标题：capsaicin
简介
.辣椒素（8-甲基-N-香草基-6-诺香草胺）是智利辣椒的活性成分，而后者是植物界中辣椒属的一种。对动物包括人类而言，辣椒素是一种刺激物，能让接触到此物的地方产生一种灼烧感。辣椒素以及其它类似的物质统称为辣椒碱，是智利辣椒的次级代谢产物，可能为该植物防御食草植物啃食的防御。纯辣椒素是疏水、无色、无臭、类似蜡状的晶状物质。
History
Capsaicin was first isolated in 1816 by P. A. Buchtholz and again 30 years later by L. T. Tresh in crystalic form, who also gave it the name capsaicin. In 1878 Hungarian doctor Endre Hogyes, who called it capsicol, also isolated it and proved that this substance is the cause of the burning feeling when in contact with mucous membrane and it also increases secretion of gastric juice. Capsaicin was first synthesized in 1930 by E. Spath and F. S. Darling. Later similar substances were isolated from chili pepper by two Japanese chemists S. Kosuge and Y. Inagaki in 1964, 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.[1]
Besides six natural capsaicinoids also one synthetic member capsaicinoid exists. It is vanillylamide of n-nonanoic acid (VNA) and it is used as a reference substance for determining capsaicinoids relative pungency.
Capsaicinoid name Abbrev. Typical
relative
amount Scoville
heat units Chemical structure 
Capsaicin C 69% 15,000,000  
Dihydrocapsaicin DHC 22% 15,000,000  
Nordihydrocapsaicin NDHC 7% 9,100,000  
Homodihydrocapsaicin HDHC 1% 8,600,000  
Homocapsaicin HC 1% 8,600,000
Natural function
Capsaicin is present in large quantities in the placental tissue which holds the seeds, the internal membranes and to a lesser extent in the other fleshy parts of the fruits of plants in the genus Capsicum. Despite popular belief, the seeds do not produce any capsaicin.[2] Unlike many such fruits which have evolved to aid in seed dispersal by attracting animals, which consume the fruits and swallow the seeds, which pass through the digestive tract and are subsequently deposited elsewhere, the seeds of Capsicum plants are predominantly dispersed by birds, in which capsaicin has analgesic properties rather than acting as an irritant. Chili pepper seeds consumed by birds pass through the digestive tract unharmed, whereas those consumed by mammals do not germinate at all. The presence of capsaicin in the fruits therefore protects them from being consumed by mammals.
It was recently discovered that the same pathway of pain utilized by capsaicin is a component of tarantula venom, becoming the first demonstrated shared target between plant and animal in defense from mammals.
Food
Because of the burning sensation caused by capsaicin when it comes in contact with human mucous membranes as found in the eye or the mouth, 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 from chili peppers. Hot sauce is an example of a product customarily containing large amounts of capsaicin and may contain chili peppers or pure capsaicin.
An effective way to relieve the burning sensation it causes is to cool the mouth and throat with dairy food or drink. Bread of all types is very effective as well. The mechanical stimulation of the mouth by chewing food will partially mask the pain sensation.
Cooling and mechanical stimulation are the only proven methods to relieve the pain, however many questionable tips are widely perpetuated, including oil and oily food (probably because capsaicin in its pure state is poorly soluble in water but soluble in oil). However, the burning sensation will slowly fade away without any measure taken. Milk is the most popular form of relief; molecularly it attracts the burning ligands away from taste receptors (Dustrophsky, 2006).
Medical
Capsaicin 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 also 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 adhesive bandages that can be applied to the back.
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 and it leads to reduction in sensation of pain and blockade of neurogenic inflammation. If capsaicin is removed, the neurons recover.
Capsaicin is being explored as a cure for diabetes by researchers in Toronto, Canada. Early work curing diabetic mice looks promising. Capsaicin was injected into 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. [5] 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.
Another study carried out at the University of Nottingham suggests capsaicin is able to trigger apoptosis in human lung cancer cells as well.[6]
Capsaicin is also used in certain medical studies as a measure of a persons tolerability to pain before that person is tested with a new drug, a painkiller for example.
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 cause death. Symptoms of overdose include difficulty breathing, blue skin, and convulsions. The large amount needed to kill an adult human and the low concentration of capsaicin in chilis make accidental poisoning by chili consumption exceedingly unlikely.
[edit] 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.[7] 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 addictive 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 swallowing it, snorting it, or injecting it would be exposed to the full power of the chemical. "Imagine snorting an extract of 50 jalape&ntilde;o 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.
Pest deterrent
Capsaicin is also used to deter pests. A common example is the use of ground-up or crushed dried chili pods in birdseed to deter squirrels, since birds are unaffected by capsaicin. Insects are also unaffected.
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). 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 the same effect that excessive heat or abrasive damage would cause, explaining why the spiciness of capsaicin is described as a burning sensation.
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, or indeed any damage to tissue at all; it causes only the sensation of one.
Acute health effects
Capsaicin is a highly irritant material requiring proper protective goggles, respirators, and proper hazmat handling procedures. It is hazardous in cases of skin contact (irritant, sensitizer), of eye contact (irritant), of ingestion, of inhalation (lung irritant, lung sensitizer). Severe over-exposure can result in death.[8] Painful exposures to capsaicin-containing peppers are among the most common plant-related exposures presented to poison centers.[9] They cause burning or stinging pain to the skin, and if ingested in large amounts by adults or small amounts by children, can produce nausea, vomiting, abdominal pain, and burning diarrhea.[9] Eye exposure produce intense tearing, pain, conjunctivitis, and blepharospasm.[9]
[edit] Treatment after exposure
The primary treatment is removal from exposure. Contaminated clothing should be removed and placed in airtight bags to prevent secondary exposure. Skin irrigation with copious cold water is used for significant dermal exposures.[9] Symptomatic treatments, such as topical ophthalmic anesthetics, nebulized bronchodilators, or oral antihistamines and corticosteroids, are indicated as appropriate in more severely affected victims.[9] Capsaicin-induced dermatitis has been treated variably with immersion in water or oil, vinegar, bleach, lidocaine gel, and topical antacid suspensions. Cold water produces earlier symptomatic relief, but oil immersion has longer-lasting benefit.[9]
References
^ Stewart C Jr, Kang BC, Liu K, Mazourek M, Moore SL, Yoo EY, Kim BD, Paran I, Jahn MM. The Pun1 gene for pungency in pepper encodes a putative acyltransferase. Plant J. 2005 Jun;42(5):675-88. [1] Accessed June 15, 2007 
^ New Mexico State University - College of Agriculture and Home Economics (2005). [http://spectre.nmsu.edu/dept/academic.html?i=1274&s=sub Chile Information - Frequently Asked Questions]. Retrieved on May 17, 2007. 
^ Siemens J, Zhou S, Piskorowski R, Nikai T, Lumpkin EA, Basbaum AI, King D, Julius D. (2006). Spider toxins activate the capsaicin receptor to produce inflammatory pain.. 
^ Dave DeWitt (1999). Burning in the Mouth, Fire in the Belly. Retrieved on May 18, 2007. 
^ American Association for Cancer Research (2006). Pepper component hot enough to trigger suicide in prostate cancer cells. Retrieved on January 27, 2007. 
^ BBC News (2007). How spicy foods can kill cancers. Retrieved on January 09, 2007. 
^ Cromie WJ (2006) "Using chili peppers to burn drug abusers" Harvard University Gazette accessed 24 January 2006 
^ Capsaicin Material Safety Data Sheet (pdf). sciencelab.com (2007). Retrieved on 2007-07-13. 
^ a b c d e f Goldfrank, L R. (ed.). Goldfrank's Toxicologic Emergencies. New York, New York: McGraw-Hill, 1167.  
Dray A (1992) "Mechanism of action of capsaicin-like molecules on sensory neurons" Life Sci 51(23):1759-65 
Garnanez RJ, McKee LH (2001) "Temporal effectiveness of sugar solutions on mouth burn by capsaicin" IFT Annual Meeting 2001 
Henkin R (1991) '"Cooling the burn from hot peppers" JAMA 266(19):2766 
Nasrawi CW, Pangborn RM (1990) "Temporal effectiveness of mouth-rinsing on capsaicin mouth-burn" Physiol Behav 47(4):617-23 
Tewksbury JJ, Nabhan GP (2001) "Seed dispersal: Directed deterrence by capsaicin in chillies" Nature 412, 403-404 (26 July 2001), doi: 10.1038/35086653 
Michael L. Kirifides1, Michael P. Kurnellas1, Larry Clark2 and Bruce P. Bryant1, "Calcium responses of chicken trigeminal ganglion neurons to methyl 
anthranilate and capsaicin" The Journal of Experimental Biology 207, 715-722 Published by The Company of Biologists 2004
Tarantula Venom, Chili Peppers Have Same "Bite," Study Finds http://news.nationalgeographic.com/news/2006/11/061108-tarantula-venom.html 
[edit] See also
Piperine, the active piquant chemical in black pepper 
Allyl isothiocyanate, the active piquant chemical in mustard, radishes, horseradish, and wasabi 
Allicin, the active piquant flavor chemical in uncooked garlic and onions (see those articles for discussion of other chemicals in them relating to pungency, and eye irritation) 
Naga Jolokia pepper, the world's most capsaicin-rich fruit 
[edit] External links
Capsaicin and Its Therapeutic Potential 
Molecule of the Month 
European Commission, opinion of the Scientific Committee on Food on capsaicin. 
An online article on popular capsaicin applications by Dave DeWitt 
A WikiHow article on How to Cool Chili Pepper Burns. 
The Straight Dope staff report: Are birds immune to hot pepper, enabling them to eat vast amounts and spread the seeds? 
Red Hot Chilies, Future of Medicine: Myth OR Real? 
[2] 
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