Gene therapy for Parkinson's disease using recombinant adeno-associated viral vectors

Implications of Gene Therapy in Dentistry and Periodontics: A Narrative Review

The relentless march of technological progress entails constant evolution and adaptation. A concerted effort is underway in medical research to unravel various diseases' cellular and molecular underpinnings. The traditional approaches to disease treatment often fall short of delivering entirely satisfactory outcomes, which has prompted a shifting spotlight on gene therapy as a versatile solution for many inherited and acquired disorders. Genes, intricate sequences of genetic code, are the complicated blueprints dictating the production of essential proteins within the human body. Remarkably, each individual's genetic makeup is uniquely distinct, with variations in these genetic sequences serving as the bedrock of our diversity. Gene therapy represents an innovative medical strategy that harnesses the power of genes themselves to function as therapeutic agents. It serves as a conduit through which defective genes are either substituted or mended with the introduction of remedial genetic material. This groundbreaking method can tackle various illnesses, from conditions originating from single-gene abnormalities to intricate disorders influenced by multiple genes. In dentistry and periodontics, gene therapy finds a promising array of applications. It contributes significantly to managing salivary gland disorders, autoimmune diseases, and the regeneration of damaged bone tissue, as well as addressing cancerous and precancerous conditions. Moreover, the possibilities extend into DNA vaccination and broader areas of oral health. The advent of gene therapy in dentistry represents a new era of significant progress, offering substantial advancements in the management of periodontal disease and the reconstruction of the dental alveolar apparatus. The aim of this narrative review is to provide a comprehensive overview of the landscape of gene therapy investigations in these disciplines, shedding light on its potential implications for oral health and treatment. With its potential to rectify the genetic underpinnings of various conditions, gene therapy offers a novel frontier in healthcare that continually shapes the landscape of medicine and holds the promise of more effective and personalised treatments.

Gene therapy in periodontics

GENES are made of DNA - the code of life. They are made up of two types of base pair from different number of hydrogen bonds AT, GC which can be turned into instruction. Everyone inherits genes from their parents and passes them on in turn to their children. Every person's genes are different, and the changes in sequence determine the inherited differences between each of us. Some changes, usually in a single gene, may cause serious diseases. Gene therapy is ‘the use of genes as medicine’. It involves the transfer of a therapeutic or working gene copy into specific cells of an individual in order to repair a faulty gene copy. Thus it may be used to replace a faulty gene, or to introduce a new gene whose function is to cure or to favorably modify the clinical course of a condition. It has a promising era in the field of periodontics. Gene therapy has been used as a mode of tissue engineering in periodontics. The tissue engineering approach reconstructs the natural target tissue by combining four elements namely: Scaffold, signaling molecules, cells and blood supply and thus can help in the reconstruction of damaged periodontium including cementum, gingival, periodontal ligament and bone.

A phase I study of aromatic L-amino acid decarboxylase gene therapy for Parkinson's disease

Gene transfer of dopamine-synthesizing enzymes into the striatal neurons has led to behavioral recovery in animal models of Parkinson's disease (PD). We evaluated the safety, tolerability, and potential efficacy of adeno-associated virus (AAV) vector-mediated gene delivery of aromatic L-amino acid decarboxylase (AADC) into the putamen of PD patients. Six PD patients were evaluated at baseline and at 6 months, using multiple measures, including the Unified Parkinson's Disease Rating Scale (UPDRS), motor state diaries, and positron emission tomography (PET) with 6-[(18)F]fluoro-L-m-tyrosine (FMT), a tracer for AADC. The short-duration response to levodopa was measured in three patients. The procedure was well tolerated. Six months after surgery, motor functions in the OFF-medication state improved an average of 46% based on the UPDRS scores, without apparent changes in the short-duration response to levodopa. PET revealed a 56% increase in FMT activity, which persisted up to 96 weeks. Our findings provide class IV evidence regarding the safety and efficacy of AADC gene therapy and warrant further evaluation in a randomized, controlled, phase 2 setting.

[Cell therapy for Parkinson disease]

Advances in the field of stem cell research have raised hopes of creating novel cell replacement therapies for Parkinson disease (PD), although double-blinded clinical trials have met with controversial success in patients implanted with fetal midbrain tissue and autopsy results have shown that some of the grafted fetal neurons displayed pathological changes typical of PD. Dopaminergic neurons have been efficiently derived from stem cells using various methods, and beneficial effects after transplantation have been demonstrated in animal models of PD. Some obstacles remain to be overcome before stem cell therapy can be routinely and safely used to treat PD in humans. A widely used prodrug/suicide gene therapy would be applied to stem cells to reduce risk of tumor formation. Since grafts were transplanted ectopically into the striatum instead of the substantia nigra in most current protocols, surviving dopaminergic neurons would not have to be the same subtype as the nigral cells. If the main mechanism underlying any functional recovery achieved by cell therapies is restoration of dopaminergic neurotransmission, then viral vector-mediated gene delivery of dopamine-synthesizing enzymes represents a more straightforward approach. Future targets for cell therapy should include some types of Parkinsonism with degeneration of striatal neurons.

Progress in transduction of cerebellar Purkinje cells in vivo using viral vectors

Expression of a foreign gene in cerebellar Purkinje cells in vivo is a powerful method for exploring the pathophysiology of the cerebellum. Although using developmental engineering many gene-modified mice have been generated, this approach is time-consuming and requires a lot of effort for crossing different lines of mice, genotyping and maintenance of animals. If a gene of interest can be transferred to and efficiently expressed in Purkinje cells of developing and mature animals, it saves much time, effort and money. Recent advances in viral vectors have markedly contributed to selective and efficient gene transfer to Purkinje cells in vivo. There are two approaches for selective gene expression in Purkinje cells: one is to take advantage of the viral tropism for Purkinje cells, which includes the tropism of adeno-associated virus and the vesicular stomatitis virus glycoprotein (VSV-G)-pseudotyped lentivirus. Another method, which might be used in combination with the first one, is utilization of a Purkinje-cell-specific promoter. Focusing mainly on these points, recent progress in viral-vector-mediated transduction of Purkinje cells in vivo is reviewed.

Over-expression of the potassium channel Kir2.3 using the dopamine-1 receptor promoter selectively inhibits striatal neurons

Dysfunction of basal ganglia circuits underlies a variety of movement disorders and neuropsychiatric conditions. Selective control of the electrical activity of striatal outflow pathways by manipulation of ion channel function presents a novel therapeutic approach. Toward this end, we have constructed and studied in vitro an adenoviral gene transfer vector that employs the promoter region of the dopamine-1 receptor to drive expression of the inward rectifier K(+) channel Kir2.3. The use of this neuronal promoter confers cell-type specificity and a physiological level of trans-gene expression in rat primary striatal cultures. The electrophysiological properties were confirmed in transfected human embryonic kidney cells, in which an inwardly-rectifying, Cs(+)-sensitive current was measured by voltage clamp. Current clamp studies of transduced striatal neurons demonstrated an increase in the firing threshold, latency to first action potential and decrease in neuronal excitability. Neurotoxin-induced activation of c-Fos, a marker of neuronal activity, was blocked in transduced neurons indicating that the decrease in electrical excitability was physiologically significant. When used in vivo, this strategy may have the potential to positively impact movement disorders by selectively changing activity of neurons belonging to the direct striatal pathway, characterized by the expression of dopamine-1 receptors.

[Utility of AAV vectors derived from novel serotypes]

AAV vector is derived from nonpathogenic virus and has a number of attractive features as a vector for human gene transfer including safety, broad tissue specificity, and low immunogenicity following gene transfer. Moreover, persistent transgene expression (for years) was demonstrated in multiple animal experiments. For these reasons, applications to a wide spectrum of diseases are expected, and several clinical trials have been conducted. Although it is too early to conclude the outcome, the efficacy of treatment was not sufficiently substantiated in most of the trials despite confirming the safety of the vector. These results are primarily due to low levels of transgene expression. One of the approaches to improve this situation is the use of alternative serotypes of AAV. Traditionally, serotype 2 was considered to be a prototype of AAV, and the majority of studies including human clinical trials have been conducted using this serotype. On the other hand, there are five "classical" serotypes, and several have been additionally discovered from tissues of primates including humans. These serotypes are considered to be valuable resources for vector development to overcome the shortcomings of serotype 2. This review focuses on the difference in expression levels and tissue specificity of various serotype-derived vectors and summarizes current status in the treatment of candidate diseases.

Gene therapeutics for periodontal regenerative medicine

There has been significant advancement in the field of periodontal tissue engineering over the past decade for the repair of tooth-supporting structures. Although encouraging results for periodontal tissue regeneration have been found in numerous clinical investigations using recombinant growth factors, limitations exist with topical protein delivery. Newer approaches seek to develop methodologies that optimize growth factor targeting to maximize the therapeutic outcome of periodontal regenerative procedures. Genetic approaches in periodontal tissue engineering show early progress in achieving delivery of growth factor genes, such as platelet-derived growth factor or bone morphogenetic protein, to periodontal lesions. Ongoing investigations in ex vivo and in vivo gene transfer to periodontia seek to examine the extent of the potential effects in stimulating periodontal tissue engineering.