Background and Objectives: S(−)-Bupivacaine has the pharmacotoxicological advantage over its antipode and racemate. The interaction with lipid membranes was compared between S(−)-, R(+)- and racemic bupivacaine.
Methods: The bupivacaine-induced changes in membrane property were determined by turbidity and fluorescence polarization measurements of membrane preparations to which bupivacaine stereoisomers of 1.0-5.0 mmol/L were applied. Liposomal membranes were made of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine without or with cholesterol (5 to 15 mol%), and nerve cell model membranes of 55 mol% different phospholipids and 45 mol% cholesterol. The purity and hydrophobic interaction of bupivacaine were analyzed by reversed-phase high-performance liquid chromatography.
Results: Both S(−)- and R(+)-bupivacaine were not different in lowering the phase transition temperature of membrane 1,2-dipalmitoyl-sn-glycero-3-phosphocholine. S(−)-, R(+)- and racemic bupivacaine disordered 100 mol% 1,2-dipalmitoyl-sn-glycero-3-phosphocholine liposomal membranes, although the potency was indistinguishable between stereoisomers. By adding cholesterol to membranes, however, the membrane-disordering effects showed stereostructure-specificity that was enhanced with increasing the cholesterol content (0 to 15 mol%). The enantio-differentiating effects resulted from neither impurities in enantiomers nor hydrophobic interaction with phosphatidylcholine acyl chains. Bupivacaine disordered nerve cell model membranes with the potency being S(−)-enantiomer < racemate < R(+)-enantiomer, which resembled their relative stereopotency in nerve and cardiac channel inhibition. Membrane-disordering stereospecificity disappeared in the membranes without containing cholesterol.
Conclusions: Bupivacaine stereostructure-specifically interacts with membranes containing cholesterol, which is consistent with the clinical features of S(−)-bupivacaine. Membrane cholesterol appears to increase the chirality of lipid bilayers and enable them to interact with S(−)-, racemic and R(+)-bupivacaine differently.
- Bupivacaine enantiomers
- Stereospecific membrane interaction
- Membrane disordering
- Lipid composition
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Supported by a grant-in-aid for Scientific Research (C) 15592145 from JSPS and a research grant from the Miyata Scientific Research Foundation. Presented in part at the International Anesthesia Research Society (IARS) 80th Clinical and Scientific Congress, March 26, 2006, San Francisco, CA.