Potential therapeutic use of olive leaf extracts obtained from the olive tree (Olea europaea) against Helicobacter pylori infection

H. pylori is one of the major human pathogens infecting approximately 50% of the world's population. Its treatment is based on the combined use of different antibiotics. In recent years, the number of antibiotic resistant strains have been increased. Therefore, new alternative therapies are required for H. pylori treatment. The aim of the present work was to evaluate the antibacterial, anti-inflammatory and antioxidant effect of olive leaf extracts against antibiotics resistant H. pylori strains. Two olive leaf extracts were used: E1, enriched in hydroxytyrosol (10%); and E2, enriched in oleuropein (20%). E1 extract showed a bactericidal effect for all evaluated H. pylori strains (7/7), while the E2 extract was bactericidal for three of the studied strains (3/7) and caused a decrease of around 1 log in colony forming units (CFU) for the rest of the strains. About antioxidant activity, both extracts reduced up to 33% the production of intracellular reactive oxygen species in human gastric AGS cells infected by H. pylori, being the antioxidant activity of the E2 extract higher than E1. Finally, E1 and E2 extracts showed anti-inflammatory activity, reducing IL-8 pro-inflammatory factor secretion by infected-AGS cells in a range of 20-74% and 71-93%, respectively. Therefore, the olive leaf extracts could be consider as a potential new candidate for H. pylori treatment, providing an alternative for the 20% of infected people with symptoms for whom antibiotic treatments are not effective. Furthermore, the recycling of olive industry by-products could also contribute to its revalorization, reducing also the environmental impact.