Contribution of RhoA/Rho-kinase/MEK1/ERK1/2/iNOS pathway to ischemia/reperfusion-induced oxidative/nitrosative stress and inflammation leading to distant and target organ injury in rats

The small G protein RhoA and its downstream effector Rho-kinase play an important role in various physiopathological processes including ischemia/reperfusion (I/R) injury. Reactive oxygen and nitrogen species produced by iNOS and NADPH oxidase are important mediators of inflammation and organ injury following an initial localized I/R event. The aim of this study was to determine whether RhoA/Rho-kinase signaling pathway increases the expression and activity of MEK1, ERK1/2, iNOS, gp91(phox), and p47(phox), and peroxynitrite formation which result in oxidative/nitrosative stress and inflammation leading to hindlimb I/R-induced injury in kidney as a distant organ and gastrocnemius muscle as a target organ. I/R-induced distant and target organ injury was performed by using the rat hindlimb tourniquet model. I/R caused an increase in the expression and/or activity of RhoA, MEK1, ERK1/2, iNOS, gp91(phox), p47(phox), and 3-nitrotyrosine and nitrotyrosine levels in the tissues. Although Rho-kinase activity was increased by I/R in the kidney, its activity was decreased in the muscle. Serum and tissue MDA levels and MPO activity were increased following I/R. I/R also caused an increase in SOD and catalase activities associated with decreased GSH levels in the tissues. Y-27632, a selective Rho-kinase inhibitor, (100µg/kg, i.p.; 1h before reperfusion) prevented the I/R-induced changes except Rho-kinase activity in the muscle. These results suggest that activation of RhoA/Rho-kinase/MEK1/ERK1/2/iNOS pathway associated with oxidative/nitrosative stress and inflammation contributes to hindlimb I/R-induced distant organ injury in rats. It also seems that hindlimb I/R induces target organ injury via upregulation of RhoA/MEK1/ERK1/2/iNOS pathway associated with decreased Rho-kinase activity.

Contribution of iNOS/sGC/PKG pathway, COX-2, CYP4A1, and gp91(phox) to the protective effect of 5,14-HEDGE, a 20-HETE mimetic, against vasodilation, hypotension, tachycardia, and inflammation in a rat model of septic shock

We have previously demonstrated that a stable synthetic analog of 20-hydroxyeicosatetraenoic acid (20-HETE), N-[20-hydroxyeicosa-5(Z),14(Z)-dienoyl]glycine (5,14-HEDGE), prevents vascular hyporeactivity, hypotension, tachycardia, and inflammation in rats treated with lipopolysaccharide (LPS) and mortality in endotoxemic mice. These changes were attributed to decreased production of inducible nitric oxide (NO) synthase (iNOS)-derived NO, cyclooxygenase (COX)-2-derived vasodilator prostanoids, and proinflammatory mediators associated with increased cyctochrome P450 (CYP) 4A1-derived 20-HETE and CYP2C23-dependent antiinflammatory mediator formation. The aim of this study was to determine whether decreased expression and activity of iNOS, soluble guanylyl cyclase (sGC), protein kinase G (PKG), COX-2, gp91(phox) (NOX2; a superoxide generating NOX enzyme), and peroxynitrite production associated with increased expression of COX-1 and CYP4A1 and 20-HETE formation in renal and cardiovascular tissues of rats contributes to the effect of 5,14-HEDGE to prevent vasodilation, hypotension, tachycardia, and inflammation in response to systemic administration of LPS. Mean arterial pressure fell by 28mmHg and heart rate rose by 47beats/min in LPS (10mg/kg, i.p.)-treated rats. Administration of LPS also increased mRNA and protein expression of iNOS and COX-2 associated with a decrease in COX-1 and CYP4A1 mRNA and protein expression. Increased NOS activity, iNOS-heat shock protein 90 complex formation (an index for iNOS activity), protein expression of phosphorylated vasodilator stimulated phosphoprotein (an index for PKG activity), gp91(phox), p47(phox) (NOXO2; organizer subunit of gp91(phox)), and nitrotyrosine (an index for peroxynitrite production) as well as cGMP (an index for sGC activity), 6-keto-PGF1α (a stable metabolite PGI2) and PGE2 levels (indexes for COX activity), and nitrotyrosine levels by LPS were also associated with decreased CYP hydroxylase activity as measured by 20-HETE formation from arachidonic acid in renal microsomes of LPS-treated rats. These effects of LPS, except iNOS mRNA and COX-1 protein expression, were prevented by 5,14-HEDGE (30mg/kg, s.c.; 1h after LPS). A competitive antagonist of vasoconstrictor effects of 20-HETE, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid (30mg/kg, s.c.; 1h after LPS) reversed the effects of 5,14-HEDGE, except iNOS and COX-1 mRNA and protein expression as well as expression of CYP4A1 mRNA. These results suggest that increased CYP4A1 expression and 20-HETE formation associated with suppression of iNOS/sGC/PKG pathway, COX-2, and gp91(phox) participate in the protective effect of 5,14-HEDGE against vasodilation, hypotension, tachycardia, and inflammation in the rat model of septic shock.

Contribution of vasoactive eicosanoids and nitric oxide production to the effect of selective cyclooxygenase-2 inhibitor, NS-398, on endotoxin-induced hypotension in rats

Our previous studies with the use of non-selective cyclooxygenase (COX) inhibitor, indomethacin, demonstrated that prostanoids produced during endotoxaemia increase inducible nitric oxide synthase (iNOS) protein expression and nitric oxide synthesis, and decrease cyctochrome P450 (CYP) 4A1 protein expression and CYP 4A activity. The results suggest that dual inhibition of iNOS and COX by indomethacin restores blood pressure presumably due to increased production of 20-hydroxyeicosatetraenoic acid (20-HETE) derived from CYP 4A in endotoxaemic rats. The present study examined whether increased levels of vasoconstrictor eicosanoids, 20-HETE, prostaglandin F(2α) (PGF(2α) )and thromboxane A(2) (TxA(2) ), would contribute to the effect of selective COX-2 inhibition to prevent endotoxin (ET)-induced fall in blood pressure associated with an increase in the production of vasodilator prostanoids, prostaglandin I(2) (PGI(2) ) and prostaglandin E(2) (PGE(2) ) and nitric oxide synthesis. Mean arterial blood pressure fell by 31 mmHg and heart rate (HR) rose by 90 beats/min. in male Wistar rats treated with ET (10 mg/kg, i.p.). The fall in mean arterial pressure and increase in HR were associated with increased levels of 6-keto-prostaglandin F(1α) (6-keto-PGF(1α) ), PGE(2) , TxB(2) , and nitrite in the serum, kidney, heart, thoracic aorta and/or superior mesenteric artery. Systemic and renal 20-HETE and PGF(2α) levels were also decreased in endotoxaemic rats. These effects of ET were prevented by a selective COX-2 inhibitor, N-(2-cyclohexyloxy-4-nitrophenyl)methansulphonamide (10 mg/kg, i.p.), given 1 hr after injection of ET. These data suggest that an increase in 20-HETE and PGF(2α) levels associated with decreased production of PGI(2) , PGE(2) , and TxA(2) , and nitric oxide synthesis contributes to the effect of selective COX-2 inhibitor to prevent the hypotension during rat endotoxaemia.

Piroxicam reverses endotoxin-induced hypotension in rats: contribution of vasoactive eicosanoids and nitric oxide

Nitric oxide (NO) produced by inducible NO synthase (iNOS) is responsible for endotoxin-induced vascular hyporeactivity and hypotension resulting in multiple organ failure. Endotoxic shock is also characterized by decreased expression of constitutive cyclooxygenase (COX-1), cytochrome P450 (CYP) 4A and endothelial NOS (eNOS). Our previous studies demonstrated that dual inhibition of iNOS and COX with a selective COX-2 inhibitor, NS-398, or a non-selective COX inhibitor, indomethacin, restores blood pressure presumably because of increased production of 20-hydroxyeicosatetraenoic acid (20-HETE) derived from arachidonic acid (AA) by CYP4A in endotoxaemic rats. The aim of this study was to investigate the effects of piroxicam, a preferential COX-1 inhibitor, on the endotoxin-induced changes in blood pressure, expression of COX-1, inducible COX (COX-2), CYP4A1, eNOS, iNOS and heat shock protein 90 (hsp90), and production of PGI(2), PGE(2), 20-HETE and NO. Injection of endotoxin (10 mg/kg, i.p.) to male Wistar rats caused a fall in blood pressure and an increase in heart rate associated with elevated renal 6-keto-PGF(1α) and PGE(2) levels as well as an increase in COX-2 protein expression. Endotoxin also caused an elevation in systemic and renal nitrite levels associated with increased renal iNOS protein expression. In contrast, systemic and renal 20-HETE levels and renal expression of eNOS, COX-1 and CYP4A1 were decreased in endotoxaemic rats. The effects of endotoxin, except for renal COX-1 and eNOS protein expression, were prevented by piroxicam (10 mg/kg, i.p.), given 1 hr after injection of endotoxin. Endotoxin did not change renal hsp90 protein expression. These data suggest that a decrease in the expression and activity of COX-2 and iNOS associated with an increase in CYP4A1 expression and 20-HETE synthesis contributes to the effect of piroxicam to prevent the hypotension during rat endotoxaemia.

A synthetic analogue of 20-HETE, 5,14-HEDGE, reverses endotoxin-induced hypotension via increased 20-HETE levels associated with decreased iNOS protein expression and vasodilator prostanoid production in rats

Nitric oxide (NO) produced by inducible NO synthase (iNOS) is responsible for endotoxin (ET)-induced hypotension and vascular hyporeactivity and plays a major contributory role in the multiorgan failure. Endotoxic shock is also associated with an increase in vasodilator prostanoids as well as a decrease in endothelial NO synthase (eNOS) and cytochrome P450 4A protein expression, and production of a vasoconstrictor arachidonic acid product, 20-hydroxyeicosatetraenoic acid (20-HETE). The aim of this study was to investigate the effects of a synthetic analogue of 20-HETE, N-[20-hydroxyeicosa-5(Z),14(Z)-dienoyl]glycine (5,14-HEDGE), on the ET-induced changes in eNOS, iNOS and heat shock protein 90 (hsp90) expression as well as 20-HETE and vasodilator prostanoid (6-keto-PGF(1alpha) and PGE(2)) production. ET-induced fall in blood pressure and rise in heart rate were associated with an increase in iNOS protein expression and a decrease in eNOS protein expression in heart, thoracic aorta, kidney and superior mesenteric artery. ET did not change hsp90 protein expression in the tissues. ET-induced changes in eNOS and iNOS protein expression were associated with increased 6-keto-PGF(1alpha) and PGE(2) levels and a decrease in 20-HETE levels, in the serum and kidney. These effects of ET on the iNOS protein expression and 6-keto-PGF(1alpha), PGE(2) and 20-HETE levels were prevented by 5,14-HEDGE. Furthermore, a competitive antagonist of vasoconstrictor effects of 20-HETE, 20-hydroxyeicosa-6(Z),15(Z)-dienoic acid, prevented the effects of 5,14-HEDGE on the ET-induced changes in systemic and renal levels of these prostanoids and 20-HETE. These data are consistent with the view that an increase in systemic and renal 20-HETE levels associated with a decrease in iNOS protein expression and vasodilator prostanoid production contributes to the effect of 5,14-HEDGE to prevent the hypotension during rat endotoxemia.