In vitro absorption studies of chlorogenic acids from coffee using the Ussing chamber model

Hydroxycinnamates are secondary plant metabolites and ubiquitous constituents of plant materials, including many foods and beverages. Hydroxycinnamates are most often conjugated with d-quinic acid, giving rise to the substance class of chlorogenic acids (CGAs). Coffee beans contain high levels of CGAs and are therefore considered the richest dietary source of this substance class. CGAs have been shown to have several beneficial health properties, including antioxidant activity, anticarcinogenic and antidiabetic potential. However, their positive effects on human health highly depend on their bioavailability. In the present study, we investigated the intestinal absorption of hydroxycinnamates using the human colon carcinoma cell line Caco-2, serving as an in vitro model for intestinal absorption. Physiological conditions were modeled using the dynamic Ussing chamber model to simulate apical/basolateral compartments of the mucosa. The test substances (5-O-caffeoylquinic acid (5-CQA), caffeoylquinic acid lactones (CQLs), caffeic (CA) and ferulic acid (FA)) were added individually to the apical compartment of the chamber to physiological concentrations. Structure-dependent absorption was observed, resulting in higher absorption efficiency for FA (12.5±1.0%; 100μM) than CA (0.33±0.13%; 100μM). A low absorption rate for 5-CQA (0.1±0.08%; 100μM) was in line with the existing literature. CQA and CQL-isomers showed comparable absorption efficiencies at 100μM (0.07±0.02%). Concentration-dependent absorption of the more hydrophobic CQLs, as well as their precursor 5-CQA, was found to be non-saturable, indicating a passive diffusion process. Overall, our results indicated that the absorption rates of hydroxycinnamates are substantially influenced by their physicochemical properties.