Mechanical stimuli such as shear stress and piezo1 stimulation generate red blood cell extracellular vesicles.

Introduction: Generating physiologically relevant red blood cell extracellular vesicles (RBC-EVs) for mechanistic studies is challenging. Herein, we investigated how to generate and isolate high concentrations of RBC-EVs in vitro via shear stress and mechanosensitive piezo1 ion channel stimulation. Methods: RBC-EVs were generated by applying shear stress or the piezo1-agonist yoda1 to RBCs. We then investigated how piezo1 RBC-EV generation parameters (hematocrit, treatment time, treatment dose), isolation methods (membrane-based affinity, ultrafiltration, ultracentrifugation with and without size exclusion chromatography), and storage conditions impacted RBC-EV yield and purity. Lastly, we used pressure myography to determine how RBC-EVs isolated using different methods affected mouse carotid artery vasodilation. Results: Our results showed that treating RBCs at 6% hematocrit with 10 µM yoda1 for 30 min and isolating RBC-EVs via ultracentrifugation minimized hemolysis, maximized yield and purity, and produced the most consistent RBC-EV preparations. Co-isolated contaminants in impure samples, but not piezo1 RBC-EVs, induced mouse carotid artery vasodilation. Conclusion: This work shows that RBC-EVs can be generated through piezo1 stimulation and may be generated in vivo under physiologic flow conditions. Our studies further emphasize the importance of characterizing EV generation and isolation parameters before using EVs for mechanistic analysis since RBC-EV purity can impact functional outcomes.

COVID-19 impairs oxygen delivery by altering red blood cell hematological, hemorheological, and oxygen transport properties.

Introduction: Coronavirus disease 2019 (COVID-19) is characterized by impaired oxygen (O2) homeostasis, including O2 sensing, uptake, transport/delivery, and consumption. Red blood cells (RBCs) are central to maintaining O2 homeostasis and undergo direct exposure to coronavirus in vivo. We thus hypothesized that COVID-19 alters RBC properties relevant to O2 homeostasis, including the hematological profile, Hb O2 transport characteristics, rheology, and the hypoxic vasodilatory (HVD) reflex. Methods: RBCs from 18 hospitalized COVID-19 subjects and 20 healthy controls were analyzed as follows: (i) clinical hematological parameters (complete blood count; hematology analyzer); (ii) O2 dissociation curves (p50, Hill number, and Bohr plot; Hemox-Analyzer); (iii) rheological properties (osmotic fragility, deformability, and aggregation; laser-assisted optical rotational cell analyzer (LORRCA) ektacytometry); and (iv) vasoactivity (the RBC HVD; vascular ring bioassay). Results: Compared to age- and gender-matched healthy controls, COVID-19 subjects demonstrated 1) significant hematological differences (increased WBC count-with a higher percentage of neutrophils); RBC distribution width (RDW); and reduced hematocrit (HCT), Hb concentration, mean corpuscular volume (MCV), and mean corpuscular hemoglobin concentration (MCHC); 2) impaired O2-carrying capacity and O2 capacitance (resulting from anemia) without difference in p50 or Hb-O2 cooperativity; 3) compromised regulation of RBC volume (altered osmotic fragility); 4) reduced RBC deformability; 5) accelerated RBC aggregation kinetics; and (6) no change in the RBC HVD reflex. Discussion: When considered collectively, homeostatic compensation for these RBC impairments requires that the cardiac output in the COVID cohort would need to increase by ∼135% to maintain O2 delivery similar to that in the control cohort. Additionally, the COVID-19 disease RBC properties were found to be exaggerated in blood-type O hospitalized COVID-19 subjects compared to blood-type A. These data indicate that altered RBC features in hospitalized COVID-19 subjects burden the cardiovascular system to maintain O2 delivery homeostasis, which appears exaggerated by blood type (more pronounced with blood-type O) and likely plays a role in disease pathogenesis.

The interactome of the N-terminus of band 3 regulates red blood cell metabolism and storage quality.

Band 3 (anion exchanger 1; AE1) is the most abundant membrane protein in red blood cells, which in turn are the most abundant cells in the human body. A compelling model posits that, at high oxygen saturation, the N-terminal cytosolic domain of AE1 binds to and inhibits glycolytic enzymes, thus diverting metabolic fluxes to the pentose phosphate pathway to generate reducing equivalents. Dysfunction of this mechanism occurs during red blood cell aging or storage under blood bank conditions, suggesting a role for AE1 in the regulation of the quality of stored blood and efficacy of transfusion, a life-saving intervention for millions of recipients worldwide. Here we leveraged two murine models carrying genetic ablations of AE1 to provide mechanistic evidence of the role of this protein in the regulation of erythrocyte metabolism and storage quality. Metabolic observations in mice recapitulated those in a human subject lacking expression of AE11-11 (band 3 Neapolis), while common polymorphisms in the region coding for AE11-56 correlate with increased susceptibility to osmotic hemolysis in healthy blood donors. Through thermal proteome profiling and crosslinking proteomics, we provide a map of the red blood cell interactome, with a focus on AE11-56 and validate recombinant AE1 interactions with glyceraldehyde 3-phosphate dehydrogenase. As a proof-of-principle and to provide further mechanistic evidence of the role of AE1 in the regulation of redox homeo stasis of stored red blood cells, we show that incubation with a cell-penetrating AE11-56 peptide can rescue the metabolic defect in glutathione recycling and boost post-transfusion recovery of stored red blood cells from healthy human donors and genetically ablated mice.

Quantifying dynamic range in red blood cell energetics: Evidence of progressive energy failure during storage.

BACKGROUND: During storage, red blood cells (RBCs) undergo significant biochemical and morphologic changes, referred to collectively as the "storage lesion". It was hypothesized that these defects may arise from disrupted oxygen-based regulation of RBC energy metabolism, with resultant depowering of intrinsic antioxidant systems. STUDY DESIGN AND METHODS: As a function of storage duration, the dynamic range in RBC metabolic response to three models of biochemical oxidant stress (methylene blue, hypoxanthine/xanthine oxidase, and diamide) was assessed, comparing glycolytic flux by NMR and UHPLC-MS methodologies. Blood was processed/stored under standard conditions (AS-1 additive solution) with leukoreduction. Over a 6-week period, RBC metabolic and antioxidant status were assessed at baseline and following exposure to the three biochemical oxidant models. Comparison was made of glycolytic flux (1 H-NMR tracking of [2-13 C]-glucose and metabolomic phenotyping with [1,2,3-13 C3 ] glucose), reducing equivalent (NADPH/NADP+ ) recycling, and thiol-based (GSH/GSSG) antioxidant status. RESULTS: As a function of storage duration, we observed the following: (1) a reduction in baseline hexose monophosphate pathway (HMP) flux, the sole pathway responsible for the regeneration of the essential reducing equivalent NADPH; with (2) diminished stress-based dynamic range in both overall glycolytic as well as proportional HMP flux. In addition, progressive with storage duration, RBCs showed (3) constraint in reducing equivalent (NADPH) recycling capacity, (4) loss of thiol based (GSH) recycling capacity, and (5) dysregulation of metabolon assembly at the cytoplasmic domain of Band 3 membrane protein (cdB3). CONCLUSION: Blood storage disturbs normal RBC metabolic control, depowering antioxidant capacity and enhancing vulnerability to oxidative injury.

A clickable probe for versatile characterization of S-nitrosothiols.

S-nitrosation of cysteine thiols (SNOs), commonly referred to as S-nitrosylation, is a cysteine oxoform that plays an important role in cellular signaling and impacts protein function and stability. Direct labeling of SNOs in cells with the flexibility to perform a wide range of cellular and biochemical assays remains a bottleneck as all SNO-targeted probes to date employ a single analytical modality such as biotin or a specific fluorophore. We therefore developed a clickable, alkyne-containing SNO probe 'PBZyn' based on the o-phosphino-benzoyl group warhead that enables multi-modal analysis via click conjugation. We demonstrate the utility of PBZyn to assay SNOs using in situ cellular imaging, protein blotting and affinity purification, as well as mass spectrometry. The flexible PBZyn probe will greatly facilitate investigation into the regulation of SNOs.

A pilot study on the kinetics of metabolites and microvascular cutaneous effects of nitric oxide inhalation in healthy volunteers.

RATIONALE: Inhaled nitric oxide (NO) exerts a variety of effects through metabolites and these play an important role in regulation of hemodynamics in the body. A detailed investigation into the generation of these metabolites has been overlooked. OBJECTIVES: We investigated the kinetics of nitrite and S-nitrosothiol-hemoglobin (SNO-Hb) in plasma derived from inhaled NO subjects and how this modifies the cutaneous microvascular response. FINDINGS: We enrolled 15 healthy volunteers. Plasma nitrite levels at baseline and during NO inhalation (15 minutes at 40 ppm) were 102 (86-118) and 114 (87-129) nM, respectively. The nitrite peak occurred at 5 minutes of discontinuing NO (131 (104-170) nM). Plasma nitrate levels were not significantly different during the study. SNO-Hb molar ratio levels at baseline and during NO inhalation were 4.7E-3 (2.5E-3-5.8E-3) and 7.8E-3 (4.1E-3-13.0E-3), respectively. Levels of SNO-Hb continued to climb up to the last study time point (30 min: 10.6E-3 (5.3E-3-15.5E-3)). The response to acetylcholine iontophoresis both before and during NO inhalation was inversely associated with the SNO-Hb level (r: -0.57, p = 0.03, and r: -0.54, p = 0.04, respectively). CONCLUSIONS: Both nitrite and SNO-Hb increase during NO inhalation. Nitrite increases first, followed by a more sustained increase in Hb-SNO. Nitrite and Hb-SNO could be a mobile reservoir of NO with potential implications on the systemic microvasculature.

Effect of plasma processing and storage on microparticle abundance, nitric oxide scavenging, and vasoactivity.

BACKGROUND: We set out to define the impact of collection, processing, and storage on plasma product microparticle (MP) abundance, potential for nitric oxide (NO) scavenging, and vasoactivity. STUDY DESIGN AND METHODS: Three currently US licensed products were tested: liquid plasma (LP), fresh frozen plasma (FFP), and solvent detergent plasma (SDP), along with a product under development, spray-dried solvent detergent plasma (SD-SDP) with/without beads. Vasoactivity was assessed in vitro using rabbit aortic vascular rings; MP abundance was determined by flow cytometry; and NO scavenging capacity/rate was determined using a biochemical NO consumption assay. All samples were analyzed unprocessed and following centrifugation at two speeds (2,500× g to remove platelets, and 25,000× g to remove microparticles). RESULTS: Significant differences in vasoactivity were observed, with SD-SDP minus beads demonstrating the greatest constriction and FFP the lowest constriction response. All products exhibited the same total NO scavenging capacity; however, significant differences were observed in the maximal rate of scavenging, with SD-SDP minus beads and FFP reacting fastest and SDP the slowest. Across all products, platelet and microparticle depletion had no effect on vasoactivity or NO scavenging (total or rate). Microparticles (RBC derived) were found only in FFP and LP, with relative abundance (LP > FFP). Additionally, storage had no effect on total or RBC-derived MP abundance, NO scavenging, or vasoactivity. CONCLUSION: Although vasoactivity differed between plasma products, we did not find similar differences in either total or RBC-derived MP abundance or NO scavenging capacity/rate.

Red blood cell phenotype fidelity following glycerol cryopreservation optimized for research purposes.

Intact red blood cells (RBCs) are required for phenotypic analyses. In order to allow separation (time and location) between subject encounter and sample analysis, we developed a research-specific RBC cryopreservation protocol and assessed its impact on data fidelity for key biochemical and physiological assays. RBCs drawn from healthy volunteers were aliquotted for immediate analysis or following glycerol-based cryopreservation, thawing, and deglycerolization. RBC phenotype was assessed by (1) scanning electron microscopy (SEM) imaging and standard morphometric RBC indices, (2) osmotic fragility, (3) deformability, (4) endothelial adhesion, (5) oxygen (O2) affinity, (6) ability to regulate hypoxic vasodilation, (7) nitric oxide (NO) content, (8) metabolomic phenotyping (at steady state, tracing with [1,2,3-13C3]glucose ± oxidative challenge with superoxide thermal source; SOTS-1), as well as in vivo quantification (following human to mouse RBC xenotransfusion) of (9) blood oxygenation content mapping and flow dynamics (velocity and adhesion). Our revised glycerolization protocol (40% v/v final) resulted in >98.5% RBC recovery following freezing (-80°C) and thawing (37°C), with no difference compared to the standard reported method (40% w/v final). Full deglycerolization (>99.9% glycerol removal) of 40% v/v final samples resulted in total cumulative lysis of ~8%, compared to ~12-15% with the standard method. The post cryopreservation/deglycerolization RBC phenotype was indistinguishable from that for fresh RBCs with regard to physical RBC parameters (morphology, volume, and density), osmotic fragility, deformability, endothelial adhesivity, O2 affinity, vasoregulation, metabolomics, and flow dynamics. These results indicate that RBC cryopreservation/deglycerolization in 40% v/v glycerol final does not significantly impact RBC phenotype (compared to fresh cells).

Hypoxia modulates the purine salvage pathway and decreases red blood cell and supernatant levels of hypoxanthine during refrigerated storage.

Hypoxanthine catabolism in vivo is potentially dangerous as it fuels production of urate and, most importantly, hydrogen peroxide. However, it is unclear whether accumulation of intracellular and supernatant hypoxanthine in stored red blood cell units is clinically relevant for transfused recipients. Leukoreduced red blood cells from glucose-6-phosphate dehydrogenase-normal or -deficient human volunteers were stored in AS-3 under normoxic, hyperoxic, or hypoxic conditions (with oxygen saturation ranging from <3% to >95%). Red blood cells from healthy human volunteers were also collected at sea level or after 1-7 days at high altitude (>5000 m). Finally, C57BL/6J mouse red blood cells were incubated in vitro with 13C1-aspartate or 13C5-adenosine under normoxic or hypoxic conditions, with or without deoxycoformycin, a purine deaminase inhibitor. Metabolomics analyses were performed on human and mouse red blood cells stored for up to 42 or 14 days, respectively, and correlated with 24 h post-transfusion red blood cell recovery. Hypoxanthine increased in stored red blood cell units as a function of oxygen levels. Stored red blood cells from human glucose-6-phosphate dehydrogenase-deficient donors had higher levels of deaminated purines. Hypoxia in vitro and in vivo decreased purine oxidation and enhanced purine salvage reactions in human and mouse red blood cells, which was partly explained by decreased adenosine monophosphate deaminase activity. In addition, hypoxanthine levels negatively correlated with post-transfusion red blood cell recovery in mice and - preliminarily albeit significantly - in humans. In conclusion, hypoxanthine is an in vitro metabolic marker of the red blood cell storage lesion that negatively correlates with post-transfusion recovery in vivo Storage-dependent hypoxanthine accumulation is ameliorated by hypoxia-induced decreases in purine deamination reaction rates.

Physiologic Impact of Circulating RBC Microparticles upon Blood-Vascular Interactions.

Here, we review current data elucidating the role of red blood cell derived microparticles (RMPs) in normal vascular physiology and disease progression. Microparticles (MPs) are submicron-size, membrane-encapsulated vesicles derived from various parent cell types. MPs are produced in response to numerous stimuli that promote a sequence of cytoskeletal and membrane phospholipid changes and resulting MP genesis. MPs were originally considered as potential biomarkers for multiple disease processes and more recently are recognized to have pleiotropic biological effects, most notably in: promotion of coagulation, production and handling of reactive oxygen species, immune modulation, angiogenesis, and in initiating apoptosis. RMPs, specifically, form normally during RBC maturation in response to injury during circulation, and are copiously produced during processing and storage for transfusion. Notably, several factors during RBC storage are known to trigger RMP production, including: increased intracellular calcium, increased potassium leakage, and energy failure with ATP depletion. Of note, RMP composition differs markedly from that of intact RBCs and the nature/composition of RMP components are affected by the specific circumstances of RMP genesis. Described RMP bioactivities include: promotion of coagulation, immune modulation, and promotion of endothelial adhesion as well as influence upon vasoregulation via influence upon nitric oxide (NO) bioavailability. Of particular relevance, RMPs scavenge NO more avidly than do intact RBCs; this physiology has been proposed to contribute to the impaired oxygen delivery homeostasis that may be observed following transfusion. In summary, RMPs are submicron particles released from RBCs, with demonstrated vasoactive properties that appear to disturb oxygen delivery homeostasis. The clinical impact of RMPs in normal and patho-physiology and in transfusion recipients is an area of continued investigation.

Antimicrobial photodynamic therapy of S. mutans biofilms attached to relevant dental materials.

BACKGROUND: Antimicrobial Photodynamic therapy (aPDT) has demonstrated efficacy in situations where conventional antibiotic therapies can be challenged such as biofilms, gram-negative bacteria, and antimicrobial resistant organisms. Surface characteristics can affect biofilm adherence and integrity and so may modify the effectiveness of aPDT. This study investigates the killing efficacy of aPDT on S. mutans biofilms grown on relevant dental substrata, examining the killing efficacy and specifically the effects of aPDT on the biofilm matrix architecture. MATERIALS AND METHODS: S. mutans (NCTC 10449) was grown in 48 hours biofilms on different substrata, specifically glass, titanium, and denture acrylic. During aPDT assays, the biofilms were treated with a purpurin based sensitizer ([25 ug/ml] in DMSO) for 30 minutes, then exposed to a 664 nm diode laser at light doses of 15, 30, and 45 J/cm2 . Colony forming unit assays were performed to determine survival following treatment. Controls for comparison in survival assays consisted of (No light/No PS; No light/PS; and No light/DMSO). MAIR-IR spectroscopy analysis was performed to investigate aPDT effects on biofilm composition before and after jet impingement. RESULTS: Survival was greatly reduced in the biofilm cultures following the aPDT assays. All light doses achieved a greater then 3-log inactivation on 48 hours biofilms grown on polished denture acrylic. The higher light doses (45 and 30 J) achieved greater than 3-log inactivation in 48 hours biofilms grown on glass. The higher light doses (30 and 45 J/cm2 ) produced a 2-log inactivation in 48 hours biofilms grown on titanium. Multiple attenuated internal reflection infrared (MAIR-IR) spectroscopy data demonstrates enhanced loss of exopolysaccharide (EPS) and Amide in the aPDT treated biofilms following jet impingement. CONCLUSION: Antimicrobial PDT experiments using a purpurin based sensitizer and laser light doses of 15, 30, and 45 J/cm2 , against S. mutans biofilm grown on different surfaces, show the effectiveness of this therapy. In CFU survival assays, a dose response to the laser is evident. While considerable disinfection was achieved on all surfaces compared to the controls, not all surfaces could be disinfected equally. MAIR-IR spectroscopy showed that aPDT groups lost more EPS and Amide versus controls, suggesting aPDT induced biofilm embrittlement, which was revealed by jet impingement. With demonstrated efficacy against various microbes and on different substrata, antimicrobial aPDT shows potential for clinical application in biofilm-mediated diseases such as peri-implantitis and periodontitis. Lasers Surg. Med. 48:995-1005, 2016. © 2016 Wiley Periodicals, Inc.

Sickle hemoglobin disturbs normal coupling among erythrocyte O2 content, glycolysis, and antioxidant capacity.

Energy metabolism in RBCs is characterized by O2-responsive variations in flux through the Embden Meyerhof pathway (EMP) or the hexose monophosphate pathway (HMP). Therefore, the generation of ATP, NADH, and 2,3-DPG (EMP) or NADPH (HMP) shift with RBC O2 content because of competition between deoxyhemoglobin and key EMP enzymes for binding to the cytoplasmic domain of the Band 3 membrane protein (cdB3). Enzyme inactivation by cdB3 sequestration in oxygenated RBCs favors HMP flux and NADPH generation (maximizing glutathione-based antioxidant systems). We tested the hypothesis that sickle hemoglobin disrupts cdB3-based regulatory protein complex assembly, creating vulnerability to oxidative stress. In RBCs from patients with sickle cell anemia, we demonstrate in the present study constrained HMP flux, NADPH, and glutathione recycling and reduced resilience to oxidative stress manifested by membrane protein oxidation and membrane fragility. Using a novel, inverted membrane-on-bead model, we illustrate abnormal (O2-dependent) association of sickle hemoglobin to RBC membrane that interferes with sequestration/inactivation of the EMP enzyme GAPDH. This finding was confirmed by immunofluorescent imaging during RBC O2 loading/unloading. Moreover, selective inhibition of inappropriately dispersed GAPDH rescues antioxidant capacity. Such disturbance of cdB3-based linkage between O2 gradients and RBC metabolism suggests a novel mechanism by which hypoxia may influence the sickle cell anemia phenotype.

Analysis of S-nitrosothiols via copper cysteine (2C) and copper cysteine-carbon monoxide (3C) methods.

This chapter summarizes the principles of RSNO measurement in the gas phase, utilizing ozone-based chemiluminescence and the copper cysteine (2C)±carbon monoxide (3C) reagent. Although an indirect method for quantifying RSNOs, this assay represents one of the most robust methodologies available. It exploits the NO detection sensitivity of ozone based chemiluminescence, which is within the range required to detect physiological concentrations of RSNO metabolites. Additionally, the specificity of the copper cysteine (2C and 3C) reagent for RSNOs negates the need for sample pretreatment, thereby minimizing the likelihood of sample contamination (false positive results), or the loss of certain highly labile RSNO species. Herein, we outline the principles of this methodology, summarizing key issues, potential pitfalls and corresponding solutions.

Direct formation of thienopyridine-derived nitrosothiols--just add nitrite!

Thienopyridines (ticlopidine, clopidogrel and prasugrel) are pro-drugs that require metabolism to exhibit a critical thiol group in the active form that binds to the P2Y12 receptor to inhibit platelet activation and prevent thrombus formation in vivo. We investigated whether these thienopyridines participate in S-nitrosation (SNO) reactions that might exhibit direct anti-platelet behaviour. Optimum conditions for in vitro formation of thienopyridine-SNO formation were studied by crushing ticlopidine, clopidogrel or prasugrel into aqueous solution and adding sodium nitrite, or albumin-SNO. Ozone-based chemiluminescence techniques were utilised to specifically detect NO release from the SNO produced. Effect on agonist-induced platelet aggregation was monitored using light transmittance in a 96 well microplate assay. Pharmaceutical grade preparations of ticlopidine, clopidogrel and prasugrel were found to exhibit significant free thiol and formed SNO derivatives directly from anionic nitrite in water under laboratory conditions without the need for prior metabolism. Thienopyridine-SNO formation was dependent on pH, duration of mixing and nitrite concentration, with prasugrel-SNO being more favourably formed. The SNO moiety readily participated in trans-nitrosation reactions with albumin and plasma. Prasugrel-SNO showed significantly better inhibition of platelet aggregation compared with clopidogrel-SNO, however when compared on the basis of SNO concentration these were equally effective (IC50=7.91 ± 1.03 v/s 10.56 ± 1.43 µM, ns). Thienopyridine-derived SNO is formed directly from the respective base drug without the need for prior in vivo metabolism and therefore may be an important additional contributor to the pharmacological effectiveness of thienopyridines not previously considered.

Characterization of Mixtures. Part 2: QSPR Models for Prediction of Excess Molar Volume and Liquid Density Using Neural Networks.

In our earlier work, we have demonstrated that it is possible to characterize binary mixtures using single component descriptors by applying various mixing rules. We also showed that these methods were successful in building predictive QSPR models to study various mixture properties of interest. Here in, we developed a QSPR model of an excess thermodynamic property of binary mixtures i.e. excess molar volume (V(E) ). In the present study, we use a set of mixture descriptors which we earlier designed to specifically account for intermolecular interactions between the components of a mixture and applied successfully to the prediction of infinite-dilution activity coefficients using neural networks (part 1 of this series). We obtain a significant QSPR model for the prediction of excess molar volume (V(E) ) using consensus neural networks and five mixture descriptors. We find that hydrogen bond and thermodynamic descriptors are the most important in determining excess molar volume (V(E) ), which is in line with the theory of intermolecular forces governing excess mixture properties. The results also suggest that the mixture descriptors utilized herein may be sufficient to model a wide variety of properties of binary and possibly even more complex mixtures.

Hypoxia limits antioxidant capacity in red blood cells by altering glycolytic pathway dominance.

The erythrocyte membrane is a newly appreciated platform for thiol-based circulatory signaling, and it requires robust free thiol maintenance. We sought to define physiological constraints on erythrocyte antioxidant defense. Hemoglobin (Hb) conformation gates glycolytic flux through the hexose monophosphate pathway (HMP), the sole source of nicotinamide adenine dinucleotide phosphate (NADPH) in erythrocytes. We hypothesized elevated intraerythrocytic deoxyHb would limit resilience to oxidative stress. Human erythrocytes were subjected to controlled oxidant (superoxide) loading following independent manipulation of oxygen tension, Hb conformation, and glycolytic pathway dominance. Sufficiency of antioxidant defense was determined by serial quantification of GSH, NADPH, NADH redox couples. Hypoxic erythrocytes demonstrated greater loss of reduction potential [Delta GSH E(hc) (mV): 123.4+/-9.7 vs. 57.2+/-11.1] and reduced membrane thiol (47.7+/-5.7 vs. 20.1+/-4.3%) (hypoxia vs. normoxia, respectively; P<0.01), a finding mimicked in normoxic erythrocytes after HMP blockade. Rebalancing HMP flux during hypoxia restored resilience to oxidative stress at all stages of the system. Cell-free studies assured oxidative loading was not altered by oxygen tension, heme ligation, or the inhibitors employed. These data indicate that Hb conformation controls coupled glucose and thiol metabolism in erythrocytes, and implicate hypoxemia in the pathobiology of erythrocyte-based vascular signaling.

Haemoglobin saturation controls the red blood cell mediated hypoxic vasorelaxation.

The vasorelaxant properties of red blood cells (RBCs) have been implicated in both the control of normal vascular tone and the protection of tissues from ischemic events. The identity of the vasorelaxant released from RBCs has yet to be elucidated, however growing evidence suggests that nitric oxide bound to the beta 93 cysteine residue of haemoglobin (SNO-Hb) may be responsible. The vasorelaxant moiety is released during the transition of haemoglobin from its R (oxygenated) to T (deoxygenated) state. We subsequently chose to assess the significance of haemoglobin saturation on the capacity of RBCs to mediate hypoxic vasorelaxation. Human RBC samples suspended in saline were manipulated in a thin film rotating tonometer, designed to rapidly change haemoglobin saturation within the time frame of circulatory transit. Various cycles of oxygenation and deoxygenation were performed. The vasorelaxant properties of the RBCs were analysed using an aortic ring bioactivity assay, wherein changes in isometric tension were recorded to study vessel relaxation. The rabbit aortic rings were preconstricted with phenylephrine under hypoxic conditions (approximately 1% O2) prior to RBC addition. Highly saturated RBCs (98.22% +/- 0.45 HbO2) elicited significantly (P<0.001) more relaxation of hypoxic blood vessels compared to those partially saturated (20.40% +/- 5.28 HbO2). Upon re-oxygenation, previously de-oxygenated RBCs were also capable of eliciting vessel relaxation, which was not significantly different from that observed with the original oxygenated RBC relaxation response. Interestingly, the relaxant capability was not simply returned from extracellular milieu upon re-oxygenation. This data provides further evidence that the conformational switch of haemoglobin from the R-state (oxygenated) to the T-state (deoxygenated) is essential for the release of the vasoactive moiety contained within red blood cells.

Blood vessel specific vaso-activity to nitrite under normoxic and hypoxic conditions.

This study uses an organ chamber bioactivity assay to characterise the direct effect of sodium nitrite upon rabbit blood vessels (aorta (Ao), inferior vena cava (IVC) and pulmonary artery (PA)) in a haemoglobin independent/variable oxygen environment. In 95% oxygen constriction to 8g (Ao), 6g (PA) and 4g (IVC) was achieved using 1 microM phenylephrine. The same constriction in 1% oxygen required 3 microM. During 95% oxygen constriction was consistent and sustained for all vessels. However under 1% oxygen PA was quick to constrict but rapidly gave up this tension whereas Ao was slower to constrict but exhibited a more sustained response. Relaxation of each vessel was assessed post constriction using 10 microM sodium nitrite. Results were expressed as a percentage loss in tension compared to the maximum achieved and corrected by controls which received no nitrite. At 95% oxygen PA relaxed greater than Ao (10.04% +/- 2.28% vs. 5.25% +/- 1.51%). IVC response was varied (2.26% +/- 9.43%). At 1% oxygen all vessels relaxed more. However the pattern was reversed with both IVC (14.20% +/- 3.63%) and PA (16.55% +/- 0.93%) relaxing less than Ao (42.20% +/- 5.21%). These results suggest that relatively low concentrations of sodium nitrite can vasodilate blood vessels. This effect is independent of haemoglobin and tissue specific.

The measurement of nitric oxide and its metabolites in biological samples by ozone-based chemiluminescence.

A plethora of publications on techniques and methodologies for measuring nitric oxide (NO) or reaction products of NO (NO metabolites) has served in recent years to complicate and confuse the majority of researchers interested in this field. Here, we provide a practical approach and summarize the key issues and corresponding solutions regarding quantification with the use of ozone-based chemiluminescence, which is the most accurate, sensitive, and widely used NO detection method. We have drawn on the vast experience of leaders in the field to produce this consensus, but the views and implications presented herein represent our own, and we limit our advice to those techniques with which we have direct experience. Hopefully, this guide will allow authors to make more informed decisions regarding NO metabolite measurement methodology, without the need for each subsequent group to rediscover previously observed advantages and pitfalls.

NO metabolite flux across the human coronary circulation.

OBJECTIVES: The theory of a red blood cell derived nitric oxide (NO) reserve conserving NO bioactivity and delivering NO as a function of oxygen demand has been the subject of much interest. We identified the human coronary circulation as an ideal model system in which to analyse NO metabolites because of its large physiological oxygen gradient. Our objective was to identify whether oxygen drove apportion between various NO metabolite species across a single vascular bed. METHODS: Plasma and red blood cell NO metabolites were assessed from the left main coronary artery, coronary sinus and pulmonary artery (providing cross heart and cross pulmonary analysis) of healthy subjects under resting conditions and following administration of an inhibitor of NO biosynthesis. Physiological parameters and angiographic data were monitored throughout the study. RESULTS: Under baseline conditions we observed significant metabolite flux upon the transit of blood across the coronary and pulmonary vascular beds. Whilst there was no net loss of NO through the coronary circulation (p=0.0759), plasma nitrite/protein NO (excluding nitrate) (p=0.0279) and red blood cell sulphanilamide labile signal (p=0.0143) decreased whereas haemoglobin-bound NO increased three-fold (p=0.005). These changes across the coronary circulation were reversed through the pulmonary circuit with red blood cell sulphanilamide labile signal (p=0.0143) and plasma nitrite/protein NO (p=0.0279) increasing and haemoglobin-bound NO decreasing. Blockade of NO synthesis increased mean arterial blood pressure (p<0.01) and reduced coronary artery diameter (p<0.05), however we observed similar apportion of NO metabolites across the heart and lung with no net loss or gain in total NO metabolites. CONCLUSIONS: For the first time in human subjects across the resting coronary circulation we reveal significant re-apportionment of NO between metabolite species which correlate with haemoglobin oxygen saturation. These changes occur even within the transit time of blood across this single vascular bed. We demonstrate no net loss/gain of NO from the total metabolite pool across the coronary circulation even where NO biosynthesis is inhibited.