Effect of propyl paraben on the dipalmitoyl phosphatidic acid vesicles

Structure of drug delivery DPPA and DPPC liposomes with ligands and their permeability through cells

Dipalmitoylphosphatidylcholine (DPPC) and 1,2-palmitoyl-phosphatidic acid (DPPA) liposomes, prepared by conventional rotary evaporation method, have similar structural organization, though they have significant differences. The similarity is that both types of lipids create standard bilayer liposomes with strong hydrophobic forces between lipids tails and with homogeneous bonds of hydrogen and electrostatic nature between hydrophilic lipids heads. By the calorimetric method, it has been shown that hydrophobic bonds break but liposomes' destruction does not occur by heating till 150 °C. As for bonds between lipid heads in liposomes, their cooperative destruction takes place at 41 °C for DPPC and 66 °C for DPPA liposomes. In the case of thermal distraction of DPPC liposomes, two so-called pre transitions peaks were observed before the main transition peak, which indicates that DPPC liposomes' structure is multilamellar. DPPA liposomes have one cooperative heat absorption peak, which points to a unilamellar structure of such liposomes. Substances of hydrophobic/hydrophilic nature, incorporated into the liposomes, are placed in hydrophobic or hydrophilic parts of liposomes, which lead to a change in calorimetric peak shapes and thermodynamic parameters. It has been shown that gold nanoparticles, incorporated into the DPPC liposomes, are able to enter Caco-2 cells. In contrast, these nanoparticles do not enter red blood cells.

Toxicological evaluation of three contaminants of emerging concern by use of the Allium cepa test

Di(2-ethylhexyl)phthalate, triclosan and propylparaben are contaminants of emerging concern that have been subjected to extensive toxicological studies, but for which limited information is currently available concerning adverse effects on terrestrial plant systems. The Allium cepa test, which is considered one of the most efficient approaches to assess toxic effects of environmental chemicals, was selected to evaluate the potential risks of these ubiquitous pollutants. Our data demonstrate that all three compounds studied may in some way be considered toxic, but different effects were noted depending on the chemical and the end point analysed. Results derived from the analysis of macroscopic parameters used in testing for general toxicity, revealed that while di(2-ethylhexyl)phthalate had no apparent effects, the other two chemicals inhibited A. cepa root growth in a dose-dependent manner. On the other hand, although all three compounds caused alterations in the mitotic index of root-tip cells, propylparaben was the only one that did not show evidence of genotoxicity in assays for chromosome aberrations and micronuclei. The results of the present study clearly indicate that sensitive plant bioassays are useful and complementary tools to determine environmental impact of contaminants of emerging concern.

Role of phosphatidic acid in the coupling of the ERK cascade

The production of phosphatidic acid plays a crucial role in the activation of the ERK cascade. This role was linked to the binding of phosphatidate to a specific polybasic site within the kinase domain of Raf-1. Here we show that phosphatidate promotes ERK phosphorylation in intact cells but does not activate Raf in vitro. The kinase suppressor of Ras (KSR) contains a sequence homologous to the phosphatidate binding site of Raf-1. Direct binding of phosphatidate to synthetic peptides derived from the sequences of the binding domains of Raf-1 and KSR was demonstrated by spectroscopic techniques. The specificity of these interactions was confirmed using synthetic lipids and mutated peptides in which the core of the phosphatidic acid binding domain was disrupted. Insulin and exogenous dioleoyl phosphatidate induced a rapid translocation of a mouse KSR1-EGFP construct to the plasma membrane of HIRcB cells. Mutation of two arginines located in the core of the putative phosphatidate binding site abolished dioleoyl phosphatidate- and insulin-induced translocation of KSR1. Overexpression of the mutant KSR1 in HIRcB cells inhibited insulin-dependent MEK and ERK phosphorylation. The addition of dioleoyl phosphatidate or insulin increased the co-localization of KSR1 and H-Ras and promoted the formation of plasma membrane patches enriched in both proteins and phosphatidic acid. These results, in conjunction with our previous work, suggest the formation of phosphatidate-enriched membrane microdomains that contain all components of the ERK cascade. We propose that these domains act as molecular scaffolds in the coupling of signaling events.

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.