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Biomedical subjects

H Herken

Publications and source records attributed to H Herken.

At least 19 recordsLinked to original sources
PubMed1989

Inhibition of biopterin synthesis and DOPA production in PC-12 pheochromocytoma cells induced by 6-aminonicotinamide.

Pheochromocytoma cells (clone PC-12) were treated with 6-aminonicotinamide. Tetrahydrobiopterin content and DOPA production of the cells were determined by reverse-phase HPLC and subsequent electrochemical detection. The same chromatographic system was used to determine total biopterin (tetrahydrobiopterin, dihydrobiopterin and quinoide dihydrobiopterin) by fluorescence detection. Tetrahydrobiopterin plays a decisive role as cofactor of tyrosine hydroxylase for the biosynthesis of DOPA and dopamine. Addition of 6-aminonicotinamide to the culture medium resulted in the accumulation of 6-phosphogluconate, suggesting that PC-12 cells synthesize 6-aminonicotinamide-adenine-dinucleotide-phosphate (6-ANADP) by a glycohydrolase localized in the endoplasmic reticulum. This substance is known to be a strong inhibitor of 6-phosphogluconate dehydrogenase and leads to a blockade of the pentose phosphate pathway. In our experiments, the synthesis of biopterins was depressed after application of 6-aminonicotinamide. The decrease of intracellular tetrahydrobiopterin and total biopterin by 6-aminonicotinamide at different concentrations was strongly correlated with a reduced cellular DOPA production. The decreased content of biopterin cofactor was compensated by addition of the precursor sepiapterin, indicating that the NADPH2-dependent reductases in biopterin synthesis are not inhibited by the antimetabolite. However, DOPA production remained suppressed at the same time. After application of NADH2, we observed an increased DOPA production though the decreased biopterin levels remained almost unchanged. The results imply that the first step in the synthesis of biopterin from GTP as well as the recycling pathways of the oxidized cofactor might be the site of action of the antimetabolite.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Aminonicotinamide↗
PubMed1987

PC12 cells: a model system for studying drug effects on dopamine synthesis and release.

PC12 cells were used as a model system to examine drug effects on dopamine synthesis and release. It could be demonstrated that KCl treatment induced release of endogenous dopamine, simultaneously DOPA synthesis was increased. Despite of the increase in DOPA synthesis the intracellular concentration of tetrahydrobiopterin (the co-factor of tyrosine hydroxylase) remained stable, indicating that the catalytic recycling of the used tetrahydrobiopterin is much more rapid than the tetrahydrobiopterin consumption by tyrosine hydroxylation. Reserpine induced a decrease of intracellular dopamine but no dopamine reached the extracellular space, instead all dopamine was depleted into the cytoplasma and metabolized to DOPAC. Nitrendipine had no effect on intracellular dopamine storage, Bay K 8644 induced a small decrease of intracellular dopamine and a small increase in DOPA production. N-(6-aminohexyl)-5-chloro-1-naphthalene sulfonamide (W7) induced a reserpine-like depletion at concentrations above 1 X 10(-6) M. The KCl-induced dopamine release and the stimulation of DOPA production were blocked by 1 X 10(-7) M nitrendipine and enhanced by 1 X 10(-7) M Bay K 8466, whereas 1 X 10(-6) M W7 had no effect on both parameters. These findings were compared to data obtained in other tissues reported in the literature indicating that PC12 cells are a useful model for studying drug effects on catecholamine synthesis and release.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed1986

Apomorphine does not decrease tissue levels of tetrahydrobiopterin in vivo.

It was reported that R(-)apomorphine and other catechols are potent inhibitors of dihydropteridine reductase in vitro. It was suggested that decreased levels of tetrahydrobiopterin may represent a mechanism by which R(-)apomorphine inhibits catecholamine synthesis in vivo. This paper demonstrates that tetrahydrobiopterin levels are not affected either in vitro (PC12 cells) or in vivo (rat liver and corpus striatum) by treatment with R(-)apomorphine, whereas DOPA (3,4-dihydroxyphenylalanine) production (PC12 cells, corpus striatum) is reduced. This indicates that R(-)apomorphine does not inhibit DOPA production by reducing 6(R)-L-erythro-tetrahydrobiopterin) levels.

Animals↗
PubMed1985

Effect of apomorphine, alpha-methylparatyrosine, haloperidol and reserpine on DOPA production in clonal cell lines (PC-12 and N1E-115).

The effect of various drugs on DOPA production in the pheochromocytoma clone PC-12 and the neuroblastoma clone N1E-115 was studied. The N1E-115 cells contain only very low amounts of dopamine due to a lack of the aromatic L-amino acid decarboxylase, whereas the PC-12 cells are rich in dopamine. alpha-Methyl-p-tyrosine and apomorphine blocked DOPA production in both cell clones. Reserpine and haloperidol reduced the intracellular dopamine in the PC-12 cells and simultaneously induced a blockade of cellular DOPA production. The released dopamine was primarily recovered as 3,4-dihydroxyphenylacetic acid indicating a release of dopamine into the cytoplasm. This transient increase of cytoplasmic dopamine by reserpine or haloperidol brings about the inhibition of DOPA production in the PC-12 cells. Our results show that the PC-12 clone especially reacts to various drugs like other in vitro systems and may serve as an additional model for studying drug effects on catecholamine biosynthesis and metabolism.

Adrenal Gland Neoplasms↗
PubMed1985

Evaluation of neurotropic drug actions on tyrosine hydroxylase activity and dopamine metabolism in clonal cell lines.

Two clonal cell lines (the pheochromocytoma clone PC-12 and the neuroblastoma clone N1E-115) were used to compare direct and indirect drug effects on tyrosine hydroxylase and dopamine turnover. Both clones contain the cofactor of tyrosine hydroxylase, tetrahydrobiopterin, in sufficient concentrations. 2,4-Diamino-6-hydroxy-pyrimidine (DAO-Pyr), an inhibitor of GTP cyclohydrolase, which is the rate-limiting enzyme in tetrahydrobiopterin biosynthesis, lowers DOPA production indicating that cofactor supply is a limiting factor for catecholamine synthesis. DOPA synthesis in the PC-12 cells can be stimulated by incubation with the natural cofactor tetrahydrobiopterin, but also by its possible precursors sepiapterin and dihydrobiopterin or the analogs methyl-tetrahydropterin and dihydropterin. The regulating enzyme for DOPA synthesis, tyrosine hydroxylase, can be inhibited by certain drugs either directly or indirectly by increasing dopamine concentrations in the cytoplasm after release from its vesicular stores. Using the neuroblastoma clone N1E-115 which lacks DOPA decarboxylase and thus contains only low levels of dopamine the site of action of certain drugs could be determined. Drugs affecting the tyrosine hydroxylase directly (alpha-methyl-para-tyrosine, apomorphine) decreased DOPA production in both clones, while drugs acting via interference with the vesicular stores (reserpine, amphetamine, nigericin) were effective only in the PC-12 cells. After total depletion of dopamine by nigericin at high concentrations or long-term incubation with 3-hydroxybenzyl-hydrazine (NSD 1015), DOPA production increased in the PC-12 cells indicating a usually occurring regulation of tyrosine hydroxylase by cytoplasmic dopamine. Dopamine concentration in the cytoplasm was calculated to be in the range of 1 X 10(-6) mol/l.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1978

Impaired dopamine function and muscular rigidity induced by 6-aminonicotinamide in rats.

In corpus striatum, 6-aminonicotinamide (6-AN), 10 mg/kg i.p. lowered the concentration of dopamine and markedly reduced the disappearance of dopamine after synthesis inhibition with alpha-methyl-p-tyrosine. In the dopamine-rich part of the limbic system, the formation of DOPA after decarboxylase inhibition with 3-hydroxybenzylhydrazine was decreased. In diencephalon, 6-AN altered neither the steady-state level nor the utilization of noradrenaline. The data suggest that the muscular rigidity induced by 6-AN may be associated with disruption of dopaminergic transmission.

6-Aminonicotinamide↗
PubMed1978

Effects of 6-aminonicotinamide on growth and acetylcholinesterase activity during differentiation of neuroblastoma cells in vitro.

Addition of 6-AN (0.01 mg/ml) to growing cultures of C-1300 neuroblastoma cells strongly reduced cell division. This growth inhibition was accompanied by a higher cell volume and a lower protein content per cell as compared to controls. Concurrently the specific activity of AChE increased markedly incontrols and 6-AN-treated cultures. During the experimental periods the specific activity of AChE was significantly higher after 6-AN. Morphologically, 6-AN-treated cultures showed characteristic signs of differentiation, i.e. enlarged, flattened cells with long branched processes. The described effect of 6-AN on growth and differentiation of neuroblastoma cells was less pronounced if cells received the antimetabolite after a subcultivation period of 5 days.

6-Aminonicotinamide↗
PubMed1978

[Clinical study of meproscillarin rates of inactivation and persistence, bioavailability and maintenance dose].

With a rate of inactivation of about 40% and a bioavailability of about 70% corresponding approximately to that of digoxin 14-hydroxy-3beta-[(4-O-methyl-alpha-L-rhamnopyranosyl)oxy]-14beta-bufa-4,20,22-trienolide (meproscillarin, Clift) is--according to our results--a new therapeutic possibility for cardiac decompensated patients, especially in the presence of renal failure. The number of side effects was low. Occasionally diarrhoea occurred which, however, only in a few cases required treatment or discontinuance of therapy.

Aged↗
PubMed1977

Distribution of acridine orange-stained RNA in neuroblastoma cells during differentiation.

Vital staining of neuroblastoma cells with acridine orange produces a bright intracellular red-orange fluorescence most probably due to the occurrence of RNA. The distribution of this fluorescence depends on the state of morphological differentiation. The fluorescence is predominantly found in the perikaryon, the growth cones, and the endings of the processes of differentiated cells. This is of special interest in respect to the biochemistry of differentiation and the function of nerve cells. Comparative autoradiographical studies with 3H-uridine demonstrate that the newly synthesised RNA is transported into the endings of the cell processes.

Acridines↗
PubMed1977

Glucose metabolism in C-1300 neuroblastoma cells after inhibition of hexose monophosphate pathway.

1. Application of 6-AN (0.01 mg/ml) leads to a strong accumulation of 6-PG in C-1300 neuroblastoma cells which, however, only amounts to one third of that found in C-6 glial cells. 2. In C-1300 neuroblastoma cells dephosphorylation of the accumulated 6-PG causes a rise of the intracellular gluconate to eight times the value found for 6-PG. It is four times higher than the gluconate content observed in C-6 glial cells. 3. Although 6-PG is a competitive inhibitor of PGI it causes no reduction of glycolytic flux and ATP content in stationary phase C-1300 neuroblastoma cells in contrast to the strong reduction of glycolytic flux and ATP content observed in C-glial cells. 4. The intracellular Glc-6-P and Fru-6-P content of C-1300 neuroblastoma cells increases by four to five times after treatment with 6-AN. Both this increase and the decrease of Fru-1,6-P2 content point to an inhibition of the phosphofructokinase. 5. In contrast to C-6 glial cells no morphological changes could be observed in C-1300 neuroblastoma cells up to 24 h after administration of 6-AN.

6-Aminonicotinamide↗