【作者】 鞠佳；

【导师】 贺高红； 吴雪梅；

【作者基本信息】 大连理工大学 ， 化学工程， 2013， 博士

【摘要】 胆红素是体内血红素的代谢产物,体内浓度较高时可对大脑和神经系统造成不可逆损害,甚至危及生命。临床多通过血液体外循环去除胆红素,然而血液中的白蛋白严重干扰胆红素的吸附与洗脱,导致胆红素吸附剂存在吸附量低、再生困难等问题。本论文以醋酸纤维素/聚乙烯基亚胺共混微孔膜(CA/PEI膜)为研究体系,提出了添加药物(去氧胆酸钠)辅助亲和膜,以及接枝长链有机胺或β-环糊精的疏水空腔改性亲和膜的方法,增加胆红素吸附量,同时提高胆红素的吸附选择性,还建立了低浓度碱液复配重氮促进剂的胆红素洗脱方法,加快吸附材料CA/PEI微孔膜的再生。首先,采用生物相容性较好的CA/PEI膜进行胆红素的吸附研究,胆红素的静态吸附实验显示：较佳的吸附实验条件为37℃、2h,在此条件下最大的游离胆红素吸附量达到41.2mg/g干膜,与文献报道的亲和膜的胆红素吸附量(25.0-63.4mg/g干膜)相当。在胆红素缓冲溶液中,吸附游离胆红素的推动力主要为静电力。在模拟血清溶液中,胆红素和白蛋白以等摩尔比复合物形式在膜上吸附,这不但导致胆红素吸附量的明显降低,仅为2.9mg/g干膜,而且降低了胆红素对白蛋白吸附选择性。此外,复合物的吸附还增加了CA/PEI膜的再生难度,常规碱液再生方法的洗脱率仅63%。为减少空间位阻大的胆红素白蛋白复合物对吸附的不利影响,选择了治疗黄疸的胆盐类药物作为吸附促进剂,研发了去氧胆酸钠等胆盐与CA/PEI膜耦合吸附血清中胆红素的新方法,在添加量较少时,效果明显优于文献报道的效果最好的促进剂苯甲酸钠。当模拟血清中人血白蛋白和胆红素的浓度同为0.163mM时,添加去氧胆酸钠的CA/PEI膜的胆红素最大吸附量提高到16.5mg/g干膜,相对于无添加情况提高了100%。血清胆红素吸附结果显示,添加去氧胆酸钠后,胆红素和白蛋白的去除率均有提高,但是胆红素的去除率提高得更加显著,因此胆红素对白蛋白的吸附选择性也略有提高。可见吸收光谱、圆二色光谱及zeta电位结果显示,在实验浓度范围内去氧胆酸钠与胆红素、白蛋白形成了三元复合物。静态实验表明去氧胆酸钠在膜上的吸附能力强于白蛋白和胆红素,并能形成多层吸附。动态实验显示预先吸附多层去氧胆酸钠的促进效果最好。基于以上研究,提出了去氧胆酸钠与CA/PEI膜耦合吸附胆红素的机理：胆红素、白蛋白、去氧胆酸钠形成的三元复合物,与PEI中胺基的相互作用更强,更容易被吸附；预先吸附在CA/PEI膜上的多层去氧胆酸钠,形成了可重排的柔性表面,延伸了亲和配基的作用距离,降低了复合物吸附的位阻效用,提高了复合物在膜上的吸附量。为了降低了胆红素白蛋白复合物在膜上吸附的位阻效应,本文进一步提出了在CA/PEI膜和聚丙烯微孔膜(PP膜)不同基膜上,接枝长链氨基酸、有机胺或引入β-环糊精的疏水空腔的方法,提高血清中胆红素的吸附量,同时提高胆红素的吸附选择性。采用戊二醛法在CA/PEI膜上接枝了具有代表性的8种氨基酸和5种有机胺,采用高碘酸钠氧化法在CA/PEI膜上接枝了疏水的环糊精空腔结构,采用紫外辐射法在PP膜上两步接枝带支链和不带支链的4种有机胺,制备出一系列具有特异性配基的改性亲和膜。其中,己二胺、三甲基己二胺、间苯二甲胺、赖氨酸改性CA/PEI膜提高了血清胆红素的吸附量和选择性：虽然改性膜的胺基含量降为原始含量的1/3,但是胆红素吸附量却提高了100%,而且白蛋白的吸附量无显著变化,因此胆红素对白蛋白的吸附选择性提高了一倍以上。基于15种改性配基的分析对比,得出以下规律：增加胺基或疏水结构有利于胆红素吸附,而羧基不利于胆红素的吸附；配基密度、空间位阻协同影响胆红素的吸附,含苯环、支链等大位阻结构的亲和配基使得胆红素白蛋白复合物难以接近膜表面,即使提高配基密度也难以提高吸附量；而具有长碳链的亲和配基,’间隔臂较长,位阻小,克服了胆红素白蛋白复合物中胆红素吸附的空间位阻,不但提高亲和膜的胆红素吸附量,而且提高了胆红素的吸附选择性。胆红素白蛋白复合物在膜上的吸附,不但导致胆红素吸附量的明显降低,还增加了胆红素洗脱的困难,限制了CA/PEI膜的重复利用。针对胆红素洗脱的问题,提出复合物拆分/洗脱的再生路线,建立了低浓度碱液复配重氮促进剂的再生体系,利用重氮促进剂(如咖啡因试剂和二羟丙茶碱)与胆红素发生相互作用,破坏胆红素与白蛋白以及膜中亲和配基的相互作用,提高胆红素的洗脱速率和洗脱程度。通过分析咖啡因试剂、胆红素、白蛋白混合溶液的吸收光谱,以及两种胆红素吸附膜的洗脱液的光谱扫描分析,证实了咖啡因试剂的拆分作用。动态洗脱实验表明,0.025M NaOH溶液复配咖啡因试剂可洗脱90%以上白蛋白结合胆红素；静态吸附洗脱循环实验显示,平均洗脱率达到85%,效果优于同浓度下常规洗脱剂NaOH。低浓度碱液复配重氮促进剂的另一优势在于不损伤膜结构,膜的机械性能基本保持不变。而且,咖啡因复配碱液对改性CA/PEI膜和添加了去氧胆酸钠的三元体系中吸附的膜也具有较好的洗脱效果。胺基改性及药物添加强化亲和膜吸附和洗脱胆红素的过程,解决了血清实验中胆红素与白蛋白形成复合物、胆红素在亲和膜上吸附容量低、洗脱困难等问题,为亲和膜去除血清胆红素临床应用提供了重要理论指导。更多还原

【Abstract】 High concentration of bilirubin (BR) in the blood results in neurotoxicity, permanent brain damage, and even death. Therefore, it is necessary to lower the amount of BR in the serum of hyperbilirubinemia patients to a normal level. Hemoperfusion is commonly used in the clinic to treat severe hyperbilirubinemia because of its biocompatibility and high efficiency. However, the particle and membrane adsorbents used in hemoperfusion demonstrated decreased BR removal and elution efficiencies due to the high affinity between BR and human albumin (HA) in the blood. In this thesis, the following experiments were conducted to explore new conditions for the improvement of BR adsorption capacity and elution efficiency. Sodium deoxycholate (SDC), a common bile salt, was used as an adsorption promoter to improve the BR adsorption capacity of the cellulose acetate/polyethyleneimine blend microporous membrane (CA/PEI membrane), and the facilitated adsorption mechanism of BR with SDC was proposed. Amino acids, β-cyclodextrin, and amines as ligands were immobilized on CA/PEI membrane or polypropylene (PP) membrane via glutaraldehyde activation, periodate oxidation, and UV induced radiation grafting to investigate the effects of chemical composition of ligand, ligand density, and steric hindrance on BR adsorption capacity. Caffeine reagent was introduced and combined with a low concentration of NaOH to enhance BR elution efficiency of CA/PEI membrane.First, CA/PEI membrane was employed to adsorb BR in BR-buffered solution, BR-HA mock solution, and the human serum. Static adsorption experiments showed, under optimized adsorption temperature and duration (37℃,2h), that the CA/PEI membrane could reach a maximum free BR adsorption capacity of70.5μmol/g dry membrane (41.2mg/g dry membrane), which was comparable to that of other affinity membranes (25.0-63.4mg/g dry membrane) investigated by other labs. The mechanism for this free BR adsorption was attributed to the electrostatic interaction between the negatively charged carboxyl groups of BR molecule and the positively charged amine groups of PEI. However, although BR could still be indirectly adsorbed by the CA/PEI membrane through the binding between the membrane and the HA-BR (1:1) complex formed in BR-HA mock solution, the high steric hindrance caused by large molecular volume of the complex decreased not only the BR adsorption capacity of the membrane to2.9mg/g dry membrane but also the adsorption selectivity of BR to HA. In addition, the BR elution efficiency of CA/PEI membrane using alkaline solution decreased to63%because of the adsorption of BR-HA complex.Second, SDC was selected as an adsorption promoter to improve the BR adsorption capacity of the CA/PEI membrane because of its biocompatibility. Static adsorption experiments demonstrated that, at the molar ratio of SDC to HA ranging from8to12in the BR-HA mock solution, the maximum BR adsorption capacity was100-200%, higher than that without SDC. For example, When the concentrations of BR and HA equalled to0.163mM (RHA/BR=1), the BR adsorption capacity reached the maximum of28.2μmol/g dry membrane (16.5mg/g dry membrane), which was100%higher than that without SDC. It was also found that BR removal efficiency and adsorption selectivity of BR to HA were improved via the addition of SDC in serum. The results also indicated that SDC was more efficiently adsorbed by the membrane than BR and HA. Absorption, circular dichroism, and zeta potential studies demonstrated that SDC could form a ternary BR-HA-SDCm complex with the BR-HA complex. Based on these results, a facilitated BR adsorption mechanism for the membrane with SDC was proposed that SDC aggregates or micelles form a quasi-multilayer on the membrane, thus increasing the approachable binding sites and elongating the distance between the BR-HA complex and the membrane. Therefore, SDC, acting as a spacer, reduced the steric hindrance of HA, which led to an improvement in the BR adsorption capacity. Results from dynamic adsorption experiments further proved the proposed facilitated adsorption mechanism.Third, amine modification was also explored on CA/PEI and PP membranes in order to enhance their serum BR adsorption capacity and adsorption selectivity of BR to HA. Amino acids, P-cyclodextrin, and amines were immobilized via glutaraldehyde activation, periodate oxidation, and UV induced radiation grafting to prepare a series of amine-modified affinity membranes. In these membranes, the BR adsorption capacity of hexamethylene diamine-,2,2,5-trimethyl hexamethylenediamine-, m-xylylenediamine-, and lysine-modified CA/PEI membrane was increased by more than100%, although the primary amine content of the modified membrane reduced to1/3of that of CA/PEI membrane. The modified membrane owned comparable HA adsorption capacity to CA/PEI membrane, and thus the adsorption selectivity of BR to HA was doubled. The experimental results also revealed that the ligand composition played a significant role in the BR adsorption. Briefly, ligands containing hydrophobic and primary amino groups enhanced the BR adsorption capacity, and ligands with acid radicals reduced the BR adsorption capacity of the modified membrane. Moreover, ligand density, ligand steric hindrance, and other factors also had great effects on the BR adsorption capacity. For example, ligands containing high steric hindrance groups, such as phenyl groups, had a negative effect on the BR adsorption capacity of the modified membrane, and naturally, the higher the ligand density was, the lower the BR adsorption capacity couldnot be. On the contrary, the BR adsorption capacity of the membrane modified with low steric hindrance ligand, like hexamethylenediamine-modified membrane, increased along with the increasing ligand density.Last, caffeine reagent was introduced and combined with a low-concentration NaOH solution (0.025M) to increase the BR elution efficiency of the CA/PEI membrane. The visible absorption spectra revealed that the caffeine reagent, as an unbinding agent in the combination eluent, could displace BR from HA and desorb the BR-HA complex from the membrane. Static adsorption-desorption cycle experiments using the combination eluent demonstrated that the average BR elution efficiency was85%, and the CA/PEI membrane maintained its mechanical properties and porous membrane structure after three cycles without any weight loss. The combination eluent could efficiently desorb BR from BR-preadsorbed membrane prepared in BR-HA mock solution with a high HA concentration or the addition of SDC. The modified CA/PEI membrane could also be efficiently regenerated using the combination eluent.In summary, this work focused on exploring various modifications of the affinity membrane to improve the BR adsorption and elution efficiency. The results could lay experimental and theoretical foundations for treatment of hyperbilirubinemia using affinity membrane in future clinical application.更多还原