An Engineered Protein as an Antidote for Carbon Monoxide Poisoning That Can Reverse Cardiovascular Collapse Through Scavenging of Carbon Monoxide and Rescue of Mitochondrial Respiration

Background: Carbon monoxide (CO) is the most common human poisoning. There is no antidote. One-third of hospitalized patients will have cardiac dysfunction and increased mortality. Little is known about the nature of cardiovascular dysfunction during acute CO poisoning. CO toxicity results from: (1) global hypoxia and decreased oxygen delivery through CO binding to hemoglobin, (2) inhibition of oxidative phosphorylation from CO binding to cytochrome c oxidase, and (3) ensuing superoxide injury. We have developed a recombinant neuroglobin molecule (rNgb) with a high affinity for CO, that can chelate CO from intrinsic heme proteins. Hypothesis: The addition of rNgb will scavenge CO from hemoglobin and cytochrome c oxidase, reversing CO-induced cardiovascular dysfunction. Methods: We inserted micromanometer-tip catheters into the left ventricle of ventilated, severely CO poisoned mice to study the mechanisms of CO-induced cardiovascular collapse. In a similar model, we measured blood pressure and heart rate of severely CO poisoned, ventilated mice through a carotid arterial catheter and treated with phosphate buffered saline (PBS) or rNgb. Hearts were isolated from these mice and we measured tissue respiration using a Clark-type oxygen electrode. We compared the respiration rates of these animals and compared with non-poisoned, sedated control mice. We also compared the enzymatic activity of electron transport chain complexes. Results and Conclusions: When compared to control mice (exposed to 21% oxygen/no CO), CO poisoned mice develop a decreased contractility index (-32.3% baseline vs. -10.8% in control, t-test, p=0.002), hypotension and death, indicating primary cardiac toxicity. CO-poisoned mice treated with PBS had heart tissue respiration that was 62.3% (+/- 7.5%) of sedated control mice (t-test, P=0.015). Treatment of mice with rNgb restored tissue respiration (P=0.037 versus PBS treated mice) similar to control values. CO poisoning reduced the activity level of complex IV in PBS treated mice (P=0.011), but levels were similar to control in rNgb treated mice. These molecular changes were associated with reversal of cardiovascular collapse in rNgb treated mice versus PBS, demonstrating the potential of rNgb as a CO poisoning antidote.