Gene therapy progress and prospects: Parkinson's disease

Potential Therapeutic Approach using Aromatic l-amino Acid Decarboxylase and Glial-derived Neurotrophic Factor Therapy Targeting Putamen in Parkinson's Disease

Parkinson's disease (PD) is a neurodegenerative illness characterized by specific loss of dopaminergic neurons, resulting in impaired motor movement. Its prevalence is twice as compared to the previous 25 years and affects more than 10 million individuals. Lack of treatment still uses levodopa and other options as disease management measures. Treatment shifts to gene therapy (GT), which utilizes direct delivery of specific genes at the targeted area. Therefore, the use of aromatic L-amino acid decarboxylase (AADC) and glial-derived neurotrophic factor (GDNF) therapy achieves an effective control to treat PD. Patients diagnosed with PD may experience improved therapeutic outcomes by reducing the frequency of drug administration while utilizing provasin and AADC as dopaminergic protective therapy. Enhancing the enzymatic activity of tyrosine hydroxylase (TH), glucocorticoid hormone (GCH), and AADC in the striatum would be useful for external L-DOPA to restore the dopamine (DA) level. Increased expression of glutamic acid decarboxylase (GAD) in the subthalamic nucleus (STN) may also be beneficial in PD. Targeting GDNF therapy specifically to the putaminal region is clinically sound and beneficial in protecting the dopaminergic neurons. Furthermore, preclinical and clinical studies supported the role of GDNF in exhibiting its neuroprotective effect in neurological disorders. Another Ret receptor, which belongs to the tyrosine kinase family, is expressed in dopaminergic neurons and sounds to play a vital role in inhibiting the advancement of PD. GDNF binding on those receptors results in the formation of a receptor-ligand complex. On the other hand, venous delivery of recombinant GDNF by liposome-based and encapsulated cellular approaches enables the secure and effective distribution of neurotrophic factors into the putamen and parenchyma. The current review emphasized the rate of GT target GDNF and AADC therapy, along with the corresponding empirical evidence.

Further Studies on Cationic Gemini Amphiphiles as Carriers for Gene Delivery-The Effect of Linkers in the Structure and Other Factors Affecting the Transfection Efficacy of These Amphiphiles

Gene therapy has the therapeutic potential to address a multitude of health problems, and it also has utility in different domains of science. However, its applications are plagued due to the absence of a suitable, safe, efficient, selective, and universal vector, which could help in delivering the desired nucleic acid cargo to the site of action. Though viral vectors are efficient, they pose various health risks. Different types of synthetic agents have been tried as nucleic acid vectors by researchers but with limited success. Gemini amphiphiles (GAs) are a class of synthetic surfactants having biscationic heads with attached hydrophilic and lipophilic groups. Herein, we synthesized two classes of GAs differing in the chemical nature and length of the linkers, head groups, and lipophilic chains. The resulting compounds were evaluated for their efficiency to transfect A549 and HeLa cell lines with a β-galactosidase reporter plasmid. A 3-oxypentyl linker, a monohydroxyethyl head group, and a tetradecyl moiety as the lipophilic chain offered the best transfection efficiency (compound 10BIII). Dioleoylphosphatidylethanolamine (DOPE) as the helper lipid improved the transfection efficacy of the GAs in the absence of serum. In the presence of serum, DOPE and cholesterol, as the helper lipids, improved the transfection efficacy of the resulting formulations. The synthesized GAs showed concentration-dependent toxicity in the MTT assay. Biodistribution studies using 99mTc-labeled lipoplexes indicated that the lipoplexes got concentrated in some vital organs such as the spleen, liver, and lungs.

Functional Polyglycidol-Based Block Copolymers for DNA Complexation

Gene therapy is an attractive therapeutic method for the treatment of genetic disorders for which the efficient delivery of nucleic acids into a target cell is critical. The present study is aimed at evaluating the potential of copolymers based on linear polyglycidol to act as carriers of nucleic acids. Functional copolymers with linear polyglycidol as a non-ionic hydrophilic block and a second block bearing amine hydrochloride pendant groups were prepared using previously synthesized poly(allyl glycidyl ether)-b-polyglycidol block copolymers as precursors. The amine functionalities were introduced via highly efficient radical addition of 2-aminoethanethiol hydrochloride to the alkene side groups. The modified copolymers formed loose aggregates with strongly positive surface charge in aqueous media, stabilized by the presence of dodecyl residues at the end of the copolymer structures and the hydrogen-bonding interactions in polyglycidol segments. The copolymer aggregates were able to condense DNA into stable and compact nanosized polyplex particles through electrostatic interactions. The copolymers and the corresponding polyplexes showed low to moderate cytotoxicity on a panel of human cancer cell lines. The cell internalization evaluation demonstrated the capability of the polyplexes to successfully deliver DNA into the cancer cells.

Highly Photoluminescent Nitrogen- and Zinc-Doped Carbon Dots for Efficient Delivery of CRISPR/Cas9 and mRNA

Safe and efficient delivery of CRISPR/Cas9 systems is still a challenge. Here we report the development of fluorescent nitrogen- and zinc-doped carbon dots (N-Zn-doped CDs) using one-step microwave-aided pyrolysis based on citric acid, branched PEI_25k, and different zinc salts. These versatile nanovectors with a quantum yield of around 60% could not only transfect large CRISPR plasmids (∼9 kb) with higher efficiency (80%) compared to PEI_25k and lipofectamine 2000 (Lipo 2K), but they also delivered mRNA into HEK 293T cells with the efficiency 20 times greater than and equal to that of PEI_25k and Lipo 2K, respectively. Unlike PEI_25k, N-Zn-doped CDs exhibited good transfection efficiency even at low plasmid doses and in the presence of 10% fetal bovine serum (FBS). Moreover, these nanovectors demonstrated excellent efficiency in GFP gene disruption by transferring plasmid encoding Cas9 and sgRNA targeting GFP as well as Cas9/sgRNA ribonucleoproteins into HEK 293T-GFP cells. Hence, N-Zn-doped CDs with remarkable photoluminescence properties and high transfection efficiency in the delivery of both CRISPR complexes and mRNA provide a promising platform for developing safe, efficient, and traceable delivery systems for biological research.

Synthesis and validation of DOPY: A new gemini dioleylbispyridinium based amphiphile for nucleic acid transfection

Nucleic acids therapeutics provide a selective and promising alternative to traditional treatments for multiple genetic diseases. A major obstacle is the development of safe and efficient delivery systems. Here, we report the synthesis of the new cationic gemini amphiphile 1,3-bis[(4-oleyl-1-pyridinio)methyl]benzene dibromide (DOPY). Its transfection efficiency was evaluated using PolyPurine Reverse Hoogsteen hairpins (PPRHs), a nucleic acid tool for gene silencing and gene repair developed in our laboratory. The interaction of DOPY with PPRHs was confirmed by gel retardation assays, and it forms complexes of 155 nm. We also demonstrated the prominent internalization of PPRHs using DOPY compared to other chemical vehicles in SH-SY5Y, PC-3 and DF42 cells. Regarding gene silencing, a specific PPRH against the survivin gene delivered with DOPY decreased survivin protein levels and cell viability more effectively than with N-[1-(2,3-Dioleoyloxy)propyl]-N,N,N-trimethylammonium methylsulfate (DOTAP) in both SH-SY5Y and PC-3 cells. We also validated the applicability of DOPY in gene repair approaches by correcting a point mutation in the endogenous locus of the dhfr gene in DF42 cells using repair-PPRHs. All these results indicate both an efficient entry and release of PPRHs at the intracellular level. Therefore, DOPY can be considered as a new lipid-based vehicle for the delivery of therapeutic oligonucleotides.

Physicochemical Properties and Biological Performance of Polymethacrylate Based Gene Delivery Vector Systems: Influence of Amino Functionalities

Physicochemical characteristics and biological performance of polyplexes based on two identical copolymers bearing tertiary amino or quaternary ammonium groups are evaluated and compared. Poly(2-(dimethylamino)ethyl methacrylate)-b-poly(oligo(ethylene glycol) methyl ether methacrylate) block copolymer (PDMAEMA-b-POEGMA) is synthesized by reversible addition fragmentation chain transfer polymerization. The tertiary amines of PDMAEMA are converted to quaternary ammonium groups by quaternization with methyl iodide. The two copolymers spontaneously formed well-defined polyplexes with DNA. The size, zeta potential, molar mass, aggregation number, and morphology of the polyplex particles are determined. The parent PDMAEMA-b-POEGMA exhibits larger buffering capacity, whereas the corresponding quaternized copolymer (QPDMAEMA-b-POEGMA) displays stronger binding affinity to DNA, yielding invariably larger in size and molar mass particles bearing greater number of DNA molecules per particle. Experiments revealed that QPDMAEMA-b-POEGMA is more effective in transfecting pEGFP-N1 than the parent copolymer, attributed to the larger size, molar mass, and DNA cargo, as well as to the effective cellular traffic, which dominated over the enhanced ability for endo-lysosomal escape of PDMAEMA-b-POEGMA.

Thermoresponsive Polyoxazolines as Vectors for Transfection of Nucleic Acids

Poly(2-oxazoline)s (POx) are an attractive platform for the development of non-viral gene delivery systems. The combination of POx moieties, exhibiting excellent biocompatibility, with DNA-binding polyethyleneimine (PEI) moieties into a single copolymer chain is a promising approach to balance toxicity and transfection efficiency. The versatility of POx in terms of type of substituent, copolymer composition, degree of polymerization, degree of hydrolysis, and chain architecture, as well as the introduction of stimuli-responsive properties, provides opportunities to finely tune the copolymer characteristics and physicochemical properties of the polyplexes to increase the biological performance. An overview of the current state of research in the POx-PEI-based gene delivery systems focusing particularly on thermosensitive POx is presented in this paper.

Nanoparticle Delivery Systems for DNA/RNA and their Potential Applications in Nanomedicine

The rapid development of nanotechnology has a great influence on the fields of biology, physiology, and medicine. Over recent years, nanoparticles have been widely presented as nanocarriers to help the delivery of gene, drugs, and other therapeutic agents with cellular targeting ability. Advances in the understanding of gene delivery and RNA interference (RNAi)-based therapy have brought increasing attention to understanding and tackling complex genetically related diseases, such as cancer, cardiovascular and pulmonary diseases, autoimmune diseases and infections. The combination of nanocarriers and DNA/RNA delivery may potentially improve their safety and therapeutic efficacy. However, there still exist many challenges before this approach can be practiced in the clinic. In this review, we provide a comprehensive summary on the types of nanoparticle systems used as nanocarriers, highlight the current use of nanocarriers in recombinant DNA and RNAi molecules delivery, and the current landscape of gene-based nanomedicine-ranging from diagnosis to therapeutics. Finally, we briefly discuss the biosafety concerns and limitations in the preclinical and clinical development of nanoparticle gene systems.

AAV2/DJ-mediated alpha-synuclein overexpression in the rat substantia nigra as early stage model of Parkinson's disease

Parkinson's disease (PD) is pathologically characterized by the progressive loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc) and alpha-synucleinopathy. We mimic the disease pathology with overexpression of either the human α-syn wildtype (α-syn-WT) or E46K mutant form (α-syn-E46K) in DA neurons of the SNpc in adult rats using AAV2/DJ as a viral vector for the first time. Transduction efficiency was compared to an equal virus titer expressing the green fluorescent protein (GFP). Motor skills of all animals were evaluated in the cylinder and amphetamine-induced rotation test over a total time period of 12 weeks. Additionally, stereological quantification of DA cells and striatal fiber density measurements were performed every 4 weeks after injection. Rats overexpressing α-syn-WT showed a progressive loss of DA neurons with 40% reduction after 12 weeks accompanied by a greater loss of striatal DA fibers. In contrast, α-syn-E46K led to this reduction after 4 weeks without further progress. Insoluble α-syn positive cytoplasmic inclusions were observed in both groups within DA neurons of the SNpc and VTA. In addition, both α-syn groups developed a characteristic worsening of the rotational behavior over time. However, only the α-syn-WT group reached statistically significant different values in the cylinder test. Summarizing these effects, we established a motor symptom animal model of PD by using AAV2/DJ in the brain for the first time. Thereby, overexpressing of α-syn-E46K mimicked a rather pre-symptomatic stage of the disease, while the α-syn-WT overexpressing animals imitated an early symptomatic stage of PD.

Cell Penetrating Peptide Conjugated Chitosan for Enhanced Delivery of Nucleic Acid

Gene therapy is an emerging therapeutic strategy for the cure or treatment of a spectrum of genetic disorders. Nevertheless, advances in gene therapy are immensely reliant upon design of an efficient gene carrier that can deliver genetic cargoes into the desired cell populations. Among various nonviral gene delivery systems, chitosan-based carriers have gained increasing attention because of their high cationic charge density, excellent biocompatibility, nearly nonexistent cytotoxicity, negligible immune response, and ideal ability to undergo chemical conjugation. However, a major shortcoming of chitosan-based carriers is their poor cellular uptake, leading to inadequate transfection efficiency. The intrinsic feature of cell penetrating peptides (CPPs) for transporting diverse cargoes into multiple cell and tissue types in a safe manner suggests that they can be conjugated to chitosan for improving its transfection efficiency. In this review, we briefly discuss CPPs and their classification, and also the major mechanisms contributing to the cellular uptake of CPPs and cargo conjugates. We also discuss immense improvements for the delivery of nucleic acids using CPP-conjugated chitosan-based carriers with special emphasis on plasmid DNA and small interfering RNA.

Comblike Polyethylenimine-Based Polyplexes: Balancing Toxicity, Cell Internalization, and Transfection Efficiency via Polymer Chain Topology

Comblike polyethylenimines with varying degrees of polymerization of both the main and side chains as well as different grafting densities were evaluated as gene delivery vectors. They were able to condense linear and plasmid DNA into nanosized polyplex particles with dimensions and surface potentials in the 130-330 nm and -30 to +15 mV ranges, respectively, depending on the amine/phosphate (N/P) ratio. The polyplexes remained stable in aqueous and buffer solutions from several hours up to several days. The moderate colloidal stability was also manifested in a relatively broad size distribution (PDI typically above 0.2) and structural polymorphism observed by transmission electron microscopy. Both the neat polymers and polyplexes displayed low cytotoxicity in WISH cells as the relative cell viability was more than 60%. Experiments with lysosomal fluorescence staining revealed that the internalization pathways and, in turn, transfection efficiency of the polyplex nanoparticles depended on the polymer chain topology. The vector systems based on the polymers of denser structure can be considered to be promising systems for gene transfection in eukaryotic cells.

shRNA targeting α-synuclein prevents neurodegeneration in a Parkinson's disease model

Multiple convergent lines of evidence implicate both α-synuclein (encoded by SCNA) and mitochondrial dysfunction in the pathogenesis of sporadic Parkinson's disease (PD). Occupational exposure to the mitochondrial complex I inhibitor rotenone increases PD risk; rotenone-exposed rats show systemic mitochondrial defects but develop specific neuropathology, including α-synuclein aggregation and degeneration of substantia nigra dopaminergic neurons. Here, we inhibited expression of endogenous α-synuclein in the adult rat substantia nigra by adeno-associated virus-mediated delivery of a short hairpin RNA (shRNA) targeting the endogenous rat Snca transcript. Knockdown of α-synuclein by ~35% did not affect motor function or cause degeneration of nigral dopaminergic neurons in control rats. However, in rotenone-exposed rats, progressive motor deficits were substantially attenuated contralateral to α-synuclein knockdown. Correspondingly, rotenone-induced degeneration of nigral dopaminergic neurons, their dendrites, and their striatal terminals was decreased ipsilateral to α-synuclein knockdown. These data show that α-synuclein knockdown is neuroprotective in the rotenone model of PD and indicate that endogenous α-synuclein contributes to the specific vulnerability of dopaminergic neurons to systemic mitochondrial inhibition. Our findings are consistent with a model in which genetic variants influencing α-synuclein expression modulate cellular susceptibility to environmental exposures in PD patients. shRNA targeting the SNCA transcript should be further evaluated as a possible neuroprotective therapy in PD.

Enhanced gene expression promoted by hybrid magnetic/cationic block copolymer micelles

We report on novel gene delivery vector systems based on hybrid polymer-magnetic micelles. The hybrid micelles were prepared by codissolution of hydrophobically surface modified iron oxide and amphiphilic polystyrene-b-poly(quaternized 2-vinylpyridine) block copolymer (PS-b-P2QVP) in organic solvent. After extensive dialysis against water, micelles with positively charged hydrophilic corona of PQVP and hydrophobic PS core were prepared, in which magnetic nanoparticles were randomly distributed. The hybrid micelles were used to form complexes with linear (salmon sperm, 2000 bp, corresponding to M(w) of 1.32 × 10(6) Da) and plasmid (pEGFP-N1, 4730 bp, corresponding to M(w) of 3.12 × 10(6) Da) DNA. The resulting magnetopolyplexes of phosphate:amine (P/N) ratios in the 0.05-20 range were characterized by light scattering, ζ-potential measurements, and transmission electron microscopy as well as cytotoxicity and gel retardation assays. The investigated systems displayed a narrow size distribution, particle dimensions below 360 nm, whereas their ζ-potential values varied from positive to negative depending of the P/N ratio. The resulting vector nanosystems exhibited low toxicity. They were able to introduce pEGFP-N1 molecules into the cells. The application of a magnetic field markedly boosted the transgene expression efficiency of the magnetopolyplexes, which was even superior to those of commercial transfectants such as Lipofectamine and dendritic polyethylenimine.

Protective and antioxidant effects of a chalconoid from Pulicaria incisa on brain astrocytes

Oxidative stress is involved in the pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS) and provide them with trophic support, such as glial-derived neurotrophic factor (GDNF). Thus, any damage to astrocytes will affect neuronal survival. In the present study, by activity-guided fractionation, we have purified from the desert plant Pulicaria incisa two protective compounds and determined their structures by spectroscopic methods. The compounds were found to be new chalcones—pulichalconoid B and pulichalconoid C. This is the first study to characterize the antioxidant and protective effects of these compounds in any biological system. Using primary cultures of astrocytes, we have found that pulichalconoid B attenuated the accumulation of ROS following treatment of these cells with hydrogen peroxide by 89% and prevented 89% of the H₂O₂-induced death of astrocytes. Pulichalconoid B exhibited an antioxidant effect both in vitro and in the cellular antioxidant assay in astrocytes and microglial cells. Pulichalconoid B also caused a fourfold increase in GDNF transcription in these cells. Thus, this chalcone deserves further studies in order to evaluate if beneficial therapeutic effect exists.

Transfection of mammalian cells using block copolypeptide vesicles

An arginine-leucine block copolypeptide (R60 L20 ) is synthesized, which is capable of forming vesicles with controllable sizes, able to transport hydrophilic cargo across the cell membrane, and exhibit relatively low cytotoxicity. The R60 L20 vesicles also possess the ability to deliver DNA into mammalian cells for transfection. Although the transfection efficiency is lower than that of the commercially available transfection agent Lipofectamine 2000, the R60 L20 vesicles are able to achieve transfection with significantly lower cytotoxicity and immunogenicity. This behavior is potentially due to its stronger interaction with DNA which subsequently provides better protection against anionic heparin.

Antioxidant and astroprotective effects of a Pulicaria incisa infusion

Oxidative stress is involved in the pathogenesis of neurodegenerative diseases such as Parkinson's and Alzheimer's diseases. Astrocytes, the most abundant glial cells in the brain, protect neurons from reactive oxygen species (ROS) and provide them with trophic support, such as glial-derived neurotrophic factor (GDNF). Thus, any damage to astrocytes will affect neuronal survival. In the present study, an infusion prepared from the desert plant Pulicaria incisa (Pi) was tested for its protective and antioxidant effects on astrocytes subjected to oxidative stress. The Pi infusion attenuated the intracellular accumulation of ROS following treatment with hydrogen peroxide and zinc and prevented the H(2)O(2)-induced death of astrocytes. The Pi infusion also exhibited an antioxidant effect in vitro and induced GDNF transcription in astrocytes. It is proposed that this Pi infusion be further evaluated for use as a functional beverage for the prevention and/or treatment of brain injuries and neurodegenerative diseases in which oxidative stress plays a role.

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.

Design of multifunctional non-viral gene vectors to overcome physiological barriers: dilemmas and strategies

Gene-based therapeutics hold great promise for medical advancement and have been used to treat various human diseases with mixed success. However, their therapeutic application in vivo is limited due largely to several physiological barriers. The design of non-viral gene vectors with the ability to overcome delivery obstacles is currently under extensive investigation. These efforts have placed an emphasis on the development of multifunctional vectors able to execute multiple tasks to simultaneously overcome both extracellular and intracellular obstacles. However, the assembly of these different functionalities into a single system to create multifunctional gene vectors faces many conflicts that largely limit the safe and efficient application of lipoplexes and polyplexes in a systemic delivery. In the review, we have described the dilemmas inherent in the design of a viable, non-viral gene vector equipped with multiple functionalities. The strategies directed towards individual delivery barriers are first summarized, followed by a focus on the design of so-called smart multifunctional vectors with the capability to overcome the delivery difficulties of gene medicines, including the so-called the "polycation dilemma", the "PEG dilemma" and the "package and release dilemma".

New non-oral drug delivery systems for Parkinson's disease treatment

INTRODUCTION

Parkinson's disease (PD) remains the only neurodegenerative disorder for which there are highly effective symptomatic therapies, but still unmet needs regarding its long-term management. Levodopa (LD) remains the most effective treatment; however, chronic use is associated with potentially disabling motor complications.

AREAS COVERED

This review highlights a variety of new non-oral drug delivery strategies for non-invasive and invasive routes of drug administration for the treatment of PD. It also includes current and future trends of liposomes, solid lipid nanoparticles and biocompatible microparticles as new non-oral drug delivery systems.

EXPERT OPINION

The long-term complications and limitations of LD treatment might be improved by changing therapy from the present pulsatile stimulation to a more constant stimulation of central dopamine receptors. Stimulation of these receptors may be possible with a new non-oral drug delivery system, with the aim of achieving long-lasting and less fluctuating drug levels, minimization of peak levels and thereby reduction of side effects.

Protective Role of rAAV-NDI1, Serotype 5, in an Acute MPTP Mouse Parkinson's Model

Defects in mitochondrial proton-translocating NADH-quinone oxidoreductase (complex I) have been implicated in a number of acquired and hereditary diseases including Leigh's syndrome and more recently Parkinson's disease. A limited number of strategies have been attempted to repair the damaged complex I with little or no success. We have recently shown that the non-proton-pumping, internal NADH-ubiquinone oxidoreductase (Ndi1) from Saccharomyces cerevisiae (baker's yeast) can be successfully inserted into the mitochondria of mice and rats, and the enzyme was found to be fully active. Using recombinant adenoassociated virus vectors (serotype 5) carrying our NDI1 gene, we were able to express the Ndi1 protein in the substantia nigra (SN) of C57BL/6 mice with an expression period of two months. The results show that the AAV serotype 5 was highly efficient in expressing Ndi1 in the SN, when compared to a previous model using serotype 2, which led to nearly 100% protection when using an acute MPTP model. It is conceivable that the AAV-serotype5 carrying the NDI1 gene is a powerful tool for proof-of-concept study to demonstrate complex I defects as the causable factor in diseases of the brain.

HSV as a vector in vaccine development and gene therapy

The very deep knowledge acquired on the genetics and molecular biology of herpes simplex virus (HSV), major human pathogen whose lifestyle is based on a long-term dual interaction with the infected host characterized by the existence of lytic and latent infections, has allowed the development of potential vectors for several applications in human healthcare. These include delivery and expression of human genes to cells of the nervous system, selective destruction of cancer cells, prophylaxis against infection with HSV or other infectious diseases and targeted infection of specific tissues or organs. Three different classes of vectors can be derived from HSV-1: replication-competent attenuated vectors, replication-incompetent recombinant vectors and defective helper-dependent vectors known as amplicons. This chapter highlights the current knowledge concerning design, construction and recent applications, as well as the potential and current limitations of the three different classes of HSV-1-based vectors.

Combinatorial evaluation of cations, pH-sensitive and hydrophobic moieties for polymeric vector design

Three combinatorial libraries of polymeric vectors were evaluated to investigate the functional roles of molecular weight (MW), cations, pH-sensitive moieties, and hydrophobic derivitization in polymer-mediated gene delivery. Four cationic and pH-sensitive moieties (imidazole, primary, secondary, and tertiary amino) and three hydrophobic residues (C4 butyl, C6 hexyl, and C8 octyl) were assessed in single and serially incremented, binary combinations. Three MWs were evaluated-10, 30, and 50 kDa. The highest levels of transfection, comparable to branched PEI (25 kDa), were achieved by 30 kDa and 50 kDa formulations containing primary amino and imidazole groups. Primary amino groups offered superior charge-neutralizing and size-condensing capacity, while imidazole groups appeared to bind with DNA via nonelectrostatically mediated interactions to produce stable polyplexes that were resistant to premature dissociation. Eight of the 10 highest-transfecting polymers possessed IC(50) values greater than the maximum concentration of free polymers exposed to cells (200 microg/ml). The results herein have identified highly efficient polymeric formulations with superb toxicity profiles and have revealed the functional roles that the investigated pendant groups play in the transfection process. The reported polymeric system offers a versatile and robust platform upon which future structure-function studies may be based to create safer and more efficient polymeric vectors.

Long-term transgene expression in mouse neural progenitor cells modified with phiC31 integrase

Stem cells can potentially be utilized in combined gene/cell therapies for neural diseases. We examined the ability of the non-viral phiC31 integrase system to promote stable transgene expression in mouse neural progenitor cells (mNPCs). phiC31 integrase catalyzes the sequence-specific integration of attB-containing plasmids into pseudo attP sites in mammalian genomes, to produce long-term transgene expression. We achieved gene transfer by co-nucleofection of a plasmid carrying the luciferase marker gene and an attB site and a plasmid expressing integrase in mNPCs that had been generated in a neurosphere preparation. Luciferase expression was quantified in live cells for 8 weeks, revealing persistence of gene expression. Sequence-specific integration at a preferred pseudo attP site in the mouse genome was detected by using PCR. Furthermore, sustained transgene expression was demonstrated in genetically modified NPCs that were cultured in conditions that promoted either growth or differentiation into neurons and astrocytes. Our results demonstrate that the phiC31 integrase system produces stable transgene expression in adult mNPCs and their progeny and may be useful in strategies for combating neurodegenerative disorders.

Viral vectors for in vivo gene transfer in Parkinson's disease: properties and clinical grade production

Because Parkinson's disease is a progressive degenerative disorder that is mainly confined to the basal ganglia, gene transfer to deliver therapeutic molecules is an attractive treatment avenue. The present review focuses on direct in vivo gene transfer vectors that have been developed to a degree that they have been successfully used in animal model of Parkinson's disease. Accordingly, the properties of recombinant adenovirus, recombinant adeno-associated virus, herpes simplex virus, and lentivirus are described and contrasted. In order for viral vectors to be developed into clinical grade reagents, they must be manufactured and tested to precise regulatory standards. Indeed, clinical lots of viral vectors can be produced in compliance with current Good Manufacturing Practices (cGMPs) regulations using industry accepted manufacturing methodologies, manufacturing controls, and quality systems. The viral vector properties themselves combined with physiological product formulations facilitate long-term storage and direct in vivo administration.

Glial cell line-derived neurotrophic factor protects astrocytes from staurosporine- and ischemia- induced apoptosis

Glial cell line-derived neurotrophic factor (GDNF) promotes the survival and functions of neurons. It has been shown to be a promising candidate in the treatment of ischemia and other neurodegenerative diseases. We transfected mouse astrocytes in primary cultures with a human GDNF gene and found that their conditioned medium could not only support the growth and survival of cultured dopaminergic neurons but also protect astrocytes from staurosporine- and ischemia-induced apoptosis. This indicated that these transfected astrocytes could release GDNF. A similar protective effect on astrocytes against apoptosis was evident when recombinant human GDNF was used. Moreover, GDNF reduced caspase-3 activity but not that of caspase-1 in cultured astrocytes after ischemia treatment. Thus, GDNF protects astrocytes from apoptosis by inhibiting the activation of caspase-3.

Dopaminergic regeneration by neurturin-overexpressing c17.2 neural stem cells in a rat model of Parkinson's disease

BACKGROUND

Genetically engineered neural stem cell (NSC) lines are promising vectors for the treatment of neurodegenerative diseases, particularly Parkinson's disease (PD). Neurturin (NTN), a member of the glial cell line-derived neurotrophic factor (GDNF) family, has been demonstrated to act specifically on mesencephalic dopaminergic neurons, suggesting its therapeutic potential for PD. In our previous work, we demonstrated that NTN-overexpressing c17.2 NSCs exerted dopaminergic neuroprotection in a rat model of PD. In this study, we transplanted NTN-c17.2 into the striatum of the 6-hydroxydopamine (6-OHDA) PD model to further determine the regenerative effect of NTN-c17.2 on the rat models of PD.

RESULTS

After intrastriatal grafting, NTN-c17.2 cells differentiated and gradually downregulated nestin expression, while the grafts stably overexpressed NTN. Further, an observation of rotational behavior and the contents of neurotransmitters tested by high-performance liquid chromatography showed that the regenerative effect of the NTN-c17.2 group was significantly better than that of the Mock-c17.2 group, and the regenerative effect of the Mock-c17.2 group was better than that of the PBS group. Further research through reverse-transcriptase polymerase chain reaction assays and in vivo histology revealed that the regenerative effect of Mock-c17.2 and NTN-c17.2 cell grafts may be attributed to the ability of NSCs to produce neurotrophic factors and differentiate into tyrosine hydroxylase-positive cells.

CONCLUSION

The transplantation of NTN-c17.2 can exert neuroregenerative effects in the rat model of PD, and the delivery of NTN by NSCs may constitute a very useful strategy in the treatment of PD.

Gene delivery to differentiated neurotypic cells with RGD and HIV Tat peptide functionalized polymeric nanoparticles

A number of neurodegenerative disorders may potentially be treated by the delivery of therapeutic genes to neurons. Nonviral gene delivery systems, however, typically provide low transfection efficiency in post-mitotic differentiated neurons. To uncover mechanistic reasons for this observation, we compared gene transfer to undifferentiated and differentiated SH-SY5Y cells using polyethylenimine (PEI)/DNA nanocomplexes. Differentiated cells exhibited substantially lower uptake of gene vectors. To overcome this bottleneck, RGD or HIV-1 Tat peptides were attached to PEI/DNA nanocomplexes via poly(ethylene glycol) (PEG) spacer molecules. Both RGD and Tat improved the cellular uptake of gene vectors and enhanced gene transfection efficiency of primary neurons up to 14-fold. RGD functionalization resulted in a statistically significant increase in vector escape from endosomes, suggesting it may improve gene delivery by more than one mechanism.

Dopaminergic neuroprotection by neurturin-expressing c17.2 neural stem cells in a rat model of Parkinson's disease

Genetically engineered neural stem cell (NSC) lines are promising vectors for the treatment of regenerative diseases, especially Parkinson's disease (PD). Neurturin (NTN), a member of the glial cell line-derived neurotrophic factor-family, has been demonstrated to act specifically on mesencephalic dopaminergic neurons, suggesting its therapeutic potential for PD. Here, we have generated a NTN-secreting c17.2 NSC line and investigated the protective effect of NTN-c17.2 on PD rat models. These NTN-releasing NSCs engrafted and integrated in the host striatum with good success, gave rise to neurons, astrocytes and oligodendrocytes, and maintained stable, high-level NTN expression. In addition, inverse transfer of NTN protein into the substantia nigra (SN) was able to protect dopaminergic neurons from 6-OHDA toxicity. Observation of rotational behavior showed that the NTN group performed significantly better than the Mock group, and the protective effect of NTN lasted for at least 4 months. HPLC tests indicated that the contents of neurotransmitters (e.g. dopamine) in the corpus striatum area of the NTN-c17.2 group and the Mock-c17.2 group were significantly higher than in the PBS group, but there was no significant difference between expression in the NTN-c17.2 and Mock-c17.2 groups. Taken together, our results suggest that transplantation of NTN-secreting NSCs exerted protective on PD rat models.

Lentiviral Manipulation of Gene Expression in Human Adult and Embryonic Stem Cells

Human stem cells could revolutionize the field of medicine by providing a diverse range of cell types for tissue replacement therapies and drug discovery. To achieve this goal, genetic tools need to be optimized and developed for controlling and manipulating stem cells ex vivo. Here we describe a lentiviral delivery system capable of high infection rates in human mesenchymal and embryonic stem cells. The lentiviral backbone was modified to express mono- and bi-cistronic transgenes and was also used to deliver short hairpin ribonucleic acid for specific silencing of gene expression in human stem cells. We show that lentiviral transduction can be used to alter gene expression without altering the genes' ability to differentiate in vitro. These vectors will enable rapid analysis of gene function in stem cells and permit the generation of knock-in / knock-out models of human disease in the rapidly developing field of gene therapy.

Human gene therapy and imaging in neurological diseases

Molecular imaging aims to assess non-invasively disease-specific biological and molecular processes in animal models and humans in vivo. Apart from precise anatomical localisation and quantification, the most intriguing advantage of such imaging is the opportunity it provides to investigate the time course (dynamics) of disease-specific molecular events in the intact organism. Further, molecular imaging can be used to address basic scientific questions, e.g. transcriptional regulation, signal transduction or protein/protein interaction, and will be essential in developing treatment strategies based on gene therapy. Most importantly, molecular imaging is a key technology in translational research, helping to develop experimental protocols which may later be applied to human patients. Over the past 20 years, imaging based on positron emission tomography (PET) and magnetic resonance imaging (MRI) has been employed for the assessment and "phenotyping" of various neurological diseases, including cerebral ischaemia, neurodegeneration and brain gliomas. While in the past neuro-anatomical studies had to be performed post mortem, molecular imaging has ushered in the era of in vivo functional neuro-anatomy by allowing neuroscience to image structure, function, metabolism and molecular processes of the central nervous system in vivo in both health and disease. Recently, PET and MRI have been successfully utilised together in the non-invasive assessment of gene transfer and gene therapy in humans. To assess the efficiency of gene transfer, the same markers are being used in animals and humans, and have been applied for phenotyping human disease. Here, we review the imaging hallmarks of focal and disseminated neurological diseases, such as cerebral ischaemia, neurodegeneration and glioblastoma multiforme, as well as the attempts to translate gene therapy's experimental knowledge into clinical applications and the way in which this process is being promoted through the use of novel imaging approaches.

Development and application of replication-incompetent HSV-1-based vectors

The replication-incompetent HSV-1-based vectors are herpesviruses in which genes that are 'essential' for viral replication have been either mutated or deleted. These deletions have substantially reduced their cytotoxicity by preventing early and late viral gene expression and, together with other deletions involving 'nonessential' genes, have also created space to introduce distinct and independently regulated expression cassettes for different transgenes. Therapeutic effects in gene therapy applications requiring simultaneous and synergic expression of multiple gene products are easily achievable with these vectors. A number of different HSV-1-based nonreplicative vectors for specific gene therapy applications have been developed so far. They have been tested in different gene therapy animal models of neuropathies (Parkinson's disease, chronic pain, spinal cord injury pain) and lysosomal storage disorders. Many replication-incompetent HSV-1-based vectors have also been used either as potential anti-herpes vaccines, as well as vaccine vectors for other pathogens in murine and simian models. Anticancer gene therapy approaches have also been successfully set up; gene therapy to other targets by using these vectors is feasible.

Viral-Mediated Temporally Controlled Dopamine Production in a Rat Model of Parkinson Disease

Regulation of gene expression is necessary to avoid possible adverse effects of gene therapy due to excess synthesis of transgene products. To reduce transgene expression, we developed a viral vector-mediated somatic regulation system using inducible Cre recombinase. A recombinant adeno-associated virus (AAV) vector expressing Cre recombinase fused to a mutated ligand-binding domain of the estrogen receptor alpha (CreER(T2)) was delivered along with AAV vectors expressing dopamine-synthesizing enzymes to rats of a Parkinson disease model. Treatment with 4-hydroxytamoxifen, a synthetic estrogen receptor modulator, activated Cre recombinase within the transduced neurons and induced selective excision of the tyrosine hydroxylase (TH) coding sequence flanked by loxP sites, leading to a reduction in transgene-mediated dopamine synthesis. Using this strategy, aromatic L-amino acid decarboxylase (AADC) activity was retained so that l-3,4-dihydroxyphenylalanine (L-dopa), a substrate for AADC, could be converted to dopamine in the striatum and the therapeutic effects of L-dopa preserved, even after reduction of TH expression in the case of dopamine overproduction. Our data demonstrate that viral vector-mediated inducible Cre recombinase can serve as an in vivo molecular switch, allowing spatial and temporal control of transgene expression, thereby potentially increasing the safety of gene therapy.

Design and development of polymers for gene delivery

The lack of safe and efficient gene-delivery methods is a limiting obstacle to human gene therapy. Synthetic gene-delivery agents, although safer than recombinant viruses, generally do not possess the required efficacy. In recent years, a variety of effective polymers have been designed specifically for gene delivery, and much has been learned about their structure-function relationships. With the growing understanding of polymer gene-delivery mechanisms and continued efforts of creative polymer chemists, it is likely that polymer-based gene-delivery systems will become an important tool for human gene therapy.

Effects of alpha-synuclein immunization in a mouse model of Parkinson's disease

Abnormal folding of alpha-synuclein (alpha-syn) is thought to lead to neurodegeneration and the characteristic symptoms of Lewy body disease (LBD). Since previous studies suggest that immunization might be a potential therapy for Alzheimer's disease, we hypothesized that immunization with human (h)alpha-syn might have therapeutic effects in LBD. For this purpose, halpha-syn transgenic (tg) mice were vaccinated with halpha-syn. In mice that produced high relative affinity antibodies, there was decreased accumulation of aggregated halpha-syn in neuronal cell bodies and synapses that was associated with reduced neurodegeneration. Furthermore, antibodies produced by immunized mice recognized abnormal halpha-syn associated with the neuronal membrane and promoted the degradation of halpha-syn aggregates, probably via lysosomal pathways. Similar effects were observed with an exogenously applied FITC-tagged halpha-syn antibody. These results suggest that vaccination is effective in reducing neuronal accumulation of halpha-syn aggregates and that further development of this approach might have a potential role in the treatment of LBD.

Neuronal expression of the transcription factor Gli1 using the Talpha1 alpha-tubulin promoter is neuroprotective in an experimental model of Parkinson's disease

Nigrostriatal neurons degenerate during Parkinson's disease. Experimentally, neurotoxins such as 6-hydroxydopamine (6-OHDA) in rodents, and MPTP in mice and non-human primates, are used to model the disease-induced degeneration of midbrain dopaminergic neurons. Glial-cell-derived neurotrophic factor (GDNF) is a very powerful neuroprotector of dopaminergic neurons in all species examined. However, recent reports have indicated the possibility that GDNF may, in the long term and if expressed in an unregulated manner, exert untoward effects on midbrain dopaminergic neuronal structure and function. Although GDNF remains a powerful neurotrophin, the search for alternative therapies based on alternative and complementary mechanisms of action to GDNF is warranted. Recently, recombinant adenovirus-derived vectors encoding the differentiation factor Sonic Hedgehog (Shh) and its downstream transcriptional activator (Gli1) were shown to protect dopaminergic neurons in the substantia nigra pars compacta from 6-OHDA-induced neurotoxicity in rats in vivo. A pancellular human CMV (hCMV) promoter was used to drive the expression of both Shh and Gli1. Since Gli1 is a transcription factor and therefore exerts its actions intracellularly, we decided to test whether expression of Gli1 within neurons would be effective for neuroprotection. We demonstrate that neuronal-specific expression of Gli1 using the neuron-specific Talpha1 alpha-tubulin (Talpha1) promoter was neuroprotective, and its efficiency was comparable to the pancellular strong viral hCMV promoter. These results suggest that expression of the transcription factor Gli1 solely within neurons is neuroprotective for dopaminergic neurons in vivo and, furthermore, that neuronal-specific promoters are effective within the context of adenovirus-mediated gene therapy-induced neuroprotection of dopaminergic midbrain neurons. Since cell-type specific promoters are known to be weaker than the viral hCMV promoter, our data demonstrate that neuronal-specific expression of transcription factors is an effective, specific, and sufficient targeted approach for neurological gene therapy applications, potentially minimizing side effects due to unrestricted promiscuous gene expression within target tissues.

Role of surgery in the treatment of motor complications

When medications no longer provide patients with Parkinson's disease a reasonable quality of life due to the presence of levodopa-associated motor fluctuations and dyskinesias, surgical treatment is often pursued. Numerous studies have examined the antiparkinsonian efficacy of procedures currently available, but surprisingly few studies have evaluated their effect on motor response complications in a systematic, controlled manner, using appropriate instruments. Nonetheless, the combined evidence from uncontrolled case series and more recent randomized controlled trials reviewed here indicates that unilateral pallidotomy, bilateral pallidal deep brain stimulation, and bilateral subthalamic deep brain stimulation all substantially alleviate levodopa-induced dyskinesias and, to a lesser extent, motor fluctuations. Incorporation of standardized, validated instruments for the quantification of motor response complications in future surgical study protocols will not only allow more accurate comparison of different interventions but also will help physicians select the most appropriate procedure for their patients.

Herpes vector-mediated gene transfer in treatment of diseases of the nervous system

Vectors constructed from recombinant herpes simplex virus (HSV) have special utility for gene transfer to the nervous system. Nonreplicating vectors created by deletion of essential immediate early genes can be propagated to high titers on complementing cell lines that provide the missing gene product(s) in trans. Direct inoculation of these vectors into neural parenchyma is effective in rodent models of brain tumor, Parkinson disease, spinal cord injury, and spinal root trauma. Subcutaneous inoculation of the HSV vectors can be used to transduce neurons of the dorsal root ganglion to provide a therapeutic effect in models of polyneuropathy and chronic regional pain. In human trials, direct injection of replication-competent HSV into brain tumors has proven safe. Human trials of nonreplicating HSV gene transfer by direct inoculation for treatment of glioblastoma and HSV gene transfer by subcutaneous inoculation for the treatment of chronic intractable pain should commence soon.

An antiaggregation gene therapy strategy for Lewy body disease utilizing β-synuclein lentivirus in a transgenic model

Current experimental gene therapy approaches for Parkinson's disease (PD) and dementia with Lewy bodies (DLB) include the use of viral vectors expressing antiapoptosis genes, neurotrophic factors and dopaminergic system enzymes. However, since increasing evidence favors a role for alpha-synuclein accumulation in the pathogenesis of these disorders, an alternative therapy might require the transfer of genes that might block alpha-synuclein accumulation. beta-Synuclein, the nonamyloidogenic homologue of alpha-synuclein, has recently been identified as a potential candidate. Thus, in vivo transfer of genes encoding beta-synuclein might provide a novel approach to the development of experimental treatments for PD and DLB. To assess this possibility and to better understand the mechanisms involved, a lentiviral vector expressing human (h) beta-synuclein (lenti-beta-synuclein) was tested in a transgenic (tg) mouse model of halpha-synuclein aggregation. This study showed that unilateral intracerebral injection of lenti-beta-synuclein reduced the formation of halpha-synuclein inclusions and the accumulation of halpha-synuclein in synapses and ameliorated the neurodegenerative alterations in the tg mice. Both in vivo and in vitro coimmunoprecipitation and immunoblot experiments show that the mechanisms of beta-synuclein neuroprotection involve binding of this molecule to halpha-synuclein and Akt, resulting in the decreased aggregation and accumulation of halpha-synuclein in the synaptic membrane. Together, these data further support a role for beta-synuclein in regulating the conformational state of alpha-synuclein and suggest that this gene transfer approach might have potential for the development of alternative therapies for PD and DLB.

Differentiation and transcription factor gene therapy in experimental parkinson's disease: sonic hedgehog and Gli-1, but not Nurr-1, protect nigrostriatal cell bodies from 6-OHDA-induced neurodegeneration

We tested the activity of the dopaminergic neuron differentiation factor sonic hedgehog, its downstream transcription factor target Gli-1, and an orphan nuclear receptor, Nurr-1, necessary for the induction of the dopaminergic phenotype of nigrostriatal neurons, in an in vivo model of nigrostriatal neurodegeneration. Our preliminary experiments demonstrated that all three constructs expressed the proper molecules and that these had the predicted biological activities in vitro. We expressed the N-terminal of sonic hedgehog (ShhN) and the Gli-1 and Nurr-1 entire coding regions from highly purified, and quality controlled, replication-defective adenoviral vectors injected into the brains of rats and used the dopaminergic growth factor GDNF as a positive control. The neurotoxin 6-hydroxydopamine was used to lesion the nigrostriatal dopaminergic innervation; RAd-ShhN and RAd-Gli-1 protected dopaminergic neuronal cell bodies in the substantia nigra, but not axonal terminals in the striatum, from 6-OHDA-induced cell death, while RAd-Nurr-1 was ineffective in protecting either cell bodies or axons. RAd-GDNF was able to protect both the dopaminergic cell bodies and the striatal axon terminals. Our results establish for the first time, to the best of our knowledge, that gene transfer of ShhN and one of its target transcription factors can selectively protect dopaminergic nigrostriatal neuronal cell bodies from a specific neurotoxic insult. Selective protection of nigrostriatal dopaminergic cell bodies by the differentiation factor ShhN and the transcription factor Gli-1 was achieved in a neurotoxic model that eliminates more than 70% of the nigral neurons under consideration. Differentiation and transcription factors can thus be used for the treatment of neurodegeneration by gene therapy.

The evolving role of genomics in shaping care for persons with dementia

Alzheimer's disease and other chronic dementing conditions remain formidable challenges for individuals, their families, and health care providers. In addition to the challenges inherent in the sheer numbers affected, the complex and relatively unpredictable progression of these disorders complicates the delivery of interventions for health care providers. Identifying genetic and environmental etiologic factors and understanding their relationship to the natural history of dementia brings health care providers closer to more effective pharmacologic treatments and perhaps cure. In the meantime, genomics research brings professional nurses closer to providing more specific, perhaps individualized, anticipatory guidance and to providing nonpharmacologic interventions in a genotype-directed way to patients with chronic dementing conditions. The emergence of a genomics-based health care environment presents an opportunity and a challenge for gerontological nurse clinicians, educators, and researchers--an opportunity to evolve practice toward a higher level of specificity and effectiveness and a challenge to do so in a equitable and sensitive manner that improves health and quality of life for all served.