Redox Rep. 2026 Dec 31;31(1):2682043. doi: 10.1080/13510002.2026.2682043. Epub 2026 Jun 2.
ABSTRACT
Human serum albumin (HSA) is the most abundant circulating protein and a central mediator of extracellular redox homeostasis. Its antioxidant function has been attributed primarily to the free thiol at cysteine residue 34 (Cys34), whose progressive oxidation-yielding nonmercaptoalbumin isoforms HNA1 and HNA2-serves as a sensitive biomarker of systemic oxidative stress. Advances in electrospray ionisation time-of-flight mass spectrometry have enabled precise quantification of Cys34 modifications, establishing cysteinylated albumin as a clinically applicable marker in chronic kidney disease, chronic liver disease, diabetes, and ageing-related functional decline. Beyond its role as a biomarker, oxidized albumin is now recognized as an active pathogenic mediator in preclinical models, with emerging evidence implicating ferroptosis as a potential mechanism of renal tubular cell injury, and contributing to cardiovascular risk and sarcopenia. A previously unrecognized dimension of albumin redox biology has also emerged: the presence of endogenous oxidized polysulfide bonds (Ox-PSS; RSS-R', n > 1) across multiple intramolecular cysteine bridges. Quantified using the newly developed Elimination Method for Sulfide from Polysulfide, albumin polysulfides are dynamically regulated by oxidative stress and are significantly depleted in chronic kidney disease and early hepatitis, even when conventional Cys34-based markers remain unchanged. Polysulfide depletion impairs both Site II drug-binding capacity and reactive oxygen species scavenging activity, with direct implications for pharmacokinetics and therapeutic efficacy. These findings collectively reframe HSA as a dynamic polysulfide reservoir and extracellular redox regulator, highlighting albumin polysulfide modulation as a compelling emerging therapeutic strategy.
PMID:42228365 | DOI:10.1080/13510002.2026.2682043