To better understand human adaptation to stress, and in particular to hypoxia, we took advantage of one of nature's experiments at high altitude (HA) and studied Ethiopians, a population that is well-adapted to HA hypoxic stress. Using whole-genome sequencing, we discovered that EDNRB (Endothelin receptor type B) is a candidate gene involved in HA adaptation. To test whether EDNRB plays a critical role in hypoxia tolerance and adaptation, we generated EdnrB knockout mice and found that when EdnrB −/+ heterozygote mice are treated with lower levels of oxygen (O 2 ), they tolerate various levels of hypoxia (even extreme hypoxia, e.g., 5% O 2 ) very well. For example, they maintain ejection fraction, cardiac contractility, and cardiac output in severe hypoxia. Furthermore, O 2 delivery to vital organs was significantly higher and blood lactate was lower in EdnrB −/+ compared with wild type in hypoxia. Tissue hypoxia in brain, heart, and kidney was lower in EdnrB −/+ mice as well. These data demonstrate that a lower level of EDNRB significantly improves cardiac performance and tissue perfusion under various levels of hypoxia. Transcriptomic profiling of left ventricles revealed three specific genes [natriuretic peptide type A (Nppa), sarcolipin (Sln), and myosin light polypeptide 4 (Myl4)] that were oppositely expressed (q < 0.05) between EdnrB −/+ and wild type. Functions related to these gene networks were consistent with a better cardiac contractility and performance. We conclude that EDNRB plays a key role in hypoxia tolerance and that a lower level of EDNRB contributes, at least in part, to HA adaptation in humans.is often referred to as a biosignature, a chemical marker in the atmosphere closely associated with life, and in a complex organism, such as humans, various physiological systems have evolved to maintain an optimal O 2 homeostasis. Arguably, humans living at high altitude (HA) for thousands of years ought to have undergone a significant level of natural selection to adjust to the challenging hypoxic condition. Human adaptation to HA hypoxia, which can be protective to tissues, can potentially be harnessed for better therapeutic modalities for sea-level diseases that involve hypoxia and ischemia in their pathogenesis. Indeed, lessons from such an "experiment in nature" can be derived from HA adaptation and can advance lowaltitude medicine (1). With the advent of newer technology including next-generation sequencing (seq), this idea has recently led to intensive efforts, and a number of publications have appeared on studies of human populations living at HA (2-4). These studies also draw added significance not only to sea-level human diseases but also to more than 140 million people living at an altitude above 2,500 m, where the hypoxic condition presents a major challenge for survival (5). Although a number of laboratory methods that mimic hypoxia adaptation using model organisms (6) have been used as tools to identify causative genetic pathways (7,8), studies in human populations living at different H...

Adaptation to hypoxia requires compensatory mechanisms that affect O transport and utilization. Decreased hemoglobin (Hb) O affinity is considered part of the physiological adaptive process to chronic hypoxia. However, this study explores the hypothesis that increased Hb O affinity can complement acute physiological responses to hypoxia by increasing O uptake and delivery compared with normal Hb O affinity during acute severe hypoxia. To test this hypothesis, Hb O affinity in mice was increased by oral administration of 2-hydroxy-6-{[(2)-1-(pyridine-3-carbonyl)piperidin-2yl] methoxy}benzaldehyde (GBT1118; 70 or 140 mg/kg). Systemic and microcirculatory hemodynamics and oxygenation parameters were studied during hypoxia in awake-instrumented mice. GBT1118 increased Hb O affinity and decreased the Po at which 50% of Hb is saturated with O (P) from 43 ± 1.1 to 18.3 ± 0.9 mmHg (70 mg/kg) and 7.7 ± 0.2 mmHg (140 mg/kg). In a dose-dependent fashion, GBT1118 increased arterial O saturation by 16% (70 mg/kg) and 40% (140 mg/kg) relative to the control group during 5% O hypoxia. In addition, a GBT1118-induced increase in Hb O affinity reduced hypoxia-induced hypotension compared with the control group. Moreover, microvascular blood flow was higher during hypoxia in GBT1118-treated groups than the control group. The increased O saturation and improved blood flow in GBT1118-treated groups preserved higher interstitial tissue Po than in the control group during 5% O hypoxia. In conclusion, increased Hb O affinity enhanced physiological tolerance to hypoxia, as evidenced by improved hemodynamics and tissue oxygenation. Therefore, pharmacologically induced increases in Hb O affinity become a potential therapeutic approach to improve tissue oxygenation in pulmonary diseases characterized by severe hypoxemia. This study establishes that pharmacological modification of hemoglobin O affinity can be a promising and novel therapeutic strategy for the treatment of hypoxic hypoxia and paves the way for the clinical development of molecules that prevent hypoxemia.

Hemorrhage impairs myocardial contractile function and decreases oxygen delivery. This study investigates how polymerized bovine hemoglobin (PolyHb) solutions affect cardiac function after resuscitation from hemorrhagic shock (HS). Hamsters were hemorrhaged and resuscitated with PolyHb at 8.5g/dL and 11.5 g/dL. Left ventricle (LV) function was assessed during shock and resuscitation using a miniaturize conductance catheter. PolyHb resuscitation had no beneficial effects in cardiac function; it increased cardiac afterload and systemic vascular resistance (SVR) of 46 and 116% for 8.5 and 11.5 g/dL, respectively. Study findings indicate that preclinical evaluation of cardiac function is essential to develop safe and efficacious alternatives to blood transfusion.

Acclimatization to hypoxia or high altitude involves physiological adaptation processes, to influence oxygen (O2) transport and utilization. Several natural products, including aromatic aldehydes and isothiocyanates stabilize the R-state of hemoglobin (Hb), increasing Hb-O2 affinity and Hb-O2 saturation. These products are a counter intuitive therapeutic strategy to increase O2 delivery during hypoxia. 5-Hydroxymethylfurfural (5-HMF) is well known Amadori compound formed during the Maillard reaction (the non-enzymatic browning and caramelization of carbohydrate-containing foods after thermal treatment), with well documented effects in Hb-O2 affinity. This study explores the therapeutic potential of 5-HMF on left ventricular (LV) cardiac function (LVCF) during hypoxia. Anesthetized Golden Syrian hamsters received 5-HMF i.v., at 100 mg/kg and were subjected to stepwise increased hypoxia (15, 10, and 5%) every 30 min. LVCF was assessed using a closed chest method with a miniaturized conductance catheter via continuous LV pressure-volume (PV) measurements. Heart hypoxic areas were studied using pimonidazole staining. 5-HMF improved cardiac indices, including stroke volume (SV), cardiac output (CO), ejection fraction (EF), and stroke work (SW) compared to the vehicle group. At 5% O2, SV, CO, EF, and SW were increased by 53, 42, 33, and 51% with 5-HMF relative to vehicle. Heart chronotropic activity was not statistically changed, suggesting that differences in LV-CF during hypoxia by 5-HMF were driven by volume dependent effects. Analysis of coronary blood flow and cardiac muscle metabolism suggest no direct pharmacological effects from 5-HMF, therefore these results can be attributed to 5-HMF-dependent increase in Hb-O2 affinity. These studies establish that naturally occurring aromatic aldehydes, such as 5-HMF, produce modification of hemoglobin oxygen affinity with promising therapeutic potential to increase O2 delivery during hypoxic hypoxia.