Summary: Researchers identify the mechanisms behind tricyclic antidepressants’ ability to help relieve nerve pain.
Researchers at Australia’s national science agency (CSIRO) have shown for the first time how tricyclic antidepressants (TCAs) work against nerve pain, paving the way for further research and new therapies to treat the debilitating condition.
Nerve pain affects 1 in 20 Australians. It is usually chronic and can be experienced for a range of reasons such as cancer, diabetes, trauma, infection, and multiple sclerosis. Its symptoms vary from shooting or throbbing pain, burning, freezing or electrical shock sensations, tingling, itchiness, oversensitivity or numbness.
Although TCAs are frequently prescribed for nerve pain, why and how they work to reduce pain hasn’t been fully understood until now.
CSIRO scientist and leader of the research, Adjunct Professor Peter Duggan, said he hoped the discovery would lead to the development of a new type of drug that worked in a similar way, without any potential side effects.
“These types of antidepressants are commonly used to treat pain, so we know they can be effective, but until now we haven’t understood what is happening at a cellular level,” Duggan said.
“Now we understand how they work, the next step is to look at developing whole new therapies that target the same nerve receptors and eliminates any potential side effects.”
The research was published in RSC Medicinal Chemistry by a multi-disciplinary team of researchers from CSIRO, The University of Queensland’s Institute for Molecular Bioscience, and Monash University to demonstrate exactly how 11 TCAs and two closely related drugs worked to block pain, and identified which ones were most effective.
Dean of the Faculty of Pain Medicine at the Australian and New Zealand College of Anaesthetists and Clinical Associate Professor at Deakin University, Michael Vagg sees the human cost of chronic pain as well as the broader social and economic impact it has for our community.
“Nerve pain is highly disabling and ruins lives. The best current treatments only work to a useful degree on every third or fourth person who receives them,” Vagg said.
“Tricyclic drugs have been used for decades in treating nerve and musculoskeletal pain and are still the most likely drugs to help despite all the effort that has been put into researching new treatments.
“We have not had any really effective new treatments for nerve pain for a long time and this work opens up the possibility of designing a new class of drugs with improved safety and effectiveness.”
With further work already underway, the team is aiming to provide the scientific basis that leads to the design of more effective drugs to improve the lives of people living with nerve pain.
About this pain research news
Author: Press Office
Contact: Press Office – CSIRO
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OriginalResearch: Open access.
“Inhibition of N-type calcium ion channels by tricyclic antidepressants—experimental and theoretical justification for their use for neuropathic pain” by Fernanda C. Cardoso et al. RSC Medicinal Chemistry
Inhibition of N-type calcium ion channels by tricyclic antidepressants—experimental and theoretical justification for their use for neuropathic pain
A number of tricyclic antidepressants (TCAs) are commonly prescribed off-label for the treatment of neuropathic pain. The blockade of neuronal calcium ion channels is often invoked to partially explain the analgesic activity of TCAs, but there has been very limited experimental or theoretical evidence reported to support this assertion.
The N-type calcium ion channel (CaV2.2) is a well-established target for the treatment of neuropathic pain and in this study a series of eleven TCAs and two closely related drugs were shown to be moderately effective inhibitors of this channel when endogenously expressed in the SH-SY5Y neuroblastoma cell line.
A homology model of the channel, which matches closely a recently reported Cryo-EM structure, was used to investigate via docking and molecular dynamics experiments the possible mode of inhibition of CaV2.2 channels by TCAs. Two closely related binding modes, that occur in the channel cavity that exists between the selectivity filter and the internal gate, were identified.
The TCAs are predicted to position themselves such that their ammonium side chains interfere with the selectivity filter, with some, such as amitriptyline, also appearing to hinder the channel’s ability to open.
This study provides the most comprehensive evidence to date that supports the notion that the blockade of neuronal calcium ion channels by TCAs is at least partially responsible for their analgesic effect.