Engineering a highly selective, hemoprotein-based scavenger as a carbon monoxide poisoning antidote with no hypertensive effect.

Abstract

Carbon monoxide (CO) poisoning causes 50,000 to 100,000 emergency department visits and ~1,500 deaths in the United States annually. Current treatments are limited to supplemental and/or hyperbaric oxygen to accelerate CO elimination. Even with oxygen therapy, nearly half of CO poisoning survivors suffer long-term cardiac and neurocognitive deficits related to slow CO clearance, highlighting a need for point of care antidotal therapies. Given the natural interaction between CO and ferrous heme, we hypothesized that the hemoprotein RcoM, a transcriptional regulator of microbial CO metabolism, would make an ideal platform for CO-selective scavenging from endogenous hemoproteins. We engineered an RcoM truncate (RcoM-HBD-CCC) that exhibits high CO affinity (<i>K</i>_a,CO = 2.8 × 10¹⁰ M^-1), remarkable selectivity for CO over oxygen (<i>K</i>_a,O2 = 1.4 × 10⁵ M^-1; <i>K</i>_a,CO/<i>K</i>_a,O2 = 1.9 × 10⁵), thermal stability (T_m = 72 °C), and slow autoxidation rate (<i>k</i>_ox = 1.1 h^-1). In a murine model of acute CO poisoning, infused RcoM-HBD-CCC accelerated CO clearance from hemoglobin in red blood cells (RBCs) and was rapidly excreted in urine. Moreover, infused RcoM-HBD-CCC elicited minimal hypertension in mice compared to infused globins (hemoglobin, myoglobin, and neuroglobin), attributed to a comparatively limited reactivity toward nitric oxide (NO) via dioxygenation [<i>k</i>_NOD(RcoM) = 6 to 8 × 10⁶ M^-1s^-1 vs <i>k</i>_NOD(Hb) = 6 to 8 × 10⁷ M^-1s^-1]. These data suggest that RcoM-HBD-CCC is a safe, selective, and efficacious CO scavenger. By limiting hypertension through minimal NO scavenging, RcoM-HBD-CCC improves end-organ adverse effects compared with other hemoprotein-based therapeutics.