Hemoglobin Oxidation Reactions in Stored Blood

Abstract

Hemoglobin (Hb) inside and outside the red blood cells (RBCs) undergoes constant transformation to an oxidized form in a process known as autoxidation. The ferrous heme iron (Fe²⁺) of the prosthetic group is spontaneously transformed into an oxidized ferric (Fe³⁺) form, but under oxidative stress conditions a higher oxidation ferryl heme (Fe⁴⁺) is also formed. Although Fe³⁺ is a non-functional form of Hb, the Fe⁴⁺ is also extremely reactive towards other biological molecules due to its high redox potential. The RBC contains an effective reductive machinery that maintains Hb in the functional form with little oxidation during its life span. The redox transformation of Hb occurs to a lesser extent in young RBCs; it may, however, have detrimental effects on the integrity of these cells during ex vivo storage or when RBCs are subjected to pathogen reduction processes. In this review, Hb oxidation reactions ("oxidative lesion") will be described, including details of how these reactions might impact the clinical use of stored or processed blood for therapeutic purposes.

Keywords: blood pathogen inactivation; blood storage; hemoglobin oxidation.

Figure 1

RBC oxidative injury during storage and pathogen inactivation conditions. Freshly stored RBCs in a standard blood bag undergo very little oxidation apart from normal spontaneous (autoxidation) reactions of Hb, resulting in little metHb accumulation (left). Reductive and antioxidant enzymes/proteins such as NADPH reductase and GSH maintain metHb to a minimum. Under prolonged storage conditions or when RBCs are exposed to UV light, Hb oxidative side reactions are increased, mainly Hb’s own pseudoperoxidative pathways (right). These pathways result in the production of ferryl Hb (HbFe⁴⁺) which attacks other biological targets including band 3, resulting in band 3 clustering. Ferryl Hb crosslinks the major RBC membranes band 3 into clusters and the ultimate release of Hb-laden microparticles (MPs), based on [18,37] with modifications.