Impact of pharmacokinetic enhancement strategies on the antimicrobial and antioxidant activities of hydroxytyrosol

Hydroxytyrosol (HTyr), a plant-derived phenolic compound found in Olea europaea L. products and by-products, is well-known for its antioxidant activity and a wide range of biological effects, including anti-inflammatory, anticancer, antiviral, cardioprotective, neuroprotective, and antibacterial properties. However, due to its high hydrophilicity, HTyr exhibits unfavorable pharmacokinetic properties, preventing its potential therapeutic use. Various strategies can be employed to address these limitations. In this study, we evaluated the effect of two specific approaches on the HTyr antimicrobial and antioxidant activities: chemical modification of HTyr by lipophilization of the alcoholic moiety and encapsulation in liposomes. Based on our experience in the synthesis and biological activities of HTyr derivatives, the attention was focused on HTyr oleate (HTyr-OL), having a C-18 unsaturated alkylic chain responsible for an increased lipophilicity compared to HTyr. This structural feature enhanced antimicrobial activity against both tested strains of S. aureus, ATCC 25923 (wild-type strain) and ATCC 33591 (MRSA), and comparable antioxidant activity against two different radicals, Galvinoxyl radical and 1,1-diphenyl-2-picrylhydrazyl radical. Moreover, liposomes as delivery systems for HTyr and HTyr-OL were developed using both natural and synthetic amphiphiles, and the impact of encapsulation on their activities was further investigated. The experimental results showed that the antimicrobial properties of HTyr and HTyr-OL against S. aureus strains were not enhanced after encapsulation in liposomes, while the high antioxidant activity of HTyr-OL was preserved when conveyed in liposomes.