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Biomedical subjects

M Naoi

Publications and source records attributed to M Naoi.

At least 109 records · Page 6Linked to original sources
PubMed1994

[Study on the metabolism of droxidopa in humans].

Supplement of the deficient neurotransmitters is one of the most effective therapies for neurodegenerative disorders. For the treatment of Parkinson's disease, L-DOPA therapy has been applied to replace dopamine, and droxidopa (L-threo-3,4-dihydroxyphenylserine) therapy to supply noradrenaline (NA). Droxidopa, an artificial amino acid, is decarboxylated by aromatic L-amino acid decarboxylase (AADC) into NA. By application for Parkinson's disease, it alleviated neurological symptoms such as freezing phenomenon, which are refractory to L-DOPA. However, as a precursor of a monoamine, droxidopa was found to be not so effective as L-DOPA; and the clinical efficiency of droxidopa is variable among patients. The metabolic pathway of droxidopa in the brain was examined using human materials. The intraventricular fluid of patients treated with droxidopa, and of control was analyzed by high-performance liquid chromatography with multi-eletrochemical detection (Neurochem). In the intraventricular fluid of the patients treated, free NA concentration increased to be 5.67 +/- 3.40 nM from non-detectable level in the control patients. The patients with higher free NA levels clinically responded better to droxidopa. However, free NA levels varied among patients; and the mechanism of the individual variance should be clarified. In the intraventricular fluid, in addition to NA, a large amount of a metabolite of droxidopa by catechol-O-methyltransferase (COMT), 3-O-methoxy-droxidopa (3OMD), was detected, followed by the metabolites by DOPS-aldolase (DOPS-ALD), protocatechualdehyde and protocatechuic acid. It indicates that considerable parts of administered droxidopa are catabolized by COMT and DOPS-ALD, but not by AADC.(ABSTRACT TRUNCATED AT 250 WORDS)

Brain↗
PubMed1993

Inhibition of tryptophan hydroxylase by 6,7-dihydroxy-N-cyanomethyl-1,2,3,4-tetrahydroisoquinoline, a cyanomethyl derivative of dopamine formed from cigarette smoke.

6,7-Dihydroxy-N-cyanomethyl-1,2,3,4-tetrahydroisoquinoline, a cyanomethyl derivative of dopamine formed from cigarette smoke, was found to inhibit the activity of tryptophan hydroxylase. The inhibition was non-competitive to the substrate L-tryptophan (the Ki value 7.25 +/- 0.81 microM), but not to the biopterin cofactor. The inhibition is irreversible. 6-Hydroxy-N-cyanomethyl-tetrahydro-beta-carboline, a cyanomethyl derivative of serotonin, is inactive towards the hydroxylase. 6,7-Dihydroxy-N-cyanomethyl-1,2,3,4-tetrahydroisoquinoline may affect the serotonin biosynthesis in vivo as a consequence of cigarette smoking.

Animals↗
PubMed1993

Branched-chain 2-oxo acid dehydrogenase complex activation by tetanic contractions in rat skeletal muscle.

Branched-chain 2-oxo acid dehydrogenase complex in rat skeletal muscle was activated by muscle contractions elicited by electrical stimulation. This activation was attributed to dephosphorylation of the phosphorylated enzyme complex, and the total enzyme activity was not altered by muscle contractions. The activation of the enzyme complex occurred in the muscle of the electrically stimulated leg, but not in the muscle of the non-stimulated (control) leg, indicating that blood components are not involved in the mechanism of the enzyme activation in the muscle. Adenine nucleotides, branched-chain amino and 2-oxo acids and lactate in the muscle were determined as possible factors modulating the enzyme complex activity through inhibition of branched-chain 2-oxo acid dehydrogenase kinase activity. The profile of enzyme activation induced by muscle contractions was different from the alteration of the adenine nucleotide concentrations but was similar to the alteration of the concentrations of branched-chain amino and 2-oxo acids in the muscle. The lactate concentration in the stimulated muscle was elevated 3-5-fold during the contractions, indicating intracellular acidification. Previous studies have shown that the 2-oxo acid derived from leucine is a potent inhibitor of the kinase. These results suggest that intracellular branched-chain 2-oxo acids increased by muscle contractions accumulate in the mitochondria due to exercise-induced acidification of the muscle cell, resulting in activation of branched-chain 2-oxo acid dehydrogenase complex by inhibition of the kinase.

3-Methyl-2-Oxobutanoate Dehydrogenase (Lipoamide)↗
PubMed1993

The effect of a heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1), on tyrosine hydroxylase mRNA in PC12h cells.

The effects of a naturally occurring heterocyclic amine, 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indol (Trp-P-1), on tyrosine hydroxylase (TH) mRNA levels were examined in PC12h cells using Northern blot analysis. Dose-dependency of Trp-P-1 for 24 h incubation gave biphasic results; 0.1 microM Trp-P-1 enhanced and 10 microM Trp-P-1 reduced TH mRNA levels. These effects were faded out in 48 h. One hundred microM Trp-P-1 caused the almost complete abolishment of TH mRNA expression as well as cell death. These results suggest the possibility that lower dose of Trp-P-1 might function as a trophic factor in contrast to neurotoxic effect in higher doses.

Animals↗
PubMed1993

Selective release of serotonin by endogenous alkaloids, 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, (R)- and (S)salsolinol, in the rat striatum; in vivo microdialysis study.

Dopamine-derived 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, (R)- and (S)salsolinol, released an enormous amount of serotonin in the rat striatum; the concentration of serotonin increased from undetectable level to 2.53 +/- 0.12 and 3.69 +/- 0.01 microM after perfusion of (R)- and (S)salsolinol, respectively. Salsolinols increased extracellular dopamine level, but to a much lesser degree than serotonin. Other naturally occurring isoquinolines with catechol structure released serotonin and dopamine, but salsolinols were the most potent and selective releaser of serotonin. Serotonin release by salsolinols may be involved in some psychiatric symptoms in L-DOPA therapy or alcoholism.

Alkaloids↗
PubMed1993

Inhibition of type A and B monoamine oxidase by 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines and their N-methylated derivatives.

6,7-Dihydroxy-1,2,3,4-tetrahydroisoquinoline (norsalsolinol) and 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline (salsolinol), and their N-methylated derivatives were found to inhibit type A and B monoamine oxidase isolated from human brain synaptosomal mitochondria. N-Methyl-norsalsolinol, (R) and (S) enantiomer of salsolinol, and N-methyl-salsolinols inhibited type A monoamine oxidase competitively to the substrate, kynuramine, and R enantiomers were more potent inhibitors than S enantiomers. The inhibition was reversible. Norsalsolinol induced positive cooperativity toward kynuramine. Both norsalsolinol and N-methyl-norsalsolinol inhibited type B oxidase non-competitively to the substrate, and their Ki values were much higher than those to type A. Types of inhibition of type A monoamine oxidase depended on the enzyme sources. Inhibition of monoamine oxidase by 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines is discussed in relation to their chemical structures.

Brain↗
PubMed1993

Simultaneous determination of in vivo hydroxylation of tyrosine and tryptophan in rat striatum by microdialysis-HPLC: relationship between dopamine and serotonin biosynthesis.

Using a microdialysis technique, the rat striatum was perfused with NSD-1015, an inhibitor of aromatic L-amino acid decarboxylase, and the amount of L-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP) accumulating in dialysate was measured as an index of in vivo activities of tyrosine hydroxylase and tryptophan hydroxylase. NSD-1015 increased the concentration of L-DOPA much higher than that of 5-HTP in a dose-related manner (1-100 mumol/L). In order to examine the relationship between dopaminergic and serotonergic neurons in the striatum, either 5-HTP or L-DOPA was injected intraperitoneally to rats pretreated with benserazide, an inhibitor of peripheral decarboxylase. 5-HTP administration increased 5-HTP, but decreased L-DOPA in a dose-dependent manner. Conversely, 5-HTP concentration decreased in an association with the increased content of L-DOPA following L-DOPA administration. The decrease of 5-HTP caused by L-DOPA administration was not as remarkable as that of L-DOPA by 5-HTP injection. These results suggest that L-DOPA and 5-HTP, the precursor amino acids for catecholamines and indoleamines, could affect mutually each other neuronal activity through the inhibition of their rate-limiting enzymes.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Naturally-occurring isoquinolines perturb monamine metabolism in the brain: studied by in vivo microdialysis.

Naturally occurring isoquinolines affected the monoamine metabolism in the rat striatum, as proved by in vivo microdialysis technique. By analysis of monoamines and their metabolites in the dialysate, dopamine-derived 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines were found to inhibit monoamine oxidase and catechol-O-methyltransferase activity. 1-Methyl- and 2-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline were found to inhibit activity of type A monoamine oxidase most markedly. To compare the structure-activity relationship, corresponding isoquinolines without a catechol structure were also examined. The inhibition by catechol isoquinolines was more manifest than those without a catechol structure. Among latter isoquinolines, N-methyl-isoquinolinium ion was the most potent inhibitor of monoamine oxidase. In addition, catechol isoquinolines increased monoamine levels in the brain. The number and the site of the methyl group are essentially required for the inhibition of monoamine oxidase and a catechol structure for that of catechol-O-methyl-transferase. These results are discussed in relation to possible involvement of these isoquinolines to the clinical features of some neuro-psychiatric diseases, such as alcoholism or in L-DOPA therapy.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1993

Changes in monoamine levels in mouse brain elicited by forced-swimming stress, and the protective effect of a new monoamine oxidase inhibitor, RS-8359.

As a stress model, a forced swimming test was applied to mice; and a typical behavioral change, an immobile posture, was recognized. This affected the brain monoamine levels significantly. The norepinephrine concentration was reduced, while that of its product was increased; and in the case of dopamine, both the amount of the amine and its product were increased. Stress increased the levels of serotonin and its product in the brain. The effects of RS-8359, (+/-)-4-(4-cyanophenyl)amino-6,7-dihydro-7-hydroxy-5H-cyclopenta[d ]- pyrimidine, a new inhibitor of type A monoamine oxidase, on the behavioral and biochemical changes caused by forced swimming were also investigated. RS-8359 significantly improved the immobile posture elicited by the forced swimming test. It reduced the increased turnover of norepinephrine and serotonin systems caused by swimming. These results suggest that the effect of RS-8359 on behavioral and biochemical changes by stress may be mainly due to its effects on norepinephrine and serotonin systems, presumably by the inhibition of type A monoamine oxidase.

Animals↗
PubMed1993

Type B monoamine oxidase and neurotoxins.

The biochemical process underlying Parkinson's disease is dopamine cell death of the nigrostriatal system. The age-dependent cell death is now proposed to be elicited by the formation of free hydroxy radicals which are formed from hydrogen peroxide, a product of oxidation of dopamine by monoamine oxidase, especially type B. The potent neurotoxin, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, was found to induce cell death by an energy crisis or oxidative stress in dopamine neurons. Other endogenous mammalian neurotoxins, monoamine-derived 1,2,3,4-tetrahydroisoquinolines and 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, have been proposed as factors accelerating dopamine cell death. N-methylated isoquinolines were found to be oxidized by monoamine oxidase, and hydroxy radicals were found to be produced by this reaction. In addition, by incubation with the N-methylated isoquinolines, ATP was depleted from a dopaminergic cell model, clonal rat pheochromocytoma PC12h cells. ATP depletion could be protected by pretreatment of the cells with monoamine oxidase inhibitors. These results suggest that oxidation of neurotoxic isoquinolines is directly involved in the oxidative stress to induce the cell death of dopamine neurons. On the other hand, 1-methyl-1,2,3,4-tetrahydroisoquinoline and 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinoline were found to inhibit the activity of monoamine oxidase, indicating that they may be neuroprotective agents in the brain. The involvement of monoamine oxidase is discussed in relation to the pathogenesis of Parkinson's disease.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1993

Cytotoxicity of dopamine-derived 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines.

The in vivo effects of dopamine-derived alkaloids, 6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines, salsolinols, and their N-methylated derivatives on a dopaminergic cell model, clonal rat pheochromocytoma PC12h cells, were examined by culture in the presence of various concentrations of the agents. The effects were evaluated in comparison with those by 1,2,3,4-tetrahydroisoquinoline and its N-methylated derivatives. Among 1,2,3,4-tetrahydroisoquinolines, only N-methylisoquinolinium ion had cytotoxic effect on PC12h cells. In general, 6,7-dihydroxyisoquinolines had more potent cytotoxic effect than N-methylisoquinolinium ion, and they reduced protein amounts of PC12h cells at 100 microM and 1 mM concentration. The specific activity of tyrosine hydroxylase, the rate-limiting enzyme in dopamine biosynthesis, decreased with these isoquinolines at concentrations lower than those required to reduce the protein amount. The toxicity of N-methylated derivatives seems to be more potent than non-methylated isoquinolines. Salsolinols were proved to be accumulated in the mitochondrial fraction of the cells after 3 days in culture. N-methyl-1,2,3,4-tetrahydroisoquinoline depleted ATP from PC12h cells and it was prevented by preincubation with an inhibitor of type-A monoamine oxidase, clorgyline. These results indicate that N-methylated and oxidized derivatives of dopamine-derived alkaloids may be potent dopaminergic neurotoxins similar to 1-methyl-4-phenylpyridinium ion in the human brain and may induce Parkinson's disease after long years of accumulation.

Animals↗
PubMed1993

N-methylated tetrahydroisoquinolines as dopaminergic neurotoxins.

N-Methylation of dopamine-derived 6,7-dihydroxyisoquinolines produces compounds whose chemical structures are similar to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). N-Methylation of 1,2,3,4-tetrahydroisoquinoline was proved by in vitro experiments using human brain homogenate as an enzyme source. By in vivo microdialysis in rat brains, N-methylation of 1-methyl-6,7-dihydroxy-1,2,3,4-tetrahydroisoquinolines (salsolinols) was also demonstrated. Among the brain regions examined, the activity of N-methylation was the highest in the substantia nigra. N-methyl-1,2,3,4-tetrahydroisoquinoline was oxidized to produce N-methyl-isoquinolinium ion by type A and type B monoamine oxidase prepared from human brain synaptosomal mitochondria. The structure of the oxidized isoquinoline is similar to that of 1-methyl-4-phenylpyridinium ion, a potent dopaminergic neurotoxin. These results indicate that these isoquinolines produced in or around dopamine neurons are N-methylated especially in substantia nigra and may be further oxidized by monoamine oxidase to produce ions. This biosynthesis pathway is quite similar to the oxidative synthesis of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. N-Methylation and oxidation of isoquinolines or other endogenous compounds may be involved in the pathogenesis of Parkinson's disease.

Animals↗
PubMed1992

Endogenous synthesis of N-methylsalsolinol, an analogue of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, in rat brain during in vivo microdialysis with salsolinol, as demonstrated by gas chromatography-mass spectrometry.

N-Methylsalsolinol, an analogue of 1,2,3,6-tetrahydropyridine, is present in the brains of patients with Parkinson's disease. To determine the metabolic pathway for the synthesis of N-Methylsalsolinol in the brain, salsolinol was perfused through the striatum or the substantia nigra of the rat brain by in vivo microdialysis. N-Methylsalsolinol was detected in the brain dialysate samples during microdialysis with salsolinol using gas chromatography-mass spectrometry with selected-ion monitoring. These results demonstrate that endogenous N-methylation of salsolinol into N-methylsalsolinol occurs in the brain in vivo.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1992

Multiple colorectal carcinomas and colorectal carcinoma associated with extracolonic malignancies.

In this study, we analyzed 149 surgical cases of colorectal cancer between January 1983 and August 1989. Thirteen cases (8.7 percent) of colorectal primary cancer associated with extracolonic primary malignancy of 14 lesions and 10 cases (6.7 percent) of multiple primary colorectal cancers were included. Among the 14 lesions of extracolonic primary malignancy, there were 6 gastric carcinomas, 2 endometrial carcinomas, 2 urinary bladder carcinomas, and one each in the esophagus, liver, bile duct and jejunum. The second tumor was not detected preoperatively in 3 of 4 cases of synchronous multiple primary colorectal carcinoma. A curative resection was done in 10 (77 percent) out of 13 cases of colorectal cancer associated with extracolonic malignancy, while 7 (88 percent) out of 8 cases of multiple colorectal cancers had a curative resection. Nine patients (69 percent) with colorectal cancer associated with extracolonic malignancy were disease-free for 2 months to 14 years. Seven patients (88 percent) with multiple colorectal cancers were disease-free for one to 22 years. We recommend, therefore, that in any patient with colorectal cancer, the entire large bowel should be thoroughly searched for any other primary tumors, by taking the existence of extracolonic tumors into account. A curative resection should be performed, and the follow-up period should be life-long.

Adenocarcinoma↗
PubMed1992

Efficacy of combination treatment--(TAE with adriamycin and ethanol)--for hepatocellular carcinoma.

Among 44 patients with hepatocellular carcinoma (HCC), combination treatment with both transhepatic arterial embolization (TAE) and ethanol injection therapy (EIT) was performed in 10 patients. Only two had tumors measuring less than 3 cm in diameter. In all, eight patients had solitary tumors and two had multiple tumors. The tumor was classified as stage I in one patient, stage II in six subjects, stage III in two patients, and stage IV in one subject prior to TAE, but one stage II case was changed to stage III after laparotomy. The clinical stage was I in two patients, II in six subjects and III in two patients. Five patients with tumors of stages I and II achieved either a complete response (CR) or partial response (PR). However, three patients with tumors of stages III and IV showed progressive disease (PD). Thus, the response rate (CR+PR) was 50%. For tumor stages I and II, the 1-, 2-, and 3-year survival values were 100%, 100%, and 83%, respectively. For tumor stages III and IV, the 1- and 2-year survival values were 75% and 25%, respectively. Combination treatment of HCC appears to be efficacious for tumor stages I and II.

Adult↗
PubMed1992

The mechanism of perturbation in monoamine metabolism by L-dopa therapy: in vivo and in vitro studies.

In the cerebrospinal fluid of the patients with Parkinson's disease treated with L-DOPA, L-3-O-methyldopa was the major metabolite of administered L-DOPA. Using a dopaminergic cell model, clonal rat phenochromocytoma PC 12h cells, and by microdialysis of the rat striatum it was proved that L-3-O-methyldopa was taken up into monoamine neurons by transport system specific for aromatic L-amino acids and inhibited transport of L-DOPA and other amino acids competitively. L-3-O-Methyldopa depleted allosteric regulation of the biopterin cofactor on activity of tyrosine hydroxylase, the rate-limiting enzyme of catecholamine synthesis. Depletion of the allostery may perturb the buffer action of endogenous L-DOPA synthesis that stabilizes dopamine level in the brain. By these mechanisms L-3-O-methyldopa may reduce clinical effectiveness of administered L-DOPA and be involved in wearing-off phenomenon. L-DOPA inhibited the activity of tryptophan hydroxylase and thus serotonin synthesis, which may be related to psychiatric side-effects in the patients under L-DOPA therapy.

Aged↗
PubMed1992

Allosteric effect of tetrahydrobiopterin cofactors on tyrosine hydroxylase activity.

Allostery of tyrosine hydroxylase was found by kinetical studies of partially purified tyrosine hydroxylase from clonal rat pheochromocytoma PC12h cells. Positive cooperativity toward the cofactors, (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin [(6R)BH4] and (6S)-L-erythro-5,6,7,8-tetrahydrobiopterin [(6S)BH4], was observed. It is indicated that biopterin might be the regulatory factor of the enzyme polymers, which changes the affinity for the cofactor itself. Moreover, the stereochemical structure of (6R)BH4, the naturally-occurring cofactor, took an important role on the kinetical properties of the enzyme in concern with L-tyrosine.

Allosteric Regulation↗