Arginase regulates red blood cell nitric oxide synthase and export of cardioprotective nitric oxide bioactivity

Abstract

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 ...

Modulation of L-Arginine-Arginase Metabolic Pathway Enzymes: Immunocytochemistry and mRNA Expression in Peripheral Blood and Tissue Levels in Head and Neck Squamous Cell Carcinomas in North East India

“…Similar to protein expression results, we could not identify ARG2 mRNA in blood ( Figure 2B). This is consistent with the recent finding that ARG2 is absent in blood circulation (Yang et al, 2013). Although, significant amount of OAT mRNA was present in both patients and controls but showed no significant difference ( Figure 3B).…”

“…No difference in ARG1 expressions with smoking (p=0.15) was observed, therefore the altered expression was due to the carcinoma (p<0.0001). Any staining of ARG 2 in blood cells were considered false positive as we did not observe any ARG2 mRNA, and also support the recent study showing absence of ARG2 in blood (Yang et al, 2013). Although we observed OAT mRNA expression in blood with no detectable difference in OAT protein or mRNA expression, which might be circulating cell free mRNA (Garcia et al, 2008).…”

“…Although, the expression of much of the genome is repressed, yet a few hundred genes whose protein products are critical for viability and normal function of mature erythrocytes continue to be expressed till the last stage of terminal maturation (Benz et al, 2010). In human blood, neutrophiles and erythrocytes represent predominant ARG1 expressing population (Yang et al, 2013). Due to diseased condition, in HNSCC patients newly synthesized RBCs might have higher expression of ARG1 and ODC as evident by immunocytochemistry.…”

Hemoglobin βCys93 is essential for cardiovascular function and integrated response to hypoxia

“…Thus, endothelium-dependent vasodilation may involve prostacyclin, H 2 S, CO, and H 2 O 2 in addition to NO/SNO (47). Similarly, in some contexts, RBC-mediated vasodilation may involve release of ATP (48) or NO bioactivity derived from erythrocytic eNOS (including SNO or nitrite) (49). Our work does not exclude roles for SNO-Hb-independent mechanisms of RBC bioactivity.…”

“…More directly, our finding that mice lacking βCys93 are subject to myocardial infarction and cardiogenic shock under hypoxia raises the possibility that RBCs may play a general role in ischemic coronary syndromes and heart failure, the most common causes of death in Western societies. A role for RBC-derived NO bioactivity in protection from myocardial damage also has been described in the context of an ex vivo model of ischemiareperfusion injury (49). That NO deficiency may be a common contributing factor in myocardial injury and death is, in fact, well accepted (54); however, current tenets hold that endothelial cells (rather than RBCs) are the root cause.…”