Chilli source of pain?

Behind the Headlines

Tuesday April 27 2010

The pain-transmitting chemicals found were similar to capsaicin

The “hot” substance found in chilli peppers is key to killing pain, reported the BBC. It said that a chemical similar to capsaicin, the active ingredient in chillies, is found in the body at sites of pain. By blocking the action of the substance, researchers hope to be able to relieve pain.

This research in mice and rats will be of interest to those working in the field of pain relief. The researchers succeeded in breeding mice without receptors for the chilli-like substance (because they had no gene to make them) and showed that these mice had no sensitivity to pain from capsaicin. The researchers say that this is a major breakthrough as it improves the understanding of how pain is transmitted and ultimately may lead to the development of new drugs.

This is early research and much further study is needed before we know if this finding can be translated into new painkillers. However, this is the sort of research that begins the process.

 

Where did the story come from?

This research was carried out by Dr Amol M Patwardhan and colleagues from the University of Texas Health Science Center at San Antonio and the University of Colorado Health Sciences Center in Texas, USA. The study was supported by grants and a Clinical and Translational Science Award. The paper was published in the peer-reviewed Journal of Clinical Investigation.

The BBC’s coverage of this story included quotes from a lead researcher, who stressed the early nature of the research.

 

What kind of research was this?

In this animal study, the researchers followed up their own previous research, which indicated that substances similar to capsaicin (found in chilli peppers) are made in the nerves of the spine in response to pain. This research aimed to further evaluate the theory that these newly discovered substances are involved in the transmission of pain sensations.

The substances, called oxidized linoleic acid metabolites (OLAMs), are metabolised forms of a fatty acid known as linoleic acid. OLAMs are released by the body when it is injured and can cause pain by stimulating receptors on the surface of cells that then transmit pain sensation. These receptors, known as TRPV1, are also called the capsaicin receptors as they are activated by a wide variety of painful physical and chemical stimuli, such as heat injury and chilli pepper. The activation of TRPV1 leads to a painful, burning sensation.

Although this is early research, this study will add to our understanding of pain and may lead to new ideas for pain-relieving drugs.

 

What did the research involve?

Capsaicin, the active ingredient in chilli peppers, is a natural irritant to humans and is associated with a burning sensation when it comes into contact with the skin. It is already used in some forms of pain relief and helps reduce pain by desensitising the body’s pain receptors to other stimuli. It is licensed for use as a cream to treat long-term nerve pain caused by conditions such as diabetes and arthritis.

This research tested the theory that the heat sensitivity of the capsaicin receptor is regulated by substances produced in the body itself. The researchers aimed to see whether this could be used to develop a new way of blocking this pain pathway. They thought that several OLAMs might react with the receptor.

The researchers first tried to produce the OLAMs by applying heat to the skin of mice and rats and performing skin biopsies. They then looked at the action of these OLAMs on the pain receptors, and how the presence of these substances affected the receptors’ response to heat. For this, they looked at the animals’ reaction, in terms of flinches, to either injections or radiant heat. They also examined how mice that had been bred to lack the receptor responded to heat.

 

What were the basic results?

The researchers say that they have shown that two of the OLAMs they looked at are formed in mouse and rat skin by exposure to painful heat.

These OLAMs and metabolites from them appeared to activate the capsaicin receptor (TRPV1). The researchers say this suggests they have found a new family of internal transmitting chemicals, which they have called endogenous TRPV1 agonists.

They say that blocking these substances substantially decreased the heat sensitivity of the receptor and the pain experienced by rats and mice.

 

How did the researchers interpret the results?

The researchers say that because OLAMs are released during cell injury, their findings suggest the existence of a new family of pain chemicals. They say this could provide the foundation for investigating new classes of analgesic drugs (painkillers).

 

Conclusion

This research explored the action of what appears to be a newly discovered family of pain-transmitting chemicals, which act on the same pain receptor as capsaicin, the “hot” ingredient in chillies.

This is early research and much further study will be needed before we know if this finding can be translated into new forms of painkillers. However, this is the sort of research that begins this important process.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

'Hot' substance in chilli peppers key to killing pain. BBC News, April 26 2010

Links to the science

Patwardhan AM, Akopian AN, Ruparel NB et alHeat generates oxidized linoleic acid metabolites that activate TRPV1 and produce pain in rodents. Journal of Clinical Investigation April 26 2010

Further reading

Derry S, Lloyd R, Moore RA, McQuay HJ. Topical capsaicin for chronic neuropathic pain in adults. Cochrane Database of Systematic Reviews 2009, Issue 4

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