Abstract 363: Endothelial Nitric Oxide Mediates Protection of Isolated Cardiomyocytes by Poloxamer 188 Against Hypoxia Reoxygenation Injury

Background: Poloxamer (P) 188, a copolymer-based cell membrane stabilizer, has been suggested to alleviate myocardial ischemia/reperfusion injury through cell membrane stabiliztion. Recent studies found that cell-to-cell interactions between endothelial cells (ECs) and cardiomyocytes (CMs) can further protect CMs: data from our co-culture model showed that ECs, at an appropriate density, promoted protection by P188 against hypoxia/reoxygenation (HR) injury evidenced by reduced release of lactate dehydrogenase (LDH) from CMs; however, the mechanism of interaction was yet to be explored. In the present study, we examined whether L-NAME, a nitric oxide (NO) synthase inhibitor, abrogates LDH release and/or Ca ²⁺ overload in CMs in the presence or absence of P188 and ECs.

Methods: Mouse coronary artery ECs, plated at densities of 25,000 per insert, were co-cultured with mouse CMs plated at confluency on the bottom of the corresponding well. Normoxic controls were kept under normal O ₂ and media conditions for 24 hours while HR groups underwent 24 h hypoxia at 0.01% O ₂ in serum- and glucose-free media, followed by 2 hr reoxygenation in normal media. P188 (300 uM), L-NAME (40 mM) or vehicle were administered upon reoxygenation. Intracellular Ca ²⁺ and LDH release were measured by standard kits. Statistics: ANOVA and SNK, alpha = 0.05.

Results: Consistent with previous observations, ECs at this low density did not affect HR-triggered LDH release or increased Ca ²⁺ in CMs by themselves; in the presence of P188, however, ECs were able to reduce LDH and Ca ²⁺ after HR (panel 1A, 2A) synergistically. L-NAME abrogated CM protection by P188 & ECs in both assays (panels 1B, 2B). Neither intervention had any effect under normoxic conditions (all panels).

Conclusion: The current data in this co-culture model suggest that protection of CMs by P188 is mediated through endothelial NO release.