Curcumin is a bright yellow chemical produced by some plants. It is the principal curcuminoid of turmeric (Curcuma longa), a member of the ginger family, Zingiberaceae. It is sold as an herbal supplement, cosmetics ingredient, food flavoring, and food coloring.
Chemically, curcumin is a diarylheptanoid, belonging to the group of curcuminoids, which are natural phenols responsible for turmeric's yellow color. It is a tautomeric compound existing in enolic form in organic solvents, and as a keto form in water. Although thoroughly studied in laboratory and clinical studies, curcumin has no confirmed medical uses, and has proved frustrating to scientists because it is unstable, not bioavailable, and unlikely to produce useful leads for drug development.
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History
It was first isolated in 1815 when Vogel and Pierre Joseph Pelletier reported the isolation of a "yellow coloring-matter" from the rhizomes of turmeric and named it curcumin. Although curcumin has been used historically in Ayurvedic medicine, its potential for medicinal properties remains unproven as a therapy when used orally.
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Uses
The most common applications are as an ingredient in dietary supplement, in cosmetics, and as flavoring for foods, such as turmeric-flavored beverages in the Indian Subcontinent and Southeast Asia. As a food additive for gold-orange coloring in turmeric and prepared foods, its E number is E100.
Annual sales of curcumin have increased since 2012, largely due to an increase in its popularity. It is present in skincare products that are marketed as containing natural ingredients or dyes, especially in Asia. The largest market is in North America, where sales exceeded US$20 million in 2014.
Chemistry
Curcumin incorporates several functional groups whose structure was first identified in 1910. The aromatic ring systems, which are phenols, are connected by two ?,?-unsaturated carbonyl groups. The diketones form stable enols and are readily deprotonated to form enolates; the ?,?-unsaturated carbonyl group is a good Michael acceptor and undergoes nucleophilic addition.
Curcumin is used as a complexometric indicator for boron. It reacts with boric acid to form a red-colored compound, rosocyanine.
Biosynthesis
The biosynthetic route of curcumin is uncertain. In 1973, Roughly and Whiting proposed two mechanisms for curcumin biosynthesis. The first mechanism involves a chain extension reaction by cinnamic acid and 5 malonyl-CoA molecules that eventually arylized into a curcuminoid. The second mechanism involves two cinnamate units coupled together by malonyl-CoA. Both use cinnamic acid as their starting point, which is derived from the amino acid phenylalanine.
Plant biosyntheses starting with cinnamic acid is rare compared to the more common p-coumaric acid. Only a few identified compounds, such as anigorufone and pinosylvin, build from cinnamic acid.
Pharmacology
Curcumin, which shows positive results in most drug discovery assays, is regarded as a false lead that medicinal chemists include among "pan-assay interference compounds" attracting undue experimental attention while failing to advance as viable therapeutic or drug leads. In vitro, curcumin inhibits certain epigenetic enzymes (the histone deacetylases: HDAC1, HDAC3, HDAC8), transcriptional co-activator proteins (the p300 histone acetyltransferase) and the arachidonate 5-lipoxygenase enzyme.
Factors that limit the bioactivity of curcumin or its analogs include chemical instability, water insolubility, absence of potent and selective target activity, low bioavailability, limited tissue distribution, extensive metabolism, and potential for toxicity.
Safety
Two preliminary clinical studies in cancer patients consuming high doses of curcumin (up to 8 grams per day for 3-4 months) showed no toxicity, though some subjects reported mild nausea or diarrhea.
Research
In vitro, curcumin exhibits numerous interference properties which may lead to misinterpretation of results. Although curcumin has been assessed in numerous laboratory and clinical studies, it has no medical uses established by well-designed clinical research. According to a 2017 review of over 120 studies, curcumin has not been successful in any clinical trial, leading the authors to conclude that "curcumin is an unstable, reactive, non-bioavailable compound and, therefore, a highly improbable lead".
Cancer studies using curcumin conducted by Bharat Aggarwal, formerly a researcher at the MD Anderson Cancer Center, were deemed fraudulent and subsequently retracted by the publisher.
Alternative medicine
Despite concerns about safety or efficacy and the absence of reliable clinical research, some alternative medicine practitioners give turmeric intravenously, supposedly as a treatment for numerous diseases. In 2017 there were two serious cases of adverse events reported - one severe allergic reaction and one death - that were caused by injection of a curcumin emulsion product administered by a naturopath.
The US government has supported $150 million in research into curcumin through the National Center for Complementary and Integrative Health, and no support has been found for curcumin as a medical treatment.
Source of the article : Wikipedia
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