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Salicylic acid (from Latin salix, willow tree) is a lipophilic monohydroxybenzoic acid, a type of phenolic acid, and a beta hydroxy acid (BHA). It has the formula C7H6O3. This colorless crystalline organic acid is widely used in organic synthesis and functions as a plant hormone. It is derived from the metabolism of salicin. In addition to serving as an important active metabolite of aspirin (acetylsalicylic acid), which acts in part as a prodrug to salicylic acid, it is probably best known for its use as a key ingredient in topical anti-acne products. The salts and esters of salicylic acid are known as salicylates. The medicinal part of the willow tree is the inner bark.
It is on the WHO Model List of Essential Medicines, the most important medications needed in a basic health system.
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Uses
Medicine
Salicylic acid as a medication is used most commonly to help remove the outer layer of the skin. As such it is used to treat warts, psoriasis, dandruff, acne, ringworm, and ichthyosis.
As with other hydroxy acids, salicylic acid is a key ingredient in many skin-care products for the treatment of seborrhoeic dermatitis, acne, psoriasis, calluses, corns, keratosis pilaris, acanthosis nigricans, ichthyosis and warts.
Manufacturing
Salicylic acid is used in the production of other pharmaceuticals, including 4-aminosalicylic acid sandulpiride landetimide (via Salethamide).
Salicylic acid was one of the original starting materials for making acetylsalicylic acid (aspirin) in 1897.
Bismuth subsalicylate, a salt of bismuth and salicylic acid, is the active ingredient in stomach relief aids such as Pepto-Bismol, is the main ingredient of Kaopectate and "displays anti-inflammatory action (due to salicylic acid) and also acts as an antacid and mild antibiotic".
Other derivatives include methyl salicylate used as a liniment to soothe joint and muscle pain and choline salicylate used topically to relieve the pain of mouth ulcers.
Chemistry
Salicylic acid has the formula C6H4(OH)COOH, where the OH group is ortho to the carboxyl group. It is also known as 2-hydroxybenzoic acid. It is poorly soluble in water (2 g/L at 20 °C). Aspirin (acetylsalicylic acid or ASA) can be prepared by the esterification of the phenolic hydroxyl group of salicylic acid with the acetyl group from acetic anhydride or acetyl chloride. Salicylic acid can also be prepared using the Kolbe-Schmitt reaction.
Other uses
Salicylic acid is used as a food preservative, a bactericidal and an antiseptic.
Sodium salicylate is a useful phosphor in the vacuum ultraviolet, with nearly flat quantum efficiency for wavelengths between 10 and 100 nm. It fluoresces in the blue at 420 nm. It is easily prepared on a clean surface by spraying a saturated solution of the salt in methanol followed by evaporation.
Body Washes With Salicylic Acid Video
Safety
Burns
As a topical agent and as a beta-hydroxy acid (and unlike alpha-hydroxy acids), salicylic acid is capable of penetrating and breaking down fats and lipids, causing moderate chemical burns of the skin at very high concentrations. It may damage the lining of pores if the solvent is alcohol, acetone or an oil. Over-the-counter limits are set at 2% for topical preparations expected to be left on the face and 3% for those expected to be washed off, such as acne cleansers or shampoo. 17% and 27% salicylic acid, which is sold for wart removal, should not be applied to the face and should not be used for acne treatment. Even for wart removal, such a solution should be applied once or twice a day - more frequent use may lead to an increase in side-effects without an increase in efficacy.
Hearing
When ingested, salicylic acid has a possible ototoxic effect by inhibiting prestin. It can induce transient hearing loss in zinc-deficient rats. An injection of salicylic acid induced hearing loss, while an injection of zinc reversed the hearing loss. An injection of magnesium in the zinc-deficient rats did not reverse the induced hearing loss.
Pregnancy
No studies examine topical salicylic acid in pregnancy. Oral salicylic acid is not associated with an increase in malformations if used during the first trimester, but in late pregnancy has been associated with bleeding, especially intracranial bleeding. The risks of aspirin late in pregnancy are probably not relevant for a topical exposure to salicylic acid, even late in the pregnancy, because of its low systemic levels. Topical salicylic acid is common in many over-the-counter dermatological agents and the lack of adverse reports suggests a low teratogenic potential.
Overdose
Salicylic acid overdose can lead to salicylate intoxication, which often presents clinically in a state of metabolic acidosis with compensatory respiratory alkalosis. In patients presenting with an acute overdose, a 16% morbidity rate and a 1% mortality rate are observed.
Allergy
Some people are hypersensitive to salicylic acid and related compounds.
Sun exposure
The United States Food and Drug Administration (FDA) recommends the use of sun protection when using skincare products containing salicylic acid (or any other BHA) on sun-exposed skin areas.
Reye's syndrome
Data support an association between exposure to salicylic acid and Reye's Syndrome. The National Reye's Syndrome Foundation cautions against the use of these and other substances similar to aspirin on children and adolescents. Epidemiological research associated the development of Reye's Syndrome and the use of aspirin for treating the symptoms of influenza-like illnesses, chicken pox, colds, etc. The U.S. Surgeon General, the FDA, the Centers for Disease Control and Prevention and the American Academy of Pediatrics recommend that aspirin and combination products containing aspirin not be given to children under 19 years of age during episodes of fever-causing illnesses.
Mechanism of action
Salicylic acid works through several different pathways. It produces its anti-inflammatory effects via suppressing the activity of cyclooxygenase (COX), an enzyme that is responsible for the production of pro-inflammatory mediators such as the prostaglandins. It does this not by direct inhibition of COX like most other non-steroidal anti-inflammatory drugs (NSAIDs) but instead by suppression of the expression of the enzyme through a mechanism not yet understood.
Salicylic acid activates adenosine monophosphate-activated protein kinase (AMPK) and this action may play a role in the anticancer effects of the compound and its prodrugs aspirin and salsalate. The antidiabetic effects of salicylic acid are likely mediated by AMPK activation primarily through allosteric conformational change that increases levels of phosphorylation.
Salicylic acid also uncouples oxidative phosphorylation, which leads to increased ADP:ATP and AMP:ATP ratios in the cell. As a consequence, salicylic acid may alter AMPK activity and work as an anti-diabetic by altering the energy status of the cell. AMPK knockout mice display an anti-diabetic effect, demonstrating at least one additional, yet unidentified action.
Salicylic acid regulates c-Myc level at both transcriptional and post-transcription levels. Inhibition of c-Myc may be an important pathway by which aspirin exerts an anti-cancer effect, decreasing the occurrence of cancer in epithelial tissues.
Plant hormone
Salicylic acid (SA) is a phenolic phytohormone and is found in plants with roles in plant growth and development, photosynthesis, transpiration, ion uptake and transport. SA also induces specific changes in leaf anatomy and chloroplast structure. SA is involved in endogenous signaling, mediating in plant defense against pathogens. It plays a role in the resistance to pathogens by inducing the production of pathogenesis-related proteins. It is involved in the systemic acquired resistance (SAR) in which a pathogenic attack on one part of the plant induces resistance in other parts. The signal can also move to nearby plants by salicylic acid being converted to the volatile ester, methyl salicylate.
Production
Salicylic acid is biosynthesized from the amino acid phenylalanine. In Arabidopsis thaliana it can be synthesized via a phenylalanine-independent pathway.
Sodium salicylate is commercially prepared by treating sodium phenolate (the sodium salt of phenol) with carbon dioxide at high pressure (100 atm) and high temperature (390 K) - a method known as the Kolbe-Schmitt reaction. Acidification of the product with sulfuric acid gives salicylic acid:
It can also be prepared by the hydrolysis of aspirin (acetylsalicylic acid) or methyl salicylate (oil of wintergreen) with a strong acid or base.
History
Hippocrates, Galen, Pliny the Elder and others knew that willow bark could ease pain and reduce fevers. It was used in Europe and China to treat these conditions. This remedy is mentioned in texts from ancient Egypt, Sumer and Assyria. The Cherokee and other Native Americans used an infusion of the bark for fever and other medicinal purposes.
In 2014, archaeologists identified traces of salicylic acid on 7th century pottery fragments found in east central Colorado. The Reverend Edward Stone, a vicar from Chipping Norton, Oxfordshire, England, noted in 1763 that the bark of the willow was effective in reducing a fever.
The active extract of the bark, called salicin, after the Latin name for the white willow (Salix alba), was isolated and named by the German chemist Johann Andreas Buchner in 1828. A larger amount of the substance was isolated in 1829 by Henri Leroux, a French pharmacist. Raffaele Piria, an Italian chemist, was able to convert the substance into a sugar and a second component, which on oxidation becomes salicylic acid.
Salicylic acid was also isolated from the herb meadowsweet (Filipendula ulmaria, formerly classified as Spiraea ulmaria) by German researchers in 1839. While their extract was somewhat effective, it also caused digestive problems such as gastric irritation, bleeding, diarrhea and even death when consumed in high doses.
Dietary sources
Salicylic acid occurs in plants as free salicylic acid and its carboxylated esters and phenolic glycosides. Several studies suggest that humans metabolize salicylic acid in measurable quantities from these plants; one study found that vegetarians not taking aspirin had urinary levels of salicylic acid roughly 5% those of patients taking 75 mg of aspirin per day, while the non-vegetarians had levels roughly one-third that of vegetarians. Dietary sources of salicylic acid and their interaction with drugs such as aspirin have not been well studied. Ongoing clinical studies of patients with aspirin-induced asthma have shown some benefits of a diet low in salicylic acid. Dietary salicylic acid may be partially responsible for the health benefits of a plant-based diet.
Studies on the salicylic content of foods are sparse and have produced distinctly different results, creating controversy. Possible causes for the discrepancies include uncontrolled and often unreported factors such as cultivation area, crop species, and harvest methods, as well as inherent issues with the studies such as poor extraction and measurement procedures and limited or low-accuracy equipment. A recent study using best practice measurement methodology significantly reduced intra-sample measurement variability but has not yet been replicated or extended.
Some results have been consistently reported. Meat, poultry, fish, eggs, oils, dairy products, sugar, cereals, and flour all have little to no salicylates. Measurable levels of salicylic acid have been found in fruits, vegetables, herbs, spices, nuts, and teas.
Source of the article : Wikipedia
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