Nigella sativa Oil Reduces LPS-Induced Microglial Inflammation: An Evaluation on M1/M2 Balance

Abstract

Objectives. The immune system plays a critical defence role against infections, injuries, and carcinogenic stimuli. As the macrophages of the brain resides in the innate immune system, microglia and their polarisation (M1/M2) play regulatory roles in inflammation in CNS, such as Parkinson’s, Alzheimer’s, dementia complex, and multiple sclerosis. Nigella sativa belongs to the Ranunculaceae family and has different anti-inflammatory and antioxidant effects. We conducted this study to evaluate the anti-inflammatory and protective properties of N. sativa oil (NSO) on the microglial cells and their polarisation (M1/M2) in the presence of LPS as a model of neuroinflammation. Methods. The protective effects of NSO (10–40 µg/ml) were studied on the LPS-induced microglial cells, and the levels of tumour necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, prostaglandin E2 (PGE2), and IL-10 were evaluated using both ELISA and gene expression methods. The levels of cyclooxygenase-2 (COX-2), inducible NOS (iNOS), and arginase-1 (Arg1) were also evaluated using the real-time PCR method. In addition, nitrite oxide (NO) and urea were measured using biochemical methods. Results. NSO decreased LPS-induced toxicity at all doses ($P$ < 0.001). NSO (10–40 μg/ml) also significantly reduced the levels of TNF-α, PGE2, IL-1β, and IL-6 in the presence of LPS ($P$ < 0.01 to 0.001). Pretreatment with NSO attenuated the levels of iNOS but increased Arg1 ($P$ < 0.001). The ratio of iNOS/Arg1 was also decreased in the presence of NSO ($P$ < 0.001) than that of the LPS group ($P$ < 0.001). Conclusion. NSO attenuated LPS-induced inflammation and increased microglia’s anti-inflammatory status. These results may prove that NSO is potentially an immunomodulator for various neurodegenerative diseases by M1 phenotype dominancy, such as Alzheimer’s and Parkinson’s diseases.