Headgroup hydration and motional order of lipids in lamellar liquid crystalline and inverted hexagonal phases of unsaturated phosphatidylethanolamine--a time-resolved fluorescence study

SYL3C aptamer-anchored microemulsion co-loading β-elemene and PTX enhances the treatment of colorectal cancer

The aim of this study is to construct a SYL3C aptamer-anchored microemulsion based on β-elemene and PTX (SYL3C/EP-MEs) for enhancement on colorectal cancer therapy. Such microemulsion is consist of encapsulated drugs (β-elemene and PTX), tumor targeting ligand (3’-end thiolated SYL3C aptamer), thiol conjugated site (maleimide-modified PEGylated 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine, mal-DOPE-PEG), pH-sensitive component (DOPE) and other necessary excipients. SYL3C/EP-MEs showed a spherical particle with an average particle size around 30 nm and a high encapsulation efficiency (>80%) for both drugs. β-elemene and PTX could be released controllably from SYL3C/EP-MEs as pH values changed. SYL3C/EP-MEs displayed a selective affinity to HT-29 cells, leading to an obvious increase in cellular uptake, cell apoptosis and cytotoxicity. In the HT-29 tumor xenograft-bearing nude mice model studies, SYL3C/EP-MEs showed an overwhelming tumor growth inhibition, the longest survival time and the lowest systemic toxicity among all the treatments. The potential mechanism of enhanced anti-cancer ability was probably associated with the induction of M1 macrophage polarization, the downregulation of mutant p53 protein and the reduction of bcl-2 protein expression. Collectively, the microemulsion codelivery of β-elemene and PTX using functionalization with SYL3C aptamer provides a novel approach for combinational colorectal cancer-targeted treatment.

Barotropic phase transition between the lamellar liquid crystal phase and the inverted hexagonal phase of dioleoylphosphatidylethanolamine

The phase transition between the lamellar liquid crystal (Lalpha) phase and the inverted hexagonal (H(II)) phase of dioleoylphosphatidylethanolamine (DOPE) in aqueous NaCl solutions was observed by means of differential scanning calorimetry (DSC) under ambient pressure and light-transmittance technique under high pressure. The pressure dependence of the transition temperature (dT/dp) and the thermodynamic quantities for the Lalpha/H(II) transition were compared with those of another phase transition found in the DOPE bilayer membrane, which is the transition from the lamellar crystal (Lc) phase to the Lalpha phase. The dT/dp value of the Lalpha/H(II) transition was about 3.5 times as large as that of the Lc/Lalpha transition while the thermodynamic quantities were significantly smaller than those of the latter to the contrary. Comparing the enthalpy and volume behavior of the Lalpha/H(II) transition with that of the Lc/Lalpha transition, we concluded that the Lalpha/H(II) transition can be regarded as the volume-controlled transition for the reconstruction of molecular packing.

Determination of L(alpha)-H(II) phase transition temperature for 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine

The thermodynamic properties of fully-hydrated lipids provide important information about the stability of membranes and the energetic interactions of lipid bilayers with membrane proteins (Nagle and Scott, Physics Today, 2:39, 1978). The lamellar/inverse hexagonal (L(alpha)-H(II)) phase transition of 1,2-dioleoyl-sn-glycero-3-phosphatidylethanolamine (DOPE) water mixtures is a first-order transition and, therefore, at constant pressure, must have a thermodynamically well-defined equilibrium transition temperature. The observed transition temperature is known to be dependent upon the rate at which the temperature is changed, which accounts for the many different values in the literature. X-ray diffraction was used to study the phase transition of fully-hydrated DOPE to determine the rate-independent transition temperature, T(LH). Samples were heated or cooled for a range of rates, 0.212 < r < 225 degrees C/hr, and the rate-dependent apparent phase transition temperatures, T(A)(r) were determined from the x-ray data. By use of a model-free extrapolation method, the transition temperature was found to be T(LH) = 3.33 +/- 0.16 degrees C. The hysteresis, /T(A)(r) - T(LH)/, was identical for heating and cooling rates, +/-r, and varied as /r/beta for beta approximately 1/4. This unexpected power-law relationship is consistent with a previous study (Tate et al., Biochemistry, 31:1081-1092, 1992) but differs markedly from the exponential behavior of activation barrier kinetics. The methods used in this study are general and provide a simple way to determine the true mesomorphic phase transition temperatures of other lipid and lyotropic systems.

Effect of cardiolipin on proton permeability of phospholipid liposomes: the role of hydration at the lipid-water interface

The effect of cardiolipin on the proton permeability of dipalmitoyl-phosphatidylcholine small unilamellar vesicles was examined by utilizing the pH-dependent fluorescence emission of 5- (and 6-) carboxyfluorescein. It has been found that the proton permeability of the phospholipid bilayer was greatly enhanced in the presence of cardiolipin, an acidic phospholipid mainly found in the inner mitochondrial membranes. In the presence of bovine heart cardiolipin, the bilayer surface hydration, as assessed with the fluorescence lifetime of 1-anilinonaphthalene-8-sulfonic acid, was increased, while hydration in the acyl chain region was not altered. In addition, the bilayer fluidity was also not affected. Taken together, these results suggest that the lipid-water interface is the major energy barrier for proton permeation of the bilayer vesicles, and alteration to properties of this interface by cardiolipin headgroup appears to be responsible for the enhanced proton permeability.

Time-resolved fluorescence reveals two binding sites of 1,8-ANS in intact human oxyhemoglobin

Time-resolved fluorescence of 1,8-anilinonaphthalene sulfonate (1,8-ANS) fluorescent probe bound to intact human oxyhemoglobin (HbO2) is investigated. Fluorescence emission spectra of 1,8-ANS in a potassium buffer solution (pH 7.4) of HbO2 undergo a substantial blue shift during first 6 ns after pulsed optical excitation at 337.1 nm. Nonexponential fluorescence kinetics of 1,8-ANS in the HbO2 solution are studied by the decay time distribution and conventional multiexponential analyses for a set of emission wavelength range of lambdaem = 455-600 nm. These fluorescence decays contain components with mean decay times of <0.5 ns, 3.1-5.5 ns, and 12.4-15.1 ns with spectrally-dependent relative contributions. The shortest decay component is assigned to free 1,8-ANS molecules in the bulk buffer environment, whereas the two longer decay components are assigned to two types of binding sites of 1,8-ANS in the HbO2 molecule presumably differing by polarity and accessibility to water molecules. The results represent the first experimental evidence of heterogeneous binding of 1,8-ANS to intact human oxyhemoglobin.

Hydration properties of lamellar and non-lamellar phases of phosphatidylcholine and phosphatidylethanolamine

Two of the most common phospholipids in biological membranes are phosphatidylcholine (PC) and phosphatidylethanolamine (PE). Over a wide range of temperatures the PCs found in biological membranes form lamellar (bilayer) phases when dispersed in excess water, whereas PEs form either lamellar or hexagonal phases depending on their hydrocarbon chain composition. This paper details the hydration properties of lamellar and hexagonal phases formed by PCs and PEs, focusing on the energetics of hydration of these phases. For the hexagonal phase, the energy of bending the lipid monolayer is a critical term, with other contributions arising from the energies of hydrating the lipid headgroups and filling voids in the interstices in the hydrocarbon region. For the lamellar phase of PC, the water content is determined by a balance between the attractive van der Waals pressure and repulsive hydration and entropic (steric) pressures. In the case of PE bilayers, recent experiments demonstrate the presence of an additional strong, short-range attractive interaction, possibly due to hydrogen-bonded water interactions between N+ H3 groups in one bilayer and the PO4- groups in the apposing bilayer. This additional attractive pressure causes apposing PE bilayers to adhere strongly and to imbibe considerably less water than PC bilayers.

Diacylglycerol and the promotion of lamellar-hexagonal and lamellar-isotropic phase transitions in lipids: implications for membrane fusion

Changes in steady-state fluorescence anisotropy of 1 -(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene TMA-DPH) are applied to the detection of lamellar-hexagonal transitions in egg phosphatidylethanolamine. Even low (2 mole%) proportions of diacylglycerol decrease the hexagonal transition temperature considerably, as confirmed by differential scanning calorimetry. Diacylglycerol is also found to promote a lamellar to "isotropic" (Q(224) cubic) transition in mixtures of phosphatidylcholine: phosphatidylethanolamine:cholesterol. This nonreversible transition is also observed by (31)P nuclear magnetic resonance and detected as a large increase in TMA-DPH steady-state anisotropy. The same technique reveals as well that lysophosphatidylcholine counteracts the effect of diacylglycerol and stabilizes the lamellar phase in both transitions. Diacylglycerol and lysophosphatidylcholine are known to respectively promote and inhibit membrane fusion in a variety of systems. These data are interpreted in support of the hypothesis of a highly bent structural fusion intermediate ("stalk"). They also show the interest of lipid-phase studies in predicting and rationalizing membrane fusion mechanisms.

The effect of N-acyl ethanolamines on phosphatidylethanolamine phase transitions studied by laurdan generalised polarisation

The effect of N-lauroylethanolamine (N-LEA) and N-oleoylethanolamine (N-OEA) on the thermal behaviour of fully hydrated egg phosphatidylethanolamine (TPE) was investigated by the steady-state fluorescence of 2-dimethylamino-(6-lauroyl)-naphtalene (laurdan) and 1-(4-trimethylaminophenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH). The parameter generalised polarisation (GP), calculated by exciting laurdan at 340 and 410 nm, revealed the gel to liquid crystalline lamellar (L alpha) as well as the L alpha to inverse hexagonal (HII) phase transitions of TPE. The L alpha to HII phase transition was not detected in TPE/N-OEA system, probably because of the formation of an intermediate Q224 cubic phase. The formation of Q224 phase in TPE/N-OEA and TPE/N-LEA systems was previously demonstrated by X-ray diffraction, but neither laurdan generalised polarisation nor TMA-DPH steady-state fluorescence anisotropy measurements revealed the presence of this phase. It is suggested that the lack of detection of the cubic phase is probably due to the similarity in dynamic characteristics and hydration levels of phospholipid headgroups in the bilayer and cubic phases.

Phases and phase transitions of the hydrated phosphatidylethanolamines

LIPIDAT is a computerized database providing access to the wealth of information scattered throughout the literature concerning synthetic and biologically derived polar lipid polymorphic and mesomorphic phase behavior. Here, a review of the LIPIDAT data subset referring to hydrated phosphatidylethanolamines (PE) is presented together with an analysis of these data. The PE subset represents 14% of all LIPIDAT records. It includes data collected over a 38-year period and consists of 1511 records obtained from 203 articles in 35 different journals. An analysis of the data in the subset has allowed us to identify trends in synthetic PE phase behavior reflecting changes in lipid chain length, chain unsaturation (number, isomeric type and position of double bonds), chain asymmetry and branching, type of chain-glycerol linkage (ether vs. ester) and headgroup modification. Also included is a summary of the data concerning the effect of pH, stereochemical purity, and different additives such as salts, saccharides, alcohols, amino adds and alkanes on PE phase behavior. Information on the phase behavior of biologically derived PE is also presented. This review includes 236 references.

Inactivation of calcium uptake by EGTA is due to an irreversible thermotropic conformational change in the calcium binding domain of the Ca(2+)-ATPase

Calcium uptake by rabbit skeletal sarcoplasmic reticulum (SR) is inhibited with an effective inactivation temperature (TI) of 37 degrees C in EGTA with no effect on ATPase activity. Since the Ca-ATPase denatures at a much higher temperature (49 degrees C) in EGTA, this suggests that a small or localized conformational change of the Ca-ATPase at 37 degrees C results in inability to accumulate calcium by the SR. Using a fluorescent analogue of dicyclohexylcarbodiimide, N-cyclohexyl-N'-[4-(dimethylamino)-alpha-naphthyl]-carbodiimide (NCD-4), the region of the calcium binding sites of the SR Ca-ATPase was labeled. Steady-state and frequency-resolved fluorescence measurements were subsequently performed on the NCD-4-labeled Ca-ATPase. Site-specific information pertaining to the hydrophobicity and segmental flexibility of the region of the calcium binding sites was derived from the steady-state fluorescence intensity, lifetime, and rotational rate of the covalently bound NCD-4 label as a function of temperature (0-50 degrees C). A reversible transition at approximately 15 degrees C and an irreversible transition at approximately 35 degrees C were deduced from the measured fluorescence parameters. The low-temperature transition agrees with the previously observed break in the Arrhenius plot of ATPase activity of the native Ca-ATPase at 15-20 degrees C. The high-temperature transition conforms well with the conformational transition, resulting in uncoupling of Ca translocation from ATP hydrolysis as predicted from the irreversible inactivation of Ca uptake at 31-37 degrees C in 1 mM EGTA.(ABSTRACT TRUNCATED AT 250 WORDS)

Infrared and time-resolved fluorescence spectroscopic studies of the polymorphic phase behavior of phosphatidylethanolamine/diacylglycerol lipid mixtures

Fourier transform infrared (FTIR) and time-resolved fluorescence spectroscopy have been employed to examine the structural dynamics of lipid fatty acyl chains and lipid/water interfacial region of a binary lipid mixture containing unsaturated phosphatidylethanolamine (PE) and diacylglycerol (DG). Infrared vibrational frequencies of the CH2 symmetric stretching and the C = O stretching bands of the lipids were measured at different lipid compositions and temperatures. For 0% DG, the lamellar gel to lamellar liquid crystalline (L beta-L alpha) and the L alpha to inverted hexagonal (L alpha-HII) phase transitions were observed at approximately 15 degrees and 55 degrees C, respectively. As the DG content increased gradually from 0% to 15%, the L alpha-HII phase transition temperature decreased drastically while the L beta-L alpha phase transition temperature decreased only slightly. At 10% DG, a merge of these two phase transitions was noticed at approximately 10 degrees C. For the composition study at 23 degrees C, the L alpha-HII transition occurred at approximately 6-10% DG as indicated by abrupt increases in both the CH2 and C = O stretching frequencies at those DG contents. Using time-resolved fluorescence spectroscopy, abrupt decreases in both the normalized long time residual and the initial slope of the anisotropy decay function of lipid probes, 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5- hexatrienyl)phenyl]ethyl]carbonyl]-3-sn-phosphatidylcholine, in these PE/DG mixtures were observed at the L alpha-HII phase transition. These changes in the anisotropy decay parameters suggested that the rotational dynamics and orientational packing of the lipids were altered at the composition-induced L alpha-HII transition, and agreed with a previous temperature-induced L alpha-HII transition study on pure unsaturated PE (Cheng (1989) Biophys. J. 55, 1025-1031). The fluorescence lifetime of water soluble probes, 8,1-anilinonapthalenes sulfonate acid, in PE/DG mixtures increased abruptly at the L alpha-HII phase transition, suggesting that the conformation and hydration of the lipid/water interfacial region also undergo significant changes at the L alpha-HII transition.