The mystery of the causes that cause itching in people could finally be solved. Harvard Medical School researchers have discovered that a common skin bacterium, Staphylococcus aureus, can directly trigger itching by acting on nerve cells. This finding could explain why persistent and intense itching often accompanies skin conditions such as eczema, according to Studyfinds.
In the experiments performed on mice, the researchers observed that the S. aureus bacteria intensified their itching. They identified a bacterial enzyme that activates a protein involved in blood clotting, thus inducing itching. Administration of an existing anti-clotting drug to mice stopped their itching.
Subsequent tests on human cells led the Boston team to believe that this anti-itch drug could be a key ingredient in the development of anti-itch creams. Published in the journal Cell, their study suggests a possible end to the long-standing itch enigma.
Previously, the itchiness associated with skin conditions such as eczema was thought to originate from inflammation of the skin. However, these new findings indicate that S. aureus alone can trigger itching through a molecular chain reaction that leads to the urge to scratch.
The researchers explain that skin conditions often disrupt the balance of microorganisms that maintain healthy skin, allowing S. aureus to grow and cause itching.
“We have identified a completely new mechanism underlying itching – the Staph aureus bacteria, which is found in almost all patients with atopic dermatitis, a chronic condition. We demonstrate that itching can be caused by the microbe itself,” says lead author Isaac Chiu, associate professor of immunology at the Blavatnik Institute at HMS, in a press release.
Dr. Chiu’s team performed experiments that demonstrated that the bacterium Staphylococcus aureus releases a chemical substance that activates a protein on the nerve fibers responsible for transmitting signals from the skin to the brain. This activation is a crucial part of the itch-cold cycle. When the mice were treated with an existing anti-clotting drug, it effectively blocked the activation of this protein, thus interrupting the cycle and reducing the urge to itch.
The experiments showed that, when the skin of the mice was exposed to S. aureus, they developed an increasingly intense itch in the following days. This itching led to scratching, which aggravated the skin lesions and spread them beyond the area of initial exposure. In addition, the mice became hypersensitive to stimuli that normally did not cause itching, a condition known as “alloknesis”, commonly found in patients with chronic skin conditions characterized by persistent itching. This hypersensitivity can also occur in people without underlying skin conditions, as can be seen from the common sensation of itching caused by wearing woolen clothes.
Because PAR1, the protein activated by S. aureus, is involved in blood clotting, the researchers tested whether an already approved anti-clotting drug that blocks it would stop the itching — which it did. Mice whose skin was exposed to S. aureus experienced rapid improvement after treatment with the drug, and their desire to scratch decreased dramatically.
Since this PAR-blocking drug is already available and used by humans, the researchers suggested that its active ingredient could be replicated as the basis for an anti-itch cream. An immediate question that still awaits an answer is whether other microbes can also trigger itching, which the researchers intend to answer in future works.
“We know that many microbes, including fungi, viruses and bacteria, are accompanied by itching, but how they cause itching is not clear,” notes Chiu.
Beyond that, the HMS team will also try to find answers as to why a microbe would cause itchiness and whether there is some sort of evolutionary benefit to it. One possibility is that pathogens hijack itching and other neural reflexes to their advantage, just as previous research has shown that the TB bacteria directly activates neurons to cause coughing, which could allow it to spread more easily from one host to another.
“It is speculation at this point, itching could be beneficial to the microbes and allow them to spread to distant areas of the body and to uninfected hosts,” concludes Deng. “Why do we eat and scratch ourselves? Does it help us or does it help the microbe? This is an aspect we could pursue in the future.”
2023-11-25 18:27:47
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