Concentration Threshold for Membrane Protection by PEO-PPO Block Copolymers with Variable Molecular Architectures

Poloxamer 188, a poly(ethylene oxide)-b-poly-(propylene oxide)-b-poly(ethylene oxide) (PEO-PPO- PEO) triblock copolymer, protects cell membranes in several injury models. However, the nature of the copolymer-membrane interaction and the mechanism of membrane protection remain unknown. Systematic variations of the block copolymer architecture.including PPO-PEO-PPO triblocks and PPO-PEO diblocks.were used to probe the mechanism and evaluate the potential for alternative architectures to yield superior protection. To test the polymers, murine myoblasts were subjected to an osmotic stress, and membrane integrity was quantified by measuring lactate dehydrogenase (LDH) leakage. These experiments exposed a concentration threshold effect where all tested polymers reach 50% leakage of LDH compared to a nontreated buffer-only control over a narrow concentration range of 0.8-4 mu M. Differences in polymer protection at lower concentrations indicate that protection increases with the PPO-PEO-PPO molecular architecture and increasing hydrophobicity.