Endothelial nitric oxide synthase in red blood cells: key to a new erythrocrine function?

Possible roles for ATP release from RBCs exclude the cAMP-mediated Panx1 pathway

Red blood cell (RBC)-derived adenosine triphosphate (ATP) has been proposed as an integral component in the regulation of oxygen supply to skeletal muscle. In ex vivo settings RBCs have been shown to release ATP in response to a number of stimuli, including stimulation of adrenergic receptors. Further evidence suggested that ATP release from RBCs was dependent on activation of adenylate cyclase (AC)/cyclic adenosine monophosphate (cAMP)-dependent pathways and involved the pannexin 1 (Panx1) channel. Here we show that RBCs express Panx1 and confirm its absence in Panx1 knockout (^-/-) RBCs. However, Panx1^-/- mice lack any decrease in exercise performance, challenging the assumptions that Panx1 plays an essential role in increased blood perfusion to exercising skeletal muscle and therefore in ATP release from RBCs. We therefore tested the role of Panx1 in ATP release from RBCs ex vivo in RBC suspensions. We found that stimulation with hypotonic potassium gluconate buffer resulted in a significant increase in ATP in the supernatant, but this was highly correlated with RBC lysis. Next, we treated RBCs with a stable cAMP analog, which did not induce ATP release from wild-type or Panx1^-/- mice. Similarly, multiple pharmacological treatments activating AC in RBCs increased intracellular cAMP levels (as measured via mass spectrometry) but did not induce ATP release. The data presented here question the importance of Panx1 for exercise performance and dispute the general assumption that ATP release from RBCs via Panx1 is regulated via cAMP.

Modulation of Local and Systemic Heterocellular Communication by Mechanical Forces: A Role of Endothelial Nitric Oxide Synthase

In this review, we discuss the role of nitric oxide (NO) as a key physiological mechanotransducer modulating both local and systemic heterocellular communication and contributing to the integrated (patho)physiology of the cardiovascular system. A deeper understanding of mechanotransduction-mediated local and systemic nodes controlling heterocellular communication between the endothelium, blood cells, and other cell types (e.g., cardiomyocytes) may suggest novel therapeutic strategies for endothelial dysfunction and cardiovascular disease. Recent Advances: Mechanical forces acting on mechanoreceptors on endothelial cells activate the endothelial NO synthase (eNOS) to produce NO. NO participates in (i) abluminal heterocellular communication, inducing vasorelaxation, and thereby regulating vascular tone and blood pressure; (ii) luminal heterocellular communication, inhibiting platelet aggregation, and controlling hemostasis; and (iii) systemic heterocellular communication, contributing to adaptive physiological processes in response to exercise and remote ischemic preconditioning. Interestingly, shear-induced eNOS-dependent activation of vascular heterocellular communication constitutes the molecular basis of all methods applied in the clinical routine for evaluation of endothelial function. Critical Issues and Future Directions: The integrated physiology of heterocellular communication is still not fully understood. Dedicated experimental models are needed to analyze messengers and mechanisms underpinning heterocellular communication in response to physical forces in the cardiovascular system (and elsewhere). Antioxid. Redox Signal. 26, 917-935.

Effect of medicinal mushrooms on blood cells under conditions of diabetes mellitus

Diabetes mellitus (DM) is the third most common non-infectious disease leading to early disability and high mortality. Moreover, the number of patients is growing every year. The main symptom of DM is hyperglycemia. Increased levels of blood glucose activate polyol, hexosamine, and protein kinase metabolic pathways cause the intensification of non-enzymatic glycosylation and nitration of macromolecules. This, in turn, leads to the development of oxidative and nitrative stresses and secondary complications, such as different kinds of micro- and macroangiopathies. Metabolic disorders caused by insulin deficiency in diabetes significantly impede the functioning of a homeostasis system, which change the physical, biochemical, morphological, and functional properties of blood cells. As a result, the oxygen-transport function of red blood cells (RBCs), rheological properties of the blood, and functions of immunocompetent cells as well as the process of apoptosis are primarily affected. Modern pharmacotherapy focuses on the search for new preparations that aim to decrease blood glucose levels. Undesirable side effects and adverse reactions caused by synthetic medicines led to the search and investigation of new preparations of natural origin. Medicinal mushrooms play an important role among such new preparations. They are a source of a large number of high- and low-molecular compounds with pronounced biological effects. Our investigations show pronounced hypoglycemic and anti-anemic action of submerged cultivated mycelium powder of medicinal mushrooms Agaricus brasiliensis (A. brasiliensis) and Ganoderma lucidum (G. lucidum) on streptozotocin-induced DM in rats. Also, we showed that mycelium powders have membrane protective properties as evidenced by the redistribution of RBC populations towards the growth of full functional cell numbers. Normalization of parameters of leukocyte formula and suppression of apoptosis of white blood cells in diabetic rats treated with A. brasiliensis and G. lucidum mycelia indicates pronounced positive effects of these strains of mushrooms. Thus, the use of medicinal mushrooms for treatment of DM and in prevention development of its secondary complications might be a new effective approach of this disease's cure. This article is aimed at summarizing and analyzing the literature data and basic achievements concerning DM type 1 treatment using medicinal mushrooms and showing the results obtained in our research.

Red Blood Cell Function and Dysfunction: Redox Regulation, Nitric Oxide Metabolism, Anemia

SIGNIFICANCE

Recent clinical evidence identified anemia to be correlated with severe complications of cardiovascular disease (CVD) such as bleeding, thromboembolic events, stroke, hypertension, arrhythmias, and inflammation, particularly in elderly patients. The underlying mechanisms of these complications are largely unidentified. Recent Advances: Previously, red blood cells (RBCs) were considered exclusively as transporters of oxygen and nutrients to the tissues. More recent experimental evidence indicates that RBCs are important interorgan communication systems with additional functions, including participation in control of systemic nitric oxide metabolism, redox regulation, blood rheology, and viscosity. In this article, we aim to revise and discuss the potential impact of these noncanonical functions of RBCs and their dysfunction in the cardiovascular system and in anemia.

CRITICAL ISSUES

The mechanistic links between changes of RBC functional properties and cardiovascular complications related to anemia have not been untangled so far.

FUTURE DIRECTIONS

To allow a better understanding of the complications associated with anemia in CVD, basic and translational science studies should be focused on identifying the role of noncanonical functions of RBCs in the cardiovascular system and on defining intrinsic and/or systemic dysfunction of RBCs in anemia and its relationship to CVD both in animal models and clinical settings. Antioxid. Redox Signal. 26, 718-742.

The Osmopressor-Induced Angiopoietin-1 Secretion in Plasma and Subsequent Activation of the Tie-2/Akt/eNOS Signaling Pathway in Red Blood Cell

BACKGROUND

Water ingestion induces the osmopressor response, which typically presents as increased total peripheral vascular resistance in young healthy subjects. A previous study has suggested that the RBC membrane receptor is involved in osmopressor stress. Recent studies have indicated nitric oxide synthase phosphorylation in RBCs. However, the main process in signaling pathway activation to elicit such a response is unknown. Herein, we hypothesized that hypo-osmotic stress following water ingestion modulates the eNOS/NO pathway, thereby alternating vascular resistance.

METHODS

We included 24 young, healthy subjects. Physiological parameters and blood samples were collected at 5 minutes before and 25 and 50 minutes after 50 ml water, 500 ml water, or 500 ml normal saline ingestion. A human receptor tyrosine kinase (RTK) phosphorylation antibody array was used to simultaneously detect and monitor the biological activation pathways in RBCs.

RESULTS

Of the 71 RTKs assayed during the osmopressor response, several RTKs were significantly upregulated, including Tie-2 and Tie-1. Plasma angiopoietin-1 levels significantly increased at 25 minutes after 500 ml water ingestion compared to those at baseline. Simultaneous phosphorylation of Tie-2, Akt, and eNOS in RBCs occurred. RBCs in vitro were stimulated with angiopoietin-1, Tie-2, or 0.8% saline and showed significant increase in Tie-2, Akt, and eNOS phosphorylation upon angiopoietin-1 treatment and enhanced activation upon cotreatment of angiopoietin-1 and 0.8% saline.

CONCLUSIONS

The hypo-osmotic stimulus of water ingestion increases angiopoietin-1 secretion and subsequently activates the Tie-2/Akt/eNOS signaling pathway in RBCs, thereby revealing a novel biological mechanism simultaneously occurring with the osmopressor response.

The microcirculation in hypoxia: The center of the battlefield for oxygen

In the past years the microcirculation has gained increasing attention not only by basic scientists, but also by clinicians and translational researchers. In the clinical scenario, it has been convincingly described that the microcirculation is a key predictor of outcome and of central pathophysiological relevance. A vast body of evidence demonstrates the central role of the smallest vessels in inflammation, hyperviscosity, cell-cell-interaction, endothelial function, tissue edema, hemodynamic and blood flow regulation and its important role in the interaction with soluble factors. A central feature of different diseases and a strong regulator of different changes is hypoxia, the lack of oxygen. Also the microcirculation is on one hand a central component responding with dynamic changes to hypoxia but also the central place where hypoxia mediates its unfavorable effects. These changes and associated interactions are the topic of this special thematic issue "Hypoxia" in Clinical Hemorheology and Microcirculation and it seems logical that important and relevant findings are presented.

Pannexin channel and connexin hemichannel expression in vascular function and inflammation

Control of blood flow distribution and tissue homeostasis depend on the tight regulation of and coordination between the microvascular network and circulating blood cells. Channels formed by connexins or pannexins that connect the intra- and extracellular compartments allow the release of paracrine signals, such as ATP and prostaglandins, and thus play a central role in achieving fine regulation and coordination of vascular function. This review focuses on vascular connexin hemichannels and pannexin channels. We review their expression pattern within the arterial and venous system with a special emphasis on how post-translational modifications by phosphorylation and S-nitrosylation of these channels modulate their function and contribute to vascular homeostasis. Furthermore, we highlight the contribution of these channels in smooth muscle cells and endothelial cells in the regulation of vasomotor tone as well as how these channels in endothelial cells regulate inflammatory responses such as during ischemic and hypoxic conditions. In addition, this review will touch on recent evidence implicating a role for these proteins in regulating red blood cell and platelet function.

Modulating Vascular Hemodynamics With an Alpha Globin Mimetic Peptide (HbαX)

The ability of hemoglobin to scavenge the potent vasodilator nitric oxide (NO) in the blood has been well established as a mechanism of vascular tone homeostasis. In endothelial cells, the alpha chain of hemoglobin (hereafter, alpha globin) and endothelial NO synthase form a macromolecular complex, providing a sink for NO directly adjacent to the production source. We have developed an alpha globin mimetic peptide (named HbαX) that displaces endogenous alpha globin and increases bioavailable NO for vasodilation. Here we show that, in vivo, HbαX administration increases capillary oxygenation and blood flow in arterioles acutely and produces a sustained decrease in systolic blood pressure in normal and angiotensin II-induced hypertensive states. HbαX acts with high specificity and affinity to endothelial NO synthase, without toxicity to liver and kidney and no effect on p50 of O2 binding in red blood cells. In human vasculature, HbαX blunts vasoconstrictive response to cumulative doses of phenylephrine, a potent constricting agent. By binding to endothelial NO synthase and displacing endogenous alpha globin, HbαX modulates important metrics of vascular function, increasing vasodilation and flow in the resistance vasculature.

Nitric oxide synthetic pathway and cGMP levels are altered in red blood cells from end-stage renal disease patients

Red blood cells (RBCs) enzymatically produce nitric oxide (NO) by a functional RBC-nitric oxide synthase (RBC-NOS). NO is a vascular key regulatory molecule. In RBCs its generation is complex and influenced by several factors, including insulin, acetylcholine, and calcium. NO availability is reduced in end-stage renal disease (ESRD) and associated with endothelial dysfunction. We previously demonstrated that, through increased phosphatidylserine membrane exposure, ESRD-RBCs augmented their adhesion to human cultured endothelium, in which NO bioavailability decreased. Since RBC-NOS-dependent NO production in ESRD is unknown, this study aimed to investigate RBC-NOS levels/activation, NO production/bioavailability in RBCs from healthy control subjects (C, N = 18) and ESRD patients (N = 27). Although RBC-NOS expression was lower in ESRD-RBCs, NO, cyclic guanosine monophosphate (cGMP), RBC-NOS Serine1177 phosphorylation level and eNOS/Calmodulin (CaM)/Heat Shock Protein-90 (HSP90) interaction levels were higher in ESRD-RBCs, indicating increased enzyme activation. Conversely, following RBCs stimulation with insulin or ionomycin, NO and cGMP levels were significantly lower in ESRD- than in C-RBCs, suggesting that uremia might reduce the RBC-NOS response to further stimuli. Additionally, the activity of multidrug-resistance-associated protein-4 (MRP4; cGMP-membrane transporter) was significantly lower in ESRD-RBCs, suggesting a possible compromised efflux of cGMP across the ESRD-RBCs membrane. This study for the first time showed highest basal RBC-NOS activation in ESRD-RBCs, possibly to reduce the negative impact of decreased NOS expression. It is further conceivable that high NO production only partially affects cell function of ESRD-RBCs maybe because in vivo they are unable to respond to physiologic stimuli, such as calcium and/or insulin.

Erythrocytes in multiple sclerosis - forgotten contributors to the pathophysiology?

Multiple sclerosis (MS) is an autoimmune disease characterised by lymphocytic infiltration of the central nervous system and subsequent destruction of myelin and axons. On the background of a genetic predisposition to autoimmunity, environmental triggers are assumed to initiate the disease. The majority of MS research has focused on the pathological involvement of lymphocytes and other immune cells, yet a paucity of attention has been given to erythrocytes, which may play an important role in MS pathology. The following review briefly summarises how erythrocytes may contribute to MS pathology through impaired antioxidant capacity and altered haemorheological features. The effect of disease-modifying therapies on erythrocytes is also reviewed. It may be important to further investigate erythrocytes in MS, as this could broaden the understanding of the pathological mechanisms of the disease, as well as potentially lead to the discovery of novel and innovative targets for future therapies.

Age and gender differences in the influences of eNOS T-786C polymorphism on arteriosclerotic parameters in general population in Japan

OBJECTIVE

The influence of T-786C polymorphism in the promoter region of endothelial nitric oxide synthase (eNOS) on arteriosclerotic parameters by age and gender were examined.

METHODS

Brachial-ankle pulse wave velocity (baPWV), heart-rate adjusted augmentation index (AIx@75), pulse pressure (PP) and albumin-creatinine ratio (ACR) were assessed as arteriosclerotic parameters in addition to non-high-density lipoprotein cholesterol (non-HDL-C) to HDL-C (non-HDL-C/HDL-C) ratio in 1499 participants. T-786C polymorphism (rs2070744) was screened using a TaqMan allelic discrimination assay. Analyses of covariance were carried.

RESULTS

Women with the non-C allele showed significantly lower AIx@75 in participants aged <65 years and baPWV in participants aged ≥65 years than those with C allele. In contrast, men with the non-C allele showed significantly higher PP in participants aged <65 years, and higher ACR and non-HDL-C/HDL-C ratio in participants aged ≥65 years. In men on cholesterol-lowering medication, the non-C allele carriers showed significantly higher non-HDL-C compared to those in the C allele carriers.

CONCLUSIONS

eNOS T-786C polymorphism is significantly associated with arteriosclerotic parameters accompanied with age and gender differences, possibly involving antioxidative and/or endothelial signaling other than inflammatory signaling.

Red cell distribution width in anemic patients undergoing transcatheter aortic valve implantation

AIM: To determine the impact of red blood cell distribution width on outcome in anemic patients undergoing transcatheter aortic valve implantation (TAVI).

METHODS: In a retrospective single center cohort study we determined the impact of baseline red cell distribution width (RDW) and anemia on outcome in 376 patients with aortic stenosis undergoing TAVI. All patients were discussed in the institutional heart team and declined for surgical aortic valve replacement due to high operative risk. Collected data included patient characteristics, imaging findings, periprocedural in hospital data, laboratory results and follow up data. Blood samples for hematology and biochemistry analysis were taken from every patient before and at fixed intervals up to 72 h after TAVI including blood count and creatinine. Descriptive statistics were used for patient’s characteristics. Kaplan-Meier survival curves were used for time to event outcomes. A recursive partitioning regression and classification was used to investigate the association between potential risk factors and outcome variables.

RESULTS: Mean age in our study population was 81 ± 6.1 years. Anemia was prevalent in 63.6% (n = 239) of our patients. Age and creatinine were identified as risk factors for anemia. In our study population, anemia per se did influence 30-d mortality but did not predict longterm mortality. In contrast, a RDW > 14% showed to be highly predictable for a reduced short- and longterm survival in patients with aortic valve disease after TAVI procedure.

CONCLUSION: Age and kidney function determine the degree of anemia. The anisocytosis of red blood cells in anemic patients supplements prognostic information in addition to that derived from the WHO-based definition of anemia.

Sevoflurane inhibits the antioxidant capacity of erythrocytes

The aim of the present study was to observe the effects of sevoflurane on the antioxidant capacity, endothelial nitric oxide synthase (eNOS) content and lifespan of erythrocytes. A 2% erythrocyte suspension was prepared from whole blood collected from healthy volunteers and then treated with sevoflurane at different concentrations (group A, 0%; group S1, 1%; group S3, 3%; and group S5, 5%), in the presence or absence of 200 µmol/l hydrogen peroxide (H₂O₂, or H in group names). In order to evaluate the effects of sevoflurane on the antioxidant capacity and NO metabolism of erythrocytes, the hemolysis rate, catalase (CAT) content and eNOS content were determined, while the labeled phosphatidylserine rate and forward scatter of erythrocytes were detected using flow cytometry. Group S3 showed the highest hemolysis rate in the absence H₂O₂, while treatment with H₂O₂ increased the hemolysis rate of groups S1 and S3 (P=0.027). The CAT content in groups treated with sevoflurane was significantly lower compared with that in the control (group A, air group). The CAT content in groups S1+H, S3+H and S5+H remained significantly lower compared with group A+H (P<0.05). The eNOS content of group A was similar to that of group S3, while the content in group S1 was similar to that in group S5. In addition, the eNOS content of groups A and S3 increased, while that of groups S1 and S5 was reduced upon H₂O₂ treatment (P<0.05). The results indicated that sevoflurane reduced the antioxidative activity of erythrocytes, decreasing the resistant ability to H₂O₂ damage and increasing the hemolysis rate. The underlying mechanism may be associated with the inhibitory effect on the CAT activity of erythrocytes. Sevoflurane also inhibited the generation of nitric oxide in erythrocytes and reduced the tolerance of erythrocytes against oxidative stress damage due to H₂O₂.

Endothelial nitric oxide synthase in the microcirculation

Endothelial nitric oxide synthase (eNOS, NOS3) is responsible for producing nitric oxide (NO)--a key molecule that can directly (or indirectly) act as a vasodilator and anti-inflammatory mediator. In this review, we examine the structural effects of regulation of the eNOS enzyme, including post-translational modifications and subcellular localization. After production, NO diffuses to surrounding cells with a variety of effects. We focus on the physiological role of NO and NO-derived molecules, including microvascular effects on vessel tone and immune response. Regulation of eNOS and NO action is complicated; we address endogenous and exogenous mechanisms of NO regulation with a discussion of pharmacological agents used in clinical and laboratory settings and a proposed role for eNOS in circulating red blood cells.

Endothelial nitric oxide synthase: From biochemistry and gene structure to clinical implications of NOS3 polymorphisms

Nitric oxide (NO) is an important vasodilator with a well-established role in cardiovascular homeostasis. While mediator is synthesized from L-arginine by neuronal, endothelial, and inducible nitric oxide synthases (NOS1,NOS3 and NOS2 respectively), NOS3 is the most important isoform for NO formation in the cardiovascular system. NOS3 is a dimeric enzyme whose expression and activity are regulated at transcriptional, posttranscriptional,and posttranslational levels. The NOS3 gene, which encodes NOS3, exhibits a number of polymorphic sites including single nucleotide polymorphisms (SNPs), variable number of tandem repeats (VNTRs), microsatellites, and insertions/deletions. Some NOS3 polymorphisms show functional effects on NOS3 expression or activity, thereby affecting NO formation. Interestingly, many studies have evaluated the effects of functional NOS3 polymorphisms on disease susceptibility and drug responses. Moreover, some studies have investigated how NOS3 haplotypes may impact endogenous NO formation and disease susceptibility. In this article,we carried out a comprehensive review to provide a basic understanding of biochemical mechanisms involved in NOS3 regulation and how genetic variations in NOS3 may translate into relevant clinical and pharmacogenetic implications.

A review and discussion of platelet nitric oxide and nitric oxide synthase: do blood platelets produce nitric oxide from L-arginine or nitrite?

The NO/sGC/cGMP/PKG system is one of the most powerful mechanisms responsible for platelet inhibition. In numerous publications, expression of functional NO synthase (NOS) in human and mouse platelets has been reported. Constitutive and inducible NOS isoforms convert L-arginine to NO and L-citrulline. The importance of this pathway in platelets and in endothelial cells for the regulation of platelet function is discussed since decades. However, there are serious doubts in the literature concerning both expression and functionality of NOS in platelets. In this review, we aim to present and critically evaluate recent data concerning NOS expression and function in platelets, and to especially emphasise potential pitfalls of detection of NOS proteins and measurement of NOS activity. Prevailing analytical problems are probably the main sources of contradictory data on occurrence, activity and function of NOS in platelets. In this review we also address issues of how these problems can be resolved. NO donors including organic nitrites (RONO) and organic nitrate (RONO2) are inhibitors of platelet activation. Endogenous inorganic nitrite (NO2 (-)), the product of NO autoxidation, and exogenous inorganic nitrite are increasingly investigated as NO donors in the circulation. The role of platelets in the generation of NO from nitrite is also discussed.

Continuous intravenous infusion of ATP in humans yields large expansions of erythrocyte ATP pools but extracellular ATP pools are elevated only at the start followed by rapid declines

The pharmacokinetics of adenosine 5'-triphosphate (ATP) was investigated in a clinical trial that included 15 patients with advanced malignancies (solid tumors). ATP was administered by continuous intravenous infusions of 8 h once weekly for 8 weeks. Three values of blood ATP levels were determined. These were total blood (erythrocyte) and blood plasma (extracellular) ATP pools along with the initial rate of release of ATP into the blood plasma. We found that values related to erythrocyte ATP pools showed great variability (diversity) among individuals (standard deviation of about 30-40% of mean at baseline). It was discovered that erythrocyte baseline ATP pool sizes are unique to each individual and that they fall within a narrow range in each individual. At the end of an 8 h continuous intravenous infusion of ATP, intracellular erythrocyte ATP pools were increased in the range of 40-60% and extracellular ATP declined from elevated levels achieved at the beginning and middle of the infusion, to baseline levels. The ability of erythrocytes to sequester exogenously administered ATP to this degree, after its initial conversion to adenosine in the blood plasma is unexpected, considering that some of the adenosine is likely to have been degraded by in vivo catabolic activities or taken up by organs. The data suggest that administration of ATP by short-term intravenous infusions, of up to 4 h, may be a favorable way for elevating extracellular ATP pools. A large fraction of the total exogenously administered ATP is sequestered into the intracellular compartments of the erythrocytes after an 8 h intravenous infusion. Erythrocytes loaded with ATP are known to release their ATP pools by the application of previously established agents or conditions applied locally or globally to circulating erythrocytes. Rapid degradation of intravenously administered ATP to adenosine and subsequent accumulation of ATP inside erythrocytes indicate the existence of very effective mechanisms for uptake of adenosine from blood plasma. These in vivo studies offer an understanding as to how both adenosine and ATP can act as purinergic transmission signals. ATP levels in blood are always accompanied by adenosine formed by catabolism of ATP. The continuous uptake of adenosine enables both to act in transmission of sometimes opposite functions.

Macrovascular and microvascular function after implantation of left ventricular assist devices in end-stage heart failure: Role of microparticles

BACKGROUND

The hemodynamic vascular consequences of implanting left ventricular assist devices (LVADs) have not been studied in detail. We investigated the effect of LVAD implantation compared with heart transplant (HTx) on microvascular and macrovascular function in patients with end-stage heart failure and evaluated whether microparticles may play a role in LVAD-related endothelial dysfunction.

METHODS

Vascular function was assessed in patients with end-stage heart failure awaiting HTx, patients who had undergone implantation of a continuous-flow centrifugal LVAD, and patients who had already received a HTx. Macrovascular function was measured by flow-mediated vasodilation (FMD) using high-resolution ultrasound of the brachial artery. Microvascular function was assessed in the forearm during reactive hyperemia using laser Doppler perfusion imaging and pulsed wave Doppler. Age-matched patients without heart failure and without coronary artery disease (CAD) (healthy control subjects) and patients with stable CAD served as control subjects. Circulating red blood cell (CD253(+)), leukocyte (CD45(+)), platelet (CD31(+)/CD41(+)), and endothelial cell (CD31(+)/CD41(-), CD62e(+), CD144(+)) microparticles were determined by flow cytometry and free hemoglobin by enzyme-linked immunosorbent assay.

RESULTS

FMD and microvascular function were significantly impaired in patients with end-stage heart failure compared with healthy control subjects and patients with stable CAD. LVAD implantation led to recovery of microvascular function, but not FMD. In parallel, increased free hemoglobin was observed along with red and white cell microparticles and endothelial and platelet microparticles. This finding indicates destruction of blood cells with release of hemoglobin and activation of endothelial cells. HTx and LVAD implantation led to similar improvements in microvascular function. FMD increased and microparticle levels decreased in patients with HTx, whereas shear stress during reactive hyperemia was similar in patients with LVADs and patients with HTx.

CONCLUSIONS

Our data suggest that LVAD support leads to significant improvements in microvascular perfusion and hemodynamics. However, destruction of blood cells may contribute to residual endothelial dysfunction potentially by increasing nitric oxide scavenging capacity.

Genetic deletion of the GATA1-regulated protein α-synuclein reduces oxidative stress and nitric oxide synthase levels in mature erythrocytes

α-Synuclein is highly expressed in neural tissue and during erythropoiesis, where the key erythroid regulator GATA1 has been found to modulate its expression. While specific α-synuclein (SNCA) mutations are known to cause autosomal dominant familial Parkinson's disease, its wild-type function remains under debate. To investigate the role of α-synuclein in murine hematopoiesis and erythropoiesis, we utilized Snca knock-out mice and analyzed erythroid compartments for maturation defects, in vivo erythrocyte survival, and erythrocyte-based reactive oxygen species (ROS) and nitric oxide synthase (NOS) levels. Our findings show that while bone marrow and spleen erythropoiesis and peripheral blood erythrocyte survival in Snca(-/-) mice was comparable to controls, the levels of ROS and of NOS-2 were significantly decreased in mature erythrocytes in these animals. These results indicate a role for α-synuclein in regulating oxidative stress in erythrocytes in vivo and could open new avenues for the investigation of its function in non-neural tissue.

Nitrosylation of c heme in cd(1)-nitrite reductase is enhanced during catalysis

The reduction of nitrite into nitric oxide (NO) in denitrifying bacteria is catalyzed by nitrite reductase. In several species, this enzyme is a heme-containing protein with one c heme and one d1 heme per monomer (cd1NiR), encoded by the nirS gene. For many years, the evidence of a link between NO and this hemeprotein represented a paradox, given that NO was known to tightly bind and, possibly, inhibit hemeproteins, including cd1NiRs. It is now established that, during catalysis, cd1NiRs diverge from "canonical" hemeproteins, since the product NO rapidly dissociates from the ferrous d1 heme, which, in turn, displays a peculiar "low" affinity for NO (KD=0.11 μM at pH 7.0). It has been also previously shown that the c heme reacts with NO at acidic pH but c heme nitrosylation was not extensively investigated, given that in cd1NiR it was considered a side reaction, rather than a genuine process controlling catalysis. The spectroscopic study of the reaction of cd1NiR and its semi-apo derivative (containing the sole c heme) with NO reported here shows that c heme nitrosylation is enhanced during catalysis; this evidence has been discussed in order to assess the potential of c heme nitrosylation as a regulatory process, as observed for cytochrome c nitrosylation in mammalian mitochondria.

Hemoglobin α in the blood vessel wall

Hemoglobin has been studied and well characterized in red blood cells for over 100 years. However, new work has indicated that the hemoglobin α subunit (Hbα) is also found within the blood vessel wall, where it appears to localize at the myoendothelial junction (MEJ) and plays a role in regulating nitric oxide (NO) signaling between endothelium and smooth muscle. This discovery has created a new paradigm for the control of endothelial nitric oxide synthase activity, nitric oxide diffusion, and, ultimately, vascular tone and blood pressure. This review discusses the current knowledge of hemoglobin׳s properties as a gas exchange molecule in the bloodstream and extrapolates the properties of Hbα biology to the MEJ signaling domain. Specifically, we propose that Hbα is present at the MEJ to regulate NO release and diffusion in a restricted physical space, which would have powerful implications for the regulation of blood flow in peripheral resistance arteries.