Focal cerebral ischemia in rats: effect of hemodilution with alpha-alpha cross-linked hemoglobin on brain injury and edema

Issues in the development of hemoglobin based oxygen carriers

Hemoglobin based oxygen carriers (HBOCs) have been developed as alternative oxygen transporting formulations for the acute treatment of anemia and ischemia. Efficacy has been demonstrated in a variety of preclinical models and selected human patients; however, a higher overall incidence of mortality and myocardial infarction in those dosed with HBOCs in later stage clinical trials has prevented widespread regulatory approval. Diagnosis of myocardial infarction is confounded by the fact that HBOCs interfere with troponin assays, as well as other clinical chemistry measurements. Analysis of data pertaining to potential toxicity mechanisms suggests that coronary vasoconstriction is an unlikely contributor, but promotion of intravascular thrombosis may occur by several mechanisms. In addition, fluid and anemia management in patients infused with HBOCs has been suboptimal. Elucidation of potential toxicity mechanisms, refinement of use protocols, and definition of improved patient inclusion/exclusion criteria remain active areas of inquiry in understanding the best manner in which to utilize HBOCs.

Frovatriptan for the Treatment of Cluster Headaches

Cluster headaches both episodic and chronic are some of the most challenging headaches to treat. Although effective treatments are now available, some patients continue to be unresponsive to standard therapy. We present 17 patients from our practice whom we treated preventively with frovatriptan, a new triptan with a long half-life. The promising results suggest that this medication may be an useful addition to our ammaterium against this painful disorder.

Transfusion of hemoglobin-based oxygen carriers in the carboxy state is beneficial during transient focal cerebral ischemia

Exchange transfusion of large volumes of hemoglobin (Hb)-based oxygen carriers can protect the brain from middle cerebral artery occlusion (MCAO). Hb in the carboxy state (COHb) may provide protection at relatively low volumes by enhancing vasodilation. We determined whether transfusion of rats with 10 ml/kg PEGylated COHb [polyethylene glycol (PEG)-COHb] at 20 min of 2-h MCAO was more effective in reducing infarct volume compared with non-carbon monoxide (CO) PEG-Hb. After PEG-COHb transfusion, whole blood and plasma COHb was <3%, indicating rapid release of CO. PEG-COHb transfusion significantly reduced infarct volume (15 ± 5% of hemisphere; mean ± SE) compared with that in the control group (35 ± 6%), but non-CO PEG-Hb did not (24 ± 5%). Chemically dissimilar COHb polymers were also effective. Induction of MCAO initially produced 34 ± 2% dilation of pial arterioles in the border region that subsided to 10 ± 1% at 2 h. Transfusion of PEG-COHb at 20 min of MCAO maintained pial arterioles in a dilated state (40 ± 5%) at 2 h, whereas transfusion of non-CO PEG-Hb had an intermediate effect (22 ± 3%). When transfusion of PEG-COHb was delayed by 90 min, laser-Doppler flow in the border region increased from 57 ± 9 to 82 ± 13% of preischemic baseline. These data demonstrate that PEG-COHb is more effective than non-CO PEG-Hb at reducing infarct volume, sustaining cerebral vasodilation, and improving collateral perfusion in a model of transient focal cerebral ischemia when given at a relatively low dose (plasma Hb concentration < 1 g/dl). Use of acellular Hb as a CO donor that is rapidly converted to an oxygen carrier in vivo may permit potent protection at low transfusion volumes.

Potential uses of hemoglobin-based oxygen carriers in critical care medicine

Hemoglobin-based oxygen carriers (HBOCs) were initially developed to provide an alternative to blood transfusion. With the realization that hemoglobin solutions not only are red blood cell substitutes but also have a number of additional properties, including hemodynamic effects related to their oncotic and nitric oxide-scavenging effects, the broader concept of "hemoglobin therapeutics" was born. Promising effects on oxygen transport and the microcirculation need to be confirmed, and the results of studies with newer, second-generation HBOCs are eagerly awaited. In the meantime, possible adverse effects need to be carefully evaluated before HBOCs can be widely used in the ICU, emergency room, or prehospital setting.

Cerebral Perfusion Pressure Elevation with Oxygen-Carrying Pressor after Traumatic Brain Injury and Hypotension in Swine

BACKGROUND

Previously, we had shown that elevation of cerebral perfusion pressure, using pressors, improved short-term outcomes after traumatic brain injury and hemorrhagic shock in swine. The current study evaluates outcomes after resuscitation with diaspirin cross-linked hemoglobin (DCLHb)--a hemoglobin-based oxygen carrier with pressor activity--in the same swine model of traumatic brain injury and hemorrhagic shock.

METHODS

Anesthetized and ventilated swine received traumatic brain injury via cortical fluid percussion (6-8 atm) followed by 45% blood volume hemorrhage. One hour later, animals were randomized to either a control group (SAL) resuscitated with normal saline equal to three times shed blood volume or to one of two experimental groups resuscitated with DCLHb. The two experimental groups consisted of a low-dose group, resuscitated with 250 mL of DCLHb (Hb1), and a high-dose group, resuscitated with 500 mL of DCLHb (Hb2). Animals were observed for 210 minutes postresuscitation. Outcomes evaluated were cerebral oxygenation by measuring partial pressure and saturation of oxygen in cerebrovenous blood; cerebral function by evaluating the preservation and magnitude of cerebrovascular carbon dioxide reactivity; and brain structural damage by semiquantitatively assessing beta amyloid precursor protein positive axons.

RESULTS

Postresuscitation, cerebral perfusion pressure was higher in the DCLHb groups (p < 0.05, Hb1 and Hb2 vs. SAL), and intracranial pressure was lower in the Hb2 group (p < 0.05 vs. SAL). Cerebrovenous oxygen level was similar in all groups (p > 0.05). At baseline, 5% carbon dioxide evoked a 16 +/- 1% increase in cerebrovenous oxygen saturation, indicating vasodilatation. At 210 minutes, this response was nearly absent in SAL (4 +/- 4%) (p < 0.05 vs. baseline) and Hb1 (1 +/- 5%), but was partially preserved in Hb2 (9 +/- 5%). There was no intergroup difference in beta amyloid precursor protein positive axons. Five of 20 SAL and 0 of 13 DCLHb animals developed brain death (flat electroencephalogram) (p = 0.05, SAL vs. DCLHb). Postresuscitation, DCLHb animals maintained higher mean pulmonary arterial pressure (28 +/- 1 mm Hg, SAL; 42 +/- 1 mm Hg, Hb1; 45 +/- 1 mm Hg, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL) and lower cardiac output (3.9 +/- 1.6 L/min, SAL; 2.6 +/- 0.1 L/min, Hb1; 2.7 +/- 0.1 L/min, Hb2) (p < 0.05, Hb1 and Hb2 vs. SAL). Three Hb2 animals died as a result of cardiac failure, and one SAL animal died as a result of irreversible shock.

CONCLUSION

In this swine model of traumatic brain injury and hemorrhagic shock, resuscitation with DCLHb maintained a higher cerebral perfusion pressure. Low-dose DCLHb (minimal increase in oxygen carriage) failed to significantly improve short-term outcome. With high-dose DCLHb (significant improvement in oxygen carriage), intracranial pressure was lower and cerebrovascular carbon dioxide reactivity was partially preserved; however, this was at the cost of poorer cardiac performance secondary to high afterload.

Recognition and treatment of cluster headache in the emergency department

Cluster headache has a dramatic presentation marked by rapidly escalating intensity of pain and prominent signs of autonomic dysfunction. Despite its distinctive features, diagnostic delay and misdiagnosis are common. Prompt recognition of this headache disorder provides an opportunity for effective treatment. This article provides a practical approach to the diagnosis and management of patients with cluster headache in the emergency room setting.

Hemoglobin solutions

OBJECTIVE

To review current knowledge about cell-free hemoglobin solutions.

DATA SOURCE

A computerized MEDLINE search was used to retrieve all studies concerning cell-free hemoglobin solutions from 1990 to 2003. The reference lists of all available review articles and primary studies were also reviewed to identify references not identified in the computerized search.

STUDY SELECTION

All clinical and experimental studies involving cell-free hemoglobin solutions were included.

DATA EXTRACTION

From the selected studies, information was obtained regarding the experimental model or the study population in which cell-free hemoglobin solutions were investigated, the type of cell-free hemoglobin solution used, their deleterious or beneficial effects, and their possible indications.

DATA SYNTHESIS

In many studies, hemoglobin solutions were considered as efficient resuscitative agents and good alternatives to red blood cell transfusion, owing to their marked vasopressor effect, coupled with their capacity to improve the microcirculation and rapidly restore metabolic parameters. The main problems identified include excessive systemic vasoconstriction and oxidative damage. Initial enthusiasm in the development of hemoglobin solutions has been tempered recently by the negative results of a U.S. multicenter trial studying the early infusion of diaspirin cross-linked hemoglobin in trauma patients. Nevertheless, the properties of diaspirin cross-linked hemoglobin (and particularly the strong vasopressor effects) cannot be attributed to all hemoglobin solutions, and results of new clinical studies are eagerly awaited to evaluate the potential benefit of such solutions in the management of trauma patients.

CONCLUSIONS

Today, we are aware of the effects of the first generation of blood substitutes. Further research is ongoing into newer solutions. One area of interest is the development of new molecular structures to decrease nitric oxide binding, thus minimizing any adverse events and maximizing potential benefits. Nevertheless, possible adverse effects need to be carefully evaluated before these agents can be widely administered.

Effect of diaspirin crosslinked hemoglobin (DCLHb HemAssist) during high blood loss surgery on selected indices of organ function

BACKGROUND

The safety of the hemoglobin based oxygen carrier diaspirin crosslinked hemoglobin (DCLHb) has been reported only in the low (50-200 mg/kg) dose range [Przybelski. R.J.; Daily, E.K.; Kisicki, J.C.; Mattia-Goldberg, C.; Bounds, M.J.; Colburn, W.A. Phase I study of the safety and pharmacologic effects of diaspirin crosslinked hemoglobin solution. Crit. Care Med. 1996, 24 (12), 1993-2000, Bloomfield, E.; Rady, M.; Popovich, M.; Esfandiari, S.; Bedocs, N. The use of diaspirin crosslinked hemoglobin (DCLHb 1996, 95, (3A), A220.]. We conducted a randomized prospective open-label trial of DCLHb and packed red blood cells (PRBCs) in high-blood loss surgical patients to show the effect of 750 ml DCLHb (approximately 1000 mg/kg) on selected indices of organ function.

METHOD

After institutional approval, 24 patients scheduled to undergo elective orthopedic or abdominal surgery, were randomized to receive either PRBCs or 10% DCLHb within 12 hours after the start of surgery. Patients with renal insufficiency, abnormal liver function, severe coronary artery disease (CAD) and ASA physical status > or = IV were excluded. The anesthetic technique was left to the judgment of the anesthesiologist. Autologous predonation and intraoperative blood conservation techniques were utilized as appropriate. The indications for blood transfusion were individualized on disease state, stage of surgery, and plasma Hb concentration. Laboratory studies were obtained preoperatively and up to 28 days postoperatively. Patients were observed daily for development of jaundice, hematuria, nausea, vomiting, gastrointestinal discomfort, cardiac, respiratory, and infectious complications. Organ effects were assessed with urinalysis, creatinine clearance, electrocardiogram (ECG), and a panel of blood and serum laboratory tests.

RESULTS

The dose of DCLHb administered ranged from 680-1500 mg/kg (mean = 999 mg/kg). Estimated blood loss was 27 +/- 13 ml/kg and 31 +/- 15 ml/kg in the control and DCLHb groups, respectively. Fewer PRBCs (1.9 +/- 1.2 vs. 3.4 +/- 2.4 units. P = 0.06) were transfused to DCLHb patients on the operative day although this difference was no longer apparent later on. In the DCLHb group, 4/12 patients avoided any allogeneic PRBC transfusion vs. none in the control group (P = 0.09). Systolic, diastolic and mean blood pressure increased moderately after DCLHb for a period of 24-30 hours. There were no occurrences of cardiac ischemia. myocardial infarction, stroke, or pulmonary edema, by clinical or laboratory parameters up to the 28th postoperative day (POD). Seven of 12 (58%) DCLHb patients had yellow skin discoloration vs. none in the PRBC group (P < 0.01). Two of four non-urologic surgery patients developed asymptomatic postoperative hemoglobinuria after DCLHb. Creatinine clearance was unchanged postoperatively. Because of hemoglobin interference, bilirubin, gamma-glutamyl transferase (GGT), and amylase could not be measured reliably on POD1; on POD2. amylase was transiently elevated to 3 times ULN along with mild elevations of bilirubin, transaminases and BUN. Mean total creatine phoshokinase (CPK) peaked at 8 times the upper limit of normal (ULN) in the DCLHb group, compared with less than twice ULN for controls. Three DCLHb patients had prolonged ileus. Two of these patients had postoperative hyperamylasemia, one of whom developed mild pancreatitis. DCLHb did not affect white blood cell count or coagulation tests.

CONCLUSION

Administration of approximately 1000 mg/kg DCLHb was associated with transient arterial hypertension, gastrointestinal side effects, laboratory abnormalities, yellow skin discoloration, and hemoglobinuria. These observations point to opportunities for improvement in future synthetic hemoglobin design.

Resuscitation from severe hemorrhagic shock after traumatic brain injury using saline, shed blood, or a blood substitute

The original purpose of this study was to compare initial resuscitation of hemorrhagic hypotension after traumatic brain injury (TBI) with saline and shed blood. Based on those results, the protocol was modified and saline was compared to a blood substitute, diaspirin cross-linked hemoglobin (DCLHb). Two series of experiments were performed in anesthetized and mechanically ventilated (FiO2 = 0.4) pigs (35-45 kg). In Series 1, fluid percussion TBI (6-8 ATM) was followed by a 30% hemorrhage. At 120 min post-TBI, initial resuscitation consisted of either shed blood (n = 7) or a bolus of 3x shed blood volume as saline (n = 13). Saline supplements were then administered to all pigs to maintain a systolic arterial blood pressure (SAP) of >100 mmHg and a heart rate (HR) of <110 beats/min. In Series 2, TBI (4-5 ATM) was followed by a 35% hemorrhage. At 60 min post-TBI, initial resuscitation consisted of either 500 mL of DCLHb (n = 6) or 500 mL of saline (n = 5). This was followed by saline supplements to all pigs to maintain a SAP of >100 mmHg and a HR of <110 beats/min. In Series 1, most systemic markers of resuscitation (e.g., SAP, HR, cardiac output, filling pressures, lactate, etc.) were normalized, but there were 0/7 vs. 5/13 deaths within 5 h (P = 0.058) with blood vs. saline. At constant arterial O2 saturation (SaO2), mixed venous O2 saturation (SvO2), cerebral perfusion pressure (CPP), and cerebral venous O2 saturation (ScvO2) were all higher, intracranial pressure (ICP) was lower, and CO2 reactivity was preserved with blood vs. saline (all P < 0.05). In Series 2, SAP, ICP, CPP, and lactate were higher with DCLHb vs. saline (all P< 0.05). Cardiac output was lower even though filling pressure was markedly elevated with DCLHb vs. saline (both P< 0.05). Neither SvO2 nor cerebrovascular CO2 reactivity were improved, and ScvO2 was lower with DCLHb vs. saline (P < 0.05). All survived at least 72 h with neuropathologic changes that included sub-arachnoid hemorrhage, midline cerebellar necrosis, and diffuse axonal injury. These changes were similar with DCLHb vs. saline. Thus, whole blood was more effective than saline for resuscitation of TBI, whereas DCLHb was no more, and according to many variables, less effective than saline resuscitation. These experimental results are comparable to those in a recent multicenter trial using DCLHb for the treatment of severe traumatic shock. Further investigations in similar experimental models might provide some plausible explanations why DCLHb unexpectedly increased mortality in patients.

Ischaemic brain oedema

Ischaemic brain oedema appears to involve two distinct processes, the relative contribution and time course of which depend on the duration and severity of ischaemia, and the presence of reperfusion. The first process involves an increase in tissue Na+ and water content accompanying increased pinocytosis and Na+, K+ ATPase activity across the endothelium. This is apparent during the early phase of infarction and before any structural damage is evident. This phenomenon is augmented by reperfusion. A second process results from a more indiscriminate and delayed BBB breakdown that is associated with infarction of both the parenchyma and the vasculature itself. Although, tissue Na+ level still seems to be the major osmotic force for oedema formation at this second stage, the extravasation of serum proteases is an additional potentially deleterious factor. The relative importance of protease action is not yet clear, however, degradation of the extracellular matrix conceivably leads to further BBB disruption and softening of the tissue, setting the stage for the most pronounced forms of brain swelling. A number of factors mediate or modulate ischaemic oedema formation, however, most current information comes from experimental models, and clinical data on this microcosmic level is lacking. Clinically significant brain oedema develops in a delayed fashion after large hemispheric strokes and is a cause of substantial mortality. Neurological signs appear to be at least as good as direct ICP measurement and neuroimaging in detecting and gauging the secondary damage produced by stroke oedema. The neuroimaging characteristics of the stroke, specifically the early involvement of greater than half of the MCA territory, are, however, highly predictive of the development of severe oedema over the subsequent hours and days. None of the available medical therapies provide substantial relief from the oedema and raised ICP, or at best, they are temporizing in most cases. Hemicraniectomy appears most promising as a method of avoiding death from brain compression, but the optimum timing and manner of patient selection are currently being investigated. All approaches to massive ischaemic brain swelling are clouded by the potential for survival with poor functional outcome. It is possible to manage blood pressure, serum osmolarity by way of selective fluid administration, and a number of other systemic factors that exaggerate brain oedema. Broad guidelines for treatment of stroke oedema can therefore be given at this time.

Regional cerebral blood flow in cats with cross-linked hemoglobin transfusion during focal cerebral ischemia

The beneficial effect of hemodilution on cerebral blood flow (CBF) during focal cerebral ischemia is mitigated by reduced arterial oxygen content (CaO2). In anesthetized cats subjected to permanent middle cerebral artery occlusion, the time course of regional CBF was evaluated after isovolemic exchange transfusion with either albumin or a tetrameric hemoglobin-based oxygen carrier. The transfusion started 30 min after arterial occlusion. We tested the hypothesis that bulk oxygen transport (CBF x CaO2) to ischemic tissue is increased by hemoglobin transfusion at a hematocrit of 18% compared with albumin-transfused cats at a hematocrit of 18% or control cats at a hematocrit of 30% and equivalent arterial pressure. In the nonischemic hemisphere, CBF increased selectively after albumin transfusion, and oxygen transport was similar among groups. In the ischemic cortex, albumin transfusion increased CBF, but oxygen transport was not increased above that of the control group. Hemoglobin transfusion increased both CBF and oxygen transport in the ischemic cortex above values in the control group, but the increase was delayed until 4 h of ischemia. Consequently, acute injury volume measured at 6 h of ischemia was not significantly attenuated. In contrast to the cortex, CBF in the ischemic caudate nucleus was not substantially increased by either albumin or hemoglobin transfusion. Therefore, in a large animal model of permanent focal ischemia in which transfusion starts 30 min after ischemia, tetrameric cross-linked hemoglobin transfusion can augment oxygen transport to the ischemic cortex, but the increase can be delayed and not necessarily provide protection. Moreover, an end-artery region such as the caudate nucleus is less likely to benefit from hemodilution.

Hemoglobin solutions--not just red blood cell substitutes

OBJECTIVE

To review current knowledge about cell-free hemoglobin solutions.

DATA SOURCES

All studies involving cell-free hemoglobin were retrieved from a computerized MEDLINE search from 1980 to 1998. We also reviewed the reference lists of all available review articles and primary studies to identify references not found in the computerized search.

STUDY SELECTION

Clinical and experimental studies in which cell-free hemoglobin solutions were studied.

DATA EXTRACTION

From the selected studies, information was obtained regarding the experimental model or the study population in which cell-free hemoglobin solutions were investigated, the type of cell-free hemoglobin solution, their deleterious or beneficial effects, and their possible indications.

DATA SYNTHESIS

In many studies, hemoglobin solutions were considered as efficient resuscitative agents and good alternatives to red blood cell transfusion, because of their marked vasopressor effect coupled with their capacity to improve the microcirculation and quickly restore metabolic parameters. Nevertheless, potential problems include an increased susceptibility to infection, immunosuppression, oxidative damage, excessive pulmonary and systemic vasoconstriction, and platelet activation.

CONCLUSIONS

Hemoglobin solutions are more than mere blood substitutes. Promising effects on oxygen transport and the microcirculation need to be confirmed, and the results of continuing research are eagerly awaited.

Effect of diaspirin cross-linked hemoglobin on endothelin-1 and blood pressure in acute ischemic stroke in man

OBJECTIVE

For almost 50 years it has been known that hemolysed blood can increase blood pressure. Although preclinical studies suggest that this pressor response is due to an interaction of hemoglobin with endothelium-derived vasoactive substances, its mechanism in humans is unknown. We investigated the involvement of endothelin-1 in the blood pressure response to the oxygen carrier diaspirin cross-linked hemoglobin (DCLHb) in stroke patients.

DESIGN

In a randomized phase II study, increasing doses of DCLHb (25, 50 and 100 mg/kg, n=8, 8 and 11, respectively) or placebo (n=26) were infused intravenously every 6 h for 72 h to patients with an acute ischemic stroke. Blood pressure and heart rate were measured every 15 min and plasma concentrations of endothelin-1, catecholamines, renin, vasopressin and atrial natriuretic peptide were measured before and 24 and 66 h after the start of the infusions.

RESULTS

In the placebo group, mean arterial pressure (MAP) was 112 (109-115) mmHg (mean and 95% confidence interval) at baseline and decreased spontaneously by 11.4 (5.4-17.5) and 12.5 (5.4-19.5) mmHg after 24 and 66 h, respectively. This decrease in MAP was attenuated in patients treated with DCLHb, reaching statistical significance in the highest dose group. The plasma endothelin-1 concentration decreased slightly in the placebo group, from 4.2 (3.1-5.3) pg/ml (median and range) at baseline to 2.4 (1.9-3.7) pg/ml after 24 h (P=0.0044) and 2.8 (1.9-3.7) pg/ml after 66 h (P=0.0042), but increased dose-dependently in response to DCLHb infusion. With the highest dose of DCLHb, the plasma endothelin-1 concentration rose from 4.8 (0.1-7.8) pg/ml at baseline to 21.2 (13.4-53.2) pg/ml after 24 h (P< 0.001) and to 27.6 (11.9-47.8) pg/ml after 66 h (P< 0.001). The increases in the plasma endothelin-1 concentration and in MAP were correlated (r=0.30, P=0.02). Other vasoactive hormones were not affected by the DCLHb infusion.

CONCLUSIONS

Infusion of DCLHb in patients with acute ischemic stroke was associated with a dose-dependent increase in plasma endothelin-1 concentration. This may underlie the attenuation by DCLHb of the natural decrease in blood pressure that we observed in these patients.

Absence of Immunogenicity of Diaspirin Cross-Linked Hemoglobin in Humans

Diaspirin cross-linked hemoglobin (DCLHb) is an intramolecularly cross-linked hemoglobin-based oxygen carrier being developed as a therapy for acute blood loss. We report here the absence of immunogenicity of DCLHb in patients enrolled in phase II and III clinical trials of DCLHb. Two very sensitive immunoassays, an enzyme-linked immunosorbent assay (ELISA) and a Western blot assay, were developed and validated for this assessment. The DCLHb-antibodies used in these assays were raised in monkeys, had similar affinities for DCLHb and native human hemoglobin (SFHb), and showed cross-reactivity for subunits of DCLHb and SFHb on the Western blot, suggesting that these antibodies were elicited as a xenogenic response to the protein. In the ELISA, the optical density of a patient sample exposed to DCLHb-coated wells was compared with that of the patient sample exposed to carbonate buffer-coated wells; an optical density ratio of 1.4 was established for discriminating between a positive (reactive) or negative DCLHb antibody response. To date, all of the more than 300 patient specimens (preinfusion and postinfusion) from clinical trials have exhibited a ratio of less than 1.4, confirming the lack of preexisting antibodies to DCLHb and clearly showing the absence of DCLHb antibodies after exposure to this new biologic entity. There has been no requirement for use of the confirmatory Western blot assay. Taken together, the results from this study indicate DCLHb is not immunogenic in humans at doses evaluated clinically.

Absence of Immunogenicity of Diaspirin Cross-Linked Hemoglobin in Humans

Diaspirin cross-linked hemoglobin (DCLHb) is an intramolecularly cross-linked hemoglobin-based oxygen carrier being developed as a therapy for acute blood loss. We report here the absence of immunogenicity of DCLHb in patients enrolled in phase II and III clinical trials of DCLHb. Two very sensitive immunoassays, an enzyme-linked immunosorbent assay (ELISA) and a Western blot assay, were developed and validated for this assessment. The DCLHb-antibodies used in these assays were raised in monkeys, had similar affinities for DCLHb and native human hemoglobin (SFHb), and showed cross-reactivity for subunits of DCLHb and SFHb on the Western blot, suggesting that these antibodies were elicited as a xenogenic response to the protein. In the ELISA, the optical density of a patient sample exposed to DCLHb-coated wells was compared with that of the patient sample exposed to carbonate buffer-coated wells; an optical density ratio of 1.4 was established for discriminating between a positive (reactive) or negative DCLHb antibody response. To date, all of the more than 300 patient specimens (preinfusion and postinfusion) from clinical trials have exhibited a ratio of less than 1.4, confirming the lack of preexisting antibodies to DCLHb and clearly showing the absence of DCLHb antibodies after exposure to this new biologic entity. There has been no requirement for use of the confirmatory Western blot assay. Taken together, the results from this study indicate DCLHb is not immunogenic in humans at doses evaluated clinically.

Structural characterization of human hemoglobin crosslinked by bis(3,5-dibromosalicyl) fumarate using mass spectrometric techniques

Diaspirin crosslinked hemoglobin (DCLHb) was analyzed by mass spectrometric-based techniques to identify the protein modifications effected by the crosslinking reaction with bis(3,5-dibromosalicyl) fumarate. DCLHb consists of two principal components. These components were isolated by size-exclusion chromatography and identified by measurement of their molecular weight using electrospray mass spectrometry and subsequent peptide mass mapping and mass spectrometric sequence analysis of their individual digests. Three major RP-HPLC fractions were observed from the major hemoglobin in DCLHb. Their MWs matched the MW of heme, intact hemoglobin beta-chain, and two hemoglobin alpha-chains crosslinked by a fumarate moiety, respectively. The minor HPLC peaks of DCLHb were also separated, and characterized by mass spectrometric methods. These minor components revealed additional details of the structural nature of covalent modification of DCLHb.

Effect of delayed albumin hemodilution on infarction volume and brain edema after transient middle cerebral artery occlusion in rats

The authors examined the effect of delayed high-concentration albumin therapy on ischemic injury in a highly reproducible model of middle cerebral artery (MCA) occlusion in rats. Male Sprague-Dawley rats weighing 270 to 320 g were anesthetized with halothane and subjected to 120 minutes of temporary MCA occlusion induced by means of a poly-L-lysine-coated intraluminal nylon suture inserted retrograde via the external carotid artery into the internal carotid artery and MCA. The agent (20% human serum albumin [HSA]) or control solution (sodium chloride 0.9%) was administered intravenously at a dosage of 1% of body weight immediately after suture removal following a 2-hour period of MCA occlusion. The animals' neurological status was evaluated during MCA occlusion (at 60 minutes) and daily for 3 days thereafter. The brains were perfusion-fixed, and infarct volumes and brain edema were determined. The HSA significantly improved the neurological score compared with saline at 24 hours after MCA occlusion. The rats treated with HSA also had significantly reduced total infarct volume (by 34%) and brain edema (by 81%) compared with saline-treated rats. There was a strong correlation between hematocrit level and brain edema (p < 0.01), and between total infarct volume or brain edema and neurological score at 24, 48, and 72 hours postinjury (p < 0.0002). These results strongly support the beneficial effect of delayed albumin therapy in transient focal ischemia and indicate its possible usefulness in treating patients with acute ischemic stroke.

Effects of diaspirin-cross-linked hemoglobin (DCLHb) on local tissue oxygen tension in striated skin muscle: an efficacy study in the hamster

Using the dorsal skin fold chamber model in the hamster, we analyzed local tissue partial oxygen pressure (PO2) in the striated skin muscle under nonischemic and postischemic conditions with a Clark-type multiwire oxygen surface electrode. Hypervolemic infusion (500 mg x kg(-1) I.V.) or isovolemic exchange transfusion (3.3 gm x kg(-1) I.V.; hematocrit 30%) with diaspirin-cross-linked hemoglobin (DCLHb) resulted in a slight decrease of the mean value of the local tissue PO2 (mm Hg) 1 hour after administration. Concomitantly, the frequency distribution curves of local tissue PO2 values were found to be more narrow (fewer values > 25 mm Hg and < 10 mm Hg). Resuscitation from severe hemorrhagic shock (bleeding of 33 ml x kg(-1) at 0.4 ml x min(-1)) with autologous blood (AuB), Dx-60, or DCLHb led to an increase of mean tissue PO2 values by 4.2-fold (p < 0.05 versus Dx-60), 1.9-fold, and 3.7-fold (p < 0.05 versus Dx-60), respectively, 2 hours after resuscitation. The reduction of tissue hypoxia (0-5 mm Hg) was significant only in the AuB- and DCLHb-treated animals. This study indicates that DCLHb effectively reverses tissue hypoxia after resuscitation from severe hemorrhagic shock by inducing a more homogeneous distribution of the local tissue PO2 levels.

Remacemide hydrochloride reduces cortical lesion volume following brain trauma in the rat

We evaluated the therapeutic effects of remacemide hydrochloride, an N-methyl-D-aspartate (NMDA) receptor-associated ionophore blocker with sodium channel blocking activity, on cortical lesion volume and memory dysfunction following parasagittal fluid-percussion brain injury in the anesthetized rat. We found that intravenous (i.v.) administration 15 min following injury of remacemide hydrochloride at both 25 and 10 mg/kg significantly reduced posttraumatic cortical lesion volume (P < 0.05), measured at 48 h postinjury using a tetrazolium salt tissue staining technique. However, neither of these doses nor the dosing regimen of 25 mg/kg i.v. 15 min postinjury plus a subcutaneous infusion over 24 h of 20 mg/kg remacemide hydrochloride improved posttraumatic memory function determined by a Morris water maze paradigm.

Effect of subarachnoid administration of alpha-alpha diaspirin crosslinked hemoglobin on cerebral blood flow in rats

As extravasated red blood cells have been implicated in the pathogenesis of perfusion deficits after subarachnoid hemorrhage, alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) might have a detrimental effect on cerebral perfusion after subarachnoid hemorrhage. We evaluated the effect of subarachnoid administration of DCLHb on cerebral blood flow (CBF). Rats were randomized to receive one of the following solutions into the cisterna magna: Control-0.3 ml of mock cerebrospinal fluid; Blood-0.3 ml of autologous blood; DCLHb-0.3 ml of 10% DCLHb. After 20-min, the area of cerebral hypoperfusion was determined (CBF < 40 ml.100g-1.min-1). The area of hypoperfusion (% area of a coronal brain section, mean +/- SD) was greater in the Blood group (58 +/- 16) than the DCLHb (16 +/- 7) and Control (5 +/- 5) groups (p < 0.05), and was greater in the DCLHb group than the Control group (p < 0.05). These data support a hypothesis that extravasation of blood from the intravascular to the subarachnoid space induces cerebral hypoperfusion. Moreover, the data support the hypothesis that although extravasated molecular hemoglobin decreases CBF, the adverse effect is not as severe as a similar volume of blood.

Metabolic quantification of lesion volume following experimental traumatic brain injury in the rat

A reliable and rapid method for quantifying lesion volume following traumatic brain injury (TBI) has vast potential in brain injury research. Staining with 2, 3, 5-triphenyltetrazolium chloride (TTC) provides for demarcation of damaged or infarcted tissue from normal, viable cerebral tissue, in which a red formazan product is formed by reduction during cellular respiration of mitochondrial dehydrogenase enzymes. The present study evaluated the use of TTC staining to quantify the cortical lesion volume in rats undergoing fluid-percussion (FP) brain injury. Male Sprague-Dawley rats (350-450 g, n = 27) were anesthetized (sodium pentobarbital, 60 mg/kg, ip) and subjected to lateral FP brain injury of mild (1.1-1.3 atm, n = 5), moderate (2.0-2.3 atm, n = 9), or high (2.4-2.6 atm, n = 8) severity, while sham (noninjured) animals (n = 5) were anesthetized and surgically prepared without injury. Forty-eight hours after injury animals were sacrificed, brains were stained with TTC, and lesion volumes were calculated. A highly significant correlation was found between cerebral cortical lesion volume (mm3) and severity of brain injury (r = 0.85; p < 0.0001). The mean (+/-SD) lesion volumes were 12.1 (+/-4.5) mm3 following mild injury, 33.8 (+/-8.6) mm3 following moderate injury, and 45.1 (+/-14.0) mm3 following severe injury. A significant difference was observed between all injury groups using a t test with Bonferroni correction (p < 0.05). These results suggest that the TTC staining technique is a useful, rapid, and reproducible method for quantification of lesion volume following lateral FP brain injury.

Cellular responses to surgical trauma, hemorrhage, and resuscitation with diaspirin cross-linked hemoglobin in rats

BACKGROUND

Resuscitation with acellular oxygen carrier solutions offers the potential advantage of improved oxygen delivery compared with crystalloid solutions, but the detailed consequences of improved resuscitation have not been fully evaluated. This study evaluated local and systemic cellular effects of trauma, hemorrhage, and resuscitation in a model of hemorrhage and surgical trauma.

METHODS

Rats with a 10 cm full-thickness incisional wound and a 15 mL/kg hemorrhage were either not resuscitated or resuscitated with blood or diaspirin cross-linked hemoglobin (DCLHb). Cellular proliferative responses were evaluated at 1.5, 6, 24, and 48 hours after wounding by labeling in vivo with 5-bromo-2'-deoxyuridine. Plasma levels of interleukin-6, tumor necrosis factor-alpha, and interferon-gamma were measured by bioassay or enzyme-linked immunosorbent assay (ELISA). Bacterial translocation was measured by culturing liver homogenates.

RESULTS

Trauma inhibited keratinocyte and hepatocyte proliferation at 1.5 and 6 hours, and stimulated subsequent proliferation of keratinocytes and liver nonparenchymal cells. DCLHb stimulated wound keratinocyte proliferation, attenuated the inhibition of hepatocyte proliferation, eliminated bacterial translocation to the liver, protected the intestine from ischemic damage, and induced a rapid increase of interleukin-6 during the early phase of injury.

CONCLUSIONS

Surgical trauma alone, or in combination with hemorrhage, modulated cell proliferation both in the wound and in the remote organs of intestine and liver. DCLHb enhanced wound healing and cell proliferation as well as, or better than, freshly drawn blood, which may be beneficial for trauma care.

Combined neuroprotection and reperfusion therapy for stroke. Effect of lubeluzole and diaspirin cross-linked hemoglobin in experimental focal ischemia

BACKGROUND AND PURPOSE

In search of a better treatment for acute ischemic stroke, we evaluated the use of lubeluzole and hemodilution with diaspirin cross-linked hemoglobin (DCLHb) therapy to test whether treatment with two complementary acting compounds provides more potent protection than either treatment alone.

METHODS

We used unilateral reversible middle cerebral artery (MCA) and common carotid artery (CCA) occlusion of various durations in Long-Evans rats to produce ischemic cortical lesions. We calculated the average maximal lesion volume (Volmax) and the time required to produce half maximal lesion size (T50) in control animals (n = 31) and evaluated the effects on cerebral perfusion and infarct size of treatment with lubeluzole (n = 23), hemodilution (to 30% hematocrit) with albumin (n = 17) or DCLHb (n = 23), and combined lubeluzole + DCLHb therapy initiated 15 minutes after MCA/CCA occlusion.

RESULTS

The Volmax produced by MCA/CCA occlusion in control animals was 138.5 +/- 7.7 mm3, and T50 was 98.5 +/- 10.2 minutes. Lubeluzole alone reduced Volmax by 53% with no significant effect on T50. In contrast to lubeluzole, DCLHb hemodilution prolonged T50 by 68% with no significant effect on Volmax. Prolongation of T50 by DCLHb was not due to hemodilution itself, since a similar degree of hemodilution with albumin had no effect. Finally, combined lubeluzole+DCLHb rescued 72% of the tissue and augmented the effect of lubeluzole alone by 40% (Volmax, 66.3 +/- 13.0 versus 39.4 +/- 12.2 mm3) while prolonging T50 by 31%.

CONCLUSIONS

Combination therapy for acute stroke using compounds with complementary action can result in more complete attenuation of neuronal damage and demonstrates the possible clinical utility of combined neuroprotective and reperfusion therapies.

Blood substitutes: fluids, drugs, or miracle solutions?

Oxygen-carrying volume-expanding solutions that can sustain life in the absence of red blood cells have been developed. Concerns about side effects, sources of hemoglobin, and the ultimate demonstration of efficacy will have to be satisfactorily addressed before anesthesiologists routinely administer such solutions in place of red cells during surgery.

Diaspirin crosslinked hemoglobin (DCLHb) does not affect the anesthetic potency of isoflurane in rats

Hemoglobin solutions are being developed as oxygen carrying fluids for multiple clinical indications. Despite an early report of accentuation of ether anesthesia, the effect of hemoglobin on anesthetic potency has not been assessed. We assessed the effect of alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) on the anesthetic requirement of isoflurane necessary to keep rats unresponsive to noxious stimuli (1.0 MAC [minimum alveolar concentration]). During isoflurane administration, each rat received one of the following fluid regimens: 44Hct/N-normal hematocrit and volume; 44Hct/H-8.0 ml of donor blood given as a hypervolemic bolus; 30Hct/H-5.0 ml of DCLHb given as an exchange transfusion and 8.0 ml as a hypervolemic bolus; or 16Hct/H-15.0 ml of DCLHb given as an exchange transfusion and 8.0 ml as a hypervolemic bolus. MAC was determined using a standard tail clamp technique. The isoflurane requirement to achieve 1.0 MAC was not different between the four groups. These results are consistent with a hypothesis that DCLHb does not change the anesthetic state.

Nitric oxide mediates the hypertensive response to a modified hemoglobin solution (DCLHb) in rats

We investigated the effect of nitric oxide synthase inhibition with L-NAME, and L-arginine (nitric oxide synthase substrate), on the hemodynamic response to a modified hemoglobin solution (DCLHb). Rats were given one of the following regimens (all groups hypervolemic except Control): Control-8.0 ml of donor blood (isovolemic exchange); HV-8.0 ml of donor blood; DCLHb-8.0 ml of DCLHb; L-NAME-30 mg.kg-1 of L-NAME followed by 8.0 ml of DCLHb; or L-Arg-8.0 ml of DCLHb followed by L-arginine (600 mg.kg-1). Mean arterial blood pressure (MABP) was continuously recorded and the change compared to baseline and expressed as delta MABP. delta MABP was greater in the HV and DCLHb groups versus the Control and L-NAME groups; and was greater in the DCLHb group versus the HV group. delta MABP was not different between the Control and L-NAME group. In the L-Arg group the initial delta MABP (after DCLHb) was similar to the DCLHb group; however, after L-arginine administration delta MABP was not different from the Control group. This study supports a hypothesis that DCLHb effects an increase in MABP by a nitric oxide related mechanism.