Epicatechin metabolites

Piskula MK, Terao J. 1998. Accumulation of (—)-epicatechin metabolites in rat plasma after oral administration and distribution of conjugation enzymes in rat tissues. J Nutr 128 1172-1178. 

Okushio K, Suzuki M, Matsumoto N, Nanjo F, Hara Y. 1999. Identification of (—)-epicatechin metabolites and their metabolic fate in the rat. Drug Metab Dispos 27 309-316. 

The strategy most widely used is the tentative qnantiiication of the procyanidin metabolites with respect to others with similar procyanidin structures. For example, the catechin and epicatechin metabolites were tentatively qnantified with its agly-cone, catechin and epicatechin, respectively. In UHPLC, the elution order of the catechin and epicatechin metabolites was considered to be the same as the elution order of catechin (first) and epicatechin (second) in their free forms. The different dimer isomer procyanidins were tentatively quantified with regard to the monomer catechin [30] or the commercial dimer [31-33,35,36,38]. 

Ottaviani, J., Momma, T., Kuhnle, G., Keen, C., and Schroeter, H. 2012. Structurally related (-)-epicatechin metabolites in humans Assessment using de novo chemically synthesized anthentic standards. Free Rad. Biol. Med. 52 1403-1412. 

The specific forms of epicatechin metabolites as well as methylated forms were measured after chocolate and cocoa consumption. This study reported much higher maximal plasma levels (4.8 pM) than all other studies as well as a 25-30% recovery rate in mine. Epicatechin was present as a mixed sulfate/ glucuronide, a sulfate conjugate, and a glucuronide conjugate. Methylated epicatechin accounted for up to 40% of the total amount of metabolites and was present as a sulfate or a mixed sulfate/glucuronide conjugate [59]. 

Absorption of (-)-epicatechin from chocolate has been studied by different authors [104-106]. Baba et al [104] found maximum levels of total EC metabolites in plasma after 2 h of chocolate or cocoa intake. Sulfate, glucuronide and sulfoglucuronide conjugates of non-methylated EC were the main metabolites present rather than methylated forms. In urine samples, excretion of total EC metabolites within 24 h was about 30% of total EC intake after chocolate and 25 % after cocoa consumption. 

LC/ESI-MS analyses were applied to determine urinary glucuronidated and sulfated tea catechins after the administration of green tea to humans, mouse and rats [109]. The major conjugates were identified as monoglucuronides and monosulfates of EGC and EC. Besides these metabolites, also G-methyl-EGC-G-glucuronides, O-sulfates and O-methyl-EC-O-sulfates in human urine were detected. Furthermore, the ring-fission metabolites of EGC and (-)-epicatechin, 5-(3 ,4 ,5 -trihydroxyphenyl)-y-valerolactone and 5-(3 ,4 -dihydroxyphenyl)- valerolactone respectively, have been detected in the monoglucuronide and monosulfate forms. 

Unno T, Tamemoto K, Yayabe F, Kakuda T. 2003. Urinary excretion of 5-(3, 4 -d i hydroxypheny 1 )-gainma-valerolactone, a ring-fission metabolite of (—)-epicatechin, in rats and its in vitro antioxidant activity. J Agric Food Chem 51 6893-6898. 

Inflammation is now recognized as a key process in atherogenesis [Libby, 2002]. The potential for dietary flavonoids to inhibit inflammatory activities is of particular interest. A potential anti-inflammatory feature of the flavonoids is the ability to inhibit the biosynthesis of eicosanoids. Selected phenolic acids and some flavonoids have been shown to inhibit both cyclooxygenase (COX) and 5-lipoxygenase (5-LO) pathways [Nijveldt et al., 2001 Takano-Ishikawa et al., 2006], Epicatechin and related flavonoids have been shown to inhibit the synthesis of pro-inflammatory cytokines in vitro [Sanbongi et al., 1997], and plasma metabolites of catechin and quercetin inhibit the adhesion of monocytes to cultured endothelial cells [Koga and Meydani, 2001]. Silymarin has been shown to inhibit the production of inflammatory cytokines, such as interleukin-1, interferon-, and tumor necrosis factor-a (TNFa), from macrophages and T-cells [Matsuda et al., 2005], Some flavonoids can inhibit neutrophil... 

Among the metabolites circulating in human blood plasma after intake of (—)-epicatechin, the major one is the glucuronide [Natsume et ah, 2003]. We suggest that the epicatechin glucuronide serves as transport metabolite, taken up into the cells and after deglucuronidation delivering the flavanol... 

Harada, M., Kan, Y., Naoki, H., Fukui, Y., Kageyama, N., Nakai, M., Miki, W., and Kiso, Y, Identification of the major antioxidative metabolites in biological fluids of the rat with ingested (+)-catechin and (-)-epicatechin. Biosci. Biotechnol. Biochem., 63, 973, 1999. 

The sample pretreatment used to determine procyanidins and their metabolites in plasma samples (from rats) is off-line solid-phase extraction (SPE) with hydrophilic-lipophilic balanced (HLB) copolymer. Both cartridges (60 mg) [31,32] and microelution SPE plates (pSPEs) (2 mg) [33,36,37] have been used as the device format. For the analysis of tissues (also from rats), such as the liver, brain, aorta artery, and adipose tissue, these were first freeze-dried and then pretreated by off-line Ll.F. (with the solution made up of methanol, water, and phosphoric acid) followed by pSPE [35-37]. The use of two sample pretreatments (LLE and pSPE) is due to the complexity of the tissue sample compared with the biofluid plasma sample. The extraction recoveries (%Rs) for determining the procyanidins catechin, epicatechin, dimer B2, and trimer in the plasma samples by pSPE [33] and SPE [31] were higher... 

Then, different procyanidin metabolites were generated, these being catechin and epicatechin in its glucuronide forms, catechin and epicatechin in its sulfate forms, methyl-catechin and methyl-epicatechin in its glucuronide forms, and methyl-calechin and methyl-epicatechin in its sulfate forms [31-33,35-39], In some studies, the aglycones, catechin, epicatechin, dimer, and trimer were also identified [31,33,35,36]. The main metabolites generated from the procyanidin-rich extract intake are shown in Table 14.3. 

Apart from these in vivo applications, a coculture system on hepatic cells was also reported for assaying the bioactivity of a procyanidin extract. In this report, different procyanidin metabolites were identified, these being catechin and epicatechin in its sulfate forms methyl-catechin and methyl-epicatechin in its sulfate forms epicatechin glucuronide, methyl-catechin, and methyl-epicatechin in its glucuronide forms and the aglycones catechin and epicatechin, epicatechin in its gallate forms, dimer and trimer [38]. 

Human absorption studies also showed that glucuronide and sulfate metabolites were found in plasma after the consumption of green tea rich in flavan-3-ols and chocolate rich in epicatechin. 

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