Indolicidin為一有潛力的抗生藥物，其具有相當廣泛的抗生活性，對抗細菌、真菌、病毒皆有不錯的能力，且是一段具有不錯經濟效益的短鏈胜肽。然而，Indolicidin對人類紅血球的溶血活性卻限制其進一步的發展。雖然，擁有低溶血血性的IL之類似物(ILK7、ILF89、ILK7F89)已經被設計，但它們的行為機制仍然不是非常清楚。本研究主要是探討其生物活性與膜擾亂之間的關係。我們藉由螢光異位向性實驗研究膜擾亂的情形，並以恆溫滴定微卡計研究胜肽與膜之間的熱變化。而我們使用兩種仿生物細胞膜的微脂粒，仿細菌細胞膜(POPG/POPC=1, PG/PC-SUVs)與仿人類紅血球細胞膜(純 POPC, PC-SUVs)。而我們進一步探討IL及其類似物對抗革蘭氏陽性菌(staphylococcus epidermidis)的活性，結果發現IL的類似物皆擁有較IL更強或相當的抗菌活性。另一方面，在POPC微脂粒的作用中，胜肽對膜的擾亂與膜擾亂焓和其溶血活性沒有很強烈的關係，所以對於溶血活性主要仍是與其胜肽吸附量有關。因此，對於抗菌活性胜膜的擾亂程度確實是一很重要的影響因素。 Indolicidin (IL) is a cationic antibacterial peptide with broad-spectrum against many pathogens; therefore, it is a potential peptide antibiotic. However, the hemolytic activity of IL limits its clinical application. Although the IL-analogues (ILK7, ILF89 and ILK7F89) with lower hemolysis have been designed, the action mechanisms of them were still under debating. In this study, we tried to examine the relationships between bioactivity and membrane perturbation. The membrane perturbation was investigated through the help of fluorescence anisotropic measurement. The membrane association enthalpy and membrane perturbation enthalpy were examined by isothermal titration calorimeter (ITC) and peptide-membrane adsorption isotherm. Two types of small unilamellar vesicles (SUVs) were used to mimic the bacterial-like membrane (POPG/POPC=1) and erythrocyte-like membrane (pure POPC). The antibacterial activity of IL and its analogues against Gram-positive bacteria (staphylococcus epidermidis) were also examined. The results revealed that IL-analogues with enhancing or similar antibacterial activity than that of IL peptide. The interaction of peptide and PG/PC-SUVs revealed that the peptide with high antibacterial activity owns strongly membrane perturbation and highly membrane perturbation enthalpy. On the contrary, as peptide and PC-SUVs interaction, the membrane perturbation of peptide action and membrane perturbation enthalpy are not strongly correlated with its hemolytic activity. Particularly, the hemolysis is related to the amounts of peptide adsorption. Consequently, the membrane perturbation suffered by peptide is an important implication on antibacterial activity.
