Gene therapy for epilepsy

Overview

Epilepsy Refers to a group of chronic neurological disorders That are caractérisée by seizures , Affecting over 50 million people, or 0.4-1% of the overall population. ^[3] [4] There is a basic understanding of the pathophysiology of epilepsy, especially of forms characterized by the onset of seizures from a specific area of ​​the brain ( partial-onset epilepsy ). Although most patients respond to medication, approximately 20% -30% do not improve with or fail to tolerate antiepileptic drugs . ^[5] [6] For such patients, surgeryto remove the epileptogenic zone may be offered in a small minority, but it is not possible that the seizures arise from brain areas that are essential for language, vision, movement or other functions. As a result, many people with epilepsy are left without any treatment options, and thus there is a strong need for the development of innovative methods for treating epilepsy.

Throughout the use of viral vector gene transfer, RNA to the epileptogenic zone, several neuropeptides , ion channels and neurotransmitter receptors have shown potential as transgenes for epilepsy treatment. Among vectors are adenovirus and adeno-associated virus vectors (AAV), which have the properties of high and efficient transduction, ease of production in high volumes, wide range of hosts, and extended gene expression. ^[7] Lentiviral vectors have also been shown.

Clinical research

Amongst the challenges of clinical translation, the possibility of immune responses to viral vectors and transgenes and the possibility of insertional mutagenesis , which can be detrimental to patient safety. ^[8] Scaling up from the volume needed for animal trials is an area of ​​difficulty, but it has been overcome in other diseases. With its size of less than 20 nm, AAV in the context of these problems, allowing for its passage through the extracellular space, leading to widespread transfection. Although it may be important for the treatment of neuronal diseases, it is important that neuronal diseases be avoided and that they are less prone to insertional mutagenesis

Viral approaches in preclinical development

In a method for treating epilepsy, the pathophysiology of epilepsy is considered. As the seizures are typically characterized by excessive excitatory neurons, the logical goal for gene therapy is to reduce excitation or enhance inhibition. Out of the viral approaches, neuropeptide transgenes being researched are somatostatin, galanin, and neuropeptide Y (NPY). However, adenosine and gamma-aminobutryic acid (GABA) and GABA receptors are gaining more momentum as well. Other transgenes being studied are potassium channels and tools for on-demand suppression of excitability ( optogenetics and chemogenetics ).

Adenosine

Adenosine is an inhibitory nucleoside that doubles up as a neuromodulator , aiding in the modulation of brain function. It has anti-inflammatory properties, in addition to neuroprotective and anti-epileptic properties. ^[6] The most prevalent theory is that there is an increased expression of adenosine kinase (ADK). The increase in adenosine kinase results in an increased metabolic rate for adenosine nucleosides. Nucleic acid deficiency in the presence of anti-epileptic properties and the overexpression of ADK, seizures are triggered, resulting in the development of epileptogenesis . ^[7] Studies have shown that ADK overexpression results fromastrogliosis following a brain injury, which can lead to the development of epileptogenesis. While ADK overexpression leads to increased susceptibility to seizures, the effects can be counteracted and moderated by adenosine. ^[9] Based on adenosine in preventing seizures, in addition to its FDA approval in the treatment of other ailments such as tachycardia and chronic pain, adenosine is an ideal target for the development of anti-epileptic gene therapies. ^[10]

Galanin

Galanin , found primarily within the central nervous system (limbic system, piriform cortex, and amygdala), plays a role in the reduction of long-term potentiation (LTP), regulating consumption habits, and inhibiting seizure activity. ^[11]Introduced back in the 1990s by Mazarati et al., Galanin has been shown to have neuroprotective and inhibitory properties. Through the use of mice are deficient in GalR1 That receptors, a picrotoxin-kindled model Was Utilized to show That galanin plays a role in modulating and Preventing hilar cell loss as well as decreasing the duration of induced seizures. ^[12]Conducted studies confirming these findings of prevention, decreasing the incidence and duration of seizures, increasing the stimulation threshold required to induce seizures, and suppressing the release of glutamate that would increase susceptibility to seizure activity. ^{[6] [11] [13]} Galanin expression can be used to reduce and reduce seizure activity and limit seizure cell death. ^[11]

Neuropeptide Y

Neuropeptide Y (NPY), which is found in the autonomic nervous system , helps modulate the hypothalamus, and therefore, consumption habits. ^[6] Experiments have been conducted to determine the effect of NPY on animal models before and after induced seizures. ^[6] [14] To evaluate-the effect prior to seizures, one study vectors inserted 8 weeks prior to kindling , showing year Increase in seizure threshold. In order to evaluate the effects after epileptogenesiswere present, the vectors were injected into the hippocampus of rats after seizures were induced. This resulted in a reduction of seizure activity. These studies established that NPY increased the seizure threshold in rats, arrested disease progression, and reduced seizure duration. ^[6] [14] After examining the effects of NPY on behavioral and physiological responses, it was discovered that it had no effect on LTP, learning, or memory. ^[14] A protocol for NPY gene transfer is being reviewed by the FDA. ^[13]

Somatostatin

Somatostatin is a neuropeptide and neuromodulator that plays a role in the regulation of hormones and aids in sleep and motor activity. It is primarily found in interneurons that modulating the firing rates of pyramidal cells primarily at a local level. They feed-forward inhibit pyramidal cells. In a series of studies where somatostatin is expressed in a rodent kindling model , it was concluded that somatostatin resulted in a decreased average duration for seizures, increasing its potential as an anti-seizure drug. ^[15]The theory in utilizing somatostatin is that if pyramidal cells are eliminated, then the feed forward, otherwise known as inhibition, is lost. Somatostatin containing interneurons carry the neurotransmitter GABA, which primarily causes hyperpolarizes the cells, which is where the feed forward theory is derived from. The hope of gene therapy is that by overexpressing somatostatin in specific cells, and increasing the GABAergic tone, it is possible to restore balance between inhibition and excitation. ^[6] [14]

Potassium channels

Kv1.1 is a voltage-gated potassium channel encoded by the KCNA1 gene. It is published in the brain and peripherals, and plays a role in controlling the excitability of neurons and the amount of neurotransmitter released from axon terminals. Successful gene therapy using lentiviral delivery of KCNA1 has been reported in a rodent model of focal motor cortex epilepsy ^[16] The treatment was well tolerated, with no detectable effect on sensorimotor coordination.

Optogenetics

A potential obstacle to clinical gene therapy is that viral vector-mediated manipulation of the genetic make-up of neurons is irreversible. An alternative approach for the use of neuron and excitability. The first such approach has been used optogenetics . Several laboratories have shown that the inhibitory light-sensitive protein Halorhodopsin can suppress seizure-like discharges in vitro and in vivo epileptic activity. ^{[17] [18] [19] [20]} A draw-back of Optogenetics Is That Light needs to be Delivered to the area of the brain conjunctival phrase the opsin. This can be achieved with laser-coupled fiber-optics or light-emitting diodes, but these are invasive.

Chemogenetics

An alternative approach for on-demand control of excitability that does not require light delivery to the brain is to use chemogenetics . This report is based on a mutated receptor in the seizure focus, which does not respond to endogenous neurotransmitters but can be activated by an exogenous drug. G-protein-coupled receptors are mutated in this way by Designer Receptors Exclusively Activated by Drugs Designer (DREADDs) . Dreadd hM4D (Gi), which is derived from the M4 muscarinic receptor. ^[21]AAV-mediated expression of hM4D (Gi) in a rodent model of focal epilepsy on its own no effect, but when activated by the drug clozapine-N-oxide it suppressed seizures. The treatment has not been detectable side effects and is, in principle, suitable for clinical translation .

Non-viral approaches

Magnetofection is done through the use of super paramagnetic iron oxide nanoparticles coated with polyethylenimine . Iron oxide nanoparticles are ideal for biomedical applications in the body due to their biodegradable, cationic, non-toxic, and FDA-approved nature. Under the conditions of the invention, the receptors of interest are coated with nanoparticles. The receptors will then be in the home. Once the particle docks, the DNA is delivered to the cell via pinocytosis or endocytosis. On delivery, the temperature is slightly increased, the lysing the iron oxide nanoparticle and releasing the DNA. Overall, the technique is useful for fighting slow vector accumulation and low concentration at target areas. The technique is also customizable to the physical and biochemical properties of the receptors by modifying the characteristics of the iron oxide nanoparticles. ^[22] [23]

Future implications

The use of gene therapy in neurological disorders Treating epilepsy Such As has presented Itself as an increasingly viable area of Ongoing research with the primary targets being white somatostatin , galanin , neuropeptide y , potassium channels , Optogenetics and chemogenetics for epilepsy. The field of gene therapy continues to grow and show promising results for the treatment of epilepsy among other diseases, providing additional methods for delivery, and finding possible methods for scaling up delivery volumes. ^[24] [25]

References