Biology subjects

Fromenty, B.

Publications and source records attributed to Fromenty, B..

5 recordsLinked to original sources

bioRxiv2024

Fatty acid-mediated induction of CYP2E1 activity in HepaRG cells is not systematically associated with exacerbated acetaminophen cytotoxicity

Hepatic cytochrome P450 2E1 (CYP2E1) is thought to contribute to the pathophysiology of metabolic dysfunction-associated steatotic liver disease (MASLD) formerly known as non-alcoholic fatty liver disease (NAFLD). Indeed, increased activity of CYP2E1 in obese subjects with fatty liver may contribute to higher oxidative stress, mitochondrial dysfunction and the progression to steatohepatitis. Besides, higher CYP2E1 activity in obesity and MASLD is deemed to increase the risk of acetaminophen (APAP)-induced hepatotoxicity because this pain reliever is metabolized by CYP2E1 to N-acetyl-p-benzoquinone imine (NAPQI), a highly toxic metabolite. Although the mechanism of MASLD-associated CYP2E1 induction is still unclear, evidence suggests that hepatic CYP2E1 activity is regulated by fatty acids (FAs). In this study, we investigated the effect of 9 FAs differing by their carbon chain length and their degree of unsaturation on CYP2E1 activity in differentiated HepaRG cells. One-week incubation with palmitic acid (PA), stearic acid (SA) and linoleic acid (LA) induced CYP2E1 activity but only LA exposure induced triglyceride accumulation. APAP hepatotoxicity was then assessed in HepaRG cells cultured with or without PA, SA or LA. Acute APAP cytotoxicity was exacerbated in presence of PA or SA and this was accompanied by more severe mitochondrial dysfunction. These effects were not observed when cells were incubated with LA. Hence, FA-mediated increased CYP2E1 activity in HepaRG cells does not necessarily require steatosis. In addition, FA-mediated CYP2E1 induction does not systematically lead to higher APAP-induced cytotoxicity. By favoring triglyceride accumulation, LA might curb APAP-induced mitochondrial dysfunction and cell death.

pharmacology and toxicology↗

bioRxiv2024

PPARgamma, a key modulator of metabolic reprogramming, stemness and chemoresistance associated with retrodifferentiation in human hepatocellular carcinomas

Human hepatocellular carcinomas (HCCs) with cancer stem cell (CSC) features are a subclass of therapeutically challenging cancers. We recently showed that retrodifferentiation of hepatic cancer cells into CSC-like cells leads to metabolic reprogramming and chemoresistance. The molecular mechanisms whereby differentiated cancer cells switch towards a CSC phenotype are poorly understood. By studying metabolic reprogramming associated with HCC cell plasticity, we identified an unsuspected role of peroxisome proliferator-activated receptor (PPAR){gamma} in hepatic CSC phenotype acquisition. Gene expression and metabolic analyses performed throughout cell differentiation/retrodifferentiation process of human HepaRG and HBG-BC2 HCC cells show that metabolic reprogramming in hepatic CSCs is associated with fragmented mitochondrial network, decreased respiration, de novo lipogenesis, fatty acid oxidation, but increased glycolysis and lipid storage. Mitochondrial genes downregulated in HepaRG-CSCs are also downregulated in the STEM HCC subclass. While PPAR is the main isoform in differentiated hepatic cells, we find high PPAR{gamma} expression in hepatic CSCs. Accordingly, nuclear localization of PPAR{gamma} is detected in human HCC tumors and PPAR{gamma}high/PPARlow expression is associated with the STEM HCC subclass and a poor outcome in human HCC cohorts. PPAR{gamma} silencing or/and inhibition of its target gene pyruvate dehydrogenase kinase 4 reactivates cell respiration, increases reactive oxygen species production and sensitizes hepatic CSCs to chemotherapy. Conversely, PPAR activation synergizes with chemotherapy to induce cell death. Targeting PPAR{gamma}, a key regulator of metabolic reprogramming and stemness in hepatic CSCs, or modulating the PPAR{gamma}/PPAR balance that finely tunes the differentiation/retrodifferentiation process in HCC deserves further investigation for antitumor therapy. Implications heading and statementPPAR{gamma}, a key regulator of metabolic reprogramming and stemness in hepatic CSC, reduces oxidative phosphorylation and reactive oxygen species production, therefore contributing to HCC chemoresistance.

cancer biology↗

bioRxiv2024

The dithiocarbamate pesticides maneb and mancozeb disturb the metabolism of lipids and xenobiotics in an in vitro model of metabolic dysfunction-associated steatotic liver disease

Pesticides are increasingly recognized to be hepatotoxic but less is known about their toxicity in metabolic dysfunction-associated steatotic liver disease (MASLD). Recent investigations reported oxidative stress-induced apoptosis in differentiated hepatocyte-like HepaRG cells after a single treatment with a 7-pesticide mixture that included chlorpyrifos, dimethoate, diazinon, iprodione, imazalil, and the dithiocarbamates maneb and mancozeb. These effects were reproduced by maneb, mancozeb, or manganese chloride (MnCl2). Herein, differentiated HepaRG cells cultured for 2 weeks without (-FA) or with (+FA) a mixture of stearic and oleic acids were treated with this 7-pesticide mixture, maneb, mancozeb, or MnCl2 along the same period. While these molecules did not induce neutral lipid accumulation in -FA-HepaRG cells, they worsened steatosis in +FA-HepaRG cells. Maneb or MnCl2 impaired very low-density lipoprotein (VLDL) secretion and increased fatty acid uptake without altering mitochondrial fatty acid oxidation and de novo lipogenesis. Reduced VLDL secretion was associated with decreased mRNA levels of apolipoproteins B and C3 and microsomal triglyceride transfer protein. Zinc supplementation restored VLDL secretion, reduced fatty acid uptake and prevented the exacerbation of steatosis in +FA-HepaRG cells treated with mancozeb or MnCl2. The mixture, maneb, or MnCl2 also reduced the mRNA expression and activity of several cytochromes P450 in +FA- and -FA-HepaRG cells. This was associated with impaired biotransformation of diazinon while chlorpyrifos metabolism was unaffected. Hence, maneb, mancozeb and MnCl2 disturb the metabolism of lipids and xenobiotics in HepaRG cells, in particular in fatty acid-exposed cells. These findings could have major pathophysiological consequences in dithiocarbamate-exposed individuals with MASLD.

pharmacology and toxicology↗

bioRxiv2023

Low concentrations of ethylene bisdithiocarbamate pesticides maneb and mancozeb impair manganese and zinc homeostasis to induce oxidative stress and caspase-dependent apoptosis in human hepatocytes

The worldwide and intensive use of phytosanitary compounds results in environmental and food contamination by chemical residues. Human exposure to multiple pesticide residues is a major health issue. Considering that the liver is not only the main organ for metabolizing pesticides but also a major target of toxicities induced by xenobiotics, we studied the effects of a mixture of 7 pesticides (chlorpyrifos-ethyl, dimethoate, diazinon, iprodione, imazalil, maneb, mancozeb) often detected in food samples. Effects of the mixture was investigated using metabolically competent HepaRG cells and human hepatocytes in primary culture. We report the strong cytotoxicity of the pesticide mixture towards hepatocytes-like HepaRG cells and human hepatocytes upon acute and chronic exposures at low concentrations extrapolated from the Acceptable Daily Intake (ADI) of each compound. Unexpectedly, we demonstrated that the manganese (Mn)-containing dithiocarbamates (DTCs) maneb and mancozeb were solely responsible for the cytotoxicity induced by the mixture. The mechanism of cell death involved the induction of oxidative stress, which led to cell death by intrinsic apoptosis involving caspases 3 and 9. Importantly, this cytotoxic effect was found only in cells metabolizing these pesticides. Herein, we unveil a novel mechanism of toxicity of the Mn-containing DTCs maneb and mancozeb through their metabolization in hepatocytes generating the main metabolite ethylene thiourea (ETU) and the release of Mn leading to intracellular Mn overload and depletion in zinc (Zn). Alteration of the Mn and Zn homeostasis provokes the oxidative stress and the induction of apoptosis, which can be prevented by Zn supplementation. Our data demonstrate the hepatotoxicity of Mn-containing fungicides at very low doses and unveil their adverse effect in disrupting Mn and Zn homeostasis and triggering oxidative stress in human hepatocytes.

pharmacology and toxicology↗

bioRxiv2023

New genome scale network modeling and mining workflow for detecting metabolic changes induced by exposure to chemicals

BackgroundThe growing abundance of in vitro omics data, coupled with the necessity to reduce animal testing in the safety assessment of chemical compounds and even eliminate it in the evaluation of cosmetics, highlights the need for adequate computational methodologies. Data from omics technologies allow the exploration of a wide range of biological processes, therefore providing a better understanding of mechanisms of action (MoA) related to chemical exposure in biological systems. However, the analysis of these large datasets remains difficult due to the complexity of modulations spanning multiple biological processes. ResultsTo address this, we propose a strategy to reduce information overload by computing, based on transcriptomics data, a comprehensive metabolic sub-network reflecting the metabolic impact of a chemical. The proposed strategy integrates transcriptomic data to a genome scale metabolic network through enumeration of condition specific metabolic models hence translating transcriptomics data into reaction activity probabilities. Based on these results, graph algorithm is applied to retrieve user readable sub-networks reflecting the possible metabolic MoA (mMoA) of chemicals. This strategy has been implemented as a three-step workflow. The first step consists in building cell condition-specific models reflecting the metabolic impact of each exposure condition while taking into account the diversity of possible optimal solutions with a partial enumeration algorithm. In a second step, we address the challenge of analyzing thousands of enumerated conditions-specific networks by computing differentially activated reactions (DARs) between the two sets of enumerated possible condition-specific models. Finally, in the third step, DARs are grouped into clusters of functionally interconnected metabolic reactions, representing possible mMoA, using the distance-based clustering and subnetwork extraction method. The first part of the workflow was exemplified on eight molecules selected for their known human hepatotoxic outcomes associated with specific MoAs well described in the literature and for which we retrieved primary human hepatocytes (PHH) transcriptomic data in Open TG-GATEs. Then, we further applied this strategy to more precisely model and visualize associated mMoA for two of these eight molecules (amiodarone and valproic acid). The approach proved to go beyond gene-based analysis by identifying mMoA when few genes are significantly differentially expressed (2 differentially expressed genes (DEGs) for amiodarone) or when very large number of genes were differentially expressed (5709 DEGs for valproic acid). In both cases, the results of our strategy well fitted evidence from the literature regarding known MoA. Beyond these confirmations, the workflow highlighted potential other unexplored mMoA. ConclusionThe proposed strategy allows toxicology experts to decipher which part of cellular metabolism is expected to be affected by the exposition to a given chemical. The approach originality resides in the combination of different metabolic modelling approaches (constraint based and graph modelling). The application to two model molecules shows the strong potential of the approach for interpretation and visual mining of complex omics in vitro data. All code is freely available as well as data to reproduce results.

bioinformatics↗