Absorption of tea catechins

Okushio, K., Matsumoto, N., Kohri, T., Suzuki, M., Nanjo, F., and Hara, Y. 1996. Absorption of tea catechins into rat portal vein. Biol. Pharm. Bull. 19(2) 326-329. 

The major absorption of tea catechins is the small intestine. EC, ECG, EGC, and EGCG were disposed at the intestinal epithelium by similar efflux and metabolism mechanisms. Intestinal epithelial membrane transport of catechins was studied via perfusion of EC and ECG in the human Caco-2 cell line. - The absorption and secretion transports of the four catechins, in the form of individual pure compounds, pure compound mixtures, and green tea extract, were studied in the human Caco-2 cell model. The results showed that the absorption transport of the four catechins in different doses was similar, but the green tea polyphenol mixtures could affect the secretion transport of individual catechins. It was suggested that the transporter competition may be responsible for the reduced efflux of EC, and metabolic competition may bring about a reduction in the formation of EGC sulfate and methylated EGC sulfate. ... 

ECG, respectively. Higher fecal recovery of tea catechins after oral administration in rats indicated incomplete absorption of green tea catechins. Intravenous administration of [4- H]-EGCG in rats resulted in 77% of the total radioactivity detected in bile within 48 h, and only 2.0% of that in the urine. °... 

It is very important to know the bioavailability and biotransformation of tea catechins in humans because the pharmacokinetics, absorption, distribution, metabolism, and excretion of green tea determine its potential bioactivities in disease prevention in... 

Metabolites of tea catechins are excreted in bile or urine. In general, small conjugates, such as monosulfates, tend to be excreted in urine, and extensively conjugated metabolites are more likely to be excreted in bile. The total amount of metabolites excreted in urine correlated roughly with maximum plasma concentrations. " The exact half-lives of tea catechins in plasma were calculated to be in the order of 2-3 h, except for EGCG, which is eliminated more slowly. " Relative urinary excretion data were used to estimate the minimal absorption rate and were consistent with the plasma kinetic data for most catechins, but for EGCG that mostly excreted in bile, the urinary excretion rate was very small (0-0.1%), and its absorption was underestimated. The urinary excretion rates of EC and EGC were 18.5 and 11.1%, respectively. The low cumulative excretion of tea catechins in human urine, which was 0-9.8%, suggested that they were extensively metabolized in the human body. 

Miyazawa T. Absorption, metabolism and antioxidative effects of tea catechins in humans. Biofactors 2000 13 55-59. 

IKEDA I, IMASATO Y, SASAKI E, NAKAYAMA M, NAGAO H, TAKEO T, YAYABE F, SUGANO M (1992) Tea catechins decrease micellar solubility and intestinal absorption of cholesterol in rats. Biochim Biophys Acta. 1127 141-6. 

Methyl xanthines in tea extracts have been widely analyzed using reversed-phase Cjg column with UV detection. They have absorption maxima at 210 and 274 nm, the latter being more often reported as it is more specihc. HPLC conditions employed varied according to the level of interferences in the extracts. Fernandez et al. reported simultaneous analysis of five catechins and three methyl xanthines by RP-18 HPLC. Without pretreatment of samples, complete separation was achieved in 18 minutes using a gradient mobile phase of water-formic acid-acetonitrile. Iso-cratic elution with methanol-0.1% ortho-phosphoric acid (20 79.9 0.1, v/v) for the analysis of the same components required 60 minutes. Such time-consuming... 

Note C is the maximum plasma concentration is the time to reach the maximum plasma concentration AUG is the area under the plasma concentration-time curve Tjq is the elimination half-life absorption in plasma (%) is the percentage of the total dose of ingested tea catechins in plasma and excretion in urine (%) is the percentage of the total dose of ingested tea catechins excreted in urine. 

Dube A, Nicolazzo JA, Larson I. Chitosan nanoparticles enhance the intestinal absorption of the green tea catechins (+)-catechin and (-)-epigallocatechin gallate. Eur J Pharm Sd. 2010 41(2) 219-25. 

Excretion of intact flavanols in urine cannot be considered a reliable indicator of absorption as it may be only a minor route of excretion. The proportion excreted in urine may also vary with dose as well as the experimental conditions. One study with three different doses of green tea catechins reported that there was no correlation between the amount of epicatechin or epigalloca-techin in urine and the areas under the curve (AUCs) in plasma [36]. 

---