The Ratner Chair of Chemistry, Casali Institute of Applied Chemistry, The Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem, Israel.
J Phys Chem B. 2011 Jun 30;115(25):8054-62. doi: 10.1021/jp2034455. Epub 2011 Jun 7.
Insulin entrapment within a monoolein-based reverse hexagonal (H(II)) mesophase was investigated under temperature-dependent conditions at acidic (pH 3) and basic (pH 8) conditions. Studying the structure of the host H(II) system and the interactions of insulin under temperature-dependent conditions has great impact on the enhancement of its thermal stabilization and controlled release for the purposes of transdermal delivery. Small angle X-ray spectroscopy (SAXS) measurements show that pH variation and/or insulin entrapment preserve the hexagonal structure and do not influence the lattice parameter. Attenuated total reflection Fourier transform spectroscopy (ATR-FTIR) spectra indicate that, although insulin interacts with hydroxyl groups of GMO in the interface region, it is not affected by pH variations. Hence different microenvironments within the H(II) mesophase were monitored by a computer-aided electron paramagnetic resonance (EPR) analysis using 5-doxylstearic acid (5-DSA) as a pH-dependent probe. The microviscosity, micropolarity, order of systems, and distribution of the probes in different microenvironments were influenced by three factors: temperature, pH, and insulin solubilization. When the temperature is increased, microviscosity and order parameters decreased at both pH 3 and 8, presenting different decrease trends. It was found that, at pH 3, the protein perturbs the lipid structure while "pushing aside" the un-ionized 5-DSA probe to fit into the narrow water cylinders. At the interface region (pH 8), the probe was distributed in two differently structured environments that significantly modifies by increasing temperature. Insulin loading within the H(II) mesophase decreased the order and microviscosity of both the microenvironments and increased their micropolarity. Finally, the EPR analysis also provides information about the unfolding/denaturation of insulin within the channel at high temperatures.
在酸性（pH 3）和碱性（pH 8）条件下，研究了在温度依赖条件下单油酸甘油酯基反向六方（H(II)）中间相内胰岛素的包埋情况。研究温度依赖条件下主体 H(II)系统的结构和胰岛素的相互作用对增强其热稳定性和控制释放以实现经皮递送具有重要影响。小角 X 射线散射（SAXS）测量表明，pH 值变化和/或胰岛素包埋保留了六方结构，并且不影响晶格参数。衰减全反射傅里叶变换光谱（ATR-FTIR）谱表明，尽管胰岛素与 GMO 的羟基在界面区域相互作用，但它不受 pH 值变化的影响。因此，使用 5-二氧代十一烷酸（5-DSA）作为 pH 依赖性探针，通过计算机辅助电子顺磁共振（EPR）分析监测 H(II)中间相内的不同微环境。微粘度、微极性、系统有序性以及探针在不同微环境中的分布受到三个因素的影响：温度、pH 值和胰岛素溶解。当温度升高时，在 pH 3 和 8 时，微粘度和有序参数均降低，呈现出不同的降低趋势。研究发现，在 pH 3 时，蛋白质会扰乱脂质结构，同时“推开”未离解的 5-DSA 探针，以适应狭窄的水筒。在界面区域（pH 8），探针分布在两个结构明显不同的环境中，这会随着温度的升高而显著改变。胰岛素在 H(II)中间相内的负载降低了两种微环境的有序性和微粘度，并增加了它们的微极性。最后，EPR 分析还提供了有关在高温下胰岛素在通道内展开/变性的信息。
