Dynamical regimes of lipids in aditivated liposomes with enhanced elasticity

ANOARDO, ESTEBAN; FRAENZA, CARLA CECILIA

Varsovia

Congreso; EUROMAR 2017-European Congress on Magnetic Resonance; 2017

The elastic properties of lipid membranes can be conveniently characterized through the bending elastic modulus k. Elasticity directly affects the deformability of a membrane, morphological and shape transitions, fusion, lipid-protein interactions, etc. It is also a critical property for the formulation of ultradeformable liposomes, and of interest for the design of theranostic liposomes for efficient drug delivery systems and/or different imaging contrast agents. A new method for the measurement of k in liposome membranes based on the fast field-cycling nuclear magnetic relaxometry technique (FFC) was recently presented [1]. A striking feature is that collective order fluctuations (OF) of the lipid molecules are an essential dynamical process that must be taken into account in order to consistently explain the observed relaxation profiles. Since the associated OF relaxation mechanism directly depends on k, its value can be obtained from the data analysis.The main goal of this work is to analyze the lipid dynamics in contrast with the elastic properties in aditivated membranes with reduced stiffness ( ~ 2KBT). Specifically, we analyze experimental relaxation dispersions obtained at different temperatures (303-328K) for liposomes of radius of 50nm, composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) or soy phosphatidylcholine (SPC) with sodium deoxycholate (SDC) added to enhance the membrane flexibility, at concentrations of 3, 10 and 20 mol%. A new dynamical regime was observed for the first time in aditivated DMPC and aditivated/non-aditivated SPC liposomes. The curious feature is discussed in terms of vesicle shape fluctuations, enhanced elasticity and lipid & additive diffusion within the membrane. Variations in κ are moderate in response to the additive concentration up to 20mol% for the both studied cases. However, we observe dramatic changes in the way diffusion and order fluctuations affect the proton spin-lattice relaxation as SDC concentration is increased, before the superelastic limit of the membrane is reached.These experiments reveals the potentiality of the FFC NMR relaxometry technique for the study of the elastic properties and formulation of ultradeformable liposomes. In particular, the technique has a huge sensitivity to pre-critical elastic behavior of the membrane.[1]- G. A. Domingez, J. Perlo, C. C. Fraenza and E. Anoardo, Measurement of the Bending Elastic Modulus in Unilamellar Vesicles Membranes by Fast Field Cycling NMR Relaxometry. Chem. Phys. Lipids 201: 21-27, 2016.