Use of an adeno-associated virus serotype Anc80 to provide durable cure of phenylketonuria in a mouse model.

Phenylketonuria (PKU) is the most common inborn error of metabolism of the liver, and results from mutations of both alleles of the phenylalanine hydroxylase gene (PAH). As such, it is a suitable target for gene therapy via gene delivery with a recombinant adeno-associated virus (AAV) vector. Here we use the synthetic AAV vector Anc80 via systemic administration to deliver a functional copy of a codon-optimized human PAH gene, with or without an intron spacer, to the Pahenu2 mouse model of PKU. Dose-dependent transduction of the liver and expression of PAH mRNA were present with both vectors, resulting in significant and durable reduction of circulating phenylalanine, reaching near control levels in males. Coat color of treated Pahenu2 mice reflected an increase in pigmentation from brown to the black color of control animals, further indicating functional restoration of phenylalanine metabolism and its byproduct melanin. There were no adverse effects associated with administration of AAV up to 5 × 1012 VG/kg, the highest dose tested. Only minor and/or transient variations in some liver enzymes were observed in some of the AAV-dosed animals which were not associated with pathology findings in the liver. Finally, there was no impact on cell turnover or apoptosis as evaluated by Ki-67 and TUNEL staining, further supporting the safety of this approach. This study demonstrates the therapeutic potential of AAV Anc80 to safely and durably cure PKU in a mouse model, supporting development for clinical consideration.

Scallop phenylalanine hydroxylase implicates in immune response and can be induced by human TNF-α.

Phenylalanine hydroxylase (PAH) is an important metabolic enzyme of aromatic amino acids, which is responsible for the irreversible oxidation of phenylalanine to tyrosine. In the present study, the full-length cDNA encoding PAH from Chlamys farreri (designated CfPAH) was cloned by using rapid amplification of cDNA ends (RACE) approaches and expression sequence tag (EST) analysis. The open reading frame of CfPAH encoded a polypeptide of 460 amino acids, and its sequence shared 64.4-74.2% similarity with those of PAHs from other animals. There were an N-terminal regulatory ACT domain and a C-terminal catalytic Biopterin_H domain in the deduced CfPAH protein. The mRNA transcripts of CfPAH could be detected in all the tested tissues, including adductor muscle, mantle, gill, gonad, haemocytes and hepatopancreas. And its expression level in haemocytes was increased significantly during 3-48 h after bacteria Vibrio anguillarum challenge with the highest level (9.1-fold, P < 0.05) at 24 h. Furthermore, the mRNA expression of CfPAH in haemocytes also increased significantly to 2.6-fold (P < 0.05) at 4 h and 3.3-fold (P < 0.05) at 6 h after the stimulation of 50.0 ng mL(-1) human TNF-α. The cDNA fragment encoding the mature peptide of CfPAH was recombined and expressed in the prokaryotic expression system, and 1 mg recombinant CfPAH protein (rCfPAH) could catalyze the conversion of 192.23 ± 32.35 nmol phenylalanine to tyrosine within 1 min (nmol min(-1) mg(-1) protein) in vitro. These results indicated collectively that CfPAH, as a homologue of phenylalanine hydroxylase in scallop C. farreri, could be induced by cytokine and involved in the immunomodulation of scallops by supplying the starting material tyrosine for the synthesis of melanin and catecholamines.

Administration-route and gender-independent long-term therapeutic correction of phenylketonuria (PKU) in a mouse model by recombinant adeno-associated virus 8 pseudotyped vector-mediated gene transfer.

Phenylketonuria (PKU) is an inborn error of metabolism caused by deficiency of the hepatic enzyme phenylalanine hydroxylase (PAH) which leads to high blood phenylalanine (Phe) levels and consequent damage of the developing brain with severe mental retardation if left untreated in early infancy. The current dietary Phe restriction treatment has certain clinical limitations. To explore a long-term nondietary restriction treatment, a somatic gene transfer approach in a PKU mouse model (C57Bl/6-Pahenu2) was employed to examine its preclinical feasibility. A recombinant adeno-associated virus (rAAV) vector containing the murine Pah-cDNA was generated, pseudotyped with capsids from AAV serotype 8, and delivered into the liver of PKU mice via single intraportal or tail vein injections. The blood Phe concentrations decreased to normal levels (< or =100 microM or 1.7 mg/dl) 2 weeks after vector application, independent of the sex of the PKU animals and the route of application. In particular, the therapeutic long-term correction in females was also dramatic, which had previously been shown to be difficult to achieve. Therapeutic ranges of Phe were accompanied by the phenotypic reversion from brown to black hair. In treated mice, PAH enzyme activity in whole liver extracts reversed to normal and neither hepatic toxicity nor immunogenicity was observed. In contrast, a lentiviral vector expressing the murine Pah-cDNA, delivered via intraportal vein injection into PKU mice, did not result in therapeutic levels of blood Phe. This study demonstrates the complete correction of hyperphenylalaninemia in both males and females with a rAAV serotype 8 vector. More importantly, the feasibility of a single intravenous injection may pave the way to develop a clinical gene therapy procedure for PKU patients.

Pteridin-dependent hydroxylases as autoantigens in autoimmune polyendocrine syndrome type I.

Autoimmune polyendocrine syndrome type I (APS I) is characterized by autoantibodies, often directed towards tissue-specific enzymes in the affected organs. We have earlier reported the identification of tryptophan hydroxylase (TPH) and tyrosine hydroxylase (TH) as autoantigens in APS I associated with intestinal dysfunction and alopecia, respectively. These two enzymes, together with phenylalanine hydroxylase (PAH), constitute the group of biopterin-dependent hydroxylases, which all are involved in the biosynthesis of neurotransmitters. A clone encoding PAH was used for in vitro transcription/translation, followed by immunoprecipitation with sera from 94 APS I patients and 70 healthy controls. Of the APS I patients, 25% had PAH antibodies, and no reactivity was detected in the controls. No association with the main clinical components of APS I was found with PAH antibodies. Altogether, 59 sera from the 94 APS I patients reacted with at least one of TPH, TH, or PAH, whereas 35 showed no reactivity. Nineteen of the sera contained antibodies towards all enzymes, 12 to TPH only and 12 to TH only. No sera showed antibodies that reacted to only PAH. An immunocompetition assay demonstrated that the reactivity against PAH represents a cross-reactivity with TPH, whereas antibodies against TPH and TH are directed towards epitopes unique for the two enzymes.

Dopaminergic modulation of motor neuron activity and neuromuscular function in Drosophila melanogaster.

Dopamine is found in both neuronal and non-neuronal tissues in the larval stage of the fruit fly, Drosophila melanogaster, and functions as a signaling molecule in the nervous system. Although dopaminergic neurons in the central nervous system (CNS) were previously thought solely to be interneurons, recent studies suggest that dopamine may also act as a neuromodulator in humoral pathways. We examined both application of dopamine on intact larval CNS-segmental preparations and isolated neuromuscular junctions (NMJs). Dopamine rapidly decreased the rhythmicity of the CNS motor activity. Application of dopamine on neuromuscular preparations of the segmental muscles 6 and 7 resulted in a dose-responsive decrease in the excitatory junction potentials (EJPs). With the use of focal, macro-patch synaptic current recordings the quantal evoked transmission showed a depression of vesicular release at concentrations of 10 microM. Higher concentrations (1 mM) produced a rapid decrement in evoked vesicular release. Dopamine did not alter the shape of the spontaneous synaptic currents, suggesting that dopamine does not alter the postsynaptic muscle fiber receptiveness to the glutaminergic motor nerve transmission. The effects are presynaptic in causing a reduction in the number of vesicles that are stimulated to be released due to neural activity.

Tryptophan hydroxylase: cloning and expression of the rat brain enzyme in mammalian cells.

A cDNA encoding full-length tryptophan hydroxylase was produced by reverse transcriptase-PCR from rat brain mRNA and expressed transiently in a human fibroblast cell line. Catalytic activity was low unless transfected cells were grown in the presence of FeSO4. Recombinant tryptophan hydroxylase was found almost exclusively within the soluble compartment of the cell and was dependent on tryptophan and tetrahydrobiopterin for activity. The catalytic activity of recombinant tryptophan hydroxylase was stimulated > 25-fold by Fe(II) and to a somewhat lesser extent by the polyanions heparin and phosphatidylserine. The enzyme was inhibited by desferrioxamine and dopamine, both of which complex iron. When extracts from transfected cells were subjected to sucrose gradient centrifugation and analytical gel filtration, the recombinant enzyme behaved the same as the native enzyme from brain. A monoclonal antibody against phenylalanine hydroxylase that cross-reacts with brain tryptophan hydroxylase was capable of immunoprecipitating the recombinant hydroxylase from solution. These data indicate that recombinant tryptophan hydroxylase expressed in mammalian cells is assembled into tetramers of approximately 220,000 daltons. Its catalytic and physical properties appear to be very similar to those of the native enzyme from brain.

Mouse models of human phenylketonuria.

Phenylketonuria (PKU) results from a deficiency in phenylalanine hydroxylase, the enzyme catalyzing the conversion of phenylalanine (PHE) to tyrosine. Although this inborn error of metabolism was among the first in humans to be understood biochemically and genetically, little is known of the mechanism(s) involved in the pathology of PKU. We have combined mouse germline mutagenesis with screens for hyperphenylalaninemia to isolate three mutants deficient in phenylalanine hydroxylase (PAH) activity and cross-reactive protein. Two of these have reduced PAH mRNA and display characteristics of untreated human PKU patients. A low PHE diet partially reverses these abnormalities. Our success in using high frequency random germline point mutagenesis to obtain appropriate disease models illustrates how such mutagenesis can complement the emergent power of targeted mutagenesis in the mouse. The mutants now can be used as models in studying both maternal PKU and somatic gene therapy.

Co-localization of serotonin and GABA in neurons of the Xenopus laevis retina.

Serotonin-synthesizing neurons in the retina of Xenopus laevis have been identified using anti-phenylalanine hydroxylase (PH) antibody which recognizes tryptophan 5-hydroxylase, the rate-limiting enzyme for serotonin synthesis. Double-labelling experiments, using anti-PH antibody and anti-serotonin antibody/5,7-dihydroxytryptamine (5,7-DHT) uptake, have shown that some serotonin-like immunoreactive/5,7-DHT-labelled neurons exhibit PH-like immunoreactivity (PH-LI) (serotonin-synthesizing neurons), but the others do not (serotonin-accumulating neurons). In the present study, triple-labelling experiments were performed using 5,7-DHT uptake and antibodies raised against GABA and PH, to determine the possible co-localization of y-aminobutyric acid (GABA) in serotonin-synthesizing and/or -accumulating neurons in the Xenopus retina. All 5,7-DHT-labelled bipolar cells lacked PH-LI; all of them were immunoreactive to GABA. In contrast, all 5,7-DHT-labelled large amacrine cells exhibited PH-LI, but none of them expressed GABA-LI. Small amacrine cells labelled with 5,7-DHT but not PH-LI exhibited GABA-LI, whilst the small amacrine cells with PH-LI lacked GABA-LI. These observations indicate that GABA is co-localized in serotonin-accumulating amacrine and bipolar cells, whereas serotonin-synthesizing large and small amacrine cells do not contain GABA-LI.

Immunological detection of phenylalanine hydroxylase protein in Drosophila melanogaster.

A monoclonal antibody raised against monkey liver phenylalanine hydroxylase (PAH) has been used to detect this protein in Drosophila melanogaster. A cross-reacting material (CRM) band of apparent molecular mass 50-52 kDa, equivalent to that deduced for the Drosophila melanogaster PAH protein based on the pah gene cDNA sequence, has been detected. This CRM was analysed throughout development and showed an equivalent pattern to that reported for PAH activity in this insect, with maxima at pupariation and at pharate adult formation. Distribution of this CRM in larval tissues, the haemolymph and the adult body is mainly restricted to the larval fat body and the adult head. Demonstration of this CRM as the PAH protein comes from the correlation between the decreased PAH enzyme activities of two mutant strains and their decreased amounts of CRM by Western blotting.

Membrane-bound phenylalanine hydroxylase of human liver.

Phenylalanine hydroxylase (EC 1.14.16.1) antigen and activity have been identified among proteins extracted with a buffer containing 0.4% Triton X-100 from adult human liver bioptate fraction, which was sedimented at 105,000 x g (n = 4). This enzyme fraction was designated as a 'membrane-bound form of phenylalanine hydroxylase'. It amounted to 5-15% of phenylalanine hydroxylase activity and 15-25% of phenylalanine hydroxylase antigen content. After immunoblotting two-dimensional gels, the soluble (cytoplasmic) form of phenylalanine hydroxylase antigen displayed three spots: one spot corresponded to the L-subunit with a molecular weight of 55,000, the two other spots corresponded to the H-subunit with a molecular weight of 57,000. Only the L-subunit was revealed in the membrane-bound enzyme form. Both phenylalanine hydroxylase activity and antigen were also demonstrated in extracts from human embryonic livers (n = 7). However, in this case the membrane-bound phenylalanine hydroxylase amounted to 85% of the antigen content. Subunit compositions of the enzymes were similar in adult and embryonic livers. The differences in the subunit compositions and enzyme activities of membrane-bound and cytoplasmic forms of phenylalanine hydroxylase in adults and embryos may be due to other functions of this enzyme in the hepatocyte membrane.

[Phenylalanine hydroxylase-like antibody in human chorionic villi]. / Fenilalaningidroksilaz-podobnyi antitel v vorsinakh khoriona cheloveka.

An antigen similar by electrophoretic mobility to liver phenylalanine hydroxylase (PH) and cross-reacting with monoclonal antibody PH8 against liver PH was detected in extracts of soluble proteins in 6 from 23 samples of chorionic villi. An antigen with electrophoretic mobility corresponding to 40-41 kDa was detected in extracts of membrane proteins from these 23 samples by immunoblotting with monoclonal antibody PH8. Its molecular weight was similar to that of major chymotryptic peptide of human liver PH. The content of the antigen varied with samples and was less than 20 ng/mg of the extracted protein. Two-dimensional gel electrophoresis revealed only 1 spot of the antigen. The antigen did not react with monoclonal antibodies PH7 and PH9 epitopes of which were located in N-terminal fragment of liver PH. These data suggest that the antigen of membrane fraction could be a PH protein without N-terminal domain.

Localization of cofactor binding sites with monoclonal anti-idiotype antibodies: phenylalanine hydroxylase.

A monoclonal anti-idiotype antibody, NS7, previously shown to mimic the binding of the pterin cofactor of phenylalanine hydroxylase (phenylalanine 4-monooxygenase, EC 1.14.16.1) has been used to localize the cofactor binding site within the phenylalanine hydroxylase catalytic domain to a 27-amino-acid sequence that is highly conserved among the three aromatic amino acid hydroxylases. The binding of NS7 to a synthetic peptide corresponding to the phenylalanine hydroxylase sequence from residue 263 to residue 289 was blocked by the competitive inhibitor of phenylalanine hydroxylase enzyme activity, 7,8-dihydro-6,7-dimethylpterin. In addition this peptide competed with native phenylalanine hydroxylase for binding to 6,7-dimethyl-5,6,7,8-tetrahydropterin conjugated to a polyglutamate carrier. Application of this simple and direct approach to other enzymes is likely to greatly facilitate the identification of ligand binding sites on enzymes, which will significantly contribute to the understanding of enzyme structure-function relationships.

The immunological evidence for a phenylalanine hydroxylase like immunoreactive protein in different human cells and tissues.

Phenylalanine hydroxylase (PAH) was purified 105-fold from human liver. The rel mol mass of the subunits in sodium dodecylsulfate-polyacrylamide gel electrophoresis was 54,000 Da and the isoelectric point was estimated to be between pH 5.0 and 5.2. The activity of purified PAH was inhibited by p-Cl-phenylalanine (p-Cl-Phe), 3-J-tyrosine (3-J-Tyr) and 6-F-tryptophane (6-F-Trp) by 73%, 26% and 10%, respectively. The Km value was 0.36 x 10(-3) mol/l for L-Phe and 5.88 x 10(-5) mol/l for the synthetic cofactor dimethyltetrahydrobiopterin (DMPH4). Polyclonal antibodies raised in rabbits against the active human enzyme showed only a slight cross-reaction with purified rat liver PAH. Using the rabbit antibodies an immunoreactive protein with the same mol mass and isoelectric point as purified human liver PAH and PAH from crude liver extract was detected in extracts from kidney, heart, spleen, brain, pancreas, lung, placenta, leucocytes, cultured skin fibroblasts and chorionic villus cells.

[The use of highly sensitive immunoblotting for detecting the phenylalanine hydroxylase antigen in human platelets]. / Primenenie immunoblottinga povyshennoi chuvstvitel'nosti dlia vyiavleniia fenilalaningidroksilaznogo antigena v trombotsitakh cheloveka.

Incubation of nitrocellulose filters containing proteins in solutions of organic alcohols (ethanol, methanol, isopropanol) enabled to increase the immunoblotting sensitivity after denaturating electrophoresis in presence of SDS. Maximal elevation of the label sensitivity (4-6-fold) was observed after incubation of these filters in 30% isopropanol within 2 hrs. The effect of sensitivity elevation appears to be caused by the antigen renaturation due to SDS washing off. The modified procedure of immunoblotting allowed to detect phenylalanine hydroxylase antigen in human thrombocytes. The antigen had electrophoretic mobility similar to that of phenylalanine hydroxylase from liver tissue; its concentration constituted less than 0.1 microgram per 1 mg of protein in thrombocytes.

[Detection of phenylalanine hydroxylase protein in human platelets. Immunochemical detection]. / Obnaruzhenie belka fenilalaningidroksilazy v trombotsitakh cheloveka. Immunokhimicheskaia identifikatsiia.

A protein reactive with anti-phenylalanine hydroxylase monoclonal antibody PH8 has been recovered from human platelet extracts. Two bands corresponding to molecular masses of about 60 kDa and 55 kDa were revealed by immunoblotting after electrophoresis according to Laemmli. Using the same antibody, a single band with a molecular mass of 60 kDa was demonstrated in extracts from human pineal gland; two similar antigens were found in human liver extracts and no antigen was found in adrenal gland extracts. Monoclonal antibodies, PH1 and PH3, did not react with these antigens during immunoblotting. Monoclonal antibodies, PH7 and PH9, reacted with the 55 kDa antigen in platelet extracts. The antigen content in platelet extracts was measured by ELISA with monoclonal antibodies relative to its content in the liver. The antigen content in platelet extracts was about 100 times as low as that in liver extracts and amounted to 100 ng/mg of protein. These findings suggest that the phenylalanine hydroxylase antigen is present in human platelets.

Structural similarities among enzyme pterin binding sites as demonstrated by a monoclonal anti-idiotypic antibody.

BALB/c mice were immunized with a synthetic co-factor of the aromatic amino acid hydroxylases, 6,7-dimethyl-5,6,7,8-tetrahydropterin, conjugated to albumin. Hybridoma cell lines isolated from the immunized mice secreted monoclonal antibodies reacting specifically with the pterin molecule and monoclonal antibodies which were found to bind phenylalanine hydroxylase. Several lines of evidence were consistent with the anti-phenylalanine hydroxylase antibodies being anti-idiotype antibodies mimicking the pterin molecule and binding to the pterin binding site of phenylalanine hydroxylase. (a) An anti-idiotype monoclonal antibody, NS7, when reimmunized into mice produced anti-pterin antibodies consistent with NS7 being an internal image anti-idiotypic antibody. (b) NS7 antibody was prevented from binding to phenylalanine hydroxylase when a competitive inhibitor of phenylalanine hydroxylase enzyme activity, 6,7-dimethyl-7,8-dihydropterin, was bound to phenylalanine hydroxylase. (c) NS7 antibody was shown to bind to a wide range of pterin-requiring enzymes: phenylalanine, tyrosine and tryptophan hydroxylases, dihydropteridine reductase, dihydrofolate reductase, and sepiapterin reductase. Thus the NS7 antibody has successfully mimicked a common portion of the pterin cofactors utilized by these enzymes and demonstrated structure homology in their pterin binding sites despite their diverse function and little amino acid sequence homology except among the three aromatic amino acid hydroxylases.

A monoclonal antibody to aromatic amino acid hydroxylases. Identification of the epitope.

PH8 monoclonal antibody has previously been shown to react with all three aromatic amino acid hydroxylases, being particularly useful for immunohistochemical staining of brain tissue [Haan, Jennings, Cuello, Nakata, Chow, Kushinsky, Brittingham & Cotton (1987) Brain Res. 426, 19-27]. Western-blot analysis of liver extracts showed that PH8 reacted with phenylalanine hydroxylase from a wide range of vertebrate species. The epitope for antibody PH8 has been localized to the human phenylalanine hydroxylase sequence between amino acid residues 139 and 155. This highly conserved region of the aromatic amino acid hydroxylases has 11 out of 17 amino acids identical in phenylalanine hydroxylase, tyrosine hydroxylase and tryptophan hydroxylase.

Distribution of monoamine-synthesizing neurons in the human medulla oblongata.

We have employed immunohistochemical and morphometric procedures to study the distribution of monoamine-synthesizing neurons in the medulla oblongata of the adult human, utilizing antibodies to tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase (PNMT), and phenylalanine hydroxylase (PH8). In the human brain, the antigen with which PH8 reacts occurs within neurons that presumably synthesize serotonin (Haan et al., '87). Neurons containing these antigens were mapped and counted in successive coronal sections with the aid of a computer-assisted procedure. The results indicate that monoamine-synthesizing neurons are distributed in the human brain in patterns broadly similar to those described for other species. TH-immunoreactive cells extended caudorostrally for approximately 32 mm commencing at the spinomedullary junction and ending 8 mm caudal to the pontomedullary junction. In coronal sections these TH-immunoreactive neurons were seen in the lateral medulla dorsal to the inferior olive extending in a continuous band to the dorsomedial medulla. Above the obex the majority of these cells apparently synthesize adrenaline since many PNMT-immunoreactive cells were also found in this region. There were few or no PNMT-immunoreactive cells caudal to the obex, indicating that the TH-immunoreactive cells in this region synthesize either noradrenaline or dopamine. Approximately 65% of these TH-immunoreactive neurons contained melanin pigment, whereas few or no PNMT-immunoreactive cells contained melanin pigment. PH8-immunoreactive cells extended throughout the rostrocaudal extent of the medulla oblongata (approximately 40 mm). In coronal sections the majority were found in the medullary raphe nuclei. However, many cells throughout the rostrocaudal extent of the medulla were found laterally intermingled with catecholamine-synthesizing neurons. Occasional neurons in the lateral medulla appeared to contain both PH8- and TH-immunoreactivity.

Full-length cDNA for rabbit tryptophan hydroxylase: functional domains and evolution of aromatic amino acid hydroxylases.

A full-length cDNA for tryptophan hydroxylase was cloned from rabbit pineal body by screening an expression library with antibody against rat phenylalanine hydroxylase, which crossreacts with rabbit tryptophan hydroxylase. Clones producing immunoreactive material contain sequences homologous to, yet distinct from, phenylalanine hydroxylase. The rabbit cDNA hybridizes to mRNA in pineal body and brainstem but not in liver. Comparison of the rabbit tryptophan hydroxylase sequence with the sequences of phenylalanine hydroxylase and tyrosine hydroxylase demonstrates that these three biopterin-dependent aromatic amino acid hydroxylases are highly homologous, reflecting a common evolutionary origin from a single primordial genetic locus. The pattern of sequence homology supports the hypothesis that the carboxyl-terminal two-thirds of the molecules constitute the enzymatic activity cores, and the amino-terminal thirds of the molecules constitute domains for substrate specificity.