Medical
Capsaicin is currently used in topical
ointments, nasal sprays (Sinol-M), as well as a high-dose
dermal patch (trade name Qutenza), to relieve the
pain of peripheral
neuropathy such as post-herpetic
neuralgia caused by
shingles.
[25] It may be used in concentrations of between 0.025% and 0.25%. It may be used as a cream for the temporary relief of minor aches and pains of
muscles and joints associated with
arthritis, simple backache, strains and
sprains, often in compounds with other
rubefacients.
[26] The treatment typically involves the application of a topical
anesthetic until the area is numb. Then the capsaicin is applied by a
therapist wearing
rubber gloves and a face mask. The capsaicin remains on the skin until the patient starts to feel the "heat", at which point it is promptly removed. Capsaicin is also available in large
bandages (plasters) that can be applied to the back.
In 2009, a landmark clinical trial performed at the Institute For Allergy & Asthma concluded that Sinol-M Nasal Spray was effective for the treatment of allergic rhinitis. This made Sinol-M the first all natural, clinically proven nasal spray for allergies.
�This study represents the first-ever capsaicin-based treatment for allergic rhinitis to be supported by prospective clinical data, and has important implications for millions of Americans who suffer from nasal allergies. This all-natural product has now been demonstrated to provide clinical effectiveness without any of the side effects associated with intra-nasal steroids and is available without a prescription� said Michael A. Kaliner, of the Institute of Asthma and Allergy in Wheaton, Maryland.
[27] There is also a Sinol-M capsaicin based nasal spray for the relief of headache pain (migraine, sinus, cluster, tension and premenstrual). This is the first OTC nasal spray for headache relief.
Capsaicin creams are used to treat
psoriasis as an effective way to reduce itching and inflammation.
[28][29]
According to animal and human studies, the oral intake of capsaicin may increase the production of heat by the body for a short time. Due to the effect on the
carbohydrates breakdown after a meal, cayenne may also be used to regulate
blood sugar levels.
[30]
Capsaicin selectively binds to a protein known as
TRPV1 that resides on the membranes of pain and heat sensing neurons.
[31][32] TRPV1 is a heat activated calcium channel, which opens between 37 and 45 �C (98.6 and 113 �F, respectively). When capsaicin binds to TRPV1, it causes the channel to open below 37 �C (
normal human body temperature), which is why capsaicin is linked to the sensation of heat. Prolonged activation of these neurons by capsaicin depletes presynaptic
substance P, one of the body's neurotransmitters for pain and heat. Neurons that do not contain TRPV1 are unaffected.
The result appears to be that the chemical mimics a burning sensation, the
nerves are overwhelmed by the influx, and are unable to report pain for an extended period of time. With chronic exposure to capsaicin,
neurons are depleted of
neurotransmitters, leading to reduction in sensation of pain and blockade of
neurogenic inflammation. If capsaicin is removed, the neurons recover.
[33][34][
citation needed]
The
American Association for Cancer Research reports studies suggesting capsaicin is able to kill
prostate cancer and
lung cancer cells by causing them to undergo
apoptosis.
[35][36] The studies were performed on tumors formed by human prostate cancer
cell cultures grown in mouse models, and showed tumors treated with capsaicin were about one-fifth the size of the untreated tumors. There have been several mouse studies conducted in Japan and China that showed natural capsaicin directly inhibits the growth of leukemic cells.
[37] Capsaicin may be able to trigger
apoptosis in human
lung cancer cells as well.
[38]
Capsaicin is also the key ingredient in the experimental drug
Adlea, which is in Phase 2 trials as a long-acting analgesic to treat post-surgical and osteoarthritic pain for weeks to months after a single injection to the site of pain.
[39] Moreover, it reduces pain resulting from
rheumatoid arthritis[40] as well as joint or muscle pain from
fibromyalgia or other causes.
Mechanism of action
The burning and painful sensations associated with capsaicin result from its chemical interaction with sensory
neurons. Capsaicin, as a member of the
vanilloid family, binds to a
receptor called the
vanilloid receptor subtype 1 (VR1).
[45] First cloned in 1997, VR1 is an
ion channel-type receptor. VR1, which can also be stimulated with heat and physical abrasion, permits
cations to pass through the
cell membrane and into the cell when activated. The resulting
depolarization of the neuron stimulates it to
signal the brain. By binding to the VR1 receptor, the capsaicin molecule produces similar sensations to those of excessive heat or abrasive damage, explaining why the spiciness of capsaicin is described as a burning sensation.
Early research showed capsaicin to evoke a strikingly long-onset current in comparison to other chemical agonists, suggesting the involvement of a significant rate-limiting factor.
[46] Subsequently, the VR1
ion channel has been shown to be a member of the superfamily of
TRP ion channels, and as such is now referred to as
TRPV1. There are a number of different
TRP ion channels that have been shown to be sensitive to different ranges of temperature and probably are responsible for our range of temperature sensation. Thus, capsaicin does not actually cause a
chemical burn, or indeed any direct tissue damage at all, when chili peppers are the source of exposure. The inflammation resulting from exposure to capsaicin is believed to be the result of the body's reaction to nerve excitement. For example, the mode of action of capsaicin in inducing bronchoconstriction is thought to involve stimulation of
C fibers [47] culminating in the release of neuropeptides. Essentially, the body inflames tissues as if it has undergone a burn or abrasion and the resulting inflammation can cause tissue damage in cases of extreme exposure, as is the case for many substances that cause the body to trigger an inflammatory response.
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