COVID-19: hemoglobin, iron, and hypoxia beyond inflammation. A narrative review

Coronavirus disease-19 (COVID-19) has been regarded as an infective-inflammatory disease, which affects mainly lungs. More recently, a multi-organ involvement has been highlighted, with different pathways of injury. A hemoglobinopathy, hypoxia and cell iron overload might have a possible additional role. Scientific literature has pointed out two potential pathophysiological mechanisms: i) severe acute respiratory syndrome-coronavirus-2 (SARS-CoV- 2) interaction with hemoglobin molecule, through CD147, CD26 and other receptors located on erythrocyte and/or blood cell precursors; ii) hepcidin-mimetic action of a viral spike protein, inducing ferroportin blockage. In this translational medicinebased narrative review, the following pathologic metabolic pathways, deriving from hemoglobin denaturation and iron metabolism dysregulation, are highlighted: i) decrease of functioning hemoglobin quote; ii) iron overload in cell/tissue (hyperferritinemia); iii) release of free toxic circulating heme; iv) hypoxemia and systemic hypoxia; v) reduction of nitric oxide; vi) coagulation activation; vii) ferroptosis with oxidative stress and lipoperoxidation; viii) mitochondrial degeneration and apoptosis. A few clinical syndromes may follow, such as pulmonary edema based on arterial vasoconstriction and altered alveolo-capillary barrier, sideroblastic-like anemia, endotheliitis, vasospastic acrosyndrome, and arterio- venous thromboembolism. We speculated that in COVID-19, beyond the classical pulmonary immune-inflammation view, the occurrence of an oxygen-deprived blood disease, with iron metabolism dysregulation, should be taken in consideration. A more comprehensive diagnostic/therapeutic approach to COVID-19 is proposed, including potential adjuvant interventions aimed at improving hemoglobin dysfunction, iron over-deposit and generalized hypoxic state.