聚乙二醇修饰脂质体的ABC现象研究进展

通常聚乙二醇(polyethylene glycol,PEG)修饰脂质体被认为几乎没有或仅有很低的免疫原性。最新的文献报道,重复注射PEG修饰脂质体发生了免疫反应。当向同一动物体内重复注射(间隔几天)PEG化脂质体时,二次注射的PEG化脂质体导致体内循环时间降低,于肝和脾的聚集量增加,这种现象称为加速血液清除(accelerated blood clearance,ABC)现象。该免疫反应使PEG化制剂的发展和临床应用面临严峻的挑战,可能造成药物或基因治疗效率的下降,甚至引起临床的毒副作用。本文综述了ABC现象的定义、验证ABC现象的方法和手段、ABC现象成因的研究进展及影响因素,并对其他PEG修饰载体是否也会发生ABC现象进行了探讨。     

聚乙二醇化脂质体引起的加速血液清除现象研究进展

目的:为聚乙二醇(PEG)化脂质体的研究和应用提供参考。方法:以"PEG""Accelerated blood clearance phenomenon""加速血液清除"等为关键词,组合查询1987-2013年在Pub Med、Elsevier Science Direct、维普数据库中相关文献,就PEG化脂质体引起的加速血液清除现象(ABC现象)的产生原因和影响因素进行归纳与总结。结果与结论:共查询到83条文献,其中有效文献37条。经分析文献发现,注射剂量、PEG的量和PEG链的长度、粒径和表面电荷、注射时间间隔以及不同动物模型、包裹药物等,均可导致不同程度的ABC现象,建议通过对PEG部分进行修饰、改变聚合物材料、包裹具有免疫抑制作用的药物以及改变注射方式等方法减弱或消除ABC现象。研究表明,对PEG的修饰和寻找PEG的替代品是比较有前途和希望的解决方案,可为日后开发一种没有免疫原性的PEG化脂质体提供一定的理论基础。     

脂质体面临的聚乙二醇“窘境”及其解决方法

聚乙二醇(polyethylene glycol,PEG)因其优越的性能被广泛应用于脂质体等纳米载体表面修饰,但随着研究的深入,PEG化脂质体也产生了相应的负面影响,如PEG链抑制靶细胞对脂质体的摄取、妨碍p H敏感脂质体细胞内的"核内体逃逸"以及对同一动物体内重复注射PEG化脂质体诱发的加速血液清除(accelerated blood clearance,ABC)现象等,这些称为PEG"窘境"(PEG dilemma)。PEG"窘境"为携载抗肿瘤药物的PEG化脂质体的靶向递送、包封基因和蛋白类药物的PEG化p H敏感脂质体发生有效的细胞内释放以及需要重复注射的PEG化脂质体都带来了严峻的挑战,因此解决PEG"窘境"刻不容缓。本文对PEG"窘境"的定义、分类和几种克服PEG"窘境"的方法进行了综述。     

聚乙二醇-脂质衍生物修饰对脂质体稳定性的影响

聚乙二醇-脂质(polyethylene glycol-lipid,PEG-lipid)衍生物具有增加脂质体的稳定性、延长其血液循环半衰期、提高其肿瘤靶向效率及增强药物疗效等优势。深入研究不同PEG-lipid衍生物修饰对脂质体的物理、化学和生物学稳定性的影响,有利于解决目前PEG化脂质体存在的问题,如静脉重复注射时引起的加速血液消除(accelerated blood clearance,ABC)现象,为开发新型靶向制剂奠定基础。本文主要综述了PEG与脂质之间的连接键如酰胺键、醚键、酯键和二硫键,脂质种类如常用的磷脂酰乙醇胺、胆固醇和二酰甘油,脂质的性质即脂肪链长度与饱和度,PEG的端基如甲氧基、羧基、氨基,PEG的相对分子质量和PEG-lipid的摩尔比对PEG化脂质体在体内外稳定性的影响。     

脂质体药物传递系统的50年发展历程概述

目的回顾脂质体50年发展过程中的重大突破及创新,并对其在药物传递系统中的卓越贡献进行综述。方法查阅国内外相关文献99篇,从发展的角度对其进行归纳、分析和总结。结果50年的技术发展与创新促进脂质体不断完善,从传统脂质体到长循环脂质体、从被动靶向到主动靶向、从小分子治疗到基因转染,使其作为一种新型载体系统在临床应用中发挥着越来越重要的作用。近些年研究发现的"加速血液清除"(accelerated blood clearance,ABC)现象极大地限制了PEG化脂质体制剂的临床应用,由此而提出减弱或消除此现象的方法也引起了人们的广泛关注。结论脂质体作为一种纳米载体,在不断发展与完善的同时,也为临床治疗提供了一种新的选择,并将在药物传递领域具有十分广阔的应用前景。     

聚乙二醇衍生化磷脂与脂质体立体稳定性

综述了聚乙二醇(PEG)衍生化磷脂的种类、分子量、用量等对脂质体立体稳定性的影响,阐明了PEG衍生化磷脂改善脂质体稳定性的机理,并对其在延长脂质体体内循环时间及在新型脂质体中的应用作了简要介绍.     

PEG化脂质体30周年回顾与反思

目的 回顾PEG化脂质体(PEGylated liposomes)首次报道至今30年来的相关研究,反思其临床安全性和有效性.方法 查阅国内外相关文献137篇,归纳、总结和分析PEG化脂质体的利弊.结果 聚乙二醇(polyethylene glycol,PEG)的修饰成功地延长了脂质体的血液循环时间,并且广泛应用于临床....     

阳离子脂质材料和聚乙二醇对脂质体细胞转染率及膜流动性的影响阳离子脂质材料和聚乙二醇对脂质体细胞转染率及膜流动性的影响

目的制备包封荧光素钠（FS）的脂质体，考察阳离子脂质材料（DC-chol）和聚乙二醇（PEG）对脂质体包封率、细胞转染率及膜流动性的影响。方法以FS作为模型物质，制备并分离脂质体，测定脂质体包封率；通过观察荧光光谱的变化考察FS与脂质体膜之间的相互作用；以HepG₂ 2.2.15为细胞模型观察脂质体对FS细胞转染率的影响；通过荧光偏振技术考察阳离子脂质材料和PEG对脂质体膜流动性的影响。结果阳离子脂质材料和PEG能提高脂质体包封率（0.64％～86.57％）、细胞转染率（2.18％～48.46％）及脂质体膜流动性，PEG分子质量的增大有利于包封率、转染率的提高，并增加脂质体膜的流动性。结论在脂质体处方中加入阳离子脂质材料和高分子量的PEG有利于提高包封率、细胞转染率及增加脂质体膜的流动性。     

二氢卟吩和全氟己烷共载脂质体的制备及其体外性质

目的 制备共载光敏剂二氢卟吩(Ce6)和氧载体全氟己烷(PFH)的长循环脂质体,对其进行表征,并进行小鼠黑色素瘤细胞摄取的初步研究.方法 采用薄膜超声分散法制备Ce6和PFH共载的PEG化长循环脂质体(Ce6-PFH@PEG-Lip),运用单因素筛选法依次筛选探头超声功率、有机溶剂种类、卵磷脂与胆固醇及DSPE-PEG...     

载药脂质体物理化学稳定性的研究进展

脂质体是一种新型药物载体，研制出稳定的脂质体是脂质体作为药物载体走向实用的前提，具有十分重要的意义。本文综述了影响脂质体物理、化学稳定性的主要因素及部分作用机制；并对改进脂质体稳定性的方法，从加入抗氧化物质、应用冰冻干燥和选择合适的磷脂种类等几个方面进行了阐述。结果表明，单纯的将脂质体的稳定性分为化学和物理稳定性是不够的，弄清楚影响脂质体稳定性的机制，找到确切的影响因素和影响程度，建立评价脂质体稳定性的可靠方法和参数，预测制剂的储存时间才是当前研究需要解决的问题所在。     

Particle size-dependent triggering of accelerated blood clearance phenomenon

A repeat-injection of polyethylene glycol-modified liposomes (PEGylated liposomes) causes a rapid clearance of them from the blood circulation in certain cases that is referred to as the accelerated blood clearance (ABC) phenomenon. In the present study, we examined whether polymeric micelles trigger ABC phenomenon or not. As a preconditioning treatment, polymeric micelles (9.7, 31.5, or 50.2nm in diameter) or PEGylated liposomes (119, 261 or 795nm) were preadministered into BALB/c mice. Three days after the preadministration [(3)H]-labeled PEGylated liposomes (127nm) as a test dose were administered into the mice to determine the biodistribution of PEGylated liposomes. At 24h after the test dose was given, accelerated clearance of PEGylated liposomes from the bloodstream and significant accumulation in the liver was observed in the mice preadministered with 50.2-795nm nanoassemblies (PEGylated liposomes or polymeric micelles). In contrast, such phenomenon was not observed with 9.7-31.5nm polymeric micelles. The enhanced blood clearance and hepatic uptake of the test dose (ABC phenomenon) were related to the size of triggering nanoassemblies. Our study provides important information for developing both drug and gene delivery systems by means of nanocarriers.     

Repeated injections of PEGylated liposomal topotecan induces accelerated blood clearance phenomenon in rats

The "accelerated blood clearance (ABC) phenomenon" of PEGylated liposomes following multiple injections has been reported recently. This immunogenicity poses a problem for research into liposomes and hinders their clinical application. However, since doxorubicin liposomes and mitoxantrone liposomes have been reported to fail to induce the ABC phenomenon, some people believe that cytotoxic drugs loaded liposomes will not produce this ABC phenomenon under multiple-dosing regimens. Nevertheless, in the present study, we report that a first injection of the PEGylated liposomal topotecan (a cell cycle-specific drug for the S phase) still produced a strong ABC phenomenon. Likewise, when the first dose of "empty" PEGylated liposomes or topotecan liposomes was increased, the ABC phenomenon of the subsequent dose was accordingly attenuated. Unlike doxorubicin and mitoxantrone, the blood clearance rate of topotecan was dramatically rapid, and the hepatic and splenic accumulations of topotecan liposomes were anomalous because of the ABC phenomenon. These findings may present new challenges to the clinical application of formulations of cytotoxic drugs loaded liposomes that require repeated administrations.     

Accelerated blood clearance (ABC) phenomenon induced by administration of PEGylated liposome

PEGylated liposomes (approximately 100 nm in diameter) lose their long-circulating characteristic upon repeated injection at certain intervals in the same animal (referred to as the "accelerated blood clearance (ABC) phenomenon"), as described by our group and by researchers in the Netherlands. Recently, it was demonstrated by our group that anti-PEG IgM, induced by the first dose of PEGylated liposomes, is responsible for the ABC phenomenon. The IgM produced in this manner then selectively bound to the surface of subsequently injected PEGylated liposomes, leading to substantial complement activation. It is generally believed that nanocarriers coated with a polymer, such as PEG, have no immunogenicity. However, unexpected immune responses occurred even in response to polymer-coated liposomes. This immunogenicity to PEGylated liposomes presents a serious concern in the development and clinical use of liposomal formulations. In this review, we demonstrate our recent observations regarding with the ABC phenomenon against liposomes.     

Accelerated blood clearance (ABC) phenomenon upon repeated injection of PEGylated liposomes

We and a Dutch group reported that "empty" PEGylated liposomes (approximately 100 nm) lose their long-circulating characteristic when they are administrated twice in the same animal with certain intervals (referred to as the accelerated blood clearance (ABC) phenomenon). Very recently, we showed that anti-PEG IgM, induced by the first dose of "empty" PEGylated liposomes, is responsible for inducing the phenomenon, based on the observation that IgM thus produced selectively binds to the surface of subsequently injected PEGylated liposomes, leading to substantial complement activation. It is generally believed that nanocarriers coated with a polymer, such as PEG, have no or lower immunogenicity. However, the results indicated evidence that unexpected immune responses occur even to such polymer-coated liposomes. Such immunogenicity of "empty" liposomes presents a serious concern in the development of liposomal formulations and their use in the clinic. In addition, through series of our studies, it was demonstrated that the magnitude of the ABC phenomenon depends on the physicochemical property of injected liposomes as a first dose, time interval between injection, lipid dose and drug-encapsulation.     

Time Interval of Two Injections and First-Dose Dependent of Accelerated Blood Clearance Phenomenon Induced by PEGylated Liposomal Gambogenic Acid: The Contribution of PEG-Specific IgM

Repeated injection of PEGylated liposomes can cause the disappearance of long circulating property because of the induction of anti-PEG IgM antibody referred to as “accelerated blood clearance (ABC) phenomenon.” Although ABC phenomenon typically occurs when entrapped drugs are chemotherapeutic agent with low cytotoxic, there is little evidence of accelerated blood clearance of PEGylated herbal-derived compound on repeated injection. Herein, we investigated the blood concentration of PEGylated liposomal gambogenic acid (PEG-GEA-L), a model PEGylated liposomal herbal extract, on its repeated injection to rats. We found time interval between injections had considerable impact on the magnitude of ABC phenomenon induced by PEG-GEA-L. When time interval was prolonged from 3 days to 7 days, ABC phenomenon could be attenuated. Furthermore, its magnitude was enhanced accompanied by a marked rise in the accumulation of PEG-GEA-L in the liver and spleen in a first-dose–dependent manner. Consistently, the level of anti-PEG IgM significantly increased with the first dose of PEG-GEA-L and decreased with the extended time interval between injections, which implies anti-PEG IgM is a major contributor to the ABC phenomenon. Notably, the increased expression of liver anti-PEG IgM was accompanied by an increased expression of efflux transporters in the induction process of the ABC phenomenon.     

Accelerated blood clearance of PEGylated liposomes containing doxorubicin upon repeated administration to dogs

The accelerated blood clearance phenomenon involving anti-PEG IgM production has been recognized as an important issue for the design and development of PEGylated liposomes. Here, we show that empty PEGylated liposomes and Doxil, PEGylated liposomes containing doxorubicin, both caused anti-PEG IgM production and thereby a rapid clearance of the second and/or third dose of Doxil in Beagle dogs in a lipid-dose, inverse-dependent manner. It appears that the pharmacokinetic profile of the second and third administration of Doxil reflected the presence of anti-PEG IgM circulating in the blood. Doxil plus an excess amount of empty PEGylated liposomes rather enhanced the production of anti-PEG IgM compared to Doxil of the same doxorubicin dose. During sequential administration, increasing the lipid dose of Doxil in each dose by the addition of empty PEGylated liposomes strongly attenuated the magnitude of the ABC phenomenon during the effectuation phase of a second and third dose of Doxil. Our results suggest that the pre-clinical study of anti-cancer drug-containing PEGylated liposomes with dogs must be carefully designed and performed with monitoring of the anti-PEG IgM and liposomal drugs circulating in the blood.     

Use of polyglycerol (PG), instead of polyethylene glycol (PEG), prevents induction of the accelerated blood clearance phenomenon against long-circulating liposomes upon repeated administration

The accelerated blood clearance (ABC) phenomenon accounts for the rapid systemic clearance of PEGylated nanocarriers upon repeated administrations. IgM production against the polyethylene glycol (PEG) coating in PEGylated liposomes is now known to be responsible for such unexpected pharmacokinetical alterations. The ABC phenomenon poses a remarkable clinical challenge by reducing the therapeutic efficacy of encapsulated drugs and causing harmful effects due to the altered tissue distribution pattern of the drugs. In this study, we investigated the in vivo performance of liposomes modified with polyglycerol (PG) upon repeated injection, and the in vivo therapeutic efficacy of such liposomes when they encapsulated a cytotoxic agent, doxorubicin (DXR). Repeated injection of PEG-coated liposomes in rats induced the ABC phenomenon, while repeated injection of PG-coated liposomes did not. In addition, DXR-containing PG-coated liposomes showed antitumor activity that was superior to that of free DXR and similar to that of DXR-containing PEG-coated liposomes upon repeated administration. These results indicate that polyglycerol (PG) might represent a promising alternative to PEG via enhancing the in vivo performance of liposomes by not eliciting the ABC phenomenon upon repeated administration.     

Differences in colloidal structure of PEGylated nanomaterials dictate the likelihood of accelerated blood clearance

PEGylated liposomes are known to exhibit accelerated clearance from systemic circulation on repeat administration (the so-called "accelerated blood clearance" or ABC effect); however, little is known about this effect for other PEGylated colloidal drug delivery systems. Furthermore, our understanding of the mechanisms by which the ABC effect is induced is limited. This article further addresses these issues by examining the impact of colloid types [polyethylene glycol (PEG)-liposomes, PEG-micelles] of varying sizes on the appearance of the ABC effect when readministered 7 days after a "priming" dose. Intravenous injection of PEG-liposomes and putative PEG-micelles induced the production of anti-PEG immunoglobulin (Ig) M, although decreasing the average particle size led to reduced IgM titres. The ABC effect was observed for PEGylated phospholipid/cholesterol-based liposomes 7 days after an initial "priming" dose of liposome; however, addition of increasing levels of PEGylated lipid to form micelles reduced the propensity of observation of the ABC effect, correlating with the reduced IgM production. The results suggest that although PEG-micelles may stimulate limited production of anti-PEG IgM, which leads to accelerated clearance of subsequently administered PEG-liposomes, PEGylated micelles themselves are not substrates for IgM binding and do not exhibit a similar ABC.     

Size-dependent induction of accelerated blood clearance phenomenon by repeated injections of polymeric micelles

An accelerated blood clearance (ABC) phenomenon is induced by repeated injections of poly(ethylene glycol)-modified (PEGylated) liposomes. We previously indicated that the phenomenon was induced by polymeric micelles possessing PEG chains like as liposomes, although, the induction mechanism of the ABC phenomenon is not fully elucidated. In the present study, we investigate whether repeat-injection of the polymeric micelles having PEG chains trigger the phenomenon or not. Two polymeric micelles, PM-30 (polymeric micelles with 33.6nm in diameter) and PM-75 (76.2nm), were prepared with PEG-poly[Asp(pentyl)] and PEG-poly[Asp(nonyl)], respectively. We firstly examined the ABC-triggering effect of these micelles, and observed that both polymeric micelles, especially PM-75, induced the production of anti-PEG IgM antibody in treated mice. Then, PM-30 or PM-75 was preadministered into mice as a preconditioning. Seven days later, AlexaFluor594-labeled PM-30 or PM-75 was administered to determine the susceptibility of the phenomenon. As a result, rapid clearance of AlexaFluor594-labeled PM-75 from the bloodstream and accumulation in the liver were observed in PM-75 pretreated mice. Although, the ABC phenomenon of AlexaFluor594-labeled PM-30 was less obvious in PM-30 pretreated mice. Our present results indicated that the repeated injections of polymeric micelles caused the ABC phenomenon in a size-dependent manner.