Systemic redox biomarkers and their relationship to prognostic risk markers in autosomal dominant polycystic kidney disease and IgA nephropathy.

BACKGROUND: Oxidative stress is evident from an early stage in chronic kidney disease (CKD). Therefore, we investigated redox biomarkers in polycystic kidney disease (ADPKD) and IgA nephropathy (IGAN). METHODS: This is a case-control study with three groups: ADPKD (n = 54), IGAN (n = 58) and healthy controls (n = 86). The major plasma aminothiols with their redox species were examined: homocysteine (Hcy), cysteinglycine (CG), cysteine (Cys) and glutathione (GSH). The redox ratio was the ratio of reduced free and oxidized aminothiols in plasma. We investigated malonedialdehyde (MDA) and advanced oxidation protein products (AOPP), and ten single nucleotide polymorphisms of antioxidant enzymes. RESULTS: Patients had elevated oxidized free Hcy and Cys with associated low redox ratios - most pronounced in IGAN. Patients with IGAN had elevated AOPP and possibly MDA. Oxidized free Hcy and Cys with redox ratios were correlated to AOPP, MDA and proteinuria. Furthermore, there was an independent relationship to parathyroid hormone (PTH). IGAN had an elevated frequency of Val16Ala SNP rs4880, which influence the function of mitochondrial superoxide dismutase 2 (p = 0.03). CONCLUSIONS: Patients with ADPKD and IGAN have evidence of oxidative stress from stage 1 to 4 - most pronounced in IGAN. In patients, aminothiol redox biomarkers were correlated to AOPP, proteinuria and PTH, which are known prognostic markers in CKD. It may be possible that oxidative stress influences PTH dysregulation in CKD. The association between IGAN and the redox related variant allele rs4880(C) might indicate a new susceptibility locus for IGAN, but this needs verification.