Alterations in phospholipid polymorphism by polyethylene glycol

Abstract

The fusogen polyethylene glycol is shown to alter the polymorphism of dimyristoyl phosphatidylcholine, soybean phosphatidylethanolamine, bovine phosphatidylserine, egg phosphatidylcholine/cholesterol mixture, dilinoleoylphosphatidylethanolamine/palmitoyl-oleoylphosphatidy lcholine mixture, and egg lysolecithin. Suspension of these lipids in 50% polyethylene glycol (mol wt = 6000) reduces both the lamellar and the hexagonal II repeat spacings as measured by X-ray diffraction. An increase in the gel to liquid crystalline and bilayer to hexagonal transition temperatures are observed by freeze-fracture, X-ray diffraction, differential scanning calorimetry and 31P NMR. Freeze-fracture electron micrographs revealed different bilayer defects depending on the physical states of the lipid. Lipidic particles in mixtures containing unsaturated phosphatidylethanolamine is eliminated. Some of the influences of polyethylene glycol on lipids may be explained by its dehydrating effect. However, other nonfusogenic dehydrating agents failed to produce similar results. These findings are consistent with the proposal that close bilayer contact and the formation of bilayer defects are associated with the fusogenic properties of polyethylene glycol.

Solid-State NMR Investigation of the Depth of Insertion of Protegrin-1 in Lipid Bilayers Using Paramagnetic Mn2+

“…However, further experiments are needed to characterize the peptide dynamics and its implication for aggregation (J. J. Buffy, A. Waring, R. I. Lehrer, and M. Hong, unpublished results). It is noteworthy that similar lipid ordering effects have been reported for gramicidin A (Cornell et al, 1988;Davis, 1986;Ge and Freed, 1999) and for water-soluble polymers such as polyethylene glycol and dextran (Boni et al, 1984). In the case of gramicidin A bound to DPPC lipids, at low concentrations of the peptide (P/L \ 1:15), both electron paramagnetic resonance spectra of spin-labeled lipids and 2 H and 13 C NMR spectra of lipid acyl chains showed increased anisotropies with increasing peptide concentrations.…”

Bending, hydration and interstitial energies quantitatively account for the hexagonal-lamellar-hexagonal reentrant phase transition in dioleoylphosphatidylethanolamine

“…We calculate the chemical potentials of lipid and water molecules in both phases, find the conditions of phase equilibrium, and reconstruct the phase diagram of the system. Comparison of the results with the experimental data illustrates a possible origin of the delicacy of this reentrant transition sequence, so far observed only in DOPE and one other lipid, soybean phosphatidylethanolamine (PE) (Boni et al, 1984), and which can be eliminated by addition of even a small amount of alkanes (Gawrisch et al, 1992) or large amounts of polar solutes (Wistrom et al, 1989). Both osmotic and gravimetric phase diagrams, derived from experimental parameters alone, show not just qualitative but excellent quantitive agreement with the experimental data.…”

The different faces of poly(ethylene glycol)

“…For example, while low molecular weight PEO generally induces cells or vesicles to adhere (depletion attraction), high molecular weight PEO causes them to repel (7)(8)(9)(10)(11). In the first case, the cells aggregate, in the second, they remain dispersed in solution (''stable'').…”