The screening diagnosis of tetrahydrobiopterin deficient phenylketonuria

Since 1990, 20 diagnostically confirmed phenylketonuria (PKU) patients have been screened with a tetrahydrobiopterin (BH4) loading test, in which plasma phenylalanine and urinary pterin metabolites were investigated, ind activity of dihydropteridine reductase (DHPR) was determined as well. The results showed that there was no statistical difference between the concentrations of plasma phenylalanine before and after BH4 (20mg/kg) administration in all patients, and values of urinary neopterin and biopterin were within the range of classic PKU. All patients but one had normal activity of DHPR in red cells. This suggests that incidence of BH4 deficiency in PKU patients amounts to five percent (1/20) which is almost the same as reported abroad.

Biopterin-dependent hyperphenylalaninemia due to deficiency of 6-pyruvoyl tetrahydropterin synthase

We describe the clinical, neurologic, and biochemical findings in 10 patients with 6-pyruvoyl tetrahydropterin synthase (6-PTS) deficiency from seven families, all of whom originate from one large tribe in Saudi Arabia. This deficiency presents with severe, early onset of failure to thrive, neurologic deterioration, and morbidity and mortality secondary to repeated episodes of bronchopneumonia or cardiorespiratory abnormalities. The urinary pterin excretion pattern indicates deficient activity of 6-PTS, which has been confirmed by direct enzyme assay in red blood cells of three patients. We treated our patients with combined use of tetrahydrobiopterin 20 mg/kg/d, L-dihydroxyphenylalanine 15 mg/kg/d, carbidopa 3.75 mg/kg/d, and L-5-hydroxytryptophan 5 mg/kg/d. Neurologic findings improved significantly in all after 5 to 24 months. Although head circumference and weight returned to the lower limit of normal in four, height normalized only in one of seven patients. Despite an unrestricted diet during combined therapy, blood phenylalanine and urinary excretion of neopterin and biopterin returned to normal.

Human carbonyl and aldose reductases: new catalytic functions in tetrahydrobiopterin biosynthesis

New catalytic functions of human carbonyl- and aldose reductase in tetrahydrobiopterin biosynthesis are proposed. 6-Pyruvoyl tetrahydropterin, an intermediate in the biosynthesis of tetrahydrobiopterin, was converted to 6-lactoyl tetrahydropterin and 1'-hydroxy-2'-oxopropyl tetrahydropterin by carbonyl reductase under anaerobic condition. 1'-Hydroxy-2'-oxopropyl tetrahydropterin was subsequently metabolized to tetrahydrobiopterin by aldose reductase. Based on these results alternative pathways for the synthesis of tetrahydrobiopterin in patients with genetic defects of sepiapterin reductase are suggested.

Long-term plasma exchange in a case of Refsum's disease

Refsum's disease (Heredopathia atactica polyneuritiformis) is caused by accumulation of phytanic acid in all body tissues due to an inherited failure of alpha-oxidation of branched chain fatty acids. Plasmapheresis has been reported to be beneficial by removal of phytanic acid from the blood. We describe a patient with Refsum's disease in whom long-term plasmapheresis did not improve clinical, biochemical or electrophysiological parameters.

7-Substituted pterins. A new class of mammalian pteridines

Three novel pteridines have been isolated from the urine of patients with a new variant of 6-(L-erythro-1',2'-dihydroxypropyl)-5,6,7,8-tetrahydropterin (tetrahydrobiopterin) deficiency, showing hyperphenylalaninemia. From the results of high performance liquid chromatography, oxidative degradation, and gas chromatography-electron impact mass spectrometry, their structures were identified as 7-(D-erythro-1',2',3'-trihydroxypropyl)-pterin (7-neopterin), 7-(L-erythro-1',2'-dihydroxypropyl)-pterin (7-biopterin), and 6-oxo-7-(L-erythro-1',2'-dihydroxypropyl)-pterin (6-oxo-7-biopterin). The ratio of biopterin to 7-biopterin in the patients' urines was 1:1, and after oral loading with tetrahydrobiopterin, 7-biopterin excretion rose parallel to biopterin. This finding suggests that 7-substituted pterins may be formed endogenously by a yet unknown isomerization reaction. The cause of hyperphenylalaninemia is still unclear. The activities of the enzymes involved in tetrahydrobiopterin biosynthesis and regeneration were found to be normal in the patients, and no effect of 7-biopterin on these enzymes was observed in vitro. However, compared with the normal cofactor, tetrahydrobiopterin, the Km values of tetrahydro-7-biopterin for phenylalanine hydroxylase and dihydropteridine reductase are 20 and 5 times higher, respectively.

Primapterin, anapterin, and 6-oxo-primapterin, three new 7-substituted pterins identified in a patient with hyperphenylalaninemia

Three unknown compounds present in the urine of a patient with mild hyperphenylalaninemia were identified to be L-erythro-7-iso-biopterin, D-erythro-7-iso-neopterin, and L-erythro-6-oxo-7-iso-biopterin. The newly identified pterins were named primapterin, anapterin, and 6-oxo-primapterin, respectively. Primapterin and anapterin are present in very low concentrations in every human urine, as well as in the liver of man and mouse, whereas 6-oxo-primapterin was detected in the patient's urine only. Substantial amounts of primapterin were excreted in the patient described. The metabolic origin of primapterin and anapterin is still obscure.

Identification of new steroids in patients with 17 alpha-hydroxylase deficiency by capillary gas chromatography/mass spectrometry

Urines of two children with 17 alpha-hydroxylase deficiency contained a number of 5-pregnane- and pregnenediols, -triols and -tetrols with a hydroxy or oxo group in position 11 of the steroid ring. They are formed mainly from progesterone via 11-hydroxyprogesterone, pregnanolone and corticosterone, respectively, or from pregnenolone. Three metabolites not previously described, 16-hydroxypregnenolone, 6,21-dihydroxypregnanediol and 6-hydroxytetrahydrocorticosterone, were identified.

Neopterin in AIDs, other immunodeficiencies, and bacterial and viral infections

An increase in total urinary neopterin was observed in 12 of 13 patients with acquired immunodeficiency syndrome (AIDS), seven of 13 patients with lymphadenopathy, one of six healthy homosexual males, seven of ten adult patients with staphylococcal pneumonia, 11 of 12 children with viral infections, four of seven children with bacterial infections, and 12 of 13 children with various immune defects. Extremely high values of total urinary neopterin and monapterin were observed in severely ill patients with AIDS and those with familial hemophagocytic lymphohistiocytosis. Neopterin excretion was normal in two AIDS patients with Kaposi's sarcoma, but without opportunistic infections at that time. On reexamination of one of these patients later on, elevated neopterin values were noted. Parallel increases in neopterin and monapterin were found, whereas biopterin was usually normal. The increase in total neopterin was mainly due to 7,8-dihydroneopterin and was accompanied by an increase in 3'-hydroxysepiapterin. Increased neopterin in urine is assumed to reflect the increase in GTP pool and GTP cyclohydrolase I activity as observed in stimulated monocytes. Thus, neopterin, as a measure of the activation of the nonspecific cellular immune system, may be used diagnostically to detect allograft rejection after transplantations and to follow-up HTLV-III positive patients.

The application of 8-aminoguanosine triphosphate, a new inhibitor of GTP cyclohydrolase I, to the purification of the enzyme from human liver

GTP cyclohydrolase I from human liver and Escherichia coli is competitively inhibited by 8-aminoguanosine triphosphate with a dissociation constant (Ki) of 0.25 mumol/l. 8-Aminoguanosine triphosphate, prepared from GTP and hydroxylamine-O-sulfonic acid, was coupled to Sepharose 4B and used as an affinity adsorbent for a 309-fold purification of GTP cyclohydrolase I from human liver. GTP cyclohydrolase I from human liver is a relatively heat-stable enzyme with a half-life of 2 min at 80 degrees C, an isoelectric point (pI) of about 5.6, and a Km for GTP of 31 mumol/l. Addition of KCl (0.3 mol/l) increased the Km to 153 mumol/l. No cofactors were required for activity. L-erythro-5,6,7,8-Tetrahydrobiopterin, L-erythro-7,8-dihydrobiopterin, L-sepiapterin and 8-aminoguanosine triphosphate were strong inhibitors.