IMECH-IR  > 非线性力学国家重点实验室
肺表面活性剂的界面吸附及其生物效应研究
Alternative TitleAdsorption of the pulmonary surfactant at interfaces and the associated bio logical effects
白轩
Thesis Advisor胡国庆
2019-11-30
Degree Grantor中国科学院大学
Place of Conferral北京
Subtype博士
Degree Discipline流体力学
Keyword肺表面活性剂 磷脂 界面吸附 生物膜 生物分子冕 分子动力学模拟
Abstract

    肺表面活性剂是由II 型肺泡细胞合成和分泌的脂质蛋白质复合物质,可以吸附在肺泡的表面,在界面处形成单层膜, 这一层膜能够将肺泡的表面张力降低到非常低 ,以维持正常的呼吸作用 。肺表面活性剂膜也是抵御吸入的纳米颗粒的第一道屏障。当纳米颗粒与肺表面活性剂膜接触时,它们可以吸附肺表面活性剂的磷脂脂和蛋白质,从而在其表面上形成称之为脂蛋白冕的结构 。该脂蛋白冕赋予了纳米颗粒新的生物识别身份,并影响纳米颗粒的生物效应。因此, 研究肺表面活性剂在表面或界面(包括空气水界面和纳米颗粒表面)上的吸附,对于研究肺表面活性剂的生物物理功能和生物效应至关重要。
    尽管目前已有许多关于肺表面活性剂 在界面或表面吸附的实验研究, 揭示肺表面活性剂在界面上的动态吸附过程仍然具有很大的挑战性。通过受限液滴表面张力测量法( Constrained Drop Surfactometry , CDS )和粗粒化分子动力学模拟,本文首先研究了肺表面活性剂 的主要成分二棕榈酰磷脂酰胆碱(dipalmitoylphosphatidylcholine DPPC )在 水气界面吸附的生物物理机制。我们发现从囊泡吸附的 DPPC 膜表现出明显比通过有机溶剂铺展的 DPPC 单层膜更高的平衡表面张力 。模拟显示,只有 DPPC 囊泡的外层能够在水气界面打开并铺展,而内层保持完整并在界面处形成反胶束的结构 。这种反胶束增加了单层膜的局部曲率,从而导致了磷脂在水气界面 的松散排序,进而形成了更高的平衡表面张力。
    通过粗粒化分子动力学模拟研究了多组分肺表面活性剂在水气界面的吸附。我们发现具有比 DPPC 更大头部基团的磷脂 在水气界面的吸附可以达到较低的表面张力。不饱和的尾巴和胆固醇可以通过稳定吸附结构的曲率以及增强倒置胶束中尾部之间的相互作用,帮助吸附的肺表面活性剂的表面张力降低到更低的值。通过包括梯度离心和高效液相色谱 质谱在内的实验技术,定量分析了纳米颗粒上吸附的天然肺表面活性剂的磷脂成分。我们发现肺表面活性剂的吸附是由肺表面活性剂薄膜和纳米颗粒表面之间的粘附能驱动的,该粘附能可以通过纳米颗粒的表面性质以及外力来调节。 同样,脂蛋白冕中的磷脂的成分不同于原始的肺表面活性剂成分,这可能是由于纳米颗粒与特定脂质之间的吸引力或脂质的弯曲模量所决定。
    使用耗散粒子动力学模拟研究了肺表面活性剂在纳米颗粒上的吸附的生物效应,即细胞膜与修饰了肺表面活性剂的纳米颗粒之间的相互作用。我们研究了肺表 面活性剂脂质和蛋白质的物理化学特性如何分别影响吸入纳米颗粒的细胞膜的 响应 。我们指出了细胞膜对脂质纳米颗粒内吞作用的几个关键因素,包括修饰脂质的变形,脂质的变形,修饰修饰脂质的密度和配体脂质的密度和配体--受体结合强度。进一步的研究表明,修修饰饰脂质的变形消耗了能量,但另一方面却促进了脂质的变形消耗了能量,但另一方面却促进了修饰的修饰的配体更紧密地与受体结合。修饰的 脂质密度控制了配体的数量和脂质纳米颗粒的疏水性,分别通过特异性和非特异性相互作用影响内吞作用 。 我们还发现与脂质相关的疏水性表面活性剂蛋白可以加速纳米颗粒的内吞过程,但是内吞作用效率主要取决于被覆表面活性剂脂质的密度。

Other Abstract

    Pulmonary surfactant is a lipid-protein complex that is synthesized and secreted by type II alveolar cells. It can adsorb at the surface of the alveolar fluid to form a pulmonary surfactant film at the interface, which can reduce the surface tension of the alveolar fluid to very low values to maintain the normal tidal breathe. The pulmonary surfactant film is also the first barrier that defences the inhaled nanoparticles. When the nanoparticles contact with the pulmonary surfactant film, they can adsorb the phospholipids and proteins of the pulmonary surfactant to form the so-called lipoprotein coronas on their surfaces. This corona defines the new identity of the nanoparticles and affect the bio-effect of the nanoparticles, such as their interactions with the alveolar cells. Therefore, study of the adsorption of the pulmonary surfactant at the surfaces or interfaces, including the air-water interface and the surface of the nanoparticles, is crucial for the biophysical functions and the bio-effect of the pulmonary surfactant.

    Although there have been many existing experimental studies on the adsorption of the pulmonary surfactant at the interfaces or surfaces. It is still challenging to reveal the molecular structure of adsorbed pulmonary surfactant and the dynamic adsorption process. Using combined experiments with constrained drop surfactometry (CDS) and coarse-grained molecular dynamics simulations, here we first studied the biophysical mechanisms of the adsorption of the dipalmitoylphosphatidylcholine (DPPC), the main component of the pulmonary surfactant, at the air-water surface. It was found that the DPPC film adsorbed from vesicles showed distinct equilibrium surface tensions from the DPPC monolayer spread via organic solvents. Our simulations revealed that only the outer leaflet of the DPPC vesicle is capable of unzipping and spreading at the air-water surface, whereas the inner leaflet remains intact and forms an inverted micelle to the interfacial monolayer. This inverted micelle increases the local curvature of the monolayer, thus leading to a loosely packed monolayer at the air-water surface and hence a higher equilibrium surface tension.

    Using the coarse-grained molecular dynamics simulations, we studied the adsorption of the multi-component pulmonary surfactant at the air-water interface. It was found that the adsorption of the phospholipids with larger head groups than DPPC can reach to a lower surface tension. The unsaturated lipid tails and cholesterols can also help reduce the surface tension of the adsorbed pulmonary surfactant to a much lower value by stabilizing the curvature of the adsorbed structure and enhancing the interactions between the tails of the inverted micelle. Through the experimental technology, including gradient centrifugation and high performance liquid chromatography-mass spectrometry, we quantificationally analyzed the phospholipid components of the adsorbed natural pulmonary surfactant on the nanoparticles. We found that the adsorption of the pulmonary surfactant was driven by the adhesion energy between the pulmonary surfactant film and the nanoparticles surface, which can be tuned by the modification of the nanoparticles and also the external forces. The additional analysis indicated that the component of the phospholipids of the corona was different from the original pulmonary component, which was possibly due to the attractions between the nanoparticles with the specific lipids and the bending modulus of the lipids.

    Using the dissipative particle dynamics simulations, we studied the bio-effect of the adsorption of the pulmonary surfactant on the nanoparticles that was the interactions between the cell membrane and the nanoparticles coated with a pulmonary surfactant layer. We investigated how the physicochemical properties of the coating pulmonary surfactant lipids and proteins affected the membrane response for inhaled nanoparticles respectively. We pinpointed several key factors in endocytosis of lipid NPs, including the deformation of the coating lipids, coating lipids density and ligand-receptor binding strength. Further studies revealed that the deformation of the coating lipids consumed energy but on the other hand promotes the coating ligands to bind with receptors more tightly. The coating lipids density controls the amount of the ligands as well as the hydrophobicity of the lipid NP, thus affecting the endocytosis kinetics through the specific and non-specific interactions respectively. It was also found that the hydrophobic surfactant proteins associated with lipids can accelerate the endocytosis process of the NPs, but the endocytosis efficiency mainly depended on the density of the coating surfactant lipids.

 

Language中文
Document Type学位论文
Identifierhttp://dspace.imech.ac.cn/handle/311007/80727
Collection非线性力学国家重点实验室
Recommended Citation
GB/T 7714
白轩. 肺表面活性剂的界面吸附及其生物效应研究[D]. 北京. 中国科学院大学,2019.
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