Oxygen-carrying Agents Research Articles

Liquid ventilation

Liquid ventilation

Haemoglobin Based Oxygen Carrier: Use in South Africa

proteins, red blood cell stroma, endotoxin, bacteria, viruses and the agents that are thought to cause transmissible spongiform encephalopathies such as bovine spongiform encephalopathy (BSE) and variant CreutzfeldJakob disease (vCJD). This process produces a sterile, pyrogen-free balanced salt solution containing glutaraldehyde cross linked bovine haemoglobin polymers, which range in size from 130 to 500 kd and have an average molecular weight of 250 kd. 3 ,4 The product’s oxygen dissociation curve is right-shifted with a P 50 of 38 mm Hg, compared to 27 mm Hg for human haemoglobin. In contrast to human haemoglobin whose oxygen affinity relies on adequate levels of 2,3diphosphoglycerate, the affinity of bovine haemoglobin for oxygen is regulated by the concentration of chloride ions in the plasma. It has a dose dependent intravascular half-life of 16 to 20 hours. When stored within a temperature range from 2° to 30° C, it is stable for at least two years, can be infused directly without reconstitution and does not require typing or cross matching. In vitro studies utilizing an artificial capillary model and mathematical simulations demonstrate that HBOC-201 acts not only as an oxygen-carrying agent in the plasma but also facilitates the uptake and release of oxygen by the patient’s own red blood cells. Furthermore, in a canine model, it was shown to take up oxygen in the lungs and release oxygen for diffusion into body tissues at a higher rate than red blood cells. On a gram-for-gram basis, the HBOC-201 haemoglobin was approximately three times more potent than stored or fresh red blood cell haemoglobin at restoring baseline tissue oxygenation following severe acute anaemia. This product has been administered to more than 800 human subjects in 22 completed or ongoing clinical trials at doses up to 1080 g (36 units) of haemoglobin, including red blood cell controlled trials in elective surgical patients where the product was administered at doses up to Until very recently, transfusion of red blood cells was the traditional method of restoring oxygen-carrying capacity in acutely anaemic patients. Blood transfusions are, however, associated with several intrinsic risks, such as bloodborne infections and allergic reactions. Upon storage, red blood cells become deficient in their ability to immediately offload oxygen and, therefore, may not be immediately effective in delivering oxygen to tissues. Various pharmacological agents, including haemoglobin solutions, have been developed as replacements for red blood cells, as intravascular volume expanders and as oxygen therapeutics. The administration of these pharmacological agents, which can assist in the delivery of oxygen to the tissues, has unfortunately been historically associated with a high incidence of toxic events such as renal failure, pancreatitis, allergic reactions and vascular events. HBOC-201 [haemoglobin glutamer-250 (bovine)] is a cell-free polymerised haemoglobin solution that not only carries oxygen in the plasma, but also enhances the ability of native red blood cells to take up and off-load oxygen. Studies in an artificial capillary model suggest that the free form in the plasma facilitates the diffusion of oxygen into the pulmonary capillary blood more rapidly and more efficiently than normal diffusion across the alveolar-capillary barrier and the red blood cell membrane. It is manufactured from a plentiful and well-controlled source material, bovine haemoglobin. Only cattle from the United States are utilized as donors, and an extensive herd-management program ensures that only certified disease-free animals less than 30 months of age are used to provide the haemoglobin. The extensive extraction and purification process used in production has been validated for the removal of potential contaminants including plasma

Monoamine-dependent production of reactive oxygen species catalyzed by pseudoperoxidase activity of human hemoglobin.

Hemoglobin (Hb) solution-based blood substitutes are being developed as oxygen-carrying agents for the prevention of ischemic tissue damage and low blood volume-shock. However, the cell-free Hb molecule has intrinsic toxicity to the tissue since harmful reactive oxygen species (ROS) are readily produced during autoxidation of Hb from the ferrous state to the ferric state, and the cell-free Hb also causes distortion in the oxidant/antioxidant balance in the tissues. There may be further hindering dangers in the use of free Hb as a blood substitute. It has been reported that Hb has peroxidase-like activity oxidizing peroxidase substrates such as aromatic amines. Here we observed the Hb-catalyzed ROS production coupled to oxidation of a neurotransmitter precursor, beta-phenylethylamine (PEA). Addition of PEA to Hb solution resulted in generation of superoxide anion (O2*-). We also observed that PEA increases the Hb-catalyzed monovalent oxidation of ascorbate to ascorbate free radicals (Asc'). The O2*- generation and Asc formation were detected by O2*--specific chemiluminescence of the Cypridina lucigenin analog and electron spin resonance spectroscopy, respectively. PEA-dependent O2*- production and monovalent oxidation of ascorbate in the Hb solution occurred without addition of H2O2, but a trace of H2O2 added to the system greatly increased the production of both O2*- and Asc*. Addition of GSH completely inhibited the PEA-dependent production of O2*- and Asc* in Hb solution. We propose that the O2*- generation and Asc* formation in the Hb solution are due to the pseudoperoxidase activity-dependent oxidation of PEA and resultant ROS may damage tissues rich in monoamines, if the Hb-based blood substitutes were circulated without addition of ROS scavengers such as thiols.

Hemoglobin-based blood substitutes: oxygen carriers, pressor agents, or oxidants?

Hemoglobin-based blood substitutes are being developed as oxygen-carrying agents for the prevention of ischemic tissue damage and hypovolemic (low blood volume) shock. The ability of cell-free hemoglobin blood substitutes to affect vascular tone through the removal of nitric oxide has also prompted an evaluation of their usefulness for maintaining blood pressure in critically ill patients. Before the clinical potential of these substitutes can be fully realized, however, concerns remain as to the intrinsic toxicity of the hemoglobin molecule, particularly the interference of the heme prosthetic group with the tissue oxidant/antioxidant balance. This review provides some insights into the complex redox chemistry of hemoglobin and places an emphasis on how current knowledge may be exploited both to selectively enhance/suppress specific chemical reaction pathway(s) and to ultimately design safer hemoglobin-based therapeutics.

Biochemical and metabolic assessments of liver graft preserved with oncotic oxygen carrier

The effect of an oxygen-carrying agent, as a component of the preservation solution, on the biochemical viability and energy metabolism of the graft in liver preservation was evaluated. Two preservation methods, simple hypothermic storage and continuous machine perfusion, both performed at 4°C for 48 h, were studied in male Lewis rats. Pyridoxylated hemoglobin-polyoxyethylene conjugate (PHP) was used as the oncotic oxygen carrier. University of Wisconsin (UW) solution served as a control solution. The test solution (PHP+UW) was a 1∶1 mixture of PHP and UW solutions with 4.0g% of hemoglobin. We observed that oxygen consumption during perfusion was significantly higher in the PHP+UW than in the UW group. Hepatic mitochondrial function and tissue adenosine-5′-triphosphate (ATP) levels were better preserved in the PHP+UW than in the UW group, and were also better preserved in continuous machine perfusion than in simple hypothermic storage. No significant differences were observed in perfusate biochemical parameters. These results indicate that the incorporation of an oxygen-carrying agent into preservation solution provides significantly better oxygen delivery to liver grafts, and may improve hepatic viability.

Synthesis of perfluoroalkyl steroids as CO-emulsifying agents for 1-bromoperfluorooctane and other perfluorocompounds

Abstract Syntheses of steroids substituted with perfluoroalkyl groups at C-3, C-7, and C-20 positions on the steroid nucleus are described. Synthetic methods employed included coupling of perfluoroalkylcopper with allylic bromides and Grignard reactions. Free radical additions of perfluoroalkyl iodide to unsaturated steroids and reaction of perfluoroalkyl Grignard reagents with 6-ketosteroid were unsuccessful. Perfluoroalkyl -substituted steroids are desired for testing as co-emulsifying agents in perfluorooctyl bromide/water emulsions which are used as blood substitutes ( synthetic blood ). A rationale for the choice of perfluorooctyl bromide as the oxygen-carrying agent in the fluorocarbon-based blood substitute and on the use of perfluoroalkyl-substituted steroids as co-emulsifying agents is also reported.

Perfluorocarbons as blood substitutes

The development of perfluorocarbon (PFC) solutions as clinically useful oxygen-carrying agents has been a slow process because PFC is immiscible in aqueous solutions, including blood. Therefore, it has been necessary to develop emulsions for IV infusions. One such emulsion (fluosol) has been the most extensively studied and has been clinically tested. It has been shown that fluosol can transport oxygen in vivo when very high inspired oxygen concentrations are used and when high arterial oxygen tensions are achieved. Furthermore, it appears that the oxygen dissolved in PFC is very effectively delivered to and used by the tissues. In severely anemic patients, the PFC may deliver a very significant portion of the total consumed oxygen. It has been difficult to prove, however, whether fluosol has been clinically beneficial. It has a limited half-life (13 hours), the amounts infused have been quite limited, and the effect on patient outcome is unclear. Further, a number of adverse effects have been related to fluosol administration, most likely related to the emulsifying agent. PFC solutions thus remain experimental. Their greatest future use may be not as a blood substitute for treatment of anemia, but rather as an agent to improve microcirculatory oxygen delivery for treatment of ischemic tissues (ie, in stroke, myocardial infarction, burns, ischemic extremities). Further development of PFC emulsions is ongoing.

Extending the limits of hemodilution on cardiopulmonary bypass using stroma-free hemoglobin solution

Ten swine were subjected to exchange transfusion to a hematocrit level of 5% with either stroma-free hemoglobin solution (SFHS) or 7% albumin solution. Myocardial performance, oxygen kinetics, and myocardial metabolism were subsequently examined using a perfused, in situ, right heart bypass, swine heart model with control of preload, afterload, and heart rate. Animals were tested during a control period (hematocrit = 30%) and following exchange transfusion with either solution to a hematocrit level of 5%. We found that myocardial performance following albumin solution exchange could not be sustained on right heart bypass, and these animals had a stroke volume of zero at a left ventricular end-diastolic pressure of 14 torr. SFHS animals had a significant drop in stroke volume at 14 torr following exchange (20 +/- 3 versus 10 +/- 4, p < 0.025), but this 50% performance level could be sustained. Coronary blood flow rose and myocardial oxygen consumption fell in both groups, although the statistically nonsignificant mean differences were less with SFHS. Arterial-coronary sinus oxygen difference fell significantly (p < 0.05) with albumin solution (7.3 +/- 0.8 versus 2.2 +/- 0.2) and nonsignificantly with SFHS (5.6 +/- 0.4 versus 4.1 +/- 0.7). Lactate production occurred in both groups, but was greater with albumin (34% +/- 6%) than with SFHS (3% +/- 16%). No changes in myocardial tissue gasses were noted in either group. Although myocardial performance decreased and some lactate production occurred with SFHS, we believe these comparative results provide promise in the eventual utilization of an oxygen-carrying agent such as SFHS to extend the limits of hemodilution to a hematocrit value of 5% or less.

Evaluation of hepatocellular and Kupffer cell function of the isolated guinea pig liver perfused by a fluorocarbon medium

A synthetic medium for isolated guinea pig liver perfusion, using a fluorocarbon (FC) emulsion as the oxygen-carrying agent, was evaluated for its capacity to maintain liver viability and function. A 10% emulsion of perfluorotributylamine (FC43) was dispersed by a nonionic detergent (Pluronic F68) in a buffered electrolyte solution. The FC43 perfusate was compared with identical media in which FC43 was either omitted or replaced by 20% isologous red cells. Damage to liver cells was assessed by hepatic flow rate, release of aspartate aminotransferase, and liver histology. Bile secretion, albumin synthesis, and galactose elimination capacity were used as indices of parenchymal cell function, and Kupffer cell activity was assessed by uptake of colloidal radioactive gold. All three perfusion media satisfactorily maintained liver cell viability, but the two media supplemented with a specific oxygen-carrying agent were associated with significantly superior parenchymal cell function (P was between 0.05 and 0.01). The performance of the FC and red cell media was not significantly different. The phagocytic activity of Kupffer cells was well sustained by all three media, but the FC medium was superior with large amounts of colloidal gold. Release of iron from hepatic parenchymal cells, with the FC medium, was similar to that reported for rat liver preparations, using a red cell perfusate.