Norepinephrine release during vasoconstriction induced by cross-linked hemoglobin

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.

Alpha adrenergic activation and hemoglobin mediated contraction in the isolated rat thoracic aorta

A primary mechanism for Hb mediated vascular contraction appears to be Hb scavenging of endothelium derive nitric oxide (NO), a potent vasodilator. In isolated rat thoracic aorta, however, Hb elicits contraction only after precontraction. The present study investigated a possible role of the alpha adrenergic activation in the Hb mediated contraction. Thoracic aortic rings harvested from normal male SD rats were prepared in a tissue bath and isometric tension changes were evaluated. In vessel rings precontracted with 50nM norepinephrine (NE), 1 microM Hb produced an additional 21.8+/-13.2% increase in tension. Pretreatment with 70nM phentolamine, an alpha adrenergic antagonist, prevented the 50nM NE induced contraction. In these vessels, subsequent treatment with 2-4 microM Hb did not elicit contraction. In vessel rings precontracted with 37mM KCl, 2 microM Hb produced an additional 21.8+/-20.1% tension increase (P<0.05). Pretreatment with phentolamine did neither prevent KCl induced contraction nor affect subsequent Hb mediated additional contraction. To test whether there is a threshold level of basal tension for Hb to trigger contraction, a group of vessel rings were passively stretched to match the tension generated by NE before Hb treatment. In these passively stretched vessel rings, Hb did not produce a significant contraction. Pretreatment with 10mM EGTA, a Ca++ chelator, significantly reduced NE induced contraction (9.7+/-5.9 vs 137.7+/-60.0%, P<0.01) but did not prevent it. EGTA also significantly reduced 2 microM Hb induced contraction (27.2+/-29.3% vs 8.9+/-7.7%, P<0.05). In contrast, pretreatment with verapamil, a Ca++ channel blocker, did not completely block NE and Hb induced contractions. In conclusion, alpha adrenergic activation is not a requisite for the Hb mediated contraction in isolated rat aortic rings. The mechanism how prior tone enhancement allows Hb mediated contraction remains unclear but results from this study suggest a factor that controls cytosolic Ca++ levels may be involved.

Effect of the blood substitute diaspirin crosslinked hemoglobin in rat mesenteric and human radial collateral arteries

The actions of the blood substitute diaspirin crosslinked hemoglobin (DCLHb) were investigated in rat (small mesenteric artery) and human (radial collateral artery) resistance vessels mounted in a wire myograph for isometric tension recording. DCLHb did not contract resting vessels from rats, but vasoconstrictor responses were observed in isolated arteries and perfused mesenteric beds prestimulated with threshold concentrations of methoxamine. The DCLHb contractile responses were greatly attenuated by N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME) or endothelial removal, whereas BQ-123 (endothelin A receptor antagonist), prazosin (alpha1-adrenoceptor antagonist), or indomethacin (cyclooxygenase inhibitor) had no effect. Endothelium-dependent relaxations to carbachol in both rat mesenteric and human radial collateral artery were inhibited by DCLHb. Relaxations to carbachol were studied in the presence of L-NAME or 25 mM KCl to investigate the effect of DCLHb on endothelium-derived hyperpolarizing factor (EDHF) and nitric oxide, respectively. In both rat and human vessels, EDHF-mediated relaxations were not affected by DCLHb preincubation, whereas the nitric oxide component of carbachol-induced relaxations was practically abolished. In conclusion, inhibition of the effects of basal nitric oxide release underpins the vasoconstrictor effects of DCLHb. DCLHb effectively abolishes the nitric oxide component of carbachol-induced relaxation, with no effect on the EDHF-mediated component in both isolated rat mesenteric and human radial collateral arteries.

Acute vasorelaxant effects of metformin and attenuation by stimulation of sympathetic agonist release

We recently discovered 1) that intravenous injection of the antidiabetic drug metformin in the rat rapidly reduces arterial pressure elevations maintained by the alpha-adrenoceptor agonist phenylephrine (PE) and 2) that direct administration of metformin to isolated rat tail arterial tissue rings rapidly relaxes PE-induced contractions. To further characterize this potential direct vasodilator action, we examined effects of metformin on contractions induced not only by PE but also by norepinephrine (NE) and by nonadrenergic agonists (5-hydroxytryptamine, 5HT; arginine vasopressin, AVP). Also, because the rat tail artery contains abundant adrenergic nerve endings we conducted these tests not only in arterial rings with nerve endings intact but in rings in which they had been removed by pretreatment with 6-hydroxydopamine. In intact rings, metformin at levels from approximately 0.2 to 20 mmol/L rapidly relaxed half-maximal contractions induced by PE and NE similarly and to a markedly greater degree than contractions induced by 5-HT (p<0.05). Metformin did not relax AVP-induced contractions. In addition, removal of adrenergic nerve endings facilitated metformin's relaxant effects (p<0.05). Thus, the acute vasodilator action of metformin appears 1) to be selectively more powerful on arterial smooth muscle contractions induced adrenergically versus nonadrenergically and 2) to be buffered by a possible metformin-induced release of endogenous NE from adrenergic nerve endings. Such results were not seen during relaxation produced by either the calcium channel inhibitor nifedipine or the nitrovasodilator nitroprusside suggesting that metformin's effects are mediated by other mechanisms.

Low-volume resuscitation with a hemoglobin-based oxygen carrier after hemorrhage improves gut microvascular oxygenation in swine

Using palladium-porphyrin quenching of phosphorescence, we investigated the influence of diaspirin cross-linked hemoglobin (DCLHb) on gut microvascular oxygen pressure (microPO2) in anesthetized pigs. Values of gut microPO2 were studied in correlation with regional intestinal as well as global metabolic and circulatory parameters. A controlled hemorrhagic shock (blood withdrawal of 40 mL/kg) was followed by resuscitation with either a combination of lactated Ringer's solution (75 mL/kg) and modified gelatin (15 mL/kg)(lactR/Gel) or 10% DCLHb (5 mL/kg). After resuscitation, gut microPO2 was similarly improved in the lactR/Gel group (from 25 +/- 10 mm Hg to 53 +/- 8 mm Hg) and the DCLHb group (from 23 +/- 9 mm Hg to 46 +/- 6 mm Hg), which was associated with increased gut oxygen delivery. However, the improvement after resuscitation with DCLHb was sustained for longer periods of time (75 vs 30 min). Mesenteric venous PO2 was increased after resuscitation with lactated Ringer's solution and modified gelatin but not with DCLHb, which was associated with an increased gut oxygen consumption in the latter group. We conclude that measurement of microPO2 by the palladium-porphyrin phosphorescence technique revealed DCLHb to be an effective carrier of oxygen to the microcirculation of the gut. Also, this effect can be achieved with a lower volume than is currently used in resuscitation procedures.

Resuscitation after hemorrhage using recombinant human hemoglobin (rHb1.1) in rats: effects on nitric oxide and prostanoid systems

OBJECTIVES

Hemoglobin-based oxygen carriers are designed to replace blood volume and to increase oxygen delivery to tissues after blood loss. The goals of the present study were two-fold: a) to determine the systemic and regional vascular effects of resuscitation with recombinant human hemoglobin (rHb1.1) in rats during controlled hemorrhage; and b) to determine whether nitric oxide (NO) or prostaglandins were involved in the observed responses.

DESIGN

Paralyzed, ventilated rats were hemorrhaged (18 mL blood/kg body weight) during halothane anesthesia and allowed to stabilize for 30 mins. Systemic and regional hemodynamics and oxygen delivery were monitored at three time points, using the radioactive microsphere method. Microspheres were first infused at the end of the hemorrhage stabilization period (t=0 min). rHb1.1 (1 g/kg body weight) or rHb1.1 diluent (phosphate buffered saline, 36 mL/kg body weight) were infused over 20 mins and microspheres were administered again, 30 mins later (t=50 mins). Saline (0.5 mL), indomethacin (5 mg/kg to inhibit cyclooxygenase), or NG-monomethyl-L-arginine (L-NMMA, 100 mg/kg, to inhibit NO synthase) were then infused in rHb1.1-treated rats and microspheres injected once more (t=80 mins).

SETTING

Research laboratory.

SUBJECTS

Male Wistar rats (n=37).

INTERVENTIONS

Recombinant human hemoglobin (rHb1.1), rHb1.1 diluent (phosphate buffered saline) resuscitation of hemorrhaged rats. Saline, L-NMMA, or indomethacin treatment after resuscitation.

MEASUREMENTS AND MAIN RESULTS

Resuscitation with rHb1.1 increased mean arterial pressure (MAP), cardiac output, and systemic oxygen delivery significantly when compared with diluent. After rHb1.1 resuscitation, regional blood flows were significantly increased in skin, kidney, spleen, and heart compared with diluent resuscitation. Compared with saline treatment after rHb1.1 resuscitation, L-NMMA increased MAP and regional resistances in virtually all tissues; indomethacin did not alter MAP, but increased resistance in the brain.

CONCLUSIONS

These data indicate that rHb1.1 resuscitation was more effective than diluent in improving systemic and regional hemodynamics and oxygen delivery, suggesting that rHb1.1 may be of benefit in the treatment of acute blood loss. Increased resistance after L-NMMA in the presence of rHb1.1 indicated that rHb1.1 resuscitation did not eliminate NO dependent circulatory control. Increased resistance after indomethacin in brain indicated that vasodilator prostanoids were important in regulating vascular resistance in these tissues after rHb1.1 resuscitation.

Regional vascular effects of rHb1.1, a hemoglobin-based oxygen carrier

The goals of this study were to determine the effects of recombinant human hemoglobin (rHb1.1, 1 g/kg i.v.) on systemic hemodynamics, regional blood flows, and regional vascular resistances in rats. Cardiac output (CO) and regional blood flow in 13 tissues were determined by using the radiolabeled-microsphere method during halothane anesthesia. Microspheres were injected at three time points: before (control, t = 0), t = 30 [10 min after a 20-min infusion of vehicle (diluent) or rHb1.1], and at t = 120 min. Infusion of diluent did not alter CO, heart rate (HR), mean arterial pressure (MAP), or systemic vascular resistance (SVR) and had minimal effects on regional blood flows. Infusion of rHb1.1 did not alter CO or HR but did increase MAP and SVR compared with diluent. Infusion of rHb1.1 increased blood flow to the heart and decreased blood flow to the gastrointestinal tract (GIT) and liver. Compared with the corresponding values in the diluent-treated rats, resistance was increased after rHb1.1 in spleen, kidney, and hepatic artery. In conclusion, rHb1.1 administration increased MAP and SVR. The vasoconstriction was heterogeneous and was associated with increased coronary blood flow and with increased regional resistance in kidney, spleen, and hepatic artery, compared with diluent-infused controls.

Initial evaluation of diaspirin cross-linked hemoglobin (DCLHb) as a vasopressor in critically ill patients

OBJECTIVE

To evaluate the hemodynamic effects and any toxicologic effects of diaspirin cross-linked hemoglobin (DCLHb) in critically ill patients.

DESIGN

A prospective, observational study.

SETTING

A seven-bed intensive care unit (ICU) in a University teaching hospital.

PATIENTS

Fourteen critically ill patients requiring vasopressor therapy to maintain adequate mean arterial pressure (MAP). All patients had secondary organ dysfunction.

INTERVENTIONS

Administration of 100 mL boluses of 10% diaspirin cross-linked hemoglobin, up to a maximum of 500 mL, given over 15 mins and separated by 60 to 90 mins.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic parameters, norepinephrine and inotropic requirements, arterial and mixed venous blood gases, urine output, and biochemical and hematologic analyses were measured before diaspirin cross-linked hemoglobin administration and at multiple time points up to 72 hrs. MAP was maintained at approximately preinfusion values and the reduction in norepinephrine requirements was used as the main end point to assess the efficacy of diaspirin cross-linked hemoglobin as a vasopressor. Diaspirin cross-linked hemoglobin demonstrated a marked vasopressor action, allowing norepinephrine requirements to be reduced from 0.29 +/- 0.15 (SD) microgram/kg/min to 0.15 +/- 0.14 and 0.07 +/- 0.10 microgram/kg/min after the first (at 1.5 hrs, p < .001) and last (at 7.5 hrs, p < .0001) boluses, respectively. These reductions in norepinephrine requirements were maintained at 24, 48, and 72 hrs (p < .01 at all time points). These hemodynamic changes began within 5 mins of starting the diaspirin cross-linked hemoglobin infusion. MAP, heart rate, central venous pressure, pulmonary artery occlusion pressure, mean pulmonary arterial pressure (MPAP), systemic vascular resistance index, and urine output did not demonstrate any significant changes from preinfusion values. Pulmonary vascular resistance index increased at 7.5 hrs despite nonsignificant increases in MPAP. Cardiac index and oxygen delivery index decreased significantly at 7.5 hrs and 24 hrs. Total plasma bilirubin increased significantly from baseline at 24 and 48 hrs, before returning to baseline values within 5 days. Platelet count was significantly reduced at 6 and 24 hrs. No other biochemical or hematologic analyses were altered significantly post diaspirin cross-linked hemoglobin.

CONCLUSIONS

This preliminary study demonstrated that diaspirin cross-linked hemoglobin is a potent vasopressor agent in critically ill patients with septicemic shock or systemic inflammatory response syndrome. This vasopressor characteristic of diaspirin cross-linked hemoglobin may have future clinical applications.