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

Does valproate therapy in epileptic patients contribute to changing atherosclerosis risk factors? The role of lipids and free fatty acids

BACKGROUND

We aimed to demonstrate the relationship between the valproate (VPA) treatment versus lipid and serum free fatty acids (FFAs) profiles to be the potential atherosclerosis risk factor in epileptic patients.

METHODS

Fasting blood samples were taken from 21 adult VPA-treated patients and 21 controls. The profiles of lipids, FFAs, clinical parameters and body mass index (BMI) were evaluated.

RESULTS

No significant differences between the study group and controls were found for any of the studied parameters. However, significant differences in the total cholesterol (CHOL), low-density-lipoprotein cholesterol (LDL), triglycerides, the CHOL/HDL (high-density-lipoprotein cholesterol) ratio, and Atherogenic Index of Plasma were observed for overweight patients when compared to those of normal weight. Patients with uncontrolled epilepsy tended to have significantly lower palmitic acid level than seizure-free patients. Oleic acid was found to be positively correlated with VPA concentration for patients with uncontrolled epilepsy, and with the dose corrected VPA concentration for all the patients. The acid was however negatively correlated with stearic acid for both the controls and the patients with uncontrolled epilepsy. PLS method revealed CHOL, LDL, triglycerides and myristic acid to be positively interrelated for the whole group under the study, whereas these parameters were found to be negatively correlated with VPA concentration, and positively with BMI. Furthermore, high sensitivity C-reactive protein was found to be negatively correlated with palmitic acid levels.

CONCLUSION

Overweight VPA-treated patients are exposed to higher risk of atherosclerosis. Alterations in FFAs are likely to depend on seizures control, and on VPA levels.

Adverse effect of valproic acid on an in vitro gastrulation model entails activation of retinoic acid signaling

Valproic acid (VPA), an antiepileptic drug, is a teratogen that causes neural tube and axial skeletal defects, although the mechanisms are not fully understood. We previously established a gastrulation model using mouse P19C5 stem cell embryoid bodies (EBs), which exhibits axial patterning and elongation morphogenesis in vitro. Here, we investigated the effects of VPA on the EB axial morphogenesis to gain insights into its teratogenic mechanisms. Axial elongation and patterning of EBs were inhibited by VPA at therapeutic concentrations. VPA elevated expression levels of various developmental regulators, including Cdx1 and Hoxa1, known transcriptional targets of retinoic acid (RA) signaling. Co-treatment of EBs with VPA and BMS493, an RA receptor antagonist, partially rescued axial elongation as well as gene expression profiles. These results suggest that VPA requires active RA signaling to interfere with EB morphogenesis.

Nephrotoxicity of sodium valproate and protective role of L-cysteine in rats at biochemical and histological levels

BACKGROUND

This study investigated whether the combination of sodium valproate (SV) with L-cysteine (LC) can decrease the SV toxicity of kidneys. SV caused alternation in oxidative/antioxidant balance.

METHODS

Biochemical estimations included the determination of oxidative stress markers like thiobarbituric acid-reactive substances in kidney tissue, and enzymatic antioxidant activities such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione reductase as well as total antioxidant capacity were evaluated in renal tissues. Creatinine and uric acid levels in the serum were also determined to assess kidney function. Pathological examination of the kidney was also performed.

RESULTS

Increasing the levels of lipid peroxidation and decreasing the enzymatic activity (SOD, CAT, and GPx) as well as total antioxidant capacity of rats was shown with different doses of SV. Impairment in renal function tests suggests a decreased glomerular filtration rate, as serum creatinine was elevated. Histopathological changes of kidney tissue treated with SV reveal the proximal and the distal convoluted tubules that show hydropic changes (small white vacuoles within the cytoplasm and the glomeruli show hypercellularity).

CONCLUSIONS

The concurrent administration of LC with SV significantly had beneficial effects on the kidney and all the above parameters have been improved.

Valproate effect on ketosis in children under ketogenic diet

INTRODUCTION

Although ketogenic diet has been proven useful in the management of intractable seizures, interactions with other medicines have been reported. This study reports two patients on co-administration with ketogenic diet and valproate appearing undesirable side effects after increase or decrease of valproate pharmaceutical levels.

METHODS

Totally 75 patients suffering from drug-resistant epilepsy were treated with ketogenic diet in our departments. Their age varied from 6 months to 9 years. All patients were followed for at least 12 months and up to five years. Clinical and laboratory variables have been regularly assessed.

RESULTS

In 75 patients treated with ketogenic diet and valproate at the same time treatment was well tolerated. Two patients presented mild to moderate undesirable effects. In these patients the removal of valproate treatment resulted in an increase of ketosis with respective clinical signs. The conversion of the diet from 4:1 to 1:1 and 2,5:1 respectively resulted in reduction of ketosis and clinical improvement.

CONCLUSION

In the majority of cases co-administration of valproate and ketogenic diet seems to be safe. In two cases, valproate appeared to have a negative effect on ketosis (and weaning it led to over-ketosis). This interaction is worthy of future study.

Valproate-Associated Parkinsonism: A Critical Review of the Literature

Valproate was first approved as an antiepileptic drug in 1962 and has since also become established as a mood stabiliser and as prophylaxis for migraine. In 1979, Lautin published the first description of a valproate-associated extrapyramidal syndrome. Many cases of valproate-associated parkinsonism have subsequently been published, but uncertainties remain concerning its prevalence, risk factors and prognosis. The aim of this paper is to provide a critical review of the existing literature on valproate-associated parkinsonism and to discuss possible mechanisms. Literature databases were searched systematically: we identified a total of 116 patients with valproate-associated parkinsonism published in case reports, case series and systematic analyses. Prevalence rates ranged widely, between 1.4 and 75 % of patients taking valproate. There was great heterogeneity with regard to clinical presentation, age of onset, valproate dose, concomitant conditions and imaging findings. In all patients apart from three, valproate plasma concentrations were within or even below the recommended reference range when the parkinsonism occurred. Parkinsonism was reversible in the majority of patients, although recovery was often prolonged and sometimes incomplete. A dopaminergic deficit was confirmed in three of six patients investigated with dopamine transporter imaging. Seven of 14 patients who were treated with dopaminergic medication had a good response. The quality of the evidence was assessed and probability of causation was examined using the Naranjo score, which ranged from 0 to 7 (median: 5.0). Several pathophysiological mechanisms, including altered gene expression and neurotransmitter signalling, enhanced neurodegeneration or unmasking subclinical dopaminergic degeneration, could theoretically lead to valproate-associated parkinsonism. Further studies are warranted to elucidate this entity and its underlying pathophysiology.

Epidrug-induced upregulation of functional somatostatin type 2 receptors in human pancreatic neuroendocrine tumor cells

Somatostatin receptors are a pivotal target for treatment of pancreatic neuroendocrine tumors (pNET), either with somatostatin analogues (SSA) or radiolabeled SSA. The highest affinity target for the most commonly used SSA is the somatostatin receptor type 2 (sst₂ ). An important factor that may complicate treatment efficacy, is the variable number of receptors expressed on pNETs. Gene expression is subject to complex regulation, in which epigenetics has a central role. In this study we explored the possible role of epigenetic modifications in the variations in sst₂ expression levels in two human pNET cell lines, BON-1 and QGP-1. We found upregulation of sst₂ mRNA after treatment with the epidrugs 5-aza-2'-deoxycytidine (5-aza-dC) and valproic acid (VPA), an increased uptake of radiolabeled octreotide, as well as increased sensitivity to the SSA octreotide in functional cAMP inhibition. At epigenetic level we observed low methylation levels of the sst₂ gene promoter region irrespective of expression. Activating histone mark H3K9Ac can be regulated with epidrug treatment, with an angle of effect corresponding to the effect on mRNA expression. Repressive histone mark H3K27me3 is not regulated by either 5-aza-dC or VPA. We conclude that epidrug treatment, in particular with combined 5-aza-dC and VPA treatment, might hold promise for improving and adding to current SSA treatment strategies of patients with pNETs.

"Watching the Detectives" report of the general assembly of the EU project DETECTIVE Brussels, 24-25 November 2015

SEURAT-1 is a joint research initiative between the European Commission and Cosmetics Europe aiming to develop in vitro- and in silico-based methods to replace the in vivo repeated dose systemic toxicity test used for the assessment of human safety. As one of the building blocks of SEURAT-1, the DETECTIVE project focused on a key element on which in vitro toxicity testing relies: the development of robust and reliable, sensitive and specific in vitro biomarkers and surrogate endpoints that can be used for safety assessments of chronically acting toxicants, relevant for humans. The work conducted by the DETECTIVE consortium partners has established a screening pipeline of functional and "-omics" technologies, including high-content and high-throughput screening platforms, to develop and investigate human biomarkers for repeated dose toxicity in cellular in vitro models. Identification and statistical selection of highly predictive biomarkers in a pathway- and evidence-based approach constitute a major step in an integrated approach towards the replacement of animal testing in human safety assessment. To discuss the final outcomes and achievements of the consortium, a meeting was organized in Brussels. This meeting brought together data-producing and supporting consortium partners. The presentations focused on the current state of ongoing and concluding projects and the strategies employed to identify new relevant biomarkers of toxicity. The outcomes and deliverables, including the dissemination of results in data-rich "-omics" databases, were discussed as were the future perspectives of the work completed under the DETECTIVE project. Although some projects were still in progress and required continued data analysis, this report summarizes the presentations, discussions and the outcomes of the project.

General pharmacokinetic/pharmacodynamic concepts of mood stabilizers in the treatment of bipolar disorder

Introduction:

Mood stabilizers are the recommended treatment for patients who receive a diagnosis of bipolar disorder. Because of the necessity of mood stabilizer treatment in patients with bipolar disorder and the extent of pharmacokinetic and pharmacodynamic principles involved, the purpose of this review is to summarize the pharmacokinetic principles of lithium in addition to the pharmacodynamics of lithium, carbamazepine, lamotrigine, and valproic acid/valproate.

Methods:

Practice guidelines, review articles, and clinical trials were located using online databases PubMed, CINAHL, IDIS, and Medline. Search terms included at least one of the following: bipolar disorder, carbamazepine, lamotrigine, lithium, mood stabilizers, pharmacokinetics, pharmacodynamics, valproate, and valproic acid. Online clinical databases Dynamed® and Lexicomp® were also used in the study.

Results:

Mood stabilizers collectively possess distinct qualities that are closely regarded before, during, and after therapeutic initiation. Individual patient characteristics, coupled with these observed traits, add to the complexity of selecting the most optimal neurologic agent. Each medication discussed uniquely contributes to both the maintenance and restoration of overall patient well-being.

Discussion:

Introduction of mood stabilizers into drug regimens is often done in the presence of an array of mitigating factors. Safety and efficacy measures are commonly used to gauge desired results. Careful monitoring of patients' responses to selected therapies is paramount for arriving at appropriate clinical outcomes.

FKBP51 inhibits GSK3β and augments the effects of distinct psychotropic medications

Psychotropic medications target glycogen synthase kinase 3β (GSK3β), but the functional integration with other factors relevant for drug efficacy is poorly understood. We discovered that the suggested psychiatric risk factor FK506 binding protein 51 (FKBP51) increases phosphorylation of GSK3β at serine 9 (pGSK3β(S9)). FKBP51 associates with GSK3β mainly through its FK1 domain; furthermore, it also changes GSK3β's heterocomplex assembly by associating with the phosphatase PP2A and the kinase cyclin-dependent kinase 5. FKBP51 acts through GSK3β on the downstream targets Tau, β-catenin and T-cell factor/lymphoid enhancing factor (TCF/LEF). Lithium and the antidepressant (AD) paroxetine (PAR) functionally synergize with FKBP51, as revealed by reporter gene and protein association analyses. Deletion of FKBP51 blunted the PAR- or lithium-induced increase in pGSK3β(S9) in cells and mice and attenuated the behavioral effects of lithium treatment. Clinical improvement in depressive patients was predicted by baseline GSK3β pathway activity and by pGSK3β(S9) reactivity to ex vivo treatment of peripheral blood mononuclear lymphocytes with lithium or PAR. In sum, FKBP51-directed GSK3β activity contributes to the action of psychotropic medications. Components of the FKBP51-GSK3β pathway may be useful as biomarkers predicting AD response and as targets for the development of novel ADs.

Drug-induced fatty liver disease: An overview of pathogenesis and management

Over the past decades, many drugs have been identified, that can potentially induce steatohepatitis in the predisposed individual. Classically this has been incriminated to amiodarone, perhexiline, and 4,4'-diethylaminoethoxyhexestrol (DH), all of which have been found to independently induce the histologic picture of non-alcoholic steatohepatitis (NASH). Pathogenetic mechanisms of hepatotoxicity although still evolving, demonstrate that mitochondrial dysfunction, deranged ATP production and fatty acid catabolism likely play an important role. Drugs like steroid hormones can exacerbate the pathogenetic mechanisms that lead to NASH, and other drugs like tamoxifen, cisplatin and irenotecan have been shown to precipitate latent fatty liver as well. Further research aiming to elucidate the pathogenesis of drug-induced steatosis and steatohepatitis is needed in order to better design therapeutic targets.

Antitumor effect of pharmacologic ascorbate in the B16 murine melanoma model

Because 5-year survival rates for patients with metastatic melanoma remain below 25%, there is continued need for new therapeutic approaches. For some tumors, pharmacologic ascorbate treatment may have a beneficial antitumor effect and may work synergistically with standard chemotherapeutics. To investigate this possibility in melanoma, we examined the effect of pharmacologic ascorbate on B16-F10 cells. Murine models were employed to compare tumor size following treatment with ascorbate, and the chemotherapeutic agents dacarbazine or valproic acid, alone or in combination with ascorbate. Results indicated that nearly all melanoma cell lines were susceptible to ascorbate-mediated cytotoxicity. Compared to saline controls, pharmacologic ascorbate decreased tumor size in both C57BL/6 (P < 0.0001) and NOD-scid tumor bearing mice (P < 0.0001). Pharmacologic ascorbate was superior or equivalent to dacarbazine as an antitumor agent. Synergy was not apparent when ascorbate was combined with either dacarbazine or valproic acid; the latter combination may have additional toxicities. Pharmacologic ascorbate induced DNA damage in melanoma cells, as evidenced by increased phosphorylation of the histone variant, H2A.X. Differences were not evident in tumor samples from C57BL/6 mice treated with pharmacologic ascorbate compared to tumors from saline-treated controls. Together, these results suggest that pharmacologic ascorbate has a cytotoxic effect against melanoma that is largely independent of lymphocytic immune functions and that continued investigation of pharmacologic ascorbate in cancer treatment is warranted.

Drug-induced liver injury in a chronic hepatitis C patient treated by peginterferon, ribavirin and simeprevir

A 56-year-old male patient with chronic hepatitis C was treated with pegylated interferon (PEG IFN)-α-2b and ribavirin (RBV) for 72 weeks in 2006. The patient achieved an early virological response (EVR); however, hepatitis C relapsed 12 weeks after discontinuation of PEG IFN and RBV. In 2012, the patient was treated with a PEG IFN/RBV/telaprevir combination therapy. After 5 days of treatment, he suffered from a telaprevir-associated skin rash on his body and four limbs. He chose to be treated with PEG IFN and RBV until 60 weeks. He again achieved EVR but no sustained virological response. In 2014, he was treated with PEG IFN/RBV/simeprevir combination therapy. He achieved rapid virological response, but after 6 weeks of therapy, a striking elevation of serum aminotransferase level was recorded with no accompanying skin rash; he was admitted to our hospital. PEG IFN/RBV/simeprevir was stopped, but sodium valproate (400 mg/day), which had been administrated for more than 10 years to prevent epilepsy was continued. Liver biopsy revealed typical features of drug-induced liver injury. After stopping PEG IFN/RBV/simeprevir, serum aminotransferase levels soon returned to the normal range. We diagnosed this case to be simeprevir-induced hepatitis clinically and histologically. Physicians need to stay alert to the possibility of drug-induced liver injury in using simeprevir.

Ultrasound-assisted dispersive liquid–liquid microextraction followed by GC–MS/MS analysis for the determination of valproic acid in urine samples

Background: Valproic acid (VPA) is an anticonvulsant drug used for the treatment of epilepsy and bipolar disorder. A method based on simultaneous derivatization and dispersive liquid–liquid microextraction followed by GC–MS/MS analysis has been developed for the determination of VPA in urine samples. Results: This optimized and validated method shows good linearity with R2 value of 0.999. LOD and LOQ of VPA was found to be 0.4 ng ml-1 and 1.4 ng ml-1, respectively. Recovery of VPA was found to be in the range of 80 to 92%. Conclusion: The developed method can find its wide applicability for the routine analysis of VPA in toxicological and clinical laboratories.

In Silico Modeling for the Prediction of Dose and Pathway-Related Adverse Effects in Humans From In Vitro Repeated-Dose Studies

Long-term repeated-dose toxicity is mainly assessed in animals despite poor concordance of animal data with human toxicity. Nowadays advanced human in vitro systems, eg, metabolically competent HepaRG cells, are used for toxicity screening. Extrapolation of in vitro toxicity to in vivo effects is possible by reverse dosimetry using pharmacokinetic modeling. We assessed long-term repeated-dose toxicity of bosentan and valproic acid (VPA) in HepaRG cells under serum-free conditions. Upon 28-day exposure, the EC50 values for bosentan and VPA decreased by 21- and 33-fold, respectively. Using EC(10) as lowest threshold of toxicity in vitro, we estimated the oral equivalent doses for both test compounds using a simplified pharmacokinetic model for the extrapolation of in vitro toxicity to in vivo effect. The model predicts that bosentan is safe at the considered dose under the assumed conditions upon 4 weeks exposure. For VPA, hepatotoxicity is predicted for 4% and 47% of the virtual population at the maximum recommended daily dose after 3 and 4 weeks of exposure, respectively. We also investigated the changes in the central carbon metabolism of HepaRG cells exposed to orally bioavailable concentrations of both drugs. These concentrations are below the 28-day EC(10) and induce significant changes especially in glucose metabolism and urea production. These metabolic changes may have a pronounced impact in susceptible patients such as those with compromised liver function and urea cycle deficiency leading to idiosyncratic toxicity. We show that the combination of modeling based on in vitro repeated-dose data and metabolic changes allows the prediction of human relevant in vivo toxicity with mechanistic insights.

M-current preservation contributes to anticonvulsant effects of valproic acid

Valproic acid (VPA) has been widely used for decades to treat epilepsy; however, its mechanism of action remains poorly understood. Here, we report that the anticonvulsant effects of nonacute VPA treatment involve preservation of the M-current, a low-threshold noninactivating potassium current, during seizures. In a wide variety of neurons, activation of Gq-coupled receptors, such as the m1 muscarinic acetylcholine receptor, suppresses the M-current and induces hyperexcitability. We demonstrated that VPA treatment disrupts muscarinic suppression of the M-current and prevents resultant agonist-induced neuronal hyperexcitability. We also determined that VPA treatment interferes with M-channel signaling by inhibiting palmitoylation of a signaling scaffold protein, AKAP79/150, in cultured neurons. In a kainate-induced murine seizure model, administration of a dose of an M-channel inhibitor that did not affect kainate-induced seizure transiently eliminated the anticonvulsant effects of VPA. Retigabine, an M-channel opener that does not open receptor-suppressed M-channels, provided anticonvulsant effects only when administered prior to seizure induction in control animals. In contrast, treatment of VPA-treated mice with retigabine induced anticonvulsant effects even when administered after seizure induction. Together, these results suggest that receptor-induced M-current suppression plays a role in the pathophysiology of seizures and that preservation of the M-current during seizures has potential as an effective therapeutic strategy.

Mechanistic review of drug-induced steatohepatitis

Drug-induced steatohepatitis is a rare form of liver injury known to be caused by only a handful of compounds. These compounds stimulate the development of steatohepatitis through their toxicity to hepatocyte mitochondria; inhibition of beta-oxidation, mitochondrial respiration, and/or oxidative phosphorylation. Other mechanisms discussed include the disruption of phospholipid metabolism in lysosomes, prevention of lipid egress from hepatocytes, targeting mitochondrial DNA and topoisomerase, decreasing intestinal barrier function, activation of the adenosine pathway, increasing fatty acid synthesis, and sequestration of coenzyme A. It has been found that the majority of compounds that induce steatohepatitis have cationic amphiphilic structures; a lipophilic ring structure with a side chain containing a cationic secondary or tertiary amine. Within the last decade, the ability of many chemotherapeutics to cause steatohepatitis has become more evident coining the term chemotherapy-associated steatohepatitis (CASH). The mechanisms behind drug-induced steatohepatitis are discussed with a focus on cationic amphiphilic drugs and chemotherapeutic agents.

Drug Induced Steatohepatitis: An Uncommon Culprit of a Common Disease

Nonalcoholic fatty liver disease (NAFLD) is a leading cause of liver disease in developed countries. Its frequency is increasing in the general population mostly due to the widespread occurrence of obesity and the metabolic syndrome. Although drugs and dietary supplements are viewed as a major cause of acute liver injury, drug induced steatosis and steatohepatitis are considered a rare form of drug induced liver injury (DILI). The complex mechanism leading to hepatic steatosis caused by commonly used drugs such as amiodarone, methotrexate, tamoxifen, valproic acid, glucocorticoids, and others is not fully understood. It relates not only to induction of the metabolic syndrome by some drugs but also to their impact on important molecular pathways including increased hepatocytes lipogenesis, decreased secretion of fatty acids, and interruption of mitochondrial β-oxidation as well as altered expression of genes responsible for drug metabolism. Better familiarity with this type of liver injury is important for early recognition of drug hepatotoxicity and crucial for preventing severe forms of liver injury and cirrhosis. Moreover, understanding the mechanisms leading to drug induced hepatic steatosis may provide much needed clues to the mechanism and potential prevention of the more common form of metabolic steatohepatitis.

Valproate therapy exacerbating intermediate phenotype of methylmalonic aciduria

A, 11-year-old male, with delayed milestones after the age of 6 months with recurrent myoclonus and generalized tonic-clonic seizures had clinical worsening after institution of valproate, was detected to have elevated serum lactate level and marked methyl malonic aciduria. Patient had remarkable improvement following withdrawal of valproate and substitution of hydroxocobalamin.

Mitochondrial Morphology and Fundamental Parameters of the Mitochondrial Respiratory Chain Are Altered in Caenorhabditis elegans Strains Deficient in Mitochondrial Dynamics and Homeostasis Processes

Mitochondrial dysfunction has been linked to myriad human diseases and toxicant exposures, highlighting the need for assays capable of rapidly assessing mitochondrial health in vivo. Here, using the Seahorse XFe24 Analyzer and the pharmacological inhibitors dicyclohexylcarbodiimide and oligomycin (ATP-synthase inhibitors), carbonyl cyanide 4-(trifluoromethoxy) phenylhydrazone (mitochondrial uncoupler) and sodium azide (cytochrome c oxidase inhibitor), we measured the fundamental parameters of mitochondrial respiratory chain function: basal oxygen consumption, ATP-linked respiration, maximal respiratory capacity, spare respiratory capacity and proton leak in the model organism Caenhorhabditis elegans. Since mutations in mitochondrial homeostasis genes cause mitochondrial dysfunction and have been linked to human disease, we measured mitochondrial respiratory function in mitochondrial fission (drp-1)-, fusion (fzo-1)-, mitophagy (pdr-1, pink-1)-, and electron transport chain complex III (isp-1)-deficient C. elegans. All showed altered function, but the nature of the alterations varied between the tested strains. We report increased basal oxygen consumption in drp-1; reduced maximal respiration in drp-1, fzo-1, and isp-1; reduced spare respiratory capacity in drp-1 and fzo-1; reduced proton leak in fzo-1 and isp-1; and increased proton leak in pink-1 nematodes. As mitochondrial morphology can play a role in mitochondrial energetics, we also quantified the mitochondrial aspect ratio for each mutant strain using a novel method, and for the first time report increased aspect ratios in pdr-1- and pink-1-deficient nematodes.

Phenoconversion of CYP2C9 in epilepsy limits the predictive value of CYP2C9 genotype in optimizing valproate therapy

Aim: Since prominent role in valproate metabolism is assigned to CYP2C9 in pediatric patients, the association between children's CYP2C9-status and serum valproate concentrations or dose-requirements was evaluated. Materials & Methods: The contribution of CYP2C9 genotype and CYP2C9 expression in children (n = 50, Caucasian) with epilepsy to valproate pharmacokinetics was analyzed. Results: Valproate concentrations were significantly lower in normal expressers with CYP2C9*1/*1 than in low expressers or in patients carrying polymorphic CYP2C9 alleles. Consistently, the dose-requirement was substantially higher in normal expressers carrying CYP2C9*1/*1 (33.3 mg/kg vs 13.8–17.8 mg/kg, p < 0.0001). Low CYP2C9 expression significantly increased the ratio of poor metabolizers predictable from CYP2C9 genotype (by 46%). Conclusion: Due to the substantial downregulation of CYP2C9 expression in epilepsy, inferring patients’ valproate metabolizing phenotype merely from CYP2C9 genotype results in false prediction.

Inflammasomes in pancreatic physiology and disease

In this review we summarize the role of inflammasomes in pancreatic physiology and disease with a focus on acute pancreatitis where much recent progress has been made. New findings have identified inducers of and cell specificity of inflammasome component expression in the pancreas, the contribution of inflammasome-regulated effectors to pancreatitis, and metabolic regulation of inflammasome activation, which are strong determinants of injury in pancreatitis. New areas of pancreatic biology will be highlighted in the context of our evolving understanding of gut microbiome- and injury-induced inflammasome priming, pyroptosis, and innate immune-mediated regulation of cell metabolism.

Sodium valproate induces mitochondrial respiration dysfunction in HepG2 in vitro cell model

Sodium valproate (VPA) is a potentially hepatotoxic antiepileptic drug. Risk of VPA-induced hepatotoxicity is increased in patients with mitochondrial diseases and especially in patients with POLG1 gene mutations. We used a HepG2 cell in vitro model to investigate the effect of VPA on mitochondrial activity. Cells were incubated in glucose medium and mitochondrial respiration-inducing medium supplemented with galactose and pyruvate. VPA treatments were carried out at concentrations of 0-2.0mM for 24-72 h. In both media, VPA caused decrease in oxygen consumption rates and mitochondrial membrane potential. VPA exposure led to depleted ATP levels in HepG2 cells incubated in galactose medium suggesting dysfunction in mitochondrial ATP production. In addition, VPA exposure for 72 h increased levels of mitochondrial reactive oxygen species (ROS), but adversely decreased protein levels of mitochondrial superoxide dismutase SOD2, suggesting oxidative stress caused by impaired elimination of mitochondrial ROS and a novel pathomechanism related to VPA toxicity. Increased cell death and decrease in cell number was detected under both metabolic conditions. However, immunoblotting did not show any changes in the protein levels of the catalytic subunit A of mitochondrial DNA polymerase γ, the mitochondrial respiratory chain complexes I, II and IV, ATP synthase, E3 subunit dihydrolipoyl dehydrogenase of pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase and glutathione peroxidase. Our results show that VPA inhibits mitochondrial respiration and leads to mitochondrial dysfunction, oxidative stress and increased cell death, thus suggesting an essential role of mitochondria in VPA-induced hepatotoxicity.

Hypothermia and valproic acid activate prosurvival pathways after hemorrhage

BACKGROUND

Therapeutic hypothermia (hypo) and valproic acid (VPA, a histone deacetylase inhibitor) have independently been shown to be protective in models of trauma and hemorrhagic shock but require logistically challenging doses to be effective. Theoretically, combined treatment may further enhance effectiveness, allowing us to use lower doses of each modality. The aim of this study was to determine whether a combination of mild hypo and VPA treatments would offer better cytoprotection compared with that of individual treatments in a hemorrhage model.

MATERIALS AND METHODS

Male Sprague-Dawley rats were subjected to 40% volume-controlled hemorrhage, kept in shock for 30 min, and assigned to one of the following treatment groups: normothermia (36°C-37°C), hypo (30 ± 2°C), normothermia + VPA (300 mg/kg), and hypo + VPA (n = 5 per group). After 3 h of observation, the animals were sacrificed, liver tissue was harvested and subjected to whole cell lysis, and levels of key proteins in the prosurvival Akt pathway were measured using Western blot.

RESULTS

Activation of the proapoptotic protein cleaved caspase-3 was significantly lower in the combined treatment group relative to normothermia (P < 0.05). Levels of the prosurvival Bcl-2 was significantly higher in the combined treatment group relative to sham, normothermia, and normothermia + VPA groups (P < 0.005). The downstream prosurvival protein phospho-GSK-3β was significantly higher in the sham, hypo, and combined treatment groups compared with that in normothermia groups with or without VPA (P < 0.05). Levels of the prosurvival β-catenin were significantly higher in the combined treatment group relative to normothermia (P < 0.01).

CONCLUSIONS

This is the first in vivo study to demonstrate that combined treatment with VPA and hypo offers better cytoprotection than these treatments given independently.

In vivo effects of naproxen, salicylic acid, and valproic acid on the pharmacokinetics of trichloroethylene and metabolites in rats

It was recently demonstrated that some drugs modulate in vitro metabolism of trichloroethylene (TCE) in humans and rats. The objective was to assess in vivo interactions between TCE and three drugs: naproxen (NA), valproic acid (VA), and salicylic acid (SA). Animals were exposed to TCE by inhalation (50 ppm for 6 h) and administered a bolus dose of drug by gavage, equivalent to 10-fold greater than the recommended daily dose. Samples of blood, urine, and collected tissues were analyzed by headspace gas chromatography coupled to an electron capture detector for TCE and metabolites (trichloroethanol [TCOH] and trichloroacetate [TCA]) levels. Coexposure to NA and TCE significantly increased (up to 50%) total and free TCOH (TCOHtotal and TCOHfree, respectively) in blood. This modulation may be explained by an inhibition of glucuronidation. VA significantly elevated TCE levels in blood (up to 50%) with a marked effect on TCOHtotal excretion in urine but not in blood. In contrast, SA produced an increase in TCOHtotal levels in blood at 30, 60, and 90 min and urine after coexposure. Data confirm in vitro observations that NA, VA, and SA affect in vivo TCE kinetics. Future efforts need to be directed to evaluate whether populations chronically medicated with the considered drugs display greater health risks related to TCE exposure.

A pilot study of plasma metabolomic patterns from patients treated with ketamine for bipolar depression: evidence for a response-related difference in mitochondrial networks

BACKGROUND AND PURPOSE

(R,S)-ketamine produces rapid and significant antidepressant effects in approximately 65% of patients suffering from treatment-resistant bipolar depression (BD). The genetic, pharmacological and biochemical differences between ketamine responders and non-responders have not been identified. The purpose of this study was to employ a metabolomics approach, a global, non-targeted determination of endogenous metabolic patterns, to identify potential markers of ketamine response and non-response.

EXPERIMENTAL APPROACH

Plasma samples from 22 BD patients were analyzed to produce metabolomic patterns. The patients had received ketamine in a placebo-controlled crossover study and the samples were obtained 230 min post-administration at which time the patients were categorized as responders or non-responders. Matching plasma samples from the placebo arm of the study were also analysed. During the study, the patients were maintained on either lithium or valproate.

KEY RESULTS

The metabolomic patterns were significantly different between the patients maintained on lithium and those maintained on valproate, irrespective of response to ketamine. In the patients maintained on lithium, 18 biomarkers were identified. In responders, lysophosphatidylethanolamines (4) and lysophosphatidylcholines (9) were increased relative to non-responders.

CONCLUSIONS AND IMPLICATIONS

The results indicate that the differences between patients who respond to ketamine and those who do not are due to alterations in the mitochondrial β-oxidation of fatty acids. These differences were not produced by ketamine administration. The data indicate that pretreatment metabolomics screening may be a guide to the prediction of response and a potential approach to the individualization of ketamine therapy.

Mitochondria, energetics, epigenetics, and cellular responses to stress

BACKGROUND

Cells respond to environmental stressors through several key pathways, including response to reactive oxygen species (ROS), nutrient and ATP sensing, DNA damage response (DDR), and epigenetic alterations. Mitochondria play a central role in these pathways not only through energetics and ATP production but also through metabolites generated in the tricarboxylic acid cycle, as well as mitochondria-nuclear signaling related to mitochondria morphology, biogenesis, fission/fusion, mitophagy, apoptosis, and epigenetic regulation.

OBJECTIVES

We investigated the concept of bidirectional interactions between mitochondria and cellular pathways in response to environmental stress with a focus on epigenetic regulation, and we examined DNA repair and DDR pathways as examples of biological processes that respond to exogenous insults through changes in homeostasis and altered mitochondrial function.

METHODS

The National Institute of Environmental Health Sciences sponsored the Workshop on Mitochondria, Energetics, Epigenetics, Environment, and DNA Damage Response on 25-26 March 2013. Here, we summarize key points and ideas emerging from this meeting.

DISCUSSION

A more comprehensive understanding of signaling mechanisms (cross-talk) between the mitochondria and nucleus is central to elucidating the integration of mitochondrial functions with other cellular response pathways in modulating the effects of environmental agents. Recent studies have highlighted the importance of mitochondrial functions in epigenetic regulation and DDR with environmental stress. Development and application of novel technologies, enhanced experimental models, and a systems-type research approach will help to discern how environmentally induced mitochondrial dysfunction affects key mechanistic pathways.

CONCLUSIONS

Understanding mitochondria-cell signaling will provide insight into individual responses to environmental hazards, improving prediction of hazard and susceptibility to environmental stressors.

Evaluation of in situ generated valproyl 1-O-β-acyl glucuronide in valproic acid toxicity in sandwich-cultured rat hepatocytes

Acyl glucuronides are reactive electrophilic metabolites implicated in the toxicity of carboxylic acid drugs. Valproyl 1-O-β-acyl glucuronide (VPA-G), which is a major metabolite of valproic acid (VPA), has been linked to the development of oxidative stress in VPA-treated rats. However, relatively little is known about the toxicity of in situ generated VPA-G and its contribution to VPA hepatotoxicity. Therefore, we investigated the effects of modulating the in situ formation of VPA-G on lactate dehydrogenase (LDH) release (a marker of necrosis), BODIPY 558/568 C12 accumulation (a marker of steatosis), and cellular glutathione (GSH) content in VPA-treated sandwich-cultured rat hepatocytes. VPA increased LDH release and BODIPY 558/568 C12 accumulation, whereas it had little or no effect on total GSH content. Among the various uridine 5'-diphospho-glucuronosyltransferase inducers evaluated, β-naphthoflavone produced the greatest increase in VPA-G formation. This was accompanied by an attenuation of the increase in BODIPY 558/568 C12 accumulation, but did not affect the change in LDH release or total GSH content in VPA-treated hepatocytes. Inhibition of in situ formation of VPA-G by borneol was not accompanied by substantive changes in the effects of VPA on any of the toxicity markers. In a comparative study, in situ generated diclofenac glucuronide was not toxic to rat hepatocytes, as assessed using the same chemical modulators, thereby demonstrating the utility of the sandwich-cultured rat hepatocyte model. Overall, in situ generated VPA-G was not toxic to sandwich-cultured rat hepatocytes, suggesting that VPA glucuronidation per se is not expected to be a contributing mechanism for VPA hepatotoxicity.

Brief report novel mechanism for valproate-induced teratogenicity

BACKGROUND

Valproic acid (VPA) is a commonly prescribed drug for those affected by epilepsy and bipolar disorders. VPA has a well known teratogenic potential, causing a variety of birth defects including neural tube defects (NTDs) and other congenital malformations, when women are treated with this medication during pregnancy. Unfortunately, the mechanism by which VPA is teratogenic remains unknown, although a range of potential mechanisms including histone deacetylase inhibition and folate antagonism have been proposed. The latter is of considerable importance, as clinicians need to know if additional folate supplements can prevent VPA-induced defects.

METHODS

We herein approach this question experimentally, using enzyme-linked immunosorbent assay assays and cell culture modeling, to demonstrate that VPA serves as a noncompetitive inhibitor of the high affinity folate receptors.

RESULTS

Binding affinities experimentally determined through enzyme-linked immunosorbent assay assays indicate that VPA serves as a noncompetitive substrate that can lessen the ability of the three primary folate forms to bind to the high affinity folate receptors. Tests in HEK293T cells indicate that the membrane-bound folate receptors of VPA treated cells bind significantly lower amounts of folic acid than do untreated cells.

CONCLUSION

If these data translate to the overall transport and subsequent bioavailability of folates, noncompetitive inhibition of the folate receptors by VPA may serve to lower the bioavailable folates in VPA treated mothers. This represents a novel mechanism by which in utero VPA exposure could be disrupting developmental processes by noncompetitively binding to the folate receptors during embryogenesis, thus inducing the wide range of defects seen in babies born to VPA treated mothers.

Gene expression markers in the zebrafish embryo reflect a hepatotoxic response in animal models and humans

The zebrafish embryo (ZFE) is a promising non-rodent model in toxicology, and initial studies suggested its applicability in detecting hepatotoxic responses. Here, we hypothesize that the detailed analysis of underlying mechanisms of hepatotoxicity in ZFE contributes to the improved identification of hepatotoxic properties of new compounds and to the reduction of rodents used for screening. ZFEs were exposed to nine reference hepatotoxicants, targeted at induction of cholestasis, steatosis and necrosis, and two non-hepatotoxic controls. Histopathology revealed various specific morphological changes in the ZFE hepatocytes indicative of cell injury. Gene expression profiles of the individual compounds were generated using microarrays. Regulation of single genes and of pathways could be linked to hepatotoxic responses in general, but phenotype-specific responses could not be distinguished. Hepatotoxicity-associated pathways included xenobiotic metabolism and oxidoreduction related pathways. Overall analysis of gene expression identified a limited set of potential biomarkers specific for a common hepatotoxicity response. This set included several cytochrome P450 genes (cyp2k19, cyp4v7, cyp2aa3), genes related to liver development (pklr) and genes important in oxidoreduction processes (zgc:163022, zgc:158614, zgc:101858 and sqrdl). In conclusion, the ZFE model allows for identification of hepatotoxicants, without discrimination into specific phenotypes.

Challenges in diagnosing a metabolic disorder: error of pyruvate metabolism or drug induced?

Certain drugs are known to cause metabolic changes resulting in altered metabolic profiles. We report here a case where a combination of antiepileptic drugs resulted in a profile that mimicked a metabolic disorder. A 16month-old female child on antiepileptic drugs (valproate and topiramate) was suspected to have the inherited metabolic disorder, dihydrolipoamide dehydrogenase deficiency, based on clinical symptoms and metabolic profile showing hyperalaninemia, elevated branched-chain amino acids, and lactate-pyruvate ratio. Suspecting that the observed metabolic changes could have also arised from medication, current medication was weaned off and replaced with levetiracetam, clonazepam, and levocarnitine (supportive therapy). Metabolic profiling conducted after 47 days showed normal alanine, branched-chain amino acids, ornithine, and lactate-pyruvate ratio, suggesting that the earlier abnormalities could have been medication induced. We stress that metabolic changes resulting from chronic medication should be considered while interpreting a positive result when investigating an inherited metabolic disorder.

Structural and energetic analysis to provide insight residues of CYP2C9, 2C11 and 2E1 involved in valproic acid dehydrogenation selectivity

Docking and molecular dynamics (MD) simulation have been two computational techniques used to gain insight about the substrate orientation within protein active sites, allowing to identify potential residues involved in the binding and catalytic mechanisms. In this study, both methods were combined to predict the regioselectivity in the binding mode of valproic acid (VPA) on three cytochrome P-450 (CYP) isoforms CYP2C9, CYP2C11, and CYP2E1, which are involved in the biotransformation of VPA yielding reactive hepatotoxic intermediate 2-n-propyl-4-pentenoic acid (4nVPA). There are experimental data about hydrogen atom abstraction of the C4-position of VPA to yield 4nVPA, however, there are not structural evidence about the binding mode of VPA and 4nVPA on CYPs. Therefore, the complexes between these CYP isoforms and VPA or 4nVPA were studied to explore their differences in binding and energetic stabilization. Docking results showed that VPA and 4nVPA are coupled into CYPs binding site in a similar conformation, but it does not explain the VPA hydrogen atom abstraction. On the other hand, MD simulations showed a set of energetic states that reorient VPA at the first ns, then making it susceptible to a dehydrogenation reaction. For 4nVPA, multiple binding modes were observed in which the different states could favor either undergo other reaction mechanism or ligand expulsion from the binding site. Otherwise, the energetic and entropic contribution point out a similar behavior for the three CYP complexes, showing as expected a more energetically favorable binding free energy for the complexes between CYPs and VPA than with 4nVPA.

Valproyl-CoA inhibits the activity of ATP- and GTP-dependent succinate:CoA ligases

BACKGROUND

Valproic acid (VPA) is an effective antiepileptic drug that may induce progressive microvesicular steatosis. The impairment of mitochondrial function may be an important metabolic effect of VPA treatment with potential adverse consequences.

OBJECTIVE

To investigate the influence of VPA on the activity of GTP- and ATP-specific succinate:CoA ligases (G-SUCL and A-SUCL).

METHODS

The GTP- and ATP-specific SUCL activities were measured in human fibroblasts in the reverse direction, i.e. the formation of succinyl-CoA. These were assessed at different concentrations of succinate in the presence of VPA, valproyl-CoA and zinc chloride, an established inhibitor of the enzymes. Activities were measured using an optimized HPLC procedure.

RESULTS

Valproyl-CoA (1 mM) inhibited the activity of A-SUCL and G-SUCL by 45-55% and 25-50%, respectively. VPA (1 mM) had no influence on the activity of the two enzymes.

DISCUSSION

Valproyl-CoA appears to affect the activity of SUCL, especially with the ATP-specific enzyme. Considering the key role of SUCL in the Krebs cycle, interference with its activity might impair the cellular energy status. Moreover, A-SUCL is bound to the nucleoside diphosphate kinase (NDPK), which is responsible for the mitochondrial (deoxy)nucleotide synthesis. An inhibition of A-SUCL might influence the activity of NDPK inducing an imbalance of nucleotides in the mitochondria and eventually mitochondrial DNA depletion. This may account for the potential liver failure associated with valproate therapy, reported in patients with deficiencies within the mitochondrial DNA replicase system such as polymerase gamma 1.

Sexually dimorphic effects of prenatal exposure to propionic acid and lipopolysaccharide on social behavior in neonatal, adolescent, and adult rats: implications for autism spectrum disorders

Emerging evidence suggests that the gut microbiome plays an important role in immune functioning, behavioral regulation and neurodevelopment. Altered microbiome composition, including altered short chain fatty acids, and/or immune system dysfunction, may contribute to neurodevelopmental disorders such as autism spectrum disorders (ASD), with some children with ASD exhibiting both abnormal gut bacterial metabolite composition and immune system dysfunction. This study describes the effects of prenatal propionic acid (PPA), a short chain fatty acid and metabolic product of many antibiotic resistant enteric bacteria, and of prenatal lipopolysaccharide (LPS), a bacterial mimetic and microbiome component, on social behavior in male and female neonatal, adolescent and adult rats. Pregnant Long-Evans rats were injected once a day with either a low level of PPA (500 mg/kg SC) on gestation days G12-16, LPS (50 μg/kg SC) on G12, or vehicle control on G12 or G12-16. Sex- and age-specific, subtle effects on behavior were observed. Both male and female PPA treated pups were impaired in a test of their nest seeking response, suggesting impairment in olfactory-mediated neonatal social recognition. As well, adolescent males, born to PPA treated dams, approached a novel object more than control animals and showed increased levels of locomotor activity compared to prenatal PPA females. Prenatal LPS produced subtle impairments in social behavior in adult male and female rats. These findings raise the possibility that brief prenatal exposure to elevated levels of microbiome products, such as PPA or LPS, can subtly influence neonatal, adolescent and adult social behavior.

Treatment of mitochondrial disorders

OPINION STATEMENT

While numerous treatments for mitochondrial disorders have been suggested, relatively few have undergone controlled clinical trials. Treatment of these disorders is challenging, as only symptomatic therapy is available. In this review we will focus on newer drugs and treatment trials in mitochondrial diseases, with a special focus on medications to avoid in treating epilepsy and ICU patient with mitochondrial disease, which has not been included in such a review. Readers are also referred to the opinion statement in A Modern Approach to the Treatment of Mitochondrial Disease published in Current Treatment Options in Neurology 2009. Many of the supplements used for treatment were reviewed in the previous abstract, and dosing guidelines were provided. The focus of this review is on items not previously covered in depth, and our discussion includes more recently studied compounds as well as any relevant updates on older compounds . We review a variety of vitamins and xenobiotics, including dichloroacetate (DCA), arginine, coenzyme Q10, idebenone, EPI-743, and exercise training. Treatment of epilepsy, which is a common feature in many mitochondrial phenotypes, warrants special consideration due to the added toxicity of certain medications, and we provide a discussion of these unique treatment challenges. Interesting, however, with only a few exceptions, the treatment strategies for epilepsy in mitochondrial cytopathies are the same as for epilepsy without mitochondrial dysfunction. We also discuss intensive care management, building upon similar reviews, adding new dimensions, and demonstrating the complexity of overall care of these patients.

A 3D in vitro model of differentiated HepG2 cell spheroids with improved liver-like properties for repeated dose high-throughput toxicity studies

Immortalized hepatocyte cell lines show only a weak resemblance to primary hepatocytes in terms of gene expression and function, limiting their value in predicting drug-induced liver injury (DILI). Furthermore, primary hepatocytes cultured on two-dimensional tissue culture plastic surfaces rapidly dedifferentiate losing their hepatocyte functions and metabolic competence. We have developed a three-dimensional in vitro model using extracellular matrix-based hydrogel for long-term culture of the human hepatoma cell line HepG2. HepG2 cells cultured in this model stop proliferating, self-organize and differentiate to form multiple polarized spheroids. These spheroids re-acquire lost hepatocyte functions such as storage of glycogen, transport of bile salts and the formation of structures resembling bile canaliculi. HepG2 spheroids also show increased expression of albumin, urea, xenobiotic transcription factors, phase I and II drug metabolism enzymes and transporters. Consistent with this, cytochrome P450-mediated metabolism is significantly higher in HepG2 spheroids compared to monolayer cultures. This highly differentiated phenotype can be maintained in 384-well microtiter plates for at least 28 days. Toxicity assessment studies with this model showed an increased sensitivity in identifying hepatotoxic compounds with repeated dosing regimens. This simple and robust high-throughput-compatible methodology may have potential for use in toxicity screening assays and mechanistic studies and may represent an alternative to animal models for studying DILI.

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.

Model steatogenic compounds (amiodarone, valproic acid, and tetracycline) alter lipid metabolism by different mechanisms in mouse liver slices

Although drug induced steatosis represents a mild type of hepatotoxicity it can progress into more severe non-alcoholic steatohepatitis. Current models used for safety assessment in drug development and chemical risk assessment do not accurately predict steatosis in humans. Therefore, new models need to be developed to screen compounds for steatogenic properties. We have studied the usefulness of mouse precision-cut liver slices (PCLS) as an alternative to animal testing to gain more insight into the mechanisms involved in the steatogenesis. To this end, PCLS were incubated 24 h with the model steatogenic compounds: amiodarone (AMI), valproic acid (VA), and tetracycline (TET). Transcriptome analysis using DNA microarrays was used to identify genes and processes affected by these compounds. AMI and VA upregulated lipid metabolism, whereas processes associated with extracellular matrix remodelling and inflammation were downregulated. TET downregulated mitochondrial functions, lipid metabolism, and fibrosis. Furthermore, on the basis of the transcriptomics data it was hypothesized that all three compounds affect peroxisome proliferator activated-receptor (PPAR) signaling. Application of PPAR reporter assays classified AMI and VA as PPARγ and triple PPARα/(β/δ)/γ agonist, respectively, whereas TET had no effect on any of the PPARs. Some of the differentially expressed genes were considered as potential candidate biomarkers to identify PPAR agonists (i.e. AMI and VA) or compounds impairing mitochondrial functions (i.e. TET). Finally, comparison of our findings with publicly available transcriptomics data showed that a number of processes altered in the mouse PCLS was also affected in mouse livers and human primary hepatocytes exposed to known PPAR agonists. Thus mouse PCLS are a valuable model to identify early mechanisms of action of compounds altering lipid metabolism.