Raman and phosphorus-31 NMR spectroscopic identification of a highly ordered lamellar phase in aqueous dispersions of 1-stearoyl-2-acetyl-sn-glycero-3-phosphorylcholine

Lipids and Membrane Microdomains: The Glycerolipid and Alkylphosphocholine Class of Cancer Chemotherapeutic Drugs

Synthetic antitumor lipids are metabolically stable lysophosphatidylcholine derivatives, encompassing a class of non-mutagenic drugs that selectively target cancerous cells. In this chapter we review the literature as relates to the clinical efficacy of these antitumor lipid drugs and how our understanding of their mode of action has evolved alongside key advances in our knowledge of membrane structure, organization, and function. First, the history of the development of this class of drugs is described, providing a summary of clinical outcomes of key members including edelfosine, miltefosine, perifosine, erufosine, and erucylphosphocholine. A detailed description of the biophysical properties of these drugs and specific drug-lipid interactions which may contribute to the selectivity of the antitumor lipids for cancer cells follows. An updated model on the mode of action of these lipid drugs as membrane disorganizing agents is presented. Membrane domain organization as opposed to targeting specific proteins on membranes is discussed. By altering membranes, these antitumor lipids inhibit many survival pathways while activating pro-apoptotic signals leading to cell demise.

Phases and phase transitions of the phosphatidylcholines

LIPIDAT (http://www.lipidat.chemistry.ohio-state.edu) is an Internet accessible, computerized relational database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior and molecular structures. Here, a review of the data subset referring to phosphatidylcholines is presented together with an analysis of these data. This subset represents ca. 60% of all LIPIDAT records. It includes data collected over a 43-year period and consists of 12,208 records obtained from 1573 articles in 106 different journals. An analysis of the data in the subset identifies trends in phosphatidylcholine phase behavior reflecting changes in lipid chain length, unsaturation (number, isomeric type and position of double bonds), asymmetry and branching, type of chain-glycerol linkage (ester, ether, amide), position of chain attachment to the glycerol backbone (1,2- vs. 1,3-) and head group modification. Also included is a summary of the data concerning the effect of pressure, pH, stereochemical purity, and different additives such as salts, saccharides, amino acids and alcohols, on phosphatidylcholine phase behavior. Information on the phase behavior of biologically derived phosphatidylcholines is also presented. This review includes 651 references.

Phase behavior of the antineoplastic ether lipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphochloline

The physicochemical properties of the antineoplastic etherphospholipid 1-O-octadecyl-2-O-methyl-glycero-3-phosphochline were examined in the concentration range 1-35% (w/w) lipid, as a function of temperature (range -10 degrees C to 40 degrees C) and of different aqueous solvents by dynamic light scattering, small- and wide-angle X-ray scattering, differential scanning calorimetry and ultrasonic speed measurements. On cooling the lipid dispersion undergoes a phase transition near 6 degrees C, transforming slowly from a micellar into a lamellar gel phase with interdigitating hydrocarbon chains. The lamellar repeat distance is nearly constant over the hydration range 65-90% buffer (d = 5.09-5.14 nm). The size of the micelles in terms of the hydrodynamic radius is 3.8 +/- 0.1 nm, the polydispersity is low. Their average shape is spherical. The electron density distribution across the micelle gives 2.5 nm for the extension of the hydrocarbon chains and 1.5 nm for the polar moiety. The existence of micelles was verified up to a concentration of 35% lipid. Throughout this concentration range size and shape do not change significantly. The kinetics of formation of the low-temperature phase is slow on cooling, increasing with increasing concentration. Upon heating the phase behavior shows a hysteresis. The extended lamellar organizations start to break down into smaller aggregates near 3 degrees C. The micellar phase is reformed near 20 degrees C.

Mixed-chain phospholipids and interdigitated bilayer systems

The lipid bilayer is a fundamental structural component for all biological membranes. The function of lipid bilayers may be considered not only to serve as a permeability barrier preventing the free flows of ions and polar molecules between the cell interior and its external environment, but also to modulate the activity of bilayer-spanning proteins or glycoproteins in biological membranes. Based on the location of the terminal methyl groups of the two hydrocarbon chains in phospholipids or glycosphingolipids, two broad categories of lipid bilayers have been recognized: (1) the noninterdigitated and (2) the interdigitated bilayers. Depending on the chain-length difference between the two hydrocarbon chains, three different types of packing models for interdigitated bilayer systems have been identified. Among the three types, the mixed interdigitated bilayer is perhaps unique, since the hydrocarbon chains in the bilayer core are observed to be interdigitated in both the gel and the liquid-crystalline states. In this communication, various experimental data supporting the chain packing characteristics of the mixed interdigitated bilayer for a large number of mixed-chain phospholipid species are considered. In addition, two types of phase diagrams for binary phospholipid mixtures obtained with mixed-chain phospholipids are also presented. These studies may be of great importance in understanding the functional control of bilayer-spanning proteins in biological membranes, and for providing basic information explaining the dynamic regulation of membrane activities in general.

Influence of PAF-acether on lecithin-oriented multibilayers monitored by ESR: interaction of PAF-acether with cholesterol

The influence of PAF-acether on natural ovolecithin oriented multibilayers is detected by ESR of intercalated 5 doxyl stearic acid. Simulation of lineshapes demonstrates an enlarged orientational distribution of the local director of the phospholipid phase and a small increase of the order parameter. The amount of PAF-acether required to destabilize the ovolecithin lamellar phase depends on the degree of hydration. By contrast, cholesterol displays an organizing effect on the PAF-acether phase. Simulation establishes a sharp orientational distribution of the local director when cholesterol reaches stoichiometric ratio relative to PAF-acether. At the same time, cholesterol increases the order parameter.

Calorimetric and fatty acid spin label study of subgel and interdigitated gel phases formed by asymmetric phosphatidylcholines

Several saturated asymmetric and symmetric phosphatidylcholines were studied by ESR spectroscopy and differential scanning calorimetry in order to determine the behavior of a fatty acid spin labeled near its terminal methyl, 16-doxylstearate, in the mixed interdigitated gel phase and the Lc subgel phase and other properties of these lipids. This spin label was motionally restricted in the mixed interdigitated gel phases of 18:10PC and 18:12PC. The motional restriction was similar to that reported earlier for fully interdigitated phases. This spin label was motionally restricted almost to the same degree in 10:18PC suggesting that this asymmetric lipid may also form a mixed interdigitated bilayer. In contrast the spin label had more motion in the gel phase of 18:14PC than in symmetric forms of PC, consistent with conclusions from X-ray diffraction studies that this less asymmetric lipid does not form a mixed interdigitated phase. The spin label was partially frozen out of the Lc subgel phases of symmetric forms of PC and 18:14PC formed by storage at low temperature. The phase behavior of the other asymmetric lipids also depended on the sample history. Storage at low temperature caused 10:18PC and 18:12PC to go into ordered phases. The enthalpy of the transition of these ordered phases to the liquid-crystalline phase was 2-2.4-times greater than that of the transition of the gel phase formed on cooling back from the liquid-crystalline phase. The temperature of this high enthalpy transition was 0.8 K below that of the lower enthalpy gel to liquid-crystalline phase transition for 18:12PC, but 4.6 K higher for 10:18PC. The spin label was frozen out of these ordered phases, as it was out of the Lc subgel phases, suggesting that 18:12PC and 10:18PC may also form an Lc phase. 18:10PC was not observed to form an ordered phase although storage of the sample at low temperatures did affect the temperature of its transition from the liquid-crystalline phase back to the gel phase upon cycling through its phase transition.

X-ray diffraction evidence for fully interdigitated bilayers of 1-stearoyllysophosphatidylcholine

X-ray diffraction experiments have been performed on 1-stearoyllysophosphatidylcholine or C(18):C(0)PC as a function of hydration at temperatures below the order/disorder transition (Tm = 26.2 degrees C). At these temperatures, hydrated C(18):C(0)PC forms lamellae. The bilayer thickness, as determined by the saturation hydration method and electron-density profile, is 35-36 A, and the average area per C(18):C(0)PC molecule at the lipid/water interface is 45.5 A2. The packing geometry of C(18):C(0)PC in the lamella is proposed to adopt a fully interdigitated model in which the long C(18) acyl chain extends across the entire hydrocarbon width of the bilayer. Thus far, three different types of interdigitated bilayers are known for phosphatidylcholines. These various types of chain interdigitation are discussed in terms of the chain length difference between the sn-1 and sn-2 acyl chains.

A Raman spectroscopic study on the effect of cholesterol on lipid packing in diether phosphatidylcholine bilayer dispersions

For assessing lipid-sterol packing characteristics in model membrane systems, the vibrational Raman spectra of 1,2-di-O-hexadecyl-sn-glycero-3-phosphocholine (DHPC) multilamellar dispersions containing 18 mol% cholesterol were examined. The thermotropic behavior of the pure diether- and cholesterol-containing bilayers were studied in both the C-H stretching (2800-3100 cm-1) and C-C stretching (1000-1200 cm-1) mode regions, spectral intervals reflecting intermolecular and intramolecular order/disorder characteristics. Pure DHPC bilayers exhibit the pretransition and gel to liquid-crystalline phase transition temperatures at approx. 31 and 42.8 degrees C, respectively. In contrast to the temperature behavior of dipalmitoylphosphatidylcholine-cholesterol bilayers in which the primary phase transition Tm, is simply broadened, Tm is increased to approx. 49.6 degrees C in the DHPC (diether PC) liposomes containing 18 mol% cholesterol. As in the saturated chain diacyl-cholesterol bilayer systems, the sterol disorders the DHPC gel phase and eliminates the pretransition, while ordering the liquid-crystalline phase. Pure diether liposomes exhibit a headgroup dehydration effect as the multilamellar dispersions are cycled slowly over a temperature range including the gel and liquid-crystalline forms. That is, on multiple passages through the phase transitions, both the gel and liquid-crystalline bilayer forms assume an increased hydrocarbon chain order. In the cholesterol-containing diether bilayers, only the disordered intra- and interchain states are formed.

Two types of hydrocarbon chain interdigitation in sphingomyelin bilayers

Vibrational Raman spectroscopic experiments have been performed as a function of temperature on aqueous dispersions of synthetic DL-erythro-N-lignoceroylsphingosylphosphocholine [C(24):SPM], a racemic mixture of two highly asymmetric hydrocarbon chain length sphingomyelins. Raman spectral peak-height intensity ratios of vibrational transitions in the C-H stretching-mode region show that the C(24):SPM-H2O system undergoes two thermal phase transitions centered at 48.5 and 54.5 degrees C. Vibrational data for fully hydrated C(24):SPM are compared to those of highly asymmetric phosphatidylcholine dispersions. The Raman data are consistent with the plausible model that the lower temperature transition can be ascribed to the conversion of a mixed interdigitated gel state (gel II) to a partially interdigitated gel state (gel I) and that the higher temperature transition corresponds to a gel I----liquid-crystalline phase transition. The observation of a mixed interdigitated gel state (gel II) at temperatures below 48.5 degrees C implies that biological membranes may have lipid domains in which some of the lipid hydrocarbon chains penetrate completely across the entire hydrocarbon width of the lipid bilayer.