Visualization of lipid domains in giant unilamellar vesicles using an environment-sensitive membrane probe based on 3-hydroxyflavone

We characterized the recently introduced environment-sensitive fluorescent membrane probe based on 3-hydroxyflavone, F2N12S, in model lipid membranes displaying liquid disordered (Ld) phase, liquid ordered (Lo) phase, or their coexistence. Steady-state fluorescence studies in large unilamellar vesicles show that the probe dual emission drastically changes with the lipid bilayer phase, which can be correlated with the difference in their hydration. Using two-photon excitation microscopy on giant unilamellar vesicles, the F2N12S probe was found to bind both Ld and Lo phases, allowing visualization of the individual phases from the fluorescence intensity ratio of its two emission bands. By using a linearly polarized excitation light, a strong photoselection was observed for F2N12S in the Lo phase, indicating that its fluorophore is nearly parallel to the lipid chains of the bilayer. In contrast, the absence of the photoselection with the Ld phase indicated no predominant orientation of the probe in the Ld phase. Comparison of the present results with those reported previously for F2N12S in living cells suggests a high content of the Lo phase in the outer leaflet of the cell plasma membranes. Taking into account the high selectivity of F2N12S for the cell plasma membranes and its suitability for both single- and two-photon excitation, applications of this probe to study membrane lateral heterogeneity in biological membranes are foreseen.     

Spatial organization of the N-terminal beta-endorphin tridecapeptide

Using conformational analysis spatial structure and conformational properties of the N-terminal tridecapeptide--endorphine molecules were investigated. Calculations were based on the fragmental analysis using non-valent, electrostatic, torsional interactions and hydrogen bonds. It was shown that tridecapeptide could exist in several low-energetical conformational states. Enkephaline fragments structure depends on the most perspective structure of free metioninenkephaline. The results can be used for conformational analysis of endorphine molecules, for structure--function relations study.     

Pharmacogenetics of community-acquired pneumonia

The rate of acetylation of xenobiotics affects the course and prognosis of infectious diseases. The efficacy of antibiotic therapy of community-acquired pneumonia in RA-patients is lower than that in LA-ones. In order to ensure the best antimicrobial effect on the onset of the disease it is required to use regimens with the maximum permissible dose of antibacterial drugs in the regions where the rapid type prevails.     

Liquid ordered phase in cell membranes evidenced by a hydration-sensitive probe: Effects of cholesterol depletion and apoptosis

Herein, using a recently developed hydration-sensitive ratiometric biomembrane probe based on 3-hydroxyflavone (F2N12S) that binds selectively to the outer leaflet of plasma membranes, we compared plasma membranes of living cells and lipid vesicles as model membranes. Through the spectroscopic analysis of the probe response, we characterized the membranes in terms of hydration and polarity (electrostatics). The hydration parameter value in cell membranes was in between the values obtained with liquid ordered (Lo) and liquid disordered (Ld) phases in model membranes, suggesting that cell plasma membranes exhibit a significant fraction of Lo phase in their outer leaflet. Moreover, two-photon fluorescence microscopy experiments show that cell membranes labeled with this probe exhibit a homogeneous lipid distribution, suggesting that the putative domains in Lo phase are distributed all over the membrane and are highly dynamic. Cholesterol depletion affected dramatically the dual emission of the probe suggesting the disappearance of the Lo phase in cell membranes. These conclusions were corroborated with the viscosity sensitive diphenylhexatriene derivative TMA-DPH, showing membrane fluidity in intact cells intermediate between those for Lo and Ld phases in model membranes, as well as a significant increase in fluidity after cholesterol depletion. Moreover, we observed that cell apoptosis results in a similar loss of Lo phase, which could be attributed to a flip of sphingomyelin from the outer to the inner leaflet of the plasma membrane due to apoptosis-driven lipid scrambling. Our data suggest a new methodology for evaluating the Lo phase in membranes of living cells.     

Metformin does not prevent DNA damage in lymphocytes despite its antioxidant properties against cumene hydroperoxide-induced oxidative stress

Metformin (1-(diaminomethylidene)-3,3-dimethyl-guanidine), which is the most commonly prescribed oral antihyperglycaemic drug in the world, was reported to have several antioxidant properties such as the inhibition of advanced glycation end-products. In addition to its use in the treatment of diabetes, it has been suggested that metformin may be a promising anti-aging agent. The present work was aimed at assessing the possible protective effects of metformin against DNA-damage induction by oxidative stress in vitro. The effects of metformin were compared with those of N-acetylcysteine (NAC). For this purpose, peripheral blood lymphocytes from aged (n = 10) and young (n = 10) individuals were pre-incubated with various concentrations of metformin (10–50 μM), followed by incubation with 15 μM cumene hydroperoxide (CumOOH) for 48 h, under conditions of low oxidant level, which do not induce cell death. Protection against oxidative DNA damage was evaluated by use of the Comet assay and the cytokinesis-block micronucleus technique. Changes in the levels of malondialdehyde + 4-hydroxy-alkenals, an index of oxidative stress, were also measured in lymphocytes. At concentrations ranging from 10 μM to 50 μM, metformin did not protect the lymphocytes from DNA damage, while 50 μM NAC possessed an effective protective effect against CumOOH-induced DNA damage. Furthermore, NAC, but not metformin, inhibited DNA fragmentation induced by CumOOH. In contrast to the lack of protection against oxidative damage in lymphocyte cultures, metformin significantly protected the cells from lipid peroxidation in both age groups, although not as effective as NAC in preventing the peroxidative damage at the highest doses. Within the limitations of this study, the results indicate that pharmacological concentrations of metformin are unable to protect against DNA damage induced by a pro-oxidant stimulus in cultured human lymphocytes, despite its antioxidant properties.