Nigella sativa Oil Reduces LPS-Induced Microglial Inflammation: An Evaluation on M ₁/M ₂ Balance

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 (M ₁/M ₂) 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 (M ₁/M ₂) in the presence of LPS as a model of neuroinflammation.

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.

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).

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.