超声微泡造影剂介导小鼠骨骼肌基因转染实验研究

目的探讨微泡造影剂在超声作用下是否可增加小鼠骨骼肌基因转染效率.方法 40只昆明小鼠随机分为4组,每组10只,第一组:在胫前肌注射造影剂与绿色荧光蛋白(GFP)质粒的混合溶液;第二组:注射与第一组相同的混合溶液后立即加超声辐照;第三组:注射GFP;第四组:在注射GFP后立即用超声辐照.7天后取小鼠胫前肌观察绿色荧光蛋白的表达情况.结果第一组与第二组有较多GFP表达,部分肌纤维绿色荧光较明亮,部分较暗淡;第三组和第四组GFP表达量较少.第一组与其余各组间的差异有显著性意义,P＜0.05;第二组与其余各组间的差异有显著性意义,P＜0.05;第三组与第四组间的差异无显著性意义,P＞0.05.结论超声微泡造影剂在超声作用下可明显增强小鼠骨骼肌的基因转染效率;未加超声波作用时,直接肌注携基因的超声微泡造影剂亦可增加小鼠骨骼肌的基因转染效率.     

Long-term expression of human alpha1-antitrypsin gene in mouse liver achieved by intravenous administration of plasmid DNA using a hydrodynamics-based procedure

The liver is an important target organ for gene transfer due to its large capacity for synthesizing serum proteins and its involvement in numerous genetic and acquired diseases. Previously, we and others have shown that an efficient gene transfer to liver cells in vivo can be achieved by an intravenous injection of plasmid DNA using a hydrodynamics-based procedure. In this study, we systematically characterized the expression of transgene encoding a secretory protein in mouse. Using human alpha1-antitrypsin (hAAT) gene as a reporter, we demonstrate that the serum level of hAAT can reach as high as 0.5 mg/ml by a simple tail vein injection of 10-50 microg plasmid DNA into a mouse. The serum hAAT reaches the peak level 1 day after DNA injection and then declines during the following 2 to 4 weeks to 2-5 microg/ml, a level which persists for at least 6 months. Southern analysis of extracted DNA and RT-PCR analysis of RNA from the liver reveal that hAAT gene is active and present as episomal form after 6 months. These results suggest that the hydrodynamics-based transfection procedure provides a valuable tool for screening genes for therapeutic purposes in whole animals.     

A combination of poloxamers increases gene expression of plasmid DNA in skeletal muscle

Intramuscular administration of plasmid DNA is a promising strategy to express therapeutic genes, however, it is limited by a relatively low level of gene expression. We report here that a non-ionic carrier, SP1017, composed of two amphiphilic block copolymers, pluronics L61 and F127, also known as poloxamers, significantly increases intramuscular expression of plasmid DNA. Two reporter genes, luciferase and beta-galactosidase, and one therapeutic gene, erythropoietin, were injected intramuscularly with and without SP1017 into C57Bl/6 and Balb/C mice and Sprague-Dawley rats. SP1017 increased gene expression by about 10-fold and maintained higher gene expression compared with naked DNA. Comparison of SP1017 with polyvinyl pyrrolidone (PVP) showed that SP1017 exhibited a significantly higher efficacy and its optimal dose was 500-fold lower. Experiments with beta-galactosidase using X-gal staining suggested that SP1017 considerably increased plasmid DNA diffusion through the tissue. SP1017 also improved expression of the erythropoietin gene leading to an increase in its systemic level and hematocrits. Previous toxicity studies have suggested that SP1017 has over a 1000-fold safety margin. Poloxamers used in SP1017 are listed in the US Pharmacopeia as inactive excipients and are widely used in a variety of clinical applications. We believe that the described system constitutes a simple and efficient gene transfer method to achieve local or systemic production of therapeutic proteins.     

Enhanced hepatocyte-selective in vivo gene expression by stabilized galactosylated liposome/plasmid DNA complex using sodium chloride for complex formation.

In this study, we demonstrated that the presence of an essential amount of sodium chloride (NaCl) during the formation of cationic liposome/plasmid DNA complexes (lipoplexes) stabilizes the lipoplexes according to the surface charge regulation (SCR) theory. Fluorescence resonance energy transfer analysis revealed that cationic liposomes in an SCR lipoplex (5 and 10 mM NaCl solution in lipoplex) increased fusion. Also, aggregation of SCR lipoplexes was significantly delayed after exposure to saline (150 mM NaCl) as a model of physiological conditions. After intraportal administration, the hepatic transfection activity of galactosylated SCR lipoplexes (5 and 10 mM NaCl solution in lipoplex) was approximately 10- to 20-fold higher than that of galactosylated conventional lipoplexes in mice. The transfection activity in hepatocytes of galactosylated SCR lipoplexes was significantly higher than that of conventional lipoplexes, and preexposure to competitive asialoglycoprotein-receptor blocker significantly reduced the hepatic gene expression, suggesting that hepatocytes are responsible for high hepatic transgene expression of the galactosylated SCR lipoplexes. Pharmacokinetic studies both in situ and in vivo demonstrated a higher tissue binding affinity and a greater expanse of intrahepatic distribution by galactosylated SCR lipoplexes. Moreover, enhanced transfection activity of galactosylated SCR lipoplexes was observed in HepG2 cells, and investigation of confocal microscopic images showed that the release of plasmid DNA in the cell was markedly accelerated. These characteristics partly explain the mechanism of enhanced in vivo transfection efficacy by galactosylated SCR lipoplexes. Hence, information in this study will be valuable for the future use, design, and development of ligand-modified lipoplexes for in vivo applications.     

CNS gene transfer mediated by a novel controlled release system based on DNA complexes of degradable polycation PPE-EA: a comparison with polyethylenimine/DNA complexes

Nonviral gene delivery systems based upon polycation/plasmid DNA complexes are quickly gaining recognition as an alternative to viral gene vectors for their potential in avoiding immunogenicity and toxicity problems inherent in viral systems. We investigated in this study the feasibility of using a controlled release system based on DNA complexed with a recently developed polymeric gene carrier, polyaminoethyl propylene phosphate (PPE-EA), to achieve gene transfer in the brain. A unique feature of this gene delivery system is the biodegradability of PPE-EA, which can provide a sustained release of DNA at different rates depending on the charge ratio of the polymer to DNA. PPE-EA/DNA complexes, naked DNA, and DNA complexed with polyethylenimine (PEI), a nondegradable cationic polymer known to be an effective gene carrier, were injected intracisternally into the mouse cerebrospinal fluid. Transgene expression mediated by naked DNA was mainly detected in the brain stem, a region close to the injection site. With either PPE-EA or PEI as a carrier, higher levels of gene expression could be detected in the cerebral cortex, basal ganglia, and diencephalons. Transgene expression in the brain mediated by PPE-EA/DNA complexes at an N/P ratio of 2 persisted for at least 4 weeks, with a significant higher level than that produced by either naked plasmid DNA or PEI/DNA at the 4-week time point. Furthermore, PPE-EA displayed much lower toxicity in cultured neural cells as compared to PEI and did not cause detectable pathological changes in the central nervous system (CNS). The results established the potential of PPE-EA as a new and biocompatible gene carrier to achieve sustained gene expression in the CNS.     

In vivo release and gene expression of plasmid DNA by hydrogels of gelatin with different cationization extents.

The objective of this paper is to investigate the in vivo release and gene expression of lacZ plasmid DNA (pSV-lacZ) by the hydrogels of cationized gelatin. Gelatin with different cationization extents was prepared by changing the amount of ethylenediamine added to aminize the carboxyl groups of gelatin with a water-soluble carbodiimide. The cationized gelatin prepared was crosslinked by various concentrations of glutaraldehyde (GA) to obtain cationized gelatin hydrogels with different cationization extents as the release carrier of plasmid DNA. When the cationized gelatin hydrogels incorporating 125I-labeled pSV-lacZ were implanted into the femoral muscle of mice, the radioactivity remaining decreased with time and the retention period was prolonged with an increase in the concentration of GA used for hydrogel preparation. In vivo experiments with 125I-labeled cationized gelatin hydrogels revealed that the higher the GA concentration, the longer the in vivo retention period of radioactivity remaining for every cationized gelatin hydrogel. Only for the hydrogels prepared from gelatin with the aminized percentages of 29.7, 41.6, and 47.8 mol.%, the time profile of pSV-lacZ retention correlated well with that of hydrogel retention. The gene expression by the cationized gelatin hydrogels incorporating pSV-lacZ depended on the aminized percentage of gelatin and was significant at the percentage of 41.6 mol.% or higher. It is possible that the pSV-lacZ was complexed with the degraded fragments of cationized gelatin and released with a positive charge, resulting in enhanced gene expression. We conclude that gelatin with a cationization extent of at least 41.6 mol.% is needed for the enhanced in vivo gene expression of plasmid DNA by the hydrogel release system.     

Enhanced expression of plasmid DNA–cationized gelatin complex by ultrasound in murine muscle

This study is an investigation to experimentally confirm that ultrasound (US) irradiation is effective in enhancing the gene expression of plasmid DNA. A cationized gelatin was prepared by introducing primary amino groups into gelatin. The plasmid of the LacZ gene was complexed with the cationized gelatin and injected into the femoral muscle of normal mice. Following US irradiation at the injected site of muscle, the gene expression of the treated muscle was evaluated to compare with that of the complex injection plus no US irradiation. US irradiation enabled the complex to significantly enhance the gene expression at the injected muscle, in contrast to naked plasmid DNA, although the extent depended on the experimental conditions, such as the injection dose of plasmid DNA, and the time period or timing of US irradiation. The gene-expressed area at the muscle was not changed by the time interval between the complex injection and US irradiation. Fluorescent microscopic observation revealed that the complex was homogeneously distributed in the muscle tissue around the injected site by US irradiation without any dissociation of plasmid DNA. The fluorescent image of plasmid DNA superposed on that of myosin heavy chain indicated intracellular localization of plasmid DNA. We demonstrated that US irradiation is a promising technique to enhance gene expression even in the normal muscle.     

Advances in plasmid gene delivery and expression in skeletal muscle

One of the most striking recent advances for plasmid delivery in vivo has been that of electropermeabilization, commonly referred to as electroporation. This physical process exposes a muscle tissue to a brief, high intensity electric field that induces temporary and reversible breakdown of the plasma membrane. During the period of membrane destabilization, a variety of molecules, including plasmids, gain intracellular access. Electroporation has been shown to improve the efficiency of plasmid gene delivery to skeletal muscle of small animals by as much as two-orders of magnitude to levels comparable to that of adenoviral gene delivery. This technology will allow the muscle to be used as a bioreactor for the secretion of therapeutic proteins into the circulation. This method of gene delivery, which is simple, efficient and reproducible, has become valuable for basic research, with great potential for gene therapy and DNA vaccination. Moreover, significant progress has been made using a variety of molecular designs to achieve regulation of gene expression by low molecular weight drugs. The enhanced efficiency of plasmid delivery by electroporation and the resultant durability of transgene expression, combined with the effectiveness of drug-dependent transgene regulation systems, provide a powerful set of tools that will be broadly applicable to the development of plasmid-based gene therapies for the treatment of human disease.     

Characterization of a targeted gene carrier, lactose-polyethylene glycol-grafted poly-L-lysine and its complex with plasmid DNA

The physicochemical properties and gene transfer ability of lactose-polyethylene glycol-grafted poly-L-lysine (Lac-PEG-PLL) were investigated. A dye displacement assay showed that plasmid DNA self-assembled with Lac-PEG-PLL, and condensation began at a <1:1 charge ratio of plasmid DNA to polymer. In atomic force microscopy, spontaneously assembled Lac-PEG-PLL/DNA complexes revealed a compact structure, with a size of about 100-200 nm. Circular dichroism spectra of Lac-PEG-PLL/DNA complexes revealed that the secondary structure of DNA was altered by complex formation and was similar to that of the poly-L-lysine/DNA complex. Lac-PEG-PLL was shown to protect DNA against nuclease action in a DNase I protection assay. The cytotoxicity test demonstrated that the complex composed of plasmid DNA and Lac-PEG-PLL had little influence on the viability of HepG2 cells, especially in comparison with that of poly-L-lysine/DNA complexes. In conclusion, our copolymer, Lac-PEG-PLI, formed complexes with plasmid DNA (on average, 150 nm), gave little cytotoxicity, and showed increased efficiency of gene transfer into hepatoma cells in vitro. Lactose-polyethylene glycol was grafted to poly-L-lysine to be used as a gene carrier for hepatoma cell targeting and to improve the solubility of the polyplexes. The average size of the carrier/DNA complexes was about 150 nm. The complexes also proved to have high resistance against nuclease attack and little cytotoxicity. The polymer also delivered plasmid DNA efficiently into a HepG2 cell line. Lac-PEG-PLL was more efficient than Lipofectin or galactose-PEG-PLL in transfection efficiency.     

质粒DNA抗原酶联免疫吸附试验检测抗双链DNA抗体的研究

目的 建立以质粒DNA为抗原的检测血清抗双链DNA(ds-DNA)抗体的酶联免疫吸附试验(ELISA)方法及探讨其临床应用价值。方法 将原核表达载体质粒pBV220用碱裂解法提取纯化DNA后，按1：150稀释包被在多聚-L-赖氨酸处理的微孔板上，以辣根过氧化物酶标记的葡萄球菌A蛋白(HRP-SPA)为酶标记物，建立检测血清抗双链DNA抗体的ELISA方法。并以短膜虫为底物的间接免疫荧光法(IIF)为参比方法，对6_4例系统性红斑狼疮(SLE)、8例混合性结缔组织病、17例类风湿性关节炎患者的血清抗ds-DNA抗体进行对比检测。结果 紫外分光法于波长260nm测DNA浓度为1．54g/L。ELISA抗ds-DNA法和IIF法检测3组患者阳性率分别为23．4％和17．2％、12．5％和12．5％、11．8％和5．9％，符合率分别为93．8％、100％、94．1％。以经典IIF法为金标准，ELISA检测抗ds-DNA抗体的特异性为93．4％，敏感性为100％。结论 用质粒DNA作抗原建立的检测血清抗ds-DNA抗体具有良好的精密度、敏感性和特异性，检出率高于IIF法，有助于对SLE的诊断和病情活动程度进行监测。     

Hepatocyte-targeted in vivo gene expression by intravenous injection of plasmid DNA complexed with synthetic multi-functional gene delivery system

To achieve hepatocyte-targeted in vivo gene expression, a carrier that controls both the tissue and intracellular distribution of DNA was designed and synthesized. A cationic polymer, poly(L-ornithine) (pOrn), was modified first with galactose, then with a fusigenic peptide (mHA2) to obtain Gal-pOrn-mHA2. When applied with Gal-pOrn-mHA2 to asialoglycoprotein receptor-positive cells, fluorescein-labeled DNA showed a diffuse profile, suggesting the release of DNA from endosomes and/or lysosomes by the carrier. Then the biodistribution and gene expression after intravenous injection of DNA complexes (10 microg DNA per mouse) were examined. After injection of [32P]DNA/Gal-pOrn-mHA2, about 60% of the radioactivity was recovered in the liver, mostly in parenchymal cells. A large amount (81 ng/g tissue) of transgene product (luciferase) was detected in the liver of mice injected with DNA/Gal-pOm-mHA2, which was 280-fold greater than that obtained with DNA/DOTMA:Chol liposomes (50 microg DNA). Prior administration of galactosylated albumin reduced the gene expression to 1/100, indicating the asialoglycoprotein receptor-mediated gene transfer in liver parenchymal cells, ie hepatocytes. The luciferase activity in hepatocytes contributed more than 95% of the total activity in all the tissues examined. Thus, hepatocyte-targeted in vivo gene expression was achieved by the intravenous injection of DNA complex with the multifunctional gene carrier.     

Sustained release of plasmid DNA using lipid microtubules and agarose hydrogel.

Non-viral gene therapy typically results in low transfection efficiencies and transient gene expression. To address these limitations, two sustained delivery systems capable of releasing functional, compacted DNA for over 50 days were designed. A luciferase plasmid was compacted with a polylysine-polyethylene glycol conjugate and released from agarose hydrogel and lipid microtubule-hydrogel delivery systems for over 50 days. The released DNA was characterized structurally using sedimentation, electron microscopy, and serum stability, and functionally using in vitro transfections. The released DNA retained its physical compaction and nuclease resistance and was converted from supercoiled to nicked and linear forms. Released compacted DNA produced significant gene expression in vitro, although at lower levels than freshly compacted DNA. Thus, hydrogels and lipid microtubules successfully provided the slow release of bioactive, compacted DNA.     

Enhanced nuclear import and transfection efficiency of plasmid DNA using streptavidin-fused importin-beta.

In order to enhance the nuclear import of exogenous genes, novel plasmid DNA/importin-beta conjugates, which consist of a biotinylated plasmid DNA and a recombinant streptavidin-fused importin-beta, were prepared. The spacer length between plasmid DNA and biotin and the number of introduced biotin were adjusted. The microinjection of plasmid DNA/importin-beta conjugates into the cytoplasm of NIH3T3 cells resulted in the nuclear localization of conjugates and the higher expression efficiency, compared to intact plasmid DNA alone. These results indicate that plasmid DNA/importin-beta conjugates would be an important tool to enhance the nuclear localization of exogenous DNA in non-viral gene delivery system.     

小鼠血管紧张素转化酶2基因表达型载体的构建及体外表达

背景:通过转基因疗法使血管紧张素转化酶2(angiotensin-converting enzyme,ACE2)过度表达来治疗心血管病是当前ACE2研究的趋势,而构建含ACE2基因的载体则能为该研究方法提供工具.目的:构建含小鼠血管紧张素转化酶2基因的真核表达载体,并验证其蛋白的表达.方法:采用RT-PCR的方法从C57小鼠肾脏扩增出ACE2基因全长cDNA序列,并通过酶切连接和转化等分子生物学方法将其定向克隆至载体pcDNA3.1/Hygro(+)上,构建小鼠ACE2基因的真核表达载体pm-ACE2,并通过酶切及测序鉴定.通过脂质体转染法将所构建的pm-ACE2转染COS7细胞,并利用Western blot检测COS7细胞中ACE2蛋白的表达.结果与结论:通过测序并与GeneBank上的小鼠血管紧张素转化酶2序列(NM_27286.3)比对,证实实验成功克隆小鼠ACE2基因全长cDNA至载体pcDNA3.1/Hygro(+)上,测序结果提示存在3处同义突变;所构建的pm-ACE2在真核细胞中具有ACE2蛋白的表达.结果提示实验成功构建了小鼠ACE2基因真核表达载体,此载体具有表达ACE2蛋白的功能.     

壳聚糖作为药物载体及基因载体的临床应用前景

甲壳素是存在于自然界中惟一能被生物降解的阳离子高分子材料,近年研究表明,它在调节机体免疫功能,降低血脂、血糖、血压,保护胃肠道等方面发挥着巨大的作用.壳聚糖是甲壳素的N-脱乙酰基衍生物,具有组织相容性好、生物学活性多样、可生物降解、无毒性、易于吸收等特点.壳聚糖作为药物载体能提高药物吸收,稳定药物成分,增加药物靶向性,增强药物缓释;它作为基因载体对DNA有一定的保护,能提高基因的表达时间.在药物载体、基因载体等研究领域壳聚糖将具有广泛的应用前景.