RESUMO
In the present investigation, the rationale for the design, synthesis, and biological evaluation of potent inhibitors of neuronal Na+ channels is described. N,N'-diaryl- and N-aryl-N-aralkylguanidine templates were locked in conformations mimicking the permissible conformations of the flexible diarylguanidinium ion (AS+, AA+, SS+). The resulting set of constrained guanidines termed "lockamers" (cyclophane, quinazoline, aminopyrimidazolines, aminoimidazolines, azocino- and tetrahydroquinolinocarboximidamides) was examined for neuronal Na+ channel blockade properties. Inhibition of [14C]guanidinium ion influx in CHO cells expressing type IIA Na+ channels showed that the aminopyrimidazoline 9b and aminoimidazoline 9d, compounds proposed to lock the N,N'-diarylguanidinium in an SS+ conformation, were the most potent Na+ channel blockers with IC50's of 0.06 microM, a value 17 times lower than that of the parent flexible compound 18d. The rest of the restricted analogues with 4-p-alkyl substituents retained potency with IC50 values ranging between 0.46 and 2.9 microM. Evaluation in a synaptosomal 45Ca2+ influx assay showed that 9b did not exhibit high selectivity for neuronal Na+ vs Ca2+ channels. The retention of significant neuronal Na+ blockade in all types of semirigid conformers gives evidence for a multiple mode of binding in this class of compounds and can possibly be attributed to a poor structural specificity of the site(s) of action. Compound 9b was also found to be the most active compound in vivo based on the high level of inhibition of seizures exhibited in the DBA/2 mouse model. The pKa value of 9b indicates that 9b binds to the channel in its protonated form, and log D vs pH measurements suggest that ion-pair partitioning contributes to membrane transport. This compound stands out as an interesting lead for further development of neurotherapeutic agents.
Assuntos
Desenho de Fármacos , Imidazóis , Neurônios/efeitos dos fármacos , Pirimidinas , Bloqueadores dos Canais de Sódio , Animais , Anticonvulsivantes/síntese química , Anticonvulsivantes/química , Anticonvulsivantes/metabolismo , Anticonvulsivantes/farmacologia , Transporte Biológico , Encéfalo/efeitos dos fármacos , Encéfalo/metabolismo , Encéfalo/ultraestrutura , Células CHO , Cálcio/metabolismo , Bloqueadores dos Canais de Cálcio/síntese química , Bloqueadores dos Canais de Cálcio/química , Bloqueadores dos Canais de Cálcio/metabolismo , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio/efeitos dos fármacos , Cricetinae , Feminino , Guanidina/metabolismo , Imidazóis/síntese química , Imidazóis/química , Imidazóis/metabolismo , Imidazóis/farmacologia , Masculino , Camundongos , Camundongos Endogâmicos DBA , Conformação Molecular , Neurônios/metabolismo , Pirimidinas/síntese química , Pirimidinas/química , Pirimidinas/metabolismo , Pirimidinas/farmacologia , Ratos , Receptores de N-Metil-D-Aspartato/metabolismo , Convulsões/prevenção & controle , Canais de Sódio/biossíntese , Relação Estrutura-Atividade , Sinaptossomos/efeitos dos fármacos , Sinaptossomos/metabolismoRESUMO
5'-Ester derivatives of the potent adenosine agonists N6-[4-[[[[4-[[[(2-acetylaminoethyl)amino]carbonyl]methyl] anilino]carbonyl]methyl]phenyl]adenosine (N-AcADAC; 1) and N6-cyclopentyladenosine (CPA; 2) were prepared as prodrugs. Both alkyl esters or carbonates (designed to enter the brain by virtue of increased lipophilicity) and 1,4-dihydro-1-methyl-3-[(pyridinylcarbonyl)oxy]esters designed to concentrate in the brain by virtue of a redox delivery system were synthesized. In the 5'-blocked form, the adenosine agonists displayed highly diminished affinity for rat brain A1-adenosine receptors in binding assays. The dihydropyridine prodrug 29 was active in an assay of locomotor depression in mice, in which adenosine agonists are highly depressant. The behavior depression was not reversible by peripheral administration of a non-central nervous system active adenosine antagonist. In an assay of the peripheral action of adenosine (i.e., the inhibition of lipolysis in rats), the parent compounds were highly potent and the dihydropyridine prodrug was much less potent.
Assuntos
Adenosina/síntese química , Pró-Fármacos/síntese química , Receptores Purinérgicos P1/efeitos dos fármacos , Adenosina/análogos & derivados , Adenosina/farmacologia , Animais , Glicerol/sangue , Masculino , Camundongos , Atividade Motora/efeitos dos fármacos , Pró-Fármacos/farmacologia , Ratos , Ratos Sprague-Dawley , Relação Estrutura-AtividadeAssuntos
Bradicinina/farmacologia , Bulbo/fisiologia , Dor , Formação Reticular/fisiologia , Potenciais de Ação , Animais , Bradicinina/administração & dosagem , Gatos , Estimulação Elétrica , Injeções Intra-Articulares , Bulbo/efeitos dos fármacos , Inibição Neural , Estimulação Física , Formação Reticular/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacosAssuntos
Dor , Medula Espinal/fisiologia , Transmissão Sináptica , Animais , Encéfalo/fisiologia , Gatos , Humanos , Nervos Periféricos/fisiologiaAssuntos
Anestésicos/farmacologia , Cicloexanos/farmacologia , Ketamina , Fenômenos Fisiológicos da Pele , Medula Espinal/fisiologia , Animais , Pressão Sanguínea/efeitos dos fármacos , Gatos , Estimulação Elétrica , Laminectomia , Microeletrodos , Pressão , Células Receptoras Sensoriais/efeitos dos fármacos , Medula Espinal/citologia , Medula Espinal/efeitos dos fármacos , Técnicas Estereotáxicas , Sinapses/fisiologia , Transmissão Sináptica/efeitos dos fármacosRESUMO
1. A method is described to study the modification in the activity of the lamina IV and V cells of the dorsal horn under the intra-arterial administration of bradykinin into the hind limb of the spinal cat.2. The modifications induced by intra-arterial injection of bradykinin preferentially affected the lamina V cells (77% of the units) and produced few changes in the lamina IV cells (16% of the units showed variations).3. 52% of the lamina V cells were activated; the mean increase in the firing rate was 700%. The mean latency of the effect was 20 sec and the mean duration was 47 sec. However, there was large variance in the excitatory effect across cells. On the other hand, for the same cell, the observed effects were perfectly reproducible and injections of physiological fluid induced no response.4. 25% of the lamina V cells were inhibited. Generally, the activity of the cell was reduced to 13% of its initial value; in some cases, a total suppression of activity was observed. The mean latency of the inhibitory effect was 12 sec and its duration 28 sec. All these units had a very wide inhibitory field (activated by stimulations of low intensity) which asymmetrically surrounds the excitatory field.5. This study confirms the role played by the lamina V cells in the transmission of nociceptive messages. The existence of inhibitory phenomena is in favour of the gate control theory described by Melzack & Wall (1965) without deciding the pre- or post-synaptic nature of these mechanisms.