Dihydroxyphenylacetate Research Articles

The Effect of Acute Hypoxia with Hypercapnia on the Monoamine Content in Symmetrical Brain Areas of Albino Mice

Changes in the activity of monoaminergic systems of the left and right hemispheres of the brain were investigated in male albino mice after acute hypoxia with hypercapnia. The concentrations of dopamine (DA), serotonin (5-HT) and their metabolites dihydroxyphenylacetic (DOPAC), homovanillic (HVA), and 5-hydroxyindoleacetic (5-HIAA) acids were measured by HPLC in the brain cortex, hippocampus, and striatum of the right and the left hemispheres. In the control mice (which were not exposed to hypoxia with hypercapnia), a higher concentration of DA in the left cortex was detected. No asymmetry in the content of other substances was identified in the investigated structures. Acute hypoxia with hypercapnia led to the right-sided increase of DA and 5-HT levels and to the left-sided reduction DOPAC in the cerebral cortex. Under the condition of hypoxia with hypercapnia, the left-sided increase of the DA content was detected in the hippocampus. In the striatum the contents of monoamines and their metabolites were insignificantly changed. It has been concluded that acute hypoxia with hypercapnia causes asymmetric changes in monoaminergic systems of the archicortex and the neocortex.

The effect of acute hypoxia with hypercapnia on the content of monoamines in symmetrical areas of the brain in albino mice

Changes in the activity of monoaminergic systems of the left and right hemispheres of the brain after acute hypoxia with hypercapnia were investigated in male albino mice. The concentrations of dopamine (DA), serotonin (5-HT) and their metabolites dihydroxyphenylacetic (DOPAC), homovanilic (HVA) and 5-hydroxyindolacetic (5-HIAA) acids were measured by HPLC in the brain cortex, hippocampus and striatum of the right and the left hemispheres. In the control mice not exposed to hypoxia with hypercapnia, a higher concentration of DA in the left cortex was detected. No asymmetry in the content of other substances has been identified in the investigated structures. Acute hypoxia with hypercapnia led to the right-sided increase of DA and 5-HT levels and to the left-sided reduction DOPAC in the cerebral cortex. Under the condition of hypoxia with hypercapnia, in the hippocampus, the left-sided increase of the DA content was revealed. In the striatum the contents of monoamines and their metabolites were insignificantly changed. It has been concluded that acute hypoxia with hypercapnia causes asymmetric changes in monoaminergic systems of the archicortex and the neocortex.

The effects of sapropterin on urinary monoamine metabolites in phenylketonuria

BackgroundSapropterin dihydrochloride (BH4, tetrahydrobiopterin) can lower plasma phenylalanine (Phe) concentrations for a subset of patients with phenylketonuria (PKU), an inborn error of metabolism. Studies suggest that monoamine neurotransmitter concentrations are low in PKU patients. Sapropterin functions as a cofactor for hydroxylases specific to Phe, tyrosine, and tryptophan metabolism, pathways essential for catecholamine and serotonin synthesis. ObjectiveThe objective of this study is to determine the impact of sapropterin on monoamine neurotransmitter status in patients with PKU. Design58 PKU subjects were provided 20mg/kg of sapropterin for 1month. Those who responded with at least a 15% decrease in plasma Phe received sapropterin for 1year, while Non-responders discontinued it. After an additional 3months, Responders who demonstrated increased Phe tolerance and decreased medical food dependence were classified as Definitive, whereas Responders unable to liberalize their diet without compromising plasma Phe control were identified as Provisional. At study visits, patients provided blood for plasma amino acids, 3-day diet records, and 12-hour urine samples analyzed for epinephrine (E), dopamine (DA), dihydroxyphenylacetate (DOPAC), homovanillic acid (HVA), 3-methoxytyramine (3MT), serotonin (5HT), and 5-hydroxyindole acetic acid (5HIAA) using HPLC with electrochemical detection. ResultsCompared with healthy non-PKU controls, subjects with PKU had significantly lower baseline concentrations of DA, HVA, 3MT, 5HT, and 5HIAA (p<0.001 for all). Medical food protein intake had a direct association with DA, HVA, 5HT, and 5HIAA during the study (p<0.05 for all), while plasma Phe had an inverse association with these markers (p<0.01 for all). DOPAC was also associated with plasma Phe throughout the year (p=0.035), although not at baseline. Patients with PKU had a significant increase in HVA (p=0.015) after 1month of sapropterin. When stratifying by Responder and Non-Responder status, significance of HVA increase in Non-responders (p=0.041) was confirmed, but not in Responders (p=0.081). A declining trend in urinary 5HIAA, significant only after controlling for plasma Phe (p=0.019), occurred for Definitive Responders during the 1-year study. ConclusionUrinary monoamine concentrations are low in patients with PKU and are influenced by oral sapropterin and medical food intake, highlighting the importance of these therapies to neurotransmitter metabolism in phenylketonuria.

Nitric oxide and DOPAC-induced cell death: From GSH depletion to mitochondrial energy crisis

The molecular mechanisms inherent to cell death associated with Parkinson's disease are not clearly understood. Diverse pathways, sequence of events and models have been explored in several studies. Recently, we have proposed an integrative mechanism, encompassing the interaction of nitric oxide (NO) and a major dopamine metabolite, dihydroxyphenylacetic (DOPAC), leading to a synergistic mitochondrial dysfunction and cell death that may be operative in PD. In this study, we have studied the sequence of events underlying the mechanisms of cell death in PC12 cells exposed to NO and DOPAC in terms of: a) free radical production; b) modulation by glutathione (GSH); c) energetic status and d) outer membrane mitochondria permeability. Using Electron Paramagnetic Resonance (EPR) it is shown the early production of oxygen free radicals followed by a depletion of GSH reflected by an increase of GSSG/GSH ratio in the cells treated with the mixture of NO/DOPAC, as compared with the cells individually exposed to each of the stimulus. Glutathione ethyl ester (GSH-EE) and N-acetylcysteine (NAC) may rescue cells from death, increasing GSH content and preventing ATP loss in cells treated with the mixture DOPAC/NO but failed to exert similar effects in the cells challenged only with NO. The depletion of GSH is accompanied by a decreased activity of mitochondrial complex I. At a later stage, the concerted action of DOPAC and NO include a rise in the ratio Bax/Bcl-2, an observation not evident when cells were exposed only to NO. The results support a free radical-induced pathway leading to cell death involving the concerted action of DOPAC and NO and the critical role of GSH in maintaining a functional mitochondria.

Estudio Electroquímico del Ácido 3,4-Dihidroxifenilacético (DOPAC) Adsorbido sobre Oro

The objective of this study was to obtain knowledge on the behavior of acid 3,4 dihydroxyphenylacetic (DOPAC) as an adsorbate and electrochemical reagent adsorbed on gold. The redox reaction characteristic of the catechol ring allows the study of the substance adsorption under open circuit conditions. The step of the procedure include adsorption, rinsing with electrolyte, and making cyclic voltammetric scan to determine the amount of adsorbed substance and its electrochemical behavior. For this, two cells were employed, one for adsorption, and the other electrochemical, both were thermostatted at 25°C. The DOPAC adsorption is weak. The adsorption bound is strengthening with the time forming a σ bound. The area per molecule of 47 A 2 , very near of that of the dopamine is

Changes in the striatal extracellular levels of dopamine and dihydroxyphenylacetic acid evoked by ammonia and N-methyl- d-aspartate: modulation by taurine

Acute hyperammonemia is associated with motor disturbances that are thought to involve striatal dopaminergic dysfunction. Discharge of striatal dopaminergic neurons is controlled by N-methyl- d-aspartate (NMDA) receptors, the excessive activation of which contributes to ammonia neurotoxicity. Here we show that ammonium chloride (‘ammonia’, extracellular concentration 5 mM) or NMDA (1 mM), when directly administered to the rat striatum via a microdialysis probe, evoke a prompt accumulation of dopamine (DA) in the microdialysates. However, while ammonia increases, NMDA decreases, the extracellular dihydroxyphenylacetate (DOPAC) level. The results point to the NMDA receptor-mediated enhancement of DA release and increased DA metabolism as two independent ways by which ammonia affects the striatal dopaminergic system. Taurine (extracellular concentration 10 mM) attenuated the NMDA- and ammonia-evoked DA release and ammonia-induced accumulation of DOPAC, reflecting two different neuroprotective mechanisms of this amino acid.

Catechol- O-methyltransferase inhibition protects against 3,4-dihydroxyphenylalanine (DOPA) toxicity in primary mesencephalic cultures: new insights into levodopa toxicity

Inhibition of catechol- O-methyltransferase (COMT) has protective effects on levodopa ( l-DOPA), but not d-DOPA toxicity towards dopamine (DA) neurons in rat primary mesencephalic cultures [Mol. Pharmacol. 57 (2000) 589]. Here, we extend our recent studies to elucidate the mechanisms of these protective effects. Thus, we investigated the effects of all main l-DOPA/DA metabolites on survival of tyrosine hydroxylase immunoreactive (THir) neurons in primary rat mesencephalic cultures. 3- O-Methyldopa, homovanillic acid, dihydroxyphenyl acetate and 3-methoxytyramine had no effects at concentrations up to 300 μM after 24 h, whereas DA was more toxic than l-DOPA with toxicity at concentrations of ≥1 μM. The coenzyme of COMT, S-adenosyl- l-methionine (SAM), and its demethylated product S-adenosylhomocystein caused no relevant alteration of THir neuron survival or l-DOPA toxicity. In contrast, inhibition of SAM synthesis by selenomethionine showed time- and dose-dependent increase of THir neuron survival, but did not affect l-DOPA toxicity. l-DOPA-induced lipid peroxidation in mesencephalic cultures was not modified by the COMT inhibitor Ro 41-0960 (1 μM). Increased contamination of the cultures with glial cells attenuated l- and d-DOPA toxicity, but caused significant enhancement of protection by COMT inhibitors against l-DOPA toxicity only. Investigations of l-DOPA uptake in rat striatal cultures using HPLC revealed a significant reduction of extracellular l-DOPA concentrations by Ro 41-0960. Our data confirm that l-DOPA toxicity towards DA neurons is mediated by an autooxidative process, which is attenuated by glial cells. In addition, we demonstrate a second mechanism of l-DOPA toxicity in vitro mediated by a COMT- and glia-dependent pathway, which is blocked by COMT inhibitors, most likely due to enhanced glial uptake of l-DOPA.

Mediation of ionotropic glutamate receptors in domoic acid-induced striatal dopamine release in rats

Our objective was to characterize the mechanism of action of intrastriatal infusion of domoic acid on extracellular dopamine levels, using in vivo dialysis in conscious and freely moving rats. The local infusion of domoic acid (500 μM) caused an increase (567.9±142.5%, versus basal) in dopamine extracellular levels associated with a decrease in its metabolites: dihydroxyphenylacetate (DOPAC) and homovanillate (HVA) (47.3±4.4% and 33.8±4.2%, respectively, compared to basal). Infusion of the amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate (AMPA/kainate) receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione (DNQX; 200 μM) reversed the effect of domoic acid infusion on striatal dopamine levels. However, the infusion of the selective non-competitive N-methyl- d-aspartate (NMDA) receptor antagonist, dizocilpine (MK-801; 50 μM), did not change significantly the effect of domoic acid on dopamine extracellular levels. In conclusion, based on results with a microdialysis technique, we suggest that domoic acid may act through AMPA/kainate receptors in striatum.

Aromatic L-amino acid decarboxylase: conformational change in the flexible region around Arg334 is required during the transaldimination process.

Aromatic L-amino acid decarboxylase (AADC) catalytic mechanism has been proposed to proceed through two consecutive intermediates (i.e., Michaelis complex and the external aldimine). Limited proteolysis of AADC that preferentially digested at the C-terminal side of Arg334 was slightly retarded in the presence of dihydroxyphenyl acetate that formed a stable Michaelis complex. On the contrary, AADC was scarcely digested in the presence of L-dopa methyl ester that formed a stable external aldimine. Similar protection by the substrate analogs was observed in the chemical modification experiment. From these results, we concluded that the region around Arg334 must be exposed and flexible in the unliganded state, and forming the Michaelis complex generated a subtle conformational change, then underwent marked conformational change during the subsequent transaldimination process prerequisite to forming the external aldimine. For further analyses, we constructed a mutant gene encoding in tandem the two peptides of AADC cleaved at the Asn327-Met328 bond inside the putative flexible region. The gene product, fragmentary AADC, was still active with L-dopa as substrate, but its k(cat) value was decreased 57-fold, and the Km value was increased 9-fold compared with those of the wild-type AADC. The absorption spectra of the fragmentary AADC in the presence of L-dopa methyl ester showed shift in the equilibrium of the transaldimination from the external aldimine to the Michaelis complex. Tryptic digestion of the fragmentary AADC removed seven amino acid residues, Met328-Arg334, and resulted in complete inactivation. Susceptibility of the fragmentary enzyme to trypsin was not changed by L-dopa methyl ester revealing the loss of appropriate conformational change in the flexible region induced by substrate binding. From these results we propose that the conformational change in the flexible region is required during the transaldimination process.

Systemic phencyclidine administration is associated with increased dopamine, GABA, and 5-HIAA levels in the dorsolateral striatum of conscious rats: an in vivo microdialysis study.

In vivo microdialysis was used to study the effects of systemically administered phencyclidine (PCP, 10 mg/kg) on the extracellular levels of dopamine, dihydroxyphenylacetate (DOPAC), homovanillate (HVA), 5-hydroxy-indolacetate (5-HIAA), gamma-aminobutyrate (GABA), glutamate, and aspartate in the rat dorsolateral striatum. In order to demarcate the effects of anesthesia, tissue trauma and gliosis, the effect of PCP was studied in both anesthetized rats with long and short probe implantation periods and in conscious rats with a long probe implantation period. PCP significantly increased the extracellular levels of dopamine in all experimental groups, though the post-implantation interval and anesthesia modulated the degree of increase. PCP increased 5-HIAA levels in both conscious and anesthetized rats after a long post-implantation period and HVA only in anesthetized rats after a long post-implantation period. Glutamate, aspartate, and DOPAC were not affected by PCP challenge but our study indicated for the first time that systemic PCP elevates extracellular GABA in conscious rats.

Decreased cortical octopamine level in basal forebrain lesioned rats: A microdialysis study

Ibotenic acid-induced lesion of the basal forebrain resulted after 13 days in a 90% reduction of octopamine (OA) in the frontoparietal cortex of adult rats, whereas dihydroxyphenylacetic (DOPAC), homovanillic (HVA) and 5-hydroxyindolacetic (5-HIAA) acids were not modified as measured by microdialysis and high-performance liquid chromatography (HPLC) with electrochemical detection. At this time, cortical choline acetyltransferase (ChAT) activity was decreased by 34%. The results are discussed with respect to possible octopamine involvement in reduced age-associated performance in neurodegenerative processes.

Altered precursor availability and metabolism of monoamines in the brain caused by the injection of physiologic saline to suckling rats: On the reliability of saline “controls” in neurochemical studies

The effect of subcutaneous injections of saline (0.9% NaCl, 10–40 μl/g b. wt) to 5- and 20-day old rats on the concentrations of tyrosine (Tyr) and tryptophan (Trp) in the serum and the brain and on the levels of biogenic amines and their metabolites in the developing brain at 6 h p.i. is described. At day 5 the concentration of Tyr in the blood was decreased (dose-dependent), but the brain concentrations of Tyr and of its amine-metabolites, dopamine (DA), norepinephrine (NE), homovanillic acid (HVA) and dihydroxyphenylacetate (DOPAC) were unaffected. In contrast, in the 20-day old rat, serum Tyr was unaffected by the saline injections, but the Tyr concentration in the brain decreased markedly at the highest saline dose. The concentrations of NE (only at maximum dose) and of DA (independent on the amount of saline injected) were elevated in the brains of saline injected 20-day old rats. The concentrations of Trp and indoles were more affected at day 5 than at day 20: slightly decreased concentration of Trp in the serum but markedly increased concentrations of brain Trp (only at maximum dose), elevated serotonin (5-HT, independent on the amount of saline injected) and 5-hydroxyindoleacetic acid (5-HIAA, at maximum dose) in the brain. If the maximum dose of 40 μl/g body weight was injected to suckling rats repeatedly during the whole suckling period (in 12 h intervals), some effects caused by one single injection of 40 μl/g disappeared (Tyr—depletion in blood or brain, increase in brain NE, DA and Trp), but other additional effects appeared (decreased DA and increased DOPAC, decreased 5-HT and 5-HIAA). The results show that saline injections do cause characteristic, age-dependent alterations of precursor availability as well as of the rate of synthesis and degradation of catecholamine and 5-HT. Repeated treatments have different effects than one single treatment on the precursor availability and the metabolism of monoamines. These alterations must be taken into account if the effects of certain “specific” treatments are compared and discussed in relation to saline “controls”.

Biochemical and behavioral evaluation of pergolide as a dopamine agonist in the rat brain

The ergot derivative pergolide was evaluated as a dopamine agonist using various behavioral and biochemical analyses. Spontaneous motor activity was decreased by small doses (O.1 mg/kg) of pergolide and increased with larger doses (above 0.5 mg/kg). Hypermotility after larger doses persisted for as long as 24 hr and was succeeded by a period of hypomotility. The doses of drug, sufficient to produce hypermotility, also produced stereotypy. With repeated daily injections (2 weeks), the period of hypermotility decreased and the ensuing period of hypomotility increased. Stereotyped behavior was similarly affected. Chronic administration of pergolide did not alter the magnitude of the behavioral responses. Levels of the dopamine (DA) metabolites, dihydroxyphenylacetate (DOPAC) and homovanillic acid (HVA), in the striatum and mesolimbic regions were decreased during the periods of hypermotility but returned to control levels during subsequent hypomotility. Activation of putative inhibitory presynaptic dopamine receptors by pergolide was studied by following accumulation of DOPA in rats treated with the dopamine neuron inhibiting agent, gamma-butyrolactone (GBL) and a DOPA-decarboxylase inhibitor. Pergolide significantly inhibited both striatal and mesolimbic accumulation of DOPA. In contrast, with changes in behavioral and metabolic indices, pergolideinduced inhibition of tyrosine hydroxylase was not affected by chronic treatment with pergolide. On the basis of both behavioral and biochemical data it is proposed that pergolide acts as a dopamine agonist with particularly long-lasting effects.

Combined administration of direct dopamine receptor agonists and l-dopa does not interfere with utilization of exogenous l-dopa in rat corpus striatum

1. 1. The effect of combined administration of L-dopa with apomorphine or with bromocriptine on rat striatal concentrations of dopamine (DA), dihydroxyphenylacetic (DOPAC) and dopa was investigated. 2. 2. Injections of apomorphine or bromocriptine alone decreased striatal DOPAC levels indicating suppression of DA turnover in nigrostriatal terminals. 3. 3. The dopa-induced elevations in striatal concentrations of DA, DOPAC and dopa were similar among animals injected with L-dopa alone or in combination with apomorphine or bromocriptine. 4. 4. These findings suggest that although direct DA receptor agonists decrease striatal DA turnover, they do not interfere with utilization of exogenous L-dopa in striatum.