Depth Distribution of Spin-Labeled Liponitroxides within Lipid Bilayers: A Combined EPR and Molecular Dynamics Approach

Abstract

The distribution in an egg–phosphatidylcholine bilayer of a series of spin-labeled nitroxides, potentially useful as targeted antioxidants, has been investigated using molecular dynamics (MD) simulations. The in silico method has been tested at first for a series of n-doxyl-phosphocholine-doped bilayers, with the doxyl moiety located at different positions (n) of the lipid chain, in analogy to electron paramagnetic resonance (EPR) spin labeling and other MD studies. As a result, a novel calibration curve has been obtained, suitable to determine the absolute membrane penetration depth of any paramagnetic solute from EPR measurements. A second series of MD simulations was then carried out on the newly synthesized series of liponitroxides (NOXs) recently tested as antioxidants against the lipid peroxidation of polyunsaturated fatty acids in membranes: their penetration depths, as determined by EPR in phosphatidylcholine liposomes, were correlated with their antioxidant efficacy. In these NOXs, a glycerol moiety is esterified with a carboxy derivative of a pyrroline nitroxide and one or two oleic acid residues. A very good agreement between the EPR experimental results and those from the current MD simulations indicates that the short distance of the nitroxide moiety from the fatty acid double bonds has been now definitively assessed; moreover, it indicates that our MD methodology could be successfully employed in the absence of nonparamagnetic species.

Systematic Quantification of Electron Transfer in a Bare Phospholipid Membrane Using Nitroxide-Labeled Stearic Acids: Distance Dependence, Kinetics, and Activation Parameters

“…SAXS shows that the thicknesses of the liposomes (ca. 5.1 nm, a result corroborated by molecular dynamics simulations), 62 is insignificantly altered when either of the probes resides in the membrane (see Supporting Information, Figure S4 ). We conclude that insertion of the phospholipids containing the SNRs does not significantly perturb the membrane structure.…”

“…The three power saturation curves (intensity vs microwave power) were obtained using a home-written program in Matlab that extracts the peak-to-peak amplitudes of the central line of the EPR spectra of the above experiments. The saturation curves were fitted using the standard equation: 27 , 61 , 62 where p 1/2 is the saturation parameter, namely, the power at which the first derivative amplitude is reduced to half of its unsaturated value, h is the homogeneity parameter, indicating the homogeneity of saturation of the resonance line (ranging from h = 1.5 for a fully homogeneous line to h = 0.5 for a fully inhomogeneous line), and A is a scaling factor that accounts for the absolute signal intensity. The dimensionless parameter (Φ) that is related to the immersion depth of the nitroxide inside the membrane can be directly calculated from the ratio of the p 1/2 parameters obtained from the fitting of the data from the three experiments described above: …”

Mechanistic Understanding from Molecular Dynamics in Pharmaceutical Research 2: Lipid Membrane in Drug Design

“…PBN [354], Quinones [145,355], Menaquinone [356,357], Lutein [358], Glutathione [359], Flavonoids [360][361][362][363][364][365][366][367][368][369][370], Liponitroxides [371] Amino acids L-phenylalanine [372][373][374][375], L-Tyrosine [374], L-Phenylglycine, Phenylacetic acid [374,376],…”

Monoalkylated Epigallocatechin-3-gallate (C18-EGCG) as Novel Lipophilic EGCG Derivative: Characterization and Antioxidant Evaluation

“…The stabilization of EGCG can be obtained by different approaches including the employment of reducing agents, structural modification and/or drug delivery systems [12][13][14]. Among these, the application of derivatization strategies designed to increase the molecule hydrophobicity and the interaction with cellular membrane [15][16][17][18][19][20] is considered as a feasible approach to improve the activity of bioactive molecules.…”