Free Dopamine Research Articles

Neurodegenerative Shielding by Curcumin and Its Derivatives on Brain Lesions Induced by 6-OHDA Model of Parkinson's Disease in Albino Wistar Rats

Study was undertaken to evaluate the neurodegenerative defending potential of curcumin (CUR), demethoxycurcumin (DMC), and bisdemethoxycurcumin (BDMC) on 6-hydroxydopamine-(6-OHDA) induced Parkinsonism model in rats. Curcuminoids were administered (60 mg/kg, body weight, per oral) for three weeks followed by unilateral injection of 6-OHDA on 22nd day (10 μg/2 μL) into the right striatum leading to extensive loss of dopaminergic cells. The behavioral observations, biochemical markers, quantification of dopamine (DA), DOPAC, and HVA followed by dopamine (D2) receptor binding assay and tyrosine hydroxylase (TH, using immunohistochemistry) were evaluated using HPLC after three weeks of lesion. Pretreated animals showed significant protection against neuronal degeneration compared to lesion animals by normalizing the deranged levels of biomarkers and showed the potency in the order CUR > DMC > BDMC. The same order of effectiveness was observed in D2 receptors binding assay and TH immunohistochemistry study. We conclude that curcuminoids appear to shield progressive neuronal degeneration from increased oxidative attack in 6-OHDA-lesioned rats through its free radical scavenging mechanism, and DA, DOPAC, and HVA enhancing capabilities in the sequence of efficacy CUR > DMC > BDMC. Further, curcuminoids may have potential utility in treatment of many more oxidative stress-induced neurodegenerative disorders.

L-DOPA induced-endogenous 6-hydroxydopamine is the cause of aggravated dopaminergic neurodegeneration in Parkinson’s disease patients

Dopamine replacement therapy by 3,4-dihydroxyphenylalanine (L-DOPA), which is the gold standard symptomatic treatment for the Parkinson’s disease (PD), frequently leads to potential debilitating side-effects such as dyskinesia. One of the most significant molecules reported to be produced endogenously in the brain is 6-hydroxydopamine (6-OHDA), contributed solely by unsequestered dopamine in neurons derived from L-DOPA. It is further demonstrated that scavengers of hydroxyl radicals such as melatonin and salicylic acid inhibited its generation. However no reports on the level of 6-OHDA and hydroxyl radicals generated in vivo in human brain is known. Oxidative stress and mitochondrial dysfunction are known to be associated with Lewy body formation, which is directly dependent on the levels of free dopamine. Therefore, it is hypothesized that L-DOPA induced increase in endogenous 6-OHDA levels will have the ability to cause oxidative stress and mitochondrial dysfunctions that eventually leads to Lewy body formation in dopaminergic neurons resulting in its degeneration. Concomitant use of potent anti-oxidants along with L-DOPA would help in attenuating the neurodegeneration caused by endogenous 6-OHDA and would ultimately delay the progression of PD.

Quantitative Determination of Free and Total Dopamine in Human Plasma by LC–MS/MS: The Importance of Sample Preparation

Two methods have been developed and validated for the determination of free and total dopamine in human plasma. They are based on solid-phase extraction of the analyte from the matrix by covalent complexation with phenylboronic acid, followed by derivatization with ethylchloroformate. The derivative is quantified by reversed-phase liquid chromatography on a C18 column and positive electrospray ionization MS/MS. The high selectivity obtained, in combination with the stable and relatively non-polar nature of the derivatized analyte, enables the reliable quantification of dopamine in the range 0.05 to 20 ng/ml in a 5 min run time, using only 100 µl of sample. Total dopamine concentrations are determined (range 1 to 400 ng/ml) by including an acidic hydrolysis step, which converts the sulphate and glucuronide conjugates to free dopamine prior to extraction. The method was applied to quantify free and total dopamine levels in human plasma after dosing with the anti-Parkinson's drug combination L-dopa/carbidopa with and without entacapone. A sensitive and selective LC-MS/MS method has been developed and validated for the determination of free and total dopamine in human plasma. This article demonstrates how essential careful optimization of the sample preparation procedures was for developing a successful method.

Iron species-mediated dopamine oxidation, proteasome inhibition, and dopaminergic cell demise: Implications for iron-related dopaminergic neuron degeneration

Iron species have been suggested to be highly involved in the pathogenesis of Parkinson disease. However, the detailed mechanism of iron-induced dopaminergic degeneration is still unclear. In this study, we demonstrate that free iron ions (trivalent or bivalent) and iron ions in stable complex with cyanide ions (K 4Fe(CN) 6 and K 3Fe(CN) 6) can induce dopamine (DA) oxidation with different profiles and subsequently lead to proteasome inhibition and even dopaminergic MN9D cell demise via different mechanisms. The free iron ions could mediate extensive DA oxidation in an iron–DA complex-dependent manner. However, iron ions in stable complex with cyanide ions could not induce, or could induce only brief, DA oxidation. Deferoxamine, a specific iron ion chelator, could disrupt iron–DA complex formation and thus abrogate free iron ion-catalyzed DA oxidation and subsequent cell toxicity. Glutathione could neither disrupt iron–DA complex formation nor influence free iron ion-catalyzed DA oxidation but could protect against iron-mediated toxicity via detoxification of toxic by-products of iron-mediated DA oxidation. The resulting DA oxidation could inhibit chymotrypsin-like, trypsin-like, and caspase-like proteasome activities. However, we demonstrated that oxidative damage was not the major toxic mechanism of MN9D cell degeneration, but it was the DA quinones derived from iron-induced DA oxidation that contributed significantly to proteasome inhibition and even dopaminergic cell demise.

Elevated Urinary Free and Deconjugated Catecholamines after Consumption of a Catecholamine-Rich Diet

The biochemical diagnosis of pheochromocytoma depends on the demonstration of elevated levels of catecholamines (i.e. epinephrine, norepinephrine, and dopamine) and their metabolites. The aim of the study was to determine the preanalytical influence of a catecholamine-rich diet on urinary free and deconjugated catecholamines in healthy volunteers with a highly specific and sensitive analytical technique. We conducted a crossover study involving 27 healthy adults in a specialist medical center. Subjects consumed catecholamine-rich nuts and fruits at fixed times on one day (about 35 micromol dopamine and 1 micromol norepinephrine) and catecholamine-poor products on another day. Urine samples were collected at timed intervals before, during, and after experimental and control interventions. We performed automated online sample preparation coupled to isotope-dilution mass spectrometry measurements of urinary concentrations of free and deconjugated catecholamines. The catecholamine-rich diet had substantial effects on urinary excretions of deconjugated dopamine (up to 20-fold increases) and norepinephrine (up to 10-fold). Dietary catecholamines had less but significant effects on urinary excretion of free dopamine and norepinephrine (up to 1.5-fold increases). Outputs of urinary free and deconjugated epinephrine remained unaffected. Urinary excretion of deconjugated norepinephrine and dopamine is strongly affected by consumption of catecholamine-rich food products, thereby increasing the likelihood of a false-positive test result during hormonal evaluation for pheochromocytoma. Measurement of deconjugated catecholamines should therefore preferably be avoided, in favor of measurement of urinary free catecholamines. In case of demonstrating increased urinary excretion of deconjugated norepinephrine and dopamine, repeated measurements are warranted with dietary restrictions prior to sample collection.

Specific oxidative stress profile associated with partial striatal dopaminergic depletion by 6-hydroxydopamine as assessed by a novel multifunctional marker molecule

Real time oxidative stress in the extracellular compartment of rat striatum was characterized by microdialysis with synthetic non-dialyzable marker molecules composed of linoleic acid, tyrosine and guanosine (N-linoleoyl tyrosine (LT) and N-linoleoyl tyrosine 2′-deoxyguanosyl ester (LTG)). Partial dopaminergic deafferentation was induced by injection of 6-hydroxydopamine (250 μg) to the left lateral ventricle, which depleted ipsilateral striatal dopamine by 46% and dopaminergic cells in left substantia nigra by 44%, 5 weeks after administration. Resting microdialysate dopamine levels in dopamine-depleted striatum were not different from sham-operated rats, although the ratio of oxidized metabolites of dopamine to free dopamine was significantly increased. Hydroperoxide and epoxy products of the linoleoyl portion of LT and LTG were detected in the striatal microdialysate by LC/MS/MS following initial separation by HPLC and were significantly increased in dopamine-depleted compared with control striatum without an increase in guanosine or tyrosine oxidation or nitration. Systemic administration of N-acetyl cysteine (350 mg/kg i.p.) decreased the increment in hydroperoxide and epoxy metabolites to levels not significantly different from control. Oxidation activity towards polyunsaturated fatty acids is present in the extracellular space of partially dopamine-denervated striatum, whereas oxidized glutathione and oxysterol levels in striatal tissue are decreased, possibly indicative of a compensatory response.

Not all partial dopamine D2 receptor agonists are the same in treating schizophrenia. Exploring the effects of bifeprunox and aripiprazole using a computer model of a primate striatal dopaminergic synapse

Species differences in physiology and unique active human metabolites contribute to the limited predictive value of preclinical rodent models for many central nervous system (CNS) drugs. In order to explore possible drivers for this translational disconnect, we developed a computer model of a dopaminergic synapse that simulates the competition among three agents and their binding to pre- and postsynaptic receptors, based on the affinities for their targets and their actual concentrations. The model includes presynaptic autoreceptor effects on neurotransmitter release and modulation by presynaptic firing frequency and is calibrated with actual experimental data on free dopamine levels in the striatum of the rodent and the primate. Using this model, we simulated the postsynaptic dopamine D2 receptor activation levels of bifeprunox and aripiprazole, two relatively similar dopamine D2 receptor agonists. The results indicate a substantial difference in dose–response for the two compounds when applying primate calibration parameters as opposed to rodent calibration parameters. In addition, when introducing the major human and rodent metabolites of aripiprazole with their specific pharmacological activities, the model predicts that while bifeprunox would result in a higher postsynaptic D2 receptor antagonism in the rodent, aripiprazole would result in a higher D2 receptor antagonism in the primate model. Furthermore, only the highest dose of aripiprazole, but not bifeprunox, reaches postsynaptic functional D2 receptor antagonism similar to 4 mg haloperidol in the primate model. The model further identifies a limited optimal window of functionality for dopamine D2 receptor partial agonists. These results suggest that computer modeling of key CNS processes, using well-validated calibration paradigms, can increase the predictive value in the clinical setting of preclinical animal model outcomes.

Synergistic dopaminergic neurotoxicity of manganese and lipopolysaccharide: differential involvement of microglia and astroglia

Overexposure to manganese is known to cause damage to basal ganglial neurons and the development of movement abnormalities. Activation of microglia and astrocytes has increasingly been associated with the pathogenesis of a variety of neurological disorders. We have recently shown that microglial activation facilitates manganese chloride (MnCl2, 10-300 microM)-induced preferential degeneration of dopamine (DA) neurons. In this study, we report that combinations of MnCl2 (1-30 microM) and endotoxin lipopolysaccharide (LPS, 0.5-2 ng/mL), at minimally effective concentrations when used alone, induced synergistic and preferential damage to DA neurons in rat primary neuron-glia cultures. Mechanistically, MnCl2 significantly potentiated LPS-induced release of tumor necrosis factor-alpha and interleukin-1 beta in microglia, but not in astroglia. MnCl2 and LPS were more effective in inducing the formation of reactive oxygen species and nitric oxide in microglia than in astroglia. Furthermore, MnCl2 and LPS-induced free radical generation, cytokine release, and DA neurotoxicity was significantly attenuated by pre-treatment with potential anti-inflammatory agents minocycline and naloxone. These results demonstrate that the combination of manganese overexposure and neuroinflammation is preferentially deleterious to DA neurons. Moreover, these findings not only shed light on the understanding of manganese neurotoxicity but may also bear relevance to the potentially multifactorial etiology of Parkinson's disease.

Analysis of Intact Glucuronides and Sulfates of Serotonin, Dopamine, and Their Phase I Metabolites in Rat Brain Microdialysates by Liquid Chromatography−Tandem Mass Spectrometry

A method for the analysis of intact glucuronides and sulfates of common neurotransmitters serotonin (5-HT) and dopamine (DA) as well as of 5-hydroxy-3-indoleacetic acid (5-HIAA), 3,4-dihydroxyphenylacetic acid (DOPAC), and homovanillic acid (HVA) in rat brain microdialysates by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was developed. Enzyme-assisted synthesis using rat liver microsomes as a biocatalyst was employed for the production of 5-HT-, 5-HIAA-, DOPAC-, and HVA-glucuronides for reference compounds. The sulfate conjugates were synthesized either chemically or enzymatically using a rat liver S9 fraction. The LC-MS/MS method was validated by determining the limits of detection and quantitation, linearity, and repeatability for the quantitative analysis of 5-HT and DA and their glucuronides, as well as of 5-HIAA, DOPAC, and HVA and their sulfate-conjugates. In this study, 5-HT-glucuronide was for the first time detected in rat brain. The concentration of 5-HT-glucuronide (1.0-1.7 nM) was up to 2.5 times higher than that of free 5-HT (0.4-2.1 nM) in rat brain microdialysates, whereas the concentration of DA-glucuronide (1.0-1.4 nM) was at the same level or lower than the free DA (1.2-2.4 nM). The acidic metabolites of neurotransmitters, 5-HIAA, HVA, and DOPAC, were found in free and sulfated form, whereas their glucuronidation was not observed.

Urinary excretion of free catecholamines in long-term treatment with dopaminergic agonists.

Urinary excretion of free adrenaline, noradrenaline and dopamine was examined in 12 patients with active acromegaly before and during long-term therapy (6-22 months) with ergoline derivatives bromocriptine (20-30 mg daily) and lisuride (1-2 mg daily). A significant fall in noradrenaline values (4.5 +/- 0.95 (SEM) nmol/h on v.s. 15.3 +/- 3.8 nmol/h before the treatment, P less than 0.01) was found in the treated patients. Adrenaline excretion rose in most patients but the difference was not significant (1.43 +/- 0.33 nmol/h on v.s. 1.02 +/- 0.36 nmol/h before the treatment, P greater than 0.05). No significant change was seen in the dopamine excretion (71.3 +/- 9.58 nmol/h on v.s. 75.0 +/- 7.0 nmol/h before the treatment, P greater than 0.05). Our studies confirm the blood pressure lowering effect of bromocriptine and lisuride even when used on a long-term basis. This effect seems to be associated with reduced sympathetic activity.

DJ-1 protects against dopamine toxicity

Parkinson's disease (PD) is a slowly progressive neurodegenerative disorder characterized by the loss of dopaminergic neurons. Dopamine is a highly toxic compound leading to generation of reactive oxygen species (ROS). DJ-1 mutations lead to early-onset inherited PD. Here, we show that DJ-1 protects against dopamine toxicity. Dopamine-exposure led to upregulation of DJ-1. Overexpression of DJ-1 increased cell resistance to dopamine toxicity and reduced intracellular ROS. Contrary effects were achieved when DJ-1 levels were reduced by siRNA. Similarly, in vivo striatal administration of 6-hydroxydopamine led to upregulation of DJ-1. Upregulation of DJ-1 was mediated by the MAP kinases pathway through activation of ERK 1, 2 in vitro and in vivo. Hence, oxidative stress, generated by free cytoplasmic dopamine, leads to upregulation of DJ-1 through the MAP kinases pathway. This mechanism elucidates how mutations in DJ-1 prompt PD and imply that modulation of DJ-1 may serve as a novel neuroprotective modality.

Abstract 3484: High Plasma Levels of Endogenous Free Dopamine Predict an Adverse Outcome in Patients with Heart Disease and Chronic Kidney Disease

Sympathetic activity is heightened in chronic kidney disease (CKD). The increased sympathetic activity is a risk of future cardiovascular disease (CVD) events. Dopamine, a precursor of norepinephrine biosynthesis, is metabolized in the kidney and excreted into urine, and its plasma levels are increased in renal dysfunction. Thus, we examined whether plasma levels of endogenous dopamine may be related to future CVD events in patients with CKD. A total of 840 patients in stable condition with chronic heart disease (622 patients with ischemic heart disease and 218 with non-ischemic heart disease) (586 patients with GFR ≥ 60 ml/min/1.73 m 2 [normal/mild CKD]; 153 patients with 60 > GFR ≥ 30 [moderate CKD]; 101 patients with 30 > GRF [advanced CKD]) were prospectively followed-up for 5 years or until one of the following CVD events: cardiac death, non-fatal myocardial infarction, unstable angina pectoris requiring unplanned revascularization, worsening heart failure requiring hospitalization, or stroke. Plasma levels of endogenous free dopamine at entry were measured by high-performance liquid chromatography. Patients with a higher stage of CKD had higher dopamine levels than patients with a lower stage (63.0 ± 5.5, 45.0 ± 5.1, and 26 ± 1.2 pg/mL, respectively, ρ = 0.54, p < 0.0001 Spearman rank correlation test). During the follow-up period, 233 patients had CVD events (cardiac death in 54, myocardial infarction in 18, others events in 161) (113 events [19%] in normal/mild CKD, 64 [42%] in moderate CKD, and 56 [55%] in advanced CKD). In patients with moderate CKD and advanced CKD, higher dopamine levels (≥ 40 pg/mL, defined by ROC analysis) were the strongest predictor of CVD events (HR 2.1 and 3.3, 95% CI 1.2 – 3.7 and 1.5 – 7.2, p = 0.006 and 0.003, respectively) in a multivariate Cox hazards analysis using plasma norepinephrine and BNP levels, hypertension, and hyperlipidemia as covariates. In contrast, dopamine levels did not have predictive value in normal/mild CKD (HR 1.2, 95% CI 0.7 – 2.0, p = 0.5). High plasma levels of endogenous free dopamine are a risk factor for future CVD in patients with CKD independently of norepinephrine levels. Increases in plasma endogenous free dopamine levels may serve as a mechanistic link between CKD and CVD.

Effects of long-term administration of a cocoa polyphenolic extract (Acticoa powder) on cognitive performances in aged rats

Numerous studies have indicated that increased vulnerability to oxidative stress may be the main factor involved in functional declines during normal and pathological ageing, and that antioxidant agents, such as polyphenols, may improve or prevent these deficits. We examined whether 1-year administration of a cocoa polyphenolic extract (Acticoa powder), orally delivered at the dose of 24 mg/kg per d between 15 and 27 months of age, affects the onset of age-related cognitive deficits, urinary free dopamine levels and lifespan in old Wistar-Unilever rats. Acticoa powder improved cognitive performances in light extinction and water maze paradigms, increased lifespan and preserved high urinary free dopamine levels. These results suggest that Acticoa powder may be beneficial in retarding age-related brain impairments, including cognitive deficits in normal ageing and perhaps neurodegenerative diseases. Further studies are required to elucidate the mechanisms of cocoa polyphenols in neuroprotection and to explore their effects in man.

Competitive enzyme-linked immunosorbent assay for the determination of catecholamine, dopamine in serum

A competitive enzyme-linked immunosorbent assay for dopamine (DA) has been optimized and characterized. DA is sensitive to oxygen and light according to a function of the pH on the DA oxidation process. The phenolic groups in DA are readily oxidisable to a quinoid form and thus, free DA deteriorates in alkaline media. Thus, effect of factors such as pH, enzyme-label with substrate, ionic strength and reaction time was considered on performance of ELISA. Assay was performed with 5 μg mL −1 of BSA–DA and 1/7500 dilution of anti-DA antibody. A dose–response curve was constructed, and a limit of detection and a dynamic range for DA were accomplished to 1.0 × 10 −9 M (0.19 μg L −1) and five orders (3.2 × 10 −8 M to 3.2 × 10 −3 M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown good agreement with correlation coefficient ( R 2 = 0.9947): Abs. (in serum) = 0.6128 × Abs. (in buffer) + 0.2926. The cross-reactivity was examined with the structurally similar compounds. And the results demonstrated that epinephrine and 3-methoxytyramine showed cross-reactivity (18.9% each), whereas 3,4-dihydroxyphenylacetic acid and homovanillic acid showed low cross-reactivity (<1%). And percent recoveries of DA in serum were quite satisfactory. This provides usefulness of the present assay to monitor DA in serum.

Estimation from PET data of transient changes in dopamine concentration induced by alcohol: support for a non-parametric signal estimation method

We previously developed a model-independent technique (non-parametric ntPET) for extracting the transient changes in neurotransmitter concentration from paired (rest & activation) PET studies with a receptor ligand. To provide support for our method, we introduced three hypotheses of validation based on work by Endres and Carson (1998 J. Cereb. Blood Flow Metab. 18 1196–210) and Yoder et al (2004 J. Nucl. Med. 45 903–11), and tested them on experimental data. All three hypotheses describe relationships between the estimated free (synaptic) dopamine curves (FDA(t)) and the change in binding potential (ΔBP). The veracity of the FDA(t) curves recovered by nonparametric ntPET is supported when the data adhere to the following hypothesized behaviors: (1) ΔBP should decline with increasing DA peak time, (2) ΔBP should increase as the strength of the temporal correlation between FDA(t) and the free raclopride (FRAC(t)) curve increases, (3) ΔBP should decline linearly with the effective weighted availability of the receptor sites. We analyzed regional brain data from 8 healthy subjects who received two [11C]raclopride scans: one at rest, and one during which unanticipated IV alcohol was administered to stimulate dopamine release. For several striatal regions, nonparametric ntPET was applied to recover FDA(t), and binding potential values were determined. Kendall rank-correlation analysis confirmed that the FDA(t) data followed the expected trends for all three validation hypotheses. Our findings lend credence to our model-independent estimates of FDA(t). Application of nonparametric ntPET may yield important insights into how alterations in timing of dopaminergic neurotransmission are involved in the pathologies of addiction and other psychiatric disorders.

Preventing effects of a novel anti-parkinsonian agent zonisamide on dopamine quinone formation

The neurotoxicity of dopamine (DA) quinones as dopaminergic neuron-specific oxidative stress is considered to play a role in the pathogenesis and/or progression of Parkinson's disease (PD), since DA quinones conjugate with several key PD pathogenic molecules ( e.g., tyrosine hydroxylase, α-synuclein and parkin) to form protein-bound quinone (quinoprotein) and consequently inhibit their functions. Zonisamide (ZNS) is used as an anti-epileptic agent but also improved the cardinal symptoms of PD in recent clinical trials in Japan. To evaluate the effects of ZNS on excess cytosolic free DA-induced quinone toxicity, we examined changes in DA quinone-related indices after ZNS treatment both in in vitro cell-free system and in cultured cells. Co-incubation of DA and ZNS in a cell-free system caused conversion of DA to stable melanin via formation of DA-semiquinone radicals and DA chrome. Long-term (5 days) treatment with ZNS decreased quinoprotein and increased DA/DOPA chromes in dopaminergic CATH.a cells. ZNS significantly inhibited quinoprotein formation induced by treatment with tetrahydrobiopterin and ketanserin that elevate cytosolic free DA in the cells. Our results suggest that the novel anti-parkinsonian agent ZNS possesses preventing effects against DA quinone formation induced by excess amount of cytosolic DA outside the synaptic vesicles.

Inhibition of VMAT-2 and DT-Diaphorase Induce Cell Death in a Substantia Nigra-Derived Cell LineAn Experimental Cell Model for Dopamine Toxicity Studies

We have induced intracellular dopamine oxidation to aminochrome in RCSN-3 cells derived from rat substantia nigra by inhibiting VMAT-2 with reserpine to increase free cytosolic dopamine concentration, to study aminochrome-dependent neurotoxicity in the absence of exogenous oxidizing agents such as metals, which may potentiate an aminochrome cytotoxic effect. The expression of VMAT-2 in RCSN-3 cells was determined by reverse transcriptase-polymerase chain reaction and immunocytochemistry. We observed double membrane bodies containing melanin when RCSN-3 cells were incubated with 100 microM dopamine by using transmission electron microscopy. No significant difference in the cell death was observed when the cells were treated 100 microM dopamine and 25 microM reserpine in the absence or presence of 100 microM dicoumarol, an inhibitor of DT-diaphorase. The lack of effect was due to the inhibitory action of 25 microM reserpine on DT-diaphorase (Ki = 24 microM). However, a significant increase in the cell death was observed when DT-diaphorase was inhibited when the cells were incubated with 1 microM reserpine and 100 microM dopamine for 12 h since at this concentration reserpine inhibits VMAT-2 but not DT-diaphorase. Under this condition, we observed (i) the formation of blebbing; (ii) chromatin condensation accompanied by the formation of massive patches in contact with the nuclear membrane; (iii) the smoothness of the cell's surface, that is, lack of surface microprojections; and (iv) mitochondrial damage characterized by disruption of cristae architecture, which remains closely packed; disorganization of the mitochondrial matrix due to separation of the outer membrane from the internal membrane and considerable enlargement of the intermembrane space; and disruption of the external mitochondrial membrane determined by transmission electron microscopy. These results support the proposed neuroprotective role of DT-diaphorase against aminochrome neurotoxicity, and it suggests that RCSN-3 cells incubated with reserpine and dopamine are an excellent and more physiological cellular experimental model to study the role of dopamine oxidation in neurotoxic effects of dopamine.

Association of High Levels of Plasma Free Dopamine With Future Coronary Events in Patients With Coronary Artery Disease

There is an intimate relationship between activation of the sympathetic nervous system and myocardial ischemia. This study examined whether plasma levels of dopamine, a precursor of norepinephrine, may provide prognostic information in coronary artery disease (CAD). Plasma levels of free dopamine were measured by high-performance liquid chromatography in 210 consecutive patients with stable CAD. The patients were prospectively followed up for a period of < or =36 months until occurrence of a clinical coronary event. Coronary events occurred in 37 patients during follow-up. In Kaplan-Meier survival analysis, higher dopamine levels (> or =30 pg/ml) resulted in a higher event probability (p<0.01). Multivariate Cox hazards analysis showed that higher dopamine levels were a significant and independent risk factor for future coronary events (hazard ratio 3.3, 95% confidence interval 1.3-8.1, p<0.01). Furthermore, patients with higher dopamine levels had lower left ventricular (LV) ejection fraction and higher levels of brain natriuretic peptide, C-reactive protein, and fibrinogen than those with lower dopamine levels. Plasma levels of free dopamine are increased in association with a decrease in LV function and an increase in inflammatory risk markers. Higher free dopamine levels are an independent risk factor for future coronary events in CAD patients.

Do Dopamine Receptors Mediate Part of MAC?

Depletion of central nervous system catecholamines, including dopamine, can decrease MAC (the minimum alveolar concentration of an inhaled anesthetic required to suppress movement in response to a noxious stimulus in 50% of test subjects); release of central nervous system catecholamines, including dopamine, can increase MAC; and increased free dopamine concentrations in the striatum can decrease MAC. Such findings suggest that dopamine receptors might mediate part of the capacity of inhaled anesthetics to provide immobility in the face of noxious stimulation. We measured the effect of blockade of D2 dopamine-mediated transmission with 0.3 mg/kg or 3.0 mg/kg droperidol on the MAC of cyclopropane, desflurane, halothane, isoflurane, or sevoflurane in rats, and the effect of 3.0 mg/kg droperidol on the dose or concentration of etomidate (an anesthetic known to act principally by enhancing the response of gamma-aminobutyric acid(A) receptors to gamma-aminobutyric acid) required to suppress movement in response to noxious stimulation. Blockade of D2 dopamine-mediated transmission with droperidol does not decrease the MAC of cyclopropane, desflurane, halothane, isoflurane, or sevoflurane or its equivalent for etomidate in rats. These data, plus data from studies by others about D1 dopamine receptors, indicate that dopamine receptors do not mediate the immobility produced by inhaled anesthetics.

L-DOPA treatment from the viewpoint of neuroprotection

With regard to the mechanism of selective dopaminergic neuronal death, experimental results of studies on the neurotoxicity of MPTP and rotenone indicate that degeneration of dopamine neurons is closely related to mitochondrial dysfunction, inflammatory process and oxidative stress, particularly with regard to the generation of quinones as dopamine neuron-specific oxidative stress. Thus, it is now clear that the presence of high levels of discompartmentalized free dopamine in dopaminergic neurons may explain the specific vulnerability of dopaminergic neurons through the generation of highly toxic quinones.