Preclinical biology of recombinant human hemoglobin, rHb1.1

Differential proteomic characterization between normal peritoneal fluid and diabetic peritoneal dialysate

BACKGROUND

Since the mechanism of comorbidity and mortality in peritoneal dialysis is unclear, a comparison of peritoneal dialysate and normal peritoneal fluid may provide clues to the biological and pathological processes involved in peritoneal damage.

METHODS

Peritoneal dialysate and control samples were collected from five diabetes mellitus (DM) patients and two patients receiving laparoscopic cholecystectomy. Proteins were separated by two-dimensional gel electrophoresis (2D-GE). After image analysis, altered gel spots between these two sample groups were subjected to tryptic digestion and mass spectrometry analysis. The results were searched against the NCBI database.

RESULTS

A total of 26 protein spots were considered altered in 2D-GE between the two sample groups. After western blotting confirmation, vitamin D-binding protein, haptoglobin and alpha-2-microglobulin were at higher levels in the DM samples, while complement C4-A and IGK@ protein were at lower levels compared to the control samples.

CONCLUSION

The loss of vitamin D-binding protein, haptoglobin and alpha-2-microglobulin may be due to a change in the permeability of the peritoneal membrane to middle-sized proteins or leakage from peritoneal inflammation. Lower levels of complement C4-A in dialysate may shed light on the beginning of peritoneal membrane scleroses.

Genomics and Blood Substitutes for 21st Century Europe (“EuroBloodSubstitutes”)

Blood transfusion is a medical intervention practised throughout the world. Blood is a biologically active material that can transmit diseases (e.g., HIV/AIDS and, perhaps, vCJD). People are becoming increasingly concerned about blood safety, despite improved screening and processing. Consequently, they are reluctant to donate blood or receive transfusions. Such problems can be solved by the development and incorporation into transfusion practices of so-called "blood substitutes" to replace some blood uses. The EuroBloodSubstitutes Project is funded by the European Union Framework 6 Programme to develop a technological platform for producing novel haem proteins and blood substitute components using micro-organisms (bacteria, fungi, yeast) as "cell factories." The Project will focus on bacteria (Escherichia coli), yeast (Pichia pastoris) and, longer-term, filamentous fungi (Aspergillus niger), all organisms used to synthesize commercially important products. The multi-centre Consortium consists of the Universities of (1) Nottingham (UK), (2) Essex (UK), (3) Denmark Technical (Denmark), (4) Lund (Sweden), (5) Milan (Italy), (6) Nancy (France), (7) Parma (Italy), (8) Rome "La Sapienza" (Italy), (9) Semmelweis (Hungary), together with (10) Alligator Bioscience, AB (Sweden), (11) LCC Engineering & Trading GmbH (Switzerland), (12) Scottish National Blood Transfusion Service (UK), and (13) Sanquin Bloodbank (The Netherlands). The EuroBloodSubstitutes Project will be informed by lay and professional stakeholders (e.g., clinicians, blood donors, patient groups, prescribers and policy makers). Outcomes of the Project are (1) the production of an information pack, decision aids and physician training aids, giving balanced overviews of the benefits and risks of transfusion of blood or potential substitutes, and (2) an interactive web site (http//:www.eurobloodsubstitutes.com) for information dissemination. This will improve knowledge and address misunderstandings about transfusion issues in a climate of changing patient expectations on blood safety and benefits of blood substitutes.

Effects of recombinant-hemoglobin solutions rHb2.0 and rHb1.1 on blood pressure, intestinal blood flow, and gut oxygenation in a rat model of hemorrhagic shock

The vasoconstriction induced by hemoglobin-based oxygen carriers (HBOCs), mainly a result of nitric oxide (NO) scavenging, until now has limited the application of HBOCs as resuscitation fluids. In this study, we tested the hypothesis that the new modified recombinant-hemoglobin solution rHb2.0, with a 20 to 30 times lesser NO-scavenging rate, would minimize vasoconstriction without adverse effects on microvascular oxygenation. Responses were compared with those to rHb1.1, a recombinant-hemoglobin solution with a wild-type NO-scavenging rate, as well as an oncotically matched albumin solution. In a fixed-pressure (40 mm Hg) rat model of hemorrhagic shock and resuscitation, rHb2.0 and albumin both restored mean arterial pressure (MAP) to baseline values, whereas rHb1.1 increased MAP to 27% above the baseline value. Mesenteric vascular resistance after resuscitation with rHb2.0 was 57% less than that with rHb1.1. rHb2.0 was found to have 55% greater intestinal oxygen delivery (Do2int ) and resulted in a 27% lower oxygen-extraction rate than did rHb1.1 after resuscitation. Intestinal microvascular Po2 , determined on the basis of oxygen-dependent quenching of palladium-porphyrin phosphorescence, revealed no difference between rHb2.0 and rHb1.1. The findings of this study confirm that the well-known pressure effect of HBOCs is caused by their effect on the NO-scavenging rate; recombinant modification of this rate did not increase MAP during resuscitation compared with baseline values. Although systemic vasoconstriction was absent, intestinal vasoconstriction almost negligible, and Do2int greater after resuscitation with rHb2.0, the effect of rHb2.0 on pH, base-excess and microvascular Po2 levels after resuscitation were comparable to those achieved with the use of the albumin solution.

Engineering blood: synthetic substitutes from fluorinated compounds

Concerns about blood safety and the logistical problems associated with conventional transfusion have fuelled the search for effective alternatives (so-called blood substitutes). Such materials include hemoglobin derivatives and those based on synthetic, highly fluorinated, inert organic compounds called perfluorochemicals (PFCs). PFCs dissolve large volumes of oxygen and other gases, are unreactive in the body, and are excreted primarily as a vapor by exhalation. Liquid PFCs are immiscible with blood and other body fluids, but can be injected safely into the bloodstream as submicron emulsions. Emulsified PFCs have been evaluated in clinical trials as temporary, intravascular tissue-oxygenating fluids. One such emulsion, a commercial perflubron-based, phospholipid-stabilized formulation, is in advanced clinical trials as an alternative to transfusing donated (allogeneic) blood during surgery. Basic and clinical studies have shown that this emulsion can adequately maintain tissue oxygenation during acute blood loss with no abnormal hemodynamic changes. The use of PFC emulsions as an efficacious, short-term transfusion alternative underpins the longer term objective of producing a totally synthetic, bioengineered blood substitute.

Benefit and risk perceptions in transfusion medicine: blood and blood substitutes

Blood transfusion is a remarkably safe, routine procedure in clinical medicine. However, little attention has focused on the perceptions of risk associated with the receipt of blood, blood products or 'blood substitutes'. It is pertinent to ask (i) what key stakeholder groups know about transfusion, (ii) how safe they perceive blood/blood products to be, (iii) how the latter information might influence their own and others' perceptions of risk linked to transfusion, and (iv) the extent to which approved blood substitutes might be preferred over autologous or donor blood. An appreciation of what stakeholders perceive to be the benefits and risks of the receipt of blood and blood substitutes will inform future transfusion strategies. To obtain such information, a programme of research has been initiated at Nottingham. Surveys have targeted key stakeholder groups, namely, UK adult blood donors and nondonors, anaesthetists, general practitioners and health care journalists. Experimental studies examining message framing and cueing have also been conducted with undergraduate students. Such research will improve misunderstandings about current issues associated with blood donation and transfusion against the backdrop of changing public trust of health care professionals and attitudes and expectations on blood safety and benefits of blood substitutes.

A double-blind study to evaluate the safety of recombinant human hemoglobin in surgical patients during general anesthesia

OBJECTIVE

To evaluate recombinant human hemoglobin (rHb1.1) in patients undergoing surgery involving general anesthesia; examine rHb1.1 for toxicity, including renal dysfunction and hypertension; and measure plasma concentrations of rHb1.1 over time.

DESIGN

Prospective, double-blinded, randomized, placebo-controlled study.

SETTING

University medical center hospital.

PARTICIPANTS

Eighteen patients having surgery under general anesthesia.

INTERVENTIONS

One of 4 escalating doses of rHb1.1 or normal saline (control) was administered by continuous infusion to patients receiving general anesthesia for elective surgical procedures. Total rHb1.1 doses ranged from 4.7 to 25.6 g.

MEASUREMENTS AND MAIN RESULTS

Clinical and laboratory data, including vital signs monitoring, hematology (white blood cell and reticulocyte count, hemoglobin, hematocrit, erythrocyte sedimentation rates, and coagulation values), renal function (serum creatinine and blood urea nitrogen), hepatic function (mean and indirect bilirubin), pancreatic function (serum amylase and lipase), and antibodies (IgG and IgM) to Escherichia coli protein, were collected at specified intervals for 7 days after infusion of rHb1.1. No serious adverse events occurred. The most frequently observed clinical event occurred during the first 24 hours after infusion and was primarily associated with surgery and anesthetic administration. A slightly higher incidence of hypertension, symptoms suggestive of pyrogenicity, mildly elevated total and indirect bilirubin, and elevated pancreatic enzymes was observed in rHb1.1 treatment groups when compared with control. Hypertension resolved within 7 hours, and laboratory values returned to normal levels by day 7.

CONCLUSION

Although the elevations in pancreatic enzymes seen in some rHb1.1-treated patients remain unexplained, the safety profile of rHb1.1 appears to be acceptable. These results support the continued clinical evaluation and development of rHb1.1.

Haptoglobin reduces renal oxidative DNA and tissue damage during phenylhydrazine-induced hemolysis

BACKGROUND

Haptoglobin knockout (Hp-/-) mice are more sensitive to phenylhydrazine-induced hemolysis than Hp+/+ mice.

METHODS

Hemolysis was induced in Hp-/- and Hp+/+ mice using phenylhydrazine. Relative renal tissue damage and function were then assessed.

RESULTS

Hp-/- mice had higher basal levels of renal lipid peroxidation, as evidenced by levels of malonaldehyde and 4-hydroxy-2(E)-nonenal (MDA/HNE). After the administration of phenylhydrazine, levels of 8-hydroxyguanine (but not other products of oxidative DNA damage) were significantly elevated in the renal DNA. There was also increased induction of heme oxygenase-1. The more severe renal damage in Hp-/- mice was also evident in the delayed erythropoietin gene expression and poorer renal clearance of 3H-inulin. This reduction in glomerular filtration function in Hp+/+ and Hp-/- mice could be restored to baseline by vasodilators (prazosin or diazoxide), implicating renal vasoconstriction as a major mechanism of acute renal failure during induced hemolysis. Precipitation of hemoglobin in the kidney was not increased in Hp-/- mice.

CONCLUSIONS

Haptoglobin appears to play an important physiological role as an antioxidant, particularly during hemolysis.

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.

Perfluorinated blood substitutes and artificial oxygen carriers

Blood transfusion is a remarkably safe, routine clinical procedure. However, the need for sophisticated blood processing, storage and cross-matching, coupled with increasing concerns about the safety of blood products, has fuelled the search for safe and efficacious substitutes. Candidate materials based on modified haemoglobin (including recombinant molecules) or highly inert, respiratory gas-dissolving perfluorinated liquids (perfluorochemicals) have been developed. The latter are immiscible in aqueous systems and must, therefore, be injected as emulsions. Second-generation perfluorochemical emulsions are available and in clinical trials as temporary intravascular oxygen carriers during surgery, thereby reducing patient exposure to donor blood. One commercial product is currently under Phase III clinical evaluation, with regulatory approval expected within 1 2 years. Other biomedical applications for perfluorochemicals and their emulsions include their use as pump-priming fluids for cardiopulmonary bypass, lung ventilation fluids, anti-cancer agents, organ perfusates and cell culture media supplements, diagnostic imaging agents and ophthalmologic tools. Novel applications for perfluorochemicals as immunomodulating agents are also being explored.

Autoxidation of pyridoxalated hemoglobin polyoxyethylene conjugate

Hemoglobin-based therapeutics are currently in clinical trials in the United States and abroad as blood replacement solutions, nitric oxide scavengers, and radiation sensitizers. The potency of the therapeutics may be influenced by the oxidation state of the iron in the heme moiety. The oxidation state is dependent upon the physical environment of the molecule and is influenced by parameters such as the chemical nature of the hemoglobin therapeutic and its formulation. Pyridoxalated hemoglobin polyoxyethylene conjugate (PHP) is one such compound currently in clinical trials in the U.S. for treatment of nitric oxide-dependent, volume refractory shock. The autoxidation rates for PHP have been determined over a range of temperatures. The oxidation events were shown to be biphasic and were similar to those observed for purified human hemoglobin (HbAo). The initial fast oxidation events were modeled with first order rate constants at 37 degrees C and determined to be 0.022 hr-1 and 0.025 hr-1 for PHP and HbAo, respectively. The autoxidation of PHP was shown to be independent of concentration from approximately 5 to 100 mg/mL.