Identification of a taurine transport inhibitory substance in sesame seeds

An ethanol extract from sesame seeds inhibited the taurine uptake in human intestinal epithelial Caco-2 cells. The uptake of such alpha-amino acids as leucine and glutamic acid was not inhibited by the extract, indicating tha t this inhibition is specific to the taurine uptake. The unknown inhibitor in the sesame extract was purified by reversed-phase HPLC by monitoring the inhibitory effect on taurine uptake. The isolated substance was identified as lysophosphatidylcholine, linoleoyl (Lyso-PC), by NMR and MS analysis. L yse-PC inhibited the taurine uptake in a dose-dependent manner with an IC50 value of approximately 200 mu M. Although Lyso-PC is known to be a surface active and cell lytic compound, neither damage nor loss of integrity of th e Caco-2 cell monolayer was apparent after treating with 200 mu M Lyso-PC. Inhibition was observed by incubating cells with Lyso-PC for only 1 min pri or to the uptake experiments. These results suggest the direct effect of Ly so-PC on the cell membrane to be the main mechanism for this inhibition. Ly so-PC may play a role in the regulation of certain intestinal transporters.