Gene expression from recombinant viral vectors in the central nervous system after blood-brain barrier disruption

Targeted transport of biotherapeutics at the blood-brain barrier

INTRODUCTION

The treatment of neurological diseases is significantly hampered by the lack of available therapeutics. A major restraint for the development of drugs is denoted by the presence of the blood-brain barrier (BBB), which precludes the transfer of biotherapeutics to the brain due to size restraints.

AREAS COVERED

Novel optimism for transfer of biotherapeutics to the brain has been generated via development of targeted therapeutics to nutrient transporters expressed by brain capillary endothelial cells (BCECs). Targeting approaches with antibodies acting as biological drug carriers allow for proteins and genetic material to enter the brain, and qualified therapy using targeted proteins for protein replacement has been observed in preclinical models and now emerging in the clinic. Viral vectors denote an alternative for protein delivery to the brain by uptake and transduction of BCECs, or by transport through the BBB leading to neuronal transduction.

EXPERT OPINION

The breaching of the BBB to large molecules has opened for treatment of diseases in the brain. A sturdier understanding of how biotherapeutics undergo transport through the BBB and how successful transport into the brain can be monitored is required to further improve the translation from successful preclinical studies to the clinic.

SHMT1 siRNA-Loaded hyperosmotic nanochains for blood-brain/tumor barrier post-transmigration therapy

The near-perivascular accumulation in solid tumors and short-lived span in circulation, derails even the most competent nanoparticles (NPs) from achieving their maximum therapeutic potential. Moreover, delivering them across the blood brain/tumor barrier (BBB/BTB) is further challenging to sought anticancer effect. To address these key challenges, we designed a linearly aligned nucleic acid-complexed polydixylitol-based polymeric nanochains (X-NCs), with inherent hyperosmotic properties enabling transmigration of the BBB/BTB and navigation through deeper regions of the brain tumor. The high aspect ratio adds shape-dependent functional aspects to parent particles by providing effective payload increment and nuclear factor of activated T cells-5 (NFAT5)-mediated cellular uptake. Therefore, serine hydroxymethyltransferase 1 (SHMT1) siRNA-loaded nanochains not only demonstrated to transmigrate the BTB, but also resulted in remarkably reducing the tumor size to 97% in the glioblastoma xenograft brain tumor mouse models. Our study illustrates how the hyperosmotic nanochains with high aspect ratio and aligned structure can accelerate a therapeutic effect in aggressive brain tumors post-transmigration of the BBB/BTB by utilizing an NFAT5 mode of uptake mechanism.

Hyperosmotic polydixylitol for crossing the blood brain barrier and efficient nucleic acid delivery

Here, we introduce a polydixylitol based highly osmotic polymer that not only transmigrates the BBB by intra-arterial infusion of osmotic polyol but also triggers cellular uptake via modulation of caveolae mediated endocytosis.

Comparison of Endovascular and Intraventricular Gene Therapy With Adeno-Associated Virus-α-L-Iduronidase for Hurler Disease

BACKGROUND

Hurler disease (mucopolysaccharidosis type I [MPS-I]) is an inherited metabolic disorder characterized by deficiency of the lysosomal enzyme α-L-iduronidase (IDUA). Currently, the only therapies for MPS-I, enzyme replacement and hematopoietic stem cell transplantation, are generally ineffective for central nervous system manifestations.

OBJECTIVE

To test whether brain-targeted gene therapy with recombinant adeno-associated virus (rAAV5)-IDUA vectors in an MPS-I transgenic mouse model would reverse the pathological hallmarks.

METHODS

Gene therapy approaches were compared using intraventricular or endovascular delivery with a marker (rAAV5-green fluorescent protein) or therapeutic (rAAV5-IDUA) vector. To improve the efficiency of brain delivery, we tested different applications of hyperosmolar mannitol to disrupt the blood-brain barrier or ependymal-brain interface.

RESULTS

Intraventricular delivery of 1 × 10 viral particles of rAAV5-IDUA with systemic 5 g/kg mannitol co-administration resulted in IDUA expression throughout the brain, with global enzyme activity >200% of the baseline level in age-matched, wild-type mice. Endovascular delivery of 1 × 10 viral particles of rAAV5-IDUA to the carotid artery with 29.1% mannitol blood-brain barrier disruption resulted in mainly ipsilateral brain IDUA expression and ipsilateral brain enzyme activity 42% of that in wild-type mice. Quantitative assays for glycosaminoglycans showed a significant decrease in both hemispheres after intraventricular delivery and in the ipsilateral hemisphere after endovascular delivery compared with untreated MPS-I mice. Immunohistochemistry for ganglioside GM3, another disease marker, showed reversal of neuronal inclusions in areas with IDUA co-expression in both delivery methods.

CONCLUSION

Physiologically relevant biochemical correction is possible with neurosurgical or endovascular gene therapy approaches for MPS-I. Intraventricular or endovascular delivery of rAAV5-IDUA was effective in reversing brain pathology, but in the latter method, effects were limited to the ipsilateral hemisphere.

Intranasal delivery of chitosan-siRNA nanoparticle formulation to the brain

Neurodegeneration is characterized by a progressive loss of neuron structure and function. Most neurodegenerative diseases progress slowly over the time. There is currently no cure available for any neurodegenerative disease, and the existing therapeutic interventions only alleviate the symptoms of the disease. The advances in the drug discovery research have come to a halt with a lack of effective means to deliver drugs at the targeted site. In addition, the route of delivering the drugs is equally important as most invasive techniques lead to postoperative complications. This chapter focuses on a non-invasive, intranasal mode of therapeutic delivery using nanoparticles, which is currently being explored. The intranasal route of delivery is a well-established route to deliver drugs via the olfactory and trigeminal neuronal pathways. It is known to be the fastest and most effective way to bypass the blood-brain barrier to reach the central nervous system. The presented chapter highlights the method of intranasal delivery in mice using chitosan-siRNA nanoparticle formulation, under mild anesthesia and the identification of successful siRNA delivery in the brain tissues, through histology and other well-established laboratory protocols.

Intranasal, siRNA Delivery to the Brain by TAT/MGF Tagged PEGylated Chitosan Nanoparticles

Neurodegeneration is characterized by progressive loss of structure and function of neurons. Several therapeutic methods and drugs are available to alleviate the symptoms of these diseases. The currently used delivery strategies such as implantation of catheters, intracarotid infusions, surgeries, and chemotherapies are invasive in nature and pose a greater risk of postsurgical complications, which can have fatal side effects. The current study utilizes a peptide (TAT and MGF) tagged PEGylated chitosan nanoparticle formulation for siRNA delivery, administered intranasally, which can bypass the blood brain barrier. The study investigates the optimal dose, duration, biodistribution, and toxicity, of the nanoparticle-siRNA formulation, in-vivo. The results indicate that 0.5 mg/kg of siRNA is delivered successfully to the hippocampus, thalamus, hypothalamus, and Purkinje cells in the cerebellum after 4 hrs of post intranasal delivery. The results indicate maximum delivery to the brain in comparison to other tissues with no cellular toxic effects. This study shows the potential of peptide-tagged PEGylated chitosan nanoparticles to be delivered intranasally and target brain tissue for the treatment of neurological disorders.

Noninvasive and targeted gene delivery into the brain using microbubble-facilitated focused ultrasound

Recombinant adeno-associated viral (rAAV) vectors are potentially powerful tools for gene therapy of CNS diseases, but their penetration into brain parenchyma is severely limited by the blood-brain barrier (BBB) and current delivery relies on invasive stereotactic injection. Here we evaluate the local, targeted delivery of rAAV vectors into the brains of mice by noninvasive, reversible, microbubble-facilitated focused ultrasound (FUS), resulting in BBB opening that can be monitored and controlled by magnetic resonance imaging (MRI). Using this method, we found that IV-administered AAV2-GFP (green fluorescence protein) with a low viral vector titer (1×10(9) vg/g) can successfully penetrate the BBB-opened brain regions to express GFP. We show that MRI monitoring of BBB-opening could serve as an indicator of the scale and distribution of AAV transduction. Transduction peaked at 3 weeks and neurons and astrocytes were affected. This novel, noninvasive delivery approach could significantly broaden the application of AAV-viral-vector-based genes for treatment of CNS diseases.

Selective stimulation of caveolae-mediated endocytosis by an osmotic polymannitol-based gene transporter

Controlling the cellular uptake mechanism and consequent intracellular route of polyplexes is important to improve the transfection efficiency of the non-viral gene delivery. Here, we report a new non-viral vector, polymannitol-based gene transporter (PMT), generated by crosslinking low molecular weight polyethylenimine with mannitol diacrylate, which has low cytotoxicity and good transfection efficiency. Interestingly, the uptake pathway of PMT/DNA complexes was shifted into caveolae-mediated endocytosis, avoiding lysosomal degradation. The mechanism of increased caveolae-mediated endocytosis of PMT/DNA complexes was found to be correlated with mechanosensing signal transduction by the hyperosmotic polymannitol part. Our results suggested that PMT, polymannitol-based gene transporter, is a safe and efficient gene delivery system with a well-modulated uptake pathway and intracellular route for gene therapy.

Challenges in drug delivery to tumors of the central nervous system: an overview of pharmacological and surgical considerations

The majority of newly diagnosed brain tumors are treated with surgery, radiation, and the chemotherapeutic temozolomide. Development of additional therapeutics to improve treatment outcomes is complicated by the blood-brain barrier (BBB), which acts to protect healthy tissue from chemical insults. The high pressure found within brain tumors adds a challenge to local delivery of therapy by limiting the distribution of bolus injections. Here we discuss various drug delivery strategies, including convection-enhanced delivery, intranasal delivery, and intrathecal delivery, as well as pharmacological strategies for improving therapeutic efficacy, such as blood-brain barrier disruption.

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.

Detection of amyloid plaques targeted by USPIO-Aβ1-42 in Alzheimer's disease transgenic mice using magnetic resonance microimaging

Amyloid plaques are one of the pathological hallmarks of Alzheimer's disease (AD). The visualization of amyloid plaques in the brain is important to monitor AD progression and to evaluate the efficacy of therapeutic interventions. Our group has developed several contrast agents to detect amyloid plaques in vivo using magnetic resonance microimaging (μMRI) in AD transgenic mice, where we used intra-carotid mannitol to enhance blood-brain barrier (BBB) permeability. In the present study, we used ultrasmall superparamagnetic iron oxide (USPIO) nanoparticles, chemically coupled with Aβ1-42 peptide to detect amyloid deposition along with mannitol for in vivo μMRI by femoral intravenous injection. A 3D gradient multi-echo sequence was used for imaging with a 100μm isotropic resolution. The amyloid plaques detected by T2*-weighted μMRI were confirmed with matched histological sections. Furthermore, two different quantitative analyses were used. The region of interest-based quantitative measurement of T2* values showed contrast-injected APP/PS1 mice had significantly reduced T2* values compared to wild-type mice. In addition, the scans were examined with voxel-based morphometry (VBM) using statistical parametric mapping (SPM) for comparison of contrast-injected AD transgenic and wild-type mice. The regional differences seen in VBM comparing USPIO-Aβ1-42 injected APP/PS1 and wild-type mice correlated with the amyloid plaque distribution histologically, contrasting with no differences between the two groups of mice without contrast agent injection in regions of the brain with amyloid deposition. Our results demonstrated that both approaches were able to identify the differences between AD transgenic mice and wild-type mice, after injected with USPIO-Aβ1-42. The feasibility of using less invasive intravenous femoral injections for amyloid plaque detection in AD transgenic mice facilitates using this method for longitudinal studies in the pathogenesis of AD.

Blood-brain barrier disruption in the treatment of brain tumors

Standard chemotherapy administered systemically has a limited efficacy in the treatment of brain tumors. One of the major obstacles in the treatment of brain neoplasias is the impediment to delivery across the intact blood-brain barrier (BBB). Many innovative approaches have been developed to circumvent this obstacle. One such strategy is BBB disruption (BBBD), which successfully increases the delivery of antineoplastic agents to the central nervous system (CNS). This chapter describes the application of the BBBD technique in rats. Different methods to evaluate and measure BBB permeability following hyperosmolar mannitol infusion including Evans blue staining, albumin immunohistochemistry, and dynamic magnetic resonance imaging are also described.

Helper-Dependent Adenoviral Vectors

Helper-dependent adenoviral vectors are devoid of all viral coding sequences, possess a large cloning capacity, and can efficiently transduce a wide variety of cell types from various species independent of the cell cycle to mediate long-term transgene expression without chronic toxicity. These non-integrating vectors hold tremendous potential for a variety of gene transfer and gene therapy applications. Here, we review the production technologies, applications, obstacles to clinical translation and their potential resolutions, and the future challenges and unanswered questions regarding this promising gene transfer technology.

Gene therapy with helper-dependent adenoviral vectors: current advances and future perspectives

Recombinant Adenoviral vectors represent one of the best gene transfer platforms due to their ability to efficiently transduce a wide range of quiescent and proliferating cell types from various tissues and species. The activation of an adaptive immune response against the transduced cells is one of the major drawbacks of first generation Adenovirus vectors and has been overcome by the latest generation of recombinant Adenovirus, the Helper-Dependent Adenoviral (HDAd) vectors. HDAds have innovative features including the complete absence of viral coding sequences and the ability to mediate high level transgene expression with negligible chronic toxicity. This review summarizes the many aspects of HDAd biology and structure with a major focus on in vivo gene therapy application and with an emphasis on the unsolved issues that these vectors still presents toward clinical application.

Macromolecular drug transport into the brain using targeted therapy

The brain forms a vascular barrier system comprised of the blood-brain barrier (BBB) and the blood-CSF barriers. Together they prevent the passage of a number of drugs from the bloodstream into the brain parenchyma, because their molecules are either hydrophilic, too large or both. In many disorders affecting the CNS, these barriers are physically intact, which limits the entry of large molecules with potentially important therapeutic implications. The BBB is the most relevant barrier against drug delivery to the brain as the area of the BBB is about 1000 times larger than that of the blood-CSF barrier. Moreover, the transport through the choroid plexus is directed to the ventricular system, only allowing the transported molecules to access cells near the ventricular and subarachnoid surfaces. This review outlines possible routes for targeted entry of macromolecules like polypeptides, siRNA and cDNA. In the vascular compartment, targeting molecules should interact specifically with proteins expressed exclusively by these barrier cells, and therefore prevent uptake elsewhere in the body. Preferably, the targeting molecule should be conjugated to a drug carrier that allows uptake of a defined cargo. However, evidence for transport of such targetable drug-carrier complexes through the barriers, in particular the BBB, is contentious, and is discussed with emphasis on the different attempts that have evinced transport through the BBB not only from blood-to-endothelium, but also from endothelium-to-brain.

Delivery of peptide and protein drugs over the blood-brain barrier. Prog Neurobiol. 2009;87:212-251. [PMID: 19395337 DOI: 10.1016/j.pneurobio.2008.12.002]

Peptide and protein (P/P) drugs have been identified as showing great promises for the treatment of various neurodegenerative diseases. A major challenge in this regard, however, is the delivery of P/P drugs over the blood-brain barrier (BBB). Intense research over the last 25 years has enabled a better understanding of the cellular and molecular transport mechanisms at the BBB, and several strategies for enhanced P/P drug delivery over the BBB have been developed and tested in preclinical and clinical-experimental research. Among them, technology-based approaches (comprising functionalized nanocarriers and liposomes) and pharmacological strategies (such as the use of carrier systems and chimeric peptide technology) appear to be the most promising ones. This review combines a comprehensive overview on the current understanding of the transport mechanisms at the BBB with promising selected strategies published so far that can be applied to facilitate enhanced P/P drug delivery over the BBB.

Effect of mesenchymal stem cell transplantation on the engraftment of human hematopoietic stem cells and leukemic cells in mice model. Int J Hematol. 2008;87:327-337. [PMID: 18293059 DOI: 10.1007/s12185-008-0041-3]

We investigated the effect of human bone marrow-derived mesenchymal stem cells on engraftment of human umbilical cord blood CD34+ cells and acute myelogenous leukemia cells and also assessed the homing capability of MSCs. Forty-two NOD/SCID mice were administered sublethal irradiation followed by various cell doses of intravenous UCB CD34+ cells with or without MSCs. Another 12 NOD/SCID mice were also sublethally irradiated followed by intravenous injection of AML cells with or without MSCs. In ten of these mice, MSCs were genetically modified with an adenoviral vector encoding eGFP gene for tracking purpose. Cotransplantation of UCB CD34+)cells and MSCs resulted in a significant increase in bone marrow engraftment after 6 weeks, and the engraftment promoting effect of MSCs was proportional to the dose of MSCs and obvious when low doses of UCB CD34+ cells were given. There was no effect of MSCs on AML cells engraftment. All of the ten mice transplanted with eGFP-transfected MSCs showed positive for eGFP in their major organs. These data demonstrate that MSCs promote engraftment of UCB CD34+ cells in bone marrow, but exert no effect on engraftment of AML cells, and are capable of homing to the major organs including bone marrow following intravenous infusion.

Nonviral approaches for neuronal delivery of nucleic acids

The delivery of therapeutic nucleic acids to neurons has the potential to treat neurological disease and spinal cord injury. While select viral vectors have shown promise as gene carriers to neurons, their potential as therapeutic agents is limited by their toxicity and immunogenicity, their broad tropism, and the cost of large-scale formulation. Nonviral vectors are an attractive alternative in that they offer improved safety profiles compared to viruses, are less expensive to produce, and can be targeted to specific neuronal subpopulations. However, most nonviral vectors suffer from significantly lower transfection efficiencies than neurotropic viruses, severely limiting their utility in neuron-targeted delivery applications. To realize the potential of nonviral delivery technology in neurons, vectors must be designed to overcome a series of extra- and intracellular barriers. In this article, we describe the challenges preventing successful nonviral delivery of nucleic acids to neurons and review strategies aimed at overcoming these challenges.

Protecting neurons from HIV-1 gp120-induced oxidant stress using both localized intracerebral and generalized intraventricular administration of antioxidant enzymes delivered by SV40-derived vectors

Human immunodeficiency virus-1 (HIV-1) is the most frequent cause of dementia in adults under 40. We sought to use gene delivery to protect from HIV-1-related neuron loss. Because HIV-1 envelope (Env) gp120 elicits oxidant stress and apoptosis in cultured neurons, we established reproducible parameters of Env-mediated neurotoxicity in vivo, then tested neuroprotection using gene delivery of antioxidant enzymes. We injected 100-500 ng mul(-1)gp120 stereotaxically into rat caudate-putamens (CP) and assayed brains for apoptosis by terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick end labeling (TUNEL) 6-h to 14-day post-injection. Peak apoptosis occurred 1 day after injection of 250 and 500 ng microl(-1)gp120. TUNEL-positive cells mostly expressed neuronal markers (NeuroTrace), although some expressed CD68 and so were most likely microglial cells. Finally, we compared neuroprotection from gp120-induced apoptosis provided by localized and generalized intra-central nervous system (CNS) gene delivery. Recombinant SV40 vectors carrying Cu/Zn superoxide dismutase (SOD1) or glutathione peroxidase (GPx1) were injected into the CP, where gp120 was administered 4-24 weeks later. Alternatively, we inoculated the vector into the lateral ventricle (LV), with or without prior intraperitoneal (i.p.) administration of mannitol. Intracerebral injection of SV(SOD1) or SV(GPx1) significantly protected neurons from gp120-induced apoptosis throughout the 24-week study. Intraventricular vector administration protected from gp120 neurotoxicity comparably, particularly if preceded by mannitol i.p. Thus, HIV-1 gp120 is neurotoxic in vivo, and intracerebral or intra-ventricular administration of rSV40 vectors carrying antioxidant enzymes is neuroprotective. These findings suggest the potential utility of both localized and widespread gene delivery in treating neuroAIDS and other CNS diseases characterized by excessive oxidative stress.

Systemic mannitol-induced hyperosmolality amplifies rAAV2-mediated striatal transduction to a greater extent than local co-infusion

Recombinant viral vectors derived from adeno-associated virus serotype 2 (rAAV2) have been investigated as highly effective vehicles for gene transfer to the central nervous system (CNS). Transduction with rAAV2 vectors results in long-term transgene expression in CNS neurons. Optimal injection parameters leading to efficient targeting and spread of the transgene to large neuroanatomical regions are important in molecular gene therapy studies of the CNS. In the present study, we reexamined the effects of both local and systemic administration of mannitol-induced hyperosmolality on facilitation of transgene expression and vector distribution in the CNS. Systemic intraperitoneal administration of mannitol prior to vector administration improved gene transfer to striatal neurons, increasing the total number of transduced cells by 400% and vector distribution by 200%. On the other hand, local coadministration of mannitol in the striatum increased the number of transduced striatal neurons by 25% and had little effect on transduction volume. In conclusion, we have demonstrated that systemic coadministration of mannitol significantly enhances transgene spread of rAAV2 viral delivery in the brain to a much greater degree than local coadministration.

Vascular transfer of adenovirus is augmented by nitric oxide in the rat heart

Reversible opening of the endothelial barrier remains a major obstacle when hearts are transfected via the coronary system. Our aim was to establish an experimental system permitting the continuous analysis of vascular transfer of virus in the intact heart. Isolated saline-perfused rat hearts were inverted and covered with a latex cap to collect interstitial transudate (IT) on the pericardial surface. Adenovirus (10(9) pfu/ml) was stably labeled with rhodamine fluorescent dye. Analysis of IT and coronary perfusate revealed that under baseline conditions, adenovirus in the IT reached 75% of its vascular concentration within 3 min. The nitric oxide-donors S-nitroso-N-acetyl penicillamine (SNAP) and bradykinin (BK) were the most effective substances to increase total IT volume and adenoviral interstitial concentration. Perfusion with 9% serum markedly reduced IT volume flow and delayed the SNAP/BK effect. Our findings demonstrate that SNAP and BK effectively increased coronary transfer of adenovirus suggesting that the inverted isolated heart is a suitable model to optimize vascular transfer of virus under standardized conditions.

Prospects for the treatment of stroke using gene therapy

Recent advances have demonstrated the use of gene therapy in the treatment of stroke in experimental animal models of focal ischemia, global ischemia and subarachnoid hemorrhage. Several different vectors for gene transfer have been studied including herpes simplex virus, adenovirus, adeno-associated virus and liposomes. Genetically modified cell lines (e.g., bone marrow-derived cells) have been studied for ex vivo gene therapy. The effects of gene transfer to several brain regions including the striatum, cortex, hippocampus, subarachnoid space and blood vessels are reviewed. Targets of gene therapy, such as molecular cascades after ischemia onset (Ca2+ influx, ATP loss, increased nitric oxide) and events associated with apoptosis are also reviewed, in addition to how gene transfer may be used to understand pathomechanisms underlying ischemic injury and the temporal therapeutic windows following ischemia within which protective effects of gene therapy have been achieved. The prospects for gene therapy for stroke are discussed in light of these findings and it is concluded that solutions to key technological problems will allow gene therapy to be a viable treatment modality.

Endovascular restorative neurosurgery: a novel concept for molecular and cellular therapy of the nervous system

The amalgam of molecular biology and neurosurgery offers immense promise for neurorestoration and the management of neurodegenerative deficiencies, developmental disorders, neoplasms, stroke, and trauma. This article summarizes present strategies for and impediments to gene therapy and stem cell therapy of the central nervous system and advances the concept of a potential new approach, namely endovascular restorative neurosurgery. The objectives of gene transfer to the central nervous system are efficient transfection of host cells, selective sustained expression of the transgene, and lack of toxicity or immune excitation. The requisite elements of this process are the identification of candidate diseases, the construction of vehicles for gene transfer, regulated expression, and physical delivery. In the selection of target disorders, the underlying genetic events to be overcome, as well as their spatial and temporal distributions, must be considered. These factors determine the requirements for the physical dispersal of the transgene, the duration of transgene expression, and the quantity of transgene product needed to abrogate the disease phenotype. Vehicles for conveying the transgene to the central nervous system include viral vectors (retroviruses, lentiviruses, adenoviruses, adeno-associated viruses, and herpes simplex virus), liposomes, and genetically engineered cells, including neural stem cells. Delivery of the transgene into the brain presents several challenges, including limited and potentially risky access through the cranium, sensitivity to volumetric changes, restricted diffusion, and the blood-brain barrier. Genetic or cellular therapeutic agents may be injected directly into the brain parenchyma (via stereotaxy or craniotomy), into the cerebrospinal fluid (in the ventricles or cisterns), or into the bloodstream (intravenously or intra-arterially). The advantages of the endovascular route include the potential for widespread distribution, the ability to deliver large volumes, limited perturbation of neural tissue, and the feasibility of repeated administration.

Effects of hypertonic saline, mannitol, and urea with regard to absorption and rebound filtration in cat skeletal muscle

OBJECTIVE

To study the effects of the hypertonic solutions 15% mannitol, 3% and 7.5% saline, and 30% urea at clinically relevant plasma concentrations with regard to absorption and rebound effects on tissue volume in skeletal muscle.

DESIGN

A prospective, experimental study.

SETTING

University laboratory.

SUBJECTS

Twenty-eight anesthetized cats.

INTERVENTIONS

The study was performed on an autoperfused and denervated cat calf muscle placed in a fluid-filled plethysmograph. Muscle volume changes and capillary filtration coefficient (reflecting capillary fluid conductivity) were measured before, during, and after intra-arterial infusion (4 mL/hr) of the hypertonic solutions. Mannitol and 3% saline have the same osmolality and were compared specifically in an attempt to distinguish osmotic effects from those specific to the compound.

MEASUREMENTS AND MAIN RESULTS

All solutions reduced muscle volume during the infusion (p < .05). The maximum volume reduction persisted after 2 hrs of infusion for 3% and 7.5% saline, whereas there was a tendency for volume recovery during the urea infusion and a complete recovery back to control for mannitol. After discontinuation of the infusions, the muscle volume increased for all four solutions, stabilizing at the initial control for 3% and 7.5% saline, whereas it increased to levels above control for mannitol and urea (p < .05). Capillary filtration coefficient was increased by hypertonic saline (p < .05) but was unaffected by mannitol and urea.

CONCLUSIONS

The effectiveness of a hypertonic solution in reducing tissue volume and its tendency to cause a rebound volume increase depends not only on the osmolality of the solution. Hypertonic saline may in the long run be superior to mannitol and urea to increase plasma volume or decrease tissue volume of an organ, because it lacks rebound effects. Alterations in capillary filtration coefficient (fluid conductivity) may reflect volume changes of the capillary endothelial cell and thereby differences in cell membrane permeability for the hypertonic solutions, also consistent with the obtained differences in tissue volume effects.

Adenovirus-mediated gene delivery to cells of the magnocellular hypothalamo-neurohypophyseal system

The objective of the present study was to define the optimum conditions for using replication-defective adenovirus (Ad) to transfer the gene for the green fluorescent protein (GFP) to the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei and cells of the neurohypophysis (NH). As indicated by characterizing cell survival over 15 days in culture and in electrophysiological whole cell patch-clamp studies, viral concentrations up to 2 x 10(7) pfu/coverslip did not affect viability of transfected PVN and NH cultured cells from preweanling rats. At 2 x 10(7) pfu, GFP gene expression was higher (40% of GFP-positive cells) and more sustained (up to 15 days). Using a stereotaxic approach in adult rats, we were able to directly transduce the PVN, SON, and NH and visualize gene expression in coronal brain slices and in the pituitary 4 days after injection of Ad. In animals receiving NH injections of Ad, the virus was retrogradely transported to PVN and SON neurons as indicated by the appearance of GFP-positive neurons in cultures of dissociated cells from those brain nuclei and by polymerase chain reaction and Western blot analyses of PVN and SON tissues. Adenoviral concentrations of up to 8 x 10(6) pfu injected into the NH did not affect cell viability and did not cause inflammatory responses. Adenoviral injection into the pituitary enabled the selective delivery of genes to the soma of magnocellular neurons. The experimental approaches described here provide potentially useful strategies for the treatment of disordered expression of the hormones vasopressin or oxytocin.

Combined injection of rAAV with mannitol enhances gene expression in the rat brain

Recombinant adeno-associated viruses (rAAV) are highly efficient vectors for gene transfer into the central nervous system (CNS). However, a major hurdle for gene delivery to the mammalian brain is to achieve high-level transduction in target cells beyond the immediate injection site. Therefore, in addition to improvements in expression cassettes and viral titers, optimal injection parameters need to be defined. Here, we show that previous studies of somatic cell gene transfer to the mammalian brain have used suboptimal injection parameters, with even the lowest reported perfusion rates still excessively fast. Moreover, we evaluated the effect of local administration of mannitol to further enhance transgene expression and vector spread. Ultraslow microperfusion of rAAV, i.e., <33 nl/min, resulted in significantly higher gene expression and less injury of surrounding tissue than the previously reported rates of 100 nl/min or faster. Co-infusion of mannitol facilitated gene transfer to neurons, increasing both the total number and the distribution of transduced cells by 200-300%. Gene transfer studies in the CNS using rAAV should use very slow infusion rates and combined injection with mannitol to maximize transduction efficiency and spread.

Recombinant human adenovirus: targeting to the human transferrin receptor improves gene transfer to brain microcapillary endothelium

Some inborn errors of metabolism due to deficiencies of soluble lysosomal enzymes cause global neurodegenerative disease. Representative examples include the infantile and late infantile forms of the ceroid lipofuscinoses (CLN1 or CLN2 deficiency, respectively) and mucopolysaccharidoses type VII (MPS VII), a deficiency of beta-glucuronidase. Treatment of the central nervous system component of these disorders will require widespread protein or enzyme replacement, either through dissemination of the protein or through dissemination of a gene encoding it. We hypothesize that transduction of brain microcapillary endothelium (BME) with recombinant viral vectors, with secretion of enzyme product basolaterally, could allow for widespread enzyme dissemination. To achieve this, viruses should be modified to target the BME. This requires (i) identification of a BME-resident target receptor, (ii) identification of motifs targeted to that molecule, (iii) the construction of modified viruses to allow for binding to the target receptor, and (iv) demonstrated transduction of receptor-expressing cells. In proof of principal experiments, we chose the human transferrin receptor (hTfR), a molecule found at high density on human BME. A nonamer phage display library was panned for motifs which could bind hTfR. Forty-three clones were sequenced, most of which contained an AKxxK/R, KxKxPK/R, or KxK motif. Ten peptides representative of the three motifs were cloned into the HI loop of adenovirus type 5 fiber. All motifs tested retained their ability to trimerize and bind transferrin receptor, and seven allowed for recombinant adenovirus production. Importantly, the fiber-modified viruses facilitated increased gene transfer (2- to 34-fold) to hTfR expressing cell lines and human brain microcapillary endothelia expressing high levels of endogenous receptor. Our data indicate that adenoviruses can be modified in the HI loop for expanded tropism to the hTfR.

Peptide-mediated transcytosis of phage display vectors in MDCK cells

Delivery of therapeutic macromolecules and gene vectors to certain tissues is hampered by endothelial or epithelial barriers. We show here that the transport of phage particles across epithelial cells can be facilitated by peptide ligands selected from a phage library of random peptides. Using MDCK cells, we identified a polycationic peptide sequence, RYRGDLGRR, containing a putative integrin-binding (RGD) motif that enhanced basal-to-apical transcytosis of peptide-bearing phage 1000- to 10,000-fold compared with phage with no peptide insert. Both the synthetic peptide RYRGDLGRR and the integrin-binding peptide GRGDSP inhibited phage transcytosis suggesting the involvement of integrins. Confocal immunofluorescence microscopy showed that following internalization at the basal cell surface, phage particles were delivered to the apical cytoplasm and released at the apical cell surface. These data suggest the feasibility of using short peptides for targeting transcytotic pathways and facilitating delivery of macromolecules across cellular barriers.

Distribution of AAV-TK following intracranial convection-enhanced delivery into rats

Adeno-associated virus (AAV)-based vectors are being tested in animal models as viable treatments for glioma and neurodegenerative disease and could potentially be employed to target a variety of central nervous system disorders. The relationship between dose of injected vector and its resulting distribution in brain tissue has not been previously reported nor has the most efficient method of delivery been determined. Here we report that convection-enhanced delivery (CED) of 2.5 x 10(8), 2.5 x 10(9), or 2.5 x 10(10) particles of AAV-thymidine kinase (AAV-TK) into rat brain revealed a clear dose response. In the high-dose group, a volume of 300 mm3 of brain tissue was partially transduced. Results showed that infusion pump and subcutaneous osmotic pumps were both capable of delivering vector via CED and that total particle number was the most important determining factor in obtaining efficient expression. Results further showed differences in histopathology between the delivery groups. While administration of vector using infusion pump had relatively benign effects, the use of osmotic pumps resulted in notable toxicity to the surrounding brain tissue. To determine tissue distribution of vector following intracranial delivery, PCR analysis was performed on tissues from rats that received high doses of AAV-TK. Three weeks following CED, vector could be detected in both hemispheres of the brain, spinal cord, spleen, and kidney.

Adenoviral gene transfer of basic fibroblast growth factor promotes angiogenesis in rat brain

Cerebral ischemic disease often causes morbidity and mortality, while the induction of new blood vessels is expected to provide a therapeutic effect in this occlusive cerebrovascular disease. In this study, we utilized two replication-deficient adenoviral vectors containing cDNA from basic fibroblast growth factor (bFGF), a well-known angiogenic factor, and examined whether biological angiogenic activity of adenovirally gene-transferred bFGF could be observed in the rat brain. One vector contained native cDNA from bFGF without the secretory signal sequence and the other contained the same cDNA fused with an interleukin-2 secretory signal sequence. After ventricular administration of these viral vectors, gene-transferred cells demonstrated a high immunoreactivity against the anti-bFGF antibody and a remarkably high concentration of bFGF was detected in the cerebrospinal fluid. A semiquantitative analysis of angiogenic activity revealed that bFGF gene transfer induced angiogenesis in normal rat brains, with a more pronounced angiogenic effect seen with the vector of a secreted form than with the vector without a secretory signal sequence. These results suggest that bFGF gene transfer using these adenoviral vectors might be useful for the treatment of ischemic cerebrovascular disease.

Hypertonic mannitol loading of NF-kappaB transcription factor decoys in human brain microvascular endothelial cells blocks upregulation of ICAM-1

BACKGROUND AND PURPOSE

An acute inflammatory response exacerbates tissue injury during acute ischemic stroke. The transcription factor nuclear factor (NF)-kappaB plays a key role in endothelial cell activation and the inflammatory response. Targeted genetic disruption of NF-kappaB activation in cerebral endothelial cells may be protective in stroke. We determined whether a NF-kappaB transcription factor decoy (TFD) could block intercellular adhesion molecule (ICAM)-1 upregulation, an indicator of endothelial cell activation.

METHODS

We modeled ischemia-reperfusion in vitro by exposing cultured human brain microvascular endothelial cells (HBMEC) to tumor necrosis factor (TNF)-alpha and conditions of hypoxia-reoxygenation (H/R). Mannitol was used to load phosphothiorated oligonucleotides containing 3 copies of the kappaB binding sequences (TFDs) into cultured HBMEC. An NF-kappaB TFD, a mutated NF-kappaB TFD, and a scrambled TFD were studied for their effect on ICAM-1 mRNA levels and surface ICAM-1 by ELISA.

RESULTS

Hyperosmolar loading with mannitol permitted rapid transfection of TFD into endothelial cell nuclei. The NF-kappaB TFD but not the mutated or scrambled TFD competed with a kappaB sequence for binding to nuclear extracts from HBMEC exposed to TNF-alpha. The NF-kappaB TFD blocked the TNF-alpha-induced and H/R-induced increase in ICAM-1 mRNA levels and the upregulation of surface ICAM-1.

CONCLUSIONS

Mannitol delivers phosphothiorated oligonucleotides into cultured HBMEC. An NF-kappaB decoy blocks both TNF-alpha-induced and H/R-induced ICAM-1 upregulation in HBMEC. Targeted genetic disruption of endothelial NF-kappaB activation may be of benefit in acute ischemic stroke.

In situ use of suicide genes for therapy of brain tumours

Suicide gene therapy represents a new therapeutic approach to the treatment of patients with otherwise incurable malignant brain tumours. This strategy involves the introduction of a gene that renders the tumour cell susceptible to an otherwise nontoxic prodrug. The most often used genetic prodrug activation system is the herpes simplex virus thymidine kinase/ganciclovir (HSV-tk/GCV) paradigm. An important aspect of this system is the 'bystander effect', the extension of cytotoxic effects to untransduced cells. For gene delivery, retroviral, adenoviral vectors and HSV-1 mutants have been used. Clinical studies have revealed that the HSV-tk/GCV approach is safe, but also that responses are observed only in very small brain tumours, indicating insufficient vector distribution and very low transduction efficiency with replication-deficient vector systems. To improve treatment efficacy, the use of replication-competent oncolytic vectors in combination with new or improved prodrug-suicide gene systems as a part of a multimodal approach is warranted. In the context of replication-competent vectors, suicide genes might also be used as fail-safe genes in the case of runaway infection.

Systemic hyperosmolality improves beta-glucuronidase distribution and pathology in murine MPS VII brain following intraventricular gene transfer

Mucopolysaccharidosis VII, a classical lysosomal storage disease, is caused by deficiency of the enzyme beta-glucuronidase. Central nervous system (CNS) manifestations are severe with accumulations of storage vacuoles in all cell types. Intraventricular gene transfer can lead to transduction of the ependyma, with production and secretion of beta-glucuronidase into the cerebral spinal fluid and underlying cortex resulting in reversal of disease pathology restricted to the periventricular areas. We tested if systemic hyperosmolality would increase the distribution of beta-glucuronidase in brain parenchyma after intraventricular virus injection. Mice were administered mannitol, intraperitoneally, 20 days after gene transfer and 1 day prior to sacrifice. Mannitol-induced systemic hyperosmolality caused a marked penetration of beta-glucuronidase into the brain parenchyma. If mannitol was administered at the time of the intraventricular injection of virus, there was penetration of vector across the ependymal cell layer, with infection of cells in the subependymal region. This also resulted in increased beta-glucuronidase activity throughout the brain. Sections of brains from beta-glucuronidase-deficient mice showed correction of cellular pathology in the subependymal region plus cortical structures away from the ventricular wall. These data indicate that virus-mediated gene transfer to the brain via the ventricles, coupled with systemic mannitol administration, can lead to extensive CNS distribution of beta-glucuronidase with concomitant correction of the storage defect. Our findings have positive therapeutic implications for the treatment of CNS disorders with gene transfer vectors and recombinant proteins.

Adenovirus-mediated kallikrein gene delivery reduces aortic thickening and stroke-induced death rate in Dahl salt-sensitive rats

BACKGROUND AND PURPOSE

Kallikrein gene delivery has been shown to attenuate hypertension, cardiac hypertrophy, and renal injury in hypertensive animal models. The aim of this study was to investigate the potential protective effects of kallikrein gene delivery in salt-induced stroke and cerebrovascular disorders.

METHODS

Adenovirus harboring the human tissue kallikrein gene (AdCMV-cHK) was delivered intravenously into Dahl salt-sensitive (DS) rats after 4 weeks of high salt loading, and blood pressure was monitored weekly for 9 weeks.

RESULTS

A single injection of AdCMV-cHK caused a significant reduction of systolic blood pressure compared with that in control rats, with or without an injection of adenovirus carrying the LacZ (control) gene (AdCMV-LacZ). A maximal blood pressure reduction of 21 mm Hg was observed 2 weeks after gene delivery. The stroke mortality rate of DS rats (AdCMV-LacZ group versus the AdCMV-cHK group) was significantly decreased: 38% versus 9% at 3 weeks and 54% versus 27% at 5 weeks after gene delivery. Kallikrein gene delivery significantly attenuated salt-induced aortic hypertrophy, as evidenced by reduced thickness of the aortic wall. Recombinant human tissue kallikrein was detected in rat serum and urine after gene transfer. Kinin-releasing activities in the brain as well as urinary kinin and cGMP levels were significantly increased in rats receiving the kallikrein gene.

CONCLUSIONS

This is the first study to demonstrate the protective effect of kallikrein gene delivery in reducing salt-induced stroke mortality and vascular dysfunction.

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.

Blood-brain barrier permeability to small and large molecules

The objective of this article is to provide the reader with an update of some of the BBB research highlights which have occurred in recent times, and to review the impact and contributions of immunogold electron microscopic studies on our understanding of the brain capillary endothelium. Glucose and monocarboxylic acids are two small molecules which this review will focus upon; and advances in immunogold characterization of the GLUT1 glucose transporter and the MCT1 and MCT2 monocarboxylic acid nutrient transporters will be discussed. Human serum albumin is chosen as a representative large molecule, and it has recently been shown that immunogold identification of this protein can serve as an indicator of compromised BBB function in a variety of pathophysiological conditions.

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.

Atrial natriuretic peptide gene delivery reduces stroke-induced mortality rate in Dahl salt-sensitive rats

Atrial natriuretic peptide (ANP) is a powerful hormone with hypotensive, natriuretic, diuretic, and many other beneficial effects. Direct infusion of ANP in therapeutics has limited success because of its short half-life in the circulation. Our previous studies have shown that ANP gene delivery attenuates hypertension, cardiac hypertrophy, and renal injury in Dahl salt-sensitive (Dahl-SS) rats. To investigate the potential therapeutic value of ANP gene delivery on salt-induced stroke and cerebrovascular disorders, an adenovirus harboring the human ANP gene (Ad.RSV-cANP) was injected into Dahl-SS rats on a high salt diet. A single intravenous injection of the ANP gene caused a significant reduction of blood pressure that lasted for more than 3 weeks. A maximal blood pressure reduction of 28 mm Hg was observed 2 weeks after gene delivery as compared with that of control rats injected with adenovirus harboring the LacZ gene under the control of the Rous sarcoma virus promoter (Ad.RSV-LacZ). Immunoreactive human ANP can be detected in the heart, lung, kidney, and brain of rats after gene delivery. The stroke mortality rate of Dahl-SS rats was significantly decreased (from 54% to 17% at 3 weeks and from 70% to 50% at 4 weeks after ANP gene delivery as compared with rats injected with control virus). ANP gene delivery also significantly attenuates salt-induced aortic hypertrophy as evidenced by reduced thickness of the aortic wall. This is the first study to demonstrate the potential of ANP gene delivery in reducing the mortality rate caused by cerebrovascular disorders and stroke. Successful application of this technology may have potential value in treating individuals with a high risk of stroke.

Mannitol at clinical concentrations activates multiple signaling pathways and induces apoptosis in endothelial cells

BACKGROUND AND PURPOSE

Hyperosmotic mannitol therapy is widely used in the clinical setting for acute and subacute reduction in brain edema, to decrease muscle damage in compartment syndrome, and to improve renal perfusion. Though beneficial rheological effects commonly are attributed to mannitol, its direct effects on endothelial cells are poorly understood.

METHODS

We studied the effect of hypertonic and hypotonic stress on bovine aortic endothelial (BAE) cells, using mannitol, urea, and sodium chloride and medium dilution in vitro.

RESULTS

Exposure to incremental osmolar concentrations of 300 mOsm of each osmotic agent increased apoptosis in BAE cells (mannitol congruent withNaCl>urea). Induced programmed cell death was detected by DAPI staining of intact cell nuclei, and by TUNEL and DNA fragmentation ladder assays. Mannitol-induced apoptosis exhibited dose dependence (42% of cells at 300 mOsm [P<0.0001] compared with 1.2% of control cells) and was also observed in bovine smooth muscle cells. Mannitol-induced apoptosis was attenuated approximately 50% in the presence of cycloheximide or actinomycin D. Hypertonic mannitol and NaCl, but not urea, increased tyrosine phosphorylation of the focal adhesion contact-associated proteins paxillin and FAK. Hypotonic medium, which did not lead to apoptosis, increased protein tyrosine phosphorylation of FAK but not of paxillin. Addition of mannitol or NaCl also produced sustained increases in c-Jun NH2-terminal kinase (JNK) activity. In addition, hypertonic mannitol increased intracellular free [Ca2+] in a dose-dependent manner. Chelation of intracellular Ca2+ with quin2-AM (10 micromol/L) inhibited mannitol-induced apoptosis approximately 50%, as to a lesser extent did inhibition of tyrosine kinase activity with herbimycin (1 micromol/L).

CONCLUSIONS

We have shown that hypertonic mannitol exposure induces endothelial cell apoptosis, accompanied by activation of tyrosine and stress kinases, phosphorylation of FAK and paxillin, and elevation of intracellular free [Ca2+]. The apoptosis is attenuated by inhibition of transcription or translation, by inhibition of tyrosine kinases, or by intracellular Ca2+ buffering. These data suggest that clinical use of the osmotic diuretic mannitol may exert direct deleterious effects on vascular endothelium.

Replication-deficient adenovirus vector transfer of gfp reporter gene into supraoptic nucleus and subfornical organ neurons

The present studies used defined cells of the subfornical organ (SFO) and supraoptic nuclei (SON) as model systems to demonstrate the efficacy of replication-deficient adenovirus (Ad) encoding green fluorescent protein (GFP) for gene transfer. The studies investigated the effects of both direct transfection of the SON and indirect transfection (i.e., via retrograde transport) of SFO neurons. The SON of rats were injected with Ad (2 x 10(6) pfu) and sacrificed 1-7 days later for cell culture of the SON and of the SFO. In the SON, GFP fluorescence was visualized in both neuronal and nonneuronal cells while only neurons in the SFO expressed GFP. Successful in vitro transfection of cultured cells from the SON and SFO was also achieved with Ad (2 x 10(6) to 2 x 10(8) pfu). The expression of GFP in in vitro transfected cells was higher in nonneuronal (approximately 28% in SON and SFO) than neuronal (approximately 4% in SON and 10% in SFO) cells. The expression of GFP was time and viral concentration related. No apparent alterations in cellular morphology of transfected cells were detected and electrophysiological characterization of transfected cells was similar between GFP-expressing and nonexpressing neurons. We conclude that (1) GFP is an effective marker for gene transfer in living SON and SFO cells, (2) Ad infects both neuronal and nonneuronal cells, (3) Ad is taken up by axonal projections from the SON and retrogradely transported to the SFO where it is expressed at detectable levels, and (4) Ad does not adversely affect neuronal viability. These results demonstrate the feasibility of using adenoviral vectors to deliver genes to the SFO-SON axis.

Extensive beta-glucuronidase activity in murine central nervous system after adenovirus-mediated gene transfer to brain

Mucopolysaccharidosis type VII (MPS VII), caused by beta-glucuronidase deficiency, is a classic lysosomal storage disease. In the central nervous system (CNS), there is widespread pathology with distention of vacuoles in neurons and glia. An approach to therapy for MPS VII would require extensive delivery of enzyme to the CNS and subsequent uptake by the affected cells. In this study we show that intrastriatal injection of recombinant adenovirus encoding beta-glucuronidase (Ad betagluc) to MPS VII or wild-type mice results in focal, intense beta-glucuronidase mRNA expression near the injection site. Further, histochemical staining for enzyme activity showed that beta-glucuronidase activity extended well beyond transduced cells. Activity was detected throughout the ipsilateral striatum as well as in the corpus callosum, ventricles, and bilateral neocortex. Similarly, after injection into the right lateral ventricle or cisterna magna, enzyme activity was present in the ependymal cells of the ventricles, in the subarachnoid spaces, and also in the underlying cortex (150-500 microm from ependyma). The distribution of enzyme was most extensive 21 days after gene transfer to normal mouse brain, with more than 50% of the hemisphere positive for beta-glucuronidase activity. Eighty-four days after adenovirus injection a substantial level of enzyme expression remained (>40% of hemisphere positive for beta-glucuronidase activity). Histological sections from striatum of beta-glucuronidase-deficient mice injected with Ad betagluc showed a marked reduction in the number of distended vacuoles in both neurons and glia, as compared with uninjected striatum. Importantly, correction was noted in both hemispheres. Our finding that a relatively small number of transduced cells produce enzyme that reaches a large proportion of the CNS has favorable implications in developing direct gene transfer therapies for lysosomal storage disorders.

Towards gene therapy for the central nervous system

Gene therapy has generated enormous scientific, medical and public interest over the last decade. Clinical trials involving approximately 2000 patients worldwide have targeted simple genetic diseases such as cystic fibrosis, muscular dystrophy, adenosine deaminase deficiency, Gaucher's disease and familial hypercholesterolemia, as well as complex acquired diseases such as cancer and AIDS. The central nervous system is a new and particularly exciting target for gene therapy because its unique properties prevent the successful treatment of many neurological disorders by conventional means. This review discusses the potential applications of in vivo gene therapy to neurological disorders that have the greatest potential for genetic treatments.