Evan Mintzer - Academia.edu (original) (raw)

Papers by Evan Mintzer

The Journal of Organic Chemistry, 2006

Analogues of cholesterol (compounds 1 and 2) and coprostanol (compound 3) containing the BODIPY f... more Analogues of cholesterol (compounds 1 and 2) and coprostanol (compound 3) containing the BODIPY fluorophore in the aliphatic tail of the free sterol have been synthesized starting with bisnorcholenic acid, cholenic acid 3beta-acetate, and lithocholic acid, respectively. An ester linkage joining the fluorophore to the sterol nucleus interfered with the ability of the fluorescent sterol to pack with phospholipids in monolayers. However, an analogue in which the linker was devoid of polar atoms exhibited a substantially similar physical behavior to cholesterol in model membranes with respect to localization in raft domains.

Journal of Controlled Release, 2014

The accumulated evidence has shown that lipids and polymers each have distinct advantages as carr... more The accumulated evidence has shown that lipids and polymers each have distinct advantages as carriers for siRNA delivery. Composite materials comprising both lipids and polymers may present improved properties that combine the advantage of each. Cationic amphiphilic macromolecules (CAMs) containing a hydrophobic alkylated mucic acid segment and a hydrophilic poly(ethylene glycol) (PEG) tail were non-covalently complexed with two lipids, 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE) and 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP), to serve as a siRNA delivery vehicle. By varying the weight ratio of CAM to lipid, cationic complexes with varying compositions were obtained in aqueous media and their properties evaluated. CAM-lipid complex sizes were relatively independent of composition, ranging from 100 to 200nm, and zeta potentials varied from 10 to 30mV. Transmission electron microscopy confirmed the spherical morphology of the complexes. The optimal N/P ratio was 50 as determined by electrophoretic mobility shift assay. The ability to achieve gene silencing was evaluated by anti-luciferase siRNA delivery to a U87-luciferase cell line. Several weight ratios of CAM-lipid complexes were found to have similar delivery efficiency compared to the gold standard, Lipofectamine. Isothermal titration calorimetry revealed that siRNA binds more tightly at pH=7.4 than pH=5 to CAM-lipid (1:10 w/w). Further intracellular trafficking studies monitored the siRNA escape from the endosomes at 24h following transfection of cells. The findings in the paper indicate that CAM-lipid complexes can serve as a novel and efficient siRNA delivery vehicle.

FEBS Letters, 2002

6-Photocholesterol, a new photoactivatable analog of cholesterol in which a diazirine functionali... more 6-Photocholesterol, a new photoactivatable analog of cholesterol in which a diazirine functionality replaces the 5,6-double bond in the steroid nucleus, was used recently to identify cholesterol-binding proteins in neuroendocrine cells [Thiele, C., Hannah, M.J., Farenholz, F. and Huttner, W.B. (2000) Nat. Cell Biol. 2, 42-49], to track the distribution and transport of cholesterol in Caenorhabditis elegans [Matyash, V., Geier, C., Henske, A., Mukherjee, S., Hirsh, D., Thiele, C., Grant, B., Maxfield, F.R. and Kurzchalia, T.V. (2001) Mol. Biol. Cell 12, 1725-1736], and to probe lipid-protein interactions in oligodendrocytes [Simons, M., Kramer, E.M., Thiele, C., Stoffel, W. and Trotter, J. (2000) J. Cell Biol. 151, 143-154]. To determine whether 6-photocholesterol is a faithful mimetic of cholesterol we analyzed the ability of this probe, under conditions in which it is not photoactivated to a carbene, to substitute for cholesterol in two unrelated assays: (1) to condense 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine monomolecular films and (2) to mediate the fusion of two alphaviruses (Semliki Forest and Sindbis) with liposomes. The results suggest that this analog is a suitable photoprobe of cholesterol.

Chemistry and Physics of Lipids, 2010

Oxidized analogs of cholesterol (oxysterols) are produced through both enzymatic and non-enzymati... more Oxidized analogs of cholesterol (oxysterols) are produced through both enzymatic and non-enzymatic pathways and have been shown to perturb membrane properties in vitro and in vivo. In the present study, the membrane behavior of two naturally occurring oxysterols, 25-hydroxycholesterol and 7-ketocholesterol, was examined in two model systems. The presence of an additional oxygen moiety was found to alter membrane properties compared to native cholesterol and to each other in lipid monolayers, composed of either pure sterol or sterol-glycerophospholipid and sterol-sphingomyelin binary films, as well as in mixed multilamellar vesicles. The ability of oxysterols to condense phosphatidylcholine and sphingomyelin films, their capacity to cause changes in in-plane elasticity moduli, and their propensity to form detergent-resistant membrane domains were all found to be dependant on the location of the oxygen functionality in the oxysterol, the chemical nature of the phospholipid in the model systems, and the oxysterol/phospholipid ratio in the membrane. The findings described in this study with respect to their biophysical/biophysiological implications provide additional insight into the activity of cytotoxic oxysterols in model membranes.

Chemistry and Physics of Lipids, 2004

The critical micelle concentrations (CMC) of lysophosphatidic acid (LPA) and sphingosylphosphoryl... more The critical micelle concentrations (CMC) of lysophosphatidic acid (LPA) and sphingosylphosphorylcholine (SPC) were measured by isothermal titration calorimetry. The CMC of LPA decreases with salt concentration and acyl chain length. In water at 25 degrees C, the CMC values of 1-acyl-2-lyso-sn-glycero-3-phosphatidic acid are 1.850, 0.540, 0.082, and 0.346 mM, respectively, when the acyl group is myristoyl, palmitoyl, stearoyl, and oleoyl. The CMC of SPC in 10 mM sodium phosphate buffer, pH 7.4, at 25 degrees C was 0.158 mM, and did not change with an increase in salt concentration.

Chemistry and Physics of Lipids, 2011

Conjugated linoleic acids (CLA) are found naturally in dairy products. Two isomers of CLA, that d... more Conjugated linoleic acids (CLA) are found naturally in dairy products. Two isomers of CLA, that differ only in the location of cis and trans double bonds, are found to have distinct and different biological effects. The cis 9 trans 11 (C9T11) isomer is believed to have anti-carcinogenic effects, while the trans 10 cis 12 (T10C12) isomer is believed to be associated with anti-obesity effects. In this paper we extend earlier Molecular Dynamics (MD) simulations of pure CLAphosphatidylcholine bilayers to investigate the comparative effects of cholesterol on bilayers composed of the two respective isomers. Simulations of phosphatidylcholine lipid bilayers in which the sn-2 chains contained one of the two isomers of CLA were performed in which, for each isomer, the simulated bilayers contained 10%, and 30% cholesterol (Chol). From MD trajectories we calculate and compare structural properties of the bilayers, including areas per molecule, thickness of bilayers, tilt angle of cholesterols, order parameter profiles, and one and twodimensional radial distribution function (RDF), as functions of Chol concentration. While the structural effect of cholesterol is approximately the same for both isomers, we find differences at an atomistic level in order parameter profiles and in two-dimensional radial distribution functions.

Biophysical Journal, 2009

bilayer and therefore plays an important role in maintaining lipid asymmetry. Leaflet composition... more bilayer and therefore plays an important role in maintaining lipid asymmetry. Leaflet composition is regulated by the active transport of lipids by membrane proteins, while thermal diffusion across a membrane tries to randomize the leaflet composition. We have measured the transbilayer diffusion rates for three different sterols over a wide range of compositions. The sterols studied were all cholesterol analogs; including dihydrocholesterol, ergosterol, a component of fungal cell membranes, and stigmasterol, an unsaturated plant sterol. Temperature was varied to determine its influence on transbilayer diffusion rates. We find that sterol structure does have an influence on the rate at which lipids move between bilayer leaflets. Transbilayer diffusion measurements were made using a sodium dithionite assay to monitor the location of lipid analogues within DMPC/sterol liposomes.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 2013

Daptomycin is a clinically important lipopeptide antibiotic that kills Gram-positive bacteria thr... more Daptomycin is a clinically important lipopeptide antibiotic that kills Gram-positive bacteria through membrane depolarization. Its activity requires calcium and the presence of phosphatidylglycerol in the target membrane. Calcium and phosphatidylglycerol also promote the formation of daptomycin oligomers, which have been assumed but not proven to be required for the bactericidal effect. Daptomycin shares substantial structural similarity with another lipopeptide antibiotic, A54145; the two have identical amino acid residues in 5 out of 13 positions and similar ones in 4 more positions. We here examined whether these conserved residues are sufficient for oligomer formation. To this end, we used fluorescence energy transfer and excimer fluorescence to detect hybrid oligomers of daptomycin and CB-182,462, a semisynthetic derivative of A54145. Mixtures of the two compounds indeed produced hybrid oligomers, but at the same time displayed a significantly less than additive antibacterial activity against Bacillus subtilis. The existence of functionally impaired oligomers indicates that oligomer formation is indeed important for antibacterial function. However, it also shows that oligomerization is not sufficient; once formed, the oligomers must take another step in order to acquire antibacterial activity. Thus, the amino acid residues shared between daptomycin and CB-182,462 suffice for formation of the oligomer, but not for its subsequent activation.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 2010

Conjugated linoleic acids (CLA) are known to exert several isomer-specific biological effects, bu... more Conjugated linoleic acids (CLA) are known to exert several isomer-specific biological effects, but their mechanisms of action are unclear. In order to determine whether the physicochemical effects of CLA on membranes play a role in their isomer-specific effects, we synthesized phosphatidylcholines (PCs) with 16:0 at sn-1 position and one of four CLA isomers (trans 10 cis 12 (A), trans 9 trans 11 (B), cis 9 trans 11 (C), and cis 9 cis 11 (D)) at sn-2, and determined their biophysical properties in monolayers and bilayers. The surface areas of the PCs with the two natural CLA (A and C) were similar at all pressures, but they differed significantly in the presence of cholesterol, with PC-A condensing more than PC-C. Liposomes of PC-A similarly showed increased binding of cholesterol compared to PC-C liposomes. PC-A liposomes were less permeable to carboxyfluorescein compared to PC-C liposomes. The PC with two trans double bonds (B) showed the highest affinity to cholesterol and lowest permeability. The two natural CLA-PCs (A and C) stimulated lecithin-cholesterol acyltransferase activity by 2-fold, whereas the unnatural CLA-PCs (B and D) were inhibitory. These results suggest that the differences in the biophysical properties of CLA isomers A and C may partly contribute to the known differences in their biological effects.

Biochimica et Biophysica Acta (BBA) - Biomembranes, 2006

The binding of the gelsolin P2 peptide (residues 150-169) with lysophosphatidic acid (LPA) and li... more The binding of the gelsolin P2 peptide (residues 150-169) with lysophosphatidic acid (LPA) and lipopolysaccharide (LPS) was investigated by isothermal titration calorimetry. P2 binds to LPS with higher affinity than to LPA. For the interaction of 1-oleoyl-LPA with P2 in the absence of salt, K(d) and deltaH degrees were 920 nM and -2.07 kcal/mol, respectively, at pH 7.4 and 25 degrees C. For the interaction of lipopolysaccharide (LPS) from P. aeruginosa with P2 under the same conditions, K(d) was 177 nM and deltaH degrees was -7.6 kcal/mol.

Langmuir, 2011

Surfactant amphiphilic macromolecules (AMs) were complexed with a 1:1 ratio of 1,2-dioleoyl-3-tri... more Surfactant amphiphilic macromolecules (AMs) were complexed with a 1:1 ratio of 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), either by a coevaporation (CE) or postaddition (PA) method, to form AM-lipid complexes with enhanced drug delivery applications. By characterizing the surfactant-lipid interactions, these heterogeneous drug delivery systems can be better controlled and engineered for optimal therapeutic outcomes. In this study, the physical interactions between DOPE:DOTAP liposomes and AM surfactants were investigated. Langmuir film balance and isothermal calorimetry studies showed cooperative intermolecular interactions between pure lipids and AM in monolayers and high thermostability of structure formed by the addition of AM micelles to DOTAP:DOPE vesicles in buffer solution respectively. Increasing the AM weight ratio in the complexes via the CE method led to complete vesicle solubilization--from lamellar aggregates, to a mixture of coexisting vesicles and micelles, to mixed micelles. Isothermal calorimetry evaluation of AM-lipid complexes shows that, at higher AM weight ratios, PA-produced complexes exhibit greater stability than complexes at lower AM weight ratios. Similar studies show that AM-lipid complexes produced by the CE methods display stronger interactions between AM-lipid components than complexes produced by the PA method. The results suggest that the PA method produces vesicles with AM molecules associated with its outer leaflet only (i.e., an AM-coated vesicle), while the CE method produces complexes ranging from mixed vesicles to mixed micelle in which the AM-lipid components are more intimately associated. These results will be helpful in the design of AM-lipid complexes as structurally defined, stable, and effective drug delivery systems.