Gene expression profiles of murine fatty liver induced by the administration of valproic acid

Inhibition of PLA2G4A attenuated valproic acid- induced lysosomal membrane permeabilization and restored impaired autophagic flux: Implications for hepatotoxicity

Valproic acid (VPA) has broad efficacy against several seizures but causes liver injury limiting its prolonged clinical use. Some studies have demonstrated that VPA-induced hepatotoxicity is characterized by microvesicular hepatic steatosis. However, novel detailed mechanisms to explain VPA-induced hepatic steatosis and experimentally rigorously validated protective agents are still lacking. In this study, 8-week-old C57BL/6J mice were gavaged with VPA (500 mg/kg/d) for 4 weeks to establish an in vivo model of VPA-induced chronic liver injury. Quantitative proteomic and non-targeted lipidomic analyses were performed to explore the underlying mechanisms of VPA-induced hepatotoxicity. As a result, VPA-induced hepatotoxicity is associated with impaired autophagic flux, which is attributed to lysosomal dysfunction. Further studies revealed that VPA-induced lysosomal membrane permeabilization (LMP), allows soluble lysosomal enzymes to leak into the cytosol, which subsequently led to impaired lysosomal acidification. A lower abundance of glycerophospholipids and an increased abundance of lysophospholipids in liver tissues of mice in the VPA group strongly indicated that VPA-induced LMP may be mediated by the activation of phospholipase PLA2G4A. Metformin (Met) acted as a potential protective agent attenuating VPA-induced liver dysfunction and excessive lipid accumulation. Molecular docking and cellular thermal shift assays demonstrated that Met inhibited the activity of PLA2G4A by directly binding to it, thereby ameliorating VPA-induced LMP and autophagic flux impairment. In conclusion, this study highlights the therapeutic potential of targeting PLA2G4A-mediated lysosomal dysfunction in VPA-induced hepatotoxicity.

Drug-Induced Fatty Liver Disease (DIFLD): A Comprehensive Analysis of Clinical, Biochemical, and Histopathological Data for Mechanisms Identification and Consistency with Current Adverse Outcome Pathways

Drug induced fatty liver disease (DIFLD) is a form of drug-induced liver injury (DILI), which can also be included in the more general metabolic dysfunction-associated steatotic liver disease (MASLD), which specifically refers to the accumulation of fat in the liver unrelated to alcohol intake. A bi-directional relationship between DILI and MASLD is likely to exist: while certain drugs can cause MASLD by acting as pro-steatogenic factors, MASLD may make hepatocytes more vulnerable to drugs. Having a pre-existing MASLD significantly heightens the likelihood of experiencing DILI from certain medications. Thus, the prevalence of steatosis within DILI may be biased by pre-existing MASLD, and it can be concluded that the genuine true incidence of DIFLD in the general population remains unknown. In certain individuals, drug-induced steatosis is often accompanied by concomitant injury mechanisms such as oxidative stress, cell death, and inflammation, which leads to the development of drug-induced steatohepatitis (DISH). DISH is much more severe from the clinical point of view, has worse prognosis and outcome, and resembles MASH (metabolic-associated steatohepatitis), as it is associated with inflammation and sometimes with fibrosis. A literature review of clinical case reports allowed us to examine and evaluate the clinical features of DIFLD and their association with specific drugs, enabling us to propose a classification of DIFLD drugs based on clinical outcomes and pathological severity: Group 1, drugs with low intrinsic toxicity (e.g., ibuprofen, naproxen, acetaminophen, irinotecan, methotrexate, and tamoxifen), but expected to promote/aggravate steatosis in patients with pre-existing MASLD; Group 2, drugs associated with steatosis and only occasionally with steatohepatitis (e.g., amiodarone, valproic acid, and tetracycline); and Group 3, drugs with a great tendency to transit to steatohepatitis and further to fibrosis. Different mechanisms may be in play when identifying drug mode of action: (1) inhibition of mitochondrial fatty acid β-oxidation; (2) inhibition of fatty acid transport across mitochondrial membranes; (3) increased de novo lipid synthesis; (4) reduction in lipid export by the inhibition of microsomal triglyceride transfer protein; (5) induction of mitochondrial permeability transition pore opening; (6) dissipation of the mitochondrial transmembrane potential; (7) impairment of the mitochondrial respiratory chain/oxidative phosphorylation; (8) mitochondrial DNA damage, degradation and depletion; and (9) nuclear receptors (NRs)/transcriptomic alterations. Currently, the majority of, if not all, adverse outcome pathways (AOPs) for steatosis in AOP-Wiki highlight the interaction with NRs or transcription factors as the key molecular initiating event (MIE). This perspective suggests that chemical-induced steatosis typically results from the interplay between a chemical and a NR or transcription factors, implying that this interaction represents the primary and pivotal MIE. However, upon conducting this exhaustive literature review, it became evident that the current AOPs tend to overly emphasize this interaction as the sole MIE. Some studies indeed support the involvement of NRs in steatosis, but others demonstrate that such NR interactions alone do not necessarily lead to steatosis. This view, ignoring other mitochondrial-related injury mechanisms, falls short in encapsulating the intricate biological mechanisms involved in chemically induced liver steatosis, necessitating their consideration as part of the AOP's map road as well.

Valproate and Short-Chain Fatty Acids Activate Transcription of the Human Vitamin D Receptor Gene through a Proximal GC-Rich DNA Region Containing Two Putative Sp1 Binding Sites

The vitamin D receptor (VDR) mediates 1,25-dihydroxyvitamin D3 pleiotropic biological actions through transcription regulation of target genes. The expression levels of this ligand-activated nuclear receptor are regulated by multiple mechanisms both at transcriptional and post-transcriptional levels. Vitamin D3 is the natural VDR activator, but other molecules and signaling pathways have also been reported to regulate VDR expression and activity. In this study, we identify valproic acid (VPA) and natural short-chain fatty acids (SCFAs) as novel transcriptional activators of the human VDR (hVDR) gene. We further report a comprehensive characterization of VPA/SCFA-responsive elements in the 5' regulatory region of the hVDR gene. Two alternative promoter DNA regions (of 2.4 and 3.8 kb), as well as subsequent deletion fragments, were cloned in pGL4-LUC reporter vector. Transfection of these constructs in HepG2 and human Upcyte hepatocytes followed by reporter assays demonstrated that a region of 107 bp (from -107 to -1) upstream of the transcription start site in exon 1a is responsible for most of the increase in transcriptional activity in response to VPA/SCFAs. This short DNA region is GC-rich, does not contain an apparent TATA box, and includes two bona fide binding sites for the transcription factor Sp1. Our results substantiate the hypothesis that VPA and SCFAs facilitate the activity of Sp1 on novel Sp1 responsive elements in the hVDR gene, thus promoting VDR upregulation and signaling. Elevated hepatic VDR levels have been associated with liver steatosis and, therefore, our results may have clinical relevance in epileptic pediatric patients on VPA therapy. Our results could also be suggestive of VDR upregulation by SCFAs produced by gut microbiota.

Effects of naringin and valproate interaction on liver steatosis and dyslipidaemia parameters in male C57BL6 mice

Valproate is a common antiepileptic drug whose adverse effects include liver steatosis and dyslipidaemia. The aim of our study was to see how natural flavonoid antioxidant naringin would interact with valproate and attenuate these adverse effects. For this reason we treated male C57BL6 mice with a combination of 150 mg/kg of valproate and 25 mg/kg naringin every day for 10 days and compared their serum triglycerides, cholesterol, LDL, HDL, VLDL, and liver PPAR-alpha, PGC-1 alpha, ACOX1, Nrf2, SOD, CAT, GSH, and histological signs of steatosis. Valproate increased lipid peroxidation parameters and caused pronounced microvesicular steatosis throughout the hepatic lobule in all acinar zones, but naringin co-administration limited steatosis to the lobule periphery. In addition, it nearly restored total serum cholesterol, LDL, and triglycerides and liver ACOX1 and MDA to control levels. and upregulated PPAR-alpha and PGC-1 alpha, otherwise severely downregulated by valproate. It also increased SOD activity. All these findings suggest that naringin modulates key lipid metabolism regulators and should further be investigated in this model, either alone or combined with other lipid regulating drugs or molecules.

RNA modifications as emerging therapeutic targets

The field of epitranscriptome, posttranscriptional modifications to RNAs, is still growing up and has presented substantial evidences for the role of RNA modifications in diseases. In terms of new drug development, RNA modifications have a great promise for therapy. For example, more than 170 type of modifications exist in various types of RNAs. Regulatory genes and their roles in critical biological process have been identified and they are associated with several diseases. Current data, for example, identification of inhibitors targeting RNA modifications regulatory genes, strongly support the idea that RNA modifications have potential as emerging therapeutic targets. Therefore, in this review, RNA modifications and regulatory genes were comprehensively documented in terms of drug development by summarizing the findings from previous studies. It was discussed how RNA modifications or regulatory genes can be targeted by altering molecular mechanisms. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications RNA Processing > RNA Editing and Modification.

Valproate inhibits mitochondrial bioenergetics and increases glycolysis in Saccharomyces cerevisiae

The widely used mood stabilizer valproate (VPA) causes perturbation of energy metabolism, which is implicated in both the therapeutic mechanism of action of the drug as well as drug toxicity. To gain insight into these mechanisms, we determined the effects of VPA on energy metabolism in yeast. VPA treatment increased levels of glycolytic intermediates, increased expression of glycolysis genes, and increased ethanol production. Increased glycolysis was likely a response to perturbation of mitochondrial function, as reflected in decreased membrane potential and oxygen consumption. Interestingly, yeast, mouse liver, and isolated bovine cytochrome c oxidase were directly inhibited by the drug, while activities of other oxidative phosphorylation complexes (III and V) were not affected. These findings have implications for mechanisms of therapeutic action and toxicity.

Monobutyrin and Monovalerin Affect Brain Short-Chain Fatty Acid Profiles and Tight-Junction Protein Expression in ApoE-Knockout Rats Fed High-Fat Diets

Monobutyrin (MB) and monovalerin (MV), esters of short-chain fatty acids (SCFAs), have previously been shown to reduce liver cholesterol and inflammation in conventional rats fed high-fat diets. This study explored the potential effects of MB and MV in hypercholesterolemic apolipoprotein E-knockout (ApoE-/-) rats. ApoE-/- rats were fed three high-fat (HF) diets, pure or supplemented with MB or MV (1%), for 5 weeks. One group of conventional rats (C) was also fed the pure high-fat diet and another group of ApoE-/- rats a low-fat (LF) diet. Blood and liver lipids, urinary lactulose/mannitol, SCFAs (blood and brain), tight junction proteins (small intestine and brain), and inflammation-related markers (blood, brain, and liver) were analyzed. MV supplementation elevated serum high-density lipoprotein (HDL) cholesterol and valeric acid concentration (p < 0.05), while the amounts of isovaleric acid in the brain were reduced (p < 0.05). MB increased butyric acid amounts in the brain, while the plasma concentration of interleukin 10 (IL-10) was lowered (p < 0.05). Both MV and MB upregulated the expression of occludin and zonula occludens-1 (ZO-1) in the brain (p < 0.05). Supplementation of MB or MV affected HDL cholesterol, the expression of tight junction proteins, and SCFA profiles. MB and MV may therefore be promising supplements to attenuate lipid metabolic disorders caused by high-fat intake and genetic deficiency.

Valproic acid affects fatty acid and triglyceride metabolism in HepaRG cells exposed to fatty acids by different mechanisms

Treatment with valproate is associated with hepatic steatosis, but the mechanisms are not fully elucidated in human cell systems. We therefore investigated the effects of valproate on fatty acid and triglyceride metabolism in HepaRG cells, a human hepatoma cell line. In previously fatty acid loaded HepaRG cells, valproate impaired lipid droplet disposal starting at 1 mM after incubation for 3 or 7 days. Valproate increased the expression of genes associated with fatty acid import and triglyceride synthesis, but did not relevantly affect expression of genes engaged in fatty acid activation. Valproate impaired mitochondrial fatty acid metabolism by inhibiting β-ketothiolase and the function of the electron transport chain, which was associated with increased mitochondrial reactive oxygen species production. Valproate increased the mitochondrial DNA copy number per HepaRG cell, possibly as a consequence of impaired mitochondrial function. Valproate decreased the hepatocellular mRNA and protein expression of the fatty acid binding protein 1 (FABP1) and of the microsomal triglyceride transfer protein (MTTP) at 1 mM and increased the hepatocellular concentration of free fatty acids. Furthermore, valproate decreased protein expression and excretion of ApoB100 in HepaRG cells at 1 mM, reflecting impaired formation and excretion of very low-density lipoprotein (VLDL). In conclusion, valproate increased the hepatocellular triglyceride content by multiple mechanisms, whereby impaired expression of FABP1 and MTTP as well as impaired VLDL formation and excretion appeared to be dominant. Valproate caused cell death mainly by apoptosis, which may be a consequence of mitochondrial oxidative stress and increased hepatocellular concentration of free fatty acids.

Regulation of Inositol Biosynthesis: Balancing Health and Pathophysiology

Inositol is the precursor for all inositol compounds and is essential for viability of eukaryotic cells. Numerous cellular processes and signaling functions are dependent on inositol compounds, and perturbation of their synthesis leads to a wide range of human diseases. Although considerable research has been directed at understanding the function of inositol compounds, especially phosphoinositides and inositol phosphates, a focus on regulatory and homeostatic mechanisms controlling inositol biosynthesis has been largely neglected. Consequently, little is known about how synthesis of inositol is regulated in human cells. Identifying physiological regulators of inositol synthesis and elucidating the molecular mechanisms that regulate inositol synthesis will contribute fundamental insight into cellular processes that are mediated by inositol compounds and will provide a foundation to understand numerous disease processes that result from perturbation of inositol homeostasis. In addition, elucidating the mechanisms of action of inositol-depleting drugs may suggest new strategies for the design of second-generation pharmaceuticals to treat psychiatric disorders and other illnesses.

Inhibitory effect of valproate sodium on pain behavior in diabetic mice involves suppression of spinal histone deacetylase 1 and inflammatory mediators

Anti-epileptic medications are included in the international guidelines for managing neuropathic pain. Valproate sodium (VPS) was recently described as "the forgotten analgesic" and has been reported to relief pain in various models of neuropathic pain. Some studies reported anti-inflammatory and histone deacetylase 1 (HDA1) inhibitory properties for sodium valproate. The aim of the current study was to investigate the modulatory effect of VPS on pain behavior and inflammatory reactions in alloxan-induced diabetic neuropathy focusing on HDA1 inhibition and glia reactivity. 28 Male Swiss albino mice were allocated into four groups, (1) vehicle group, (2) alloxan-diabetic group, (3 & 4) alloxan+VPS (25 or 50 mg/kg) groups. VPS was given daily for 5 weeks by oral gavage. Pain behavior demonstrated increased allodynia (von-Frey filaments) and hyperalgesia (hot-plate test) in alloxan-diabetic mice that was reduced significantly by at least one of VPS doses. Sciatic nerves in diabetic mice showed increased histopathology score, increased silver staining for the nerves-indicating myelopathy- and a decrease in immunostaining for nerve growth factor. Spinal cord of diabetic mice showed greater histopathologic score, increased CD11b and glia fibrillary acidic protein (GFAP) immunostaining than vehicle treated mice. Molecular investigations highlighted greater content of spinal histone deacetylases, tumor necrosis factor-α (TNF-α) and interlukin-1β (IL1β) that were favorably modified by VPS. Overall, the current data confirmed that the pain killing and anti-inflammatory activity of VPS is at least partly mediated through inhibition of spinal HDA1 and glia reactivity. These findings support the view of inviting antiepileptics for treating neuropathies.

Strain and interindividual differences in lamotrigine-induced liver injury in mice

Lamotrigine (LTG) has been widely prescribed as an antipsychotic drug, although it causes idiosyncratic drug-induced liver injury in humans. LTG is mainly metabolized by UDP-glucuronosyltransferase, while LTG undergoes bioactivation by cytochrome P450 to a reactive metabolite; it is subsequently conjugated with glutathione, suggesting that reactive metabolite would be one of the causes for LTG-induced liver injury. However, there is little information regarding the mechanism of LTG-induced liver injury in both humans and rodents. In this study, we established an LTG-induced liver injury mouse model through co-administration with LTG and a glutathione synthesis inhibitor, l-buthionine-(S,R)-sulfoximine. We found an increase in alanine aminotransferase (ALT) levels (>10 000 U/L) in C57BL/6J mice, with apparent interindividual differences. On the other hand, a drastic increase in ALT was not noted in BALB/c mice, suggesting that the initiation mechanism would be different between the two strains. To examine the cause of interindividual differences, C57BL/6J mice that were co-administered LTG and l-buthionine-(S,R)-sulfoximine were categorized into three groups based on ALT values: no-responder (ALT <100 U/L), low-responder (100 U/L < ALT < 1000 U/L) and high-responder (ALT >1000 U/L). In the high-responder group, induction of hepatic oxidative stress, inflammation and damage-associated molecular pattern molecules in mRNA was associated with vacuolation and karyorrhexis in hepatocytes. In conclusion, we demonstrated that LTG showed apparent strain and interindividual differences in liver injuries from the aspects of initiation and exacerbation mechanisms. These results would support interpretation of the mechanism of LTG-induced liver injury observed in humans.

Zinc Deficiency and Oxidative Stress Involved in Valproic Acid Induced Hepatotoxicity: Protection by Zinc and Selenium Supplementation

Valproic acid (VPA) is an antiepileptic drug, which its usage is limited due to its hepatotoxicity. The present study was conducted to investigate the efficacy of zinc (Zn) and selenium (Se), necessary trace elements, against VPA-induced hepatotoxicity in Wistar rats. The animals were divided into five groups: control, VPA 200 mg/kg, VPA + Zn (100 mg/kg), VPA + Se (100 mg/kg), and VPA + Zn + Se. The administration of VPA for four consecutive weeks resulted in decrease in serum level of Zn in rats. Also, an increase in liver marker enzymes (ALT and AST) and also histological changes in liver tissue were shown after VPA administration. Oxidative stress was evident in VPA group by increased lipid peroxidation (LPO), protein carbonyl (PCO), glutathione (GSH) oxidation, and reducing total antioxidant capacity. Zn and Se (100 mg/kg) administration was able to protect against deterioration in liver enzyme, abrogated the histological change in liver tissue, and suppressed the increase in oxidative stress markers. Zn and combination of Zn plus Se treatment showed more protective effects than Se alone. These results imply that Zn and Se should be suggested as effective supplement products for the prevention of VPA-induced hepatotoxicity.

Protective effects of fennel oil extract against sodium valproate-induced hepatorenal damage in albino rats

Foeniculum vulgare (Apiaceae) is commonly known as fennel. This herb is well-known worldwide and traditionally used as curative herbal therapy for the treatment of epileptic disease, seizurescarminative, digestive, lactogogue, diuretic, treating respiratory and gastrointestinal disorders. The aim of present study is to investigate the possible effect of fennel oil against the toxicity of Sodium-Valproic (SVP) in albino rats. In order to assess the protection of fennel oil on SVP induced hepato- and nephro-toxicity, male albino rats were treated with 1 ml/kg b.w fennel oil 3 days/week for 6 weeks. The biochemical analyses of hepatic enzymes were evaluated by estimating blood biomarkers of liver and renal damage along with histological examination. The results obtained from this work showed that treating animals with SVP lead to many histopathological alterations in the liver and kidney tissues. The effect appeared in the liver tissue include leukocyte infiltrations, cytoplasmic vacuolization of the hepatocytes, fatty degeneration and congestion of blood vessels. This commonly used chemical (SVP) caused some unwanted effects on the kidney cortex which histologically observed as degeneration in renal tubules, atrophy of the glomeruli and edema. Biochemical results also revealed an abnormal increase in the enzyme level of AST, SAT, ALP, bilirubin, creatinine and urea-nitrogen, with a noticed decrease in total protein content. However, the results of treated rats with SVP plus fennel oil showed some positive histopathological changes in both the liver and kidney tissues. These results have confirmed that fennel oil has positive effects on the histological structure of the liver and kidney and the biochemical levels of AST, ALT, ALP, bilirubin, total proteins, creatinine and urea. It is concluded that fennel oil has various pharmacological properties including antioxidant, anti-cancer activity, anti-inflammatory. These valuable effects might be due to the presence of aromatic compounds trans-anethole. This useful properties of fennel plant could be due to its antioxidant activity that prevents the toxicity of SVP.

HDACi Valproic Acid (VPA) and Suberoylanilide Hydroxamic Acid (SAHA) Delay but Fail to Protect against Warm Hepatic Ischemia-Reperfusion Injury

BACKGROUND

Histone deacetylases (HDAC) catalyze N-terminal deacetylation of lysine-residues on histones and multiple nuclear and cytoplasmic proteins. In various animal models, such as trauma/hemorrhagic shock, ischemic stroke or myocardial infarction, HDAC inhibitor (HDACi) application is cyto- and organoprotective and promotes survival. HDACi reduce stress signaling, cell death and inflammation. Hepatic ischemia-reperfusion (I/R) injury during major liver resection or transplantation increases morbidity and mortality. Assuming protective properties, the aim of this study was to investigate the effect of the HDACi VPA and SAHA on warm hepatic I/R.

MATERIAL AND METHODS

Male Wistar-Kyoto rats (age: 6-8 weeks) were randomized to VPA, SAHA, vehicle control (pre-) treatment or sham-groups and underwent partial no-flow liver ischemia for 90 minutes with subsequent reperfusion for 6, 12, 24 and 60 hours. Injury and regeneration was quantified by serum AST and ALT levels, by macroscopic aspect and (immuno-) histology. HDACi treatment efficiency, impact on MAPK/SAPK-activation and Hippo-YAP signaling was determined by Western blot.

RESULTS

Treatment with HDACi significantly enhanced hyperacetylation of Histone H3-K9 during I/R, indicative of adequate treatment efficiency. Liver injury, as measured by macroscopic aspect, serum transaminases and histology, was delayed, but not alleviated in VPA and SAHA treated animals. Importantly, tissue destruction was significantly more pronounced with VPA. SAPK-activation (p38 and JNK) was reduced by VPA and SAHA in the early (6h) reperfusion phase, but augmented later on (JNK, 24h). Regeneration appeared enhanced in SAHA and VPA treated animals and was dependent on Hippo-YAP signaling.

CONCLUSIONS

VPA and SAHA delay warm hepatic I/R injury at least in part through modulation of SAPK-activation. However, these HDACi fail to exert organoprotective effects, in this setting. For VPA, belated damage is even aggravated.

Study of Valproic Acid-Enhanced Hepatocyte Steatosis

Valproic acid (VPA) is one of the most widely used antiepilepsy drugs. However, several side effects, including weight gain and fatty liver, have been reported in patients following VPA treatment. In this study, we explored the molecular mechanisms of VPA-induced hepatic steatosis using FL83B cell line-based in vitro model. Using fluorescent lipid staining technique, we found that VPA enhanced oleic acid- (OLA-) induced lipid accumulation in a dose-dependent manner in hepatocytes; this may be due to upregulated lipid uptake, triacylglycerol (TAG) synthesis, and lipid droplet formation. Real-time PCR results showed that, following VPA treatment, the expression levels of genes encoding cluster of differentiation 36 (Cd36), low-density lipoprotein receptor-related protein 1 (Lrp1), diacylglycerol acyltransferase 2 (Dgat2), and perilipin 2 (Plin2) were increased, that of carnitine palmitoyltransferase I a (Cpt1a) was not affected, and those of acetyl-Co A carboxylase α (Acca) and fatty acid synthase (Fasn) were decreased. Furthermore, using immunofluorescence staining and flow cytometry analyses, we found that VPA also induced peroxisome proliferator-activated receptor γ (PPARγ) nuclear translocation and increased levels of cell-surface CD36. Based on these results, we propose that VPA may enhance OLA-induced hepatocyte steatosis through the upregulation of PPARγ- and CD36-dependent lipid uptake, TAG synthesis, and lipid droplet formation.

High-calorie diet inflates steatogenic effects of valproic acid in mice

Valproic acid (VPA) is an anti-epileptic drug used in patients with convulsive seizures and psychic disorders. Despite its therapeutic use, VPA administration is associated with several side effects of which hepatosteatosis (lipid deposition in liver >10% of organ weight) is of concern. Recently, the consumption of western-type diet rich in fat and simple sugar has increased, the pathological consequences of which has been linked to the escalating incidence of metabolic disorders. The hypothesis of the study is that the metabolic stress induced by high-calorie diet may potentiate VPA-induced hepatosteatosis. Two groups of Swiss Mus musculus male mice weighing 25-35 g were fed either normal chow or high fat and high fructose diet (HFFD) and maintained for 30 days. On the 16th day of the experiment, VPA (100 mg/kg bw) administration was initiated in one set of animals from each group and the other set was left without VPA treatment. Assays were done in the hemolysate, plasma and liver tissue of mice after the experimental period. Deregulated lipid metabolism, loss of insulin sensitivity, enhanced CYP2E1 activity and oxidative damage, and diminution of cellular antioxidants were observed in animals that received HFFD and VPA. HFFD-fed mice are sensitized to VPA toxicity than the normal chow-fed counterparts. The results of this study show that preformed metabolic derangements due to high-energy diet may infuriate VPA-induced hepatosteatosis and insulin resistance.

Strategies, models and biomarkers in experimental non-alcoholic fatty liver disease research

Non-alcoholic fatty liver disease encompasses a spectrum of liver diseases, including simple steatosis, steatohepatitis, liver fibrosis and cirrhosis and hepatocellular carcinoma. Non-alcoholic fatty liver disease is currently the most dominant chronic liver disease in Western countries due to the fact that hepatic steatosis is associated with insulin resistance, type 2 diabetes mellitus, obesity, metabolic syndrome and drug-induced injury. A variety of chemicals, mainly drugs, and diets is known to cause hepatic steatosis in humans and rodents. Experimental non-alcoholic fatty liver disease models rely on the application of a diet or the administration of drugs to laboratory animals or the exposure of hepatic cell lines to these drugs. More recently, genetically modified rodents or zebrafish have been introduced as non-alcoholic fatty liver disease models. Considerable interest now lies in the discovery and development of novel non-invasive biomarkers of non-alcoholic fatty liver disease, with specific focus on hepatic steatosis. Experimental diagnostic biomarkers of non-alcoholic fatty liver disease, such as (epi)genetic parameters and '-omics'-based read-outs are still in their infancy, but show great promise. In this paper, the array of tools and models for the study of liver steatosis is discussed. Furthermore, the current state-of-art regarding experimental biomarkers such as epigenetic, genetic, transcriptomic, proteomic and metabonomic biomarkers will be reviewed.

An effective assessment of valproate sodium-induced hepatotoxicity with UPLC-MS and (1)HNMR-based metabonomics approach

Valproate sodium is one of the most prescribed antiepileptic drugs. However, valproate sodium has various side effects, especially its toxicity on liver. Current markers for toxicity reflect mostly the late stages of tissue damage; thus, more efficient methods for toxicity evaluation are desired. To evaluate the toxicity of valproate sodium on liver, we performed both UPLC-MS and (1)HNMR-based metabonomics analysis of serum samples from 34 epileptic patients (age: 42.0±18.6, 18 male/16 female) after valproate sodium treatment. Compared to conventional markers, the serum metabolic profiles provided clear distinction of the valproate sodium induced normal liver function and abnormal liver function in epileptic patients. Through multivariate statistical analysis, we identified marker metabolites associated with the hepatotoxicity induced by valproate sodium, such as glucose, lactate, acetoacetate, VLDL/LDL, lysophosphatidylcholines, phosphatidylcholines, choline, creatine, amino acids, N-acetyl glycoprotein, pyruvate and uric acid. This metabonomics approach may provide effective way to evaluate the valproate sodium-induced toxicity in a manner that can complement current measures. This approach is expected to find broader application in other drug-induced toxicity assessment.

Determination of liver specific toxicities in rat hepatocytes by high content imaging during 2-week multiple treatment

DILI is a major safety issue during drug development and one of the leading causes for market withdrawal. Despite many efforts made in the past, the prediction of DILI using in vitro models remains very unreliable. In the present study, the well-established hepatocyte Collagen I-Matrigel™ sandwich culture was used, mimicking chronic drug treatment after multiple incubations for 14 days. Ten drugs associated with different types of specific preclinical and clinical liver injury were evaluated at non-cytotoxic concentrations. Mrp2-mediated transport, intracellular accumulation of neutral lipids and phospholipids were selected as functional endpoints by using Cellomics™ Arrayscan® technology and assessed at five timepoints (day 1, 3, 7, 10, 14). Liver specific functional impairments after drug treatment were enhanced over time and could be monitored by HCI already after few days and before cytotoxicity. Phospholipidosis-inducing drugs Chlorpromazine and Amiodarone displayed the same response as in vivo. Cyclosporin A, Chlorpromazine, and Troglitazone inhibited Mrp2-mediated biliary transport, correlating with in vivo findings. Steatosis remained difficult to be reproduced under the current in vitro testing conditions, resulting into false negative and positive responses. The present results suggest that the repeated long-term treatment of rat hepatocytes in the Collagen I-Matrigel™ sandwich configuration might be a suitable tool for safety profiling of the potential to induce phospholipidosis and impair Mrp2-mediated transport processes, but not to predict steatosis.

Effect of chronic valproic Acid treatment on hepatic gene expression profile in wfs1 knockout mouse

Valproic acid (VPA) is a widely used anticonvulsant and mood-stabilizing drug whose use is often associated with drug-induced weight gain. Treatment with VPA has been shown to upregulate Wfs1 expression in vitro. Aim of the present study was to compare the effect of chronic VPA treatment in wild type (WT) and Wfs1 knockout (KO) mice on hepatic gene expression profile. Wild type, Wfs1 heterozygous, and homozygous mice were treated with VPA for three months (300 mg/kg i.p. daily) and gene expression profiles in liver were evaluated using Affymetrix Mouse GeneChip 1.0 ST array. We identified 42 genes affected by Wfs1 genotype, 10 genes regulated by VPA treatment, and 9 genes whose regulation by VPA was dependent on genotype. Among the genes that were regulated differentially by VPA depending on genotype was peroxisome proliferator-activated receptor delta (Ppard), whose expression was upregulated in response to VPA treatment in WT, but not in Wfs1 KO mice. Thus, regulation of Ppard by VPA is dependent on Wfs1 genotype.

Combined effects of a high-fat diet and chronic valproic acid treatment on hepatic steatosis and hepatotoxicity in rats

AIM

To investigate the potential interactive effects of a high-fat diet (HFD) and valproic acid (VPA) on hepatic steatosis and hepatotoxicity in rats.

METHODS

Male SD rats were orally administered VPA (100 or 500 mg·kg⁻¹·d⁻¹) combined with HFD or a standard diet for 8 weeks. Blood and liver samples were analyzed to determine lipid levels and hepatic function biomarkers using commercial kit assays. Low-molecular-weight compounds in serum, urine and bile samples were analyzed using a metabonomic approach based on GC/TOF-MS.

RESULTS

HFD alone induced extensive hepatocyte steatosis and edema in rats, while VPA alone did not cause significant liver lesions. VPA significantly aggravated HFD-induced accumulation of liver lipids, and caused additional spotty or piecemeal necrosis, accompanied by moderate infiltration of inflammatory cells in the liver. Metabonomic analysis of serum, urine and bile samples revealed that HFD significantly increased the levels of amino acids, free fatty acids (FFAs) and 3-hydroxy-butanoic acid, whereas VPA markedly decreased the levels of amino acids, FFAs and the intermediate products of the tricarboxylic acid cycle (TCA) compared with the control group. HFD aggravated VPA-induced inhibition on lipid and amino acid metabolism.

CONCLUSION

HFD magnifies VPA-induced impairment of mitochondrial β-oxidation of FFAs and TCA, thereby increases hepatic steatosis and hepatotoxicity. The results suggest the patients receiving VPA treatment should be advised to avoid eating HFD.

Mechanisms of amiodarone and valproic acid induced liver steatosis in mouse in vivo act as a template for other hepatotoxicity models

Liver injury is the leading cause of drug-induced toxicity. For the evaluation of a chemical compound to induce toxicity, in this case steatosis or fatty liver, it is imperative to identify markers reflective of mechanisms and processes induced upon exposure, as these will be the earliest changes reflective of disease. Therefore, an in vivo mouse toxicogenomics study was completed to identify common pathways, nuclear receptor (NR) binding sites, and genes regulated by three known human steatosis-inducing compounds, amiodarone (AMD), valproic acid (VPA), and tetracycline (TET). Over 1, 4, and 11 days of treatment, AMD induced changes in clinical chemistry parameters and histopathology consistent with steatosis. Common processes and NR binding sites involved in lipid, retinol, and drug metabolism were found for AMD and VPA, but not for TET, which showed no response. Interestingly, the pattern of enrichment of these common pathways and NR binding sites over time was unique to each compound. Eleven biomarkers of steatosis were identified as dose responsive and time sensitive to toxicity for AMD and VPA. Finally, this in vivo mouse study was compared to an AMD rat in vivo, an AMD mouse primary hepatocyte, and a VPA human primary hepatocyte study to identify concordance for steatosis. We conclude that concordance is found on the process level independent of species, model or dose*time point.

A simple transcriptomic signature able to predict drug-induced hepatic steatosis

It is estimated that only a few marketed drugs are able to directly induce liver steatosis. However, many other drugs may exacerbate or precipitate fatty liver in the presence of other risk factors or in patients prone to non-alcoholic fatty liver disease. On the other hand, current in vitro tests for drug-induced steatosis in preclinical research are scarce and not very sensitive or reproducible. In the present study, we have investigated the effect of well-characterized steatotic drugs on the expression profile of 47 transcription factors (TFs) in human hepatoma HepG2 cells and found that these drugs are able to up- and down-regulate a substantial number of these factors. Multivariate data analysis revealed a common TF signature for steatotic drugs, which consistently and significantly repressed FOXA1, HEX and SREBP1C in cultured cells. This signature was also observed in the livers of rats and in cultured human hepatocytes. Therefore, we selected these three TFs as predictive biomarkers for iatrogenic steatosis. With these biomarkers, a logistic regression analysis yielded a predictive model, which was able to correctly classify 92 % of drugs. The developed algorithm also predicted that ibuprofen, nifedipine and irinotecan are potential steatotic drugs, whereas troglitazone is not. In summary, this is a sensitive, specific and simple RT-PCR test that can be easily implemented in preclinical drug development to predict drug-induced steatosis. Our results also indicate that steatotic drugs affect expression of both common and specific subsets of TF and lipid metabolism genes, thus generating complex transcriptomic responses that cause or contribute to steatosis in hepatocytes.

Integrative analysis of proteomic and transcriptomic data for identification of pathways related to simvastatin-induced hepatotoxicity

Hepatocytes are used widely as a cell model for investigation of xenobiotic metabolism and the toxic mechanism of drugs. Simvastatin is the first statin drug used extensively in clinical practice for control of elevated cholesterol or hypercholesterolemia. However, it has also been reported to cause adverse effects in liver due to cellular damage. In this study, for proteomic and transcriptomic analysis, rat primary hepatocytes were exposed to simvastatin at IC20 concentration for 24 h. Among a total of 607 differentially expressed proteins, 61 upregulated and 29 downregulated proteins have been identified in the simvastatin-treated group. At the mRNA level, results of transcriptomic analysis revealed 206 upregulated and 41 downregulated genes in the simvastatin-treated group. Based on results of transcriptomic and proteomic analysis, NRF2-mediated oxidative stress response, xenobiotics by metabolism of cytochrome P450, fatty acid metabolism, bile metabolism, and urea cycle and inflammation metabolism pathways were focused using IPA software. Genes (FASN, UGT2B, ALDH1A1, CYP1A2, GSTA2, HAP90, IL-6, IL-1, FABP4, and ABC11) and proteins (FASN, CYP2D1, UG2TB, ALDH1A1, GSTA2, HSP90, FABP4, and ABCB11) related to several important pathways were confirmed by real-time PCR andWestern blot analysis, respectively. This study will provide new insight into the potential toxic pathways induced by simvastatin.

Gene expression in liver injury caused by long-term exposure to titanium dioxide nanoparticles in mice

Although liver toxicity induced by titanium dioxide nanoparticles (TiO(2) NPs) has been demonstrated, very little is known about the molecular mechanisms of multiple genes working together underlying this type of liver injury in mice. In this study, we used the whole-genome microarray analysis technique to determine the gene expression profile in the livers of mice exposed to 10 mg/kg body weight TiO(2) NPs for 90 days. The findings showed that long-term exposure to TiO(2) NPs resulted in obvious titanium accumulation in the liver and TiO(2) NP aggregation in hepatocyte nuclei, an inflammatory response, hepatocyte apoptosis, and liver dysfunction. Furthermore, microarray data showed striking changes in the expression of 785 genes related to the immune/inflammatory response, apoptosis, oxidative stress, the metabolic process, response to stress, cell cycle, ion transport, signal transduction, cell proliferation, cytoskeleton, and cell differentiation in TiO(2) NP-exposed livers. In particular, a significant reduction in complement factor D (Cfd) expression following long-term exposure to TiO(2) NPs resulted in autoimmune and inflammatory disease states in mice. Therefore, Cfd may be a potential biomarker of liver toxicity caused by TiO(2) NPs exposure.

A proteomic analysis of the functional effects of fatty acids in NIH 3T3 fibroblasts

Previous studies have demonstrated that long chain fatty acids influence fibroblast function at sub-lethal concentrations. This study is the first to assess the effects of oleic, linoleic or palmitic acids on protein expression of fibroblasts, as determined by standard proteomic techniques. The fatty acids were not cytotoxic at the concentration used in this work as assessed by membrane integrity, DNA fragmentation and the MTT assay but significantly increased cell proliferation. Subsequently, a proteomic analysis was performed using two dimensional difference gel electrophoresis (2D-DIGE) and MS based identification. Cells treated with 50 μM oleic, linoleic or palmitic acid for 24 h were associated with 24, 22, 16 spots differentially expressed, respectively. Among the identified proteins, α-enolase and far upstream element binding protein 1 (FBP-1) are of importance due to their function in fibroblast-associated diseases. However, modulation of α-enolase and FBP-1 expression by fatty acids was not validated by the Western blot technique.

In-depth identification of pathways related to cisplatin-induced hepatotoxicity through an integrative method based on an informatics-assisted label-free protein quantitation and microarray gene expression approach

Cisplatin is used widely for treatment of a variety of cancer diseases. Recently, however, the use of cisplatin is restricted because of its adverse effects such as hepatotoxicity. There is no study with current proteomics technology to evaluate cisplatin-induced hepatotoxicity, even if some studies have reported on the hepatotoxicity. In this study, proteomic as well as genomic analyses have been used for identification of proteins and genes that respond to cisplatin treatment in rat primary hepatocytes. To investigate the hepatotoxic effects of cisplatin, rat primary hepatocytes were treated with an IC(20) concentration for 24 h. From proteomic analysis based on label-free quantitation strategy, cisplatin induced 76 up-regulated and 19 down-regulated proteins among 325 distinct proteins. In the mRNA level, genomic analysis revealed 72 up-regulated and 385 down-regulated genes in the cisplatin-treated group. Based on these two analyses, 19 pathways were commonly altered, whereas seven pathways were identified only by proteomic analysis, and 19 pathways were identified only by genomic analysis. Overall, this study explained the mechanism of cisplatin-induced hepatotoxicity with two points of view: well known pathways including drug metabolism, fatty acid metabolism, and glycolysis/TCA cycle and little known pathways including urea cycle and inflammation metabolism, for hepatotoxicity of other toxic agents. Up-regulated proteins detected by proteomic analysis in the cisplatin-treated group: FBP1 (fructose 1,6-bisphosphatase 1), FASN (fatty acid synthase), CAT (catalase), PRDX1 (peroxiredoxin-1), HSPD1 (60-kDa heat shock protein), MDH2 (malate dehydrogenase 2), and ARG1 (arginase 1), and also down-regulated proteins in the cisplatin-treated group: TPM1 (tropomyosin 1), TPM3 (tropomyosin 3), and CTSB (cathepsin B), were confirmed by Western blot analysis. In addition, up-regulated mRNAs detected by microarray analysis in the cisplatin-treated group: GSTA2, GSTT2, YC2, TXNRD1, CYP2E1, CYP2C13, CYP2D1, ALDH17, ARG1, ARG2, and IL-6, and also down-regulated mRNAs: CYP2C12, CYP26B1, TPM1, and TPM3, were confirmed by RT-PCR analysis. In case of PRDX1, FASN, and ARG1, they were further confirmed by immunofluorescence analysis. Through the integrated proteomic and genomic approaches, the present study provides the first pathway map related to cisplatin-induced hepatotoxicity, which may provide new insight into the mechanism of hepatotoxicity.

New insights on the mechanisms of valproate-induced hyperammonemia: inhibition of hepatic N-acetylglutamate synthase activity by valproyl-CoA

BACKGROUND & AIMS

Hyperammonemia is a frequent side-effect of valproic acid (VPA) therapy, which points to an imbalance between ammoniagenesis and ammonia disposal via the urea cycle. The impairment of this liver-specific metabolic pathway induced either by primary genetic defects or by secondary causes, namely associated with drugs administration, may result in accumulation of ammonia. To elucidate the mechanisms which underlie VPA-induced hyperammonemia, the aim of this study was to evaluate the effect of both VPA and its reactive intermediate, valproyl-CoA (VP-CoA), on the synthesis of N-acetylglutamate (NAG), a prime metabolite activator of the urea cycle.

METHODS

The amount of NAG in livers of rats treated with VPA was quantified by HPLC-MS/MS. The NAG synthase (NAGS) activity was evaluated in vitro in rat liver mitochondria, and the effect of both VPA and VP-CoA was characterized.

RESULTS

The present results clearly show that VP-CoA is a stronger inhibitor of NAGS activity in vitro than the parent drug VPA. The hepatic levels of NAG were significantly reduced in VPA-treated rats as compared with control tissues.

CONCLUSIONS

These data strongly suggest that the hyperammonemia observed in patients under VPA treatment may result from a direct inhibition of the NAGS activity by VP-CoA. The subsequent reduced availability of NAG will impair the flux through the urea cycle and compromise the major role of this pathway in ammonia detoxification.

The mechanistic basis for the induction of hepatic steatosis by xenobiotics

INTRODUCTION

Hepatic steatosis is the histological observation of numerous lipid inclusions due to an excess accumulation of triacylglycerols. They are a concern with new therapeutic candidates because they signify altered lipid metabolism that can progress to more serious liver toxicity.

AREAS COVERED

This article is based on an article search using the PubMed database from 1987 to 2011 and confirms associations for several previously marketed drugs with four basic hepatocellular mechanisms. The article also describes how these mechanisms are controlled by master regulators of lipid metabolism, which include gene transcription factors, nuclear receptors, hormonal signaling, energy sensing proteins, endoplasmic reticulum stress signaling and certain key metabolic intermediates.

EXPERT OPINION

Drug-induced hepatic steatosis is typically not detectable by conventional means other than invasive histological examinations. By understanding the basic mechanisms, key regulators and energy signaling systems of the liver, the investigator is better equipped to avoid xenobiotics with steatogenic potential in the drug discovery or early development process. There are now a number of methods for detecting this potential, specifically gene expression or metabolomic profiling and pathway analysis or mechanism-based in vitro systems.

Gene expression profiling of murine hepatic steatosis induced by tamoxifen

Tamoxifen is an antiestrogenic agent used widely in the treatment of estrogen receptor-positive breast cancer. However, hepatic steatosis has been reported during clinical trials of tamoxifen. To explore the mechanism responsible for this tamoxifen-induced hepatic steatosis, we used microarray analysis to profile the gene expression pattern of mouse liver after tamoxifen treatment. Tamoxifen was administered orally as a single dose of 10mg/kg (low dose), 50mg/kg (medium dose), or 100mg/kg (high dose) to C57BL/6 mice, and the livers were removed 2h, 4h, 8h, and 24h later. From microarray data obtained from the liver samples, 414 genes were selected as tamoxifen-responsive genes (P<0.05, two-way ANOVA; cutoff ≥ 1.5-fold response). These genes were classified into three groups: 308 of the 414 genes showed a time-dependent response, nine genes showed a dose-dependent response, and 97 genes showed a time- and dose-dependent response. Most of the 308 time-dependent-responsive genes were associated predominantly with the biological processes involved in lipid metabolism. Overrepresented transcription factor binding site analysis showed that the following nuclear receptors that are important in lipid and carbohydrate metabolism were overrepresented: the androgen receptor (AR), nuclear receptor subfamily 2 group F member 1 (NR2F1), hepatocyte nuclear factor 4α (HNF4α), and retinoic acid receptor-related orphan receptor alpha 1 (RORα1). Reporter gene analysis further revealed that tamoxifen repressed the 5α-dihydrotestosterone-induced activation of the AR and the intrinsic transactivation function of RORα1, HNF4α, and NR2F1. Taken together, these data provide a better understanding of the molecular mechanism underlying tamoxifen-induced steatogenic hepatotoxicity and useful information for predicting steatogenic hepatotoxicity.

p21 Promotes oncolytic adenoviral activity in ovarian cancer and is a potential biomarker

The oncolytic adenovirus dl922-947 replicates selectively within and lyses cells with a dysregulated Rb pathway, a finding seen in > 90% human cancers. dl922-947 is more potent than wild type adenovirus and the E1B-deletion mutant dl1520 (Onyx-015). We wished to determine which host cell factors influence cytotoxicity. SV40 large T-transformed MRC5-VA cells are 3-logs more sensitive to dl922-947 than isogenic parental MRC5 cells, confirming that an abnormal G1/S checkpoint increases viral efficacy. The sensitivity of ovarian cancer cells to dl922-947 varied widely: IC₅₀ values ranged from 51 (SKOV3ip1) to 0.03 pfu/cell (TOV21G). Cells sensitive to dl922-947 had higher S phase populations and supported earlier E1A expression. Cytotoxicity correlated poorly with both infectivity and replication, but well with expression of p21 by microarray and western blot analyses. Matched p21+/+ and -/- Hct116 cells confirmed that p21 influences dl922-947 activity in vitro and in vivo. siRNA-mediated p21 knockdown in sensitive TOV21G cells decreases E1A expression and viral cytotoxicity, whilst expression of p21 in resistant A2780CP cells increases virus activity in vitro and in intraperitoneal xenografts. These results highlight that host cell factors beyond simple infectivity can influence the efficacy of oncolytic adenoviruses. p21 expression may be an important biomarker of response in clinical trials.

Single valproic acid treatment inhibits glycogen and RNA ribose turnover while disrupting glucose-derived cholesterol synthesis in liver as revealed by the [U-C(6)]-d-glucose tracer in mice

Previous genetic and proteomic studies identified altered activity of various enzymes such as those of fatty acid metabolism and glycogen synthesis after a single toxic dose of valproic acid (VPA) in rats. In this study, we demonstrate the effect of VPA on metabolite synthesis flux rates and the possible use of abnormal (13)C labeled glucose-derived metabolites in plasma or urine as early markers of toxicity. Female CD-1 mice were injected subcutaneously with saline or 600 mg/kg) VPA. Twelve hours later, the mice were injected with an intraperitoneal load of 1 g/kg [U-(13)C]-d-glucose. (13)C isotopomers of glycogen glucose and RNA ribose in liver, kidney and brain tissue, as well as glucose disposal via cholesterol and glucose in the plasma and urine were determined. The levels of all of the positional (13)C isotopomers of glucose were similar in plasma, suggesting that a single VPA dose does not disturb glucose absorption, uptake or hepatic glucose metabolism. Three-hour urine samples showed an increase in the injected tracer indicating a decreased glucose re-absorption via kidney tubules. (13)C labeled glucose deposited as liver glycogen or as ribose of RNA were decreased by VPA treatment; incorporation of (13)C via acetyl-CoA into plasma cholesterol was significantly lower at 60 min. The severe decreases in glucose-derived carbon flux into plasma and kidney-bound cholesterol, liver glycogen and RNA ribose synthesis, as well as decreased glucose re-absorption and an increased disposal via urine all serve as early flux markers of VPA-induced adverse metabolic effects in the host.

Cytometric analysis for drug-induced steatosis in HepG2 cells

Drugs are capable of inducing hepatic lipid accumulation. When fat accumulates, lipids are primarily stored as triglycerides which results in steatosis and provides substrates for lipid peroxidation. An in vitro multiparametric flow cytometry assay was performed in HepG2 cells by using fluorescent probes to analyze cell viability (propidium iodide, PI), lipid accumulation (BODIPY493/503), mitochondrial membrane potential (tetramethyl rhodamine methyl ester, TMRM) and reactive oxygen species generation (ROS) (2',7'-dihydrochlorofluorescein diacetate, DHCF-DA) as functional markers. All the measurements were restricted to live cells by gating the cells that excluded PI or those that exhibited the typical forward and side scatter features of live cells. The assay was qualified by analyzing a number of selected model drugs with a well documented induction of steatosis in vivo using different mechanisms as positive controls and several non-steatosic compounds as negative controls. For the cytometric screening assay, the concentrations tested were up to the corresponding IC(10) value determined by the MTT assay. Among the parameters analyzed, increased BODIPY fluorescence was the most sensitive and selective marker of drug-induced steatosis. However, a more consistent predictive approach was the combination of two endpoints: lipid accumulation and ROS generation. The assay correctly identified 100% of steatosis-positive and steatosis-negative compounds, and a high steatosis risk was predicted for amiodarone, doxycycline, tetracycline and valproate treatments at therapeutic doses. The results suggest that this cell-based assay may be a useful approach to identify the potential of drug candidates to induce steatosis.

Toxicogenomic biomarkers for liver toxicity

Toxicogenomics (TGx) is a widely used technique in the preclinical stage of drug development to investigate the molecular mechanisms of toxicity. A number of candidate TGx biomarkers have now been identified and are utilized for both assessing and predicting toxicities. Further accumulation of novel TGx biomarkers will lead to more efficient, appropriate and cost effective drug risk assessment, reinforcing the paradigm of the conventional toxicology system with a more profound understanding of the molecular mechanisms of drug-induced toxicity. In this paper, we overview some practical strategies as well as obstacles for identifying and utilizing TGx biomarkers based on microarray analysis. Since clinical hepatotoxicity is one of the major causes of drug development attrition, the liver has been the best documented target organ for TGx studies to date, and we therefore focused on information from liver TGx studies. In this review, we summarize the current resources in the literature in regard to TGx studies of the liver, from which toxicologists could extract potential TGx biomarker gene sets for better hepatotoxicity risk assessment.

Valproic acid metabolism and its effects on mitochondrial fatty acid oxidation: a review

Valproic acid (VPA; 2-n-propylpentanoic acid) is widely used as a major drug in the treatment of epilepsy and in the control of several types of seizures. Being a simple fatty acid, VPA is a substrate for the fatty acid beta-oxidation (FAO) pathway, which takes place primarily in mitochondria. The toxicity of valproate has long been considered to be due primarily to its interference with mitochondrial beta-oxidation. The metabolism of the drug, its effects on enzymes of FAO and their cofactors such as CoA and/or carnitine will be reviewed. The cumulative consequences of VPA therapy in inborn errors of metabolism (IEMs) and the importance of recognizing an underlying IEM in cases of VPA-induced steatosis and acute liver toxicity are two different concepts that will be emphasized.