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A team in Japan has used UV spectroscopy and microscopy to study the interaction between liposome clusters and endocrine-disrupting chemicals (EDCs) as a model of how living cell plasma membranes might be affected. The work could lead to the development of a universal detector for EDCs. Yuko Nakane and Izumi Kubo of the Faculty of Engineering, at Soka University, Hachioji, Tokyo, Japan, explain how plasma membranes are important biological structures and functional components of the cell. These membranes fit the so-called fluid-mosaic model in which a lipid bilayer carries various proteins. By using materials that mimic this structure in the laboratory it is possible to determine how a cellular plasma membrane might behave when challenged with particular chemical and physical stresses. One such chemical stress are EDCs. These are now widely dispersed in the environment and have been a serious cause for concern for more than two decades in terms of their impact on individual species, ecosystems as a whole, and the health of people exposed to them. They have gained notoriety as synthetic compounds inadvertently released into the environment that have apparently affected reproductive function and embryonic development in many species. EDCs include nonylphenol (a cleaning agent and spermicide), benzophenone (used in the print industry), bisphenol A (a polymer additive), benzyl butyl phthalate and dimethylphthalate (both plasticizers), Lauric acid (a fatty acid used in cosmetics), and Triton-X100 (a non-ionic detergent). Most worryingly, those concerned with these compounds say, is that they have effects on reproduction and development at much lower concentrations than other pollutants and also become persistent through bioaccumulation. The researchers add that there are several analytical techniques for detecting these compounds, such as high performance liquid chromatography and gas chromatography. However, these require bulky equipment and complicated sample pre-treatment. "EDCs are structurally diverse and there is a continuous market-driven evolution in the type of chemical compounds produced," the researchers explain, "So a universal method of detection of EDCs is required." Various biomimetic models have previously been created for medical diagnostics, food testing, and environmental monitoring, the researchers explain in the October issue of the journal Colloids and Surfaces, but most are complicated or have other shortcomings. The researchers explain that EDCs can permeate the cell plasma membrane prior to binding to the specific endocrine receptor. "This phenomenon led us to the idea that EDCs should interact with the liposome cluster and that the effect of this interaction could be detected by characterization of the clusters," they add. Other researchers have investigated related effects for studying the effects of environmental organic pollutants including diverse EDCs. However, the researchers report, these various techniques, while often useful, fall short of a viable universal detector for any EDC because they require specialist equipment, take several days to run, and are generally involve complicated procedures. A detection method based simply on the interaction between liposome and EDC has not previously been reported, the team says, and could point the way forward to a universal EDC detector. Now, Nakane and Kubo have turned to liposome (vesicles), which have been widely used to model lipid bilayers. They have worked with previously described cationic liposomes and bacteriorhodopsin (bR), which are reportedly stable as well as forming large complexes that mimic cellular membranes even more keenly. "In this study, we regarded the complexes as a liposome cluster [about 10 micrometres across]," the researchers explain, "We used small unilamellar liposomes, homogeneous in size, to observe the effect of EDCs." The team has used this model to investigate, using UV-Vis spectroscopy and microscopy how such a membrane model is affected by interaction with EDCs. They have now demonstrated that the interaction of EDC with a liposome cluster can be tracked easily using conventional UV-Vis spectroscopy to reveal the structural changes correlated with the spectra. The use of a liposome cluster, rather than individual liposomes, the researchers add, was expected to make the system viable through an intrinsic amplification not seen with non-assembled liposomes. "The liposome cluster was large enough to observe under a microscope and to be detected using UV-Vis spectroscopy without special instruments," they explain, "while requiring less response time than the evaluation methods using individual liposomes." Related links:
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Kubo, searching for a universal EDC detector |
