Abstract PR450

Abstract

Background & Objectives: While more than half of currently used drugs are chiral compounds, stereoisomers exhibit remarkable differences in their beneficial and adverse effects. Besides receptor and ion channel proteins, amphiphilic drugs target membrane-constituting lipids. The purpose of our study is to discriminate the membrane interactivity between enantiomers of anesthetic agents because their mechanism-based differentiation has pharmacological and clinical implications. Materials & Methods: Biomimetic membranes were prepared with phospholipids and sterols to mimic the lipid compositions of neuronal and cardiomyocyte membranes. They were treated with stereoisomers (S(–)-enantiomer, R(+)-enantiomer or racemate of local anesthetic bupivacaine and dextro-enantiomer, levo-enantiomer or racemate of sedative/analgesic medetomidine) at 1–200 μM, followed by measuring fluorescence polarization with different probes to determine the drug-membrane interactivity to change membrane fluidity and the drug-acting region in lipid bilayers. Results: All drugs interacted with lipid bilayers to increase the fluidity of membranes. Although the interactions with membranes consisting of phospholipids alone were not discriminated between stereoisomers, the membranes containing ~40 mol% cholesterol ((3β)-cholest-5-en-3-ol) showed the relative potencies of membrane interactivity being R(+)-bupivacaine > racemic bupivacaine > S(–)-bupivacaine, and dexmedetomidine > racemic medetomidine > levomedetomidine at clinically-relevant concentrations, correlating to those of their pharmacological activity and cardiotoxicity. Fluidity changes induced by R(+)-bupivacaine and dexmedetomidine were greatest at the membrane region close to the ester linkages of phospholipids. In contrast, the membranes prepared with epicholesterol (3α-cholesterol) reversed the rank order of membrane interactivity to be S(–)-enantiomer > racemate > R(+)-enantiomer of bupivacaine, and levo-enantiomer > racemate > dextro-enantiomer of medetomidine. Cholesterol with several chiral centers is oriented in lipid bilayers with a hydroxyl moiety anchoring to phospholipid polar heads and an alkyl chain extending into hydrophobic cores. Its 3β-hydroxyl group appears to be responsible for the enantioselective interactions of anesthetic agents with chiral lipid membranes. Conclusion: The opposite configuration allows stereoisomers to be discriminated by enantioselectively interacting with neuronal and cardiomyocyte membranes containing chiral cholesterol. The membrane interactivity would be useful for predicting comparative activity and toxicity of anesthetic enantiomers. Disclosure of Interest: None declared