Effect of polyphenolic extracts from leaves of Mediterranean forage crops on enzymes involved in the oxidative stress, and useful for alternative cancer treatments

In this investigation, we report the ability of polyphenolic extracts from leaves of Lotus ornithopodioides, Hedysarum coronarium, Medicago sativa, and Cichorium intybus to affect the activity of key enzymes involved in the cellular redox balance, such as catalase (CAT) and xanthine oxidase (XO). The tested extracts presented a different polyphenol composition; in fact, while L. ornithopodioides and H. coronarium extracts mainly contained condensed tannins (HcCT and LoCT, respectively), M. sativa, and C. intybus extracts were richer in flavonoids (CiF and MsF, respectively). These condensed tannins (CTs) or flavonoids-containing extracts, had a similar although moderate inhibition strength towards CAT (IC50 28–53 μM) with mixed inhibition mechanisms. On the other hand, among the four extracts, MsF caused a clear dose-dependent reduction of the XO activity (IC50 15 μM), followed at a distance by CiF (IC50 83 μM). Interestingly, both flavonoid-containing extracts displayed a competitive inhibition mechanism. Vice versa, those containing CT resulted almost ineffective in the inhibition of XO activity. Finally, we evaluated the effects exerted by these plant extracts on the viability of human gastric cancer cells. Using MKN-28 and AGS as a cellular model for this investigation, we found that, among the four extracts, MsF was endowed with the highest cytotoxicity, thus suggesting its putative use in anticancer treatments.