Hemoglobin-based oxygen carrier preserves submaximal exercise capacity in humans

Hemoglobin-Based Oxygen Carriers: Potential Applications in Solid Organ Preservation

Ameliorating graft injury induced by ischemia and hypoxia, expanding the donor pool, and improving graft quality and recipient prognosis are still goals pursued by the transplant community. The preservation of organs during this process from donor to recipient is critical to the prognosis of both the graft and the recipient. At present, static cold storage, which is most widely used in clinical practice, not only reduces cell metabolism and oxygen demand through low temperature but also prevents cell edema and resists apoptosis through the application of traditional preservation solutions, but these do not improve hypoxia and increase oxygenation of the donor organ. In recent years, improving the ischemia and hypoxia of grafts during preservation and repairing the quality of marginal donor organs have been of great concern. Hemoglobin-based oxygen carriers (HBOCs) are “made of” natural hemoglobins that were originally developed as blood substitutes but have been extended to a variety of hypoxic clinical situations due to their ability to release oxygen. Compared with traditional preservation protocols, the addition of HBOCs to traditional preservation protocols provides more oxygen to organs to meet their energy metabolic needs, prolong preservation time, reduce ischemia–reperfusion injury to grafts, improve graft quality, and even increase the number of transplantable donors. The focus of the present study was to review the potential applications of HBOCs in solid organ preservation and provide new approaches to understanding the mechanism of the promising strategies for organ preservation.

Comparison of the Pharmacokinetic Properties of Hemoglobin-Based Oxygen Carriers

Hemoglobin (Hb) is an ideal material for use in the development of an oxygen carrier in view of its innate biological properties. However, the vascular retention of free Hb is too short to permit a full therapeutic effect because Hb is rapidly cleared from the kidney via glomerular filtration or from the liver via the haptogloblin-CD 163 pathway when free Hb is administered in the blood circulation. Attempts have been made to develop alternate acellular and cellular types of Hb based oxygen carriers (HBOCs), in which Hb is processed via various routes in order to regulate its pharmacokinetic properties. These HBOCs have been demonstrated to have superior pharmacokinetic properties including a longer half-life than the Hb molecule in preclinical and clinical trials. The present review summarizes and compares the pharmacokinetic properties of acellular and cellular type HBOCs that have been developed through different approaches, such as polymerization, PEGylation, cross-linking, and encapsulation.

A safety and efficacy evaluation of hemoglobin-based oxygen carrier HBOC-201 in a randomized, multicenter red blood cell controlled trial in noncardiac surgery patients

BACKGROUND

We present the results of a previously unpublished hemoglobin-based oxygen carrier (HBOC) study conducted in 1998-1999.

METHODS

In a multicenter, randomized, single-blind, comparative study of HBOC-201 versus allogeneic red blood cell (RBC) transfusions, no-cardiac surgery patients received HBOC-201 to a maximum of 7 units (n = 83) or RBCs (n = 77). Patients could be switched to RBCs for safety or any other reason. The efficacy end points were elimination and/or reduction of allogeneic RBC transfusions for 28 days.

RESULTS

The proportion of patients in the HBOC-201 group that avoided RBC transfusion was 0.427 (95% confidence interval, 0.321-0.533). Subjects in the HBOC-201 group received on average 3.2 units of RBCs versus 4.4 units in the control arm (P = 0.004). Seventy-nine (95.2%) subjects in the HBOC-201 group and 72 (93.5%) in the RBC group experienced adverse events (AEs), judged to be associated with study treatment in 59 (71.1%) and 18 (23.4%) subjects, respectively. Thirty-day mortality, 5 (6.0%) vs 4 (5.2%) patients (P = 1.00), incidence of serious AEs, 24 (28.9%) vs 20 (26.0%) (P = 0.73), or time to intensive care unit (log-rank P = 0.15) or hospital discharge (log-rank P = 0.53) were similar for the HBOC-201 and RBC groups, respectively.

CONCLUSIONS

Up to 7 units of HBOC-201 infused over the course of 6 days resulted in RBC transfusion avoidance in 43% of patients. There were no notable differences in mortality and serious AEs incidence. The use of HBOC-201 was associated with a notable excess of nonserious AEs.

Transfusion protocol in trauma

Blood and blood components are considered drugs because they are used in the treatment of diseases. As with any drug, adverse effects may occur, necessitating careful consideration of therapy. Like any other therapeutic decision, the need for transfusion should be considered on the basis of risks and benefits and alternative treatments available to avoid over- and under-transfusion. This review is focused on the blood transfusion protocol in trauma patients with hemorrhagic shock. Besides, issues related to emergency and massive transfusion have also been elaborated. We conducted a comprehensive MEDLINE search and reviewed the relevant literature, with particular reference to emergency medical care in trauma.

The biochemistry of drugs and doping methods used to enhance aerobic sport performance

Optimum performance in aerobic sports performance requires an efficient delivery to, and consumption of, oxygen by the exercising muscle. It is probable that maximal oxygen uptake in the athlete is multifactorial, being shared between cardiac output, blood oxygen content, muscle blood flow, oxygen diffusion from the blood to the cell and mitochondrial content. Of these, raising the blood oxygen content by raising the haematocrit is the simplest acute method to increase oxygen delivery and improve sport performance. Legal means of raising haematocrit include altitude training and hypoxic tents. Illegal means include blood doping and the administration of EPO (erythropoietin). The ability to make EPO by genetic means has resulted in an increase in its availability and use, although it is probable that recent testing methods may have had some impact. Less widely used illegal methods include the use of artificial blood oxygen carriers (the so-called ‘blood substitutes’). In principle these molecules could enhance aerobic sports performance; however, they would be readily detectable in urine and blood tests. An alternative to increasing the blood oxygen content is to increase the amount of oxygen that haemoglobin can deliver. It is possible to do this by using compounds that right-shift the haemoglobin dissociation curve (e.g. RSR13). There is a compromise between improving oxygen delivery at the muscle and losing oxygen uptake at the lung and it is unclear whether these reagents would enhance the performance of elite athletes. However, given the proven success of blood doping and EPO, attempts to manipulate these pathways are likely to lead to an ongoing battle between the athlete and the drug testers.

Resuscitation from hemorrhagic shock comparing standard hemoglobin-based oxygen carrier (HBOC)-201 versus 7.5% hypertonic HBOC-201

BACKGROUND

Hemoglobin-based oxygen carrier (HBOC) resuscitation has been associated with increased systemic and pulmonary vascular resistances (SVR, PVR), which may result in reduced blood flow and severe pulmonary hypertension. The physiologic and immunologic properties of 7.5% hypertonic saline solution (HTS), such as reduction of SVR and PVR, as well as inhibition of neutrophil and endothelial activation may be beneficial in reducing some of these undesirable effects of HBOCs. The aim of this study was to evaluate the hemodynamic effects of the HBOC and HBOC-201 suspended in 7.5% hypertonic saline solution (HT-HBOC) when compared with standard HBOC resuscitation.

METHODS

Thirty-two domestic crossbred pigs (50-60 kg) were hemorrhaged to a mean arterial pressure (MAP) of 35 mm Hg +/- 5 mm Hg for 45 minutes and resuscitated to a baseline mean arterial pressure using the following groups: (1) sham, no hemorrhage; (2) shed blood + lactated Ringer's solution; (3) standard HBOC-201; (4) hypertonic saline 7.5%; (5) hypertonic 7.5% HBOC-201. After resuscitation, observation was continued for 4 hours. Hemodynamic variables, oxygen consumption, and arterial blood gases were monitored continuously. Data were analyzed using analysis of variance.

RESULTS

SVR (p = 0.001), PVR (p = 0.001), and MPAP (p = 0.01) were significantly reduced in the HT-HBOC group compared with the standard HBOC group.

CONCLUSION

In this model of hemorrhagic shock, hypertonic HBOC-201- resuscitated pigs had significantly reduced SVR and PVR, as well as mean pulmonary artery pressure (MPAP) and increased cardiac output. HT-HBOC may be beneficial in reducing the undesirable effects of standard HBOC-201. The mechanisms of these beneficial effects need to be investigated.

The Swedish Blood Pass project

Manipulation of the blood's oxygen carrying capacity (CaO(2)) through reinfusion of red blood cells, injections of recombinant erythropoietin or by other means results in an increased maximal oxygen uptake and concomitantly enhanced endurance performance. Therefore, there is a need to establish a system--"A Blood Pass"--through which such illegal and unethical methods can be detected. Venous blood samples were taken under standardized conditions from 47 male and female Swedish national and international elite endurance athletes four times during the athletic year of the individual sport (beginning and end of the preparation period and at the beginning and during peak performance in the competition period). In these samples, different hematological values were determined. ON(hes) and OFF(hre) values were calculated according to the formula of Gore et al. A questionnaire regarding training at altitude, alcohol use and other important factors for hematological status was answered by the athletes. There were some individual variations comparing hematological values obtained at different times of the athletic year or at the same time in the athletic year but in different years. However, the median values of all individual hematological, ON(hes) and OFF(hre), values taken at the beginning and the end of the preparation or at the beginning and the end of the competition period, respectively, as well as median values for the preparation and competition periods in the respective sport, were all within the 95% confidence limit (CI) of each comparison. It must be mentioned that there was no gender difference in this respect. This study shows that even if there are some individual variations in different hematological values between different sampling times in the athletic year, median values of important hematological factors are stable over time. It must be emphasized that for each blood sample, the 95% CI in each athlete will be increasingly narrower. The conclusion is that there is a physiological basis for establishing an individual-based "Blood Pass" system, mainly for athletes competing at the international level. On indications of manipulations of hemoglobin concentration and red cell mass by deviations from established "Blood Pass" data, more specific methods can be applied.

Biochemistry, physiology, and complications of blood doping: facts and speculation

Competition is a natural part of human nature. Techniques and substances employed to enhance athletic performance and to achieve unfair success in sport have a long history, and there has been little knowledge or acceptance of potential harmful effects. Among doping practices, blood doping has become an integral part of endurance sport disciplines over the past decade. The definition of blood doping includes methods or substances administered for non-medical reasons to healthy athletes for improving aerobic performance. It includes all means aimed at producing an increased or more efficient mechanism of oxygen transport and delivery to peripheral tissues and muscles. The aim of this review is to discuss the biochemistry, physiology, and complications of blood doping and to provide an update on current antidoping policies.

Electrophoretic, size-exclusion high-performance liquid chromatography and liquid chromatography-electrospray ionization ion trap mass spectrometric detection of hemoglobin-based oxygen carriers

Hemoglobin-based oxygen carriers (HBOCs) are blood substitutes based on hemoglobin of either bovine or human origin and they can potentially be misused in elite sports to improve endurance performance. Recently, three methods have been proposed in doping control analysis to allow HBOCs screening and identification by application of electrophoresis, size-exclusion chromatography coupled with HPLC and LC coupled with tandem mass spectrometry (LC/MSMS). In view of the Athens 2004 Olympic Games, modifications were introduced in order to increase the specificity of these methods. The sample preparation protocols of the electrophoretic and SEC-HPLC methods were modified with the introduction of sequential ultra filtration steps to remove all heme containing material below 100 kDa, thus leaving only HBOCs material for analysis. Furthermore, a modification of the LC/MSMS methodology was introduced to allow full scan MS-MS spectra of peptide segments arising from the tryptic digestion of bovine HBOCs. These relatively simple methodological modifications have major impact, as far as time and cost effectiveness is concerned in doping control procedures, because they provide a useful tool in order to identify which suspect samples from the initial visual screening are due to hemolysis and exclude them from further analysis.

Coagulation patterns following haemoglobin-based oxygen carrier resuscitation in severe uncontrolled haemorrhagic shock in swine

Massive blood loss due to penetrating trauma and internal organ damage can cause severe haemorrhagic shock (HS), leading to a severely compromised haemostatic balance. This study evaluated the effect of bovine polymerized haemoglobin (Hb) (Hb-based oxygen carrier, HBOC) resuscitation on haemostasis in a swine model of uncontrolled HS. Following liver injury/HS, swine received HBOC (n= 8), Hextend (HEX) (n= 8) or no resuscitation (NON) (n= 8). Fluids were infused to increase mean arterial pressure above 60 mmHg and to reduce heart rate to baseline. At 4 h, the animals were eligible for blood transfusions. Prothrombin time (PT), activated partial thromboplastin time, fibrinogen, thromboelastography (TEG) and platelet function analyser closure time (PFA-CT) were compared by using mixed statistical model. At 4 h, blood loss (% estimated blood volume) was comparable for HBOC (65.5 +/- 18.5%) and HEX (80.8 +/- 14.4%) and less for NON (58.7 +/- 10.1%; P < 0.05). Resuscitation-induced dilutional coagulopathy was observed with HBOC and HEX, as indicated by reduced haematocrit, platelets and fibrinogen (P < 0.05). At 4 h, PT was higher in HEX than in HBOC groups (P < 0.01). In the early hospital phase, a trend to increased TEG reaction time and PFA-CT indicates that dilutional effects persist in HBOC and HEX groups. PFA-CT returned to baseline later with HBOC than with HEX (48 vs. 24 h) following blood transfusion. At 4 h, all surviving HEX animals (n= 3) required transfusion, in contrast to no HBOC (n= 7) or NON (n= 1) animals. In this severe uncontrolled HS model, successful resuscitation with HBOC produced haemodilutional coagulopathy less than or similar to that produced by resuscitation with HEX.

A polymerized bovine hemoglobin oxygen carrier preserves regional myocardial function and reduces infarct size after acute myocardial ischemia

The purpose of this study was to test if HBOC-201, a hemoglobin-based oxygen-carrying solution, can decrease infarct size (or Inf) during acute, severe myocardial ischemia and reperfusion. To test the impact of HBOC-201 on infarct size, ischemia was produced in 18 dogs by coronary stenosis to achieve 80-95% flow reduction for 195 min along with pacing 10% above the spontaneous heart rate, followed by 180 min of reperfusion. Animals were randomized to intravenous infusion of HBOC-201 (1 g/kg) (n=6), normal saline (NS) (n=6), or phenylephrine (Phe) (n=6, as a control for the increased blood pressure seen with HBOC-201), given 15 min after the start of ischemia. Amount of infarct was quantified as the ratio between area at risk (AAR) and Inf after Evans blue and 2,3,5-triphenyltetrazolium chloride staining. Hearts were divided into five layers from base (layer A) to apex (layer E) and photographed for digital image analysis of AAR and Inf. Regional myocardial function (RMF) was also measured after 60 min of ischemia and 15 min of reperfusion. Inf/AAR was significantly reduced after HBOC-201 therapy (4.4+/-2.2%) vs. NS (26.0+/-3.6%) and Phe (25.7+/-4.1%) (both, P<0.05). RMF after reperfusion was restored to 92% of baseline with HBOC-201 compared with 11% of baseline after NS (P<0.05) and 49% after Phe (P=not significant). HBOC-201 administration after induction of severe myocardial ischemia by acute coronary stenosis reduces infarct size and improves myocardial viability.

Cardioprotection before revascularization in ischemic myocardial injury and the potential role of hemoglobin-based oxygen carriers

Despite the availability of interventional catheterization for patients with acute coronary syndromes, there is an unavoidable delay until the occluded coronary artery(s) can be revascularized, during which time persistent ischemia may lead to irreversible myocardial damage despite subsequently high patency rates. Accordingly, there has been an intense effort to develop early interventions that will preserve the viability of ischemic myocardium before revascularization. A number of novel strategies have been studied, including hemoglobin-based oxygen carriers. These compounds transport oxygen in the plasma to help maintain more normal oxygen delivery to the myocardium supplied by a thrombosed vessel, and they also release oxygen to tissue more efficiently than intraerythrocytic hemoglobin.

Circulation Kinetics and Organ Distribution of Hb-Vesicles Developed as a Red Blood Cell Substitute

Phospholipid vesicles encapsulating concentrated human hemoglobin (Hb-vesicles, HbV), also known as liposomes, have a membrane structure similar to that of red blood cells (RBCs). These vesicles circulate in the bloodstream as an oxygen carrier, and their circulatory half-life times (t(1/2)) and biodistribution are fundamental characteristics required for representation of their efficacy and safety as a RBC substitute. Herein, we report the pharmacokinetics of HbV and empty vesicles (EV) that do not contain Hb, in rats and rabbits to evaluate the potential of HbV as a RBC substitute. The samples were labeled with technetium-99m and then intravenously infused into animals at 14 ml/kg to measure the kinetics of HbV elimination from blood and distribution to the organs. The t(1/2) values were 34.8 and 62.6 h for HbV and 29.3 and 57.3 h for EV in rats and rabbits, respectively. At 48 h after infusion, the liver, bone marrow, and spleen of both rats and rabbits had significant concentrations of HbV and EV, and the percentages of the infused dose in these three organs were closely correlated to the circulatory half-life times in elimination phase (t(1/2beta)). Furthermore, the milligrams of HbV per gram of tissue correlated well between rats and rabbits, suggesting that the balance between organ weight and body weight is a fundamental factor determining the pharmacokinetics of HbV. This factor could be used to estimate the biodistribution and the circulation time of HbV in humans, which is estimated to be equal to that in rabbit.

Confirmation and quantification of hemoglobin-based oxygen carriers in equine and human plasma by hyphenated liquid chromatography tandem mass spectrometry

Oxyglobin (OXY) and Hemopure (HMP) are produced from bovine hemoglobin (Hb) and were developed for the treatment of anemia in animal and human patients, respectively. Hemolink (HML) is a blood substitute of human Hb origin under development. The ability of these agents to carry oxygen in circulating blood and their promise to improve oxygen delivery to tissues supports the potential for their abuse in equine and human athletes. To deter athletes from abuse of these agents, a method has been developed for the detection, confirmation and quantification of OXY, HMP, and HML in equine and human plasma. OXY, HMP, and HML were extracted from equine or human plasma by solid-phase extraction using Bond Elut ENV cartridges and were digested by trypsin at 37 degrees C for 3 h. The tryptic digests were analyzed by LC-MS/MS, and tryptic peptides specific for bovine and human Hbs were targeted. OXY and HMP were detected, quantified, and confirmed using the y14 ion and b8 ion of the tryptic peptide from bovine Hb alpha chain residues 69-90, and HML was quantified using the tryptic peptide from human Hb alpha chain residues 63-91. The limit of detection for OXY in equine plasma and HML in human and equine plasma was 50 and 250 microg/mL for HMP in human and equine plasma. The limit of confirmation was 250 microg/mL for OXY in equine plasma, 500 microg/mL for HML in human and equine plasma, and 1000 microg/mL for HMP in human and equine plasma. The linear range for quantification was 50-5000 microg/mL for OXY in equine plasma and for HML in human and equine plasma, and 250-5000 microg/mL for HMP in human and equine plasma. The intraday and interday CV were less than 17% for quantification of OXY in equine plasma with external calibration. OXY was stable for more than 30 days at -20 and -70 degrees C. OXY was detected and quantified in equine plasma up to 24 h following administration of a very low dose of OXY (32.5 g in 2 x 125 mL per horse), and its presence in equine plasma was confirmed up to 12 h postadministration.

Doping with Artificial Oxygen Carriers

There is a long history of science seeking to develop artificial substitutes for body parts damaged by disease or trauma. While defective teeth and limbs are commonly replaced by imitations without major loss of functionality, the development of a substitute for red blood cells has proved elusive. There is a permanent shortage of donor blood in western societies. Nevertheless, despite whole blood transfusions carrying measurable risks due to immunogenicity and the transmission of blood-borne infectious diseases, red blood cells are still relatively inexpensive, well tolerated and widely available. Researchers seeking to develop products that are able to meet and perhaps exceed these criteria have responded to this difficult challenge by adopting many different approaches. Work has focussed on two classes of substances: modified haemoglobin solutions and perfluorocarbon emulsions. Other approaches include the creation of artificial red cells, where haemoglobin and supporting enzyme systems are encapsulated into liposomes. Haemoglobin is ideally suited to oxygen transport when encased by the red cell membrane; however, once removed, it rapidly dissociates into dimers and is cleared by the kidney. Therefore, it must be stabilised before it can be safely re-infused into humans. Modifications concomitantly alter the vascular half-life, oxygen affinity and hypertensive characteristics of raw haemoglobin, which can be sourced from outdated blood stores, genetically-engineered Escherichia coli or even bovine herds. In contrast, perfluorocarbons are entirely synthetic molecules that are capable of dissolving oxygen but biologically inert. Since they dissolve rather than bind oxygen, their capacity to serve as a blood substitute is determined principally by the oxygen pressure gradients in the lung and at the target tissue. Blood substitutes have important potential areas of clinical application including red cell replacement during surgery, emergency resuscitation of traumatic blood loss, oxygen therapeutic applications in radiography (oxygenation of tumour cells is beneficial to the effect of certain chemotherapeutic agents), other medical applications such as organ preservation, and finally to meet the requirements of patients who cannot receive donor blood because of religious beliefs. Given the elite athlete's historical propensity to experiment with novel doping strategies, it is likely that the burgeoning field of artificial oxygen carriers has already attracted their attention. Scientific data concerning the performance benefits associated with blood substitutes are virtually nonexistent; however, international sporting federations have been commendably proactive in adding this category to their banned substance lists. The current situation is vulnerable to exploitation by immoral athletes since there is still no accepted methodology to test for the presence of artificial oxygen carriers.

Detection of hemoglobin-based oxygen carriers in human serum for doping analysis: screening by electrophoresis

BACKGROUND

Hemoglobin-based oxygen carriers (HBOCs) have recently been included in the International Olympic Committee and World Anti-Doping Agency lists of substances and methods prohibited in sports. To enforce this rule and deter abuse of HBOCs in elite sports, it is necessary to develop HBOC-specific screening and confirmation tests that are the usual steps in antidoping control analysis.

METHODS

We developed a screening method based on electrophoresis of serum samples cleared of haptoglobin (Hp). Four successive steps (immunoprecipitation of Hp, electrophoresis of the cleared serum, Western blotting of the separated proteins, and detection of hemoglobin-related molecules based on the peroxidase properties of the heme moiety), provided electropherograms that could be easily interpreted in terms of the presence of HBOCs. This method was tested with serum samples enriched with various types of HBOCs: polymerized, conjugated, and cross-linked hemoglobins. It was also applied to blood samples collected from 12 healthy volunteers who had been infused with either 30 or 45 g of Hemopure, a glutaraldehyde-polymerized bovine hemoglobin.

RESULTS

The method clearly detected the presence in serum of the various types of HBOCs tested and demonstrated no possible confusion with endogenous hemoglobin that may be present in cases of hemolysis. The test was able to detect Hemopure for 4-5 days after administration of 45 g to healthy individuals.

CONCLUSIONS

The electrophoretic method is a simple, fast, and sensitive procedure that appears to fulfill the criteria of a screening test for the presence of HBOCs in antidoping control samples.

Clinical application of a hemoglobin-based oxygen-carrying solution

Oxyglobin, a hemoglobin-based oxygen-carrying fluid, is indicated in the treatment of anemia in dogs and may be life saving if compatible red blood cells are not available for transfusion. The colloidal properties of Oxyglobin allow for expansion of the circulatory volume, which may be helpful in patients with hypovolemia, especially hemorrhagic shock. Oxyglobin's colloidal properties can also lead to circulatory overload, with development of pulmonary edema and pleural effusion, however, necessitating careful monitoring of the rate of administration and of the respiratory rate and effort of the patient. Measurement of total or plasma hemoglobin concentration can be used as an aid in monitoring patients receiving Oxyglobin.

Drugs for increasing oxygen and their potential use in doping: a review

Blood oxygenation is a fundamental factor in optimising muscular activity. Enhancement of oxygen delivery to tissues is associated with a substantial improvement in athletic performance, particularly in endurance sports. Progress in medical research has led to the identification of new chemicals for the treatment of severe anaemia. Effective and promising molecules have been created and sometimes used for doping purposes. The aim of this review is to present methods, and drugs, known to be (or that might be) used by athletes to increase oxygen transport in an attempt to improve endurance capacity. These methods and drugs include: (i) blood transfusion; (ii) endogenous stimulation of red blood cell production at altitude, or using hypoxic rooms, erythropoietins (EPOs), EPO gene therapy or EPO mimetics; (iii) allosteric effectors of haemoglobin; and (iv) blood substitutes such as modified haemoglobin solutions and perfluorochemicals. Often, new chemicals are used before safety tests have been completed and athletes are taking great health risks. Such new chemicals have also created the need for new instrumental strategies in doping control laboratories, but not all of these chemicals are detectable. Further progress in analytical research is necessary.

Arterial oxygenation and oxygen delivery after hemoglobin-based oxygen carrier infusion in canine hypovolemic shock: a dose-response study

OBJECTIVE

To compare effects of 6% hetastarch (Hextend) and hemoglobin-based oxygen carrier hemoglobin glutamer-200 (Hb-200) (bovine; Oxyglobin) on hemodynamics, arterial oxygen content, and systemic oxygen delivery in a canine hemorrhagic shock model.

DESIGN

Randomized laboratory investigation.

SETTING

University surgical research facility.

SUBJECTS

Twenty-four anesthetized healthy, adult, mongrel dogs (28 +/- 1 kg; 7 female, 17 male).

INTERVENTIONS

Dogs were instrumented for determinations of heart rate, arterial, central venous, pulmonary arterial, and pulmonary arterial occlusion pressures, and cardiac index. Total solids, colloid oncotic pressure, arterial oxygen content, Hb, lactate, pH, and blood gases were analyzed in blood samples. Recordings were made before, after 1 hr of hemorrhagic shock, and immediately and 3 hrs after infusion of either 30 mL/kg hetastarch (group 1), 10 mL/kg Hb-200 + 20 mL/kg hetastarch (group 2), 20 mL/kg Hb-200 + 10 mL/kg hetastarch (group 3), or 30 mL/kg Hb-200 (group 4).

MEASUREMENTS AND MAIN RESULTS

Hemorrhage (35 +/- 1 mL/kg) reduced mean arterial pressure to 50 mm Hg and caused significant decreases in total Hb, mean pulmonary arterial pressure, cardiac index and systemic oxygen delivery, increases in heart rate and systemic vascular resistance, and lactic acidosis. In group 1, hetastarch infusion was accompanied by increases of pulmonary arterial pressure, cardiac index, and blood oxygen extraction above baseline, and decreases of systemic vascular resistance, total Hb, total solids, arterial oxygen content, and systemic oxygen delivery below baseline (p <.05). Other data returned to baseline. In groups 2 to 4, hemodynamic functions (except pulmonary arterial pressure) recovered, yet neither total Hb (i.e., plasma and red blood cell Hb) nor arterial oxygen content increased despite increases in plasma Hb of 2 to 5 g/dL and proportionate increases in total solids. Systemic oxygen delivery improved dose-dependently with Hb-200 but did not return to baseline (p <.05), reaching values comparable to hetastarch group only at 30 mL/kg Hb-200. In all groups, oxygen extraction remained above baseline. Metabolic acidosis and lactatemia resolved significantly faster in groups 2 to 4, and colloid oncotic pressure after resuscitation was greater in groups 2 to 4 than in controls (p <.05).

CONCLUSIONS

In hemorrhagic shock, Hb-200 infusion may not improve oxygen delivery more than hetastarch, likely due to hemodilution caused by its high colloid oncotic pressure, but may facilitate diffusive oxygen transport to tissues.

The use of haemoglobin glutamer-250 (HBOC-201) as an oxygen bridge in patients with acute anaemia associated with surgical blood loss

For the treatment of substantial blood loss in surgery, allogeneic blood is transfused to maintain stability and organ perfusion and function. Continued concerns about the availability, safety, efficacy and storage-related problems of allogeneic blood products have led to an intense effort to find alternatives that can serve the same physiologic functions. Haemoglobin-based oxygen carriers (HBOCs) are compounds that can match the oxygen-carrying capacity of red blood cells (RBCs), and several HBOCs have reached advanced stages of development and clinical testing. Multi-centre, randomised, Phase III, controlled trials have demonstrated the safety and efficacy of haemoglobin glutamer-250 (bovine) (Hemopure), Biopure Corporation, Cambridge, MA, USA), also known as HBOC-201. HBOC-201 is bovine-derived, modified haemoglobin that has been ultrapurified to remove any plasma proteins, RBC stroma and potential pathogenic material. During the manufacturing process, crosslinking and polymerisation stabilise the haemoglobin molecule, which increases its vascular persistence as well as the efficiency of oxygen transport to tissue. Results from clinical trials indicate that HBOC-201 can be used as an oxygen 'bridge' for patients experiencing anaemia due to surgical blood loss, until their own red blood cells are replenished or have regenerated (haematinic effect). HBOC-201 is generally well-tolerated and is approved for use in South Africa, where it is indicated for use in adult surgical patients who are acutely anaemic, and is used to eliminate, delay or reduce the need for allogeneic RBCs. A Biologics License Application for HBOC-201 is currently under review by the US FDA.

Hemoglobin solutions and tissue oxygenation

Oxygen (O2) delivery to tissues plays an important role in determining microcirulatory autoregulatory responses. The balance between O2 delivery by whole blood and tissue O2 consumption likely has evolved based on regulatory processes designed to accommodate the encapsulation of hemoglobin (Hb) within red blood cells (RBCs). The hemodynamic, rheologic, and physical properties of blood, or an alternate O2-carrying solution, can have important consequences for O2 delivery to tissue. The development of acellular hemoglobin-based oxygen carriers (HBOC) requires reassessment of the O2 loading and unloading charactistics of Hb. the effects of altering the rheologic properties of blood, and the impact of these changes on microcirculatory autoregulation and tissue oxygenation. A variety of experimental and clinical studies have demonstrated beneficial effects of HBOCs. However, mechanisms responsible for HBOC-facilitated, O2-dependent autoregulatory changes in the microcirculation have not been completely elucidated.

Hemoglobin-based oxygen carriers

Three types of materials have been studied as candidate blood substitutes: the perfluorocarbons, modified hemoglobins, and liposome-encapsulated hemoglobin. Progress has been greatest with the hemoglobin-based oxygen carriers. Hemoglobin is a highly active molecule; hence, modification has been required to avoid potential deleterious effects. Although there has been considerable progress toward bringing such a product to the clinic, its development has challenged understanding of oxygen delivery and use. The study of these molecules has provided new insights into basic physiologic processes.

The use of bovine hemoglobin glutamer-250 (Hemopure) in surgical patients: results of a multicenter, randomized, single-blinded trial

Hemoglobin-based oxygen carrier-201 (HBOC-201, hemoglobin glutamer-250 [bovine], Hemopure; Biopure Corporation, Cambridge, MA) is polymerized hemoglobin of bovine origin being developed as an oxygen therapeutic. In this study, we evaluated the tolerability of a single intraoperative dose of HBOC-201 in surgical patients. In a single-blinded, multicenter study, 81 patients were randomized to receive either a single infusion of HBOC-201 (55 patients) or an equivalent volume of lactated Ringer's solution (26 patients). Forty-two patients originally assigned to the HBOC-201 group received the entire planned treatment of only one of the following doses: 0.6, 0.9, 1.2, 1.5, 2.0, or 2.5 g/kg of body weight. Thirteen of the 55 patients in the HBOC-201-assigned group did not reach the trigger point for transfusion administration, and they were not included in the analysis. We studied clinical outcomes and compared hematologic findings, blood chemistry values, and blood use in the two treatment groups. There were no patient deaths in this study. No pattern of clinically significant laboratory abnormalities could be attributed to exposure to HBOC-201. In the HBOC-201 group, 2 patients had a transient increased concentration of serum transaminases and 6 had transient skin discoloration. One patient in the HBOC-201 group had mast cell degranulation with hypotension. Postoperatively, methemoglobin plasma concentrations increased in the HBOC-201 group in a dose-dependent manner, reaching maximal values of 3.7% +/- 3.2% (average of all doses given) on postoperative day 3. There was no difference in the mean number of allogeneic blood units transfused in the 2 groups (3.3 +/- 1.8 and 3.7 +/- 4.1 for the lactated Ringer's solution and HBOC-201 groups, respectively) over the course of hospitalization. The intraoperative administration of HBOC-201, up to a maximum of 245 g, was generally well tolerated. There was no relationship between HBOC-201 use and the number of allogeneic blood units transfused over the entire hospitalization course. The administration of HBOC-201 was associated with a delayed (third postoperative day) dose-dependent increase in the plasma methemoglobin concentration. We conclude that the intraoperative use of HBOC-201 was generally well tolerated.

IMPLICATIONS

The intraoperative use of hemoglobin glutamer-250 (bovine) (HBOC-201, Hemopure was generally well tolerated. The administration of HBOC-201 was associated with a delayed increase in the plasma methemoglobin concentrations.

Fetal oxygen content is restored after maternal hemorrhage and fluid replacement with polymerized bovine hemoglobin, but not with hetastarch, in pregnant sheep

We investigated the ability of hemoglobin-based oxygen carrying solutions (HBOCs) to alleviate fetal hypoxemia from maternal hemorrhage. Fifteen pregnant ewes (132-day gestational age) were hemorrhaged 20 mL/kg over 1 h; they were randomized to receive 20 mL/kg IV of HBOC, hetastarch (HTS), or autologous blood (BLD) (n = 5 each) over 30 min and were monitored for 2 h. Hemorrhage significantly (P < or = 0.05) decreased maternal mean blood pressure (from 98 to 48 mm Hg, median), arterial oxygen content (from 12.2 to 11.1 mL/dL), and fetal arterial oxygen content (from 8.1 to 3.9 mL/dL). Fluid replacement restored maternal blood pressure in all groups, although maternal oxygen content immediately returned to baseline only after BLD or HBOC. Maternal oxygen saturation decreased after HBOC (from 98% to 88%). Fetal oxygen content rapidly returned to baseline with either BLD (7.1 mL/dL) or HBOC (8.0 mL/dL) but was never restored with HTS (4.7 mL/dL), and, 60 min after fluid replacement, it was higher with HBOC (8.3 mL/dL) than with HTS (4.7 mL/dL). Fetal plasma-free hemoglobin did not change after HBOC. In conclusion, maternal fluid replacement with HBOC or BLD effectively restored fetal oxygenation, primarily by restoring maternal oxygen content, whereas HTS did not.

IMPLICATIONS

Hemoglobin solutions eliminate many limitations of blood transfusions. Our results show that fluid replacement with either blood or a hemoglobin solution, compared with hetastarch, restored fetal oxygenation in pregnant ewes after hemorrhage. If applicable to women, these results suggest a potential for the use of hemoglobin solutions in obstetrics.

Absence of immunopathology associated with repeated IV administration of bovine Hb-based oxygen carrier in dogs

BACKGROUND

A Hb-based oxygen carrier, HBOC-301, is licensed by the FDA for use as a single-dose product to treat anemia in canines. The objective of this study was to investigate the immunopathologic consequences of multiple doses of HBOC-301.

STUDY DESIGN AND METHODS

HBOC-301 was administered intravenously at 1.3 g per kg (10 mL/kg) nine times over 50 weeks to each of eight splenectomized beagles. During interim weeks, HBOC-301-specific IgG antibody was quantified in serum by immunoassay. Immunofluorescence studies were performed on thin sections of control and test dog livers and kidneys to detect any IgG, IgM, IgA, or C3 deposition. Physiology (p50) studies evaluated the capacity of circulating HBOC-301-specific IgG antibody to competitively block the binding of oxygen to HBOC-301.

RESULTS

HBOC-301-specific IgG antibody was detected in seven of eight HBOC-301-treated dogs by Week 6. Peak antibody levels occurred by Week 10 (after the third dose). Immunofluorescence studies detected comparable IgG, IgA, IgM, or C3 deposition patterns in the kidneys and livers of both control and test dogs, which indicated no selective antibody-mediated deposition from multiple HBOC-301 administrations. Moreover, HBOC-301-specific IgG antibody in serum was unable to inhibit oxygen binding to the HBOC-301 in vitro, which indicated that circulating antibody did not diminish the oxygen-binding capacity of HBOC-301.

CONCLUSION

The immunologic, histologic, and physiologic data support the safety of multidose administration of HBOC-301 in canines.

Current aspects in pharmacology of modified hemoglobins

Blood substitutes are products that are designed to replace whole blood (or) red blood cells in the field of transfusion medicine. There are two major classes that belong to this new therapeutics: (i) modified hemoglobins and (ii) perfluorocarbons. Modified hemoglobins have made tremendous progress in the past decade and are being considered for a wide variety of conditions like trauma, elective surgery, oxygenation of tumors to make them more sensitive to radiation therapy, stroke etc. Although, these agents are primarily used for oxygen delivery, their pharmacological actions have been significantly important. Several mechanisms are being explored to explain these pharmacological effects. Modified hemoglobins suffer several drawbacks including hypertension, renal toxicity, and pulmonary hypertension that restrict their development. This review deals with the clinical status and pharmacological actions of modified hemoglobins presently in advanced stages of development and some of the newer generation hemoglobin based therapeutics are also discussed.

Hemoglobin-based oxygen carriers: development and clinical potential

This article addresses issues involved in the development of hemoglobin-based oxygen carriers and provides a focused overview of the 4 hemoglobin-based oxygen carriers with emergency medicine application currently in clinical trials.

Oxygen carriers as blood substitutes. Past, present, and future

Prospects for safe and effective blood substitutes are promising, based on clinical trial results of soluble hemoglobin solutions and emulsion of perfluorocarbins. Advantages of blood substitutes include sterilization of viral and bacterial contaminants, room temperature storage, a long shelf life, and absence of ABO and other red cell antigens. Projected arenas for their use include not only military applications but also trauma medicine and elective surgical settings, coupled with acute normovolemic hemodilution. Applications of perfluorocarbons are limited by the need for 100% FIO2. A significant challenge facing development of hemoglobin solutions is their effect on vascular tone through smooth muscle constriction. Development of second or third generation hemoglobin solutions may be necessary so that hemoglobin solutions more closely mimic cellular hemoglobin's nitric oxide binding properties. Optimizing O2 delivery to ischemic tissues and organs may lead to regulatory approval of these agents in this setting before their approval as blood substitutes.

Effect of cross-linked hemoglobin transfusion on endothelial-dependent dilation in cat pial arterioles

We determined whether addition of hemoglobin to the plasma would inhibit endothelial-dependent dilation in brain where tight endothelial junctions limit hemoglobin extravasation. Pial arteriolar diameter was measured by intravital microscopy through closed cranial windows in anesthetized cats either without transfusion (hematocrit = 32%) or after exchange transfusion with an albumin or sebacyl-cross-linked human hemoglobin solution (hematocrit = 18%). Dilation of small, medium, and large arterioles to acetylcholine and ADP was not significantly altered by hemoglobin transfusion. The dilatory responses were inhibited by the nitric oxide synthase inhibitor NG-nitro-L-arginine, although significant dilation to 30 microM acetylcholine persisted in small arterioles in the control and albumin-transfused group but not in the hemoglobin-transfused group. The dilatory response to the nitric oxide donor 3-morpholinosydnonimine was unaffected by albumin or hemoglobin transfusion, but the response to nitroprusside was reduced by one-third after hemoglobin transfusion. When cross-linked hemoglobin was superfused through the cranial window, the acetylcholine response became inhibited at a hemoglobin concentration of 0.1 microM and was completely blocked at 10 microM. Because this concentration is substantially less than the 500 microM hemoglobin concentration in plasma after transfusion when there was no inhibition of the acetylcholine response, hemoglobin permeation of the blood-brain barrier was considered negligible. We conclude that exchange of red cell-based hemoglobin with plasma-based hemoglobin does not produce a more effective sink for endothelial-derived nitric oxide evoked by agonist receptor-mediated activation. Furthermore, decreased hematocrit does not affect agonist-evoked endothelial-dependent dilation.

Prediction of microcirculatory oxygen transport by erythrocyte/hemoglobin solution mixtures

A mathematical model has been developed to predict oxygen transport by erythrocyte/acellular hemoglobin solution mixtures flowing in arteriolar-sized vessels (20 to 100 micron diameter). The model includes erythrocyte and extracellular hemoglobin solution phases, radial hematocrit and velocity gradients, axial convection, and radial diffusion of both oxygen and oxyhemoglobin. Model simulations were compared with experimental data from an in vitro capillary model where all of the geometric, physical, and transport parameters are known accurately. A new approach to shear augmentation of transport in 25-micron-diameter conduits was developed. Comparison of theory with experiment suggests that shear augmentation in this flow regime is primarily an extracellular phenomenon produced by cell-cell interactions. Negligible shear augmentation was seen in erythrocyte suspensions in plasma due to the relatively low solubility of oxygen in the plasma phase. Good agreement was found between the theoretical simulations and experimental data for release experiments even neglecting shear augmentation. However, treatment of shear augmentation significantly improved agreement between theoretical simulations and experimental data for oxygen uptake. The model was used to determine the effects on oxygen transport of varying extracellular hemoglobin concentration and extracellular hemoglobin oxygen binding characteristics. It is known that hemoglobin solutions transport oxygen more efficiently than erythrocyte suspensions of the same overall hemoglobin content. Model simulations show that erythrocyte/hemoglobin solution mixtures with 30% extracellular hemoglobin transport oxygen with virtually the same efficiency as pure hemoglobin solutions of the same overall hemoglobin content. Additional simulations predict that erythrocyte/hemoglobin solution mixtures transport oxygen more efficiently than Rbc suspensions, even if the extracellular hemoglobin has a high oxygen affinity.

The effects of increased doses of bovine hemoglobin on hemodynamics and oxygen transport in patients undergoing preoperative hemodilution for elective abdominal aortic surgery

In two consecutive studies (Study A and Study B), we evaluated the effects of increasing doses of HBOC-201, a bovine hemoglobin-based oxygen carrier, on hemodynamics and oxygen transport in patients undergoing preoperative hemodilution for elective abdominal aortic surgery. After the induction of anesthesia and the exchange of 1 L of blood for 1 L of lactated Ringer's solution, 24 patients (12 in each study) were randomly assigned to receive, within 30 min, a predetermined volume of either HBOC-201 or 6% hydroxyethyl starch (Study A 6.9 mL/kg; Study B 9.2 mL/kg). Monitored variables included systemic and pulmonary arterial pressures, arterial and mixed venous blood gases, and calculations of cardiac index (CI), systemic (SVRI) and pulmonary (PVRI) vascular resistance indices, oxygen delivery index (DO2I), oxygen consumption index (VO2I), and oxygen extraction ratio (O2ER). In both studies, the infusion of HBOC-201 was associated with increases in SVRI (Study A 121%; Study B 71%) and PVRI (Study A 70%; Study B 53%) and with a decrease in CI (29% both studies). Hemodilution with HBOC-201 maintained the arterial oxygen content at levels higher than hemodilution with hydroxyethyl starch, but the advantage of a greater oxygen-carrying capacity was offset by the increase in SVRI, with a resulting net decrease in both CI and DO2I (Study A 30%; Study B 28%); VO2I was maintained by increased O2ER. In terms of hemodynamics and oxygen transport, hemodilution with bovine hemoglobin in these doses provided no apparent benefit over hemodilution with hydroxyethyl starch.

IMPLICATIONS

Bovine hemoglobin in doses ranging between 55 and 97 g of hemoglobin increased vascular resistance and decreased cardiac output in anesthetized surgical patients. In terms of hemodynamics and oxygen transport, hemodilution with bovine hemoglobin in these doses provided no apparent benefit over hemodilution with hydroxyethyl starch.

Oxygen transport by erythrocyte/hemoglobin solution mixtures in an in vitro capillary as a model of hemoglobin-based oxygen carrier performance

Oxygen transport behavior of erythrocyte/extracellular hemoglobin mixtures flowing in microvessels was studied as a model of hemoglobin-based oxygen carrier (HBOC) performance. An experimental in vitro 25-microm-diameter capillary model was used to provide detailed oxygen flux measurements for hemoglobin solutions, erythrocyte suspensions, and erythrocyte/hemoglobin solution mixtures. The experimental apparatus includes computerized data acquisition and control coupled to a dual wavelength microspectrophotomer. This apparatus had been previously validated by good agreement of experimental measurements with predictive mathematical models of oxygen transport for either erythrocyte suspensions or hemoglobin solutions. The experimental methodology was extended to measurement of oxygen transport in erythrocyte/hemoglobin solutions. The hemoglobin solutions consisted of either purified or gluteraldehyde polymerized bovine hemoglobin. Dose-response plots were generated by varying the extracellular to intracellular hemoglobin ratio while holding the overall hemoglobin concentration constant. Measurements were also made on unmixed erythrocyte suspensions and hemoglobin solutions to generate limiting cases for comparison. Direct comparison of experimental results showed that both types of hemoglobin solutions were substantially more efficient than erythrocyte suspension in uptake and release of oxygen. Increased extracellular hemoglobin concentration increased oxygen transport efficiency for both uptake and release, even when total hemoglobin concentration was held constant. When only 10% of the total hemoglobin was extracellular, approximately half of the increased efficiency of pure hemoglobin solutions was reached. When 50% of the total hemoglobin was extracellular, the increased efficiency was virtually equal to that of pure hemoglobin solutions.

The current status of haemoglobin-based blood substitutes

Haemoglobin-based red cell substitutes have recently passed a myriad of safety studies and are now undergoing efficacy evaluation. There are numerous potential benefits with use of these solutions: they are readily available and have a long shelf-life; do not require typing and cross-matching; are free of viral or bacterial contamination; lack the immunosuppressive effects of blood; and have a much lower viscosity than blood. One-third of the 10 million units of blood transfused in the United States each year is utilized in the emergency setting. Therefore, a safe, effective substitute for blood should have significant impact upon the way we resuscitate bleeding patients. In this article, the current status of the various haemoglobin-based red cell substitutes is reviewed.

The effects of a blood-salvaging device on blood containing a hemoglobin-based oxygen carrier, HBOC-201

OBJECTIVES

Hemoglobin-based oxygen carriers will be used concurrently with intraoperative blood salvage. The effects of salvage and processing on blood containing one such solution (HBOC-201; Biopure Corp, Boston, MA) were studied.

DESIGN

Prospective, randomized.

SETTING

Laboratory.

INTERVENTIONS

Sixteen blood units from healthy volunteers had either HBOC (1,500 mg/dL; n = 10) or normal saline (equivalent volume; n = 6) added. All units were salvaged and processed using a blood salvage device. Samples were analyzed for the concentration and molecular weight distribution of plasma hemoglobin and red cell morphology presalvage (pre) and following processing and washing (post 1). Five of the HBOC units underwent a second 1,000 mL wash (post 2).

MEASUREMENTS AND MAIN RESULTS

Processing and washing decreased the concentration of plasma hemoglobin (mg/dL) in HBOC units (1311 +/- 265 pre to 27.8 +/- 19.6 post 1 to 6.5 +/- 2.19 post 2), but did not change the plasma hemoglobin concentration in saline units (2.05 +/- 1.27 pre v 3.18 +/- 0.79 post 1). Total plasma hemoglobin in HBOC units (6.56 +/- 2.19) was significantly greater than in saline units (3.18 +/- 0.79), even after the second wash (post 2). The concentration of unstable hemoglobin in the plasma phase was not different between groups. Red cell morphology was altered by the salvage process but was not different between groups.

CONCLUSIONS

Salvage and processing of blood containing HBOC yield concentrated red cells that are indistinguishable from those obtained from blood without HBOC. Residual HBOC remains but is unchanged from the HBOC initially administered.