Involvement of endoplasmic reticulum stress response and IRE1-mediated ASK1/JNK/Mcl-1 pathways in silver nanoparticle-induced apoptosis of human retinal pigment epithelial cells

Spinosin inhibits activated hepatic stellate cell to attenuate liver fibrosis by targeting Nur77/ASK1/p38 MAPK signaling pathway

AIM

Liver fibrosis remains a great challenge in the world. Spinosin (SPI), a natural flavonoid-C-glycoside, possesses various pharmacological activities including anti-inflammatory and anti-myocardial fibrosis effects. In this study, we investigate whether SPI can be a potential lead for the treatment of liver fibrosis and explore whether the orphan nuclear receptor Nur77, a negative regulator of liver fibrosis development, plays a critical role in SPI's action.

METHODS

A dual luciferase reporter system of α-SMA was established to evaluate the effect of SPI on hepatic stellate cell (HSC) activation in LX2 and HSC-T6 cells. A mouse model of CCl4-induced liver fibrosis was used to test the efficacy of SPI against liver fibrosis. The expression levels of Nur77, inflammatory cytokines and collagen were determined by Western blotting and qPCR. Potential kinase pathways involved were also analyzed. The affinity of Nur77 with SPI was documented by fluorescence titration.

RESULTS

SPI can strongly suppress TGF-β1-mediated activation of both LX2 and HSC-T6 cells in a dose-dependent manner. SPI increases the expression of Nur77 and reduces TGF-β1-mediated phosphorylation levels of ASK1 and p38 MAPK, which can be reversed by knocking out of Nur77. SPI strongly inhibits collagen deposition (COLA1) and reduces inflammatory cytokines (IL-6 and IL-1β), which is followed by improved liver function in the CCl4-induced mouse model. SPI can directly bind to R515 and R563 in the Nur77-LBD pocket with a Kd of 2.14 μM.

CONCLUSION

Spinosin is the major pharmacological active component of Ziziphus jujuba Mill. var. spinosa which has been frequently prescribed in traditional Chinese medicine. We demonstrate here for the first time that spinosin is a new therapeutic lead for treatment of liver fibrosis by targeting Nur77 and blocking the ASK1/p38 MAPK signaling pathway.

Emerging mechanisms of the unfolded protein response in therapeutic resistance: from chemotherapy to Immunotherapy

The accumulation of unfolded or misfolded proteins in the endoplasmic reticulum (ER) causes ER stress and activates the unfolded protein response (UPR). As an adaptive cellular response to hostile microenvironments, such as hypoxia, nutrient deprivation, oxidative stress, and chemotherapeutic drugs, the UPR is activated in diverse cancer types and functions as a dynamic tumour promoter in cancer development; this role of the UPR indicates that regulation of the UPR can be utilized as a target for tumour treatment. T-cell exhaustion mainly refers to effector T cells losing their effector functions and expressing inhibitory receptors, leading to tumour immune evasion and the loss of tumour control. Emerging evidence suggests that the UPR plays a crucial role in T-cell exhaustion, immune evasion, and resistance to immunotherapy. In this review, we summarize the molecular basis of UPR activation, the effect of the UPR on immune evasion, the emerging mechanisms of the UPR in chemotherapy and immunotherapy resistance, and agents that target the UPR for tumour therapeutics. An understanding of the role of the UPR in immune evasion and therapeutic resistance will be helpful to identify new therapeutic modalities for cancer treatment. Video Abstract.

Intricate subcellular journey of nanoparticles to the enigmatic domains of endoplasmic reticulum

It is evident that site-specific systemic drug delivery can reduce side effects, systemic toxicity, and minimal dosage requirements predominantly by delivering drugs to particular pathological sites, cells, and even subcellular structures. The endoplasmic reticulum (ER) and associated cell organelles play a vital role in several essential cellular functions and activities, such as the synthesis of lipids, steroids, membrane-associated proteins along with intracellular transport, signaling of Ca2+, and specific response to stress. Therefore, the dysfunction of ER is correlated with numerous diseases where cancer, neurodegenerative disorders, diabetes mellitus, hepatic disorder, etc., are very common. To achieve satisfactory therapeutic results in certain diseases, it is essential to engineer delivery systems that can effectively enter the cells and target ER. Nanoparticles are highly biocompatible, contain a variety of cargos or payloads, and can be modified in a pliable manner to achieve therapeutic effectiveness at the subcellular level when delivered to specific organelles. Passive targeting drug delivery vehicles, or active targeting drug delivery systems, reduce the nonselective accumulation of drugs while reducing side effects by modifying them with small molecular compounds, antibodies, polypeptides, or isolated bio-membranes. The targeting of ER and closely associated organelles in cells using nanoparticles, however, is still unsymmetrically understood. Therefore, here we summarized the pathophysiological prospect of ER stress, involvement of ER and mitochondrial response, disease related to ER dysfunctions, essential therapeutics, and nanoenabled modulation of their delivery to optimize therapy.

Nanosilver: An Old Antibacterial Agent with Great Promise in the Fight against Antibiotic Resistance

Antibiotic resistance in bacteria is a major problem worldwide that costs 55 billion USD annually for extended hospitalization, resource utilization, and additional treatment expenditures in the United States. This review examines the roles and forms of silver (e.g., bulk Ag, silver salts (AgNO3), and colloidal Ag) from antiquity to the present, and its eventual incorporation as silver nanoparticles (AgNPs) in numerous antibacterial consumer products and biomedical applications. The AgNP fabrication methods, physicochemical properties, and antibacterial mechanisms in Gram-positive and Gram-negative bacterial models are covered. The emphasis is on the problematic ESKAPE pathogens and the antibiotic-resistant pathogens of the greatest human health concern according to the World Health Organization. This review delineates the differences between each bacterial model, the role of the physicochemical properties of AgNPs in the interaction with pathogens, and the subsequent damage of AgNPs and Ag+ released by AgNPs on structural cellular components. In closing, the processes of antibiotic resistance attainment and how novel AgNP-antibiotic conjugates may synergistically reduce the growth of antibiotic-resistant pathogens are presented in light of promising examples, where antibiotic efficacy alone is decreased.

Multi-walled carbon nanotube induced liver injuries possibly by promoting endoplasmic reticulum stress in Cyprinus carpio

The mass production and discharge of carbon nanotubes (CNTs) to the water environment are of great concern since they threaten the health of organisms in the aquatic ecosystem. CNTs induce multi-organ injuries in fish, but limited literature is available regarding the mechanisms involved. In the present study, juvenile common carp (Cyprinus carpio) were exposed to multi-walled carbon nanotubes (MWCNTs) (0.25 mg L^-1 and 2.5 mg L^-1) for four weeks. MWCNTs caused dose-dependent alterations in the pathological morphology of liver tissues. Ultrastructural changes manifested as nuclear deformation, chromatin condensation, endoplasmic reticulum (ER) disorderly arrangement, mitochondria vacuolation, and mitochondrial membrane destruction. TUNEL analysis indicated that the apoptosis rate in hepatocytes markedly increased upon exposure to MWCNTs. Moreover, the apoptosis was confirmed by significant upregulation of mRNA levels of apoptosis-related genes (Bcl-2, XBP1, Bax, and caspase3) in MWCNTs-exposure groups, except for Bcl-2 expression which was not significantly changed in HSC groups (2.5 mg L^-1 MWCNTs). Furthermore, real-time PCR assay indicated the increased expression of ER stress (ERS) marker genes (GRP78, PERK, and eIF2α) in the exposure groups compared to the control groups, suggesting that the PERK/eIF2α signaling pathway involved in the injuries of the liver tissue. Overall, the results above indicate that MWCNTs induce ERS by activating the PERK/eIF2α pathway in the liver of common carp, and resulted in the initiation of apoptosis procedure.

Apoptin causes apoptosis in HepG-2 cells via Ca2+ imbalance and activation of the mitochondrial apoptotic pathway

BACKGROUND

Apoptin is derived from the chicken anemia virus and exhibits specific cytotoxic effects against tumor cells. Herein, we found that Apoptin induced a strong and lasting endoplasmic reticulum (ER) stress response, Ca²⁺ imbalance, and triggered the mitochondrial apoptotic pathway. The aim of this study was to explore the mechanisms by which Apoptin exhibited anti-tumor effects in HepG-2 cells.

METHODS

The intracellular levels of calcium (Ca²⁺ ) were induced by ER stress and determined by electron microscopy, flow cytometry, and fluorescence staining. The mitochondrial injury was determined by mitochondrial membrane potential and electron microscopy. Western blotting was used to investigate the levels of key proteins in ER stress and the apoptotic pathway in mitochondria. The relationship between Ca²⁺ levels and apoptosis in Apoptin-treated cells was analyzed using a Ca²⁺ chelator (BAPTA-AM), flow cytometry, and fluorescence staining. We also investigated the in vivo effects of Ca²⁺ imbalance on the mitochondrial apoptotic pathway using tumor tissues xenografted on nude mice.

RESULTS

This study showed that Apoptin induced a strong and long- lasting ER stress and injury, which subsequently led to an imbalance of cellular Ca²⁺ levels, a reduction in the mitochondrial membrane potential, a significant extent image in the mitochondrial structure, and an increase in the expression levels of Smac/Diablo and Cyto-C.

CONCLUSIONS

In summary, Apoptin induced apoptosis in HepG-2 cells via Ca²⁺ imbalance and activation of the mitochondrial apoptotic pathway. This study provided a new direction for antitumor research in Apoptin.

Endoplasmic Reticulum Stress in Hepatitis B Virus and Hepatitis C Virus Infection

Endoplasmic reticulum (ER) stress, a type of cellular stress, always occurs when unfolded or misfolded proteins accumulating in the ER exceed the protein folding capacity. Because of the demand for rapid viral protein synthesis after viral infection, viral infections become a risk factor for ER stress. The hepatocyte is a cell with large and well-developed ER, and hepatitis virus infection is widespread in the population, indicating the interaction between hepatitis viruses and ER stress may have significance for managing liver diseases. In this paper, we review the process that is initiated by the hepatocyte through ER stress against HBV and HCV infection and explain how this information can be helpful in the treatment of HBV/HCV-related diseases.

Low-dose silver nanoparticles plus methyl mercury exert embryotoxic effects on mouse blastocysts via endoplasmic reticulum stress and mitochondrial apoptosis

The health and environmental impacts of the increasing commercial use of silver nanoparticles (AgNPs) are a growing concern. Methyl mercury (MeHg) is a potent toxin that biotransforms from mercury or inorganic mercury compounds in waterways and causes dangerous environmental contamination. However, the potential interactions and combined effects of AgNPs and MeHg are yet to be established. In the current study, we showed that low/non-embryotoxic doses of AgNPs and MeHg interact synergistically to induce embryotoxicity and further explored the underlying mechanisms affecting mouse embryo development. Notably, co-treatment with noncytotoxic concentrations of AgNPs (10 μM) and MeHg (0.1 μM) triggered apoptotic processes and embryotoxicity in mouse blastocysts and evoked intracellular reactive oxygen species (ROS) generation, which was effectively blocked by preincubation with 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (trolox), a classic antioxidant. Further experiments demonstrated that ROS serve as a key upstream inducer of endoplasmic reticulum (ER) stress and mitochondria-dependent apoptotic processes in AgNP/MeHg-induced injury of mouse embryo implantation and pre- and postimplantation development. Our results collectively indicate that AgNP and MeHg at non-embryotoxic concentrations can synergistically evoke ROS, ultimately causing embryotoxicity through promotion of ER stress and mitochondria-dependent apoptotic signaling cascades.

Tanshinone Protects against Spinal Cord Ischemia-Reperfusion Injury by Inhibiting JNK Activity

Spinal cord reperfusion injury as a secondary damage after primary spinal cord injury is an important factor causing nerve cell damage. In this study, we aim to investigate the effects and mechanisms of tanshinone (TAE) in the rabbit spinal cord during ischemia-reperfusion. New Zealand white rabbits were randomly divided into 3 groups: sham-operated group (5 rabbits), ischemia-reperfusion group (0.9% TAE was administered intraperitoneally 30 min before ischemia, and 4 groups of 5 rabbits each according to different time periods of reperfusion: group A reperfused for 0.5 h, group B reperfused for 2 h, group C reperfused for 8 h, and group D reperfused for 24 h), and TAE group (an ischemia-reperfused for 24 h). Group A was reperfused for 0.5 h, group B for 2 h, group C for 8 h, group D for 24 h, and group TAE (TAE was applied 30 min before ischemia reperfusion, grouped as ischemia-reperfusion group). The expression of JNK (c-Jun NH2-terminal Kinase) and phosphorylation-JNK (p-JNK) in spinal cord tissues of each group were detected by Western blot. Light and electron microscopy showed that early apoptosis started in group B in the ischemia-reperfusion group, while early apoptosis appeared only in group D in the tanshinone intervention group. Western blot showed that p-JNK expression started in group B in the ischemia-reperfusion group and gradually increased with the prolongation of ischemia time, while p-JNK expression only increased in group D in the tanshinone intervention group. In the tanshinone intervention group, p-JNK was activated only in group D and its activity was less than that in the ischemia-reperfusion group; the protein expression of JNK did not change significantly in both groups. Spinal cord ischemia-reperfusion can cause spinal cord injury by activating the signaling molecule JNK (MRPKs family), and early tanshinone intervention can partially inhibit this injury. Our finding provides a new idea and theoretical basis for clinical treatment of spinal cord ischemia-reperfusion injury.

Potential Biomarkers and Drugs for Nanoparticle-Induced Cytotoxicity in the Retina: Based on Regulation of Inflammatory and Apoptotic Genes

The eye is a superficial organ directly exposed to the surrounding environment. Thus, the toxicity of nanoparticle (NP) pollutants to the eye may be potentially severer relative to inner organs and needs to be monitored. However, the cytotoxic mechanisms of NPs on the eyes remain rarely reported. This study was to screen crucial genes associated with NPs-induced retinal injuries. The gene expression profiles in the retina induced by NPs [GSE49371: Au20, Au100, Si20, Si100; GSE49048: presumptive therapeutic concentration (PTC) TiO₂, 10PTC TiO₂] and commonly used retinal cell injury models (optic nerve injury procedure: GSE55228, GSE120257 and GSE131486; hypoxia exposure: GSE173233, GSE151610, GSE135844; H₂O₂ exposure: GSE122270) were obtained from the Gene Expression Omnibus database. A total of 381 differentially expressed genes (including 372 mRNAs and 9 lncRNAs) were shared between NP exposure and the optic nerve injury model when they were compared with their corresponding controls. Function enrichment analysis of these overlapped genes showed that Tlr2, Crhbp, Ccl2, Cxcl10, Fas, Irf8, Socs3, Stat3, Gbp6, Casp1 and Syk were involved in inflammatory- and apoptotic-related processes. Protein-protein interaction network analysis revealed eight of them (Tlr2, Ccl2, Cxcl10, Irf8, Socs3, Stat3, Casp1 and Syk) were hub genes. Moreover, Socs3 could interact with upstream Stat3 and downstream Fas/Casp1/Ccl2/Cxcl10; Irf8 could interact with upstream Tlr2, Syk and downstream Cxcl10. Competing endogenous RNAs network analysis identified Socs3, Irf8, Gdf6 and Crhbp could be regulated by lncRNAs and miRNAs (9330175E14Rik-mmu-miR-762-Socs3, 6430562O15Rik-mmu-miR-207-Irf8, Gm9866-mmu-miR-669b-5p-Gdf6, 4933406C10Rik-mmu-miR-9-5p-Crhbp). CMap-CTD database analyses indicated the expression levels of Tlr2, Ccl2, Cxcl10, Fas, Irf8, Socs3, Stat3, Gbp6, Casp1 and Syk could be reversed by folic acid. Crhbp and Gdf6 were also verified to be downregulated, while Tlr2, Ccl2, Irf8, Socs3 and Stat3 were upregulated in hypoxia/H₂O₂-induced retinal injury models. Hereby, our findings suggest that Crhbp, Irf8, Socs3 and Gdf6 as well as their upstream mRNAs, lncRNAs and miRNAs may be potential monitoring biomarkers and therapeutic targets for NP-induced retinal injuries. Folic acid supplementation may be a preventive and therapeutic approach.

Cytotoxicity of Metal-Based Nanoparticles: From Mechanisms and Methods of Evaluation to Pathological Manifestations

Metal-based nanoparticles (NPs) are particularly important tools in tissue engineering-, drug carrier-, interventional therapy-, and biobased technologies. However, their complex and varied migration and transformation pathways, as well as their continuous accumulation in closed biological systems, cause various unpredictable toxic effects that threaten human and ecosystem health. Considerable experimental and theoretical efforts have been made toward understanding these cytotoxic effects, though more research on metal-based NPs integrated with clinical medicine is required. This review summarizes the mechanisms and evaluation methods of cytotoxicity and provides an in-depth analysis of the typical effects generated in the nervous, immune, reproductive, and genetic systems. In addition, the challenges and opportunities are discussed to enhance future investigations on safer metal-based NPs for practical commercial adoption.

Lentinan inhibited colon cancer growth by inducing endoplasmic reticulum stress-mediated autophagic cell death and apoptosis

Lentinan (SLNT) has been shown to be directly cytotoxic to cancer cells. However, this direct antitumour effect has not been thoroughly investigated in vivo, and the mechanism remains unclear. We aimed to examine the direct antitumour effect of SLNT on human colon cancer and the mechanism in vivo and in vitro. SLNT significantly inhibited tumour growth and induced autophagy and endoplasmic reticulum stress (ERS) in HT-29 cells and tumour-bearing nonobese diabetic (NOD)/severe combined immunodeficiency (SCID) mice. Experiments with the autophagy inhibitors chloroquine (CQ) and 3-methyladenine (3-MA) showed that autophagy facilitated the antitumour effect of SLNT. Moreover, ERS was identified as the common upstream regulator of SLNT-induced increases in Ca2+concentrations, autophagy and apoptosis by using ERS inhibitors. In summary, our study demonstrated that SLNT exerted direct antitumour effects on human colon cancer via ERS-mediated autophagy and apoptosis, providing a novel understanding of SLNT as an anti-colon cancer therapy.

The crosstalk between DRP1-dependent mitochondrial fission and oxidative stress triggers hepatocyte apoptosis induced by silver nanoparticles

Previous studies have revealed that the liver is the main target organ of deposition for engineered nanoparticles. The hepatotoxicity of silver nanoparticles (AgNPs), the widely used antimicrobial nanoparticles, has been of great interest. However, little is known about the regulatory mechanism of the mitochondria in AgNP-induced hepatotoxicity. In the present study, we found that AgNPs, rather than silver ions, induced mitochondrial dynamics disorders, oxidative stress, and mitochondria-dependent hepatocyte apoptosis in mice. Using human hepatocellular carcinoma (HepG2) cells, we confirmed that the interaction between dynamin-related protein 1 (DRP1)-dependent mitochondrial fission and oxidative stress promoted mitochondrial damage and mitochondria-dependent apoptosis induced by AgNPs, as determined by the elimination of DRP1 or addition of N-acetylcysteine (NAC). Interestingly, the crosstalk between DRP1-dependent mitochondrial fission and oxidative stress also activated mitophagy and autophagy flux blocking. Phosphatase and tensin homolog (PTEN)-induced putative kinase 1 (PINK1) gene silencing contributed to the aggravation of mitochondrial damage, oxidative stress, and apoptosis. These results revealed that the interplay between mitochondrial fission and oxidative stress induced mitophagy defects and triggered AgNP-induced mitochondria-dependent apoptosis in liver cells both in vivo and in vitro. Our findings provide a perspective for the mechanism of hepatotoxicity induced by exposure to metal NPs.

Malvidin and its derivatives exhibit antioxidant properties by inhibiting MAPK signaling pathways to reduce endoplasmic reticulum stress in ARPE-19 cells

Malvidin (MV) and its derivatives, such as malvidin-3-O-guaiacol (Mv3C) and malvidin-3-O-6-(acrylic acid-(2-hydroxy,4-carboxy-cyclohexanol)ester)-guaiacol (Mv3ACEC), are natural compounds with antioxidant properties. However, the basic mechanisms underlying their functional activities are unclear. In this study, we show that MV, Mv3C, and Mv3ACEC inhibit reactive oxygen species production and malondialdehyde content, promote glutathione peroxidase activity, and increase superoxide dismutase levels in ARPE-19 cells treated with H₂O₂. Western blotting and immunofluorescence analysis revealed that MV, Mv3C, and Mv3ACEC regulate mitogen-activated protein kinase signal transduction pathways related to endoplasmic reticulum stress. Interestingly, Mv3C and Mv3ACEC showed greater beneficial properties than MV. Our results show that MV and its derivatives have potential as therapeutic compounds for ocular diseases associated with oxidative stress, such as age-related macular degeneration.

Silver nanoparticles induce apoptosis via NOX4-derived mitochondrial reactive oxygen species and endoplasmic reticulum stress in colorectal cancer cells

Aim: To investigate the anticancer mechanisms of silver nanoparticles (AgNPs) in colorectal cancer. Methods: Anticancer effects of AgNPs were determined in colorectal cancer HCT116 cells and xenograft mice using cellular and molecular methods. Results: AgNPs induced mitochondrial reactive oxygen species production, mitochondrial dysfunction and endoplasmic reticulum (ER) stress responses through NOX4 and led to HCT116 cell apoptosis. Pretreatment with DPI or 4-PBA significantly inhibited mitochondrial reactive oxygen species production, apoptosis, ER stress response, NOX4 expression and mitochondrial dysfunction in AgNP-treated HCT116 cells. AgNPs also significantly suppressed HCT116 cell-based xenograft tumor growth in nude mice by inducing apoptosis and ER stress responses. Conclusion: AgNPs exert anticancer effects against colorectal cancer via ROS- and ER stress-related mitochondrial apoptosis pathways.

Endoplasmic Reticulum Stress Contributes to Gefitinib-Induced Apoptosis in Glioma

Adequate stress on the Endoplasmic Reticulum (ER) with the Unfolded Protein Response (UPR) could maintain glioma malignancy. Uncontrolled ER stress, on the other hand, predisposes an apoptosis-dominant UPR program. We studied here the proapoptotic actions of the Epidermal Growth Factor Receptor (EGFR) inhibitor gefitinib, with the focus on ER stress. The study models were human H4 and U87 glioma cell lines. We found that the glioma cell-killing effects of gefitinib involved caspase 3 apoptotic cascades. Three branches of ER stress, namely Activating Transcription Factor-6 (ATF6), Protein Kinase R (PKR)-Like ER Kinase (PERK), and Inositol-Requiring Enzyme 1 (IRE1), were activated by gefitinib, along with the elevation of intracellular free Ca²⁺, Reactive Oxygen Species (ROS), and NADPH Oxidase2/4 (NOX2/4). Specifically, elevated IRE1 phosphorylation, Tumor Necrosis Factor (TNF) Receptor-Associated Factor-2 (TRAF2) expression, Apoptosis Signal-Regulating Kinase-1 (Ask1) phosphorylation, c-Jun N-Terminal Kinase (JNK) phosphorylation, and Noxa expression appeared in gefitinib-treated glioma cells. Genetic, pharmacological, and biochemical studies further indicated an active ROS/ER stress/Ask1/JNK/Noxa axis causing the glioma apoptosis induced by gefitinib. The findings suggest that ER-stress-based therapeutic targeting could be a promising option in EGFR inhibitor glioma therapy, and may ultimately achieve a better patient response.