Nitric oxide enhances endothelin production in pancreas transplantation

The cytoprotective effects of addition of activated protein C into preservation solution on small-for-size grafts in rats

Small-for-size liver grafts are a serious obstacle for partial orthotopic liver transplantation. Activated protein C (APC), a potent anticoagulant serine protease, is known to have cell-protective properties due to its anti-inflammatory and antiapoptotic activities. This study was designed to examine the cytoprotective effects of a preservation solution containing APC on small-for-size liver grafts, with special attention paid to ischemia-reperfusion injury and shear stress in rats. APC exerted cytoprotective effects, as evidenced by (1) increased 7-day graft survival; (2) decreased initial portal pressure and improved hepatic microcirculation; (3) decreased levels of aminotransferase and improved histological features of hepatic ischemia-reperfusion injury; (4) suppressed infiltration of neutrophils and monocytes/macrophages; (5) reduced hepatic expression of tumor necrosis factor alpha and interleukin 6; (6) decreased serum levels of hyaluronic acid, which indicated attenuation of sinusoidal endothelial cell injury; (7) increased hepatic levels of nitric oxide via up-regulated hepatic endothelial nitric oxide synthesis expression together with down-regulated hepatic inducible nitric oxide synthase expression; (8) decreased hepatic levels of endothelin 1; and (9) reduced hepatocellular apoptosis by down-regulated caspase-8 and caspase-3 activities. These results suggest that a preservation solution containing APC is a potential novel and safe product for small-for-size liver transplantation, alleviating graft injury via anti-inflammatory and antiapoptotic effects and vasorelaxing conditions.

The endothelin receptor antagonist TAK-044 in the treatment of reperfusion injury in organ transplantation

Ischaemia and reperfusion are complex interrelated events that involve the vascular endothelium. The endothelium produces endothelin (ET), the most potent vasoconstrictor identified to date. During ischaemia, endothelial transcription of ET is increased, leading to strong and sustained vasoconstriction. Ischaemia and reperfusion are indispensable parts of solid organ transplantation. Various experimental data discussed in this review show an efficacy of the mixed ET(A/B) antagonist TAK-044 in the treatment of reperfusion injury. The overall safety and tolerability of TAK-044 in humans seems to be excellent. Large clinical randomised trials on the use of TAK-044 in the treatment of reperfusion injury in different clinical situations are missing, nevertheless, the future for ET antagonists is promising.

Strategies to modulate the deleterious effects of endothelin in hepatic ischemia-reperfusion

BACKGROUND

This study evaluates whether bosentan (endothelin [ET] receptor antagonist) or preconditioning (mechanism that inhibits the postischemic ET release) could reduce the microvascular disorders and the injurious effects of tumor necrosis factor (TNF) associated with hepatic ischemia-reperfusion (I/R).

METHODS

Hepatic I/R was induced in rats and the effects of bosentan or preconditioning on the deleterious effects of ET in hepatic I/R were evaluated. Transaminase and TNF levels in plasma; edema, vascular permeability, lactate, ET, and TNF levels in liver; and edema and myeloperoxidase activity levels in lung were measured after hepatic reperfusion.

RESULTS

The administration of bosentan or the induction of preconditioning previous to I/R attenuated the increase in vascular permeability, edema and lactate levels observed in liver after I/R. However, the addition of ET before preconditioning abolished its benefits. Preconditioning prevented both the increase in hepatic TNF and its release from the liver into the systemic circulation. This resulted in an attenuation of liver and lung damage. Addition of ET or TNF to the preconditioned group abolished the benefits of preconditioning, whereas the previous inhibition of TNF release with GdCl3 in the preconditioned group pretreated with ET did not modify the effects of preconditioning. The inhibition of ET with bosentan prevented the increase of both hepatic and plasma TNF, thus attenuating the liver and lung injury, whereas TNF addition abolished the benefits of bosentan.

CONCLUSIONS

These findings suggest that both bosentan and preconditioning, by inhibition of ET could attenuate the microvascular disorders and the deleterious effect of TNF on the liver and lung elicited by hepatic I/R.

Evolution of streptozotocin-pancreatic damage in the rat: modulatory effect of endothelins on the nitridergic and prostanoid pathway

Many lines of evidence indicate that an increased pancreatic production of nitric oxide (NO) and prostaglandins (PGs) is found in the pancreas of streptozotocin-diabetic rats and that endothelins (ETs) are closely related to the nitridergic and prostanoid pathway in several tissues. In the present study the relationship between NO, ETs, and PGs has been explored in isolated pancreatic tissue from streptozotocin-diabetic rats. Pancreatic ET levels are higher in pancreatic tissues from diabetic (D) rats compared to control (C) animals. The addition of nitric oxide synthase (NOS) inhibitors (1 mM N(G)-nitro-l-arginine methyl ester, 600 microM N(G)-monomethyl-l-arginine) in the incubating medium reduces and NO donors (SIN-1, 300 microM spermine suppress, NONOate 100 microM) increases ET levels in pancreatic slices from C and D animals. PGE(2) (10(-7) M) increases and indomethacin (10(-6) M) decreases ET pancreatic production only in D but not in C tissues when added into the incubating bath. When tissues are incubated in the presence of endothelin 1 (ET-1) (10(-7) M), NOS activity is higher in C pancreas, while the ET-receptor antagonist bosentan (B) decreases NOS levels in D but not in C tissues. When pancreatic arachidonic acid (AA) conversion to prostaglandins was explored, ET-1 increased PGF(2alpha), PGE(2), and TXB(2) levels in C but not in D tissues. B abolishes TXB(2) increment due to the diabetic state, but failed in modulating AA conversion to 6-keto PGF(1alpha), PGF2(alpha) and PGE(2) in D pancreas. Our results show an alteration in AA metabolism, ET production, and NO increment associated with pancreatic damage due to streptozotocin.