*3.3. The Role of Urolithin A as a Direct Free Radical Scavenger*

The direct antioxidant and reducing activities of urolithin A were measured by different free radical scavenging methods. To verify this fact, reference antioxidants such as gallic acid and ascorbic (vitamin C) acid were also tested and IC50 values were calculated (Figure 8).

The antioxidant activity measured by the ORAC assay was 13.1 μmol TE/mg for urolithin A; this result reflects a great antioxidant capacity to neutralize peroxyl radicals compared to other high-content urolithin A extracts, such as pomegranate, the activity of which was 0.49 μmol TE/mg.

**Figure 8.** *Cont.*


**Figure 8.** Antioxidant activity of urolithin A against physiological (superoxide) and synthetic (DPPH) radicals. IC50 were calculated by non-linear regression. (**A**) Urolithin A scavenges superoxide radicals generated by the xanthine/xanthine oxidase system. (**B**) DPPH inhibition of urolithin A. Gallic acid and ascorbic acid were used as reference antioxidants.

On the other hand, both in the inhibition of superoxide radicals and DPPH, urolithin A showed a dose-dependent curve reaching the maximum inhibition (100%). The reference compounds achieved better activity in terms of potency. IC50 values were 0.26 ± 0.21 μM for gallic acid and 5.01 ± 5.01 μM for urolithin A (in the superoxide radical), while they were 3.10 ± 3.11 μM for gallic acid, 14.81 ± 14.90 μM for ascorbic acid, and 152.66 ± 35.01 μM for urolithin A (DPPH radical).
