New frontiers in transfusion biology: identification and significance of mediators of morbidity and mortality in stored red blood cells

Transfusion immunomodulation--the case for leukoreduced and (perhaps) washed transfusions

During the last three decades, a growing body of clinical, basic science and animal model data has demonstrated that blood transfusions have important effects on the immune system. These effects include: dysregulation of inflammation and innate immunity leading to susceptibility to microbial infection, down-regulation of cellular (T and NK cell) host defenses against tumors, and enhanced B cell function that leads to alloimmunization to blood group, histocompatibility and other transfused antigens. Furthermore, transfusions alter the balance between hemostasis and thrombosis through inflammation, nitric oxide scavenging, altered rheologic properties of the blood, immune complex formation and, no doubt, several mechanisms not yet elucidated. The net effects are rarely beneficial to patients, unless they are in imminent danger of death due to exsanguination or life threatening anemia. These findings have led to appeals for more conservative transfusion practice, buttressed by randomized trials showing that patients do not benefit from aggressive transfusion practices. At the risk of hyperbole, one might suggest that if the 18th and 19th centuries were characterized by physicians unwittingly harming patients through venesection and bleeding, the 20th century was characterized by physicians unwittingly harming patients through current transfusion practices. In addition to the movement to more parsimonious use of blood transfusions, an effort has been made to reduce the toxic effects of blood transfusions through modifications such as leukoreduction and saline washing. More recently, there is early evidence that reducing the storage period of red cells transfused might be a strategy for minimizing adverse outcomes such as infection, thrombosis, organ failure and mortality in critically ill patients particularly at risk for these hypothesized effects. The present review will focus on two approaches, leukoreduction and saline washing, as means to reduce adverse transfusion outcomes.

Effects of pre-storage leukoreduction on stored red blood cells signaling: a time-course evaluation from shape to proteome

The introduction of pre-storage leukoreduction in the preparation of standard RBCs intended for transfusion provided significant improvement in the quality of labile products and their post transfusion viability and effects, although the literature data are controversial. To elucidate the issue of the probable leukoreduction effects on RBCs storage lesion, we evaluated various storage quality measures in RBCs stored in either leukoreduced (L) or non-leukoreduced (N) units, with emphasis to senescence and oxidative stress associated modifications. Our data suggest that the residual leukocytes/platelets of the labile products represent a stressful storage factor, countering the structural and functional integrity of stored RBCs. Hemolysis, irreversible echinocytosis, microvesiculation, removal signaling, ROS/calcium accumulation, band 3-related senescence modifications, membrane proteome stress biomarkers as well as emergence of a senescence phenotype in young RBCs that is disproportionate to their age, are all encountered more or mostly in N-RBCs compared to the L-RBCs, either for a part or for the whole of the storage period. The partial, yet significant, alleviation of so many storage-related manifestations in the L-RBCs compared to the N-RBCs, is presented for the first time and provides a rational mechanistic interpretation of the improved storage quality and transfusions observed by the introduction of pre-storage leukoreduction. This article is part of a Special Issue entitled: Integrated omics.

Stored red blood cell transfusions: Iron, inflammation, immunity, and infection

The potential adverse effects of transfusion of red blood cells after prolonged storage have been hotly debated. During refrigerated storage, red blood cells are damaged, a process known as the red blood cell "storage lesion." We hypothesized that the delivery of a bolus of iron derived from these rapidly cleared, damaged, red blood cells is responsible for some of the adverse effects of transfusion. Iron may play a role in producing a pro-inflammatory response to transfused red blood cells, potentially through the effects of reactive oxygen species on stress pathways and inflammasome activation. Furthermore, the excess iron may impair the host's ability to combat infection by its innate iron-withholding pathways. This symposium paper summarizes the background for the "iron hypothesis" as it relates to transfusion of red blood cells after prolonged refrigerated storage. It also includes a summary of the data from recent murine and human studies, and concludes with a discussion of several unresolved questions arising from these published studies.

Pulmonary hypertension in lambs transfused with stored blood is prevented by breathing nitric oxide

BACKGROUND

During extended storage, erythrocytes undergo functional changes. These changes reduce the viability of erythrocytes leading to release of oxyhemoglobin, a potent scavenger of nitric oxide. We hypothesized that transfusion of ovine packed erythrocytes (PRBC) stored for prolonged periods would induce pulmonary vasoconstriction in lambs, and that reduced vascular nitric oxide concentrations would increase this vasoconstrictor effect.

METHODS

We developed a model of autologous stored blood transfusion in lambs (n = 36). Leukoreduced blood was stored for either 2 days (fresh PRBC) or 40 days (stored PRBC). Fresh or stored PRBC were transfused into donors instrumented for awake hemodynamic measurements. Hemodynamic effects of PRBC transfusion were also studied after infusion of N-nitro-L-arginine methyl-ester (25 mg/kg) or during inhalation of nitric oxide (80 ppm).

RESULTS

Cell-free hemoglobin levels were higher in the supernatant of stored PRBC than in supernatant of fresh PRBC (Mean ± SD, 148 ± 20 vs. 41 ± 13 mg/dl, respectively, P < 0.001). Pulmonary artery pressure during transfusion of stored PRBC transiently increased from 13 ± 1 to 18 ± 1 mmHg (P < 0.001) and was associated with increased plasma hemoglobin concentrations. N-nitro-L-arginine methyl-ester potentiated the increase in pulmonary arterial pressure induced by transfusing stored PRBC, whereas inhalation of nitric oxide prevented the vasoconstrictor response.

CONCLUSIONS

Our results suggest that patients with reduced vascular nitric oxide levels because of endothelial dysfunction may be more susceptible to adverse effects of transfusing blood stored for prolonged periods. These patients might benefit from transfusion of fresh PRBC, when available, or inhaled nitric oxide supplementation to prevent the pulmonary hypertension associated with transfusion of stored PRBC.

Microparticles from stored red blood cells activate neutrophils and cause lung injury after hemorrhage and resuscitation

BACKGROUND

Transfusion of stored blood is associated with increased complications. Microparticles (MPs) are small vesicles released from RBCs that can induce cellular dysfunction, but the role of RBC-derived MPs in resuscitation from hemorrhagic shock is unknown. In the current study, we examined the effects of RBC-derived MPs on the host response to hemorrhage and resuscitation.

STUDY DESIGN

MPs were isolated from murine packed RBC units, quantified using flow cytometry, and injected into healthy mice. Separate groups of mice underwent hemorrhage and resuscitation with and without packed RBC-derived MPs. Lungs were harvested for histology and neutrophil accumulation and assessed by myeloperoxidase content. Human neutrophils were treated with human RBC-derived MPs and CD11b expression, superoxide production, and phagocytic activity were determined.

RESULTS

Stored murine packed RBC units contained increased numbers of RBC-derived MPs compared with fresh units. Hemorrhaged mice resuscitated with MPs demonstrated substantially increased pulmonary neutrophil accumulation and altered lung histology compared with mice resuscitated without MPs. Intravenous injection of MPs into normal mice resulted in neutrophil priming, evidenced by increased neutrophil CD11b expression. Human neutrophils treated with RBC-derived MPs demonstrated increased CD11b expression, increased superoxide production, and enhanced phagocytic ability compared with untreated neutrophils.

CONCLUSIONS

Stored packed RBC units contain increased numbers of RBC-derived MPs. These MPs appear to contribute to neutrophil priming and activation. The presence of MPs in stored units can be associated with adverse effects, including lung injury, after transfusion.

Haemolysis and sublethal injury of RBCs after routine blood bank manipulations

OBJECTIVES

To determine the extent of RBC sublethal injury in male donor units as measured by both the mechanical fragility index (MFI) and percentage haemolysis after RBCs underwent leucoreduction (LR), irradiation (IRRAD), and washing.

BACKGROUND

RBCs frequently undergo post-collection processing to meet certain recipient's special needs. The extent of haemolysis and sublethal injury following these interventions has not been fully characterised.

METHODS

Eight to ten day old male, AS-5 RBCs underwent either LR, IRRAD or washing. A control group of male, AS-5 RBCs were unmanipulated. The MFI, percent haemolysis, and plasma free haemoglobin (PFHb) were measured immediately after manipulation and, for a series of irradiated RBCs, 28 days after irradiation (IRRAD28).

RESULTS

The MFI of the washed units was significantly higher than unmanipulated, LR, IRRAD, IRRAD28 units (P < 0·0001). The percent haemolysis was highest in the IRRAD28 units (1·4%) followed by the washed units (0·74%); the other three units demonstrated significantly less haemolysis (P < 0·0001). The largest mean total amount of PFHb per unit was found in the IRRAD28 units (500·5 mg/unit) followed by the washed units (149·8 mg/unit); the mean total amount of PFHb in the three other types of units was significantly less than that found in both the IRRAD28 and washed units (P at least < 0·001).

CONCLUSION

There is a significant quantity of PFHb in IRRAD28 RBC units, and potentially in washed allogeneic RBC units. Clinical correlation is required to determine if this quantity of PFHb and the transfusion of potentially fragile RBCs causes adverse events.