| Ceruloplasmin is a liver-derived multicopper ferroxidase of the multicopper oxidase family that circulates in plasma as the main copper‑binding protein and functions at the interface of copper handling, iron export, and antioxidant defense. The mature secreted protein adopts a six-domain β‑sandwich architecture that coordinates multiple copper ions organized into a mononuclear type I copper site and a spatially separated trinuclear center composed of type II and type III copper atoms, an arrangement that supports long‑range intramolecular electron transfer during substrate oxidation and oxygen reduction. Ferrous iron binds near the type I copper center, is oxidized to ferric iron through copper‑dependent electron transfer, and the resulting electrons are relayed via conserved cysteine and histidine residues to the trinuclear copper cluster, where molecular oxygen undergoes a four‑electron reduction to water; this ferroxidase cycle generates ferric iron suitable for loading onto transferrin and maintains an iron gradient that favors efflux from storage cells. In hepatocytes and other tissues with mobilizable iron stores, ceruloplasmin associates functionally with the iron exporter ferroportin so that its surface ferroxidase activity couples directly to iron release, and genetic or acquired loss of ceruloplasmin activity reduces cell‑to‑plasma iron flux and causes hypoferremia despite normal or increased tissue iron stores. Aceruloplasminemia, caused by loss‑of‑function mutations in the CP gene, exemplifies this mechanism and is characterized by iron accumulation in liver, pancreas, and brain with low plasma iron and transferrin saturation, linking the absence of ceruloplasmin ferroxidase activity to impaired iron mobilization and secondary neurodegeneration and diabetes. Plasma ceruloplasmin also behaves as a positive acute‑phase reactant whose levels increase in inflammation and tissue injury, and its ability to oxidize diverse substrates and scavenge reactive oxygen species contributes to antioxidant protection in vascular and metabolic disease states. A GPI‑anchored form of ceruloplasmin is expressed on astrocytes, where it supports ferroportin‑mediated iron efflux at the blood–brain interface and in neural tissue; defects in this astrocytic ceruloplasmin–ferroportin system associate with regional brain iron overload and are implicated in neurodegenerative conditions where iron‑driven oxidative stress is prominent. Transcriptional and translational control of ceruloplasmin expression, including cytokine‑inducible pathways and GAIT element–mediated translational silencing, links systemic inflammatory cues to copper and iron handling capacity. |
