Ferric Reducing Ability of Tears in Healthy Subjects—Diurnal Variation and Dependence on Defined Demographic Data

A comparison of native and non-urate Total Antioxidant Capacity of fasting plasma and saliva among middle-aged and older subjects

OBJECTIVES

As plasma and salivary total antioxidant capacity (TAC) is mainly contributed by uric acid (UA), the present study measures non-urate TAC (Nu-TAC). The aim of the study was to correlate plasma native TAC, Nu-TAC and UA with their salivary analogues, and compare the UA contribution in both body fluids using two different methods.

METHODS

The study involved 55 middle-aged and older subjects (66.7 ± 4.5 years). TAC was determined simultaneously with two methods (ferric reducing ability of plasma - FRAP, 2.2-diphenyl-1-picryl-hydrazyl - DPPH and countertypes for saliva - FRAS and DPPHS test), with and without UA (native TAC and Nu-TAC, respectively). Plasma UA and salivary UA (SUA) were assessed.

RESULTS

Subjects with increased FRAP, DPPH and UA had higher FRAS, DPPHS and SUA, respectively (P < 0.05). Plasma Nu-TAC indices did not correlate with salivary Nu-TAC. The contribution of UA to the plasma and salivary DPPH tests was similar: 75.7 ± 10.3% and 75.2 ± 14.0%, respectively. However, the contribution of UA to FRAS was higher than that for FRAP (71.6 ± 13.9% vs. 64.0 ± 8.1%; P < 0.001).

DISCUSSION

Our findings suggest that saliva is a good predictor for native plasma TAC but not for Nu-TAC. UA level is comparably dominant in saliva and in plasma according to DPPH, but lower in plasma according to FRAP.

Non-enzymatic antioxidant capacity assays: Limitations of use in biomedicine

The 'Total antioxidant capacity' (TAC) is a parameter frequently used for characterization of food products and of the antioxidant status of the body. This mini-review shows shortcomings of TAC assays and points of concern that should be considered when performing and interpreting results of such assays. The term TAC is not optimal since the assay measures only part of antioxidant capacity, usually excluding enzymatic activities. Antioxidant and oxidant-regenerating enzymes in blood cells and the blood vessel wall have a profound impact on the antioxidant properties of blood plasma, which is not reflected in the in vitro assays of isolated plasma. The term 'Non-enzymatic antioxidant capacity' (NEAC) is suggested as more relevant than TAC. NEAC is estimated by various methods, which yield different values and results obtained using different methods do not always show satisfactory correlation. One reason for the discrepancy of results is the use of different oxidants in NEAC assays. The use of hydroxyl radical as the oxidant is not recommended in view of the high and non-specific reactivity of this species.

Ferric reducing antioxidant power and square wave voltammetry for assay of low molecular weight antioxidants in blood plasma: performance and comparison of methods

The purpose of the present study was to employ two methods—square wave voltammetry (SWV) performed on screen printed sensors and ferric reducing antioxidant power (FRAP)—as suitable tools for the assay of low-molecular-weight antioxidants (LMWAs). LMWAs were assayed by both methods and the resulting data were statistically compared. Plasma samples from five Cinereous vultures accidentally intoxicated with lead were used to represent real biological matrices with different levels of LMWAs. Blood was collected from the birds prior to and one month after treatment with Ca-EDTA. SWV resulted in two peaks. The first peak, with the potential value of 466 ± 15 mV, was recognized as ascorbic and uric acids, while the second one (743 ± 30 mV) represented glutathione, tocopherol, ascorbic acid and in a minor effect by uric acid, too. Contribution of individual antioxidants was recognized by separate assays of LMWA standards. Correlation between peaks 1 and 2 as well as the sum of the two peaks and FRAP was analysed. While peak 1 and the sum of peaks were in close correlation to FRAP results (correlation coefficient of 0.97), the relation between peak 2 and FRAP may be expressed using a correlation coefficient of 0.64. The determination of thiols by the Ellman assay confirmed the accuracy of SWV. Levels of glutathione and other similar structures were stable in the chosen model and it may be concluded that SWV is appropriate for assay of LMWAs in plasma samples. The methods employed in the study were advantageous in minimal sample volume consumption and fast acquisition of results.