Using Caffeine And Free Amino Acids To Enhance The Transepithecial Transport Of Catechins In Caco-2 Cells

Tea polyphenols,especially catechins,possess health-promoting functions.A large number of epidemiological investigations and animal experiments have shown that the health function of drinking tea can prevent metabolic syndrome.However,many studies have shown that catechins such as epigallocatechin gallate(EGCG),epicatechin gallate(ECG)and epicatechin(EC)had the low bioavailability.This contradiction triggered us to speculate that the interaction of the catechins with other components in tea could alter their absorption and further contribute to the health effects of tea.Therefore this study investigated whether the absorption of catechins are affected by tea bioactive compounds such as caffeine and the three amino acids(theanine,serine,and glycine)using the Caco-2 monolayer cell model by ultra-performance liquid chromatography.Furthermore,the main efflux transporters reported for polyphenols as multi-drug resistance protein 2(MRP2),P-glycoprotein(P-gp)and breast-cancer-resistant protein(BCRP),and monocarboxylate transporter 1(MCT1)were investigated by western blotting.The results showed that:1.Each of EGCG,ECG,and ECat the concentration of 50μM were actively effluxed in Caco-2 monolayer cells.2.The active efflux of EGCG and EC was related to the increased expression of efflux protein MRP2 and P-gp,while ECG efflux was related to the increased expression of P-gp,but had no significant effect on MRP2.3.Interestingly,co-transportation of 50μM EGCG,ECG or EC with 2.5 mM caffeine,500μM theanine,2.0mM serine and 2.0mM glycine,respectively,increased their transepithelial transport and significantly decreased their efflux ratio values,which led to the significant increase of transepithelial transport of catechins.4.Moreover,the addition of caffeine and the three amino acids decreased the expression of both MRP2 and P-gp induced by EGCG and also decreased the expression of P-gp induced by ECG or EC,respectively.In contrast,only glycine,not caffeine,theanine and serine decreased the expression of MRP2 induced by EC.5.Both EGCG alone and the co-treatment of EGCG with caffeine and the three amino acids were not affected the expression of BCRP.However,ECG alone decreased the expression of BCRP,while co-treatment had no significant effect.EC had no effct on the expression of BCRP,whereas the co-treatment of EC with caffeine and the three amino acids decreased the expression of BCRP.6.Both EGCG and EC did not affect the expression of MCT1.However,ECG increased the expression of MCT1.The co-treatment of the three catechins with caffeine and the three amino acids respectively had no effect on the expression of MCT1.