Albumin

Albumin (ALB) is the most abundant plasma protein, serving multiple transport and regulatory functions. It binds diverse ligands including water, ions (calcium, magnesium, zinc), fatty acids, hormones, and bilirubin, and regulates blood colloidal osmotic pressure (UniProt: P02768). As the major zinc transporter in plasma, albumin typically binds approximately 80% of circulating zinc, with a binding affinity rank order of zinc > calcium > magnesium.

Albumin is primarily synthesized in the liver and circulates in blood, though its presence in cerebrospinal fluid and brain tissue reflects its role in systemic mineral and ligand homeostasis. Genetic variants in ALB cause rare disorders including familial dysalbuminemic hyperthyroxinemia and analbuminemia, characterized by altered thyroid hormone or severe albumin deficiency (UniProt: P02768).

In Alzheimer's disease, albumin is significantly down-regulated in post-mortem AD brain tissue compared to age-matched controls (mean log2 fold-change: −0.87) across multiple subcellular fractions (Chaparral AD proteomics). This reduction may reflect altered systemic-central nervous system transport or local brain metabolic changes associated with neurodegeneration, though the mechanistic significance requires further investigation.