Please use this identifier to cite or link to this item: http://hdl.handle.net/1843/MCSC-7C6T5Y
Type: Tese de Doutorado
Title: Mecanismos envolvidos no aumento da concentração plasmática de Sb a partir das composições de antimoniato de meglumina com ciclodextrina, visando o tratamento oral das leishmanioses
Authors: Patricia Silveira Martins
First Advisor: Frederic Jean Georges Frezard
First Referee: Miriam Teresa Paz Lopes
Second Referee: Marcelo Matos Santoro
Third Referee: Tania Maria de Almeida Alves
metadata.dc.contributor.referee4: Bartira Rossi Bergmann
Abstract: O antimoniato de meglumina (AM), complexo de antimonio pentavalente (Sb(V)) com N-metil-D-glucamina (NMG), tem sido usado como medicamento de primeira escolha no tratamento das leishmanioses. De administracao parenteral, recentemente foi relatadoque a associacao entre o AM e a s-ciclodextrina (s-CD) e capaz de tornar esse antimonial ativo por via oral em modelo de leishmaniose cutanea. Contudo, como o AM e altamente soluvel em agua e, muito provavelmente, nao interage com a cavidade hidrofobica da s-CD, os mecanismos responsaveis pelo aumento de absorcao oral doantimonial na composicao AM/s-CD diferem daqueles que atuam nos complexos de inclusao farmaco/s-CD convencionais. A presente tese propos fornecer dados sobre o modo de acao da composicao AM/s-CD. Para tal, o AM e a composicao AM/s-CD foram caracterizados do ponto de vista fisico-quimico e sua absorcao por via oral e permeacao em modelo lipidico de membrana foram estudadas. Sabendo-se que oprocesso de preparo da composicao AM/s-CD se da em duas etapas, em que a mistura equimolar AM + s-CD e aquecida, a 55oC por 48 horas, e em seguida liofilizada, foram avaliados os efeitos do aquecimento e da liofilizacao nas caracteristicas fisico-quimicasdaquela composicao. Medidas de osmolaridade e analise por ESI-MS de solucoes aquosas do AM e da mistura equimolar AM + s-CD comprovaram que o aquecimento promove a dissociacao do AM em especies de baixo peso molecular (Sb-NMG 1:1) e aformacao do complexo ternario NMG-Sb-s-CD. Analises por dicroismo circular e ESIMS permitiram mostrar que a etapa de liofilizacao promove associacoes multiplas entre o AM e a s-CD, incluindo a formacao de complexos (NMG-Sb)2-s-CD e (NMG-Sb-s-CD)2. Estudos de absorcao de Sb por via oral em camundongos a partir das misturas AM + s-CD nao aquecida, AM + s-CD aquecida e AM + s-CD aquecida e liofilizadaindicaram que a etapa de aquecimento aumenta menos que duas vezes o nivel de Sb no soro de animais, enquanto a etapa de liofilizacao aumenta esse nivel de duas a tres vezes. Foi desenvolvido e avaliado um modelo lipidico de membrana, consistindo em lipossomas contendo glutationa reduzida, para o estudo de permeacao de Sb(V) atravesde bicamada lipidica. Este modelo permitiu determinar um coeficiente de permeabilidade para o antimoniato de potassio, cujo valor foi de 0,82 x 10-10 cm s-1, a 37oC, para membrana de fosfatidilcolina de soja, valor proximo do relatado na literatura para aquele do ion Cl-. A comparacao da velocidade de permeacao do AM com aquela da composicao AM/s-CD nao mostrou diferenca significativa nas condicoes deconcentracao e de temperatura utilizados neste modelo. Esses resultados comprovam que o aquecimento, seguido de liofilizacao da mistura AM + s-CD sao necessarios para o aumento significativo na absorcao oral de Sb para essa composicao. Um estudo porDC revelou ainda que essa composicao atua como um sistema de liberacao prolongada do AM, podendo alterar seu sitio de absorcao, uma vez que a s-CD se mantem intacta por todo o trato gastrointestinal ate o colon. Em adicao as novas informacoes obtidas sobre os mecanismos envolvidos no aumento de concentracao plasmatica de Sb nacomposicao AM/À-CD, o presente trabalho permitiu propor duas novas formulacoes para a administracao oral do Sb: uma que consiste no AM pre-aquecido, potencialmente menos toxico e de menor custo, em comparacao as composicoes AM/s-CD; e a outra que consiste numa composicao AM/s-CD mais soluvel em relacao a composicao 1:1, epotencialmente menos toxica e de menor custo.
Abstract: Meglumine antimoniate (MA), complex of pentavalent antimony (Sb(V)) with Nmethyl-D-glucamine (NMG), is currently an agent of choice for the treatment of leishmaniases. This compound is considered inactive when given enterally and is subject to rapid renal clearance after parenteral administration, requiring a multiple dosing regimen. Recently, it was reported that the association of MA to ß-cyclodextrin (ß-CD) enhances the oral absorption of Sb and renders this drug active by the oral routein a model of cutaneous leishmaniasis. However, since MA is highly water-soluble and, most probably, does not interact with the internal hydrophobic cavity of ß-CD, the mechanism responsible for the enhanced oral absorption of Sb in the MA/ß-CD composition is expected to differ from that involved in conventional inclusion drug/ß-CD complexes. The main objective of the present thesis was to investigate the mode ofaction of the MA/ß-CD composition. For that, MA and the MA/ß-CD composition were physicochemically characterized and their oral absorption in mice and their permeation across a lipid bilayer model were investigated. Since the preparation of MA/ß-CD composition consists in a two-step process, involving the heating of an equimolar MA +ß-CD mixture at 55oC for 48 h followed by the freeze-drying of the mixture, the effects of heating and of freeze-drying on the physicochemical characteristics of the resulting composition were evaluated. Osmolarity measurements and ESI mass spectrometry analyses of aqueous MA solutions and equimolar MA/ß-CD mixture indicated that theheating step induces the dissociation of MA into species of low molecular weight (1:1Sb-NMG complex) and the formation of ternary NMG-Sb-ß-CD complexes. Circular dichroism and ESI mass spectrometric analyses showed that the freeze-drying step promotes multiple associations between MA and ß-CD, including the formation of (NMG-Sb)2-ß-CD and (NMG-Sb-CD)2 complexes. Oral absorption of Sb in mice from MA+ß-CD physical mixture, heated MA/ß-CD and heated and freeze-dried MA/ß-CDindicated that the heating process increases by less than 2-fold Sb concentration in the serum of mice, while the freeze-drying step enhances significantly by 2- to 3-fold the Sb level. A lipid bilayer model, consisting of glutathione (GSH)-containing liposomes made from phosphatidylcholine, was developed in order to evaluate the permeation of Sb(V) across the lipid bilayer. This model allowed the determination of the permeability coefficient of antimoniate. Its value was found to be equal to 0.82 x 10-10 cm s-1, which is close to the value reported for Cl- ion. The comparison between the permeation rates of MA and of MA/ß-CD composition did not show significant difference under the conditions of concentration and temperature used in this model. A circular dichroismexperiment indicated that the MA/ß-CD composition acts as a sustained release system of the antimonial drug, MA. Since cyclodextrins are poorly digested in the small intestine, the association of MA with ß-CD may change the drug absorption site. In addition to the new insights achieved into the mode of action of the MA/ß-CD composition, the present work led us to propose also two new formulations for the oral administration of Sb: one which consists in pre-heated MA and is potentially less toxicand of lower cost, when compared to MA/ß-CD compositions; the other which consists in a MA/ß-CD composition, exhibits a higher solubility in comparison to 1:1 MA/ß-CD composition and is potentially less toxic and of lower cost.
Subject: Leishmaniose
Tratamento parenteral
language: Português
Publisher: Universidade Federal de Minas Gerais
Publisher Initials: UFMG
Rights: Acesso Aberto
URI: http://hdl.handle.net/1843/MCSC-7C6T5Y
Issue Date: 9-Feb-2007
Appears in Collections:Teses de Doutorado

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