Studying lipid flip-flop in asymmetric liposomes using 1H NMR and TR-SANS.

The specific spatial and temporal distribution of lipids in membranes play a crucial role in determining the biochemical and biophysical properties of the system. In nature, the asymmetric distribution of lipids is a dynamic process with ATP-dependent lipid transporters maintaining asymmetry, and passive transbilayer diffusion, that is, flip-flop, counteracting it. In this chapter, two probe-free techniques, 1H NMR and time-resolved small angle neutron scattering, are described in detail as methods of investigating lipid flip-flop rates in synthetic liposomes that have been generated with an asymmetric bilayer composition.

Investigating the cut-off effect of n-alcohols on lipid movement: a biophysical study.

Cellular membranes are responsible for absorbing the effects of external perturbants for the cell's survival. Such perturbants include small ubiquitous molecules like n-alcohols which were observed to exhibit anesthetic capabilities, with this effect tapering off at a cut-off alcohol chain length. To explain this cut-off effect and complement prior biochemical studies, we investigated a series of n-alcohols (with carbon lengths 2-18) and their impact on several bilayer properties, including lipid flip-flop, intervesicular exchange, diffusion, membrane bending rigidity and more. To this end, we employed an array of biophysical techniques such as time-resolved small angle neutron scattering (TR-SANS), small angle X-ray scattering (SAXS), all atomistic and coarse-grained molecular dynamics (MD) simulations, and calcein leakage assays. At an alcohol concentration of 30 mol% of the overall lipid content, TR-SANS showed 1-hexanol (C6OH) increased transverse lipid diffusion, i.e. flip-flop. As alcohol chain length increased from C6 to C10 and longer, lipid flip-flop slowed by factors of 5.6 to 32.2. Intervesicular lipid exchange contrasted these results with only a slight cut-off at alcohol concentrations of 30 mol% but not 10 mol%. SAXS, MD simulations, and leakage assays revealed changes to key bilayer properties, such as bilayer thickness and fluidity, that correlate well with the effects on lipid flip-flop rates. Finally, we tie our results to a defect-mediated pathway for alcohol-induced lipid flip-flop.

Diagnosis of pelvic inflammatory disease (PID): intra-operative findings and comparison of vaginal and intra-abdominal cultures.

INTRODUCTION: Pelvic inflammatory disease (PID) is frequent in adolescents and younger women. Diagnosis is usually based on the clinical findings, and the threshold for empiric antibiotic therapy should be low. However, at least in cases of resistance toward therapy or deterioration of symptoms, laparoscopic evaluation can be helpful. METHODS: We searched the hospital charts for in-house patients who were treated for PID or tubo-ovarian abscess between 2007 and 2010. In cases with both vaginal and intra-abdominal bacterial cultures, results of those were compared. RESULTS: 73 patients with suspected PID or tubo-ovarian abscess were included. Median patients' age was 40 years (18-88), 18 of 73 (24.7 %) patients had an IUD at the time of consultation. 58 patients underwent laparoscopy or laparotomy. In 41 patients (70.7 %) tubo-ovarian abscess could be confirmed, four patients had differential gynecologic diagnoses, and two patients appendicitis. In vaginal swabs, most frequent bacteria were Streptococcus sp. (28.5 %), Escherichia coli (22.2 %), Enterococcus faecalis (15.9 %), and Staphylococcus sp. (9.5 %). In eight patients (11 %) Chlamydia trachomatis could be found, there was no case of Neisseria gonorrhea. In 33 patients both vaginal and abdominal cultures were available. In nine cases (27.3 %), identical bacteria could be found, however, 11 cases (33.3 %) showed different results. CONCLUSION: In severe cases of PID, laparoscopic evaluation and taking an intra-abdominal bacterial culture are helpful for the confirmation of diagnosis, accurate microbiologic testing and specific therapy.