Collecting dietary intake data is associated with challenges due to the subjective nature of self–administered instruments. Biomarkers may objectively estimate the consumption of specific dietary items or help assess compliance in dietary intervention studies. Our aim was to use a panel of plasma and urine biomarkers to assess the validity of self-reported dietary intake using a modified Mediterranean Diet Scale (mMDS) among firefighters participating in Feeding America’s Bravest (FAB), an MD cluster-randomized controlled trial. In our nested biomarker pilot study, participants were randomly selected from both the MD intervention group (n = 24) and the control group (n = 24) after 12-months of dietary intervention. At baseline data collection for the pilot study (t = 12-months of FAB), participants in the control group crossed-over to receive the MD intervention (active intervention) for 6-months. Participants in the intervention group continued in a self-sustained continuation phase (SSP) of the intervention. Food frequency questionnaires (FFQ), 13-item-mMDS questionnaires, 40 plasma fatty acids, inflammatory biomarkers and urinary hydroxytyrosol and tyrosol were analyzed at both time points. Spearman’s correlation, t-tests and linear regression coefficients were calculated using SAS software. Overall, the mMDS derived from the FFQ was highly correlated with the specific 13-domain-mMDS (r = 0.74). The concordance between the two questionnaires for low and high adherence to MD was high for all the participants in the parent trial (κ = 0.76). After 6 months of intervention in the pilot study, plasma saturated fatty acid decreased in both groups (active intervention: −1.3 ± 1.7; p = 0.002; SSP: −1.12 ± 1.90; p = 0.014) and oleic acid improved in the SSP (p = 0.013). Intake of olive oil was positively associated with plasma omega-3 (p = 0.004) and negatively with TNF-α (p < 0.001) at baseline. Choosing olive oil as a type of fat was also associated with higher levels of plasma omega-3 (p = 0.019) at baseline and lower TNF-α (p = 0.023) at follow up. Intake of red and processed meats were associated with lower serum omega-3 (p = 0.04) and fish consumption was associated with lower IL-6 at baseline (p = 0.022). The overall mMDS was associated with an increase in plasma omega-3 (p = 0.021). Good correlation was found between nutrient intake from the FFQ and the corresponding plasma biomarkers (omega-3, EPA and DHA). In this MD randomized controlled trial, some key plasma biomarkers were significantly associated with key MD diet components and the overall mMDS supporting the validity of the mMDS questionnaire as well as compliance with the intervention.

Olive oil phenols (OOPs) are associated with the prevention of many human cancers. Some of these have been shown to inhibit cell proliferation and induce apoptosis. However, no systematic comparative study exists for all the investigated compounds under the same conditions, due to difficulties in their isolation or synthesis. Herein are presented innovative methods for large-scale selective extraction of six major secoiridoids from olive oil or leaves enabling their detailed investigation. The cytotoxic/antiproliferative bioactivity of these six compounds was evaluated on sixteen human cancer cell lines originating from eight different tissues. Cell viability with half-maximal effective concentrations (EC50) was evaluated after 72 h treatments. Antiproliferative and pro-apoptotic effects were also assessed for the most bioactive compounds (EC50 ≤ 50 μΜ). Oleocanthal (1) showed the strongest antiproliferative/cytotoxic activity in most cancer cell lines (EC50: 9–20 μΜ). The relative effectiveness of the six OOPs was: oleocanthal (1) > oleuropein aglycone (3a,b) > ligstroside aglycone (4a,b) > oleacein (2) > oleomissional (6a,b,c) > oleocanthalic acid (7). This is the first detailed study comparing the bioactivity of six OOPs in such a wide array of cancer cell lines, providing a reference for their relative antiproliferative/cytotoxic effect in the investigated cancers.

Several individual olive oil phenols (OOPs) and their secoiridoid derivatives have been shown to exert anti-proliferative and pro-apoptotic activity in treatments of human cancer cell lines originating from several tissues. This study evaluated the synergistic anti-proliferative/cytotoxic effects of five olive secoiridoid derivatives (oleocanthal, oleacein, oleuropein aglycone, ligstroside aglycone and oleomissional) in all possible double combinations and of total phenolic extracts (TPEs) on eleven human cancer cell lines representing eight cell-culture-based cancer models. Individual OOPs were used to treat cells for 72 h in half of their EC50 values for each cell line and their synergistic, additive or antagonistic interactions were evaluated by calculating the coefficient for drug interactions (CDI) for each double combination of OOPs. Olive oil TPEs of determined OOPs’ content, originating from three different harvests of autochthonous olive cultivars in Greece, were evaluated as an attempt to investigate the efficacy of OOPs to reduce cancer cell numbers as part of olive oil consumption. Most combinations of OOPs showed strong synergistic effect (CDIs < 0.9) in their efficacy, whereas TPEs strongly impaired cancer cell viability, better than most individual OOPs tested herein, including the most resistant cancer cell lines evaluated.