The thiol antioxidant 1,2-dithiole-3-thione stimulates the expression of heat shock protein 70 in dopaminergic PC12 cells

In Parkinson's disease (PD), the pathogenic factors oxidative stress and protein aggregation interact and culminate in the apoptotic death of (mainly catecholaminergic) neurons. The dithiolethiones comprise thiol antioxidants that are well known for their activation of the expression of a wide collection of cytoprotective genes, including genes coding for antioxidant enzymes. Given the observation that heat shock proteins (HSPs), in particular the heat shock protein 72 (HSP72), protects against cellular degeneration in various models of PD, the ability of the unsubstituted dithiolethione 1,2-dithiole-3-thione (D3T) to stimulate heat shock protein gene and protein expression was studied using the dopaminergic PC12 cell line. As anticipated, D3T stimulated the expression of the antioxidant enzyme NAD(P)H:quinone oxidoreductase 1 (NQO1). Quantitative PCR analysis revealed that D3T stimulates the expression of the inducible, cytoplasmic HSP72. Moreover, D3T strongly potentiated HSP72 gene and protein expression in heat-stressed cells. Taken together, our data show that, in addition to antioxidant enzymes, D3T stimulates the expression of HSP72, a chaperone shown to be neuroprotective in various models of PD, in particular under conditions of cellular stress. Thus, the broad range manipulation of endogenous cellular defense mechanisms, through D3T, may represent an innovative approach to therapeutic intervention in PD.

Changed distribution pattern of the constitutive rather than the inducible HSP70 chaperone in neuromelanin-containing neurones of the Parkinsonian midbrain

Aberrant protein aggregation has been recognized as an important factor in the degeneration of melanized dopaminergic neurones in Parkinson's disease (PD). The constitutive (HSP73) and (heat)-inducible (HSP72) proteins of the heat shock 70 family form a major defence system against pathological protein aggregation. However, the distribution patterns of these chaperones in nigral neuromelanin-laden neurones are largely unknown. The present study determined the distribution of HSP72 and HSP73 in control and Parkinsonian substantia nigra, using immunohistochemistry. In the neuromelanin-laden neurones of controls, HSP72 was nondetectable, whereas HSP73 was weakly expressed in both the cytosol and the nucleus. Surprisingly, in PD subjects, marked nuclear HSP73, but not HSP72 immunoreactivity was observed, while cytosolic immunoreactivity of the two chaperones resembled the labelling pattern observed in controls. Furthermore, HSP73 immunoreactivity was observed in a subset of the Lewy bodies (LBs) detected in the substantia nigra of PD subjects, whereas only few of these LBs were labelled with HSP72. Interestingly, HSP72 and to a lesser extent HSP73 immunoreactivity was much stronger in nonmelanized neurones as compared with melanized neurones in this area. Thus, we conclude that the distribution pattern of HSP73 rather than HSP72 is changed in the nigral neuromelanin-laden neurones of PD subjects as compared with control subjects. The impaired ability of aged, dopaminergic neurones to express high levels of chaperones, may contribute to the preferential vulnerability of the latter cells in PD.

The antioxidant anethole dithiolethione inhibits monoamine oxidase-B but not monoamine oxidase A activity in extracts of cultured astrocytes

Anethole dithiolethione (ADT) is a clinically available, pluripotent antioxidant proposed as a neuroprotectant for Parkinson's disease (PD). Here, using extracts from cultured astrocytes, containing both monoamine oxidase (MAO) A and B activity, we demonstrate that ADT concentration-dependently inhibits MAO-B activity in a clinically relevant concentration range (0.03-30 microM, IC-50 = 0.5 microM) without affecting MAO A activity. Considering the alleged contribution of MAO activity in general, and MAO-B in particular, to oxidative stress and neurodegeneration in PD, our data further support the neuroprotective potential of ADT.

Expression of NAD(P)H:quinone oxidoreductase in the normal and Parkinsonian substantia nigra

Dopamine (DA) autooxidation, and consequent formation of neurotoxic DA-derived quinones and reactive oxygen species, has been implicated in dopaminergic cell death and, hence, in the pathogenesis of Parkinson's disease (PD). Stimulation of pathways involved in the detoxication of DA-quinones in the brain is hypothesized to be an effective means to limit oxidative stress and to confer neuroprotection in PD. In this respect, the inducible flavoprotein NAD(P)H:quinone oxidoreductase (NQO1) is of particular interest as it is directly implicated in the detoxication of DA-quinones and, in addition, has broad spectrum anti-oxidant properties. To study the potential pathophysiological role of NQO1 in PD, the cellular expression of NQO1 was examined in the mesencephalon of PD patients and age-matched controls. In the substantia nigra pars compacta (SNpc), NQO1 was found to be expressed in astroglial and endothelial cells and, albeit less frequently, also in dopaminergic neurons. Moreover, while overt NQO1 immunoreactivity was absent in the surrounding nervous tissue, in the Parkinsonian SNpc a marked increase in the astroglial and neuronal expression of NQO1 was consistently observed.

Tissue transglutaminase catalyzes the formation of alpha-synuclein crosslinks in Parkinson's disease

In Parkinson's disease (PD), conformational changes in the alpha-synuclein monomer precede the formation of Lewy bodies. We examined postmortem PD and undiseased (control) substantia nigra for evidence of pathological crosslinking of alpha-synuclein by tissue transglutaminase (tTG) using immunohistochemistry, immunoprecipitation, and Western blot. Consistent with previous reports, we found that both tTG and its substrate-characteristic N(epsilon)-(gamma-glutamyl)-lysine crosslink are increased in PD nigral dopamine neurons. Furthermore, both the tTG protein and its substrate crosslink coprecipitated with alpha-synuclein in extracts of PD substantia nigra. Unexpectedly, the isodipeptide crosslink was detected in the alpha-synuclein monomer as well as in higher molecular mass oligomers of alpha-synuclein. Although the intramolecularly crosslinked alpha-synuclein monomer was present in control tissue, it was highly enriched in PD substantia nigra. Conversely, significantly less uncrosslinked alpha-synuclein remained in the postimmunoprecipitate lysate of PD tissue than in control. Crosslinked alpha-synuclein, formed at the expense of the total alpha-synuclein monomer, correlated with disease progression. These results demonstrate that much of the alpha-synuclein monomer in PD nigra is crosslinked by tTG and thus may be functionally impaired. This modification appears to be an early step in PD pathogenesis, preceding the aggregation of alpha-synuclein in Lewy bodies.

SKF 83959 is an antagonist of dopamine D1-like receptors in the prefrontal cortex and nucleus accumbens: a key to its antiparkinsonian effect in animals?

SKF 83959 that has a unique antiparkinson profile in animal models of Parkinson's disease is an in vitro dopamine D1 antagonist of receptors coupled to adenylyl cyclase. We hypothesized that SKF 83959, among others, interacts with dopamine D1 receptors coupled to adenylyl cyclase in the nucleus accumbens and the prefrontal cortex. Effects of intra-accumbal injections of SKF 83959 on locomotor activity were compared to effects of the dopamine D1 agonist SKF 81297 and the dopamine D1 antagonist SCH 39166. Similarly to SCH 39166, SKF 83959 did not affect locomotor activity, but counteracted SKF 81297-induced locomotor activity. Effects of unilateral intra-prefrontal injections of SKF 83959 on rotational behaviour were compared to the effects of the dopamine D1 agonist SKF 81297 and the dopamine D1 antagonists SCH 23390 and SCH 39166 in rats selected on basis of their high locomotor response to novelty and pretreated with a subcutaneous injection of 0.75 mg/kg dexamphetamine. Like SCH 39166 and SCH 23390, SKF 83959 induced a bias for contralateral rotating and blocked the SKF 81297-induced bias for ipsilateral rotating. In conclusion, SKF 83959 is an in vivo antagonist of dopamine D1 receptors that are coupled to adenylyl cyclase in the nucleus accumbens and the prefrontal cortex. The role of these receptors in the antiparkinson profile of SKF 83959 is discussed.

The neuroprotective effects of CGP 3466B in the best in vivo model of Parkinson's disease, the bilaterally MPTP-treated rhesus monkey

The propargylamine CGP 3466B prevents dopamine cell death both in vitro and in rodent models of Parkinson's disease. The present study investigates the efficacy of this compound to prevent the behavioral consequences of dopaminergic cell death in the best animal model of Parkinson's disease, the bilaterally MPTP-treated monkey. Rhesus monkeys were bilaterally treated with MPTP, using a two-step procedure: 2.50 mg MPTP was infused into the left carotid artery followed by a second bolus of 1.25 mg into the right carotid artery, 8 weeks later. Subcutaneous injection of either 0.014 mg/kg CGP 3466B (n = 4) or its solvent (distilled water; n = 4), twice daily for fourteen days, started two hours after the second MPTP infusion. A Parkinson rating scale was assessed for the evaluation of the effects. After the first MPTP treatment, the monkeys developed mild to moderate parkinsonian symptoms. The second MPTP treatment strongly increased the severity of Parkinson scores in all control monkeys, as assessed on day 3, 7, 14, 21, 28 and 35 after the second MPTP treatment. In contrast, CGP 3466B nearly completely prevented the increase of parkinsonian symptoms after the second MPTP treatment. The therapeutic effects of CGP 3466B were still present after a washout period of 3 weeks, implying that the effects were not symptomatic. These data are the first to show that the systemic administration of CGP 3466B is able to prevent the development of MPTP-induced motor symptoms in primates. This compound may have great value for inhibiting the progression of the neurodegenerative process in patients with Parkinson's disease.

Systemic administration of the propargylamine CGP 3466B prevents behavioural and morphological deficits in rats with 6-hydroxydopamine-induced lesions in the substantia nigra

The ability of CGP 3466B to attenuate the behavioural and morphological consequences of experimentally induced cell death was investigated in a recently updated animal model of Parkinson's disease. 6-Hydroxydopamine was infused bilaterally into the substantia nigra pars compacta of rats that were pretreated with desimipramine. Treatment with CGP 3466B (0.0014-1.4 mg/kg, injected subcutaneously) or its solvent was begun 2 h after the 6-OHDA injection, and maintained twice daily for 14 days. After a washout period of 14 days, changes in motor behaviour were evaluated, using the open field test (analysis of normal and abnormal stepping, e.g.) and the paw test (analysis of retraction time of limbs). Changes in learning and memory were evaluated with the help of the Morris water maze task. Following immunocytochemical staining of tyrosine hydroxylase, the extent of the lesion was quantified using a computerized system. CGP 3466B prevented all deficits produced by 6-hydroxydopamine (6-OHDA), though at different doses. It prevented: abnormal stepping (0.0014-0.014 mg/kg); increased forelimb and hindlimb retraction time (0.014-0.14 mg/kg and 0.0014-0.14 mg/kg, respectively); delayed learning (1.4 mg/kg); and reduced tyrosine hydroxylase immunoreactivity in the substantia nigra (0.0014-0.014 mg/kg). CGP 3466B (0.0014-0.14 mg/kg) induced no deficits in sham-treated rats. CGP 3466B (1.4 mg/kg), however, did not show any benefit on motor deficits in 6-OHDA-lesioned rats, and induced abnormal movements and decreased the tyrosine hydroxylase immunoreactivity in the substantia nigra pars compacta and the ventral tegmental area of sham-lesioned animals. It is concluded that CGP 3466B prevents all 6-OHDA-induced behavioural and immunocytochemical deficits, though at different doses. CGP 3466B is suggested to be a valuable agent for inhibiting the dopaminergic degeneration in patients with Parkinson's disease.

Sub-chronic administration of the dopamine D(1) antagonist SKF 83959 in bilaterally MPTP-treated rhesus monkeys: stable therapeutic effects and wearing-off dyskinesia

RATIONALE

SKF 83959 acts as a D(1) antagonist in vitro but has been claimed to induce anti-parkinsonian effects after acute administration in MPTP-treated marmosets.

OBJECTIVE

The aim of the present study was to evaluate the therapeutic and undesired effects of sub-chronic administration of SKF 83959 in bilaterally MPTP-treated rhesus monkeys and to compare these effects with the effects of l-dopa and the dopamine agonist SKF 82958.

METHODS

MPTP was given in the left carotid artery (2.5 mg) and 6 weeks later, the right carotid artery (1.25 mg). The monkeys (n = 4) had previously been treated chronically with l-dopa (22 days, 10 mg/kg) and SKF 82958 (22 days, 1 mg/kg). Three months after the last administration of SKF 82958, SKF 83959 was given in a dose of 0.5 mg/kg from day 1 to day 15 and in a dose of 1.0 mg/kg from day 16 to day 18.

RESULTS

SKF 83959 increased goal-directed limb movements in all animals, including those unresponsive to l-dopa. This therapeutic effect did not diminish during treatment. With respect to body displacement and undesired effects, a large variation in the response to SKF 83959 was found: a large increase in body displacement co-occurred with oro-facial dyskinesia (n = 2), whereas a small increase in body displacement co-occurred with dystonia (n = 2). In contrast to the undesired effects of l-dopa, the dyskinetic effects of SKF 83959 were primarily limited to the first treatment day. Unlike l-dopa and SKF 82958, SKF 83959 did not induce epileptoid behaviour.

CONCLUSION

Sub-chronic administration of SKF 83959 induced both clear-cut therapeutic effects that remained stable in time, and a limited number of dyskinetic effects that wore off during the treatment. The dopamine D(1) antagonist SKF 83959 may be considered as an alternative treatment in Parkinson's disease, especially in those patients who do not respond to L-dopa.

The validity of the pretreated, unilaterally MPTP-treated monkeys as a model of Parkinson's disease: a detailed behavioural analysis of the therapeutic and undesired effects of the D2 agonist quinpirole and the D1 agonist SKF 81297

The goal of this study was to evaluate the validity of the pretreated, unilaterally MPTP-treated monkey as an animal model of Parkinson's disease (PD). For that purpose, a detailed ethogram was developed and assessed in four male rhesus monkeys that had received MPTP (2.5 mg) in the carotid artery contralateral to the dominant limb. Subsequently, the behavioural effects of the dopamine D2 agonist quinpirole and the dopamine D1 agonist SKF 81297 were studied. The ethogram was found to allow a clear-cut and objective separation of drug-induced behaviours into therapeutic and undesired effects in the MPTP-treated monkeys. Saline-treated monkeys predominantly displayed ipsilateral goal-directed fore-limb movements, and distinct types of ipsilaterally directed rotations. Although quinpirole and SKF 81297 increased motor behaviours, such as body displacement, contralateral fore-limb movements and contralateral rotational behaviours, assessment of the new detailed ethogram revealed that this increase was completely due to the activation of abnormal, non-goal-directed behaviours, such as dyskinetic fore-limb movements, pivoting and shuffling. Moreover, the new ethogram made clear that the drug treatments induced not only dyskinesia and dystonia, but also epileptoid behaviour, which was confirmed by EEG analysis. In summary, the detailed behavioural analysis showed that this model does not adequately predict the clinical effects of the D2 agonist. It is concluded that the pretreated, unilaterally MPTP-treated monkey is not a valid model to predict the therapeutic and undesired effects of dopaminergic drugs in humans.

The predictive validity of the drug-naive bilaterally MPTP-treated monkey as a model of Parkinson's disease: effects of L-DOPA and the D1 agonist SKF 82958

The aim of this study was twofold: (1) to study the predictive validity of the drug-naive, bilaterally MPTP-treated monkey as an animal model of Parkinson's disease (PD), and (2) to investigate the therapeutic and undesired effects of the D1 agonist SKF 82958 as compared to L-DOPA treatment, in drug-naive and L-DOPA pretreated monkeys. A detailed ethogram was used, allowing the separation of therapeutic and undesired effects. Eight weeks after bilateral intracarotid MPTP administration, SKF 82958 (1 mg/kg, n = 4, SKF 82958, naive group) or methyl-L-DOPA + carbi-dopa (10 + 2.5 mg/kg, n = 4, L-DOPA group) was administered intramuscularly for 22 days. After a drug-free period of eight weeks, the L-DOPA group was treated with SKF 82958 for 22 days (SKF 82959, 1 mg/kg, n=4, pretreated). All drug treatments increased the parameters used classically to evaluate dopaminergic drugs, namely body displacement, dyskinesia and dystonia. However, the new detailed analysis revealed that L-DOPA, but not SKF 82958, had therapeutic effects, reflected by an increase in goal-directed fore-limb use. SKF 82958, but not L-DOPA, induced additional undesired effects; including epileptoid behaviours in both drug-naive and drug-pretreated monkeys. In one L-DOPA-unresponsive monkey, SKF 82958 did induce minor therapeutic effects, as well as undesired effects. Although the effects of SKF 82958 on fore-limb movements, rotational behaviours and body displacement were comparable in the naive and pretreated group, SKF 82958 re-initiated undesired effects in the L-DOPA pretreated group from day one. It is concluded that the bilaterally MPTP-treated monkey is an animal model with predictive validity for PD: it adequately predicts the therapeutic effects and undesired effects of L-DOPA. Furthermore, it is concluded that SKF 82958 is less effective than L-DOPA in the treatment of PD, because it did not induce therapeutic effects, but instead elicited several undesired effects.

The alleged dopamine D1 receptor agonist SKF 83959 is a dopamine D1 receptor antagonist in primate cells and interacts with other receptors

So far, no clear correlation has been found between the effects of dopamine D1 receptor agonists on motor behavior in primate models of Parkinson's disease and their ability to stimulate adenylate cyclase in rats, the benzazepine SKF 83959 (3-methyl-6-chloro-7,8-hydroxy-1-[3-methylphenyl]-2,3,4,5-tetrahydro-]H- 3-benzazepine) being the most striking example. Since this discrepancy might be attributed to: (A) the different species used to study these effects or (B) the interaction of SKF 83959 with other catecholamine receptors, the aims of this study were: (1) to study the ability of SKF 83959 to stimulate adenylate cyclase in cultured human and monkey glial cells equipped with dopamine D1 receptors and (2) to evaluate the affinity for and the functional interaction of SKF 83959 with other catecholamine receptors. Binding studies revealed that SKF 83959 displayed the highest affinity for the dopamine D1 receptor (pKi=6.72) and the alpha2-adrenoceptor (pKi=6.41) and moderate affinity for the dopamine D2 receptor and the noradrenaline transporter. In monkey and human cells, SKF 83959 did not stimulate cyclic adenosine monophosphate (cAMP) formation to a significant extent, but antagonized very potently the dopamine-induced stimulation of cAMP formation in both cell types. The compound stimulated basal dopamine outflow and inhibited depolarization-induced acetylcholine release only at concentrations > 10 microM. Finally, SKF 83959 concentration dependently increased electrically evoked noradrenaline release, indicating that it had alpha2-adrenoceptor blocking activity and interfered with the noradrenaline transporter. In conclusion, SKF 83959 is a potent dopamine D1 receptor and alpha2-adrenoceptor antagonist. Thus, the anti-parkinsonian effects of SKF 83959 in primates are not mediated by striatal dopamine D1 receptors coupled to adenylate cyclase in a stimulatory way.

[123I]FP-CIT binds to the dopamine transporter as assessed by biodistribution studies in rats and SPECT studies in MPTP-lesioned monkeys

[123I]FP-CIT (N-omega-fluoropropyl-2 beta-carbomethoxy-3 beta-(4-iodophenyl)-tropane), a radioiodinated cocaine analogue, was evaluated as an agent for the in vivo labeling of dopamine (DA) transporters by biodistribution studies in rats and by single photon emission computed tomography (SPECT) studies in unilateral 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkeys. In rats, intravenous injection of [123I]FP-CIT resulted in high accumulation of radioactivity in the striatum. Less pronounced uptake was seen in brain areas with high densities of serotonergic uptake sites. While striatal uptake of radioactivity after injection of [123I]FP-CIT was displaced significantly by GBR12,909 but not by fluvoxamine, the opposite was observed in brain areas known to be rich of serotonin transporters. Monkeys which were unilaterally treated with neurotoxic doses of MPTP showed severe loss of striatal [123I]FP-CIT uptake at the side of treatment. The results of this study indicate that [123I]FP-CIT, although not being a selective radioligand, binds specifically to the striatal DA transporter in vivo and thus suggest that [123I]FP-CIT promises to be a suitable radioligand for SPECT imaging of DA transporters in humans.

Exposure to chronic psychosocial stress and corticosterone in the rat: effects on spatial discrimination learning and hippocampal protein kinase Cgamma immunoreactivity

Previous reports have demonstrated a striking increase of the immunoreactivity of the gamma-isoform of protein kinase C (PKCgamma-ir) in Ammon's horn and dentate gyrus (DG) of rodent hippocampus after training in a spatial orientation task. In the present study, we investigated how 8 days of psychosocial stress affects spatial discrimination learning in a hole board and influences PKCgamma-ir in the hippocampal formation. The acquisition of both reference memory and working memory was significantly delayed in the stressed animals during the entire training period. With respect to cellular plasticity, the training experience in both nonstressed and stressed groups yielded enhanced PKCgamma-ir in the CA1 and CA3 regions of the posterior hippocampus but not in subfields of the anterior hippocampus. Stress enhanced PKCgamma-ir in the DG and CA3 pyramidal cells of the anterior hippocampus. In stressed animals that were subsequently trained, the PKCgamma-ir was increased in the posterior CA1 region to the same level as that found in nonstressed trained animals. Stress apparently abrogated the PKCgamma-ir training response in the CA3 region. In a second experiment, the elevation of plasma corticosterone levels to values that are found during stress did not significantly influence reference memory scores but slightly and temporarily affected working memory. The training-induced enhancement of PKCgamma-ir in the CA1 region was similar in trained and corticosterone-treated trained animals, but the learning-induced PKCgamma-ir response in the posterior CA3 area was absent after corticosterone pretreatment. These results reveal that prolonged psychosocial stress causes spatial learning deficits, whereas artificial elevation of corticosterone levels to the levels that occur during stress only mildly affects spatial memory performance. The spatial learning deficits following stress are reflected only in part in the redistribution of hippocampal PKCgamma-ir following training.