Efficient therapeutic gene expression in cultured rat hippocampal neurons mediated by human foamy virus vectors: a potential for the treatment of neurological diseases

Challenges and prospects in geriatric epilepsy treatment: the role of the blood-brain barrier in pharmacotherapy and drug delivery

The blood-brain barrier (BBB) is pivotal in maintaining neuronal physiology within the brain. This review delves into the alterations of the BBB specifically in the context of geriatric epilepsy. We examine how age-related changes in the BBB contribute to the pathogenesis of epilepsy in the elderly and present significant challenges in pharmacotherapy. Subsequently, we evaluate recent advancements in drug delivery methods targeting the BBB, as well as alternative approaches that could bypass the BBB's restrictive nature. We particularly highlight the use of neurotropic viruses and various synthetic nanoparticles that have been investigated for delivering a range of antiepileptic drugs. Additionally, the advantage and limitation of these diverse delivery methods are discussed. Finally, we analyze the potential efficacy of different drug delivery approaches in the treatment of geriatric epilepsy, aiming to provide insights into more effective management of this condition in the elderly population.

Gene Therapy Repairs for the Epileptic Brain: Potential for Treatment and Future Directions

Epilepsy is a syndrome specified by frequent seizures and is one of the most prevalent neurological conditions, and that one-third of people of epilepsy are resistant to available drugs. Surgery is supposed to be the main treatment for the remedy of multiple drug-resistant epilepsy, but it is a drastic procedure. Advancement in genomic technologies indicates that gene therapy can make such surgery unnecessary. The considerable number of new studies show the significance of mutation in mammalian target of rapamycin pathway, NMDA receptors, GABA receptors, potassium channels and G-protein coupled receptors. Illustration of the meticulous drug in epilepsy targeting new expression of mutations in SCN8A, GRIN2A, GRIN2D and KCNT1 are conferred. Various methods are utilized to express a gene in a precise area of the brain; Transplantation of cells in an ex vivo approach (fetal cells, fibroblasts, immortalized cells), nonviral vector delivery and viral vector delivery like retrovirus, herpes simplex virus adenovirus and adeno-related virus. Gene therapy has thus been explored to generate anti-epileptogenic, anti-seizure and disease-modifying effects. Specific targeting of the epileptogenic region is facilitated by gene therapy, hence sparing the adjacent healthy tissue and decreasing the adverse effects that frequently go hand in hand with antiepileptic medication.

Gene therapy for neuropathic pain using dorsal root ganglion-targeted helper-dependent adenoviral vectors with GAD67 expression

INTRODUCTION

Currently available medications for neuropathic pain are of limited efficacy. Moreover, they are administered systemically and are associated with significant side effects. Ideally, one can circumvent systemic side effects if such treatment can be administered by delivery of the therapeutic agent directly to the diseased neurons. Towards this end, we previously reported the production of a recombinant helper-dependent adenovirus (HDAd) armed with a tissue-specific homing peptide to deliver transgenes targeting sensory neurons with high efficacy.

OBJECTIVES

To develop an effective gene therapy for neuropathic pain by producing a dorsal root ganglion (DRG)-targeted HDAd vector that specifically expresses glutamic acid decarboxylase (GAD) 67 (HDAd-DRG-GAD67).

METHODS

We produced spinal nerve transection (SNT) mice as a neuropathic pain model and delivered HDAd-DRG-GAD67 by injection into spinal nerve or intrathecally to these animals. We evaluated the therapeutic efficacy by measuring ion channel gene expression and quantifying mechanical allodynia, a representative symptom of neuropathic pain, in treated animals.

RESULTS

Glutamic acid decarboxylase expression by HDAd-DRG-GAD67 reduced allodynia significantly in SNT mice. In addition, HDAd-DRG-GAD67 had a much greater transduction efficacy and expressed the therapeutic gene for a much longer time and at a lower dose of viral particles than wild-type HDAd. We found that SNT induced the upregulation of Cav3.2 mRNA in the DRG and GAD67 overexpression suppressed the elevation. Furthermore, the HDAd-DRG-GAD67-induced allodynia amelioration occurred even when we delayed intrathecal delivery of the therapeutic vector to day 7 after SNT.

CONCLUSION

HDAd-mediated DRG-targeted gene therapy delivering GAD67 is an efficacious treatment for neuropathic pain in SNT mice.

Gene therapy for chronic neuropathic pain: how does it work and where do we stand today?

OBJECTIVES

Chronic neuropathic pain has been an enigma to physicians and researchers for decades. A better understanding of its pathophysiology has given us more insight into its various mechanisms and possible treatment options. We now have an understanding of the role of various ionic channels, biologically active molecules involved in pain, and also the intricate pain pathways where possible interventions might lead to substantial pain relief. The recent research on laboratory animals using virus-based vectors for gene transfer at targeted sites is very promising and may lead to additional human clinical trials. However, one needs to be aware that this "novel" approach is still in its infancy and that many of its details need to be further elucidated. The purpose of this article is to thoroughly review the current available literature and analyze the deficiencies in our current knowledge.

DESIGN

Literature review.

METHODS

After an extensive online literature search, a total of 133 articles were selected to synthesize a comprehensive review about chronic neuropathic pain and gene therapy in order to understand the concepts and mechanisms.

RESULTS

Most of the studies have shown benefits of gene therapy in animal models, and recently, phase 1 human trials using herpes simplex virus vector have started for intractable cancer pain.

CONCLUSION

Although animal data have shown safety and efficacy, and initial human trials have been promising, additional studies in humans are required to more completely understand the actual benefits and risks of using gene therapy for the treatment of chronic neuropathic pain.

Cell and gene therapies for refractory epilepsy

Despite recent advances in the development of antiepileptic drugs, refractory epilepsy remains a major clinical problem affecting up to 35% of patients with partial epilepsy. Currently, there are few therapies that affect the underlying disease process. Therefore, novel therapeutic concepts are urgently needed. The recent development of experimental cell and gene therapies may offer several advantages compared to conventional systemic pharmacotherapy: (i) Specificity to underlying pathogenetic mechanisms by rational design; (ii) specificity to epileptogenic networks by focal delivery; and (iii) avoidance of side effects. A number of naturally occurring brain substances, such as GABA, adenosine, and the neuropeptides galanin and neuropeptide Y, may function as endogenous anticonvulsants and, in addition, may interact with the process of epileptogenesis. Unfortunately, the systemic application of these compounds is compromised by limited bioavailability, poor penetration of the blood-brain barrier, or the widespread systemic distribution of their respective receptors. Therefore, in recent years a new field of cell and gene-based neuropharmacology has emerged, aimed at either delivering endogenous anticonvulsant compounds by focal intracerebral transplantation of bioengineered cells (ex vivo gene therapy), or by inducing epileptogenic brain areas to produce these compounds in situ (in vivo gene therapy). In this review, recent efforts to develop GABA-, adenosine-, galanin-, and neuropeptide Y- based cell and gene therapies are discussed. The neurochemical rationales for using these compounds are discussed, the advantages of focal applications are highlighted and preclinical cell transplantation and gene therapy studies are critically evaluated. Although many promising data have been generated recently, potential problems, such as long-term therapeutic efficacy, long-term safety, and efficacy in clinically relevant animal models, need to be addressed before clinical applications can be contemplated.

Foamy virus as a gene transfer vector to the central nervous system

Engineered foamy virus (FV) vectors have been lauded for their superior safety profiles and stable integration patterns compared to their gammaretroviral counterparts. The drawback has been the belief that FV incorporation is cell cycle-dependent, thereby limiting its utility in post-mitotic tissues such as the central nervous system. In this brief communication, we challenged this theory by examining FV in vivo. We injected equal titers of FV and lentivirus (LV) into the adult rat brain and found that at 1 week, FV transduced a significantly greater volume of bromodeoxyuridine (BrdU)-negative brain parenchyma than did LV. By 8 weeks, however, the volume of transduced tissue was greatly reduced--comparable to LV-and restricted to BrdU+. Taken together, these data implicate a role for FV in short-term gene delivery strategies to the CNS.

Gene therapy in epilepsy

Results from animal models suggest gene therapy is a promising new approach for the treatment of epilepsy. Several candidate genes such as neuropeptide Y and galanin have been demonstrated in preclinical studies to have a positive effect on seizure activity. For a successful gene therapy-based treatment, efficient delivery of a transgene to target neurons is also essential. To this end, advances have been made in the areas of cell transplantation and in the development of recombinant viral vectors for gene delivery. Recombinant adeno-associated viral (rAAV) vectors in particular show promise for gene therapy of neurological disorders due to their neuronal tropism, lack of toxicity, and stable persistence in neurons, which results in robust, long-term expression of the transgene. rAAV vectors have been recently used in phase I clinical trials of Parkinson's disease with an excellent safety profile. Prior to commencement of phase I trials for gene therapy of epilepsy, further preclinical studies are ongoing including evaluation of the therapeutic benefit in chronic models of epileptogenesis, as well as assessment of safety in toxicological studies.

A novel human foamy virus mediated gene transfer of GAD67 reduces neuropathic pain following spinal cord injury

Neuropathic pain is a long-lasting clinical problem that is often refractory to medical management. Gene transfer of specific genes for therapeutic benefit offers a novel approach to the treatment of neuropathic pain. In this study, we tested whether the transfer of the glutamic acid decarboxylase (GAD) gene to dorsal root ganglion (DRG) cells would attenuate below-injury level central neuropathic pain after spinal cord injury (SCI) by using a novel human foamy virus (HFV) vector to achieve release of gamma-aminobutyric acid (GABA). Subcutaneous inoculation of a replication-defective HFV vector, which expresses GAD (vector rdvGAD67) for 7days after T13 spinal cord hemisection, reversed mechanical allodynia and thermal hyperalgesia evoked by SCI. The antiallodynic effect lasted 6 weeks and was reestablished by reinoculation. We also found that subcutaneous inoculation of rdvGAD67 resulted in enhanced production of GAD and tonical GABA release from transduced DRG neurons. These results suggest that HFV-mediated gene transfer to DRG could be employed to treat below-injury level central neuropathic pain after incomplete SCI.

Recombinant human foamy virus, a novel vector for neurological disorders gene therapy, drives production of GAD in cultured astrocytes

Human foamy virus (HFV), with its nonpathogenic nature and several unique features for gene transfer, is a promising vector system for neurological disorders gene therapy. The question of whether HFV vectors can be developed for the expression of therapeutic genes in primary astrocytes of the brain may be of interest. First, efficient expression for foreign genes, which is critical for the potentials of HFV-derived vector in gene therapy, was successfully demonstrated in rat-cultured astrocytes by the enhanced green fluorescent protein (EGFP) transduction through an HFV vector bearing an EGFP expression cassette. Second, HFV vectors containing human glutamic acid decarboxylase (GAD) complementary DNA, which encodes an inhibitory neurotransmitter gamma-aminobutyric acid (GABA)-producing enzyme, were used to examine the function of GAD on GABA synthesis in cultured astrocytes. We found that the transduction of GAD vector resulted in isoform-specific expression of GAD, synthesis of a significant amount of GABA and tonical GABA release, and behavioral recovery in rat Parkinson's disease (PD) models. These results suggested that HFV vector had the ability to transduce astrocytes and HFV vector-derived GAD expression in astrocytes provided a potential strategy for the treatment of neurological disorders associated with hyperexcitable or diminished inhibitory activity.