The effects of thromboxane synthase inhibition on reperfusion injury and endothelin-1,2 levels in allograft kidney transplantation in rats

Renal functional responses to ischaemia-reperfusion injury in normotensive and hypertensive rats following non-selective and selective cyclo-oxygenase inhibition with nitric oxide donation

1. Acute renal failure develops as a result of periods of renal ischaemia during cardiovascular surgery or hypovolaemic shock. The present study investigated the importance of endogenous prostaglandin production and nitric oxide (NO) in the renal haemodynamic and excretory responses to ischaemia-reperfusion both normally and in the hypertensive state by chronic administration of cyclo-oxygenase (COX) inhibitors. 2. Male Wistar and stroke-prone spontaneously hypertensive rats (SHRSP) were subjected to 30 min renal ischaemia and 2 h reperfusion following 7 day treatment with vehicle, aspirin, NO-aspirin or celecoxib. 3. Renal blood flow was higher in the SHRSP treatment groups. Renal ischaemia increased blood pressure in all Wistar groups except that given aspirin, had no effect in the SHRSP and did not change renal blood flow in any group. Glomerular filtration rate was reduced throughout the reperfusion period in both rat strains. The postischaemic diuresis in the Wistar was enhanced by COX-2 inhibition, but not by aspirin or NO-aspirin. Urine flow increased in SHRSP during the postischaemic period, which was blunted by aspirin and NO-aspirin, but not by celecoxib. There was a postischaemic increase in fractional sodium excretion, the magnitude of which was unaltered by any drug in the Wistar rats, but was blunted by aspirin, NO-aspirin and celecoxib in SHRSP. 4. These results suggest that products of COX activity contribute to the renal responses to ischaemia-reperfusion injury, but in different ways, in SHRSP, which may reflect variations in renal prostaglandin and NO production in the hypertensive state.

Endothelin-1 blockade prevents COX2 induction and TXA2 production in the fructose hypertensive rat

Feeding rats with a high fructose diet results in insulin resistance and hypertension. Fructose-hypertensive rats (FHR) have increased vascular levels of endothelin-1 (ET-1) and thromboxane (TXA2). We have previously shown that chronic treatment with either the dual endothelin receptor blocker, bosentan, or the thromboxane synthase inhibitor, dazmegrel, prevented fructose-induced increases in blood pressure, suggesting that both ET-1 and TXA2 play important roles in the development of hyperinsulinemia/insulin resistance-associated hypertension. In this study, we investigated the potential interrelationship between ET-1 and TXA2 in the development of fructose-induced hypertension in vivo. Male Wistar rats were fed on a high fructose diet for 9 weeks. Either bosentan or dazmegrel treatment (daily by oral gavage) was initiated 3 weeks after the start of fructose feeding for a total duration of 6 weeks. At the end of drug treatment, blood and aorta were collected from each animal. Plasma thromboxane B2 (TXB2), a stable TXA2 metabolite, increased significantly in FHR and was reduced to control level by both chronic bosentan and dazmegrel treatment. Protein expression of cyclooxygenase 2 (COX2) was elevated significantly in FHR aortas and treatment with bosentan and dazmegrel corrected these changes. These results indicate that the actions of ET-1 in the aorta of FHR may be mediated through COX2-derived TXA2. Bosentan may prevent the development of hypertension in fructose-fed rats through inhibition of COX2 induction and subsequently the reduction in plasma TXA2.

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 A2 (PLA2) is a key enzyme that initiates this reaction. In this study, we tested our hypothesis that a type II PLA2 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 (n=6) was untreated and served as a control group. LY329722 was administered to animals in group 2 (n=6) intravenously (0.2 mg x kg(-1) x hr(-1)) for 60 min before ischemia, and to animals in group 3 (n=6) for 60 min starting 15 min before reperfusion (0.2 mg x kg(-1) x hr(-1)). Animal survival, systemic and splanchnic hemodynamics, hepatic tissue blood flow, liver functions, energy metabolism, hepatic venous thromboxane B2 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 B2, and endothelin-1 release, prevented hepatic phospholipid degradation and tumor necrosis factor-alpha 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 PLA2 inhibitor, LY329722, attenuated hepatic I/R injury caused by a 2-hr THVE model in dogs.