Pro-Oxidative and Inflammatory Actions of Extracellular Hemoglobin and Heme: Molecular Events and Implications for Alzheimer's and Parkinson Disease

Hemoglobin (Hb) and heme, which are typically confined within red blood cells (RBCs), are essential for intravascular transport of gases and nutrients. However, these molecules acquire secondary functions upon exposure to the extracellular environment. Hb and heme generate reactive oxygen species (ROS), which are potent pro-inflammatory agents that contribute to oxidative stress and cellular damage. These events are relevant to neurodegenerative processes, where oxidative stress, irregular deposition of protein aggregates, and chronic inflammation are key pathological features. Extracellular Hb, heme, and oxidative stress derived from hemorrhagic events or RBC lysis may contribute to increased blood-brain barrier (BBB) permeability. These events allow Hb and heme to interact with neuroimmune cells and pathological protein aggregates, further amplifying pro-inflammatory signaling and the progression of Alzheimer's disease (AD) and Parkinson disease (PD). Chronic neuroinflammation, oxidative stress, and mitochondrial dysfunction lead to neuronal degeneration. Here, we sought to elucidate the pro-oxidative and inflammatory actions of extracellular Hb and heme, emphasizing their potential impact on AD and PD development.