Neuroinflammation and microglial activation are pathological markers of a number of central nervous system (CNS) diseases. Chronic activation of microglia induces the release of excessive amounts of reactive oxygen species (ROS) and pro-inflammatory cytokines. Additionally, chronic microglial activation has been implicated in several neurodegenerative diseases, including Alzheimer's disease and Parkinson's disease. Thymoquinone (TQ) has been identified as one of the major active components of the natural product Nigella sativa seed oil. TQ has been shown to exhibit anti-inflammatory, anti-oxidative, and neuroprotective effects. In this study, lipopolysaccharide (LPS) and interferon gamma (IFNγ) activated BV-2 microglial cells were treated with TQ (12.5 μM for 24 h). We performed quantitative proteomic analysis using Orbitrap/Q-Exactive Proteomic LC-MS/ MS (Liquid chromatography-mass spectrometry) to globally assess changes in protein expression between the treatment groups. Furthermore, we evaluated the ability of TQ to suppress the inflammatory response using ELISArray™ for Inflammatory Cytokines. We also assessed TQ's effect on the gene expression of NFκB signaling targets by profiling 84 key genes via real-time reverse transcription (RT2) PCR array. Our results indicated that TQ treatment of LPS/IFNγ-activated microglial cells significantly increased the expression of 4 antioxidant, neuroprotective proteins: glutaredoxin-3 (21 fold; p < 0.001), biliverdin reductase A (15 fold; p < 0.0001), 3-mercaptopyruvate sulfurtransferase (11 fold; p < 0.01), and mitochondrial lon protease (> 8 fold; p < 0.001) compared to the untreated, activated cells. Furthermore, TQ treatment significantly (P < 0.0001) reduced the expression of inflammatory cytokines, IL-2 = 38%, IL-4 = 19%, IL-6 = 83%, IL-10 = 237%, and IL-17a = 29%, in the activated microglia compared to the untreated, activated which expression levels were significantly elevated compared to the control microglia: IL-2 = 127%, IL-4 = 151%, IL-6 = 670%, IL-10 = 133%, IL-17a = 127%. Upon assessing the gene expression of NFκB signaling targets, this study also demonstrated that TQ treatment of activated microglia resulted in > 7 fold down-regulation of several NFκB signaling targets genes, including interleukin 6 (IL6), complement factor B (CFB), chemokine (C–C motif) ligand 3 (CXCL3), chemokine (C–C) motif ligand 5 (CCL5) compared to the untreated, activated microglia. This modulation in gene expression counteracts the > 10-fold upregulation of these same genes observed in the activated microglia compared to the controls. Our results show that TQ treatment of LPS/IFNγ-activated BV-2 microglial cells induce a significant increase in expression of neuroprotective proteins, a significant decrease in expression inflammatory cytokines, and a decrease in the expression of signaling target genes of the NFκB pathway. Our findings are the first to show that TQ treatment increased the expression of these neuroprotective proteins (biliverdin reductase-A, 3-mercaptopyruvate sulfu...

Both neuroinflammation and microglial activation are pathological markers of a number of central nervous system (CNS) diseases. During chronic activation of the microglial cells, the induced release of excessive amounts of reactive oxygen species (ROS) and pro-inflammatory cytokines have been implicated in several neurodegenerative diseases such as Alzheimer’s disease. Thymoquinone (TQ), a major bioactive compound of the natural product Nigella sativa seed, has been shown to be effective against numerous oxidative stress-induced and inflammatory disorders as well as possess neuroprotective properties. In this study, we investigated the antioxidant effects of TQ on LPS/IFNγ or H2O2-activated BV-2 microglia by assessing the levels of specific oxidative stress markers, the activities of selected antioxidant enzymes, as well as profiling 84 key genes related to oxidative stress via real-time reverse transcription (RT2) PCR array. Our results showed that in the LPS/IFNγ-activated microglia TQ significantly decreased the cellular production of both superoxide and nitric oxide 4-fold (p<0.0001) and 6 fold (p<0.0001), respectfully. In the H2O2-activated microglia, TQ also significantly decreased the cellular production of superoxide 3-fold (p<0.0001) and significantly decreased hydrogen peroxide levels ~20% (p<0.05). Moreover, TQ treatment significantly decreased the levels oxidative stress in the activated BV-2 as evidenced by the assessed levels of lipid hydroperoxides and glutathione. TQ significantly decreased the levels of lipid hydroperoxides 2-fold (p<0.0001) and significantly increased the levels of antioxidant glutathione 2.5-fold (p<0.0001) in the LPS/IFNγ-activated BV-2 cells. In the H2O2-activated microglia, TQ significantly decreased lipid hydroperoxides 8-fold (p<0.0001) and significantly increased glutathione 15% (p<0.05). Activities of antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT), in the TQ-treated microglial cells also reflected a reduced oxidative stress status in the cellular environment. SOD and CAT activities were 6 fold (p<0.0001) and 5 fold (p<0.0001) lower, respectfully, for the LPS/INFγ-activated microglia treated with TQ in comparison to those that were not. For the H2O2-activated microglia treated with TQ, SOD and CAT activities were 5 fold (p<0.0001) and 3 fold (p<0.01) lower, respectfully, compared to the untreated. Furthermore, RT2 PCR array profiling of the selected 84 genes related to oxidative stress confirmed that TQ treatment in the LPS/IFNγ-activated microglia downregulates specific pro-oxidant genes, upregulates specific anti-oxidant genes, and enhances the up- or downregulation of specific genes related to the cells’ natural antioxidant defense against LPS/IFNγ activation. These findings suggest that TQ may be utilized as an effective therapeutic agent for delaying the onset and/or slowing/preventing the progression of microglia-derived neurodegeneration propagated by excessive oxidative stress in the CNS.

Alzheimer’s disease (AD) is the most common cause of neurodegeneration and dementia in the elderly. Dysregulated, chronic activation of microglia, the brain’s resident macrophages, induces the release of excessive amounts of pro-inflammatory cytokines which has been implicated in the early stages of AD pathology. Therefore, suppressing the expression of these inflammatory mediators may decrease or delay the progression of AD. Many natural compounds derived from plants have shown anti-inflammatory activity. The naturally occurring 1,2,3,4,6 Penta-O-Galloyl-β-D-Glucose (PGG), is a polyphenolic compound highly enriched in Rhus chinensis Millplant. It is a potent anti-inflammatory agent that act through the inhibition of many cytokines in different experimental models. In the present study, we investigated the role of PGG as an anti-inflammatory agent in LPS/IFNγ activated BV-2 microglia cells. Mouse cytokine antibody arrays were used to assess the effect of PGG on the release of pro-inflammatory cytokines, and ELISA experiments were performed to validate the results from the arrays. The results obtained from the cytokine arrays, and ELISA assays showed that PGG decreased the expression of monocyte chemotactic protein-5 (MCP-5) 8-fold, and pro-matrix metalloproteinase 9 (Pro MMP-9) 10-fold. Both of these cytokines are upregulated during the inflammatory process and have been shown to be involved in brain injury, inflammation, and neurodegeneration. Therefore, these findings suggest that the anti-inflammatory effect of PGG on activated microglia involving the attenuation of MCP-5 and ProMMP-9 cytokines.