Harvard scientists discover the reason you can't stop itching
The reason people with eczema often can’t stop itching has been discovered for the first time by Harvard scientists.
Persistent itching is a condition that plagues millions of people with skin conditions such as dermatitis and eczema but the cause has evaded experts until now, and the team at Harvard said a pre-existing blood-clotting drug could help cure the issue.
A study has now discovered the common bacteria Staphylococcus aureus is to blame for the phenomenon as it triggers a chain reaction that sends a constant itching message to the brain.
It is the first time scientists have known that bacteria alone can lead to itching. Previous work showed the microbe, which is often found on the skin naturally, thrives on the skin of people with eczema and similar conditions.
Fresh experiments found this imbalance allows the bacteria to release an enzyme which then activates a protein in the skin that in turn sends itchy signals from the skin to the brain.
This can persist until the balance of the skin’s microbial ecosystems is restored and sufferers often scratch constantly for relief but this leads to tearing and damaging of skin.
“We’ve identified an entirely novel mechanism behind itch — the bacterium Staph aureus, which is found on almost every patient with the chronic condition atopic dermatitis,” said Dr Isaac Chiu, study co-author and associate professor of immunology at Harvard Medical School.
The discovery of this chain reaction revealed that the skin bacteria and inflammation from medical conditions are related, but can be separated and targeted independently.
“When we started the study, it was unclear whether the itch was a result of inflammation or not,” study first author Dr Liwen Deng said.
“We show that these things can be decoupled, that you don’t necessarily have to have inflammation for the microbe to cause itch, but that the itch exacerbates inflammation on the skin.”
Vorapaxar effective in stopping itching
The team used human cells, lab tests and animal models to identify the specific enzyme (V8) and protein (PAR1) involved in the itching biochemical cascade and found there is already a drug which could help.
PAR1 antagonists, such as Vorapaxar made by MSD, have previously been developed and approved because they play a role in stopping blood clotting and reduce the risk of strokes in people with heart conditions.
Studies on mice made to itch with Staph aureus and then treated with Vorapaxar found the drug was effective at stopping excessive scratching.
The authors suggest it is possible the drug, or similar ones that work in the same way, could be turned from a pill into a cream and repurposed to treat persistent itching.
“Targeting PAR1 abrogates itch, leading to improved skin pathology. Our findings uncover a role for bacterial proteases in itch and PAR1 as a candidate for therapeutic development,” the authors write in the paper, published in Cell.
They add: “PAR1 could be an attractive candidate to target for itch therapies. Vorapaxar is currently FDA-approved for prevention of thrombotic cardiovascular events.
“Future development of topical application of such PAR1 antagonists could avoid adverse events caused by systemic delivery.”
Discovery should help to find new treatment
Dr Emma Wedgeworth, consultant dermatologist and British Skin Foundation spokesman, said: “Whilst we have previously recognised that Staph aureus plays an important role in eczema, its contribution to itch has not previously been recognised.
“Hopefully this understanding will translate into new treatment options helping to tackle the misery of itch and eczema.”
Andrew Proctor, chief executive of the National Eczema Society, told The Telegraph: “For the millions of children and adults with atopic eczema, relentless itch is one of the most difficult things about living with this complex condition.
“It often leads to the painful ‘itch-scratch cycle’, where you scratch to relieve the itch, then the skin is damaged and it becomes even more itchy, with even greater temptation to scratch. It can be so uncomfortable and debilitating, and you often can’t sleep properly because the itch keeps you awake at night.”
