Transition temperature cholesterol effect

The development of monoalkyl phosphate as a low skin irritating anionic surfactant is accented in a review with 30 references on monoalkyl phosphate salts, including surface-active properties, cutaneous effects, and applications to paste and liquid-type skin cleansers, and also phosphorylation reactions from the viewpoint of industrial production [26]. Amine salts of acrylate ester polymers, which are physiologically acceptable and useful as surfactants, are prepared by transesterification of alkyl acrylate polymers with 4-morpholinethanol or the alkanolamines and fatty alcohols or alkoxylated alkylphenols, and neutralizing with carboxylic or phosphoric acid. The polymer salt was used as an emulsifying agent for oils and waxes [70]. Preparation of pharmaceutical liposomes with surfactants derived from phosphoric acid is described in [279]. Lipid bilayer vesicles comprise an anionic or zwitterionic surfactant which when dispersed in H20 at a temperature above the phase transition temperature is in a micellar phase and a second lipid which is a single-chain fatty acid, fatty acid ester, or fatty alcohol which is in an emulsion phase, and cholesterol or a derivative. 

Recently, due to increased interest in membrane raft domains, extensive attention has been paid to the cholesterol-dependent liquid-ordered phase in the membrane (Subczynski and Kusumi 2003). The pulse EPR spin-labeling DOT method detected two coexisting phases in the DMPC/cholesterol membranes the liquid-ordered and the liquid-disordered domains above the phase-transition temperature (Subczynski et al. 2007b). However, using the same method for DMPC/lutein (zeaxanthin) membranes, only the liquid-ordered-like phase was detected above the phase-transition temperature (Widomska, Wisniewska, and Subczynski, unpublished data). No significant differences were found in the effects of lutein and zeaxanthin on the lateral organization of lipid bilayer membranes. We can conclude that lutein and zeaxanthin—macular xanthophylls that parallel cholesterol in its function as a regulator of both membrane fluidity and hydrophobicity—cannot parallel the ability of cholesterol to induce liquid-ordered-disordered phase separation. 

Cholesterol s presence in liposome membranes has the effect of decreasing or even abolishing (at high cholesterol concentrations) the phase transition from the gel state to the fluid or liquid crystal state that occurs with increasing temperature. It also can modulate the permeability and fluidity of the associated membrane—increasing both parameters at temperatures below the phase transition point and decreasing both above the phase transition temperature. Most liposomal recipes include cholesterol as an integral component in membrane construction. 

Biological membranes Fluidity and order parameters Determination of the phase transition temperature Effect of additives (e.g. cholesterol)... 

Pyrene has been used to investigate the extent of water penetration into micelles and to accurately determine critical micellar concentrations (Kalyanasundaram, 1987). Polarity studies of silica or alumina surfaces have also been reported. In lipid vesicles, measurement of the ratio Ii/Iui provides a simple tool for determination of phase transition temperatures and also the effect of cholesterol addition. 

Fig. 11. Evidence that a membrane-associated immunochemical reaction (complement fixation) depends on the mobility of the target hapten (IX) in the plane of a model membrane. The extent of the immunochemical reaction, complement fixation, is measured by A Absorbance at 413 nm. Temperature is always 32°C, which is above the chainmelting temperature (23°C) of dimyristoylphosphatidylcholine used for the data given in A and below the chain-melting transition temperature (42°C) of dipalmitoylphosphatidyl-choline used for the data in B. Thus A refers to a fluid membrane and B refers to a solid membrane. The numbers by each curve are equal to c, the mole % of spin-label hapten IX in the plane of the lipid membrane. It will be seen that complement fixation, as measured by A Absorbance at 413 nm is far more effective in the fluid membrane than in the solid membrane at low hapten concentrations (i.e., c 0.3 mo e%). In C the lipid membrane host is a 50 50 mole ratio mixture of cholesterol and dipalmitoylphosphatidylcholine. The immunochemical data suggest that this membrane is in a state of intermediate fluidity. Specific affinity-purified IgG molecules were used in these experiments. (For further details, see Ref. 5.)... 

An obvious hypothesis is that this unusual membrane lipid composition is related directly to membrane function in some way. Within the restricted area of lipid bilayers, lipid composition is known to be an important determinant of physical properties. There are several prominent examples. First, the temperature at which the hydrocarbon chains melt when assembled in bilayers (the gel-to-liquid-crystalline transition temperature, marks an abrupt change in many of the physical properties of such bilayer systems for example, water permeability through such bilayers increases by several orders of magnitude above the transition. Second, the presence of cholesterol within bilayers composed of amphipathic lipids has a profound effect on lipid motion, mechanical properties (such as resistance to shear), and permeability to water. 

The occurrence of cholesterol and related sterols in the membranes of eukaryotic cells has prompted many investigations of the effect of cholesterol on the thermotropic phase behavior of phospholipids (see References 23-25). Studies using calorimetric and other physical techniques have established that cholesterol can have profound effects on the physical properties of phospholipid bilayers and plays an important role in controlling the fluidity of biological membranes. Cholesterol induces an intermediate state in phospholipid molecules with which it interacts and, thus, increases the fluidity of the hydrocarbon chains below and decreases the fluidity above the gel-to-liquid-crystalline phase transition temperature. The reader should consult some recent reviews for a more detailed treatment of cholesterol incorporation on the structure and organization of lipid bilayers (23-25). 

In this work, we have analyzed the phase behavior of various freeze-dried mixtures of DPPE, DPPC, and cholesterol and have examined the effects of trehalose addition to these liposomes. Generally, dehydration leads to increase in transition temperature of the phospholipids and also to phase separation. Addition of trehalose, however, can prevent the increase in transition temperature and phase separation freeze-dried DPPC-cholesterol liposomes exhibit only one transition and their retention capability increases by more than 40%. Further studies on the phase separation and stability of multicomponent model membranes will be required to understand better its relation to the survival of cells to freeze-drying procedures. 

The effects of cholesterol on phospholipid dispersions in water have been studied by a variety of biophysical techniques. These have created an understanding of the cholesterol condensation eff t in molecular terms. Such studies have been made above and below the main phosphohpid melting transition temperature (7 ) at which the phosphohpid changes from the l-)8 gel phase to the L-a hquid-crystalline phase. 

In a recent study, a dose-response relationship was found between THC and the transition temperature shift for lecithins [113]. The cholesterol content was again found to influence this effect. 

Cholesterol has an interesting effect on membrane fluidity. As seen in Figure 10.12b, cholesterol does not change the transition temperature of a membrane, but rather broadens the range of the transition considerably. It has been hypothesized that this broadening occurs because cholesterol can both stiffen the membrane above the transition temperature and inhibit regularity in structure formation below the transition temperature. Thus, it blurs the distinction between the gel and fluid state. 

Another example demonstrates the effect of formation of a network of hydrogen bonds between linkages on the phase transition temperatures and molecular mobility of cholesterol-containing polymers ... 

Cholesterol in membrane bilayers has an important modulatory effect on the bilayer phase of phospholipids [2,15]. The sterol interacts strongly with phospholipids and keeps them in an intermediate fluid condition. Thus, above its transition temperature, the presence of cholesterol tends to increase the packing and rigidity of bilayers [19], and below its transition temperature, it expands and fluidizes the bilayers [20]. 

Papahadjopoulos, D., Jacobson, K., Nir, S. and Isac, T. (1973). Phase transitions in phospholipid vesicles fluorescence polarization and permeability measurements concerning the effect of temperature and cholesterol, Biophys. Biochim. Acta, 311, 330-348. 

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