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

Inhibition of astrocytic DRD2 suppresses CNS inflammation in an animal model of multiple sclerosis

Astrocyte activation is associated with progressive inflammatory demyelination in multiple sclerosis (MS). The molecular mechanisms underlying astrocyte activation remain incompletely understood. Recent studies have suggested that classical neurotransmitter receptors are implicated in the modulation of brain innate immunity. We investigated the role of dopamine signaling in the process of astrocyte activation. Here, we show the upregulation of dopamine D2 receptor (DRD2) in reactive astrocytes in MS brain and noncanonical role of astrocytic DRD2 in MS pathogenesis. Mice deficient in astrocytic Drd2 exhibit a remarkable suppression of reactive astrocytes and amelioration of experimental autoimmune encephalomyelitis (EAE). Mechanistically, DRD2 regulates the expression of 6-pyruvoyl-tetrahydropterin synthase, which modulates NF-κB activity through protein kinase C-δ. Pharmacological blockade of astrocytic DRD2 with a DRD2 antagonist dehydrocorybulbine remarkably inhibits the inflammatory response in mice lacking neuronal Drd2. Together, our findings reveal previously an uncharted role for DRD2 in astrocyte activation during EAE-associated CNS inflammation. Its therapeutic inhibition may provide a potent lever to alleviate autoimmune diseases.

Protective effects of (6R)-5,6,7,8-tetrahydro-l-biopterin on local ischemia/reperfusion-induced suppression of reactive hyperemia in rat gingiva

We herein investigated the regulatory mechanism in the circulation responsible for rat gingival reactive hyperemia (RH) associated with ischemia/reperfusion (I/R). RH was analyzed using a laser Doppler flowmeter. RH and I/R were elicited by gingival compression and release with a laser Doppler probe. RH increased in a time-dependent manner when the duration of compression was between 30 s and 20 min. This increase was significantly suppressed by N^ω-nitro-l-arginine-methyl-ester (l-NAME), 7-nitroindazole (7-NI), and 2,4-diamino-6-hydroxypyrimidine (DAHP). However, RH was markedly inhibited following 60 min of compression. This inhibition was significantly decreased by treatments with superoxide dismutase (SOD), (6R)-5,6,7,8-tetrahydro-l-biopterin (BH₄), and sepiapterin. The luminescent intensity of superoxide anion (O₂^•−)-induced 2-methyl-6-(4-methoxyphenyl)-3,7-dihydroimidazo-[1,2-a] pyrazine-3-one (MCLA) was markedly decreased by SOD and BH₄, but only slightly by sepiapterin. BH₄ significantly decreased O₂^•− scavenging activity in a time-dependent manner. These results suggested that nitric oxide (NO) secreted by the nitrergic nerve played a role in regulating local circulation in rat gingiva. This NO-related regulation of local circulation was temporarily inhibited in the gingiva by the I/R treatment. The decrease observed in the production of NO, which was caused by suppression of NO synthase (NOS) activity subsequent to depletion of the NOS co-factor BH₄ by O₂^•−, played a partial role in this inhibition.

Different SNP combinations in the GCH1 gene and use of labor analgesia

Background

The aim of this study was to investigate if there is an association between different SNP combinations in the guanosine triphosphate cyclohydrolase (GCH1) gene and a number of pain behavior related outcomes during labor. A population-based sample of pregnant women (n = 814) was recruited at gestational week 18. A plasma sample was collected from each subject. Genotyping was performed and three single nucleotide polymorphisms (SNP) previously defined as a pain-protective SNP combination of GCH1 were used.

Results

Homozygous carriers of the pain-protective SNP combination of GCH1 arrived to the delivery ward with a more advanced stage of cervical dilation compared to heterozygous carriers and non-carriers. However, homozygous carriers more often used second line labor analgesia compared to the others.

Conclusion

The pain-protective SNP combination of GCH1 may be of importance in the limited number of homozygous carriers during the initial dilation of cervix but upon arrival at the delivery unit these women are more inclined to use second line labor analgesia.

Consideration of gene therapy for paediatric neurotransmitter diseases

The paediatric neurotransmitter diseases (PNDs) are a group of inborn errors of metabolism characterized by abnormalities of neurotransmitter synthesis or metabolism. Although some children may react favourably to neurotransmitter augmentation treatment, optimal response is not universal and other modes of treatment should be sought. The genes involved in many of the currently known monoamine PNDs have been utilized in pre-clinical and in phase I clinical trials in Parkinson disease (PD) and the basic principles could be applied to the therapy of PNDs with some modifications regarding the targeting and distribution of vectors. However, issues that go beyond neurotransmitter replacement are important considerations in PD and even more so in PNDs. Understanding the pathophysiology of PNDs including abnormal development resulting from the neurotransmitter deficiency will be critical for rational therapeutic approaches. Better animal models of PNDs are necessary to test gene therapy before clinical trials can be attempted.

The fate of intravenously administered tetrahydrobiopterin and its implications for heterologous gene therapy of phenylketonuria

Tetrahydrobiopterin (BH(4)) is a required cofactor for the enzymatic activity of phenylalanine hydroxylase (PAH) and is synthesized de novo from GTP in several tissues. Heterologous expression of PAH in tissues other than liver is a potential novel therapy for human phenylketonuria that is completely dependent upon BH(4) supply in the PAH-expressing tissue. Previous experiments with liver PAH-deficient transgenic mice that expressed PAH in skeletal muscle demonstrated transient correction of hyperphenylalaninemia only with hourly parenteral BH(4) administration. In this report, the fate of intravenously administered BH(4) is examined. The conclusions are that (1) BH(4) administered intravenously is rapidly taken up by liver and kidney, and (2) uptake of BH(4) into muscle is relatively low. The levels of BH(4) achieved in skeletal muscle following IV injection are only 10% of the amount expected were BH(4) freely and equally distributed across all tissues. The half-life of BH(4) in muscle is approximately 30 min, necessitating repeated injections to maintain muscle BH(4) content sufficient to support phenylalanine hydroxylation. The efficacy of heterologous muscle-directed gene therapy for the treatment of PKU will likely be limited by the BH(4) supply in PAH-expressing muscle.

Comparison of epidermal keratinocytes and dermal fibroblasts as potential target cells for somatic gene therapy of phenylketonuria

Phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase (PAH) and increased levels of phenylalanine. PAH requires the cofactor BH(4) to function and the rate-limiting step in the synthesis of BH(4) is GTP cyclohydrolase I (GTP-CH). The skin is a potential target tissue for PKU gene therapy. We have previously shown that overexpression of PAH and GTP-CH in primary human keratinocytes leads to high levels of phenylalanine clearance without BH(4) supplementation [Gene Ther. 7 (2000) 1971]. Here, we investigate the capacity of fibroblasts, another cell type from the skin, to metabolize phenylalanine. After retroviral gene transfer of PAH and GTP-CH both normal and PKU patient fibroblasts were able to metabolize phenylalanine, however, in lower amounts compared to genetically modified keratinocytes. Further comparative analyses between keratinocytes and fibroblasts revealed a higher copy number of transgenes in keratinocytes and also a higher metabolic capacity.

Development of a skin-based metabolic sink for phenylalanine by overexpression of phenylalanine hydroxylase and GTP cyclohydrolase in primary human keratinocytes

Phenylketonuria, PKU, is caused by deficiency of phenylalanine hydroxylase (PAH) resulting in increased levels of phenylalanine in body fluids. PAH requires the non-protein cofactor BH4 and the rate-limiting step in the synthesis of BH4 is GTP cyclohydrolase I (GTP-CH). Here we show that overexpression of the two enzymes PAH and GTP-CH in primary human keratinocytes leads to high levels of phenylalanine clearance without BH4 supplementation. Integration of multiple PAH and GTP-CH transgenes were achieved after optimized retroviral transduction. Phenylalanine clearance was measured ex vivo in primary human keratinocytes cotransduced with PAH and GTP-CH (more than 370 nmol/24 h/106 cells), a level exceeding that of a human liver cell line (HepG2 cells). Cells overexpressing either one of the enzymes alone did not clear significant amounts of phenylalanine. Transfer of the two genes into the same cell was not necessary, since cocultivation of cells transduced separately with PAH and GTP-CH also resulted in phenylalanine clearance. Thus the experiments indicate metabolic cooperation between cells overexpressing PAH and cells overexpressing GTP-CH, possibly due to intercellular transport of synthesized BH4.

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.