Presence Of Stearate Research Articles

Free Fatty Acids Modulate Thrombin Mediated Fibrin Generation Resulting in Less Stable Clots.

Upon platelet activation, free fatty acids are released at the stage of thrombus formation, but their effects on fibrin formation are largely unexplored. Our objective was to characterize the kinetic effects of fatty acids on thrombin activity, as well as the structural and mechanical properties of the resultant fibrin clots. Thrombin activity on fibrinogen was followed by turbidimetry and detailed kinetic characterization was performed using a fluorogenic short peptide substrate. The viscoelastic properties of fibrin were measured with rotatory oscillation rheometer, whereas its structure was analyzed with scanning electron microscopy (SEM). In turbidimetric assays of fibrin generation, oleate and stearate at physiologically relevant concentrations (60–600 μM) produced a bell-shaped inhibitory dose response, increasing 10- to 30-fold the time to half-maximal clotting. Oleate inhibited thrombin activity on a short peptide substrate according to a mixed-type inhibitor pattern (a 9-fold increase of the Michaelis constant, Km and a 20% decrease of the catalytic constant), whereas stearate resulted in only a minor (15%) drop in the catalytic constant without any change in the Km. Morphometric analysis of SEM images showed a 73% increase in the median fiber diameter in the presence of stearate and a 20% decrease in the presence of oleate. Concerning the viscoelastic parameters of the clots, storage and loss moduli, maximal viscosity and critical shear stress decreased by 32–65% in the presence of oleate or stearate, but loss tangent did not change indicating decreased rigidity, higher deformability and decreased internal resistance to shear stress. Our study provides evidence that free fatty acids (at concentrations comparable to those reported in thrombi) reduce the mechanical stability of fibrin through modulation of thrombin activity and the pattern of fibrin assembly.

Effect of modified layered double hydroxide on the flammability and mechanical properties of polypropylene

Abstract Copper-aluminum layered double hydroxides (Cu-LDHs) and nickel-aluminum layered double hydroxides (Ni-LDHs) were synthesized using co-precipitation method. LDHs were organically modified by long chain sodium stearate. Polypropylene (PP)/layered double hydroxides (LDHs) and polypropylene (PP)/organically-modified layered double hydroxides (m.Cu-LDHs or m.Ni-LDHs) were prepared through the melt bending of the PP with either nanosized LDHs or m.LDHs without any other additives. The effect of stearate on the dispersibility of LDHs was investigated by X-ray diffraction (XRD). The surface morphology of LDHs was also studied using scanning electron microscope (SEM), and the thermal stability properties of PP/LDHs composites were studied by thermogravimetric analysis (TGA). The mechanical properties of the PP/LDH composites, tensile strength, and modulus of elasticity were investigated. The flammability properties were investigated using the cone calorimeter test. The intercalation of modified LDHs was determined by XRD in the presence of stearate. Results showed that modified LDHs presented good disperasbility in the PP matrix. The thermal stability of PP has been improved by up to 6% using m.Ni-LDHS. Unmodified and modified nanosized LDHs decreased the fire growth rate of PP from 10.8 kW/m2.s to 4.1 kW/m2.s and 4.5 kW/m2.s, respectively.

A cellular model to study drug-induced liver injury in nonalcoholic fatty liver disease: Application to acetaminophen

Obesity and nonalcoholic fatty liver disease (NAFLD) can increase susceptibility to hepatotoxicity induced by some xenobiotics including drugs, but the involved mechanisms are poorly understood. For acetaminophen (APAP), a role of hepatic cytochrome P450 2E1 (CYP2E1) is suspected since the activity of this enzyme is consistently enhanced during NAFLD. The first aim of our study was to set up a cellular model of NAFLD characterized not only by triglyceride accumulation but also by higher CYP2E1 activity. To this end, human HepaRG cells were incubated for one week with stearic acid or oleic acid, in the presence of different concentrations of insulin. Although cellular triglycerides and the expression of lipid-responsive genes were similar with both fatty acids, CYP2E1 activity was significantly increased only by stearic acid. CYP2E1 activity was reduced by insulin and this effect was reproduced in cultured primary human hepatocytes. Next, APAP cytotoxicity was assessed in HepaRG cells with or without lipid accretion and CYP2E1 induction. Experiments with a large range of APAP concentrations showed that the loss of ATP and glutathione was almost always greater in the presence of stearic acid. In cells pretreated with the CYP2E1 inhibitor chlormethiazole, recovery of ATP was significantly higher in the presence of stearate with low (2.5mM) or high (20mM) concentrations of APAP. Levels of APAP-glucuronide were significantly enhanced by insulin. Hence, HepaRG cells can be used as a valuable model of NAFLD to unveil important metabolic and hormonal factors which can increase susceptibility to drug-induced hepatotoxicity.

A transcription factor that senses fatty acid structure

Bacteria regulate their membrane biophysical properties by the coordinated synthesis of saturated and unsaturated fatty acids. In Pseudomonas aeruginosa, unsaturated fatty acids are produced by the de novo fatty acid biosynthetic pathway anaerobically, or by oxidative desaturation of the existing fatty acids catalyzed by Δ9 desaturases DesA and DesB. DesA introduces the double bond into phospholipid acyl chains, whilst DesB desaturates acyl‐CoAs. A transcriptional repressor DesT regulates the expression of desCB operon. The expression level of desCB is strongly and selectively up‐regulated in a ΔdesT deletion strain. Both electrophoresis mobility shift assay and DNase I footprinting analysis demonstrated the existence of two DesT binding sites in the desT‐desCB promoter region, P1 and P2. The binding of purified DesT to P2 was enhanced by unsaturated acyl‐CoAs, whereas saturated acyl‐CoAs prevented DesT interaction with P2. The biological importance of this interaction was verified by the up‐regulation of desCB in cells grown in the presence of stearate and their repression when oleate was present. This unique ligand selectivity allows DesT to sense the physical properties of the cellular acyl‐CoA pool and modulate the expression of the acyl‐CoA Δ9‐desaturase system accordingly. (Supported by GM34496 and ALSAC)

Suppressed catalytic efficiency of plasmin in the presence of long‐chain fatty acids

Thrombi, which are dissolved primarily by plasmin (EC 3.4.21.7.), contain up to millimolar concentrations of fatty acids and these are known to affect the action of the protease. In the present study the modulation of plasmin activity was characterized quantitatively in a continuous amidolytic assay based on synthetic plasmin substrate (Spectrozyme-PL). A novel numerical procedure was applied for identification of kinetic parameters and their confidence intervals, with Monte Carlo simulation of the reaction progress curves, providing adequate grounds for discrimination of different models of the enzyme action. All three fatty acids caused a 10–20-fold increase in the Michaelis constant on Spectrozyme-PL (baseline value 5.9 μm). The catalytic constant decreased from 5.8·s−1 to 2.4–2.8·s−1 in the presence of arachidonate and oleate, but increased to 14.8·s−1 in the presence of stearate, implying enhancement of plasmin activity at saturating substrate concentrations. However, based on the ratio of the catalytic and Michaelis constants, all three fatty acids acted as inhibitors of plasmin with various degrees of potency, showing concentration dependence in the range of 10–65 μm for oleate and arachidonate, and 115–230 μm for stearate. The reported effects of the three fatty acids require the presence of kringle 5 in the structure of the protease; miniplasmin (des-kringle 1-4 plasmin) is as sensitive to fatty acids as plasmin, whereas the activity of microplasmin (des-kringle 1-5 plasmin) is not affected.

A Pseudomonas aeruginosa transcription factor that senses fatty acid structure

Cells regulate their membrane phospholipid biophysical properties by the co-ordinated synthesis of saturated and unsaturated fatty acids. In bacteria, unsaturated fatty acids are produced by the de novo fatty acid biosynthetic pathway anaerobically, or by oxidative desaturation of the existing fatty acids catalysed by desaturases. A transcriptional repressor in Pseudomonas aeruginosa, DesT (PA4890), regulates the expression of an acyl-CoA desaturase operon (desCB, PA4889 and PA4888). The desCB operon is located adjacent to desT and is transcribed in the opposite direction. The expression level of desCB is strongly and selectively upregulated in a DeltadesT-deletion strain. Both electrophoresis mobility shift assay and DNase I footprinting analysis demonstrated the existence of two DesT binding sites in the desT-desCB promoter region, P1 and P2. The binding of purified DesT to P2 was enhanced by unsaturated acyl-CoAs, whereas saturated acyl-CoAs prevented DesT interaction with P2. The biological importance of this interaction was verified by the upregulation of desCB and desT in cells grown in the presence of stearate and their repression when oleate was present. This unique ligand selectivity allows DesT to sense the physical properties of the cellular acyl-CoA pool and modulate the expression of the acyl-CoA Delta9-desaturase system to adjust fatty acid desaturation activity accordingly.

Characterization of Pseudomonas aeruginosa DesT (PA4890), a transcriptional factor sensing long‐chain acyl‐CoAs

Cells regulate their membrane phospholipid biophysical properties by coordinated synthesis of saturated and unsaturated fatty acids. In bacteria, unsaturated fatty acids are produced by the de novo fatty acid biosynthetic pathway anaerobically, or by oxidative desaturation of the existing fatty acids catalyzed by desaturases. In this study, we have identified and characterized a unique transcriptional repressor in Pseudomonas aeruginosa, DesT (PA4890), which regulates the expression of an acyl-CoA desaturase operon (desCB, PA4889 and PA4888). The desCB operon is located immediately upstream of desT and is transcribed to the opposite direction to desT. Both Affymetrix array and quantitative real-time PCR analyses demonstrated that desC and desB expression were strongly and selectively up-regulated in a ΔdesT deletion strain. The purified recombinant DesT bound to the desCB promoter region at two distinct sites with different affinities. The interaction of DesT with the high-affinity binding site (Kd = 0.35 ± 0.03 nM) was enhanced by unsaturated acyl-CoAs such as palmitoleoyl-CoA and oleoyl-CoA (Kd = 0.10 ± 0.01 nM), whereas saturated acyl-CoAs such as myristoyl-CoA and palmitoyl-CoA prevented DesT interaction with the high-affinity site. CoA, short-chain acyl-CoAs, free fatty acids and acyl-ACPs did not influence DesT-DNA interactions in vitro. Binding to the low-affinity site was not regulated. Accordingly, the expression of desB was up-regulated in cells grown in the presence of stearate and repressed when oleate was present. Thus, DesT senses the composition of the cellular acyl-CoA pool to either increase or decrease the expression of the acyl-CoA Δ9 desaturase system to adjust fatty acid metabolism to the composition of the exogenous fatty acid pool.

Extracellular metabolites of hydrocarbon-oxidizing bacteria as a substrate for sulfate reduction

The relationship between bacterial oxidation of hydrocarbons and sulfate reduction was studied in the experimental system with liquid paraffin was used as a source of organic compounds inoculated with silt taken from a reservoir. Pseudomonads dominated in the hydrocarbon-oxidizing silt bacteriocenosis. However, Rhodococcus and Arthrobacteria amounted to not more than 3%. Arthrobacteria dominated the microbial association formed in the paraffin film of the model system. Sulfate-reducing bacteria were represented by genera Desulfomonas, Desulfotomaculum, and Desulfovibrio. The growth of sulfate-reducing bacteria in media containing with paraffin, successive products of its oxidation (cetyl alcohol, stearate, and acetate), and extracellular metabolites of hydrocarbon-reducing bacteria was studied. The data showed that sulfate-reducing bacteria did not use paraffin or cetyl alcohol as growth substrates. However, active growth of sulfate-reducing bacteria was observed in the presence of stearate and extracellular water-soluble or lipid metabolites of Arthrobacteria.

Photodegradation of PVC stabilized by Ba, Ca, Cd and Zn stearates

Films of unplasticized PVC containing Ba, Ca, Cd or Zn stearate at 5 mmol/100 g PVC and prepared by pressing at 190° were exposed to radiation of 300–420 nm wavelength with emission maximum at 345 nm. I.R. spectroscopy and coulometric chloride determinations were employed to monitor changes in the amounts of stearate, stearic acid, carbonyl groups and chloride ions in the films during photodegradation. The point at which the characteristic absorption maxima of the stearates vanish decreases in the order CdSt2, ZnSt2, BaSt2, CaSt2. HCl is found to split from the polymer and CO groups to form from the beginning of the exposure. The courses of the formation of stearic acid and chloride ions differ for the various stearates. The formation of CO groups is not favoured by the presence of stearates. The increase in the CO group content of the polymer is related to the amount of the chemically unchanged stearate in the mixture.

Etude de la stabilisation du polychlorure de vinyle avec des molecules modeles—IV. Composes epoxydes

Chloro-4-hexene-2 (C4H2), a model compound for the study of polyvinylchloride stabilization, reacts with epoxy compounds in dichloroethane but not in tetrahydrofuran. In the latter case, the reaction is catalysed by zinc chloride but this compound is also a catalyst for the polymerization of the epoxy function. The zinc chloride is then modified so that the kinetic laws for etherification and dehydrochlorination of C4H2 are more complex than when the catalyst is CdCl2, as previously studied by Anderson and McKenzie. With zinc and calcium stearate, one also observes esterification of C4H2, the three reactions being competitive. The synergistic effect of epoxy in the presence of stearate is induced chiefly by modification of ZnCl2 through the initiation reaction for the polymerization. Therification, as well as esterification, may be reversed by HCl which regenerates C4H2; this fact explains the catastrophic character of degradation after the stabilizer has been consumed. The results of the study on model compounds can be applied to the degradation of PVC upon mastication in a Brabender plastograph.