Hydroxytyrosol glucuronides protect renal tubular epithelial cells against H2O2 induced oxidative damage

Hydroxytyrosol (2-(3′,4′-dihydroxyphenyl)ethanol; HT), the most active ortho-diphenolic compound, present either in free or esterified form in extravirgin olive oil, is extensively metabolized in vivo mainly to O-methylated, O-sulfated and glucuronide metabolites. We investigated the capacity of three glucuronide metabolites of HT, 3′-O-β-d-glucuronide and 4′-O-β-d-glucuronide derivatives and 2-(3′,4′-dihydroxyphenyl)ethanol-1-O-β-d-glucuronide, in comparison with the parent compound, to inhibit H2O2 induced oxidative damage and cell death in LLC-PK1 cells, a porcine kidney epithelial cell line. H2O2 treatment exerted a toxic effect inducing cell death, interacting selectively within the pro-death extracellular-signal relate kinase (ERK 1/2) and the pro-survival Akt/PKB signaling pathways. It also produced direct oxidative damage initiating the membrane lipid peroxidation process. None of the tested glucuronides exhibited any protection against the loss in renal cell viability. They also failed to prevent the changes in the phosphorylation states of ERK and Akt, probably reflecting their inability to enter the cells, while HT was highly effective. Notably, pretreatment with glucuronides exerted a protective effect at the highest concentration tested against membrane oxidative damage, comparable to that of HT: the formation of malondialdehyde, fatty acid hydroperoxides and 7-ketocholesterol was significantly inhibited.

► Hydroxytyrosol glucuronides were tested against H2O2 induced toxicity in renal cells. ► H2O2 induced cell death, interacting with intracellular signaling ERK 1/2 and Akt/PKB. ► Membrane lipid peroxidation was highlighted by hydroperoxydes and 7-keto detection. ► Contrary to hydroxytyrosol glucuronides did not enter the cells and act against death. ► Glucuronides protected cells against membrane oxidative damage as the parent compound.