Caracterização farmacológica do efeito da crotamina sobre o músculo esquelético de camundongo empregando ensaios ex vivo e in vivo
Arquivos
Data
2017
Autores
Lima, Sunamita de Carvalho 
Orientadores
Hayashi, Mirian Akemi Furuie
Tipo
Dissertação de mestrado
Título da Revista
ISSN da Revista
Título de Volume
Resumo
Apesar dos vários estudos científicos conduzidos até o momento, visando entender e explorar as diferentes funções e atividades biológicas da crotamina, pouco se sabe ainda sobre o mecanismo de ação envolvido no seu efeito sobre o tecido muscular. Embora a ação da crotamina sobre a musculatura esquelética tenha sido a principal motivação para a sua descoberta e para a realização dos primeiros experimentos farmacológicos com o intuito de identificar os principais alvos e mecanismo de ação deste polipeptídeo, apenas o envolvimento dos canais de Na+ foi sugerido até o momento, mas que também foi descartado como alvo por outros pesquisadores empregando técnicas eletrofisiológicas, que permitiram demonstrar que este peptídeo não atua diretamente sobre as subunidades alfa dos canais de Na+ humanos expressos em células renais HEK293. Por outro lado, considerando que a crotamina bloqueia os canais de K+ voltagem-dependente encontrados em células excitáveis, propomos realizar concomitantemente estudos ex vivo e in vivo com o intuito de avaliar a possível importância da ação da crotamina sobre estes canais iônicos para promoção da síndrome da paralisia das patas traseiras em camundongos. Verificamos pela primeira vez uma resposta dose-dependente para a paralisia induzida pela crotamina, no qual a imobilização foi observada mais rapidamente para as maiores doses utilizadas. E ainda, ativadores e/ou bloqueadores de canais de Na+ ou K+ afetam tanto o efeito inotrópico positivo em musculatura esquelética isolada, como no tempo decorrido para a observação da síndrome da paralisia dos membros traseiros de camundongos promovidos pela administração da crotamina. Embora não tenha sido possível identificar os fatores determinantes para a imobilização seletiva dos membros posteriores dos camundongos, a comprovação do envolvimento dos canais de Na+ e K+ no aumento de força de contração promovido pela crotamina permitem sugerir possíveis novas aplicações para esta molécula, como o seu uso em disfunções musculares características, como as presentes na caquexia e fadiga muscular, observados em pacientes com câncer e sob tratamento com quimioterápicos.
In spite of several scientific studies conducted in order to understand and explore the different biological functions and activities of crotamine, the accumulated knowledge about the mechanism of action involved in crotamine effect on skeletal muscle is still very limited. Although crotamine effect on skeletal muscle was the main motivation for its discovery and also for the first pharmacological experiments aiming the identification of the main targets and most relevant mechanism of action of this toxin, only the involvement of Na+ channels was reported up to date, but that was also soon after refuted as potential target by others after using electrophysiological techniques, which allowed demonstrating that this peptide does not act directly on the alpha subunits of human Na+ channels expressed in HEK293 kidney cells. On the other hand, considering that crotamine blocks voltage-dependent K+ channels found in excitable cells, we conducted side-by-side both ex vivo and in vivo studies aiming to evaluate the potential importance of crotamine effect on these ion channels for the paralysis of mice hind limbs. We show here for the first time, a dose-dependent response for the paralysis elicited by crotamine, in which the immobilization was observed quicker after administration of higher doses of crotamine. In addition, the Na+ or K+ channel activators and/or blockers affected both the positive inotropic effect in isolated skeletal muscle assay as well as the hind limb paralysis syndrome triggered by crotamine in mice. Although it was not possible to identify which factors determined this selective immobilization of mice hind limbs, the confirmation of the involvement of both Na+ and K+ channels for the increased muscle contraction force induced by crotamine allow us to suggest possible new application for this molecule in the therapy of skeletal muscle dysfunctions, as those reported in patients with cancer under chemotherapy treatment, including in cachexia and muscle fatigue.
In spite of several scientific studies conducted in order to understand and explore the different biological functions and activities of crotamine, the accumulated knowledge about the mechanism of action involved in crotamine effect on skeletal muscle is still very limited. Although crotamine effect on skeletal muscle was the main motivation for its discovery and also for the first pharmacological experiments aiming the identification of the main targets and most relevant mechanism of action of this toxin, only the involvement of Na+ channels was reported up to date, but that was also soon after refuted as potential target by others after using electrophysiological techniques, which allowed demonstrating that this peptide does not act directly on the alpha subunits of human Na+ channels expressed in HEK293 kidney cells. On the other hand, considering that crotamine blocks voltage-dependent K+ channels found in excitable cells, we conducted side-by-side both ex vivo and in vivo studies aiming to evaluate the potential importance of crotamine effect on these ion channels for the paralysis of mice hind limbs. We show here for the first time, a dose-dependent response for the paralysis elicited by crotamine, in which the immobilization was observed quicker after administration of higher doses of crotamine. In addition, the Na+ or K+ channel activators and/or blockers affected both the positive inotropic effect in isolated skeletal muscle assay as well as the hind limb paralysis syndrome triggered by crotamine in mice. Although it was not possible to identify which factors determined this selective immobilization of mice hind limbs, the confirmation of the involvement of both Na+ and K+ channels for the increased muscle contraction force induced by crotamine allow us to suggest possible new application for this molecule in the therapy of skeletal muscle dysfunctions, as those reported in patients with cancer under chemotherapy treatment, including in cachexia and muscle fatigue.
Descrição
Citação
LIMA, Sunamita de Carvalho. Caracterização farmacológica do efeito da crotamina sobre o músculo esquelético de camundongo empregando ensaios ex vivo e in vivo. 2017. [84] p. Dissertação (Mestrado em Farmacologia) - Escola Paulista de Medicina (EPM), Universidade Federal de São Paulo (UNIFESP), São Paulo, 2017