The theory that red blood cells (RBCs) generate and release nitric oxide (NO)-like bioactivity has gained considerable interest. However, it remains unclear whether it can be produced by endothelial NO synthase (eNOS), which is present in RBCs, and whether NO can escape scavenging by hemoglobin. The aim of this study was to test the hypothesis that arginase reciprocally controls NO formation in RBCs by competition with eNOS for their common substrate arginine and that RBC-derived NO is functionally active following arginase blockade. We show that rodent and human RBCs contain functional arginase 1 and that pharmacological inhibition of arginase increases export of eNOS-derived nitrogen oxides from RBCs under basal conditions. The functional importance was tested in an ex vivo model of myocardial ischemiareperfusion injury. Inhibitors of arginase significantly improved postischemic functional recovery in rat hearts if administered in whole blood or with RBCs in plasma. By contrast, arginase inhibition did not improve postischemic recovery when administered with buffer solution or plasma alone. The protective effect of arginase inhibition was lost in the presence of a NOS inhibitor. Moreover, hearts from eNOS −/− mice were protected when the arginase inhibitor was given with blood from wildtype donors. In contrast, when hearts from wild-type mice were given blood from eNOS −/− mice, the arginase inhibitor failed to protect against ischemia-reperfusion. These results strongly support the notion that RBCs contain functional eNOS and release NO-like bioactivity. This process is under tight control by arginase 1 and is of functional importance during ischemia-reperfusion.is a biological messenger that is a key regulator of cardiovascular function by inducing vasodilation, inhibition of platelet aggregation, and leukocyte adhesion (1). Reduced bioavailability of endothelium-derived NO is closely associated with development of several cardiovascular diseases including atherosclerosis, ischemia-reperfusion injury, and hypertension. The vascular effects of NO have traditionally been considered to be mediated by endothelium-derived NO after formation by the constitutively expressed endothelial NO synthase (eNOS). An alternative source of NO is nitrite that can be converted to NO in cardiac tissue during ischemia or hypoxia (2-4). In 1996, Stamler and colleagues suggested a role for red blood cells (RBCs) in exporting NO bioactivity and regulating blood flow (5). In this model, RBCs contain NO in the form of S-nitrosylated hemoglobin, which is in equilibrium with small nitrosothiols that are exported preferentially under deoxygenated conditions (5, 6). RBCs thereby provide NO-based vasodilatory activity through S-nitrosothiols when deoxygenated. It was also suggested that the source of RBC NO is eNOS (5). However, it was assumed that eNOS was exclusively vascular in origin, and mechanisms regulating RBC formation and export of NO bioactivity have been a matter of significant debate over the years (7). Another mechanism for ...

Inhibition of arginase protects from myocardial infarction by a mechanism that is dependent on NOS activity and bioavailability of NO by shifting arginine utilization from arginase towards NOS. These findings suggest that targeting of arginase is a promising future therapeutic strategy for protection against myocardial IR injury.

Myocardial ischaemia–reperfusion injury can be significantly reduced by an episode(s) of ischaemia–reperfusion applied prior to or during myocardial ischaemia (MI) to peripheral tissue located at a distance from the heart; this phenomenon is called remote ischaemic conditioning (RIc). Here, we compared the efficacy of RIc in protecting the heart when the RIc stimulus is applied prior to, during and at different time points after MI. A rat model of myocardial ischaemia–reperfusion injury involved 30 min of left coronary artery occlusion followed by 120 min of reperfusion. Remote ischaemic conditioning was induced by 15 min occlusion of femoral arteries and conferred a similar degree of cardioprotection when applied 25 min prior to MI, 10 or 25 min after the onset of MI, or starting 10 min after the onset of reperfusion. These RIc stimuli reduced infarct size by 54, 56, 56 and 48% (all P < 0.001), respectively. Remote ischaemic conditioning applied 30 min into the reperfusion period was ineffective. Activation of sensory nerves by application of capsaicin was effective in establishing cardioprotection only when elicited prior to MI. Vagotomy or denervation of the peripheral ischaemic tissue both completely abolished cardioprotection induced by RIc applied prior to MI. Cardioprotection conferred by delayed remote postconditioning was not affected by either vagotomy or peripheral denervation. These results indicate that RIc confers potent cardioprotection even if applied with a significant delay after the onset of myocardial reperfusion. Cardioprotection by remote preconditioning is critically dependent on afferent innervation of the remote organ and intact parasympathetic activity, while delayed remote postconditioning appears to rely on a different signalling pathway(s).

Bulhak AA, Jung C, Ö stenson C, Lundberg JO, Sjö quist P, Pernow J. PPAR-␣ activation protects the type 2 diabetic myocardium against ischemia-reperfusion injury: involvement of the PI3-kinase/Akt and NO pathway. Am J Physiol Heart Circ Physiol 296: H719 -H727, 2009. First published January 16, 2009 doi:10.1152/ajpheart.00394.2008.-Several clinical studies have shown the beneficial cardiovascular effects of fibrates in patients with diabetes and insulin resistance. The ligands of peroxisome proliferatoractivated receptor-␣ (PPAR-␣) reduce ischemia-reperfusion injury in nondiabetic animals. We hypothesized that the activation of PPAR-␣ would exert cardioprotection in type 2 diabetic Goto-Kakizaki (GK) rats, involving mechanisms related to nitric oxide (NO) production via the phosphatidylinositol 3-kinase (PI3K)/Akt pathway. GK rats and agematched Wistar rats (n Ն 7) were given either 1) the PPAR-␣ agonist WY-14643 (WY), 2) dimethyl sulfoxide (DMSO), 3) WY and the NO synthase inhibitor N G -nitro-L-arginine (L-NNA), 4) L-NNA, 5) WY and the PI3K inhibitor wortmannin, or 6) wortmannin alone intravenously before a 35-min period of coronary artery occlusion followed by 2 h of reperfusion. Infarct size (IS), expression of endothelial NO synthase (eNOS), inducible NO synthase, and Akt as well as nitrite/ nitrate were determined. The IS was 75 Ϯ 3% and 72 Ϯ 4% of the area at risk in the Wistar and GK DMSO groups, respectively. WY reduced IS to 56 Ϯ 3% in Wistar (P Ͻ 0.05) and to 46 Ϯ 5% in GK rats (P Ͻ 0.001). The addition of either L-NNA or wortmannin reversed the cardioprotective effect of WY in both Wistar (IS, 70 Ϯ 5% and 65 Ϯ 5%, respectively) and GK (IS, 66 Ϯ 4% and 64 Ϯ 4%, P Ͻ 0.05, respectively) rats. The expression of eNOS and eNOS Ser1177 in the ischemic myocardium from both strains was increased after WY. The expression of Akt, Akt Ser473, and Akt Thr308 was also increased in the ischemic myocardium from GK rats following WY. Myocardial nitrite/nitrate levels were reduced in GK rats (P Ͻ 0.05). The results suggest that PPAR-␣ activation protects the type 2 diabetic rat myocardium against ischemia-reperfusion injury via the activation of the PI3K/Akt and NO pathway.peroxisome proliferator-activated receptor-␣ ligand; endothelial function; phosphatidylinositol 3-kinase