Permeation of bile acids across artificial lipid membranes and Caco-2 monolayers

The permeation behavior of free bile acids (BA) with different numbers of h ydroxyl groups as well as of the glycine and taurine conjugates was studied in vitro using artificial lipid membranes and Caco-2 monolayers. The trans port across artificial lipid membranes depends strongly on the lipophilicit y of the BA applied. Free BA permeated to a higher degree than the: conjuga ted derivatives. The taurine conjugate was transported only to a very low e xtent. A distinct influence of the pH value in the donor medium on the perm eation of the BA was observed. The transport rate decreased with increasing pH. Using Caco-2 monolayers, it was found that only unconjugated BA could permeate to a higher extent.