Prevention of the pulmonary vasoconstrictor effects of HBOC-201 in awake lambs by continuously breathing nitric oxide

Abstract

Background: Hemoglobin-based oxygen-carrying solutions (HBOC) provide emergency alternatives to blood transfusion to carry oxygen to tissues without the risks of disease transmission or transfusion reaction. Two primary concerns hampering the clinical acceptance of acellular HBOC are the occurrence of systemic and pulmonary vasoconstriction and the maintenance of the heme-iron in the reduced state (Fe2+). We recently demonstrated that pretreatment with inhaled nitric oxide prevents the systemic hypertension induced by HBOC-201 (polymerized bovine hemoglobin) infusion in awake mice and sheep without causing methemoglobinemia. However, the impact of HBOC-201 infusion with or without inhaled nitric oxide on pulmonary vascular tone has not yet been examined.

Methods: The pulmonary and systemic hemodynamic effects of breathing nitric oxide both before and after the administration of HBOC-201 were determined in healthy, awake lambs.

Results: Intravenous administration of HBOC-201 (12 ml/kg) induced prolonged systemic and pulmonary vasoconstriction. Pretreatment with inhaled nitric oxide (80 parts per million [ppm] for 1 h) prevented the HBOC-201--induced increase in mean arterial pressure but not the increase of pulmonary arterial pressure, systemic vascular resistance, or pulmonary vascular resistance. Pretreatment with inhaled nitric oxide (80 ppm for 1 h) followed by breathing a lower concentration of nitric oxide (5 ppm) during and after HBOC-201 infusion prevented systemic and pulmonary vasoconstriction without increasing methemoglobin levels.

Conclusions: These findings demonstrate that pretreatment with inhaled nitric oxide followed by breathing a lower concentration of the gas during and after administration of HBOC-201 may enable administration of an acellular hemoglobin substitute without vasoconstriction while preserving its oxygen-carrying capacity.

Fig. 1

Mean arterial pressure (MAP; A), systemic vascular resistance (SVR; B), mean pulmonary arterial pressure (PAP; C), pulmonary vascular resistance (PVR; D), cardiac output (E) of awake lambs after an intravenous infusion of pre-warmed (37°C) autologous whole blood (12 ml/kg; n=6), intravenous HBOC-201 (n=5), or HBOC-201 (12 ml/kg) after pretreatment with breathing 80 ppm nitric oxide at FiO₂=0.3 for 1 h (iNO; n=6). All lambs breathed at FiO₂=0.3. *p<0.05 HBOC-201 differs from autologous whole blood and from HBOC-201 after inhaled nitric oxide, †p<0.05 autologous whole blood differs from HBOC-201 with or without pretreatment by inhaled nitric oxide, ‡p<0.05 HBOC-201 differs from autologous whole blood.

Fig. 2

Changes in plasma methemoglobin level after breathing nitric oxide at ascending concentrations for 15 min at each nitric oxide level, all after infusion of HBOC-201 (12 ml/kg) in awake lambs (n=4). *p<0.05 differs from the changes in methemoglobin level induced by breathing 0.5 ppm nitric oxide for 15 min.

Fig. 3

Mean arterial pressure (MAP; A), mean pulmonary arterial pressure (PAP; B), systemic vascular resistance (SVR; C), pulmonary vascular resistance (PVR; D), Cardiac output (E), and plasma methemoglobin concentration (F) of awake lambs after infusion of autologous whole blood (n=6), intravenous HBOC-201 (n=5), or HBOC-201 (12 ml/kg) after pretreatment by breathing 80 ppm nitric oxide for 1 h followed by continuously breathing 5 ppm nitric oxide for 2 h (high/low nitric oxide, n=6). *p<0.05 HBOC-201 differs from autologous whole blood and from HBOC-201 after high/low inhaled nitric oxide, †p<0.05 autologous whole blood differs from HBOC-201 with or without high/low inhaled nitric oxide, ‡p<0.05 HBOC-201 differs from autologous whole blood, §p<0.05 differs from autologous whole blood and HBOC-201.

Fig. 4

Mean arterial pressure (MAP; A), mean pulmonary arterial pressure (PAP; B), systemic vascular resistance (SVR; C), pulmonary vascular resistance (PVR; D), cardiac output (E), and plasma methemoglobin concentration (F) of awake lambs after infusion of 37°C autologous whole blood (12 ml/kg) (n=6), after intravenous HBOC-201 (n=5), or HBOC-201 (12 ml/kg) after pretreatment with a sodium nitrite infusion (1 mg/kg over 5 min; n=4). *p<0.05 HBOC-201 differs from autologous blood and from HBOC-201 after nitrite, †p<0.05 autologous whole blood differs from HBOC-201 with or without nitrite infusion, ‡p<0.05 HBOC-201 after nitrite differs from autologous whole blood, §p<0.05 differs from before nitrite administration.

Fig. 5

Plasma nitrate (A) and nitrite (B) levels in awake lambs after infusion of intravenous HBOC-201 alone (n=3), intravenous HBOC-201 with pretreatment by inhaled nitric oxide (80 ppm, 1 h; n=3), intravenous HBOC-201 with pretreatment by inhaled nitric oxide (80 ppm, 1 h) followed by continuously breathing nitric oxide (5 ppm, 2 h; n=5; high/low iNO), or intravenous HBOC-201 after nitrite infusion (n=4). *p<0.05 HBOC-201 with pretreatment by inhaled nitric oxide and HBOC-201 with high/low inhaled nitric oxide differ from HBOC-201 alone, †p<0.05 HBOC-201 after nitrite bolus differs from HBOC-201 alone, ‡p<0.05 HBOC-201 after nitrite bolus differs from its own baseline.