In the present study, we have observed that the phenol fraction of VOO in vivo is able to repress the expression of several genes related to inflammation pathways in patients with MetS during postprandial period (Additional File 1). This finding draws interest since pro-inflammatory state remains as one component of MetS  and low-grade inflammation is often associated with endothelial dysfunction , which by itself is associated to the development of atherosclerosis .
The PTGS2 gene encodes prostaglandin-endoperoxide synthase 2 (COX-2), an inducible isozyme involved in prostaglandin biosynthesis using arachidonic acid as substrate. In macrophages, and other cells, COX-2 activity is rapidly increased by various stimuli, such as pro-inflammatory cytokine IL1β. Substantial evidence indicates that up regulated PTGS2 expression and prostaglandin synthesis indeed influence chronic inflammatory conditions . De la Puerta et al. observed that murine macrophages showed significantly reduced IL1β production and COX-2 activity after olive oil-enriched diet . Recently, it has been demonstrated that hydroxytyrosol, one of the most important phenol compounds found in virgin olive oil, attenuates in vitro LPS-induced transcription of PTGS2 . Our study showed that in vivo intake of phenol-rich virgin olive oil in humans is associated with a decreased expression of both IL1B and PTGS2, as compared to low-phenol olive oil intake. Those effects could contribute to reduced inflammation during postprandial state in agreement with anti-inflammatory effects observed after VOO-rich MD consumption [8, 9].
The cytokine-cytokine interaction pathway contains a network of proteins (chemokines and their receptors) involved in the recruitment and activation of leukocytes during inflammatory response. Expression of genes such as CCL3, CXCL1, CXCL2, CXCL3, CXCR4, IL1B, IL6, and OSM is described under-expressed after acute intake of phenol-rich olive oil in our intervention study on diet. CCL3 gene, which codes for macrophage inflammatory protein-1 (MIP-1), has been implicated in monocyte infiltration of adipose tissue, an action that could significantly influence a pro-inflammatory pattern within endothelial cells . CXCL1, CXCL2 (MIP2A), and further, CXCL3 (MIP2B) are genes for small and structurally related chemokines that regulate cell trafficking of various types of leukocytes through interactions with a subset of G protein-coupled receptors. Elgazar-Carmon et al. have demonstrated in mice that early neutrophil infiltration of adipose tissue may be mediated by CXCL1, a process that would precede macrophage infiltration after long-term consumption of a high-fat diet . IL6 encodes a cytokine which is secreted to serum and induces a transcriptional response involved in a wide variety of inflammation-associated conditions, including MetS and type 2 diabetes mellitus (T2DM) . On the other hand, it has been proposed that IL6 and OSM, which encodes oncostatin M, a growth regulator and member of the IL6 group of cytokines, can contribute to the increased cardiovascular risk in obese patients by up regulating PAI -1 in adipose tissue .
Activation of NF-κB and MAPK pathway, a cascade of phosphorilation events that result in the activation of transcription factors like CREB and AP-1, synergize for expression of inflammatory genes through coordinate bindings of transcription factors to κB and AP-1 sites which have been found together in the promoters of e.g. IL6 and TNF-α, and many other inflammatory genes . Chemokine repression found in our study could be consequence of phenols interaction with this inflammation signaling system, since expression of some genes involved in NF-κB/MAPK/AP-1 signaling pathways was also modulated after phenol-rich olive oil based breakfast. NF-κB is a transcription factor activated by pro-inflammatory cytokines  and oxidative stress mediators . Recently Pierce et al. have demonstrated that NF-κB activation is important in mediating vascular endothelial dysfunction in obese humans . The product of SGK1 gene, encoding a serum/glucocorticoid regulated kinase with a role in stress response and by itself being a downstream target for PI3K signaling, enhances nuclear NF-κB activity by phosphorylating an inhibitory kinase IKKα ; so repression on expression of SGK1 gene by olive oil phenols would decrease the NF-κB activation. In addition, NFKBIA gene, which encodes to IκBα, a member of an inhibitory IκB family that retains NFκB into the cytoplasm, remained under-expressed after acute intake of phenol-rich olive oil. It has been reported that NF-κB binds to the IκBα promoter in order to activate its transcription . Thus, this negative feedback mechanism results in rapid cycles of inhibition and stimulation of NF-κB where a decrease on NF-κB activation is accompanied by a reduction on NFKBIA gene expression, as observed in our results. The hypothesis that NF-κB activation is decreased by olive oil phenols is also supported by two in vivo studies which showed reduced NF-κB activation after olive oil consumption [8, 9]. Additionally, in vitro studies showing attenuated NF-κB activation by resveratrol support the hypothesis that this pathway employs a shared mechanism by which polyphenols reduce expression of genes encoding inflammatory cytokines and adhesion molecules .
After intake of virgin olive oil with high content in phenolic compounds we found a decreased postprandial expression of DUSP1 and DUSP2. Those genes encode dual serine-threonine phosphatases, which down regulate members of p38, MAPK/ERK and SAPK/JNK, the three final effectors of the MAPK pathway . In addition, TRIB1, another gene repressed by phenol-rich olive oil, is involved in MAPK signaling, participating in the activation of ERK proteins  and being up regulated in human atherosclerotic plaques . Thus, reduction of TRIB1 expression by olive oil phenols could promote decreased ERK activation. This observation agrees with in vitro studies demonstrating that phenol compounds of green tea down regulate PTGS2 expression by decreasing ERK and p38 MAPK activation . Our results allow us to hypothesize that olive oil phenols influence activation of AP-1, which consists of a variety of heterodimers of Jun, Fos and activating transcription factor families , by means of two different mechanisms: a) one direct, involving repression of JUN, JUNB and FOSB as observed after phenol-rich olive oil intake; and/or b) another one indirect, through MAPK pathway, where the relative intensity and duration of activation determine the type of response.
Lastly, biomedical literature and text mining tasks were performed to identify interactions of differentially expressed genes in PBMCs as response to phenol-rich VOO with conditions clustered around MetS such as obesity, hypertension, dyslipemia, hyperglycemia, or T2DM. Recently, Chen et al. have described a macrophage-enriched gene network (MEGN) of ~1237 genes referred as having causal relationship with complex-disease traits associated with MetS . Thirteen genes share our set of differentially expressed genes in PBMCs after acute intake of phenol-rich olive oil and MEGN: JUN, RGS1, CXCL2, ANXA3, RASGEF1B, CD83, CA2, EGR2, DIAPH3, CCL3, and TLR7, PSAP and IFIT3. De Mello et al. assessed individuals with both impaired glucose metabolism and MetS on how long-term weight loss affects expression of cytokines in PBMCs. Weight reduction resulted in a decrease in of IL1B expression . Kaiser et al. showed by microarrays analysis in PBMCs a set of 22 over-expressed genes in T1DM and T2DM compared to healthy subjects . Interestingly, 8 of the identified 22 over-expressed genes in T2DM were repressed by olive oil phenols, according to our intervention study (IL1B, EGR2, EGR3, PTGS2, FOSB, CXCL1, SGK, and TRIB1). In addition, PBEF1, another gene involved in the pathogenesis of T2DM , was also found repressed after consumption of phenols-rich olive oil. Taken together, this finding could lead to potential therapeutic implications in T2DM.