β-Αminoisobutyric acid (BAIBA) is a β-amino acid discovered in the 1950’s as a waste product of valine and thymine biotransformation. In the early 2000s, we discovered that BAIBA could promote hepatic fatty acid oxidation (FAO) and ketogenesis, reduce fatty liver and body fatness, and improve glucose intolerance in obese mice, in a leptin-dependent manner. A few years later, another team reported that BAIBA was a myokine acting on white adipocytes to induce browning and confirmed that it could promote hepatic FAO. Since then, other researchers have borne out that BAIBA is a bona fide myokine whose circulating levels could serve as a biomarker in certain metabolic states and diseases. Moreover, further investigations showed that BAIBA could act on cells other than hepatocytes and adipocytes, including osteocytes, endothelial and neuronal cells, myocytes, and cardiomyocytes. In these cells, BAIBA exerts its metabolic and cytoprotective effects via different signaling pathways involving, for instance, AMP-activated protein kinase, protein kinase A, peroxisome proliferator-activated receptor γ coactivator 1, and peroxisome proliferator-activated receptors α and δ. Overall, these studies provide strong evidence that BAIBA presents favorable effects on different conditions associated with obesity and diabetes. This could make BAIBA a potential druggable compound since it presents an apparent good safety profile, while derivatives are currently being developed to enhance BAIBA biodistribution. This narrative review aims to tell the fascinating history of BAIBA, which spans 75 years.

Mitochondrial activity is necessary for the maintenance of many liver functions. In particular, mitochondrial fatty acid oxidation (FAO) is required for energy production and lipid homeostasis. This key metabolic pathway is finely tuned by the mitochondrial respiratory chain (MRC) activity and different transcription factors such as peroxisome proliferator-activated receptor α (PPARα). Many drugs have been shown to cause mitochondrial dysfunction, which can lead to acute and chronic liver lesions. While severe inhibition of mitochondrial FAO would eventually cause microvesicular steatosis, hypoglycemia, and liver failure, moderate impairment of this metabolic pathway can induce macrovacuolar steatosis, which can progress in the long term to steatohepatitis and cirrhosis. Drugs can impair mitochondrial FAO through several mechanisms including direct inhibition of FAO enzymes, sequestration of coenzyme A and L-carnitine, impairment of the activity of one or several MRC complexes and reduced PPARα expression. In drug-induced macrovacuolar steatosis, non-mitochondrial mechanisms can also be involved in lipid accumulation including increased de novo lipogenesis and reduced very-low-density lipoprotein secretion. Nonetheless, mitochondrial dysfunction and subsequent oxidative stress appear to be key events in the progression of steatosis to steatohepatitis. Patients suffering from metabolic dysfunction-associated steatotic liver disease (MASLD) and treated with mitochondriotoxic drugs should be closely monitored to reduce the risk of acute liver injury or a faster transition of steatosis to steatohepatitis. Therapies based on the mitochondrial cofactor L-carnitine, the antioxidant N-acetylcysteine, or thyromimetics might be useful to prevent or treat drug-induced mitochondrial dysfunction, steatosis, and steatohepatitis.

Pesticides are increasingly recognized to be hepatotoxic, but less is known about their toxicity in metabolic dysfunction-associated steatotic liver disease (MASLD). Herein, differentiated HepaRG cells cultured for 2 weeks without (-FA) or with (+FA) a mixture of fatty acids were treated with different pesticides, including maneb and mancozeb, during the same period. While maneb and mancozeb did not induce neutral lipid accumulation in -FA-HepaRG cells, they worsened steatosis in +FA-HepaRG cells. MnCl2 treatment reproduced these effects. Maneb or MnCl2 impaired very low-density lipoprotein (VLDL) secretion and increased fatty acid uptake. Zinc supplementation restored VLDL secretion, reduced fatty acid uptake, and prevented steatosis worsening in +FA-HepaRG cells treated with mancozeb or MnCl2. 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. These findings could have major pathophysiological consequences in dithiocarbamate-exposed individuals with MASLD.

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)γ in hepatic CSC phenotype acquisition. Gene expression and metabolic analyses performed throughout the cell differentiation/retrodifferentiation process of human HepaRG and HBG-BC2 HCC cells show that metabolic reprogramming in hepatic CSCs is associated with a fragmented mitochondrial network, decreased respiration, de novo lipogenesis, and fatty acid oxidation, but increased glycolysis and lipid storage. Mitochondrial genes downregulated in HepaRG-CSCs are also downregulated in the STEM HCC subclass. While PPARα is the main isoform in differentiated hepatic cells, we find high PPARγ expression in hepatic CSCs. Accordingly, nuclear localization of PPARγ is detected in human HCC tumors, and PPARγhigh/PPARαlow expression is associated with the STEM HCC subclass and a poor outcome in human HCC cohorts. PPARγ 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, PPARα activation synergizes with chemotherapy to induce cell death. Targeting PPARγ, a key regulator of metabolic reprogramming and stemness in hepatic CSCs, or modulating the PPARγ/PPARα balance that finely tunes the differentiation/retrodifferentiation process in HCC deserves further investigation for anti-tumor therapy.

Identification of Endocrine-Disrupting Chemicals (EDCs) in a regulatory context requires a high level of evidence. However, lines of evidence (e.g. human, in vivo, in vitro or in silico) are heterogeneous and incomplete for quantifying evidence of the adverse effects and mechanisms involved. To date, for the regulatory appraisal of metabolism-disrupting chemicals (MDCs), no harmonised guidance to assess the weight of evidence has been developed at the EU or international level. To explore how to develop this, we applied a formal Expert Knowledge Elicitation (EKE) approach within the European GOLIATH project. EKE captures expert judgment in a quantitative manner and provides an estimate of uncertainty of the final opinion. As a proof of principle, we selected one suspected MDC -triphenyl phosphate (TPP) - based on its related adverse endpoints (obesity/adipogenicity) relevant to metabolic disruption and a putative Molecular Initiating Event (MIE): activation of peroxisome proliferator activated receptor gamma (PPARγ). We conducted a systematic literature review and assessed the quality of the lines of evidence with two independent groups of experts within GOLIATH, with the objective of categorising the metabolic disruption properties of TPP, by applying an EKE approach. Having followed the entire process separately, both groups arrived at the same conclusion, designating TPP as a “suspected MDC” with an overall quantitative agreement exceeding 85%, indicating robust reproducibility. The EKE method provides to be an important way to bring together scientists with diverse expertise and is recommended for future work in this area.

The development of in vitro models that recapitulate critical liver functions is essential for accurate assessments of drug toxicity. Although liver organoids can be used for drug discovery and toxicology, they are limited by (i) the lack of expression and activity of xenobiotic-metabolizing enzymes, and (ii) the difficulty of mimicking non-alcoholic fatty liver disease (NAFLD, which influences the expression of these enzymes) in vitro. Here, we generated three-dimensional multi-cell-type liver organoids (hereafter "HML organoids") from HepaRG cells, primary human macrophages, and hepatic-stellate-cell-derived LX-2 cells. We also developed an NAFLD model by culturing HML organoids for 9 days with a mixture of stearic and oleic acids. The exposed organoids showed typical features of steatosis and expressed fibrosis markers. We subsequently used HML and NAFLD-HML organoids to model drug-induced liver injury. By estimating the IC50 and benchmark doses, we were able to improve the in vitro detection of drugs likely to be toxic in fatty livers. Thus, HML and NAFLD-HML organoids exhibited most of the liver's functions and are relevant in vitro models of drug metabolism, drug toxicity, and adverse drug event in NAFLD.

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. ### Competing Interest Statement The authors have declared no competing interest.

BACKGROUND:The antineoplastic drug busulfan can induce different hepatic lesions including cholestasis and sinusoidal obstruction syndrome. However, hepatic steatosis has never been reported in patients.OBJECTIVES:This study aimed to determine whether busulfan could induce steatosis in primary human hepatocytes (PHH) and differentiated HepaRG cells.METHODS:Neutral lipids were determined in PHH and HepaRG cells. Mechanistic investigations were performed in HepaRG cells by measuring metabolic fluxes linked to lipid homeostasis, reduced glutathione (GSH) levels, and expression of genes involved in lipid metabolism and endoplasmic reticulum (ER) stress. Analysis of two previous transcriptomic datasets was carried out.RESULTS:Busulfan induced lipid accumulation in HepaRG cells but not in six different batches of PHH. In HepaRG cells, busulfan impaired VLDL secretion, increased fatty acid uptake, and induced ER stress. Transcriptomic data analysis and decreased GSH levels suggested that busulfan-induced steatosis might be linked to the high expression of glutathione S-transferase (GST) isoenzyme A1, which is responsible for the formation of the hepatotoxic sulfonium cation conjugate. In keeping with this, the GST inhibitor ethacrynic acid and the chemical chaperone tauroursodeoxycholic acid alleviated busulfan-induced lipid accumulation in HepaRG cells supporting the role of the sulfonium cation conjugate and ER stress in steatosis.CONCLUSION:While the HepaRG cell line is an invaluable tool for pharmacotoxicological studies, it might not be always an appropriate model to predict and mechanistically investigate drug-induced liver injury. Hence, we recommend carrying out toxicological investigations in both HepaRG cells and PHH to avoid drawing wrong conclusions on the potential hepatotoxicity of drugs and other xenobiotics.

Drug-induced liver injury (DILI) represents a major issue for pharmaceutical companies, being a potential cause of black-box warnings on marketed pharmaceuticals, or drug withdrawal from the market. Lipid accumulation in the liver also referred to as steatosis, may be secondary to impaired mitochondrial fatty acid oxidation (mtFAO). However, an overall causal relationship between drug-induced mtFAO inhibition and the occurrence of steatosis in patients has not yet been established with a high number of pharmaceuticals. Hence, 32 steatogenic and 13 nonsteatogenic drugs were tested for their ability to inhibit mtFAO in isolated mouse liver mitochondria. To this end, mitochondrial respiration was measured with palmitoyl-l-carnitine, palmitoyl-CoA + l-carnitine, or octanoyl- l-carnitine. This mtFAO tri-parametric assay was able to predict the occurrence of steatosis in patients with a sensitivity and positive predictive value above 88%. To get further information regarding the mechanism of drug-induced mtFAO impairment, mitochondrial respiration was also measured with malate/glutamate or succinate. Drugs such as diclofenac, methotrexate, and troglitazone could inhibit mtFAO secondary to an impairment of the mitochondrial respiratory chain, whereas dexamethasone, olanzapine, and zidovudine appeared to impair mtFAO directly. Mitochondrial swelling, transmembrane potential, and production of reactive oxygen species were also assessed for all compounds. Only the steatogenic drugs amiodarone, ketoconazole, lovastatin, and toremifene altered all these 3 mitochondrial parameters. In conclusion, our tri-parametric mtFAO assay could be useful in predicting the occurrence of steatosis in patients. The combination of this assay with other mitochondrial parameters could also help to better understand the mechanism of drug-induced mtFAO inhibition.

La stéatose hépatique (non-alcoholic fatty liver [NAFL]) est caractérisée par une accumulation excessive de triglycérides dans le foie et touche aujourd'hui un quart de la population mondiale. Bien que souvent bénigne, la NAFL peut progressivement évoluer vers une stéatohépatite non alcoolique (non-alcoholic steatohepatitis [NASH]), une lésion potentiellement plus grave définie par la présence concomitante d'une NAFL, de lésions nécro-inflammatoires évolutives et d'un ballonnement hépatocytaire. La NASH peut elle-même être à l'origine d'une cirrhose voire d'un carcinome hépatocellulaire. Une meilleure compréhension des mécanismes d'aggravation de la NAFL vers la NASH représente donc un enjeu majeur de santé publique. Plusieurs études ont mis en évidence que le cytochrome P450 2E1 (CYP2E1) pourrait être impliqué dans ces mécanismes d'aggravation. L'induction du CYP2E1 a en effet pour particularité de générer des espèces réactives de l'oxygène (EROs) qui sont sources d'un stress oxydant propice à l'aggravation de la NAFL en NASH. Des travaux ont rapporté le rôle de certains acides gras (AGs) parmi les facteurs métaboliques susceptibles d'activer le CYP2E1, en particulier dans un contexte d'obésité et/ou de NAFL. Outre son rôle potentiel dans l'aggravation de la NAFL en NASH, le CYP2E1 est impliqué dans la toxicité hépatique du paracétamol (PRC), observée généralement après un surdosage (> 10 g/j) intentionnel ou non, et plus rarement au cours de traitements à des doses pharmacologiques (3–4 g/j). Ainsi, le PRC pourrait être plus toxique dans un contexte de NAFL et d'obésité. Afin d'identifier plus précisément l'impact de différents AGs sur l'induction du CYP2E1, la NAFL et sur la toxicité du PRC, la lignée d'hépatocarcinome humain HepaRG a été utilisée. Ces cellules ont été traitées pendant une semaine par neuf AGs différents (150 μM). Un traitement par le PRC (10 ou 20 mM) pendant les 24 dernières heures a également été réalisé. L'activité du CYP2E1 a été significativement induite par les AGs palmitique (PA), stéarique (SA) et linoléique (LA) dans notre modèle. Pour le PA et le SA, les mécanismes impliqués passeraient par une augmentation de la stabilité de la protéine CYP2E1. Concernant la NAFL, uniquement le LA a favorisé une accumulation significative de triglycérides intracellulaires ainsi que l'expression de certains gènes représentatifs des gouttelettes lipidiques. Pour cet AG, l'accumulation des triglycérides pourrait s'expliquer par une augmentation de l'entrée des AGs dans les hépatocytes par le transporteur CD36/FAT et une diminution de la b-oxydation mitochondriale. Les effets de ces trois AGs sur le stress oxydant, le stress du réticulum endoplasmique et la fonction mitochondriale ont ensuite été évalués. Après une semaine de traitement, aucune variation de stress cellulaire n'a été mesurée. En revanche, une diminution de la respiration maximale a été observée en réponse aux AGs PA et SA. Enfin, une potentialisation de la toxicité du PRC a été observée avec les AGs PA et SA mais pas avec le LA. Le stress oxydant a ensuite été évalué au vu de son importance dans l'hépatotoxicité du PRC. Une potentialisation de la production d'EROs ainsi qu'une altération de la réponse antioxydante ont été mises en évidence avec les AGs PA et SA. Trois AGs inducteurs du CYP2E1 (c.-à-d. PA, SA et LA) ont été identifiés. De façon intéressante, ces AGs n'ont pas tous le même impact sur la NAFL dans nos conditions expérimentales puisque seul le LA entraînait une stéatose. En effet, le métabolisme lipidique hépatocytaire s'effectue de manière différente selon le traitement en AG. De plus, une potentialisation de la toxicité du PRC avec les AGs PA et SA et un stress oxydant avec ces deux AGs ont également été mis en évidence. Ainsi, la sensibilité accrue à l'hépatotoxicité du PRC dans un contexte de nutrition hyperlipidique et de NAFL pourrait en partie être expliquée par l'induction du CYP2E1, qui cependant peut s'observer expérimentalement de façon indépendante de l'accumulation des triglycérides intracellulaires.

Supplemental Table 5 provides the lists of genes significantly deregulated between HepaRG-Spheres and HepaRG-D10 cells and between HepaRG-SP and HepaRG-D10 cells.

The epidemic of obesity, type 2 diabetes and nonalcoholic liver disease (NAFLD) favors drug consumption, which augments the risk of adverse events including liver injury. For more than 30 years, a series of experimental and clinical investigations reported or suggested that the common pain reliever acetaminophen (APAP) could be more hepatotoxic in obesity and related metabolic diseases, at least after an overdose. Nonetheless, several investigations did not reproduce these data. This discrepancy might come from the extent of obesity and steatosis, accumulation of specific lipid species, mitochondrial dysfunction and diabetes-related parameters such as ketonemia and hyperglycemia. Among these factors, some of them seem pivotal for the induction of cytochrome P450 2E1 (CYP2E1), which favors the conversion of APAP to the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI). In contrast, other factors might explain why obesity and NAFLD are not always associated with more frequent or more severe APAP-induced acute hepatotoxicity, such as increased volume of distribution in the body, higher hepatic glucuronidation and reduced CYP3A4 activity. Accordingly, the occurrence and outcome of APAP-induced liver injury in an obese individual with NAFLD would depend on a delicate balance between metabolic factors that augment the generation of NAPQI and others that can mitigate hepatotoxicity.

De nombreuses investigations ont mis en évidence la présence de dysfonctions mitochondriales au cours de la stéatose hépatique non alcoolique (NAFLD). Tandis que les oxydations mitochondriales sont plutôt augmentées au cours de la simple stéatose, ces adaptations métaboliques disparaissent lors de la stéatohépatite non alcoolique (NASH). La dégradation des fonctions mitochondriales se poursuit ensuite pendant la cirrhose. Ces dysfonctions mitochondriales semblent être, au moins en partie, la conséquence de l’inflammation. Les patients souffrant de NAFLD devraient être dissuadés de consommer de l’alcool, une molécule présentant de nombreux effets délétères sur les mitochondries.

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.

Mucosal healing has emerged as a therapeutic goal to achieve lasting clinical remission in ulcerative colitis. Intestinal repair in response to inflammation presumably requires higher energy supplies for the restoration of intestinal barrier and physiological functions. However, epithelial energy metabolism during intestinal mucosal healing has been little studied, whereas inflammation-induced alterations have been reported in the main energy production site, the mitochondria. The aim of the present work was to assess the involvement of mitochondrial activity and the events influencing their function during spontaneous epithelial repair after colitis induction in mouse colonic crypts. The results obtained show adaptations of colonocyte metabolism during colitis to ensure maximal ATP production for supporting energetic demand by both oxidative phosphorylation and glycolysis in a context of decreased mitochondrial biogenesis and through mitochondrial function restoration during colon epithelial repair. In parallel, colitis-induced mitochondrial ROS production in colonic epithelial cells was rapidly associated with transient expression of GSH-related enzymes. Mitochondrial respiration in colonic crypts was markedly increased during both inflammatory and recovery phases despite decreased expression of several mitochondrial respiratory chain complex subunits after colitis induction. Rapid induction of mitochondrial fusion was associated with mitochondrial function restoration. Finally, in contrast with the kinetics expression of genes involved in mitochondrial oxidative metabolism and in glycolysis, the expression of glutaminase was markedly reduced in the colonic crypts both during colitis and repair phases. Overall, our data suggest that the epithelial repair after colitis induction is characterized by a rapid and transient increased capacity for mitochondrial ATP production in a context of apparent restoration of mitochondrial biogenesis and metabolic reorientation of energy production. The potential implication of energy production adaptations within colonic crypts to sustain mucosal healing in a context of altered fuel supply is discussed.

In the current article the aims for a constructive way forward in Drug-Induced Liver Injury (DILI) are to highlight the most important priorities in research and clinical science, therefore supporting a more informed, focused, and better funded future for European DILI research. This Roadmap aims to identify key challenges, define a shared vision across all stakeholders for the opportunities to overcome these challenges and propose a high-quality research program to achieve progress on the prediction, prevention, diagnosis and management of this condition and impact on healthcare practice in the field of DILI. This will involve 1. Creation of a database encompassing optimised case report form for prospectively identified DILI cases with well-characterised controls with competing diagnoses, biological samples, and imaging data; 2. Establishing of preclinical models to improve the assessment and prediction of hepatotoxicity in humans to guide future drug safety testing; 3. Emphasis on implementation science and 4. Enhanced collaboration between drug-developers, clinicians and regulatory scientists. This proposed operational framework will advance DILI research and may bring together basic, applied, translational and clinical research in DILI.

Originally developed as an antianginal agent, amiodarone is now commonly prescribed as a broad-spectrum antiarrhythmic. However, long-term treatment with this pharmaceutical is limited by many drug-drug interactions and various adverse effects affecting different organs and tissues such as the heart, liver, lung, and thyroid. Amiodarone-induced hepatotoxicity includes hepatic cytolysis, cholestasis, and steatosis, a liver lesion which can occur secondary to an impairment of mitochondrial fatty acid oxidation. In this chapter, the discovery of the fact that amiodarone could inhibit this major metabolic pathway in the late 1980s is described. In addition, the fact that this antiarrhythmic drug had a dual effect on oxidative phosphorylation depending on the concentrations applied to isolated mouse liver mitochondria is uncovered. Moreover, the way these mitochondrial effects might favor in some patients the progression of steatosis to steatohepatitis is discussed. Finally, other works showing that amiodarone can alter mitochondrial functions in other tissues such as the lung and thyroid are briefly mentioned.

Fatty liver diseases can result from common metabolic diseases, as well as from xenobiotic exposure and excessive alcohol use, all of which have been shown to exert toxic effects on hepatic mitochondrial functionality and dynamics. Invasive or complex methodology limits large-scale investigations of mitochondria in human livers. Nevertheless, abnormal mitochondrial function, such as impaired fatty acid oxidation and oxidative phosphorylation, drives oxidative stress and has been identified as an important feature of human steatohepatitis. On the other hand, hepatic mitochondria can be flexible and adapt to the ambient metabolic condition to prevent triglyceride and lipotoxin accumulation in obesity. Experience from studies on xenobiotics has provided important insights into the regulation of hepatic mitochondria. Increasing awareness of the joint presence of metabolic disease-related (lipotoxic) and alcohol-related liver diseases further highlights the need to better understand their mutual interaction and potentiation in disease progression. Recent clinical studies have assessed the effects of diets or bariatric surgery on hepatic mitochondria, which are also evolving as an interesting therapeutic target in non-alcoholic fatty liver disease. This review summarises the current knowledge on hepatic mitochondria with a focus on fatty liver diseases linked to obesity, type 2 diabetes and xenobiotics.

L'excès d'acide linoléique (LA) alimentaire (> 4 % de l'apport calorique journalier) est associé à des effets délétères qui dépendent du modèle étudié. Il augmente notamment la prévalence de l'adiposité et du surpoids chez l'homme et possède des rôles pro-adipogéniques trans-générationnels chez la souris mais également pro-inflammatoires et pro-stéatosants chez le rat, ce dernier effet étant aussi retrouvé sur le modèle hépatocellulaire HepaRG. Ces effets nécessitent une compréhension plus précise des voies/mécanismes impactés par l'action directe de cet acide gras, ou indirecte, médiée par des métabolites issus de la conversion du précurseur. Cette étude cherche à répondre à cette problématique en explorant en premier lieu l'effet pro-stéatosant du LA, ainsi que celui de 4 métabolites d'intérêt dont 2 Oxlams (oxydized linoleic acid metabolites) : le 9-HODE (9-HydroxyOctaDecadienoic Acid) et le 13-HODE, ainsi que 2 CLAs (conjugated linoleic acid) : le c9,t11 C18:2 (acide ruménique) et le t10,c12 C18:2. Des cellules HepaRG ont été cultivées durant 35 jours (2 semaines de prolifération puis 3 semaines de différenciation) puis incubées durant 1 semaine en présence de différents traitements contenant respectivement les 5 molécules d'intérêt identifiées (LA/9-HODE/13-HODE/c9,t11 C18:2/t10,c12 C18:2) à différentes concentrations, comparées à un contrôle négatif (milieu de différenciation classique à 1,75 % de DMSO). À l'issue de ces traitements, des tests de dosage des triglycérides et de viabilité cellulaire ont été réalisés. Les ARNm codants pour des gènes associés au métabolisme lipidique ont été quantifiés par RTqPCR. Les cellules ont développé une stéatose marquée par l'accumulation de triglycérides intracellulaires pour les traitements LA/c9,t11 C18:2 et dans une moindre mesure t10,c12 C18:2 à 150 μM chacun, sans toxicité cellulaire associée. En revanche aucune accumulation de triglycérides n'a été observée pour les traitements aux HODEs pour les 3 concentrations testées à 125 nM, 250 nM et 500 nM. L'exploration au niveau transcriptionnel semble montrer une variabilité des mécanismes induits dans la mise en place de cette stéatose en fonction des différents traitements. L'expression de MTTP (sécrétion des VLDL) est plus fortement diminuée pour c9,t11 C18:2, au niveau du stress du réticulum endoplasmique (RE) les expressions de DDIT3 et de HSPA5 sont respectivement augmentées pour t10,c12 C18:2 et diminuées pour le LA. CPT1 (bêta-oxydation mitochondriale) est quant à lui plus fortement exprimé pour t10,c12 C18:2. Notre étude montre un effet pro-stéatosant du LA mais aussi des métabolites conjugués associés sur le modèle étudié. Les résultats de l'analyse des expressions géniques permettent de formuler des hypothèses sur les mécanismes sous-jacents expliquant la mise en place d'une stéatose. En fonction des différentes molécules d'intérêt, on observe notamment un impact plus marqué sur la voie de sécrétion des VLDL pour l'acide ruménique, sur la voie du stress du RE pour l'acide linoléique et t10,c12 C18:2, lui-même contrebalancé par une hausse de la bêta-oxydation mitochondriale. Par la suite, des analyses seront réalisées sur d'autres voies du métabolisme et à d'autres échelles (expressions protéiques, activité enzymatiques …) pour compléter ces premières observations.