Department of Bioengineering, 501 Rhodes Engineering Center, Clemson University, Clemson, SC 29634, USA.
Biomaterials. 2010 Feb;31(6):1036-44. doi: 10.1016/j.biomaterials.2009.10.017. Epub 2009 Oct 27.
Although albumin (Alb) is the most abundant plasma protein, it is considered to be non-adhesive to platelets, as it lacks any known amino acid sequences for binding platelet receptors. Recent studies have suggested that platelets adhere to adsorbed Alb by mechanisms linked to its conformational state. To definitively address this issue we used circular dichroism (CD) spectropolarimetry to characterize the conformation of Alb adsorbed on a broad range of surface chemistries from a wide range of Alb solution concentrations, with platelet adhesion examined using a lactate dehydrogenase (LDH) assay and scanning electron microscopy (SEM). Our results prove that platelets bind to adsorbed Alb through receptor-mediated processes, with binding sites in Alb exposed and/or formed by adsorption-induced protein unfolding. Most importantly, beyond a critical degree of unfolding, the platelet adhesion levels correlated strongly with the adsorption-induced unfolding in Alb. The blockage of Arg-Gly-Asp (RGD) specific platelet receptors using an Arg-Gly-Asp-Ser (RGDS) peptide led to significant inhibition of platelet adhesion to adsorbed Alb, with the extent of inhibition and morphology of adherent platelets being similar for both Alb and Fg. Chemical neutralization of arginine (Arg) residues in the adsorbed Alb layer inhibited platelet-Alb interactions significantly, indicating that Arg residues play a prominent role in mediating platelet adhesion to Alb. These results provide deeper insight into the molecular mechanisms that mediate the interactions of platelets with adsorbed proteins, and how to control these interactions to improve the blood compatibility of biomaterials for cardiovascular applications.
尽管白蛋白 (Alb) 是最丰富的血浆蛋白，但它被认为对血小板没有粘性，因为它缺乏与血小板受体结合的任何已知氨基酸序列。最近的研究表明，血小板通过与 Alb 构象状态相关的机制粘附在吸附的 Alb 上。为了明确解决这个问题，我们使用圆二色性 (CD) 旋光光谱法来表征 Alb 在广泛的表面化学性质上从广泛的 Alb 溶液浓度下吸附的构象，使用乳酸脱氢酶 (LDH) 测定法和扫描电子显微镜 (SEM) 检查血小板粘附。我们的结果证明，血小板通过受体介导的过程与吸附的 Alb 结合，吸附诱导的蛋白展开暴露和/或形成 Alb 中的结合位点。最重要的是，超过一定程度的展开后，血小板粘附水平与 Alb 中的吸附诱导展开密切相关。使用 Arg-Gly-Asp-Ser (RGDS) 肽阻断 Arg-Gly-Asp (RGD) 特异性血小板受体导致血小板对吸附 Alb 的粘附显著抑制，吸附的 Alb 和 Fg 上的血小板粘附的抑制程度和形态相似。吸附 Alb 层中精氨酸 (Arg) 残基的化学中和显著抑制了血小板-Alb 相互作用，表明 Arg 残基在介导血小板与 Alb 相互作用中起重要作用。这些结果深入了解了介导血小板与吸附蛋白相互作用的分子机制，以及如何控制这些相互作用以提高心血管应用中生物材料的血液相容性。
