Membrane interactivity of charged local anesthetic derivative and stereoselectivity in membrane interaction of local anesthetic enantiomers

Abstract

With respect to the membrane lipid theory as a molecular mechanism for local anesthetics, two critical subjects, the negligible effects of charged drugs when applied extracellularly and the stereoselective effects of enantiomers, were verified by paying particular attention to membrane components, phospholipids with the anionic property, and cholesterol with several chiral carbons. The membrane interactivities of structurally-different anesthetics were determined by their induced fluidity changes of liposomal membranes. Lidocaine (3.0 μmol/mL) fluidized phosphatidylcholine membranes, but not its quaternary derivative QX-314 (3.0 μmol/mL). Similarly to the mother molecule lidocaine, however, QX-314 fluidized phosphatidylserine-containing nerve cell model membranes and acidic phospholipids-constituting membranes depending on the acidity of membrane lipids. Positively charged local anesthetics are able to act on lipid bilayers by ion-pairing with anionic (acidic) phospholipids. Bupivacaine (0.75 mol/mL) and ropivacaine (0.75 and 1.0 μmol/mL) fluidized nerve cell model membranes with the potency being S(−)-enantiomer < racemate < R(+)-enantiomer (P < 0.01, vs antipode and racemate) and cardiac cell model membranes with the potency being S(−)-ropivacaine < S(−)-bupivacaine < R(+)-bupivacaine (P < 0.01). However, their membrane effects were not different when removing cholesterol from the model membranes. Stereoselectivity is producible by cholesterol which increases the chirality of lipid bilayers and enables to discriminate anesthetic enantiomers. The membrane lipid interaction should be reevaluated as the mode of action of local anesthetics.

Drinking-Related Tetrahydroharmans Counteract the Membrane Effects of Local Anesthetic Lidocaine

“…Lidocaine induces larger fluidity changes in DPPC membranes than in POPC/cholesterol membranes, suggesting that membrane fluidization depends on the lipid composition. Its membrane effects are consistent with the previous reports of local anesthetics to fluidize artificial and synaptosomal membranes [33,40]. The membrane-acting concentrations (0.1-2 mg/mL) of lidocaine are lower than or almost correspond to its clinically used concentrations.…”

“…Since PNA is subject to the rotational restriction imparted by membrane fluidity or rigidity, drugs acting on lipid bilayers to produce more fluid membranes facilitate the probe rotation to emit the absorbed light in all directions, decreasing fluorescence polarization. Fluorescence polarization of the membrane suspensions was measured by an RF-540 spectrofluorometer (Shimadzu, Kyoto, Japan) equipped with a polarizer at 350 nm for excitation and 425 nm for emission as reported previously [33]. Polarization values were calculated by the formula (I V V − GI V H )/(I V V + GI V H ), in which I is the fluorescence intensity and the subscripts V and H refer to the vertical and horizontal orientations of the excitation and emission polarizers, respectively [38].…”

Do local anesthetics interact preferentially with membrane lipid rafts? Comparative interactivities with raft-like membranes

“…Such structure-dependence and stereoselectivity are also found in LA-induced physicochemical changes of cardiomyocyte model membranes prepared with CL and cholesterol [10,14,18]. The DPH polarization changes in biomimetic membranes were 2.71, 2.44, 2.19, 1.59, 1.22, and 1.10 times larger than those in raft-3 model membranes for R(?…”

“…Raft model membranes devoid of CL are disadvantageous for the intensive interaction with LAs. Cholesterol with several chiral carbons is responsible for discriminating the membrane effects between stereoisomeric LAs [14]. Although raft model membranes contain cholesterol, similarly to biomimetic membranes, they did not produce the discriminable interactivities of bupivacaine enantiomers.…”

“…Lidocaine and prilocaine were obtained from Sigma-Aldrich (St Louis, MO, USA). After the reaction at 37°C for 30 min, membrane interactivities were determined by measuring DPH fluorescence polarization at 360 nm for excitation and at 430 nm for emission [14]. Compared with controls, a decrease of polarization is indicative of membrane disordering.…”