Dopamine visualized in the basal ganglia of living man

The neurotransmitter dopamine has biological attributes that make it amenable to study by positron emission tomography, unlike many of the 40 or so neurotransmitters that have been identified in the brain. Dopamine deficiency in the nigrostriatal system is a characteristic of Parkinson's disease, and a disturbance of dopamine metabolism is still widely held to be responsible for the syndrome of schizophrenia. Despite its importance in the regulation of locomotion and mood, it has been impossible to visualize the intracerebral distribution of dopamine and measure its regional metabolism in man. In the first demonstration of the regional distribution of a neurotransmitter in the brain of conscious normal man, we show here that L-3,4-dihydroxyphenylalanine (L-dopa) labelled in the 6-position with the positron-emitting radionuclide fluorine-18, localizes specifically in the dopaminergic pathways of the human brain where its turnover could be measured atraumatically by positron emission tomography.

Mice lacking dopamine D4 receptors are supersensitive to ethanol, cocaine, and methamphetamine

The human dopamine D4 receptor (D4R) has received considerable attention because of its high affinity for the atypical antipsychotic clozapine and the unusually polymorphic nature of its gene. To clarify the in vivo role of the D4R, we produced and analyzed mutant mice (D4R-/-) lacking this protein. Although less active in open field tests, D4R-/- mice outperformed wild-type mice on the rotarod and displayed locomotor supersensitivity to ethanol, cocaine, and methamphetamine. Biochemical analyses revealed that dopamine synthesis and its conversion to DOPAC were elevated in the dorsal striatum from D4R-/- mice. Based on these findings, we propose that the D4R modulates normal, coordinated and drug-stimulated motor behaviors as well as the activity of nigrostriatal dopamine neurons.

Dopamine-, L-DOPA-, adrenaline-, and noradrenaline-induced growth of Au nanoparticles: assays for the detection of neurotransmitters and of tyrosinase activity

The neurotransmitters dopamine (1), L-DOPA (2), adrenaline (3), and noradrenaline (4) mediate the generation and growth of Au nanoparticles (Au-NPs). The plasmon absorbance of the Au-NPs allows the quantitative colorimetric detection of the neurotransmitters. Neurotransmitters 1, 2, and 4 are sensed with a detection limit of 2.5 x 10(-6) M, whereas the detection limit for analyzing 3 corresponds to 2 x 10(-5) M. The neurotransmitter-mediated growth of the Au-NPs is also used to probe the activity of tyrosinase. The later biocatalyst oxidizes tyrosine to L-DOPA that mediates the growth of the Au-NPs. The analysis of tyrosinase activity is important for detecting melanoma cells and Parkinson disease.

Flow injection chemiluminometric determination of epinephrine, norepinephrine, dopamine and L-dopa

A method is proposed for the determination of 0.0500-1.00 microgram ml-1 of epinephrine and L-dopa and 0.100-1.00 micrograms ml-1 of norepinephrine and dopamine by their chemiluminogenic oxidation with potassium permanganate in acidic medium, in the presence of formaldehyde, which greatly improves the sensitivity. Flow injection allows the measurement of 80 solutions per hour. The method was also optimized for a continuous-flow system. Comparative results from numerous organic compounds proved the necessity for electron-donating groups on the benzene ring for sensitive chemiluminescent characteristics.

Cytosolic catechols inhibit alpha-synuclein aggregation and facilitate the formation of intracellular soluble oligomeric intermediates

Aberrant aggregation of alpha-synuclein (alpha-syn) to form fibrils and insoluble aggregates has been implicated in the pathogenic processes of many neurodegenerative diseases. Despite the dramatic effects of dopamine in inhibiting the formation of alpha-syn fibrils by stabilization of oligomeric intermediates in cell-free systems, no studies have examined the effects of intracellular dopamine on alpha-syn aggregation. To study this process and its association with neurodegeneration, intracellular catechol levels were increased to various levels by expressing different forms of tyrosine hydroxylase, in cells induced to form alpha-syn aggregates. The increase in the steady-state dopamine levels inhibited the formation of alpha-syn aggregates and induced the formation of innocuous oligomeric intermediates. Analysis of transgenic mice expressing the disease-associated A53T mutant alpha-syn revealed the presence of oligomeric alpha-syn in nondegenerating dopaminergic neurons that do contain insoluble alpha-syn. These data indicate that intraneuronal dopamine levels can be a major modulator of alpha-syn aggregation and inclusion formation, with important implications on the selective degeneration of these neurons in Parkinson's disease.

Developmental differences in dopamine synthesis inhibition by (+/-)-7-OH-DPAT

Dopamine synthesis modulation by the D2-family agonist (+/-)-7-OH-DPAT was explored in striatum, accumbens, and prefrontal cortex of 10-40 day old rats using the gamma-butyrolactone (GBL) autoreceptor model. GBL produced an age-dependent increase in dopamine synthesis that was inhibited by (+/-) 7-OH-DPAT (0.1-13.5 mg/kg) at all ages and antagonized by eticlopride in the nucleus accumbens and striatum. The ID50 of (+/-) 7-OH-DPAT increased with age, suggesting decreased autoreceptor sensitivity with maturation. In prefrontal cortex, (+/-) 7-OH-DPAT inhibited synthesis between 10-30 days, with no evidence of autoreceptor function at 40 days. Dopamine synthesis was also inhibited with the D3/D2 agonist quinpirole at 15 days of age in vivo and yielded similar results to those obtained with (+/-) 7-OH-DPAT. Finally, under conditions that result in low D2 receptor affinity, D3 specificity was examined in vitro at 15 days with (+/-) 7-OH-DPAT, which produced comparable (yet more potent) effects to those observed in vivo. These findings illustrate D3 autoreceptor-like activity in ascending dopamine regions and provide further support for transient prefrontal cortex autoreceptor-like function that recedes by puberty.

Determination of catecholamines by flow-injection analysis and high-performance liquid chromatography with chemiluminescence detection

A chemiluminescence (CL) detection of catecholamines [norepinephrine (NE), epinephrine (E), dopamine (DA) and L-dopa (LD)] is described for the flow-injection (FI) and high-performance liquid chromatographic (HPLC) determination of these compounds. The detection method is based on the inhibition effect of catecholamines (CAs) on the CL reaction of luminol with iodine in the alkaline medium. The proposed FI method allows the determination of CAs in pharmaceutical preparations for the purpose of drug quality control. The calibration curves show good linearity in the concentration range of: 1.1-20.0 microg l(-1) (NE), 0.5-5.0 microg l(-1) (E), 0.6-9.0 microg l(-1) (DA) and 0.6-10.0 microg l(-1) (LD). The limits of detection (defined as a signal-to-noise ratio of 3) are: 0.34 microg l(-1) (NE), 0.15 microg l(-1) (E) and 0.18 microg l(-1) (DA, LD). The HPLC procedure was successfully applied for the determination of catecholamines (NE, E, DA) in human urine after solid-phase extraction (SPE). In a simple run time CAs can be determined in 20 min. The chromatographic linear ranges are: 5.0-72.0 microg l(-1) (NE), 5.0-48.0 microg l(-1) (E) and 5.0-96.0 microg l(-1) (DA). The limits of detection for three urinary CAs are: 0.71 microg l(-1) (NE), 0.26 microg l(-1) (E) and 0.73 microg l(-1) (DA).

A disposable electrochemical sensor for the rapid determination of levodopa

Levodopa (L-dopa), the biological precursor of catecholamines, is the most widely prescribed drug in the treatment of Parkinson's disease. The present work presents a proposal for the application of a gold screen-printed electrode an electrochemical sensor for monitoring L-dopa in stationary solution and a flow system. Using the electrooxidation of L-dopa at +0.63 V in acetate buffer pH 3.0 on a gold screen-printed electrode it is possible to obtain a linear calibration curve from 9.9 x 10(-5) to 1.2 x 10(-3) mol L(-1) and a detection limit of 6.8 x 10(-5) mol L(-1). Under amperometric conditions (E(app) = 0.8 V; flow rate = 14.1 mL min(-1); pH 3.0), an analytical calibration graph for l-dopa was obtained from 1.0 x 10(-6) mol L(-1) 6.6 x 10(-4) mol L(-1) with a detection limit of 9.9 x 10(-7) mol L(-1). The method was successfully applied to the determination of L-dopa in commercial dosage forms without any pre-treatment.

Brain transplantation of human neural stem cells transduced with tyrosine hydroxylase and GTP cyclohydrolase 1 provides functional improvement in animal models of Parkinson disease

Parkinson disease is a neurodegenerative disease characterized by loss of midbrain dopaminergic neurons resulting in movement disorder. Neural stem cells (NSC) of the CNS have recently aroused a great deal of interest, not only because of their importance in basic research of neural development, but also for their therapeutic potential in neurological disorders. We have recently generated an immortalized human NSC cell line, HB1.F3, via retrovirus-mediated v-myc transfer. This line is capable of self-renewal, is multipotent, and expresses cell specific markers for NSC, ATP-binding cassettes transporter (ABCG2) and nestin. Next, we co-transduced the F3 NSC line with genes encoding tyrosine hydroxylase (TH) and GTP cyclohydrolase 1 (GTPCH1) in order to generate dopamine-producing NSC. The F3.TH.GTPCH human NSC line expresses TH and GTPCH phenotypes as determined by RT-PCR, western blotting and immunocytochemistry, and shows a 800 to 2000-fold increase in production of L-dihydroxyphenyl alanine in HPLC analysis. A marked improvement in amphetamine-induced turning behavior was observed in parkinsonian rats implanted with F3.TH.GTPCH cells, but not in control rats receiving F3 NSC. In the animals showing functional improvement, a large number of TH-positive F3.TH.GTPCH NSC were found at injection sites. These results indicate that human NSC, genetically transduced with TH and GTPCH1 genes, have great potential in clinical utility for cell replacement therapy in patients suffering from Parkinson disease.

Immunocytochemical localization of L-dopa and dopamine in the brain of the chicken (Gallus domesticus)

A light microscopic immunocytochemical study, with antisera against dihydroxyphenylalanine (L-DOPA) and dopamine (DA), revealed the dopaergic and dopaminergic systems in the brain of the chicken (Gallus domesticus). L-DOPA- and DA-immunoreactive (ir) elements are similarly distributed throughout the entire brain. Virtually all regions of the brain contained a dense innervation by L-DOPA- and DA-immunopositive varicose fibers. The neuronal cell bodies immunoreactive for the two monoamines were confined to more restricted regions, the hypothalamus, the midbrain and the brainstem. In the hypothalamus, DA- and L-DOPA-ir neurons were subdivided into a medial periventricular and a lateral group. The medial group starts at the level of the anterior commissure, in the ventral part of the nucleus periventricularis hypothalami, and continues in a more dorsal periventricular position caudally into the dorsal tuberal hypothalamic region. Densely labeled cerebrospinal fluid contacting cells can be observed in the paraventricular organ. The lateral group consists of immunopositive neurons loosely arranged in the lateral hypothalamic area and in the nucleus mamillaris lateralis. Most of the dopaminergic cell groups, identified in the hypothalamus of mammals, could be observed in the chicken, with the exception of the tuberoinfundibular group. The majority of L-DOPA- and DA-ir perikarya is, however, situated in the mesencephalic tegmentum, in the area ventralis of Tsai and in the nucleus tegmenti pedunculo-pontinus, pars compacta, the avian homologues of, respectively, the ventral tegmental area and the substantia nigra of mammals. In the pons, dense groups of cells are found in the locus coeruleus and in the nucleus subcoeruleus ventralis and dorsalis. A few labeled cells appear in and around the nucleus olivaris superior in the most caudal part of the metencephalic tegmentum. In the medulla oblongata, L-DOPA- and DA-ir cells can be seen at the level of the nucleus of the solitary tract and in a ventrolateral complex. A comparison with tyrosine hydroxylase (TH) immunocytochemistry revealed TH-immunopositive neurons greatly outnumbering the cells exhibiting DA and L-DOPA immunoreactivity. These results are discussed in relation to catecholaminergic systems previously reported in avian species and in the mammalian brain.

High-performance liquid chromatography with electrochemical detection for the determination of levodopa, catecholamines and their metabolites in rat brain dialysates

A high-performance liquid chromatographic assay with electrochemical detection is described for the simultaneous determination of levodopa, 3-O-methyldopa, dopamine, dihydroxyphenylacetic acid, homovanillic acid, 3-methoxytyramine, noradrenaline, adrenaline, 3-methoxy-4-hydroxyphenylethylene glycol and 5-hydroxyindoleacetic acid in rat brain dialysates. Samples are obtained in vivo using the microdialysis technique. Microdialysis probes are placed in the brain area to be studied and neurochemicals are collected by perfusion of the probe with modified Ringer's solution. Direct injection of the dialysates allows rapid and reliable results to be obtained.

Phosphate-modified TiO2 nanoparticles for selective detection of dopamine, levodopa, adrenaline, and catechol based on fluorescence quenching

For the first time, an aqueous solution, comprising 6-nm phosphate-modified titanium dioxide (P-TiO2) nanoparticles (NPs) and fluorescein, has been used for sensing dopamine (DA), levodopa (L-DOPA), adrenaline, and catechol. The complexes obtained by means of chelation of surface Ti(IV) ions with an enediol group exhibit strong absorption at 428 nm; thus, they can be designed as efficient quenchers for fluorescein. The fluorescence of a fluorescein solution containing 1.4 mM P-TiO2 NPs at pH 8.0 decreases if the solution comprises DA, L-DOPA, adrenaline, and catechol, but not noradrenaline, ascorbic acid, and salicylic acid. We consider that P-TiO2 NPs have a number of advantages over bare TiO2 NPs, such as ease of preparation, high selectivity, and high stability. By measuring fluorescence quenching, the limits of detection at a signal-to-noise ratio of 3 are calculated as 33.5, 81.8, 20.3, and 92.1 nM for DA, L-DOPA, adrenaline, and catechol, respectively. In contrast, UV-vis absorption reveals the relatively poor sensitivity of these compounds. We have validated the applicability of our method by means of analyses of DA in urine samples. High-performance liquid chromatography in combination with an electrochemical cell has been used to further confirm our results. We believe that this approach has great potential for diagnostic purposes.

Development of electrochemical biosensor based on tyrosinase immobilized in composite biopolymeric film

An electrochemical enzyme electrode for dopa and dopamine was developed via an easy and effective immobilization method. The enzyme tyrosinase was extracted from a plant source Amorphophallus companulatus and immobilized in a novel composite of two biopolymers: agarose and guar gum. This composite matrix-containing enzyme forms a self-adhering layer on the active surface of glassy carbon electrode, making it a selective and sensitive phenol sensor. Dopa and dopamine were determined by the direct reduction of biocatalytically liberated quinone species at -0.18V versus Ag/AgCl (3M KCl). The analytical characteristics of this sensor, including linear range, lower detection limit, pH, and storage stability, are described. It has reusability up to 15 cycles and a shelf life of more than 2 months.

Identification of catecholamines in the immune system by electrospray ionization mass spectrometry

The first evidence that catecholamines might be present in the immune system was provided by capillary electrophoresis combined with electrochemical detection. Here, we present the first structural characterization of the endogenous catecholamines isolated from human peripheral blood mononuclear cells. Dopamine, L-DOPA and norepinephrine were detected and were identified with electrospray ionization mass spectrometry by determination of the protonated molecular species of each catecholamine and their major fragments generated in the electrospray source with a nozzle-skimmer voltage method. This technique, in conjunction with accurate mass measurement, allowed us to identify in an unfractionated sample the content of catecholamines in extracted cells in a quantitative manner, with structure-specific methodology. The data unambiguously confirm our previous tentative findings, and also strengthen the importance of the regulatory function of catecholamines in the immune system and the existence of an autocrine loop, where lymphocytes may down-regulate their own activity.

Flow Injection Determination of levodopa in tablets using a solid-phase reactor containing lead(IV) dioxide immobilized

A flow injection spectrophotometric procedure was developed for determining levodopa in tablets. The determination of this drug was carried out by reacting it with lead(IV) dioxide immobilized in polyester resin packed in a solid-phase reactor and the dopachrome yielded was monitored at 520 nm. The analytical curve for levodopa was linear in the concentration range from 1.0x10(-4) to 1.0x10(-3) mol l(-1) with a detection limit of 8.0x10(-5) mol l(-1). The relative standard deviation (R.S.D.) was 0.2% for a solution containing 4.0x10(-4) mol l(-1) levodopa (n=10), and 90 determinations per hour were obtained.

Effects of wild-type and mutated copper/zinc superoxide dismutase on neuronal survival and L-DOPA-induced toxicity in postnatal midbrain culture

Mutations in the free radical-scavenging enzyme copper/zinc superoxide dismutase (Cu/Zn-SOD) are associated with neuronal death in humans and mice. Here, we examine the effects of human wild-type (WT SOD) and mutant (Gly93 --> Ala; G93A) Cu/Zn-SOD enzyme on the fate of postnatal midbrain neurons. One-week-old cultures from transgenic mice expressing WT SOD enzyme had significantly more midbrain neurons and fewer necrotic and apoptotic neurons than nontransgenic cultures. In contrast, 1-week-old cultures from transgenic G93A mice expressing mutant SOD enzyme had significantly fewer midbrain neurons and more necrotic and apoptotic neurons than nontransgenic cultures. To subject postnatal midbrain neurons to oxidative stress, cultures were incubated with L-DOPA. L-DOPA at 200 microM caused approximately 50% loss of tyrosine hydroxylase (TH)-positive neurons in nontransgenic cultures and even greater loss in transgenic G93A cultures; no alterations were noted in GABA neuron numbers. In contrast, 200 microM L-DOPA did not cause any significant reductions in TH-positive or GABA neuron numbers in transgenic WT SOD cultures. L-DOPA at 50 microM had opposite effects, in that it significantly increased TH-positive, but not GABA neuron numbers in transgenic WT SOD and G93A and in nontransgenic cultures. These results indicate that increased amounts of WT SOD enzyme promote cell survival and protect against L-DOPA-induced dopaminergic neurotoxicity, whereas increased amounts of mutated Cu/Zn-SOD enzyme have inverse effects. As the spontaneous loss and L-DOPA-induced loss of postnatal dopaminergic midbrain neurons appear to be mediated by free radicals, our study supports the view that mutated Cu/Zn-SOD enzyme kills cells by oxidative stress.

Simultaneous determination of levodopa, carbidopa and their metabolites in human plasma and urine samples using LC-EC

In this study levodopa (L-DOPA), carbidopa (C-DOPA) and their metabolites were resolved from other endogenous components present in human plasma and urine and determined quantitatively. The developed technique involved the use of a second pump, a switching valve, and a pre-column in the LC system in order to perform on-line sample clean-up and enrichment. This procedure is dependent on an effective removal of the many interfering matrix components that vitiate HPLC analysis. Several unknown endogenous electroactive compounds, present in plasma, were eliminated by the purification step, or suppressed by the pre-treatment or detection conditions. The analyses were separated on an Octyl-bonded reversed-phase column followed by amperometric detection using a carbon fibre microelectrode flow cell operated at +0.8 V versus silver/silver phosphate reference electrode. The cell was compatible with the mobile and the stationary phase used in the flow system without any complex surface reaction. The peak currents obtained for the different analytes were directly proportional to the analyse over the concentration range 0.02-4.0 microg ml(-1). Using this method, the minimum detectable concentration was estimated to be 5 and 8 ng ml(-1) for L-DOPA and C-DOPA, respectively. Recovery studies performed on human plasma samples ranged from 93.83 to 89.76%, with a relative standard deviation of < 6%. The intra- and inter-assay coefficients of variation were < 7%. The accuracy of the assay, which was defined as the percentage difference between the mean concentration found and the theoretical (true) concentration, was 12% or better. The electrochemical pre-treatment regime described in this work permitted a longer application of the same microelectrode. The method showed a good agreement with other available methods described in the introduction and offers the advantages of being simple, less time and labour consuming, does not require additional solvents for extraction, inexpensive and suitable for routine analysis and kinetic purposes.

Simultaneous determination of levodopa and benserazide by stopped-flow injection analysis and three-way multivariate calibration of kinetic-spectrophotometric data

The simultaneous determination of levodopa and benserazide in pharmaceutical formulations is described, based on the application of multidimensional partial least-squares regression to the kinetic-spectrophotometric data provided by diode-array detection within a stopped-flow injection method where analytes react with periodate. Flow injection parameters were adequately optimized. Accurate analysis is performed with no sample pre-treatment steps, and with minimum experimental effort. Satisfactory recovery results were obtained on a number of synthetic and commercial samples, in the latter case including the comparison with liquid chromatography measurements.

Determination of l-dopa using electropolymerized 3,3′,3″,3‴-tetraaminophthalocyanatonickel(II) film on glassy carbon electrode

Electropolymerized film of 3,3',3'',3'''-tetraaminophthalocyanatonickel(II) (p-Ni(II)TAPc) on glassy carbon (GC) electrode was used for the selective and stable determination of 3,4-dihydroxy-L-phenylalanine (L-dopa) in acetate buffer (pH 4.0) solution. Bare GC electrode fails to determine the concentration of L-dopa accurately in acetate buffer solution due to the cyclization reaction of dopaquinone to cyclodopa in solution. On the other hand, p-Ni(II)TAPc electrode successfully determines the concentration of L-dopa accurately because the cyclization reaction was prevented at this electrode. It was found that the electrochemical reaction of L-dopa at the modified electrode is faster than that at the bare GC electrode. This was confirmed from the higher heterogeneous electron transfer rate constant (k(0)) of L-dopa at p-Ni(II)TAPc electrode (3.35 x 10(-2) cms(-1)) when compared to that at the bare GC electrode (5.18 x 10(-3) cms(-1)). Further, it was found that p-Ni(II)TAPc electrode separates the signals of ascorbic acid (AA) and L-dopa in a mixture with a peak separation of 220 mV. Lowest detection limit of 100 nM was achieved at the modified electrode using amperometric method. Common physiological interferents like uric acid, glucose and urea does not show any interference within the potential window of L-dopa oxidation. The present electrode system was also successfully applied to estimate the concentration of L-dopa in the commercially available tablets.

Flow injection spectrophotometric determination of L-Dopa and carbidopa in pharmaceutical formulations using a crude extract of sweet potato root [Ipomoea batatas (L.) Lam.] as enzymatic source

A flow injection (FI) spectrophotometric method is proposed for the determination of L-dopa and carbidopa in pharmaceutical formulations. After selection of the extraction medium (e.g., buffer-to-tissue ratio, pH, buffer concentration, protective agents and/or stabilizers) and storage conditions, crude extract of sweet potato root [Ipomoea batatas (L.) Lam.] was used as an enzymatic source of polyphenol oxidase (Tyrosinase; catechol oxidase; EC.1.14.18.1) directly in the carrier. This enzyme catalyses the oxidation of these catecholamines to the corresponding dopaquinone. Further, dopaquinone undergoes a rapid spontaneous auto-oxidation to leucodopachrome, which is in turn oxidized to dopachrome; this last compound has a strong absorption at 480 and 360 nm for L-dopa and carbidopa, respectively. For the optimum extraction conditions found the enzyme activity of the crude extract did not vary for at least 5 months when stored at 4 degrees C and decreased by only 4-5% during an 8 h working period at 25 degrees C. The results obtained for L-dopa and carbidopa by the proposed enzymatic FI method were in close agreement with the label values (r1 = 0.9699 and r2 = 0.9999) and also with those obtained using a pharmacopeial method (r3 = 0.9675). The throughput was 26 samples h-1, and 2.30 ml of crude extract were consumed in each determination, corresponding to only 72 mg of the original sweet potato root. The detection limit (three times the signal blank/slope) was 1.5 x 10(-5) and 2.0 x 10(-5) mol l-1 for L-dopa and carbidopa, respectively; the recovery of L-dopa and carbidopa from three samples ranged from 98.6 to 106.3% of the added amount.

Simultaneous measurement of 5-hydroxytryptophan and L-dihydroxyphenylalanine by high-performance liquid chromatography with electrochemical detection. Measurement of serotonin and catecholamine turnover in discrete brain regions

A sensitive method, using reversed-phase high-performance liquid chromatography with electrochemical detection, which allows the measurement of both 5-hydroxytryptophan and L-dihydroxyphenylalanine is described. This method, used in conjunction with the administration in vivo of an L-aromatic amino acid decarboxylase inhibitor, allows the simultaneous measurement of serotonin and catecholamine synthesis rates in small discrete brain regions.

Simple assay procedure for tyrosine hydroxylase activity by high-performance liquid chromatography employing coulometric detection with minimal sample preparation

A simple assay procedure for tyrosine hydroxylase activity in crude tissue samples was devised that requires minimal sample preparation and use of high-performance liquid chromatography with coulometric electrochemical detection. After incubation of enzyme samples, such as human brain homogenates or rat pheochromocytoma PC12h cells, with L-tyrosine and a tetrahydropterin cofactor, in the presence or absence of p-bromobenzyloxyamine, an inhibitor of aromatic L-amino acid decarboxylase, the reaction was terminated by addition of an equal volume of 0.1 M perchloric acid. For quantitation of L-DOPA produced, the sample was centrifuged, filtered and directly applied to the chromatographic apparatus connected to a coulometric electrochemical detector. This method makes redundant a time-consuming step in the previous methods, purification and concentration of L-DOPA or dopamine using alumina. The reaction conditions for the assay of tyrosine hydroxylase activity in brain homogenates and PC12h cells were re-examined by this method. Both tyrosine hydroxylase samples required a naturally occurring cofactor, (6R)-L-erythro-5,6,7,8-tetrahydrobiopterin [(6R)BH4], catalase and NSD-1055 for the full activity, and tyrosine hydroxylase in human brain homogenates required Fe2+ ions for its full activity. (6R)BH4 proved to be a more effective cofactor than a synthetic cofactor, (6RS)-methyl-5,6,7,8-tetrahydropterin, which is commonly used for this assay.

Aromatic L-amino acid decarboxylase deficiency: clinical features, diagnosis, and treatment of a second family

Aromatic L-amino acid decarboxylase deficiency is an inborn error of metabolism that leads to combined serotonin and catecholamine deficiency, first described by Hyland et al in 1990. The clinical features, biochemical findings, and treatment of the second family with this condition are reported. Our male patient presented with developmental delay, extreme hypotonia, oculogyric crises, and irritability. The diagnosis of this inborn error of biogenic amine metabolism was accomplished by determining low concentrations of homovanillic, 5-hydroxyindoleacetic acid, and 3-methoxy-4-hydroxyphenyl-ethyleneglycol in cerebrospinal fluid with normal biopterin metabolism and increased L-dopa, in plasma, cerebrospinal fluid, and urine. Greatly reduced activity of aromatic L-amino acid decarboxylase in plasma confirmed this diagnosis. Combined treatment with pyridoxine, tranylcypromine, and bromocriptine produced some clinical improvement.