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Hemoglobin-Based Artificial Blood: New Polymeric Derivatives of Hemoglobin with Low Oxygen Affinity. Int J Artif Organs 2018. [DOI: 10.1177/039139889101400107] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Naito Y, Sakai H, Inoue S, Kawaguchi M. Hemoglobin Vesicles prolong the time to circulatory collapse in rats during apnea. BMC Anesthesiol 2017; 17:44. [PMID: 28288573 PMCID: PMC5348749 DOI: 10.1186/s12871-017-0338-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2016] [Accepted: 03/07/2017] [Indexed: 11/10/2022] Open
Abstract
Background Hemoglobin vesicles (HbV) are hemoglobin-based oxygen carriers manufactured by liposome encapsulation of hemoglobin molecules. We hypothesised that the infusion of oxygenated HbV could prolong the time to circulatory collapse during apnea in rats. Methods Twenty-four Sprague-Dawley rats were randomly divided into four groups (Air, Oxy, NS and HbV). The rats were anaesthetized with isoflurane and the trachea was intubated using 14-gauge intravenous catheters. Rats in the Air group were mechanically ventilated with 1.5% isoflurane in room air, and those in other groups received 1.5% isoflurane in 100% oxygen. Mechanical ventilation was withdrawn 1 min after the administration of rocuronium bromide to induce apnea. After 30 s, 6 mL saline and HbV boluses were infused at a rate of 0.1 mL/s in the NS and HbV groups, respectively. Circulatory collapse was defined as a pulse pressure < 20 mmHg and the time to reach this point (PP20) was compared between the groups. The results were analysed via a one-way analysis of variance and post-hoc Holm–Sidak test. Results PP20 times were 30.4 ± 4.2 s, 67.5 ± 9.7 s, 95 ± 17.3 s and 135 ± 38.2 s for the Air (ventilated in room air with no fluid bolus), Oxy (ventilated with 100% oxygen with no fluid bolus), NS (ventilated with 100% oxygen with a normal saline bolus), and HbV (ventilated in 100% oxygen with an HbV bolus) groups, respectively, and differed significantly between the four groups (P = 0.0001). The PP20 times in the HbV group were significantly greater than in the Air (P = 0.0001), Oxy (P = 0.007) and NS (P = 0.04) groups. Conclusion Infusion of oxygenated HbV prolongs the time to circulatory collapse during apnea in rats. Electronic supplementary material The online version of this article (doi:10.1186/s12871-017-0338-y) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Yusuke Naito
- Department of Anesthesiology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan.
| | - Hiromi Sakai
- Department of Chemistry, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, Japan
| | - Satoki Inoue
- Department of Anesthesiology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan
| | - Masahiko Kawaguchi
- Department of Anesthesiology, Nara Medical University, 840 Shijo-cho, Kashihara, Nara, 634-8522, Japan
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Banerjee A, Bandopadhyay R. Use of dextran nanoparticle: A paradigm shift in bacterial exopolysaccharide based biomedical applications. Int J Biol Macromol 2016; 87:295-301. [DOI: 10.1016/j.ijbiomac.2016.02.059] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2016] [Revised: 02/18/2016] [Accepted: 02/23/2016] [Indexed: 12/27/2022]
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Chang TMS. Red blood cell replacement, or nanobiotherapeutics with enhanced red blood cell functions? ARTIFICIAL CELLS NANOMEDICINE AND BIOTECHNOLOGY 2015; 43:145-7. [DOI: 10.3109/21691401.2015.1047557] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
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Chang TMS. Evolution of Artificial Cells Using Nanobiotechnology of Hemoglobin Based RBC Blood Substitute as an Example. ACTA ACUST UNITED AC 2009; 34:551-66. [PMID: 17090428 DOI: 10.1080/10731190600973808] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The original artificial red blood cells have evolved into oxygen carriers in the form of polyhemoglobin and conjugated hemoglobin. Clinical conditions requiring only oxygen carriers are responding well to these types of oxygen carriers without the need for a complete artificial red blood cell. For those conditions requiring more than just oxygen carriers, new generations of polyhemoglobin containing antioxidant enzymes are being developed. Though a complete artificial red blood cell comparable to red blood cell is still a dream, development in lipid membrane artificial red blood cells and biodegradable polymeric nano artificial red blood cells are steps towards this possibility. The many years of neglect on basic research in the area of blood substitutes have resulted in the lack of important basic knowledge needed for the rapid development of blood substitutes suitable for clinical use. This is further hampered by the mistaken conception that blood substitute is a single entity. We need to look at blood substitutes as consisting of progressively more complicated entities, e.g. oxygen carriers, oxygen carriers with antioxidant activity, and complete red blood cell substitutes. Each of these entities is not applicable to all clinical conditions, but is suitable for specific applications.
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Chang TM. Artificial Cell Including Blood Substitute and Biomicroencapsulation: from Ideas to Applications. ACTA ACUST UNITED AC 2009. [DOI: 10.3109/10731199409117661] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
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Abstract
In this brief review, basic principles and recent progresses on the development of therapeutic substitutes for major blood components are briefly discussed with primary focus on the red cell substitutes.
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Kim HW, Greenburg AG. Artificial Oxygen Carriers as Red Blood Cell Substitutes: A Selected Review and Current Status. Artif Organs 2004; 28:813-28. [PMID: 15320945 DOI: 10.1111/j.1525-1594.2004.07345.x] [Citation(s) in RCA: 105] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Two distinct approaches are being explored in red blood cell substitute (RCS) development: hemoglobin-based oxygen carriers (HBOCs) and perfluorocarbon-based oxygen carriers (PFBOCs). HBOCs are based on intra- and/or intermolecularly "engineered" human or animal hemoglobins (Hbs), optimized for O2 delivery and longer intravascular circulation. Some are currently being evaluated in Phase II/III clinical studies. PFBOCs are aqueous emulsions of perfluorocarbon derivatives that dissolve relatively large amounts of O2. A PFBOC based on a 60% (wt/vol) emulsion of perfluorooctyl bromide has been evaluated in Phase II/III clinical trials. Although current PFBOC products generally require patients to breathe O2 enriched air, they render certain advantages since they are totally synthetic. This article provides a short review of the basic principles, approaches, and current status of RCS development. Results of preclinical and clinical studies including recent Phase II/III clinical studies are discussed.
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Affiliation(s)
- Hae Won Kim
- Department of Surgery, Brown University Medical School, The Miriam Hospital, Providence, RI 02906, USA.
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Abstract
Polyhemoglobin is already well into the final stages of clinical trials in humans with one approved for routine clinical use in South Africa. Conjugated hemoglobin is also in ongoing clinical trials. Meanwhile, recombinant Hb has been modified to modulate the effects of nitric oxide. Other systems contain antioxidant enzymes for those clinical applications that may have potential problems related to ischemia-reperfusion injuries. Other developments are based on hemoglobin-lipid vesicles and also the use of nanotechnology and biodegradable copolymers to prepare nanodimension artificial red blood cells containing hemoglobin and complex enzyme systems.
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Affiliation(s)
- Thomas Ming Swi Chang
- Artificial Cells and Organs Research Centre, MSSS-FRSQ Research Group on Blood Substitutes in Transfusion Medicine, McGill University, Montreal, Quebec, Canada
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Abstract
Polyhaemoglobins (PolyHb) and perfluorochemicals are in advanced phase III clinical trials and conjugated haemoglobins in phase II clinical trial. New recombinant human haemoglobin with no vasoactivity is being developed. A soluble macromolecule of PolyHb-catalase-superoxide dismutase is being studied as an oxygen carrier with antioxidant properties. New artificial red blood cells that are more like RBC are being developed. One is based on haemoglobin lipid vesicles. A more recent one is based on nano-dimension artificial red blood cells containing haemoglobin and RBC enzymes with membrane formed from composite copolymer of polyethylene glycol-polylactic acid. Their circulation time is double that of PolyHb.
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Affiliation(s)
- T M S Chang
- Artificial Cells & Organs Research Center, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
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Riess JG. Oxygen carriers ("blood substitutes")--raison d'etre, chemistry, and some physiology. Chem Rev 2001; 101:2797-920. [PMID: 11749396 DOI: 10.1021/cr970143c] [Citation(s) in RCA: 544] [Impact Index Per Article: 23.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Affiliation(s)
- J G Riess
- MRI Institute, University of California at San Diego, San Diego, CA 92103, USA.
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Abstract
Soluble polymerized haemoglobin (polyhaemoglobin) is now in a phase III clinical trials. Patients have received up to 20 units (10 litres) in trauma surgery and other surgery. Polyhaemoglobin can be stored for more than 1 year. Haemoglobin solutions have no blood group antigen and can be used as a 'universal donor' oxygen carrier. They can also be sterilized. With a circulation half-life of 24 hours they are undergoing trials for peri-operative use. For conditions with potential for ischaemia-reperfusion injuries, a new polyhaemoglobin-superoxide dismutase-catalase, which can reduce oxygen radicals, is being developed. Recombinant human haemoglobin has been tested in clinical trials, and a new type of recombinant human haemoglobin that has low affinity for nitric oxide is being developed for clinical trials. To increase the circulation time, artificial red blood cells have been prepared with a bilayer lipid membrane (haemoglobin liposomes) or with a biodegradable polymer membrane-like polylactide (haemoglobin nanocapsules). Synthetic chemicals such as perfluorochemicals are also being developed and tested in clinical trials as red blood cell substitutes.
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Affiliation(s)
- T M Chang
- Artificial Cells and Organs Research Centre, Department of Physiology, McGill University, Montreal, Canada
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Abstract
Dextrans are glucose polymers which have been used for more than 50 years as plasma volume expanders. Recently, however, dextrans have been investigated for delivery of drugs, proteins/enzymes, and imaging agents. These highly water soluble polymers are available commercially as different molecular weights (M(W)) with a relatively narrow M(W) distribution. Additionally, dextrans contain a large number of hydroxyl groups which can be easily conjugated to drugs and proteins by either direct attachment or through a linker. In terms of pharmacokinetics, the intact polymer is not absorbed to a significant degree after oral administration. Therefore, most of the applications of dextrans as macromolecular carriers are through injectable routes. However, a few studies have reported the potential of dextrans for site (colon)-specific delivery of drugs via the oral route. After the systemic administration, the pharmacokinetics of the conjugates of dextran with therapeutic/imaging agents are significantly affected by the kinetics of the dextran carrier. Animal and human studies have shown that both the distribution and elimination of dextrans are dependent on the M(W) and charge of these polymers. Pharmacodynamically, conjugation with dextrans has resulted in prolongation of the effect, alteration of toxicity profile, and a reduction in the immunogenicity of drugs and/or proteins. A substantial number of studies on dextran conjugates of therapeutic/imaging agents have reported favorable alteration of pharmacokinetics and pharmacodynamics of these agents. However, most of these studies have been carried out in animals, with only a few being extended to humans. Future studies should concentrate on barriers for the clinical use of dextrans as macromolecular carriers for delivery of drugs, proteins, and imaging agents.
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Affiliation(s)
- R Mehvar
- School of Pharmacy, Texas Tech University Health Sciences Center, 1300 Coulter, Amarillo, TX 79106, USA.
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Chang TM. Modified hemoglobin blood substitutes: present status and future perspectives. BIOTECHNOLOGY ANNUAL REVIEW 1999; 4:75-112. [PMID: 9890139 DOI: 10.1016/s1387-2656(08)70068-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Biotechnological techniques of cross-linking and microencapsulation of hemoglobin result in blood substitutes that can replace red blood cells. Unlike red blood cells they can be sterilized by pasteurization, ultrafiltration and chemical means. This removes microorganisms responsible for AIDS, hepatitis, etc. Since they are free of red blood cell blood group antigens, there is no need for cross-matching or typing. This saves time and facilities and allows on-the-spot transfusion such as the infusion of salt solution. Furthermore, they can be stored for a long time. Hemoglobin for modification can be extracted from human red blood cells. Other sources of hemoglobin include bovine hemoglobin and recombinant human hemoglobin. Clinical trials are ongoing testing the possible uses of cross-linked hemoglobin in cardiac, orthopedic, trauma and other types of surgery. It is also being tested for the replacement of lost blood in severe bleeding due to trauma or other causes. Cross-linked hemoglobins are first generation blood substitutes that only fulfil some of the functions of red blood cells. New generations of more complete red blood cell substitutes are being developed. These include cross-linked hemoglobin-catalase-superoxide dismutase and microencapsulated hemoglobin-enzyme systems.
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Affiliation(s)
- T M Chang
- Department of Physiology, McGill University, Montreal, Québec, Canada.
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Abstract
Artificial cells are prepared in the laboratory for medical and biotechnological applications. Encapsulated cells are being studied for the treatment of diabetes, liver failure, and other conditions. More recently, there have been extensive studies into the use of encapsulated genetically engineered cells for gene therapy. We recently found that daily orally administered artificial cells, each containing a genetically engineered microorganism, can lower the elevated urea level in uremic rats to normal levels. This may solve the final obstacle of the lack of an effective oral urea removal system for the simple and inexpensive oral treatment of uremia. This is important because 85% of the world's uremic population cannot afford standard dialysis. Other areas of artificial cell application include use in hemoperfusion. Red blood cell substitutes based on modified hemoglobin are already in Phase 3 clinical trials in patients. Artificial cells containing enzymes are being developed for clinical trial in hereditary enzyme deficiency disease and other diseases. They are also being investigated for drug delivery and for use in other applications in biotechnology, chemical engineering, and medicine.
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Affiliation(s)
- T M Chang
- Artificial Cells & Organs Research Centre, Faculty of Medicine, McGill University, Montreal, Canada
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Chang TM. Modified hemoglobin-based blood substitutes: crosslinked, recombinant and encapsulated hemoglobin. Vox Sang 1998; 74 Suppl 2:233-41. [PMID: 9704450 DOI: 10.1111/j.1423-0410.1998.tb05425.x] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Native hemoglobin in the form of stroma-free hemoglobin cannot be used as blood substitute. Hemoglobin has to be modified either molecularly or encapsulated. First generation molecularly modified ultrapure hemoglobins are now in clinical trial--some in Phase III. There are a number of these. Polyhemoglobin is formed by crosslinking hemoglobin molecules intermolecularly and intramolecularly. A crosslinked single hemoglobin molecule is formed by crosslinking hemoglobin intramolecularly. Recombinant hemoglobin from E.coli is formed by fusion of the subunits of each hemoglobin molecule. Conjugated hemoglobin is formed by crosslinking each hemoglobin molecule to soluble polymers. A second generation system formed by crosslinking hemoglobin-superoxide dismutase-catalase is being developed. A third generation hemoglobin-based blood substitute is based on microencapsulated hemoglobin, artificial red blood cells, that more closely resemble a complete red blood cell.
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Affiliation(s)
- T M Chang
- Artificial Cells & Organs Research Centre, Faculty of Medicine, McGill University, Montreal, Quebec, Canada.
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Chang TM. Recent and future developments in modified hemoglobin and microencapsulated hemoglobin as red blood cell substitutes. ARTIFICIAL CELLS, BLOOD SUBSTITUTES, AND IMMOBILIZATION BIOTECHNOLOGY 1997; 25:1-24. [PMID: 9083622 DOI: 10.3109/10731199709118893] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Affiliation(s)
- T M Chang
- Faculty of Medicine, McGill University, Montreal, Quebec, Canada
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Abstract
Chemically modified haemoglobin solutions represent a potential alternative to the transfusion of donor blood. The theoretical advantages of these products include an oxygen delivery potential greater than that of conventional plasma expanders, prolonged shelf-life, universal compatibility and the absence of pathogenic viruses. Principal concerns have been safety issues including renal toxicity, coagulopathy and vasoactivity. The proposed indications for these solutions are primarily resuscitation of patients in haemorrhagic shock and perioperative haemodilution during elective surgery. Three products have now undergone phase I safety trials in human subjects and phase II safety and efficacy trials are planned in the near future.
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Affiliation(s)
- J E Ogden
- Propharma Consultants, Nottingham, UK
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Affiliation(s)
- H Xue
- Robertson Institute of Biotechnology, Department of Genetics, University of Glasgow, Scotland
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Sherman IA, Dlugosz JA, Perelman V, Hsia CJ, Wong LT, Condie RM. Systemic hemodynamic and hepatic microvascular responses to a 33% blood volume exchange with whole blood, stroma-free hemoglobin, and oxypolyhemoglobin solutions. BIOMATERIALS, ARTIFICIAL CELLS, AND IMMOBILIZATION BIOTECHNOLOGY : OFFICIAL JOURNAL OF THE INTERNATIONAL SOCIETY FOR ARTIFICIAL CELLS AND IMMOBILIZATION BIOTECHNOLOGY 1993; 21:537-51. [PMID: 8260579 DOI: 10.3109/10731199309117656] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Little is known about the microvascular effects of blood replacement solutions. This study was undertaken to develop an animal model suitable for studies of the microcirculatory effects of such solutions and to investigate microvascular responses to isovolemic transfusion with stroma-free hemoglobin (SFH), whole donor blood, or a new potential blood substitute solution containing oxypolyhemoglobin (OPH) as an oxygen carrier. Hamster livers were exposed and the microcirculation studied using intravital epifluorescent video microscopy. 33% blood volume replacement with SFH elevated systemic blood pressure by 25 Torr. Accompanying this increase in pressure was a 36% decrease in sinusoidal blood flow velocity and a 10% decrease in terminal hepatic venular diameters. Terminal portal venular diameters did not change. Decrease in liver sinusoidal perfusion was not due to neutrophil mediated injury, as myeloperoxidase activity in jejunum, liver, kidney, and lung remained unchanged. The reduction in perfusion was likely due to systemic vasoconstriction produced by SFH. In contrast, transfusion with whole blood did not change any of the measured parameters showing the excellent stability of the model. OPH transfused animals exhibited only a small 10 Torr transient increase in MAP 15 min post-transfusion. By 30 min MAP returned to the pre-infusion value. No significant changes were observed in either venular diameters or sinusoidal velocities in this group of animals. These results demonstrate suitability of this model for studies of the microcirculatory and hemodynamic effects of blood replacement solutions. Furthermore, OPH solution produced only minor transient disturbances in microvascular and systemic parameters.
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Affiliation(s)
- I A Sherman
- Aron M. Rappaport Microcirculation Laboratory, Sunnybrook Health Science Centre, University of Toronto, Ontario, Canada
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Xue H, Wu XF, Wong JT. Properties of hemoglobin and dextran-hemoglobin rightshifted by oxidized inositol tetrakisphosphate. Artif Organs 1992; 16:427-31. [PMID: 10078288 DOI: 10.1111/j.1525-1594.1992.tb00545.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Phytate was digested by wheat bran phytase to yield inositol tetrakisphosphate. Periodate-oxidized inositol tetrakisphosphate (oxyIP4) was coupled by means of reductive alkylation to hemoglobin and the covalent dextran-hemoglobin conjugate to yield the rightshifted (rs) compounds rsHb and rsDxHb, respectively. The variations of the oxygen dissociation curves of these molecules with pH and temperature were compared to those of hemoglobin. The variations with pH were found to be less pronounced for these rightshifted forms. An extensive decrease in the half-saturation oxygen tension was observed, however, with both rsHb and rsDxHb, as in the case of unmodified Hb. Modification of hemoglobin by oxyIP4 at the polyphosphate site was suggested by the lack of a further rightshifting effect of phytate on rsHb, and by the similarity between the difference spectrum of rs-methemoglobin and the difference spectrum induced by the addition of phytate.
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Affiliation(s)
- H Xue
- Department of Biochemistry, University of Toronto, Canada
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Abstract
Increasing concern over viral contamination of blood is spurring the development of a blood substitute which can effectively replace the oxygen-carrying capabilities of transfused erythrocytes. Solutions of chemically modified haemoglobin represent one option being evaluated for this role. More recently, recombinant-DNA techniques have enabled production of human haemoglobin in host expression systems, and progress is being made towards the creation of a genetically engineered molecule incorporating the properties required of a blood substitute.
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Affiliation(s)
- J E Ogden
- Delta Biotechnology Ltd, Nottingham, UK
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Chang TM. Blood substitutes based on modified hemoglobin prepared by encapsulation or crosslinking: an overview. BIOMATERIALS, ARTIFICIAL CELLS, AND IMMOBILIZATION BIOTECHNOLOGY : OFFICIAL JOURNAL OF THE INTERNATIONAL SOCIETY FOR ARTIFICIAL CELLS AND IMMOBILIZATION BIOTECHNOLOGY 1992; 20:159-79. [PMID: 1391433 DOI: 10.3109/10731199209119634] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Modified hemoglobin consists of (1) encapsulated hemoglobin and (2) crosslinked hemoglobin (polyhemoglobin, intramolecularly cross-linked hemoglobin and conjugated hemoglobin). There have been new advances in all types of modified hemoglobins. Modified hemoglobins are effective in hemorrhagic shock. However, it is important to define hemorrhagic shock models and experimental designs. Important progress has been made in research on vasoactivities, organ perfusion, organ preservation, biodistribution, hematology, complement activation immunology and other areas. A preclinical screening test may bridge the gap between animal safety studies and injection into human. Potential new sources of hemoglobin included bovine hemoglobin, recombinant human hemoglobin and synthetic heme.
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Affiliation(s)
- T M Chang
- Artificial Cells and Organs Research Centre, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
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Affiliation(s)
- T M Chang
- Artificial Cells and Organs Research Centre, Faculty of Medicine, McGill University, Montreal, Quebec, Canada
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