DSPE-PEG衍生物属性和长循环脂质体的研究及应用介绍

药物载运系统是药学的重要研究内容之一。常见的药物载体有脂质体、病毒、脂质微球、多聚复合物及蛋白多肽类等。控释和靶向脂质体制剂是目前药物运载系统的研究热点。脂质体具有低毒、易制备、既能作为水溶性药物的载体又能作为脂溶性药物的载体、适用于多种给药途径、提高药物的稳定性、实现靶向性给药等优点。但是当脂质体进入体内后,由于血浆中的调理素对脂质体的特异性调理作用,以及网状内皮系统(RES)细胞与脂质体的非特异性疏水作用,使其易被RES细胞摄取、清除,在血液循环中的半衰期较短(一般为30min),主动靶向性和稳定性较差,其应用受到限制。对脂质体表面行聚乙二醇(polyethyleneglycol,PEG)修饰后,得到长循环脂质体(Longcirculationliposome,LCL),可以延长脂质体的半衰期和提高它在血液循环中的稳定性、改变脂质体的生物学分布,并具有靶向性      PEG是由乙二醇单体聚合而成的线性高分子材料,分子组成为HO-CH2-CH2(OCH2CH2O)n-CH2-CH2-OH。PEG延长脂质体血循环半衰期的机理如下。PEG分子中存在的大量乙氧基能够与水形成氢键,使PEG具有水溶性和高柔顺性,在脂质体表面形成一层水化膜;PEG在脂质体表面交错重叠覆盖,形成致密的蘑菇状、毛刷状或烙饼状构象云,构成空间位阻,阻碍某些蛋白质的吸附和细胞的黏附,并掩盖脂质体表面的疏水性结合位点,降低血浆蛋白与脂质体之间的范德华力,阻碍血浆成分接近脂质体,从而有效地躲避RES的识别和吞噬,使脂质体在血循环中的半衰期明显延长[3] 。与不含PEG的脂质体相比,DSPE-PEG-脂质体在体外血浆的稳定性高,与血浆成分的吸附慢;体内血循环清除时间延长30%[4,5],因此PEG修饰的这种脂质体具有长循环、隐形和立体稳定的特点。

在PEG-脂质复合物中,由于单纯PEG或PEG-硬脂酸与脂质体的连接不牢固,不能有效降低RES对脂质体的摄取。PEG-二棕榈酰磷脂酰甘油酯和PEG-*延长脂质体T1/2的能力较单纯PEG或PEG-硬脂酸强,但低于DSPE-PEG。PEG与DSPE通过氨基甲酸酯键相连,有两个饱和脂酰基链,亲脂端为DSPE,亲水端为PEG,与脂质体的连接牢固,保护脂质体不被破坏的能力zui强。因此制作LCL的基本方法是在脂质体的磷脂双层外加上DSPE-PEG。      PEG与脂质体的连接方法有两种:一种是以共价键偶联在已制备好的脂质体表面;另一种是以疏水性取代基的疏水作用吸附或结合在脂质体的表面。这两种方法中结合或吸附的聚合物的疏水链部分暴露于溶液中,以保护脂质体不与血液中的血浆蛋白发生作用。

PEG对脂质体的立体保护作用取决于PEG的分子量、链长、柔性、亲水性、磷脂的组成、不同的添加剂以及形成的LCL的粒径。制备LCL较佳的处方为:较低浓度的短链或中长链的PEG,不含有不饱和键、碳原子数为16或更少的磷脂酰*,*的浓度大于30%。一般而言,PEG链越长(分子质量达5000),脂质体的循环时间越长;但对于胶态脂质体,分子质量在1000～2000之间的PEG长循环效果[6]。DSPE-PEG浓度为5～7mol/L时,血液循环时间zui长。由PEG-750-DSPE、PEG-2000-DSPE或PEG-5000-DSPE为成膜材料制备的LCL静脉注射后,血浆T1/2分别为0.7、1.7和6.2h,而脂质体血浆半衰期(T1/2)为0.5h。因此随PEG分子量增加,LCL血浆T1/2延长。粒径在160～220nm的PEG-LCL的长循环作用zui明显。

PEG脂质材料产品介绍：

Research and application of DSPE-PEG derivative properties and long-circulating liposomes

Drug delivery system is one of the important research contents in pharmacy. Common drug carriers include liposomes, viruses, lipid microspheres, multimeric complexes and protein polypeptides. Controlled-release and targeted liposome formulations are the current research hotspots for drug delivery systems. Liposomes have the advantages of low toxicity, easy preparation, can be used as a carrier for both water-soluble drugs and lipid-soluble drugs, suitable for various administration routes, improve the stability of drugs, and achieve targeted drug delivery. However, after the liposome enters the body, due to the specific opsonization of the liposome by the opsonins in the plasma and the non-specific hydrophobic interaction between the reticuloendothelial system (RES) cells and the liposome, the liposome is easily absorbed by the RES cells. Uptake, clearance, short half-life in blood circulation (usually 30min), poor active targeting and poor stability, its application is limited. Long circulation liposome (LCL) can be obtained by modifying the surface of liposomes with polyethylene glycol (PEG), which can prolong the half-life of liposomes, improve its stability in blood circulation, and change lipids. Biological distribution of plastids with targeting

PEG is a linear polymer material polymerized by ethylene glycol monomer, and its molecular composition is HO-CH2-CH2(OCH2CH2O)n-CH2-CH2-OH. The mechanism by which PEG prolongs the blood circulation half-life of liposomes is as follows. A large number of ethoxy groups in PEG molecules can form hydrogen bonds with water, making PEG water-soluble and highly flexible, forming a layer of hydration film on the surface of liposomes; PEG overlaps and overlaps on the surface of liposomes, forming dense The mushroom-shaped, brush-shaped or pancake-shaped conformation cloud constitutes steric hindrance, hinders the adsorption of certain proteins and cell adhesion, and masks the hydrophobic binding sites on the surface of liposomes, reducing the interaction between plasma proteins and liposomes. The intervening van der Waals force prevents plasma components from approaching liposomes, thereby effectively avoiding the recognition and phagocytosis of RES, and prolonging the half-life of liposomes in the blood circulation significantly [3]. Compared with liposomes without PEG, DSPE-PEG-liposomes have high stability in plasma in vitro, slow adsorption to plasma components, and prolonged blood circulation clearance time by 30% in vivo[4,5], so PEG-modified liposomes have high stability in plasma. This liposome is characterized by long circulation, stealth and steric stability.

In the PEG-liposome complex, the uptake of RES to liposomes cannot be effectively reduced due to the weak connection between simple PEG or PEG-stearic acid and liposomes. The ability of PEG-dipalmitoyl phosphatidylglyceride and PEG-* to prolong liposome T1/2 was stronger than that of simple PEG or PEG-stearic acid, but lower than that of DSPE-PEG. PEG and DSPE are connected by carbamate bonds, there are two saturated fatty acyl chains, the lipophilic end is DSPE, the hydrophilic end is PEG, the connection with the liposome is firm, and the ability to protect the liposome from being destroyed is the strongest . Therefore, the basic method of making LCL is to add DSPE-PEG to the phospholipid bilayer of liposome.

There are two ways to connect PEG to liposomes: one is to couple on the surface of the prepared liposome by covalent bond; the other is to adsorb or bind to the liposome by the hydrophobic interaction of hydrophobic substituents. s surface. The hydrophobic chain moieties of the bound or adsorbed polymers in both methods are exposed in solution to protect the liposomes from interacting with plasma proteins in the blood.

The steric protective effect of PEG on liposomes depends on the molecular weight, chain length, flexibility, hydrophilicity, phospholipid composition, different additives and particle size of the LCLs formed. The best formula for preparing LCL is: low concentration of short-chain or medium-long chain PEG, no unsaturated bond, phosphatidyl* with 16 or less carbon atoms, and the concentration of * is greater than 30%. In general, the longer the PEG chain (molecular mass up to 5000), the longer the circulation time of liposomes; but for colloidal liposomes, PEG with molecular mass between 1000 and 2000 has a long circulation effect [6]. When the concentration of DSPE-PEG was 5～7mol/L, the blood circulation time was the longest. After intravenous injection of LCL prepared with PEG-750-DSPE, PEG-2000-DSPE or PEG-5000-DSPE as film-forming materials, the plasma T1/2 were 0.7, 1.7 and 6.2 h, respectively, while the plasma half-life of liposomes (T1 /2) is 0.5h. Therefore, with the increase of PEG molecular weight, LCL plasma T1/2 prolonged. The long-circulation effect of PEG-LCL with a particle size of 160-220 nm is the most obvious.