Summary: Gene therapy that inhibits targeted nerve cell signals effectively improves symptoms of neuropathic pain without negative side effects in mouse models of spinal cord injury or peripheral nerve damage.
An international team of researchers, led by scientists at University of California San Diego School of Medicine, report that a gene therapy that inhibits targeted nerve cell signaling effectively reduced neuropathic pain with no detectable side effects in mice with spinal cord or peripheral nerve injuries.
The findings, published in the May 5, 2022 online issue of Molecular Therapy, represent a potential new treatment approach for a condition that may affect more than half of patients who suffer spinal cord injuries. Neuropathy involves damage or dysfunction in nerves elsewhere in the body, typically resulting in chronic or debilitating numbness, tingling, muscle weakness and pain.
There are no singularly effective remedies for neuropathy. Pharmaceutical therapies, for example, often require complex, continuous delivery of drugs and are associated with undesirable side effects, such as sedation and motor weakness. Opioids can be effective, but can also lead to increased tolerance and risk of misuse or abuse.
Because physicians and researchers are able to pinpoint the precise location of a spinal cord injury and origin of neuropathic pain, there has been much effort to develop treatments that selectively target impaired or damaged neurons in the affected spinal segments.
In recent years, gene therapy has proven an increasingly attractive possibility. In the latest study, researchers injected a harmless adeno-associated virus carrying a pair of transgenes that encode for gamma-aminobutyric acid or GABA into mice with sciatic nerve injuries and consequential neuropathic pain. GABA is a neurotransmitter that blocks impulses between nerve cells; in this case, pain signals.
The delivery and expression of the transgenes — GAD65 and VGAT — was restricted to the area of sciatic nerve injury in the mice and, as a result, there were no detectable side effects, such as motor weakness or loss of normal sensation. The production of GABA by the transgenes resulted in measurable inhibition of pain-signaling neurons in the mice, which persisted for at least 2.5 months after treatment.
“One of the prerequisites of a clinically acceptable antinociceptive (pain-blocking) therapy is minimal or no side effects like muscle weakness, general sedation or development of tolerance for the treatment,” said senior author Martin Marsala, MD, professor in the Department of Anesthesiology in the UC San Diego School of Medicine.
“A single treatment invention that provides long-lasting therapeutic effect is also highly desirable. These finding suggest a path forward on both.”
Co-authors include: Takahiro Tadokoro, UC San Diego, University of Ryukyus, Japan and Neurgain Technologies, San Diego; Mariana Bravo-Hernandez, Yoshiomi Kobayashi, Oleksandr Platoshyn, Michael Navarro, Atsushi Miyanohara, Tetsuya Yoshizumi, Michiko Shigyo, Rajiv Reddy and Joseph Ciacci, all at UC San Diego; Silvia Marsala, UC San Diego and Neurgain Technologies, San Diego; Kirill Agashkov and Volodymyr Krotov, both at Bogomoletz Institute of Physiology, Ukraine; Stefan Juhas, Jana Juhasova, Duong Nguyen, Helena Kupcova Skalnikova and Jan Motlik, all at Czech Academy of Sciences; Shawn P. Driscoll, Thomas D. Glenn and Samuel L. Pfaff, all at Salk Institute for Biological Studies; Taratorn Kemthong and Suchinda Malaivijitnond, both at Chulalongkorn University, Thailand; Zoltan Tomori and Ivo Vanicky, both at Slovak Academy of Sciences; Manabu Kakinohana. University of Ryukyus; and Pavel Belan, Kyiv Academic University, Ukraine.
About this SCI and gene therapy research news
Author: Scott La Fee Source: UCSD Contact: Scott La Fee – UCSD Image: The image is in the public domain
Second-order spinal cord excitatory neurons play a key role in spinal processing and transmission of pain signals to the brain. Exogenously-induced change in developmentally-imprinted excitatory neurotransmitter phenotype of these neurons to inhibitory has not yet been achieved.
Here we use a subpial dorsal horn-targeted delivery of AAV (adeno-associated virus) vector(s) encoding GABA (gamma-Aminobutyric acid,) synthesizing-releasing inhibitory machinery in mice with neuropathic pain. Treated animals showed a progressive and complete reversal of neuropathic pain (tactile and brush-evoked pain behavior) which persisted for minimum 2.5 months post-treatment.
The mechanism of this treatment effect results from the switch of excitatory to preferential inhibitory neurotransmitter phenotype in dorsal horn nociceptive neurons and a resulting increase in inhibitory activity in regional spinal circuitry after peripheral nociceptive stimulation.
No detectable side effects (such as sedation, motor weakness or loss of normal sensation) were seen between 2-13 months post-treatment in naive adult mice, pigs and non-human primates.
The use of this treatment approach may represent a potent and safe treatment modality in patients suffering from spinal cord- or peripheral nerve-injury induced neuropathic pain.