Abstract 344: Reconstituted High-density Lipoprotein (rHDL) Directly Modulates Inflammatory Cells after Myocardial Infarction in Mice

Aim: We have recently demonstrated that reconstituted high-density lipoprotein (rHDL) delivered immediately after myocardial infarction reduces infarct size and improves heart function in mice ( Heywood SE, Sci Transl Med, 2017 ). We now examine potential immunomodulatory actions of HDL that may underlie these effects. Methods: In male C57BL/6 mice, a single intravenous bolus of rHDL (CSL-111, 80mg/kg of human apoA-I, or saline) was delivered at the time of reperfusion following 30mins of surgically-induced ischemia. Effects on the inflammatory response were studied throughout the 5 days post ischemia-reperfusion. Results: Twenty-four hours after ischemia-reperfusion, rHDL reduced the number of circulating leukocytes (versus saline p<0.05) and increased the number in spleen (p<0.05). rHDL inhibited the recruitment cascade of the entire spectrum of inflammatory cells into the left ventricle (LV) including neutrophils (1 day post ischemia), T and B cells (3 days after), and monocytes (5 days after) (p<0.05 for all). This was associated with lower cardiac expression of chemokines that attract neutrophils (CXCL1, CXCL2, CXCL5) and monocytes (CCL2) (ELISA, p<0.05 for all). Histochemistry at 6 and 24 hours after ischemia-reperfusion showed fluorescently labeled rHDL localized to the infarct and peri-infarct regions. There were also greater quantities of rHDL (human apoA-I) in the LV and spleen of mice subjected to ischemia versus sham-operated mice (ELISA, p<0.05); no rHDL was observed in the right ventricle. In addition, flow cytometry studies using the fluorescent rHDL indicated binding to both circulating leukocytes as well as those recruited into the ischemic LV (mostly neutrophils and monocytes). rHDL had a greater association with the circulating pro-inflammatory monocyte subtype (Ly6C high ) than the anti-inflammatory subtype (Ly6C low ; p<0.05) 24 hours post ischemia. Furthermore, there was less recruitment of Ly6C High monocytes 5 days post ischemia in the LV of mice treated with rHDL (p<0.05). Conclusion: rHDL limits the myocardial post-ischemic inflammatory response by effects in both the LV and by directly modulating inflammatory cells. These finding suggest a novel treatment modality for acute coronary syndromes.