therapy on kidney function have been studied. These data suggest that agalsidase alfa may stabilize kidney function in these patients.

Expanded clinical and molecular spectrum of guanidinoacetate methyltransferase (GAMT) deficiency

Guanidinoacetate methyltransferase (GAMT) deficiency is a disorder of creatine biosynthesis, characterized by excessive amounts of guanidinoacetate in body fluids, deficiency of creatine in the brain, and presence of mutations in the GAMT gene. We present here 8 new patients with GAMT deficiency along with their clinical, biochemical and molecular data. The age at diagnosis of our patients ranges from 0 to 14 years. The age of onset of seizures usually ranges from infancy to 3 years. However, one of our patients developed seizures at age 5; progressing to myoclonic epilepsy at age 8 years and another patient has not developed seizures at age 17 years. Five novel mutations were identified: c.37ins26 (p.G13PfsX38), c.403G>T (p.D135Y), c.507_521dup15 (p.C169_S173dup), c.402C>G (p.Y134X) and c.610_611delAGinsGAA (p.R204EfsX63). Six patients had the c.327G>A (last nucleotide of exon 2) splice-site mutation which suggests that this is one of the most common mutations in the GAMT gene, second only to the known Portuguese founder mutation, c.59G>C (p.W20S). Our data suggests that the clinical presentation can be variable and the diagnosis may be overlooked due to unawareness of this disorder. Therefore, GAMT deficiency should be considered in the differential diagnosis of progressive myoclonic epilepsy as well as in unexplained developmental delay or regression with dystonia, even if the patient has no history of seizures. As more patients are reported, the prevalence of GAMT deficiency will become known and guidelines for prenatal diagnosis, newborn screening, presymptomatic testing and treatment, will need to be formulated.

Management of a patient with holocarboxylase synthetase deficiency

We investigated in a patient with holocarboxylase synthetase deficiency, the relation between the biochemical and genetic factors of the mutant protein with the pharmacokinetic factors of successful biotin treatment. A girl exhibited abnormal skin at birth, and developed in the first days of life neonatal respiratory distress syndrome and metabolic abnormalities diagnostic of multiple carboxylase deficiency. Enzyme assays showed low carboxylase activities. Fibroblast analysis showed poor incorporation of biotin into the carboxylases, and low transfer of biotin by the holocarboxylase synthetase enzyme. Kinetic studies identified an increased Km but a preserved Vmax. Mutation analysis showed the child to be a compound heterozygote for a new nonsense mutation Q379X and for a novel missense mutation Y663H. This mutation affects a conserved amino acid, which is located the most 3' of all recorded missense mutations thus far described, and extends the region of functional biotin interaction. Treatment with biotin 100mg/day gradually improved the biochemical abnormalities in blood and in cerebrospinal fluid (CSF), corrected the carboxylase enzyme activities, and provided clinical stability and a normal neurodevelopmental outcome. Plasma concentrations of biotin were increased to more than 500 nM, thus exceeding the increased Km of the mutant enzyme. At these pharmacological concentrations, the CSF biotin concentration was half the concentration in blood. Measuring these pharmacokinetic variables can aid in optimizing treatment, as individual tailoring of dosing to the needs of the mutation may be required.

Organic anion transporter 3 contributes to the regulation of blood pressure

Renal organic anion transporters (OAT) are known to mediate the excretion of many drugs, but their function in normal physiology is not well understood. In this study, mice lacking organic anion transporter 3 (Oat3) had a 10 to 15% lower BP than wild-type mice, raising the possibility that Oat3 transports an endogenous regulator of BP. The aldosterone response to a low-salt diet was blunted in Oat3-null mice, but baseline aldosterone concentration was higher in these mice, suggesting that aldosterone dysregulation does not fully explain the lower BP in the basal state; therefore, both targeted and global metabolomic analyses of plasma and urine were performed, and several potential endogenous substrates of Oat3 were found to accumulate in the plasma of Oat3-null mice. One of these substrates, thymidine, was transported by Oat3 expressed in vitro. In vivo, thymidine, as well as two of the most potent Oat3 inhibitors that were characterized, reduced BP by 10 to 15%; therefore, Oat3 seems to regulate BP, and Oat3 inhibitors might be therapeutically useful antihypertensive agents. Moreover, polymorphisms in human OAT3 might contribute to the genetic variation in susceptibility to hypertension.

Multiple organic anion transporters contribute to net renal excretion of uric acid

Excretion of uric acid, a compound of considerable medical importance, is largely determined by the balance between renal secretion and reabsorption. The latter process has been suggested to be principally mediated by urate transporter 1 (URAT1; slc22a12), but the role of various putative urate transporters has been much debated. We have characterized urate handling in mice null for RST, the murine ortholog of URAT1, as well as in those null for the related organic anion transporters Oat1 and Oat3. Expression of mRNA of other putative urate transporters (UAT, MRP2, MRP4, Oatv1) was unaffected in the knockouts, as were general indexes of renal function (glomerular filtration rate, fractional excretion of fluid and electrolytes). While mass spectrometric analyses of urine and plasma revealed significantly diminished renal reabsorption of urate in RST-null mice, the bulk of reabsorption, surprisingly, was preserved. Oat1- and Oat3-null mice manifested decreased secretion rather than reabsorption, indicating that these related transporters transport urate in the "opposite" direction to RST. Moreover, metabolomic analyses revealed significant alteration in the concentration of several molecules in the plasma and urine of RST knockouts, some of which may represent additional substrates of RST. The results suggest that RST, Oat1, and Oat3 each contribute to urate handling, but, at least in mice, the bulk of reabsorption is mediated by a transporter(s) that remains to be identified. We discuss the data in the context of recent human genetic studies that suggest that the magnitude of the contribution of URAT1 to urate reabsorption might vary with ethnic background.

Potential misdiagnosis of 3-methylcrotonyl-coenzyme A carboxylase deficiency associated with absent or trace urinary 3-methylcrotonylglycine

We report 2 patients with isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency whose urine was devoid of, or contained only trace, 3-methylcrotonylglycine, the pathognomonic marker for this disorder. The first patient, a girl with trisomy 21, was detected through newborn screening with an elevated 5 carbon hydroxycarnitine species level, and the second patient came to clinical attention at the age of 5 months because of failure to thrive and developmental delay. Investigation of urinary organic acids revealed an elevated 3-hydroxyisovaleric acid level but no demonstrable 3-methylcrotonylglycine in both patients. Enzyme studies in cultured fibroblasts confirmed isolated 3-methylcrotonyl-coenzyme A carboxylase deficiency with residual activities of 5% to 7% and 12% of the median control value, respectively. Incorporation of 14C-isovaleric acid into intact fibroblasts was essentially normal, showing that the overall pathway was at least partially functional and potentially explaining the absence of 3-methylcrotonylglycine in urine. Mutation analysis of the MCCA and MCCB genes revealed that both patients were compound heterozygous for a missense mutation, MCCB-c.1015G-->A (p.V339M), and a second mutation that leads to undetectable MCCB messenger (poly A+) RNA. Absent or trace 3-methylcrotonylglycine levels in urine raises the potential for misdiagnosis in the clinical biochemical genetics laboratory based solely on urine organic acid analysis using combined gas chromatography-mass spectrometry.

Metabolomics identifies perturbations in human disorders of propionate metabolism

BACKGROUND

We applied untargeted mass spectrometry-based metabolomics to the diseases methylmalonic acidemia (MMA) and propionic acidemia (PA).

METHODS

We used a screening platform that used untargeted, mass-based metabolomics of methanol-extracted plasma to find significantly different molecular features in human plasma samples from MMA and PA patients and from healthy individuals. Capillary reverse phase liquid chromatography (4 microL/min) was interfaced to a TOF mass spectrometer, and data were processed using nonlinear alignment software (XCMS) and an online database (METLIN) to find and identify metabolites differentially regulated in disease.

RESULTS

Of the approximately 3500 features measured, propionyl carnitine was easily identified as the best biomarker of disease (P value 1.3 x 10(-18)), demonstrating the proof-of-concept use of untargeted metabolomics in clinical chemistry discovery. Five additional acylcarnitine metabolites showed significant differentiation between plasma from patients and healthy individuals, and gamma-butyrobetaine was highly increased in a subset of patients. Two acylcarnitine metabolites and numerous unidentified species differentiate MMA and PA. Many metabolites that do not appear in any public database, and that remain unidentified, varied significantly between normal, MMA, and PA, underscoring the complex downstream metabolic effects resulting from the defect in a single enzyme.

CONCLUSIONS

This proof-of-concept study demonstrates that metabolomics can expand the range of metabolites associated with human disease and shows that this method may be useful for disease diagnosis and patient clinical evaluation.

Pharmacokinetics of cysteamine bitartrate following gastrointestinal infusion

AIMS

Although cysteamine was first used in the treatment of cystinosis in 1976 and approved by the FDA as cysteamine bitartrate (Cystagon) in 1994, surprisingly little pharmacological data are available for this compound. Cysteamine and its related drugs are currently being evaluated for the treatment of Huntington's and Parkinson's disease. The aim of te study was to understand the pharmacokinetics of cysteamine bitartrate following gastrointestinal infusion.

METHOD

Cysteamine bitartrate was delivered through a naso-enteric catheter into the stomach (n = 8), small intestine (n = 8) and caecum (n = 4) of normal subjects. Plasma cysteamine concentrations were determined using LC-MS/MS.

RESULTS

The rate and extent of drug absorption were assessed by comparing AUC(0, infinity), C(max) and t(max), among the gastrointestinal infusion sites. Total cysteamine exposure, expressed as area under the curve (AUC(0, infinity)) was greatest when the drug was infused into the small intestine (4331.3 +/- 1907.6 min x microM) followed by stomach (3901.9 +/- 1591.9 min x microM) and caecum (3141.4 +/- 1627.6 min x microM). Cysteamine infusion into the small intestine resulted in the most rapid rise to maximal plasma concentrations (t(max) = 21 +/- 0.56 min); t(max) was delayed to 50 +/- 26 min and 64 +/- 26 min after gastric and caecal infusion, respectively. The maximum cysteamine plasma concentration (C(max)) was reached after infusion of the drug into the small intestine (51 +/- 21 microM), which was higher than plasma C(max) concentrations after gastric (39 +/- 16 microM) and caecal infusion (23 +/- 15 microM).

CONCLUSIONS

The pharmacokinetic data generated help extend our understanding of cysteamine.

Analysis of coenzyme Q in human blood and tissues

The major coenzyme Q species in humans is the decaprenyl quinoid derivative coenzyme Q10 (CoQ10), and its measurement is somewhat challenging owing to its hydrophobicity and tendency to be oxidized. There are three major methods which are suited for analysis of CoQ10: HPLC-coupled UV or electrochemical detection, and tandem mass spectrometry. The techniques are discussed, and results of these applications to determine CoQ10 concentrations in various human fluids and tissues are summarized.