Oxidative stress and proinflammatory cytokines are factors affecting multiple sclerosis (MS) disease progression. Oleacein (OLE), an olive secoiridoid, possesses powerful antioxidant and anti-inflammatory activities, which suggests its potential application to treat neuroinflammatory disorders. Herein, we investigated the impact of OLE on the main clinic-pathological features of experimental autoimmune encephalomyelitis (EAE), an animal model for MS, including paralysis, demyelination, central nervous system (CNS) inflammation/oxidative stress and blood-brain barrier (BBB) breakdown.
Methods: Mice were immunized with the myelin oligodendrocyte glycoprotein peptide, MOG35-55, to induce EAE, and OLE was administrated from immunization day. Serum, optic nerve, spinal cord and cerebellum were collected to evaluate immunomodulatory activities at a systemic level, as well as within the CNS. Additionally, BV2 microglia and the retinal ganglion cell line RGC-5 were used to confirm the direct effect of OLE on CNS-resident cells.
Results: We show that OLE treatment effectively reduced clinical score and histological signs typical of EAE. Histological evaluation confirmed a decrease in leukocyte infiltration, demyelination, BBB disruption and superoxide anion accumulation in CNS tissues of OLE-treated EAE mice compared to untreated ones. OLE significantly decreased expression of proinflammatory cytokines (IL-13, TNFα, GM-CSF, MCP-1 and IL-1β), while it increased the anti-inflammatory cytokine IL-10. Serum levels of anti-MOG35-55 antibodies were also lower in OLE-treated EAE mice. Further, OLE significantly diminished the presence of oxidative system parameters, while upregulated the ROS disruptor, Sestrin-3. Mechanistically, OLE prevented NLRP3 expression, phosphorylation of p65-NF-κB and reduced the synthesis of proinflammatory mediators induced by relevant inflammatory stimuli in BV2 cells. OLE did not affect viability or the phagocytic capabilities of BV2 microglia. In addition, apoptosis of RGC-5 induced by oxidative stressors was also prevented by OLE.
Conclusion: Altogether, our results show that the antioxidant and anti-inflammatory OLE has neuroprotective effects in the CNS of EAE mice, pointing out this natural product as a candidate to consider for research on MS treatments.
Keywords: EAE; EVOO; cytokines; inflammation; multiple sclerosis; oleacein; oxidative stress; polyphenol; secoiridoid.