RESUMO
A novel adenosine A(2A) receptor selective antagonist, KW-6002 [(E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methyl-3,7-dihydro-1H-purine-2,6-dione], possesses antiparkinsonian activities in rodent and primate models. In the present study, we investigated the distribution of [14C]KW-6002 in forebrain after oral administration at pharmacologically effective doses. Also, we monitored the effects of the compound on preproenkephalin (PPE) and preprotachykinin (PPT) gene expression in rat striatum. The highest level of radioactivity was observed in the striatum after oral administration of [14C]KW-6002; 30 min after 0.1 and 0.3 mg/kg, the density values in the striatum were 2.45 and 2.43 times higher than those in a reference region (frontal cortex), respectively. At the dose of 3 mg/kg, p.o., the ratio was only 1.58 and the compound was distributed more extensively in the brain. The distribution pattern and intensity of radioactivity were maintained even 90 min after the administration of [14C]KW-6002. Oral administration of KW-6002 (0.3 and 3 mg/kg/day) to rats for 14 days reversed the increased gene expression of PPE in striatum that had been depleted of dopamine by prior treatment with 6-hydroxydopamine (6-OHDA). On the other hand, KW-6002 did not alter the decreased gene expression of PPT in 6-OHDA-treated rats. These results are the first to show directly that orally administered KW-6002 is distributed selectively to the striatum and that it modulates the activity of striatopallidal enkephalin-containing neurons but not striatonigral substance P-containing neurons.
Assuntos
Antagonistas Adrenérgicos/farmacocinética , Corpo Estriado/efeitos dos fármacos , Antagonistas de Receptores Purinérgicos P1 , Purinas/farmacocinética , Administração Oral , Animais , Radioisótopos de Carbono , Corpo Estriado/citologia , Corpo Estriado/fisiologia , Encefalinas/genética , Expressão Gênica/efeitos dos fármacos , Masculino , Neurônios/efeitos dos fármacos , Neurônios/fisiologia , Oxidopamina , Transtornos Parkinsonianos/tratamento farmacológico , Precursores de Proteínas/genética , RNA Mensageiro/análise , Ratos , Ratos Sprague-Dawley , Receptor A2A de Adenosina , Simpatolíticos , Taquicininas/genética , Distribuição TecidualRESUMO
Adenosine A2A receptors are abundant in the caudate-putamen and involved in the motor control in several species. In MPTP-treated monkeys, A2A receptor-blockade with an antagonist alleviates parkinsonian symptoms without provoking dyskinesia, suggesting this receptor may offer a new target for the antisymptomatic therapy of Parkinson's disease. In the present study, a significant neuroprotective effect of A2A receptor antagonists is shown in experimental models of Parkinson's disease. Oral administration of A2A receptor antagonists protected against the loss of nigral dopaminergic neuronal cells induced by 6-hydroxydopamine in rats. A2A antagonists also prevented the functional loss of dopaminergic nerve terminals in the striatum and the ensuing gliosis caused by MPTP in mice. The neuroprotective property of A2A receptor antagonists may be exerted by altering the packaging of these neurotoxins into vesicles, thus reducing their effective intracellular concentration. We therefore conclude that the adenosine A2A receptor may provide a novel target for the long-term medication of Parkinson's disease, because blockade of this receptor exerts both acutely antisymptomatic and chronically neuroprotective activities.