Atividade antifosfolipásica A2 da harpalicina 2, uma isoflavona isolada de Harpalyce brasiliana Benth

• Ano de defesa: 2012
• Autor(a) principal: Ximenes, Rafael Matos
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Palavras-chave em Português: Receptores da Fosfolipase A2; Venenos
• Link de acesso: http://www.repositorio.ufc.br/handle/riufc/4038

Secretory phospholipases A2 (sPLA2, EC 3.1.1.4) hydrolyses the sn-2 ester bond of phospholipids, releasing fatty acids and lysophospholipids. The expression of these enzymes is found to be elevated in many pathological conditions, such as rheumatoid arthritis, sepsis, atherosclerosis, and cancer. Moreover, sPLA2s are the main toxic components of some snake venoms, being the mainly responsible for the local tissue damage. Harpalycin 2 is an isoflavona isolated from the leaves of Harpalyce brasiliana Benth., a snakeroot used in folk medicine to treat snake bites and inflammation in Northeast of Brazil. The aim of this study was evaluate the effect of harpalycin 2 in the enzymatic, edematogenic, and myotoxic activities of sPLA2s isolated from Bothrops pirajai (PrTX-III), Crotalus durissus terrificus (Cdt F15), Apis mellifera (Apis), and Naja naja (Naja) venoms. Futher, the effect on the platelet aggregation induced by PrTX-III as a result of the treatment with harpalycin 2 was also evaluated. Harpalycin 2 inhibited all sPLA2s tested, with inhibition percentages of 58.7, 78.8, 87.7, and 88.1 % for PrTX-III, Cdt F15, Apis, and Naja, respectively. The early phase of the edema induced by sPLA2s administration was also inhibited by harpalycin 2, as well as the myotoxicity. When assayed specifically with the PrTX-III, in comparison with two standard sPLA2 inhibitor, aristolochic acid (Aris Ac) and p-bromophenacyl bromide (p-BPB), the IC50 of harpalycin 2 on the enzymatic activity was 11.34 ± 0.28 μg/mL. Conformational changes as a slightly unfolding and the transition from the dimeric to the monomeric form were also observed after treatment with the harpalycin 2, with no changes in the molecular mass of the protein. In the platelet aggregation assays, the harpalycin 2 incubated with the PrTX-III inhibited the aggregation when compared to the untreated protein. The inhibitory effect of Aris Ac and p-BPB were lower than that of harpalycin 2, which also inhibited the aggregation induced by arachidonic acid. The docking results, using the crystallographic structures of the sPLA2s taken from the Protein Data Bank, showed a trend between the GOLD scores and the percentages of catalytic activity and platelet aggregation inhibition, showing the formation of hydrogen bonds between harpalycin 2 and important residues in the active site of the sPLA2s, as His48. In conclusion, these results showed the inhibitory effect of harpalycin 2 on the enzymatic and toxic activities of sPLA2s, corroborating, at least in part, the use of H. brasiliana in folk medicine.