Differences in the Neuroprotective Effect of Orally Administered Virgin Olive Oil (Olea europaea) Polyphenols Tyrosol and Hydroxytyrosol in Rats

The neuroprotective effect of virgin olive oil (VOO) polyphenols has been related to their antioxidant effect. The main objective was to analyze how tyrosol and hydroxytyrosol contribute to the antioxidant and neuroprotective effects of VOO in a model of hypoxia-reoxygenation in rat brain slices. Rats were treated per os (po) (10 or 20 mg/kg/day) with hydroxytyrosol ethyl ether (HTEE), tyrosol ethyl ether (TEE), or 3,4-di-o-methylidene-hydroxytyrosol ethyl ether (MHTEE), used as a negative control for antioxidant effects. Lipid peroxidation was inhibited with HTEE, TEE, and MHTEE (from 5.0 +/- 1.5 to 2.6 +/- 1.5, 4.5 +/- 1.5, and 4.8 +/- 1.5 nmol/mg protein, respectively). However, all three compounds had similar neuroprotective effects: from 2.8 +/- 0.07 to 1.8 +/- 0.02 arbitrary units for HTEE, 1.4 +/- 0.09 arbitrary units for TEE, and 1.3 +/- 0.2 arbitrary units for MHTEE. All three compounds inhibited 3-nitrotyrosine production (from 3.7 +/- 0.3 to 1.2 +/- 0.03 nmol/0.1 g tissue for HTEE, 1.0 +/- 0.2 nmol/0.1 g tissue for TEE, and 1.3 +/- 0.1 nmol/0.1 g tissue for MHTEE), prostaglandin E2 production (from 55.7 +/- 2.2 to 46.4 +/- 1.9 pg/0.1 g tissue for HTEE, 24.7 +/- 1.3 pg/0.1 g tissue for TEE, and 27.6 +/- 2.6 pg/0.1 g tissue for MHTEE), whereas only HTEE inhibited IL1 beta production (from 35.7 +/- 1.5 to 21.6 +/- 0.8 pg/0.1 g tissue). Pearson correlation coefficients related neuroprotective effect with an antioxidant effect for HTEE (R = 0.72, p < 0.001), and inhibition of nitrosative stress (R = 0.78, 0.67, and 0.66 for HTEE, TEE, and MHTEE, respectively, p < 0.001) and inflammatory mediators (R = 0.72, 0.79, and 0.64 for HTEE, TEE, and MHTEE, respectively, p < 0.001) with all three compounds.