br Introduction The chronic inflammation
Introduction The chronic inflammation is one of the leading events involved in the aetiology of many chronic-degenerative diseases including diabetes, atherosclerosis, arthritis and cancer (Coussens and Werb, 2002). Monocytes/macrophages lineage plays an important role during inflammation through the secretion of different soluble mediators such as prostaglandin E2 (PGE2) and tumour necrosis factor alpha (TNF-α). These mediators are involved both in the initiation and resolution of the inflammatory process, and play also a role in its maintenance during chronic diseases (Bradley, 2008). In fact, PGE2 is able to cause hyperalgesia and vasodilatation during acute inflammation but also to avoid long-term inflammatory effects by suppressing monocytes TNF-α production (James et al., 2001). TNF-α, “the master regulator of pro-inflammatory cytokines production”, acts modulating the PGE2 secretion and protecting host from pathogenic invasion (Parameswaran and Patial, 2010). Therefore, an accurate regulation of the production of these two mediators is very important for a physiological inflammation process. Some vegetal phenols are able to modulate the production of these two key inflammatory mediators (Richard et al., 2005, Shalini et al., 2012). Regarding olive oil phenols, it has been shown that both hydroxytyrosol (3,4-dihydroxyphenyl ethanol, DPE), the principal phenol alcohol present in olive oil, and the olive waste water containing different phenols, were able to reduce the TNF-α level both in vivo, in a murine animal model, and in vitro, in THP-1 human monocytic cell line (Bitler et al., 2005). Moreover, the inhibitory effect of DPE on PGE2 production was demonstrated in murine macrophages cell lines RAW264.7 and J774 (Richard et al., 2011, Maiuri et al., 2005). In addition, Trefiletti et al. (2011) have demonstrated that the 1-phenyl-6,7-dihydroxy-isochroman, an ortho-diphenol recently identified in extra virgin olive oil, was able to inhibit the production of both PGE2 and TNF-α in LPS-activated human monocytes. We have recently reported that in LPS-activated human monocytes DPE reduces both the COX-2 gene ro5 mg and PGE2 secretion while it increases the TNF-α accumulation in the culture medium (Rosignoli et al., 2013). In the present study we investigated whether these effects were related to each other attempting to clarify the possible mechanisms involved. Our findings demonstrated that: (a) DPE was able to increase the TNF-α gene expression in LPS activated monocytes; (aa) the reduced PGE2 accumulation is involved in the DPE-mediated increase of TNF-α production; (aaa) the DPE-mediated increase of TNF-α production was inhibited by forskolin, an activator of adenylate cyclase.
Materials and methods
Results and discussion The beneficial effects of olive oil on human health have been attributed to several biological activities of its phenols. In particular, the chemopreventive activities of olive oil phenols have been deeply investigated (Fabiani et al., 2006, Fabiani et al., 2011, Fabiani et al., 2012). Recently we have published a study demonstrating that DPE is able to modulate the production of some inflammatory mediators. In particular, we have observed that DPE dose-dependently (50–200μM) inhibits the COX-2 gene expression and PGE2 accumulation in the culture medium of LPS-activated human monocytes. In the same experimental conditions, it was demonstrated that DPE increased the TNF-α secretion in the culture medium as evaluated by an EIA kit (Rosignoli et al., 2013). In the present work we have investigated whether these effects were related to each other, clarifying the possible mechanisms involved. To this end, the experiments were carried out using 100μM of DPE since it was the dose showing the higher effect without citotoxicity on human monocytes.
Conclusions DPE and NSAIDs (rofecoxib and celecoxib) show a similar behavior in the modulation of PGE2 and TNF, although NSAIDs are efficient at lower doses. However, the experimental evidences reported in the present investigation suggest that DPE could be used as a natural drug for the treatment of inflammation. Furthermore, our findings indirectly suggest that cAMP may be involved also in the NSAIDs-dependent TNF increment. Finally, since the side effects of selective inhibitors of COX-2 may be mediated by the increment of TNF, it may be suggested that these adverse effect could be reduced, in vivo, by molecules that can regulate the levels of cAMP. Further experiments are underway in our lab to confirm in vivo the effects of DPE on the regulation of PGE2 and TNF-α production.