Absorption of catechin auto‐oxidation dimers by confluent Caco‐2 cell monolayers

Abstract

Formation of homo‐ and hetero‐dimers through auto‐oxidation of epigallocatechin gallate (EGCG) and epigallocatechin (EGC) under simulated digestion has been reported. However, little data exists regarding potential absorption of these dimers. The objective of this study was to first demonstrate intestinal absorption of these dimers in vitro in order to characterize their potential relevance in vivo. Dimers generated by pH‐induced (pH 7.0) auto‐oxidation of catechin reactants (0.3 mM) in saline were incubated on highly differentiated Caco‐2 cell monolayers for 3 h. HPLC analysis of cell extracts with electrochemical array detection and MS/MS characterization indicated the presence of the EGCG homodimers theasinensin (m/z 913) and P‐2 (m/z 883) as well as Phase‐II conjugated metabolites of EGC homodimers (m/z 689 and 593) in the cells. These results indicate that catechin auto‐oxidation dimers formed through food processing or potentially through digestive reactions may be absorbed by human intestinal epithelial cells. Furthermore, catechin dimers appear to be substrates for the Phase‐II detoxification pathways known to metabolize monomeric catechins. These observations suggest that the potential digestive formation and subsequent absorption of catechin auto‐oxidation dimers in vivo warrants further investigation. (Supported by NIH grant CA119210‐01A1).