Lack of dependence of amine or prostaglandin biosynthesis on absolute cerebral level of pteridine cofactor

Tetrahydrobiopterin and total biopterin content of neuroblastoma (N1E-115, N2A) and pheochromocytoma (PC-12) clones and the dependence of catecholamine synthesis on tetrahydrobiopterin concentration in PC-12 cells

Tetrahydrobiopterin content was determined in several clonal cell lines by reversed-phase HPLC and subsequent electrochemical detection. The same chromatography system was used to determine the total biopterin (tetrahydrobiopterin and 7,8-dihydrobiopterin) by fluorescence detection. The catecholamine-producing clones neuroblastoma N1E-115 and pheochromocytoma PC-12 contained 96 and 60 ng tetrahydrobiopterin/mg protein, respectively. The corresponding amount for the neuroblastoma clone N2A was 36 ng/mg protein. The tetrahydrobiopterin content in C-6 glioma cells was below the limit of detection. The total biopterin is about 20% above the tetrahydrobiopterin content. Tetrahydrobiopterin and biopterin from the cells were identified by coelution with standard solutions and by potential-current relationship or emission and excitation spectra, respectively. Addition of 2,4-diamino-6-hydroxypyrimidine, an inhibitor of biopterin synthesis from GTP, to the culture medium of PC-12 cells resulted in a dose-dependent decrease of tetrahydrobiopterin and total biopterin content within 4 h, suggesting that the cells are capable of synthesising the biopterin which was found. A decrease in intracellular tetrahydrobiopterin levels by different concentrations of 2,4-diamino-6-hydroxypyrimidine reduces the cellular production of dihydroxyphenylalanine after inhibition of aromatic L-amino acid decarboxylase, indicating that the concentration of tetrahydrobiopterin might be a limiting factor for catecholamine synthesis in catecholamine-producing cells.

Cerebrospinal fluid hydroxylase cofactor in schizophrenia

Cerebrospinal fluid levels of pterin cofactor were measured in off-medication schizophrenic patients and normal control subjects as one aspect of monoamine physiology in schizophrenia. Pterin cofactor is essential for the hydroxylation of several substances including tyrosine, the rate-limiting step in the synthesis of dopamine and norepinephrine. No significant differences were found. Platelet monoamine oxidase activity correlated significantly with pterin levels in male schizophrenic and in female control subjects.

Biopterin. VII. Inhibition of synthesis of reduced biopterins and its bearing on the function of cerebral tryptophan-5-hydroxylase in vivo

Repeated intraventricular injections of 2,4-diamino-6-hydroxypyrimidine (DAO-Pyr), inhibitor of D-erythro-q-dihydroneopterin triphosphate synthetase, inhibited q-BH2 synthesis from GTP, markedly increased accumulation of 2-amino-4-hydroxy-5 (or -6)-formamido-6-triphosphoribosylaminopyrimidine (FPyd-P3) and brought about a 60% decrease in the in vivo of reduced biopterin (BH2 and BH4) pool in the brain. Nevertheless, there was no effect on the rate of hydroxylation of L-tryptophan or on the 5-hydroxytryptamine level in rat brain. These data emphasized the significance of the rate of hydrogen transfer and the limitation of the concept of "unsaturation" (i.e., the absolute amount of the carrier pterin molecule) for the synthesis of neurotransmitters in vivo.