Markers of oxidative protein damage in plasma and urine of type 2 diabetic patients

This study aims to measure selected markers of oxidative protein damage (OPD) in patients with type 2 diabetes mellitus (T2DM) in order to estimate their utility as indicators of oxidative stress (OS) and to search for possible associations between them. The concentrations of advanced oxidation protein products (AOPP) and total sulphydryl (TSH) and reactive carbonyl (RCO) groups are measured in the plasma (P) and urine (U) of 60 patients and 22 controls using spectrophotometric methods. Significantly higher plasma concentrations of AOPP (P < 0.001), RCO groups (P < 0.01) and their P/U indexes (P < 0.001) as well as urinary levels of the RCO and TSH groups (P < 0.001) were observed in the diabetic patients compared with the controls. In contrast, the plasma levels and P/U index of the TSH groups were significantly lower (P < 0.001). A progressive increase in AOPP (plasma, urine and P/U index) in the course of albuminuria was noted, but significant differences among the subgroups of patients (with normoalbuminuria, microalbuminuria and macroalbuminuria) were found only in plasma. Plasma levels of all the measured parameters of OPD showed significant changes in T2DM patients compared with the control group. The largest increase was observed for AOPP. As the urinary AOPP concentration was not significantly different to that of the controls, it cannot be recommended as a marker of oxidative stress for monitoring the development of diabetic nephropathy. The P/U indexes did not provide any more information than the plasma concentrations of the studied markers.