Effects of Genetic Deletion of Soluble Epoxide Hydrolase on Cardiac Function and Inflammation in Acute Lipopolysaccharide Injury
Creators: Sosnowski, Deanna
Publisher: name: University of Alberta Library
Year: 2022

<p>Acute inflammatory syndromes, such as endotoxemia, elicit detrimental multi-organ responses resulting in cardiac dysfunction often leading to death.  Emerging evidence suggests epoxylipids can exert cardioprotective effects by modulating the NOD-like receptor family pyrin domain containing 3 (NLRP3) inflammasome pathway.  However, these beneficial epoxylipids may be metabolized by soluble epoxide hydrolase (sEH).  This study investigated whether cardiomyocyte-specific sEH-knockdown can attenuate inflammation and cardiac dysfunction in a model of acute lipopolysaccharide (LPS) injury via modulation of the NLRP3 inflammasome pathway.<br>
Cardiomyocyte-targeted sEH-knockdown mice were produced by crossing Ephx2-floxed and Cre recombinase expressing mice. Male sEH(Myo -/-) (knockdown) and sEH(Myo +/+) (Cre control) mice were given tamoxifen (45 mg/kg, 6 i.p injections over 8 days) 5 weeks prior to LPS injection (10mg/kg, i.p.).  Wild type (WT) and global sEH null mice were subjected to LPS treatment as comparators.  Echocardiography was conducted pre-injection and 6 or 24 hours post-LPS.  Plasma cytokine levels were determined with multi-plex assays.   Neonatal rat cardiomyocytes were treated with LPS (1 µg/mL), 19, 20-epoxydocosapentaenoic acid (EDP, 1 µM) or sEH inhibitor, trans-4-[4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid (tAUCB, 10 µM), for 6 hours.  NLRP3 and pro-IL-1β expression was assessed using immunoblotting.  Extracellular release of MCP-1 and TNF-α were determined by ELISA.  Caspase-1 activity was assessed by a fluorometric peptide substrate cleavage assay.  Macrophage infiltration into the myocardium was assessed by immunohistochemical staining for CD68.<br>
All groups experienced a decline in cardiac systolic function at 6 hours post-LPS.   At 24 hours after LPS administration, the decline in cardiac function plateaued in mice with global and cardiomyocyte-specific sEH deletion while sEH expressing mice continued to deteriorate further.  Plasma levels of pro-inflammatory cytokines post-LPS exposure were attenuated in mice lacking sEH.  Cardiomyocytes treated with LPS had increased NLRP3 inflammasome and pro-IL-1β expression, which was not attenuated by co-treatment with 19,20-EDP or tAUCB.  However, caspase-1 activity and the release of IL-1β, MCP-1 and TNF-α were reduced in 19,20-EDP and tAUCB treated cardiomyocytes.  This was associated with reduced macrophage infiltration into the myocardium of LPS-treated sEH null and sEH(Myo -/-) mice.<br>
In summary, cardiomyocyte-specific sEH deletion protects cardiac function and limits pro-inflammatory responses post-LPS exposure by limiting local cardiac inflammation and the activation of the systemic immune response.  sEH inhibition does not prevent the expression of NLRP3 inflammasome machinery in cardiomyocytes but attenuates downstream activation of the pathway leading to release of fewer chemoattractant factors and recruitment of immune cells to the heart.  Thus, limiting the inflammatory cascade to reduce LPS-induced cardiac and inflammatory injury. </p>