Quantitation of 3,4-dihydroxyphenylacetaldehyde and 3, 4-dihydroxyphenylglycolaldehyde, the monoamine oxidase metabolites of dopamine and noradrenaline, in human tissues by microcolumn high-performance liquid chromatography

Prodromal Parkinson's disease and the catecholaldehyde hypothesis: Insight from olfactory bulb organotypic cultures

Parkinson's disease (PD) is a progressive, neurodegenerative disorder with an increasing incidence, unknown etiology, and is currently incurable. Advances in understanding the pathological mechanisms at a molecular level have been slow, with little attention focused on the early prodromal phase of the disease. Consequently, the development of early-acting disease-modifying therapies has been hindered. The olfactory bulb (OB), the brain region responsible for initial processing of olfactory information, is particularly affected early in PD at both functional and molecular levels but there is little information on how the cells in this region are affected by disease. Organotypic and primary OB cultures were developed and characterized. These platforms were then used to assess the effects of 3,4-dihydroxyphenylacetylaldehyde (DOPAL), a metabolite of dopamine present in increased levels in post-mortem PD tissue and which is thought to contribute to PD pathogenesis. Our findings showed that DOPAL exposure can recapitulate many aspects of PD pathology. Oxidative stress, depolarization of mitochondrial membranes, and neurodegeneration were all induced by DOPAL addition, as were measured transcriptomic changes consistent with those reported in PD clinical studies. These olfactory models of prodromal disease lend credence to the catecholaldehyde hypothesis of PD and provide insight into the mechanisms by which the OB may be involved in disease progression.

Anti-VEGF Effect of Bioactive Indolic Compounds and Hydroxytyrosol Metabolites

Angiogenesis is a key process involved in both cancer and cardiovascular diseases, the vascular endothelial growth factor (VEGF) and its VEGF receptor-2 (VEGFR-2) being the main triggers. The aim of this study was to determine the molecular mechanism underlying the potent inhibition of VEGF signaling by hydroxytyrosol (HT) metabolites and indolic compounds and establish a relation between their structure and bioactivity. Experiments involved the evaluation of their potential to inhibit VEGF on human umbilical vein endothelial cells (HUVECs) by ELISA assay and their subsequent effect on the downstream signaling pathway (PLCγ1, Akt, and endothelial nitric oxide synthetase (eNOS)) by Western blot. Respectively, 3,4-dihydroxyphenylacetaldehyde (DOPAL) (100 µM) and indole pyruvic acid (IPy) (1 mM) were capable of inhibiting VEGFR-2 activation with an IC50 value of 119 µM and 1.037 mM. The anti-angiogenic effect of DOPAL and IPy is mediated via PLCγ1. Additionally, DOPAL significantly increases eNOS phosphorylation, while IPy maintained it. These data provide for the first time evidence of the anti-angiogenic effect of DOPAL and IPy for future use as potential bioactive food ingredients.

A model of dopamine and serotonin-kynurenine metabolism in cortisolemia: Implications for depression

A major factor contributing to the etiology of depression is a neurochemical imbalance of the dopaminergic and serotonergic systems, which is caused by persistently high levels of circulating stress hormones. Here, a computational model is proposed to investigate the interplay between dopaminergic and serotonergic-kynurenine metabolism under cortisolemia and its consequences for the onset of depression. The model was formulated as a set of nonlinear ordinary differential equations represented with power-law functions. Parameter values were obtained from experimental data reported in the literature, biological databases, and other general information, and subsequently fine-tuned through optimization. Model simulations predict that changes in the kynurenine pathway, caused by elevated levels of cortisol, can increase the risk of neurotoxicity and lead to increased levels of 3,4-dihydroxyphenylaceltahyde (DOPAL) and 5-hydroxyindoleacetaldehyde (5-HIAL). These aldehydes contribute to alpha-synuclein aggregation and may cause mitochondrial fragmentation. Further model analysis demonstrated that the inhibition of both serotonin transport and kynurenine-3-monooxygenase decreased the levels of DOPAL and 5-HIAL and the neurotoxic risk often associated with depression. The mathematical model was also able to predict a novel role of the dopamine and serotonin metabolites DOPAL and 5-HIAL in the ethiology of depression, which is facilitated through increased cortisol levels. Finally, the model analysis suggests treatment with a combination of inhibitors of serotonin transport and kynurenine-3-monooxygenase as a potentially effective pharmacological strategy to revert the slow-down in monoamine neurotransmission that is often triggered by inflammation.

A novel LC-MS/MS method for quantification of unstable endogenous 3,4-dihydroxyphenylacetaldehyde in rat brain after chemical derivatization

3,4-dihydroxyphenylacetaldehyde (DOPAL), a toxic intermediary metabolite of dopamine (DA), causes catecholaminergic neurodegeneration via covalent binding with functional proteins or other biomolecules. Accurate quantification of DOPAL is essential to investigate the etiological factors associated with DOPAL and the pathogenetic role of DOPAL in Parkinson's disease (PD). However, no validated quantitative methods are available. Quantification of DOPAL in biosample is challenging since it is a reactive endogenous aldehyde with poor ionization efficiency and chromatographic behavior in the LC-MS system. Here, a sensitive, simple, and robust UPLC-MS/MS method has been established and validated for the determination of DOPAL in rat brain tissue specimens. DOPAL was found to be unstable in biosample due to reactive aldehyde whereas it was stable in acidic condition. The analyte was stabilized by pH and temperature control during the sample preparation and derivatization. Then, a chemical derivatization method that can be readily performed in acidic conditions and at low temperature was employed using 2-hydrazino-4-(trifluoromethyl)-pyrimidine (HTP) to block the reactive aldehyde and improve the detection sensitivity (about 100-fold increase) and chromatographic retention. Bovine serum albumin was used as a surrogate matrix, which was validated by the parallelism assay and post-column infusion experiment. This method was fully validated and the lower limit of quantification (LLOQ) was 0.5 ng/mL. With the method, a significant increase of DOPAL level was found in striatum region of rats received 6-hydroxydopamine (6-OHDA) injection for 12 h, indicating DOPAL may play a pathogenic role in 6-OHDA-induced PD model.

Delta-secretase cleavage of Tau mediates its pathology and propagation in Alzheimer's disease

Alzheimer’s disease (AD) is a progressive neurodegenerative disease with age as a major risk factor. AD is the most common dementia with abnormal structures, including extracellular senile plaques and intraneuronal neurofibrillary tangles, as key neuropathologic hallmarks. The early feature of AD pathology is degeneration of the locus coeruleus (LC), which is the main source of norepinephrine (NE) supplying various cortical and subcortical areas that are affected in AD. The spread of Tau deposits is first initiated in the LC and is transported in a stepwise manner from the entorhinal cortex to the hippocampus and then to associative regions of the neocortex as the disease progresses. Most recently, we reported that the NE metabolite DOPEGAL activates delta-secretase (AEP, asparagine endopeptidase) and triggers pathological Tau aggregation in the LC, providing molecular insight into why LC neurons are selectively vulnerable to developing early Tau pathology and degenerating later in the disease and how δ-secretase mediates the spread of Tau pathology to the rest of the brain. This review summarizes our current understanding of the crucial role of δ-secretase in driving and spreading AD pathologies by cleaving multiple critical players, including APP and Tau, supporting that blockade of δ-secretase may provide an innovative disease-modifying therapeutic strategy for treating AD.

The identification of an enzyme that plays a critical role in the progression of Alzheimer’s disease (AD) could lead to novel therapeutic interventions. In the earliest stage of AD, the build-up of Tau protein aggregates causes degeneration of a site in the brainstem. These abnormal Tau accumulations then spread to other parts of the brain. Recent research suggests that an enzyme called delta-secretase cleaves Tau and other key molecules, making Tau more prone to forming aggregates and thus facilitating disease progression. Keqiang Ye and co-workers at Emory University School of Medicine in Atlanta, USA, reviewed current understanding of the role of delta-secretase in AD pathology. Studies show that delta-secretase expression levels are high in aged mice and AD brains. Inhibiting delta-secretase could therefore limit neurodegeneration and alleviate cognitive deficits in patients.

Effect of ALDH2 on Sleep Disturbances in Patients with Parkinson's Disease

Monoamine neurotransmitters play essential roles in the regulation of arousal and sleep. Impaired metabolism of monoamine neurotransmitters could result in the accumulation of neurotoxic aldehyde metabolites and, hence, neuronal degeneration. Aldehyde dehydrogenases play an important role in the metabolism of the neurotoxic aldehyde metabolites, including the aldehyde metabolites of dopamine, serotonin, and noradrenaline. Deficient aldehyde dehydrogenase 2 (ALDH2) has been suggested to result in the accumulation of these biogenic aldehydes. An ALDH2 single nucleotide polymorphism (SNP), rs671 (A), results in significantly reduced ALDH2 enzyme activity. A total of 83 Parkinson’s disease (PD) patients were recruited in this study. In addition to the genotypes of rs671, the patients were assessed with the PD sleep scale-2nd version (PDSS-2) and the Epworth sleepiness scale (ESS) for symptoms of daytime and nocturnal sleep disturbances. The patients carrying rs671 (A) had more frequent dozing while lying down to rest in the afternoon (ESS item5) (F = 7.308, p = 0.008) than the rs671 (GG) patients. The patients with rs671 (A) reported a trend toward more frequent difficulty staying asleep than the patients with rs671 (GG). (F = 3.278, p = 0.074). The results indicate that patients carrying allele rs671 (A) are more likely to experience impairment in the regulation of arousal and sleep. The results also support the hypothesis that the accumulation of neurotoxic monoamine neurotransmitter aldehyde metabolites secondary to reduced ALDH2 enzyme activity may cause more severe monoaminergic neuronal loss and, hence, more severe symptoms in the regulation of wakefulness and sleep.

Biogenic Aldehyde-Mediated Mechanisms of Toxicity in Neurodegenerative Disease

Oxidative decomposition of several biomolecules produces reactive aldehydes. Monoamine neurotransmitters are enzymatically converted to aldehydes via monoamine oxidase followed by further metabolism such as carbonyl oxidation/reduction. Elevated levels of aldehyde intermediates are implicated as factors in several pathological conditions, including Parkinson's disease. The biogenic aldehydes produced from dopamine, norepinephrine and serotonin are known to be toxic, generate reactive oxygen species and/or cause aggregation of proteins such as α-synuclein. Polyunsaturated lipids undergo oxidative decomposition to produce biogenic aldehydes, including 4-hydroxy-2-nonenal and malondialdehyde. These lipid aldehydes, some including an α,β-unsaturated carbonyl, target important proteins such as α-synuclein, proteasome degradation and G-protein-coupled signaling. Overproduction of biogenic aldehydes is a hypothesized factor in neurodegeneration; preventing their formation or scavenging may provide means for neuroprotection.

Inactivation of glyceraldehyde-3-phosphate dehydrogenase by the dopamine metabolite, 3,4-dihydroxyphenylacetaldehyde

BACKGROUND

The aldehyde metabolite of dopamine, 3,4-dihydroxyphenylacetaldehyde (DOPAL) is an endogenous neurotoxin implicated in Parkinson's Disease. Elucidating protein targets of DOPAL is essential in understanding it's pathology. The enzyme, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a target of DOPAL.

METHODS

GAPDH activity was measured via reduction of NAD⁺ cofactor (340 nm). Protein aggregation was assessed with SDS-PAGE methods and specific modification via chemical probes.

RESULTS

Low micromolar levels of DOPAL caused extensive GAPDH aggregation and irreversibly inhibited enzyme activity. The inactivation of GAPDH was dependent on both the catechol and aldehyde moieties of DOPAL. It is suggested that Cys are modified and oxidized by DOPAL.

CONCLUSIONS

The mechanism by which DOPAL modifies GAPDH can serve as a mechanistic explanation to the pathological events in Parkinson's Disease.

Catecholamine autotoxicity. Implications for pharmacology and therapeutics of Parkinson disease and related disorders

Several neurodegenerative diseases involve loss of catecholamine neurons-Parkinson disease is a prototypical example. Catecholamine neurons are rare in the nervous system, and why they are vulnerable in PD and related disorders has been mysterious. Accumulating evidence supports the concept of "autotoxicity"-inherent cytotoxicity of catecholamines and their metabolites in the cells in which they are produced. According to the "catecholaldehyde hypothesis" for the pathogenesis of Parkinson disease, long-term increased build-up of 3,4-dihydroxyphenylacetaldehyde (DOPAL), the catecholaldehyde metabolite of dopamine, causes or contributes to the eventual death of dopaminergic neurons. Lewy bodies, a neuropathologic hallmark of PD, contain precipitated alpha-synuclein. Bases for the tendency of alpha-synuclein to precipitate in the cytoplasm of catecholaminergic neurons have also been mysterious. Since DOPAL potently oligomerizes and aggregates alpha-synuclein, the catecholaldehyde hypothesis provides a link between alpha-synucleinopathy and catecholamine neuron loss in Lewy body diseases. The concept developed here is that DOPAL and alpha-synuclein are nodes in a complex nexus of interacting homeostatic systems. Dysfunctions of several processes, including decreased vesicular sequestration of cytoplasmic catecholamines, decreased aldehyde dehydrogenase activity, and oligomerization of alpha-synuclein, lead to conversion from the stability afforded by negative feedback regulation to the instability, degeneration, and system failure caused by induction of positive feedback loops. These dysfunctions result from diverse combinations of genetic predispositions, environmental exposures, stress, and time. The notion of catecholamine autotoxicity has several implications for treatment, disease modification, and prevention. Conversely, disease modification clinical trials would provide key tests of the catecholaldehyde hypothesis.

L-threo-dihydroxyphenylserine corrects neurochemical abnormalities in a Menkes disease mouse model

OBJECTIVE

Menkes disease is a lethal neurodegenerative disorder of infancy caused by mutations in a copper-transporting adenosine triphosphatase gene, ATP7A. Among its multiple cellular tasks, ATP7A transfers copper to dopamine beta hydroxylase (DBH) within the lumen of the Golgi network or secretory granules, catalyzing the conversion of dopamine to norepinephrine. In a well-established mouse model of Menkes disease, mottled-brindled (mo-br), we tested whether systemic administration of L-threo-dihydroxyphenylserine (L-DOPS), a drug used successfully to treat autosomal recessive norepinephrine deficiency, would improve brain neurochemical abnormalities and neuropathology.

METHODS

At 8, 10, and 12 days of age, wild-type and mo-br mice received intraperitoneal injections of 200μg/g body weight of L-DOPS, or mock solution. Five hours after the final injection, the mice were euthanized, and brains were removed. We measured catecholamine metabolites affected by DBH via high-performance liquid chromatography with electrochemical detection, and assessed brain histopathology.

RESULTS

Compared to mock-treated controls, mo-br mice that received intraperitoneal L-DOPS showed significant increases in brain norepinephrine (p < 0.001) and its deaminated metabolite, dihydroxyphenylglycol (p < 0.05). The ratio of a non-beta-hydroxylated metabolite in the catecholamine biosynthetic pathway, dihydroxyphenylacetic acid, to the beta-hydroxylated metabolite, dihydroxyphenylglycol, improved equivalently to results obtained previously with brain-directed ATP7A gene therapy (p < 0.01). However, L-DOPS treatment did not arrest global brain pathology or improve somatic growth, as gene therapy had.

INTERPRETATION

We conclude that (1) L-DOPS crosses the blood-brain barrier in mo-br mice and corrects brain neurochemical abnormalities, (2) norepinephrine deficiency is not the cause of neurodegeneration in mo-br mice, and (3) L-DOPS treatment may ameliorate noradrenergic hypofunction in Menkes disease.

Trivalent copper chelate-luminol chemiluminescence system for highly sensitive CE detection of dopamine in biological sample after clean-up using SPE

A transition metal chelate unstable at a high oxidation state, diperiodatocuprate (III) (K₅[Cu(HIO₆)₂], DPC), was synthesized and applied in the luminol-based chemiluminescence (CL) system for highly sensitive CE end-column detection of dopamine (DA). This method was based on the fact that DA enhanced the CL emission resulting from the reaction between luminol and DPC in alkaline medium. The DPC-luminol-DA CL system showed very intensive emission and very fast kinetic characteristics, thus resulting in a high sensitivity in flow-through detection mode for CE. Under optimal conditions, the linear range was 1.0 × 10⁻⁸-5.0 × 10⁻⁵ g/mL (R² = 0.9984) with a limit of detection of 6.0 × 10⁻⁹ g/mL (S/N = 3). The RSDs of the peak height and the migration time were about 4.2 and 2.4% for a standard sample at 3.0 × 10⁻⁶ g/mL (n = 5), respectively. The presented method has been successfully used for the determination of DA in commercial preparation and human urine samples after clean-up using SPE.

Quantum dot-enhanced chemiluminescence detection for simultaneous determination of dopamine and epinephrine by capillary electrophoresis

A sensitive method based on quantum dot (QD)-enhanced capillary electrophoresis-chemiluminescence (CE-CL) detection was developed for simultaneous determination of dopamine (DA) and epinephrine (E). In this work, CdTe QD was added into the running buffer of CE to catalyze the post-column CL reaction between luminol and hydrogen peroxide, achieving higher CL emission. Negative peaks were produced due to the inhibitory effects on CL emission from DA and E eluted from the electrophoretic capillary. The decrease in CL intensity was proportional to the concentration of DA and E in the range of 8.0 × 10(-8)-5.0 × 10(-6)M and 4.0 × 10(-8)-5.0 × 10(-6)M, respectively. Detection limits for DA and E were 2.3 × 10(-8)M and 9.3 × 10(-9)M, respectively. Using this method, the levels of DA and E in human urine from healthy donors were determined.

The neurotoxicity of DOPAL: behavioral and stereological evidence for its role in Parkinson disease pathogenesis

BACKGROUND

The etiology of Parkinson disease (PD) has yet to be fully elucidated. We examined the consequences of injections of 3,4-dihydroxyphenylacetaldehyde (DOPAL), a toxic metabolite of dopamine, into the substantia nigra of rats on motor behavior and neuronal survival.

METHODS/PRINCIPAL FINDINGS

A total of 800 nl/rat of DOPAL (1 µg/200 nl) was injected stereotaxically into the substantia nigra over three sites while control animals received similar injections of phosphate buffered saline. Rotational behavior of these rats was analyzed, optical density of striatal tyrosine hydroxylase was calculated, and unbiased stereological counts of the substantia nigra were made. The rats showed significant rotational asymmetry ipsilateral to the lesion, supporting disruption of dopaminergic nigrostriatal projections. Such disruption was verified since the density of striatal tyrosine hydroxylase decreased significantly (p<0.001) on the side ipsilateral to the DOPAL injections when compared to the non-injected side. Stereological counts of neurons stained for Nissl in pars compacta of the substantia nigra significantly decreased (p<0.001) from control values, while counts of those in pars reticulata were unchanged after DOPAL injections. Counts of neurons immunostained for tyrosine hydroxylase also showed a significant (p=0.032) loss of dopaminergic neurons. In spite of significant loss of dopaminergic neurons, DOPAL injections did not induce significant glial reaction in the substantia nigra.

CONCLUSIONS

The present study provides the first in vivo quantification of substantia nigra pars compacta neuronal loss after injection of the endogenous toxin DOPAL. The results demonstrate that injections of DOPAL selectively kills SN DA neurons, suggests loss of striatal DA terminals, spares non-dopaminergic neurons of the pars reticulata, and triggers a behavioral phenotype (rotational asymmetry) consistent with other PD animal models. This study supports the "catecholaldehyde hypothesis" as an important link for the etiology of sporadic PD.

Protein reactivity of 3,4-dihydroxyphenylacetaldehyde, a toxic dopamine metabolite, is dependent on both the aldehyde and the catechol

Dopamine (DA) has been implicated as an endogenous neurotoxin to explain selective neurodegeneration, as observed for Parkinson's disease (PD). However, previous work demonstrated that 3,4-dihydroxyphenylacetaldehyde (DOPAL) was more toxic than DA. DOPAL is generated as a part of DA catabolism via the activity of monoamine oxidase, and the mechanism of DOPAL toxicity is proposed to involve protein modification. Previous studies have demonstrated protein reactivity via the aldehyde moiety; however, DOPAL contains two reactive functional groups (catechol and aldehyde), both with the potential for protein adduction. The goal of this work was to determine whether protein modification by DOPAL occurs via a thiol-reactive quinone generated from oxidation of the catechol, which is known to occur for DA, or if the aldehyde forms adducts with amine nucleophiles. To accomplish this objective, the reactivity of DOPAL toward N-acetyl-lysine (NAL), N-acetyl-cysteine (NAC), and two model proteins was determined. In addition, several DOPAL analogues were obtained and used for comparison of reactivity. Results demonstrate that at pH 7.4 and 37 degrees C, the order of DOPAL reactivity is NAL >> NAC and the product of NAL and DOPAL is stable in the absence of reducing agent. Moreover, DOPAL will react with model proteins, but in the presence of amine-selective modifiers citraconic anhydride and 2-iminothiolane hydrochloride, the reactivity of DOPAL toward the proteins is diminished. In addition, DOPAL-mediated protein cross-linking is observed when a model protein or a protein mixture (i.e., mitochondria lysate) is treated with DOPAL at concentrations of 5-100 microM. Protein cross-linking was diminished in the presence of ascorbate, suggesting the involvement of a quinone in DOPAL-mediated protein modification. These data indicate that DOPAL is highly reactive toward protein nucleophiles with the potential for protein cross-linking.

Lipid Peroxidation Products Inhibit Dopamine Catabolism Yielding Aberrant Levels of a Reactive Intermediate

Recent work indicates that oxidative stress is a factor in Parkinson's disease (PD); however, it is unknown how this condition causes selective dopaminergic cell death. The neurotransmitter dopamine (DA) has been implicated as an endogenous neurotoxin to explain the selective neurodegeneration. DA undergoes catabolism by monoamine oxidase (MAO) to the reactive intermediate 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is further oxidized to 3,4-dihydroxyphenylacetic (DOPAC) acid via mitochondrial aldehyde dehydrogenase (ALDH). Previous studies found DOPAL to be more toxic than DA, and the major lipid peroxidation products, that is, 4-hydroxynonenal (4HNE) and malondialdehyde (MDA), potently inhibit ALDH. The hypothesis of this work is that lipid peroxidation products inhibit DOPAL oxidation, yielding aberrant levels of the reactive aldehyde intermediate. Treatment of striatal synaptosomes with 2-100 microM 4HNE or 2-50 microM MDA impaired DOPAL oxidation, resulting in elevated [DOPAL]. The aberrant concentration of DOPAL yielded an increase in protein modification by the DA-derived aldehyde, evident via staining of proteins with nitroblue tetrazolium (NBT). Pretreatment of synaptosomes with an MAO inhibitor significantly decreased NBT staining. On the basis of NBT staining, the order of protein reactivity for DA and metabolites was found to be DOPAL>>DOPAC>DA. Mass spectrometric analysis of a model peptide reacted with DOPAL revealed the adduct to be a Schiff base product. In summary, these data demonstrate the sensitivity of DA catabolism to the lipid peroxidation products 4HNE and MDA even at low, physiologic levels and suggest a mechanistic link between oxidative stress and generation of aberrant levels of an endogenous and protein reactive dopaminergic toxin relevant to PD.

Neurotoxicity and metabolism of the catecholamine-derived 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde: the role of aldehyde dehydrogenase

Aldehydes are highly reactive molecules formed during the biotransformation of numerous endogenous and exogenous compounds, including biogenic amines. 3,4-Dihydroxyphenylacetaldehyde is the aldehyde metabolite of dopamine, and 3,4-dihydroxyphenylglycolaldehyde is the aldehyde metabolite of both norepinephrine and epinephrine. There is an increasing body of evidence suggesting that these compounds are neurotoxic, and it has been recently hypothesized that neurodegenerative disorders may be associated with increased levels of these biogenic aldehydes. Aldehyde dehydrogenases are a group of NAD(P)+ -dependent enzymes that catalyze the oxidation of aldehydes, such as those derived from catecholamines, to their corresponding carboxylic acids. To date, 19 aldehyde dehydrogenase genes have been identified in the human genome. Mutations in these genes and subsequent inborn errors in aldehyde metabolism are the molecular basis of several diseases, including Sjögren-Larsson syndrome, type II hyperprolinemia, gamma-hydroxybutyric aciduria, and pyridoxine-dependent seizures, most of which are characterized by neurological abnormalities. Several pharmaceutical agents and environmental toxins are also known to disrupt or inhibit aldehyde dehydrogenase function. It is, therefore, possible to speculate that reduced detoxification of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde from impaired or deficient aldehyde dehydrogenase function may be a contributing factor in the suggested neurotoxicity of these compounds. This article presents a comprehensive review of what is currently known of both the neurotoxicity and respective metabolism pathways of 3,4-dihydroxyphenylacetaldehyde and 3,4-dihydroxyphenylglycolaldehyde with an emphasis on the role that aldehyde dehydrogenase enzymes play in the detoxification of these two aldehydes.

Inhibition of the oxidative metabolism of 3,4-dihydroxyphenylacetaldehyde, a reactive intermediate of dopamine metabolism, by 4-hydroxy-2-nonenal

Recent evidence indicates a role for oxidative stress and resulting products, e.g. 4-hydroxy-2-nonenal (4HNE) in the pathogenesis of Parkinson's disease (PD). 4HNE is a known inhibitor of mitochondrial aldehyde dehydrogenase (ALDH2), an enzyme very important to the dopamine (DA) metabolic pathway. DA undergoes monoamine oxidase-catalyzed oxidative deamination to 3,4-dihydroxyphenylacetaldehyde (DOPAL), which is metabolized primarily to 3,4-dihydroxyphenylacetic acid (DOPAC) via ALDH2. The biotransformation of DOPAL is critical as previous studies have demonstrated this DA-derived aldehyde to be a reactive electrophile and toxic to dopaminergic cells. Therefore, 4HNE produced via oxidative stress may inhibit ALDH2-mediated oxidation of the endogenous neurotoxin DOPAL. To test this hypothesis, ALDH2 in various model systems was treated with 4HNE and activity toward DOPAL measured. Incubation of human recombinant ALDH2 with 4HNE (1.5-30 microM) yielded inhibition of activity toward DOPAL. Furthermore, ALDH2 in rat brain mitochondrial lysate as well as isolated rat brain mitochondria was also sensitive to the lipid peroxidation product at low micromolar, as evident by a decrease in the rate of DOPAL to DOPAC conversion measured using HPLC. Taken together, these data indicate that 4HNE at low micromolar inhibits mitochondrial biotransformation of DOPAL to DOPAC, and generation of the lipid peroxidation product may represent a mechanism yielding aberrant levels of DOPAL, thus linking oxidative stress to the uncontrolled production of an endogenous neurotoxin relevant to PD.

Interaction of alpha-synuclein and dopamine metabolites in the pathogenesis of Parkinson's disease: a case for the selective vulnerability of the substantia nigra

Parkinson's disease (PD) is the most common movement disorder. Major disease symptoms are due to the loss of dopaminergic (DA) neurons in substantia nigra (SN). The pathologic hallmark of PD is Lewy bodies (LBs) in the SN and the major protein in LBs is alpha-synuclein (AS). A plethora of evidence points towards the culpability of AS in the pathogenesis of PD including: (1) linkage of AS mutations to familial forms of PD, (2) triplication of the AS locus causing PD, and (3) overexpression of AS in transgenic mice and Drosophila leads to PD-like phenotypes. Studies of purified AS have revealed its ability to interact with diverse molecules including monoamines. Monoamine metabolism is associated with oxidative stress conditions that may contribute to DA-AS interactions promoting aggregation and neuronal damage. However, in order to explain the selective vulnerability of DA neurons there needs to be a link between DA metabolism and AS aggregation. Since only the DA neurons contain significant amounts of DA, this has been hypothesized to account for the selective vulnerability of SN neurons. However, DA itself may not be toxic at physiologic relevant doses, so it is probable that other DA metabolites may play a major role in AS aggregation. In this review, we discuss the role of the DA metabolite 3,4-dihydroxyphenylacetaldehyde to provide a plausible link between DA production and metabolism, AS aggregation and the pathogenesis of PD.

Simple Analysis Used in Diagnosis and Follow-up of Schizophrenic Patients (Patent)

Dopamine acts as neurotransmitter in the central and peripheral sympathetic nervous system. Determination of dopamine (DO) was performed by spectrophotometric analysis depending on the formation of new colored compound. The proposed procedure was efficient in quantitative determination of DO as pure material in pharmaceutical preparations and in urine samples. DO concentration in urine sample of patient confirms the affection with schizophrenia and the proposed procedure was used to facilitate diagnosis and followup of schizophrenic patients. It is recommended to apply the proposed procedures as routine analysis in pharmaceutical companies for quality control and in analytical laboratories to diagnose and follow up schizophrenia.

MPTP and SNpc DA neuronal vulnerability: role of dopamine, superoxide and nitric oxide in neurotoxicity. Minireview

Parkinson disease (PD) is a common neurodegenerative disease of unknown origin that is characterized, mainly, by a significant reduction in the number of dopamine neurons in the substantia nigra pars compacta (SNpc) of the brain and a dramatic reduction in dopamine levels in the corpus striatum. For reasons that we do not know, the dopamine neuron seems to be more vulnerable to damage than any other neuron in the brain. Although hypotheses of damage to the dopamine neuron include oxidative stress, growth factor decline, excitotoxicity, inflammation in the SNpc and protein aggregation, oxidative stress in the nigrostriatal dopaminergic system garners a significant amount of attention. In the oxidative stress hypothesis of PD, superoxide, nitric oxide and dopamine all conspire to create an environment that can be detrimental to the dopamine neuron. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), the tool of choice for investigations into the mechanisms involved in the death of dopamine neurons in PD, has been used extensively in attempts to sort out what happens in and around the dopamine neuron. Herein, we review the roles of dopamine, superoxide and nitric oxide in the demise of the dopamine neuron in the MPTP model of PD as it relates to the death of the dopamine neuron noted in PD.

3,4-Dihydroxyphenylacetaldehyde is the toxic dopamine metabolite in vivo: implications for Parkinson's disease pathogenesis

In Parkinson's disease (PD), there is a highly selective loss of dopamine (DA) neurons in the substantia nigra (SN) greater than in the ventral tegmental area (VTA). The simplest explanation for selective DA neuron loss in PD is that DA is toxic and, because only DA neurons contain significant amounts of DA, this highly localized synthesis of DOPAL accounts for selective vulnerability of DA neurons. However, the large concentrations of DA required to produce in vivo toxicity cast doubt on its role in PD pathogenesis. Alpha-synuclein (alpha-syn) is the major component of the Lewy body, the pathological marker of PD, and is genetically linked to the disease. Recent studies indicate that alpha-syn neurotoxicity is mediated by a free radical generating metabolite of DA. Here we test the hypothesis that 3,4-dihydroxyphenylacetaldehyde (DOPAL), the monamine oxidase metabolite of DA, mediates DA toxicity in vivo. We injected DOPAL, DA and its oxidative, reduced and methylated metabolites into rat SN and VTA. Five days post-surgery, the injection sites were evaluated in Nissl preparations and with tyrosine hydroxylase (for DA neurons), neuronal nuclear antigen (for neurons) and glial fibrillary acidic protein (for astrocytes) immunoreactivities. Lesion size in SN vs. VTA was compared using morphometry. DOPAL at concentrations as low as 100 ng was toxic to DA SN neurons>DA VTA neurons>glia. Neither DA nor its other metabolites showed evidence of neurotoxicity at fivefold higher doses. However, 20 microg of DA produced lesions in the SN and VTA. We conclude that DOPAL is the toxic DA metabolite in vivo. Implications for a unified hypothesis for PD pathogenesis are discussed.

Determination of catecholamines and metanephrines in urine by capillary electrophoresis-electrospray ionization-time-of-flight mass spectrometry

A method successfully coupling capillary electrophoretic separation to time-of-flight mass spectrometric (TOFMS) detection for the simultaneous analysis of catecholamines (dopamine, norepinephrine, and epinephrine) and their O-methoxylated metabolites (3-methoxytyramine, normetanephrine, and metanephrine) is described. The inner capillary wall was coated with polyvinyl alcohol in order to obtain baseline resolution of catecholamines and metanephrines and to ensure reproducibility without extensive restorative washing of the capillary. Using electrokinetic injection, detection limits of 0.3 microM for dopamine and norepinephrine, 0.2 microM for 3-methoxytyramine and normetanephrine, and 0.1 microM for epinephrine and metanephrine were achieved with standard solutions. The usefulness of this approach was demonstrated by applying the developed method to the analysis of a spot collection of human urine from a healthy volunteer. The catecholamines and metanephrines were removed from the urine samples and preconcentrated by simultaneous SPE on cation-exchange sorbents. The recoveries of all analytes, with the exception of epinephrine (75%), were over 80%. Catecholamines and metanephrines in the urine samples were quantitated using 3,4-dihydroxybenzylamine as an internal standard. Submicromolar concentrations, consistent with the catecholamine and metanephrine levels reported for normal human urine, were detected.

3,4-Dihydroxyphenylacetaldehyde and hydrogen peroxide generate a hydroxyl radical: possible role in Parkinson's disease pathogenesis

3,4-Dihydroxyphenylacetaldehyde (DOPAL) and 3,4-dihydroxyphenylglycolaldehyde (DOPEGAL), the monoamine oxidase (MAO) metabolites of dopamine (DA) and norepinephrine (NE), respectively, are toxic to catecholamine (CA) neurons in vitro and in vivo. DOPEGAL generates a free radical and activates mitochondrial permeability transition, a mechanism implicated in neuron death. To determine if DOPAL and other DA metabolites generate the hydroxyl radical in the presence of H(2)O(2), we used HPLC-EC to detect salicylate hydroxylation products. To determine the relative reducing capacity of DOPAL and DOPEGAL we used cyclic voltammetry to measure their reduction potentials. Results indicate that DOPAL, but not DOPEGAL, DA or other DA metabolites, generates hydroxyl radicals. Atomic absorption spectroscopy and heavy metal screening indicate that this result is not due to contamination of DOPAL with iron or other heavy metals. DOPAL reduction potential (161 mV) is lower than that of DOPEGAL (235 mV). DOPAL is present in human substantia nigra. The implications of these findings to CA neuronal death in degenerative brain diseases are discussed.

Catecholamine monoamine oxidase a metabolite in adrenergic neurons is cytotoxic in vivo

3,4-Dihydroxyphenylglycolaldehyde is the monoamine oxidase-A metabolite of two catecholamine neurotransmitters, epinephrine and norepinephrine. This aldehyde metabolite and its synthesizing enzymes increase in cell bodies of catecholamine neurons in Alzheimer's disease. To test the hypothesis that 3,4-dihydroxyphenylglycolaldehyde, but not epinephrine or its major metabolite 4-hydroxy-3-methoxyphenylglycol, is a neurotoxin, we injected 3,4-dihydroxyphenylglycolaldehyde onto adrenergic neurons in the rostral ventrolateral medulla. Injections of epinephrine or 4-hydroxy-3-methoxyphenylglycol were made into the same area of controls. A dose response and time study were performed. Adrenergic neurons were identified by their content of the epinephrine synthesizing enzyme, phenylethanolamine N-methyltransferase, immunohistochemically. Apoptosis was evaluated by in situ terminal deoxynucleotidyl-transferase mediated dUTP nick end label staining. Injection of 3,4-dihydroxyphenylglycolaldehyde in amounts as low as 50 ng results in loss of adrenergic neurons and apoptosis after 18 h. The degree of neurotoxicity is dose and time dependent. Doses of 3,4-dihydroxyphenylglycolaldehyde 10-fold higher produce necrosis. Neither epinephrine nor 4-hydroxy-3-methoxyphenylglycol are toxic. A 2.5 microg injection of 3,4-dihydroxyphenylglycolaldehyde is toxic to cortical neurons but not glia. Active uptake of the catecholamine-derived aldehyde into differentiated PC-12 cells is demonstrated. Implications of these findings for catecholamine neuron death in neurodegenerative diseases are discussed.