Division of Clinical Nephrology and Rheumatology, Niigata University Graduate School of Medical and Dental Sciences, Niigata 951-8510, Japan.
Institute for Protein Research, Osaka University, Yamadaoka 3-2, Suita, Osaka 565-0871, Japan.
Toxins (Basel). 2021 Feb 4;13(2):116. doi: 10.3390/toxins13020116.
Protein-bound uremic toxins (PBUTs) are difficult to remove using conventional dialysis treatment owing to their high protein-binding affinity. As pH changes the conformation of proteins, it may be associated with the binding of uremic toxins. Albumin conformation at pH 2 to 13 was analyzed using circular dichroism. The protein binding behavior between indoxyl sulfate (IS) and albumin was examined using isothermal titration calorimetry. Albumin with IS, and serum with IS, p-cresyl sulfate, indole acetic acid or phenyl sulfate, as well as serum from hemodialysis patients, were adjusted pH of 3 to 11, and the concentration of the free PBUTs was measured using mass spectrometry. Albumin was unfolded at pH < 4 or >12, and weakened interaction with IS occurred at pH < 5 or >10. The concentration of free IS in the albumin solution was increased at pH 4.0 and pH 11.0. Addition of human serum to each toxin resulted in increased free forms at acidic and alkaline pH. The pH values of serums from patients undergoing hemodialysis adjusted to 3.4 and 11.3 resulted in increased concentrations of the free forms of PBUTs. In conclusion, acidic and alkaline pH conditions changed the albumin conformation and weakened the protein binding property of PBUTs in vitro.
蛋白质结合型尿毒症毒素（PBUTs）由于其与蛋白质的高亲和力而难以通过常规透析治疗去除。由于 pH 值改变了蛋白质的构象，因此它可能与尿毒症毒素的结合有关。使用圆二色性分析了 pH 值为 2 到 13 的白蛋白构象。使用等温滴定量热法研究了间苯硫酸（IS）与白蛋白之间的蛋白质结合行为。将 IS 与白蛋白、血清中的对甲酚硫酸盐、吲哚乙酸或苯硫酸以及血液透析患者的血清的 pH 值调节为 3 到 11，并使用质谱法测量游离 PBUTs 的浓度。当 pH 值 < 4 或 >12 时，白蛋白发生去折叠，当 pH 值 < 5 或 >10 时，与 IS 的相互作用减弱。在 pH 值为 4.0 和 11.0 时，白蛋白溶液中游离 IS 的浓度增加。将人血清添加到每种毒素中，在酸性和碱性 pH 值下会增加游离形式。将接受血液透析的患者的血清 pH 值分别调节至 3.4 和 11.3，导致游离形式的 PBUTs 浓度增加。总之，酸性和碱性 pH 值条件改变了白蛋白构象，并削弱了 PBUTs 在体外的蛋白质结合特性。
