Study On Transmembrane Transport Of Water-solubilityβ-glycyrrhizic Acid Across Human Intestinal Epithelial Caco-2Cells

Licorice is a famous traditional Chinese medicine. Modern pharmacology study shows that the glycyrrhizic acid is a main active ingredient in licorice, and it can produce the same effect as the adrenal cortical hormone. It can be used for human aging resistance, anti-inflammatory, reduce blood press, enhance immunity, improve the physiological function and restrain cancer cell growth. However, preliminary studies suggested that glycyrrhizin acid was not significantly absorbed after oral administration, and pharmacokinetic studies yielded low plasma concentrations of the active ingredient. It is necessary to investigate whether the observed low oral bioavailability is due to poor absorption. Therefore, we studied the transepithelial flux of water-solubility P-glycyrrhizic acid using the human colonic cell line Caco-2, a well established model of human intestinal absorption, and the results showed that:1. Caco-2cell model was authenticated by determination of TEER of Caco-2cell monolayers. The results indicated that in our laboratory, Caco-2cells had reached integrated confluence and formed differentiated monolayers21days after seeding. TEER of the cells reached300Ωcm2and met the requirement of drug transport. So this model can be an in vitro model that investigated intestinal permeability and transport of water-solubility P-glycyrrhizic acid.2. Methyl thiazoly tetrazolium chromatometry was applied to study the cytotoxicity of water-solubility P-glycyrrhizic acid in Caco-2cells. The results showed that compared with the control group, drug solution concentration lower than60μM had no toxicity to Caco-2cell. While drug solution concentration higher than60μM was toxical to Caco-2cell.3. The flux of water-solubility P-glycyrrhizic acid (0.75-30.1μM) across the Caco-2cell layer was linear with time for up to3hr. The data indicated that water-solubility β-glycyrrhizic acid was primarily absorbed by passive diffusion across the Caco-2cell membranes.4. The Papp for BL to AP transport decreased from54.3±6.3×10-6cm/s,(mean±SE) to17.1±4.2×10-6cm/s water-solubility β-glycyrrhizic acid. The Papp for AP to BL transport was fairly constant (15.6±3.4×10-6) throughout the concentration range studied.5. Verapamil and tetrandrine reduced the efflux by about50-60%. Concomitant with this inhibition we observed a about2.6-fold increase in the AP to BL flux. It was shown that water-solubility P-glycyrrhizic acid is a substrate of P-gp.6. This was15.6±3.4×10-6cm/sec for water-solubility β-glycyrrhizin acid. According to previous studies, a Papp value of>10×10-6cm/s in Caco-2cells suggest good drug absorption in vivo.In summary, it is hypothesized that the low oral bioavailability of water-solubility β-glycyrrhizic acid may be more dependent on its hydrolysis.