2,3,7,8-Tetrachlorodibenzo-p-dioxin induced autophagy in a bovine kidney cell line

A cytotoxicity and mechanistic investigation of mono- and di-chloro naphthalenes

Polychlorinated naphthalenes (PCNs) were characterized as persistent organic pollutants (POPs) that were widely distributed in the environment. Although the striking in vivo toxicity of these pollutants towards both animals and humans was well documented, their cytotoxicity and mechanism of action have not been extensively investigated. In this study, the in vitro antiproliferative activity of mono- and di-chloronaphthalenes as representative PCNs were evaluated and the results indicated strong growth inhibitory effects against mammalian cells, especially the human breast MCF-10A cell and human hepatic HL-7702 cells. 2-Chloronaphthalene with the most potent antiproliferative effects within the tested PCNs, which showed IC50 values ranging from 0.3 mM to 1.5 mM against selected human cell lines, was investigated for its working mechanisms. It promoted cellular apoptosis of MCF-10A cells upon the concentration of 200 μM. It also induced the autophagy of MCF-10A cells in a dose-dependent manner, resulting in cell death via the interaction of autophagy and apoptosis. Thus, these findings supported the theoretical foundation for interventional treatment of PCNs toxicity and also provided implications for the use of chemopreventive agents against the toxic chlorinated naphthalenes in the environments.

Antiviral activity of Taurisolo® during bovine alphaherpesvirus 1 infection

Bovine alphaherpesvirus 1 (BoAHV-1), the pathogen causing Infectious Bovine Rhinotracheitis (IBR) and predisposing to polymicrobial infections in cattle, provokes farm economic losses and trading restrictions in the world. However, nontoxic antiviral agents for BoAHV-1 infection are still unavailable, but plant extracts, such as flavonoid derivatives possess activity against BoAHV-1. Taurisolo®, a nutraceutical produced by Aglianico grape pomace, has recently shown promising antiviral activity. Herein, the potential activity of Taurisolo® during BoAHV-1 infection in Madin Darby bovine kidney (MDBK) cells was tested. Taurisolo® enhanced cell viability and reduced morphological death signs in BoAHV-1-infected cells. Moreover, Taurisolo® influenced the expression of bICP0, the key regulatory protein of BoAHV-1, and it strongly diminished virus yield. These effects were associated with an up-regulation of aryl hydrocarbon receptor (AhR), a transcription factor involved in microbial metabolism and immune response. In conclusion, our findings indicate that Taurisolo® may represent a potential antiviral agent against BoAHV-1 infection. Noteworthy, AhR could be involved in the observed effects and become a new target in antiviral therapy.

The Relationship between Typical Environmental Endocrine Disruptors and Kidney Disease

Endocrine disrupting chemicals (EDCs) are exogenous substances that alter the endocrine function of an organism, to result in adverse effects on growth and development, metabolism, and reproductive function. The kidney is one of the most important organs in the urinary system and an accumulation point. Studies have shown that EDCs can cause proteinuria, affect glomeruli and renal tubules, and even lead to diabetes and renal fibrosis in animal and human studies. In this review, we discuss renal accumulation of select EDCs such as dioxins, per- and polyfluoroalkyl substances (PFAS), bisphenol A (BPA), and phthalates, and delineate how exposures to such EDCs cause renal lesions and diseases, including cancer. The regulation of typical EDCs with specific target genes and the activation of related pathways are summarized.

Effectiveness of the Fungal Metabolite 3-O-Methylfunicone towards Canine Coronavirus in a Canine Fibrosarcoma Cell Line (A72)

Canine coronavirus (CCoV), an alphacoronavirus, may cause self-limiting enteric disease in dogs, especially in puppies. The noteworthy plasticity of coronaviruses (CoVs) occurs through mutation and recombination processes, which sometimes generate new dangerous variants. The ongoing SARS-CoV-2 pandemic and the isolation of a novel canine-feline recombinant alphacoronavirus from humans emphasizes the cross-species transmission ability of CoVs. In this context, exploring antiviral compounds is essential to find new tools for fighting against CoVs infections. Fungi produce secondary metabolites, which are often developed as antibiotics, fungicides, hormones, and plant growth regulators. Previous examinations of benzo-γ-pyrone 3-O-methylfunicone (OMF), obtained from Talaromyces pinophilus, showed that it reduces the infectivity of hepatitis C virus and bovine herpesvirus 1. Based on this evidence, this study evaluated the antiviral ability of OMF against CCoV infection in a canine fibrosarcoma (A72) cell line. During CCoV infection, a non-toxic dose of OMF markedly increased features of cell viability. Moreover, OMF induced a significant reduction in virus yield in the presence of an intense downregulation of the viral nucleocapsid protein (NP). These findings occurred in the presence of a marked reduction in the aryl hydrocarbon receptor (AhR) expression. Taken together, preliminary findings suggest that OMF inhibiting AhR shows promising activity against CCoV infection.

Eucalyptol relieves imidacloprid-induced autophagy through the miR-451/Cab39/AMPK axis in Ctenopharyngodon idellus kidney cells†

Imidacloprid (IMI) is a widely used neonicotinoid insecticide that has toxic effects on nontarget organisms. 1,8-Cineole (eucalyptol) is purified from essential oils in several aromatic plants and can prevent xenobiotic toxicity. The kidney is a major organ for xenobiotic elimination and thus has high risk of exposure. The purpose of this research was to clarify the effect of IMI exposure on autophagy in fish kidney cells, determine the potential of eucalyptol to provide cytoprotection from the toxicity of the neonicotinoid pesticide IMI, and identify its mechanism of action. Therefore, the Ctenopharyngodon idellus kidney cell line (CIK cell) was treated with 20 mg/L IMI and/or 20 μM eucalyptol for 48 h as the research objective. The results showed that IMI exposure induced autophagy accompanied by advanced autophagy markers BNIP3, Beclin1 and LC3Ⅱ/Ⅰ in CIK cells, reduced the levels of miR-451, increased the expression of Cab39 and AMPK, inhibited AKT/mTOR signaling, and activated the JNK pathway. Eucalyptol treatment alleviated IMI-induced autophagy and relieved the activation of autophagy-associated signals. These results indicate that eucalyptol could alleviate IMI-induced autophagy through the miR-451/Cab39/AMPK axis in fish kidney cells. These results partly explained the mechanism of biological threat on fish under IMI exposure and the potential application value of EUC in aquaculture.

Antiviral Property of the Fungal Metabolite 3-O-Methylfunicone in Bovine Herpesvirus 1 Infection

Bovine herpesvirus type-1 (BoHV-1) is a widespread pathogen that provokes infectious rhinotracheitis and polymicrobial infections in cattle, resulting in serious economic losses to the farm animal industry and trade restrictions. To date, non-toxic active drugs against BoHV-1 are not available. The exploitation of bioactive properties of microbial products is of great pharmaceutical interest. In fact, fungi are a promising source of novel drugs with a broad spectrum of activities and functions, including antiviral properties. Hence, the potential antiviral properties of 3-O-methylfunicone (OMF), a secondary metabolite produced by Talaromyces pinophilus, were evaluated on BoHV-1. In this study, during BoHV-1 infection in bovine cells (MDBK), the non-toxic concentration of 5 µM OMF considerably reduced signs of cell death and increased cell proliferation. Furthermore, OMF significantly decreased the virus titer as well as the cytopathic effect and strongly inhibited the expression of bICP0, the major regulatory protein in the BoHV-1 lytic cycle. These findings were accompanied by a considerable up-regulation in the expression of the aryl hydrocarbon receptor (AhR), a multifunctional transcription factor also linked to the host’s response to a herpesvirus infection. Overall, our results suggest that by involving AhR, OMF shows potential against a BoHV-1 infection.

MG-132 interferes with iron cellular homeostasis and alters virulence of bovine herpesvirus 1

Bovine herpesvirus 1 (BoHV-1) requires an iron-replete cell host to replicate efficiently. BoHV-1 infection provokes an increase in ferritin levels and a decrease of transferrin receptor 1 (TfR-1) expression, ultimately lowering iron pool extent. Thus, cells try to limit iron availability for virus spread. It has been demonstrated that MG-132, a proteasome inhibitor, reduces BoHV-1 release. Since ferritin, the major iron storage protein in mammalian cells, undergoes proteasome-mediated degradation, herein, the influence of MG-132 on iron metabolism during BoHV-1 infection was examined. Following infection in bovine cells (MDBK), MG-132 reduced cell death and viral yield. Western blot analysis showed a significant ferritin accumulation, likely due to the inhibition of its proteasome-mediated degradation pathway. In addition, the concomitant down-regulation of TfR-1 expression, observed during infection, was counteracted by proteasome inhibitor. This trend may be explained by enhanced acidic vesicular organelles, detected by acridine orange staining, determining a reduction of intracellular pH, that promotes new synthesis of TfR-1 degraded in a recycling pathway. In addition, MG-132 influences cellular iron distribution during BoHV-1 infection, as revealed by Perls' Prussian blue staining. However, cellular iron content, evaluated by Atomic Absorption Spectrophotometry, resulted essentially unaltered. These findings reveal that MG-132 may contribute to limit cellular iron availability for virus replication thereby enhancing cell survival.

Bovine herpesvirus-1 infection in mouse neuroblastoma (Neuro-2A) cells

Bovine herpesvirus 1 (BoHV-1) is an important cattle pathogen, that may cause rhinotracheitis, abortions and shipping fever. Virus establishes latency in sensory neurons, but periodically could reactivate. Recent studies identified mouse neuroblastoma (Neuro-2A) cells as a novel cell culture model to study factors that regulate BoHV-1 productive infection in neuronal cells. Herein, following BoHV-1 infection in Neuro-2A, a reduced cell viability occurred. Membrane damage and death morphological alterations, features of apoptosis and necrosis, were distinguished in infected cells. In addition, biochemical signs of apoptosis (caspase 3 activation and PARP cleavage) were observed. These results were accompanied by incomplete autophagy due to enhanced amounts of autophagic markers (LC3-II, ATG5 and Beclin 1), in the presence of increased levels of p62. Interestingly, protein expression of viral infected cell protein 0 (bICP0) was detected in Neuro-2A cells, although BoHV-1 inefficiently replicates in these cells, because just low levels of viral yield were found. Taken together, our results suggest that BoHV-1 may exert its potential neurotoxicity through a combined mechanism of necrosis and apoptosis. Moreover, incomplete autophagy occurred during BoHV-1 replication in Neuro-2A cells, which were favourable for viral persistence.

Relevance of autophagy markers to cytotoxicity of zinc compounds in macrophages

Autophagy molecules such as microtubule-associated protein light chain 3 (LC3) and p62/SQSTM1 have been used as biomarkers of protective or conversely adverse effects of exposure to toxicants. In the present study we show changes in LC3-II (a lipidated form of LC3-I) and p62 levels in response to zinc compounds and some other toxicants in J774.1 murine macrophages. The cytotoxicity of either ZnO or ZnSO₄ largely depended on the concentration of FBS or albumin in the culture medium. Accordingly, these authophagy markers were more remarkably increased when the cells were exposed to ZnO or ZnSO₄ in the absence of FBS. We next addressed lysosomal function impairment and changes in LC3-II and p62 levels following exposure to TiO₂, ZnO, and ZnSO₄. Lysosomal pH was quickly decreased by autolysosome inhibitors such as bafilomycin A1 and chloroquine, while TiO₂, ZnO and ZnSO₄ did not decrease lysosomal pH. However, the amounts of LC3-II and p62 and the LC3-II/LC3-I ratio were increased either by the lysosomal inhibitors and the Zn compounds. LC3-II and p62 levels were increased after exposure to arsenite and lipopolysaccharide (LPS). The p62 and phospho-p62 levels were also increased by either ZnSO₄ and bafilomycin A1 in HEK293 cells stably expressing RFP-LC3. The current observations suggest that LC3-II and p62 levels were increased as consequences of early effects of toxicants without changing lysosomal pH.

Autophagy role in environmental pollutants exposure

During the last decades, the potential harmfulness derived from the exposure to environmental pollutants has been largely demonstrated, with associated damages ranging from geno- and cyto-toxicity to tissue malfunction and alterations in organism physiology. Autophagy is an evolutionarily-conserved cellular mechanism essential for cellular homeostasis, which contributes to protect cells from a wide variety of intracellular and extracellular stressors. Due to its pivotal importance, its correct functioning is directly linked to cell, tissue and organismal fitness. Environmental pollutants, particularly industrial compounds, are able to impact autophagic flux, either by increasing it as a protective response, by blocking it, or by switching its protective role toward a pro-cell death mechanism. Thus, the understanding of the effects of chemicals exposure on autophagy has become highly relevant, offering new potential approaches for risk assessment, protection and preventive measures to counteract the detrimental effects of environmental pollutants on human health.

Disturbances in H+ dynamics during environmental carcinogenesis

Despite the improvement of diagnostic methods and anticancer therapeutics, the human population is still facing an increasing incidence of several types of cancers. According to the World Health Organization, this growing trend would be partly linked to our environment, with around 20% of cancers stemming from exposure to environmental contaminants, notably chemicals like polycyclic aromatic hydrocarbons (PAHs). PAHs are widespread pollutants in our environment resulting from incomplete combustion or pyrolysis of organic material, and thus produced by both natural and anthropic sources; notably benzo[a]pyrene (B[a]P), i.e. the prototypical molecule of this family, that can be detected in cigarette smoke, diesel exhaust particles, occupational-related fumes, and grilled food. This molecule is a well-recognized carcinogen belonging to group 1 carcinogens. Indeed, it can target the different steps of the carcinogenic process and all cancer hallmarks. Interestingly, H⁺ dynamics have been described as key parameters for the occurrence of several, if not all, of these hallmarks. However, information regarding the role of such parameters during environmental carcinogenesis is still very scarce. The present review will thus mainly give an overview of the impact of B[a]P on H⁺ dynamics in liver cells, and will show how such alterations might impact different aspects related to the finely-tuned balance between cell death and survival processes, thereby likely favoring environmental carcinogenesis. In total, the main objective of this review is to encourage further research in this poorly explored field of environmental molecular toxicology.

Autophagy in exposure to environmental chemicals

Autophagy is a catabolic pathway, which breaks down old and damaged cytoplasmic material into basic biomolecules through lysosome-mediated digestion thereby recycling cellular material. In this way, autophagy prevents the accumulation of damaged cellular components inside cells and reduces metabolic stress and toxicity. The basal level of autophagy is generally low but essential for maintaining the turnover of proteins and other molecules. The level is, however, increased in response to various stress conditions including chemical stress. This elevation in autophagy is intended to restore energy balance and improve cell survival in stress conditions. However, aberrant and/or deficient autophagy may also be involved in the aggravation of chemical-caused insults. Thus, the overall role of autophagy in chemical-induced toxicity is complex and only a limited number of environmental chemicals have been studied from this point of view. Autophagy is associated with many of the chemical-caused cytotoxic mechanisms, including mitochondrial dysfunction, DNA damage, oxidative stress, changes in the endoplasmic reticulum, impairment of lysosomal functions, and inflammation. This mini-review describes autophagy and its involvement in the responses to some common environmental exposures including airborne particulate matter, nanoparticles and tobacco smoke as well as to some common single environmental chemicals.

27-Deoxyactein prevents 2,3,7,8-tetrachlorodibenzo-p-dioxin-induced cellular damage in MC3T3-E1 osteoblastic cells

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a well-known environmental contaminant that exerts its toxicity through a variety of signaling mechanisms. The present study evaluated the effects of 27-deoxyactein, one of the major constituents isolated from Cimicifuga racemosa, on TCDD-induced toxicity in osteoblastic MC3T3-E1 cells. TCDD reduced cell survival, markedly increased apoptosis, and enhanced autophagy activity. However, pre-treatment with 27-deoxyactein attenuated all TCDD-induced effects and significantly decreased intracellular calcium (Ca²⁺) concentrations, the collapse of the mitochondrial membrane potential (MMP), the level of reactive oxygen species (ROS), and cardiolipin peroxidation compared to the TCDD-treated controls. Additionally, TCDD-induced increases in the levels of aryl hydrocarbon receptor (AhR), cytochrome P450 1A1 (CYP1A1), and extracellular signal-regulated kinase (ERK) were significantly inhibited by 27-deoxyactein. The mRNA levels of superoxide dismutase (SOD), ERK1, and nuclear factor kappa B (NF-κB) were also effectively restored by pre-treatment with 27-deoxyactein. Furthermore, 27-deoxyactein significantly increased the expressions of genes associated with osteoblast differentiation, including alkaline phosphatase (ALP), osteocalcin, bone sialoprotein (BSP), and osterix. Taken together, the present findings demonstrate the preventive effects of 27-deoxyactein on TCDD-induced damage in osteoblasts.

Elimination of dysfunctional mitochondria through mitophagy suppresses benzo[a]pyrene-induced apoptosis

Mitophagy, a special type of autophagy, plays an important role in the mitochondria quality control and cellular homeostasis. In this study, we examined the molecular mechanism of mitophagy induction with benzo[a]pyrene (B[a]P), a ubiquitous polycyclic aromatic hydrocarbon, which acts as a prosurvival response against apoptotic cell death. Our study showed that B[a]P displayed higher cytotoxicity in autophagy-deficient HaCaT cells as compared to control. Further, we showed that B[a]P triggered the Beclin-1-dependent autophagy through the mammalian target of rapamycin (mTOR)/AMP-activated protein kinase (AMPK) pathway. Moreover, our study indicated that the B[a]P-induced autophagy was initiated through the activation of cytochrome P450 1B1 (CYP1B1) and the aryl hydrocarbon receptor (AhR) in HaCaT cells. Intriguingly, the B[a]P-induced Beclin-1-mediated mitophagy was suppressed in CYP1B1 and AhR knockdown HaCaT cells, indicating a crucial role of B[a]P activation in the mitophagy induction to regulate cell death. B[a]P was shown to increase the mitochondrial dysfunction and decrease the mitochondrial membrane potential, resulting in depletion of ATP level along with the inhibition of the oxygen consumption rate in HaCaT cells. Importantly, the supplementation of methyl pyruvate compensated for the B[a]P-induced drop in the ATP level and mitigated the reactive oxygen species burden and autophagy. Mechanistically, B[a]P inhibited the manganese superoxide dismutase (MnSOD) activity and we found that the activated mitochondrial CYP1B1 interacted with MnSOD, inflicting mitophagy to protect from B[a]P-induced apoptosis. In summary, our study reveals mitophagy induction as a cellular protection mechanism against B[a]P-triggered toxicity and carcinogenesis.

2,3,7,8-Tetrachlorodibenzo-p-dioxin influences bovine herpesvirus 1 replication through upregulation of SIRT3 and cytoskeletal reorganization

Infection of kidney cells (MDBK) with Bovine Herpesvirus 1 (BoHV-1) is affected by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which accelerates BoHV-1-induced apoptosis and increases virus replication. Herein, to elucidate the mechanism through TCDD modifies BoHV-1 infection, we analyzed the modulation of a members of Sirtuin proteins family in MDBK cells. We found that mitochondrial SIRT3 was upregulated during infection. This change was accompanied by cytoskeletal rearrangements and cell extensions. All these trends were drastically modified by TCDD. We hypothesize that, taken together, these results might further clarify the processes responsible for the action of TCDD on the BoHV-1 replication, resulting in enhanced virus production.

MG-132 reduces virus release in Bovine herpesvirus-1 infection

Bovine herpesvirus 1 (BoHV-1) can provoke conjunctivitis, abortions and shipping fever. BoHV-1 infection can also cause immunosuppression and increased susceptibility to secondary bacterial infections, leading to pneumonia and occasionally to death. Herein, we investigated the influence of MG-132, a proteasome inhibitor, on BoHV-1 infection in bovine kidney (MDBK) cells. Infection of MDBK cells with BoHV-1 induces apoptotic cell death that enhances virus release. Whereas, MG-132 inhibited virus-induced apoptosis and stimulated autophagy. Protein expression of viral infected cell protein 0 (bICP0), which is constitutively expressed during infection and is able to stimulate Nuclear factor kappa B (NF-κB), was completely inhibited by MG-132. These results were accompanied by a significant delay in the NF-κB activation. Interestingly, the efficient virus release provoked by BoHV-1-induced apoptosis was significantly reduced by MG-132. Overall, this study suggests that MG-132, through the activation of autophagy, may limit BoHV-1 replication during productive infection, by providing an antiviral defense mechanism.

Synergistic cellular effects including mitochondrial destabilization, autophagy and apoptosis following low-level exposure to a mixture of lipophilic persistent organic pollutants

Humans are exposed to multiple exogenous environmental pollutants. Many of these compounds are parts of mixtures that can exacerbate harmful effects of the individual mixture components. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), is primarily produced via industrial processes including incineration and the manufacture of herbicides. Both endosulfan and TCDD are persistent organic pollutants which elicit cytotoxic effects by inducing reactive oxygen species generation. Sublethal concentrations of mixtures of TCDD and endosulfan increase oxidative stress, as well as mitochondrial homeostasis disruption, which is preceded by a calcium rise and, in fine, induce cell death. TCDD+Endosulfan elicit a complex signaling sequence involving reticulum endoplasmic destalilization which leads to Ca2+ rise, superoxide anion production, ATP drop and late NADP(H) depletion associated with a mitochondrial induced apoptosis concomitant early autophagic processes. The ROS scavenger, N-acetyl-cysteine, blocks both the mixture-induced autophagy and death. Calcium chelators act similarly and mitochondrially targeted anti-oxidants also abrogate these effects. Inhibition of the autophagic fluxes with 3-methyladenine, increases mixture-induced cell death. These findings show that subchronic doses of pollutants may act synergistically. They also reveal that the onset of autophagy might serve as a protective mechanism against ROS-triggered cytotoxic effects of a cocktail of pollutants in Caco-2 cells and increase their tumorigenicity.

2,3,7,8-tetrachlorodibenzo-p-dioxin and the viral infection

Exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a widespread highly toxic environmental contaminant, suppresses immune response and leads to an increased susceptibility to infectious agents. In particular, several studies have provided evidence that TCDD decreases resistance to numerous viruses. Indeed, in vivo and in vitro investigations showed that the presence of TCDD is able to interfere with the replication of both human and animal viruses, such as influenza A viruses, coxsackie virus B3, immunodeficiency virus type-1 (HIV-1), cytomegalovirus (CMV), herpes simplex II, and bovine herpesvirus 1. Moreover, TCDD could induce an exacerbation of latent infection produced by HIV-1, CMV or Epstein-Barr virus. In this review, we first describe the general effects of TCDD exposure on mammalian cells, then we focus on its influence on the viral infections. Overall, the available data support the concept that TCDD exposure may act as an additional risk factor in promoting of viral diseases.

Eicosapentaenoic acid prevents TCDD-induced oxidative stress and inflammatory response by modulating MAP kinases and redox-sensitive transcription factors

BACKGROUND AND PURPOSE

Oxidative stress and subsequent activation of inflammatory responses is a widely accepted consequence of exposure to environmental toxins. TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin), a well-known environmental toxin, exerts its toxicity through many signalling mechanisms, with liver being the principal organ affected. However, an effective antidote to TCDD-induced toxicity is unknown. The present study evaluated the effect of eicosapentaenoic acid (EPA), an n3 fatty acid, on TCDD-induced toxicity.

EXPERIMENTAL APPROACH

In cultures of HepG2 cells, the EPA/AA ratio was determined using gas chromatography, oxidative stress and inflammatory responses through reactive oxygen species (ROS) levels, antioxidant status, [Ca(2+) ]i , nuclear migration of two redox-sensitive transcription factors, NF-κB p65 and Nrf-2, expression of MAP kinase (p-Erk, p-p38), NF-κB p65, COX-2 and Nrf-2. Cellular changes in ΔΨm, acidic vesicular organelle formation, cell cycle analysis and scanning electron microscopy analysis were performed.

KEY RESULTS

EPA offered significant cytoprotection by increasing EPA/AA ratios in cell membranes, inhibiting ROS generation, enhancing antioxidant status and modulating nuclear translocation of redox-sensitive transcription factors (NF-κB p65 and Nrf-2) and expression of NF-κB p65, COX-2 and Nrf-2. Furthermore, TCDD-induced upstream events of MAPK phosphorylation, the increase in [Ca(2+) ]i levels and cell surface changes in microvilli were significantly inhibited by EPA. EPA treatment maintained ΔΨm and prevented formation of acidic vesicular organelles.

CONCLUSION AND IMPLICATIONS

The present study demonstrates for the first time some underlying molecular mechanisms of cytoprotection exerted by EPA against TCDD-induced oxidative stress and inflammatory responses.

Differential regulatory functions of three classes of phosphatidylinositol and phosphoinositide 3-kinases in autophagy

Autophagy is an evolutionarily conserved and exquisitely regulated self-eating cellular process with important biological functions. Phosphatidylinositol 3-kinases (PtdIns3Ks) and phosphoinositide 3-kinases (PI3Ks) are involved in the autophagic process. Here we aim to recapitulate how 3 classes of these lipid kinases differentially regulate autophagy. Generally, activation of the class I PI3K suppresses autophagy, via the well-established PI3K-AKT-MTOR (mechanistic target of rapamycin) complex 1 (MTORC1) pathway. In contrast, the class III PtdIns3K catalytic subunit PIK3C3/Vps34 forms a protein complex with BECN1 and PIK3R4 and produces phosphatidylinositol 3-phosphate (PtdIns3P), which is required for the initiation and progression of autophagy. The class II enzyme emerged only recently as an alternative source of PtdIns3P and autophagic initiator. However, the orthodox paradigm is challenged by findings that the PIK3CB catalytic subunit of class I PI3K acts as a positive regulator of autophagy, and PIK3C3 was thought to be an amino acid sensor for MTOR, which curbs autophagy. At present, a number of PtdIns3K and PI3K inhibitors, including specific PIK3C3 inhibitors, have been developed for suppression of autophagy and for clinical applications in autophagy-related human diseases.

Association of dioxin and other persistent organic pollutants (POPs) with diabetes: epidemiological evidence and new mechanisms of beta cell dysfunction

The worldwide explosion of the rates of diabetes and other metabolic diseases in the last few decades cannot be fully explained only by changes in the prevalence of classical lifestyle-related risk factors, such as physical inactivity and poor diet. For this reason, it has been recently proposed that other "nontraditional" risk factors could contribute to the diabetes epidemics. In particular, an increasing number of reports indicate that chronic exposure to and accumulation of a low concentration of environmental pollutants (especially the so-called persistent organic pollutants (POPs)) within the body might be associated with diabetogenesis. In this review, the epidemiological evidence suggesting a relationship between dioxin and other POPs exposure and diabetes incidence will be summarized, and some recent developments on the possible underlying mechanisms, with particular reference to dioxin, will be presented and discussed.

Oxidative stress-induced autophagy: role in pulmonary toxicity

Autophagy is an evolutionarily conserved catabolic process important in regulating the turnover of essential proteins and in elimination of damaged organelles and protein aggregates. Autophagy is observed in the lung in response to oxidative stress generated as a consequence of exposure to environmental toxicants. Whether autophagy plays role in promoting cell survival or cytotoxicity is unclear. In this article recent findings on oxidative stress-induced autophagy in the lung are reviewed; potential mechanisms initiating autophagy are also discussed. A better understanding of autophagy and its role in pulmonary toxicity may lead to the development of new strategies to treat lung injury associated with oxidative stress.

2,3,7,8-Tetrachlorodibenzo-p-dioxin stimulates proliferation of HAPI microglia by affecting the Akt/GSK-3β/cyclin D1 signaling pathway

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental toxin that induces apoptosis of neurons and a pro-inflammatory response in microglial cells. First, we found that TCDD induced proliferation of HAPI microglial cells in a dose- and time-dependent manner. Flow cytometry analysis showed that this proliferation by TCDD was due to mainly enhancing the G1 to S phase transition. Next, it was found that TCDD treatment led to up-regulation of cyclin D1, which induces cell cycle progression from G1 to S phase, in a time-dependent manner. As for molecular mechanism, we revealed that TCDD was capable of inducing Akt phosphorylation and activation, resulting in phosphorylation and inactivation of glycogen synthase kinase-3β (GSK-3β). Inactivated GSK-3β attenuated proteasomal degradation of cyclin D1 by reducing Thr(286)-phosphorylated cyclin D1 levels. Moreover, inactivated GSK-3β increased cyclin D1 gene transcription by increasing its transcription factor β-catenin in the nucleus. Further, blockage of phosphoinositide 3-kinase/Akt kinase with their specific inhibitors, LY294002 and Akt 1/2 kinase inhibitor, significantly reduced TCDD-enhanced proliferation of HAPI microglial cells. In conclusion, TCDD stimulates proliferation of HAPI microglial cells by affecting the Akt/GSK-3β/cyclin D1 signaling pathway.

Impairment of autophagy: from hereditary disorder to drug intoxication

At first, the molecular mechanism of autophagy was unveiled in a unicellular organism Saccharomyces cerevisiae (budding yeast), followed by the discovery that the basic mechanism of autophagy is conserved in multicellular organisms including mammals. Although autophagy was considered to be a non-selective bulk protein degradation system to recycle amino acids during periods of nutrient starvation, it is also believed to be an essential mechanism for the selective elimination of proteins/organelles that are damaged under pathological conditions. Research advances made using autophagy-deficient animals have revealed that impairments of autophagy often underlie the pathogenesis of hereditary disorders such as Danon, Parkinson's, Alzheimer's, and Huntington's diseases, and amyotrophic lateral sclerosis. On the other hand, there are many reports that drugs and toxicants, including arsenic, cadmium, paraquat, methamphetamine, and ethanol, induce autophagy during the development of their toxicity on many organs including heart, brain, lung, kidney, and liver. Although the question as to whether autophagic machinery is involved in the execution of cell death or not remains controversial, the current view of the role of autophagy during cell/tissue injury is that it is an important, often essential, cytoprotective reaction; disturbances in cytoprotective autophagy aggravate cell/tissue injuries. The purpose of this review is to provide (1) a gross summarization of autophagy processes, which are becoming more important in the field of toxicology, and (2) examples of important studies reporting the involvement of perturbations in autophagy in cell/tissue injuries caused by acute as well as chronic intoxication.

2,3,7,8-Tetrachlorodibenzo-p-dioxin promotes BHV-1 infection in mammalian cells by interfering with iron homeostasis regulation

Mammalian cells require iron to satisfy metabolic needs or to accomplish specialized functions, and DNA viruses, like bovine herpesvirus 1 (BHV-1), require an iron-replete host to efficiently replicate, so that iron bioavailability is an important component of viral virulence. Cellular iron metabolism is coordinately controlled by the Iron Regulatory Proteins (IRP1 and IRP2), whose activity is affected by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a current and persistent environmental contaminant. Considering that TCDD enhances BHV-1 replication, herein we analyzed the effects of TCDD on iron metabolism during BHV-1 infection in MDBK cells, and presented evidences of a divergent modulation of IRP1 and IRP2 RNA-binding capacity. Moreover, an up-regulation of transferrin receptor 1 (TfR1) and a concomitant down-regulation of ferritin were observed. This scenario led to an expansion of the labile iron pool (LIP) and induces a significant enhance of viral titer, as confirmed by increased levels of BHV-1 infected cell protein 0 (bICP0), the major transcriptional regulatory protein of BHV-1. Taken together, our data suggest that TCDD increases the free intracellular iron availability thereby promoting the onset of BHV-1 infection and rendering bovine cells more vulnerable to the virus.

Autophagy in toxicology: cause or consequence?

Research on autophagy and its effects on cell metabolism and physiology has increased dramatically during recent years. Multiple forms of autophagy have been characterized, and many of the genes involved in the regulation of this process have been identified. The importance of autophagy for embryonic development and maintenance of tissue homeostasis in the adult organism has been demonstrated convincingly, and several human diseases have been linked to deficiencies in autophagy. Most often, autophagy serves as a protective mechanism, but persistent activation of autophagy can result in cell death. This is true for many toxic agents. In fact, there are ample examples of cross talk between autophagy and other modes of cell death after exposure to toxicants. However, the relative contribution of autophagy to the overall toxicity of these compounds is not always clear, and further research is needed to clarify the toxicological significance of this process.