GTP Cyclohydrolase Functions in Fish Color Formation / 中国生物化学与分子生物学报

Guanosine triphosphate cyclohydrolase (GTP cyclohydrolase,Gch) is a protease with a GTP- cyclohydro domain, which is widely found in vertebrates and invertebrates.Mammals and birds only have Gch 1.In teleost and amphibian, other two paralogs (Gch2 and Gch3) also exists besides Gchl, which also displayed functional differences.Gch is a rate-limiting enzyme that ultimately synthesized the tetrahydrobiopterin (BH4) using guanosine triphosphate as a substrate.BH4 is an essential coenzyme of aromatic amino acid hydroxylase and contributes to the synthesis of various hormones and neurotransmitters.The Gch is an initial step in the catalysis of various pterin biosynthesis and plays important roles in a series of physiological and pathological processes, such as skin pigmentation, ocular pigmentation, methotrexate, folic acid, and tetrahydrobiopterin.The physiological function of Gch is inextricably linked to the biosynthesis of BH4.As the only rate-limiting enzyme in BH4 biosynthesis, the activity of Gch is a useful indicator for the development of neurons and pigment cells.Besides, it is also an important marker of pigment synthesis and neurotransmitter biosynthesis.Nowadays, the functions of Geh in pathogenesis of tumor and cardiovascular diseases have been widely concerned, while the researches on the pigmentation and color formation are mainly concentrated in insects, and rarely in teleost.Therefore, this article summarized the characteristics of Gch genes, protein and the functions of Gch in fish coloration, which has important guiding significance for further illustration the mechanism of Gch in teleost pigmentation and fish color genetic improvements.

Metabolic Control in Patients With Phenylketonuria Pre- and Post-Sapropterin Loading Test

Abstract In Portugal, tetrahydrobiopterin (BH4)-responsive patients with phenylketonuria (PKU) are identified using a loading test (LT). Phenylalanine/natural protein (Phe/NP) intake is increased to elevate blood Phe prior to the LT. In a longitudinal retrospective study, the impact of Phe/NP titration post-LT in 58 patients (19.6 + 8.2 years) with PKU during 4 study periods (SPs) was examined. In SP1 (2010-2013), patients were diet treated only; in SP2 (2014), the Phe/NP titration was followed by the LT in SP3 (2015). In SP4 (2016), patients received diet treatment only (n » 49) or BH4 þdiet (n » 9). The median percentage blood Phe within the target range was higher in SP1 versus SP4 (64 [28-85] vs 45 [0-66]; P < .001). Our results suggest that transient Phe/NP titration, associated with a deliberate increase in NP, may adversely affect metabolic control. Controlled studies are necessary to examine the longer term impact of temporary increased NP with BH4 LT in non-BH4-responsive patients.

Alternative Therapies for PKU

Abstract The phenylalanine (PHE)-restricted diet has improved in quality and diversity over time and has proven to be effective in all patients. Nevertheless, this treatment imposes a heavy social and economic burden to patient and family and impacts quality of life. Sustained adherence to PHE restriction is difficult to maintain. Moreover, even patients with phenylketonuria (PKU) with normal intelligence quotient (IQ) have lower IQ than matched individuals without PKU and can have deficits in multiple other aspects of neuropsychological function, including cognitive and executive function, working memory. They can also have behavior problems, depression, and low self-esteem. In recent years, alternative treatments for PKU have been developed and their use has been indicated for some patients who are candidates for options besides traditional treatment. Sapropterindihydrochloride, large neutral amino acids, and glycomacropeptide are alternative treatment options in use for selected patients. The aim of this article is to review the current knowledge of these new approaches to PKU treatment.

Effects of Sodium Arsenite on mRNA Expression of GTP Cyclohydrolase and 6-pyruvoyl-tetrahydropterin Synthase in Chang Liver Cells / 环境与健康杂志

Objective To study the effects of sodium arsenite on the mRNA expression of GTP cyclohydrolase (GTPCH) and 6-pyruvoyl-tetrahydropterin synthase (PTPS) in Chang liver cells. Methods Human Chang liver cells were cultured with sodium arsenite at doses of 0, 50, 200 and 400 ?mol/L for 12 hours. Cell viability was tested by MTT assay, and the expression of mRNA of GTPCH and PTPS was detected by RT-PCR. Results Cell viability in 50 ?mol/L group was almost the same as that in control, while the viability in the other two groups were significantly lower than that in control. All of the mRNA expression levels in the three groups were significantly lower than that in control with dose-dependent manner. Conclusion The down-regulated expression of GTPCH and PTPS, the main enzymes of the synthesis of BH4, induced by sodium arsenite exposure may be related with arsenic related skin depigmentation.

Endothelial Dysfunction-Its Molecular Mechanism and Potential Implication in Therapy

Endothelial dysfunction is known to be early stage of atherosclerosis and its presence leads to poor prognosis. Recently many basic researchs were done to elucidate the basic mechanism related to endothelial nitric oxide synthase (eNOS). eNOS is composed of dimer, between which calmodulin binding domain is located. This area plays important role in producing NO with BH4 (tetrahydrobiopteryn as a co factor). In the presence of excess of superoxide from NADPH oxidase, NO binds with superoxide to be peroxynitrite. BH4 is converted to BH2 in the presence of peroxynitrite and eNOSdimer dissociates to monomer, which is called uncoupling. Uncoupled eNOS produces superoxide and it results in endothelial dysfunction. NO deficiency is related to the decreased number of peripheral endothelial progenitor cell and HDL-cholesterol is known to stimulate eNOS. This would be new field of research relating eNOS to atherogenesis and eNOS's role in prevention of cardiovascular disease.

Study on the Protective Effects of 6R-Tetrahydrobiopterin on the Oxidative Neuronal Injury in Mouse Cortical Cultures

OBJECTIVE: 6R-Tetrahydrobiopterin(BH4) is a cofactor for the aromatic amino acid hydroxylases which is essential for the biosynthesis of catecholamines and serotonin. It also acts as a cofactor for nitric oxide synthase, and stimulates the release of some neurotransmitters such as dopamine, serotonin, acetylcholine and glutamate. Recently, it has been reported that BH4 could induce cellular proliferation and enhance neuronal survival. This study was performed to investigate the antioxidative effect of BH4 on the various oxidative insults in mouse cerebral cortical cell cultures. METHODS: Iron ion(FeCl2), zinc ion(ZnCl2), sodium nitroprusside(SNP) and buthionine sulfoximine(BSO, a glutathione depletor) were used as oxidants. Cell death was assessed by measurement of lactate dehydrogenase efflux to bathing media at the end of exposure. RESULT: All 4 oxidants induced neuronal cell death associated with cell body swelling, which was markedly inhibited by trolox(100nM), a vitamin E analog. BH4(10-100nM) markedly inhibited the neuronal cell death induced by all 4 oxidants(20nM Cu2+, 20nM Zn2+, 1nM SNP or 1mM BSO). However, BH4 failed to inhibit the neuronal cell death induced by 24hr exposure to 20nM NMDA. CONCLUSION: These results suggest that BH4 has antioxidative action independently of any actions of enzyme cofactor.

Pterin & DHPR measurement and DNA analysis in Korean PKU patients

Phenylketonuria is metabolic disorder that results from a deficiency of the hepatic phenylalanine hydroxylase. But among patients with hyperphenylalaninemia, the defect resides in one of the enzymes necessary for production or recycling of tetrahydrobiopterin (BH4). The reduction of BH4 affects not only phenylalanine metabolism but also formation of the tyrosine related neurotransmitter, dopamin and tryptophan related neurotransmitter, serotonin. Administration of L-dopa and 5-hydroxytriptophan seems to be the most effective treatment and may prevent irreversible neurologic damage if started early in life in hyperphenylalaninemia due to deficiency of cofactor BH4. Therefore, all patients with PKU and hyperphenylalaninemia should be tested for BH4 deficiency as early as passible. So we measured reduced forms of biopterin in urines of 19 phenylketonuria patients by Funkushima and Nixon method and 13 of PKU patients measured dihydropterin reductase (DHPR) in white blood cells by modified Narisawa method. We could not find abnormal pterin patterns of cofactor BH4 and normal value of DHPR. All Korean 19 PKU children were classic PKU. A missense mutation has been identified in the phenylalanine hydroxylase (PAH) gene of 16 Koran PKU patients. 5 mutations (IVS4, Y204 C, R243Q, Y356 X, R413 P) have been identified. The frequency of these mutations was found to be 50% of PKU alleles. The IVS4 mutation had a high frequency in Korea and southern China, due to the result of the founder effect and genetic drift. the R413 P mutation, which may have originated in the regions surrounding the Baikal, expanded to northen China and Japan. We were not able to find Caucasian mutations in Korean ptiets. PKU mutations occured after racial divergence between Caucasian and Mongoloids. We observed that PKU patients with Y 204 C and R413 P mutations showed mild mild clinical phenotype but IVS4 mutation had severe mental retardation. the establishment of genotype will therefore aid in the prediction of clinical phenotypes in patients with this disease. So, pterin and DHPR measurement and DNA analsis will be useful for prognosis and proper treatment of PKU patients.