Oleuropein (OLE), a main constituent of olive, displays a pleiotropic beneficial dynamic in health and disease, based mainly on its antioxidant and hypolipidemic properties, and its capacity to protect myocardium during ischemia. Furthermore, OLE activates peroxisome proliferator-activated receptor (PPARα) in neurons and astrocytes, providing neuroprotection against noxious biological reactions that are induced following cerebral ischemia. Current study investigated the effect of OLE in the regulation of various neural plasticity indices, emphasizing the role of PPARα. For this purpose, 129/Sv wild-type (WT) and Pparα-null mice were treated with OLE for three weeks. The present findings revealed that chronic treatment with OLE up-regulated the brain-derived neurotrophic factor (BDNF) and its receptor TrkB in the prefrontal cortex (PFC) of mice via activation of ERK1/2, AKT and PKA/CREB signaling pathways. No similar effects were observed in the hippocampus. The OLE-induced effects on BDNF and TrkB appear to be mediated by PPARα, because no similar alterations were observed in the PFC of Pparα-null mice. Notably, OLE did not affect the neurotrophic factors NT3 and NT4/5 in both brain tissues. Fenofibrate though, a selective PPARα agonist, up-regulated BDNF and NT3 in the PFC of mice, whereas the drug induced NT4/5 in both brain sites tested. Interestingly, OLE provided neuroprotection in differentiated human SH-SY5Y cells against β-amyloid and H2O2 toxicity independently from PPARα activation. In conclusion, OLE and similar drugs acting either as PPARα agonists or via PPARα independent mechanisms could improve synaptic function/plasticity mainly in the PFC and to a lesser extent in the hippocampus, thus beneficially affecting cognitive functions.

Neurotoxicity belongs to the leading factors inducing neurodegeneration-related diseases, such as Alzheimer’s (AD) and Parkinson’s disease. In particular, accumulation of β-amyloid proteins in the brain, a hallmark in AD, induces oxidative stress and neurotoxicity. The use of antioxidants in AD is not sufficiently effective and other pharmacological approaches tested failed to cure, prevent or retard the progression of the disease. Clinical studies indicated that several medicinal plants display beneficial effects by improving memory and cognitive functions of patients with mild and moderate AD. In this study, the potential antioxidant and neuroprotective properties of Olea europea, Crocus sativus and Salvia spp extracts, as well as their main active compounds on cell viability was evaluated using an in vitro model of AD, the differentiated human SH-SY5Y neuroblastoma cells to cholinergic neurons. Their effects were assessed against the H2O2- and β-amyloid- induced cell toxicity using the MTS test. Current findings indicated that Salvia fruticosa, S. officinalis, S. argentea leaf extracts and the active compounds, oleuropein, trans-crocin-3 and -4 display significant dose-dependent antioxidant and neuroprotective properties. It is of note though that the total phenolic fragment of Olea europea leaf extract includes several toxic compounds, such as oleocanthal, that markedly reduce cell viability and exacerbate the H2O2- and Aβ-induced cell toxicity. In addition, the Crocus sativus hydrophilic and diethyl ether extracts and all their active compounds tested markedly increased the H2O2-induced cell toxicity. In conclusion, the medicinal plants tested contain several compounds displaying dose-dependent effects against H2O2- and Aβ-induced neurotoxicity and could be used in AD, but they also contain several neurotoxic agents.

Oleuropein (Ole), a secoiridoid glucoside present in Olea europaea leaves, gained the interest of many scientists thanks to its several biological properties, including the anticancer one. We verified whether Ole might potentiate cytotoxicity of conventional drugs used to treat melanoma, disclosing new potential therapeutic strategy. We tested the cytotoxic action of Ole alone or in combination with chemotherapeutics on A375 human melanoma cells. We found that Ole was able, at a dose of 500 μM, to stimulate apoptosis in melanoma cells, while at a non-toxic dose of 250 μM, it affected cell proliferation and induced the downregulation of pAKT/pS6 pathway. 250 μM Ole did not potentiate the effect of Vemurafenib (PLX4032), but it succeeded in increase the cytotoxic effect of Dacarbazine (DTIC). The mayor effect was found in the association between Ole and Everolimus (RAD001), also on PLX4032-resistant BRAF melanoma cells, possibly cooperating in the inhibition of pAKT/pS6 pathway. Of interest, an olive leaf extract enriched in equimolar Ole was more effective and able to further improve DTIC and, particularly, RAD001 efficacy on BRAF melanoma cells than Ole alone. Therefore, Ole represents a natural product able to potentiate a wide array of chemotherapeutics against BRAF melanoma cells affecting pAKT/pS6 pathway.

Abstract: Oleuropein, the major compound of olive leaves, has been reported to exert numerous pharmacological properties, including anti-inflammatory, antidiabetic and anticancer. The purpose of this study is to evaluate, for the first time, the effect of oleuropein-rich leaf extracts (ORLE) in already-developed colon tumours colon tumours arising in an Apc (adenomatous polyposis coli) mutated PIRC rats (F344/NTac-Apcam1137). Here, we were able to investigate in parallel the anti-cancer effect of ORLE, both in vivo and in vitro, and its anti-inflammatory effect on macrophages, which represents a critical and abundant population in most solid tumours microenvironment. We found that in vivo ORLE treatment promoted apoptosis and attenuated iNOS activity both in colon tumours as in peritoneal macrophages of PIRC rats. We confirmed in vitro using primary RAW264.7 cells: ORLE reduced iNOS activity in parallel with COX-2 and pro-inflammatory cytokines, such as IL-1, IL-6 and TGF-. These findings suggest that ORLE possess a strong anti-inflammatory activity, which could be crucial for dampening the pro-tumourigenic activity elicited by a chronic inflammatory state generated by either tumour cells or tumour-associated macrophages.