Hemoglobin A0 and alpha-crosslinked hemoglobin (alpha-DBBF) potentiate agonist-induced platelet aggregation through the platelet thromboxane receptor

Endothelin-1 contributes to hemoglobin glutamer-200-mediated hepatocellular dysfunction after hemorrhagic shock

Hemoglobin glutamer-200 (HbG) might be an alternative to human blood. However, artificial oxygen carriers are initially successful to restore oxygen supply but may induce organ dysfunction and increase mortality several days after application in terms of delayed side effects. Impairment of microcirculation and an inflammatory cytokine response through induction of endothelin (ET) 1 may contribute. We investigated the role of HbG for the therapy of hemorrhagic shock and for delayed side effects in a model of hemorrhagic shock and reperfusion (H/R). To analyze early effects, Sprague-Dawley rats (n = 8/group) were resuscitated after hemorrhagic shock (1 h) with shed blood or HbG followed by reperfusion (2 h). Hemorrhagic shock and reperfusion decreased liver microcirculation and hepatic function in both shock groups to the same extent. Thus, HbG was not superior to shed blood regarding resuscitation end points after hemorrhagic shock. To determine delayed effects, rats (n = 8/group) were pretreated with Ringer's solution (vehicle) or HbG (1 g/kg) 24 h before H/R. Endothelin receptors were blocked with bosentan. Subsequently, ET-1 expression, inflammatory response, sinusoidal perfusion, hepatocellular function (plasma disappearance rate of indocyanine green [PDRICG]), and redox state [NAD(P)H] were analyzed. After vehicle pretreatment, H/R increased ET-1, hepatocellular injury, NAD(P)H, and cytokine levels. Sinusoidal perfusion and PDRICG decreased. After HbG pretreatment, a further increase of ET-1 and hepatocellular injury was observed, whereas PDRICG further decreased. Application of bosentan after HbG but not after vehicle pretreatment significantly improved PDRICG and liver perfusion, whereas NAD(P)H and hepatocellular injury decreased. Furthermore, cytokine release changed to an anti-inflammatory response. These data suggest an HbG-dependent increase of ET-1, which may contribute to delayed side effects under shock conditions.

Influence of heme-based solutions on stress protein expression and organ failure after hemorrhagic shock

OBJECTIVE

Hemoglobin-based oxygen carriers (e.g., diaspirin-cross-linked hemoglobin [DCLHb] and hemoglobin glutamer-200 [HbG]) may have potential in the treatment of hemorrhagic shock. The nitric oxide scavenging and direct vasoconstrictive side effects of free hemoglobin of currently available preparations may increase organ injury after shock in contrast to non-oxygen-carrying heme solutions (e.g., hemin arginate [HAR]). However, both classes of substances might induce the protective enzyme heme oxygenase (HO)-1, particularly in the liver. The aim of the study was to assess the role of pretreatment with DCLHb, HbG, or HAR on HO-1 expression and organ injury after hemorrhagic shock.

DESIGN

Prospective controlled laboratory study.

SETTING

Animal research laboratory at a university hospital.

SUBJECTS

Male Sprague-Dawley rats (200-300 g body weight, n = 5-12/group).

INTERVENTIONS

Twenty-four hours after different doses of DCLHb, HbG (each 1, 2, or 3 g/kg of body weight), or HAR (5, 25, or 75 mg/kg of body weight), the protein expression of HO-1 and heat shock protein-70 in liver, kidney, heart, lungs, and aorta was determined. Twenty-four hours after pretreatment with DCLHb, HbG, or HAR, rats were subjected to hemorrhage (mean arterial blood pressure, 35-40 mm Hg for 1 or 2 hrs)/resuscitation (5 or 4 hrs, respectively). Animals treated with Ringer's solution (30 mL/kg of body weight) served as controls. In additional experiments, HO activity was blocked with tin mesoporphyrin-IX.

MEASUREMENTS AND MAIN RESULTS

DCLHb, HbG, and HAR dose-dependently induced HO-1 protein but not heat shock protein-70. Pretreatment with DCLHb or HbG shortened the onset of decompensation in shock (DCLHb, 40 +/- 11 mins; HbG, 36 +/- 4 mins) compared with vehicle (68 +/- 4 mins, p < .05) and HAR pretreatment (81 +/- 7 mins, p < .05). High doses of DCLHb pretreatment increased mortality (2 hrs of shock, 80%; p < .05 vs. vehicle or HAR). Pretreatment with HAR led to higher shed blood volumes (p < .05) and higher hepatocellular ATP levels (2 hrs of shock, p < .05 vs. DCLHb and HbG). Blockade of HO activity by tin mesoporphyrin-IX abolished the protection mediated by HAR.

CONCLUSIONS

Although DCLHb, HbG, and HAR induce HO-1 in the absence of an unspecific stress response, only HAR pretreatment protects against shock-induced organ failure. Although the underlying mechanisms of positive HAR priming are not completely understood, the induction of HO-1 expression and the lack of nitric oxide scavenging through HAR may play an important role.

Hemolink, an o-raffinose cross-linked haemoglobin-based oxygen carrier, does not affect activation and function of human platelets in whole blood in vitro

Haemoglobin-based oxygen carriers (HBOCs) are anticipated to be safe and efficient alternatives to RBC transfusions. Haemoglobin (Hb) raffimer (Hemolink; Hemosol, Toronto, ON, Canada) is polymerized human Hb, cross-linked with o-raffinose. As administration of cell-free Hb may affect blood cells and tissues, this study was focused on evaluating effects of Hb raffimer on human platelets in whole blood in vitro. Citrated blood from healthy donors was incubated with Hb raffimer to achieve raffimer concentrations of 2-50 vol percentage (2-50 g/l). Platelet activation, phosphatidylserine exposure and microparticle generation were measured by flow cytometry. Aperture closure time on collagen/ADP- and collagen/epinephrine-coated membranes was determined by a platelet function analyser (PFA-100). We found that addition of Hb raffimer to blood samples up to 50 vol % did not affect human platelets as measured by various markers of platelet activation (CD42b, CD41, PAC-1, CD62, CD63), procoagulant activity (annexin V) and microparticle formation; differences between Hb raffimer- and lactated Ringer's-diluted blood were not significant. Similarly, no adverse effect of Hb raffimer on closure time was observed at concentrations up to 50 vol %, in comparison with Ringer's solution. These data indicate that exposure of human blood to high concentrations of Hb raffimer in vitro did not cause platelet activation nor affect platelet function.

o-Raffinose cross-linked hemoglobin improves the hemostatic defect associated with anemia and thrombocytopenia in rabbits

Several different preparations of cross-linked hemoglobin (CLHb) are being evaluated for their efficacy and safety as red cell substitutes in a variety of preclinical and clinical settings. Because CLHb is known to sequester nitric oxide (NO) and inhibit NO-mediated processes, we hypothesized that CLHb would have a hemostatic effect by enhancing platelet reactivity, inducing vasoconstriction, or both. Infusion of o-raffinose CLHb shortened the prolonged microvascular bleeding time and decreased blood loss from ear incisions in rabbits rendered anemic and thrombocytopenic. Moreover, this hemostatic effect persisted for at least 24 hours after infusion. Phenylephrine induced a degree of vasoconstriction similar to that induced by CLHb but did not shorten the bleeding time or decrease blood loss, suggesting that vasoconstriction alone cannot account for the hemostatic effect of CLHb. There was no evidence of CLHb-induced activation of coagulation in vivo, since infusion of CLHb did not increase circulating levels of thrombin-antithrombin complex. In vitro, CLHb abolished the inhibitory effect of the NO donor 3-morpholinosydnonimine on platelet aggregation and enhanced the aggregation of stimulated but not resting platelets. This potentiating effect was not attenuated by the addition of superoxide dismutase or catalase. To evaluate the potential arterial thrombogenicity of CLHb, a model of carotid artery thrombosis was developed in rabbits without thrombocytopenia or anemia. Compared with albumin infusion, CLHb infusion shortened the time to complete carotid occlusion. These data suggest that CLHb may shift the thromboregulatory balance toward clot formation, resulting in decreased bleeding in anemic and thrombocytopenic rabbits and possibly increasing arterial thrombogenicity in normal rabbits.

o-Raffinose cross-linked hemoglobin improves the hemostatic defect associated with anemia and thrombocytopenia in rabbits

Several different preparations of cross-linked hemoglobin (CLHb) are being evaluated for their efficacy and safety as red cell substitutes in a variety of preclinical and clinical settings. Because CLHb is known to sequester nitric oxide (NO) and inhibit NO-mediated processes, we hypothesized that CLHb would have a hemostatic effect by enhancing platelet reactivity, inducing vasoconstriction, or both. Infusion of o-raffinose CLHb shortened the prolonged microvascular bleeding time and decreased blood loss from ear incisions in rabbits rendered anemic and thrombocytopenic. Moreover, this hemostatic effect persisted for at least 24 hours after infusion. Phenylephrine induced a degree of vasoconstriction similar to that induced by CLHb but did not shorten the bleeding time or decrease blood loss, suggesting that vasoconstriction alone cannot account for the hemostatic effect of CLHb. There was no evidence of CLHb-induced activation of coagulation in vivo, since infusion of CLHb did not increase circulating levels of thrombin-antithrombin complex. In vitro, CLHb abolished the inhibitory effect of the NO donor 3-morpholinosydnonimine on platelet aggregation and enhanced the aggregation of stimulated but not resting platelets. This potentiating effect was not attenuated by the addition of superoxide dismutase or catalase. To evaluate the potential arterial thrombogenicity of CLHb, a model of carotid artery thrombosis was developed in rabbits without thrombocytopenia or anemia. Compared with albumin infusion, CLHb infusion shortened the time to complete carotid occlusion. These data suggest that CLHb may shift the thromboregulatory balance toward clot formation, resulting in decreased bleeding in anemic and thrombocytopenic rabbits and possibly increasing arterial thrombogenicity in normal rabbits.

Site-specific modifications and toxicity of blood substitutes. The case of diaspirin cross-linked hemoglobin

Safe and effective hemoglobin-based blood substitutes may be advantageous over conventional therapies for certain clinical settings requiring short term blood replacement such as emergency resuscitation and hemodilution in surgery. Many advances have been made in developing these oxygen therapeutics, however safety concerns continue to slow their clinical progress. An important and often overlooked consideration in evaluating the safety of modified hemoglobins is the impact of chemical and/or genetic modifications on the redox chemistry of these proteins. Diaspirin cross-linked hemoglobin (DBBF-Hb) has been extensively evaluated in vitro and in animal models, and thus represents a useful model to explore possible correlations between structural-functional alterations and toxicity of hemoglobin-based blood substitutes.