Research Articles
Rapid determination of liposome–water partition coefficients (Klw) using liposome electrokinetic chromatography (LEKC)

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ABSTRACT

Liposome Electrokinetic Chromatography (LEKC) provides a simple and facile approach for determining liposome–water partition coefficients, Klw. LEKC is a Capillary Electrophoresis (CE) technique where liposomes are incorporated into a buffer solution and act as a pseudostationary phase providing sites of interaction for solutes. The retention factors of solutes in LEKC are directly proportional to Klw. This article describes how LEKC can be used to determine Klw for both neutral and charged solutes. The Klw values for a group of neutral aromatic compounds, β‐blockers, and other drugs are reported. In addition, the usefulness of two quantitative structure partition relationships (QSPR) for estimation of Klw is demonstrated. One is the logarithmic linear relationship between liposome water and octanol–water partition coefficients (Pow). The other is the Linear Solvation Energy Relationship (LSER). The calculated Klw values from the two QSPR agree nicely with the observed values and with one another. © 2002 Wiley‐Liss Inc. and the American Pharmaceutical Association J Pharm Sci 91:1601–1612, 2002

Section snippets

INTRODUCTION

There has been a great deal of interest in investigating partitioning behavior of solutes into lipid bilayers and biological activity.1,2 Due to difficulties associated with investigating solute interactions with biological cell membranes, different chemical models have been proposed in Quantitative Structure Activity Relationships (QSAR) studies. Collander showed the distribution of drugs in membranes was related to their partition coefficients in aqueous–organic solvents.3 Over the past 4

Chemicals

Dipalmitoyl‐L‐α‐phosphotidylcholine (DPPC), dipalmitoyl‐L‐α‐phosphotidylglycerol (sodium salt) (DPPG), and cholesterol (Chol) were purchased from Sigma Chemical Co. (St. Louis, MO). The acidic form of HEPES (N‐[2‐Hydroxyethyl] piperazine‐N′‐[2‐ethanesulfonic acid]) was purchased from Sigma Chemical Co. (St. Louis, MO), while chloroform and the basic form of HEPES (N‐[2‐Hydroxyethyl] piperazine‐N′‐[2‐ethanesulfonic acid](Na salt)) were purchased from Fluka (Buchs, Switzerland). Sodium Phosphate

PROCEDURES

The capillary was rinsed in the following manner prior to use each day: a 10‐min rinse with Milli‐Q water; a 20‐min rinse with 1.0 M NaOH; a 10‐min rinse with Milli‐Q water; a 10‐min rinse with methanol; another 10‐min rinse with Milli‐Q water; and a 20‐min rinse with the liposome solution. Furthermore, the Milli‐Q water, methanol, 1.0 M NaOH, and liposome solution were all filtered through a 0.45‐μm filter disk (Scientific Resources Inc.) prior to use. The capillary was vacuum‐rinsed with the

Determination of Klw

The retention factors (k) for uncharged solutes were calculated from the retention time data using the following eq. 1k=(trteo)(teo*(1(trtlip)))where teo is the retention time of the unretained solute (methanol), tr is the retention time of the solute, and tlip is the retention time of the liposome marker (decanophenone).

The liposomes used in this work were Small Unilamelar Vesicles (SUVs) that were composed of 24 % anionic DiPalmitoylPhosphotidylGlycerol (DPPG), 46 % zwitterionic

CONCLUSION

LEKC provides remarkable advantages for investigations of drug interactions with lipid bilayers. It combines the biomimic nature of artitficial lipid bilayer membranes with capabilities of a chromatographic technique such as small sample size, lack of sample purity requirements, speed, and automation. The only shortcoming of this technique is the existence of an elution window that limits the dynamic range for uncharged solutes. This problem can be obviated for charged drugs by using neutrally

Acknowledgements

A research grant from the U.S. National Institutes of Health (GM 38738) is gratefully acknowledged.

REFERENCES (23)

  • R. Collander

    The partition of organic compounds between higher alcohols and water

    Acta Chem Scand

    (1951)
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