Hydroxytyrosol (HT) is the component primarily responsible for the
neuroprotective effect of extra virgin
olive oil (EVOO). However, it is less effective on its own than the demonstrated
neuroprotective effect of EVOO, and for this reason, it can be postulated that there is an interaction between several of the
polyphenols of EVOO. The objective of the study was to assess the possible interaction of four EVOO
polyphenols (HT,
tyrosol, dihydroxyphenylglycol, and
oleocanthal) in an experimental model of
hypoxia-reoxygenation in rat brain slices. The
lactate dehydrogenase (LDH) efflux, lipid peroxidation, and
peroxynitrite production were determined as measures of cell death, oxidative stress, and nitrosative stress, respectively. First, the
polyphenols were incubated with the brain slices in the same proportions that exist in EVOO, comparing their effects with those of HT. In all cases, the cytoprotective and
antioxidant effects of the combination were greater than those of HT alone. Second, we calculated the concentration-effect curves for HT in the absence or presence of each
polyphenol.
Tyrosol did not significantly modify any of the variables inhibited by HT. Dihydroxyphenylglycol only increased the cytoprotective effect of HT
at 10 µM, while it increased its
antioxidant effect at 50 and 100 µM and its inhibitory effect on
peroxynitrite formation at all the concentrations tested.
Oleocanthal increased the cytoprotective and
antioxidant effects of HT but did not modify its inhibitory effect on nitrosative stress. The results of this study show that the EVOO
polyphenols DHPG and OLC increase the cytoprotective effect of HT in an experimental model of
hypoxia-reoxygenation in rat brain slices, mainly due to a possibly synergistic effect on HT's
antioxidant action. These results could explain the greater
neuroprotective effect of EVOO than of the
polyphenols alone.