Photochem. & Photophys. Appl. Lab, Laser Bio-Medical Applications Section, Raja Ramanna Center for Advanced Technology , Indore, M.P. India 452013.
Homi Bhabha National Institute , Training School Complex, Anushakti Nagar, Mumbai 400094, India.
Langmuir. 2017 Aug 22;33(33):8302-8310. doi: 10.1021/acs.langmuir.7b01783. Epub 2017 Aug 8.
The effect of addition of curcumin on the adsorption and transport characteristics of a cationic dye, LDS, across negatively charged bilayers composed of POPG and DPPG lipids were investigated by the interface selective second harmonic (SH) spectroscopic technique. Curcumin induced changes in the SH electric field signal of the LDS ions (E (LDS)) were observed to depend critically on the bilayer acyl chain saturation/unsaturation ratio (S/U). Following earlier works, the increase in the E (LDS) signal is attributed to the release of the Na counterions present in the head group region of the bilayer by curcumin and the decay of the E (LDS) signal is attributed to the bilayer intercalated state of curcumin. While the changes observed in the E (LDS) signal in the presence of POPG liposomes were consistent with our earlier study ( Varshney, G. K. et al. Langmuir , 2016 , 32 , 10415 - 10421 ), they were significantly different for DPPG liposomes, following curcumin addition. While the increase in the E (LDS) signal in the presence of POPG liposomes, is marginal (∼10-20%) and instantaneous (<1 s) followed by a rapid decay (completed within ∼100 s), in the presence of DPPG liposomes it was observed to increase slowly and at saturation shows a substantial increase (100-200%), following curcumin addition. When liposomes consisting of a mixture of POPG and DPPG lipids are used, curcumin induced kinetic characteristics of the E (LDS) signal showed a mixture of the individual kinetic characteristics observed for the unsaturated (POPG) and saturated (DPPG) liposomes. The observed kinetic trends of the E (LDS) signal following curcumin addition are explained on the basis of the relative strength of the Na-POPG and Na-DPPG interaction. Higher ordering of the lipid acyl chain region in DPPG liposome makes the Na-DPPG interaction much stronger than the Na-POPG interaction. Further, it is proposed that, in POPG-DPPG liposomes, individual domains of POPG and DPPG lipids exist at low temperature as suggested by the observed temperature dependent kinetic characteristics of the E (LDS) signal following curcumin addition. These domains are dependent on the S/U ratio and phase state of the bilayer. The gel phase was observed to be more conducive for individual domain formation. Results presented in this work not only support the notion that biological activity of curcumin is associated with its bilayer altering properties, but more interestingly it provides a qualitative insight about how bilayer phase separation can be achieved by modulating the hydrophobic interactions between the lipid acyl chains.
通过界面选择性二次谐波（SH）光谱技术研究了姜黄素对带负电荷的由 POPG 和 DPPG 脂质组成的双层中阳离子染料 LDS 的吸附和输运特性的影响。观察到姜黄素诱导的 LDS 离子（E（LDS））的 SH 电场信号变化取决于双层酰基链饱和度/不饱和度比（S/U）。根据早期的研究，E（LDS）信号的增加归因于姜黄素从双层头部区域释放存在的 Na 抗衡离子，而 E（LDS）信号的衰减归因于姜黄素的双层插入状态。虽然在存在 POPG 脂质体时观察到的 E（LDS）信号变化与我们早期的研究一致（Varshney，G.K.等人，Langmuir，2016，32，10415-10421），但在添加姜黄素后，对于 DPPG 脂质体，它们的差异非常显著。在存在 POPG 脂质体时，E（LDS）信号的增加是微不足道的（∼10-20%）且瞬时（<1 s），随后迅速衰减（在∼100 s 内完成），而在存在 DPPG 脂质体时，它的增加缓慢，在达到饱和时会显示出明显的增加（100-200%），在添加姜黄素后。当使用由 POPG 和 DPPG 脂质组成的混合物的脂质体时，E（LDS）信号的姜黄素诱导的动力学特征显示出对不饱和（POPG）和饱和（DPPG）脂质体观察到的个体动力学特征的混合物。在添加姜黄素后，E（LDS）信号的观察到的动力学趋势基于 Na-POPG 和 Na-DPPG 相互作用的相对强度进行解释。DPPG 脂质体中脂酰链区域的更高有序性使得 Na-DPPG 相互作用比 Na-POPG 相互作用强得多。此外，据推测，在 POPG-DPPG 脂质体中，正如添加姜黄素后观察到的 E（LDS）信号的温度依赖性动力学特征所表明的那样，POPG 和 DPPG 脂质的单独域在低温下存在。这些域取决于 S/U 比和双层的相态。观察到凝胶相更有利于单个域的形成。本工作中提出的结果不仅支持姜黄素的生物活性与其改变双层的特性有关的观点，而且更有趣的是，它提供了关于如何通过调节脂质酰基链之间的疏水相互作用来实现双层相分离的定性见解。
