Nitric oxide pathway activation and impaired red blood cell deformability with hypercholesterolemia

Nitric oxide bioavailability for red blood cell deformability in the microcirculation: A review of recent progress

The rheological properties of red blood cells (RBCs) play an important role in their microcirculation. RBCs can elastically deform in response to mechanical forces to pass through narrow vessels for effective gas exchange in peripheral tissues. Decreased RBC deformability is observed in lifestyle-related diseases such as diabetes mellitus, hypercholesterolemia, and hypertension, which are pathological conditions linked to increased oxidative stress and decreased nitric oxide (NO) bioavailability. Redox-sensitive cysteine residues on RBC cytoskeletal proteins, such as α- and β-spectrins, responsible for membrane flexibility, are affected by prolonged oxidative stress, leading to reversible and irreversible oxidative modifications and decreased RBC deformability. However, endogenously, and exogenously generated NO protects RBC membrane flexibility from further oxidative modification by shielding redox-sensitive cysteine residues with a glutathione cap. Recent studies have shown that nitrate-rich diets and moderate exercise can enhance NO production to increase RBC deformability by increasing the interplay between RBCs and vascular endothelium-mediated NO bioavailability for microcirculation. This review focuses on the molecular mechanism of RBC- and non-RBC-mediated NO generation, and how diet- and exercise-derived NO exert prophylactic effects against decreased RBC deformability in lifestyle-related diseases with vascular endothelial dysfunction.

A new perspective on NO pathway in sepsis and ADMA lowering as a potential therapeutic approach

The nitric oxide pathway plays a critical role in vascular homeostasis. Increased levels of systemic nitric oxide (NO) are observed in preclinical models of sepsis and endotoxemia. This has led to the postulation that vasodilation by inducible nitric oxide synthase (iNOS) generated NO may be a mechanism of hypotension in sepsis. However, contrary to the expected pharmacological action of a nitric oxide synthase (NOS) inhibitor, clinical studies with L-NAME produced adverse cardiac and pulmonary events, and higher mortality in sepsis patients. Thus, the potential adverse effects of NO in human sepsis and shock have not been fully established. In recent years, the emerging new understanding of the NO pathway has shown that an endogenously produced inhibitor of NOS, asymmetric dimethylarginine (ADMA), a host response to infection, may play an important role in the pathophysiology of sepsis as well as organ damage during ischemia–reperfusion. ADMA induces microvascular dysfunction, proinflammatory and prothrombotic state in endothelium, release of inflammatory cytokines, oxidative stress and mitochondrial dysfunction. High levels of ADMA exist in sepsis patients, which may produce adverse effects like those observed with L-NAME. Several studies have demonstrated the association of plasma ADMA levels with mortality in sepsis patients. Preclinical studies in sepsis and ischemia–reperfusion animal models have shown that lowering of ADMA reduced organ damage and improved survival. The clinical finding with L-NAME and the preclinical research on ADMA “bed to bench” suggest that ADMA lowering could be a potential therapeutic approach to attenuate progressive organ damage and mortality in sepsis. Testing of this approach is now feasible by using the pharmacological molecules that specifically lower ADMA.

A Therapeutic Extracorporeal Device for Specific Removal of Pathologic Asymmetric Dimethylarginine from the Blood

INTRODUCTION

Blood levels of uremic toxin, asymmetric dimethylarginine (ADMA), are strongly associated with mortality in sepsis, renal failure, and cardiovascular and renal disease patients.

METHODS

An extracorporeal approach to reduce pathological ADMA was developed. The dimethylarginine dimethylaminohydrolase (DDAH) was immobilized on agarose beads to prepare a cartridge. The efficacy of cartridge for ADMA lowering in blood was investigated.

RESULTS

The DDAH beads and cartridge reduced ADMA from solution or plasma. The magnitude of ADMA removal was dependent on the quantity of DDAH linked to the beads and the flow rate. When tested in association with plasmapheresis, the DDAH-cartridge was highly effective in ADMA removal from the blood and improved the arginine/ADMA ratio in a pig model.

CONCLUSION

A new, safe, and effective extracorporeal approach to lower ADMA was developed which may have application in improving outcomes in patients with vascular complications and risk of mortality associated with high ADMA.

Protein kinase A activity and NO are involved in the regulation of crucian carp (Carassius carassius) red blood cell osmotic fragility

Activation of the cAMP pathway by β-adrenergic stimulation and cGMP pathway by activation of guanylate cyclase substantially affects red blood cell (RBC) membrane properties in mammals. However, whether similar mechanisms are involved in RBC regulation of lower vertebrates, especially teleosts, is not elucidated yet. In this study, we evaluated the effects of adenylate cyclase activation by epinephrine and forskolin, guanylate cyclase activation by sodium nitroprusside, and the role of Na⁺/H⁺-exchanger in the changes of osmotic fragility and regulatory volume decrease (RVD) response in crucian carp RBCs. Western blot analysis of protein kinase A and protein kinase G substrate phosphorylation revealed that changes in osmotic fragility were regulated via the protein kinase A, but not protein kinase G signaling pathway. At the same time, the RVD response in crucian carp RBCs was not affected either by activation of adenylate or guanylate cyclase. Adenylate cyclase/protein kinase A activation significantly decreased RBC osmotic fragility, i.e., increased cell rigidity. Inhibition of Na⁺/H⁺-exchanger by amiloride had no effect on the epinephrine-mediated decrease of RBC osmotic fragility. NO donor SNP did not activate guanylate cyclase, however affected RBCs osmotic fragility by protein kinase G-independent mechanisms. Taken together, our data demonstrated that the cAMP/PKA signaling pathway and NO are involved in the regulation of crucian carp RBC osmotic fragility, but not in RVD response. The authors confirm that the study has no clinical trial.

Stepwise immobilization of keratin-dopamine conjugates and gold nanoparticles on PET sheets for potential vascular graft with the catalytic generation of nitric oxide

Gold nanoparticles(AuNPs) are capable to catalyze the nitric oxide (NO) generation from endogenous and exogenous donors, thereby promoting re-endothelialization and inhibiting intimal hyperplasia and thrombosis. Herein, keratin-dopamine conjugates were synthesized and then immobilized on the surface of the pre-aminolyzed poly(ethylene terephthalate) (PET) via self-polymerization of dopamine residue, following by the formation of AuNPs in situ without extra reductant. The modified PET sheets(PET-AuNPs) could promote the growth of HUVECs while inhibit the proliferation of HUASMCs due to their catalytic generation of NO from GSNO. In addition, these sheets exhibited antibacterial properties and good blood compatibility without hemolysis. Taken together, this strategy for designing prosthetic vascular grafts to treat cardiovascular diseases has great potential.

Cardiovascular Disorders Triggered by Obstructive Sleep Apnea-A Focus on Endothelium and Blood Components

Obstructive sleep apnea (OSA) is known to be an independent cardiovascular risk factor. Among arousal from sleep, increased thoracic pressure and enhanced sympathetic activation, intermittent hypoxia is now considered as one of the most important pathophysiological mechanisms contributing to the development of endothelial dysfunction. Nevertheless, not much is known about blood components, which justifies the current review. This review focuses on molecular mechanisms triggered by sleep apnea. The recurrent periods of hypoxemia followed by reoxygenation promote reactive oxygen species (ROS) overproduction and increase inflammatory response. In this review paper we also intend to summarize the effect of treatment with continuous positive airway pressure (CPAP) on changes in the profile of the endothelial function and its subsequent potential clinical advantage in lowering cardiovascular risk in other comorbidities such as diabetes, atherosclerosis, hypertension, atrial fibrillation. Moreover, this paper is aimed at explaining how the presence of OSA may affect platelet function and exert effects on rheological activity of erythrocytes, which could also be the key to explaining an increased risk of stroke.

Stress erythropoiesis in atherogenic mice

Bone marrow erythropoiesis is mainly homeostatic and a demand of oxygen in tissues activates stress erythropoiesis in the spleen. Here, we show an increase in the number of circulating erythrocytes in apolipoprotein E-/- mice fed a Western high-fat diet, with similar number of circulating leukocytes and CD41+ events (platelets). Atherogenic conditions increase spleen erythropoiesis with no variations of this cell lineage in the bone marrow. Spleens from atherogenic mice show augmented number of late-stage erythroblasts and biased differentiation of progenitor cells towards the erythroid cell lineage, with an increase of CD71+CD41CD34-CD117+Sca1-Lin- cells (erythroid-primed megakaryocyte-erythroid progenitors), which is consistent with the way in which atherogenesis modifies the expression of pro-erythroid and pro-megakaryocytic genes in megakaryocyte-erythroid progenitors. These data explain the transiently improved response to an acute severe hemolytic anemia insult found in atherogenic mice in comparison to control mice, as well as the higher burst-forming unit-erythroid and colony forming unit-erythroid capacity of splenocytes from atherogenic mice. In conclusion, our work demonstrates that, along with the well stablished enhancement of monocytosis during atherogenesis, stress erythropoiesis in apolipoprotein E-/- mice fed a Western high fat diet results in increased numbers of circulating red blood cells.

Hypercholesterolemia and hypertriglyceridemia as biochemical markers of disease in companion rabbits

BACKGROUND

Inflammation has important effects on lipid metabolism, but the relationship between hyperlipidemia, inflammation, and disease remains unknown in rabbits. While rabbits are sensitive to dietary hypercholesterolemia, the etiology of hyperlipidemia when fed non-atherogenic diets is uncertain.

OBJECTIVES

This study aimed to determine the association between hypercholesterolemia and patient characteristics, diseases, and select CBC and biochemistry analytes in rabbits, and to measure plasma lipoprotein lipid fractions in rabbits with inflammatory and other diseases.

METHODS

Complete blood count and plasma biochemistry data, including total cholesterol concentrations, were evaluated in 531 companion rabbits. Lipoprotein cholesterol fractions (non-high-density lipoprotein cholesterol [non-HDLc] and high-density lipoprotein [HDLc]) and triglycerides were measured using a colorimetric enzymatic assay in archived plasma from a subset of 267 rabbits. Rabbits were categorized by age, sex, spay/neuter status, breed, diet status (fed atherogenic dietary components or not), the organ system affected by disease, and the pathologic process.

RESULTS

Cholesterol was associated with fibrinogen (P = 0.01), globulins (P < 0.01), and heterophil (P < 0.01) concentrations. Adjusting for diet, rabbits with severe infection or sepsis (odds ratio [OR] = 13.25, 95% CI = 5.83-30.12), renal failure (OR = 14.42, 95% CI = 5.69-36.54), and hepatopathy (OR = 8.55, 95% CI = 3.55-20.62) had increased risks of hypercholesterolemia. Increased non-HDLc and triglyceride concentrations were also associated with these three disease states (P < 0.05).

CONCLUSIONS

Hyperlipidemia is associated with biochemical and CBC markers of inflammation, and with severe infection or sepsis, renal failure, and hepatopathy. Independent of diet, increased cholesterol, non-HDLc, and triglycerides are indicators of disease in companion rabbits.

Chitosan treatment abrogates hypercholesterolemia-induced erythrocyte's arginase activation

This study aimed to evaluate the protective effect of chitosan (CS) against hypercholesterolemia (HC) induced arginase activation and disruption of nitric oxide (NO) biosynthesis using erythrocytes as cellular model. Human erythrocytes were isolated and classified into eight groups. Next, cells were treated with l-arginine (l-ARG), N^ω-nitro-l-arginine methyl ester (l-NAME), CS or CS + l-ARG in the presence of normal plasma or cholesterol enriches plasma. Then, erythrocytes were incubated at 37 °C for 24 h. The present results revealed that, HC induced significant increase of cholesterol inclusion into erythrocytes membrane compared to control. Moreover, HC caused significant decrease in nitric oxide synthase (NOS) activity similar to l-NAME; however, arginase activity and arginase/NOS ratio significantly increased compared to control. On contrast, treatment of HC with, l-arginine, CS or CS plus l-arginine prevents HC induced cholesterol loading into erythrocytes membrane, NOS inhibition and arginase activation. This study suggested that CS could be protective agent against HC induced disruption of erythrocyte’s oxidative status and arginase activation.

Poikilocytosis in rabbits: prevalence, type, and association with disease

Rabbits (Oryctolagus cuniculus) are a popular companion animal, food animal, and animal model of human disease. Abnormal red cell shapes (poikilocytes) have been observed in rabbits, but their significance is unknown. The objective of this study was to investigate the prevalence and type of poikilocytosis in pet rabbits and its association with physiologic factors, clinical disease, and laboratory abnormalities. We retrospectively analyzed blood smears from 482 rabbits presented to the University of California-Davis Veterinary Medical Teaching Hospital from 1990 to 2010. Number and type of poikilocytes per 2000 red blood cells (RBCs) were counted and expressed as a percentage. Acanthocytes (>3% of RBCs) were found in 150/482 (31%) rabbits and echinocytes (>3% of RBCs) were found in 127/482 (27%) of rabbits, both healthy and diseased. Thirty-three of 482 (7%) rabbits had >30% acanthocytes and echinocytes combined. Mild to moderate (>0.5% of RBCs) fragmented red cells (schistocytes, microcytes, keratocytes, spherocytes) were found in 25/403 (6%) diseased and 0/79 (0%) healthy rabbits (P = 0.0240). Fragmentation and acanthocytosis were more severe in rabbits with inflammatory disease and malignant neoplasia compared with healthy rabbits (P<0.01). The % fragmented cells correlated with % polychromasia, RDW, and heterophil, monocyte, globulins, and fibrinogen concentrations (P<0.05). Echinocytosis was significantly associated with renal failure, azotemia, and acid-base/electrolyte abnormalities (P<0.05). Serum cholesterol concentration correlated significantly with % acanthocytes (P<0.0001), % echinocytes (P = 0.0069), and % fragmented cells (P = 0.0109), but correlations were weak (Spearman ρ <0.02). These findings provide important insights into underlying pathophysiologic mechanisms that appear to affect the prevalence and type of naturally-occurring poikilocytosis in rabbits. Our findings support the need to carefully document poikilocytes in research investigations and in clinical diagnosis and to determine their diagnostic and prognostic value.

Blood viscosity as a sensitive indicator for paclitaxel induced oxidative stress in human whole blood

In this study, the in vitro effects of paclitaxel (PTX) and Cremophor-EL (CrEL) on blood viscosity and oxidative stress markers were investigated. Whole-blood samples were collected from healthy volunteers and co-incubated with PTX, CrEL or their combination then compared with control blood samples. After a 24 h incubation time, the whole-blood viscosity (WBV), erythrocyte sedimentation rate (ESR), levels of whole-blood malondialdehyde (MDA), protein carbonyl content (PCC) and reduced glutathione (GSH) were determined. Moreover, plasma nitrite and plasma sialic acid (SA) values were measured. The present results revealed that the incubation of blood samples with PTX, CrEL or PTX plus CrEL significantly increased the values of WBV, ESR, MDA and PCC compared to control samples. In contrast, a significant decrease in levels of GSH, SA and nitrite was observed after incubation of blood samples with tested agents compared to control. The effects of tested agents on the measured parameters were more pronounced in the case of blood samples treated with PTX plus CrEL. The present study demonstrates that PTX-induced oxidative stress is associated with an increase of WBV.

Reduced erythrocyte deformability associated with hypoargininemia during Plasmodium falciparum malaria

The mechanisms underlying reduced red blood cell (RBC) deformability during Plasmodium falciparum (Pf) malaria remain poorly understood. Here, we explore the possible involvement of the L-arginine and nitric oxide (NO) pathway on RBC deformability in Pf-infected patients and parasite cultures. RBC deformability was reduced during the acute attack (day0) and returned to normal values upon convalescence (day28). Day0 values correlated with plasma L-arginine levels (r = 0.69; p = 0.01) and weakly with parasitemia (r = −0.38; p = 0.006). In vitro, day0 patient's plasma incubated with ring-stage cultures at 41°C reduced RBC deformability, and this effect correlated strongly with plasma L-arginine levels (r = 0.89; p < 0.0001). Moreover, addition of exogenous L-arginine to the cultures increased deformability of both Pf-free and trophozoite-harboring RBCs. NO synthase activity, evidenced in Pf-infected RBCs, induced L-arginine-dependent NO production. These data show that hypoargininemia during P.falciparum malaria may altogether impair NO production and reduce RBC deformability, particularly at febrile temperature.

Xuezhikang, extract of red yeast rice, improved abnormal hemorheology, suppressed caveolin-1 and increased eNOS expression in atherosclerotic rats

Background

Xuezhikang is the extract of red yeast rice, which has been widely used for the management of atherosclerotic disease, but the molecular basis of its antiatherosclerotic effects has not yet been fully identified. Here we investigated the changes of eNOS in vascular endothelia and RBCs, eNOS regulatory factor Caveolin-1 in endothelia, and hemorheological parameters in atherosclerotic rats to explore the protective effects of Xuezhikang.

Methodology/Principal Findings

Wistar rats were divided into 4 groups (n = 12/group) group C, controls; group M, high-cholesterol diet (HCD) induced atherosclerotic models; group X, HCD+Xuezhikang; and group L, HCD +Lovastatin. In group X, Xuezhikang inhibited oxidative stress, down-regulated caveolin-1 in aorta wall (P<0.05), up-regulated eNOS expression in vascular endothelia and erythrocytes (P<0.05), increased NOx (nitrite and nitrate) in plasma and cGMP in erythrocyte plasma and aorta wall (P<0.05), increased erythrocyte deformation index (EDI), and decreased whole blood viscosity and plasma viscosity (P<0.05), with the improvement of arterial pathology.

Conclusions/Significance

Xuezhikang up-regulated eNOS expression in vascular endothelia and RBCs, increased plasma NOx and improved abnormal hemorheology in high cholesterol diet induced atherosclerotic rats. The elevated eNOS/NO and improved hemorheology may be beneficial to atherosclerotic disease.

Nitric oxide influences red blood cell velocity independently of changes in the vascular tone

Nitric oxide (NO) plays a key role in regulation of vascular tone and blood flow. In the microcirculation blood flow is strongly dependent on red blood cells (RBC) deformability. In vitro NO increases RBC deformability. This study hypothesized that NO increases RBC velocity in vivo not only by regulating vascular tone, but also by modifying RBC deformability. The effects of NO on RBC velocity were analysed by intra-vital microscopy in the microcirculation of the chorioallantoic membrane (CAM) of the avian embryo at day 7 post-fertilization, when all vessels lack smooth muscle cells and vascular tone is not affected by NO. It was found that inhibition of enzymatic NO synthesis and NO scavenging decreased intracellular NO levels and avian RBC deformability in vitro. Injection of a NO synthase-inhibitor or a NO scavenger into the microcirculation of the CAM decreased capillary RBC velocity and deformation, while the diameter of the vessels remained constant. The results indicate that scavenging of NO and inhibition of NO synthesis decrease RBC velocity not only by regulating vascular tone but also by decreasing RBC deformability.

Quantification of arginine and its metabolites in human erythrocytes using liquid chromatography-tandem mass spectrometry

Erythrocytes may affect several physiological processes because they are scavengers, vehicles, and (as recently highlighted) a producer of nitric oxide (NO). NO bioavailability is linked to arginine, its metabolic products ornithine and citrulline, and methylarginines. Here we describe a liquid chromatography-tandem mass spectrometry method for the simultaneous quantification of analytes involved in the Arg/NO metabolic pathway in erythrocytes. Calibration functions were linear, and the interday coefficients of variation were less than 10%. Limit of quantification values make this method suitable for low concentration samples. The method presented here allows easy sample preparation and provides a valuable tool for the evaluation of the Arg/NO metabolic pathway in erythrocytes.