Glycaemic control is the main focus of managing diabetes and its complications. Hyperglycaemia induces oxidative stress favouring cellular damage and subsequent diabetic complications. The present study was conducted to compare the plasma total antioxidant capacity (TAC) and individual antioxidant marker antioxidant status of type 2 diabetics (T2D) with good ((+) GC) and poor ((-) GC) glycaemic control with prediabetic (PDM) and normoglycaemic (NG) individuals. T2D (n=147), PDM (n=47), and NGC (n=106) were recruited as subjects. T2D and PDM had lower plasma TAG than NG subjects. T2D and PDM had significantly higher GPx activity and plasma MDA concentrations than NG. PDM showed the highest SOD activity. T2D (-) GC showed significantly elevated GPx activity and higher MDA level and significantly lower SOD activity among all study groups. Lower plasma TAC and higher plasma MDA indicate the presence of oxidative stress in T2D and PDM. Elevated GPx activity in T2D, PDM, and particularly in T2D (-) GC suggests a compensatory response to counteract excess lipid peroxidation in the hyperglycaemic state. Decline in SOD activity advocates the presence of glycation and excess lipid peroxidation in T2D.

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ObjectiveOxygen radical absorbance capacity (ORAC) assay measures the quenching of fluorescent probe by peroxyl radicals. Antioxidants present in biological systems block the quenching of fluorescence probe. We experienced the dynamic quenching of fluorescein, the fluorescence probe used in ORAC assay by the human plasma while plasma ORAC assay was optimized. Therefore, for the first time, we report the quenching of fluorescein by human plasma at the initial point of ORAC assay.ResultsAqueous whole and non-protein fractions of plasma were used in the analysis. Since the both fractions showed a similar pattern of quenching at the initial stage, quenched percentage of fluorescein was calculated and added to each sample in subsequent analysis. Addition of extra 20% fluorescein allowed plasma samples to quench the required amount of fluorescein and follow the normal decay curves afterwards. Further, change of fluorescein quenching (ΔF/F0) disclosed a dose dependent linear relationship with plasma (R2 = 0.8). It can be speculated that dynamic quenching exhibited by human plasma biomolecule/s at the initial stage would be of non-protein aqueous phase molecule/s. We suggest initiating further studies to detect, identify and quantify the fluorescein quenching biomolecules present in human plasma for further improvements in plasma ORAC assay.

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