PARTITIONING INTO LIPOSOMES

The octanol-water partition model has several limitations notably, it is not very biological. The alternative use of liposomes (which are vesicles with walls made of a phospholipid bilayer) has become more widespread [149,162,275, 380—4441. Also, liposomes contain the main ingredients found in all biological membranes. 

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Figure 5.6 The difference between liposome-water and octanol-water partitioning as a function of the octanol-water partition coefficient for a series of unrelated structures [149,385,386,429]. For example, acyclovir partitions into liposomes over 3000 times more strongly than into octanol, and amiodarone partitions into liposomes 100 times more weakly than into octanol. [Avdeef, A., Curr. Topics Med. Chem., 1, 277-351 (2001). Reproduced with permission from Bentham Science Publishers, Ltd.]...

Permeability is perhaps the most widely studied of the biological components of Figure 16.5 and as a result has led to a number of in silico models of this component [48], There are various experimental systems designed to give some measure of permeability ranging in complexity from partition into liposomes to permeability across Caco-2 cells (see Chapter 7). In silico models of Caco-2 cell permeability have been constructed [49], but the question may be asked why model the model of human absorption [50]. It may be better to measure, and make models of, more fundamental factors that affect permeability. 

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