Capsaicin (pronounced /kæpˈseɪəsɪn/ ) (8-methyl- N -vanillyl-6-nonenamide, (CH 3 ) 2 CHCH=CH(CH 2 ) 4 CONHCH 2 C 6 H 3 -4-(OH)-3-(OCH 3 )) 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 any tissue with which it comes into contact. Capsaicin and several related compounds are called capsaicinoids and are produced as a secondary metabolite by chili peppers, probably as deterrents against certain herbivores and fungi. Pure capsaicin is a hydrophobic, colorless, odorless, crystalline to waxy compound.
History
The compound was first extracted (albeit in impure form) in 1816 by Christian Friedrich Bucholz (1770-1818). He called it "capsicin". Capsaicin was first isolated in pure, crystalline form in 1876 by John Clough Thresh (1850-1932), who gave it the name "capsaicin". In 1873 German pharmacologist Rudolf Buchheim (1820-1879) and in 1878 the Hungarian doctor Endre Hőgyes stated that "capsicol" (partially purified capsaicin) caused the burning feeling when in contact with mucous membranes and increased secretion of gastric juice. The structure of capsaicin was partly elucidated by E. K. Nelson in 1919. Capsaicin was first synthesized in 1930 by E. Spath and S. F. Darling. In 1961, similar substances were isolated from chili peppers by the Japanese chemists S. Kosuge and Y. Inagaki, who named them capsaicinoids.
Capsaicinoids
Capsaicin is the main capsaicinoid in chili peppers, followed by dihydrocapsaicin. These two compounds are also about twice as potent to the taste and nerves 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.
Capsaicin is believed to be synthesized in the interlocular septa of chili peppers by addition of a branched-chain fatty acid to vanillylamine. Biosynthesis depends on the gene AT3 , which resides at the pun1 locus, and which encodes a putative acyltransferase.
Besides the six natural capsaicinoids, one synthetic member of the capsaicinoid family exists. Vanillylamide of n-nonanoic acid (VNA) is used as a reference substance for determining the relative pungency of capsaicinoids.
Natural function
Capsaicin is present in large quantities in the placental tissue (which holds the seeds), the internal membranes and, to a lesser extent, the other fleshy parts of the fruits of plants in the genus Capsicum . Contrary to popular belief, the seeds themselves do not produce any capsaicin, although the highest concentration of capsaicin can be found in the white pith around the seeds.
The seeds of Capsicum plants are predominantly dispersed by birds. Birds do not have the receptor to which capsaicin binds, so it does not function as an irritant for them. Chili pepper seeds consumed by birds pass through the digestive tract and can germinate later, but mammals have molars, which destroy seeds and prevent them from germinating. Thus, natural selection may have led to increasing capsaicin production because it makes the plant less likely to be eaten by animals that do not help it reproduce. However, there is evidence that capsaicin first evolved as an anti-fungal agent.
In 2006 it was discovered that tarantula venom activates the same pathway of pain as is activated by capsaicin, the first demonstrated case of such a shared pathway in both plant and animal anti-mammal defense.
Uses
Food
Because of the burning sensation caused by capsaicin when it comes in contact with mucous membranes, it is commonly used in food products to give them added spice or "heat" (pungency). In high concentrations capsaicin will also cause a burning effect on other sensitive areas of skin. The degree of heat found within a food is often measured on the Scoville scale.
Cold milk is the most effective solution against the burning sensation (due to casein having a detergent effect on capsaicin) and cold sugar solution (10%) at 20°C/68°F is almost as effective. The burning sensation will slowly fade away in about 6–8 hours if no actions are taken.
It is common for people to experience pleasurable and even euphoriant effects from eating capsaicin-flavored foods. Folklore among self-described "pepperheads" attributes this to pain-stimulated release of endorphins, a different mechanism from the local receptor overload that makes capsaicin effective as a topical analgesic. In support of this theory, there is some evidence that the effect can be blocked by naloxone and other compounds that compete for receptor sites with endorphins and opiates.
Medical
Further information: Health risks of chili consumption and Health benefits of chili consumptionCapsaicin is currently used in topical ointments to relieve the pain of peripheral neuropathy such as post-herpetic neuralgia caused by shingles. It may be used in concentrations of between 0.025% and 0.075%. 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. 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 that can be applied to the back.
In 1997, a research team led by David Julius of UCSF showed that capsaicin selectively binds to a protein known as TRPV1 that resides on the membranes of pain and heat sensing neurons. TRPV1 is a heat activated calcium channel, which opens between 37 and 45 °C. 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.
Capsaicin is being explored as a possible prophylaxis for Type 1 diabetes by researchers in Toronto, Canada; capsaicin was injected subcutaneously affecting pancreatic sensory nerves of mice with Type 1 diabetes because of a suspected link between the nerves and diabetes.
The American Association for Cancer Research reports studies suggesting capsaicin is able to kill prostate cancer cells by causing them to undergo apoptosis. 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 clinical studies conducted in Japan and China that showed natural capsaicin directly inhibits the growth of leukemic cells.
Another study carried out at the University of Nottingham suggests capsaicin is able to trigger apoptosis in human lung cancer cells as well.
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 osteoarthritis pain for weeks to months after a single injection to the site of pain.
Proposed 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, opioid prescription drugs such as OxyContin or stimulant drugs such as Adderall XR release their active chemical over time, but when crushed and snorted, taken as a suppository, chewed, or injected, the larger than normal dosage is absorbed all at once and a much stronger effect is produced that can be highly habit forming and dangerous due to the higher risk of overdose. 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 chewing 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.
Less-lethal force
Capsaicin is also the active ingredient in riot control and personal defense pepper spray chemical agents. When the spray comes in contact with skin, especially eyes or mucous membranes, it is very painful, and breathing small particles of it as it disperses
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