阳离子脂质体介导的基因转移机制

背景:与病毒载体相比,许多天然与合成的阳离子类脂以脂质体的形式用于基因转移,具有无免疫原性、易生产、质粒免受核酸酶降解和无致瘤性等优点,并且作为病毒载体的有效替代物,阳离子脂质体能用于细胞的体内和体外转染.目的:介绍阳离子脂质体介导的基因转移机制研究进展.方法:由第一作者用计算机检索中国期刊全文数据库(CNKI:1987/2010)和PubMed (1987/2010)数据库,检索词分别为"基因治疗、阳离子脂质体、基因转移、机制"和"gene therapy,cationic liposome,gene transfer,mechanism",语言分别设定为中文和英文.从阳离子脂质体基因转染和基因转移机制进行总结,综述了阳离子脂质体介导的基因转移机制.结果与结论:共检索到108篇,按纳入和排除标准对文献进行筛选,共纳入20篇文章.综述了阳离子脂质体介导的基因转移机制,包括阳离子脂质体/DNA复合物的形成、细胞吸收、内含体释放和复合物解体以及细胞核摄入等方面的研究内容.结果提示,对类脂构效关系和基因转移机制的研究,是提高阳离子脂质体转染效率和优化基因治疗的关键.     

聚合物基因载体的设计与优化

目的：随着基因治疗研究的不断深入，选择更安全和更有效的基因转移载体已成为基因治疗成功的关键。为此本文就聚合物基因载体的设计与优化进行综述。 资料来源：应用计算机检索PUBMED1990—01／2005-12期间的相关文章，检索词为“gene therapy，non-viral vectors，cationic polymer／DNA complex”，并限定文章语言种类为English。同时计算机检索万方中国全文期刊数据库1990～01／2005—12期间的相关文章，检索词为“基因治疗，非病毒载体，阳离子聚合物／基因复合物”，并限定文章语言种类为中文。 资料选择：对资料进行初审，并查看每篇文献后的引文。纳入标准：文章所述内容应与聚合物基因载体的设计及优化研究相关。排除标准：重复研究或Meta分析类文章。 资料提炼：共收集到60篇相关文献，28篇文献符合纳入标准，排除的32篇文献为内容陈旧或重复。符合纳入标准的28篇文献中，26篇涉及基因转移体系，2篇涉及Polyplex转染过程中的问题以及聚合物载体的优化。 资料综合：本文首先简要介绍了两类基因转移体系：病毒载体转移体系和非病毒转移体系，以及非病毒转移体系的分类。然后详细介绍了聚合物基因载体的发展现状，列举了几类近年设计的新型阳离子聚合物载体，指出其优点和不足、结构与功能的关系，以及优化的方法。最后介绍了以阳离子聚合物作为基因载体进行细胞转染的机制，并探讨了如何对聚合物基因载体进行优化。 结论：在非病毒转移体系中，聚合物基因载体由于其设计灵活及具有很好的生物相容性等优点而在人类基因治疗中具有很大的潜力。然而低转染效率限制了其在临床上的应用。随着对聚合物基因转移机制的进一步理解，聚合物基因转移体系将成为人类基因治疗的有力工具。     

脂质体在基因治疗中的应用研究及进展

背景：脂质体是常用的安全的基因载体,然而由于其本身组成及结构的原因,应用和发展受到了限制,其转染效率和治疗效果成为基因治疗研究中最为重要的参考因素。目的：回顾脂质体在基因治疗中的应用以及研究进展。方法：由第一作者计算机检索1995/2011中国期刊全文数据库、CALIS全国医学文献/服务系统以及康健循证医学知识仓库,中英文检索词分别为＂脂质体、基因、转染＂和＂liposome、gene、transfection＂。结果与结论：脂质体作为基因载体较病毒载体具有安全性高,免疫原性小,毒性小,容易制备等优点已成功应用于很多体外及动物体内实验,但由于其转染效率低,靶向性低等缺点使其发展受到了很大限制,所以目前脂质体在基因治疗中的研究热点在于提高脂质体的转染效率,在靶细胞和靶器官达到治疗浓度才能有更好的治疗效果。     

聚合物基因载体的设计与优化

目的:随着基因治疗研究的不断深入,选择更安全和更有效的基因转移载体已成为基因治疗成功的关键。为此本文就聚合物基因载体的设计与优化进行综述。资料来源:应用计算机检索PUBMED1990-01/2005-12期间的相关文章,检索词为“genetherapy,non-viralvectors,cationicpolymer/DNAcomplex”,并限定文章语言种类为English。同时计算机检索万方中国全文期刊数据库1990-01/2005-12期间的相关文章,检索词为“基因治疗,非病毒载体,阳离子聚合物/基因复合物”,并限定文章语言种类为中文。资料选择:对资料进行初审,并查看每篇文献后的引文。纳入标准:文章所述内容应与聚合物基因载体的设计及优化研究相关。排除标准:重复研究或Meta分析类文章。资料提炼:共收集到60篇相关文献,28篇文献符合纳入标准,排除的32篇文献为内容陈旧或重复。符合纳入标准的28篇文献中,26篇涉及基因转移体系,2篇涉及Polyplex转染过程中的问题以及聚合物载体的优化。资料综合:本文首先简要介绍了两类基因转移体系:病毒载体转移体系和非病毒转移体系,以及非病毒转移体系的分类。然后详细介绍了聚合物基因载体的发展现状,列举了几类近年设计的新型阳离子聚合物载体,指出其优点和不足、结构与功能的关系,以及优化的方法。最后介绍了以阳离子聚合物作为基因载体进行细胞转染的机制,并探讨了如何对聚合物基因载体进行优化。结论:在非病毒转移体系中,聚合物基因载体由于其设计灵活及具有很好的生物相容性等优点而在人类基因治疗中具有很大的潜力。然而低转染效率限制了其在临床上的应用。随着对聚合物基因转移机制的进一步理解,聚合物基因转移体系将成为人类基因治疗的有力工具。     

壳聚糖纳米粒子基因载体的研究现状

背景：壳聚糖纳米粒子因其独有特性作为基因载体的研究日益增多。目的：综述了壳聚糖纳米粒子作为基因载体的研究进展,进一步促进基因治疗的效果。方法：应用计算机检索web of science数据库和中国学术期刊数据库中2000-01/2011-04关于壳聚糖及其衍生物作为基因载体研究的文章,在标题和摘要中以＂chitosan,gene＂或＂壳聚糖;基因＂为检索词进行检索。选择内容与基因载体和壳聚糖相关的文章,初检得到120篇文献,根据纳入标准选择31篇文章进行综述。结果与结论：壳聚糖基因纳米粒子作为非病毒基因述文章的数量、主要结载体将在基因治疗领域中发挥举足轻重的作用,今后壳聚糖转基因体系的研究将更为深入。如何标记、可视跟踪壳聚糖DNA复合物进入不同细胞的过程,明确其基因转染机制,进一步提高基因转染效率,使其尽快进入基因治疗临床应用是今后研究的主要方向。     

周围神经损伤修复与再生中的基因治疗

背景：周围神经损伤后功能恢复不够理想。基因治疗为其功能修复提供了新的方法。目的：从功能基因、转染载体选择、基因翻译因子生物学效应3方面进行综述,为周围神经损伤的基因治疗研究提供参考。方法：由第一作者应用计算机检索PubMed和中国期刊全文数据库（CNKI）2006/2010相关文献。在标题、摘要、关键词中以＂peripheral nerve injury,gene therapy,virus vector＂或＂周围神经损伤、基因治疗、病毒载体＂为检索词进行检索。选择与周围神经损伤的基因治疗有关的文献,同一领域文献则选择近期发表及发表在权威杂志的文章。结果与结论：共检索到35篇文章,按纳入和排除标准对文献进行筛选,保留20篇文章进行综述。目前,周围神经损伤的基因治疗技术已经日趋成熟,如转基因的腺病毒表达的骨形态发生蛋白7和Ad-32Ep65-Flag基因等,有望成为临床修复周围神经损伤的重要手段。     

阳离子聚合物基因载体的理论研究

目的:介绍阳离子聚合物非病毒基因载体的种类,并分析它们各自的特点和作用.资料来源:以基因治疗,非病毒载体,阳离子聚合物,壳聚糖,环糊精为检索词,检索清华同方数据库(1980-01/2009-01).以gene therapy,non-viral vectors,Cationic polymer,chitosan,cyclodextrin为检索词,检索sciencedirect数据库(1980-01/2009-01).文献检索语种限制为英文和中文.资料选择:纳入阳离子聚合物作为非病毒基因载体的实验研究,排除其他形式基因载体的研究.结局评价指标:①细胞毒性.②基因表达率.③转染效率.结果:计算机初检得到154篇文献,根据纳入排除标准,对阳离子聚合物作为菲病毒基因载体的种类和治疗作用进行分析.目前,应用于基因治疗的载体主要有病毒载体和非病毒载体两种.病毒载体转染效率高,但存在免疫原性高、毒性大、目的基因容量小、靶向特异性差、制备较复杂及费用较高等缺点.因此,人们愈来愈重视非病毒载体的研究.阳离子聚合物作为非病毒基因载体显示出巨大的优势和潜力.它不但可以降低药物在细胞内的蓄积和毒性,还可以通过自身的降解来控制基因的释放.阳离子聚合物用作非病毒基因治疗载体包括多聚赖氨酸类共聚物、聚氨酯、聚乙烯亚胺阳离子共聚物、聚磷腈类、壳聚糖类及其衍生物和环糊精及其衍生物.结论:阳离子非病毒载体相比于其他非病毒载体,具有毒性低,基因转染率高,释药可控制等优点,是一种相对安全、高效的非病毒基因载体.     

壳聚糖纳米粒子基因载体的研究现状

背景:壳聚糖纳米粒子因其独有特性作为基因载体的研究日益增多.目的:综述了壳聚糖纳米粒子作为基因载体的研究进展,进一步促进基因治疗的效果.方法:应用计算机检索web of science 数据库和中国学术期刊数据库中2000-01/2011-04 关于壳聚糖及其衍生物作为基因载体研究的文章,在标题和摘要中以"chitosan,gene"或 "壳聚糖;基因"为检索词进行检索.选择内容与基因载体和壳聚糖相关的文章,初检得到120 篇文献,根据纳入标准选择31 篇文章进行综述.结果与结论:壳聚糖基因纳米粒子作为非病毒基因述文章的数量、主要结载体将在基因治疗领域中发挥举足轻重的作用,今后壳聚糖转基因体系的研究将更为深入.如何标记、可视跟踪壳聚糖DNA 复合物进入不同细胞的过程,明确其基因转染机制,进一步提高基因转染效率,使其尽快进入基因治疗临床应用是今后研究的主要方向.     

三种阳离子脂质体介导血管内皮细胞基因转染效率的比较

目的:评价不同阳离子脂质体介导基因转染血管内皮细胞的转染效率。方法:实验于2006-12/2007-02在中山大学生化实验室及广州市创伤外科研究所完成。采用增强型绿色荧光蛋白基因为报告基因,分别采用Lipofectin、Lipofectamine、Dosper3种不同的阳离子脂质体为载体,转染人脐静脉血管内皮细胞。在24孔板中,每孔加入人脐静脉血管内皮细胞悬液(1×106个细胞),各孔分别加入3种不同阳离子脂质体增强型绿色荧光蛋白质粒复合物,分别于培养24,48h后用荧光显微镜及流式细胞仪测定增强型绿色荧光蛋白在细胞内的表达及转染效率。结果:3种不同阳离子介导的增强型绿色荧光蛋白基因转染的人脐静脉血管内皮细胞内均有绿色荧光蛋白表达,24h后明显,48h后达高峰。Dosper介导组绿色荧光细胞百分比明显高于Lipofectin介导组及Lipofectamine介导组,差异有非常显著意义(P<0.01)。结论:Dosper介导的血管内皮细胞基因转染效率较高,较适合作为血管内皮细胞的基因转染载体。     

聚酰胺纳米分子介导survivin反义寡核苷酸诱导结肠癌细胞凋亡

背景:传统的病毒载体及非病毒载体在基因治疗中均存在明显的缺点,采用纳米材料作为反义寡核苷酸载体有望获得更好更安全的基因转导,提高基因治疗的有效性和安全性.实验拟采用聚酰胺纳米分子介导反义寡核苷酸阻断survivin表达,诱导大肠癌凋亡.目的:探讨聚酰胺树形分子高聚合物介导survivin反义寡核苷酸(survivin antisense oligonucleotide,survivin-asODN)转染结直肠癌SW620细胞的可行性以及对结直肠癌SW620细胞survivin表达、细胞凋亡的影响.设计、时间及地点:肿瘤基因治疗体外实验,于2007-09/2008-05在上海交通大学微纳米科学技术研究院生物纳米工程研究室及南方医科大学珠江医院中心实验室完成.材料:人结直肠癌细胞株SW620购自中国科学院上海细胞研究所,聚酰胺树形分子由上海交通大学微纳米研究院生物纳米工程研究室崔大祥教授提供,转染试剂脂质体LipofectamineTM 2000购自美国Invitrogen公司.survivin-asODN由上海生工公司合成.方法:采用300 μg/L survivin-asODN和4.06 μg/L聚酰胺制备聚酰胺反义基因复合物,同时制备阳离子脂质体反义基因复合物作为对照.透射电镜观察复合物的形态,激光散射粒径分析仪测定粒径,zeta电位分析仪测定zeta电位,离心法和紫外分光光度仪测定复合物的的包封率、载药率和体外DNA释放速度.将上述两种基因转染复合物转染结直肠癌细胞,测定其转染效率;Western blotting检测转染后细胞中survivin蛋白的表达:流式细胞术检测两组细胞的凋亡率.主要观察指标:阳离子脂质体-survivin-asODN复合物及聚酰胺-survivin-asODN复合物的粒经,zeta电位,基因载药率,包封率,释放率,转染后survivin表达率及对凋亡的诱导率.结果:聚酰胺-survivin-asODN复合物的粒径小于脂质体-survivin-asODN复合物的粒径(P<0.01),但zeta电位高于后者(P<0.05);基因载药率、包封率两组差异无显著性意义:聚酰胺对DNA持续释放14 d,但脂质体只持续5 d.聚酰胺-survivin-asODN转染结直肠癌细胞的效果强于脂质体survivin-asODN(P<0.05).转染后结直肠癌细胞survivin蛋白的表达低于脂质体复合物(P<0.05),细胞的凋亡率高于脂质体复合物(P<0.05).结论:聚酰胺能将survivin-asODN高效递送到结直肠癌SW620细胞,降低survivin蛋白表达并诱导结直肠癌细胞凋亡.     

Enhanced cationic liposome-mediated transfection using the DNA-binding peptide mu (mu) from the adenovirus core

Promising advances in nonviral gene transfer have been made as a result of the production of cationic liposomes formulated with synthetic cationic lipids (cytofectins) that are able to transfect cells. However few cationic liposome systems have been examined for their ability to transfect CNS cells. Building upon our earlier use of cationic liposomes formulated from 3beta-[N-(N',N'-dimethylaminoethane)carbamoyl] cholesterol (DC-Chol) and dioleoyl-L-alpha-phosphatidyl-ethanolamine (DOPE), we describe studies using two cationic viral peptides, mu (mu) and Vp1, as potential enhancers for cationic liposome-mediated transfection. Mu is derived from the condensed core of the adenovirus and was selected to be a powerful nucleic acid charge neutralising and condensing agent. Vp1 derives from the polyomavirus and harbours a classical nuclear localisation signal (NLS). Vp1 proved disappointing but lipopolyplex mixtures formulated from pCMVbeta plasmid, mu peptide and DC-Chol/DOPE cationic liposomes were able to transfect an undifferentiated neuronal ND7 cell line with beta-galactosidase reporter gene five-fold more effectively than lipoplex mixtures prepared from pCMVbeta plasmid and DC-Chol/DOPE cationic liposomes. Mu was found to give an identical enhancement to cationic liposome-mediated transfection of ND7 cells as poly-L-lysine (pLL) or protamine sulfate (PA). The enhancing effects of mu were found to be even greater (six- to 10-fold) when differentiated ND7 cells were transfected with mu-containing lipopolyplex mixtures. Differentiated ND7 cells represent a simple ex vivo-like post-mitotic CNS cell system. Successful transfection of these cells bodes well for transfection of primary neurons and CNS cells in vivo. These findings have implications for experimental and therapeutic uses of cationic liposome-mediated delivery of nucleic acids to CNS cells.     

Effect of DNA/liposome mixing ratio on the physicochemical characteristics, cellular uptake and intracellular trafficking of plasmid DNA/cationic liposome complexes and subsequent gene expression.

In order to identify the important factors involved in cationic liposome-mediated gene transfer, in vitro transfection efficiencies by plasmid DNA complexed with DOTMA/DOPE liposomes at different DNA/liposome mixing ratios were evaluated using four types of cultured cells with respect to their physicochemical properties. Significant changes were observed in the particle size and zeta potential of the complexes as well as in their structures, assessed by atomic force microscopy, which depended on the mixing ratio. In transfection experiments, except for RAW 264.7 cells (mouse macrophages), efficient gene expression was obtained in MBT-2 cells (mouse bladder tumor), NLH3T3 cells (mouse fibroblasts) and HUVEC (human umbilical vein endothelial cells) at an optimal ratio of 1:5, 1:7.5 or 1:5, respectively. On the other hand, cellular uptake of the [32P]DNA/liposome complexes increased in all cell types with an increase in the mixing ratio, which was not reflected by the transfection efficiency. The cellular damage determined by MTT assay was minimal even at the highest DNA/liposome ratio (1:10), indicating that the lower gene expression level at the higher ratio was not due to cytotoxicity induced by the complex. An ethidium bromide intercalation assay showed that the release of plasmid DNA from the complex, following the addition of negatively charged liposomes, was restricted as the mixing ratio increased. Furthermore, confocal microscopic studies using HUVEC showed that the 1:5 complexes exhibited a dispersed distribution in the cytoplasm whereas a punctuate intracellular distribution was observed for the 1:10 complexes. This suggests that there was a significant difference in intracellular trafficking, probably release from the endosomes or lysosomes, of the plasmid DNA/cationic liposome complexes between these mixing ratios. Taken together, these findings suggest that the DNA/liposome mixing ratio significantly affects the intracellular trafficking of plasmid DNA complexed with the cationic liposomes, which is an important determinant of the optimal mixing ratio in cationic liposome-mediated transfection.     

Intracytoplasmic gene delivery for in vitro transfection with cytoskeleton-specific immunoliposomes.

A novel and highly efficient method of in vitro gene transfection has been developed. This method employs direct intracytoplasmic gene delivery into embryonic cardiocytes using neutral cytoskeletal-antigen specific immunoliposomes (CSIL). These immunoliposomes target cardiocytes specifically under reversible hypoxic conditions. Two independent reporter genes, pGL2 and pSV-beta-galactosidase, were used to verify CSIL-transfection (CSIL-fection). The efficiency of CSIL-fection with firefly luciferase pGL2 vector was 30+ times greater than controls consisting of hypoxic cardiocytes treated with plain liposomes (PL) or normoxic cardiocytes treated with CSIL, PL or naked DNA. CSIL-fection was also compared to cationic liposome transfection. Net cationic liposome transfection appeared to be more efficient than CSIL-fection for pGL2 vectors. However, a smaller number of viable cells was observed in the cationic liposome treated cultures than in the CSIL treated cultures. Therefore, to determine whether more cells were transfected with cationic liposomes or CSIL, pSV-beta-galactosidase vector was used. CSIL-fection with pSV-beta-galactosidase vector produced at least 40 times more transfected cells than those transfected with cationic liposomes. No transfection with pSV-beta-galactosidase vectors was obtained with IgG-liposome, PL or naked DNA treatments. Targeted enhanced efficiency of transfection by this novel method could have practical therapeutic applications in the genetic modification of cells ex vivo that could then be reimplanted into patients for gene therapy.     

Cationic liposomes as non-viral carriers of gene medicines: resolved issues, open questions, and future promises

The clinical success of gene therapy is critically dependent on the development of efficient and safe gene delivery reagents, popularly known as "transfection vectors." The transfection vectors commonly used in gene therapy are mainly of two types: viral and non-viral. The efficiencies of viral transfection vectors are, in general, superior to their non-viral counterparts. However, the myriads of potentially adverse immunogenic aftermaths associated with the use of viral vectors are increasingly making the non-viral gene delivery reagents as the vectors of choice. Among the existing arsenal of non-viral gene delivery reagents, the distinct advantages associated with the use of cationic transfection lipids include their: (a) robust manufacture; (b) ease in handling and preparation techniques; (c) ability to inject large lipid:DNA complexes; and (d) low immunogenic response. The present review highlights the major achievements in the area of designing efficacious cationic transfection lipids, some of the more recent advances in the field of cationic liposomes-mediated gene transfer and targeted gene delivery, some unresolved issues and challenges in liposomal gene delivery, and future promises of cationic liposomes as gene-carriers in non-viral gene therapy.     

Remarkable induction of apoptosis in cancer cells by a novel cationic liposome complexed with a bcl-2 antisense oligonucleotide.

We reported recently a novel cationic cholesterol derivative with a hydroxyethylamino head group, cholesteryl-3beta-carboxyamidoethylene-N-hydroxyethylamine (I) for liposome-mediated gene transfection [FEBS Lett., 408 (1997) 232]. In the present paper we have studied whether this novel cationic liposome is prominent in nature to suppress cell growth of human cancer cells. Bcl-2 antisense phosphorothioate oligonucleotides (AS-ODNs) were complexed with the cationic liposomes with the derivative (I) and they were introduced into human cervix epithelial carcinoma cell lines HeLa, and mouse fibroblast NIH3T3 cells. An AS-ODNs targeting/bcl-2 gene induced probably apoptosis (including necrosis in some cases) in HeLa and NIH3T3 cells, however, nonsense oligonucleotides (NS-ODNs) corresponding to a scrambled-sequence control hardly induced apoptosis. Induction of apoptosis was much greater than that by commercially available DC-Chol liposomes. Fluorescence intensities of FITC-conjugated bcl-2 AS-ODNs were specifically found in the nucleus. The intensity of the AS-ODNs was mostly consistent with the amounts of Bcl-2 proteins observed by Western blot analysis in the target cells. The results showed the possibility that this new cationic cholesterol derivative might be very promising to be used for liposome-mediated gene targeting in vitro and in vivo.     

Polycation liposomes, a novel nonviral gene transfer system, constructed from cetylated polyethylenimine

A novel gene transfer system was developed by using liposomes modified with cetylated polyethylenimine (PEI, MW 600). This polycation liposome, PCL, showed remarkable transfection efficiency as monitored by the expression of the GFP reporter gene. Most conventional cationic liposomes require phosphatidylethanolamine or cholesterol as a component, although PCLs did not. Egg yolk phosphatidylcholine- and dipalmitoylphosphatidylcholine-based PCL were as effective as dioleoylphosphatidylethanolamine-based PCLs for gene transfer. Concerning the cytotoxicity against COS-1 cells and hemolytic activity, the PCL was superior to conventional cationic liposome preparations. Furthermore, the transfection efficacy of PCLs was enhanced, instead of being diminished, in the presence of serum. Effective gene transfer was observed in all eight malignant and two normal cells line tested, as well as in COS-1 cells. We also examined the effect of the molecular weight of PEI on PCL-mediated gene transfer, and observed that PEI with a MW of 1800 Da was as effective as that with one of 600, but that PEI of 25,000 was far less effective. Finally, an in vivo study was done in which GFP was effectively expressed in mouse liver after injection of PCL via the portal vein. Thus, PCL represents a new system useful for transfection and gene therapy.     

骨髓间充质干细胞对脑胶质瘤的趋瘤效应

背景：骨髓间充质干细胞在体内、外均具有较强的向胶质瘤趋向性迁移的能力,可作为基因靶向胶质瘤治疗的理想载体。目的：在复习相关文献的基础上,探讨骨髓间充质干细胞向脑胶质瘤定向迁移的机制。方法：由第一作者对CNKI和PUBMED数据库进行检索,英文关键词为＂mesenchymal stem cells,bone marrow,glioma＂,中文检索词为＂间充质干细胞,骨髓,胶质瘤＂。共检索到51篇相关文献,根据入选标准最终剩余27篇文章进行归纳总结。结果与结论：骨髓间充质干细胞对胶质瘤具有较强的趋化性迁移的能力,这与胶质瘤细胞分泌的某些细胞因子和骨髓间充质干细胞表面相应受体之间的相互作用有关。增强骨髓间充质干细胞表面相关受体的表达有助于增强其趋瘤效应,进而增强抗胶质瘤作用。     

Cationic liposome-mediated DNA transfection in organotypic explant cultures of the ventral mesencephalon.

We have examined the potential of cationic liposomes as a tool for approaches to gene therapy in the CNS. Our previous work has shown that cationic liposomes formulated from 3 beta-[N-(N',N'-dimethylaminoethane)carbamoyl] cholesterol (DC-Chol) and dioleoyl-L-alpha-phosphatidylethanolamine (DOPE) could achieve high transfection levels in a neuronal cell line (McQuillin et al. Neuroreport 1997; 8: 1481-1484). We therefore wished to assess transfection efficiencies in organotypic cultures from the brain with a reporter plasmid expressing E. coli beta-galactosidase in order to mimic an in vivo model. Explant cultures were generated according to the method of Stoppini et al (J Neurosci Meth 1991; 37: 173-182) with slight modifications. Brain slices were maintained on transparent porous membranes and were observed to maintain their intrinsic connectivity and cytoarchitecture to a large degree over periods of up to 6 weeks in culture. CNS tissue was obtained from rats at birth or 5 days after birth. After transfection beta-galactosidase expression was detected in cells of both neuronal and non-neuronal morphology. Control cultures were exposed to liposome alone and a plasmid that had the beta-galactosidase gene insert removed. Only low levels of endogenous beta-galactosidase reactivity were seen in these control cultures. DC-Chol/DOPE-mediated transfection was confirmed using a RT-PCR protocol capable of differentiating between untranscribed plasmid DNA and RNA generated from the transfected vector. These results suggest that cationic liposomes, particularly DC-Chol/DOPE liposomes, will be useful as delivery agents for gene transfer to CNS cells in vitro and possibly in vivo.     

Extracellular and intracellular barriers in non-viral gene delivery.

Complexes of DNA with cationic lipids and cationic polymers are frequently used for gene transfer. Extracellular interactions of the complexes with anionic glycosaminoglycans (GAGs) may interfere with gene transfer. Interactions of GAGs with carrier DNA complexes have been studied using tests for DNA relaxation (ethidium bromide intercalation), DNA release (electrophoresis), and transfection (pCMVbGal transfer into RAA smooth muscle cells). Several cationic lipid formulations (DOTAP, DOTAP/Chol, DOTAP/DOPE, DOTMA/DOPE, DOGS) and cationic polymers (fractured dendrimer, polyethylene imines 25 and 800 kDa, polylysines 20 and 200 kDa) were tested. Polycations condensed DNA more effectively than monovalent lipids. Hyaluronic acid did not release or relax DNA in any complex, but it inhibited transfection by some polyvalent systems (PEI, dendrimers, DOGS). Gene transfer by other carriers was not affected by hyaluronic acid. Sulfated GAGs (heparan sulfate, chondroitin sulfates B and C) completely blocked transfection, except in the case of liposomes with DOPE. Sulfated GAGs relaxed and released DNA from some complexes, but these events were not prerequisites for the inhibition of transfection. Furthermore, preliminary results suggest that cell surface GAGs, particularly heparan sulfate, inhibit gene transfer by cationic lipids and polymers.