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Capsaicin

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Capsaicin
Chemical structure of capsaicin
Systematic name (E)-N- (4-hydroxy-
3-methoxybenzyl) -
8-methylnon-6-enamide
Molecular formula C18H27NO3
SMILES CC(C)/C=C/CCCCC(NCC1=CC
(OC)=C(O)C=C1)=O
CAS number [404-86-4]
Molecular mass 305.41 g/mol
Melting point 62 - 65 °C

The chemical compound capsaicin (8-methyl-N-vanillyl-6-nonenamide) is the active component of chili peppers, which are plants belonging to the genus Capsicum. It is an irritant for mammals including humans and produces a sensation of burning in the mouth. Capsaicin and several related compounds are called capsaicinoids and are produced as a secondary metabolite by chili peppers, probably as deterrents against herbivores. Birds are generally not sensitive to capsaicinoids. Pure capsaicin is a lipophilic colorless odorless crystalline to waxy compound.

Capsaicinoids

Capsaicin is the main capsaicinoid in chili peppers, followed by dihydrocapsaicin. These two compounds are also about twice as hot as the minor capsaicinoids nordihydrocapsaicin, homodihydrocapsaicin, and homocapsaicin. Dilute solutions of pure capsaicinoids produced different types of pungency; however, these differences were not noted using more concentrated solutions.

Capsaicinoid name Abbrev. Typical
relative
amount		 Scoville
heat units		 Chemical structure
Capsaicin C 69% 15,000,000 Chemical structure of capsaicin
Dihydrocapsaicin DHC 22% 15,000,000 Chemical structure of dihydrocapsaicin
Nordihydrocapsaicin NDHC 7% 9,100,000 Chemical structure of nordihydrocapsaicin
Homodihydrocapsaicin HDHC 1% 8,600,000 Chemical structure of homodihydrocapsaicin
Homocapsaicin HC 1% 8,600,000 Chemical structure of homocapsaicin

Uses

Food

Because of the burning sensation caused by capsaicin when it comes in contact with human flesh, it is commonly used in food products to give them added spice or "heat" (piquancy). The degree of heat found within a food is measured on the Scoville scale. Typically the capsaicin is obtained by using chili peppers as the source. Another common source is hot sauces (which may contain pure capsaicin or chili peppers). These sources are preferred over pure capsaicin for reasons of safety resulting from the lower concentration.

The most effective ways to relieve the burning sensation is to cool the mouth and throat with cool food or cool beverages like yogurt, ice cream, or milk, or something sugary, like juice, sugar, or candy. Since capsaicin in its pure state is poorly soluble in water, but good in fat, oils, and pure alcohol, an often-heard advice is to eat fatty foods like buttered bread or beverages like whole milk or whipped cream, assuming that these would carry away the capsaicin and thus reduce the source of the burning. The value of this practice is questionable and the burning sensation will slowly fade away without any measure taken.

The effect of consuming cool beverages or fatty foods to relieve the burning sensation stems from their molecular status as non-polar solvents. Due to water's molecular polarity, it is not an efficient allevation from the burning sensation.

Medical

Capsaicin was originally used in topical ointments to relieve the pain of peripheral neuropathy, for example post-herpetic neuralgia caused by Herpes zoster ("Shingles"). This original use is reflected in the name of Rodlen Laboratories' capsaicin cream, Zostrix. Today, capsaicin creams are indicated for the temporary relief of minor aches and pains of muscles and joints associated with arthritis, simple backache, strains and sprains.

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. The result appears to be that the nerves are overwhelmed from the burning sensation and are unable to report pain for an extended period of time. With chronic exposure to capsaicin, neurons are depleted of neurotransmitters. This leads to reduction in sensation of pain and blockade of neurogenic inflammation. If capsaicin is removed, the neurons recover.

The American Association for Cancer Research reports studies showing that Capsaicin is a killer of androgen-independent prostate cancer cells (PMID 16540674). [1]

Intranasal administration of capsaicin has shown some promise in treating certain kinds of headaches. [2] It may also be helpful in treating chronic sinus infections. [3]

Non-lethal force

Capsaicin is also the active ingredient in the chemical riot control agent pepper spray. When the spray comes in contact with skin, especially eyes or mucous membranes it is very painful. Refer to the Scoville scale for a comparison of pepper spray to other sources of Capsaicin.

In large quantities, capsaicin can be a lethal poison. Symptoms of overdose include difficulty breathing, blue skin, and convulsions. While the large amount needed to kill an adult human being and the low concentration of capsaicin in chilis make accidental poisoning by chili consumption exceedingly unlikely, capsaicin has been implicated in some cases of infanticide in India.

Possible drug abuse deterrent

Clifford Woolf, the Richard J. Kitz Professor of Anesthesia Research at Harvard Medical School has suggested using Capsaicin to deter abuse of certain extended-release drugs such as OxyContin and Ritalin. When taken as prescribed, morphine-based prescription drugs such as OxyContin release their opioids over time, but when crushed and snorted, swallowed, or injected intravenously, the drugs produce an intense high that is highly addictive. Woolf has argued that adding Capsaicin into the capsules would be a safe way to deter abuse. A person taking the capsule in the prescribed way (i.e., swallowing it whole) would suffer no ill effects from the additive. However, a person crushing it would expose the irritant. Anyone then swallowing it, snorting it, or injecting it would be exposed to the full power of the chemical. "Imagine snorting an extract of 50 jalapeño peppers and you get the idea", Woolf said in an interview with the Harvard University Gazette. As of 2006, Woolf's proposal is still in the preliminary stages of development and the additive has not yet entered the production stage. Notably, as with many other anti-abuse measures it can be largely defeated by a simple cold water extraction.

Pest deterrent

Capsaicin is also used to deter pests, both insects and animals. A common example would be the use of ground-up or crushed dried chili pods in bird feed to deter squirrels, since birds are unaffected by capsaicin.

Mechanism of action

The burning and painful sensations associated with capsaicin result from capsaicin's chemical interaction with sensory neurons. Capsaicin, as a member of the vanilloid family, binds to a receptor called the vanilloid receptor subtype 1 (VR1). 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 from outside when activated. The resulting "depolarization" of the neuron stimulates it to signal the brain. By binding to the VR1 receptor, the capsaicin molecule produces the same effect that excessive heat or abrasive damage would cause, explaining why the spiciness of capsaicin is described as a burning sensation.

With chronic exposure to capsaicin, neurons are depleted of neurotransmitters. This leads to reduction in sensation of pain and blockade of neurogenic inflammation. If capsaicin is removed, the neurons recover.

The VR1 ion channel has subsequently 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; it causes only the sensation of one.

Capsaicin "high"

The "capsaicin high" is a euphoric sensation caused by the consumption of large quantities of capsaicin from capsaicin-laden foods. It is theorised that the pain induced by capsaicin causes the human body to release endorphins. Eventually, enough are released to create a sensation that is frequently compared to "runner's high".

References

See also

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