Capsaicin
Capsaicin (/kæpˈseɪ.ɪsɪn/ (INN); 8-methyl-N-vanillyl-6-nonenamide) is an 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 secondary metabolites by chili peppers, probably as deterrents against certain mammals and fungi. Pure capsaicin is a hydrophobic, colorless, highly pungent, crystalline to the waxy solid compound.
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 provide added spice or "heat" (piquancy), usually in the form of spices such as chili powder and paprika. In high concentrations, capsaicin will also cause a burning effect on other sensitive areas, such as skin or eyes. The degree of heat found within a food is often measured on the Scoville scale. Because people enjoy the heat, there has long been a demand for capsaicin-spiced products like curry, chili con carne, and hot sauces such as Tabasco sauce and salsa.
It is common for people to experience pleasurable and even euphoric effects from ingesting capsaicin. Folklore among self-described "chiliheads" attributes this to the pain-stimulated release of endorphins, a different mechanism from the local receptor overload that makes capsaicin effective as a topical analgesic.
Contents
Research and pharmaceutical use
Capsaicin is used as an analgesic in topical ointments and dermal patches to relieve pain, typically in concentrations between 0.025% and 0.1%. It may be applied in cream form for the temporary relief of minor aches and pains of muscles and joints associated with arthritis, backache, strains and sprains, often in compounds with other rubefacients.
It is also used to reduce the symptoms of peripheral neuropathy, such as post-herpetic neuralgia caused by shingles. Capsaicin transdermal patch (Qutenza) for the management of this particular therapeutic indication (pain due to post-herpetic neuralgia) was approved as a therapeutic by the U.S. FDA, but a subsequent application for Qutenza to be used as an analgesic in HIV neuralgia was refused. One 2017 review of clinical studies having limited quality found that high-dose topical capsaicin (8%) compared with control (0.4% capsaicin) provided moderate to substantial pain relief from post-herpetic neuralgia, HIV-neuropathy, and diabetic neuropathy.
Although capsaicin creams have been used to treat psoriasis for reduction of itching, a review of six clinical trials involving topical capsaicin for treatment of pruritus concluded there was insufficient evidence of effect.
There is insufficient clinical evidence to determine the role of ingested capsaicin on several human disorders, including obesity, diabetes, cancer and cardiovascular diseases.
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 (TRPV1).[54] First cloned in 1997, TRPV1 is an ion channel-type receptor.[55] TRPV1, which can also be stimulated with heat, protons and physical abrasion, permits cations to pass through the cell membrane when activated. The resulting depolarization of the neuron stimulates it to signal the brain. By binding to the TRPV1 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 long-onset current in comparison to other chemical agonists, suggesting the involvement of a significant rate-limiting factor.[56] Subsequent to this, the TRPV1 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[57] culminating in the release of neuropeptides. In essence, 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.
Toxicity
Acute health effects
Capsaicin is a strong irritant requiring proper protective goggles, respirators, and proper hazardous material-handling procedures. Capsaicin takes effect upon skin contact (irritant, sensitizer), eye contact (irritant), ingestion, and inhalation (lung irritant, lung sensitizer). LD50 in mice is 47.2 mg/kg.
Painful exposures to capsaicin-containing peppers are among the most common plant-related exposures presented to poison centers. 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. Eye exposure produces intense tearing, pain, conjunctivitis, and blepharospasm.
Effects on weight loss and regain
As of 2007 there was no evidence showing that weight loss is directly correlated with ingesting capsaicin. Well-designed clinical studies had not been performed because the pungency of capsaicin in prescribed doses under research prevents subject compliance. A 2014 meta-analysis of further trials that had been run, found weak, uneven evidence suggesting that consuming capsaicin before a meal might slightly reduce the amount of food that people eat and might drive food choice toward carbohydrates.
Reference
1. "Capsaicin", from Wikipeida
