Annual Report of Activities CNC 2008 - Center for Neuroscience and ...

Membrane Toxicity | Head: Maria Amália JuradoObjectivesThe main purpose of our research has been to findout more about the particular role played by lipidsand the lipid‐bilayer component of cell membranesin health and disease conditions. The emphasis ison biophysical properties of the lipid‐bilayer andon the way they affect membrane functions, that isa lipidomics approach. Advances in the elucidationof the aspects of lipid‐bilayer structure and dynamicspotentially involved in abnormal membranefunctioning and disease have been built uponexperimental approaches considering a serial stepwiseincrease in biological complexity, from modelmembranes prepared with synthetic and nativemembrane lipids, to subcellular fractions (biologicalmembranes, mitochondria, protoplasts) and prokaryoticand eukaryotic cell cultures. The area of researchhas included the study of a wide range ofbiological and chemical compounds, such as DNA,sterols, surfactants, drugs, environmental pollutantsand nanomaterials.To investigate how membrane composition, structureand dynamics are involved in cell functioning ordysfunction, the group has been developing differentexperimental strategies, namely: a) To elucidate how cellfunctioning and pharmacological/toxicological effects ofmembrane‐active drugs are influenced by diet‐inducedmembrane lipid composition changes, in rats, and byalterations of membrane lipids as a response toenvironmental stress, in bacteria; b) To identifyalterations of the physical properties of the lipid bilayerrelated with cell malfunctioning and disease.Additionally, the group has been also interested on thecharacterization of DNA physical interactions with lipidmembranes, envisaging to contribute to the ameliorationof liposomal gene delivery systems and to further clarifythe biophysical principles, which govern efficientliposome‐mediated transfection.Fig.1. Interaction of chemical agents with membranes. Smallmolecules interact with the membrane surface, in fluid (A) and lipidraft (B) domains, or penetrate in the membrane core (C).Nanostructures such as fullerenes (D) or lipid‐based DNA vectors(E) establish different interactions with the membrane, dependingon their size, surface chemistry and charge.Main AchievementsA large experience has been accumulated in our labconcerning pesticides effects on membrane physicalproperties using different model systems. Aparticularly important aspect of this work is theestimation of the partition coefficients of thecompounds in model and native membranes. Thesestudies are instrumental to evaluate their potential foruptake and accumulation in living cells. Thereafter,biophysical techniques, fluorescence spectroscopy,differential scanning calorimetry and magneticresonance spectroscopy ( 31 P‐NMR), have helped tocharacterise the perturbations promoted by thecompounds across the bilayer thickness and toidentify their potential accumulation in differentiatedregions of the heterogeneous membrane structure,allowing to predict a preferential interaction onspecific lipid‐protein environments.On the basis of collected data and knowledge, thesestudies have been extended to a variety ofcompounds whose physical‐chemical characteristicsmake them presumable disturbers of membraneproperties. Thus, the cellular effects of differentchemical compounds with pharmacological ortoxicological interest have been correlated to theirability to affect and modulate lipid‐membraneorganisation. Alterations induced in the structuralorder and organisation of lipid membranes haveshown to be strictly correlated with adverse effects onbioenergetics, cell growth and viability, suggesting tobe involved in xenobiotic mechanisms of actionfocused on the target cells and/or on xenobiotic nonselectiveside‐effects.We emphasise the following conclusive aspects:Bacterial models can be used as a suitable researchapproach to assess unspecific membrane cytotoxiceffects mediated by pesticides or drugs;Lipid composition changes induced by physical orchemical stress in bacteria have indicated thatrather than fluidity (the lipid membrane microstructure),other membrane properties, such asstructural heterogeneity and curvature stress,directly account for cell function impairment.Alterations of the structural order and organisation ofmembrane lipids, disturbance of the bilayer lateralpressure profile and induction or remodelling of amembrane microphase pattern have beenidentified as common strategies for a variety ofdrugs and environmental pollutants to alter thehomeostatic equilibrium of biological systems.51