Enhancement Of Membrane Fluidity Research Articles

The role of altered lipid composition and distribution in liver fibrosis revealed by multimodal nonlinear optical microscopy.

Intracellular lipid accumulation is commonly seen in fibrotic livers, but its exact role in liver fibrosis remains elusive. Here, we established a multimodal nonlinear optical microscopy to quantitatively map distribution of biomolecules in fibrotic livers. Our data revealed that unsaturated triglycerides were predominantly accumulated in central vein area during liver fibrosis but not in portal vein area. Moreover, the lipid homeostasis was remarkably dysregulated in the late-stage compared to the early-stage fibrosis, including increased unsaturated triglycerides with decreased lipid unsaturation degree and decreased membrane fluidity. Such alterations were likely due to up-regulated lipogenesis, desaturation, and peroxidation, which consequently led to endoplasmic reticulum stress and cell death. Inspiringly, injured hepatocyte could be rescued by remodeling lipid homeostasis via either supply of unsaturated fatty acids or enhancement of membrane fluidity. Collectively, our study improves current understanding of the role of lipid homeostasis in fibrosis and open opportunities for treatment.

Antifungal Activity and Action Mechanism of Ginger Oleoresin Against Pestalotiopsis microspora Isolated From Chinese Olive Fruits

Pestalotiopsis microspora (P. microspora) is one of dominant pathogenic fungi causing rotten disease in harvested Chinese olive (Canarium album Lour.) fruits. The purposes of this study were to evaluate the antifungal activities of ginger oleoresin (GO) against P. microspora and to illuminate the underlying action mechanisms. The in vitro assays indicate that GO exhibited strong antifungal activity against mycelial growth of P. microspore, and with 50%-inhibition concentration (EC50) and 90%-inhibition concentration (EC90) at 2.04 μL GO and 8.87 μL GO per mL propylene glycol, respectively, while the minimal inhibitory concentration (MIC) and minimal fungicidal concentration were at 10 μL GO and 30 μL GO per mL propylene glycol, respectively. Spore germination of P. microspora was inhibited by GO in a dose-dependent manner, and with 100% inhibition rate at the concentration of 8 μL GO per mL propylene glycol. Compared to the control, the cellular membrane permeability of P. microspora increased due to severe leakage of intercellular electrolytes, soluble proteins, and total sugars with the treatments (EC50, EC90) by GO during incubation. In addition, analysis of fatty acid contents and compositions in cellular membrane by GC-MS indicated that GO could significantly promote the degradation or peroxidation of unsaturated fatty acids in P. microspore, resulting in the enhancement of membrane fluidity. Moreover, observations of microstructure further showed the damage to plasma membrane and morphology of P. microspora caused by GO, which resulted in distortion, sunken and shriveled spores and mycelia of the pathogen. Furthermore, in vivo assay confirmed that over 3 MIC GO treatments remarkably suppressed disease development in P. microspore inoculated-Chinese olive fruit. These results demonstrate that owing to its strong antifungal activity, GO can be used as a promising antifungal agent to inhibit the growth of pathogenic fungi in Chinese olives.

A Membrane-Bound Biosensor Visualizes Shear Stress-Induced Inhomogeneous Alteration of Cell Membrane Tension

SummaryCell membrane is the first medium from where a cell senses and responds to external stress stimuli. Exploring the tension changes in cell membrane will help us to understand intracellular force transmission. Here, a biosensor (named MSS) based on fluorescence resonance energy transfer is developed to visualize cell membrane tension. Validity of the biosensor is first verified for the detection of cell membrane tension. Results show a shear stress-induced heterogeneous distribution of membrane tension with the biosensor, which is strengthened by the disruption of microfilaments or enhancement of membrane fluidity, but weakened by the reduction of membrane fluidity or disruption of microtubules. These findings suggest that the MSS biosensor is a beneficial tool to visualize the changes and distribution of cell membrane tension. Besides, cell membrane tension does not display obvious polar distribution, indicating that cellular polarity changes do not first occur on the cell membrane during mechanical transmission.

Mechanism of the Action of Didecyldimethylammonium chloride (DDAC) against Escherichia coli and Morphological Changes of the Cells

The antibacterial activity of a disinfectant with geminated twin long-chain alkyl groups, didecyldimethylammonium chloride (DDAC), was investigated. The minimum inhibitory concentration (MIC) value of DDAC against Eschrichia coil was revealed to be a small value, 1.3 mg/L, by using the specific growth rates, mu, obtained from the cultivation in a liquid nutrient broth (NB) medium. The relationship between the leakage of proteins or beta-galactosidase and the DDAC concentration showed that the leakage of intracellular macromolecules occurs at around 3 - 4 mg/L DDAC. Furthermore, the effect of DDAC on the enhancement of membrane fluidity was examined by using liposomes labeled with a fluorescent probe. It was shown that the phase transition occurs at around 3 mg/L DDAC. The bleb formation of E. coli cells in the presence of DDAC was also examined by use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). However, bleb formation was not observed at around 3 mg/L DDAC but at concentrations higher than 50 mg/L. These results suggested that the action of DDAC toward the cell membrane causes the leakage of the intracellular molecules and the subsequent death of the cells. Thus the bleb formation seemed to be a result of the action of the DDAC toward the cell membrane but not to be a reason for the death of the cells.

Cytotoxic and genotoxic effects of tert-butyl hydroperoxide on Chinese hamster B14 cells

The organic hydroperoxide, tert-butyl hydroperoxide (t-BHP), is a useful model compound to study mechanisms of oxidative cell injury. In the present work, we examined the features of the interactions of this oxidant with Chinese hamster B14 cells. The aim of our study was to reveal a possible role of structural modifications in membranes and loss of DNA integrity in t-BHP-induced cell injury and death. The tert-butyl hydroperoxide treatment (100–1000μM, 37°C for 1h) did not decrease cell viability (as measured by cell-specific functional activity with an MTT test), but completely prevented cell growth. We observed intracellular reduced glutathione (GSH) oxidation and total glutathione (GSH+GSSG) depletion, a slight increase in the level of lipid-peroxidation products, an enhancement of membrane fluidity, intracellular potassium leakage and a significant decrease of membrane potential. At oxidant concentrations of 100–1500μM, a significant damage to DNA integrity was observed as revealed by the Comet assay. The inhibition of cell proliferation (cell-growth arrest) may be explained by genotoxicity of t-BHP, by disturbance of the cellular redox-equilibrium (GSH oxidation) and by structural membrane modifications, which result in ion-non-selective pore formation. The disturbance in passive membrane permeability and the DNA damage may be the most dramatic cell impairments induced by t-BHP treatment. The presence of another oxidant, hypochlorous acid (HOCl), completely prevented t-BHP-induced DNA strand breaks, perhaps due to extracellular oxidation of t-BHP by HOCl.

Enhancement of membrane fluidity in cholesterol-poor endothelial cells pre-treated with simvastatin.

We examined the membrane fluidity of the cholesterol-poor bovine carotid artery endothelial cells (BAEC). Cholesterol-poor BAEC were obtained by treating the cells with 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors under 10% low density lipoprotein (LDL)-deficient serum condition for 2 days. Simvastatin reduced the intracellular cholesterol content significantly at a concentration of 0.1 microgram/ml. The reduction in the cholesterol content was accompanied by the enhancement of the cell membrane fluidity which was measured by a photobleaching technique. Additional data suggested that the reduction in cholesterol content referred to the reduction in the proliferation of BAEC.

Effect of Bothrops asper (Fer-De-Lance) snake venom on erythrocyte membrane. A comparative study

1. The effect of Bothrops asper venom on erythrocytes of different species, sheep erythrocyte ghost vesicles and liposomes made of phospholipids from sheep erythrocytes was studied. 2. B. asper venom had a direct hemolytic effect on mouse erythrocytes, but no lytic activity on goat, rabbit, horse, toad and sheep erythrocytes. Human erythrocytes were lysed only in the presence of bovine serum albumin and Ca 2+. 3. Although the phospholipase A 2 activity in the venom might be involved in the lytic effect on mouse erythrocytes, there is also evidence of direct lytic factor(s) acting in the absence of calcium ions. 4. Sheep erythrocytes were modified in order to study the basis of their resistance. Enhancement of membrane fluidity and variation of pH were of no consequence for the resistance of sheep erythrocytes to the action of venom. 5. The reorganization of membranes that takes place during ghost or liposome preparation made them susceptible to B. asper venom-induced disruption. Thus the resistance of sheep erythrocytes seems related to the accessibility of the target.

Nasal absorption enhancers for biosynthetic human growth hormone in rats.

The effects of several prospective absorption enhancers were assessed on the nasal absorption of biosynthetic human growth hormone (hGH) in the rat. These enhancers function by alternative mechanisms that include enzyme inhibition, reduction in mucus viscosity, and enhancement of membrane fluidity. The levels of plasma hGH achieved were determined by an enzyme-linked immunosorbent assay. The increase in peak height was calculated relative to nasal administration of hGH alone without any enhancers and the relative bioavailability was calculated with reference to subcutaneous injection data. A lysophospholipid, lysophosphatidylcholine, gave the highest peak concentration, with an increase in peak height of 450% and a relative bioavailability of 25.8%. However, the greatest increase in AUC (291%) was achieved with the aminopeptidase inhibitor, amastatin, which gave a relative bioavailability of 28.9%. A mucolytic agent, N-acetyl-L-cysteine, and a transmembrane fatty acid transporter, palmitoyl-DL-carnitine, were also found to promote the nasal absorption of hGH in this model, with relative bioavailabilities of 12.2 and 22.1%, respectively. Bestatin, an enzyme inhibitor, was not an effective absorption enhancer for hGH in this model.