Abstract
Serum albumin is the most abundant circulating protein in mammals including humans. It has three isoforms according to the redox state of the free cysteine residue at position 34, named as mercaptalbumin (reduced albumin), non-mercaptalbumin-1 and -2 (oxidized albumin), respectively. The serum albumin redox state has long been viewed as a biomarker of systemic oxidative stress, as the redox state shifts to a more oxidized state in response to the severity of the pathological condition in various diseases such as liver diseases and renal failures. However, recent ex vivo studies revealed oxidized albumin per se could aggravate the pathological conditions. Furthermore, the possibility of the serum albumin redox state as a sensitive protein nutrition biomarker has also been demonstrated in a series of animal studies. A paradigm shift is thus ongoing in the research field of the serum albumin. This article provides an updated overview of analytical techniques for serum albumin redox state and its association with human health, focusing on recent findings.
Highlights
Antioxidants 2021, 10, 503. https://Albumin (ALB) is the most abundant protein in serum, which has a molecular weight of approx. 66 kDa and is normally present at 35–45 g/L [1]
The UV absorbance at 215 nm involves an interference with the separation of human mercaptalbumin (HMA) and human non-mercaptalbumin-1 (HNA-1) by uric acid [33], which is a critical obstacle especially for the determination of serum ALB redox state in chronic kidney disease (CKD) patients [34]
A recent study by Fujii et al, 2019 is notable as it demonstrated the association between serum ALB redox state and renal function in community-dwelling general population without CKD or its pretreatment [74], suggesting that serum ALB redox state would be even useful as an indicator of renal function in broad population
Summary
Albumin (ALB) is the most abundant protein in serum, which has a molecular weight of approx. 66 kDa and is normally present at 35–45 g/L (approx. 0.6 mM) [1]. Whereas small thiols Cys and glutathione (GSH) are the major antioxidants contributing to intracellular redox homeostasis, the most abundant thiol in plasma is the Cys residue in ALB, which exerts anti-oxidative activity and circumvent systemic oxidative stress. The thiol group of Cys residue is redox-active as described above, and the redox state state grants the heterogeneity of serum ALB isoforms. The UV absorbance at 215 nm involves an interference with the separation of HMA and HNA-1 by uric acid [33], which is a critical obstacle especially for the determination of serum ALB redox state in chronic kidney disease (CKD) patients [34]. While the use of HPLC systems are enough to determine the ratios of reduced and oxidized serum ALB isoforms, they are not able to characterize chemical structures of the post-translational modifications in oxidized ALB isoforms
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