Acellular Hemoglobin Impairs Cardiomyocyte Excitation-Contraction Coupling

Heart failure is a significant complication of chronic intravascular hemolysis, a condition characterized by red blood cells (RBCs) breakdown, leading to the release of acellular hemoglobin (Hb) and its oxidized form, methemoglobin (MetHb), into the bloodstream. Acellular Hb promotes nitric oxide (NO) scavenging, oxidative stress, inflammation, iron overload, and functional tissue impairment. This study investigates the direct impact of Hb and MetHb on cardiomyocyte function by assessing calcium transients, fractional shortening, and reactive oxygen species (ROS) formation. The study also evaluated the effects of polymerized Hb, NO scavenging, and antioxidant therapy using N-acetylcysteine (NAC) on cardiomyocyte contractility. Our results show that acellular Hb and MetHb impair cardiomyocyte function by prolonging calcium transient half-life, reducing contractility, and increasing ROS production. Polymerization of Hb and antioxidant supplementation offered partial protection but did not fully mitigate these effects. Inhibiting NO synthase did not increase Hb toxicity, indicating that NO scavenging is not the sole toxicity pathway. These findings demonstrate that Hb-induced cardiomyocyte dysfunction involves a multifactorial mechanism, including NO scavenging, oxidative stress, and disrupted calcium dynamics. Although Hb polymerization and antioxidants offer limited protection, novel multi-target strategies are essential to address Hb toxicity in hemolytic disorders and the use of Hb-based oxygen carriers.