Endoplasmic reticulum stress contributes to arsenic trioxide-induced intrinsic apoptosis in human umbilical and bone marrow mesenchymal stem cells

Mechanisms Associated with Cognitive and Behavioral Impairment Induced by Arsenic Exposure

Arsenic (As) is a metalloid naturally present in the environment, in food, water, soil, and air; however, its chronic exposure, even with low doses, represents a public health concern. For a long time, As was used as a pigment, pesticide, wood preservative, and for medical applications; its industrial use has recently decreased or has been discontinued due to its toxicity. Due to its versatile applications and distribution, there is a wide spectrum of human As exposure sources, mainly contaminated drinking water. The fact that As is present in drinking water implies chronic human exposure to this metalloid; it has become a worldwide health problem, since over 200 million people live where As levels exceed safe ranges. Many health problems have been associated with As chronic exposure including cancer, cardiovascular diseases, gastrointestinal disturbances, and brain dysfunctions. Because As can cross the blood-brain barrier (BBB), the brain represents a target organ where this metalloid can exert its long-term toxic effects. Many mechanisms of As neurotoxicity have been described: oxidative stress, inflammation, DNA damage, and mitochondrial dysfunction; all of them can converge, thus leading to impaired cellular functions, cell death, and in consequence, long-term detrimental effects. Here, we provide a current overview of As toxicity and integrated the global mechanisms involved in cognitive and behavioral impairment induced by As exposure show experimental strategies against its neurotoxicity.

Mitochondrial Oxidative Stress Is the General Reason for Apoptosis Induced by Different-Valence Heavy Metals in Cells and Mitochondria

This review analyzes the causes and consequences of apoptosis resulting from oxidative stress that occurs in mitochondria and cells exposed to the toxic effects of different-valence heavy metals (Ag+, Tl+, Hg2+, Cd2+, Pb2+, Al3+, Ga3+, In3+, As3+, Sb3+, Cr6+, and U6+). The problems of the relationship between the integration of these toxic metals into molecular mechanisms with the subsequent development of pathophysiological processes and the appearance of diseases caused by the accumulation of these metals in the body are also addressed in this review. Such apoptosis is characterized by a reduction in cell viability, the activation of caspase-3 and caspase-9, the expression of pro-apoptotic genes (Bax and Bcl-2), and the activation of protein kinases (ERK, JNK, p53, and p38) by mitogens. Moreover, the oxidative stress manifests as the mitochondrial permeability transition pore (MPTP) opening, mitochondrial swelling, an increase in the production of reactive oxygen species (ROS) and H2O2, lipid peroxidation, cytochrome c release, a decline in the inner mitochondrial membrane potential (ΔΨmito), a decrease in ATP synthesis, and reduced glutathione and oxygen consumption as well as cytoplasm and matrix calcium overload due to Ca2+ release from the endoplasmic reticulum (ER). The apoptosis and respiratory dysfunction induced by these metals are discussed regarding their interaction with cellular and mitochondrial thiol groups and Fe2+ metabolism disturbance. Similarities and differences in the toxic effects of Tl+ from those of other heavy metals under review are discussed. Similarities may be due to the increase in the cytoplasmic calcium concentration induced by Tl+ and these metals. One difference discussed is the failure to decrease Tl+ toxicity through metallothionein-dependent mechanisms. Another difference could be the decrease in reduced glutathione in the matrix due to the reversible oxidation of Tl+ to Tl3+ near the centers of ROS generation in the respiratory chain. The latter may explain why thallium toxicity to humans turned out to be higher than the toxicity of mercury, lead, cadmium, copper, and zinc.

Arsenic trioxide induces expression of BCL-2 expression via NF-κB and p38 MAPK signaling pathways in BEAS-2B cells during apoptosis

Inorganic arsenic compounds are environmental toxicants that are widely distributed in air, water, and food. B-cell lymphoma 2 (BCL-2) is an oncogene having anti-apoptotic function. In this study, we clarify that BCL-2, as a pro-apoptotic factor, participates in As₂O₃-induced apoptosis in BEAS-2B cells. Specifically, As₂O₃ stimulated the expression of BCL-2 mRNA and protein in a dose-dependent manner which was highly accumulated in the nucleus of BEAS-2B cell together with chromatin condensation and DNA fragmentation during apoptosis. Mechanistically, the process described above is mediated through the NF-κB and p38 MAPK signaling pathways, which can be abated by corresponding inhibitors, such as BAY11-7082 and SB203580, respectively. Additionally, BAY11-7082, actinomycin D, and cycloheximide have inhibitory effects on As₂O₃-induced expression of BCL-2 mRNA and protein, and restore the cell viability of BEAS-2B cells. Suppression of BCL-2 protein activation by ABT-199 also restored viability of BEAS-2B cell in As₂O₃-induced apoptosis. Furthermore, As₂O₃ increased the level of BCL-2 phosphorylation. These results suggest that in BEAS-2B cells, As₂O₃-induced apoptosis is mainly dominated by BCL-2 upregulation, nuclear localization and phosphorylation. The study presented here provides a novel insight into the molecular mechanism of BCL-2-induced apoptosis.

Potential therapeutic compounds from traditional Chinese medicine targeting endoplasmic reticulum stress to alleviate rheumatoid arthritis

Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease which affects about 0.5-1% of people with symptoms that significantly impact a sufferer's lifestyle. The cells involved in propagating RA tend to display pro-inflammatory and cancer-like characteristics. Medical drug treatment is currently the main avenue of RA therapy. However, drug options are limited due to severe side effects, high costs, insufficient disease retardation in a majority of patients, and therapeutic effects possibly subsiding over time. Thus there is a need for new drug therapies. Endoplasmic reticulum (ER) stress, a condition due to accumulation of misfolded proteins in the ER, and subsequent cellular responses have been found to be involved in cancer and inflammatory pathologies, including RA. ER stress protein markers and their modulation have therefore been suggested as therapeutic targets, such as GRP78 and CHOP, among others. Some current RA therapeutic drugs have been found to have ER stress-modulating properties. Traditional Chinese Medicines (TCMs) frequently use natural products that affect multiple body and cellular targets, and several medicines and/or their isolated compounds have been found to also have ER stress-modulating capabilities, including TCMs used in RA treatment by Chinese Medicine practitioners. This review encourages, in light of the available information, the study of these RA-treating, ER stress-modulating TCMs as potential new pharmaceutical drugs for use in clinical RA therapy, along with providing a list of other ER stress-modulating TCMs utilized in treatment of cancers, inflammatory diseases and other diseases, that have potential use in RA treatment given similar ER stress-modulating capacity.

Feasibility of Sijunzi Tang (Chinese medicine) to enhance protein disulfide isomerase activities for reactivating malate dehydrogenase deactivated by polycyclic aromatic hydrocarbons

The objective of this research is to investigate the enzymatic activities between protein disulfide isomerase (PDI) found in animals and plants and the properties found in a commonly used Chinese medicine called Sijunzi Tang. During the investigation, PDI, which is a monomer with a molecular mass of 57.0 kDa, was used to reactivate malate dehydrogenase (MDH). However, with the interference of polycyclic aromatic hydrocarbons (PAHs), evidence indicates that such chemicals are carcinogenic, mutagenic, and toxic to humans. The enzymatic activity of PDI found in animal's liver and plant was 1657 folds of purification; 0.284 unit/mg of enzyme activity, and 5694.4 folds of purification; 1.00 unit/mg of enzyme activity, respectively. PDI extracted in treated animal and plant tissue revealed 2.40% and 80.44% of regaining MDH enzymatic activity, respectively. Although in its initial phase of investigation, it is assumed that the properties found in Sijunzi Tang can help regain enzymatic activity in those affected by xenobiotic substances, thus, making it a potential ingredient in assisting with PDI functions.

CUDC-101 overcomes arsenic trioxide resistance via caspase-dependent promyelocytic leukemia-retinoic acid receptor alpha degradation in acute promyelocytic leukemia

Although arsenic trioxide (ATO) treatment has transformed acute promyelocytic leukemia (APL) from the most fatal to the most curable hematological cancer, many high-risk APL patients who fail to achieve a complete molecular remission or relapse become resistant to ATO. Herein, we report that 7-(4-(3-ethynylphenylamino)-7-methoxyquinazolin-6-yloxy)-N-hydroxyheptanamide (CUDC-101) exhibits specific anticancer effects on APL and ATO-resistant APL in vitro and in vivo, while showing negligible cytotoxic effect on the noncancerous cells including normal CD34 cells and bone marrow mesenchymal stem cells from APL patients. Further mechanistic studies show that CUDC-101 triggers caspase-dependent degradation of the promyelocytic leukemia-retinoic acid receptor alpha fusion protein. As a result, APL and ATO-resistant APL cells undergo apoptosis upon CUDC-101 treatment and this apoptosis-inducing effect is even stronger than that of ATO. Finally, using a xenograft mouse model, we demonstrated that CUDC-101 significantly represses leukemia development in vivo. In conclusion, these results suggested that CUDC-101 can serve as a potential candidate drug for APL, particularly for ATO-resistant APL.

Endoplasmic Reticulum Stress Induced by Toxic Elements-a Review of Recent Developments

Endoplasmic reticulum of all eukaryotic cells is a membrane-bound organelle. Under electron microscope it appears as parallel arrays of "rough membranes" and a maze of "smooth vesicles" respectively. It performs various functions in cell, i.e., synthesis of proteins to degradation of xenobiotics. Bioaccumulation of drugs/chemicals/xenobiotics in the cytosol can trigger ER stress. It is recognized by the accumulation of unfolded or misfolded proteins in the lumen of ER. Present review summarizes the present status of knowledge on ER stress caused by toxic elements, viz arsenic, cadmium, lead, mercury, copper, chromium, and nickel. While inorganic arsenic may induce various glucose-related proteins, i.e., GRP78, GRP94 and CHOP, XBP1, and calpains, cadmium upregulates GRP78. Antioxidants like ascorbic acid, NAC, and Se inhibit the expression of UPR. Exposure to lead also changes ER stress related genes, i.e., GRP 78, GRP 94, ATF4, and ATF6. Mercury too upregulates these genes. Nickel, a carcinogenic element upregulates the expression of Bak, cytochrome C, caspase-3, caspase-9, caspase-12, and GADD 153. Much is not known on ER stress caused by nanoparticles. The review describes inter-organelle association between mitochondria and ER. It also discusses the interdependence between oxidative stress and ER stress. A cross talk amongst different cellular components appears essential to disturb pathways leading to cell death. However, these molecular switches within the signaling network used by toxic elements need to be identified. Nevertheless, ER stress especially caused by toxic elements still remains to be an engaging issue.

In Silico Pharmacoepidemiologic Evaluation of Drug-Induced Cardiovascular Complications Using Combined Classifiers

Drug-induced cardiovascular complications are the most common adverse drug events and account for the withdrawal or severe restrictions on the use of multitudinous postmarketed drugs. In this study, we developed new in silico models for systematic identification of drug-induced cardiovascular complications in drug discovery and postmarketing surveillance. Specifically, we collected drug-induced cardiovascular complications covering the five most common types of cardiovascular outcomes (hypertension, heart block, arrhythmia, cardiac failure, and myocardial infarction) from four publicly available data resources: Comparative Toxicogenomics Database, SIDER, Offsides, and MetaADEDB. Using these databases, we developed a combined classifier framework through integration of five machine-learning algorithms: logistic regression, random forest, k-nearest neighbors, support vector machine, and neural network. The totality of models included 180 single classifiers with area under receiver operating characteristic curves (AUC) ranging from 0.647 to 0.809 on 5-fold cross-validations. To develop the combined classifiers, we then utilized a neural network algorithm to integrate the best four single classifiers for each cardiovascular outcome. The combined classifiers had higher performance with an AUC range from 0.784 to 0.842 compared to single classifiers. Furthermore, we validated our predicted cardiovascular complications for 63 anticancer agents using experimental data from clinical studies, human pluripotent stem cell-derived cardiomyocyte assays, and literature. The success rate of our combined classifiers reached 87%. In conclusion, this study presents powerful in silico tools for systematic risk assessment of drug-induced cardiovascular complications. This tool is relevant not only in early stages of drug discovery but also throughout the life of a drug including clinical trials and postmarketing surveillance.

Effect of bis(hydroxymethyl) alkanoate curcuminoid derivative MTH-3 on cell cycle arrest, apoptotic and autophagic pathway in triple-negative breast adenocarcinoma MDA-MB-231 cells: An in vitro study

Curcumin has been shown to exert potential antitumor activity in vitro and in vivo involved in multiple signaling pathways. However, the application of curcumin is still limited because of its poor hydrophilicity and low bio-availability. In the present study, we investigated the therapeutic effects of a novel and water soluble bis(hydroxymethyl) alkanoate curcuminoid derivative, MTH-3, on human breast adenocarcinoma MDA-MB-231 cells. This study investigated the effect of MTH-3 on cell viability, cell cycle and induction of autophagy and apoptosis in MDA-MB-231 cells. After 24-h treatment with MTH-3, a concentration-dependent decrease in MDA-MB-231 cell viability was observed, and the IC₅₀ value was 5.37±1.22 μM. MTH-3 significantly triggered G₂/M phase arrest and apoptosis in MDA-MB-231 cells. Within a 24-h treatment, MTH-3 decreased the CDK1 activity by decreasing CDK1 and cyclin B1 protein levels. MTH-3-induced apoptosis was further confirmed by morphological assessment and Annexin V/PI staining assay. Induction of apoptosis caused by MTH-3 was accompanied by an apparent increase of DR3, DR5 and FADD and, as well as a marked decrease of Bcl-2 and Bcl-xL protein expression. MTH-3 also decreased the protein levels of Ero1, PDI, PERK and calnexin, as well as increased the expression of IRE1α, CHOP and Bip that consequently led to ER stress and MDA-MB-231 cell apoptosis. In addition, MTH-3-treated cells were involved in the autophagic process and cleavage of LC3B was observed. MTH-3 enhanced the protein levels of LC3B, Atg5, Atg7, Atg12, p62 and Beclin-1 in MDA-MB-231 cells. Finally, DNA microarray was carried out to investigate the level changes of gene expression modulated by MTH-3 in MDA-MB-231 cells. Taken together, our results suggest that MTH-3 might be a novel therapeutic agent for the treatment of triple-negative breast cancer in the near future.

Arsenic trioxide exposure impairs testicular morphology in adult male mice and consequent fetus viability

The acute promyelocytic leukemia (APL) is a rare disease, affecting 0.1/100,000 individuals globally. Despite significant advances in APL therapy, some patients still experience relapsed disease. Currently, arsenic trioxide (As₂O₃) was found to be effective in relapsed APL treatment and considered as standard treatment for these cases. However, it has been shown that exposure to As₂O₃ may exert adverse effects on the male reproductive system since this substance might also induce apoptosis of other important cell types including stem cells. Studies demonstrated that treatment with this metallic substance decreased plasma levels of testosterone and interfered with sperm parameters such as concentration, motility, and viability. In addition, As₂O₃ was found to produce significant damage to spermatocytes, which may be associated with testicular toxicity and consequent inhibition of spermatogenesis. The aim of this study was to determine sub-chronic treatment effects of As₂O₃ on sperm and testicular morphology, androgen receptor (AR) immunoreactivity in testes and epididymis, in addition to evaluation of fertility parameters in adult male mice. Thirty adult Swiss mice were divided into three experimental groups: control; received distilled water (vehicle) while treated received 0.3 or 3 mg/kg/day As₂O₃ subcutaneously, for 5 days per week, followed by 2 days of interruption, for 5 weeks. Results showed that As₂O₃ (1) decreased spermatozoa number, (2) produced seminiferous epithelium degeneration and exfoliation of germ cells tubule lumen (3) altered nucleus/cytoplasm proportion of Leydig cells and (4) reduced AR immunoreactivity in both Leydig and epithelial epididymal cells. Further, fetal viability tests demonstrated an increase in post-implantation loss in females that were mated with As₂O₃-treated males. Data indicate that As₂O₃ exposure altered the spermatogenic process and subsequently fetal viability.

Epigallocatechin gallate sensitizes cisplatin-resistant oral cancer CAR cell apoptosis and autophagy through stimulating AKT/STAT3 pathway and suppressing multidrug resistance 1 signaling

Epigallocatechin gallate (EGCG) is a green tea polyphenol that presents anticancer activities in multiple cancer cells, but no available report was addressed for the underling molecular mechanism of cytotoxic impacts on drug-resistant oral squamous cell carcinoma cells. In the present study, the inhibitory effects of EGCG were experienced on cisplatin-resistant oral cancer CAR cells. EGCG inhibited cell viability in a time- and concentration-dependent manner by a sulforhodamine B (SRB) assay. EGCG induced CAR cell apoptosis and autophagy by 4',6-diamidino-2-phenylindole (DAPI) dye, acridine orange (AO) staining and green fluorescent protein (GFP)-tagged LC3B assay, respectively. EGCG also significantly enhanced caspase-9 and caspase-3 activities by caspase activity assay. EGCG markedly increased the protein levels of Bax, cleaved caspase-9, cleaved caspase-3, Atg5, Atg7, Atg12, Beclin-1, and LC3B-II, as well as significantly decreased the expression of Bcl-2, phosphorylated AKT (Ser473) and phosphorylation of STAT3 on Tyr705 by western blotting in CAR cells. Importantly, the protein and gene expression of multidrug resistance 1 (MDR1) were dose-dependently inhibited by EGCG. Overall, downregulation of MDR1 levels and alterations of AKT/STAT3 signaling contributed to EGCG-induced apoptosis and autophagy in CAR cells. Based on these results, EGCG has the potential for therapeutic effect on oral cancer and may be useful for long-term oral cancer prevention in the future. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 845-855, 2017.

ATF4 regulates arsenic trioxide-mediated NADPH oxidase, ER-mitochondrial crosstalk and apoptosis

Arsenic is a mitochondrial toxin, and its derivatives, such as arsenic trioxide (ATO), can trigger endoplasmic reticulum (ER) and the associated unfolded protein response (UPR). Here, we show that arsenic induction of the UPR triggers ATF4, which is involved in regulating this ER-mitochondrial crosstalk that is important for the molecular pathogenesis of arsenic toxicity. Employing ATF4+/+ and ATF4-/- MEFs, we show that ATO induces UPR and impairs mitochondrial integrity in ATF4+/+ MEF cells which is largely ablated upon loss of ATF4. Following ATO treatment, ATF4 activates NADPH oxidase by promoting assembly of the enzyme components Rac-1/P47phox/P67phox, which generates ROS/superoxides. Furthermore, ATF4 is required for triggering Ca++/calpain/caspase-12-mediated apoptosis following ATO treatment. The IP3R inhibitor attenuates Ca++/calpain-dependent apoptosis, as well as reduces m-ROS and MMP disruption, suggesting that ER-mitochondria crosstalk involves IP3R-regulated Ca++ signaling. Blockade of m-Ca++ entry by inhibiting m-VDAC reduces ATO-mediated UPR in ATF4+/+ cells. Additionally, ATO treatment leads to p53-regulated mitochondrial apoptosis, where p53 phosphorylation plays a key role. Together, these findings indicate that ATO-mediated apoptosis is regulated by both ER and mitochondria events that are facilitated by ATF4 and the UPR. Thus, we describe novel mechanisms by which ATO orchestrates cytotoxic responses involving interplay of ER and mitochondria.

New insights into the unfolded protein response in stem cells

The unfolded protein response (UPR) is an evolutionarily conserved adaptive mechanism to increase cell survival under endoplasmic reticulum (ER) stress conditions. The UPR is critical for maintaining cell homeostasis under physiological and pathological conditions. The vital functions of the UPR in development, metabolism and immunity have been demonstrated in several cell types. UPR dysfunction activates a variety of pathologies, including cancer, inflammation, neurodegenerative disease, metabolic disease and immune disease. Stem cells with the special ability to self-renew and differentiate into various somatic cells have been demonstrated to be present in multiple tissues. These cells are involved in development, tissue renewal and certain disease processes. Although the role and regulation of the UPR in somatic cells has been widely reported, the function of the UPR in stem cells is not fully known, and the roles and functions of the UPR are dependent on the stem cell type. Therefore, in this article, the potential significances of the UPR in stem cells, including embryonic stem cells, tissue stem cells, cancer stem cells and induced pluripotent cells, are comprehensively reviewed. This review aims to provide novel insights regarding the mechanisms associated with stem cell differentiation and cancer pathology.

Role of endoplasmic reticulum stress in drug-induced toxicity

Drug‐induced toxicity is a key issue for public health because some side effects can be severe and life‐threatening. These adverse effects can also be a major concern for the pharmaceutical companies since significant toxicity can lead to the interruption of clinical trials, or the withdrawal of the incriminated drugs from the market. Recent studies suggested that endoplasmic reticulum (ER) stress could be an important event involved in drug liability, in addition to other key mechanisms such as mitochondrial dysfunction and oxidative stress. Indeed, drug‐induced ER stress could lead to several deleterious effects within cells and tissues including accumulation of lipids, cell death, cytolysis, and inflammation. After recalling important information regarding drug‐induced adverse reactions and ER stress in diverse pathophysiological situations, this review summarizes the main data pertaining to drug‐induced ER stress and its potential involvement in different adverse effects. Drugs presented in this review are for instance acetaminophen (APAP), arsenic trioxide and other anticancer drugs, diclofenac, and different antiretroviral compounds. We also included data on tunicamycin (an antibiotic not used in human medicine because of its toxicity) and thapsigargin (a toxic compound of the Mediterranean plant Thapsia garganica) since both molecules are commonly used as prototypical toxins to induce ER stress in cellular and animal models.