IMPORTANCE OF PROSTAGLANDIN E2 RECEPTORS IN LIVER ISCHEMIA REPERFUSION INJURY

Abstract

O184 Aims: Prostaglandin E2 (PGE2) mediates a variety of both innate and adaptive immunity through four receptors; EP1, EP2, EP3 and EP4. Recent studies have suggested the importance and distinct role of each receptor in various disease conditions. We investigated the significance of PGE2 receptors and therapeutic efficacy of selective agonist for each receptor in hepatic ischemia/reperfusion injury (I/R injury). Methods: We utilized a commonly used murine hepatic I/R injury model. Seventy percent partial hepatic ischemia was performed for 90 or 120 minutes in male C57BL/6 mice. Results: First, we evaluated the local expression of EPs in the liver. All receptors expressed in the naïve liver. EP4 expression was significantly upregulated after 6h of reperfusion following 90 minutes of ischemia (p=0.008), while EP3 expression was downregulated. EP1 and EP2 expression was not changed during I/R injury. Then, we evaluated the effect of selective agonist for each receptor on liver damage. EP1, EP2 and EP3 agonist treatment did not show significant effect on liver function. By contrast, EP4 agonist treatment significantly inhibited hepatic injury compared to control at 6 h of reperfusion (sAST: 854±117 vs. 4683±1043: p=0.030, sALT:1535±292 vs. 6252±1638: p=0.025, sLDH:3884±569 vs. 19653±4917: p=0.037). Histological analysis also confirmed this protective effect of EP4 agonist. Massive cellular infiltration and extensive hepatic cellular necrosis was observed in control mice, while the lobular architecture was well preserved and there was few necrosis in EP4 agonist treated mice. Furthermore, we evaluated the number of neutrophils in the liver as a hallmark of hepatic I/R injury using MPO staining. The recruitment of neutrophils was significantly inhibited in EP-4 agonist treated mice (n=6, p=0.028 vs. control). To address the underlying mechanisms, we evaluated local expression of cytokine, chemokine and adhesion molecule using quantative real-time PCR. EP4 agonist treatment significantly down-regulated the local expression of several pro-inflammatory cytokine (TNF-α, IL-1β and IFN-γ, p=0.0002, p=0.0007 and p=0.0001, respectively vs control), chemokine (MCP-1 and IP-10, p=0.006 and p=0.008) and adhesion molecule (E-selectin and ICAM-1, p=0.011 and p=0.024) after 2h of reperfusion following 90 minutes of ischemia. By sharp contrast, IL-10, an anti-inflammatory cytokine, was significantly up-regulated (p=0.037 vs. control). Finally, the removal of shunt liver after 120 minutes of ischemia resulted in the death of 86 % of mice treated with saline within 48 h. By sharp contrast, 80% of mice treated with EP-4 agonist survived (P=0.016 compared to control). Conclusions: This study demonstrates for the first time the inhibitory role of EP4 receptor in hepatic I/R injury and therapeutic efficacy of selective EP4 agonist for the protection of the liver injury.