The worldwide epidemic of obesity and insulin resistance favors nonalcoholic fatty liver disease (NAFLD). Insulin resistance (IR) in the adipose tissue increases lipolysis and the entry of ...nonesterified fatty acids (NEFAs) in the liver, whereas IR‐associated hyperinsulinemia promotes hepatic de novo lipogenesis. However, several hormonal and metabolic adaptations are set up in order to restrain hepatic fat accumulation, such as increased mitochondrial fatty acid oxidation (mtFAO). Unfortunately, these adaptations are usually not sufficient to reduce fat accumulation in liver. Furthermore, enhanced mtFAO without concomitant up‐regulation of the mitochondrial respiratory chain (MRC) activity induces reactive oxygen species (ROS) overproduction within different MRC components upstream of cytochrome c oxidase. This event seems to play a significant role in the initiation of oxidative stress and subsequent development of nonalcoholic steatohepatitis (NASH) in some individuals. Experimental investigations also pointed to a progressive reduction of MRC activity during NAFLD, which could impair energy output and aggravate ROS overproduction by the damaged MRC. Hence, developing drugs that further increase mtFAO and restore MRC activity in a coordinated manner could ameliorate steatosis, but also necroinflammation and fibrosis by reducing oxidative stress. In contrast, physicians should be aware that numerous drugs in the current pharmacopoeia are able to induce mitochondrial dysfunction, which could aggravate NAFLD in some patients. (Hepatology 2013;58:1497–1507)
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Although acetaminophen (APAP) is usually considered as a safe drug, this painkiller can lead to acute liver failure after overdoses. Moreover, there is evidence that the maximum recommended dosage ...can induce hepatic cytolysis in some individuals. Several predisposing factors appear to enhance the risk and severity of APAP‐induced liver injury including chronic alcoholic liver disease and nonalcoholic fatty liver disease (NAFLD), which refers to a large spectrum of hepatic lesions linked to obesity. In contrast, obesity by itself does not seem to be associated with a higher risk of APAP‐induced liver injury. Since 1987, seven studies dealt with APAP‐induced hepatotoxicity in rodent models of NAFLD and five of them found that this liver disease was associated with higher APAP toxicity. Unfortunately, these studies did not unequivocally established the mechanism(s) whereby NAFLD could favour APAP hepatotoxicity, although some investigations suggested that pre‐existent induction of hepatic cytochrome P450 2E1 (CYP2E1) could play a significant role by increasing the generation of N‐acetyl‐p‐benzoquinone imine (NAPQI), the toxic metabolite of APAP. Moreover, pre‐existent mitochondrial dysfunction associated with NAFLD could also be involved. In contrast, some investigations suggested that factors that could reduce the risk and severity of APAP hepatotoxicity in obesity and NAFLD include higher hepatic APAP glucuronidation, reduced CYP3A4 activity and increased volume of body distribution. Thus, the occurrence and the outcome of APAP‐induced liver injury in an obese individual with NAFLD might depend on a delicate balance between metabolic factors that can be protective and others that favour large hepatic levels of NAPQI.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, UILJ, UKNU, UL, UM, UPUK
Numerous investigations have shown that mitochondrial dysfunction is a major mechanism of drug-induced liver injury, which involves the parent drug or a reactive metabolite generated through ...cytochromes P450. Depending of their nature and their severity, the mitochondrial alterations are able to induce mild to fulminant hepatic cytolysis and steatosis (lipid accumulation), which can have different clinical and pathological features. Microvesicular steatosis, a potentially severe liver lesion usually associated with liver failure and profound hypoglycemia, is due to a major inhibition of mitochondrial fatty acid oxidation (FAO). Macrovacuolar steatosis, a relatively benign liver lesion in the short term, can be induced not only by a moderate reduction of mitochondrial FAO but also by an increased hepatic de novo lipid synthesis and a decreased secretion of VLDL-associated triglycerides. Moreover, recent investigations suggest that some drugs could favor lipid deposition in the liver through primary alterations of white adipose tissue (WAT) homeostasis. If the treatment is not interrupted, steatosis can evolve toward steatohepatitis, which is characterized not only by lipid accumulation but also by necroinflammation and fibrosis. Although the mechanisms involved in this aggravation are not fully characterized, it appears that overproduction of reactive oxygen species by the damaged mitochondria could play a salient role. Numerous factors could favor drug-induced mitochondrial and metabolic toxicity, such as the structure of the parent molecule, genetic predispositions (in particular those involving mitochondrial enzymes), alcohol intoxication, hepatitis virus C infection, and obesity. In obese and diabetic patients, some drugs may induce acute liver injury more frequently while others may worsen the pre-existent steatosis (or steatohepatitis).
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
There has been growing evidence that phase I metabolizing enzymes cytochromes P450 (CYPs) are not only located in the endoplasmic reticulum but also in other subcellular compartments and particularly ...in mitochondria. The presence of CYPs in these organelles raises questions regarding their metabolic role and their possible deleterious effects on the respiratory chain complexes and mitochondrial DNA. This review will focus on one particular CYP, CYP2E1, which represents a significant source of reactive oxygen species and is involved in the metabolism of small molecule substrates including ethanol, drugs and carcinogens. Since hepatic CYP2E1 expression is increased in different physiopathological situations such as type 2 diabetes, obesity and ethanol intoxication, the presence of significant levels of this CYP within the mitochondria could have major deleterious effects. This review recalls the main data that brought to the fore the presence of CYP2E1 in mitochondria and the mechanism of its targeting in this organelle. The potential pathological consequences linked to the presence of CYP2E1 in mitochondria will be subsequently discussed.
Cytochrome P4502E1 (CYP2E1) is an enzyme involved in the metabolism of ethanol, drugs and carcinogens. It produces reactive oxygen species and is increased in diabetes, obesity and ethanol intoxication. This review recalls the data assessing the presence of CYP2E1 in mitochondria and the mechanism of its targeting. The potential pathological consequences linked to its presence in mitochondria are also discussed
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
Drugs induce cholestasis by diverse and still poorly understood mechanisms in humans. Early hepatic effects of chlorpromazine (CPZ), a neuroleptic drug known for years to induce intrahepatic ...cholestasis, were investigated using the differentiated human hepatoma HepaRG cells. Generation of reactive oxygen species (ROS) was detected as early as 15 minutes after CPZ treatment and was associated with an altered mitochondrial membrane potential and disruption of the pericanalicular distribution of F‐actin. Inhibition of 3H‐taurocholic acid efflux was observed after 30 minutes and was mostly prevented by N‐acetyl cysteine (NAC) cotreatment, indicating a major role of oxidative stress in CPZ‐induced bile acid (BA) accumulation. Moreover, 24‐hour treatment with CPZ decreased messenger RNA (mRNA) expression of the two main canalicular bile transporters, bile salt export pump (BSEP) and multidrug resistance protein 3 (MDR3). Additional CPZ effects included inhibition of Na+‐dependent taurocholic cotransporting polypeptide (NTCP) expression and activity, multidrug resistance‐associated protein 4 (MRP4) overexpression and CYP8B1 inhibition that are involved in BA uptake, basolateral transport, and BA synthesis, respectively. These latter events likely represent hepatoprotective responses which aim to reduce intrahepatic accumulation of toxic BA. Compared to CPZ effects, overloading of HepaRG cells with high concentrations of cholic and chenodeoxycholic acids induced a delayed oxidative stress and, similarly, after 24 hours it down‐regulated BSEP and MDR3 in parallel to a decrease of NTCP and CYP8B1 and an increase of MRP4. By contrast, low BA concentrations up‐regulated BSEP and MDR3 in the absence of oxidative stress. Conclusion: These data provide evidence that, among other mechanisms, oxidative stress plays a major role as both a primary causal and an aggravating factor in the early CPZ‐induced intrahepatic cholestasis in human hepatocytes. (HEPATOLOGY 2013)
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A frequent mechanism for drug-induced liver injury (DILI) is the formation of reactive metabolites that trigger hepatitis through direct toxicity or immune reactions. Both events cause mitochondrial ...membrane disruption. Genetic or acquired factors predispose to metabolite-mediated hepatitis by increasing the formation of the reactive metabolite, decreasing its detoxification, or by the presence of critical human leukocyte antigen molecule(s). In other instances, the parent drug itself triggers mitochondrial membrane disruption or inhibits mitochondrial function through different mechanisms. Drugs can sequester coenzyme A or can inhibit mitochondrial β-oxidation enzymes, the transfer of electrons along the respiratory chain, or adenosine triphosphate (ATP) synthase. Drugs can also destroy mitochondrial DNA, inhibit its replication, decrease mitochondrial transcripts, or hamper mitochondrial protein synthesis. Quite often, a single drug has many different effects on mitochondrial function. A severe impairment of oxidative phosphorylation decreases hepatic ATP, leading to cell dysfunction or necrosis; it can also secondarily inhibit ß-oxidation, thus causing steatosis, and can also inhibit pyruvate catabolism, leading to lactic acidosis. A severe impairment of β-oxidation can cause a fatty liver; further, decreased gluconeogenesis and increased utilization of glucose to compensate for the inability to oxidize fatty acids, together with the mitochondrial toxicity of accumulated free fatty acids and lipid peroxidation products, may impair energy production, possibly leading to coma and death. Susceptibility to parent drug-mediated mitochondrial dysfunction can be increased by factors impairing the removal of the toxic parent compound or by the presence of other medical condition(s) impairing mitochondrial function. New drug molecules should be screened for possible mitochondrial effects.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Drug‐induced liver injury occurs in general after several weeks and is often unpredictable. It is characterized by a large spectrum of lesions that includes steatosis and phospholipidosis. Many drugs ...such as amiodarone and tetracycline have been reported to cause phospholipidosis and/or steatosis. In this study, acute and chronic hepatic effects of these two drugs were investigated using well‐differentiated human hepatoma HepaRG cells. Accumulation of typical lipid droplets, labeled with Oil Red O, was observed in hepatocyte‐like HepaRG cells after repeat exposure to either drug. Amiodarone caused the formation of additional intracytoplasmic vesicles that did not stain in all HepaRG cells. At the electron microscopic level, these vesicles appeared as typical lamellar bodies and were associated with an increase of phosphatidylethanolamine and phosphatidylcholine. A dose‐dependent induction of triglycerides (TG) was observed after repeat exposure to either amiodarone or tetracycline. Several genes known to be related to lipogenesis were induced after treatment by these two drugs. By contrast, opposite deregulation of some of these genes (FASN, SCD1, and THSRP) was observed in fat HepaRG cells induced by oleic acid overload, supporting the conclusion that different mechanisms were involved in the induction of steatosis by drugs and oleic acid. Moreover, several genes related to lipid droplet formation (ADFP, PLIN4) were up‐regulated after exposure to both drugs and oleic acid. Conclusion: Our results show that amiodarone causes phospholipidosis after short‐term treatment and, like tetracycline, induces vesicular steatosis after repeat exposure in HepaRG cells. These data represent the first demonstration that drugs can induce vesicular steatosis in vitro and show a direct relationship between TG accumulation and enhanced expression of lipogenic genes. (HEPATOLOGY 2011;)
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Alzheimer's amyloid precursor protein 695 (APP) is a plasma membrane protein, which is known to be the source of the toxic amyloid β (Aβ) peptide associated with the pathogenesis of Alzheimer's ...disease (AD). Here we demonstrate that by virtue of its chimeric NH2-terminal signal, APP is also targeted to mitochondria of cortical neuronal cells and select regions of the brain of a transgenic mouse model for AD. The positively charged residues at 40, 44, and 51 of APP are critical components of the mitochondrial-targeting signal. Chemical cross-linking together with immunoelectron microscopy show that the mitochondrial APP exists in NH2-terminal inside transmembrane orientation and in contact with mitochondrial translocase proteins. Mutational studies show that the acidic domain, which spans sequence 220-290 of APP, causes the transmembrane arrest with the COOH-terminal 73-kD portion of the protein facing the cytoplasmic side. Accumulation of full-length APP in the mitochondrial compartment in a transmembrane-arrested form, but not lacking the acidic domain, caused mitochondrial dysfunction and impaired energy metabolism. These results show, for the first time, that APP is targeted to neuronal mitochondria under some physiological and pathological conditions.
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BFBNIB, NUK, PNG, UL, UM, UPUK
Human hepatoma HepaRG cells express most drug metabolizing enzymes and constitute a pertinent in vitro alternative cell system to primary cultures of human hepatocytes in order to determine drug ...metabolism and evaluate the toxicity of xenobiotics. In this work, we established novel transgenic HepaRG cells transduced with lentiviruses encoding the reporter green fluorescent protein (GFP) transcriptionally regulated by promoter sequences of cytochromes P450 (CYP) 1A1/2, 2B6 and 3A4 genes. Here, we demonstrated that GFP-biosensor transgenes shared similar expression patterns with the corresponding endogenous CYP genes during proliferation and differentiation in HepaRG cells. Interestingly, differentiated hepatocyte-like HepaRG cells expressed GFP at higher levels than cholangiocyte-like cells. Despite weaker inductions of GFP expression compared to the strong increases in mRNA levels of endogenous genes, we also demonstrated that the biosensor transgenes were induced by prototypical drug inducers benzo(a)pyrene and phenobarbital. In addition, we used the differentiated biosensor HepaRG cells to evidence that pesticide mancozeb triggered selective cytotoxicity of hepatocyte-like cells. Our data demonstrate that these new biosensor HepaRG cells have potential applications in the field of chemicals safety evaluation and the assessment of drug hepatotoxicity.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Hepatic steatosis (i.e. lipid accumulation) and steatohepatitis have been related to diverse etiologic factors, including alcohol, obesity, environmental pollutants. However, no study has so far ...analyzed how these different factors might interplay regarding the progression of liver diseases. The impact of the co-exposure to the environmental carcinogen benzoapyrene (BaP) and the lifestyle-related hepatotoxicant ethanol, was thus tested on in vitro models of steatosis (human HepaRG cell line; hybrid human/rat WIF-B9 cell line), and on an in vivo model (obese zebrafish larvae). Steatosis was induced prior to chronic treatments (14, 5 or 7 days for HepaRG, WIF-B9 or zebrafish, respectively). Toxicity and inflammation were analyzed in all models; the impact of steatosis and ethanol towards BaP metabolism was studied in HepaRG cells. Cytotoxicity and expression of inflammation markers upon co-exposure were increased in all steatotic models, compared to non steatotic counterparts. A change of BaP metabolism with a decrease in detoxification was detected in HepaRG cells under these conditions. A prior steatosis therefore enhanced the toxicity of BaP/ethanol co-exposure in vitro and in vivo; such a co-exposure might favor the appearance of a steatohepatitis-like state, with the development of inflammation. These deleterious effects could be partly explained by BaP metabolism alterations.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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