Salicylic acid-induced effects in the mixed-lipid (dipalmitoyl phosphatidylcholine–dipalmitoyl phosphatidylethanolamine) model membrane

Acetylsalicylic acid (aspirin) and salicylic acid interaction with the human erythrocyte membrane bilayer induce in vitro changes in the morphology of erythrocytes

Despite the well-documented information, there are insufficient reports concerning the effects of salicylate compounds on the structure and functions of cell membranes, particularly those of human erythrocytes. With the aim to better understand the molecular mechanisms of the interaction of acetylsalicylic acid (ASA) and salicylic acid (SA) with cell membranes, human erythrocyte membranes and molecular models were utilized. These consisted of bilayers of dimyristoylphosphatidylcholine (DMPC) and dimyristoylphosphatidylethanolamine (DMPE), representative of phospholipid classes located in the outer and inner monolayers of the human erythrocyte membrane, respectively. The capacity of ASA and SA to perturb the multibilayer structures of DMPC and DMPE was evaluated by X-ray diffraction while DMPC unilamellar vesicles (LUV) were studied by fluorescence spectroscopy. Moreover, we took advantage of the capability of differential scanning calorimetry (DSC) to detect the changes in the thermotropic phase behavior of lipid bilayers resulting from ASA and SA interaction with PC and PE molecules. In an attempt to further elucidate their effects on cell membranes, the present work also examined their influence on the morphology of intact human erythrocytes by means of defocusing and scanning electron microscopy, while isolated unsealed human erythrocyte membranes (IUM) were studied by fluorescence spectroscopy. Results indicated that both salicylates interact with human erythrocytes and their molecular models in a concentration-dependent manner perturbing their bilayer structures.

Interaction of propyl paraben with dipalmitoyl phosphatidylcholine bilayer: A differential scanning calorimetry and nuclear magnetic resonance study

The influence of the preservative, propyl paraben (PPB) on the biophysical properties of dipalmitoyl phosphatidyl choline (DPPC) vesicles, both in multilamellar vesicle (MLV) and unilamellar vesicle (ULV) forms, has been studied using DSC and ((1)H and (31)P) NMR. The mechanism by which PPB interacts with DPPC bilayers was found to be independent of the morphological organization of the lipid bilayer. Incorporation of PPB in DPPC vesicles causes a significant depression in the transition temperature and enthalpy of both the pre-transition (PT) and the gel to liquid crystalline transition. The presence of the PPB also reduces the co-operativity of these transitions. However, at high PPB concentration the PT disappears. DSC and NMR findings indicate that: (i) PPB is bound strongly to the lipid bilayer leading to increased headgroup fluidity due to reduced headgroup-headgroup interaction and (ii) the PPB molecules are intercalated between the DPPC polar headgroups with its alkyl chain penetrate into the co-operative region. MLV incorporated with high PPB concentration shows additional transitions whose intensity increases with increasing PPB concentration. This phase segregation observed could probably be due to co-existence of PPB-rich and PPB-poor phospholipid domains within the bilayers. The effect of inclusion of cholesterol in the PPB-free and PPB-doped DPPC dispersion was also studied. Equilibration studies suggest that PPB molecules are very strongly bound and remain intercalated between the polar headgroup for prolonged time.

Effect of propyl paraben on the dipalmitoyl phosphatidic acid vesicles

The effect of the preservative propyl paraben (PPB) on the phase transition and dynamics of dipalmitoyl phosphatidic acid (DPPA)-buffer (pH 7.4/9.3) vesicles has been studied using DSC and ((1)H and (31)P) NMR. These investigations were carried out with DPPA dispersion in both multilamellar vesicular (MLV) and unilamellar vesicular (ULV) forms. DSC results indicate that the mechanism by which PPB interact with the DPPA vesicles is similar in MLV and ULV and is independent of pH of the buffer used to form the dispersion. However, for a given concentration of PPB, the perturbation in DPPA bilayer is more when the dispersion is prepared in buffer pH 7.4. PPB affected both the thermotropic phase transition and the molecular mobility of the DPPA membrane. In the presence of PPB, the gel to liquid crystalline phase transition temperature (T(m)) of the DPPA vesicles decreases hence increases membrane fluidity due to reduced headgroup-headgroup interaction. For all concentrations, the PPB molecules seem to get intercalated between the polar groups of the phospholipids with its alkyl chain penetrating into the co-operative region. At high PPB concentration, additional transitions are observed whose intensity increases with increasing PPB concentration. The large enthalpy values obtained at high PPB concentration suggest that presence of PPB makes the DPPA bilayer more ordered (rigid). The interesting finding obtained with MLV is that the stable gel phase of DPPA-buffer (pH 9.3/7.4) system in the presence of high PPB concentration becomes a metastable gel phase, this metastable gel phase on equilibration at 25 degrees C or when cooled to -20 degrees C transforms to a stable crystalline phase(s). The intensity of this new phase(s) increases with increasing PPB concentration. However, the transition temperatures of these new phases are not significantly changed with increasing PPB concentration. The effect of inclusion of cholesterol in the PPB-free and PPB-doped DPPA dispersion was also studied.