ABSTRACT
Membrane-resealing agents such as poloxamer P188 improve the outcome in experimental brain injury paradigms; however, whether membrane resealing is a key mechanism for protection has not been shown in vivo. We previously reported that Kollidon VA64, a polymeric membrane-resealing agent, reduces cell membrane permeability and improves brain edema, brain tissue damage, and functional outcome after controlled cortical impact in mice, without rescuing resealed cells from death. To reconcile these disparate findings, we used a dual-pulse labeling protocol to determine membrane-resealing kinetics by VA64/P188 in vivo. Membrane resealing after controlled cortical impact in mice by intravenous or intracerebroventricular VA64 and poloxamer P188 was transient, with most cells becoming repermeabilized within 2 hours, even with multiple-dose paradigms that maintained high VA64 blood levels. Moreover, VA64 reduced cytotoxic brain edema in a water intoxication model devoid of plasmalemma permeability (P<0.05 versus P188, VA30, mannitol, and vehicle). We conclude that VA64 reduces cytotoxic and traumatic brain edema independent of membrane resealing. The results suggest that classic membrane-resealing agents such as poloxamer P188, and the newly discovered VA64, exert protective effects in central nervous system injury paradigms by mechanisms other than or in addition to maintaining permeable cell membranes sealed.
Subject(s)
Brain Edema/prevention & control , Brain Injuries/drug therapy , Cell Membrane Permeability/drug effects , Neuroprotective Agents , Pyrrolidines , Vinyl Compounds , Animals , Brain Edema/etiology , Brain Edema/metabolism , Brain Injuries/complications , Brain Injuries/metabolism , Disease Models, Animal , Dose-Response Relationship, Drug , Injections, Intravenous , Male , Mice , Mice, Inbred Strains , Neuroprotective Agents/pharmacokinetics , Neuroprotective Agents/pharmacology , Neuroprotective Agents/therapeutic use , Pyrrolidines/pharmacokinetics , Pyrrolidines/pharmacology , Pyrrolidines/therapeutic use , Vinyl Compounds/pharmacokinetics , Vinyl Compounds/pharmacology , Vinyl Compounds/therapeutic useABSTRACT
Loss of plasma membrane integrity is a feature of acute cellular injury/death in vitro and in vivo. Plasmalemma-resealing agents are protective in acute central nervous system injury models, but their ability to reseal cell membranes in vivo has not been reported. Using a mouse controlled cortical impact (CCI) model, we found that propidium iodide-positive (PI+) cells pulse labeled at 6, 24, or 48 hours maintained a degenerative phenotype and disappeared from the injured brain by 7 days, suggesting that plasmalemma permeability is a biomarker of fatal cellular injury after CCI. Intravenous or intracerebroventricular administration of Kollidon VA64, poloxamer P188, or polyethylene glycol 8000 resealed injured cell membranes in vivo (P<0.05 versus vehicle or poloxamer P407). Kollidon VA64 (1 mmol/L, 500 µL) administered intravenously to mice 1 hour after CCI significantly reduced acute cellular degeneration, chronic brain tissue damage, brain edema, blood-brain barrier damage, and postinjury motor deficits (all P<0.05 versus vehicle). However, VA64 did not rescue pulse-labeled PI+ cells from eventual demise. We conclude that PI permeability within 48 hours of CCI is a biomarker of eventual cell death/loss. Kollidon VA64 reduces secondary damage after CCI by mechanisms other than or in addition to resealing permeable cells.
