Fatty Acid Hydroxytyrosyl Esters: Structure/Antioxidant Activity Relationship by ABTS and in Cell-Culture DCF Assays

Abstract

A large series of hydroxytyrosyl esters of C2-C18 fatty acids with increasing lipophilicity was prepared by a new highly efficient method based on acylation of methylorthoformate-protected hydroxytyrosol. All products were tested for relative antioxidant effect using ABTS assays in ethanolic medium and DCF assays in L6 cells. No linear correlation between lipophilicity and antioxidant effect was found. ABTS assays showed a growing antioxidant capacity, with respect to hydroxytyrosol, only for medium-sized ester chains (C4-C10) and a nearly constant capacity for the higher homologues. This has been rationalized by molecular dynamics experiments in terms of partial shielding of the catecholic hydroxyls by long-chain esters. A similar and dose-dependent pattern was observed in DCF assays in L6 cells, but a sharp antioxidant activity drop resulted for long-chain esters, probably due to membrane entrapment.

Protection of Cells against Oxidative Stress by Nanomolar Levels of Hydroxyflavones Indicates a New Type of Intracellular Antioxidant Mechanism

“…The method used was a standard assay based on the intracellular fluorescent probe DCF [39]–[42]. For L6 myoblasts the medium was discarded and cells were washed twice with 5 ml phosphate buffered saline (PBS) containing 5.0 mM glucose (PBS-glucose), at 37°C.…”

Carbon nanotubes supported tyrosinase in the synthesis of lipophilic hydroxytyrosol and dihydrocaffeoyl catechols with antiviral activity against DNA and RNA viruses

“…18 For example, the limited accessibility of highly hydrophilic catechols to specific intracellular targets has been improved by the synthesis of lipophilic derivatives possessing long carbon alkyl side chains. 19,20,21 In the case of bioactive hydroxytyrosol and dihydrocaffeic acid derivatives, 22,23 which are characterized by the concomitant presence of alcoholic and ortho-diphenol groups, 24,25 the side-chain functionalization requires expensive and tedious protection/deprotection sequences. As an alternative, we described the synthesis of lipophilic catechols by selective oxidation of side-chain functionalized phenol derivatives, using tyrosinase supported on Eupergit C250L resin (Tyr/ECM), by sequential deposition of alternatively charged poly(allylamine hydrochloride) (PAH) and polystyrene sulfonate (PSS).…”

Biological Properties of Hydroxytyrosol and Its Derivatives

“…This confirms that antioxidant capacity does not depend only on lipophilicity. A possible explanation could be related to the fact that the conformational freedom of the ester chain increases with the acyl chain length, and this could result in folded structures in which catechol hydroxyls are shielded (Tofani et al, 2010;Pereira-Caro et al, 2009;Medina et al, 2009). …”

“…Dichlorodihydrofluorescein (DCF) fluorometric assay on whole cells, carried out to check the antioxidant activity of a large serie of hydroxytyrosyl esters (Tofani et al, 2010) on rat muscle cells, showed that hydroxytyrosol esters had a better antioxidant activity compared to HT due to the better penetration into the cells of the lipophilic derivatives.…”