Tamoxifen effect on L-DOPA induced response complications in parkinsonian rats and primates

The contribution of striatal protein kinase C (PKC) isoform changes in levodopa (L-DOPA) induced motor response complications in parkinsonian rats was investigated and the ability of tamoxifen, an antiestrogen with a partial PKC antagonist property, to prevent these response alterations in 6-hydroxydopamine (6-OHDA) lesioned rats as well as in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treated cynomologous monkeys was studied. Following treatment of adult male rats with L-DOPA twice daily for 3 weeks, protein levels of left (lesioned) and right (intact) striatal PKC isoforms were measured. Western blot analysis showed increased protein expression of both the novel PKC epsilon isoform and the atypical PKC lambda isoform ipsilateral to the lesion (174+/-17% for epsilon, 140+/-9% for lambda, of intact striatum in 6-OHDA lesioned plus chronic L-DOPA treated animals) in acute L-DOPA treated rats. No enhancement was observed in PKC immunoreactivity for other isoforms. Tamoxifen (5.0 mg/kg p.o.) significantly attenuated the L-DOPA induced augmentation of protein expression of PKC epsilon and PKC lambda, but had no effect on immunoreactivity for other PKC isoforms. In chronic L-DOPA treated parkinsonian rats, tamoxifen prevented (5.0 mg/kg p.o.) as well as ameliorated (5.0 mg/kg p.o.) the characteristic shortening in duration of motor response to L-DOPA challenge. In MPTP lesioned primates, similar to the ameliorative effect seen in rats, tamoxifen (1 and 3 mg/kg p.o) reduced the appearance of L-DOPA induced dyskinesia by 61% and 55% respectively (p<0.05). These results suggest that changes in specific striatal PKC isoforms contribute to the pathogenesis of L-DOPA induced motor complications and further that drugs able to selectively inhibit these signaling kinases might provide adjunctive benefit in the treatment of Parkinson's disease.

Combined blockade of AMPA and NMDA glutamate receptors reduces levodopa-induced motor complications in animal models of PD

AMPA and NMDA receptors, abundantly expressed on striatal medium spiny neurons, have been implicated in the regulation of corticostriatal synaptic efficacy. To evaluate the contribution of both glutamate receptor types to the pathogenesis of motor response alterations associated with dopaminergic treatment, we studied the ability of the selective AMPA receptor antagonist GYKI-47261 and the selective NMDA receptor antagonists, MK-801 and amantadine, to mitigate these syndromes in rodent and primate models of Parkinson's disease. The effects of GYKI-47261 and amantadine (or MK-801), alone and in combination, were compared for their ability to modify dyskinesias induced by levodopa. In rats, simultaneous administration of subthreshold doses of AMPA and NMDA receptor antagonists completely normalized the wearing-off response to acute levodopa challenge produced by chronic levodopa treatment (P < 0.05). In primates, the glutamate antagonists GYKI-47261 and amantadine, co-administered at low doses (failing to alter dyskinesia scores), reduced levodopa-induced dyskinesias by 51% (P < 0.05). The simultaneous AMPA and NMDA receptor blockade acts to provide a substantially greater reduction in the response alterations induced by levodopa than inhibition of either of these receptors alone. The results suggest that mechanisms mediated by both ionotropic glutamate receptors make an independent contribution to the pathogenesis of these motor response changes and further that a combination of both drug types may provide relief from these disabling complications at lower and thus safer and more tolerable doses than required when either drug is used alone.

Translating A2A antagonist KW6002 from animal models to parkinsonian patients

Improving the translation of novel findings from basic laboratory research to better therapies for neurologic disease constitutes a major challenge for the neurosciences. This brief review of aspects of the development of an adenosine A2A antagonist for use in the management of Parkinson's disease (PD) illustrates approaches to some of the relevant issues. Adenosine A2A receptors, highly expressed on striatal medium spiny neurons, signal via kinases whose aberrant activation has been linked to the appearance of parkinsonian signs after dopaminergic denervation and to the motor response complications produced by dopaminomimetic therapy. To assess the ability of A2A receptor blockade to normalize certain of these kinases and thus benefit motor dysfunction, the palliative and prophylactic effects of the selective antagonist KW6002 were first evaluated in rodent and primate models. In hemiparkinsonian rats, KW6002 reversed the intermittent L-dopa treatment-induced, protein kinase A-mediated hyperphosphorylation of striatal alpha-amino-3-hydroxy-5-methyl-4-isoxazole proprionic acid receptor GluR1 S845 residues and the concomitant shortening in motor response duration. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkeys, coadministration of KW6002 with daily apomorphine injections acted prophylactically to prevent dyskinesia onset. These and related preclinical observations guided the design of a limited, randomized, controlled, proof-of-concept study of the A2A antagonist in patients with moderately advanced PD. Although KW6002 alone or in combination with a steady-state IV infusion of optimal-dose L-dopa had no effect on parkinsonian severity, the drug potentiated the antiparkinsonian response to low-dose L-dopa with fewer dyskinesias than produced by optimal-dose L-dopa alone. KW6002 also safely prolonged the efficacy half-time of L-dopa. The results suggest that drugs capable of selectively blocking adenosine A2A receptors could confer therapeutic benefit to L-dopa-treated parkinsonian patients and warrant further evaluation in phase II studies. They also illustrate a strategy for successfully bridging a novel approach to PD therapy from an evolving research concept to pivotal clinical trials.

A2A antagonist prevents dopamine agonist-induced motor complications in animal models of Parkinson’s disease

Adenosine A(2A) receptors, abundantly expressed on striatal medium spiny neurons, appear to activate signaling cascades implicated in the regulation of coexpressed ionotropic glutamatergic receptors. To evaluate the contribution of adenosinergic mechanisms to the pathogenesis of the response alterations induced by dopaminergic treatment, we studied the ability of the selective adenosine A(2A) receptor antagonist KW-6002 to prevent as well as palliate these syndromes in rodent and primate models of Parkinson's disease. In rats, KW-6002 reversed the shortened motor response produced by chronic levodopa treatment while reducing levodopa-induced hyperphosphorylation at S845 residues on AMPA receptor GluR1 subunits. In primates, KW-6002 evidenced modest antiparkinsonian activity when given alone. Once-daily coadministration of KW-6002 with apomorphine prevented the development of dyskinesias, which appeared in control animals 7-10 days after initiating apomorphine treatment. Animals initially given apomorphine plus KW-6002 for 3 weeks did not begin to manifest apomorphine-induced dyskinesias until 10-12 days after discontinuing the A(2A) antagonist. These results suggest that KW-6002 can attenuate the induction as well as the expression of motor response alterations to chronic dopaminergic stimulation in parkinsonian animals, possibly by blocking A(2A) receptor-stimulated signaling pathways. Our findings strengthen the rationale for developing A(2A) antagonists as an early treatment strategy for Parkinson's disease.

Adenosine A(2A) receptor antagonist treatment of Parkinson's disease

BACKGROUND

Observations in animal models suggest that A(2A) antagonists confer benefit by modulating dopaminergic effects on the striatal dysfunction associated with motor disability. This double-blind, placebo-controlled, proof-of-principle study evaluated the pathogenic contribution and therapeutic potential of adenosine A(2A) receptor-mediated mechanisms in Parkinson disease (PD) and levodopa-induced motor complications.

METHODS

Fifteen patients with moderate to advanced PD consented to participate. All were randomized to either the selective A(2A) antagonist KW-6002 or matching placebo capsules in a 6-week dose-rising design (40 and 80 mg/day). Motor function was rated on the Unified PD Rating Scale.

RESULTS

KW-6002 alone or in combination with a steady-state IV infusion of each patient's optimal levodopa dose had no effect on parkinsonian severity. At a low dose of levodopa, however, KW-6002 (80 mg) potentiated the antiparkinsonian response by 36% (p < 0.02), but with 45% less dyskinesia compared with that induced by optimal dose levodopa alone (p < 0.05). All cardinal parkinsonian signs improved, especially resting tremor. In addition, KW-6002 prolonged the efficacy half-time of levodopa by an average of 47 minutes (76%; p < 0.05). No medically important drug toxicity occurred.

CONCLUSIONS

The results support the hypothesis that A(2A) receptor mechanisms contribute to symptom production in PD and that drugs able to selectively block these receptors may help palliate symptoms in levodopa-treated patients with this disorder.

Serotonin 5-HT1A agonist improves motor complications in rodent and primate parkinsonian models

BACKGROUND

Serotoninergic transmission in the basal ganglia is known to influence dopaminergic mechanisms and motor function.

OBJECTIVE

To evaluate the possibility that serotoninergic 5-HT1A autoreceptors (by regulating the release of serotonin as well as dopamine formed from exogenous levodopa) affect the response alterations complicating levodopa treatment of PD.

METHODS

The 5-HT1A receptor agonist sarizotan (EMD128130) was systemically administered alone and together with levodopa to parkinsonian rats and nonhuman primates.

RESULTS

In 6-hydroxydopamine-lesioned rats, sarizotan (2.5 mg/kg PO) had no effect on the acute rotational response to levodopa but did attenuate the shortening in motor response duration induced by chronic levodopa treatment. In 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-lesioned monkeys, sarizotan (2 mg/kg PO) alone had no effect on parkinsonian severity or on the antiparkinsonian response to levodopa. In contrast, the same dose of sarizotan reduced levodopa-induced choreiform dyskinesias by 91 +/- 5.9%. In both species, the motoric effects of sarizotan were blocked by the selective 5-HT1A antagonist WAY100635 (0.1 mg/kg SC), indicating that the observed sarizotan responses were probably mediated at the 5-HT1A autoreceptor.

CONCLUSION

Pharmaceuticals acting to stimulate 5-HT1A receptors could prove useful in the treatment of the motor response complications in parkinsonian patients.

Continuous transdermal dopaminergic stimulation in advanced Parkinson's disease

The objective of the study was to determine the safety and efficacy of increasing doses of Rotigotine CDS in patients with advanced Parkinson's disease. The development of motor complications in Parkinson's disease has been linked to intermittent stimulation of dopamine receptors. Continuous, noninvasive, dopaminergic stimulation has not been available to date. Rotigotine CDS is a lipid-soluble D2 dopamine agonist in a transdermal delivery system that could fill this void. This inpatient study consisted of a 2-week dose escalation phase followed by a 2-week dose maintenance phase at the highest dose (80 cm2). Each individual's L-Dopa dose was back-titrated as feasible. The primary outcome measure was L-Dopa dose, and secondary outcome measures included early morning "off"-L-Dopa Unified Parkinson's Disease Rating Scale motor scores by a blinded evaluator and motor fluctuation data obtained from patient diaries ("on" without dyskinesia, "on" with dyskinesia, and "off"). Seven of 10 subjects provided data that could be evaluated. There were two administrative dropouts, and one individual was eliminated from the study because of recrudescence of hallucinations. The median daily L-Dopa dose decreased from 1,400 to 400 mg (p = 0.018, Wilcoxon test). Unified Parkinson's Disease Rating Scale motor scores were unchanged. Although diary variables improved in most individuals, only the reduction in "off" time attained statistical significance. Adverse effects were mild and consisted mainly of dopaminergic side effects and local skin reactions. The data suggest that Rotigotine CDS is an effective treatment for advanced Parkinson's disease and permits patients to substantially lower L-Dopa doses without loss of antiparkinsonian efficacy. Full-scale controlled clinical trials are warranted. In addition to potential therapeutic benefits, this drug can be used to test the hypothesis that continuous dopaminergic stimulation from the initiation of Parkinson's disease therapy will limit the development of motor complications.

White matter MRI hyperintensities in a hundred and twenty-nine consecutive migraine patients

The most frequently reported abnormal MRI finding in migraine is the presence of high signal white matter foci (WMF) on long TR images. Recently, WMF have been distinguished in periventricular WMF (PVF), when contiguous to ventricles, and deep WMF (DF), when far from these. DF, but not PVF, appear positively correlated with cerebrovascular risk factors and are called leukoaraiosis. In this study the MRI examination was performed in 129 consecutive migraine patients (83 of them had migraine without aura and 46 migraine with aura). In 19.3% of the migraineurs studied we observed WMF on T2 weighted images strictly localized in the deep white matter (DF). No PVF were observed. These findings were independent of the type of migraine and did not correlate with age, sex, disease duration, or frequency of attacks. The presence in a subgroup of migraineurs of leukoaraiosis (DF), for which a vascular genesis has been hypothesized, suggests that migraine could represent, a cerebrovascular risk factor in these patients.