Tejero, Jesús

The clinical benefit of blood transfusion is undeniable, and yet reliance on donated blood products has several shortcomings. These include risks of supply shortages due to reliance on volunteer donors, short storage life, and potential infectious disease transmission. Immune response complications to donated blood cannot be completely avoided, despite significant advances in testing. Many of these limitations are exacerbated in low-income countries. For decades, cell-free hemoglobin-based blood substitutes have been developed and tested as potential substitutes for red blood cell transfusions. Early studies found that purified, native hemoglobin exhibited significant safety risks, such as hypertension from excessive vasoconstriction and evidence of multiple organ toxicities. These effects are likely in part due to the reactive heme center, which will scavenge nitric oxide, generate reactive oxygen species, and may drive sterile inflammation. Numerous strategies have been explored to further modify hemoglobin in the hope of creating a safe and well-tolerated blood substitute. Despite some promising results in preliminary studies, large-scale clinical trials have continued to show elevated rates of adverse events and/or a failure to meet specified clinical endpoints. As a result, no hemoglobin-based oxygen carrier (HBOC) has obtained US Food and Drug Administration approval for clinical use. This review focuses on the history of HBOC development, the lessons that have been learned from prior failures of HBOC programs, and the status of ongoing artificial oxygen carrier development efforts.

Abstract Cytoglobin is a highly conserved redox sensor heme protein with unknown physiological function. Unexpectedly, genetic deletion of zebrafish cytoglobin (cygb2) causes cardiac and gastro-intestinal tract laterality defects, modeling Kartagener’s syndrome, which in humans is associated with low airway epithelial nitric oxide (NO) production. Cygb2 co-localized with cilia and the NO synthase Nos2b in the Kupffer’s vesicle (KV) laterality organ and the structure and function of cilia were disrupted in cygb2 mutants, abolishing fluid flow within the KV. Abnormal ciliary function and organ laterality was phenocopied by depletion of nos2band gucy1a, the canonical NO receptor soluble guanylate cyclase (sGC) homolog in fish, and rescued by exposing cygb2 mutant embryos to an NO donor or an sGC stimulator and with over-expression of nos2b. Consistent with a conserved role in the modulation of ciliary function, cytoglobin knock out in the mouse also impaired airway epithelial ciliary structure and beat frequency. This is the first evidence that cytoglobin is essential for normal development stage-specific NO signaling, ciliogenesis and cilia motility, required for the establishment of left-right patterning.