In vivo expression of recombinant vascular endothelial growth factor in rabbit carotid artery increases production of superoxide anion

OBJECTIVE

Vascular endothelial growth factor (VEGF) is one of the most important pro-angiogenic cytokines. Ability of VEGF to stimulate formation of superoxide anion in vivo has not been studied. We hypothesized that in vivo expression of recombinant VEGF in the rabbit carotid artery increases production of superoxide anion.

METHODS AND RESULTS

Plaque-forming units (10(9)) of adenovirus-encoding human VEGF165 (AdVEGF) or beta-galactosidase (AdLacZ) were delivered into the lumen of rabbit carotid arteries. Three days after gene delivery, expression of recombinant proteins was detected in endothelium and smooth muscle cells. Endothelium-dependent relaxations to acetylcholine were impaired in AdVEGF-transduced arteries (P<0.01; n=5). Treatment with superoxide dismutase mimetic, Mn(III) tetra(4-benzoic acid) porphyrin chloride (10(-5) mol/L), improved relaxations to acetylcholine (P<0.01; n=5). Western blot analysis demonstrated increased expression of p47(phox) in AdVEGF-transduced arteries (P<0.05; n=8). Lucigenin chemiluminescence showed significantly higher production of superoxide anion in AdVEGF-transduced arteries (P<0.05; n=5 to 10).

CONCLUSIONS

Our results suggest that in vivo expression of recombinant VEGF in the vascular endothelium increases local production of superoxide anion. Superoxide anion appears to be an important mediator of vascular effects of VEGF in vivo.

Long-term follow-up of a patient with mild tetrahydrobiopterin-responsive phenylketonuria

We report on the long-term follow-up of the first Italian patient with the tetrahydrobiopterin (BH4)-responsive type of phenylalanine hydroxylase deficiency (R243X/Y414C genotype). The patient was diagnosed by the newborn screening for phenylketonuria (PKU) and with a positive BH4 loading test. Introduction of BH4 (initially 10 and later 20 mg/kg/day) in addition to reduced low-phenylalanine diet resulted in therapeutic plasma phenylalanine concentrations (<340 micromol/L). Very good compliance and no side effects in this patient demonstrate the great potential of BH4 in the treatment of some patients with mild PKU.

Genetic engineering of Escherichia coli for production of tetrahydrobiopterin

Tetrahydrobiopterin (BH4) is an essential cofactor for various enzymes in mammals. In vivo, it is synthesized from GTP via the three-step pathway of GTP cyclohydrolase I (GCHI), 6-pyruvoyl-tetrahydropterin synthase (PTPS) and sepiapterin reductase (SPR). BH4 is a medicine used to treat atypical hyperphenylalaninemia. It is currently synthesized by chemical means, which consists of many steps, and requires costly materials and complicated procedures. To explore an alternative microbial method for BH4 production, we utilized recombinant DNA technology to construct recombinant Escherichia coli (E. coli) strains carrying genes expressing GCHI, PTPS and SPR enzymes. These strains successfully produced BH4, which was detected as dihydrobiopterin and biopterin, oxidation products of BH4. In order to increase BH4 productivity we made further improvements. First, to increase the de novo GTP supply, an 8-azaguanine resistant mutant was isolated and an additional guaBA operon was introduced. Second, to augment the activity of GCHI, the folE gene from E. coli was replaced by the mtrA gene from Bacillus subtilis. These modifications provided us with a strain showing significantly higher productivity, up to 4.0 g of biopterin/L of culture broth. The results suggest the possibility of commercial BH4 production by our method.

Overexpression of V-1 prevents nitric oxide-induced cell death: involvement of enhanced tetrahydrobiopterin biosynthesis

Previously we reported that the synthesis of catecholamines, dopamine, and noradrenaline was enhanced by overexpression of V-1 protein, a neuronal protein active in the initial stage of development of the rat cerebellum, in the neuronal cell line PC12D, a model of dopamine cells (Yamakuni et al. [1998] J. Biol. Chem. 273:27051-27054). To investigate the physiological role of this protein, we examined the effect of V-1 overexpression on cell toxicity induced by nitric oxide (NO) used at low concentrations. Two clones of PC12D cells overexpressing V-1, transfectants termed V1-46 and V1-69, were significantly more resistant to NOR3 (an NO donor) but not to etoposide (an inhibitor of topoisomerase II)-induced apoptotic cell death than the control cells (termed C-7 and C-9) that had been transfected with the vector alone. The addition of L-DOPA, dopamine, or noradrenaline to the medium did not abolish NOR3-induced cell death in PC12D cells. Moreover, pretreatment of V1-46 and V1-69 cells with L-alpha-methyl-p-tyrosine (alpha-MPT), an inhibitor of tyrosine hydroxylase, to inhibit catecholamine biosynthesis did not affect the resistance to NO toxicity. These results indicate that the catecholamine levels increased by V-1 overexpression did not produce the protection against NOR3-induced toxicity. We further showed that overexpression of V-1 enhanced the synthesis of (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (BH(4)). In addition, pretreatment with BH(4) or with sepiapterin, which is converted to BH(4) intracellularly, significantly protected PC12D cells in a dose-dependent manner. The increased BH(4) synthesis by V-1 overexpression was dose dependently inhibited by pretreatment with diaminohydroxypyrimidine (DAHP), an inhibitor of GTP-cyclohydrolase I, which is the rate-limiting enzyme for the biosynthesis of BH(4), concomitantly with the loss of protective effect afforded by V-1 overexpression. Furthermore, the addition of BH(4) or sepiapterin to DAHP-pretreated V146 and V1-69 cells restored cell viability. Taken together, these results indicate that V1 protein plays an important role in protection against cell death induced by NO at low levels by promoting the synthesis of BH(4). Moreover, these findings suggest the up-regulation of V1 expression as a possible therapeutic target for protection against the insult of NO-induced oxidative stress.

The 245 kb amplified chromosome of Leishmania (V.) braziliensis contains a biopterin transporter gene

Leishmania (V.) braziliensis M2903 presents a small linear and stable 245 kb chromosome originating from a genomic amplification. Similar amplifications present in other species of Leishmania contain a gene coding for a biopterin transporter. Since Leishmania is auxotrophic for this metabolite, this amplification could result from the need to better capture biotpterin from growth media under specific circumstances. In this paper we show that this gene is also present in L. (V.) braziliensis small chromosome, which shares sequences with other genomic amplifications already described.

Genetics and biochemistry of dopa-responsive dystonia: significance of striatal tyrosine hydroxylase protein loss

Notwithstanding the discovery of GCH1 and TH mutations in autosomal-dominant and autosomal-recessive DRD, respectively, a therapeutic trial with levodopa is still the most practical approach to the diagnosis of DRD. The trial needs to be considered in all children with dystonic and/or parkinsonian symptoms or with unexplained gait disorders. Further accumulation of patients with TH-deficient DRD (the mild form of TH deficiency) is necessary to establish the clinical characteristics of this disorder. Regarding GTPCH-deficient DRD, there remain important unresolved issues, including questions of incomplete penetrance of GCH1 mutations, female predominance of affected subjects, and intrafamilial phenotypic variation. A clarification of the mechanism of striatal TH protein loss in GTPCH-deficient DRD may provide a new clue to the pathogenesis of this major form of DRD.

6R-Tetrahydrobiopterin induces dopamine synthesis in a human neuroblastoma cell line, LA-N-1. A cellular model of DOPA-responsive dystonia

Dopa-responsive dystonia (DRD) is an extrapyramidal disorder caused by deficit of 5,6,7,8-tetrahydrobiopterin (BH4), cofactor for tyrosine hydroxylase (TH). In these patients the nigrostriatal dopaminergic neurons normally express TH and the cellular machinery for the dopamine uptake. LA-N-1 is a human neuroblastoma cell line expressing tyrosine hydroxylase. Here we show that LA-N-1 cells are able to take up exogenous dopamine (DA) by an high-affinity mechanism; significant amounts of serotonin and its metabolite 5HIAA, but neither DA nor its metabolites, DOPAC and HVA, could be measured in the cell culture homogenate. 5,6,7,8-Tetrahydrobiopterin, cofactor for both tyrosine and tryptophan hydroxylases, is able to activate dopamine synthesis and also decreases the content of 5HIAA by 50%, indicating that LA-N-1 might be a useful model for studying dopamine-serotonin interaction in cultured cells and the neuronal mechanism of DRD.

Brain biopterin and tyrosine hydroxylase in asymptomatic dopa-responsive dystonia

It is assumed that brain biopterin and dopamine loss should not be as severe in asymptomatic dopa-responsive dystonia caused by GCH1 mutations as it is in symptomatic dopa-responsive dystonia. However, the actual status of dopaminergic systems in asymptomatic cases is unknown. In the autopsied putamen of an asymptomatic GCH1 mutation carrier, we found that brain biopterin loss (-82%) paralleled that reported in dopa-responsive dystonia patients (-84%). However, tyrosine hydroxylase protein and dopamine levels (-52 and -44%, respectively) were not as severely affected as in symptomatic patients (exceeding -97 and -88%, respectively). Our data suggest that the extent of striatal tyrosine hydroxylase protein loss may be critical in determining dopa-responsive dystonia symptomatology.

Structures of tetrahydrobiopterin binding-site mutants of inducible nitric oxide synthase oxygenase dimer and implicated roles of Trp457

To better understand potential roles of conserved Trp457 of the murine inducible nitric oxide synthase oxygenase domain (iNOS(ox); residues 1-498) in maintaining the structural integrity of the (6R)-5,6,7,8-tetrahydrobiopterin (H(4)B) binding site located at the dimer interface and in supporting H(4)B redox activity, we determined crystallographic structures of W457F and W457A mutant iNOS(ox) dimers (residues 66-498). In W457F iNOS(ox), all the important hydrogen-bonding and aromatic stacking interactions that constitute the H(4)B binding site and that bridge the H(4)B and heme sites are preserved. In contrast, the W457A mutation results in rearrangement of the Arg193 side chain, orienting its terminal guanidinium group almost perpendicular to the ring plane of H(4)B. Although Trp457 is not required for dimerization, both Trp457 mutations led to the increased mobility of the N-terminal H(4)B binding segment (Ser112-Met114), which might indicate reduced stability of the Trp457 mutant dimers. The Trp457 mutant structures show decreased pi-stacking with bound pterin when the wild-type pi-stacking Trp457 position is occupied with the smaller Phe457 in W457F or positive Arg193 in W457A. The reduced pterin pi-stacking in these mutant structures, relative to that in the wild-type, implies stabilization of reduced H(4)B and destabilization of the pterin radical, consequently slowing electron transfer to the heme ferrous-dioxy (Fe(II)O(2)) species during catalysis. These crystal structures therefore aid elucidation of the roles and importance of conserved Trp457 in maintaining the structural integrity of the H(4)B binding site and of H(4)B-bound dimers, and in influencing the rate of electron transfer between H(4)B and heme in NOS catalysis.

Tetrahydrobiopterin deficiencies without hyperphenylalaninemia: diagnosis and genetics of dopa-responsive dystonia and sepiapterin reductase deficiency

DOPA responsive dystonia (DRD) and sepiapterin reductase (SR) deficiency are inherited disorders of tetrahydrobiopterin (BH4) metabolism characterized by the signs and symptoms related to monoamine neurotransmitter deficiency. In contrast to classical forms of BH4 deficiency DRD and SR deficiency present without hyperphenylalaninemia and thus cannot be detected by the neonatal screening for phenylketonuria (PKU). While DRD is mostly caused by autosomal dominant mutations in the GTP cyclohydrolase I gene (GCH1), SR deficiency is an autosomal recessive disease. The most important biochemical investigations for the diagnosis of these neurological diseases includes CSF investigations for neurotransmitter metabolites and pterins as well as neopterin and biopterin production in cytokine-stimulated fibroblasts. Discovery of SR deficiency opened new insights into alternative pathways of the cofactor BH4 via carbonyl, aldose, and dihydrofolate reductases. As a consequence of the low dihydrofolate reductase activity in the brain, dihydrobiopterin intermediate accumulates and inhibits tyrosine and tryptophan hydroxylases and uncouples nitric oxide synthase (nNOS), leading to neurotransmitter deficiency and possibly also to neuronal cell death.

Homomeric and heteromeric interactions between wild-type and mutant phenylalanine hydroxylase subunits: evaluation of two-hybrid approaches for functional analysis of mutations causing hyperphenylalaninemia

Phenylketonuria (PKU) is caused by mutations in the phenylalanine hydroxylase gene (PAH), while mutations in genes encoding the two enzymes (dihydropteridine reductase, DHPR, and pterin-4-alpha-carbinolamine dehydratase, PCD) required for recycling of its cofactor, tetrahydrobiopterin (BH(4)), cause other rarer disease forms of hyperphenylalaninemia. We have applied a yeast two-hybrid method, in which protein--protein interactions are measured by four reporter gene constructs, to the analysis of six PKU-associated PAH missense mutations (F39L, K42I, L48S, I65T, A104D, and R157N). By studying homomeric interactions between mutant PAH subunits, we show that this system is capable of detecting quite subtle aberrations in PAH oligomerization caused by missense mutations and that the observed results generally correlate with the severity of the mutation as determined by other expression systems. The mutant PAH subunits are also shown in this system to be able to interact with wild-type PAH subunits, pointing to an explanation for apparent dominant negative effects previously observed in obligate heterozygotes for PKU mutations. Based on our findings, the applications and limitations of two-hybrid approaches in understanding mechanisms by which PAH missense mutations exert their pathogenic effects are discussed. We have also used this technique to demonstrate homomeric interactions between wild-type DHPR subunits and between wild-type PCD subunits. These data provide a basis for functional studies on HPA-associated mutations affecting these enzymes.

Reconstitution of a metabolic pathway with triple-cistronic IRES-containing retroviral vectors for correction of tetrahydrobiopterin deficiency

BACKGROUND

Tetrahydrobiopterin (BH4) is an essential cofactor for catecholamine and serotonin neurotransmitter biosynthesis. BH4 biosynthesis is carried out in a three-enzyme pathway involving GTP cyclohydrolase I (GTPCH), 6-pyruvoyl-tetrahydropterin synthase (PTPS) and sepiapterin reductase (SR). Treatment of genetic defects leading to BH4 deficiency requires neurotransmitter replacement since synthetic cofactor does not efficiently penetrate the blood-brain barrier. Autologous fibroblasts transplanted into the brain as depository cells for drug delivery might offer an alternative. However, normal fibroblasts do not express GTPCH, and fibroblasts from PTPS patients lack two biosynthetic enzymes for BH4 production.

METHODS

We engineered primary fibroblasts by the use of triple-cistronic, retroviral vectors for cofactor production.

RESULTS

Constitutive SR activity in these cells enabled BH4 biosynthesis by transducing GTPCH and PTPS cDNAs together with a selective marker coupled in a single transcript with two IRES-elements in tandem. Upon reaching a critical concentration (> 400 pmol/mg protein) of intracellular BH4, the fibroblasts efficiently released cofactor even under non-dividing conditions.

CONCLUSION

The use of triple-cistronic vectors for single transduction to reconstitute metabolic pathways or to treat multi-genetic diseases may be useful for engineering, for instance, depository cells for various organs, including the nervous system.

Dopa-responsive dystonia: recent advances and remaining issues to be addressed

It is evident from this review that there is much that we know and much that we still do not know about DRD. In terms of diagnosis and clinical management, there is general agreement that patients with childhood-onset dystonic symptoms of unknown etiology should be treated initially with levodopa with the later addition, if necessary, of other medications (for example, BH4, 5-hydroxytryptophan). Although the results of molecular genetic and CSF studies are, at this time, unlikely to significantly alter clinical management of the patient, these analyses could be useful in providing information on prognosis (that is, DRD versus progressive neurodegenerative disorders or more severe metabolic disorders). It is also clear that notwithstanding the discovery of GCH1 and hTH mutations responsible for DRD, there remain many important unresolved issues regarding this disorder, including questions of female predominance, phenotypic heterogeneity, and presence of childhood-onset dystonia versus the expected parkinsonism resulting from a striatal DA deficit. We are confident that answers to these interesting questions on DRD will, in addition to providing clarification of the mechanisms of this disorder, provide exciting information relating to the pathogenesis of other types of dystonia as well as PD and to long-standing issues regarding a role of DA and serotonin in normal human brain development.

Maternal and zygotic control of serotonin biosynthesis are both necessary for Drosophila germband extension

In the accompanying paper, we report that Drosophila gastrulae genetically depleted for the 5-HT(2Dro) serotonin receptor or for serotonin show abnormal germband extension. In wild-type gastrulae, peaks of both the 5-HT(2Dro) receptor and serotonin coincide precisely with the onset of germband extension. Here, we assessed the genetic requirement for this peak of serotonin. We report the characterisation of the serotonin content of individual Drosophila embryos, progeny from flies heterozygous for mutations in genes that are involved in the serotonin synthesis pathway and include the GTP-cyclohydrolase, tryptophan hydroxylase and DOPA decarboxylase loci. The peak of serotonin synthesis at the beginning of germband extension appears strictly dependent upon the maternal deposition of biopterins, products of GTP-cyclohydrolase and cofactors of tryptophan hydroxylase and upon the zygotic synthesis of both tryptophan hydroxylase and DOPA decarboxylase enzymes. Mutant embryos with an impairment in this peak of serotonin synthesis die with a cuticular organisation which is also observed in embryos deficient for the 5-HT(2Dro) receptor. This characteristic cuticular phenotype is thus the hallmark of desynchronisation of the morphogenetic movements during gastrulation. Together, these findings provide additional support for the notion that serotonin, acting through the 5-HT(2Dro) receptor, is necessary for proper gastrulation.

Pterins in human hair follicle cells and in the synchronized murine hair cycle

Human dermal papilla cells (HDPC) express mRNA for the key enzymes for de novo synthesis/recycling and regulation of the pterin (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin (6BH4). HDPC had significantly higher enzyme activities and 6BH4 levels in a comparative study with dermal fibroblasts, epidermal melanocytes, and keratinocytes under in vitro conditions. In addition, a significantly more rapid uptake of 14C-L-phenylalanine was demonstrated in HDPC compared with fibroblasts, whereas the differences in turnover to L-tyrosine were insignificant, suggesting a pooling of L-phenylalanine in HDPC. These results suggested that HDPC driven 6BH4 synthesis could be of major functional importance in the hair cycle. In order to follow this hypothesis in vivo, expression of enzyme activities and levels of the produced cofactor during the synchronized hair cycle were determined employing the murine model C57BL/6. These data revealed a significantly increased de novo synthesis for 6BH4 via GTP-cyclohydrolase I concomitant with high levels of 6BH4, and the induction of phenylalanine hydroxylase activities during the telogen/early anagen stage (days 0-1). Pterin levels and enzyme activities fall on day 3 and plateau during the rest of the entire cycle. In addition, thioredoxin reductase and glutathione reductase activities were measured, where the latter enzyme remained constant but thioredoxin reductase activities showed a biphasic behavior. The first peak coincided with the induction of 6BH4 de novo synthesis at the beginning of the hair cycle. The second peak was observed at mid-anagen, when melanogenesis takes place. Taken together, our results show the presence of autocrine pterin synthesis/recycling in human hair follicle cells under in vitro conditions, and a possible role for 6BH4 in the synchronized murine hair cycle.

Retrovirus-mediated double transduction of the GTPCH and PTPS genes allows 6-pyruvoyltetrahydropterin synthase-deficient human fibroblasts to synthesize and release tetrahydrobiopterin

The tetrahydrobiopterin (BH4) cofactor is essential for the aromatic amino acid hydroxylases that are involved in phenylalanine degradation and catecholamine and serotonin biosynthesis. Furthermore, BH4 is an essential and limiting cofactor for all types of nitric oxide synthases. BH4 deficiency results in hyperphenylalaninemia and monoamine neurotransmitter depletion associated with progressive mental retardation and is most commonly due to autosomal recessive mutations in 6-pyruvoyltetrahydropterin synthase (PTPS), the second enzyme for cofactor biosynthesis. Due to the relatively poor blood-brain barrier penetration of the cofactor, conventional therapy requires, besides oral doses of synthetic BH4, administration of neurotransmitter precursors and an aromatic amino acid decarboxylase inhibitor. The outcome of this therapy is not always beneficial. In this study we transduced into primary patient fibroblasts the human cDNAs for the BH4 biosynthetic enzymes GTP cyclohydrolase I and PTPS, expressed from different retroviral vectors. This allowed BH4 biosynthesis in originally PTPS-deficient cells. Moreover, the double-transduced fibroblasts released between 200 and 800 pmol of BH4/10(6) cells/day. Such engineered fibroblasts may be grafted into the central nervous system and used as depository cells for constitutive delivery of BH4.

Mutation analysis of the 6-pyruvoyl-tetrahydropterin synthase gene in Chinese hyperphenylalaninemia caused by tetrahydrobiopterin synthesis deficiency

Hyperphenylalaninemia (HPA) may be caused by deficiency of phenylalanine hydroxylase or tetrahydrobiopterin (BH4), the essential cofactor for the aromatic amino acid hydroxylases. 6-Pyruvoyl-tetrahydropterin synthase (PTPS) deficiency is a major cause of BH4 deficient HPA. In this study, seven single base mutations at nucleotides 73 (C>G), 155 (A>G), 166 (G>A), 209 (T>A), 259 (C>T), 286 (G>A), and 317 (C>T) on PTPS cDNA were detected in Chinese PTPS-deficient HPA by polymerase chain reaction and solid phase DNA sequencing. These nucleotide alterations result in R25G, N52S, V56M, V70D, P87S, D96N, and T106M amino acid substitutions, respectively. The R25G, V56M, V70D, and T106M were novel mutations found in PTPS gene. By analysis of 38 PTPS mutant alleles from 19 unrelated Chinese PTPS-deficient HPA families, the allele frequency of these mutations in Chinese PTPS-deficient HPA were determined to be approximately 5.3% (R25G), 34.2% (N52S), 7.9% (V56M), 2.6% (V70D), 36.8% (P87S), 7.9% (D96N), and 2.6% (T106M), respectively. Two common mutations, N52S and P87S, were found to account for 71% of the Chinese PTPS mutant alleles. The N52S mutation accounts for 48% of the southern Chinese PTPS mutation, but only one (9%) of the northern Chinese PTPS mutant allele was found to be N52S, which suggested that the N52S mutation might be southern Chinese. Clinically, the V56M mutation was found to associate with the mild form of PTPS deficiency. However, the R25G, N52S, P87S, and D96N were found mainly in the patients with severe clinical symptom. Using polymerase chain reaction-based mutation analysis, a fetus at risk of PTPS deficiency was diagnosed prenatally to be a carrier of N52S mutation.

Impairment of the nitric oxide/cyclic GMP pathway in cerebellar slices prepared from the hph-1 mouse

In this study, the effect of tetrahydrobiopterin deficiency on the nitric oxide/cGMP pathway has been investigated in cerebellar slices derived from the hph-1 mouse. This animal displays a partial deficiency of tetrahydrobiopterin. Basal levels of cGMP were significantly reduced (-29.5%) in the hph-1 mouse cerebellum compared to controls. Following kainate stimulation (500 microM) cGMP levels increased in both control and hph-1 preparations but were again significantly lower (-29.1%) in the hph-1 mouse. Exposure of slices to the nitric oxide donors, S-nitroso-N-acetylpenicillamine and S-nitroso-glutathione, revealed no difference in cGMP accumulation between the two groups. These findings suggest that the cerebellar nitric oxide/cGMP pathway may be impaired in partial tetrahydrobiopterin deficiency states due to diminished nitric oxide formation.

Preliminary studies on the molecular basis of hyperphenylalaninemia in Egypt

Mutation analysis at the phenylalanine hydroxylase (PAH) locus was undertaken in 56 Egyptian hyperphenylalaninemic patients. Selected screening for 11 known mutations and denaturing Gradient gel electrophoresis (DGGE) analysis of the entire coding sequence and exon/intron boundaries led to the identification of a new mutation (I224T), four previously described mutations, and several polymorphisms. Overall, 18 mutant alleles could thus be characterized. In contrast to the high mutation detection rate typical of the DGGE-based scanning approach, only 6 of 16 mutant alleles tested were identified. Since BH4 deficiency could not be excluded in any of these patients, the latter results may be explained by the occurrence of mutations affecting the genes controlling the synthesis and recycling of tetrahydrobiopterin: the cofactor of PAH. An alternative hypothesis is also discussed.

Tetrahydrobiopterin and inherited hyperphenylalaninemias

Tetrahydrobiopterin deficiency, a variant of hyperphenylalaninemia, may be caused by deficiency of one of the following enzymes: guanosine triphosphate cyclohydrolase 1,6-pyruvoyltetrahydropterin synthase, dihydropteridin reductase and pterin-4a-carbinolamine dehydratase. The first two enzymes are involved in the biosynthesis of tetrahydrobiopterin, the last two in its regeneration. Although these diseases are rare, early detection by selective screening is essential for the treatment and outcome. Tetrahydrobiopterin deficiencies are very heterogenous ranging from mild forms requiring only marginal if any treatment to severe forms which are in some cases very difficult to treat. All variants of tetrahydrobiopterin deficiency can be differentiated from the classical phenylketonuria (PKU) by measurement of pterin metabolites in patients' urine, tetrahydrobiopterin loading test, and by dihydropteridine reductase activity in erythrocytes from the Guthrie card.

Stimulus-dependent production of cytokines and pterins by peripheral blood mononuclear cells

The cytokine profiles produced by peripheral blood mononuclear cell (PBMC) cultures were dependent upon the nature of the stimulus used. Powerful lymphocyte activators such as mitogens induced rapid cell proliferation together with the production of both inflammatory (IL-1 alpha, IL-1 beta, IL-6 and TNF alpha) and immune (IFN-gamma, TNF-alpha and TNF-beta) cytokines, and immune activation markers (soluble IL-2 receptor, neopterin and xanthopterin). Bacterial endotoxin failed to induce cell proliferation but resulted in the rapid production of inflammatory cytokines together with a short burst of IFN-gamma production, without the production of the other immune cytokines or activation markers. Alloantigen stimulation gave a typical immune cytokine and marker profile, with little or no production of inflammatory cytokines. Re-call antigens (candida and PPD) induced maximal cell proliferation at days 5 to 6, but induced little or no production of inflammatory cytokines. Markedly different immune cytokine profiles were obtained with these re-call antigens. Candida induced an early burst of IFN-gamma production on day 1 followed by later production of TNF-alpha. In cultures stimulated with PPD, both IFN-gamma and TNF-alpha were detected from day 2. With both re-call antigens, the levels of production of the activation markers were equivalent to the proliferative responses obtained.

[The metabolic basis of the hyperphenylalaninemias and tyrosinemia]

The hyperphenylalaninemias are caused by the defect of either phenylalanine hydroxylase (PAH) or tetrahydrobiopterin (BH4) cofactor. The former is diagnosed as phenylketonuria (PKU) or benign hyperphenylalaninemia, based on the serum phenylalanine values. The latter, so called malignant hyperphenylalaninemia, includes three enzyme defects, dihydropteridine reductase (DHPR), 6-pyruvoyl tetrahydropterin synthase (PT PS) and guanosine triphosphate cyclohydrolase (GTP-CH). Excess phenylalanine and its metabolites cause brain damage before 6 years of age. Deficiency of BH4 impairs two other hydroxylases (tyrosine and tryptophan), and severe neurological symptoms develop because of the lack of neurotransmitters. Tyrosinemia I, II, and III are different enzyme defects, fumarylacetoacetate hydrolyase (FAH), hepatic tyrosine aminotransferase (TAT), and 4-hydroxyphenylpyruvate acid oxidase, respectively. Tyrosinemia I is associated with severe involvement of the liver, kidney and central nervous system. Tyrosinemia II has mental retardation, palmar hyperkeratosis and corneal ulcers. Tyrosinemia III has mild mental retardation but no eye or skin manifestations.