Effect of angiotensin II non-peptide AT(1) antagonist losartan on phosphatidylethanolamine membranes

On the Rational Drug Design for Hypertension through NMR Spectroscopy

Antagonists of the AT1receptor (AT1R) are beneficial molecules that can prevent the peptide hormone angiotensin II from binding and activating the specific receptor causing hypertension in pathological states. This review article summarizes the multifaced applications of solid and liquid state high resolution nuclear magnetic resonance (NMR) spectroscopy in antihypertensive commercial drugs that act as AT1R antagonists. The 3D architecture of these compounds is explored through 2D NOESY spectroscopy and their interactions with micelles and lipid bilayers are described using solid state 13CP/MAS, 31P and 2H static solid state NMR spectroscopy. Due to their hydrophobic character, AT1R antagonists do not exert their optimum profile on the AT1R. Therefore, various vehicles are explored so as to effectively deliver these molecules to the site of action and to enhance their pharmaceutical efficacy. Cyclodextrins and polymers comprise successful examples of effective drug delivery vehicles, widely used for the delivery of hydrophobic drugs to the active site of the receptor. High resolution NMR spectroscopy provides valuable information on the physical-chemical forces that govern these drug:vehicle interactions, knowledge required to get a deeper understanding on the stability of the formed complexes and therefore the appropriateness and usefulness of the drug delivery system. In addition, it provides valuable information on the rational design towards the synthesis of more stable and efficient drug formulations.

Effect of Statins on the Nanomechanical Properties of Supported Lipid Bilayers

Many drugs and other xenobiotics may reach systemic concentrations where they interact not only with the proteins that are their therapeutic targets but also modify the physicochemical properties of the cell membrane, which may lead to altered function of many transmembrane proteins beyond the intended targets. These changes in bilayer properties may contribute to nonspecific, promiscuous changes in membrane protein and cell function because membrane proteins are energetically coupled to their host lipid bilayer. It is thus important, for both pharmaceutical and biophysical reasons, to understand the bilayer-modifying effect of amphiphiles (including therapeutic agents). Here we use atomic force microscopy topography imaging and nanomechanical mapping to monitor the effect of statins, a family of hypolipidemic drugs, on synthetic lipid membranes. Our results reveal that statins alter the nanomechanical stability of the bilayers and increase their elastic moduli depending on the lipid bilayer order. Our results also suggest that statins increase bilayer heterogeneity, which may indicate that statins form nanometer-sized aggregates in the membrane. This is further evidence that changes in bilayer nanoscale mechanical properties may be a signature of lipid bilayer-mediated effects of amphiphilic drugs.

Effect of dietary fibers on losartan uptake and transport in Caco-2 cells

The objective of this study was to assess the effect of dietary fibers on the transport of losartan, an angiotensin II type 1 receptor blocker, in small intestinal cells. Using Caco-2 cells in vitro, losartan uptake and transport were evaluated in the presence of various fibers (cellulose, chitosan, sodium alginate and glucomannan). Dietary fibers caused a decrease in the uptake of losartan, with chitosan causing a significant reduction. Chitosan and glucomannan significantly reduced the transport of losartan, while cellulose or sodium alginate did not. Dietary fibers also reduced the level of free losartan; however, this did not correlate with the observed reduction in losartan uptake and transport. In summary, chitosan had the greatest inhibitory effect on losartan uptake and transport, and this potential interaction should be considered in patients taking losartan. Copyright © 2016 John Wiley & Sons, Ltd.

Understanding the interaction between valsartan and detergents by NMR techniques and molecular dynamics simulation

Valsartan (VST) is one of the Angiotensin II receptor antagonists, which is widely used in clinical hypertension treatment. It is believed that VST incorporates into biological membranes before it binds to AT(1) receptor. Herein the interactions between VST and detergents, mimicking the membrane environment, were investigated by using nuclear magnetic resonance (NMR) techniques and molecular dynamics (MD) simulation. We observed that VST has two conformers (trans and cis) exchanging slowly in DPC (dodecyl-phosphocholine) micelles, a widely used detergent. The changes of chemical shifts, relaxation rates, and self-diffusion coefficients of VST protons indicate that both conformers have strong interactions with DPC. NOE cross peaks and MD simulation reveal that DPC interacts with VST not only through the hydrophobic lipid chain, but also the hydrophilic headgroup, locating VST at the charged headgroup and upper part of the micelles. Our results are in good agreement with the Raman spectroscopic studies of VST in the DPPC (dipalmitoyl-phosphatidylcholine) bilayers by Potamitis et al. (Biochim. Biophys. Acta. 2011). The concentration ratio of trans over cis conformers is 0.94, showing that two conformers have the same affinities with the detergent, which is significantly smaller than our previous results obtained in SDS (sodium dodecyl sulfate) micelles. MD simulation suggested that the cis conformer has slightly lower binding free energy than the trans conformer when interacting with DPC. The conformational change of VST was further investigated in two detergents, CTAB (hexadecyltrimethylammonium bromide) and Tween-20 (polysorbate 20). Ratios of conformer A and B in the presence of detergents are in the order of DPC, CTAB < Tween-20 < SDS, which is correlated with the charge characters of their head groups. NMR investigations and MD simulations indicate that the electrostatic interaction plays an essential role in the binding process of VST with detergents, and the hydrophobic interaction influences the packing of the drug in the micelles. These results may be of help in understanding delivery processes of sartan drugs in cell membranes.

Molecular simulation study of structural and dynamic properties of mixed DPPC/DPPE bilayers

Molecular dynamics simulations have been used to study structural and dynamic properties of fully hydrated mixed 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) bilayers at 0, 25, 50, 75, and 100 mol % DPPE. Simulations were performed for 50 ns at 350 K and 1 bar for the liquid-crystalline state of the mixtures. Results show that the average area per headgroup reduces from 0.65 +/- 0.01 nm(2) in pure DPPC to 0.52 +/- 0.01 nm(2) in pure DPPE systems. The lipid tails become more ordered with increasing DPPE concentration, resulting in a slight increase in membrane thickness (3.43 +/- 0.01 nm in pure DPPC to 4.00 +/- 0.01 nm in pure DPPE). The calculated area per headgroup and order parameter for pure DPPE deviates significantly from available experimental measurements, suggesting that the force field employed requires further refinement. In-depth analysis of the hydrogen-bond distribution in DPPE molecules shows that the amine groups strongly interact with the phosphate and carbonyl groups through inter/intramolecular hydrogen bonds. This yields a bilayer structure with DPPE headgroups preferentially located near the lipid phosphate and ester oxygens. It is observed that increasing DPPE concentrations causes competitive hydrogen bonding between the amine groups (hydrogen-donor) and the phosphate/carbonyl groups or water (hydrogen-acceptor). Due to the increasing number of hydrogen-donors from DPPE molecules with increasing concentration, DPPE becomes more hydrated. Trajectory analysis shows that DPPE molecules in the lipid mixtures move laterally and randomly around the membrane surface and the movement becomes more localized with increasing DPPE concentrations. For the conditions and simulation time considered, no aggregation or phase separation was observed between DPPC and DPPE.

Effects of a short-chain ceramide on bilayer domain formation, thickness, and chain mobililty: DMPC and asymmetric ceramide mixtures

An important part of natural ceramides contain asymmetric hydrocarbon chains. We have used calorimetry, atomic force microscopy, and electron paramagnetic resonance to study the effect of ceramide chain asymmetry in mixtures of C8Cer with DMPC as a model system of hydrocarbon chain disparity. A phase diagram is provided along with information on the thickness of the membrane and the mobility of the chains at different temperatures both below and above the phase transition temperature of the mixtures. The results indicate a partial interdigitation of C8Cer chains in the gel phase, producing a correlation between the organization of both hemilayers. Our data suggest that the effects of ceramides on biomembranes may be bimodal and similar to those of cholesterol.

Incorporation of the V-ATPase inhibitors concanamycin and indole pentadiene in lipid membranes. Spin-label EPR studies

The incorporation of concanamycin A, a potent inhibitor of vacuolar ATPases, into membranes of dimyristoyl phosphatidylcholine has been studied by using EPR of spin-labelled lipid chains. At an inhibitor/lipid ratio of 1:1 mol/mol, concanamycin A broadens the chain-melting transition of the phospholipid bilayer membrane, and effects the lipid chain motion in the fluid phase. The outer hyperfine splitting of a spin label at the C-5 position and the line widths of a spin label at the C-14 position of the lipid chain are increased by concanamycin A. Considerably larger membrane perturbations are caused by equimolar admixture of a designed synthetic 5-(5,6-dichloro-2-indolyl)-2,4-pentadienoyl V-ATPase inhibitor. These results indicate that concanamycin A intercalates readily between the lipid chains in biological membranes, with minimal perturbation of the bilayer structure. Essentially identical results are obtained with concanamycin A added to preformed membranes as a concentrated solution in DMSO, or mixed with lipid in organic solvent prior to membrane formation. Therefore, the common mode of addition in V-ATPase inhibition assays ensures incorporation of concanamycin into the lipid bilayer milieu, which provides an efficient channel of access to the transmembrane domains of the V-ATPase.