Platyconic Acid A, Platycodi Radix-Derived Saponin, Suppresses TGF-1-induced Activation of Hepatic Stellate Cells via Blocking SMAD and Activating the PPAR Signaling Pathway

New Perspectives on Chinese Medicine in Treating Hepatic Fibrosis: Lipid Droplets in Hepatic Stellate Cells

Hepatic fibrosis (HF) is a wound healing response featuring excessive deposition of the extracellular matrix (ECM) and activation of hepatic stellate cells (HSCs) that occurs during chronic liver injury. As an initial stage of various liver diseases, HF is a reversible pathological process that, if left unchecked, can escalate into cirrhosis, liver failure, and liver cancer. HF is a life-threatening disease presenting morbidity and mortality challenges to healthcare systems worldwide. There is no specific and effective anti-HF therapy, and the toxic side effects of the available drugs also impose a heavy financial burden on patients. Therefore, it is significant to study the pathogenesis of HF and explore effective prevention and treatment measures. Formerly called adipocytes, or fat storage cells, HSCs regulate liver growth, immunity, and inflammation, as well as energy and nutrient homeostasis. HSCs in a quiescent state do not proliferate and store abundant lipid droplets (LDs). Catabolism of LDs is characteristic of the activation of HSCs and morphological transdifferentiation of cells into contractile and proliferative myofibroblasts, resulting in the deposition of ECM and the development of HF. Recent studies have revealed that various Chinese medicines (e.g., Artemisia annua, turmeric, Scutellaria baicalensis Georgi, etc.) are able to effectively reduce the degradation of LDs in HSCs. Therefore, this study takes the modification of LDs in HSCs as an entry point to elaborate on the process of Chinese medicine intervening in the loss of LDs in HSCs and the mechanism of action for the treatment of HF.

PPARγ signaling in hepatocarcinogenesis: Mechanistic insights for cellular reprogramming and therapeutic implications

Liver cancer or hepatocellular carcinoma (HCC) is leading cause of cancer-related mortalities globally. The therapeutic approaches for chronic liver diseases-associated liver cancers aimed at modulating immune check-points and peroxisome proliferator-activated receptor gamma (PPARγ) signaling pathway during multistep process of hepatocarcinogenesis that played a dispensable role in immunopathogenesis and outcomes of disease. Herein, the review highlights PPARγ-induced effects in balancing inflammatory (tumor necrosis factor alpha (TNF-α), interleukin (IL)-6, IL-1) and anti-inflammatory cytokines (IL-10, transforming growth factor beta (TGF-β), and interplay of PPARγ, hepatic stellate cells and fibrogenic niche in cell-intrinsic and -extrinsic crosstalk of hepatocarcinogenesis. PPARγ-mediated effects in pre-malignant microenvironment promote growth arrest, cell senescence and cell clearance in liver cancer pathophysiology. Furthermore, PPARγ-immune cell axis of liver microenvironment exhibits an immunomodulation strategy of resident immune cells of the liver (macrophages, natural killer cells, and dendritic cells) in concomitance with current clinical guidelines of the European Association for Study of Liver Diseases (EASL) for several liver diseases. Thus, mechanistic insights of PPARγ-associated high value targets and canonical signaling suggest PPARγ as a possible therapeutic target in reprogramming of hepatocarcinogenesis to decrease burden of liver cancers, worldwide.

Platycodon grandiflorum (Jacq.) A. DC.: A review of phytochemistry, pharmacology, toxicology and traditional use

BACKGROUND

The traditional Chinese medicine Platycodon grandiflorum (Jacq.) A. DC. (PG, balloon flower) has medicinal and culinary value. It consists of a variety of chemical components including triterpenoid saponins, polysaccharides, flavonoids, polyphenols, polyethylene glycols, volatile oils and mineral components, which have medicinal and edible value.

PURPOSE

The ultimate goal of this review is to summarize the phytochemistry, pharmacological activities, safety and uses of PG in local and traditional medicine.

METHODS

A comprehensive search of published literature up to March 2022 was conducted using the PubMed, China Knowledge Network and Web of Science databases to identify original research related to PG, its active ingredients and pharmacological activities.

RESULTS

Triterpene saponins are the primary bioactive compounds of PG. To date, 76 triterpene saponin compounds have been isolated and identified from PG. In addition, there are other biological components, such as flavonoids, polyacetylene and phenolic acids. These extracts possess antitussive, immunostimulatory, anti-inflammatory, antioxidant, antitumor, antiobesity, antidepressant, and cardiovascular system activities. The mechanisms of expression of these pharmacological effects include inhibition of the expression of proteins such as MDM and p53, inhibition of the activation of enzymes, such as AKT, the secretion of inflammatory factors, such as IFN-γ, TNF-α, IL-2 and IL-1β, and activation of the AMPK pathway.

CONCLUSION

This review summarizes the chemical composition, pharmacological activities, molecular mechanism, toxicity and uses of PG in local and traditional medicine over the last 12 years. PG contains a wide range of chemical components, among which triterpene saponins, especially platycoside D (PD), play a strong role in pharmacological activity, representing a natural phytomedicine with low toxicity that has applications in food, animal feed and cosmetics. Therefore, PG has value for exploitation and is an excellent choice for treating various diseases.

The anti-inflammatory effects of Akkermansia muciniphila and its derivates in HFD/CCL4-induced murine model of liver injury

Inflammation plays a critical role in the promotion of hepatocyte damage and liver fibrosis. In recent years the protective role of Akkermansia muciniphila, a next-generation beneficial microbe, has been suggested for metabolic and inflammatory disorders. In this study, we aimed to evaluate the effects of live and pasteurized A. muciniphila and its extra cellular vesicles (EVs) on inflammatory markers involved in liver fibrosis in a mouse model of a high-fat diet (HFD)/carbon tetrachloride (CCl₄)-induced liver injury. Firstly, the responses of hepatic stellate cells (HSCs) to live and pasteurized A. muciniphila and its EVs were examined in the quiescent and LPS-activated LX-2 cells. Next, the anti-inflammatory effects of different forms of A. muciniphila were examined in the mouse model of HFD/CCl₄-induced liver injury. The gene expression of various inflammatory markers was evaluated in liver, colon, and white adipose tissues. The cytokine secretion in the liver and white adipose tissues was also measured by ELISA. The results showed that administration of live and pasteurized A. muciniphila and its EVs leads to amelioration in HSCs activation. Based on data obtained from the histopathological analysis, an improvement in gut health was observed through enhancing the epithelium and mucosal layer thickness and strengthening the intestinal integrity in all treatments. Moreover, live A. muciniphila and its EVs had inhibitory effects on liver inflammation and hepatocytes damage. In addition, the tissue cytokine production and inflammatory gene expression levels revealed that live A. muciniphila and its EVs had more pronounced anti-inflammatory effects on liver and adipose tissues. Furthermore, EVs had better effects on the modulation of gene expression related to TLRs, PPARs, and immune response in the liver. In conclusion, the present results showed that oral administration of A. muciniphila and its derivatives for four weeks could enhance the intestinal integrity and anti-inflammatory responses of the colon, adipose, and liver tissues and subsequently prevent liver injury in HFD/CCL₄ mice.

Kaempferol 3-O-gentiobioside, an ALK5 inhibitor, affects the proliferation, migration, and invasion of tumor cells via blockade of the TGF-β/ALK5/Smad signaling pathway

Overactivation of TGF-β/ALK5/Smad signaling pathway has been observed in the advanced stage of various human malignancies. As a key component of TGF-β/ALK5/Smad signaling pathway transduction, TGF-β type I receptor (also known as ALK5) has emerged as a promising therapeutic target for cancer treatment. In this study, to discover a novel ALK5 inhibitor, a commercial natural products library was screened using docking-based virtual screening, followed by luciferase reporter assay. A flavonoid glycoside kaempferol 3-O-gentiobioside (KPF 3-O-G) was identified as a potent ALK5 inhibitor through directly bound to the ATP-site of ALK5, resulting in the inhibitory effects on phosphorylation and translocation of Smad2 and expression of Smad4. Additionally, we found that KPF 3-O-G reduced cell proliferation and inhibited TGF-β-induced cell migration and invasion. Moreover, western blotting and immunofluorescent analysis showed that KPF 3-O-G significantly reversed the TGF-β-induced EMT biomarkers, including upregulation of E-cadherin and downregulation of N-cadherin, vimentin, and snail. In vivo study showed that KPF 3-O-G administration reduced tumor growth in human ovarian cancer xenograft mouse model, without obvious toxic effect. This study provided novel insight into the anticancer effects of KPF-3-O-G and indicated that KPF-3-O-G might be developed as potential therapeutics for cancer treatment after further validation.

Natural products and analogs as preventive agents for metabolic syndrome via peroxisome proliferator-activated receptors: An overview

Natural products and synthetic analogs have drawn much attention as potential therapeutical drugs to treat metabolic syndrome. We reviewed the underlying mechanisms of 32 natural products and analogs with potential pharmacological effects in vitro, and especially in rodent models and/or patients, that usually act on the PPAR pathway, along with other molecular targets. Recent outstanding total syntheses or semisyntheses of these lead compounds are stated. In general, they can activate the transcriptional activity of PPARα, PPARγ, PPARα/γ, PPARβ/δ, PPARα/δ, PPARγ/δ and panPPAR as weak, partial agonists or selective PPARγ modulators (SPPARγM), which may be useful for managing obesity, type 2 diabetes (T2D), dyslipidemia and non-fatty liver disease (NAFLD). Terpenoids is the largest group of compounds that act as potential modulators on PPARs and are comprised from small lipophilic cannabinoids to lipophilic pentacyclic triterpenes and polar saponins. Shikimates-phenylpropanoids include polar heterocyclic flavonoids and phenolic compounds containing at least one C3-C6 unit and usually a double bond on the propyl chain. Quercetin (19), resveratrol (24) and curcumin (27), stand out from this group for exhibiting beneficial effects on patients. Alkaloids, the minor group of potential modulators on PPARs, include berberine (30), which has been widely explored in preclinical and clinical studies for its potential beneficial effects on T2D and dyslipidemia. However, large-scale clinical trials may be warranted for the promising compounds.

The Anti-fibrotic Effects of Heat-Killed Akkermansia muciniphila MucT on Liver Fibrosis Markers and Activation of Hepatic Stellate Cells

Hepatic stellate cell (HSC) activation is a key phenomenon in development of liver fibrosis. Recently, Akkermansia muciniphila has been introduced as a next-generation microbe residing in the mucosal layer of the human gut. Due to the probable risks associated with the use of live probiotics, the tendency to use heat-killed bacteria has been raised. Herein, we investigated the potential anti-fibrotic effects of heat-killed A. muciniphila MucT on activation of HSCs. The human LX-2 cells were stimulated by various concentrations of LPS to evaluate the optimal concentration for HSC activation. Cell viability of LX-2 cells treated with LPS and heat-killed A. muciniphila MucT was measured by MTT assay. Scanning electron microscopy was used to analyze the morphology of heat-killed bacteria. Quiescent and LPS-stimulated LX-2 cells were coinfected with heat-killed A. muciniphila MucT. The gene expression of α-SMA, TIMP, Col1, TGF-β, TLR4, and PPARγ was analyzed using quantitative real-time PCR. Our results showed that LPS treatment led to a significant increase in fibrosis markers in a concentration-independent manner (P < 0.0001), and significantly downregulated the expression of PPARγ (P < 0.0001). The heat-killed A. muciniphila MucT could significantly modulate the expression of fibrosis markers particularly in MOI 10 (P < 0.0001), and reversed the HSC activation in LPS-stimulated LX-2 cells. In conclusion, we demonstrated that heat-killed A. muciniphila MucT was safe and capable to ameliorate LPS-induced HSC activation through modulation of fibrosis markers. Further in vivo studies are required to validate the anti-fibrotic properties of heat-killed A. muciniphila MucT.

Regulation of peroxisome proliferator-activated receptor-gamma activity affects the hepatic stellate cell activation and the progression of NASH via TGF-β1/Smad signaling pathway

Development of liver fibrosis is associated with activation of quiescent hepatic stellate cells (HSCs) into myofibroblasts (activated HSCs), which produce excessive extracellular matrix. Peroxisome proliferator-activated receptor-gamma (PPAR-γ) exerts protective effects on hepatic inflammation and fibrosis. The current study was to explore the function of PPAR-γ on HSC activation and progression of nonalcoholic steatohepatitis (NASH). Our study found that HSCs were gradually activated during the progression of methionine-choline-deficient (MCD) diet-induced NASH, accompanied by decreased PPAR-γ expression and activated TGF-β1/Smad signaling pathway in the liver. PPAR-γ agonist was found to inhibit primary HSCs and NIH/3T3 fibroblast activation and reverted their phenotypical morphology induced by TGF-β1 in vitro. In addition to this, PPAR-γ agonist decreased expression of TGF-β1 and phosphorylation of Smad2/3 while increased expression of Smad7. In vivo, rosiglitazone, a PPAR-γ agonist, inhibited HSC activation and alleviated liver fibrosis and inflammation similarly via inhibiting the activation of TGF-β1/Smad signaling pathway. In parallel, rosiglitazone alleviated hepatic lipid accumulation and peroxidation, beneficial to reverse of NASH. From these findings, it can be concluded that the gradual activation of HSCs is crucial to the progression of NASH and modulating PPAR-γ expression can affect HSC activation via TGF-β1/Smad signaling pathway and thereby influence hepatic fibrogenesis.

PPAR-Mediated Toxicology and Applied Pharmacology

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor family, attract wide attention as promising therapeutic targets for the treatment of multiple diseases, and their target selective ligands were also intensively developed for pharmacological agents such as the approved drugs fibrates and thiazolidinediones (TZDs). Despite their potent pharmacological activities, PPARs are reported to be involved in agent- and pollutant-induced multiple organ toxicity or protective effects against toxicity. A better understanding of the protective and the detrimental role of PPARs will help to preserve efficacy of the PPAR modulators but diminish adverse effects. The present review summarizes and critiques current findings related to PPAR-mediated types of toxicity and protective effects against toxicity for a systematic understanding of PPARs in toxicology and applied pharmacology.