Botanical Polyphenols Mitigate Microglial Activation and Microglia-Induced Neurotoxicity: Role of Cytosolic Phospholipase A2

Abstract

Microglia play a significant role in the generation and propagation of oxidative/nitrosative stress, and are the basis of neuroinflammatory responses in the central nervous system. Upon stimulation by endotoxins such as lipopolysaccharides (LPS), these cells release pro-inflammatory factors which can exert harmful effects on surrounding neurons, leading to secondary neuronal damage and cell death. Our previous studies demonstrated the effects of botanical polyphenols to mitigate inflammatory responses induced by LPS, and highlighted an important role for cytosolic phospholipase A2 (cPLA2) upstream of the pro-inflammatory pathways (Chuang et al. in J Neuroinflammation 12(1):199, 2015. doi: 10.1186/s12974-015-0419-0 ). In this study, we investigate the action of botanical compounds and assess whether suppression of cPLA2 in microglia is involved in the neurotoxic effects on neurons. Differentiated SH-SY5Y neuroblastoma cells were used to test the neurotoxicity of conditioned medium from stimulated microglial cells, and WST-1 assay was used to assess for the cell viability of SH-SY5Y cells. Botanicals such as quercetin and honokiol (but not cyanidin-3-O-glucoside, 3CG) were effective in inhibiting LPS-induced nitric oxide (NO) production and phosphorylation of cPLA2. Conditioned medium from BV-2 cells stimulated with LPS or IFNγ caused neurotoxicity to SH-SY5Y cells. Decrease in cell viability could be ameliorated by pharmacological inhibitors for cPLA2 as well as by down-regulating cPLA2 with siRNA. Botanicals effective in inhibition of LPS-induced NO and cPLA2 phosphorylation were also effective in ameliorating microglial-induced neurotoxicity. Results demonstrated cytotoxic factors from activated microglial cells to cause damaging effects to neurons and potential use of botanical polyphenols to ameliorate the neurotoxic effects.

Unveiling anti-oxidative and anti-inflammatory effects of docosahexaenoic acid and its lipid peroxidation product on lipopolysaccharide-stimulated BV-2 microglial cells

“…Taken together, results from our study with BV-2 microglial cells, as well as studies with smooth muscle and endothelial cells, clearly demonstrate that exogenous 4-HHE and 4-HNE are capable of enhancing the Nrf2 anti-oxidative activity and suppressing the LPS-induced oxidative/inflammatory responses [ 37 – 39 ]. The effective concentration ranges for these alkenals to enhance Nrf2/HO-1 and to suppress the LPS pathways are comparable to those observed with quercetin, a botanical polyphenol enriched in berries [ 31 , 46 ]. In fact, due to the electrophilic properties of these alkenals, their ability to offer adaptive responses can be shown in a number of cell systems [ 28 , 47 ].…”

“…2 in Chuang’s paper). Based on the presence of Toll-like receptors as well as mitogen-activated protein kinase (MAPK)-induced cPLA 2 pathways in both primary and BV-2 cells, numerous studies have used BV-2 cells to study the effects of botanical polyphenols and other factors on neuroinflammation [ 29 – 31 ].…”

Small-molecule inhibitors as potential therapeutics and as tools to understand the role of phospholipases A2

“…1) and honokiol (13, Fig. 1), were effective in inhibiting LPS-induced NO production and phosphorylation of GIVA cPLA 2 indicating a potential use of botanical polyphenols to ameliorate the neurotoxic effects [50].…”

N‐acetylcysteine targets 5 lipoxygenase‐derived, toxic lipids and can synergize with prostaglandin E2 to inhibit ferroptosis and improve outcomes following hemorrhagic stroke in mice

“…30 that regulate a diverse set of homeostatic and inflammatory processes. Because NAC appeared to be targeting oxidized lipids, we used structurally diverse, but well-characterized, pharmacological tools to further understand how hemin kills neurons.…”

“…Following brain injury, AA is liberated by increases in calcium-dependent, phospholipase A2 or phospholipase C activity. 30 Released AA can be oxidized nonenzymatically by oxidants or enzymatically (by cyclooxygenase [COX], lipoxygenase, or epoxygenase enzymes) to produce bioactive lipid mediators (isoprostanes, hydroxynonenol, malondialdehye, hydroxyl-PUFAs [HETEs], epoxy-PUFAs [EETs], prostaglandins, and leukotrienes) that regulate a diverse set of homeostatic and inflammatory processes. 31 We performed a systematic characterization of AA metabolizing enzymes involved in hemin-induced toxicity by using a cassette of known, but diverse, chemical inhibitors.…”