HIF prolyl hydroxylase (HIF-PH1/2/3)

Class

HIF prolyl hydroxylase inhibitor (HIF-PHI)

Pathway

Hypoxia-inducible factor (HIF) / erythropoietin pathway

HIF prolyl hydroxylases (PHD1, PHD2, PHD3) are enzymes that use molecular oxygen to modify hypoxia-inducible factor (HIF), a transcription factor that governs cellular adaptation to low oxygen. Under normal oxygen levels, these enzymes hydroxylate HIF-alpha subunits, marking them for rapid degradation. When oxygen is scarce, hydroxylation slows, HIF accumulates, and it activates genes involved in oxygen delivery and metabolism, including erythropoietin (EPO), the hormone that stimulates red blood cell production, along with genes governing iron handling and blood vessel formation. HIF-PH inhibitors act as pharmacological mimics of hypoxia: by blocking the hydroxylase active site, they stabilize HIF even when oxygen is plentiful, prompting the body to increase endogenous EPO production and improve iron availability for red cell formation. This mechanism is exploited primarily in anemia associated with chronic kidney disease, where diseased kidneys produce insufficient EPO. Because the approach works upstream of EPO itself, promoting a more physiological hormone response rather than delivering a fixed exogenous dose, it represents an alternative to injectable erythropoiesis-stimulating agents. The broader HIF pathway also touches metabolism, vascular biology, and cellular stress responses, so modulation carries effects that extend beyond erythropoiesis alone.