Extracellular Hemoglobin: Modulation of Cellular Functions and Pathophysiological Effects

Abstract

Hemoglobin is essential for maintaining cellular bioenergetic homeostasis through its ability to bind and transport oxygen to the tissues. Besides its ability to transport oxygen, hemoglobin within erythrocytes plays an important role in cellular signaling and modulation of the inflammatory response either directly by binding gas molecules (NO, CO, and CO₂) or indirectly by acting as their source. Once hemoglobin reaches the extracellular environment, it acquires several secondary functions affecting surrounding cells and tissues. By modulating the cell functions, this macromolecule becomes involved in the etiology and pathophysiology of various diseases. The up-to-date results disclose the impact of extracellular hemoglobin on (i) redox status, (ii) inflammatory state of cells, (iii) proliferation and chemotaxis, (iv) mitochondrial dynamic, (v) chemoresistance and (vi) differentiation. This review pays special attention to applied biomedical research and the use of non-vertebrate and vertebrate extracellular hemoglobin as a promising candidate for hemoglobin-based oxygen carriers, as well as cell culture medium additive. Although recent experimental settings have some limitations, they provide additional insight into the modulatory activity of extracellular hemoglobin in various cellular microenvironments, such as stem or tumor cells niches.

Keywords: cell culture additives; differentiation; extracellular hemoglobin; hemolysis; oxygen carriers.

Figure 1

Scheme illustrating the mechanisms of action of endogenous extracellular hemoglobin: (A) extravascular translocation of hemoglobin, (B) prooxidative reactivity of hemoglobin in plasma or within tissues after extravasation, (C) release of hemin from Hb-Fe³⁺ as the main product of oxidative reactions and (D) hemin induced changes in cell activation, gene expression, and metabolism.

Figure 2

Schematic presentation of the potential use of vertebrates and invertebrates’ hemoglobin preparations in biomedicine and biotechnology (left side of the scheme), emphasizing already commercially available cell culture additives based on invertebrate hemoglobin (HEMOXCell^®, HEMOXYCarriers^®, HEMARINA SA, Morlaix, France). Up-to-date research on the impact of such hemoglobin preparation on mesenchymal stromal cell (MSC) cultures could significantly contribute to a better understanding of the onset and progression of pathological conditions involving extracellular hemoglobin as presented on the right side of the scheme.

Figure 3

Targets of extracellular hemoglobin and its derivatives relevant for pathophysiology of several diseases (see Section 4). Extracellular hemoglobin and/or its derivatives induce (a) neutrophil activation characterized by elevated ROS production, increased production of pro-inflammatory cytokines, (b) neutrophil and monocytes chemotaxis, (c) endothelial cell activation characterized by NF-κB activation, elevated ROS production, and increased expression of adhesion molecules and pro-inflammatory cytokines. (d) Macrophages elevated ROS production and pro-inflammatory cytokine production, (e) astrocytes reduced ROS accumulation and apoptosis rate characterized by upregulation and nuclear translocation of Nrf2 and HO-1 upregulation, (f) MSC reduced osteogenesis, chondrogenesis and adipogenesis. (NF-κB, nuclear factor kappa B; ROS, reactive oxygen species; TLR2, toll-like receptor 2; TLR4, toll-like receptor 4, Nrf2, erythroid 2 related factor; HO-1 hem oxygenase-1; MSC-mesenchymal stromal cells).