catechin

File:Catechin numbered.svg

Catechin possesses two benzene rings (called the A and B rings) and a dihydropyran heterocycle (the C ring) with a hydroxyl group on carbon 3. The A ring is similar to a resorcinol moiety while the B ring is similar to a catechol moiety. There are two chiral centers on the molecule on carbons 2 and 3. Therefore, it has four diastereoisomers. Two of the isomers are in trans configuration and are called catechin and the other two are in cis configuration and are called epicatechin.

The most common catechin isomer is (+)-catechin. The other stereoisomer is (−)-catechin or ent-catechin. The most common epicatechin isomer is (−)-epicatechin (also known under the names L-epicatechin, epicatechol, (−)-epicatechol, L-acacatechin, L-epicatechol, epicatechin, 2,3-cis-epicatechin or (2R,3R)-(−)-epicatechin).

The different epimers can be separated using chiral column chromatography.{{cite journal | vauthors = Rinaldo D, Batista JM, Rodrigues J, Benfatti AC, Rodrigues CM, dos Santos LC, Furlan M, Vilegas W | display-authors = 6 | title = Determination of catechin diastereomers from the leaves of Byrsonima species using chiral HPLC-PAD-CD | journal = Chirality | volume = 22 | issue = 8 | pages = 726–733 | date = August 2010 | pmid = 20143413 | doi = 10.1002/chir.20824 }}

Making reference to no particular isomer, the molecule can just be called catechin. Mixtures of the different enantiomers can be called (±)-catechin or DL-catechin and (±)-epicatechin or DL-epicatechin.

Catechin and epicatechin are the building blocks of the proanthocyanidins, a type of condensed tannin.

File:(+)-Catechin.png|(+)-catechin (2R,3S)

File:Catechin.png|(−)-catechin (2S,3R)

File:(-)-Epicatechin.svg|(−)-epicatechin (2R,3R)

File:(+)-epicatechin.svg|(+)-epicatechin (2S,3S)

File:Catechin above.PNG

Moreover, the flexibility of the C-ring allows for two conformation isomers, putting the B-ring either in a pseudoequatorial position (E conformer) or in a pseudoaxial position (A conformer). Studies confirmed that (+)-catechin adopts a mixture of A- and E-conformers in aqueous solution and their conformational equilibrium has been evaluated to be 33:67.{{cite journal | vauthors = Kríz Z, Koca J, Imberty A, Charlot A, Auzély-Velty R | title = Investigation of the complexation of (+)-catechin by beta-cyclodextrin by a combination of NMR, microcalorimetry and molecular modeling techniques | journal = Organic & Biomolecular Chemistry | volume = 1 | issue = 14 | pages = 2590–2595 | date = July 2003 | pmid = 12956082 | doi = 10.1039/B302935M }}

As flavonoids, catechins can act as antioxidants when in high concentration in vitro, but compared with other flavonoids, their antioxidant potential is low.{{cite journal | vauthors = Pietta PG | title = Flavonoids as antioxidants | journal = Journal of Natural Products | volume = 63 | issue = 7 | pages = 1035–1042 | date = July 2000 | pmid = 10924197 | doi = 10.1021/np9904509 | s2cid = 23310671 }} The ability to quench singlet oxygen seems to be in relation with the chemical structure of catechin, with the presence of the catechol moiety on ring B and the presence of a hydroxyl group activating the double bond on ring C.{{cite journal | vauthors = Tournaire C, Croux S, Maurette MT, Beck I, Hocquaux M, Braun AM, Oliveros E | title = Antioxidant activity of flavonoids: efficiency of singlet oxygen (¹Δ_g) quenching | journal = Journal of Photochemistry and Photobiology. B, Biology | volume = 19 | issue = 3 | pages = 205–215 | date = August 1993 | pmid = 8229463 | doi = 10.1016/1011-1344(93)87086-3 }}

Electrochemical experiments show that (+)-catechin oxidation mechanism proceeds in sequential steps, related with the catechol and resorcinol groups and the oxidation is pH-dependent. The oxidation of the catechol 3′,4′-dihydroxyl electron-donating groups occurs first, at very low positive potentials, and is a reversible reaction. The hydroxyl groups of the resorcinol moiety oxidised afterwards were shown to undergo an irreversible oxidation reaction.{{cite journal |doi=10.1016/j.aca.2004.05.038 |title=Catechin electrochemical oxidation mechanisms |year=2004 | vauthors = Janeiro P, Oliveira Brett AM |journal=Analytica Chimica Acta |volume=518 |issue=1–2 |pages=109–115|bibcode=2004AcAC..518..109J |hdl=10316/5128 |hdl-access=free }}

The laccase–ABTS system oxidizes (+)-catechin to oligomeric products{{cite journal |doi=10.1016/j.enzmictec.2006.09.018 |title=The laccase/ABTS system oxidizes (+)-catechin to oligomeric products | date = April 2007 | vauthors = Osman AM, Wong KK, Fernyhough A |journal=Enzyme and Microbial Technology |volume=40 |issue=5 |pages=1272–1279}} of which proanthocyanidin A2 is a dimer.

File:Spectre UV-vis catechine.PNG

(+)-Catechin and (−)-epicatechin as well as their gallic acid conjugates are ubiquitous constituents of vascular plants, and frequent components of traditional herbal remedies, such as Uncaria rhynchophylla. The two isomers are mostly found as cacao and tea constituents, as well as in Vitis vinifera grapes.{{cite journal | vauthors = Aizpurua-Olaizola O, Ormazabal M, Vallejo A, Olivares M, Navarro P, Etxebarria N, Usobiaga A | title = Optimization of supercritical fluid consecutive extractions of fatty acids and polyphenols from Vitis vinifera grape wastes | journal = Journal of Food Science | volume = 80 | issue = 1 | pages = E101–E107 | date = January 2015 | pmid = 25471637 | doi = 10.1111/1750-3841.12715 }}{{cite journal |doi=10.1021/ja01344a026 |year=1932 | vauthors = Freudenberg K, Cox RF, Braun E |title=The Catechin of the Cacao Bean |journal=Journal of the American Chemical Society |volume=54 |issue=5 |pages=1913–1917}}{{cite web|url=http://archives.cf.ocha.ac.jp/en/researcher/tsujimura_michiyo.html|title=Michiyo Tsujimura (1888–1969)|access-date=10 November 2015|archive-date=21 November 2015|archive-url=https://web.archive.org/web/20151121161332/http://archives.cf.ocha.ac.jp/en/researcher/tsujimura_michiyo.html}}

{{main|Phenolic content in tea|Phenolic content in wine}}

The main dietary sources of catechins in Europe and the United States are tea and pome fruits.{{cite journal | vauthors = Chun OK, Chung SJ, Song WO | title = Estimated dietary flavonoid intake and major food sources of U.S. adults | journal = The Journal of Nutrition | volume = 137 | issue = 5 | pages = 1244–1252 | date = May 2007 | pmid = 17449588 | doi = 10.1093/jn/137.5.1244 | doi-access = free }}{{cite journal | vauthors = Vogiatzoglou A, Mulligan AA, Lentjes MA, Luben RN, Spencer JP, Schroeter H, Khaw KT, Kuhnle GG | display-authors = 6 | title = Flavonoid intake in European adults (18 to 64 years) | journal = PLoS One | volume = 10 | issue = 5 | pages = e0128132 | year = 2015 | pmid = 26010916 | pmc = 4444122 | doi = 10.1371/journal.pone.0128132 | doi-access = free | bibcode = 2015PLoSO..1028132V }}

Catechins and epicatechins are found in cocoa,{{cite journal | vauthors = Kwik-Uribe C, Bektash RM | title = Cocoa flavanols – measurement, bioavailability and bioactivity | journal = Asia Pacific Journal of Clinical Nutrition | volume = 17 | issue = Suppl. 1 | pages = 280–283 | date = 2008 | pmid = 18296356 | url = http://apjcn.nhri.org.tw/server/APJCN/17%20Suppl%201//280.pdf }} which, according to one database, has the highest content (108 mg/100 g) of catechins among foods analyzed, followed by prune juice (25 mg/100 ml) and broad bean pod (16 mg/100 g). Açaí oil, obtained from the fruit of the açaí palm (Euterpe oleracea), contains (+)-catechins (67 mg/kg).{{cite journal | vauthors = Pacheco-Palencia LA, Mertens-Talcott S, Talcott ST | title = Chemical composition, antioxidant properties, and thermal stability of a phytochemical enriched oil from Açaí (Euterpe oleracea Mart.) | journal = Journal of Agricultural and Food Chemistry | volume = 56 | issue = 12 | pages = 4631–4636 | date = June 2008 | pmid = 18522407 | doi = 10.1021/jf800161u }}

Catechins are diverse among foods, from peaches{{cite journal | vauthors = Cheng GW, Crisosto CH | year = 1995 | title = Browning Potential, Phenolic Composition, and Polyphenoloxidase Activity of Buffer Extracts of Peach and Nectarine Skin Tissue | journal = Journal of the American Society for Horticultural Science | volume = 120 | issue = 5 | pages = 835–838 | doi = 10.21273/JASHS.120.5.835 | doi-access = free }} to green tea and vinegar.{{cite web|url=http://phenol-explorer.eu/contents/food/29|title=Polyphenols in green tea infusion|publisher=Phenol-Explorer, v3.5|date=2014|access-date=1 November 2014}}{{cite journal |doi=10.1007/BF01192948 |title=Analysis of polyphenolic compounds of different vinegar samples |year=1994 | vauthors = Gálvez MC, Barroso CG, Pérez-Bustamante JA |journal=Zeitschrift für Lebensmittel-Untersuchung und -Forschung |volume=199 |issue=1 |pages=29–31|s2cid=91784893 }} Catechins are found in barley grain, where they are the main phenolic compound responsible for dough discoloration.{{cite journal | vauthors = Quinde-Axtell Z, Baik BK | title = Phenolic compounds of barley grain and their implication in food product discoloration | journal = Journal of Agricultural and Food Chemistry | volume = 54 | issue = 26 | pages = 9978–9984 | date = December 2006 | pmid = 17177530 | doi = 10.1021/jf060974w }} The taste associated with monomeric (+)-catechin or (−)-epicatechin is described as slightly astringent, but not bitter.{{cite journal |doi=10.1016/S0950-3293(98)00049-4 |title=Oral sensations associated with the flavan-3-ols (+)-catechin and (−)-epicatechin |year=1999 | last1 = Kielhorn |first1=S. |last2=Thorngate |first2=J. H. III |journal=Food Quality and Preference |volume=10 |issue=2 |pages=109–116}}

File:Biosynthesis_of_4-hydroxycinnamoyl-CoA.png

The biosynthesis of catechin begins with ma 4-hydroxycinnamoyl CoA starter unit which undergoes chain extension by the addition of three malonyl-CoAs through a PKSIII pathway. 4-Hydroxycinnamoyl CoA is biosynthesized from L-phenylalanine through the Shikimate pathway. L-Phenylalanine is first deaminated by phenylalanine ammonia lyase (PAL) forming cinnamic acid which is then oxidized to 4-hydroxycinnamic acid by cinnamate 4-hydroxylase. Chalcone synthase then catalyzes the condensation of 4-hydroxycinnamoyl CoA and three molecules of malonyl-CoA to form chalcone. Chalcone is then isomerized to naringenin by chalcone isomerase which is oxidized to eriodictyol by flavonoid 3′-hydroxylase and further oxidized to taxifolin by flavanone 3-hydroxylase. Taxifolin is then reduced by dihydroflavanol 4-reductase and leucoanthocyanidin reductase to yield catechin. The biosynthesis of catechin is shown below{{cite journal | vauthors = Rani A, Singh K, Ahuja PS, Kumar S | title = Molecular regulation of catechins biosynthesis in tea [Camellia sinensis (L.) O. Kuntze] | journal = Gene | volume = 495 | issue = 2 | pages = 205–210 | date = March 2012 | pmid = 22226811 | doi = 10.1016/j.gene.2011.12.029 }}{{cite journal | vauthors = Punyasiri PA, Abeysinghe IS, Kumar V, Treutter D, Duy D, Gosch C, Martens S, Forkmann G, Fischer TC | display-authors = 6 | title = Flavonoid biosynthesis in the tea plant Camellia sinensis: properties of enzymes of the prominent epicatechin and catechin pathways | journal = Archives of Biochemistry and Biophysics | volume = 431 | issue = 1 | pages = 22–30 | date = November 2004 | pmid = 15464723 | doi = 10.1016/j.abb.2004.08.003 }}{{cite book | vauthors = Dewick PM |title=Medicinal Natural Products: A Biosynthetic Approach |edition=3rd |year=2009 |publisher=John Wiley & Sons |location=UK |isbn=978-0-470-74167-2}}{{page needed|date=July 2013}}

Leucocyanidin reductase (LCR) uses 2,3-trans-3,4-cis-leucocyanidin to produce (+)-catechin and is the first enzyme in the proanthocyanidin (PA) specific pathway. Its activity has been measured in leaves, flowers, and seeds of the legumes Medicago sativa, Lotus japonicus, Lotus uliginosus, Hedysarum sulfurescens, and Robinia pseudoacacia.{{cite journal | vauthors = Skadhauge B, Gruber MY, Thomsen KK, Von Wettstein D |date=April 1997 |title=Leucocyanidin Reductase Activity and Accumulation of Proanthocyanidins in Developing Legume Tissues |journal=American Journal of Botany |volume=84 |issue=4 |pages=494–503 |jstor=2446026 |doi=10.2307/2446026}} The enzyme is also present in Vitis vinifera (grape).{{cite journal | vauthors = Maugé C, Granier T, d'Estaintot BL, Gargouri M, Manigand C, Schmitter JM, Chaudière J, Gallois B | display-authors = 6 | title = Crystal structure and catalytic mechanism of leucoanthocyanidin reductase from Vitis vinifera | journal = Journal of Molecular Biology | volume = 397 | issue = 4 | pages = 1079–1091 | date = April 2010 | pmid = 20138891 | doi = 10.1016/j.jmb.2010.02.002 }}

File:Biosynthesis of catechin.png

Catechin oxygenase, a key enzyme in the degradation of catechin, is present in fungi and bacteria.{{cite journal|url=http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20008a2f_353.pdf |title=Biodegradation of Catechin |first1=M. |last1=Arunachalam |first2=M. |last2=Mohan Raj |first3=N. |last3=Mohan |first4=A. |last4=Mahadevan |journal=Proceedings of the Indian National Science Academy |volume=B69 |issue=4 |pages=353–370 |date=2003 |archive-url=https://web.archive.org/web/20120316083221/http://www.new.dli.ernet.in/rawdataupload/upload/insa/INSA_1/20008a2f_353.pdf |archive-date=2012-03-16 }}

Among bacteria, degradation of (+)-catechin can be achieved by Acinetobacter calcoaceticus. Catechin is metabolized to protocatechuic acid (PCA) and phloroglucinol carboxylic acid (PGCA).{{cite journal | vauthors = Arunachalam M, Mohan N, Sugadev R, Chellappan P, Mahadevan A | title = Degradation of (+)-catechin by Acinetobacter calcoaceticus MTC 127 | journal = Biochimica et Biophysica Acta (BBA): General Subjects| volume = 1621 | issue = 3 | pages = 261–265 | date = June 2003 | pmid = 12787923 | doi = 10.1016/S0304-4165(03)00077-1 }} It is also degraded by Bradyrhizobium japonicum. Phloroglucinol carboxylic acid is further decarboxylated to phloroglucinol, which is dehydroxylated to resorcinol. Resorcinol is hydroxylated to hydroxyquinol. Protocatechuic acid and hydroxyquinol undergo intradiol cleavage through protocatechuate 3,4-dioxygenase and hydroxyquinol 1,2-dioxygenase to form [[3-Carboxy-cis,cis-muconic acid|β-carboxy-cis,cis-muconic acid

]] and maleyl acetate.{{cite journal | doi = 10.1023/A:1008254812074 | year = 1997 | vauthors = Hopper W, Mahadevan A | journal = Biodegradation | title=Degradation of catechin by Bradyrhizobium japonicum|volume = 8 | issue = 3 | pages = 159–165| s2cid = 41221044 }}

Among fungi, degradation of catechin can be achieved by Chaetomium cupreum.{{cite journal | vauthors = Sambandam T, Mahadevan A | title = Degradation of catechin and purification and partial characterization of catechin oxygenase from Chaetomium cupreum | journal = World Journal of Microbiology & Biotechnology | volume = 9 | issue = 1 | pages = 37–44 | date = January 1993 | pmid = 24419836 | doi = 10.1007/BF00656513 | s2cid = 1257624 }}

File:Epicatechin metabolites.png

File:Schematic representation of (−)-epicatechin metabolism in humans as a function of time post-oral intake.jpg

Catechins are metabolised upon uptake from the gastrointestinal tract, in particular the jejunum,{{cite journal | vauthors = Actis-Goretta L, Lévèques A, Rein M, Teml A, Schäfer C, Hofmann U, Li H, Schwab M, Eichelbaum M, Williamson G | display-authors = 6 | title = Intestinal absorption, metabolism, and excretion of (−)-epicatechin in healthy humans assessed by using an intestinal perfusion technique | journal = The American Journal of Clinical Nutrition | volume = 98 | issue = 4 | pages = 924–933 | date = October 2013 | pmid = 23864538 | doi = 10.3945/ajcn.113.065789 | doi-access = free }} and in the liver, resulting in so-called structurally related epicatechin metabolites (SREM).{{cite journal | vauthors = Ottaviani JI, Momma TY, Kuhnle GK, Keen CL, Schroeter H | title = Structurally related (−)-epicatechin metabolites in humans: assessment using de novo chemically synthesized authentic standards | journal = Free Radical Biology & Medicine | volume = 52 | issue = 8 | pages = 1403–1412 | date = April 2012 | pmid = 22240152 | doi = 10.1016/j.freeradbiomed.2011.12.010 | doi-access = free }} The main metabolic pathways for SREMs are glucuronidation, sulfation and methylation of the catechol group by catechol-O-methyl transferase, with only small amounts detected in plasma.{{cite web|url=http://lpi.oregonstate.edu/mic/dietary-factors/phytochemicals/flavonoids|title=Flavonoids|publisher=Linus Pauling Institute, Oregon State University, Corvallis|date=2016|access-date=24 July 2016}} The majority of dietary catechins are however metabolised by the colonic microbiome to gamma-valerolactones and hippuric acids which undergo further biotransformation, glucuronidation, sulfation and methylation in the liver.

The stereochemical configuration of catechins has a strong impact on their uptake and metabolism as uptake is highest for (−)-epicatechin and lowest for (−)-catechin.{{cite journal | vauthors = Ottaviani JI, Momma TY, Heiss C, Kwik-Uribe C, Schroeter H, Keen CL | title = The stereochemical configuration of flavanols influences the level and metabolism of flavanols in humans and their biological activity in vivo | journal = Free Radical Biology & Medicine | volume = 50 | issue = 2 | pages = 237–244 | date = January 2011 | pmid = 21074608 | doi = 10.1016/j.freeradbiomed.2010.11.005 }}

Biotransformation of (+)-catechin into taxifolin by a two-step oxidation can be achieved by Burkholderia sp.{{cite journal | vauthors = Matsuda M, Otsuka Y, Jin S, Wasaki J, Watanabe J, Watanabe T, Osaki M | title = Biotransformation of (+)-catechin into taxifolin by a two-step oxidation: primary stage of (+)-catechin metabolism by a novel (+)-catechin-degrading bacteria, Burkholderia sp. KTC-1, isolated from tropical peat | journal = Biochemical and Biophysical Research Communications | volume = 366 | issue = 2 | pages = 414–419 | date = February 2008 | pmid = 18068670 | doi = 10.1016/j.bbrc.2007.11.157 }}

(+)-Catechin and (−)-epicatechin are transformed by the endophytic filamentous fungus Diaporthe sp. into the 3,4-cis-dihydroxyflavan derivatives, (+)-(2R,3S,4S)-3,4,5,7,3′,4′-hexahydroxyflavan (leucocyanidin) and (−)-(2R,3R,4R)-3,4,5,7,3′,4′-hexahydroxyflavan, respectively, whereas (−)-catechin and (+)-epicatechin with a (2S)-phenyl group resisted the biooxidation.{{cite journal | vauthors = Shibuya H, Agusta A, Ohashi K, Maehara S, Simanjuntak P | title = Biooxidation of (+)-catechin and (−)-epicatechin into 3,4-dihydroxyflavan derivatives by the endophytic fungus Diaporthe sp. isolated from a tea plant | journal = Chemical & Pharmaceutical Bulletin | volume = 53 | issue = 7 | pages = 866–867 | date = July 2005 | pmid = 15997157 | doi = 10.1248/cpb.53.866 | doi-access = free }}

Leucoanthocyanidin reductase (LAR) uses (2R,3S)-catechin, NADP⁺ and H₂O to produce 2,3-trans-3,4-cis-leucocyanidin, NADPH, and H⁺. Its gene expression has been studied in developing grape berries and grapevine leaves.{{cite journal | vauthors = Bogs J, Downey MO, Harvey JS, Ashton AR, Tanner GJ, Robinson SP | title = Proanthocyanidin synthesis and expression of genes encoding leucoanthocyanidin reductase and anthocyanidin reductase in developing grape berries and grapevine leaves | journal = Plant Physiology | volume = 139 | issue = 2 | pages = 652–663 | date = October 2005 | pmid = 16169968 | pmc = 1255985 | doi = 10.1104/pp.105.064238 | jstor = 4281902 }}

• (2R,3S)-Catechin-7-O-β-D-glucopyranoside can be isolated from barley (Hordeum vulgare L.) and malt.{{cite journal |doi=10.1007/s00217-002-0498-x |title=Identification of a new flavanol glucoside from barley (Hordeum vulgare L.) and malt |year=2002 | vauthors = Friedrich W, Galensa R |journal=European Food Research and Technology |volume=214 |issue=5 |pages=388–393|s2cid=84221785 }}
• Epigeoside (catechin-3-O-α-L-rhamnopyranosyl-(1–4)-β-D-glucopyranosyl-(1–6)-β-D-glucopyranoside) can be isolated from the rhizomes of Epigynum auritum.{{cite journal | vauthors = Jin QD, Mu QZ | title = [Study on glycosidal constituents from Epigynum auritum] | language = zh | journal = Yao Xue Xue Bao (Acta Pharmaceutica Sinica) | volume = 26 | issue = 11 | pages = 841–845 | year = 1991 | pmid = 1823978 }}

File:Inter-species differences in (-)-epicatechin metabolism.pdf

Only limited evidence from dietary studies indicates that catechins may affect endothelium-dependent vasodilation which could contribute to normal blood flow regulation in humans.{{cite journal | vauthors = Hooper L, Kay C, Abdelhamid A, Kroon PA, Cohn JS, Rimm EB, Cassidy A | title = Effects of chocolate, cocoa, and flavan-3-ols on cardiovascular health: a systematic review and meta-analysis of randomized trials | journal = The American Journal of Clinical Nutrition | volume = 95 | issue = 3 | pages = 740–751 | date = March 2012 | pmid = 22301923 | doi = 10.3945/ajcn.111.023457 | doi-access = free }}{{cite journal | vauthors = Ellinger S, Reusch A, Stehle P, Helfrich HP | title = Epicatechin ingested via cocoa products reduces blood pressure in humans: a nonlinear regression model with a Bayesian approach | journal = The American Journal of Clinical Nutrition | volume = 95 | issue = 6 | pages = 1365–1377 | date = June 2012 | pmid = 22552030 | doi = 10.3945/ajcn.111.029330 | doi-access = free }} Green tea catechins may improve blood pressure, especially when systolic blood pressure is above 130 mmHg.{{cite journal | vauthors = Khalesi S, Sun J, Buys N, Jamshidi A, Nikbakht-Nasrabadi E, Khosravi-Boroujeni H | title = Green tea catechins and blood pressure: a systematic review and meta-analysis of randomised controlled trials | journal = European Journal of Nutrition | volume = 53 | issue = 6 | pages = 1299–1311 | date = September 2014 | pmid = 24861099 | doi = 10.1007/s00394-014-0720-1 | s2cid = 206969226 }}{{cite journal | vauthors = Aprotosoaie AC, Miron A, Trifan A, Luca VS, Costache II | title = The Cardiovascular Effects of Cocoa Polyphenols—An Overview | journal = Diseases | volume = 4 | issue = 4 | page = 39 | date = December 2016 | pmid = 28933419 | pmc = 5456324 | doi = 10.3390/diseases4040039 | doi-access = free }}

Due to extensive metabolism during digestion, the fate and activity of catechin metabolites responsible for this effect on blood vessels, as well as the actual mode of action, are unknown.{{cite journal | vauthors = Schroeter H, Heiss C, Balzer J, Kleinbongard P, Keen CL, Hollenberg NK, Sies H, Kwik-Uribe C, Schmitz HH, Kelm M | display-authors = 6 | title = (−)-Epicatechin mediates beneficial effects of flavanol-rich cocoa on vascular function in humans | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 103 | issue = 4 | pages = 1024–1029 | date = January 2006 | pmid = 16418281 | pmc = 1327732 | doi = 10.1073/pnas.0510168103 | doi-access = free | bibcode = 2006PNAS..103.1024S }}

Catechin and its metabolites can bind tightly to red blood cells and thereby induce the development of autoantibodies, resulting in haemolytic anaemia and renal failure.{{cite book | vauthors = Martinez SE, Davies NM, Reynolds JK |date=2013 |title= Methods of Analysis, Preclinical and Clinical Pharmacokinetics, Safety, and Toxicology|chapter=Toxicology and Safety of Flavonoids|publisher=John Wiley & Son |page=257 |isbn= 978-0-470-57871-1}} This resulted in the withdrawal of the catechin-containing drug Catergen, used to treat viral hepatitis,{{cite book | vauthors = Bode JC |editor1-first=Lajos |editor1-last=Okolicsányi |editor2-first=Géza |editor2-last=Csomós |editor3-first=Gaetano |editor3-last=Crepaldi |date=1987 |title=Assessment and Management of Hepatobiliary Disease |location= Berlin |publisher=Springer-Verlag |page= 371|isbn=978-3-642-72631-6|doi=10.1007/978-3-642-72631-6|s2cid=3167832 }} from market in 1985.{{cite journal|title=Ruhen der Zulassung für Catergen|trans-title=Suspension of approval for Catergen|lang=de|journal=Deutsches Ärzteblatt|volume=82|issue=38|page=2706|url=https://www.aerzteblatt.de/pdf/82/38/a2706.pdf}}

Catechins from green tea can be hepatotoxic{{Cite web | author = Health Canada|date=2017-11-15 |title=Summary Safety Review – Green tea extract-containing natural health products – Assessing the potential risk of liver injury (hepatotoxicity) |url=https://www.canada.ca/en/health-canada/services/drugs-health-products/medeffect-canada/safety-reviews/green-tea-extract-containing-natural-health-products-assessing-potential-risk-liver-injury.html |access-date=2022-05-06 |website=www.canada.ca}} and the European Food Safety Authority has recommended not to exceed 800 mg per day.{{cite journal | vauthors = Younes M, Aggett P, Aguilar F, Crebelli R, Dusemund B, Filipič M, Frutos MJ, Galtier P, Gott D, Gundert-Remy U, Lambré C, Leblanc JC, Lillegaard IT, Moldeus P, Mortensen A, Oskarsson A, Stankovic I, Waalkens-Berendsen I, Woutersen RA, Andrade RJ, Fortes C, Mosesso P, Restani P, Arcella D, Pizzo F, Smeraldi C, Wright M | display-authors = 6 | title = Scientific opinion on the safety of green tea catechins | journal = EFSA Journal | volume = 16 | issue = 4 | pages = e05239 | date = April 2018 | pmid = 32625874 | pmc = 7009618 | doi = 10.2903/j.efsa.2018.5239 }}

One limited meta-analysis showed that increasing consumption of green tea and its catechins to seven cups per day provided a small reduction in prostate cancer.{{cite journal | vauthors = Guo Y, Zhi F, Chen P, Zhao K, Xiang H, Mao Q, Wang X, Zhang X | display-authors = 6 | title = Green tea and the risk of prostate cancer: A systematic review and meta-analysis | journal = Medicine | volume = 96 | issue = 13 | pages = e6426 | date = March 2017 | pmid = 28353571 | pmc = 5380255 | doi = 10.1097/MD.0000000000006426 }}

Nanoparticle methods are under preliminary research as potential delivery systems of catechins.{{cite journal | vauthors = Ye JH, Augustin MA | title = Nano- and micro-particles for delivery of catechins: Physical and biological performance | journal = Critical Reviews in Food Science and Nutrition | volume = 59 | issue = 10 | pages = 1563–1579 | year = 2018 | pmid = 29345975 | doi = 10.1080/10408398.2017.1422110 | author-link2 = Mary Ann Augustin | s2cid = 29522787 }}

Catechins released into the ground by some plants may hinder the growth of their neighbors, a form of allelopathy.{{cite book | chapter-url=http://6e.plantphys.net/essay23.07.html| chapter = Secondary Metabolites and Allelopathy in Plant Invasions: A Case Study of Centaurea maculosa| vauthors = Broz AK, Vivanco JM, Schultz MJ, Perry LG, Paschke MW |date=2006|publisher=Sinauer Associates | title = Plant Physiology and Development | edition = 6th | veditors = Taiz L, Zeiger E, Møller IM, Murphy A }} Centaurea maculosa, the spotted knapweed often studied for this behavior, releases catechin isomers into the ground through its roots, potentially having effects as an antibiotic or herbicide. One hypothesis is that it causes a reactive oxygen species wave through the target plant's root to kill root cells by apoptosis.{{cite journal | vauthors = Bais HP, Vepachedu R, Gilroy S, Callaway RM, Vivanco JM | title = Allelopathy and exotic plant invasion: from molecules and genes to species interactions | journal = Science | volume = 301 | issue = 5638 | pages = 1377–1380 | date = September 2003 | pmid = 12958360 | doi = 10.1126/science.1083245 | s2cid = 26483595 | bibcode = 2003Sci...301.1377B }} Most plants in the European ecosystem have defenses against catechin, but few plants are protected against it in the North American ecosystem where Centaurea maculosa is an invasive, uncontrolled weed.

Catechin acts as an infection-inhibiting factor in strawberry leaves.{{cite journal | vauthors = Yamamoto M, Nakatsuka S, Otani H, Kohmoto K, Nishimura S | title = (+)-Catechin acts as an infection-inhibiting factor in strawberry leaf | journal = Phytopathology | volume = 90 | issue = 6 | pages = 595–600 | date = June 2000 | pmid = 18944538 | doi = 10.1094/PHYTO.2000.90.6.595 }} Epicatechin and catechin may prevent coffee berry disease by inhibiting appressorial melanization of Colletotrichum kahawae.{{cite journal | vauthors = Chen Z, Liang J, Zhang C, Rodrigues CJ | title = Epicatechin and catechin may prevent coffee berry disease by inhibition of appressorial melanization of Colletotrichum kahawae | journal = Biotechnology Letters | volume = 28 | issue = 20 | pages = 1637–1640 | date = October 2006 | pmid = 16955359 | doi = 10.1007/s10529-006-9135-2 | s2cid = 30593181 }}

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{{wiktionary|Catechin|catechine}}

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{{Flavanol}}

Category:Flavanols

Category:Catechols

Category:Nutrition