Heterogeneous lung surfactant morphologies: effect on alveolar dynamics, and role in promoting acute respiratory distress syndrome

摘要 天然肺表面活性物质(LS)由脂类和蛋白质的混合物组成，它们共同具有 降低肺泡表面张力，因此对正常呼吸至关重要。而确切的机制是 急性肺损伤(ALI)及其更严重的形式--急性呼吸窘迫综合征(ARDS)目前 表面活性抑制蛋白、酶、脂肪酸和溶质对LS的失活作用尚不清楚 被认为起到了贡献作用。已发表的和初步的工作表明，即使是一小部分 ARDS相关组分可按以下数量级改变单分子膜的表面粘度和弹性 强度：当添加饱和脂肪酸时，磷脂单分子层硬度增加数千倍 或者白蛋白被吸附，而当添加1-2%的胆固醇时，会减少100-1000倍。 这些结果提示了ARDS进展的一种合理的机械机制，而且中央 拟议项目的假设：ARDS的流变性(例如粘性和弹性)- 失活的LS在ARDS的级联中起着中心的致病作用，并且在RS治疗中无法 有效逆转ARDS进展。最初对肺的侮辱通过以下途径引入血液蛋白质 肺泡壁通透性增加，PLA2酶水平升高，作为炎症反应的一部分。 先前的结果表明，这两种情况中的任何一种都会产生异质的、流变性的弹性。 肺深处的区域：通过消化磷脂产生溶脂和脂肪酸的PLA2，以及血液 蛋白质通过吸附。连续介质力学中的众所周知的现象表明，弹性 LS内部的异质性强烈地抵抗了呼吸过程中自然发生的曲率变化，并且 甚至可能“破裂”或“皱缩”，而不是平滑地变形。这种反常的变形会因此产生 强烈的局部机械应力作用于肺泡上皮，促进进一步的组织损伤和 炎症，最终导致更高水平的蛋白质和PLA2。值得注意的是，假设的机制是 物理起源，并源自这些组件在LS单层中的组织如何影响其 能够流动和变形。仅靠化学分析是无法发现这种机制的。 为了验证这一假设，LS失活因子(血液蛋白质、脂肪酸、酶)对 LS型单分子膜的流变学将使用同类技术中的第一项技术进行测量，以及组件 (如天然或合成表面活性蛋白质、单不饱和脂肪酸、胆固醇)可降低或 逆转失活。利用新的实验技术和理论，分子组成 失活LS与弹性非均质性有关，弹性非均质性与各向异性肺泡有关 通货膨胀和通货紧缩。最后，我们将研究非均相单分子膜的混合和演化。 确定化解、扰乱或取代这些弹性异质性的策略，并最终指导 治疗性配方。

Abstract Native lung surfactant (LS) consists of a mixture of lipids and proteins that together posses the ability to lower the alveolar surface tension, and thus is essential for normal breathing. While the exact mechanisms of acute lung injury (ALI), and its more severe form, acute respiratory distress syndrome (ARDS), are currently not well understood, LS inactivation by surface active inhibitory proteins, enzymes, fatty acids and lyso-lipids are believed to play a contributing role. Published and preliminary work reveals that even small fractions of ARDS-implicated components may change the surface viscosity and elasticity of monolayers by orders of magnitude: thousand-fold increases in phospholipid monolayer stiffness when saturated fatty acids are added or albumin adsorbs, whereas 100-1000-fold decreases occur when 1-2% cholesterol is added. These results suggest a plausible mechanical mechanism for ARDS progression, and the central hypothesis of the proposed project: that the rheological (e.g. viscous and elastic) properties of ARDS- inactivated LS play a central, causative role in the ARDS cascade, and in the inability of RS therapies to effectively reverse ARDS progression. An initial insult to the lung introduces blood proteins through permeabilized alveolar walls, and heightened levels of the enzyme PLA2, as part of the inflammatory response. Previous results suggest that either of these situations would create heterogeneous, rheologically elastic domains deep in the lung: PLA2 by digesting phospholipids to produce lyso-lipids and fatty acids, and blood proteins through adsorption. Well-known phenomena in continuum mechanics suggest that elastic heterogeneities within the LS strongly resist the curvature changes that occur naturally during respiration, and may even `crack' or `crumple' rather than deform smoothly. Such abnormal deformations would thus exert strong, localized mechanical stresses on the alveolar epithelium, promoting further tissue damage and inflammation, and ultimately to greater levels of protein and PLA2. Notably, the hypothesized mechanism is physical in origin, and derives from how the organization of these components in the LS monolayer affects their ability to flow and deform. Such a mechanism could not be uncovered from chemical assays alone. To test this hypothesis, the impact of LS-inactivating factors (blood proteins, fatty acids, enzymes) on the rheology of model LS monolayers will be measured with first-of-their-kind techniques, as well components (e.g. natural or synthetic surfactant proteins, mono-unsaturated fatty acids, cholesterol) that may reduce or reverse the inactivation. Using both novel experimental techniques and theory, the molecular composition of inactivated LS will be related to elastic heterogeneities, and elastic heterogeneities to anisotropic alveolar inflation and deflation. Finally, the mixing and evolution of heterogeneous monolayers will be studied to identify strategies to dissolve, disrupt or displace these elastic heterogeneities, and ultimately guiding therapeutic formulations.