Interaction of piroxicam and meloxicam with DMPG/DMPC mixed vesicles: Anomalous partitioning behavior

Interaction of Oxicam Derivatives with the Artificial Models of Biological Membranes-Calorimetric and Fluorescence Spectroscopic Study

The modified 1,2-benzothiazine analogues designed as new drug candidates and discussed in this paper are oxicam derivatives. Oxicams are a class of non-steroidal anti-inflammatory drugs (NSAIDs). Their biological target is cyclooxygenase (COX), a membrane protein associated with the phospholipid bilayer. In recent decades, it has been proven that the biological effect of NSAIDs may be closely related to their interaction at the level of the biological membrane. These processes are often complicated and the biological membranes themselves are very complex. Therefore, to study these mechanisms, simplified models of biological membranes are used. To characterize the interaction of six oxicam derivatives with DPPC, DMPC and EYPC, artificial models of biological membranes (multi-bilayers or liposomes), differential scanning calorimetry (DSC) and fluorescence spectroscopy techniques were applied. In spectroscopic measurements, two fluorescent probes (Laurdan and Prodan) localized in different membrane segments were used. All tested oxicam derivatives interacted with the lipid bilayers and may penetrate the artificial models of biological membranes. They intercalated into the lipid bilayers and were located in the vicinity of the polar/apolar membrane interface. Moreover, a good drug candidate should not only have high efficiency against a molecular target but also exhibit strictly defined ADMET parameters, therefore these activities of the studied compounds were also estimated.

Toxicity inhibitors protect lipid membranes from disruption by Aβ42

Although the precise molecular factors linking amyloid β-protein (Aβ) to Alzheimer's disease (AD) have not been deciphered, interaction of Aβ with cellular membranes has an important role in the disease. However, most therapeutic strategies targeting Aβ have focused on interfering with Aβ self-assembly rather than with its membrane interactions. Here, we studied the impact of three toxicity inhibitors on membrane interactions of Aβ42, the longer form of Aβ, which is associated most strongly with AD. The inhibitors included the four-residue C-terminal fragment Aβ(39-42), the polyphenol (-)-epigallocatechin-3-gallate (EGCG), and the lysine-specific molecular tweezer, CLR01, all of which previously were shown to disrupt different steps in Aβ42 self-assembly. Biophysical experiments revealed that incubation of Aβ42 with each of the three modulators affected membrane interactions in a distinct manner. Interestingly, EGCG and CLR01 were found to have significant interaction with membranes themselves. However, membrane bilayer disruption was reduced when the compounds were preincubated with Aβ42, suggesting that binding of the assembly modulators to the peptide attenuated their membrane interactions. Importantly, our study reveals that even though the three tested compounds affect Aβ42 assembly differently, membrane interactions were significantly inhibited upon incubation of each compound with Aβ42, suggesting that preventing the interaction of Aβ42 with the membrane contributes substantially to inhibition of its toxicity by each compound. The data suggest that interference with membrane interactions is an important factor for Aβ42 toxicity inhibitors and should be taken into account in potential therapeutic strategies, in addition to disruption or remodeling of amyloid assembly.

Minimal effect of lipid charge on membrane miscibility phase behavior in three ternary systems

Giant unilamellar vesicles composed of a ternary mixture of phospholipids and cholesterol exhibit coexisting liquid phases over a range of temperatures and compositions. A significant fraction of lipids in biological membranes are charged. Here, we present phase diagrams of vesicles composed of phosphatidylcholine (PC) lipids, which are zwitterionic; phosphatidylglycerol (PG) lipids, which are anionic; and cholesterol (Chol). Specifically, we use DiPhyPG-DPPC-Chol and DiPhyPC-DPPG-Chol. We show that miscibility in membranes containing charged PG lipids occurs over similarly high temperatures and broad lipid compositions as in corresponding membranes containing only uncharged lipids, and that the presence of salt has a minimal effect. We verified our results in two ways. First, we used mass spectrometry to ensure that charged PC/PG/Chol vesicles formed by gentle hydration have the same composition as the lipid stocks from which they are made. Second, we repeated the experiments by substituting phosphatidylserine for PG as the charged lipid and observed similar phenomena. Our results consistently support the view that monovalent charged lipids have only a minimal effect on lipid miscibility phase behavior in our system.

Interaction of nonsteroidal anti-inflammatory drugs with membranes: in vitro assessment and relevance for their biological actions

Nonsteroidal anti-inflammatory drugs (NSAIDs) are among the most commonly used drugs in the world due to their anti-inflammatory, analgesic and antipyretic properties. Nevertheless, the consumption of these drugs is still associated with the occurrence of a wide spectrum of adverse effects. Regarding the major role of membranes in cellular events, the hypothesis that the biological actions of NSAIDs may be related to their effect at the membrane level has triggered the in vitro assessment of NSAIDs-membrane interactions. The use of membrane mimetic models, cell cultures, a wide range of experimental techniques and molecular dynamics simulations has been providing significant information about drugs partition and location within membranes and also about their effect on diverse membrane properties. These studies have indeed been providing evidences that the effect of NSAIDs at membrane level may be an additional mechanism of action and toxicity of NSAIDs. In fact, the pharmacokinetic properties of NSAIDs are closely related to the ability of these drugs to interact and overcome biological membranes. Moreover, the therapeutic actions of NSAIDs may also result from the indirect inhibition of cyclooxygenase due to the disturbing effect of NSAIDs on membrane properties. Furthermore, increasing evidences suggest that the disordering effects of these drugs on membranes may be in the basis of the NSAIDs-induced toxicity in diverse organ systems. Overall, the study of NSAIDs-membrane interactions has proved to be not only important for the better understanding of their pharmacological actions, but also for the rational development of new approaches to overcome NSAIDs adverse effects.

Surface electrostatics of lipid bilayers by EPR of a pH-sensitive spin-labeled lipid

Many biophysical processes such as insertion of proteins into membranes and membrane fusion are governed by bilayer electrostatic potential. At the time of this writing, the arsenal of biophysical methods for such measurements is limited to a few techniques. Here we describe a, to our knowledge, new spin-probe electron paramagnetic resonance (EPR) approach for assessing the electrostatic surface potential of lipid bilayers that is based on a recently synthesized EPR probe (IMTSL-PTE) containing a reversibly ionizable nitroxide tag attached to the lipids' polar headgroup. EPR spectra of the probe directly report on its ionization state and, therefore, on electrostatic potential through changes in nitroxide magnetic parameters and the degree of rotational averaging. Further, the lipid nature of the probe provides its full integration into lipid bilayers. Tethering the nitroxide moiety directly to the lipid polar headgroup defines the location of the measured potential with respect to the lipid bilayer interface. Electrostatic surface potentials measured by EPR of IMTSL-PTE show a remarkable (within ±2%) agreement with the Gouy-Chapman theory for anionic DMPG bilayers in fluid (48°C) phase at low electrolyte concentration (50 mM) and in gel (17°C) phase at 150-mM electrolyte concentration. This agreement begins to diminish for DMPG vesicles in gel phase (17°C) upon varying electrolyte concentration and fluid phase bilayers formed from DMPG/DMPC and POPG/POPC mixtures. Possible reasons for such deviations, as well as the proper choice of an electrostatically neutral reference interface, have been discussed. Described EPR method is expected to be fully applicable to more-complex models of cellular membranes.

Differentiating oxicam nonsteroidal anti-inflammatory drugs in phosphoglyceride monolayers

Meloxicam, piroxicam, and tenoxicam belong to a highly potent oxicam group of nonsteroidal anti-inflammatory drugs. Whereas the structurally similar oxicams have different pharmacokinetics, treatment efficiency, and adverse effects, their common mechanism of action is the inhibition of a membrane enzyme, cyclooxygenase. Because the prerequisite for accessing the cyclooxygenase by the drugs is interaction with the membrane, the focus of the current study was a comparison of how meloxicam, piroxicam, and tenoxicam interact with lipid monolayers used as models of biological membranes. The monolayers were formed with 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol), 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, 1,2-myristoyl-sn-glycero-3-phosphoethanolamine, and 1,2-dilauroyl-sn-glycero-3-phosphoethanolamine. These systems were examined via surface pressure and surface electrical potential measurements, polarization modulation infrared reflection adsorption spectra, and Brewster angle microscopy. The three oxicams are differentiated in the monolayers; meloxicam shows the highest ability to modify membrane fluidity and surface potential, followed by piroxicam and tenoxicam. The dissimilarity of the biological activity of the oxicams may be linked to different interaction with the membrane, as revealed by the present study.

Meloxicam and meloxicam-beta-cyclodextrin complex in model membranes: effects on the properties and enzymatic lipolysis of phospholipid monolayers in relation to anti-inflammatory activity

Meloxicam, a nonsteroidal anti-inflammatory drug (NSAID), is known as a selective cyclooxygenase-2 inhibitor. Cyclooxygenase-2 is a membrane protein, functionally coupled to an interfacial enzyme, phospholipase A2. Consequently, it may be supposed that the interactions of NSAIDs with lipid membranes play a role in the anti-inflammatory process. In order to investigate the mechanism of this process, Langmuir films formed with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dilauroyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, or 1,2-myristoyl-sn-glycero-3-phosphoethanolamine were exposed to meloxicam and its beta-cyclodextrin inclusion complex. The monolayers were studied by measuring surface pressure, electric surface potential, Brewster angle micrographs, polarization-modulation infrared reflection-absorption spectra, and phospholipase A2 activity; the inclusion complex was studied using molecular modeling. The results obtained show that the monolayers formed in the presence of meloxicam and its complex are expanded and more liquid-like compared to pure lipids. Both compounds modify hydration of the lipid polar heads, orientation of the molecules, morphology of the domains, and the rate of lipolysis catalyzed by phospholipase A2. The latter effect may be involved in the anti-inflammatory activity of meloxicam. Importantly, the effects observed with the meloxicam-beta-cyclodextrin complex are more pronounced compared to those of the free meloxicam. This observation may be relevant for developing new meloxicam preparations with increased bioavailability.

Interaction of Oxicam NSAIDs with lipid monolayer: anomalous dependence on drug concentration

Surface pressure (pi) versus specific molecular area (A) isotherms of Langmuir monolayers of dimyristoylphosphatidylcholine (DMPC) lipid on pure water were studied in pristine form and in presence of three non-steroidal anti-inflammatory drugs, meloxicam (MX), piroxicam (PX) and tenoxicam (TX) in the subphase. Data were taken at three drug/lipid (D/L) ratios of 0.026, 0.05, and 0.1. Integration of drug to the lipid monolayer was measured by the increase in A (Delta A) of DMPC monolayer due to the presence of drugs. All three drugs could be integrated in the monolayer resulting in a positive value of Delta A for D/L ratio of 0.026. Above this D/L value, there is an anomalous, monotonic decrease in Delta A for MX and TX resulting, finally, in negative Delta A values. For PX, however, decrease in Delta A values at D/L of 0.05 is partially compensated at D/L of 0.1. We have tentatively explained these observations by invoking two competing forces in the overall drug-lipid interaction. One of these is an 'in-plane' force that tends to integrate the drug molecule to the plane formed by the lipid monolayer and the other is an 'out-of-plane' force that perturbs the drug and the lipid molecules such that the monolayer plane is no longer well defined.