Investigation of Drug Partitioning and Transfer between Artificial Membranes Using Different Techniques

One of the most important factors influencing oral absorption is the permeability of the monolayer of the intestinal epithelial cells lining the gastrointestinal tract. As well, the understanding of the mechanism and the factors influencing the drug release from the drug delivery system and transfer to the site of the action to be up taken by the body cells is prerequisite for drug formulation. Thereby, the partitioning of structurally diverse compounds using different artificial membranes had been investigated. In addition, the factors influencing liposomal formulation of a photosensitizing agent (Temoporfin; mTHPC) and the kinetics of transfer between donor liposomes and acceptor liposomes. IAM.PC.DD2 and XBridgeTM Shield RP18, were chosen using RP-HPLC. The lipophilicity indices obtained from the two membranes were compared to log Poct. In terms of mTHPC transfer, the parameters studied were total lipid content, temperature, charge of donor vesicles, and finally donor fatty acyl chain structure regarding the length and saturation. The results showed that the retention of the ionized compounds on IAM.PC.DD2 is controlled not only by lipophilicity, but also by electrostatic interactions between charged solutes and phospholipids. Positively charged compounds are more retained than negatively charged solutes. For the XbridgeTM shield RP18 phase, the log Kw values highly correlated with log Poct values. The retention on the XbridgeTM shield RP18 phase and partitioning in n-octanol/water are controlled by the same balance of structural properties, namely the Van der Waals volume (Vw), H-bond acceptor basicity (β) and dipolarity/polarizability (π*). With respect to mTHPC transfer between liposomal membranes, the obtained results are consistent with a first order kinetics in which the transfer may proceed through liposome collisions or through the aqueous phase. Thermodynamics calculations indicated that the transfer process is entropically controlled. Positively charged liposomes showed transfer rate faster than negatively charged liposomes. A potential relationship between transfer rate and membrane rigidity was evident since


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