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

Preparation of Artificial Red Blood Cells (Hemoglobin Vesicles) Using the Rotation-Revolution Mixer for High Encapsulation Efficiency

Hemoglobin vesicles (Hb-V) are artificial red blood cells encapsulating highly concentrated hemoglobin (Hb) in liposomes comprising phospholipids, cholesterol, negatively charged lipids, and polyethylene glycol (PEG)-conjugated phospholipids. Safety and efficacy of Hb-V as a transfusion alternative have been extensively studied. For this study, we prepared Hb-V using the kneading method with a rotation-revolution mixer as an alternative to the conventional extrusion method. We optimized the kneading operation parameters to obtain Hb-V with a high yield. Results show that the Hb encapsulation efficiency was increased dramatically up to 74.2%, which is higher than that of the extrusion method (20%) because the kneading method enabled mixing of a highly concentrated carbonylhemoglobin (HbCO) solution (40 g/dL) and a considerably large amount of powdered lipids in only 10 min. The high viscosity of the Hb-lipid mixture paste (ca. 10³-10⁵ cP) favorably induces frictional heat by kneading and increases the paste temperature (ca. 60 °C), which facilitates lipid dispersion and liposome formation. During the kneading operation using a thermostable HbCO solution, Hb denaturation was prevented. Hb-V prepared using this method showed no marked changes in particle sizes, Hb denaturation, or Hb leakage from liposomes during two years of long-term storage-stability tests. Collectively, these results demonstrate that the kneading method using a rotation-revolution mixer shows good potential as a new method to produce Hb-V.

Haemoglobin-loaded metal organic framework-based nanoparticles camouflaged with a red blood cell membrane as potential oxygen delivery systems

Metal organic frameworks are used to protect hemoglobin from denaturation thus preserving its excellent oxygen-binding and releasing properties. Decorating with cell membranes minimizes protein adsorption holding potential for long circulation.   

Low modulus biomimetic microgel particles with high loading of hemoglobin

We synthesized extremely deformable red blood cell-like microgel particles and loaded them with bovine hemoglobin (Hb) to potentiate oxygen transport. With similar shape and size as red blood cells (RBCs), the particles were fabricated using the PRINT (particle replication in nonwetting templates) technique. Low cross-linking of the hydrogel resulted in very low mesh density for these particles, allowing passive diffusion of hemoglobin throughout the particles. Hb was secured in the particles through covalent conjugation of the lysine groups of Hb to carboxyl groups in the particles via EDC/NHS coupling. Confocal microscopy of particles bound to fluorescent dye-labeled Hb confirmed the uniform distribution of Hb throughout the particle interior, as opposed to the surface conjugation only. High loading ratios, up to 5 times the amount of Hb to polymer by weight, were obtained without a significant effect on particle stability and shape, though particle diameter decreased slightly with Hb conjugation. Analysis of the protein by circular dichroism (CD) spectroscopy showed that the secondary structure of Hb was unperturbed by conjugation to the particles. Methemoglobin in the particles could be maintained at a low level and the loaded Hb could still bind oxygen, as studied by UV-vis spectroscopy. Hb-loaded particles with moderate loading ratios demonstrated excellent deformability in microfluidic devices, easily deforming to pass through restricted pores half as wide as the diameter of the particles. The suspension of concentrated particles with a Hb concentration of 5.2 g/dL showed comparable viscosity to that of mouse blood, and the particles remained intact even after being sheared at a constant high rate (1000 1/s) for 10 min. Armed with the ability to control size, shape, deformability, and loading of Hb into RBC mimics, we will discuss the implications for artificial blood.

Stroma-free hemoglobin from bovine blood

Isolation and purification of bovine hemoglobin (HbBv) was carried out after reaction of whole blood with carbon monoxide. Washing/centrifugation steps were used to eliminate leukocytes, platelets, and plasma proteins. Hypotonic media and ultrasound radiation were used to lyse red blood cells. Lyse by ultrasound was shown to lead to solutions at the highest concentrations in HbBv, and the least concentrations in major phospholipids contaminants. Additional purification procedures were performed to remove membrane proteins and phospholipids. In the first case, proteins were denatured by thermal treatment, and filtered. To eliminate phospholipids, liquid chromatography was used with strong anion exchangers. Purity of HbBv was evaluated by normal phase high performance liquid chromatography (HPLC), electrophoresis, and size-exclusion HPLC.

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.

Purification and characterization of human hemoglobin: effect of the hemolysis conditions

Human hemoglobin was isolated and purified by anion exchange chromatography. To isolate hemoglobin, outdated red blood cells (RBC) were transformed into carbonylhemoglobin, by reaction with carbon monoxide, and submitted to washing/centrifugation procedures, to eliminate other plasma proteins. Albumin was quantified in each supernatant, by the bromcresol green method. Hemolysis was performed in three different hypotonic media (water, 0.01 M NaCl and 5 mM Tris/HCl buffer at pH 7.4), at 8 degrees C for 24 h. Sonication for 5 min was also used to lyse RBC. After isolation of hemoglobin, additional purification was carried out by anion exchange chromatography on AG MP-1, Q-SFF and both exchangers. Hemoglobin concentration of hemolysates and of purified solutions were determined by the hemiglobincyanide method. Residual phospholipids were extracted from the four different hemolysates, as well as from the purified hemoglobin solutions, and were analyzed by high performance liquid chromatography. Native and SDS-polyacrylamide gel electrophoresis experiments were performed on purified hemoglobin samples to verify the presence of proteins other than hemoglobin. According to the results, the hemolysis conditions have influence on the purification of hemoglobin.

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.

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.

Faith, identity, and leukemia: when blood products are not an option

Shortly before his death in 1995, Kenneth B. Schwartz, a cancer patient at Massachusetts General Hospital, founded the Kenneth B. Schwartz Center. The Schwartz Center is a non-profit organization dedicated to supporting and advancing compassionate health care delivery, which provides hope to the patient, support to caregivers, and sustenance to the healing process. The center sponsors the Schwartz Center Rounds, a monthly multidisciplinary forum where caregivers reflect on important psychosocial issues faced by patients, their families, and their caregivers and gain insight and support from fellow staff members. When a competent adult patient refuses lifesaving treatment for religious or personal reasons, caregivers have a legal obligation to respect this decision. A patient's refusal of treatment adds particular challenges to the delivery of compassionate care. The case of a 50-year-old Jehovah's Witness with acute myelocytic leukemia who declined blood product support is presented. Respecting her religious beliefs during chemotherapy required balancing risk and benefit, watching her suffer while unable to intervene with what the staff saw as simple treatment, and eventually undertaking a complicated grief process. Jehovah's Witness beliefs regarding blood products are reviewed. Caregiver roles and responsibilities are discussed in the context of psychosocial, legal, familial, and ethical issues.

A second-generation blood substitute (perflubron emulsion) increases the blood solubility of modern volatile anesthetics in vitro

Perfluorocarbon-based emulsions increase the blood solubility of isoflurane, enflurane, and halothane, with a maximal effect reported for the less soluble isoflurane. Current volatile anesthetics are less soluble and may be more affected by this phenomenon. Perflubron (Oxygent(TM)) is a perfluorocarbon-based emulsion in late-stage clinical testing in surgical patients for use as a temporary oxygen carrier. We tested the hypothesis that perflubron increases the solubility of isoflurane, sevoflurane, and desflurane, as reflected by their blood/gas partition coefficient (lambda(Bl:g)). Fresh whole-blood samples were drawn from eight volunteers and mixed with perflubron to obtain concentrations of 1.2%, 1.8%, and 3.6% by volume (equivalent to in vivo doses of 1.8 to 5.4 g/kg, which represent up to twice the intended clinical dose range). By using the double-extraction method, we demonstrated increased lambda(Bl:g) for isoflurane, sevoflurane, and desflurane. However, the solubility in blood does not really change, because volatile anesthetics are actually partitioning into perflubron. Increasing the amount of emulsion in the blood consequently increases the amount of gas carried, as reflected by the measured linear correlation between the lambda(Bl:g) values of all three volatile anesthetics and perflubron doses. Even though the increase ranges from 0.9 (desflurane) to 2.6 (sevoflurane) times the normal value, the apparent lack of clinical implications in current trials with perflubron may trigger further in vivo experiments.

IMPLICATIONS

Perflubron increases the in vitro solubility of volatile anesthetics when present in the blood at clinically relevant concentrations. Volatile anesthetics actually partition into the emulsion, but the solubility in the blood does not change. Further studies are needed to assess whether perflubron will affect the pharmacokinetics of volatile anesthetics in vivo.

Perioperative blood salvage as an alternative to predonating blood for primary total knee and hip arthroplasty

A total of 200 consecutive patients who underwent primary total knee or hip arthroplasty were reviewed to assess the efficacy of perioperative blood salvage and retransfusion. Five of 132 (3.8%) patients undergoing total knee arthroplasty and 3 of 68 (4.4%) patients undergoing total hip arthroplasty required allogeneic transfusion in addition to retransfusion of salvaged autologous blood. The risk of receiving allogeneic transfusion in addition to retransfusion of salvaged blood was 1.2% (2 of 173) in patients with a preoperative hematocrit of > or=37%. The risk of requiring allogeneic transfusion was 22% (6 of 27) in patients with a preoperative hematocrit of <or=37% (P<or=.01). Perioperative blood salvage is safe and cost-effective and makes it possible to discontinue the practice of predonating blood for primary total knee arthroplasty and total hip arthroplasty in patients with a preoperative hematocrit >37%.

Systemic and renal hemodynamics after moderate hemodilution with HbOCs in anesthetized rabbits

Hb-based O(2)-carrying solutions (HbOCs) have been developed as red blood cell substitutes for use in patients undergoing hemodilution. Variously modified Hb with diverse solution properties have been shown to produce variable hemodynamic responses. We examined, through pulsed-Doppler velocimetry, the systemic and renal hemodynamic effects of dextran-benzene-tetracarboxylate-conjugated (Hb-Dex-BTC), bis(3,5-dibromosalicyl)fumarate cross-linked (alphaalpha-Hb), and o-raffinose-polymerized (o-raffinose-Hb) Hb perfused in rabbits after moderate hemodilution (30% hematocrit), and we compared the effects of these Hb solutions with the effects elicited by plasma volume expanders. In addition, vascular hindrance (resistance/blood viscosity at 128.5 s(-1)) was calculated to determine whether a moderate decrease in the viscosity of blood mixed with HbOCs may impair vasoconstriction as a result of autoregulation after infusion of cell-free Hb. No changes were observed in renal hemodynamics after hemodilution with reference or Hb solutions. Increase in blood pressure and vascular resistance was found with Hb-Dex-BTC and alphaalpha-Hb (for 180 min) and, to a lesser extent, with o-raffinose-Hb (for 120 min). Furthermore, Hb-Dex-BTC (high viscosity) and o-raffinose-Hb (medium viscosity) induced comparable increases in vascular hindrance (from 0.091 to 0. 159 and from 0.092 to 0.162 cm(-1), respectively) but far less than that produced by alphaalpha-Hb (low viscosity, from 0.092 to 0.200 cm(-1)). These results suggest that maintaining the viscosity of blood by infusing solutions with high viscosity makes it possible to limit vasoconstriction due to autoregulation mechanisms and mainly caused by hemodilution per se.