A novel biochromatographic Oatp2 column to study the transmembrane transport of statins.

In a previous paper, using a biophysical model system to study the passive diffusion of the statin molecules through the cell membrane, our group demonstrated that statins could cross biological membrane by passive diffusion (Sarr et al. [40]). However, in the liver, the uptake of statins would also be mediated by organic anion transporting polypeptides (Oatps) like Oatp2 a member of this family. Thus, a novel biochromatographic approach was developed in our laboratory to study the transmembrane transport of statins and an Oatp2 inhibitor via this carrier family. For this, the Oatp2 protein was immobilized via its amino groups on a chromatographic support using an "in situ" immobilization technique. For the first time, using this novel biochromatographic concept, the effect of magnesium chloride salt (MgCl(2)) on the pharmacomolecule-Oatp2 binding was investigated. It was shown an Mg(2+)-dependent pharmacomolecule-protein association and a potential facilitated diffusion of these pharmacomolecules into biological membrane. This association process was due to the central positive potential pore of the Oatp2. Indeed, at pH 7.4, all the pharmacomolecules studied were ionized (i.e. negatively charged) and so interact with this positive potential pore. However, an increase of the Mg(2+) concentration led a decrease of the pharmacomolecule-Oatp2 association attributed to ion pair formations between the Mg(2+) cation and molecules. Moreover, the decrease of this affinity could be explained by an ion attraction between the Cl(-) anion of the MgCl(2) salt and the positively charged pore of the protein. This novel biochromatographic column could be useful to find a specific reversible inhibitor for these transporters and so open new perspectives to be investigated.