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Certain anesthetics have been suggested to protect against the pathological states associated with oxidative stress. We compared the antioxidant and membrane activities of propofol (2,6-diisopropylphenol) and its related compounds to address the structure-activity relationship especially in a lipid membrane phase. They were studied for the effects on 1,1-diphenyl-2-picrylhydrazyl radicals, nitro blue tetrazolium reduction by superoxide anions and membrane lipid peroxidation by peroxynitrite, and also for the induced changes in membrane fluidity of liposomes. 2-Isopropylphenols scavenged free radicals with the potency being propofol>2,5-diisopropylphenol>2-isopropylphenol>2,4-diisopropylphenol, but not 3- and 4-isopropylphenols and 1,3- and 1,4-diisopropylbenzenes. The tested compounds showed no significant superoxide dismutase-like effects. Propofol inhibited membrane lipid peroxidation more intensively than 2,5-diisopropylphenol, 2,4-diisopropylphenol and 2-isopropylphenol. Despite structurally resembling antioxidant alpha-tocopherol, 2,6-dimethylphenol was less potent than propofol. Propofol produced 50% inhibition of the lipid peroxidation in unsaturated phosphatidylcholine liposomal membranes and cell-mimetic membranes at 4.0 and 10.1 microM, respectively. Propofol and 2-alkylphenolic compounds interacted with membranes to increase their fluidity with the potency correlating with lipid peroxidation inhibiting activity. The 2-isopropylphenol structure is a requisite for both lipid peroxidation inhibition and membrane fluidity modification. The structure-specific membrane interactivity appears to be one of possible antioxidant mechanisms for propofol., (Copyright 2009 Elsevier B.V. All rights reserved.)

While bupivacaine is more cardiotoxic than other local anesthetics, the mechanistic background for different toxic effects remains unclear. Several cardiotoxic compounds act on lipid bilayers to change the physicochemical properties of membranes. We comparatively studied the interaction of local anesthetics with lipid membranous systems which might be related to their structure-selective cardiotoxicity. Amide local anesthetics (10-300 microM) were reacted with unilamellar vesicles which were prepared with different phospholipids and cholesterol of varying lipid compositions. They were compared on the potencies to modify membrane fluidity by measuring fluorescence polarization. Local anesthetics interacted with liposomal membranes to increase the fluidity. Increasing anionic phospholipids in membranes enhanced the membrane-fluidizing effects of local anesthetics with the potency being cardiolipin>>phosphatidic acid>phosphatidylglycerol>phosphatidylserine. Cardiolipin was most effective on bupivacaine, followed by ropivacaine. Local anesthetics interacted differently with biomimetic membranes consisting of 10mol% cardiolipin, 50mol% other phospholipids and 40mol% cholesterol with the potency being bupivacaine>>ropivacaine>lidocaine>prilocaine, which agreed with the rank order of cardiotoxicity. Bupivacaine significantly fluidized 2.5-12.5mol% cardiolipin-containing membranes at cardiotoxicologically relevant concentrations. Bupivacaine is considered to affect lipid bilayers by interacting electrostatically with negatively charged cardiolipin head groups and hydrophobically with phospholipid acyl chains. The structure-dependent interaction with lipid membranes containing cardiolipin, which is preferentially localized in cardiomyocyte mitochondrial membranes, may be a mechanistic clue to explain the structure-selective cardiotoxicity of local anesthetics.

As a novel approach to the mode of medicinal action of garlic, its constituents were comparatively studied with respect to their interactions with membrane lipids to modify the membrane fluidity. Allyl derivatives rigidified tumor cell and platelet model membranes consisting of unsaturated phospholipids and cholesterol at 20-500 muM with the potency being diallyl trisulfide (DATS) > diallyl disulfide (DADS) by preferentially acting on the hydrocarbon cores of lipid bilayers. They were also effective in rigidifying candida cell model membranes prepared with ergosterol and phospholipids at 100-500 microM with the potency being DADS > DATS > diallyl sulfide (DAS), but not bacteria cell model membranes without ergosterol. Alliin, a precursor of these DASs, was not active on any membranes at 500 microM. Both relative intensity and selectivity in membrane effects correlated with those in antiproliferative, antiplatelet and antimicrobial effects. In cell culture experiments, membrane-active DASs inhibited the growth of tumor cells cultured for 24 and 48 h at 20-500 muM to show the potency being DATS > DADS, together with rigidifying cell membranes by acting on their deeper regions more intensively. However, membrane-inactive allyl derivatives were not growth-inhibitory on tumor cells. The membrane lipid interactions of DASs appear to be one of possible mechanisms underlying different effects of garlic.

Inflammation is clinically well known to decrease the efficiency of local anesthesia, an effect which has been explained mechanistically by tissue acidosis in the literature. However, recent studies offer no support to such a pharmacopathological background for anesthetic failure. Because inflammatory cells produce significant amounts of peroxynitrite, the peroxynitrite could interact with local anesthetics to decrease their effects. To examine this speculated interaction, we determined whether membrane fluidization, as one mode of local anesthetic action, was influenced by peroxynitrite. The membrane effects were analyzed by measuring the fluorescence polarization of liposomes prepared with 1, 2-dipalmitoylphosphatidylcholine. Although lidocaine, at a clinically relevant concentration, fluidized liposomal membranes, its fluidizing potency was reduced to 43.6 +/- 4.4% and 58.4 +/- 7.5% of that in membranes without peroxynitrite when membranes were pretreated with 50 and 250 microM peroxynitrite, respectively, for 15 min. A significant inhibition of membrane fluidization of 27.5 +/- 6.8%, was also observed after reaction for 5 min. Peroxynitrite released by inflammatory cells may affect local anesthesia through a possible interaction with lidocaine, inhibiting its membrane-fluidizing effect.

Inflammation frequently decreases local anesthetic effects, especially in dental anesthesia in patients with pulpitis and periodontitis. The pharmacokinetics and the mode of action of local anesthetics are closely associated with the hydrophobic interactions between these drugs and lipid bilayers that change the membrane physicochemical property, fluidity. A lipid oxidant, peroxynitrite, is produced by inflammatory cells, and it may act on nerve cell membranes and affect anesthetic efficacy. With respect to this speculated action, we addressed whether peroxynitrite acted on membrane-constituting lipids to decrease the membrane interactivity of lidocaine. Membrane fluidity changes were determined by measuring the fluorescence polarization of liposomes prepared with different phospholipids. Peroxynitrite (0.1-50 microM) rigidified nerve-cell model membranes consisting of unsaturated phospholipids, as well as liposomal membranes consisting of 1,2-dioleoylphosphatidylcholine and 1-stearoyl-2-arachidonylphosphatidylcholine, but peroxynitrite did not rigidify 1, 2-dipalmitoylphosphatidylcholine liposomal membranes. The pretreatment of nerve-cell model membranes with peroxynitrite (0.1-50 microM) decreased the membrane-fluidizing effects of lidocaine (5.0 mg x ml(-1)) to 63%-86% of the control (not treated with peroxynitrite) depending on the peroxynitrite concentration. As one of the mechanisms of the local anesthetic failure associated with inflammation, inflammatory peroxynitrite may affect local anesthesia by acting on membrane-constituting unsaturated phospholipids.

In addition to interacting with functional proteins such as receptors, ion channels, and enzymes, a variety of drugs mechanistically act on membrane lipids to change the physicochemical properties of biomembranes as reported for anesthetic, adrenergic, cholinergic, non-steroidal anti-inflammatory, analgesic, antitumor, antiplatelet, antimicrobial, and antioxidant drugs. As well as these membrane-acting drugs, bioactive plant components, phytochemicals, with amphiphilic or hydrophobic structures, are presumed to interact with biological membranes and biomimetic membranes prepared with phospholipids and cholesterol, resulting in the modification of membrane fluidity, microviscosity, order, elasticity, and permeability with the potencies being consistent with their pharmacological effects. A novel mechanistic point of view of phytochemicals would lead to a better understanding of their bioactivities, an insight into their medicinal benefits, and a strategic implication for discovering drug leads from plants. This article reviews the membrane interactions of different classes of phytochemicals by highlighting their induced changes in membrane property. The phytochemicals to be reviewed include membrane-interactive flavonoids, terpenoids, stilbenoids, capsaicinoids, phloroglucinols, naphthodianthrones, organosulfur compounds, alkaloids, anthraquinonoids, ginsenosides, pentacyclic triterpene acids, and curcuminoids. The membrane interaction's applicability to the discovery of phytochemical drug leads is also discussed while referring to previous screening and isolating studies. [ABSTRACT FROM AUTHOR]

Catechins originating from green tea have been used in plaque inhibition for caries prevention and treatment for liver damage because of their antibacterial activity against cariogenic bacteria and protective activity on hepatic cells. The effects of catechins on membrane fluidity were studied by a fluorescence polarization method using liposomes prepared with dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine to assess their pharmacological mechanism at μmol/l levels found in human body fluids after clinical application. All eight catechins tested, ranging from 1 to 1,000 μmol/l, significantly reduced membrane fluidity in both hydrophilic and hydrophobic regions of lipid bilayers. Catechin gallate esters were superior in fluidity reduction to the corresponding nonesters. The fluidity-reducing degree was different between the cis and trans forms, suggesting the stereospecific activity of catechins. A reference antiplaque agent, chlorhexidine, similarly reduced membrane fluidity at the antibacterial concentration. (+)-Catechin (250 μmol/l) and (–)-epigallocatechin gallate (2.5 μmol/l) significantly prevented the membrane fluidization induced by hepatotoxic chloroform. These results indicate that the reduction in membrane fluidity is responsible for the antiplaque and hepatoprotective effects of green tea catechins. [ABSTRACT FROM AUTHOR]