Regulatory mechanisms of natural compounds from traditional Chinese herbal medicines on the microglial response in ischemic stroke.

BACKGROUND: Development of clinically effective neuroprotective agents for stroke therapy is still a challenging task. Microglia play a critical role in brain injury and recovery after ischemic stroke. Traditional Chinese herbal medicines (TCHMs) are based on a unique therapeutic principle, have various formulas, and have long been widely used to treat stroke. Therefore, the active compounds in TCHMs and their underlying mechanisms of action are attracting increasing attention in the field of stroke drug development. PURPOSE: To summarize the regulatory mechanisms of TCHM-derived natural compounds on the microglial response in animal models of ischemic stroke. METHODS: We searched studies published until 10 April 2023 in the Web of Science, PubMed, and ScienceDirect using the following keywords: natural compounds, natural products or phytochemicals, traditional Chinese Medicine or Chinese herbal medicine, microglia, and ischemic stroke. This review was prepared according to PRISMA (Preferred Reporting Item for Systematic Reviews and Meta-Analysis) guidelines. RESULTS: Natural compounds derived from TCHMs can attenuate the M1 phenotype of microglia, which is involved in the detrimental inflammatory response, via inhibition of NF-κB, MAPKs, JAK/STAT, Notch, TLR4, P2X7R, CX3CR1, IL-17RA, the NLRP3 inflammasome, and pro-oxidant enzymes. Additionally, the neuroprotective response of microglia with the M2 phenotype can be enhanced by activating Nrf2/HO-1, PI3K/AKT, AMPK, PPARγ, SIRT1, CB2R, TREM2, nAChR, and IL-33/ST2. Several clinical trials showed that TCHM-derived natural compounds that regulate microglial responses have significant and safe therapeutic effects, but further well-designed clinical studies are needed. CONCLUSIONS: Further research regarding the direct targets and potential pleiotropic or synergistic effects of natural compounds would provide a more reasonable approach for regulation of the microglial response with the possibility of successful stroke drug development.

Galangin inhibits programmed cell death-ligand 1 expression by suppressing STAT3 and MYC and enhances T cell tumor-killing activity.

BACKGROUND: The flavonoid galangin (3,5,7-trihydroxyflavone) is derived from the root of Alpinia officinarum Hance, an edible and medicinal herb. Galangin has many biological activities, such as anti-inflammatory, anti-microbial, anti-viral, anti-obesogenic, and anti-oxidant effects. However, the anti-tumor mechanism of galangin remains unclear. PURPOSE: To elucidate the anti-tumor mechanisms of galangin in vitro and in vivo. METHODS: MTT, western blotting, immunoprecipitation, RT-PCR, and immunofluorescence assays were used to assess the mechanism of galangin inhibiting PD-L1 expression. The effect of galangin on T cell activity was analyzed in Hep3B/T cell co-cultures. Colony formation, EdU, migration, and invasion assays were performed to explore the effect of galangin on cancer progression and metastasis. Anti-tumor effects of galangin were investigated in a xenograft model. RESULTS: Galangin inhibited PD-L1 expression dose-dependently, which plays a major role in tumor progression. Moreover, galangin blocked STAT3 activation through the JAK1/JAK2/Src signaling pathway and Myc activation through the Ras/RAF/MEK/ERK signaling pathway. Galangin reduced PD-L1 expression by suppressing STAT3 and Myc cooperatively. Galangin increased the killing effect of T cells on tumor cells in Hep3B/T cell co-cultures. Moreover, galangin inhibited tumor cell proliferation, migration, and invasion through PD-L1. In vivo experiments showed that galangin suppressed tumor growth. CONCLUSION: Galangin enhances T-cell activity and inhibits tumor cell proliferation, migration, and invasion through PD-L1. The current study emphasizes the anti-tumor properties of galangin, offering new insights into the development of tumor therapeutics targeting PD-L1.

Panaxadiol inhibits IL-1ß secretion by suppressing zinc finger protein 91-regulated activation of non-canonical caspase-8 inflammasome and MAPKs in macrophages.

ETHNOPHARMACOLOGICAL RELEVANCE: The use of Panax ginseng C.A.Mey. in traditional Chinese medicine dates back to about 5000 years ago thanks to its several beneficial and healing properties. Panaxadiol is a triterpenoid sapogenin monomer found in the roots of Panax ginseng C.A.Mey. and has been proven to have various bio-activities such as anti-inflammatory, anti-tumour and neuroprotective effects. AIM OF THE STUDY: The present study focuses on investigating the inflammation inhibitory effect and mechanism of panaxadiol by regulating zinc finger protein 91-regulated activation of non-canonical caspase-8 inflammasome and MAPKs in macrophages. MATERIALS AND METHODS: In vitro, the underlying mechanisms by which panaxadiol inhibits ZFP91-regulated IL-1ß expression were investigated using molecular docking, western blotting, RT-PCR, ELISA, immunofluorescence, and immunoprecipitation assays. In vivo, colitis was induced by oral administration of DSS in drinking water, and peritonitis was induced by an intraperitoneal injection of alum. Recombinant adeno-associated virus (AAV serotype 9) vector was used to establish ZFP91 knockdown mouse. RESULTS: We confirmed that panaxadiol inhibited IL-1ß secretion by suppressing ZFP91 in macrophages. Further analysis revealed that panaxadiol inhibited IL-1ß secretion by suppressing ZFP91-regulated activation of non-canonical caspase-8 inflammasome. Meanwhile, panaxadiol inhibited IL-1ß secretion by suppressing ZFP91-regulated activation of MAPKs. In vivo, prominent anti-inflammatory effects of panaxadiol were demonstrated in a DSS induced acute colitis mouse model and in an alum-induced peritonitis model by suppressing ZFP91-regulated secretion of inflammatory mediators, consistent with the results of the AAV-ZFP91 knockdown in mice. CONCLUSIONS: We report for the first time that panaxadiol inhibited IL-1ß secretion by suppressing ZFP91-regulated activation of non-canonical caspase-8 inflammasome and MAPKs, providing evidence for anti-inflammation mechanism of panaxadiol treatment for inflammatory diseases.

Formononetin represses cervical tumorigenesis by interfering with the activation of PD-L1 through MYC and STAT3 downregulation.

A. membranaceus is a traditional Chinese medicine that regulates blood sugar levels, suppresses inflammation, protects the liver, and enhances immunity. In addition, A. membranaceus is also widely used in diet therapy and is a well-known health tonic. Formononetin is a natural product isolated from A. membranaceus that has multiple biological functions, including anti-cancer activity. However, the mechanism by which formononetin inhibits tumor growth is not fully understood. In this present study, we demonstrated that formononetin suppresses PD-L1 protein synthesis via reduction of MYC and STAT3 protein expression. Furthermore, formononetin markedly reduced the expression of MYC protein via the RAS/ERK signaling pathway and inhibited STAT3 activation through JAK1/STAT3 pathway. Co-immunoprecipitation experiments illustrated that formononetin suppresses protein expression of PD-L1 by interfering with the interaction between MYC and STAT3. Meanwhile, formononetin promoted PD-L1 protein degradation via TFEB and TFE3-mediated lysosome biogenesis. T cell killing assay revealed that formononetin could enhance the activity of cytotoxic T lymphocytes (CTLs) and restore ability to kill tumor cells in a co-culture system of T cells and tumor cells. In addition, formononetin inhibited cell proliferation, tube formation, cell migration, and promoted tumor cell apoptosis by suppressing PD-L1. Finally, the inhibitory effect of formononetin on tumor growth was confirmed in a murine xenograft model. The present study revealed the anti-tumor potential of formononetin, and the findings should support further research and development of anti-cancer drugs for cervical cancer.

Convallatoxin inhibits IL-1ß production by suppressing zinc finger protein 91 (ZFP91)-mediated pro-IL-1ß ubiquitination and caspase-8 inflammasome activity.

BACKGROUND AND PURPOSE: ZFP91 positively regulates IL-1ß production in macrophages and may be a potential therapeutic target to treat inflammatory-related diseases. We investigated whether this process is modulated by convallatoxin, which is a cardiac glycoside isolated from the traditional Chinese medicinal plant Adonis amurensis Regel et Radde. EXPERIMENTAL APPROACH: In vitro, the mechanisms by which convallatoxin inhibits ZFP91-regulated IL-1ß expression were investigated using molecular docking, western blotting, RT-PCR, ELISA, immunofluorescence and immunoprecipitation assays.In vivo, mice liver injury was induced by an intraperitoneal injection of D-GalN and LPS, colitis was induced by oral administration of dextran sulfate sodium (DSS) in drinking water and peritonitis was induced by an intraperitoneal injection of alum. KEY RESULTS: We confirmed that convallatoxin inhibited the release of IL-1ß by down-regulating ZFP91. Importantly, we found that convallatoxin significantly reduced K63-linked polyubiquitination of pro-IL-1ß regulated by ZFP91 and decreased the efficacy of pro-IL-1ß cleavage. Moreover, convallatoxin suppressed ZFP91-mediated activation of the non-canonical cysteine-requiring aspartate protease-8 (caspase-8) inflammasome and MAPK signalling pathways in macrophages. Furthermore, we showed that ZFP91 promoted the assembly of the caspase-8 inflammasome complex, whereas convallatoxin treatment reversed this result. Mice in vivo studies further demonstrated that convallatoxin ameliorated D-GalN/LPS-induced liver injury, DSS-induced colitis and alum-induced peritonitis by down-regulating ZFP91. CONCLUSION AND IMPLICATIONS: We show for the first time that convallatoxin-mediated inhibition of ZFP91 is an important regulatory event that prevents inappropriate inflammatory responses to maintain immune homeostasis. This mechanism provides new insight for the development of convallatoxin as a novel anti-inflammatory drug targeting ZFP91. LINKED ARTICLES: This article is part of a themed issue on Inflammation, Repair and Ageing. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.9/issuetoc.

Usnic acid suppresses cervical cancer cell proliferation by inhibiting PD-L1 expression and enhancing T-lymphocyte tumor-killing activity.

The programmed cell death 1 (PD-1)/programmed death ligand 1 (PD-L1) pathway is abnormally expressed in cervical cancer cells. Moreover, PD-1/PD-L1 blockade reduces the apoptosis and exhaustion of T cells and inhibits the development of malignant tumors. Usnic acid is a dibenzofuran compound originating from Usnea diffracta Vain and has anti-inflammatory, antifungal, and anticancer activities. However, the molecular mechanism of its antitumor effects has not been fully elucidated. In this work, we first observed that usnic acid decreased the expression of PD-L1 in HeLa cells and enhanced the cytotoxicity of co-cultured T cells toward tumor cells. Usnic acid inhibited PD-L1 protein synthesis by reducing STAT3 and RAS pathways cooperatively. It was subsequently shown that usnic acid induced MiT/TFE nuclear translocation through the suppression of mTOR signaling pathways, and promoted the biogenesis of lysosomes and the translocation of PD-L1 to the lysosomes for proteolysis. Furthermore, usnic acid inhibited cell proliferation, angiogenesis, migration, and invasion, respectively, by downregulating PD-L1, thereby inhibiting tumor growth. Taken together, our results show that usnic acid is an effective inhibitor of PD-L1 and our study provide novel insights into the mechanism of its anticancer targeted therapy.

Britannin stabilizes T cell activity and inhibits proliferation and angiogenesis by targeting PD-L1 via abrogation of the crosstalk between Myc and HIF-1α in cancer.

BACKGROUND: Programmed cell death-ligand 1 (PD-L1) is overexpressed in tumor cells, which causes tumor cells to escape T cell killing, and promotes tumor cell survival, cell proliferation, migration, invasion, and angiogenesis. Britannin is a natural product with anticancer pharmacological effects. PURPOSE: In this work, we studied the anticancer potential of britannin and explored whether britannin mediated its effect by inhibiting the expression of PD-L1 in tumor cells. METHODS: In vitro, the mechanisms underlying the inhibition of PD-L1 expression by britannin were investigated by MTT assay, homology modeling and molecular docking, RT-PCR, western blotting, co-immunoprecipitation, and immunofluorescence. The changes in tumor killing activity, cell proliferation, cell cycle, migration, invasion, and angiogenesis were analyzed by T cell killing assays, EdU labeling, colony formation, flow cytometry, wound healing, matrigel transwell invasion, and tube formation, respectively. In vivo, the antitumor activity of britannin was evaluated in the HCT116 cell xenograft model. RESULTS: Britannin reduced the expression of PD-L1 in tumor cells by inhibiting the synthesis of the PD-L1 protein but did not affect the degradation of the PD-L1 protein. Britannin also inhibited HIF-1α expression through the mTOR/P70S6K/4EBP1 pathway and Myc activation through the Ras/RAF/MEK/ERK pathway. Mechanistically, britannin inhibited the expression of PD-L1 by blocking the interaction between HIF-1α and Myc. In addition, britannin could enhance the activity of cytotoxic T lymphocytes and inhibit tumor cell proliferation and angiogenesis by inhibiting PD-L1. Finally, in vivo observations were confirmed by demonstrating the antitumor activity of britannin in a murine xenograft model. CONCLUSION: Britannin inhibits the expression of PD-L1 by blocking the interaction between HIF-1α and Myc. Moreover, britannin stabilizes T cell activity and inhibits proliferation and angiogenesis by inhibiting PD-L1 in cancer. The current work highlights the anti-tumor effect of britannin, providing insights into the development of cancer therapeutics via PD-L1 inhibition.

Erianin regulates programmed cell death ligand 1 expression and enhances cytotoxic T lymphocyte activity.

ETHNOPHARMACOLOGICAL RELEVANCE: Dendrobium chrysotoxum Lindl is a cultivation of Dendrobium which belongs to the family of Orchidaceae. D. chrysotoxum Lindl is a traditional Chinese medicine with a wide range of clinical applications including tonic, astringent, analgesic and anti-inflammatory properties as early as the 28th century B.C. Erianin is a representative index component for the quality control of the D. chrysotoxum Lindl, which is included in the Pharmacopoeia of the People's Republic of China (2020 version). AIM OF THE STUDY: To clarify the anti-tumour mechanisms of erianin in vitro and in vivo. MATERIALS AND METHODS: We detected the anti-tumour activity of erianin using in vitro HeLa cell models and in vivo cervical cancer xenograft models. We performed MTT, western blot, RT-PCR, homology modeling, flow cytometry, and immunoprecipitation assays to study the proteins, genes, and pathways related to erianin's anti-tumour activity. LysoTracker Red staining was performed to detect lysosome function. Transwell, wound healing, tube formation, colony formation and EdU labelling assays were performed to determine cell proliferation, migration and invasion abilities, respectively. Cytotoxic T lymphocytes ability was confirmed using HeLa/T-cell co-culture model. RESULTS: Experimental data demonstrated that erianin inhibited PD-L1 expression and induced the lysosomal degradation of PD-L1. Erianin suppressed HIF-1α synthesis through mTOR/p70S6K/4EBP1 pathway, and inhibited RAS/Raf/MEK/MAPK-ERK pathway. Immunoprecipitation experiments demonstrated that erianin reduced the interaction between RAS and HIF-1α. Experiments using a co-cultivation system of T cells and HeLa cells confirmed that erianin restored cytotoxic T lymphocytes ability to kill tumour cells. Erianin inhibited PD-L1-mediated angiogenesis, proliferation, invasion and migration. The anti-proliferative effects of erianin were supported using in vivo xenotransplantation experiments. CONCLUSIONS: Collectively, these results revealed previously unknown properties of erianin and provided a new basis for improving the efficacy of immunotherapy against cervical cancer and other malignant tumours through PD-L1.

Panaxadiol inhibits programmed cell death-ligand 1 expression and tumour proliferation via hypoxia-inducible factor (HIF)-1α and STAT3 in human colon cancer cells.

Panaxadiol is a triterpenoid sapogenin monomeric compound found in the roots of Panax ginseng and has a variety of biological activities such as neuroprotective and anti-tumour functions. However, the mechanisms how panaxadiol exerts the anticancer effects remain unknown. The current study aimed to investigate the potential activity of panaxadiol on programmed cell death-ligand 1 (PD-L1) expression and tumour proliferation in human colon cancer cells and to identify the underlying mechanism. Results showed that panaxadiol showed little cytotoxicity as assessed by a cytotoxicity assay and significantly inhibited PD-L1 expression at the protein and mRNA level in a dose-dependent manner. Furthermore, panaxadiol supressed the hypoxia-induced synthesis of hypoxia-inducible factor (HIF)-1α via the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) pathways without affecting HIF-1α degradation. Simultaneously, panaxadiol inhibited STAT3 activation through the JAK1, JAK2, and Src pathways. Moreover, pre-treatment with panaxadiol enhanced the activity of cytotoxic T lymphocytes (CTL) and regained their capacity of tumour cell killing in a T cell and tumour cell co-culture system. Immunoprecipitation showed that panaxadiol inhibited PD-L1 expression by blocking the interaction between HIF-1α and STAT3. The inhibitory effect of panaxadiol on tumour proliferation was further demonstrated by colony formation and EdU labelling assays. The anti-proliferative effect of panaxadiol was also proved by a xenograft assay in vivo. Taken together, the current work highlights the anti-tumour effect of panaxadiol, providing insights into development of cancer therapeutic through PD-L1 inhibition.

Quercetin-3-O-α-l-arabinopyranoside protects against retinal cell death via blue light-induced damage in human RPE cells and Balb-c mice.

Age-related macular degeneration (AMD) is among the increasing number of diseases causing irreversible blindness in the elderly. Dry AMD is characterized by the accumulation of lipofuscin in retinal pigment epithelium (RPE) cells. N-Retinylidene-N-retinylethanolamine (A2E), a component of lipofuscin, is oxidized to oxo-A2E under blue light illumination, leading to retinal cell death. The aim of this study was to investigate the protective effect and mechanism of quercetin-3-O-α-l-arabinopyranoside (QA) against blue light (BL)-induced damage in both RPE cells and mice models. Treatment by QA inhibited A2E uptake in RPE cells, as determined by a decrease in fluorescence intensity. QA also protected A2E-laden RPE cells against BL-induced apoptosis. QA inhibited C3 complement activation and poly (ADP-ribose) polymerase (PARP) cleavage, as determined by western blotting. QA showed an inhibitory effect on AP1 and NF-kB activity as estimated in a reporter gene assay. In addition, QA activated the gene expression of aryl hydrocarbon receptor target genes (CYP1A1, CYP1B1) in TCDD-treated RPE cells. In the mice model, oral administration of QA protected against retinal degeneration induced by BL exposure as determined by histological analyses (thickness of retinal layers and immunostaining for caspase-3). In addition, QA inhibited apoptosis and inflammation via inhibition of NF-kB p65 translocation, C3 activation, and PARP cleavage. Collectively, these results revealed the protective mechanism of QA against BL-induced retinal damage both in vitro and in vivo.