Tuesday, June 4, 2013

Key to chronic eczema itch may lie in special ion channel

Recently scientists reported the discovery of an “itch molecule” (Nppb)  responsible for conveying the itch signal across the synapse from sensory neurons in the skin to neurons in the dorsal horn of the spinal cord.

The media made a great deal of this study, which laid out a substantial model for how we feel itch.

Something I hadn’t noticed, though, was that the Science study considered only a subset of neurons involved in sensing itch—those that are activated by histamine. These neurons, at the itch-sensing end, have a type of ion channel called “TRPV1” that detects histamine and other substances, or “pruritogens,” that induce itch.

An ion channel is a kind of gate that opens when a key--such as a histamine molecule--binds to it. The open gate lets in sodium or potassium ions. When this happens to ion channels in a neuron, the neuron sends an electrical pulse down its length, transmitting information, such as a sensation of itch.

But there are other triggers for itch besides histamine. “Histamine-independent” itch is particularly important in the chronic itch experienced by eczema patients. (And that's why antihistamines don't do us any good.)

Histamine-independent itch is transmitted by neurons that possess TRPA1 ion channels. A new study, published in the Journal of Neuroscience, shows that mice only feel chronic itch if they have neurons expressing TRPA1 channels. Strikingly, the scientists show that knocking out TRPV1 channels (the histamine-dependent kind) does not affect the ability of mice to feel chronic itch.

As a model of chronic itch, the researchers shaved the cheeks of lab mice and exposed the skin to drying chemicals over a period of a few days. The mice scratched their cheeks and developed classic signs of dry, itchy skin--unless their TRPA1 channels had either been genetically deleted or inhibited by a drug,in which cases they hardly scratched at all.

The researchers were also interested in whether the itch-scratch cycle affected the sensation of itch. If you don’t scratch an itch, does it get better or worse? The answer appears to be that if you (or, by proxy, a lab mouse) have an itch on your back that you can only scratch by rubbing it against the wall, it may torment you, but when measured by objective standards, skin that you don’t scratch ends up in better shape.

We can draw two practical conclusions from this work, which was led by Diana Bautista at UC Berkeley: that blocking TRPA1 channels with a drug in cream or ointment form could be a potential solution to the chronic itch of eczema; and that it really does appear that if you can break the itch-scratch cycle, your skin will be better off.

Now, we all know how difficult it is to stop scratching. It’s not as easy as saying that you’ll stop. But this type of research certainly highlights the positive feedback of habit-reversal, which uses psychiatric techniques to reduce habitual scratching. Scratch less…and you’ll feel less itchy.

I do have one question: does the molecule Nppb, reported in the Science paper two weeks ago, transmit chronic itch signals as well as histamine-induced itch? If so, it is still a valuable target for further research into eczema therapies.


  1. Interesting post.

    I once posted on a eczema forum titled "What will happen if a person with eczema's skin start to get itchy but does not scratch it for the next couple of days ?"

    and the top post is "Nonsense, this isn't possible!" I can totally understand their situation. It's hard stop scratching the itch. It is like a intensive version of Chinese water torture in my opinion.

    Now reading this post, it might just give me an idea what I could do as of right now as we wait for more news of new research in itch and ezcema. Maybe I will attempt to stop scratching and still continue to apply topical steroids once a week and hopefully the attempt will produce a similar results as reflect in this newer research that you mentioned.

  2. Well good luck with that!

    When I've had bad flareups I have tied myself in knots trying not to scratch. But you can't control what you do when you sleep, so I would wake up in the morning having scratched everywhere. It's a big part of the problem.

    1. Yes, I experience sleep scratching too. At least I have those creams to help me suppress the itch(for a few days) as of now..

  3. Hey Spanish Key,
    I found this awhile ago:
    This might be an interesting news that we are trying to find but
    there is like only two online article about it so it made me a bit *skeptical* about this finding.
    Here is one of the article :

  4. This is good stuff. Thanks for posting the links, Ryan. I had not thought to look for other efforts--and these came out only recently. I'll look into them.

    1. No problems! These news are like finding another fitting piece of the jigsaw puzzle and we are slowly completing the whole picture of this eczema and itch mystery. I hope these research will bring new and better treatments than what we currently have for any people suffering from chronic itching.

      There is also another article that I found that explains more in dept of the new research clearly that you might be interested in:
      It's cool to find similar terms from your posts in these articles, it is like I am starting to get familiarize in some of the terms in dermatology.

    2. I downloaded the paper. It looks like an important result. It's always hard in science to figure out what people have done before and what, exactly, the "new" research adds. But these scientists are high profile and so is the journal, so it's likely that this is significant.

      Nice graphic for the Harvard story! More true than the artist probably knows.