Close relationship between redox state of human serum albumin and serum cysteine levels in non-diabetic CKD patients with various degrees of renal function

Aims: Human mercaptalbumin (HMA) acts as a covalent-carrier protein for sulfur-containing amino acids, cysteine, and glutathione. In addition, its sulfhydryl residue reacts with peroxyl radicals. In this study, we evaluated the redox state of human serum albumin and its relationship with serum amino thiol levels in non-diabetic chronic kidney disease (CKD) patients with various degrees of renal function. Materials and methods: High performance liquid chromatography (HPLC) and gas chromatography-mass spectrometry (GC-MS) with selected ion monitoring were used to analyze serum samples collected from 37 non-dialysis patients with primary glomerulonephritis without diabetes mellitus (DM) or other systemic diseases (non-diabetic CKD patients). Results: Total cysteine and homocysteine plasma levels increased with decreasing renal function and showed a significant negative correlation with glomerular filtration rate. The protein-bound ratio of serum cysteine also changed with the degree of renal dysfunction. The HPLC fraction of human mercaptalbumin (HMA) (%) was significantly lower in nondiabetic CKD patients than in healthy subjects. The redox state of human serum albumin (i. e., HMA %) correlated significantly with the total serum cysteine level. Conclusion: The HPLC fraction of HMA (%) closely correlated with the serum cysteine level in non-diabetic CKD patients. An increase in oxidized cysteine with impaired renal function and a reduced plasma redox capacity associated with a decrease in the reduced form of serum albumin (HMA %) may be important risk factors for promoting long-term complications in patients with renal dysfunction.