The asymmetric distribution of lipids between the two bilayer leaflets represents a typical feature of biological membranes. The loss of this asymmetry, for example the exposure of negatively charged lipids on the extracellular membrane leaflet of mammalian cells, is involved in apoptosis and occurs in tumor cells. Thus, the controlled production of asymmetric liposomes helps to better understand such crucial cellular processes. Here, we present an approach that allows us to design asymmetric model-membrane experiments on a rational basis and predict the fraction of exchanged lipid. In addition, we developed a label-free and nondestructive assay to quantify the asymmetric uptake of negatively charged lipids in terms of the zeta potential. This significantly enhances the applicability, impact, and predictive power of model membranes.
The functional roles of the lipid asymmetry of biomembranes are attracting increasing attention. This study characterizes the activity of surfactants to induce transmembrane flip-flop of lipids and thus ''scramble'' this asymmetry. Detergentinduced lipid scrambling of liposomes mimicking the charge asymmetry of bacterial membranes with 20 mol % of 1-palmitoyl-2oleoyl-sn-glycero-3-phospho-rac-glycerol in the outer leaflet only was quantified by z-potential measurements for octaethylene glycol dodecyl ether (C 12 EO 8 ), octyl glucoside (OG), and dodecyl maltoside. Membrane leakage was separately measured by the fluorescence lifetime-based calcein leakage assay and the onset of the membrane-to-micelle transition by isothermal titration calorimetry. Partition coefficients and partial molar areas were obtained as well. For the quickly membrane-permeant C 12 EO 8 and OG, leakage proceeds at a rather sharp threshold content in the membrane, which is well below the onset of solubilization and little dependent on incubation time; it is accompanied by fast lipid scrambling. However, unlike leakage, flip-flop is a relaxation process that speeds up gradually from taking weeks in the detergent-free membrane to minutes or less in the leaking membrane. Hence, after 24 h of incubation, 10 mol % of C 12 EO 8 or 50 mol % of OG in the membrane suffice for virtually complete lipid scrambling, whereas leakage remains below 10% for up to 14 mol % of C 12 EO 8 and 88 mol % of OG. There is thus a concentration window in which lipid scrambling proceeds without leakage. This implies that lipid scrambling must be considered a possible mode of action of antimicrobial peptides and other membrane-active drugs or biomolecules. A related, detergentbased protocol for scrambling the lipid asymmetry of liposomes and maybe cells without compromising their overall integrity would be a very valuable tool to study functions of lipid asymmetry.
Purpose We examined how migration background is associated with awareness and usage of psycho-oncology services. Methods Oncologists in community-based practices and outpatient clinics asked their patients and their relatives to complete a questionnaire. Migrants were purposely over-sampled. The questionnaire was provided in Arabic, English, Farsi, French, German, Hindi, Kurdish, Pashto, Russian, Somali, Turkish, Urdu, and Vietnamese. Results From 9 collaborators, 177 participants were enrolled (130 with and 47 without migration background). The existence of outpatient cancer counselling centres was known to 38% of the participants without and 32% with migration background, self-help groups to 32 vs. 12%, and psychotherapy to 43 vs. 25%. Respondents from the Near and Middle East were less likely to know about psychotherapy (odds ratio (OR) 0.1, p = 0.01); those from the Commonwealth of the Independent States or former Yugoslavia were less often informed about self-help groups (OR 0.1, p = 0.06). Migrants retrieved information less frequently from the internet than non-migrants (10 vs. 25%). At least one service had been used by 27% of migrants and 42% of non-migrants (OR 0.5, p = 0.06). After adjusting for gender, age, education, and patient-relative status, there was no evidence for an association between migration background and service use. Conclusions Migrants should be better informed about psychotherapy and self-help groups, in particular the ones coming from the Near or Middle East and the Commonwealth of the Independent States or former Yugoslavia. The under-use of psychosocial services can largely be explained by confounding factors. Therefore, these factors must always be taken into account when analysing the use of psychosocial services in the aforementioned populations.
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