Direct plasmid mediated transfection of adult murine brain cells in vivo using cationic liposomes

In vivo methods for acute modulation of gene expression in the central nervous system

Accurate and timely expression of specific genes guarantees the healthy development and function of the brain. Indeed, variations in the correct amount or timing of gene expression lead to improper development and/or pathological conditions. Almost forty years after the first successful gene transfection in in vitro cell cultures, it is currently possible to regulate gene expression in an area-specific manner at any step of central nervous system development and in adulthood in experimental animals in vivo, even overcoming the very poor accessibility of the brain. Here, we will review the diverse approaches for acute gene transfer in vivo, highlighting their advantages and disadvantages with respect to the efficiency and specificity of transfection as well as to brain accessibility. In particular, we will present well-established chemical, physical and virus-based approaches suitable for different animal models, pointing out their current and future possible applications in basic and translational research as well as in gene therapy.

The neurotoxicity of gene vectors and its amelioration by packaging with collagen hollow spheres

Over the last twenty years there have been several reports on the use of nonviral vectors to facilitate gene transfer in the mammalian brain. Whilst a large emphasis has been placed on vector transfection efficiency, the study of the adverse effects upon the brain, caused by the vectors themselves, remains completely overshadowed. To this end, a study was undertaken to study the tissue response to three commercially available transfection agents in the brain of adult Sprague Dawley rats. The response to these transfection agents was compared to adeno-associated viral vector (AAV), PBS and naked DNA. Furthermore, the use of a collagen hollow sphere (CHS) sustained delivery system was analysed for its ability to reduce striatal toxicity of the most predominantly studied polymer vector, polyethyleneimine (PEI). The size of the gross tissue loss at the injection site was analysed after immunohistochemical staining and was used as an indication of acute toxicity. Polymeric vectors showed similar levels of acute brain toxicity as seen with AAV, and CHS were able to significantly reduce the toxicity of the PEI vector. In addition; the host response to the vectors was measured in terms of reactive astrocytes and microglial cell recruitment. To understand whether this gross tissue loss was caused by the direct toxicity of the vectors themselves an in vitro study on primary astrocytes was conducted. All vectors reduced the viability of the cells which is brought about by direct necrosis and apoptosis. The CHS delivery system reduced cell necrosis in the early stages of post administration. In conclusion, whilst polymeric gene vectors cause acute necrosis, administration in the brain causes adverse effects no worse than that of an AAV vector. Furthermore, packaging the PEI vector with CHS reduces surface charge and direct toxicity without elevating the host response.

A synopsis on the role of tyrosine hydroxylase in Parkinson's disease

Parkinson's disease (PD) is a common chronic progressive neurodegenerative disorder in elderly people. A consistent neurochemical abnormality in PD is degeneration of dopaminergic neurons in substantia nigra pars compacta, leading to a reduction of striatal dopamine (DA) levels. As tyrosine hydroxylase (TH) catalyses the formation of L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of DA, the disease can be considered as a TH-deficiency syndrome of the striatum. Problems related to PD usually build up when vesicular storage of DA is altered by the presence of either α-synuclein protofibrils or oxidative stress. Phosphorylation of three physiologically-regulated specific sites of N-terminal domain of TH is vital in regulating its kinetic and protein interaction. The concept of physiological significance of TH isoforms is another interesting aspect to be explored further for a comprehensive understanding of its role in PD. Thus, a logical and efficient strategy for PD treatment is based on correcting or bypassing the enzyme deficiency by the treatment with L-DOPA, DA agonists, inhibitors of DA metabolism or brain grafts with cells expressing a high level of TH. Neurotrophic factors are also attracting the attention of neuroscientists because they provide the essential neuroprotective and neurorestorative properties to the nigrostriatal DA system. PPAR-γ, a key regulator of immune responses, is likewise a promising target for the treatment of PD, which can be achieved by the use of agonists with the potential to impact the expression of pro- and anti-inflammatory cytokines at the transcriptional level in immune cells via expression of TH. Herein, we review the primary biochemical and pathological features of PD, and describe both classical and developing approaches aimed to ameliorate disease symptoms and its progression.

Barriers to carrier mediated drug and gene delivery to brain tumors

Brain tumor patients face a poor prognosis despite significant advances in tumor imaging, neurosurgery and radiation therapy. Potent chemotherapeutic drugs fail when used to treat brain tumors because biochemical and physiological barriers limit drug delivery into the brain. In the past decade a number of strategies have been introduced to increase drug delivery into the brain parenchyma. In particular, direct drug administration into the brain tumor has shown promising results in both animal models and clinical trials. This technique is well suited for the delivery of liposome and polymer drug carriers, which have the potential to provide a sustained level of drug and to reach cellular targets with improved specificity. We will discuss the current approaches that have been used to increase drug delivery into the brain parenchyma in the context of fluid and solute transport into, through and from the brain, with a focus on liposome and polymer drug carriers.

Colloidal carriers and blood–brain barrier (BBB) translocation: A way to deliver drugs to the brain?

The major problem in drug delivery to the brain is the presence of the blood-brain barrier (BBB) which limits drug penetration even if in certain pathological situations the BBB is partly disrupted. Therefore, various strategies have been proposed to improve the delivery of drugs to this tissue. This review presents the status of the BBB in healthy patients and in pathologies like neurodegenerative, cerebrovascular and inflammatory diseases. The second part of this article aims to review the invasive and non-invasive strategies developed to circumvent the BBB and deliver drugs into the brain. The use of nanotechnologies (liposomes, nanoparticles) is especially discussed in the ultimate part of the review evidencing their potentiality as non-invasive technique in the brain delivery of drugs with the possibility to target specific brain tissue thanks to ligand linked to carrier surface.

Distribution in brain of liposomes after convection enhanced delivery; modulation by particle charge, particle diameter, and presence of steric coating

We have investigated the role of diameter, charge, and steric shielding on the brain distribution of liposomes infused by convection enhanced delivery (CED) using both radiolabeled and fluorescent-labeled particles. Liposomes of 40 and 80-nm diameter traveled the same distance but penetrated significantly less than a 10-kDa dextran; whereas 200-nm-diameter liposomes penetrated less than 80 nm liposomes. A neutral liposome shielded by polyethylene glycol (PEG; 2 kDa; 10% by mole) penetrated significantly farther than an unshielded liposome. Even when shielded with PEG, positive surface charge (10% by mole) significantly reduced the penetration radius compared to a neutral or negative charged liposome (10% by mole). A mathematical CED model including a term for liposome cell binding was applied to analyze the radius of particle penetration. Neutral liposomes had a binding constant of k=0.0010+/-0.0002 min-1, whereas for positive charged liposomes k increased 50-fold. The binding constant was independently verified using a degradable lipid radiolabel that eliminated from the brain with a 9.9+/-2.0 h half-life, equivalent to the calculated elimination constant k=0.0012+/-0.0002 min-1. During CED, liposomes accumulated in a subpopulation of perivascular cells within the brain. A non-degradable lipid radiolabel showed that lipid components remained within these perivascular brain cells for at least 2 days. To reduce this uptake, 100-fold molar excess of non-labeled liposomes were co-infused with labeled liposomes, which significantly increased liposome penetration. These studies suggest that optimization of therapeutic CED using particles such as drug-loaded liposomes, polymeric nanoparticles, non-viral DNA complexes, and viruses will require a strategy to overcome particle binding and clearance by cells within the CNS.

Improving lipoplex-mediated gene transfer into C6 glioma cells and primary neurons

The development of methodologies for gene transfer into the central nervous system is crucial for gene therapy of neurological disorders. In this study, different cationic liposome formulations were used to transfer DNA into C6 glioma cells and primary hippocampal and cortical neurons by varying the nature of the helper lipid (DOPE, Chol) or a mixture of DOPE and cholesterol (Chol) associated to DOTAP. In addition, the effect of the lipid/DNA (+/-) charge ratio, the association of the ligand transferrin to the lipoplexes, and the stage of differentiation of the primary cells on the levels of transfection activity, transfection efficiency, and duration of gene expression were evaluated. Mechanistic studies were also performed to investigate the route of delivery of the complexes into neurons. Our results indicate that DOTAP:Chol (1:1 mol ratio) was the best formulation to transfer a reporter gene into C6 glioma cells, primary hippocampal neurons, and primary cortical neurons. The use of transferrin-associated lipoplexes resulted in a significant enhancement of transfection activity, as compared to plain lipoplexes, which can be partially attributed to the promotion of their internalization mediated by transferrin. While for hippocampal neurons the levels of luciferase gene expression are very low, for primary cortical neurons the levels of transgene expression are high and relatively stable, although only 4% of the cells has been transfected. The stage of cell differentiation revealed to be critical to the levels of gene expression. Consistent with previous findings on the mechanisms of cell internalization, the experiments with inhibitors of the endocytotic pathway clearly indicate that transferrin-associated lipoplexes are internalized into primary neurons by endocytosis. Promising results were obtained in terms of the levels and duration of gene expression, particularly in cortical neurons when transfected with the Tf-associated lipoplexes, this finding suggesting the usefulness of these lipid-based carriers to deliver genes within the CNS.

Feline immunodeficiency virus vectors. Gene transfer to mouse retina following intravitreal injection

BACKGROUND

Transduction of the murine retinal pigmented epithelium (RPE) with adenovirus vectors requires technically difficult and invasive subretinal injections. This study tested the hypothesis that recombinant vectors based on feline immunodeficiency virus (FIV) could access the retina following intravitreal injection.

METHODS

FIV vectors expressing E. coli beta-galactosidase (FIVbetagal) were injected alone, or in combination with adenovirus vectors expressing eGFP, into the vitreous of normal mice and eyes evaluated for transgene expression. In further studies, the utility of FIV-mediated gene transfer to correct lysosomal storage defects in the anterior and posterior chambers of eyes was tested using recombinant FIV vectors expressing beta-glucuronidase. FIVbetagluc vectors were injected into beta-glucuronidase-deficient mice, an animal model of mucopolysacharridoses type VII.

RESULTS

The results of this study show that similar to adenovirus, both corneal endothelium and cells of the iris could be transduced following intravitreal injection of FIVbetagal. However, in contrast to adenovirus, intravitreal injection of FIVbetagal also resulted in transduction of the RPE. Immunohistochemistry following an intravitreal injection of an AdeGFP (adenovirus expressing green fluorescent protein) and FIVbetagal mixture confirmed that both viruses mediated transduction of corneal endothelium and cells of the iris, while only FIVbetagal transduced cells in the retina. Using the beta-glucuronidase-deficient mouse, the therapeutic efficacy of intravitreal injection of FIVbetagluc (FIV expressing beta-glucuronidase) was tested. Intravitreal injection of FIVbetagluc to the eyes of beta-glucuronidase-deficient mice resulted in rapid reduction (within 2 weeks) of the lysosomal storage defect within the RPE, corneal endothelium, and the non-pigmented epithelium of the ciliary process. Transgene expression and correction of the lysosomal storage defect remained for at least 12 weeks, the latest time point tested.

CONCLUSION

These studies demonstrate that intravitreal injection of FIV-based vectors can mediate efficient and lasting transduction of cells in the cornea, iris, and retina.

Vehicles for oligonucleotide delivery to tumours

The vasculature of a tumour provides the most effective route by which neoplastic cells may be reached and eradicated by drugs. The fact that a tumour's vasculature is relatively more permeable than healthy host tissue should enable selective delivery of drugs to tumour tissue. Such delivery is relevant to carrier-mediated delivery of genetic medicine to tumours. This review discusses the potential of delivering therapeutic oligonucleotides (ONs) to tumours using cationic liposomes and cyclodextrins (CyDs), and the major hindrances posed by the tumour itself on such delivery. Cationic liposomes are generally 100-200 nm in diameter, whereas CyDs typically span 1.5 nm across. Cationic liposomes have been used for the introduction of nucleic acids into mammalian cells for more than a decade. CyD molecules are routinely used as agents that engender cholesterol efflux from lipid-laden cells, thus having an efficacious potential in the management of atherosclerosis. A recent trend is to employ these oligosaccharide molecules for delivering nucleic acids in cells both in-vitro and in-vivo. Comparisons are made with other ON delivery agents, such as porphyrin derivatives (< 1 nm), branched chain dendrimers (approximately 10 nm), polyethylenimine polymers (approximately 10 nm), nanoparticles (20-1,000 nm) and microspheres (> 1 microm), in the context of delivery to solid tumours. A discourse on how the chemical and physical properties of these carriers may affect the uptake of ONs into cells, particularly in-vivo, forms a major basis of this review.

Effects of liposome-mediated gene transfer of VEGF in ischemic rat gracilis muscle

The purpose of the current study was to determine the effects of vascular endothelial growth factor (VEGF) on muscle flap survival and vascularity in a rat gracilis ischemia-reperfusion model. A total of 12 adult male Wistar rats were divided into two groups (n = 6). The experimental group received the plasmid encoding VEGF(165) cDNA plus lipofectamine (cationic liposome) injected directly to the gracilis muscle following 4 h of ischemia. The control group received lipofectamine only. The viability and vascularity of the flaps were evaluated after 7 days of reperfusion. The data demonstrated that the VEGF plasmid- and lipofectamine-treated muscle flaps had significantly greater total survival and capillary count 7 days after reperfusion compared with the flaps treated only with lipofectamine. These results indicate that VEGF exerts a protective effect on ischemic skeletal muscle flaps.

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.

Atomic force microscopy imaging of DNA-cationic liposome complexes optimised for gene transfection into neuronal cells

BACKGROUND

Cationic liposomes represent an important gene delivery system due to their low immunogenicity, but are relatively inefficient, with optimisation of DNA-liposome complexes (lipoplexes) for transfection necessary for each cell type of interest. There have been few studies examining optimisation in neuronal cell types or determining how the structure of lipoplexes affects transfection efficiency.

METHODS

Four commercially available cationic liposome formulations were used to optimise transfection efficiency in neuronal cells. The DNA to liposome ratio and the amount of DNA used in transfections were varied. Transfection efficiency was determined by the percentage of cells positive for the micro-galactosidase reporter gene product. The structure of lipoplexes was studied using atomic force microscopy. Lipoplexes were characterised further using dynamic light scattering to determine size and fluorescence techniques to show DNA compaction.

RESULTS

Optimal transfection conditions were found to differ between immortalised cell lines and primary cells. High transfection efficiencies in immortalised cell lines were achieved predominantly with multivalent cationic liposomes while primary neuronal cells showed optimal transfection efficiency with monovalent cationic liposomes. The structure of lipoplexes was observed with atomic force microscopy and showed globular complexes for multivalent cationic liposomes, while monovalent liposomes gave less compact structures. In support of this finding, high levels of DNA compaction with multivalent liposomes were observed using fluorescence quenching measurements for all DNA to liposome ratios tested. One monovalent liposome showed increasing levels of compaction with increasing liposome amount. Dynamic light scattering showed little change in complex size when the different lipoplexes were studied.

CONCLUSIONS

Optimisation of transfection efficiency was different for cell lines and primary neurons. Immortalised cells showed optimal transfection with multivalent liposomes while primary neurons showed optimal transfection with monovalent liposomes. The charge ratio of the monovalent liposome was below one, suggesting a different mechanism of lipoplex binding and uptake in primary neurons. The structure of lipoplexes, as

Aspartoacylase gene transfer to the mammalian central nervous system with therapeutic implications for Canavan disease

With the ultimate goal of developing safe and effective in vivo gene therapy for the treatment of Canavan disease and other neurological disorders, we developed a non-viral lipid-entrapped, polycation-condensed delivery system (LPD) for central nervous system gene transfer, in conjunction with adeno-associated virus (AAV)-based plasmids containing recombinant aspartoacylase (ASPA). The gene delivery system was tested in healthy rodents and primates, before proceeding to preliminary studies in 2 children with Canavan disease. Toxicity and expression testing was first carried out in human 293 cells, which demonstrated effective transduction of cells and high levels of functional ASPA activity. We performed in vivo toxicity and expression testing of LPD/pAAVaspa and LPD/pAAVlac in rodents, which demonstrated widespread gene expression for more than 10 months after intraventricular delivery, and local expression in deep brain nuclei and white matter tracts for more than 6 months after intraparenchymal injections, with no significant adverse effects. We also performed intraventricular delivery of LPD/pAAVaspa to 2 cynomologous monkeys, with 2 additional monkeys receiving LPD and saline controls. None of the monkeys demonstrated significant adverse effects, and at 1 month the 2 LPD/pAAVaspa monkeys were positive for human ASPA transcript by reverse transcriptase polymerase chain reaction of brain tissue punches. Finally, we performed the first in vivo gene transfer study for a human neurodegenerative disease in 2 children with Canavan disease to assess the in vivo toxicity and efficacy of ASPA gene delivery. Our results suggest that LPD/pAAVaspa is well tolerated in human subjects and is associated with biochemical, radiological, and clinical changes.

Sustained production of beta-glucuronidase from localized sites after AAV vector gene transfer results in widespread distribution of enzyme and reversal of lysosomal storage lesions in a large volume of brain in mucopolysaccharidosis VII mice

The lysosomal storage disorders are a large group of inherited diseases that involve central nervous system degeneration. The disease in the brain has generally been refractory to treatment, which will require long-term correction of lesions dispersed throughout the central nervous system to be effective. A promising approach is somatic gene therapy but the methods have so far been inadequate because they have only achieved short-term or localized improvements. A potential approach to overcome these limitations is to obtain sustained high level expression and secretion of the missing normal enzyme from a small group of cells for export to neighboring diseased cells, which might allow the therapeutic protein to reach distal sites. We tested this in a mouse model of mucopolysaccharidosis VII (Sly disease) using an adeno-associated virus vector. After a single treatment the vector continuously produced the normal enzyme from infected cells at the injection sites. The secreted enzyme was disseminated along most of the neuraxis, resulting in widespread reversal of the hallmark pathology. An extensive sphere of correction surrounding the transduction sites was created, suggesting that a limited number of appropriately spaced sites of gene transfer may provide overlapping spheres of enzyme diffusion to cover a large volume of brain tissue.

Lipid mediated gene delivery in the adult rat brain: quantitative analysis of expression

Gene transfer into the adult brain is potentially an attractive alternative to commonly employed transgenic approaches. DNA-lipid complexes have been used to obtain brain gene transfer, but data are sparse to indicate to what extent this results in significant expression of functional protein. Here, an expression construct encoding the functional reporter, chloramphenicol-acetyl-transferase (CAT), was complexed to a novel biodegradable lipid, and delivered into the rat brain. CAT-activity was assayed in tissue extracts to allow a precise quantitation of functional enzyme protein. Following bilateral intraventricular (i.c.v.) injection, robust enzyme activity was found in all brain regions studied, peaking at 4 weeks. Other routes of administration, e.g. intra-parenchymal injection or chronic infusion of complexes, resulted in marginal or no activity. Presence of CAT mRNA and plasmid DNA in tissue extracts was confirmed at 4 weeks post i.c.v. administration. In agreement with previous studies, labelled lipid-DNA complexes were mainly found in the ventricular ependyma. Present data support the feasibility of lipid mediated brain gene transfer, and outline some of its anatomical and temporal limitations.

Lipoplexes and tumours. A review

The need for genotherapy to refocus its attention on to laboratory evaluation of better methods rather than proceeding to the clinic with semi-apt tools for genetic transfer has been highlighted in clinical study reports documented to date. Quintessential for tumour genotherapy is the ability to target abnormal cells, hence reducing exposure of normal cells to genetic material whilst maximizing gene dosage to tumour cells. This becomes increasingly important as genotherapy establishes itself in the clinic alongside the older modes of treatment. This review has discussed the applicability of lipoplexes for genotherapy of solid tumours. Lipoplexes have been used extensively for gene transfer into cells, such as cancerous cells, deficient for a certain gene product. While cationic liposomes have many advantages over other forms of delivery mechanisms, several problems hinder their use in-vivo. A closer examination of the physical limitations of current lipoplex preparations, the development and testing of novel formulations, combined with more attention to the cellular processes of cell membrane breaching and nuclear entry, may enhance gene delivery. Essential for tumour genotherapy is the ability to target these lipoplexes into tumour sites whilst reducing gene dosage to other normal tissues. Development of a better lipofection agent may indeed require a collaboration of the fields of physiology, cell biology, molecular biology, biochemistry, chemistry and membrane physics.

Liposome-mediated NGF gene transfection following neuronal injury: potential therapeutic applications

We have systematically investigated the therapeutic potential of cationic liposome-mediated neurotrophic gene transfer for treatment of CNS injury. Following determination of optimal transfection conditions, we examined the effects of dimethylaminoethane-carbamoyl-cholesterol (DC-Chol) liposome-mediated NGF cDNA transfection in injured and uninjured primary septo-hippocampal cell cultures and rat brains. In in vitro studies, we detected an increase of NGF mRNA in cultures 1 day after transfection. Subsequent ELISA and PC12 cell biological assays confirmed that cultured cells secreted soluble active NGF into the media from day 2 after gene transfection. Further experiments showed that such NGF gene transfection reduced the loss of chol- ine acetyltransferase (ChAT) activity in cultures following calcium-dependent depolarization injury. In in vivo studies, following intraventricular injections of NGF cDNA complexed with DC-Chol liposomes, ELISA detected nine- to 12-fold increases of NGF in rat CSF. Further studies showed that liposome/NGF cDNA complexes could attenuate the loss of cholinergic neuronal immunostaining in the rat septum after traumatic brain injury (TBI). Since deficits in cholinergic neurotransmission are a major consequence of TBI, our studies demonstrate for the first time that DC-Chol liposome-mediated NGF gene transfection may have therapeutic potential for treatment of brain injury.

Gene therapy for cerebrovascular disease

OBJECTIVE

To review the principles of and the experimental and clinical results of gene therapy for cerebrovascular disease.

METHODS

Literature review.

RESULTS

Vectors for gene transfer into the brain or into the cerebral vasculature include naked plasmid deoxyribonucleic acid, cationic liposomes, and viruses such as adenovirus, retrovirus, adeno-associated virus, and herpes simplex virus. Experiments using these vectors showed that intra- or perivascular application to systemic arteries can lead to transfection and expression of a foreign transgene in the adventitia and the endothelium. Intrathecal administration can lead to transfection and foreign transgene expression in leptomeningeal cells as well as in fibroblasts of blood vessel adventitia. Biological effects demonstrated thus far include increased nitric oxide production by transfection of cerebral arterial adventitia with adenovirus expressing nitric oxide synthase. Adenoviruses carrying foreign genes have been used to decrease neuronal damage in cerebral ischemia and to decrease blood pressure in spontaneously hypertensive rats. Vectors and therapeutic applications for gene therapy are evolving rapidly.

CONCLUSION

Gene therapy for cerebrovascular disease is likely to have clinical application in the near future and will have a major impact on neurosurgery. Neurosurgeons will need to be aware of the literature in this area.

Neural transplantation for Parkinson's disease

1. Neural transplantation is one promising approach for the treatment of Parkinson's disease. Fetal substantia nigra cells are a good source of dopamine, but in order to avoid ethical and immunological problems, adrenal medullary chromaffin cells have been investigated as an alternative source. 2. Grafted adrenal medullary chromaffin cells can provide dopamine as well as several neurotrophic factors that affect dopaminergic neurons in the brain. 3. We review experimental studies for application of neural transplantation techniques in Parkinson's disease, including immunological studies, cryopreservation, microvasculature, donor tissue, and direct gene delivery studies performed in our laboratory. Our clinical experience and new approach involving a polymer-encapsulated cell grafting procedure are also described.

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.

Up- and down-expression of the dopamine transporter by plasmid DNA transfer in the rat brain

The functional role of the dopamine transporter (DAT) in central dopaminergic neurotransmission was assessed further by investigating the consequences on dopamine (DA) turn-over of up- and down-regulation of this protein induced by a non-viral gene transfer approach. For this purpose, expression plasmids containing the sense or antisense coding sequence of DAT complexed with the cationic polymer, polyethylenimine (PEI), were injected into the rat substantia nigra, the brain region containing the majority of DA cell bodies. Before in vivo injection, the efficacies of the different DNA constructs were assessed by transfection studies into LLC-PK1 cells. Stereotaxic administration of the sense plasmid complexed to PEI induced, 3 days later, a significant increase in the immunoautoradiographic labelling by anti-DAT antibodies of the substantia nigra and various DA projection areas. These effects were associated with a significantly enhanced capacity of striatal synaptosomes to take up [3H]-DA and lasted up to 14 days postinjection. In contrast, 7 days after intranigral administration of the antisense plasmid complexed to PEI, we observed a significant decrease of DAT immunolabelling in the substantia nigra and [3H]-DA uptake by striatal synaptosomes. Whereas DA turnover in the striatum was unaltered 3 days after intranigral administration of the sense plasmid, it was increased 7 days after intranigral administration of the antisense construct. These data indicate that non-viral transfer of the sense or antisense coding sequence of DAT can be used as a novel approach to induce long-term changes in central DA neurotransmission.

In vivo gene transfer into the adult mammalian central nervous system by continuous injection of plasmid DNA-cationic liposome complex

Previously reported methods of liposome-mediated direct in vivo gene transfer have been inefficient, especially when performed with highly differentiated, quiescent cells of the adult mammalian central nervous system (CNS). We have therefore improved these procedures based upon a novel concept. Following continuous injection of plasmid DNA-cationic liposome complex which contained a reporter gene encoding E. coli beta-galactosidase into the striatum of adult rats, the expression of transgene was dramatically elevated without any adverse effects. This new technique may enable a wide application of liposome-mediated gene transfer technology not only to basic analysis of gene functions in the brain but also for clinical treatment of certain CNS disorders.

Antisense strategies in neurobiology

The use of antisense oligodeoxynucleotides, targeted to the transcripts encoding biologically active proteins in the nervous system, provides a novel and highly selective means to further our understanding of the function of these proteins. Recent studies of these agents also suggest the possibility of their being used therapeutically for a variety of diseases involving neuronal tissue. In this paper we review studies showing the in vitro and in vivo effects of antisense oligodeoxynucleotides as they relate to neurobiological functions. Particular attention is paid to the behavioral and biochemical effects of antisense oligodeoxynucleotides directed to the various subtypes of receptors for the neurotransmitter dopamine. An example is also provided showing the effects of a plasmid vector expressing an antisense RNA targeted to the calmodulin mRNAs in the PC12 pheochromocytoma cell line. The advantages of antisense oligodeoxynucleotides over traditional pharmacological treatments are assessed, and the advantages of using vectors encoding antisense RNA over the use of antisense oligodeoxynucleotides are also considered. We also describe the criteria that should be used in designing antisense oligodeoxynucleotides and several controls that should be employed to assure their specificity of action.

DC-Chol liposome-mediated gene transfer in rat spinal cord

We examined the potential of non-viral vector-mediated gene transfection in the rat spinal cord. Reporter gene (beta-gal) or brain-derived neurotrophic factor (BDNF) cDNA containing a pCMV promoter complexed with DC-Chol liposomes was injected into the intact rat spinal cord gray matter. RT-PCR confirmed the increased expression of BDNF mRNA in the injection areas. X-gal staining demonstrated the localized expression of beta-gal reporter genes. No overt tissue damage caused by DC-Chol liposome/DNA complex injections was detected. These results suggest that cationic liposome-mediated delivery can be a practical method for gene transfer in spinal cord.

In vitro and in vivo gene delivery mediated by a synthetic polycationic amino polymer

A synthetic polyamino polymer with a glucose backbone was used for gene transfer in vitro and in vivo. Gene transfer in vitro to various human carcinoma cell lines was achieved with an efficiency superior to a commercially available cationic liposome preparation. The polymer was resistant to inhibition by serum, which allowed for efficient gene transfer in vivo. Direct Intracranial tumor injection using this reagent resulted in reporter gene expression levels comparable to those achieved by a recombinant adenoviral vector. Thus, this compound represents a new class of agent that may have broad utility for gene transfer and gene therapy applications.

Gene therapy for central nervous system injury: the use of cationic liposomes: an invited review

This paper briefly reviews general principles of gene therapy with emphasis on the therapeutic potential of cationic liposome-mediated neurotrophin gene transfer to treat central nervous system (CNS) injury. Current developments in studies of gene therapy for CNS injury are both impressive and promising. Ex vivo gene transfer into the CNS is relatively mature in animal studies following more than a decade of experimental studies. In vivo gene transfer into the CNS has gained more attention recently. Although progress has been made using viral vectors, rapid advances in transfection technologies employing cationic liposomes, together with the relatively low toxicity of these nonviral vector systems, suggest that liposomes may have significant potential for clinical applications. Although many investigators have recognized that gene therapy may be useful for treatment of certain genetic defect diseases or cancer, gene therapy for CNS injury is relatively novel. In contrast to genetic defect disorders, temporary induction of transgenes may have therapeutic applications for CNS injuries such as stroke and trauma. Employing gene transfer techniques to achieve therapeutically useful levels of expression of neurotrophins in the CNS could provide a new strategy for treatment of the traumatically injured CNS.

Cellular and molecular neurosurgery: pathways from concept to reality--part II: vector systems and delivery methodologies for gene therapy of the central nervous system

Different vector systems that have been used and/or specifically developed for central nervous system (CNS) gene transfer studies are briefly discussed along with their advantages and disadvantages with respect to potential clinical application. These include retroviruses, recombinant herpes simplex virus, adenoviruses, adenoassociated viruses, encapsulation of plasmid deoxyribonucleic acid into cationic liposomes, and neural and oliogodendroglial stem cells. Particular attention has been paid to relate the modality of a specific CNS gene therapy to the strategy for adequate delivery of genetic material to the brain for either global or localized CNS neurodegenerative chronic disorder, as well as for CNS tumors and stroke. Techniques to circumvent the "impermeable" blood-brain barrier and how to breach the more versatile blood-brain-tumor barrier to deliver the genetic material to the target CNS cells are reviewed and include the following: 1) local stereotactic CNS injection/infusion of viral vectors, administration of vector producer cells, or cell replacement; 2) local administration of genetic material into the cerebrospinal fluid ventriculocisternal system; 3) osmotic opening of the blood-brain barrier; 4) local intra-arterial infusion; and 5) administration of blood-brain-tumor barrier permeabilizers, such as a bradykinin B2 agonist RMP-7. It is concluded that gene therapy for several brain disorders holds great potential, as suggested mainly by in vitro experiments and, to some extent, by a limited number of animal experiments. However, several drawbacks currently hamper the application of gene therapy under the clinical setting. The problems associated with gene therapy that still present major obstacles are as follows: 1) inefficient transfection of host cells by viral vectors; 2) restricted delivery of genetic material across vascular barriers of the CNS and brain tumors; 3) nonselective expression of the transgene; and 4) in situ CNS regulation of the transgene expression in a therapeutically controlled manner, as imposed by the course and phenotype of the CNS disease.

Lipofectin-facilitated transfer of cholecystokinin gene corrects behavioral abnormalities of rats with audiogenic seizures

To evaluate the potential for lipofectin-mediated central nervous system gene transfer, the plasmid coding for cholecystokinin was administered intracerebroventricularly to rats, which have congenital audiogenic seizures and high responses to peripheral electric stimulation-induced analgesia. Previous studies had shown that low brain cholecystokinin levels may be the neurochemical variable of rat's audiogenic seizure and high responses to the analgesia because cholecystokinin is an anticonvulsant and anti-opioid neuropeptide. Gene transfer of cholecystokinin corrected the increased susceptibility to audiogenic seizures and the high responses to analgesia for about one week. Similar administration of plasmid expressing beta-galactosidase indicated that the vector mainly transfected ependymal cells lining the ventricle and pia mater cells. The increased cholecystokinin messenger RNA and immunoreactivity in the hippocampus following stereotactic intrahippocampal administration of cholecystokinin plasmid was also demonstrated with in situ hybridization and immunohistochemistry techniques. These results suggest that lipofectin-mediated gene transfer will be useful for studies of brain function, the modification of behavior and gene therapy for central nervous system disorders.

Gene therapeutic strategies for neuroprotection: implications for Parkinson's disease

Gene transfer methodologies are being explored as strategies to restore and preserve neuronal function in Parkinson's Disease. This technology represents a new therapeutic modality, holding promise for continuous and localized delivery, of neuroprotective molecules. Two primary approaches for gene transfer have emerged: in vivo and ex vivo. Recent advances in the construction and characterization of gene transfer vectors have generated more efficient vehicles to deliver and express candidate therapeutic genes. Direct gene transfer into the CNS can be achieved with replication-deficient viral vectors of several types: adenovirus, adeno-associated virus, and herpes simplex virus. These vector systems are being evaluated in models of Parkinson's disease. Strategies to deliver genes include those that either augment dopamine biosynthesis or attenuate loss of dopaminergic neurons. A discussion of the various approaches is detailed.

Cationic lipid-mediated NGF gene transfection increases neurofilament phosphorylation

We examined the effect of cationic lipid-mediated gene transfection of nerve growth factor (NGF) in primary septo-hippocampal cell cultures. Rat NGF cDNA was subcloned into a pUC19-based plasmid containing a CMV promoter. Two days after NGF gene transfection in primary cell cultures, ELISA confirmed increases in NGF protein secretion from transfected cells. To study the biological effect of cationic lipid-mediated NGF gene transfection, we analyzed the amount of neurofilament protein from NGF-transfected cell cultures. Western blot and immunohistochemical analyses detected significant increases in the phosphorylated form of neurofilament proteins in the cultures after cationic lipid-mediated NGF cDNA transfection. Cationic lipid-mediated NGF cDNA transfection did rot cause significant changes in the total amount of neurofilament protein. Our studies suggest that cationic lipid-mediated NGF gene transfection can increase neurofilament phosphorylation but not total neurofilament protein.

Hypoxanthine-guanine phosphoribosyltransferase (HPRT) expression in the central nervous system of HPRT-deficient mice following adenoviral-mediated gene transfer

In this study we show that recombinant adenovirus can augment hypoxanthine-guanine phosphoribosyltransferase (HPRT) levels in the central nervous system (CNS) of HPRT-deficient mice. Recombinant adenovirus containing the cDNA for rat HPRT (rHPRT) expressed from the Rous sarcoma virus LTR (RSV LTR) was constructed (AdRSVrHPRT). AdRSVrHPRT was injected into the right caudate nucleus of 7-week-old HPRT-deficient mice. Brains were analyzed for gene transfer, transgene expression and function by DNA PCR, in situ RNA hybridization, and enzyme bioactivity. The results show that rHPRT cDNA delivered by an adenoviral vector can augment HPRT levels in brain tissue and documents the utility of gene transfer to restore HPRT activity in an HPRT-deficient CNS.

Cationic lipid-mediated delivery and expression of prepro-neuropeptide Y cDNA after intraventricular administration in rat: feasibility and limitations

The utility of in vivo lipofection for delivery and expression of a neuropeptide gene in the adult rat brain was explored. Prepro-neuropeptide Y (NPY) cDNA was cloned into the episomal eucaryotic expression vector pCEP4. This construct was complexed to lipofectamine or lipofectin. Complexed DNA was injected into the lateral ventricles of adult rats. Brains were removed for analysis following various time intervals. Polymerase chain reaction (PCR) reactions were designed for specific detection of endogenous and vector derived NPY sequence, respectively. PCR of DNA preparations from 5 major brain regions (frontal and parietal cortex, striatum, hypothalamus, brain stem) demonstrated presence of vector DNA up to 1 month (longest interval studied) in all brain regions. Reverse-transcription (RT-) PCR of DNase treated RNA-preparations from brain tissue demonstrated presence of both vector-derived and endogenous NPY mRNA in treated animals, while only endogenous mRNA was detected in controls. In situ hybridization histochemistry indicated scattered patches of vector uptake into tissue in the vicinity of the CSF compartment, but not into deeper located structures. Weight gain was not affected, indicating that the expression levels achieved may not be sufficient to play a functional role, and/or may need to be targeted to specific brain areas. These findings suggest a potential for cationic lipid mediated gene transfer in the brain as an experimental tool and as a possible future therapeutic principle, but also indicate the need for optimization of delivery strategies in order to achieve functionally relevant expression levels.

Parameters influencing the introduction of plasmid DNA into cells by the use of synthetic amphiphiles as a carrier system

Parameters that affect cellular transfection as accomplished by introducing DNA via carriers composed of cationic synthetic amphiphiles, have been investigated, with the aim to obtain insight into the mechanism of DNA translocation. Such insight may be exploited in optimizing carrier properties of synthetic amphiphiles for molecules other than nucleic acids. In the present work, the interaction of vesicles composed of the cationic amphiphile dioleyloxy-propyl-trimethylammonium chloride (DOTMA) with cultured cells was examined. The results show that optimal transfection is dependent on the concentration of lipid, which determines the efficiency of vesicle interaction with the target cell membrane, as well as the toxicity of the amphiphiles towards the cell. A low lipid/DNA ratio prevents the complex from interacting with the cell surface, whereas at a relatively high amphiphile concentration the complex becomes toxic. Translocation efficiency is independent of the initial vesicle size but is affected by the size of the DNA. An incubation time of the DNA/amphiphile complex and cells of approx. 2-4 h is required for obtaining efficient transfection. In conjunction with observations on DNA/amphiphile complex-induced hemolysis of erythrocytes, a mechanism of DNA-entry is proposed which involves translocation of the nucleic acids through pores across the membranes rather than delivery via fusion or endocytosis. Dioleoylphosphatidylethanolamine, a phospholipid frequently used in a mixture with DOTMA ('lipofectin') strongly facilitates this pore formation. Translocation of the DNA is effectively prevented when the cells are pretreated with Ca2+ or pronase. These observations suggest that Ca(2+)-sensitive cell surface proteins play a role in amphiphile-mediated DNA translocation.

Phenotype correction in retinal pigment epithelium in murine mucopolysaccharidosis VII by adenovirus-mediated gene transfer

We have studied the use of adenovirus-mediated gene transfer to reverse the pathologic changes of lysosomal storage disease caused by beta-glucuronidase deficiency in the eyes of mice with mucopolysaccharidosis VII. A recombinant adenovirus carrying the human beta-glucuronidase cDNA coding region under the control of a non-tissue-specific promoter was injected intravitreally or subretinally into the eyes of mice with mucopolysaccharidosis VII. At 1-3 weeks after injection, the treated and control eyes were examined histochemically for beta-glucuronidase expression and histologically for phenotypic correction of the lysosomal storage defect. Enzymatic expression was detected 1-3 weeks after injection. Storage vacuoles in the retinal pigment epithelium (RPE) were still present 1 week after gene transfer but were reduced to undetectable levels by 3 weeks in both intravitreally and subretinally injected eyes. There was minimal evidence of ocular pathology associated with the viral injection. These data indicate that adenovirus-mediated gene transfer to the eye may provide for adjunctive therapy for lysosomal storage diseases affecting the RPE in conjunction with enzyme replacement and/or gene therapies for correction of systemic disease manifestations. The data also support the view that recombinant adenovirus may be useful as a gene therapy vector for retinal degenerations that result from a primary genetic defect in the RPE cells.

Rescue of injury-induced neurofilament loss by BDNF gene transfection in primary septo-hippocampal cell cultures

We employed primary septo-hippocampal cell cultures to determine the ability of liposome-mediated BDNF gene transfection to facilitate recovery of neurofilament loss caused by depolarization injury. After BDNF gene transfection in uninjured cultures, RT-PCR and immunohistochemical staining confirmed increases in BDNF mRNA and protein in transfected cells. Three days after depolarization injury, Western blot and immunohistochemical analyses detected significant loss of neurofilament proteins in non-transfected cultures, while BDNF transfection produced marked increases in neurofilament proteins following either pre-injury transfection or transfection 24 h following injury. Immunohistochemical studies also detected enhanced immunolabeling of BDNF and total neurofilament protein (phosphorylated and non-phosphorylated) in injured neurons following BDNF transfection or administration of exogenous BDNF protein, compared to untransfected, injured controls.

Sustained expression of functional nerve growth factor in primary septo-hippocampal cell cultures by liposome-mediated gene transfer

We examined liposome-mediated gene transfection of nerve growth factor (NGF) in primary central nervous system cultures. RT-PCR analyses detected increased expression of NGF mRNA one day after liposome-mediated NGF gene transfection. ELISA studies detected large increases in NGF protein in cells and in culture medium after NGF gene transfection. Cells continued to secrete NGF into the medium for at least 2 weeks. NGF bioassays confirmed that the NGF secreted after gene transfection was biologically active.

Optimizing liposome-mediated gene transfer in primary rat septo-hippocampal cell cultures

Although liposomes have been widely employed to transfect DNA into a variety of cell types, no previous studies have systematically examined conditions producing optimal liposomal-mediated transfection of DNA into central nervous system (CNS) cells. Thus, we used the beta-galactosidase (beta-gal) reporter gene to examine factors influencing the efficiency of liposome-mediated gene transfection in CNS cell cultures. Our results indicate that without increasing the amounts of DNA, increased liposome concentrations within certain limits enhanced transfection efficiency. However, higher liposome levels could produce cell lysis. Without increasing liposome concentrations, increased amounts of DNA did not improve transfection efficiency. Employing the optimal concentration (1 microgram DNA/3 microliters liposomes/well), beta-gal gene expression was sustained for at least two weeks after transfection in primary septo-hippocampal cultures.