Curcumin Suppresses Neuroinflammation; a Systematic Review of Preclinical Studies

Curcumin, the active ingredient of turmeric, has showed anti-inflammatory properties in many disorders including esophagitis, rheumatoidarthritis and ulcerative colitis. However, poor bioavailability of curcumin in the brain has limited its use in neuroinflammatory disorders. Meanwhile, the protective actions of curcumin against some neuroinflammatory disorders have been documented, including Parkinson s disease and depression. The aim of this study was to review in vivo and in vitro studies that investigated the anti-neuroinflammatory properties of curcumin. We performed a systematic review to comprehensively assess the effects of curcumin in experimental models of neuroinflammation. We searched the PubMed, Cochrane and Scopus databases up to April 2019. Search keywords were curcumin,turmeric and neuroinflammation. Ninety-four studies met our inclusion criteria. Irrelevant titles were excluded and eventually 29 articles were reviewed. Only in one of these articles, curcumin did not show any anti-neuroinflammatory effect. Eight articles demonstrated protective effect of curcumin against Alzheimer s disease. In two of these articles, Nano particles were used to increase the poor bioavailability of curcumin, which was successful. Apigenin, showed synergistic effect with curcumin against Alzheimer s disaese. In addition, resveratrol and piperine showed synergistic effects with curcumin. Piperine increased the protective effects of curcumin in models ofdepression and Parkinson s disease. Furthermore, curcumin inhibited the neuroinflammation in models of Parkinson s disease (four articles), radiculopathy (two articles), chronic alcohol-induced cognitive deficits (two articles), and epilepsy (one articles). Suppressing NF- κB signalling pathways in activated microglial cells, inhibiting oxidative-nitrosative stress, and protecting axons from degeneration, were the main mechanisms underlying neuroprotective and anti-neuroinflammatory properties of curcumin. Conclusion: current preclinical evidences show that curcumin has significant antineuroinflammatory and neuroprotective properties.Novel delivery systems, especially Nano technology,has improved its poor bioavailability. Hence, curcumin can be a potential candidate for developing new antineuroinflammatory drugs. Future clinical studies are required to confirm these results.