PCB28 and PCB52 induce hepatotoxicity by impairing the autophagic flux and stimulating cell apoptosis in vitro

Inhalation of 2,2',5,5'-tetrachlorobiphenyl (PCB52) causes changes to the gut microbiome throughout the gastrointestinal tract

Polychlorinated biphenyls (PCBs), such as PCB52, are hazardous environmental contaminants present in indoor and outdoor environments. Oral PCB exposure affects the colon microbiome; however, it is unknown if inhalation of PCBs alters the intestinal microbiome. We hypothesize that sub-acute inhalation of PCB52 affects microbial communities depending on the location in the (GI) gastrointestinal tract and the local profiles of PCB52 and its metabolites present in the GI tract following mucociliary clearance and biliary or intestinal excretion. Sprague-Dawley rats were exposed via nose-only inhalation 4 h per day, 7 days per week, for 4 weeks to either filtered air or PCB52. After 28 days, differences in the microbiome and levels of PCB52 and its metabolites were characterized throughout the GI tract. PCB52 inhalation altered taxa abundances and predicted functions altered throughout the gut, with most alterations occurring in the large intestine. PCB52 and metabolite levels varied across the GI tract, resulting in differing PCB × microbiome networks. Thus, the presence of different levels of PCB52 and its metabolites in different parts of the GI tract has varying effects on the composition and predicted function of microbial communities. Future studies need to investigate whether these changes lead to adverse outcomes.

Gestational PCB52 exposure induces hepatotoxicity and intestinal injury by activating inflammation in dam and offspring mice: A maternal and progeny study

Although Polychlorinated biphenyl (PCB) levels are decreased in the environment, the adverse effects of gestational exposure on the mother and offspring cannot be ignored due to the vulnerability of the fetus. In the present study, pregnant Balb/c mice were administered PCB52 (1 mg/kg BW/day) or corn oil vehicle by gavage until parturition. In the dams, PCB52 caused histopathological changes in the liver, higher serum levels of aminotransferase and alanine aminotransferase, and activated apoptosis and autophagy, suggesting hepatotoxicity. Overexpressed indicators of TLR4 pathway were observed in the liver of PCB52-exposed dams, indicated hepatic inflammation. Moreover, PCB52 exposure weakened the intestinal barrier and triggered inflammatory response, which might contribute to the hepatic inflammation by gut-liver axis. In the pups, prenatal PCB52 exposure affected the sex ratio at birth and reduced birth length and weights. Similar to the dams, prenatal PCB52 exposure induced hepatotoxicity in the pups without gender difference. Consistent with the alteration of gut microbiota, intestinal inflammation was confirmed, accompanying the disruption in the intestinal barrier and the activation of apoptosis and autophagy in the PCB52-exposed pups. Intestinal injury might be responsible for hepatotoxicity at least in part. Taken together, these findings suggested that gestational PCB52 exposure induced hepatic and intestinal injury in both maternal and offspring mice by arousing inflammation.

Gestational exposure to GenX induces hepatic alterations by the gut-liver axis in maternal mice: A similar mechanism as PFOA

GenX is an alternative to perfluorooctanoic acid (PFOA) and was included in the accession list of Substances of Very High Concern in 2019. Gestational GenX exposure induces maternal hepatotoxicity in animals. However, the mechanisms of GenX toxicity have not been explored. In the present study, pregnant Balb/c mice were administered with PFOA (1 mg/kg BW/day), GenX (2 mg/kg BW/day), or Milli-Q water by gavage during gestation. Similar hepatic pathological changes, including enlargement of hepatocytes, cytoplasm loss, nucleus migration, inflammatory cell infiltration, and reduction of glycogen storage, were observed in PFOA and GenX groups. Increased expression levels of indicators of the TLR4 pathway indicated activation of inflammation in the liver of maternal mice after exposure to PFOA or GenX, consistent with the pathological changes. Overexpression of cleaved PARP-1, cleaved caspase 3, Bax and decreased Bcl-2 proteins indicated activation of apoptosis, whereas overexpression of ULK-1, p62, beclin-1, LC3-II proteins and downregulation of p-mTOR implied that PFOA and GenX exposure initiated autophagy. Decreased secretion of mucus, reduced expression levels of tight junction proteins, and higher serum levels of lipopolysaccharide indicated disruption of the intestinal barrier. Translocation of lipopolysaccharide may be recognized by TLR4, thus triggering inflammatory pathway in the maternal liver. In summary, gestational exposure to PFOA or GenX induced maternal hepatic alterations through the gut-liver axis.

Escalating dose-multiple binge methamphetamine treatment elicits neurotoxicity, altering gut microbiota and fecal metabolites in mice

Methamphetamine (METH) is an addictive and illegal psychostimulant drug that can cause multiple organ dysfunction, especially in the central nervous system (CNS). Gut microbiota have been implicated in development of various CNS-related diseases, via the gut-brain axis (GBA). However, effect of METH in the alteration of gut microbiota and fecal metabolites is unclear, whereas the relationship with METH-induced neurotoxicity remains unknown. In the current study, we investigated effect of METH on neurotoxicity in striatum and colonic damage by exposing BALB/c mice to an escalating dose-multiple binge regimen, and then analyzed protein expression using Western blot analysis. We further detected and sequenced the 16 S rRNA gene in fecal samples, and performed ultra-high-performance liquid chromatography-mass spectrometry (UHPLC-MS)-based metabolomics to analyze gut microbes and fecal metabolites. Exposure to METH significantly downregulated tyrosine hydroxylase (TH) proteins, but upregulated MAOA, Beclin1, Atg5, and LC3-Ⅱ. METH up-regulated inflammation-related factors, such as caspase1, TNF-α and IL-18, by activating the toll-like receptors 4 (TLR4)/myeloid differentiation factor 88 (Myd88)/nuclear factor κB (NF-κB) pathway and reduced occludin protein expression. In addition, METH exposure changed α and β diversities of gut microbiota. Specifically, METH exposure elevated relative abundances of pathogenic bacteria, but reduced those of probiotics. Metabolomics, combined with enrichment analyses revealed that METH exposure altered fecal metabolites. Our findings suggest that METH exposure induced autophagy in the CNS, elevated intestinal autophagy flora, leading to accumulation of fecal metabolites in the autophagy pathway, and causing enteritis. Moreover, METH promoted intestinal inflammation by increasing the relative abundance of the pathogenic bacteria in the intestinal tract, and reduced intestinal TJ protein expression.

GBE attenuates arsenite-induced hepatotoxicity by regulating E2F1-autophagy-E2F7a pathway and restoring lysosomal activity

Arsenic is an environmental toxicant. Its overdose can cause liver damage. Autophagy has been reported to be involved in arsenite (iAs³⁺ ) cytotoxicity and plays a dual role in cell proliferation and cell death. However, the effect and molecular regulative mechanisms of iAs³⁺ on autophagy in hepatocytes remains largely unknown. Here, we found that iAs³⁺ exposure lead to hepatotoxicity by inducing autophagosome and autolysosome accumulation. On the one hand, iAs³⁺ promoted autophagosome synthesis by inhibiting E2F1/mTOR pathway in L-02 human hepatocytes. On the other, iAs³⁺ blocked autophagosome degradation partially via suppressing the expression of INPP5E and Rab7 as well as impairing lysosomal activity. More importantly, autophagosome and autolysosome accumulation induced by iAs³⁺ increased the protein level of E2F7a, which could further inhibit cell viability and induce apoptosis of L-02 cells. The treatment of Ginkgo biloba extract (GBE) effectively reduced autophagosome and autolysosome accumulation and thus alleviated iAs³⁺ -induced hepatotoxicity. Moreover, GBE could also protect lysosomal activity, promote the phosphorylation level of E2F1 (Ser364 and Thr433) and Rb (Ser780) as well as suppress the protein level of E2F7a in iAs³⁺ -treated L-02 cells. Taken together, our data suggested that autophagosome and autophagolysosome accumulation play a critical role for iAs³⁺ -induced hepatotoxicity, and GBE is a promising candidate for intervening iAs³⁺ induced liver damage by regulating E2F1-autophagy-E2F7a pathway and restoring lysosomal activity.

N-acetylcysteine alleviates PCB52-induced hepatotoxicity by repressing oxidative stress and inflammatory responses

Polychlorinated biphenyls (PCBs), particularly low chlorinated congeners in our environment, can induce human hepatotoxicity. However, the mechanisms by which PCBs cause hepatotoxicity remain elusive. Moreover, there are no effective treatments for this condition. In this study, 40 μM PCB52 was administered to rat (Brl-3A) and human hepatocytes (L-02) for 48 h following the N-acetylcysteine (NAC)/saline pretreatment. A significant decrease in cell viability was observed in PCB52-treated cells relative to the control. Besides, PCB52 significantly increased reactive oxygen species (ROS) levels and malondialdehyde (MDA) contents, suggesting induction of oxidative stress. The expression of Traf6, MyD88, and Tnf in Brl-3A cells and that of MYD88, TNF, and IL1B in L-02 cells were significantly upregulated by PCB52. Consistently, overexpression of TLR4, MyD88, Traf6, and NF-κB p65 proteins was observed in PCB52-treated cells, indicating activation of inflammatory responses. Nevertheless, no changes in kelch-like ECH-associated protein 1 (keap1), nuclear factor-erythroid 2-related factor (nrf2), and heme oxygenase-1 proteins were observed in PCB52-treated cells, indicating non-activation of the keap1/nrf2 pathway. Pretreatment with NAC significantly ameliorated PCB52 effects on cell viability, ROS levels, MDA contents and expression of inflammatory elements at both RNA and protein levels. However, no changes in keap1, nrf2 and HO-1 protein levels were detected following NAC pretreatment. Taken together, with non-activated keap1/nrf2 pathway, PCB52-induced oxidative stress and inflammatory responses could be responsible for its hepatotoxicity. These effects were effectively attenuated by NAC pretreatment, which scavenges ROS and dampens inflammatory responses. This study might provide novel strategies for the treatment of the PCBs-associated hepatotoxic effects.

Polychlorinated biphenyl quinone induces hepatocytes iron overload through up-regulating hepcidin expression

Polychlorinated biphenyls (PCBs) are infamous industry by-products or additives, and increasing evidences demonstrated that their exposure is associate with adverse effects on human health. Liver, as the dominate site for xenobiotic metabolism, is apt to be the primary target of PCBs insult. Although PCBs' hepatic toxic effects have been extensively studied, however, the biotransformation of PCBs in liver and the toxicities of associated PCB metabolites are neglected at some extent. Thus, we choose 2,3,5-trichloro-6-phenyl-[1,4]-benzoquinone (PCB29-pQ), a surrogate PCB29 metabolite, and evaluated its contribution on hepatotoxicity. In the current study, we discovered PCB29-pQ-induced lipid peroxidation and iron overload both in vivo and in vitro. Further mechanistic research confirmed iron overload is caused by reactive oxygen species (ROS)-driven hepcidin disorder in hepatic cells, and the increase of hepcidin is regulated by the translocation of nuclear factor erythroid 2-related factor 2 (Nrf2).

Luteolin alleviates methamphetamine-induced neurotoxicity by suppressing PI3K/Akt pathway-modulated apoptosis and autophagy in rats

Methamphetamine (METH) is a highly addictive stimulant that results in serious and persistent neurotoxic effects. Studies have indicated that luteolin, a flavonoid, may confer neuroprotection against neurotoxicity. Nevertheless, the effects of luteolin on METH-induced neurotoxicity have not been sufficiently verified. In the present study, Sprague Dawley rats were pretreated with luteolin (100 mg/kg) or sodium dodecyl sulfate water, followed by administration of METH (15 mg/kg) or saline. Rat striata were then collected for RNA-sequencing and subsequent analyses. A total of 347 differentially expressed genes (DEGs) were identified in the METH group with 20 pathways, including the phosphoinositol 3 kinase (PI3K)/protein kinase B (Akt), found to be enriched by the KEGG analysis. Seventy-five of the 347 DEGs were modulated in luteolin-pretreated rats, which were enriched into 12 pathways, containing the PI3K/Akt. Results further showed that luteolin pretreatment significantly repressed the METH-induced increases of PI3K, Akt, p-Akt, p53, Bax, caspase 3, normalized the ratio of p-Akt/Akt, and autophagy-related proteins (Beclin1, Atg5 and LC3-II) expression. Taken together, these findings indicate that luteolin attenuates METH-induced apoptosis and autophagy by suppressing the PI3K/Akt pathway. In this case, it exerts protection against METH-induced neurotoxicity. This provides a platform for development of potential therapies for METH treatment.

Concentrations and risks of polychlorinated biphenyls (PCBs) in transformer oils and the environment of a power plant in the Niger Delta, Nigeria

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Soils and water resources around the power plant are contaminated with PCBs.

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The hepta- and octa-PCB homologues were dominant in the samples.

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Exposure to PCBs in soils from the power plant could cause human health risk.

The concentrations of Ʃ14 PCBs were determined, with the aid of gas chromatography-mass spectrometry (GC–MS), in transformer/turbine oils, soils, groundwater, and drainage water collected within a power plant in the Niger Delta of Nigeria. The Ʃ14 PCB concentrations in the transformer oils, drainage water, groundwater and soils ranged from 484 to 48506 mg kg⁻¹, 0.99 to 2.95 mg L⁻¹, 0.16 to 0.56 mg L⁻¹ and from 8.4 to 510 mg kg⁻¹ respectively. The congener distribution patterns in these samples indicate the dominance of highly chlorinated homologues (hepta- and octa-PCBs). The Σ14 PCB concentrations in the transformer oils were above the provisional definition of low persistent organic pollutant (POP) content for PCBs of 50 mg kg⁻¹ as defined in the guidelines on the management of POP waste of the Basel Convention. The concentrations of Ʃ14 PCBs in the soils were above the Dutch guideline value of 1000 μg kg⁻¹ and the estimated incremental lifetime cancer risks relating to exposure of humans to PCBs in soils indicate serious health risks. There is therefore a need to implement a surveillance programme in the vicinity of power plants to determine the impacts on the adjacent ecosystem.

Interplay Between Autophagy and Apoptosis in Lycorine Hydrochloride-Induced Cytotoxicity of HCT116 Cells

The aim of this study was to investigate the antitumor effect of lycorine hydrochloride (LH) and discuss the correlation between LH-induced apoptosis and autophagy in the human colorectal cancer cell line HCT116. Here the results by the Cell Counting Kit-8 and colony formation assays showed that LH concentration-dependently decreased cell viability and colony formation in HCT116 cells, suggesting inhibition of cell proliferation by LH. By flow cytometry, LH was found to increase apoptotic rate in HCT116 cells. Mechanistically, Western blot results revealed that LH increased the expression of the protein of Bax and Caspase-3, and decreased Bcl-2 proteins expression. Moreover, the reverse transcriptase quantitative polymerase chain reaction and Western blot analysis also showed that LH increased the expression of Beclin-1 and LC3B-II/LC3B-I ratio, indicating that autophagy was induced by LH. LH induced autophagy via downregulating phospho-mammalian target of rapamycin and upregulating phospho-AMPK (5′ adenosine monophosphate-activated protein kinase). Furthermore, to understand the role of LH-induced autophagy and its association with apoptosis, cells were analyzed after Beclin-1 small interfering RNA transfection. The results indicated that the proapoptotic ability of LH was increased by inhibition of autophagy. In conclusion, the present investigation suggested that LH induced apoptosis and autophagy in HCT116 cells via the mitochondrial and AMPK/mTOR pathways. The suppression of autophagy promoted LH-induced apoptosis by modulating Beclin-1 and Bcl-2.

PCB52 induces hepatotoxicity in male offspring through aggravating loss of clearance capacity and activating the apoptosis: Sex-biased effects on rats

Polychlorinated biphenyls (PCBs), a kind of persistent organic pollutant, can induce hepatotoxicity in mammals. However, PCB-induced hepatotoxicity in offspring and the underlying mechanisms have been rarely studied. In the present study, Wistar rats were administered with corn oil or PCB52 (1 mg/kg body weight/day, by gavage) from gestational day 7 to postnatal day 21. In the PCB52-treated group, birth body lengths and weights were significantly decreased compared with the control group, suggesting developmental toxicity. Cytoplasmic injury in hepatocytes was observed in PCB52-treated male offspring, while no pathologic change was observed in female offspring, suggesting sex-biased hepatotoxicity. Furthermore, using an RNA-Seq method, coincided with the sexual bias, 454 differential expression genes (DEGs) were screened out in liver tissues of PCB52-treated male offspring, while 10 DEGs were screened out in female offspring. By KEGG annotation analysis, 4 in 12 significant pathways in male offspring were metabolism-related. In the present study, together with cytoplasmic injury of hepatocytes, decreased metabolic enzymes both at RNA and protein levels might aggravate loss of clearance capacity of hepatocytes and induce hepatotoxicity. Moreover, over-expressed peroxisome proliferator-activated receptor delta and mitogen-activated protein kinase 9 might activate apoptosis, which was verified by the augments of cleaved poly ADP-ribose polymerase 1 and caspase 3 in PCB52-treated male offspring. Taken together, PCB52 had developmental toxicity and induced sex-biased hepatotoxicity. The hepatotoxicity in male offspring might be attributed to the aggravated loss of clearance capacity and activation of apoptosis.

Autophagy impairment contributes to PBDE-47-induced developmental neurotoxicity and its relationship with apoptosis

Apoptosis is involved in 2,2',4,4'- tetrabromodiphenyl ether (PBDE-47)-induced developmental neurotoxicity. However, little is known about the role of autophagy, especially its relationship with apoptosis underlying such neurotoxic process.

Methods: Using female Sprague-Dawley rats exposed to low-dose PBDE-47 (0.1, 1.0 and 10 mg/kg/day) from pre-pregnancy until weaning of offspring to mimic human exposure, we investigated the effects of PBDE-47 on autophagy and apoptosis in relation to cognitive impairment of adult offspring rats. We also evaluated relationship between autophagy and apoptosis using neuroendocrine pheochromocytoma (PC12) cells, a widely used neuron-like cell line for neuronal development.

Results: In vivo, perinatal exposure to PBDE-47 induced memory deficits in adult rats. This is accompanied by hippocampal neuronal loss partly as a result of apoptosis, as evidenced by caspase-3 activation and PARP cleavage. Further study identified that PBDE-47 triggered autophagic vesicles accumulation, increased levels of microtubule-associated protein 1 light chain 3 (LC3)-II, an essential protein for autophagosomes formation, and autophagy substrate sequestosome 1 (SQSTM1/p62), but reduced levels of autophagy-related protein (ATG) 7, a key protein for autophagosomes elongation, suggestive of autophagy impairment. These findings were further demonstrated by an in vitro model of PBDE-47-treated PC12 cells. Mechanistically, autophagy alteration is more sensitive to PBDE-47 treatment than apoptosis induction. Importantly, while stimulation of autophagy by the chemical inducer rapamycin and adenovirus-mediated Atg7 overexpression aggravated PBDE-47-induced apoptosis and cell death, inhibition of autophagy by the chemical inhibitor wortmannin and siRNA knockdown of Atg7 reversed PBDE-47-produced detrimental outcomes. Interestingly, blockage of apoptosis by caspase-3 inhibitor Ac-DEVD-CHO ameliorated PBDE-47-exerted autophagy impairment and cell death, though in combination with autophagy inhibitor did not further promote cell survival.

Conclusion: Our data suggest that autophagy impairment facilitates apoptosis, which, in turn, disrupts autophagy, ultimately resulting in cell death, and that autophagy may act as a promising therapeutic target for PBDE-47-induced developmental neurotoxicity.