Adverse Effects of RBC Transfusions: A Unifying Hypothesis
Condition: Healthy Volunteers
Study type: Interventional
Phase: Phase 2

Summary: 
      Transfusion of red blood cells is often used in critically ill patients with low red blood
      cell counts to prevent disease progression and death. Recent studies suggest that the use of
      "aged" versus "fresh" red blood cells are associated with worse clinical outcomes. There is
      evidence that red blood cells work with the cells lining our blood vessels to produce a
      variety of substances that normally cause arteries to relax and increase blood supply. Two of
      these substances are called nitric oxide (NO) and endothelium-derived hyperpolarizing factor
      (EDHF). The investigators are trying to determine the nature of these substances in human
      beings when they are transfused "aged" versus "fresh" red blood cells. It is their thought
      that "aged" red blood cells have less of the substances (NO and EDHF) that naturally relax
      our arteries and further changes the blood supply. One way to determine this is to transfuse
      a subject's own "aged" and "fresh" red blood cells and inject substances such as L-NMMA (L-NG
      monomethyl arginine) and TEA (tetraethylammonium chloride), which block the production of NO
      and EDHF respectively, and then, study what happens to the blood flow.

      There is evidence that red blood cells produce NO, which normally causes arteries to relax
      and increase blood supply. The investigators will try to determine the nature of NO in red
      blood cells and whether the amount of this substance is altered because of different blood
      processing and storage techniques. It is their thought that "aged" red blood cells have less
      NO that naturally relaxes our arteries and further changes the blood supply. This study is
      designed to determine the most ideal way of storing and processing blood.
    

Detailed description: 
      Transfusion of red blood cells (RBCs) is often effective at preventing morbidity and
      mortality in anemic patients. In contrast, recent studies indicate that some RBC components
      may have functional defects ("RBC storage lesions") that actually cause morbidity and
      mortality when transfused. For example, patients transfused with RBCs stored >14 days have
      statistically worse outcomes than those receiving "fresher" RBC units. In addition to the age
      of stored RBCs, the volume transfused may be important. The TRICC study showed that specific
      patients whose transfusions were limited by a restrictive trigger (RBCs transfusions only
      when hemoglobin [Hb] < 7 g/dL) had significantly better outcomes than those transfused with a
      more liberal trigger ([Hb] < 10 g/dL Hb). This finding has been particularly difficult to
      understand since conventional wisdom suggests that an elevated [Hb] should be beneficial
      because it supports increased O2 delivery. Recipient-specific factors may also contribute to
      the occurrence of these adverse events. Unfortunately, these events have been difficult to
      investigate because up to now they have existed only as "statistical occurrences" of
      increased morbidity and mortality in large data sets. There are currently no clinical or
      laboratory methods to detect or study them in individual patients.

      The microcirculation is composed of a continuum of small vessels including small arterioles,
      capillaries, and post-capillary venules. The microcirculation represents an
      actively-adjusting vascular circuit that matches blood flow (and O2 delivery) to local tissue
      oxygen demands. While the physiologic mechanisms that match O2 delivery to local requirements
      are incompletely understood, endothelium-derived nitric oxide (NO) clearly plays an important
      role. Interestingly, recent work has revealed that in addition to transporting O2 and CO2,
      the RBC also controls local NO concentrations and thus may also play a surprisingly important
      role in regulating blood flow in the microcirculation.

      Herein, the investigators bring together previously unconnected data to propose a unifying
      hypothesis, centered on insufficient NO bioavailability (INOBA), to explain the increased
      morbidity and mortality observed in some patients following RBC transfusion. In this model,
      variables associated with RBC units (storage time; 2,3-DPG concentration) and transfusion
      recipients (endothelial dysfunction; hematocrit [Hct]) collectively lead to changes in NO
      levels in vascular beds. Under certain circumstances, these variables are "aligned" such that
      NO concentrations are markedly reduced, leading to vasoconstriction, decreased local blood
      flow and insufficient O2 delivery to end organs. Under these circumstances, the likelihood of
      morbidity and mortality escalates. The INOBA hypothesis is attractive because of its
      explanatory power and because it leads to a number of readily testable predictions, which
      will be investigated in the following aims:

      Aim 1: To investigate the effects of blood processing and storage (using standard
      FDA-approved conditions) on NO production and scavenging by human RBCs/Hb in vitro. Using
      sensitive biochemical assays (electron spin resonance [ESR]) and a rat aortic ring in vitro
      bioassay, the investigators will test the effects of RBC storage time, leukoreduction, and
      irradiation on NO synthesis and/or scavenging by intact RBCs and free Hb. Modifications such
      as washing and rejuvenation will be investigated as possible approaches to correct
      abnormalities in NO bioavailability.

      Aim 2: To transfuse healthy volunteers and investigate the effects of storage-related RBC
      changes on blood flow, tissue oxygenation, and biomarkers of cardiovascular function. The
      investigators will determine whether RBCs prepared and stored under conditions that alter NO
      bioavailability in vitro (Aim 1) inhibit NO-mediated vasodilation, reduce tissue perfusion,
      and decrease tissue O2 delivery in healthy transfusion recipients in vivo. The role of
      2,3-DPG depletion as well as exercise-induced O2 demand will also be investigated with these
      specialized experimental systems.
    

Intervention name(s): Fresh blood; Aged blood
Intervention type(s): Biological; Biological
Intervention description(s): For fresh transfusions, a whole blood unit will be drawn from volunteers, processed, and then reinfused on the same day during the study. For impaired and repaired transfusions, the volunteers will be brought to the blood bank to donate; then, after processing and the appropriate length of storage (eg, 28 days), they will return for the FBF studies. Since recipients of fresh transfusions are relatively anemic after donation and before reinfusion, recipients of impaired/repaired transfusions should also be mildly anemic for the study. Thus, they will donate another whole blood unit prior to beginning the study course, they will be transfused with their stored unit during the study, and then the autologous unit collected at the beginning of the day will be reinfused at the end of the day after the study is complete.; In a separate aim, the FMD assay will be used to investigate NO-mediated vasodilation in patients with CVD who are receiving transfusions. Over 60% of blood orders for cardiology patients at Emory are for 2 units or more. Therefore, when a 2-unit order is placed on a consented patient, they will be issued both fresh (< 7 days) and impaired (> 28 days) compatible units from inventory. Prior to starting transfusions, the patient will be randomized to either receive the fresh or the older unit first. All RBC units will be ACD/AS1. Units will also be leukoreduced and/or irradiated, if either of those modifications were found to impair NO bioavailability in prior studies. If washing or rejuvenation were found to be successful in significantly "repairing" NO bioavailability in previous aims, some patients may also receive impaired and repaired (> 28 days; washed or rejuvenated) RBC transfusions.
Intervention model: Single Group Assignment
Masking: None (Open Label)
Primary purpose: Treatment
Keywords: Blood Transfusions