title: Stereospecific interaction of bupivacaine enantiomers with lipid membranes.
abstract: OBJECTIVE
  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.
authors.affiliation: Department of Anesthesiology, Asahi University School of Dentistry, Mizuho, Gifu, Japan. makikai@dent.asahi-u.ac.jp
authors.forename: Maki
authors.initials: M
authors.lastname: Mizogami
authors.forename: Hironori
authors.initials: H
authors.lastname: Tsuchiya
authors.forename: Takahiro
authors.initials: T
authors.lastname: Ueno
authors.forename: Masanori
authors.initials: M
authors.lastname: Kashimata
authors.forename: Ko
authors.initials: K
authors.lastname: Takakura
mesh_terms: D000779:Anesthetics, Local / Q000494:pharmacology*; D002045:Bupivacaine / Q000494:pharmacology*; D002462:Cell Membrane / Q000737:chemistry / Q000187:drug effects*; D002851:Chromatography, High Pressure Liquid; D006860:Hydrogen Bonding; D008051:Lipid Bilayers / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry; D008563:Membrane Lipids / Q000737:chemistry*; D044367:Phase Transition; D013237:Stereoisomerism
chemical_list: D000779:Anesthetics, Local; D008051:Lipid Bilayers; D008081:Liposomes; D008563:Membrane Lipids; D002045:Bupivacaine