Tea catechin auto-oxidation dimers are accumulated and retained by Caco-2 human intestinal cells

Despite the presence of bioactive catechin B-ring auto-oxidation dimers in tea, little is known regarding their absorption in humans. Our hypothesis for this research is that catechin auto-oxidation dimers are present in teas and are absorbable by human intestinal epithelial cells. Dimers (theasinensins [THSNs] and P-2 analogs) were quantified in commercial teas by high-performance liquid chromatography-mass spectrometry. (−)-Epigallocatechin (EGC) and (−)-epigallocatechin gallate (EGCG) homodimers were present at 10 to 43 and 0 to 62 μmol/g leaf, respectively. The EGC-EGCG heterodimers were present at 0 to 79 μmol/g. The potential intestinal absorption of these dimers was assessed using Caco-2 intestinal cells. Catechin monomers and dimers were detected in cells exposed to media containing monomers and preformed dimers. Accumulation of dimers was significantly greater than monomers from test media. Three-hour accumulation of EGC and EGCG was 0.19% to 0.55% and 1.24% to 1.35%, respectively. Comparatively, 3-hour accumulation of the EGC P-2 analog and THSNs C/E was 0.89% ± 0.28% and 1.53% ± 0.36%, respectively. Accumulation of P-2 and THSNs A/D was 6.93% ± 2.1% and 10.1% ± 3.6%, respectively. The EGCG-EGC heterodimer P-2 analog and THSN B 3-hour accumulation was 4.87% ± 2.2% and 4.65% ± 2.8%, respectively. One-hour retention of P-2 and THSNs A/D was 171% ± 22% and 29.6% ± 9.3% of accumulated amount, respectively, suggesting intracellular oxidative conversion of THSNs to P-2. These data suggest that catechin dimers present in the gut lumen may be readily absorbed by intestinal epithelium.