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München, Germany

Santos-sierra S.,Innsbruck Medical University | Kirchmair J.,University of Innsbruck | Perna A.M.,University of Innsbruck | Reiss D.,Ludwig Maximilians University of Munich | And 8 more authors.
Human Molecular Genetics | Year: 2012

Phenylketonuria (PKU) is caused by inherited phenylalanine-hydroxylase (PAH) deficiency and, in many genotypes, it is associated with protein misfolding. The natural cofactor of PAH, tetrahydrobiopterin (BH 4), can act as a pharmacological chaperone (PC) that rescues enzyme function. However, BH 4 shows limited efficacy in some PKU genotypes and its chemical synthesis is very costly. Taking an integrated drug discovery approach which has not been applied to this target before, we identified alternative PCs for the treatment of PKU. Shape-focused virtual screening of the National Cancer Institute's chemical library identified 84 candidate molecules with potential to bind to the active site of PAH. An in vitro evaluation of these yielded six compounds that restored the enzymatic activity of the unstable PAHV106A variant and increased its stability in cell-based assays against proteolytic degradation. During a 3-day treatment study, two compounds (benzylhydantoin and 6-amino-5-(benzylamino)-uracil) substantially improved the in vivo Phe oxidation and blood Phe concentrations of PKU mice (Pah enu1). Notably, benzylhydantoin was twice as effective as tetrahydrobiopterin. In conclusion, we identified two PCs with high in vivo efficacy that may be further developed into a more effective drug treatment of PKU. © The Author 2012. Published by Oxford University Press. All rights reserved. Source


Lagler F.B.,Innsbruck Medical University | Gersting So.W.,Ludwig Maximilians University of Munich | Zsifkovits C.,Innsbruck Medical University | Steinbacher A.,Ludwig Maximilians University of Munich | And 7 more authors.
Biochemical Pharmacology | Year: 2010

Phenylketonuria (PKU), an autosomal recessive disease with phenylalanine hydroxylase (PAH) deficiency, was recently shown to be a protein misfolding disease with loss-of-function. It can be treated by oral application of the natural PAH cofactor tetrahydrobiopterin (BH4) that acts as a pharmacological chaperone and rescues enzyme function in vivo. Here we identified Pahenu1/2 bearing a mild and a severe mutation (V106A/F363S) as a new mouse model for compound heterozygous mild PKU. Although BH4 treatment has become established in clinical routine, there is substantial lack of knowledge with regard to BH4 pharmacodynamics and the effect of the genotype on the response to treatment with the natural cofactor. To address these questions we applied an elaborate methodological setup analyzing: (i) blood phenylalanine elimination, (ii) blood phenylalanine/tyrosine ratios, and (iii) kinetics of in vivo phenylalanine oxidation using 13C-phenylalanine breath tests. We compared pharmacodynamics in wild-type, Pahenu1/1, and Pahenu1/2 mice and observed crucial differences in terms of effect size as well as effect kinetics and dose response. Results from in vivo experiments were substantiated in vitro after overexpression of wild-type, V106A, and F263S in COS-7 cells. Pharmacokinetics did not differ between Pahenu1/1 and Pahenu1/2 indicating that the differences in pharmacodynamics were not induced by divergent pharmacokinetic behavior of BH4. In conclusion, our findings show a significant impact of the genotype on the response to BH4 in PAH deficient mice. This may lead to important consequences concerning the diagnostic and therapeutic management of patients with PAH deficiency underscoring the need for individualized procedures addressing pharmacodynamic aspects. © 2010 Elsevier Inc. Source


Gersting S.W.,Ludwig Maximilians University of Munich | Lagler F.B.,Innsbruck Medical University | Eichinger A.,Ludwig Maximilians University of Munich | Kemter K.F.,Ludwig Maximilians University of Munich | And 10 more authors.
Human Molecular Genetics | Year: 2010

The recent approval of sapropterin dihydrochloride, the synthetic form of 6[R]-L-erythro-5,6,7,8-tetrahydrobiopterin (BH4), for the treatment of phenylketonuria (PKU) as the first pharmacological chaperone drug initiated a paradigm change in the treatment of monogenetic diseases. Symptomatic treatment is now replaced by a causal pharmacological therapy correcting misfolding of the defective phenylalanine hydroxylase (PAH) in numerous patients. Here, we disclose BH4 responsiveness in Pahenu1, a mouse model for PAH deficiency. Loss of function resulted from loss of PAH, a consequence of misfolding, aggregation, and accelerated degradation of the enzyme. BH4 attenuated this triad by conformational stabilization augmenting the effective PAH concentration. This led to the rescue of the biochemical phenotype and enzyme function in vivo. Combined in vitro and in vivo analyses revealed a selective pharmaceutical action of BH4 confined to the pathological metabolic state. Our data provide new molecular-level insights into the mechanisms underlying protein misfolding with loss of function and support a general model of pharmacological chaperone-induced stabilization of protein conformation to correct this intracellular phenotype. Pahenu1 will be essential for pharmaceutical drug optimization and to design individually tailored therapies. © The Author 2010. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org. Source


Ensenauer R.,Ludwig Maximilians University of Munich | Fingerhut R.,Laboratory Becker | Maier E.M.,Ludwig Maximilians University of Munich | Polanetz R.,Ludwig Maximilians University of Munich | And 3 more authors.
Clinical Chemistry | Year: 2011

BACKGROUND: Electrospray ionization-tandem mass spectrometry (ESI-MS/MS) has been used in the Bavarian newborn screening (NBS) program since 1999. The use of ESI-MS/MS has led to the inclusion of isovaleric acidemia (IVA) into NBS. We retrospectively evaluated data on more than 1.6 million newborns screened during 9.5 years. METHODS: Acylcarnitines from whole blood spotted on filter paper were converted to their corresponding butyl esters, and the samples were analyzed by use of ESI-MS/MS with stable isotope labeled internal standards. RESULTS: A total of 24 individuals with IVA were detected by use of a multiparametric threshold criteria panel including isovalerylcarnitine (C5) and the ratios of C5 to octanoyl-, butyryl-, and propionylcarnitine. A cutoff set at the 99.99th percentile for isolated C5 or at the 99th percentile for C5 plus at least 2 ratios resulted in a positive predictive value for IVA screening of 7.0% and an overall recall rate of 0.024%. Adjusted reference ranges for age and birth weight were applied, and the incidence of IVA in the study population was calculated to be 1 in 67 000. Missed cases were not brought to our attention. IVA was also detectable in cord blood and early postnatal blood samples. CONCLUSIONS: IVA can be reliably detected in NBS through acylcarnitine analysis in dried blood spots by using multiparametric threshold criteria. Further improvement (positive predictive value 13.0%, recall rate 0.01%) can be achieved by using more stringent recall criteria. In view of the potentially life-threatening natural course of IVA in early life, presymptomatic diagnosis may thus prevent mortality and morbidity. © 2011 American Association for Clinical Chemistry. Source


Ensenauer R.,Ludwig Maximilians University of Munich | Fingerhut R.,Laboratory Becker | Fingerhut R.,University of Zurich | Schriever S.C.,Ludwig Maximilians University of Munich | And 9 more authors.
Journal of Lipid Research | Year: 2012

Quantitative analysis of mitochondrial FA β-oxidation (FAO) has drawn increasing interest for defining lipid-induced metabolic dysfunctions, such as in obesity-induced insulin resistance, and evaluating pharmacologic strategies to improve β-oxidation function. The aim was to develop a new assay to quantify β-oxidation function in intact mitochondria and with a low amount of cell material. Cell membranes of primary human fibroblasts were permeabilized with digitonin prior to a load with FFA substrate. Following 120 min of incubation, the various generated acylcarnitines were extracted from both cells and incubation medium by protein precipitation/desalting and subjected to solid-phase extraction. A panel of 30 acylcarnitines per well was quantified by MS/MS and normalized to citrate synthase activity to analyze mitochondrial metabolite flux. Pretreatment with bezafibrate and etomoxir revealed stimulating and inhibiting regulatory effects on β-oxidation function, respectively. In addition to the advantage of a much shorter assay time due to in situ permeabilization compared with whole-cell incubation systems, the method allows the detection of multiple acylcarnitines from an only limited amount of intact cells, particularly relevant to the use of primary cells. This novel approach facilitates highly sensitive, simple, and fast monitoring of pharmacological effects on FAO. Copyright © 2012 by the American Society for Biochemistry and Molecular Biology, Inc. Source

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