Cevc Gregor, Schätzlein Andreas, Richardsen Holger
Medizinische Biophysik, Technische Universität München, Ismaningerstr 22, D-81675 Munich, Germany.
Biochim Biophys Acta. 2002 Aug 19;1564(1):21-30. doi: 10.1016/s0005-2736(02)00401-7.
The stability of various aggregates in the form of lipid bilayer vesicles was tested by three different methods before and after crossing different semi-permeable barriers. First, polymer membranes with pores significantly smaller than the average aggregate diameter were used as the skin barrier model; dynamic light scattering was employed to monitor vesicle size changes after barrier passage for several lipid mixtures with different bilayer elasticities. This revealed that vesicles must adapt their size and/or shape, dependent on bilayer stability and elasto-mechanics, to overcome an otherwise confining pore. For the mixed lipid aggregates with highly flexible bilayers (Transfersomes), the change is transient and only involves vesicle shape and volume adaptation. The constancy of ultradeformable vesicle size before and after pores penetration proves this. This is remarkable in light of the very strong aggregate deformation during an enforced barrier passage. Simple phosphatidylcholine vesicles, with less flexible bilayers, lack such capability and stability. Conventional liposomes are therefore fractured during transport through a semi-permeable barrier; as reported by other researchers, liposomes are fragmented to the size of a narrow pore if sufficient pressure is applied across the barrier; otherwise, liposomes clog the pores. The precise outcome depends on trans-barrier flux and/or on relative vesicle vs. pore size. Lipid vesicles applied on the skin behave accordingly. Mixed lipid vesicles penetrate the skin if they are sufficiently deformable. If this is the case, they cross inter-cellular constrictions in the organ without significant composition or size modification. To prove this, we labelled vesicles with two different fluorescent markers and applied the suspension on intact murine skin without occlusion. The confocal laser scanning microscopy (CLSM) of the skin then revealed a practically indistinguishable distribution of both labels in the stratum corneum, corroborating the first assumption. To confirm the second postulate, we compared vesicle size in the starting suspension and in the blood after non-invasive transcutaneous aggregate delivery. Size exclusion chromatograms of sera from the mice that received ultradeformable vesicles on the skin were undistinguishable from the results measured with the original vesicle suspension. Taken together, the results support our previous postulate that ultradeformable vesicles penetrate the skin intact, that is, without permanent disintegration.
在穿过不同的半透膜屏障之前和之后，通过三种不同的方法测试了脂质双层囊泡形式的各种聚集体的稳定性。首先，使用孔径明显小于平均聚集体直径的聚合物膜作为皮肤屏障模型；采用动态光散射来监测几种具有不同双层弹性的脂质混合物在通过屏障后的囊泡大小变化。这表明囊泡必须根据双层稳定性和弹性力学来调整其大小和/或形状，以克服原本狭窄的孔隙。对于具有高度柔性双层的混合脂质聚集体（传递体），这种变化是短暂的，仅涉及囊泡形状和体积的调整。超可变形囊泡在穿过孔隙前后大小的恒定证明了这一点。鉴于在强制通过屏障期间聚集体发生了非常强烈的变形，这一点很显著。双层柔性较小的简单磷脂酰胆碱囊泡缺乏这种能力和稳定性。因此，传统脂质体在通过半透膜屏障运输过程中会破裂；正如其他研究人员所报道的，如果在屏障上施加足够的压力，脂质体会破碎成狭窄孔隙的大小；否则，脂质体会堵塞孔隙。确切的结果取决于跨屏障通量和/或脂质体与孔隙大小的相对关系。应用于皮肤的脂质囊泡也有相应表现。如果混合脂质囊泡具有足够的可变形性，它们就能穿透皮肤。如果是这种情况，它们会穿过器官中的细胞间狭窄处，而不会有明显的组成或大小改变。为了证明这一点，我们用两种不同的荧光标记物标记囊泡，并将悬浮液涂抹在未封闭的完整小鼠皮肤上。然后，对皮肤进行共聚焦激光扫描显微镜（CLSM）检查，结果显示角质层中两种标记物的分布几乎无法区分，这证实了第一个假设。为了证实第二个假设，我们比较了起始悬浮液中的囊泡大小和无创经皮递送聚集体后血液中的囊泡大小。在皮肤上接受超可变形囊泡的小鼠血清的尺寸排阻色谱图与用原始囊泡悬浮液测量的结果无法区分。综上所述，这些结果支持了我们之前的假设，即超可变形囊泡完整地穿透皮肤，也就是说，不会发生永久性崩解。
