High speed atomic force microscopy to investigate the interactions between toxic Aß1-42 peptides and model membranes in real time: impact of the membrane composition.

Due to an aging population, neurodegenerative diseases have become a major health issue, the most common being Alzheimer's disease. The mechanisms leading to neuronal loss still remain unclear but recent studies suggest that soluble Aß oligomers have deleterious effects on neuronal membranes. Here, high-speed atomic force microscopy was used to assess the effect of oligomeric species of a variant of Aß1-42 amyloid peptide on model membranes with various lipid compositions. Results showed that the peptide does not interact with membranes composed of phosphatidylcholine and sphingomyelin. Ganglioside GM1, but not cholesterol, is required for the peptide to interact with the membrane. Interestingly, when they are both present, a fast disruption of the membrane was observed. It suggests that the presence of ganglioside GM1 and cholesterol in membranes promotes the interaction of the oligomeric Aß1-42 peptide with the membrane. This interaction leads to the membrane's destruction in a few seconds. This study highlights the power of high-speed atomic force microscopy to explore lipid-protein interactions with high spatio-temporal resolution.

Interaction of Aß1-42 peptide or their variant with model membrane of different composition probed by infrared nanospectroscopy.

Toxicity of Aß peptides involved in Alzheimer's disease is linked to the interaction of intermediate species with membranes. Nanoscale Infrared Spectroscopy enhances the study of the morphology and the secondary structure of the peptides as fibers or oligomers interacting with membranes of different compositions, with nanometer scale resolution. Membrane models are used to investigate the role of different lipids in their interactions with Aß peptides. This work clearly brings to light that the presence of cholesterol in membranes is favorable to the interaction with Aß peptides in oligomers or aggregates.

A randomized study of etoposide and carboplatin with or without paclitaxel in the treatment of small cell lung cancer.

Small cell lung cancer accounts for 20% to 25% of all lung cancer cases and is initially responsive to combination chemotherapy. However, the majority of patients relapse, and at that point their disease is highly resistant to chemotherapy. The combination of etoposide with either cisplatin or carboplatin is regarded as the standard of care for these patients. Previous studies have documented the activity of paclitaxel (Taxol; Bristol-Myers Squibb Company, Princeton, NJ) at doses of 135 to 250 mg/m2 administered over 1, 3, or 24 hours as either a single agent or in combination with etoposide and a platinum compound. Studies adding paclitaxel to etoposide/carboplatin (EP) have demonstrated complete responses in both limited and extensive disease, but all have been in single-arm phase II studies. Preliminary data also suggest the possibility of a dose-response curve for the combination. We recently began a randomized phase II/III comparison of the standard EP to EP plus paclitaxel for newly diagnosed patients with limited or extensive small cell lung cancer. Carboplatin in this study is dosed according to area under the concentration-time curve as calculated by the Calvert formula. The study compares EP (carboplatin area under the concentration-time curve of 6 intravenously [IV] over 30 to 60 minutes on day 1, with etoposide 120 mg/m2 IV days 1 to 3) versus EP plus paclitaxel (paclitaxel 200 mg/m2 IV 1-hour infusion on day 1, carboplatin area under the concentration-time curve of 6 IV over 30 to 60 minutes on day 1, and etoposide 50/100 mg orally on alternating days 1 to 10). The design, inclusion criteria, and staging of patients in this study will be presented with initial accrual and patient characteristics. Randomized studies of this type are essential if the true role of this new combination is to be fully evaluated.

Myopic photorefractive keratectomy in eyes with atypical inferior corneal steepening.

PURPOSE: To evaluate the visual and refractive results of photorefractive keratectomy (PRK) in eyes with atypical inferior corneal steepening (AICS). SETTING: Department of Ophthalmology, Hôpital Morvan, University of Breast, France. METHODS: Using videokeratopography, we screened 310 eyes that had PRK from November 1992 through November 1993 and found that 35 eyes exhibited topographic patterns consistent with AICS with no clinical findings. The results at 6 months and 1 year were compared with those of 185 eyes with normal topography treated concurrently. RESULTS: There were no statistically significant differences between the two groups in mean spherical equivalent, mean uncorrected visual acuity, and mean best spectacle-corrected visual acuity 6 months and 1 year after PRK. CONCLUSION: After 1 year, PRK in eyes with AICS appeared to give results similar to those in eyes with normal topography. Further follow-up is needed.

[Amebic keratitis]. / Les kératites amibiennes.

Amoebic keratitis is an uncommon pathology mainly implicated in eye infection in contact lens wearers. The offending parasite is a free-living amoeba of the genus Acanthamoeba. Diagnosis is often delayed because clinical signs are confusing especially at the onset. Samples for parasitic tests should be taken not only for the infection site but also from the lenses and cleaning products. A standard treatment of amoebic keratitis has not been established. Several drugs are theoretically active but achieve inconsistent results. Recently keratitis has been observed at a seemingly high incidence in developing countries but epidemiologic data is still scarce.

Kinetic study of interaction between [14C]amphotericin B derivatives and human erythrocytes: relationship between binding and induced K+ leak.

The relationship between polyene antibiotic binding to red cells and their membrane permeabilization was studied using two 14C-labelled amphotericin B (AmB) derivatives: N-fructosyl AmB and N-acetyl methyl ester AmB. The binding kinetics of both derivatives were determined on whole red cells and ghosts. The resulting experimental points were well fitted by monoexponential functions, and the characteristic t1/2 for both derivatives were calculated from these functions. At 2 X 10(-5) M, the half time t1/2 for N-acetyl methyl ester AmB (30.2 min) which forms aqueous aggregates was longer than the t1/2 for the more soluble species N-fructosyl AmB (4.5 min). At lower concentrations (10(-7) M), the t1/2 for N-acetyl methyl ester AmB (6.3 min) in a more solubilized form was close to that of N-fructosyl AmB (7.9 min). These results suggest that only solubilized species bound to red cell membranes and that disaggregation of aggregates is the limiting step in the binding process. The permeabilization of red cell membranes by N-fructosyl AmB, measured as intracellular K+ leak, was not instantaneous and at 10 degrees C external K+ was only detected 20 min after antibiotic addition. In contrast, binding occurs without lag time. Consequently, different mecanisms underlie binding and K+ permeability inducement. Absorption spectroscopy data showed that bound antibiotic is located in the hydrophobic membrane interior and that this penetration of the membrane by AmB derivatives occurs without lag time. Consequently, the lag time occurring for K+ permeability inducement would be due to some steps subsequent to binding and probably located in the hydrophobic membrane interior. This statement is further supported by the observation that the lag time is sensitive to changes in membrane fluidity as shown here by the break between 20 and 30 degrees C in the slope of the Arrhenius plot for the lag time, coinciding with the phase transition in red cell membranes.

Relationship between ionophoric and haemolytic activities of perimycin A and vacidin A, two polyene macrolide antifungal antibiotics.

The ionophoric and hemolytic activities of two antifungal aromatic heptaenes: vacidin A and perimycin A, were studied on human red blood cells. Measurements of hemolysis, K+ influx and efflux, H+ movement and potential difference across the cell membrane, show that the hemolytic activity, being related to the K+ permeability induced by the polyene, is strongly dependent on the ability of this polyene to induce H+ movement. It was shown that: (1) both antibiotics have approximately the same efficiency in inducing K+ permeability, but a 100-fold difference in their hemolytic activity; (2) their hemolytic activity is related to their ability to induce H+ movement; (3) the protonophoric activity requires the existence of a free carboxyl group in the macrolide ring, as in vacidin A. The hemolytic activity is determined by the intrinsic efficiency of a K+/H+ exchange induced by this polyene. With perimycin A, which lacks the free carboxyl group, the hemolytic activity is dependent on the Cl- conductive flux which slows down the K+ flux.