Effects of nitric oxide on red blood cell deformability

Hawthorn special extract WS® 1442 increases red blood cell NO-formation without altering red blood cell deformability

WS(®) 1442 is a special extract of hawthorn leaves with flowers used for the treatment of mild cardiac failure. The activation of endothelial nitric oxide synthase (eNOS) has been shown to contribute to its vasodilating properties. Quite recently it has been demonstrated that red blood cells (RBCs) express a functional NO-synthase (rbcNOS) and rbcNOS activation has been associated with increased RBC deformability. The aim of the present study was to determine whether WS(®) 1442 is able to activate rbcNOS, to induce NO-formation in RBC and to alter RBC-deformability. Blood from healthy volunteers was incubated with WS(®) 1442 (25-100 μg/ml) for up to 30 min. RbcNOS activation was detected by immunohistochemical staining of phosphorylated rbcNOS and NO-formation was examined by diaminofluorescein (DAF) fluorescence. RBC deformability was measured by a laser assisted optical rotational cell analyzer. Serine 1177 of RbcNOS (rbcNOS Ser(1177)) was time- and concentration-dependently phosphorylated by WS(®) 1442. Rates of rbcNOS Ser(1177) phosphorylation were up to 149% higher in RBCs treated with WS(®) 1442 in comparison to control (DMSO 0.05%). WS(®) 1442 induced a time-dependent increase in NO-formation in RBCs which reached its maximum after 5 min. An increase in shear stress (0.3-50 Pa) caused an increase in RBC deformability. WS(®) 1442 did not change either basal or maximal RBC-deformability or shear stress sensitivity of RBC at normoxia.

CONCLUSION

WS(®) 1442 activates rbcNOS and causes NO-formation in RBCs. WS(®) 1442-dependent NO-formation however does not affect RBC-deformability at normoxia.

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.

Shear stress activation of nitric oxide synthase and increased nitric oxide levels in human red blood cells

Red blood cells (RBC) play an important role in the balance between generation and scavenging of nitric oxide (NO) and hence its local bioavailability and influence on vasomotor control. Previous studies have reported increased NO levels in RBC suspensions subsequent to exposure to shear forces; the present study was designed to further investigate changes in intracellular NO concentration and possible mechanisms involved for RBC exposed to well-controlled shear forces. Attached human RBC were subjected to shear stresses up to 0.1Pa in a parallel-plate flow channel; fluorescent methods were used to monitor changes in intracellular NO and calcium concentrations. Intracellular NO concentration, estimated by the fluorescence level of 4-amino-5-methylamino-2',7'-difluorofluorescein diacetate (DAF-FM), increased sharply within 30s following the application of shear stress between 0.013 and 0.1Pa. This increase was only partially prevented by the absence of l-arginine and by the presence of l-N-acetyl-methyl-arginine (L-NAME), strongly suggesting that this response was in part related to the activation of NO-synthase (NOS) enzyme. The increase in intracellular NO concentration under shear stress was also inhibited by calcium chelation in the suspending medium, indicating the role of calcium entry for NOS activation. Increases of intracellular calcium concentrations under the same shearing conditions were demonstrated by monitoring Fluo-3/AM fluorescence in RBC exposed to shear stress. Serine 1177 phosphorylated NOS protein, the activated form of the enzyme determined by immunohistochemistry, was found to be significantly increased following the exposure of RBC to 0.1Pa shear stress for 1min. These data confirm that RBC possess a NOS enzyme that is actively synthesizing NO and activated by effective shear forces. The data also suggest that there may be additional (e.g., non-enzymatic) NO generating mechanisms in RBC that are also enhanced under shear stress.

Increased erythrocyte antioxidant status protects against smoking induced hemolysis in moderate smokers

Cigarette smoking is common in societies worldwide and has been identified as injurious to human health. Human red blood cells are important targets for electrophilic and oxidant foreign compounds. In the present study, the possible role of antioxidant status on smoking-induced erythrocyte hemolysis of smokers was studied. Erythrocyte superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) activities, reduced glutathione (GSH) level, erythrocyte membrane lipid peroxidation, total cholesterol and phospholipids were determined. Further, nitrite/nitrate levels (NO2/NO3) in both plasma and erythrocyte lysate were measured. Results showed increased plasma and erythrocyte membrane lipid peroxidation and nitrite/nitrate levels in smokers. The activities of SOD, CAT and GPx were also increased with reduced glutathione (GSH) level in smokers. No significant change was observed in smokers red cell hemolysis and cholesterol/phospholipid (C/P) ratio compared to controls. Erythrocyte membrane lipid peroxidation was positively correlated with SOD ( r = 0.482, p < 0.01) and GPx ( r = 0.368, p < 0.018) in smokers. Increased levels of nitrite/nitrate and antioxidant status of erythrocytes might be playing a crucial role in protecting red cell from free radical damage induced by cigarette smoke.

Chronic cigarette smoking alters erythrocyte membrane lipid composition and properties in male human volunteers

Cigarette smoking is a major lifestyle factor influencing the health of human beings. The present study investigates smoking induced alterations on the erythrocyte membrane lipid composition, fluidity and the role of nitric oxide. Thirty experimental and control subjects (age 35+/-8) were selected for the study. Experimental subjects smoke 12+/-2 cigarettes per day for 7-10 years. In smokers elevated nitrite/nitrate levels in plasma and red cell lysates were observed. Smokers showed increased hemolysis, erythrocyte membrane lipid peroxidation, protein carbonyls, C/P ratio (cholesterol and phospholipid ratio), anisotropic (gamma) value with decreased Na(+)/K(+)-ATPase activity and sulfhydryl groups. Alterations in smokers erythrocyte membrane individual phospholipids were also evident from the study. Red cell lysate nitric oxide positively correlated with C/P ratio (r=0.565) and fluorescent anisotropic (gamma) value (r=0.386) in smokers. Smoking induced generation of reactive oxygen/nitrogen species might have altered erythrocyte membrane physico-chemical properties.

Hydroxyurea stimulates the release of ATP from rabbit erythrocytes through an increase in calcium and nitric oxide production

Hydroxyurea, a proven therapy for sickle cell disease, is known to improve blood flow and reduce vaso-occlusive crises, although its exact mechanism of action is not clear. The objective of this study was to determine if hydroxyurea results in an increase of ATP release from the red blood cell (RBC) via the drug's ability to stimulate nitric oxide (NO) production in these cells. A system enabling the flow of RBCs through microbore tubing was used to investigate ATP release from the RBC. Incubation of rabbit RBCs (7% hct) with 50 microM hydroxyurea resulted in a significant increase in the release of ATP from these cells. This level of ATP release was not detected in the absence of flow. Studies also showed that increments in hydroxyurea and NO (from spermine NONOate) resulted in an initial increase in ATP release, followed by a decrease in this release at higher concentrations of hydroxyurea and the NO donor. Incubation with L-NAME abolished the effect of the hydroxyurea, suggesting that NO production by the RBC was involved. Indeed, in the presence of 50 microM hydroxyurea, the amount of total Ca(2+) measured (by atomic absorption spectroscopy) in a 7% solution of RBCs increased from 363+/-47 ng/ml and 530+/-52 ng/ml. Finally, EPR studies suggest that an increase in nitrosylated Hb in the RBC is only measured for those studies involving hydroxyurea and a Ca(2+)-containing buffer.

A clinical cardiology perspective of thrombophilias

Thrombophilias, an inherited and/or acquired predisposition to vascular thrombosis beyond hemostatic needs are common in cardiovascular medicine and include systemic disorders such as coronary atherosclerosis, atrial fibrillation, exogenous obesity, metabolic syndrome, collagen vascular disease, human immunodeficiency virus, blood replacement therapy and several commonly used medications. A contemporary approach to patients with suspected thrombophilias, in addition to a very selective investigation for gain-of-function and loss-of-function gene mutations affecting thromboresistance, must consider prevalent diseases and management decisions encountered regularly by cardiologists in clinical practice. An appropriate recognition of common disease states as thrombophilias will also stimulate platforms for much needed scientific investigation.

High fat diets modulate nitric oxide biosynthesis and antioxidant defence in red blood cells from C57BL/6 mice

The consumption of a high fat (HF) diet is considered a risk factor for the development of obesity. On the other hand, a monounsaturated HF diet has beneficial cardiometabolic effects. Since nitric oxide (NO) modulates vascular homeostasis, we investigate whether HF diets that vary in fatty acid composition have a different effect on theL-arginine-NO pathway and oxidative stress in C57BL/6 mice red blood cells (RBC). The olive oil diet induced an activation of L-arginine transport compared to other diets. NO synthase (NOS) activity was increased in all unsaturated HF diets (olive, sunflower and canola oils). Moreover, the expression of endothelial NOS (eNOS) and inducible NOS (iNOS) was increased in the olive oil group. In contrast, NOS activity from the lard group was decreased associated with diminished l-arginine transport. Olive oil also induced superoxide dismutase activation. Inhibition of the L-arginine-NO pathway in the lard group could contribute to cardiovascular diseases, while unsaturated HF diets may have a protector effect via enhanced NO bioavailability.

Erythrocyte deformability and nitric oxide metabolites in athletes before and after a cardiopulmonary test

OBJECTIVE

To evaluate erythrocyte deformability, nitric oxide metabolites, and their modifications induced by exercise in athletes who practised different sports.

DESIGN

This evaluation was effected before and after cardiopulmonary test, using a cycloergometer.

SETTING

The study was performed in the Department of Internal Medicine, Cardiovascular and Renal Diseases of the University of Palermo.

PARTICIPANTS

We enrolled 62 male athletes who practised endurance (n = 23), mixed (n = 20), and power (n = 19) sports and 20 sedentary male subjects as controls.

ASSESSMENT OF RISK FACTORS

No subject had diabetes or hypertension or dyslipidemia. Five control subjects and 14 athletes were smokers.

MAIN OUTCOME MEASURES

Erythrocyte deformability was examined as elongation index (EI) using a diffractometer. The nitric oxide metabolites (nitrite + nitrate = NOx) were evaluated employing the Griess reagent.

RESULTS

In the whole group, an increase in EI and NOx was present. Subdividing the whole group into 3 subgroups, we noted an increase in EI and NOx only in endurance and mixed athletes. The EI before and after the cardiopulmonary test significantly decreased in the whole group and in power athletes but not in endurance and mixed athletes. Before and after the test, NOx did not significantly change in the whole group and in the 3 subgroups.

CONCLUSIONS

In athletes who practised endurance and mixed sports, we observed an increase of NOx level and an increase of erythrocyte deformability. The latter did not change after an exercise test in the same subgroups, whereas it decreased in power athletes.

Effect of 3,4,5,6-tetrahydroxyxanthone on erythrocyte deformability in apolipoprotein E-deficient mice

Previous investigations have indicated that reduced erythrocyte deformability may be an important factor contributing to the development of atherosclerosis, and endogenous asymmetric dimethylarginine (ADMA) might be an important contributor to reduction of erythrocyte deformability in atherosclerosis. In this study, the effect of 3,4,5,6-tetrahydroxyxanthone (1), a kind of polyphenolic compound, on erythrocyte deformability in apolipoprotein E-deficient (apoE-/-) mice was evaluated. After treatment with compound 1 (10 or 20 mg/kg per day) for 4 weeks, erythrocyte deformability, antioxidant enzymes activity, erythrocyte dimethylarginine dimethylaminohydrolase (DDAH) activity, the plasma level of ADMA and malondialdehyde (MDA) level were determined. Treatment with compound 1 (10 or 20 mg/kg) increased erythrocyte deformability, antioxidant enzymes activity concomitantly, a decrease in the plasma levels of MDA and ADMA, and an increase in erythrocyte DDAH activity. The present result suggests that the beneficial effect of 1 on the erythrocyte deformability, besides inhibiting lipid peroxidation, may be related to reduction of ADMA concentration via an increase in DDAH activity.

Role of hemoglobin oxygenation in the modulation of red blood cell mechanical properties by nitric oxide

It has been previously demonstrated that both externally generated and internally synthesized nitric oxide (NO) can affect red blood cell (RBC) deformability. Further studies have shown that the RBC has active NO synthesizing mechanisms and that these mechanisms may play role in maintaining normal RBC mechanical properties. However, hemoglobin within the RBC is known to be a potent scavenger of NO; oxy-hemoglobin scavenges NO faster than deoxy-hemoglobin via the dioxygenation reaction to nitrate. The present study aimed at investigating the role of hemoglobin oxygenation in the modulation of RBC rheologic behavior by NO. Human blood was obtained from healthy volunteers, anticoagulated with sodium heparin (15 IU/mL), and the hematocrit was adjusted to 0.4 L/L by adding or removing autologous plasma. Several two mL aliquots of blood were equilibrated at room temperature (22+/-2 degrees C) with moisturized air or 100% nitrogen by a membrane gas exchanger, The NO donor sodium nitroprusside (SNP), at a concentration range of 10(-7)-10(-4)M, was added to the equilibrated aliquots which were maintained under the same conditions for an additional 60 min. The effect of the non-specific NOS inhibitor l-NAME was also tested at a concentration of 10(-3)M. RBC deformability was measured using an ektacytometer with an environment corresponding to that used for the prior incubation (i.e., oxygenated or deoxygenated). Our results indicate an improvement of RBC deformability with the NO donor SNP that was much more pronounced in the deoxygenated aliquots. SNP also had a more pronounced effect on RBC aggregation for deoxygenated RBC. Conversely, l-NAME had no effect on deoxygenated blood but resulted in impaired deformability, with no change in aggregation for oxygenated blood. These findings can be explained by a differential behavior of hemoglobin under oxygenated and deoxygenated conditions; the influence of oxygen partial pressure on NOS activity may also play a role. It is therefore critical to consider the oxygenation state of intracellular hemoglobin while studying the role of NO as a regulator of RBC mechanical properties.

Effect of thrombocytapheresis on blood rheology in healthy donors: role of nitric oxide

Platelet transfusions are increasingly being used to treat thrombocytopenic conditions. Because of anticoagulation, changes in blood composition and extracorporeal circulation, donor apheresis may cause alterations in hemorheology. This study aimed at investigating the effects of thrombocytapheresis on donor blood rheology. The effect of nitric oxide (NO) on donor red blood cell (RBC) deformability after thrombocytapheresis was also studied. Platelets were collected by a Haemonetics MCS 3p cell seperator. Blood samples were obtained before and 15 min after thrombocytapheresis. RBC deformability and aggregation were measured using an ektacytometer, whole blood viscosity (WBV) was determined with a cone-plate rotational viscometer. Donor RBCs were shown to be less deformable at all stress levels except 0.30 Pa after thrombocytapheresis and NO donor sodium nitroprusside (SNP, 10(-6) M) reversed the reduced deformability caused by thrombocytapheresis. It was observed that donor apheresis induces a decrement in RBC aggregation and WBV measured at standard hematocrit (Hct). No significant alterations were observed in WBV values determined at native Hct values. Thrombocytapheresis also resulted in a decrement in fibrinogen, total protein, cholesterol and albumin levels whereas Hct was found to be increased and serum glucose, triglyceride, hemoglobin levels unaltered after apheresis. These results suggest that, thrombocytapheresis causes alterations in hemorheological parameters and hence in the perfusion of the microvasculature of the donors and NO appears to have a protective effect on the impairment observed in RBC deformability.

Oxygen-dependent ion transport in erythrocytes

The present contribution reviews current knowledge of apparently oxygen-dependent ion transport in erythrocytes and presents modern hypotheses on their regulatory mechanisms and physiological roles. In addition to molecular oxygen as such, reactive oxygen species, nitric oxide, carbon monoxide, regional variations of cellular ATP and hydrogen sulphide may play a role in the regulation of transport, provided that they are affected by oxygen tension. It appears that the transporter molecules themselves do not have direct oxygen sensors. Thus, the oxygen level must be sensed elsewhere, and the effect transduced to the transporter. The possible pathways involved in the regulation of transport, including haemoglobin as a sensor, and phosphorylation/dephosphorylation reactions both in the transporter and its upstream effectors, are discussed.

Nitric oxide production pathways in erythrocytes and plasma

Nitric oxide (NO) is a potent regulator of vascular tone and hemorheology. The signaling function of NO was largely unappreciated until approximately 30 years ago, when the endothelium-derived relaxing factor (EDRF) was identified as NO. Since then, NO from the endothelium has been considered the major source of NO in the vasculature and a contributor to the paracrine regulation of blood hemodynamics. Because NO is highly reactive, and its half-life in vivo is only a few seconds (even less in the bloodstream), any NO bioactivity derived from the intraluminal region has traditionally been considered insignificant. However, the availability and significance of NO signaling molecules derived from intraluminal sources, particularly erythrocytes, have gained attention in recent years. Multiple potential sources of NO bioactivity have been identified in the blood, but unresolved questions remain concerning these proposed sources and how the NO released via these pathways actually interacts with intravascular and extravascular targets. Here we review the hypotheses that have been put forward concerning blood-borne NO and its contribution to hemorheological properties and the regulation of vascular tone, with an emphasis on the quantitative aspects of these processes.

Intensive exercise induces changes of endothelial nitric oxide synthase pattern in human erythrocytes

The synthesis of nitric oxide (NO) in the circulation has been attributed exclusively to the vascular endothelium, especially to endothelial cells. Recently, it has been demonstrated that red blood cells (RBCs) express the endothelial NOS isoform (eNOS). In addition, RBCs have been assumed to metabolize large quantities of NO due to their high content of hemoglobin. In addition to its known action on endothelial cells, NO seems to possess cardiovascular effects via regulation of RBC deformability. To get a better understanding of the question whether RBCs endothelial NOS (eNOS) is affected by intensive exercise undertaken by elite athletes, the present study aimed to investigate eNOS content, activated eNOS, phosphorylation states of eNOS (eNOSSer(116), eNOSSer(1177), eNOSThr(495)) and nitrotyrosine in erythrocytes of international-class field hockey players following a two-day long intensive training camp. Blood samples were taken before and immediately after the training camp. The athletes were required to complete at least two training sessions per day. The results showed that eNOS content, activated eNOS, eNOSSer(1177), and nitrotyrosine were significantly (p<0.05) down-regulated after the training camp. In contrast, eNOSSer(116), and eNOSThr(495) did not show significant changes, although eNOSThr(495) (p=0.081) tended to decrease. Hemoglobin and hematocrit were significantly decreased after training camp. In conclusion, this study gains new insights into a possible down-regulation of eNOS and NO production in human RBCs following high intensity exercises. It can be speculated that the reduction of eNOS and the combined reduction of eNOS activity influence erythrocyte deformability and lead subsequently to a rheological impairment.

RBC NOS: regulatory mechanisms and therapeutic aspects

Nitric oxide (NO), one of the most important vascular signaling molecules, is primarily produced by endothelial NO synthase (eNOS). eNOS is tightly regulated by its substrate l-arginine, cofactors and diverse interacting proteins. Interestingly, an NO synthase (NOS) was described within red blood cells (RBC NOS), and it was recently shown to significantly contribute to the intravascular NO pool and to regulate physiologically relevant mechanisms. However, the regulatory mechanisms and clinical implications of RBC NOS are unknown. The aim of this review is to highlight intracellular RBC NOS interactions and the role of RBC NOS in RBC homeostasis. Furthermore, macro- and microvascular diseases affected by RBC-derived NO are discussed.

C-peptide and its C-terminal fragments improve erythrocyte deformability in type 1 diabetes patients

Aims/hypothesis. Data now indicate that proinsulin C-peptide exerts important physiological effects and shows the characteristics of an endogenous peptide hormone. This study aimed to investigate the influence of C-peptide and fragments thereof on erythrocyte deformability and to elucidate the relevant signal transduction pathway. Methods. Blood samples from 23 patients with type 1 diabetes and 15 matched healthy controls were incubated with 6.6 nM of either human C-peptide, C-terminal hexapeptide, C-terminal pentapeptide, a middle fragment comprising residues 11–19 of C-peptide, or randomly scrambled C-peptide. Furthermore, red blood cells from 7 patients were incubated with C-peptide, penta- and hexapeptides with/without addition of ouabain, EDTA, or pertussis toxin. Erythrocyte deformability was measured using a laser diffractoscope in the shear stress range 0.3–60 Pa. Results. Erythrocyte deformability was impaired by 18–25% in type 1 diabetic patients compared to matched controls in the physiological shear stress range 0.6–12 Pa (P < .01–.001). C-peptide, penta- and hexapeptide all significantly improved the impaired erythrocyte deformability of type 1 diabetic patients, while the middle fragment and scrambled C-peptide had no detectable effect. Treatment of erythrocytes with ouabain or EDTA completely abolished the C-peptide, penta- and hexapeptide effects. Pertussis toxin in itself significantly increased erythrocyte deformability. Conclusion/interpretation. C-peptide and its C-terminal fragments are equally effective in improving erythrocyte deformability in type 1 diabetes. The C-terminal residues of C-peptide are causally involved in this effect. The signal transduction pathway is Ca²⁺-dependent and involves activation of red blood cell Na⁺, K⁺-ATPase.

Neither a nitric oxide donor nor potassium channel blockage inhibit RBC mechanical damage induced by a roller pump

Red blood cells (RBC) are exposed to various levels of shear stresses when they are exposed to artificial flow environments, such as extracorporeal flow circuits and hemodialysis equipment. This mechanical trauma affects RBC and the resulting effect is determined by the magnitude of shear forces and exposure time. It has been previously demonstrated that nitric oxide (NO) donors and potassium channel blockers could prevent the sub-hemolytic damage to RBC, when they are exposed to 120 Pa shear stress in a Couette shearing system. This study aimed at testing the effectiveness of NO donor sodium nitroprussid (SNP, 10^-4 M) and non-specific potassium channel blocker tetraethylammonium (TEA, 10^-7 M) in preventing the mechanical damage to RBC in a simple flow system including a roller pump and a glass capillary of 0.12 cm diameter. RBC suspensions were pumped through the capillary by the roller pump at a flow rate that maintains 200 mmHg hydrostatic pressure at the entrance of the capillary. An aliquot of 10 ml of RBC suspension of 0.4 L/L hematocrit was re-circulated through the capillary for 30 minutes. Plasma hemoglobin concentrations were found to be significantly increased (~7 folds compared to control aliquot which was not pumped through the system) and neither SNP nor TEA prevented this hemolysis. Alternatively, RBC deformability assessed by laser diffraction ektacytometry was not altered after 30 min of pumping and both SNP and TEA had no effect on this parameter. The results of this study indicated that, in contrast with the findings in RBC exposed to a well-defined magnitude of shear stress in a Couette shearing system, the mechanical damage induced by a roller pump could not be prevented by NO donor or potassium channel blocker.

Impaired nitric oxide bioavailability and L-arginine reversible endothelial dysfunction in adults with falciparum malaria

Severe falciparum malaria (SM) is associated with tissue ischemia related to cytoadherence of parasitized erythrocytes to microvascular endothelium and reduced levels of NO and its precursor, l-arginine. Endothelial function has not been characterized in SM but can be improved by l-arginine in cardiovascular disease. In an observational study in Indonesia, we measured endothelial function using reactive hyperemia-peripheral arterial tonometry (RH-PAT) in 51 adults with SM, 48 patients with moderately severe falciparum malaria (MSM), and 48 controls. The mean RH-PAT index was lower in SM (1.41; 95% confidence interval [CI] = 1.33-1.47) than in MSM (1.82; 95% CI = 1.7-2.02) and controls (1.93; 95% CI = 1.8-2.06; P < 0.0001). Endothelial dysfunction was associated with elevated blood lactate and measures of hemolysis. Exhaled NO was also lower in SM relative to MSM and controls. In an ascending dose study of intravenous l-arginine in 30 more patients with MSM, l-arginine increased the RH-PAT index by 19% (95% CI = 6-34; P = 0.006) and exhaled NO by 55% (95% CI = 32-73; P < 0.0001) without important side effects. Hypoargininemia and hemolysis likely reduce NO bioavailability. Endothelial dysfunction in malaria is nearly universal in severe disease, is reversible with l-arginine, and likely contributes to its pathogenesis. Clinical trials in SM of adjunctive agents to improve endothelial NO bioavailability, including l-arginine, are warranted.

Evolution of adverse changes in stored RBCs

Recent studies have underscored questions about the balance of risk and benefit of RBC transfusion. A better understanding of the nature and timing of molecular and functional changes in stored RBCs may provide strategies to improve the balance of benefit and risk of RBC transfusion. We analyzed changes occurring during RBC storage focusing on RBC deformability, RBC-dependent vasoregulatory function, and S-nitrosohemoglobin (SNO-Hb), through which hemoglobin (Hb) O(2) desaturation is coupled to regional increases in blood flow in vivo (hypoxic vasodilation). Five hundred ml of blood from each of 15 healthy volunteers was processed into leukofiltered, additive solution 3-exposed RBCs and stored at 1-6 degrees C according to AABB standards. Blood was subjected to 26 assays at 0, 3, 8, 24 and 96 h, and at 1, 2, 3, 4, and 6 weeks. RBC SNO-Hb decreased rapidly (1.2 x 10(-4) at 3 h vs. 6.5 x 10(-4) (fresh) mol S-nitrosothiol (SNO)/mol Hb tetramer (P = 0.032, mercuric-displaced photolysis-chemiluminescence assay), and remained low over the 42-day period. The decline was corroborated by using the carbon monoxide-saturated copper-cysteine assay [3.0 x 10(-5) at 3 h vs. 9.0 x 10(-5) (fresh) mol SNO/mol Hb]. In parallel, vasodilation by stored RBCs was significantly depressed. RBC deformability assayed at a physiological shear stress decreased gradually over the 42-day period (P < 0.001). Time courses vary for several storage-induced defects that might account for recent observations linking blood transfusion with adverse outcomes. Of clinical concern is that SNO levels, and their physiological correlate, RBC-dependent vasodilation, become depressed soon after collection, suggesting that even "fresh" blood may have developed adverse biological characteristics.

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

The pathophysiological effects of the activation or inhibition of the nitric oxide (NO)-mediated pathway on the deformability of red blood cells (RBC) were evaluated in the presence of hypercholesterolemia induced in rabbits fed a cholesterol-rich diet. RBC deformability was assessed using a microchannel array flow analyzer system. The maximum passage time (MPT) by flowing a suspension of RBC through the microchannels was used as an index of RBC deformability. During cholesterol feeding for 12 weeks, MPT gradually increased with no significant elevation in the serum asymmetric dimethylarginine (ADMA) and arginine/ADMA ratio. The reduction in RBC deformability associated with hypercholesterolemia was significantly improved during incubation with each of three different NO pathway activators: a NO donor, 8-bromo-cyclic GMP, and arginine; however, no additional reduction was observed with ADMA administration. The inhibition of NO synthase due to ADMA caused a significant reduction in the deformability of normal RBC, which was reversed with NO pathway activation. These results suggest that impaired RBC deformability may be associated with a dysfunction in the NO pathway that is partially dependent upon the accumulation of ADMA in RBC, and exogenous NO pathway activators may improve the microcirculation by restoring RBC deformability in the presence of hypercholesterolemia.

Effect of asymmetric dimethylarginine on atherogenesis and erythrocyte deformability in apolipoprotein E deficient mice

Previous investigations have shown that the level of asymmetric dimethylarginine (ADMA) was increased in hypercholesterolemic animal and humans, and the decreased erythrocyte deformability has been suggested to be a factor contributing to atherogenesis. In the present study, we investigated the effect of ADMA, endogenous or exogenous, on atherogenesis and erythrocyte deformability in apolipoprotein E deficient (ApoE-/-) mice. On a regular chow diet, ApoE-/- mice or C57BL/6 J mice at 12 weeks of age were treated with ADMA (5 mg/kg/day) for 4 weeks. Atherosclerotic lesion area, erythrocyte deformability, plasma lipids and asymmetric dimethylarginine (ADMA) level were determined. Plasma concentrations of triglyceride (TG), low-density lipoprotein-cholesterol (LDL-C), total cholesterol (TC), ADMA, and atherosclerotic lesion area were significantly increased, and the level of plasma high-density lipoprotein-cholesterol (HDL-C), erythrocyte deformability in ApoE-/- mice were markedly decreased compared with that of C57BL/6J mice (P<0.05 or P<0.01). Exogenous ADMA treatment increased the plasma TG level, produced atherosclerotic lesions, and decreased erythrocyte deformability in C57BL/6J mice (P<0.05 or P<0.01). Treatment with exogenous ADMA further increased the plasma TG level and lesion areas, and decreased erythrocyte deformability in ApoE-/- mice. In vitro, exogenous ADMA caused a decrease of erythrocyte deformability in a concentration-dependent manner, and the effect of ADMA was reversed by L-arginine. The present results suggest that endogenous ADMA is an important contributor to the development of atherosclerosis and that reduction of erythrocyte deformability and impaired endothelial function induced by ADMA may be an important factor facilitating atherosclerotic lesions.

Asymmetric dimethylarginine reduced erythrocyte deformability in streptozotocin-induced diabetic rats

To investigate the effect of asymmetric dimethylarginine on erythrocyte deformability in streptozotocin-induced diabetic rats, a single intraperitoneal injection of streptozotocin (STZ, 65 mg/kg) in male Sprague-Dawley rats was carried out to induce diabetes and normal erythrocytes were incubated with asymmetric dimethylarginine or aortic rings from diabetic rats in the presence of L-arginine or vitamin E. We found that erythrocyte deformability was significantly decreased in diabetic rats. The levels of asymmetric dimethylarginine in plasma and erythrocytes of diabetic rats were elevated significantly from 2-week diabetic duration to 8-week diabetic duration. Nitric oxide in erythrocytes was decreased at 8-week diabetic duration while plasma nitric oxide remained unchanged all along. The content of malondialdehyde in erythrocytes of diabetic rats was increased. After incubation of erythrocytes with asymmetric dimethylarginine (10(-6) M) for 30 min, erythrocyte deformability and nitric oxide level in erythrocytes were decreased markedly. Reactive oxygen species and malondialdehyde production in erythrocytes were promoted by asymmetric dimethylarginine. Both L-arginine and vitamin E reversed the effects of asymmetric dimethylarginine. After incubation of erythrocytes with aortic rings from diabetic rats, erythrocyte deformability was decreased, which was attenuated by L-arginine. These results indicated that reduction of erythrocyte deformability in diabetic rats was associated with promoted oxidant stress as well as impaired nitric oxide synthesis by elevation of asymmetric dimethylarginine.

Effect of penicillin G-induced epileptic seizures on hemorheological parameters in rats

Normally, cerebral blood flow (CBF) is quantitatively coupled to cerebral metabolic rate like other tissues and maintained basically by altering vascular geometry and appropriate perfusion pressure. However, the rheological properties of the blood are important factors for effective tissue perfusion. Although a lot of studies have reported that hemorheological parameters are affected by a wide range of pathophysiological conditions, to our knowledge no research related to the effects of epileptic seizures on hemorheological parameters has been carried out. Thus, the aim of this study was to explore possible changes in rheological parameters including red blood cell (RBC) deformability, rigidity and aggregation, whole blood and plasma viscosity during epileptic seizures induced by penicillin G in rats. Eighteen female albino rats were divided into three groups that included sham operated controls (Group S), epileptic group (Group E), intraperitoneal penicillin group (Group IPP). Epilepsy was induced by intracortical injections of penicillin G. Hemorheological studies had been carried out 3 h after the induction of epilepsy. Among the studied hemorheological parameters, only RBC deformability was found to be different in the E group compared to S group. Epileptic seizures led to an increase in RBC deformability in the E group. In conclusion, these results suggest that in addition to an increase in CBF, RBC deformability may also improve to better match brain metabolic demands during seizures.

Hemorheologic profile in systemic sclerosis: role of NOS3 -786T > C and 894G >T polymorphisms in modulating both the hemorheologic parameters and the susceptibility to the disease

OBJECTIVE

Microvascular disorders are relevant in systemic sclerosis (SSc). Hyperviscosity, due to alterations of blood cells and plasma components, may play a role in the pathogenesis of microcirculatory disorders. An impaired availability of nitric oxide, related to polymorphisms in NOS3, the gene for endothelial cell nitric oxide synthase, might influence erythrocyte deformability. We undertook this study to investigate the hemorheologic profile in SSc and the role of NOS3 polymorphisms in modulating the hemorheologic status of SSc patients.

METHODS

We studied 113 consecutive SSc patients (75 with limited cutaneous SSc [lcSSc] and 38 with diffuse cutaneous SSc [dcSSc]) and 113 healthy controls. The hemorheologic profile was obtained by assessing whole blood viscosity (WBV; at shear rates of 0.512 and 94.5 seconds(-1)), plasma viscosity (PLV; at a shear rate of 94.5 seconds(-1)), and erythrocyte deformability index (DI). We determined NOS3 polymorphisms by molecular analysis.

RESULTS

A marked alteration of hemorheologic parameters was found both in patients with lcSSc and in those with dcSSc compared with controls (P < 0.0001). In multivariate analysis, rheologic variables were significantly associated with the disease (for WBV at a shear rate of 94.5 seconds(-1), odds ratio [OR] 5.4, 95% confidence interval [95% CI] 1.4-19.9, P = 0.01; for PLV, OR 2.8, 95% CI 1.2-6.5, P = 0.01; for DI, OR 3.9, 95% CI 1.4-10.8, P = 0.007), and NOS3 -786C and 894T alleles significantly affected the DI (for -786C allele, OR 2.3, 95% CI 1.01-5.4, P = 0.04; for 894T allele, OR 2.2, 95% CI 1.01-4.8, P = 0.04). The simultaneous presence of the -786C and 894T alleles represented a susceptibility factor for SSc (OR 2.8, 95% CI 1.4-5.7, P = 0.004).

CONCLUSION

Our findings document an altered rheologic profile in SSc and demonstrate a relationship between this alteration and NOS3 polymorphisms, thus shedding light on a potential novel mechanism influencing the microcirculation in this disease.

Direct measurement of the impact of impaired erythrocyte deformability on microvascular network perfusion in a microfluidic device

The ability of red blood cells (RBCs, erythrocytes) to deform and pass through capillaries is essential for continual flow of blood in the microvasculature, which ensures an adequate supply of oxygen and nutrients, prompt removal of metabolic waste products, transport of drugs and hormones, and traffic of circulating cells to and from all living tissues. This paper presents a novel tool for evaluating the impact of impaired deformability of RBCs on the flow of blood in the microvasculature by directly measuring perfusion of a test microchannel network with dimensions and topology similar to the real microcirculation. The measurement of microchannel network perfusion is compared with RBC filtration -- a conventional assay of RBC deformability. In contrast to RBC filterability, network perfusion depends linearly on RBC deformability modulated by graded exposure to glutaraldehyde, showing a higher sensitivity to small changes of deformability. The direct measurement of microchannel network perfusion represents a new concept for the field of blood rheology and should prove beneficial for basic science and clinical applications.

Increased deformability of red blood cells is associated with a deletion polymorphism of the angiotensin-converting enzyme gene

Angiotensin-converting enzyme (ACE) plays important roles in the renin-angiotensin system. ACE converts angiotensin I to angiotensin II and also inactivates bradykinin, thereby modulating the vascular tone. A polymorphism of the ACE gene, located on chromosome 17, has been found in intron 16, and is characterized by the presence (insertion [I]) or absence (deletion [D]) of a 287-base-pair Alu repeat. Individuals with the D allele of the ACE gene have higher ACE levels and are at higher risk of cardiovascular events. We aimed to investigate the possible relationship between the I/D polymorphism of the ACE gene and hemorheological parameters, including red blood cell (RBC) deformability. The study was performed on 28 healthy young volunteers (13 women and 15 men, mean age 24 +/- 2). The prevalence of the I and D alleles was 30.4% and 69.6%, respectively. The I/I genotype (II) was found in 21.4%, I/D genotype (ID) in 17.9%, and D/D genotype (DD) in 60.7% of the subjects tested. No significant relationship between ACE I/D polymorphism and RBC aggregation or whole blood and plasma viscosity was observed. In contrast, RBC deformability was significantly increased in the subjects with the DD genotype compared with the II (p < 0.05) or the ID (p < 0.01) genotype, and in the subjects with the D allele compared with the I allele (p < 0.01). We suggest that RBC deformability of individuals with the D allele, who have higher risk for cardiovascular pathologies, may have been increased by a compensatory mechanism.

Red blood cells and hemoglobin in hypoxic pulmonary vasoconstriction

Nitric oxide (NO) plays an important role in the modulation of hypoxic pulmonary vasoconstriction; in turn, red blood cells (RBCs) augment HPV by hemoglobin-mediated oxidation and inactivation of NO. In addition, scavenging of reactive oxygen species by RBCs may play a role in augmentation of HPV. NO delivery and/or production by RBCs does not appear to be important in the control of pulmonary vasomotor tone. This review will discuss regulation of HPV by RBCs with an emphasis on hemoglobin-NO interactions. In addition, the review will discuss how biologic (S-nitrosation) or pharmacologic (cross-linking) modification of hemoglobin may affect pulmonary circulatory-hemoglobin interactions.

Mechanisms involved in the swelling of erythrocytes caused by Pacific and Caribbean ciguatoxins

The mechanisms underlying the swelling of frog red blood cells (RBC), induced by Pacific (P-CTX-1) and Caribbean (C-CTX-1) ciguatoxins (CTXs), were investigated by measuring the length, width and surface of their elliptic shape. P-CTX-1 (0.5 to 5 nM) and C-CTX-1 (1 nM) induced RBC swelling within 60 min. The CTXs-induced RBC swelling was blocked by apamin (1 microM) and by Sr(2+) (1 mM). P-CTX-1-induced RBC swelling was prevented and inhibited by H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (27 microM), an inhibitor of soluble guanylate cyclase (sGC), and NOS blockade by NG methyl-l-arginine (l-NMA; 10 microM). Cytochalasin D (cytD, 10 microM) increased RBC surface and mimicked CTX effect but did not prevent the P-CTX-1-induced l-NMA-sensitive extra increase. Calculations revealed that P-CTX-1 and cytD increase RBC total surface envelop and volume. These data strongly suggest that the molecular mechanisms underlying CTXs-induced RBC swelling involve the NO pathway by an activation of the inducible NOS, leading to sGC activation which modulates intracellular cGMP and regulates L-type Ca(2+) channels. The resulting increase in intracellular Ca(2+) content, in turn, disrupts the actin cytoskeleton, which causes a water influx and triggers a Ca(2+)-activated K(+) current through SK2 isoform channels.

Erythrocyte signal transduction pathways, their oxygenation dependence and functional significance

Erythrocytes play a key role in human and vertebrate metabolism. Tissue O2 supply is regulated by both hemoglobin (Hb)-O2 affinity and erythrocyte rheology, a key determinant of tissue perfusion. Oxygenation-deoxygenation transitions of Hb may lead to re-organization of the cytoskeleton and signalling pathways activation/deactivation in an O2-dependent manner. Deoxygenated Hb binds to the cytoplasmic domain of the anion exchanger band 3, which is anchored to the cytoskeleton, and is considered a major mechanism underlying the oxygenation-dependence of several erythrocyte functions. This work discusses the multiple modes of Hb-cytoskeleton interactions. In addition, it reviews the effects of Mg2+, 2,3-diphosphoglycerate, NO, shear stress and Ca2+, all factors accompanying the oxygenation-deoxygenation cycle in circulating red cells. Due to the extensive literature on the subject, the data discussed here, pertain mainly to human erythrocytes whose O2 affinity is modulated by 2,3-diphosphoglycerate, ectothermic vertebrate erythrocytes that use ATP, and to bird erythrocytes that use inositol pentaphosphate.

Association between hematological parameters and high-density lipoprotein cholesterol

PURPOSE OF REVIEW

The ability of high-density lipoprotein cholesterol to reverse atherosclerosis and reduce cardiovascular disease has been shown in several randomized controlled trials. One mechanism by which high-density lipoprotein cholesterol protects the vascular system includes hemorheology, the study of blood flow.

RECENT FINDINGS

Blood viscosity, or the resistance of flow, can be altered by red blood cell aggregation, red blood cell deformability, and plasma viscosity. Elevated high-density lipoprotein cholesterol levels may improve all of these rheological mediators. An infusion of recombinant high-density lipoprotein cholesterol can immediately release nitric oxide, a potent vasodilator and responder to changes in rheology, into the arteries by activation of endothelial nitric oxide synthase. The stimulation of nitric oxide release by high-density lipoprotein cholesterol may also alter blood rheology.

SUMMARY

In this article, we will review hemorheology, particularly blood viscosity along with other hemorheological factors, and examine their association with high-density lipoprotein cholesterol.

cGMP (guanosine 3′,5′-cyclic monophosphate) transport across human erythrocyte membranes

Human erythrocytes produce cGMP that can be eliminated by phosphodiesterases or active efflux transporters. The efflux can be studied under controlled conditions as ATP-dependent uptake into inside-out membrane vesicles. However, widely differing values for the transport rates have been reported. We have here examined factors that influence the uptake rates measured and thus may explain these discrepancies. Both the ionic composition of the buffer used during uptake and the mode of vesicle preparation were found to affect the observed transport rates. Furthermore it was apparent that different blood donors expressed on their erythrocytes different amounts of both MRP4 and MRP5, transporters that have been putatively linked to cGMP efflux across erythrocyte membranes. These differences in expression were reflected in differences in rates of cGMP uptake into inside-out erythrocyte membrane vesicles. Calculations based on the transport rates observed using vesicles suggest that efflux may be the principal means for eliminating cGMP from human erythrocytes.

Nitric oxide scavenging by hemoglobin regulates hypoxic pulmonary vasoconstriction

Although the importance of red blood cells in augmenting hypoxic pulmonary vasoconstriction has been recognized for decades, only recently has it become clear that this occurs primarily because of the inactivation of nitric oxide (NO) by hemoglobin. This interaction between red blood cells, NO, and the pulmonary circulation is critical in understanding the effects of anemia and polycythemia on pulmonary blood flow distribution, gas exchange, and global O2 delivery and in understanding the development of hemoglobin-based oxygen carriers. This review will discuss the proposed mechanisms for initiation of hypoxic pulmonary vasoconstriction and regulation of hypoxic pulmonary vasoconstriction by red blood cells with an emphasis on hemoglobin-NO interactions. In addition, the review will discuss how biologic (S-nitrosation) or pharmacologic (cross-linking) modification of hemoglobin may affect pulmonary circulatory-hemoglobin interactions.

Red blood cell physiology in critical illness

OBJECTIVE

Reduction in red blood cell mass, as well as structural and functional alterations of erythrocytes, occurs in critical illness. This review discusses these changes in red blood cell physiology, emphasizing the pathogenesis of anemia in intensive care unit patients.

DATA SOURCE

Studies published in biomedical journals.

DATA SYNTHESIS AND CONCLUSION

Anemia in intensive care unit patients resembles the anemia of chronic disease, being characterized by diminished erythropoietin production relative to decreased hematocrit, altered iron metabolism, and impaired proliferation and differentiation of erythroid progenitors in the bone marrow. Inflammatory mediators play a major role in the development of insufficient erythropoiesis and altered iron metabolism. Furthermore, a proinflammatory milieu promotes structural and functional alterations of erythrocytes, impairing their deformability and possibly impairing microvascular perfusion. Collectively, these changes in red blood cell physiology can impair oxygen transport to tissues and, thereby, might contribute to the development of multiple organ failure in critical illness.

Bench-to-bedside review: microvascular dysfunction in sepsis--hemodynamics, oxygen transport, and nitric oxide

The microcirculation is a complex and integrated system that supplies and distributes oxygen throughout the tissues. The red blood cell (RBC) facilitates convective oxygen transport via co-operative binding with hemoglobin. In the microcirculation oxygen diffuses from the RBC into neighboring tissues, where it is consumed by mitochondria. Evidence suggests that the RBC acts as deliverer of oxygen and 'sensor' of local oxygen gradients. Within vascular beds RBCs are distributed actively by arteriolar tone and passively by rheologic factors, including vessel geometry and RBC deformability. Microvascular oxygen transport is determined by microvascular geometry, hemodynamics, and RBC hemoglobin oxygen saturation. Sepsis causes abnormal microvascular oxygen transport as significant numbers of capillaries stop flowing and the microcirculation fails to compensate for decreased functional capillary density. The resulting maldistribution of RBC flow results in a mismatch of oxygen delivery with oxygen demand that affects both critical oxygen delivery and oxygen extraction ratio. Nitric oxide (NO) maintains microvascular homeostasis by regulating arteriolar tone, RBC deformability, leukocyte and platelet adhesion to endothelial cells, and blood volume. NO also regulates mitochondrial respiration. During sepsis, NO over-production mediates systemic hypotension and microvascular reactivity, and is seemingly protective of microvascular blood flow.