2,4-dichlorophenol induces ER stress-mediated apoptosis via eIF2α dephosphorylation in vitro

Effects of 2,4-dichlorophenol on non-specific immunity, histopathological lesions, and redox balance in African Catfish, clarias gariepinus (Burchell, 1822)

The toxic effects of 2, 4-dichlorophenol (2, 4-DCP) on aquatic organisms are well-established; however, the details regarding the mechanisms underlying the toxicity, especially immunotoxicity are poorly understood. Consequently, the aim of this study was to investigate the histopathologic, oxidative stress and immunotoxic effects attributed to exposure to sublethal concentrations of 2,4-DCP in the African catfish, Clarias gariepinus. Juvenile C. gariepinus were exposed to 0.4, 0.8, or 1.6 mg/L 2, 4-DCP for 28 days after which blood and head kidney were extracted for the determination of various nonspecific innate immune parameters while the liver was excised for histopathology examination and measurement of oxidative stress biomarkers. Control fish were maintained in water spiked 10 µL/L ethanol, representing the solvent control. A significant increase was noted in the activities of lactate dehydrogenase and superoxide dismutase as well as in levels of lipid peroxidation and DNA fragmentation in a dose-dependent manner, with higher adverse effects observed at the highest concentration tested (1.6 mg/L). The total white blood cells (WBC) count was significantly elevated in fish exposed to 2,4-DCP compared to control. Myeloperoxidase content was decreased significantly in fish exposed to 2,4-DCP especially at the highest concentration (1.6 mg/L) compared to controls. The respiratory burst activity did not differ markedly amongst groups. Histopathological lesions noted included edema, leucocyte infiltration, and depletion of hemopoietic tissue in the head kidney of exposed fish. There was significant upregulation in the mRNA expression of tumor necrosis factor (TNF-α) and heat shock protein 70 (HSP 70) but downregulation of major histocompatibility complex 2 (MHC 2) in exposed fish. Data demonstrated that exposure to 2,4-DCP resulted in histopathological lesions, oxidative stress, and compromised immune system in C. gariepinus.

Time-course transcriptome analysis discloses PFDMO2OA (C8 HFPO-TA)-induced developmental malformations and cardiovascular toxicities in zebrafish

PFDMO2OA (C8 HFPO-TA), a novel substitute for perfluorooctanoic acid (PFOA), has been frequently detected in surface waters. However, information on its toxicity remains scarce. In the present study, zebrafish embryos were exposed to varying concentrations of PFDMO2OA, ranging from 80 to 800 mg/L, until 120 h post-fertilization (hpf) to explore its potential developmental toxicities. The LC50 value for mortality was 505.9 mg/L, comparable to that of PFOA (over 500 mg/L), suggesting a lack of safety of PFDMO2OA compared to PFOA. At 120 hpf, PFDMO2OA exposure led to various malformations in embryos, including uninflated swim bladder, yolk sac oedema, spinal deformation, and pigmentation changes, with pericardial oedema being prominent. Analysis using O-dianisidine stain indicated a decline in erythrocytes over time. Transcriptome analysis further revealed the cardiovascular toxicity caused by PFDMO2OA at the molecular level. Time-course differential analysis pointed to the apoptosis dependent on disrupted mitochondrial function as a significant contributor to erythrocyte disappearance, as confirmed by the TUNEL stain. Therefore, the present findings suggest that PFDMO2OA induces developmental malformations and cardiovascular toxicities in zebrafish embryos, demonstrating a toxic potency comparable to that of PFOA. The results further highlight the significance of evaluating the health risks associated with PFDMO2OA.

Endocrine-Disrupting Chemicals and Their Adverse Effects on the Endoplasmic Reticulum

There is growing concern regarding the health and safety issues of endocrine-disrupting chemicals (EDCs). Long-term exposure to EDCs has serious adverse health effects through both hormone-direct and hormone-indirect ways. Accordingly, some EDCs can be a pathogen and an inducer to the susceptibility of disease, even if they have a very low affinity on the estrogen receptor, or no estrogenic effect. Endoplasmic reticulum (ER) stress recently attracted attention in this research area. Because ER and ER stress could be key regulators of the EDC’s adverse effects, such as the malfunction of the organ, as well as the death, apoptosis, and proliferation of a cell. In this review, we focused on finding evidence which shows that EDCs could be a trigger for ER stress and provide specific examples of EDCs, which are known to cause ER stress currently.

Monobutyl phthalate can induce autophagy and metabolic disorders by activating the ire1a-xbp1 pathway in zebrafish liver

Monobutyl phthalate (MBP) can exist in biological organisms for a long time because of its excellent fat solubility, and it has been found to have certain toxic effects. In this study, the acute effects of MBP on endoplasmic reticulum (ER) stress and metabolism in the zebrafish liver were studied. After continuous exposure to MBP (5 and 10 mg / L) for 96 h, ER damage and the appearance of apoptotic bodies and autophagosomes were found in liver. This is because MBP stimulated the ire-xbp1 pathway of ER stress, thus leading to apoptosis and autophagy. Also, through analysis of metabolic enzymes and genes, it was found that the activated ire-xbp1 pathway could promote lipid synthesis and cause the accumulation of lipid droplets. The gene pparγ related to lipid storage affected the level of insulin, which can also further affect the glucose metabolism process, that is, glycolysis and aerobic respiration were inhibited. And the pentose phosphate pathway (PPP) was activated as a compensation mechanism to alleviate glycogen accumulation. The abnormal supply of energy and the death of excessive cells will eventually severely damage the zebrafish liver. This study will enrich the knowledge about the toxic effects of MBP.

tmbim4 protects against triclocarban-induced embryonic toxicity in zebrafish by regulating autophagy and apoptosis

Triclocarban (TCC), an antibacterial agent widely used in personal care products, can affect embryonic development. However, the specific molecular mechanism of TCC-induced embryonic developmental damage remains unclear. In this study, TCC exposure was found to increase the expression of tmbim4 gene in zebrafish embryos. The tmbim4 mutant embryos are more susceptible to TCC exposure than wild-type (WT) embryos, with tmbim4 overexpression reducing TCC-induced embryonic death in the former. Exposure of tmbim4 mutant larvae to 400 μg/L TCC substantially increased apoptosis in the hindbrain and eyes. RNA-sequencing of WT and tmbim4 mutant larvae indicated that knockout of the tmbim4 gene in zebrafish affects the autophagy pathway. Abnormalities in autophagy can increase apoptosis and TCC exposure caused abnormal accumulation of autophagosomes in the hindbrain of tmbim4 mutant zebrafish embryos. Pretreatment of TCC-exposed tmbim4 mutant zebrafish embryos with autophagosome formation inhibitors, substantially reduced the mortality of embryos and apoptosis levels. These results indicate that defects in the tmbim4 gene can reduce zebrafish embryo resistance to TCC. Additionally, apoptosis induced by abnormal accumulation of autophagosomes is involved in this process.

Adverse effects of pesticides on the functions of immune system

Pesticides are chemical substances used to kill unwanted fungi, weeds and insects. In many countries, there is currently concern regarding the adverse effects of pesticides on health. It has been reported that pesticides may cause cancer, respiratory diseases, organ diseases, system failures, nervous system disorders and asthma, which are closely connected with immune disorders. Therefore, this study reviewed the immunotoxicity of pesticides that are currently used or prohibited from being used, especially their effects on leukocytes such as T cells, B cells, NK cells and macrophages. These immune cells play crucial roles in innate and adaptive immune systems to protect hosts. Pesticides are known to have possible toxicological modes of action to induce oxidative stress, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress in living organisms. According to previous studies, pesticides such as atrazine (ATR), organophophorus (OP) compounds, carbamates, and pyrethroids were shown to inhibit the survival and growth of leukocytes by inducing apoptosis or cell cycle arrest and interfering with the specific immunological functions of each type of immune cells. These results suggest the immunotoxicity of pesticides toward specific immune cells. To substantiate the overall immunocompromised effects of pesticides, there is a need to collect and thoroughly analyze additional information regarding other immunological toxicities.

Endoplasmic reticulum stress is involved in 2,4-dichlorophenol-induced hepatotoxicity

2,4-Dichlorophenol (2,4-DCP) is an environmental pollutant exhibiting a wide spectrum of toxic effects. We investigated the toxic effects and potential mechanisms underlying 2,4-DCP-induced hepatotoxicity. In vitro, 2,4-DCP caused hepatotoxicity manifested by a decrease in cell viability and inhibition of colony formation. Bip and CHOP expression was up-regulated at the mRNA and protein levels. Moreover, 2,4-DCP induced eIF2α phosphorylation and Xbp1 mRNA splicing, indicating that endoplasmic reticulum (ER) stress was activated after exposure of HL7702 cells to 2,4-DCP for 12 hr. Furthermore, the mitochondrial membrane potential collapsed and apoptosis was triggered after exposure to 2,4-DCP for 24 hr. In vivo, 2,4-DCP caused histological changes in the liver, and dramatically elevated the serum alanine transaminase (ALT) and aspartate aminotransferase (AST) levels of mice. ER stress was also triggered in the liver of mice on days 1 and 3. The ER stress inhibitor TUDCA could partly relieve the liver damage, as indicated by the restoration of serum ALT and AST levels. Taken together, our results demonstrated that ER stress may serve as an early warning mechanism against 2,4-DCP-induced hepatotoxicity, and severe ER stress may lead to apoptosis.

The toxic effects of chlorophenols and associated mechanisms in fish

Chlorophenols (CPs) are ubiquitous contaminants in the environment primarily released from agricultural and industrial wastewater. These compounds are not readily degraded naturally, and easily accumulate in organs, tissues and cells via food chains, further leading to acute and chronic toxic effects on aquatic organisms. Herein, we review the available literature regarding CP toxicity in fish, with special emphasis on the potential toxic mechanisms. CPs cause oxidative stress via generation of reactive oxygen species, induction of lipid peroxidation and/or oxidative DNA damage along with inhibition of antioxidant systems. CPs affect immune system by altering the number of mature B cells and macrophages, while suppressing phagocytosis and down-regulating the expression of immune factors. CPs also disrupt endocrine function by affecting hormone levels, or inducing abnormal gene expression and interference with hormone receptors. CPs at relatively higher concentrations induce apoptosis via mitochondria-mediated pathway, cell death receptor-mediated pathway, and/or DNA damage-mediated pathway. CPs at relatively lower concentrations promote cell proliferation, and foster cancers-prone environment by increasing the rate of point mutations and oxidative DNA lesions. These toxic effects in fish are induced directly by CPs per se or indirectly by their metabolic products. In addition, recent studies on the alteration of DNA methylation by CPs through high-throughput DNA sequencing analysis provide new insights into our understanding of the epigenetic mechanisms underlying CPs toxicity.

Endoplasmic reticulum stress signaling in mammalian oocytes and embryos: life in balance

Mammalian oocytes and embryos are exquisitely sensitive to a wide range of insults related to physical stress, chemical exposure, and exposures to adverse maternal nutrition or health status. Although cells manifest specific responses to various stressors, many of these stressors intersect at the endoplasmic reticulum (ER), where disruptions in protein folding and production of reactive oxygen species initiate downstream signaling events. These signals modulate mRNA translation and gene transcription, leading to recovery, activation of autophagy, or with severe and prolonged stress, apoptosis. ER stress signaling has recently come to the fore as a major contributor to embryo demise. Accordingly, agents that modulate or inhibit ER stress signaling have yielded beneficial effects on embryo survival and long-term developmental potential. We review here the mechanisms of ER stress signaling, their connections to mammalian oocytes and embryos, and the promising indications that interventions in this pathway may provide new opportunities for improving mammalian reproduction and health.