Membrane Sealing:Biopolymers for Tissue Electroporation

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Disruption of the cell membrane lipid bilayer structure is a common cause of tissue necrosis in many illnesses, including high-energy trauma. Loss of membrane ionic barrier function is followed by rapid metabolic energy exhaustion and then acute cellular necrosis. Electrical shock induced tissue injury is superb model for this type of cell injury because membrane damage occurs by electroporation, exposure to high temperatures and possibly high-power acoustic stresses (Appendices I and II). Because of the relatively large size of the cells, skeletal muscle and nerve are especially vulnerable to the direct electrical mechanisms of cellular membrane damage (electroporation and electroconformational protein denaturation). Theoretical, experimental and clinical data all indicate that membrane damage by electroporation is a significant cause of much of the skeletal muscle and nerve injury that results (Appendix II). Our lab and others have shown that poloxamer surfactants (Poloxamer 188 and Poloxamine 1107) reduce acute necrosis mediated by membrane disruption (Appendix III, Sharma et al. 1996, Merchant et al. 1998, Hannig et al. 2000). Thus, we postulate that these surfactants can be used to substantially reduce tissue necrosis following electroporation to result in significantly improved tissue survival and function. We propose to determine how effective intravenous Poloxamer 188 with and without cofactors are in sealing electroporated skeletal muscle cell membranes in vivo and in improving functional recovery. We propose to assess outcomes using quantitative real- time functional assay measurement techniques (surface electromyography and radiopharmaceutical imaging) as well as by standard histological and biochemical markers reflective of membrane integrity and tissue necrosis. Furthermore, on the basis of completed experiments, we postulate that antioxidants (i.e. ascorbate) may protect poloxamers from oxidative degradation to enhance its efficacy, and propose that MgATP will enhance responsiveness to membrane sealing. A basic need also addressed in this proposal is the refinement and calibration of real-time surface electromyography and radiopharmaceutical imaging as tools for quantifying therapeutic responses to membrane sealing therapy and for real-time assessment in clinical studies. Such diagnostic tools would be of tremendous clinical value because rapid detection, discrimination, and localization of tissue injury would accelerate and guide clinical therapy. Although we choose electroporation as the experimental model to test in vivo membrane sealing, these results and experimental methods will be directly relevant to other diseases characterized by membrane permeabilization, e.g. ischemia-reperfusion, freeze-thaw and mechanical trauma.