ATTENUATION OF ISCHEMIA AND REPERFUSION INJURY OF CANINE LIVERS BY INHIBITION OF TYPE II PHOSPHOLIPASE A2 WITH LY3297221

Background. Membrane phospholipid breakdown, caused by ischemia and reperfusion (I/R) of the liver, releases free fatty acids including arachidonic acids and lysophospholipids, which serve as precursors of various inflammatory lipid derivatives. Phospholipase A 2 (PLA2) is a key enzyme that initiates this reaction. In this study, we tested our hypothesis that a type II PLA 2 inhibitor, LY329722, could attenuate hepatic I/R injury caused by a 2-hr total hepatic vascular exclusion (THVE) in dogs. Methods. Eighteen beagle dogs, subjected to a 2-hr THVE, were divided into three groups. Group 1 (n56) was untreated and served as a control group. LY329722 was administered to animals in group 2 (n56) intravenously (0.2 mg·kg 21 ·hr 21 ) for 60 min before ischemia, and to animals in group 3 (n56) for 60 min starting 15 min before reperfusion (0.2 mg·kg 21 ·hr 21 ). Animal survival, systemic and splanchnic hemodynamics, hepatic tissue blood flow, liver functions, energy metabolism, hepatic venous thromboxane B 2 and endothelin-1 levels, phospholipid levels and tumor necrosis factor-a mRNA expression in liver tissue, and histopathologic findings were evaluated. Results. Two-week animal survival was 33% (two of six) in group 1, and 100% (six of six) in groups 2 and 3. LY329722 improved systemic and splanchnic hemodynamics, hepatic tissue blood flow, and energy metabolism, reduced liver enzyme, thromboxane B 2, and endothelin-1 release, prevented hepatic phospholipid degradation and tumor necrosis factor-a mRNA expression, and lessened histopathologic damage and the number of neutrophil infiltrating into the liver tissue. Conclusion. The present study demonstrated that a type II PLA 2 inhibitor, LY329722, attenuated hepatic I/R injury caused by a 2-hr THVE model in dogs. Phospholipase A 2 (PLA2) accelerates breakdown of membrane phospholipids of the heart, liver, and kidney under warm ischemia (1‐3), and leads to the release of free fatty acids including arachidonic acid, and lysophospholipids. The arachidonic acids are metabolized via the cyclooxygenase pathway to thromboxane (TX) A 2 and prostaglandins (PGs), or via 5-lipoxygenase pathway to leukotrienes. Lysophospholipids are metabolized to platelet-activating factor (PAF) by acetyltransferase. Most of these lipid derivatives have proinflammatory and vasoconstrictive actions and contribute to postischemic organ dysfunction, which is attenuated by nonspecific PLA 2 inhibitors ( 4‐6 ). PLA 2 is classified generally into two subtypes: cPLA2 and sPLA 2 (7). cPLA2 is involved in the breakdown of membrane phospholipids of intracellular organelles. Of the secretory PLA 2 (sPLA2), type I PLA2 is contained in the exocrine pancreas and type II PLA 2 is involved in inflammatory events, particularly the ischemia and reperfusion (I/R) injury of the heart, liver, kidney, and intestine (8 ‐11). LY329722 is a novel selective type II PLA 2 inhibitor (12), which is derived from synthetic LY315920/S-5920 (13). In this study, we tested whether LY329722 could attenuate hepatic I/R injury caused by a 2-hr total hepatic vascular exclusion (THVE) in dogs.