Dopamine Conjugate Research Articles

Dopamine-induced oxidative stress in neurons with glutathione deficit: implication for schizophrenia

Glutathione (GSH) is the main non-protein antioxidant and plays a critical role in protecting cells from damage by reactive oxygen species (ROS) generated by dopamine (DA) metabolism. We reported a decrease of GSH levels ([GSH]) in CSF and in prefrontal cortex in vivo in schizophrenics [Eur. J. Neurosci. 12 (2000) 3721]. A GSH deficit may lead to membrane peroxidation and microlesions around dopaminergic terminals, resulting in loss of connectivity. To test this hypothesis, we studied the effect of DA in cultured cortical neurons with low [GSH]. DA alone decreased [GSH] by 40%. This effect appears to result from direct conjugation of DA semiquinone/quinone with GSH. Ethacrynic acid (EA) decreased [GSH] in a concentration-dependent manner. When added to EA, DA further lowers [GSH]. As this additional decrease is blocked by superoxide dismutase (SOD) or D 1/D 2 receptor antagonists, it likely involves the generation of superoxide via activation of DA receptors. It also reduces the mitochondrial membrane potential. Most interestingly, a significant decrease in number of neuronal processes (spines analogous) was induced by 24-h application of DA only in low [GSH]. These data, compatible with our hypothesis, is consistent with the dendritic spines reduction reported in schizophrenia and could be related to abnormalities in synaptic connectivity.

5-s-Cysteinyl-conjugates of catecholamines induce cell damage, extensive DNA base modification and increases in caspase-3 activity in neurons.

A decrease in reduced glutathione levels in dopamine containing nigral cells in Parkinson's disease may result from the formation of cysteinyl-adducts of catecholamines, which in turn exert toxicity on nigral cells. We show that exposure of neurons (CSM 14.1) to 5-S-cysteinyl conjugates of dopamine, L-DOPA, DOPAC or DHMA causes neuronal damage, increases in oxidative DNA base modification and an elevation of caspase-3 activity in cells. Damage to neurons was apparent 12-48 h of post-exposure and there were increases in caspase-3 activity in neurons after 6 h. These changes were paralleled by large increases in pyrimidine and purine base oxidation products, such as 8-OH-guanine suggesting that 5-S-cysteinyl conjugates of catecholamines are capable of diffusing into cells and stimulating the formation of reactive oxygen species (ROS), which may then lead to a mechanism of cell damage involving caspase-3. Indeed, intracellular ROS were observed to rise sharply on exposure to the conjugates. These results suggest one mechanism by which oxidative stress may occur in the substantia nigra in Parkinson's disease.

Electron paramagnetic resonance study on free radical scavenging and/or generating activity of dopamine-4-O-sulfate.

The free radical scavenging and/or generating activity of dopamine-4-O-sulfate was examined and compared with that of dopamine. In humans, dopamine mostly exists in two isomeric forms of sulfate ester conjugates as metabolites; i.e., dopamine-3-O-sulfate and dopamine-4-O-sulfate in the circulation. Dopamine is generally believed to be oxidized by molecular oxygen or another reactive oxygen species under physiological conditions, to form oxidized dopamine derivatives that are cytotoxic. However, it is not known whether dopamine conjugates are generated on interaction with reactive oxygen species or not. In the present study, we measured the susceptibility to oxidization of dopamine-4-O-sulfate by using electron paramagnetic resonance (EPR) spectroscopy and optical absorption spectrometry. Dopamine was easily oxidized and dopamine-derived radicals appeared, whereas dopamine-4-O-sulfate was not oxidized under physiological conditions. Furthermore, dopamine-4-O-sulfate did not react with a strong oxidizing agent, sodium periodate. These results suggest that dopamine-4-O-sulfate has resistance against autoxidation, and seems to be a stable metabolite of dopamine.

Glutathione Transferase M2-2 Catalyzes Conjugation of Dopamine and Dopa o-Quinones

Human glutathione transferase M2-2 prevents the formation of neurotoxic aminochrome and dopachrome by catalyzing the conjugation of dopamine and dopa o-quinone with glutathione. NMR analysis of dopamine and dopa o-quinone-glutathione conjugates revealed that the addition of glutathione was at C-5 to form 5-S-glutathionyl-dopamine and 5-S-glutathionyl-dopa, respectively. Both conjugates were found to be resistant to oxidation by biological oxidizing agents such as O2, H2O2, and O•−2, and the glutathione transferase-catalyzed reaction can therefore serve a neuroprotective antioxidant function.

Iron- and manganese-catalyzed autoxidation of dopamine in the presence of L-cysteine: possible insights into iron- and manganese-mediated dopaminergic neurotoxicity.

Iron(II/III) and manganese(II) both catalyze the autoxidation of the neurotransmitter dopamine (DA) in the presence of L-cysteine (CySH) in buffered aqueous solution at pH 7.4. Fe2+/Fe3+ and CySH together generate the hydroxyl (HO.) and cysteinyl thiyl (CyS.) radicals. DA is oxidized by HO. to DA semiquinone radical species that either react with CyS. to give 5-S-cysteinyldopamine (5-S-CyS-DA), 2-S-CyS-DA, and 6-S-CyS-DA or disproportionate to DA-o-quinone that reacts with CySH to give the same cysteinyl conjugates of DA. The major product of this initial reaction is 5-S-CyS-DA. However, 5-S-CyS-DA can be further oxidized by HO. to an o-quinone (2) that undergoes intramolecular cyclization to an o-quinone imine (3). The latter intermediate is the precursor of the dihydrobenzothiazine (DHBT) 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1, 4-benzothiazine-3-carboxylic acid (DHBT-1) and several other cyclized products. However, cysteinyl conjugates of DA can also be oxidized by HO. in a one-electron abstraction reaction that leads to DA thiyl radicals. Reactions of these radicals with CyS. or DA semiquinone radicals lead to some novel DA disulfides and thioethers, respectively. The Mn(II)-catalyzed oxidation of DA generates DA-o-quinone that is scavenged by CySH to give 5-S-CyS-DA (major initial product) with lower yields of other cysteinyldopamines. Subsequent Mn(II)-catalyzed oxidation of 5-S-CyS-DA gives o-quinone 2 and thence o-quinone imine 3 that serve as the precursors of DHBT-1 and several other DHBTs. Organic or oxygen radicals do not play significant roles in the Mn(II)-catalyzed oxidation of DA in the presence of CySH. Recent studies have demonstrated that DHBT-1 can be accumulated by brain mitochondria and evoke irreversible inhibition of NADH-coenzyme Q reductase (complex I). Furthermore, iron, manganese, and alterations in glutathione and CySH metabolism have been implicated in the selective degeneration of nigrostriatal dopaminergic neurons in idiopathic and chemically induced Parkinson's disease (PD). Because DHBT-1 is formed in both the iron- and manganese-catalyzed oxidation of DA in the presence of CySH and a defect in mitochondrial complex I respiration contributes to dopaminergic neuronal cell death in PD, the results of this investigation are discussed in terms of their possible implications to an understanding of the neuropathological processes in idiopathic and chemically induced parkinsonism.

Optimization of the hydrolysis of conjugated L-DOPA, dopamine and dihydroxyphenylacetic acid in human urine for assay by high-performance liquid chromatography with electrochemical detection.

Conjugates of the catechol compounds, L-dihydroxyphenylalanine (L-DOPA), dopamine and dihydroxyphenylacetic acid in human urine were analysed using the isocratic ion-pair reversed-phase HPLC method with electrochemical detection. Acid hydrolysis, using 4 mol/l HCl for 60 min, was more effective than treatment with sulphatase for the generation of free catechols. Free (non-conjugated) catechols already present, as well as those produced by either of the hydrolysis procedures, were adsorbed onto aluminium oxide and extracted in acid solution. The repeatability of the technique for within and between-batch urine analysis was less than 2% and 8%, respectively. Free urinary dopamine (and dihydroxyphenylacetic acid) concentrations were much higher in the urine of patients treated with L-DOPA for Parkinson's disease than in healthy volunteers. At high dopamine (and dihydroxyphenylacetic acid) levels the conjugation capacity was apparently exceeded, since the overall percent conjugation of L-DOPA, dopamine and dihydroxyphenylacetic acid was decreased "concentration dependently" where the concentrations of free catechols were increased. Both in the control group and L-DOPA-treated groups, enzymatic hydrolysis was much less effective than acid hydrolysis in generating free catechols. This indicated that there were other, non-sulphated conjugates in the urine, accounting for between 66 and 100% of total conjugates.

Redox cycling activity of monoamine-serotonin binding protein conjugates

It has been shown recently that the covalent binding of labelled dopamine and serotonin to serotonin binding proteins (SBP) from bovine frontal cortex is potently inhibited by their related neurotoxins. The present study reveals that the monoamine-SBP conjugates of serotonin, dopamine, and related toxins are able to catalyse redox cycling reactions. Using an improved method to detect quinoproteins in SDS-PAGE gels, we were also able to demonstrate that the redox cycling activity corresponded to two major protein components with molecular weights of 45 and 56 kDa. The covalent monoamine-SBP conjugates may be referred to as “artificial quinoproteins.”

Synthesis, redox properties, in vivo formation, and neurobehavioral effects of N-acetylcysteinyl conjugates of dopamine: possible metabolites of relevance to Parkinson's disease.

A very early event in the pathogenesis of idiopathic Parkinson's disease (PD) has been proposed to be an elevated translocation of L-cysteine (CySH) and/or glutathione (GSH) into pigmented dopaminergic cell bodies in the substantia nigra (SN) in which cytoplasmic dopamine (DA) is normally autoxidized to DA-o-quinone as the first step in a reaction leading to black neuromelanin polymer. Such an elevated influx of CySH and GSH would be expected to initially result in formation of 5-S-cysteinyldopamine (5-S-CyS-DA) and 5-S-glutathionyldopamine (5-S-Glu-DA), respectively, and might account for the massive irreversible loss of GSH and progressive depigmentation of SN cells that occurs in the Parkinsonian brain. However, 5-S-Glu-DA has not been detected in the Parkinsonian brain. Furthermore, although the 5-S-CyS-DA/DA and 5-S-CyS-DA/homovanillic acid concentration ratios increase significantly in the SN and cerebrospinal fluid, respectively, of PD patients, the absolute concentrations of 5-S-CyS-DA are extremely low and similar to those measured in age-matched control patients. One explanation for these observations is that 5-S-CyS-DA might be intraneuronally oxidized to more complex cysteinyldopamines and a number of dihydrobenzothiazines (DHBTs) and benzothiazines (BTs). Similarly, 5-S-Glu-DA might be intraneuronally oxidized to more complex glutathionyldopamines. In this investigation, however, it is demonstrated that 5-S-Glu-DA is rapidly metabolized in rat brain to 5-S-CyS-DA and 5-S-(N-acetylcysteinyl) dopamine (5) in reactions mediated by gamma-glutamyl transpeptidase (gamma-GT) and cysteine conjugate N-acetyltransferase. Similarly, 5-S-CyS-DA is metabolized to 5 in rat brain although more slowly than 5-S-Glu-DA. These reactions occur most rapidly in the midbrain, a region that contains the SN. Furthermore, 5, 2-S-(N-acetylcysteinyl)dopamine (6) and 2,5-di-S-(N-acetylcysteinyl)-dopamine (9) are toxic when administered into mouse brain having LD50 values of 14, 25, and 42 micrograms, respectively, and evoke a profound hyperactivity syndrome. These results suggest that the failure to detect 5-S-Glu-DA and the presence of only very low levels of 5-S-CyS-DA in Parkinsonian SN tissue and CSF might be related to both their intraneuronal oxidation and extraneuronal metabolism to N-acetylcysteinyl conjugates of DA. Furthermore, the toxic properties and neurobehavioral responses evoked by 5, 6, and 9 raise the possibility that these N-acetylcysteinyl conjugates of DA, in addition to certain cysteinyldopamines, DHBTs and BTs, might include endotoxins that contribute to SN cell death and other neuronal damage that occurs in PD. Methods are described for the synthesis of several N-acetylcysteinyl conjugates of DA, and their redox behaviors have been studied using cyclic voltammetry.

Influence of glutathione on the oxidation chemistry of the catecholaminergic neurotransmitter dopamine

In this study it is demonstrated that dopamine- o-quinone (DA- o-quinone), generated by the electrochemically driven oxidation of the catecholaminergic neurotransmitter dopamine (DA) at physicological pH, is rapidly scavenged by glutathione (GSH) to give, initially, 5- S-glutathionyldopamine (5- S-Glu-DA). The latter conjugate is more easily oxidized than DA to an o-quinone that reacts further with free GSH to give 2,5-bi- S-glutathionyldopamine ( 6), an even more easily oxidized compound. The proximate oxidation product of 6, o-quinone ( 7), is the precursor of 2,5,6-tri- S-glutathionyldopamine ( 8) and 4,7-bi- S-glutathionyl-5,6,dihydroxyindole ( 16). A p-quinone methide tautomer of o-quinone 7 is the precursor of glutathionyl conjugates of DA which contain a glutathionyl residue substituted in the ethylamino side-chain of the neurotransmitter. In the presence of equimolar or greater concentrations of GSH the normal oxidation pathway of DA to insoluble black indolic melanin polymer is blocked. The potential relevance of the in-vitro oxidation of DA in the presence of free GSH to an understanding of the degeneration of nigrostriatal dopaminergic neurons in idiopathic Parkinson's disease is discussed.

Iron- and peroxide-dependent conjugation of dopamine with cysteine: oxidative routes to the novel brain metabolite 5- S- cysteinyldopamine

The mechanism of formation of 5- S- cysteinyldopamine (5- S- CDA), a putative index of oxidative stress in dopaminergic regions of the brain, was investigated by comparing the ability of a number of neurochemically relevant oxidising systems to promote the conjugation of dopamine with cysteine in vitro. Autoxidation of the catecholamine proceeds at relatively slow rate in the physiological pH range, and is little affected by 1 mM Fe 2+-EDTA complex. In the presence of cysteine, however, the Fe 2+-induced autoxidation is hastened, affording little amounts of 5- S- CDA. Formation of the adduct is completely suppressed by ascorbic acid. Hydrogen peroxide, in the presence of Fe 2+-EDTA (Fenton-type oxidation) or peroxidase, promotes a relatively efficient conversion of dopamine to 5- S- CDA and the minor isomer 2- S- CDA. Noteworthy, 15-hydroperoxyeicosatetraenoic acid (arachidonic acid hydroperoxide, HPETE), in the presence of Fe 2+-EDTA complex, can also mediate 5- S- CDA formation, whilst superoxide radicals are little effective. Overall, these results suggest that ferrous ions, hydrogen peroxide and lipoperoxides may play an important role in 5- S- CDA generation.

Reactions of Cysteine and Cysteinyl Derivatives with Dopamine-o-quinone and Further Insights into the Oxidation Chemistry of 5-S-Cysteinyldopamine: Potential Relevance to Idiopathic Parkinson′s Disease

Recent studies suggest that elevated rates of autoxidation of dopamine (DA) in the cytoplasm of neuromelanin-pigmented dopaminergic cell bodies in the substantia nigra (SN) and/or reactions of its proximate oxidation product, DA-o-quinone, with glutathione (GSH) or L-cysteine (CySH) might yield endotoxins that play roles in the pathogenesis of idiopathic Parkinson′s Disease (PD). In this study the reactions between DA-o-quinone and CySH and some cysteine derivatives have been studied. The reactions between DA-o-quinone and CySH or cysteine methyl ester are rapid and give the corresponding 5-S-cysteinyl conjugates of DA as the predominant products. By contrast, the reaction between the sterically hindered D-penicillamine methyl ester (PME) and DA-o-quinone is much slower to give, initially, a mixture of the 2-S-, 5-S-, and 6-S-PME conjugates of DA. These conjugates are then further oxidized by unreacted DA-o-quinone to give a complex mixture of products which include 7-(2-aminoethyl)-5-hydroxy-2,2-dimethyl-1,4-benzothiazine-3-carboxylic acid methyl ester (13). Large increases in the 5-S-cysteinyldopamine (5-S-CyS-DA)/DA concentration ratio have been measured in the Parkinsonian SN and have been interpreted to reflect elevated rates of DA autoxidation in this structure that degenerates in PD. However, the present study reveals that at physiological pH 5-S-CyS-DA is not only more easily oxidized than DA but a bicyclic o-quinone imine (5) intermediate is formed that can chemically oxidize the former conjugate in a reaction that leads to 7-(2-aminoethyl)-3,4-dihydro-5-hydroxy-2H-1,4-benzothiazine-3-carboxylic acid (6). Compound 6 is lethal when administered into the brains of mice. However, this putative dihydrobenzothiazine endotoxin is even more easily oxidized than 5-S-CyS-DA in a rather complex reaction that ultimately forms 7-(2-aminoethyl)-5-hydroxy-1,4-benzothiazine-3-carboxylic acid (15). Although this benzothiazine could not be isolated it was identified by comparison of its electrochemical and spectroscopic properties in solution with those of 13. The results of this study suggest that benzothiazine 15 might serve as a better analytical marker molecule than 5-S-CyS-DA for either elevated rates of DA autoxidation and/or for roles of GSH and CySH in the neurodegenerative mechanisms in the SN that contribute to PD.

Metabolism of dopamine prodrug, docarpamine.

Docarpamine is a dopamine prodrug which has been selected from a large number of dopamine derivatives in order to develop an orally effective dopamine. The pharmacokinetics and metabolism after oral administration of docarpamine were studied in rats and dogs. The maximum concentration of free dopamine in plasma after oral administration of docarpamine to rats and dogs was 13 and 4-6 times, respectively, higher than those of dopamine (DA). In the first pass metabolism study in dogs, the main metabolic pathways after oral administration of docarpamine were catechol ester hydrolysis in the small intestine, and amide hydrolysis and conjugation in the liver. Conversion rates from docarpamine to DA in various rat tissue homogenates were in the order of the liver > small intestine > blood. The concentrations of DA conjugate and 3,4-dihydroxyphenylacetic acid in plasma after oral administration of DA to dogs were higher than those of docarpamine. This result indicates that protected groups of the docarpamine molecule suppress the first pass metabolism of orally administered dopamine. In conclusion, the findings of this study suggest that docarpamine can be used as an oral dopamine prodrug. The main first pass metabolism after oral administration of docarpamine are catechol ester hydrolysis in the small intestine, and amide hydrolysis and conjugation in the liver. Free dopamine, which is a pharmacologically active form, is mainly produced in the liver.

Detection of putative dopamine receptors in neurites outgrowing from locust central nervous system explants using anti-idiotypic dopamine antibodies

Organotypic cultures established from the third thoracic ganglion of locust embryo have been used to investigate dopamine receptors. In this in vitro system, neurites emerge directly from the explants and form a dense network around the explants, presenting cell surface freely exposed for experimental labelling. Polyclonal anti-idiotypic antibodies raised in rabbits to antibodies against dopamine conjugate, and previously found to bind to dopamine receptors, have been used to investigate putative dopamine receptors in these neurites. Immunocytochemical detection by light microscopy employing immunofluorescence labelling, was correlated with electron microscopy, using peroxidase staining. In addition to a location for dopamine receptors on the neurite surface, intracellular binding sites were also found in neurites. This internal labelling might represent an intracellular pool of dopamine receptor precursors. The labelling was specific in that it was not present when the anti-idiotypic dopamine antibodies were replaced with non-immune serum or when preincubation with conjugated dopamine preceded incubation with anti-idiotypic dopamine antibodies.

Drug targeting to the kidney with low molecular weight proteins

This paper reviews the design of a drug targeting strategy for renal specific delivery and endorenal release of drugs using low-molecular-weight proteins (LMWPs). In general, LMWPs are known to be filtered and subsequently reabsorbed by the proximal tubular cells of the kidneys. Within these cells LMWPs are catabolized in lysosomes due to prevalence of proteolytic enzymes and pH of 4-5. As such, these LMWPs might serve as drug carriers that release drugs site-specifically in the kidneys. The ability of the kidney to release the parent drug from drug-LMWP conjugates and drug-spacer derivatives by enzymatic or chemical hydrolysis of the connecting bond has been tested by incubation experiments in renal cortex homogenates and lysosomal lysates. Drug-LMWP conjugates of naproxen, sulfamethoxazole and dopamine have also been studied in vivo. The pharmacokinetics of these conjugates have been examined in freely moving rats and compared to those obtained after injection of equivalent doses of unreacted mixtures of drug and protein. In addition, the disposition of the drug-conjugated LMWP has been studied by radioactive-imaging with a gamma-camera. These studies demonstrated that the kidneys are the main site of uptake of drug-conjugated LMWPs and that the drugs are renally uncoupled and finally excreted in the urine. gamma-Camera experiments revealed a predominant renal uptake of radio-iodinated drug-conjugated LMWPs. Coadministration of an excess of the native LMWP resulted in a pronounced decrease of urinary (parent) drug excretion, suggesting competition for proximal tubular uptake between the LMWP and the drug-conjugated LMWP. Endorenal parent drug release from the LMWP was demonstrated for drugs with carboxyl groups and amino groups. The NSAID, naproxen, was shown to be released from the LMWP conjugate in vivo, provided that coupling via its carboxyl group was performed via an ester bond using a L-lactic acid spacer. If naproxen was directly coupled to the protein via an amide linkage, renal proteolysis of the LMWP-conjugated drug gave rise to the formation of a naproxen-lysine derivative. Interestingly, this product has been demonstrated to be at least as active in inhibiting prostaglandin synthesis as naproxen itself. Sulfamethoxazole was shown to be endorenally released from a drug-LMWP conjugate, if its primary amino group was coupled to the LMWP via an acid-sensitive spacer. Apart from the altered kinetics of the drug itself, the selective renal distribution was further demonstrated by the absence of its hepatically formed metabolite N-4-acetylsulfamethoxazole in urine. This metabolite was abundantly present in the control experiments after injection of the drug in its uncoupled form. Parent drug regeneration in the kidney was further demonstrated for a dopamine-LMWP conjugate, linked through its amino group via a similar acid-sensitive spacer. Within a relatively low dose range of lysozyme, a dose-dependent endorenal dopamine release could be demonstrated. In principle, drugs released within the proximal tubular cell may leave this cell at the basolateral membrane (blood site) or at the brush-border membrane (urine site). Renal delivery of LMWP-conjugated naproxen resulted in detectable plasma levels of the parent drug. In contrast, in the case of LMWP-conjugated sulfamethoxazole and dopamine, no (increase in) plasma levels of the free drugs were measured.

Demonstration of immunoglobulin G with affinity for dopamine in cerebrospinal fluid from psychotic patients

Using an enzyme-linked immunosorbent assay, significantly raised concentrations of immunoglobulin G with affinity for the neurotransmitter dopamine were demonstrated in cerebrospinal fluid psychotic patients. We have varied the antigen presentation in order to find a conjugate with low unspecific binding. The conjugation of dopamine to carbodiimide-activated poly- L-glutamic acid and that to activated succinimide ester of biotin are described. The use of glutaraldehyde conjugation is not recommended because of the risk of formation of tetrahydroisoquinolines. A strong correlation ( r = 0.94, P < 0.001) between the results obtained with dopamine conjugated to poly- L-glutamic acid and dopamine conjugated to biotin was observed. Forty-two human cerebrospinal fluid samples from 20

Identification and quantification of γ-glutamyl conjugates of biogenic amines in the nervous system of the snail, Helix aspersa, by gas chromatography—negative-ion chemical ionisation mass spectrometry

The γ-glutamyl conjugates of p-octapamine and dopamine were identified unambiguously for the first time and quantified in a single cerebral ganglion or pleural plus pedal ganglia of the snail, Helix aspersa, by gas chromatography—negative-ion chemical ionisation mass spectrometry. A new method was used for synthesis of γ-glutamylamine standards. The concentration of γ-glutamyltyramine was found to be low in the tissues, therefore it was used as an internal standard. The γ-glutamylamines were extracted with water and derivatised with pentafluoropropionic anhydride and trifluoroethanol. Under negative-ion chemical ionisation conditions, the trifluoroethyl and pentafluoropropionyl derivatives produced significant ions which were sufficiently abundant to be suitable for selective ion monitoring. The method had a limit of detection of ca. 80 pg of γ-glutamyl conjugate per tissue and calibration curves were linear over the range examined.

1H and 13C NMR of 3-O and 4-O conjugates of dopamine and other catecholamines.

Dopamine and its conjugates are widely distributed among biological species and are utilized for a variety of functions. Insects metabolize dopamine for cuticle melanization and sclerotization. Among the most abundant dopamines found in the larval and pupal development stages of Manduca sexta, the tobacco hornworm, are N-acetyldopamine and N-beta-alanyldopamine. In addition, glycosylated derivatives of these dopamines are found mainly in the hemolymph just prior to cuticulogenesis. The 1H and 13C NMR resonances of dopamine, its 3-O-methyl, 4-O-methyl, N-acetyl, and N-beta-alanyl derivatives, norepinephrine, 4-O-(beta-D-glucuronopyranosyl)dopamine, and the glycosylated products of N-beta-alanyldopamine and dopamine have largely been assigned. Assignments were based on one- and two-dimensional NMR analyses of the above compounds combined with that of specifically enriched [C7-13C]dopamine. 1H NMR showed that the major glycosylated natural product isolated from M. sexta pupal hemolymph was a 3-O-glycosyl derivative of N-beta-alanyldopamine. 13C NMR confirmed that the carbohydrate was D-glucose probably in a beta-linkage. 1H NMR of the aromatic ring protons provided the most definitive method to distinguish 3-O- from 4-O-derivatives of dopamine. In addition, the 3-O-glucosyl conjugate of N-beta-alanyldopamine had unique chemical shifts and coupling patterns compared to those of 4-O-(beta-D-glucuronosyl)- and 3-O-(beta-D-glucopyranosyl)dopamine.

Human brain phenolsulfotransferase. Regional distribution in Parkinson's disease

Brain phenolsulfotransferase (PST) in 105.000 x g supernatant fractions prepared from post mortem human brain catalyzes the sulfate conjugation of dopamine (DA). Using 50 microM DA, the PST activity was linear up to one hour. The KM value for DA was 3.1 microM. Higher concentrations of DA from 25 b microM up caused inhibition of PST activity. Assessment of regional distribution in normal brain using 20 microM DA concentration revealed the highest PST activities in temporal and frontal cortex. About ten times lower activities were measured in parietal and occipital lobe, amygdala, hypothalamus, and hippocampus, whereas the nucleus accumbens, nucleus basalis of Meynert, caudate nucleus, and substantia nigra showed the lowest activities (about 1% of those in frontal and parietal cortex). In the brains of subjects with Parkinson's disease (PD) treated with levodopa, a significant reduction of PST activities was observed in hypothalamus, frontal and temporal cortex, amygdaloid nucleus, occipital and parietal cortex (between 20 and 38.8% of controls). Depletion of PST activity was less severe in hippocampus (46% of controls), nucleus accumbens, putamen, and substantia nigra (67 and 72% of controls, respectively). No changes were observed in the nucleus basalis of Meynert, while PST activity was increased in the caudate nucleus (174 to 203% of controls). The presented data indicate that on PD brain the PST activity is reduced in areas of the cerebral isocortex and limbic system, while in the basal ganglia it is either mildly reduced (putamen) or increased (caudate nucleus). Selective changes of PST activity in PD brain may indicate an important function of this enzyme in the metabolism and/or storage of DA under pathological conditions.

Determination of γ-glutamyl conjugates of monoamines by means of high-performance liquid chromatography with electrochemical detection and application to gastropod tissues

Catabolism of aminergic neurotransmitters in gastropods appears to be primarily by means of γ-glutamyl conjugation rather than by oxidative deamination as is typical of vertebrates. High-performance liquid chromatography with electrochemical detection was used to develop a method for the routine measurement of γ-glutamyl conjugates of dopamine and 5-hydroxytryptamine in gastropod tissues.

Sulphate conjugation in human liver: Direct measurement of N-acetyldopamine-sulphate

The overall three-step sulphate conjugating activity of the human liver was determined by the direct measurement of N-acetyldopamine (NADA)-sulphate from ATP and inorganic sulphate. NADA-sulphate was separated from NADA and quantified by HPLC-ECD (high-pressure liquid chromatography-electrochemical detection). The overall sulphate conjugation of NADA showed a pH optimum of 8.0 with apparent K m values for sodium sulphate and NADA of 103 μM and 4.8 μM, respectively. The optimum concentration of ATP was 5 mM and that for Mg 2+ ions was 7mM. The specific activities of 17 samples of human liver, measured by this HPLC-ECD procedure ranged from 940 to 23,128 pmol NADA-suphate/hr/mg protein. A comparison of these values with those determined by the radiometric method developed previously showed a direct correlation coefficient, r = 0.89. The rates of overall sulphate conjugation of NADA and dopamine measured in these samples by the radiometric assay procedure were also significantly correlated with r = 0.82.