Phytochemicals and botanical extracts regulate NF-κB and Nrf2/ARE reporter activities in DI TNC1 astrocytes

Abstract

The increase in oxidative stress and inflammatory responses associated with neurodegenerative diseases has drawn considerable attention towards understanding the transcriptional signaling pathways involving NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) and Nrf2 (Nuclear Factor Erythroid 2-like 2). Our recent studies with immortalized murine microglial cells (BV-2) demonstrated effects of botanical polyphenols to inhibit lipopolysaccharide (LPS)-induced nitric oxide (NO) and enhance Nrf2-mediated antioxidant responses (Sun et al., 2015). In this study, an immortalized rat astrocyte (DI TNC1) cell line expressing a luciferase reporter driven by the NF-κB or the Nrf2/Antioxidant Response Element (ARE) promoter was used to assess regulation of these two pathways by phytochemiscals such as quercetin, rutin, cyanidin, cyanidin-3-O-glucoside, as well as botanical extracts from Withania somnifera (Ashwagandha), Sutherlandia frutescens (Sutherlandia) and Euterpe oleracea (Açaí). Quercetin effectively inhibited LPS-induced NF-κB reporter activity and stimulated Nrf2/ARE reporter activity in DI TNC1 astrocytes. Cyanidin and the glycosides showed similar effects but only at much higher concentrations. All three botanical extracts effectively inhibited LPS-induced NF-κB reporter activity. These extracts were capable of enhancing ARE activity by themselves and further enhanced ARE activity in the presence of LPS. Quercetin and botanical extracts induced Nrf2 and HO-1 protein expression. Interestingly, Ashwagandha extract was more active in inducing Nrf2 and HO-1 expression in DI TNC1 astrocytes as compared to Sutherlandia and Açaí extracts. In summary, this study demonstrated NF-kB and Nrf2/ARE promotor activities in DI TNC1 astrocytes, and further showed differences in ability for specific botanical polyphenols and extracts to down-regulate LPS-induced NF-kB and up-regulate the NRF2/ARE activities in these cells.

The Role of the Nrf2/ARE Antioxidant System in Preventing Cardiovascular Diseases

“…This includes extracts of Withania somnifera (Ashwagandha), Sutherlandia frutescens (Sutherlandia) and Euterpe oleracea (açaí) [14]. There is also at least one dietary supplement that appears to activate the Nrf2/ARE signaling system.…”

Quercetin as an Emerging Anti-Melanoma Agent: A Four-Focus Area Therapeutic Development Strategy

“…In DB-1 melanoma cells overexpressing tyrosinase, quercetin administration led to significant increase of p53 protein and the number of cells in apoptosis compared to untreated cells (8). In particular, quercetin may potentiate p53-dependent apoptosis in melanocytic cells via stimulation of nuclear factor E2-related factor 2 (Nrf2) transcriptional activity, which has been observed in various cell types including human hepatoblastoma HepG2 cells (85, 86), human BJ foreskin fibroblasts and skin HaCaT keratinocytes (87), rat DI TNC1 astrocytes (88), and UVA-irradiated mouse B16F10 melanoma cells (89). Nrf2 is a basic leucine zipper (bZIP) transcription factor that induces the expression of several genes involved in cellular redox reactions, drug metabolism and transport, energy metabolism, and intracellular iron homeostasis in response to oxidative and electrophilic stress (90).…”

“…Quercetin has been demonstrated to induce Nrf2-mediated ARE activation in vitro in human hepatoblastoma HepG2 cells (85, 86), human BJ foreskin fibroblasts and skin HaCaT keratinocytes (87), rat DI TNC1 astrocytes (88), and UVA-irradiated mouse B16F10 melanoma cells (89). Tanigawa et al demonstrated the ability of quercetin treatment to upregulate ARE transcription by regulating both Nrf2 and Keap1 in HepG2 cells (85).…”

“…It was suggested that the refractory response to upregulation of GSTP1 protein in HaCaT by activated Nrf2 is likely due to constitutively high expression in these types of cells, indicating a potentially distinct role of GSTP1 in HaCaT keratinocytes compared to normal cells (87). In immortalized rat DI TNC1 astrocytes, a range of quercetin concentrations (2.5–10 μM) attenuated lipopolysaccharide (LPS)-induced NF-κB activity and upregulated Nrf2 activity in both the presence and absence of LPS (88). Treatment with 10 μM of quercetin led to ~20-fold and 25-fold increase in Nrf2 activity in LPS-free and LPS-containing media, respectively, as determined by luciferase assay (88).…”

“…In immortalized rat DI TNC1 astrocytes, a range of quercetin concentrations (2.5–10 μM) attenuated lipopolysaccharide (LPS)-induced NF-κB activity and upregulated Nrf2 activity in both the presence and absence of LPS (88). Treatment with 10 μM of quercetin led to ~20-fold and 25-fold increase in Nrf2 activity in LPS-free and LPS-containing media, respectively, as determined by luciferase assay (88). …”