Inhaled nitric oxide attenuates the adverse effects of transfusing stored syngeneic erythrocytes in mice with endothelial dysfunction after hemorrhagic shock

Navigating Hemolysis, Hemoglobin Toxicity, and Its Renal Implications in Cardiac Surgery

Cardiopulmonary bypass–induced hemolysis is linked to acute kidney injury in cardiac surgery. Emerging therapies targeting cell-free hemoglobin (CFHb), like haptoglobin, nitric oxide (NO), and antioxidants, show promise in reducing kidney injury, highlighting the need for further research.

Toxic effects of cell-free hemoglobin on the microvascular endothelium: implications for pulmonary and nonpulmonary organ dysfunction

Levels of circulating cell-free hemoglobin are elevated during hemolytic and inflammatory diseases and contribute to organ dysfunction and severity of illness. Though several studies have investigated the contribution of hemoglobin to tissue injury, the precise signaling mechanisms of hemoglobin-mediated endothelial dysfunction in the lung and other organs are not yet completely understood. The purpose of this review is to highlight the knowledge gained thus far and the need for further investigation regarding hemoglobin-mediated endothelial inflammation and injury to develop novel therapeutic strategies targeting the damaging effects of cell-free hemoglobin.

Clinical use of inhaled nitric oxide: Local and systemic applications

Upon the FDA approval for inhaled nitric oxide (iNO) in 1999 to treat persistent pulmonary hypertension in neonates, iNO has proven to be a beneficial therapeutic in multiple diseases. We aim to review applications of iNO that have modeled its protective and therapeutic attributes, as well as highlight preliminary studies that could allude to future avenues of use. Numerous publications have reported specific incidences where iNO therapy has proved advantageous, while some applications have potential after further validation. Establishing guidelines on dosing, duration, and defined clinical uses are crucial for the future of iNO. Delivery of iNO has been controlled by a sole distributor, and comes with high cost, and lack of portability. A shift in patents has allowed for new designs for iNO device synthesis, with many new developments of iNO medical devices that will likely change the future of iNO in a medical setting.

Old, older, the oldest: red blood cell storage and the potential harm of using older red blood cell concentrates

PURPOSE OF REVIEW

Over the last decades, clinical studies have suggested that transfusion of red blood cells (RBCs) might negatively impact patient outcomes. Even though large randomized clinical trials did not show differences in mortality when transfusing fresh versus standard-issue RBC units, data imply that RBCs at the very end of storage could elicit negative effects.

RECENT FINDINGS

Certain alterations of RBCs during cold storage -- such as an increase of potassium and lactate in the storage solution -- have been discovered a century ago. In recent years, proteomic and metabolomic studies have shed more light into pathophysiological changes of RBCs during storage and have helped to specify the definition of old blood. These advancements are now utilized to increase the quality of stored RBCs and devise therapeutic strategies (e.g. nitric oxide, haptoglobin, or reduction of the iron load) when transfusing old blood.

SUMMARY

Further research to improve the quality of RBC units and to study populations potentially at risk is warranted. Until the question whether transfusion of old blood is detrimental for specific patient populations has been answered, a deliberate use of RBC transfusion should be implemented.

RBC Storage Lesion Studies in Humans and Experimental Models of Shock

The finding of toxicity in a meta-analysis of observational clinical studies of transfused longer stored red blood cells (RBC) and ethical issues surrounding aging blood for human studies prompted us to develop an experimental model of RBC transfusion. Transfusing older RBCs during canine pneumonia increased mortality rates. Toxicity was associated with in vivo hemolysis with release of cell-free hemoglobin (CFH) and iron. CFH can scavenge nitric oxide, causing vasoconstriction and endothelial injury. Iron, an essential bacterial nutrient, can worsen infections. This toxicity was seen at commonly transfused blood volumes (2 units) and was altered by the severity of pneumonia. Washing longer-stored RBCs mitigated these detrimental effects, but washing fresh RBCs actually increased them. In contrast to septic shock, transfused longer stored RBCs proved beneficial in hemorrhagic shock by decreasing reperfusion injury. Intravenous iron was equivalent in toxicity to transfusion of longer stored RBCs and both should be avoided during infection. Storage of longer-stored RBCs at 2 °C instead of higher standard temperatures (4-6 °C) minimized the release of CFH and iron. Haptoglobin, a plasma protein that binds CFH and increases its clearance, minimizes the toxic effects of longer-stored RBCs during infection and is a biologically plausible novel approach to treat septic shock.

Improved flowing behaviour and gas exchange of stored red blood cells by a compound porous structure

Storage lesions in red blood cells (RBCs) hinder efficient circulation and tissue oxygenation. The absence of flow mechanics and gas exchange may contribute to this problem. To test if in vitro compensation of flow mechanics and gas exchange helps RBC recovery, three-dimensional polydimethylsiloxane (PDMS) porous structures were fabricated with a sugar mould, simulating lung alveoli. RBC suspensions were passed through the porous structure cyclically, simulating in vivo blood circulation. Acid-base indices, partial gas pressures, ions, glucose and RBC indices were analyzed. An atomic force microscope was used to investigate local mechanical properties of intact RBCs. RBCs suspensions that passed through the porous structures had a higher pH and oxygen partial pressure, and a lower potassium concentration and carbon dioxide partial pressure. Meantime they had better biochemical properties relative to static samples, namely, they exhibited a more homogenous distribution of Young's Modulus. RBCs that passed through a PDMS porous structure were healthier than static ones, giving hints to prevent RBC storage lesions.

Inhaled nitric oxide

Nitric oxide (NO) is a gas that induces relaxation of smooth muscle cells in the vasculature. Because NO reacts with oxyhaemoglobin with high affinity, the gas is rapidly scavenged by oxyhaemoglobin in red blood cells and the vasodilating effects of inhaled NO are limited to ventilated regions in the lung. NO therefore has the unique ability to induce pulmonary vasodilatation specifically in the portions of the lung with adequate ventilation, thereby improving oxygenation of blood and decreasing intrapulmonary right to left shunting. Inhaled NO is used to treat a spectrum of cardiopulmonary conditions, including pulmonary hypertension in children and adults. However, the widespread use of inhaled NO is limited by logistical and financial barriers. We have designed, developed and tested a simple and economic NO generation device, which uses pulsed electrical discharges in air to produce therapeutic levels of NO that can be used for inhalation therapy. LINKED ARTICLES: This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc.

Nitric Oxide Decreases Acute Kidney Injury and Stage 3 Chronic Kidney Disease after Cardiac Surgery

RATIONALE

No medical intervention has been identified that decreases acute kidney injury and improves renal outcome at 1 year after cardiac surgery.

OBJECTIVES

To determine whether administration of nitric oxide reduces the incidence of postoperative acute kidney injury and improves long-term kidney outcomes after multiple cardiac valve replacement requiring prolonged cardiopulmonary bypass.

METHODS

Two hundred and forty-four patients undergoing elective, multiple valve replacement surgery, mostly due to rheumatic fever, were randomized to receive either nitric oxide (treatment) or nitrogen (control). Nitric oxide and nitrogen were administered via the gas exchanger during cardiopulmonary bypass and by inhalation for 24 hours postoperatively.

MEASUREMENTS AND MAIN RESULTS

The primary outcome was as follows: oxidation of ferrous plasma oxyhemoglobin to ferric methemoglobin was associated with reduced postoperative acute kidney injury from 64% (control group) to 50% (nitric oxide group) (relative risk [RR], 0.78; 95% confidence interval [CI], 0.62-0.97; P = 0.014). Secondary outcomes were as follows: at 90 days, transition to stage 3 chronic kidney disease was reduced from 33% in the control group to 21% in the treatment group (RR, 0.64; 95% CI, 0.41-0.99; P = 0.024) and at 1 year, from 31% to 18% (RR, 0.59; 95% CI, 0.36-0.96; P = 0.017). Nitric oxide treatment reduced the overall major adverse kidney events at 30 days (RR, 0.40; 95% CI, 0.18-0.92; P = 0.016), 90 days (RR, 0.40; 95% CI, 0.17-0.92; P = 0.015), and 1 year (RR, 0.47; 95% CI, 0.20-1.10; P = 0.041).

CONCLUSIONS

In patients undergoing multiple valve replacement and prolonged cardiopulmonary bypass, administration of nitric oxide decreased the incidence of acute kidney injury, transition to stage 3 chronic kidney disease, and major adverse kidney events at 30 days, 90 days, and 1 year. Clinical trial registered with ClinicalTrials.gov (NCT01802619).

Older Blood Is Associated With Increased Mortality and Adverse Events in Massively Transfused Trauma Patients: Secondary Analysis of the PROPPR Trial

STUDY OBJECTIVE

The transfusion of older packed RBCs may be harmful in critically ill patients. We seek to determine the association between packed RBC age and mortality among trauma patients requiring massive packed RBC transfusion.

METHODS

We analyzed data from the Pragmatic, Randomized Optimal Platelet and Plasma Ratios trial. Subjects in the parent trial included critically injured adult patients admitted to 1 of 12 North American Level I trauma centers who received at least 1 unit of packed RBCs and were predicted to require massive blood transfusion. The primary exposure was volume of packed RBC units transfused during the first 24 hours of hospitalization, stratified by packed RBC age category: 0 to 7 days, 8 to 14 days, 15 to 21 days, and greater than or equal to 22 days. The primary outcome was 24-hour mortality. We evaluated the association between transfused volume of each packed RBC age category and 24-hour survival, using random-effects logistic regression, adjusting for total packed RBC volume, patient age, sex, race, mechanism of injury, Injury Severity Score, Revised Trauma Score, clinical site, and trial treatment group.

RESULTS

The 678 patients included in the analysis received a total of 8,830 packed RBC units. One hundred patients (14.8%) died within the first 24 hours. On multivariable analysis, the number of packed RBCs greater than or equal to 22 days old was independently associated with increased 24-hour mortality (adjusted odds ratio [OR] 1.05 per packed RBC unit; 95% confidence interval [CI] 1.01 to 1.08): OR 0.97 for 0 to 7 days old (95% CI 0.88 to 1.08), OR 1.04 for 8 to 14 days old (95% CI 0.99 to 1.09), and OR 1.02 for 15 to 21 days old (95% CI 0.98 to 1.06). Results of sensitivity analyses were similar only among patients who received greater than or equal to 10 packed RBC units.

CONCLUSION

Increasing quantities of older packed RBCs are associated with increased likelihood of 24-hour mortality in trauma patients receiving massive packed RBC transfusion (≥10 units), but not in those who receive fewer than 10 units.

Iron accelerates hemoglobin oxidation increasing mortality in vascular diseased guinea pigs following transfusion of stored blood

Non-transferrin-bound iron (NTBI) and free hemoglobin (Hb) accumulate in circulation following stored RBC transfusions. This study investigated transfusion, vascular disease, and mortality in guinea pigs after stored RBC transfusion alone and following cotransfusion with apo-transferrin (apo-Tf) and haptoglobin (Hp). The effects of RBC exchange transfusion dose (1, 3, and 9 units), storage period (14 days), and mortality were evaluated in guinea pigs with a vascular disease phenotype. Seven-day mortality and the interaction between iron and Hb as cocontributors to adverse outcome were studied. Concentrations of iron and free Hb were greatest after transfusion with 9 units of stored RBCs compared with fresh RBCs or stored RBCs at 1- and 3-unit volumes. Nine units of stored RBCs led to mortality in vascular diseased animals, but not normal animals. One and 3 units of stored RBCs did not cause a mortality effect, suggesting the concomitant relevance of NTBI and Hb on outcome. Cotransfusion with apo-Tf or Hp restored survival to 100% following 9-unit RBC transfusions in vascular diseased animals. Our data suggest that increases in plasma NTBI and Hb contribute to vascular disease-associated mortality through iron-enhanced Hb oxidation and enhanced tissue injury.

Pulmonary and Systemic Vascular Resistances After Cardiopulmonary Bypass: Role of Hemolysis

OBJECTIVES

Prolonged cardiopulmonary bypass (CPB) is associated with hemolysis, resulting in increased plasma oxyhemoglobin and vascular nitric oxide depletion. The authors hypothesized that hemolysis associated with CPB would reduce nitric oxide bioavailability, resulting in high pulmonary and systemic vascular resistances that after CPB would normalize gradually over time, due to clearance of plasma oxyhemoglobin. The authors also investigated whether prolonged CPB (≥140 min) produced increased levels of hemolysis and greater pulmonary and systemic vasoconstriction.

DESIGN

Prospective cohort study.

SETTING

Single-center university hospital.

PATIENTS

The study comprised 50 patients undergoing elective cardiac surgery requiring CPB.

INTERVENTIONS

Plasma hemoglobin and plasma nitric oxide consumption were measured before surgery and after CPB. Pulmonary and systemic hemodynamics were measured after CPB. The effects of short (<140 min) and prolonged (≥140 min) CPB on these parameters were considered.

MEASUREMENTS AND MAIN RESULTS

Pulmonary and systemic vascular resistances and plasma hemoglobin and nitric oxide consumption were highest at 15 minutes after CPB and then decreased over time. Pulmonary and systemic vascular resistances and plasma hemoglobin and plasma nitric oxide consumption were higher in patients requiring prolonged CPB. The reduction in plasma nitric oxide consumption from 15 minutes to 4 hours after CPB was correlated independently with the reductions in pulmonary and systemic vascular resistances.

CONCLUSIONS

Prolonged CPB was associated with increased plasma hemoglobin and plasma nitric oxide consumption and pulmonary and systemic vascular resistances. The reduction in plasma nitric oxide consumption at 4 hours after CPB was an independent predictor of the concomitant reductions in pulmonary and systemic vascular resistances.

The red cell storage lesion(s): of dogs and men

The advent of preservative solutions permitted refrigerated storage of red blood cells. However, the convenience of having red blood cell inventories was accompanied by a disadvantage. Red cells undergo numerous physical and metabolic changes during cold storage, the "storage lesion(s)". Whereas controlled clinical trials have not confirmed the clinical importance of such changes, ethical and operational issues have prevented careful study of the oldest stored red blood cells. Suggestions of toxicity from meta-analyses motivated us to develop pre-clinical canine models to compare the freshest vs the oldest red blood cells. Our model of canine pneumonia with red blood cell transfusion indicated that the oldest red blood cells increased mortality, that the severity of pneumonia is important, but that the dose of transfused red blood cells is not. Washing the oldest red blood cells reduces mortality by removing senescent cells and remnants, whereas washing fresher cells increases mortality by damaging the red blood cell membrane. An opposite effect was found in a model of haemorrhagic shock with reperfusion injury. Physiological studies indicate that release of iron from old cells is a primary mechanism of toxicity during infection, whereas scavenging of cell-free haemoglobin may be beneficial during reperfusion injury. Intravenous iron appears to have toxicity equivalent to old red blood cells in the pneumonia model, suggesting that intravenous iron and old red blood cells should be administered with caution to infected patients.

Intravascular hemolysis and the pathophysiology of sickle cell disease

Hemolysis is a fundamental feature of sickle cell anemia that contributes to its pathophysiology and phenotypic variability. Decompartmentalized hemoglobin, arginase 1, asymmetric dimethylarginine, and adenine nucleotides are all products of hemolysis that promote vasomotor dysfunction, proliferative vasculopathy, and a multitude of clinical complications of pulmonary and systemic vasculopathy, including pulmonary hypertension, leg ulcers, priapism, chronic kidney disease, and large-artery ischemic stroke. Nitric oxide (NO) is inactivated by cell-free hemoglobin in a dioxygenation reaction that also oxidizes hemoglobin to methemoglobin, a non-oxygen-binding form of hemoglobin that readily loses heme. Circulating hemoglobin and heme represent erythrocytic danger-associated molecular pattern (eDAMP) molecules, which activate the innate immune system and endothelium to an inflammatory, proadhesive state that promotes sickle vaso-occlusion and acute lung injury in murine models of sickle cell disease. Intravascular hemolysis can impair NO bioavailability and cause oxidative stress, altering redox balance and amplifying physiological processes that govern blood flow, hemostasis, inflammation, and angiogenesis. These pathological responses promote regional vasoconstriction and subsequent blood vessel remodeling. Thus, intravascular hemolysis represents an intrinsic mechanism for human vascular disease that manifests clinical complications in sickle cell disease and other chronic hereditary or acquired hemolytic anemias.

Red blood cell transfusion and its effect on microvascular dysfunction in shock states

Among critically ill patients, red blood cell (RBC) transfusion is often prescribed for anemia in the absence of active or recent bleeding. The failure of RBC transfusion to improve physiological parameters and clinical outcomes in this setting may be explained by current understanding of the relationship between the RBCs and the microcirculation. It is now evident that the circulating RBCs contribute to microcirculatory hypoxic vasodilation by regulated nitric oxide (NO)-dependent vasodilation, thereby facilitating delivery of oxygen to oxygen-deprived tissue. The structural and functional changes in RBCs during storage, collectively known as the storage lesion, result in circulating RBCs that may not function as expected after transfusion. In recent years, there has been a significant focus on the dysfunctional interaction between stored RBCs and the microcirculation, with emphasis on understanding the mechanisms that drive erythrocyte NO-mediated vasodilation. The development of technology that allows noninvasive observation of the microcirculation in humans has allowed for direct observation of the microcirculation immediately before and after RBC transfusion. The current understanding of RBC NO-mediated vasodilation and the results of direct observation of the microcirculation in the setting of RBC transfusion are reviewed.

Haptoglobin or Hemopexin Therapy Prevents Acute Adverse Effects of Resuscitation After Prolonged Storage of Red Cells

BACKGROUND

Extracellular hemoglobin and cell-free heme are toxic breakdown products of hemolyzed erythrocytes. Mammals synthesize the scavenger proteins haptoglobin and hemopexin, which bind extracellular hemoglobin and heme, respectively. Transfusion of packed red blood cells is a lifesaving therapy for patients with hemorrhagic shock. Because erythrocytes undergo progressive deleterious morphological and biochemical changes during storage, transfusion of packed red blood cells that have been stored for prolonged intervals (SRBCs; stored for 35-40 days in humans or 14 days in mice) increases plasma levels of cell-free hemoglobin and heme. Therefore, in patients with hemorrhagic shock, perfusion-sensitive organs such as the kidneys are challenged not only by hypoperfusion but also by the high concentrations of plasma hemoglobin and heme that are associated with the transfusion of SRBCs.

METHODS

To test whether treatment with exogenous human haptoglobin or hemopexin can ameliorate adverse effects of resuscitation with SRBCs after 2 hours of hemorrhagic shock, mice that received SRBCs were given a coinfusion of haptoglobin, hemopexin, or albumin.

RESULTS

Treatment with haptoglobin or hemopexin but not albumin improved the survival rate and attenuated SRBC-induced inflammation. Treatment with haptoglobin retained free hemoglobin in the plasma and prevented SRBC-induced hemoglobinuria and kidney injury. In mice resuscitated with fresh packed red blood cells, treatment with haptoglobin, hemopexin, or albumin did not cause harmful effects.

CONCLUSIONS

In mice, the adverse effects of transfusion with SRBCs after hemorrhagic shock are ameliorated by treatment with either haptoglobin or hemopexin. Haptoglobin infusion prevents kidney injury associated with high plasma hemoglobin concentrations after resuscitation with SRBCs. Treatment with the naturally occurring human plasma proteins haptoglobin or hemopexin may have beneficial effects in conditions of severe hemolysis after prolonged hypotension.

Perioperative Red Blood Cell Transfusion: What We Do Not Know

Objective:

Blood transfusion saves lives but may also increase the risk of injury. The objective of this review was to evaluate the possible adverse effects related to transfusion of red blood cell (RBC) concentrates stored for prolonged periods.

Data Sources:

The data used in this review were mainly from PubMed articles published in English up to February 2015.

Study Selection:

Clinical and basic research articles were selected according to their relevance to this topic.

Results:

The ex vivo changes to RBC that occur during storage are collectively called storage lesion. It is still inconclusive if transfusion of RBC with storage lesion has clinical relevance. Multiple ongoing prospective randomized controlled trials are aimed to clarify this clinical issue. It was observed that the adverse events related to stored RBC transfusion were prominent in certain patient populations, including trauma, critical care, pediatric, and cardiac surgery patients, which leads to the investigation of underlying mechanisms. It is demonstrated that free hemoglobin toxicity, decreasing of nitric oxide bioavailability, and free iron-induced increasing of inflammation may play an important role in this process.

Conclusion:

It is still unclear whether transfusion of older RBC has adverse effects, and if so, which factors determine such clinical effects. However, considering the magnitude of transfusion and the widespread medical significance, potential preventive strategies should be considered, especially for the susceptible recipients.

Effects of Aged Stored Autologous Red Blood Cells on Human Endothelial Function

RATIONALE

A major abnormality that characterizes the red cell "storage lesion" is increased hemolysis and reduced red cell lifespan after infusion. Low levels of intravascular hemolysis after transfusion of aged stored red cells disrupt nitric oxide (NO) bioavailabity, via accelerated NO scavenging reaction with cell-free plasma hemoglobin. The degree of intravascular hemolysis post-transfusion and effects on endothelial-dependent vasodilation responses to acetylcholine have not been fully characterized in humans.

OBJECTIVES

To evaluate the effects of blood aged to the limits of Food and Drug Administration-approved storage time on the human microcirculation and endothelial function.

METHODS

Eighteen healthy individuals donated 1 U of leukopheresed red cells, divided and autologously transfused into the forearm brachial artery 5 and 42 days after blood donation. Blood samples were obtained from stored blood bag supernatants and the antecubital vein of the infusion arm. Forearm blood flow measurements were performed using strain-gauge plethysmography during transfusion, followed by testing of endothelium-dependent blood flow with increasing doses of intraarterial acetylcholine.

MEASUREMENTS AND MAIN RESULTS

We demonstrate that aged stored blood has higher levels of arginase-1 and cell-free plasma hemoglobin. Compared with 5-day blood, the transfusion of 42-day packed red cells decreases acetylcholine-dependent forearm blood flows. Intravascular venous levels of arginase-1 and cell-free plasma hemoglobin increase immediately after red cell transfusion, with more significant increases observed after infusion of 42-day-old blood.

CONCLUSIONS

We demonstrate that the transfusion of blood at the limits of Food and Drug Administration-approved storage has a significant effect on the forearm circulation and impairs endothelial function. Clinical trial registered with www.clinicaltrials.gov (NCT 01137656).

Transfused older stored red blood cells improve the clinical course and outcome in a canine lethal hemorrhage and reperfusion model

BACKGROUND

In canine models, transfused older stored red blood cells (RBCs) hemolyze in vivo resulting in significantly increased intravascular cell-free hemoglobin (CFH) and non-transferrin-bound iron (NTBI). During canine bacterial pneumonia with septic shock, but not in controls, older stored RBCs were associated with significantly increased lung injury and mortality. It is unknown if in shock without infection transfusion of older RBCs will result in similar adverse effects.

STUDY DESIGN AND METHODS

Two-year-old purpose-bred beagles (n = 12) were transfused similar quantities of either older (42-day) or fresher (7-day) stored universal donor canine RBCs 2.5 hours after undergoing controlled hemorrhage (55 mL/kg).

RESULTS

With older transfused RBCs, CFH (p < 0.0001) and NTBI (p = 0.004) levels increased, but lung injury (p = 0.01) and C-reactive protein levels (p = 0.002) declined and there was a trend toward lower mortality (18% vs. 50%). All three deaths after transfused fresher RBCs resulted from hepatic fractures. Lowered exogenous norepinephrine requirements (p < 0.05) and cardiac outputs (p < 0.05) after older transfused RBCs were associated with increased CFH levels that have known vasoconstrictive nitric oxide scavenging capability.

CONCLUSIONS

In hemorrhagic shock, older RBCs altered resuscitation physiology but did not worsen clinical outcomes. Elevated CFH may lower norepinephrine requirements and cardiac outputs ameliorating reperfusion injuries. With hemorrhagic shock, NTBI levels persist in contrast to the increased clearance, lung injury, and mortality in the previously reported infection model. These preclinical data suggest that whereas iron derived from older RBCs promotes bacterial growth, worsening septic shock mortality during infection, release of CFH and NTBI during hemorrhagic shock is not necessarily harmful.

Red blood cell washing, nitrite therapy, and antiheme therapies prevent stored red blood cell toxicity after trauma-hemorrhage

Transfusion of stored red blood cells (RBCs) is associated with increased morbidity and mortality in trauma patients. Pro-oxidant, pro-inflammatory, and nitric oxide (NO) scavenging properties of stored RBCs are thought to underlie this association. In this study we determined the effects of RBC washing and nitrite and antiheme therapy on stored RBC-dependent toxicity in the setting of trauma-induced hemorrhage. A murine (C57BL/6) model of trauma-hemorrhage and resuscitation with 1 or 3 units of RBCs stored for 0-10 days was used. Tested variables included washing RBCs to remove lower MW components that scavenge NO, NO-repletion therapy using nitrite, or mitigation of free heme toxicity by heme scavenging or preventing TLR4 activation. Stored RBC toxicity was determined by assessment of acute lung injury indices (airway edema and inflammation) and survival. Transfusion with 5 day RBCs increased acute lung injury indexed by BAL protein and neutrophil accumulation. Washing 5 day RBCs prior to transfusion did not decrease this injury, whereas nitrite therapy did. Transfusion with 10 day RBCs elicited a more severe injury resulting in ~90% lethality, compared to <15% with 5 day RBCs. Both washing and nitrite therapy significantly protected against 10 day RBC-induced lethality, suggesting that washing may be protective when the injury stimulus is more severe. Finally, a spectral deconvolution assay was developed to simultaneously measure free heme and hemoglobin in stored RBC supernatants, which demonstrated significant increases of both in stored human and mouse RBCs. Transfusion with free heme partially recapitulated the toxicity mediated by stored RBCs. Furthermore, inhibition of TLR4 signaling, which is stimulated by heme, using TAK-242, or hemopexin-dependent sequestration of free heme significantly protected against both 5 day and 10 day mouse RBC-dependent toxicity. These data suggest that RBC washing, nitrite therapy, and/or antiheme and TLR4 strategies may prevent stored RBC toxicities.

Effects of inhalation of low-dose nitrite or carbon monoxide on post-reperfusion mitochondrial function and tissue injury in hemorrhagic shock swine

Introduction

Tissue reperfusion following hemorrhagic shock may paradoxically cause tissue injury and organ dysfunction by mitochondrial free radical expression. Both nitrite and carbon monoxide (CO) may protect from this reperfusion injury by limiting mitochondrial free radial production. We explored the effects of very small doses of inhaled nitrite and CO on tissue injury in a porcine model of hemorrhagic shock.

Methods

Twenty pigs (mean wt. 30.6 kg, range 27.2 to 36.4 kg) had microdialysis catheters inserted in muscle, peritoneum, and liver to measure lactate, pyruvate, glucose, glycerol, and nitrite. Nineteen of the pigs were bled at a rate of 20 ml/min to a mean arterial pressure of 30 mmHg and kept between 30 and 40 mmHg for 90 minutes and then resuscitated. One pig was instrumented but not bled (sham). Hemorrhaged animals were randomized to inhale nothing (control, n = 7), 11 mg nitrite (nitrite, n = 7) or 250 ppm CO (CO, n = 5) over 30 minutes before fluid resuscitation. Mitochondrial respiratory control ratio was measured in muscle biopsies. Repeated measures from microdialysis catheters were analyzed in a random effects mixed model.

Results

Neither nitrite nor CO had any effects on the measured hemodynamic variables. Following inhalation of nitrite, plasma, but not tissue, nitrite increased. Following reperfusion, plasma nitrite only increased in the control and CO groups. Thereafter, nitrite decreased only in the nitrite group. Inhalation of nitrite was associated with decreases in blood lactate, whereas both nitrite and CO were associated with decreases in glycerol release into peritoneal fluid. Following resuscitation, the muscular mitochondrial respiratory control ratio was reduced in the control group but preserved in the nitrite and CO groups.

Conclusions

We conclude that small doses of nebulized sodium nitrite or inhaled CO may be associated with intestinal protection during resuscitation from severe hemorrhagic shock.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-0903-z) contains supplementary material, which is available to authorized users.

Autologous transfusion of stored red blood cells increases pulmonary artery pressure

RATIONALE

Transfusion of erythrocytes stored for prolonged periods is associated with increased mortality. Erythrocytes undergo hemolysis during storage and after transfusion. Plasma hemoglobin scavenges endogenous nitric oxide leading to systemic and pulmonary vasoconstriction.

OBJECTIVES

We hypothesized that transfusion of autologous blood stored for 40 days would increase the pulmonary artery pressure in volunteers with endothelial dysfunction (impaired endothelial production of nitric oxide). We also tested whether breathing nitric oxide before and during transfusion could prevent the increase of pulmonary artery pressure.

METHODS

Fourteen obese adults with endothelial dysfunction were enrolled in a randomized crossover study of transfusing autologous, leukoreduced blood stored for either 3 or 40 days. Volunteers were transfused with 3-day blood, 40-day blood, and 40-day blood while breathing 80 ppm nitric oxide.

MEASUREMENTS AND MAIN RESULTS

The age of volunteers was 41 ± 4 years (mean ± SEM), and their body mass index was 33.4 ± 1.3 kg/m(2). Plasma hemoglobin concentrations increased after transfusion with 40-day and 40-day plus nitric oxide blood but not after transfusing 3-day blood. Mean pulmonary artery pressure, estimated by transthoracic echocardiography, increased after transfusing 40-day blood (18 ± 2 to 23 ± 2 mm Hg; P < 0.05) but did not change after transfusing 3-day blood (17 ± 2 to 18 ± 2 mm Hg; P = 0.5). Breathing nitric oxide decreased pulmonary artery pressure in volunteers transfused with 40-day blood (17 ± 2 to 12 ± 1 mm Hg; P < 0.05).

CONCLUSIONS

Transfusion of autologous leukoreduced blood stored for 40 days was associated with increased plasma hemoglobin levels and increased pulmonary artery pressure. Breathing nitric oxide prevents the increase of pulmonary artery pressure produced by transfusing stored blood. Clinical trial registered with www.clinicaltrials.gov (NCT 01529502).

Immunosuppressive/anti-inflammatory cytokines directly and indirectly inhibit endothelial dysfunction--a novel mechanism for maintaining vascular function

Endothelial dysfunction is a pathological status of the vascular system, which can be broadly defined as an imbalance between endothelium-dependent vasoconstriction and vasodilation. Endothelial dysfunction is a key event in the progression of many pathological processes including atherosclerosis, type II diabetes and hypertension. Previous reports have demonstrated that pro-inflammatory/immunoeffector cytokines significantly promote endothelial dysfunction while numerous novel anti-inflammatory/immunosuppressive cytokines have recently been identified such as interleukin (IL)-35. However, the effects of anti-inflammatory cytokines on endothelial dysfunction have received much less attention. In this analytical review, we focus on the recent progress attained in characterizing the direct and indirect effects of anti-inflammatory/immunosuppressive cytokines in the inhibition of endothelial dysfunction. Our analyses are not only limited to the importance of endothelial dysfunction in cardiovascular disease progression, but also expand into the molecular mechanisms and pathways underlying the inhibition of endothelial dysfunction by anti-inflammatory/immunosuppressive cytokines. Our review suggests that anti-inflammatory/immunosuppressive cytokines serve as novel therapeutic targets for inhibiting endothelial dysfunction, vascular inflammation and cardio- and cerebro-vascular diseases.

Adverse effects of hemorrhagic shock resuscitation with stored blood are ameliorated by inhaled nitric oxide in lambs*

OBJECTIVES

Transfusion of stored RBCs is associated with increased morbidity and mortality in trauma patients. Plasma hemoglobin scavenges nitric oxide, which can cause vasoconstriction, induce inflammation, and activate platelets. We hypothesized that transfusion of RBCs stored for prolonged periods would induce adverse effects (pulmonary vasoconstriction, tissue injury, inflammation, and platelet activation) in lambs subjected to severe hemorrhagic shock and that concurrent inhalation of nitric oxide would prevent these adverse effects.

DESIGN

Animal study.

SETTING

Research laboratory at the Massachusetts General Hospital, Boston, MA.

SUBJECTS

Seventeen awake Polypay-breed lambs.

INTERVENTIONS

Lambs were subjected to 2 hours of hemorrhagic shock by acutely withdrawing 50% of their blood volume. Lambs were resuscitated with autologous RBCs stored for 2 hours or less (fresh) or 39 ± 2 (mean ± SD) days (stored). Stored RBCs were administered with or without breathing nitric oxide (80 ppm) during resuscitation and for 21 hours thereafter.

MEASUREMENTS AND MAIN RESULTS

We measured hemodynamic and oxygenation variables, markers of tissue injury and inflammation, plasma hemoglobin concentrations, and platelet activation. Peak pulmonary arterial pressure was higher after resuscitation with stored than with fresh RBCs (24 ± 4 vs 14 ± 2 mm Hg, p < 0.001) and correlated with peak plasma hemoglobin concentrations (R = 0.56, p = 0.003). At 21 hours after resuscitation, pulmonary myeloperoxidase activity was higher in lambs resuscitated with stored than with fresh RBCs (11 ± 2 vs 4 ± 1 U/g, p = 0.007). Furthermore, transfusion of stored RBCs increased plasma markers of tissue injury and sensitized platelets to adenosine diphosphate activation. Breathing nitric oxide prevented the pulmonary hypertension and attenuated the pulmonary myeloperoxidase activity, as well as tissue injury and sensitization of platelets to adenosine diphosphate.

CONCLUSIONS

Our data suggest that resuscitation of lambs from hemorrhagic shock with autologous stored RBCs induces pulmonary hypertension and inflammation, which can be ameliorated by breathing nitric oxide.

Assessing murine resistance artery function using pressure myography

Pressure myograph systems are exquisitely useful in the functional assessment of small arteries, pressurized to a suitable transmural pressure. The near physiological condition achieved in pressure myography permits in-depth characterization of intrinsic responses to pharmacological and physiological stimuli, which can be extrapolated to the in vivo behavior of the vascular bed. Pressure myograph has several advantages over conventional wire myographs. For example, smaller resistance vessels can be studied at tightly controlled and physiologically relevant intraluminal pressures. Here, we study the ability of 3(rd) order mesenteric arteries (3-4 mm long), preconstricted with phenylephrine, to vaso-relax in response to acetylcholine. Mesenteric arteries are mounted on two cannulas connected to a pressurized and sealed system that is maintained at constant pressure of 60 mmHg. The lumen and outer diameter of the vessel are continuously recorded using a video camera, allowing real time quantification of the vasoconstriction and vasorelaxation in response to phenylephrine and acetylcholine, respectively. To demonstrate the applicability of pressure myography to study the etiology of cardiovascular disease, we assessed endothelium-dependent vascular function in a murine model of systemic hypertension. Mice deficient in the α1 subunit of soluble guanylate cyclase (sGCα1(-/-)) are hypertensive when on a 129S6 (S6) background (sGCα1(-/-S6)) but not when on a C57BL/6 (B6) background (sGCα1(-/-B6)). Using pressure myography, we demonstrate that sGCα1-deficiency results in impaired endothelium-dependent vasorelaxation. The vascular dysfunction is more pronounced in sGCα1(-/-S6) than in sGCα1(-/-B6) mice, likely contributing to the higher blood pressure in sGCα1(-/-S6) than in sGCα1(-/-B6) mice. Pressure myography is a relatively simple, but sensitive and mechanistically useful technique that can be used to assess the effect of various stimuli on vascular contraction and relaxation, thereby augmenting our insight into the mechanisms underlying cardiovascular disease.

Hemoglobin infusion does not alter murine pulmonary vascular tone

Plasma hemoglobin (Hb) scavenges endothelium-derived nitric oxide (NO), producing systemic and pulmonary vasoconstriction in many species. We hypothesized that i.v. administration of murine cell-free Hb would produce pulmonary vasoconstriction and enhance hypoxic pulmonary vasoconstriction (HPV) in mice. To assess the impact of plasma Hb on basal pulmonary vascular tone in anesthetized mice we measured left lung pulmonary vascular resistance (LPVRI) before and after infusion of Hb at thoracotomy. To confirm the findings obtained at thoracotomy, measurements of right ventricular systolic pressure (RVSP) and systemic arterial pressure (SAP) were obtained in closed-chest wild-type mice. To elucidate whether pretreatment with Hb augments HPV we assessed the increase in LPVRI before and during regional lung hypoxia produced by left mainstem bronchial occlusion (LMBO) in wild-type mice pretreated with Hb. Infusion of Hb increased SAP but did not change pulmonary arterial pressure (PAP), left lung pulmonary arterial flow (QLPA) or LPVRI in either wild-type or diabetic mice with endothelial dysfunction. Scavenging of NO by plasma Hb did not alter HPV in wild-type mice. Inhibition of NO synthase with l-NAME did not change the basal LPVRI, but augmented HPV during LMBO. Our data suggest that scavenging of NO by plasma Hb does not alter pulmonary vascular tone in mice. Therefore, generation of NO in the pulmonary circulation is unlikely to be responsible for the low basal pulmonary vascular tone of mice.