Free extracellular heme (Heme)

Free extracellular heme is a potent pro-oxidant and pro-inflammatory molecule released from hemoproteins, primarily hemoglobin, during hemolysis or tissue injury [1]. While heme is essential as a prosthetic group in proteins like hemoglobin and cytochromes, its "free" or "labile" form in the extracellular space is highly toxic [2]. It promotes the generation of reactive oxygen species (ROS) via Fenton chemistry and acts as a damage-associated molecular pattern (DAMP) by activating Toll-like receptor 4 (TLR4) [3]. This leads to vascular dysfunction, sterile inflammation, and organ damage in conditions such as sickle cell disease, sepsis, and malaria [4]. Therapeutic strategies focus on neutralizing free heme using endogenous scavengers like hemopexin or developing synthetic binders to mitigate its pathological effects [5]. Sources: [1] Chiabrando et al. (2014) Front Pharmacol; [2] Wagener et al. (2003) Pharmacol Rev; [3] Belcher et al. (2014) J Clin Invest; [4] Schaer et al. (2013) Blood; [5] Detter et al. (2023) JCI Insight.

Other names

Labile hemeNon-protein-bound hemeFerriprotoporphyrin IXExtracellular hemeHeme B

Sequestration and neutralization of extracellular heme to prevent oxidative damage and TLR4-mediated inflammatory signaling.