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  1. Science & Research (Biologics)

Evaluating the Safety and Efficacy of Hemoglobin-based Blood Substitutes


Abdu I. Alayash, Ph.D., D.Sc. headshot

Abdu I. Alayash, Ph.D., D.Sc.

Office of Blood Research and Review
Division of Blood Components and Devices
Laboratory of Biochemistry and Vascular Biology



Dr. Alayash joined CBER in 1989, beginning as a Senior Staff Fellow in the Office of Blood Research and Review (OBRR). Dr. Alayash is the Chief of the Laboratory of Biochemistry and Vascular Biology (LBVB), which he established in 2004.  Dr. Alayash obtained his PhD in Biochemistry (1978) as well as a DSc in Biochemistry (2011) from the University of Essex, Colchester, United Kingdom. In 2013, Dr. Alayash was awarded an honorary doctorate from Lund University, Sweden for research accomplishments in the field of blood substitutes. He is a member of the FDA Senior Biomedical Research and Biomedical Product Assessment Service (SBRBPAS).

General Overview

The development of a safe and effective blood substitute would greatly improve the emergency treatment of accident victims and wounded soldiers, as well as patients undergoing elective surgeries, especially when blood is not available. These products, also known as "hemoglobin-based oxygen carriers" (HBOCs), have undergone extensive testing in animals and in humans over the last 3 decades. HBOCs use the natural oxygen-carrying molecule, hemoglobin (Hb), to carry oxygen throughout the body. However, because the Hb used for HBOCs is no longer inside red blood cells (RBCs), it tends to be toxic in the blood. This cell-free Hb can cause high blood pressure; Hb can also escape blood vessels and damage the kidneys and other organs. Because there was no   scientific and/or regulatory historical precedent, understanding how free Hb behaves outside the protective environment of an RBC becomes a very challenging problem facing industrial and the scientific communities. Our laboratory is trying to a) understand the complexities associated with the interaction of Hb with the vascular system and b) attempt to overcome toxicities.

We have successfully used the body's own defense mechanisms, such as plasma-derived haptoglobin (oxidized Hb scavenger) and hemopexin (heme scavenger) against Hb oxidative toxicity in animal models. Further, we have embarked on a two-prong strategy. First, we explored naturally occurring mutants of human Hb, which are considered experiments in nature that have evolved over the years to resist oxidation or have developed into a full hematological disorder. Second, we utilized this knowledge to design approaches to increase or decrease these reactions in acellular oxygen therapeutics that will result in oxidatively stable and safe protein. For example, we have recently discovered that Hb Providence is a very stable protein. We have introduced the Providence mutation into a newly designed HBOC, which shows a remarkable resistance to oxidation. This is a critical element in the design of safe and effective oxygen therapeutics.

Several manufacturers and research institutions are now designing second-generation blood substitutes that are oxidatively stable and could potentially be effective lifesaving oxygen therapeutics. Our work therefore is contributing to the regulatory and research efforts of CBER to support development of safe and effective products that improve public health in the U.S. and worldwide. Using our extensive expertise with Hb oxygen transport and reduction-oxidation (redox) chemistry, we have begun a pilot study on the effects of COVID-19 infection on oxygen homeostasis and other signaling pathways.

Scientific Overview

HBOCs have many potential advantages over human blood, including availability, compatibility, and long-term storage. However, they also raise a number of concerns, including toxicity. The basis of HBOC toxicity is poorly understood; most research done by industry is proprietary, and there is only minimal exchange of information among investigators. The focus of research in this program is on the structural-functional characterization of modified Hb in relation to its redox chemistry and toxicity. Specifically, we study the potential contributions of Hb-based reactive intermediates to oxidative and signaling cascades both in vitro and in vivo. We have also investigated several potential molecular interventions to directly or indirectly control Hb toxicity in vitro and in vivo.

To date, our major contributions to the field of HBOCs include: 1) fully characterizing (biochemical and biophysical) all HBOCs that have been tested in humans; 2) defining toxicological pathways that arise from and are driven by the heme prosthetic group of the molecule; we have indeed recently confirmed that heme acts as Damage Associated Molecular Pattern (DAMP) molecule that triggers inflammatory events; 3) correlating various redox and oxygenation states of free Hb and Hb-laden microparticles from sickle cell blood with mitochondrial respiration and dysfunction; 4) designing protective molecular strategies to suppress or control Hb oxidative side reactions, including the use of oxidatively stable mutant Hb as a potential HBOC prototype; 5) defining the impact of SAR-COV-2 spike protein binding on cellular and subcellular oxygen sensing and mitochondrial functions in human pulmonary arterial endothelial cells. Our mission-oriented laboratory research on the safety and efficacy evaluation of HBOCs has been published in major peer-reviewed journals and presented at national and international meetings.

Important Links


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    Changes in hemoglobin oxidation and band 3 during blood storage impact oxygen sensing and mitochondrial bioenergetic pathways in the human pulmonary arterial endothelial cell model.
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    The impact of COVID-19 infection on oxygen homeostasis: a molecular perspective.
    Alayash AI
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    Jana S, Heaven MR, Alayash AI
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    Beta-cysteine 93 in human hemoglobin: a gateway to oxidative stability in health and disease.
    Alayash AI
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    Targeting the red cell enzyme pyruvate kinase with a small allosteric molecule AG-348 may correct underlying pathology of a glycolytic enzymopathy.
    Alayash AI
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    Voxelotor treatment of a patient with sickle cell disease and very severe anemia.
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    Redox chemistry of hemoglobin-associated disorders.
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    Evaluation of stem cell-derived red blood cells as a transfusion product using a novel animal model.
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    Sustained treatment of sickle cell mice with haptoglobin increases HO-1 and H-ferritin expression and decreases iron deposition in the kidney without improvement in kidney function.
    Shi PA, Choi E, Chintagari NR, Nguyen J, Guo X, Yazdanbakhsh K, Mohandas N, Alayash AI, Manci EA, Belcher JD, Vercellotti GM
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    Oxidized ferric and ferryl forms of hemoglobin trigger mitochondrial dysfunction and injury in alveolar type I cells.
    Chintagari NR, Jana S, Alayash AI
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    Oxidative instability of hemoglobin E (beta26 Glu-->Lys) is increased in the presence of free alpha subunits and reversed by alpha-hemoglobin stabilizing protein (AHSP): relevance to HbE/beta-thalassemia.
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    Differential heme release from various hemoglobin redox states and the upregulation of cellular heme oxygenase-1.
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