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Summary: The pathophysiologic mechanism of sickle cell disease (SCD) involves polymerization of deoxygenated haemoglobin S (HbS), leading to red blood cell (RBC) sickling, decreased RBC deformability, microvascular obstruction, haemolysis, anaemia and downstream clinical complications. Pharmacological increase in the concentration of oxygenated HbS in RBCs has been shown to be a novel approach to inhibit HbS polymerization and reduce RBC sickling and haemolysis. We report that GBT021601, a small molecule that increases HbS‐oxygen affinity, inhibits HbS polymerization and prevents RBC sickling in blood from patients with SCD. Moreover, in a murine model of SCD (SS mice), GBT021601 reduces RBC sickling, improves RBC deformability, prolongs RBC half‐life and restores haemoglobin levels to the normal range, while improving oxygen delivery and increasing tolerance to severe hypoxia. Notably, oral dosing of GBT021601 in animals results in higher levels of Hb occupancy than voxelotor and suggests the feasibility of once‐daily dosing in humans. In summary, GBT021601 improves RBC health and normalizes haemoglobin in SS mice, suggesting that it may be useful for the treatment of SCD. These data are being used as a foundation for clinical research and development of GBT021601. [ABSTRACT FROM AUTHOR]

Background: Hemolysis releases toxic cell‐free hemoglobin (Hb), heme, and iron, which overwhelm their natural scavenging mechanisms during acute or chronic hemolytic conditions. This study describes a novel strategy to purify a protein cocktail containing a comprehensive set of scavenger proteins for potential treatment of hemolysis byproducts. Study Design and Methods: Tangential flow filtration was used to purify a protein cocktail from Human Cohn Fraction IV (FIV). A series of in vitro assays were performed to characterize composition and biocompatibility. The in vivo potential for hemolysis byproduct mitigation was assessed in a hamster exchange transfusion model using mechanically hemolyzed blood plasma mixed with the protein cocktail or a control colloid (dextran 70 kDa). Results: A basis of 500 g of FIV yielded 62 ± 9 g of a protein mixture at 170 g/L, which bound to approximately 0.6 mM Hb, 1.2 mM heme, and 1.2 mM iron. This protein cocktail was shown to be biocompatible in vitro with red blood cells and platelets and exhibits nonlinear concentration dependence with respect to viscosity and colloidal osmotic pressure. In vivo assessment of the protein cocktail demonstrated higher iron transport to the liver and spleen and less to the kidney and heart with significantly reduced renal and cardiac inflammation markers and lower kidney and hepatic damage compared to a control colloid. Discussion Taken together, this study provides an effective method for large‐scale production of a protein cocktail suitable for comprehensive reduction of hemolysis‐induced toxicity. [ABSTRACT FROM AUTHOR]

Microvascular fluid exchange is primarily dependent on Starling forces and both the active and passive myogenic response of arterioles and post‐capillary venules. Arterioles are classically considered resistance vessels, while venules are considered capacitance vessels with high distensibility and low tonic sympathetic stimulation at rest. However, few studies have investigated the effects of modulating interstitial hydrostatic pressure, particularly in the context of hemorrhagic shock. The objective of this study was to investigate the mechanics of arterioles and functional capillary density (FCD) during application of negative tissue interstitial pressure after 40% total blood volume hemorrhagic shock. In this study, we characterized systemic and microcirculatory hemodynamic parameters, including FCD, in hamsters instrumented with a dorsal window chamber and a custom‐designed negative pressure application device via intravital microscopy. In large arterioles, application of negative pressure after hemorrhagic shock resulted in a 13 ± 11% decrease in flow compared with only a 7 ± 9% decrease in flow after hemorrhagic shock alone after 90 minutes. In post‐capillary venules, however, application of negative pressure after hemorrhagic shock resulted in a 31 ± 4% decrease in flow compared with only an 8 ± 5% decrease in flow after hemorrhagic shock alone after 90 minutes. Normalized FCD was observed to significantly improve after application of negative pressure after hemorrhagic shock (0.66 ± 0.02) compared to hemorrhagic shock without application of negative pressure (0.50 ± 0.04). Our study demonstrates that application of negative pressure acutely improves FCD during hemorrhagic shock, though it does not normalize FCD. These results suggest that by increasing the hydrostatic pressure gradient between the microvasculature and interstitium, microvascular perfusion can be transiently restored in the absence of volume resuscitation. This study has significant clinical implications, particularly in negative pressure wound therapy, and offers an alternative mechanism to improve microvascular perfusion during hypovolemic shock. [ABSTRACT FROM AUTHOR]

Background: Hemoglobin (Hb)‐based oxygen (O2) carriers (HBOCs) are being developed as alternatives to red blood cells and blood when these products are unavailable. Clinical trials of previous HBOC generations revealed side effects, including hypertension and vasoconstriction, that were not observed in preclinical studies. Large molecular weight (MW) polymerized bovine Hb (PolybHb) represents a new class of HBOC with promising results. We evaluated the safety profile of PolybHb after an exchange transfusion (ET) in guinea pigs (GPs). This study compares changes in indices of cardiac, inflammatory, and organ function after ET with high (R‐state) and low (T‐state) O2 affinity PolybHb with high MW. Study Design and Methods: Guinea pigs underwent a 20% ET with PolybHb. To assess the implication of PolybHb ET on the microcirculation, hamsters instrumented with a dorsal window chamber were subjected to a similar volume ET. Results: T and R‐state PolybHb did not induce significant alterations in cardiac function. T‐state PolybHb induced mild vasoconstriction shortly after transfusion, while R‐state did not have acute effects on microvascular tone. Conclusion: Large MW PolybHbs were found to be safe and efficacious in increasing O2 carrying capacity and the O2 affinity of the PolybHb did not affect O2 delivery or extraction by tissues in relevant preclinical models. In conclusion, these results suggest that both T‐state and R‐state PolybHb are safe and do not impair O2 delivery. The results are encouraging and support further evaluation of high MW PolybHbs and their future feasibility compared to allogenic blood in a trauma model. [ABSTRACT FROM AUTHOR]

New Findings What is the central question of this study? The purpose of the present study was to determine the effects of exercise-induced haemoconcentration and hyperthermia on blood viscosity., What is the main finding and its importance? Exercise-induced haemoconcentration, increased plasma viscosity and increased blood aggregation, all of which increased blood viscosity, were counterbalanced by increased red blood cell (RBC) deformability (e.g. RBC membrane shear elastic modulus and elongation index) caused by the hyperthermia. Thus, blood viscosity remained unchanged following prolonged moderate-intensity exercise in the heat., Previous studies have reported that blood viscosity is significantly increased following exercise. However, these studies measured both pre- and postexercise blood viscosity at 37°C even though core and blood temperatures would be expected to have increased during the exercise. Consequently, the effect of exercise-induced hyperthermia on mitigating change in blood viscosity may have been missed. The purpose of this study was to isolate the effects of exercise-induced haemoconcentration and hyperthermia and to determine their combined effects on blood viscosity. Nine subjects performed 2 h of moderate-intensity exercise in the heat (37°C, 40% relative humidity), which resulted in significant increases from pre-exercise values for rectal temperature (from 37.11 ± 0.35 to 38.76 ± 0.13°C), haemoconcentration (haematocrit increased from 43.6 ± 3.6 to 45.6 ± 3.5%) and dehydration (change in body weight = −3.6 ± 0.7%). Exercise-induced haemoconcentration significantly ( P < 0.05) increased blood viscosity by 9% (from 3.97 to 4.33 cP at 300 s−1), whereas exercise-induced hyperthermia significantly decreased blood viscosity by 7% (from 3.97 to 3.69 cP at 300 s−1). When both factors were considered together, there was no overall change in blood viscosity (from 3.97 to 4.03 cP at 300 s−1). The effects of exercise-induced haemoconcentration, increased plasma viscosity and increased red blood cell aggregation, all of which increased blood viscosity, were counterbalanced by increased red blood cell deformability (e.g. red blood cell membrane shear elastic modulus and elongation index) caused by the hyperthermia. Thus, blood viscosity remained unchanged following prolonged moderate-intensity exercise in the heat. [ABSTRACT FROM AUTHOR]

New Findings What is the central question of this study? The aim was to evaluate the effect of perfusion pressure on blood flow in small arterioles. The hypothesis was that blood flow regulates the thickness of the red-cell-free layer and, therefore, blood flow determines blood apparent viscosity and local vascular resistance in vascular networks with limited myogenic or metabolic regulation of blood flow., What is the main finding and its importance? Reduced perfusion pressures lowered volumetric flow rates and increased local vascular resistance, due to increased blood apparent viscosity. Thus, the local vascular resistance of small arterioles with limited myogenic or metabolic regulation of blood flow, appeared to be determined by changes in blood rheology rather than blood vessel diameter., The study of blood flow regulation is important to understand and resolve pathological conditions. As blood is a complex non-Newtonian multiphase system, the foundations of blood rheological properties have been obtained mostly in viscometers. However, blood rheological behaviour in vivo depends on the concentration of red blood cells (RBCs), their mechanical properties and the RBC hydrodynamics, including RBC migration away from the vessel wall in shear flow. This migration promotes the formation of a RBC-depleted zone, or cell-free layer (CFL), which reduces the apparent viscosity of blood. We hypothesize that perfusion pressure determines blood apparent viscosity in microvessels, as shear rate affects axial migration of RBCs by influencing the CFL thickness. In this study, we analysed the effects of perfusion pressure on blood flow in individual arterioles within the rat cremaster muscle preparation. Perfusion pressures to this microvascular bed were controlled by occlusions of the iliac artery using a pressure cuff. Blood flow measurements were obtained from direct measurements of blood flow velocity profile, as well as determination of CFL thickness using intravital microscopy. Our results indicate that perfusion pressure determines shear rates and the CFL thickness and its variations. In addition, blood flow reduction increased local vascular resistance by augmenting blood apparent viscosity rather than vascular hindrance. In conclusion, blood rheology could act as an intrinsic mechanism to further limit blood flow to tissue with limited myogenic and metabolic responses at low perfusion pressures. [ABSTRACT FROM AUTHOR]