Gene expression profiling of the PPAR-alpha agonist ciprofibrate in the cynomolgus monkey liver

MASLD/MASH and type 2 diabetes: two sides of the same coin? From single PPAR to pan-PPAR agonists

Type 2 diabetes (T2D) and metabolic dysfunction-associated steatotic liver disease (MASLD), mainly related to nutrition and lack of physical activity, are both very common conditions, share several disease pathways and clinical manifestations, and increasingly co-occur with disease progression. Insulin resistance is an upstream node in the biology of both conditions and triggers liver parenchymal injury, inflammation and fibrosis. Peroxisome proliferator-activated receptor (PPAR) nuclear transcription factors are master regulators of energy homeostasis - insulin signaling in liver, adipose and skeletal muscle tissue - and affect immune and fibrogenesis pathways. Among distinct yet overlapping effects, PPARα regulates lipid metabolism and energy expenditure, PPAR β/δ has anti-inflammatory effects and increases glucose uptake by skeletal muscle, while PPARγ improves insulin sensitivity and exerts direct antifibrotic effects on hepatic stellate cells. Together PPARs thus represent pharmacological targets across the entire biology of MASH. Single PPAR agonists are approved for hypertriglyceridemia (PPARα) and T2D (PPARγ), but these, as well as dual PPAR agonists, have shown mixed results as anti-MASH treatments in clinical trials. Agonists of all three PPAR isoforms have the potential to improve the full disease spectrum from insulin resistance to fibrosis, and correspondingly to improve cardiometabolic and hepatic health, as has been shown (phase II data) with the pan-PPAR agonist lanifibranor.

Treating NASH by targeting peroxisome proliferator-activated receptors

The pathophysiology of non-alcoholic steatohepatitis (NASH) encompasses a complex set of intra- and extrahepatic driving mechanisms, involving numerous metabolic, inflammatory, vascular and fibrogenic pathways. The peroxisome proliferator-activated receptors (PPARs) α, β/δ and γ belong to the nuclear receptor family of ligand-activated transcription factors. Activated PPARs modulate target tissue transcriptomic profiles, enabling the body's adaptation to changing nutritional, metabolic and inflammatory environments. PPARs hence regulate several pathways involved in NASH pathogenesis. Whereas single PPAR agonists exert robust anti-NASH activity in several preclinical models, their clinical effects on histological endpoints of NASH resolution and fibrosis regression appear more modest. Simultaneous activation of several PPAR isotypes across different organs and within-organ cell types, resulting in pleiotropic actions, enhances the therapeutic potential of PPAR agonists as pharmacological agents for NASH and NASH-related hepatic and extrahepatic morbidity, with some compounds having already shown clinical efficacy on histological endpoints.

Peroxisome Proliferator-Activated Receptor Activation in Precision-Cut Bovine Liver Slices Reveals Novel Putative PPAR Targets in Periparturient Dairy Cows

Metabolic challenges experienced by dairy cows during the transition between pregnancy and lactation (also known as peripartum), are of considerable interest from a nutrigenomic perspective. The mobilization of large amounts of non-esterified fatty acids (NEFA) leads to an increase in NEFA uptake in the liver, the excess of which can cause hepatic accumulation of lipids and ultimately fatty liver. Interestingly, peripartum NEFA activate the Peroxisome Proliferator-activated Receptor (PPAR), a transcriptional regulator with known nutrigenomic properties. The study of PPAR activation in the liver of periparturient dairy cows is thus crucial; however, current in vitro models of the bovine liver are inadequate, and the isolation of primary hepatocytes is time consuming, resource intensive, and prone to errors, with the resulting cells losing characteristic phenotypical traits within hours. The objective of the current study was to evaluate the use of precision-cut liver slices (PCLS) from liver biopsies as a model for PPAR activation in periparturient dairy cows. Three primiparous Jersey cows were enrolled in the experiment, and PCLS from each were prepared prepartum (−8.0 ± 3.6 DIM) and postpartum (+7.7± 1.2 DIM) and treated independently with a variety of PPAR agonists and antagonists: the PPARα agonist WY-14643 and antagonist GW-6471; the PPARδ agonist GW-50156 and antagonist GSK-3787; and the PPARγ agonist rosiglitazone and antagonist GW-9662. Gene expression was assayed through RT-qPCR and RNAseq, and intracellular triacylglycerol (TAG) concentration was measured. PCLS obtained from postpartum cows and treated with a PPARγ agonist displayed upregulation of ACADVL and LIPC while those treated with PPARδ agonist had increased expression of LIPC, PPARD, and PDK4. In PCLS from prepartum cows, transcription of LIPC was increased by all PPAR agonists and NEFA. TAG concentration tended to be larger in tissue slices treated with PPARδ agonist compared to CTR. Use of PPAR isotype-specific antagonists in PCLS cultivated in autologous blood serum failed to decrease expression of PPAR targets, except for PDK4, which was confirmed to be a PPARδ target. Transcriptome sequencing revealed considerable differences in response to PPAR agonists at a false discovery rate-adjusted p-value of 0.2, with the most notable effects exerted by the PPARδ and PPARγ agonists. Differentially expressed genes were mainly related to pathways involved with lipid metabolism and the immune response. Among differentially expressed genes, a subset of 91 genes were identified as novel putative PPAR targets in the bovine liver, by cross-referencing our results with a publicly available dataset of predicted PPAR target genes, and supplementing our findings with prior literature. Our results provide important insights on the use of PCLS as a model for assaying PPAR activation in the periparturient dairy cow.

Review article: vascular effects of PPARs in the context of NASH

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors known to regulate glucose and fatty acid metabolism, inflammation, endothelial function and fibrosis. PPAR isoforms have been extensively studied in metabolic diseases, including type 2 diabetes and cardiovascular diseases. Recent data extend the key role of PPARs to liver diseases coursing with vascular dysfunction, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

AIM

This review summarises and discusses the pathobiological role of PPARs in cardiovascular diseases with a special focus on their impact and therapeutic potential in NAFLD and NASH.

RESULTS AND CONCLUSIONS

PPARs may be attractive for the treatment of NASH due to their liver-specific effects but also because of their efficacy in improving cardiovascular outcomes, which may later impact liver disease. Assessment of cardiovascular disease in the context of NASH trials is, therefore, of the utmost importance, both from a safety and efficacy perspective.

An evaluation of maternal serum dynamic thiol-disulfide homeostasis and ischemia modified albumin changes in pregnant women with COVID-19

Objective:

It is thought that oxidative stress, free radicals, reactive oxygen species and reactive nitrogen species affect the pathophysiology of coronavirus disease-2019 (COVID-19). This study aimed to evaluate the oxidative status in pregnant patients with COVID-19 infection according to the changes seen in the levels of maternal serum thiol-disulfide and ischemia-modified albumin (IMA).

Materials and Methods:

A study group was formed of 40 pregnant women with confirmed COVID-19 infection (study group) and a control group of 40 healthy pregnant women with no risk factors determined. In this prospective, case-controlled study, analyses were made of the maternal serum native thiol, total thiol, disulfide, IMA, and disulfide/native thiol concentrations.

Results:

The maternal serum native thiol and total thiol concentrations in the study group were determined to be statistically significantly lower (p=0.007 and p=0.006, respectively), and the disulfide/native thiol ratio was higher but not to a level of statistical significance (p=0.473). There was no difference between the two groups regarding IMA levels (p=0.731).

Conclusion:

The thiol-disulfide balance was seen to shift in the oxidant direction in pregnancies with COVID-19, which might support the view that ischemic processes play a role in the etiopathogenesis of this novel disease.

Transcriptomic analyses of livers from mice exposed to 1,4-dioxane for up to 90 days to assess potential mode(s) of action underlying liver tumor development

1,4-Dioxane is a volatile organic compound with industrial and commercial applications as a solvent and in the manufacture of other chemicals. 1,4-Dioxane has been demonstrated to induce liver tumors in chronic rodent bioassays conducted at very high doses. The available evidence for 1,4-dioxane-induced liver tumors in rodents aligns with a threshold-dependent mode of action (MOA), with the underlying mechanism being less clear in the mouse than in rats. To gain a better understanding of the underlying molecular mechanisms related to liver tumor development in mice orally exposed to 1,4-dioxane, transcriptomics analysis was conducted on liver tissue collected from a 90-day drinking water study in female B6D2F₁/Crl mice (Lafranconi et al., 2020). Using tissue samples from female mice exposed to 1,4-dioxane in the drinking water at concentrations of 0, 40, 200, 600, 2,000 or 6,000 ppm for 7, 28, and 90 days, transcriptomic analyses demonstrate minimal treatment effects on global gene expression at concentrations below 600 ppm. At higher concentrations, genes involved in phase II metabolism and mitotic cell cycle checkpoints were significantly upregulated. There was an overall lack of enrichment of genes related to DNA damage response. The increase in mitotic signaling is most prevalent in the livers of mice exposed to 1,4-dioxane at the highest concentrations for 90 days. This finding aligns with phenotypic changes reported by Lafranconi et al. (2020) after 90-days of exposure to 6,000 ppm 1,4-dioxane in the same tissues. The transcriptomics analysis further supports overarching study findings demonstrating a non-mutagenic, threshold-based, mitogenic MOA for 1,4-dioxane-induced liver tumors.

Coagulopathy in Malnourished Mice Is Sexually Dimorphic and Regulated by Nutrient-Sensing Nuclear Receptors

Liver dysfunction, including coagulopathy, is a prominent feature of protein-energy malnutrition. To identify mechanisms underlying malnutrition-associated coagulopathy, we administered a low-protein low-fat diet to lactating dams and examined hepatic transcription and plasma coagulation parameters in young adult weanlings. Malnutrition impacted body composition to a greater extent in male versus female mice. Transcriptional profiles suggested opposing effects of nutrient-sensing nuclear receptors, namely induction of peroxisome proliferator-activated receptor α (PPARα) targets and repression of farnesoid-X-receptor (FXR) targets. Coagulopathy with decreased synthesis of fibrinogen-α (FGA) and factor 11 (F11) was observed in malnourished male animals but not female animals. In primary mouse hepatocytes, FXR agonist increased and PPARα agonist decreased Fga and F11 messenger RNA expression. Nuclear receptor DNA response elements were identified in the Fga and F11 gene regulatory regions, and opposing effects of FXR and PPARα were confirmed with luciferase assays. Unexpectedly, hepatic PPARα protein was markedly depleted in malnourished male liver and was not enriched on Fga or F11 response elements. Rather, there was loss of FXR binding at these response elements. Reduced PPARα protein was associated with loss of hepatocyte peroxisomes, which are necessary for bile acid biosynthesis, and with decreased concentrations of bile acids that function as FXR ligands, most notably the FXR agonist chenodeoxycholic acid. Conclusion: Malnutrition impairs growth and liver synthetic function more severely in male mice than in female mice. Malnourished male mice are coagulopathic and exhibit decreased hepatocyte peroxisomes, FXR agonist bile acids, FXR binding on Fga and F11 gene regulatory elements, and coagulation factor synthesis. These effects are absent in female mice, which have low baseline levels of PPARα, suggesting that nutrient-sensing nuclear receptors regulate coagulation factor synthesis in response to host nutritional status in a sex-specific manner.

Alzheimer's Disease: Protective Effects of Mycobacterium vaccae, a Soil-Derived Mycobacterium with Anti-Inflammatory and Anti-Tubercular Properties, on the Proteomic Profiles of Plasma and Cerebrospinal Fluid in Rats

BACKGROUND

Alzheimer's disease (AD) is an inflammatory neurodegenerative disease that may be associated with prior bacterial infections. Microbial "old friends" can suppress exaggerated inflammation in response to disease-causing infections or increase clearance of pathogens such as Mycobacterium tuberculosis, which causes tuberculosis (TB). One such "old friend" is Mycobacterium vaccae NCTC 11659, a soil-derived bacterium that has been proposed either as a vaccine for prevention of TB, or as immunotherapy for the treatment of TB when used alongside first line anti-TB drug treatment.

OBJECTIVE

The goal of this study was to use a hypothesis generating approach to explore the effects of M. vaccae on physiological changes in the plasma and cerebrospinal fluid (CSF).

METHODS

Liquid chromatography-tandem mass spectrometry-based proteomics were performed in plasma and CSF of adult male rats after immunization with a heat-killed preparation of M. vaccae NCTC 11659 or borate-buffered saline vehicle. Gene enrichment analysis and analysis of protein-protein interactions were performed to integrate physiological network changes in plasma and CSF. We used RT-qPCR to assess immune and metabolic gene expression changes in the hippocampus.

RESULTS

In both plasma and CSF, immunization with M. vaccae increased proteins associated with immune activation and downregulated proteins corresponding to lipid (including phospholipid and cholesterol) metabolism. Immunization with M. vaccae also increased hippocampal expression of interleukin-4 (IL-4) mRNA, implicating anti-inflammatory effects in the central nervous system.

CONCLUSION

M. vaccae alters host immune activity and lipid metabolism. These data are consistent with the hypothesis that microbe-host interactions may protect against possible infection-induced, inflammation-related cognitive impairments.

Hepatocyte p53 ablation induces metabolic dysregulation that is corrected by food restriction and vertical sleeve gastrectomy in mice

P53 has been implicated in the pathogenesis of obesity and diabetes; however, the mechanisms and tissue sites of action are incompletely defined. Therefore, we investigated the role of hepatocyte p53 in metabolic homeostasis using a hepatocyte-specific p53 knockout mouse model. To gain further mechanistic insight, we studied mice under two complementary conditions of restricted weight gain: vertical sleeve gastrectomy (VSG) or food restriction. VSG or sham surgery was performed in high-fat diet-fed male hepatocyte-specific p53 wild-type and knockout littermates. Sham-operated mice were fed ad libitum or food restricted to match their body weight to VSG-operated mice. Hepatocyte-specific p53 ablation in sham-operated ad libitum-fed mice impaired glucose homeostasis, increased body weight, and decreased energy expenditure without changing food intake. The metabolic deficits induced by hepatocyte-specific p53 ablation were corrected, in part by food restriction, and completely by VSG. Unlike food restriction, VSG corrected the effect of hepatocyte p53 ablation to lower energy expenditure, resulting in a greater improvement in glucose homeostasis compared with food restricted mice. These data reveal an important new role for hepatocyte p53 in the regulation of energy expenditure and body weight and suggest that VSG can improve alterations in energetics associated with p53 dysregulation.

Transcriptomic Analysis of Gonadal Adipose Tissue in Male Mice Exposed Perinatally to 2,2',4,4'-Tetrabromodiphenyl Ether (BDE-47)

For the majority of lipophilic compounds, adipose tissue is traditionally considered as a storage depot and only rarely as a target organ. Meanwhile, abnormalities in adipose tissue physiology induced by chemical exposure may contribute to the current epidemic of obesity and metabolic diseases. Polybrominated diphenyl ethers (PBDEs) are a group of lipophilic flame retardants found in the majority of human samples in North America. Their ability to alter the physiology of adipose tissue is unknown. We exposed pregnant mice to 0.2 mg/kg body weight/day of BDE-47 perinatally. Transcriptomic changes in gonadal adipose tissue were analyzed in male offspring using the RNA-seq approach with subsequent bioinformatic analysis. The expression of genes of coagulation and complement cascade, de novo lipogenesis, and xenobiotic metabolism was altered in response to BDE-47 exposure. The affected molecular network included the following hubs: PPARα, HNF1A, and HNF4. These findings suggest that adipose tissue should be considered a target tissue for BDE-47, in addition to its role as a storage depot. This study also builds a background for a targeted search of sensitive phenotypic endpoints of BDE-47 exposure, including lipid profile parameters and coagulation factors in circulation. Additional studies are needed to investigate the role of PBDEs as an obesogen.

The PPARα-dependent rodent liver tumor response is not relevant to humans: addressing misconceptions

A number of industrial chemicals and therapeutic agents cause liver tumors in rats and mice by activating the nuclear receptor peroxisome proliferator-activated receptor α (PPARα). The molecular and cellular events by which PPARα activators induce rodent hepatocarcinogenesis have been extensively studied elucidating a number of consistent mechanistic changes linked to the increased incidence of liver neoplasms. The weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis is summarized here. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators. The key events (KE) identified in the MOA are PPARα activation (KE1), alteration in cell growth pathways (KE2), perturbation of hepatocyte growth and survival (KE3), and selective clonal expansion of preneoplastic foci cells (KE4), which leads to the apical event-increases in hepatocellular adenomas and carcinomas (KE5). In addition, a number of concurrent molecular and cellular events have been classified as modulating factors, because they potentially alter the ability of PPARα activators to increase rodent liver cancer while not being key events themselves. These modulating factors include increases in oxidative stress and activation of NF-kB. PPARα activators are unlikely to induce liver tumors in humans due to biological differences in the response of KEs downstream of PPARα activation. This conclusion is based on minimal or no effects observed on cell growth pathways and hepatocellular proliferation in human primary hepatocytes and absence of alteration in growth pathways, hepatocyte proliferation, and tumors in the livers of species (hamsters, guinea pigs and cynomolgus monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Despite this overwhelming body of evidence and almost universal acceptance of the PPARα MOA and lack of human relevance, several reviews have selectively focused on specific studies that, as discussed, contradict the consensus opinion and suggest uncertainty. In the present review, we systematically address these most germane suggested weaknesses of the PPARα MOA.

Crosstalk between Receptor and Non-receptor Mediated Chemical Modes of Action in Rat Livers Converges through a Dysregulated Gene Expression Network at Tumor Suppressor Tp53

Chemicals, toxicants, and environmental stressors mediate their biologic effect through specific modes of action (MOAs). These encompass key molecular events that lead to changes in the expression of genes within regulatory pathways. Elucidating shared biologic processes and overlapping gene networks will help to better understand the toxicologic effects on biological systems. In this study we used a weighted network analysis of gene expression data from the livers of male Sprague-Dawley rats exposed to chemicals that elicit their effects through receptor-mediated MOAs (aryl hydrocarbon receptor, orphan nuclear hormone receptor, or peroxisome proliferator-activated receptor-α) or non-receptor-mediated MOAs (cytotoxicity or DNA damage). Four gene networks were highly preserved and statistically significant in each of the two MOA classes. Three of the four networks contain genes that enrich for immunity and defense. However, many canonical pathways related to an immune response were activated from exposure to the non-receptor-mediated MOA chemicals and deactivated from exposure to the receptor-mediated MOA chemicals. The top gene network contains a module with 33 genes including tumor suppressor TP53 as the central hub which was slightly up-regulated in gene expression compared to control. Although, there is crosstalk between the two MOA classes of chemicals at the TP53 gene network, more than half of the genes are dysregulated in opposite directions. For example, Thromboxane A Synthase 1 (Tbxas1), a cytochrome P450 protein coding gene regulated by Tp53, is down-regulated by exposure to the receptor-mediated chemicals but up-regulated by the non-receptor-mediated chemicals. The regulation of gene expression by the chemicals within MOA classes was consistent despite varying alanine transaminase and aspartate aminotransferase liver enzyme measurements. These results suggest that overlap in toxicologic pathways by chemicals with different MOAs provides common mechanisms for discordant regulation of gene expression within molecular networks.

Nutrient-sensing nuclear receptors PPARα and FXR control liver energy balance

The nuclear receptors PPARα (encoded by NR1C1) and farnesoid X receptor (FXR, encoded by NR1H4) are activated in the liver in the fasted and fed state, respectively. PPARα activation induces fatty acid oxidation, while FXR controls bile acid homeostasis, but both nuclear receptors also regulate numerous other metabolic pathways relevant to liver energy balance. Here we review evidence that they function coordinately to control key nutrient pathways, including fatty acid oxidation and gluconeogenesis in the fasted state and lipogenesis and glycolysis in the fed state. We have also recently reported that these receptors have mutually antagonistic impacts on autophagy, which is induced by PPARα but suppressed by FXR. Secretion of multiple blood proteins is a major drain on liver energy and nutrient resources, and we present preliminary evidence that the liver secretome may be directly suppressed by PPARα, but induced by FXR. Finally, previous studies demonstrated a striking deficiency in bile acid levels in malnourished mice that is consistent with results in malnourished children. We present evidence that hepatic targets of PPARα and FXR are dysregulated in chronic undernutrition. We conclude that PPARα and FXR function coordinately to integrate liver energy balance.

PPARα (Peroxisome Proliferator-activated Receptor α) Activation Reduces Hepatic CEACAM1 Protein Expression to Regulate Fatty Acid Oxidation during Fasting-refeeding Transition

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is expressed at high levels in the hepatocyte, consistent with its role in promoting insulin clearance in liver. CEACAM1 also mediates a negative acute effect of insulin on fatty acid synthase activity. Western blot analysis reveals lower hepatic CEACAM1 expression during fasting. Treating of rat hepatoma FAO cells with Wy14,643, an agonist of peroxisome proliferator-activated receptor α (PPARα), rapidly reduces Ceacam1 mRNA and CEACAM1 protein levels within 1 and 2 h, respectively. Luciferase reporter assay shows a decrease in the promoter activity of both rat and mouse genes by Pparα activation, and 5'-deletion and block substitution analyses reveal that the Pparα response element between nucleotides -557 and -543 is required for regulation of the mouse promoter activity. Chromatin immunoprecipitation analysis demonstrates binding of liganded Pparα toCeacam1promoter in liver lysates ofPparα(+/+), but notPparα(-/-)mice fed a Wy14,643-supplemented chow diet. Consequently, Wy14,643 feeding reduces hepatic Ceacam1 mRNA and CEACAM1 protein levels, thus decreasing insulin clearance to compensate for compromised insulin secretion and maintain glucose homeostasis and insulin sensitivity in wild-type mice. Together, the data show that the low hepatic CEACAM1 expression at fasting is mediated by Pparα-dependent mechanisms. Changes in CEACAM1 expression contribute to the coordination of fatty acid oxidation and insulin action in the fasting-refeeding transition.

Fenofibrate increases radiosensitivity in head and neck squamous cell carcinoma via inducing G2/M arrest and apoptosis

Radiation therapy is an important treatment for head and neck squamous cell carcinoma (HNSCC). However, how to promote radiation sensitivity in HNSCC remains a challenge. This study aimed to investigate the radiosensitizing effects of fenofibrate on HNSCC and explore the underlying mechanisms. HNSCC cell lines CNE-2 and KB were subjected to ionizing radiation (IR), in the presence or absence of fenofibrate treatment. Cell growth and survival, apoptosis and cell cycle were evaluated. In addition, CNE-2 cells were xenografted into nude mice and subjected to IR and/ or fenofibrate treatment. The expression of cyclinB and CDK1 was detected by Western blotting. Our results showed that fenofibrate efficiently radiosensitized HNSCC cells and xenografts in mice, and induced apoptosis and G2/M arrest via reducing the activity of the CDK1/cyclinB1 kinase complex. These data suggest that fenofibrate could be a promising radiosensitizer for HNSCC radiotherapy.

Influence of fenofibrate treatment on triacylglycerides, diacylglycerides and fatty acids in fructose fed rats

Fenofibrate (FF) lowers plasma triglycerides via PPARα activation. Here, we analyzed lipidomic changes upon FF treatment of fructose fed rats. Three groups with 6 animals each were defined as control, fructose-fed and fructose-fed/FF treated. Male Wistar Unilever Rats were subjected to 10% fructose-feeding for 20 days. On day 14, fenofibrate treatment (100 mg/kg p.o.) was initiated and maintained for 7 days. Lipid species in serum were analyzed using mass spectrometry (ESI-MS/MS; LC-FT-MS, GC-MS) on days 0, 14 and 20 in all three groups. In addition, lipid levels in liver and intestine were determined. Short-chain TAGs increased in serum and liver upon fructose-feeding, while almost all TAG-species decreased under FF treatment. Long-chain unsaturated DAG-levels (36:1, 36:2, 36:4, 38:3, 38:4, 38:5) increased upon FF treatment in rat liver and decreased in rat serum. FAs, especially short-chain FAs (12:0, 14:0, 16:0) increased during fructose-challenge. VLDL secretion increased upon fructose-feeding and together with FA-levels decreased to control levels during FF treatment. Fructose challenge of de novo fatty acid synthesis through fatty acid synthase (FAS) may enhance the release of FAs ≤ 16:0 chain length, a process reversed by FF-mediated PPARα-activation.

Mechanism of action of anti-hypercholesterolemia drugs and their resistance

Coronary artery disease is one of the leading causes of death worldwide. One of the significant causes of this disease is hypercholesterolemia which is the result of various genetic alterations that are associated with the accumulation of specific classes of lipoprotein particles in plasma. A number of drugs are used to treat hypercholesterolemia like statin, fibrate, bile acid sequestrants, niacin, ezetimibe, omega-3 fatty acids and natural extracts. It has been observed that these drugs show diverse response in different individuals. The present review explains the mechanism of action of these drugs as well as mechanism of its lesser effectiveness or resistance in some individuals. There are various identified genetic variations that are associated with diversity in the drugs response. Therefore, present study helps to understand the ethiology of drug mechanism and resistance developed against drugs used to treat hypercholesterolemia.

Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPARα) as a case study

Several therapeutic agents and industrial chemicals induce liver tumors in rodents through the activation of the peroxisome proliferator-activated receptor alpha (PPARα). The cellular and molecular events by which PPARα activators induce rodent hepatocarcinogenesis has been extensively studied and elucidated. This review summarizes the weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis and identifies gaps in our knowledge of this MOA. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators including a phthalate ester plasticizer di(2-ethylhexyl) phthalate (DEHP) and the drug gemfibrozil. While biologically plausible in humans, the hypothesized key events in the rodent MOA, for PPARα activators, are unlikely to induce liver tumors in humans because of toxicodynamic and biological differences in responses. This conclusion is based on minimal or no effects observed on growth pathways, hepatocellular proliferation and liver tumors in humans and/or species (including hamsters, guinea pigs and cynomolgous monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Overall, the panel concluded that significant quantitative differences in PPARα activator-induced effects related to liver cancer formation exist between rodents and humans. On the basis of these quantitative differences, most of the workgroup felt that the rodent MOA is "not relevant to humans" with the remaining members concluding that the MOA is "unlikely to be relevant to humans". The two groups differed in their level of confidence based on perceived limitations of the quantitative and mechanistic knowledge of the species differences, which for some panel members strongly supports but cannot preclude the absence of effects under unlikely exposure scenarios.

PPARα-mediated responses in human adult liver stem cells: In vivo/in vitro and cross-species comparisons

The peroxisome proliferator-activated receptor α (PPARα) is a ligand-activated transcription factor that regulates a variety of biological processes including lipid metabolism and energy homeostasis. Peroxisome proliferators (PPs) are carcinogens in rodents, while humans are resistant to peroxisome proliferation and carcinogenesis. In this study, we examined the differential gene expression elicited by clofibrate (CLO) and WY-14,643 (WY) in C57BL/6 mouse liver compared to responses in human HepG2 hepatoma and HL1-1 adult stem cells. Mice were gavaged with sesame oil, 300mg/kg CLO or WY for 2, 4, 8, 12, 18 or 24h, or daily for 4 or 14 days. Although no significant changes in body weight gain were observed, WY induced relative liver weight at 4 and 14 days. Genome-wide hepatic gene expression analysis identified 719 and 1443 differentially expressed unique genes elicited by CLO and WY, respectively (|fold change|>1.5, P1(t)>0.99). Functional analysis associated the gene expression changes with lipid metabolism, transport, cell cycle and immune response. Most differentially expressed genes were in common to both treatments and clustered together only at early time points (2-8h). Complementary QRT-PCR studies in human HL1-1 and HepG2 cells treated with 50μM WY or DMSO for 1, 2, 4, 8, 12, 24 or 48h identified a minimal number of conserved orthologous responses (e.g., Pdk4, Adfp and Angptl4) while some genes (i.e., Bmf, a tumor suppressor) exhibited induction in human cells but repression in mice. These data suggest that PPs elicit species-specific PPARα-mediated gene expression.

Inhibition of mitogen-activated protein kinase Erk1/2 promotes protein degradation of ATP binding cassette transporters A1 and G1 in CHO and HuH7 cells

Signal transduction modulates expression and activity of cholesterol transporters. We recently demonstrated that the Ras/mitogen-activated protein kinase (MAPK) signaling cascade regulates protein stability of Scavenger Receptor BI (SR-BI) through Proliferator Activator Receptor (PPARα) -dependent degradation pathways. In addition, MAPK (Mek/Erk 1/2) inhibition has been shown to influence liver X receptor (LXR) -inducible ATP Binding Cassette (ABC) transporter ABCA1 expression in macrophages. Here we investigated if Ras/MAPK signaling could alter expression and activity of ABCA1 and ABCG1 in steroidogenic and hepatic cell lines. We demonstrate that in Chinese Hamster Ovary (CHO) cells and human hepatic HuH7 cells, extracellular signal-regulated kinase 1/2 (Erk1/2) inhibition reduces PPARα-inducible ABCA1 protein levels, while ectopic expression of constitutively active H-Ras, K-Ras and MAPK/Erk kinase 1 (Mek1) increases ABCA1 protein expression, respectively. Furthermore, Mek1/2 inhibitors reduce ABCG1 protein levels in ABCG1 overexpressing CHO cells (CHO-ABCG1) and human embryonic kidney 293 (HEK293) cells treated with LXR agonist. This correlates with Mek1/2 inhibition reducing ABCG1 cell surface expression and decreasing cholesterol efflux onto High Density Lipoproteins (HDL). Real Time reverse transcriptase polymerase chain reaction (RT-PCR) and protein turnover studies reveal that Mek1/2 inhibitors do not target transcriptional regulation of ABCA1 and ABCG1, but promote ABCA1 and ABCG1 protein degradation in HuH7 and CHO cells, respectively. In line with published data from mouse macrophages, blocking Mek1/2 activity upregulates ABCA1 and ABCG1 protein levels in human THP1 macrophages, indicating opposite roles for the Ras/MAPK pathway in the regulation of ABC transporter activity in macrophages compared to steroidogenic and hepatic cell types. In summary, this study suggests that Ras/MAPK signaling modulates PPARα- and LXR-dependent protein degradation pathways in a cell-specific manner to regulate the expression levels of ABCA1 and ABCG1 transporters.

Reelin is involved in the crypt-villus unit homeostasis

Intestinal myofibroblasts secrete substances that control organogenesis and wound repair of the intestine. The myofibroblasts of the rat small intestine express reelin and the present work explores whether reelin regulates crypt-villus unit homeostasis using normal mice and mice with the reelin gene disrupted (reeler). The results reveal that mouse small intestine expresses reelin, its receptors apolipoprotein E receptor 2 (ApoER2) and very low-density lipoprotein receptor (VldlR) and the reelin effector protein Disabled-1 (Dab1) and that reelin expression is restricted to myofibroblasts. The absence of reelin significantly reduces epithelial cell proliferation, migration, and apoptosis and the number of Paneth cells. These effects are observed during the suckling, weaning, and adult periods. The number of Goblet cells is increased in the 2-month-old reeler mice. The absence of reelin also expands the extracellular space of the adherens junctions and desmosomes without significantly affecting either the tight-junction structure or the epithelial paracellular permeability. In conclusion, this is the first in vivo work showing that the absence of reelin alters intestinal epithelium homeostasis.

Comparative gene expression profiling in human-induced pluripotent stem cell--derived cardiocytes and human and cynomolgus heart tissue

Cardiotoxicity is one of the leading causes of drug attrition. Current in vitro models insufficiently predict cardiotoxicity, and there is a need for alternative physiologically relevant models. Here we describe the gene expression profile of human-induced pluripotent stem cell-derived cardiocytes (iCC) postthaw over a period of 42 days in culture and compare this profile to human fetal and adult as well as adult cynomolgus nonhuman primate (NHP, Macaca fascicularis) heart tissue. Our results indicate that iCC express relevant cardiac markers such as ion channels (SCN5A, KCNJ2, CACNA1C, KCNQ1, and KCNH2), tissue-specific structural markers (MYH6, MYLPF, MYBPC3, DES, TNNT2, and TNNI3), and transcription factors (NKX2.5, GATA4, and GATA6) and lack the expression of stem cell markers (FOXD3, GBX2, NANOG, POU5F1, SOX2, and ZFP42). Furthermore, we performed a functional evaluation of contractility of the iCC and showed functional and pharmacological correlations with myocytes isolated from adult NHP hearts. These results suggest that stem cell-derived cardiocytes may represent a novel in vitro model to study human cardiac toxicity with potential ex vivo and in vivo translation.

Gene expression profiling of the synergy of 5-aza-2'-deoxycytidine and paclitaxel against renal cell carcinoma

Background

Renal cell carcinoma (RCC) is one of the most common kidney cancers and is highly resistant to chemotherapy. We previously demonstrated that 5-aza-2^′-deoxycytidine (DAC) could significantly increase the susceptibility of renal cell carcinoma (RCC) cells to paclitaxel (PTX) treatment in vitro, and showed the synergy of DAC and PTX against RCC. The purpose of this study is to investigated the gene transcriptional alteration and investigate possible molecular mechanism and pathways implicated in the synergy of DAC and PTX against RCC.

Methods

cDNA microarray was performed and coupled with real-time PCR to identify critical genes in the synergistic mechanism of both agents against RCC cells. Various patterns of gene expression were observed by cluster analysis. IPA software was used to analyze possible biological pathways and to explore the inter-relationships between interesting network genes.

Results

We found that lymphoid enhancer-binding factor 1 (LEF1), transforming growth factor β-induced (TGFBI), C-X-C motif ligand 5 (CXCL5) and myelocytomatosis viral related oncogene (c-myc) may play a pivotal role in the synergy of DAC and PTX. The PI3K/Akt pathway and other pathways associated with cyclins, DNA replication and cell cycle/mitotic regulation were also associated with the synergy of DAC and PTX against RCC.

Conclusion

The activation of PI3K/Akt-LEF1/β-catenin pathway could be suppressed synergistically by two agents and that PI3K/Akt-LEF1/β-catenin pathway is participated in the synergy of two agents.

Chronic exposure to contaminated drinking water stimulates PPAR expression in mice livers

Mice were fed with source water (SW) and tap water (TW) for 90 d to evaluate hepatotoxicity induced by the drinking water. Histopathologic observation showed no obvious damage to hepatic tissue in the SW and TW groups. However, microarray analysis indicated that the SW and TW exposures affected many metabolic pathways, among which PPAR (peroxisome proliferator-activated receptors) signaling was most susceptible. Immunohistochemical staining demonstrated that both PPAR-α and PPAR-γ were significantly increased in the exposure groups compared to control. Enzyme-linked immunosorbent assay revealed that PPAR-α expression level was increased from 23.37±0.53 ng g(-1) liver weight in control group to 26.60±1.43 ng g(-1) liver weight in SW group and 27.68±1.10 ng g(-1) liver weight in TW group (p<0.05). For PPAR-γ, the expression level was also significantly enhanced from 0.83±0.07 ng g(-1) liver weight in control group to 1.11±0.20 ng g(-1) liver weight in SW group and 1.16±0.07 ng g(-1) liver weight in TW group (p<0.05). The SW and DW posed no obvious hepatotoxicity on mice and PPAR-α/-γ could be used as a novel biomarker to assess public health risk induced by slightly contaminated drinking water.

Liver hypertrophy: a review of adaptive (adverse and non-adverse) changes--conclusions from the 3rd International ESTP Expert Workshop

Preclinical toxicity studies have demonstrated that exposure of laboratory animals to liver enzyme inducers during preclinical safety assessment results in a signature of toxicological changes characterized by an increase in liver weight, hepatocellular hypertrophy, cell proliferation, and, frequently in long-term (life-time) studies, hepatocarcinogenesis. Recent advances over the last decade have revealed that for many xenobiotics, these changes may be induced through a common mechanism of action involving activation of the nuclear hormone receptors CAR, PXR, or PPARα. The generation of genetically engineered mice that express altered versions of these nuclear hormone receptors, together with other avenues of investigation, have now demonstrated that sensitivity to many of these effects is rodent-specific. These data are consistent with the available epidemiological and empirical human evidence and lend support to the scientific opinion that these changes have little relevance to man. The ESTP therefore convened an international panel of experts to debate the evidence in order to more clearly define for toxicologic pathologists what is considered adverse in the context of hepatocellular hypertrophy. The results of this workshop concluded that hepatomegaly as a consequence of hepatocellular hypertrophy without histologic or clinical pathology alterations indicative of liver toxicity was considered an adaptive and a non-adverse reaction. This conclusion should normally be reached by an integrative weight of evidence approach.

Conservation and divergence of chemical defense system in the tunicate Oikopleura dioica revealed by genome wide response to two xenobiotics

Background

Animals have developed extensive mechanisms of response to xenobiotic chemical attacks. Although recent genome surveys have suggested a broad conservation of the chemical defensome across metazoans, global gene expression responses to xenobiotics have not been well investigated in most invertebrates. Here, we performed genome survey for key defensome genes in Oikopleura dioica genome, and explored genome-wide gene expression using high density tiling arrays with over 2 million probes, in response to two model xenobiotic chemicals - the carcinogenic polycyclic aromatic hydrocarbon benzo[a]pyrene (BaP) the pharmaceutical compound Clofibrate (Clo).

Results

Oikopleura genome surveys for key genes of the chemical defensome suggested a reduced repertoire. Not more than 23 cytochrome P450 (CYP) genes could be identified, and neither CYP1 family genes nor their transcriptional activator AhR was detected. These two genes were present in deuterostome ancestors. As in vertebrates, the genotoxic compound BaP induced xenobiotic biotransformation and oxidative stress responsive genes. Notable exceptions were genes of the aryl hydrocarbon receptor (AhR) signaling pathway. Clo also affected the expression of many biotransformation genes and markedly repressed genes involved in energy metabolism and muscle contraction pathways.

Conclusions

Oikopleura has the smallest number of CYP genes among sequenced animal genomes and lacks the AhR signaling pathway. However it appears to have basic xenobiotic inducible biotransformation genes such as a conserved genotoxic stress response gene set. Our genome survey and expression study does not support a role of AhR signaling pathway in the chemical defense of metazoans prior to the emergence of vertebrates.

The PPARα agonists fenofibrate and CP-778875 cause increased β-oxidation, leading to oxidative injury in skeletal and cardiac muscle in the rat

Weak peroxisome proliferator-activated receptor (PPAR) α agonists (fibrates) are used to treat dyslipidemia. This study compared the effects of the potent and selective PPARα agonist CP-778875 on peroxisomal β-oxidation and cardiac and/or skeletal muscle injury with those of the weak PPARα agonist fenofibrate. We hypothesized that these muscle effects are mediated through the PPARα receptor, leading to increased β-oxidation and consequent oxidative stress. CP-778875 (5 or 500 mg/kg) and fenofibrate (600 or 2,000→1,200 mg/kg, dose lowered because of intolerance) were administered to rats for six weeks. Standard end points, serum troponin I, heart and skeletal muscle β-oxidation of palmitoyl-CoA, and acyl co-oxidase (AOX) mRNA were assessed. Both compounds dose-dependently increased the incidence and/or severity of cardiomyocyte degeneration and necrosis, heart weight, troponin I, and skeletal muscle degeneration. Mean heart β-oxidation (3.4- to 5.1-fold control) and AOX mRNA (2.4- to 3.2-fold control) were increased with CP-778875 500 mg/kg and both doses of fenofibrate. β-Oxidation of skeletal muscle was not affected by either compound; however, a significant increase in AOX mRNA (1.6- to 2.1-fold control) was observed with CP-778875 500 mg/kg and both doses of fenofibrate. Taken together, these findings were consistent with PPARα agonism and support the link between increased cardiac and skeletal muscle β-oxidation and resultant muscle injury in the rat.

Comparative transcriptomic and metabolomic analysis of fenofibrate and fish oil treatments in mice

Elevated circulating triglycerides, which are considered a risk factor for cardiovascular disease, can be targeted by treatment with fenofibrate or fish oil. To gain insight into underlying mechanisms, we carried out a comparative transcriptomics and metabolomics analysis of the effect of 2 wk treatment with fenofibrate and fish oil in mice. Plasma triglycerides were significantly decreased by fenofibrate (−49.1%) and fish oil (−21.8%), whereas plasma cholesterol was increased by fenofibrate (+29.9%) and decreased by fish oil (−32.8%). Levels of various phospholipid species were specifically decreased by fish oil, while levels of Krebs cycle intermediates were increased specifically by fenofibrate. Plasma levels of many amino acids were altered by fenofibrate and to a lesser extent by fish oil. Both fenofibrate and fish oil upregulated genes involved in fatty acid metabolism and downregulated genes involved in blood coagulation and fibrinolysis. Significant overlap in gene regulation by fenofibrate and fish oil was observed, reflecting their property as high or low affinity agonist for peroxisome proliferator-activated receptor-α, respectively. Fenofibrate specifically downregulated genes involved in complement cascade and inflammatory response. Fish oil specifically downregulated genes involved in cholesterol and fatty acid biosynthesis and upregulated genes involved in amino acid and arachidonic acid metabolism. Taken together, the data indicate that despite being similarly potent toward modulating plasma free fatty acids, cholesterol, and triglyceride levels, fish oil causes modest changes in gene expression likely via activation of multiple mechanistic pathways, whereas fenofibrate causes pronounced gene expression changes via a single pathway, reflecting the key difference between nutritional and pharmacological intervention.

UPLC-MS-based urine metabolomics reveals indole-3-lactic acid and phenyllactic acid as conserved biomarkers for alcohol-induced liver disease in the Ppara-null mouse model

Since the development and prognosis of alcohol-induced liver disease (ALD) vary significantly with genetic background, identification of a genetic background-independent noninvasive ALD biomarker would significantly improve screening and diagnosis. This study explored the effect of genetic background on the ALD-associated urinary metabolome using the Ppara-null mouse model on two different backgrounds, C57BL/6 (B6) and 129/SvJ (129S), along with their wild-type counterparts. Reversed-phase gradient UPLC-ESI-QTOF-MS analysis revealed that urinary excretion of a number of metabolites, such as ethylsulfate, 4-hydroxyphenylacetic acid, 4-hydroxyphenylacetic acid sulfate, adipic acid, pimelic acid, xanthurenic acid, and taurine, were background-dependent. Elevation of ethyl-β-d-glucuronide and N-acetylglycine was found to be a common signature of the metabolomic response to alcohol exposure in wild-type as well as in Ppara-null mice of both strains. However, increased excretion of indole-3-lactic acid and phenyllactic acid was found to be a conserved feature exclusively associated with the alcohol-treated Ppara-null mouse on both backgrounds that develop liver pathologies similar to the early stages of human ALD. These markers reflected the biochemical events associated with early stages of ALD pathogenesis. The results suggest that indole-3-lactic acid and phenyllactic acid are potential candidates for conserved and pathology-specific high-throughput noninvasive biomarkers for early stages of ALD.

Comparative gene expression profiles induced by PPARγ and PPARα/γ agonists in rat hepatocytes

Species-differential toxic effects have been described with PPARα and PPARγ agonists between rodent and human liver. PPARα agonists (fibrates) are potent hypocholesterolemic agents in humans while they induce peroxisome proliferation and tumors in rodent liver. By contrast, PPARγ agonists (glitazones) and even dual PPARα/γ agonists (glitazars) have caused idiosyncratic hepatic and nonhepatic toxicities in human without evidence of any damage in rodent during preclinical studies. The mechanisms involved in such differences remain largely unknown. Several studies have identified the major target genes of PPARα agonists in rodent liver while no comprehensive analysis has been performed on gene expression changes induced by PPARγ and dual PPARα/γ agonists. Here, we investigated transcriptomes of rat hepatocytes after 24h treatment with two PPARγ (troglitazone and rosiglitazone) and two PPARα/γ (muraglitazar and tesaglitazar) agonists. Although, hierarchical clustering revealed a gene expression profile characteristic of each PPAR agonist class, only a limited number of genes was specifically deregulated by glitazars. Functional analyses showed that many genes known as PPARα targets were also modulated by both PPARγ and PPARα/γ agonists and quantitative differences in gene expression profiles were observed between these two classes. Moreover, most major genes modulated in rat hepatocytes were also found to be deregulated in rat liver after tesaglitazar treatment. Taken altogether, these results support the conclusion that differential toxic effects of PPARα and PPARγ agonists in rodent liver do not result from transcriptional deregulation of major PPAR target genes but rather from qualitative and/or quantitative differential responses of a small subset of genes.

Gene Expression Profiling in Wild-Type and PPARα-Null Mice Exposed to Perfluorooctane Sulfonate Reveals PPARα-Independent Effects

Perfluorooctane sulfonate (PFOS) is a perfluoroalkyl acid (PFAA) and a persistent environmental contaminant found in the tissues of humans and wildlife. Although blood levels of PFOS have begun to decline, health concerns remain because of the long half-life of PFOS in humans. Like other PFAAs, such as, perfluorooctanoic acid (PFOA), PFOS is an activator of peroxisome proliferator-activated receptor-alpha (PPARα) and exhibits hepatocarcinogenic potential in rodents. PFOS is also a developmental toxicant in rodents where, unlike PFOA, its mode of action is independent of PPARα. Wild-type (WT) and PPARα-null (Null) mice were dosed with 0, 3, or 10 mg/kg/day PFOS for 7 days. Animals were euthanized, livers weighed, and liver samples collected for histology and preparation of total RNA. Gene profiling was conducted using Affymetrix 430_2 microarrays. In WT mice, PFOS induced changes that were characteristic of PPARα transactivation including regulation of genes associated with lipid metabolism, peroxisome biogenesis, proteasome activation, and inflammation. PPARα-independent changes were indicated in both WT and Null mice by altered expression of genes related to lipid metabolism, inflammation, and xenobiotic metabolism. Such results are similar to studies done with PFOA and are consistent with modest activation of the constitutive androstane receptor (CAR), and possibly PPARγ and/or PPARβ/δ. Unique treatment-related effects were also found in Null mice including altered expression of genes associated with ribosome biogenesis, oxidative phosphorylation, and cholesterol biosynthesis. Of interest was up-regulation of Cyp7a1, a gene which is under the control of various transcription regulators. Hence, in addition to its ability to modestly activate PPARα, PFOS induces a variety of PPARα-independent effects as well.

Molecular Mechanisms and Genome-Wide Aspects of PPAR Subtype Specific Transactivation. PPAR Res. 2010;2010:pii: 169506. [PMID: 20862367 PMCID: PMC2938449 DOI: 10.1155/2010/169506]

The peroxisome proliferator-activated receptors (PPARs) are central regulators of fat metabolism, energy homeostasis, proliferation, and inflammation. The three PPAR subtypes, PPARα, β/δ, and γ activate overlapping but also very different target gene programs. This review summarizes the insights into PPAR subtype-specific transactivation provided by genome-wide studies and discusses the recent advances in the understanding of the molecular mechanisms underlying PPAR subtype specificity with special focus on the regulatory role of AF-1.

Triclosan: a critical review of the experimental data and development of margins of safety for consumer products

Triclosan (2,4,4'-trichloro-2'-hydroxy-diphenyl ether) is an antibacterial compound that has been used in consumer products for about 40 years. The tolerability and safety of triclosan has been evaluated in human volunteers with little indication of toxicity or sensitization. Although information in humans from chronic usage of personal care products is not available, triclosan has been extensively studied in laboratory animals. When evaluated in chronic oncogenicity studies in mice, rats, and hamsters, treatment-related tumors were found only in the liver of male and female mice. Application of the Human Relevance Framework suggested that these tumors arose by way of peroxisome proliferator-activated receptor alpha (PPARalpha) activation, a mode of action not considered to be relevant to humans. Consequently, a Benchmark Dose (BMDL(10)) of 47 mg/kg/day was developed based on kidney toxicity in the hamster. Estimates of the amount of intake from in the use of representative personal care products for men, women, and children were derived in two ways: (1) using known or assumed triclosan levels in various consumer products and assumed usage patterns (product-based estimates); and (2) using upper bound measured urinary triclosan levels from human volunteers (biomonitoring-based estimates) using data from the Centers for Disease Control and Prevention. For the product-based estimates, the margin of safety (MOS) for the combined exposure estimates of intake from the use of all triclosan-containing products considered were approximately 1000, 730, and 630 for men, women, and children, respectively. The MOS calculated from the biomonitoring-based estimated intakes were 5200, 6700, and 11,750 for men, women, and children, respectively. Based on these results, exposure to triclosan in consumer products is not expected to cause adverse health effects in children or adults who use these products as intended.

Effect of a Large Dose of Di (2-ethylhexyl) phthalate (DEHP) on Hepatic Peroxisome in Cynomolgus Monkeys (Macaca Fascicularis)

To elucidate the effect of a large dose of di (2-ethylhexyl) phthalate (DEHP), a plasticizer and peroxisome proliferator-activated receptor-α (PPARα) agonist, on hepatic peroxisomes, we orally administered 1,000 mg/kg/day, once daily, to 3 male and 4 female cynomolgus monkeys for 28 days consecutively. Light-microscopic and electron microscopic examinations of the liver were carried out in conjunction with measurement of the hepatic fatty acid β-oxidation system (FAOS), carnitine acetyltransferase (CAT) and carnitine palmitoyltransferase (CPT) activities, which are peroxisomal and/or mitochondrial enzyme activities. Electron microscopically, enlargement of the mitochondria was observed with lamellar orientation of the cristae along the major axis. Although the number of peroxisomes showed a tendency to increase when compared with those in a biopsied specimen before treatment, no abnormality in morphology was observed. A slight increase in CPT activity was noted at termination. No changes were noted in hepatic FAOS or CAT activity. In conclusion, although repeated oral treatment of cynomolgus monkeys with a large dose of DEHP induced a subtle increase in the numbers of peroxisomes with slight enlargements of the mitochondria, this low-sensitivity response to peroxisome proliferators in cynomolgus monkeys was considered to be closer to the response in humans than that in rodents.

Hepatic Enzyme Induction

Hepatic enzyme induction is generally an adaptive response associated with increases in liver weight, induction of gene expression, and morphological changes in hepatocytes. The additive growth and functional demands that initiated the response to hepatic enzyme induction cover a wide range of stimuli including pregnancy and lactation, hormonal fluctuations, dietary constituents, infections associated with acute-phase proteins, as well as responses to exposure to xenobiotics. Common xenobiotic enzyme inducers trigger pathways involving the constitutive androstane receptor (CAR), the peroxisome proliferator-activated receptor (PPAR), the aryl hydrocarbon receptor (AhR), and the pregnane-X-receptor (PXR). Liver enlargement in response to hepatic enzyme induction is typically associated with hepatocellular hypertrophy and often, transient hepatocyte hyperplasia. The hypertrophy may show a lobular distribution, with the pattern of lobular zonation and severity reflecting species, strain, and sex differences in addition to effects from specific xenobiotics. Toxicity and hepatocarcinogenicity may occur when liver responses exceed adaptive changes or induced enzymes generate toxic metabolites. These undesirable consequences are influenced by the type and dose of xenobiotic and show considerable species differences in susceptibility and severity that need to be understood for assessing the potential effects on human health from similar exposures to specific xenobiotics.

Use of transcriptomics in understanding mechanisms of drug-induced toxicity

Adverse drug reactions (ADRs) are an important clinical issue and a serious public health risk. Understanding the underlying mechanisms is critical for clinical diagnosis and management of different ADRs. Toxicogenomics can reveal impacts on biological pathways and processes that had not previously been considered to be involved in a drug response. Mechanistic hypotheses can be generated that can then be experimentally tested using the full arsenal of pharmacology, toxicology, molecular biology and genetics. Recent transcriptomic studies on drug-induced toxicity, which have provided valuable mechanistic insights into various ADRs, have been reviewed with a focus on nephrotoxicity and hepatotoxicity. Related issues have been discussed, including extrapolation of mechanistic findings from experimental model systems to humans using blood as a surrogate tissue for organ damage and comparative systems biology approaches.

Role of Esrrg in the fibrate-mediated regulation of lipid metabolism genes in human ApoA-I transgenic mice

We have used a new ApoA-I transgenic mouse model to identify by global gene expression profiling, candidate genes that affect lipid and lipoprotein metabolism in response to fenofibrate treatment. Multilevel bioinformatical analysis and stringent selection criteria (2-fold change, 0% false discovery rate) identified 267 significantly changed genes involved in several molecular pathways. The fenofibrate-treated group did not have significantly altered levels of hepatic human APOA-I mRNA and plasma ApoA-I compared with the control group. However, the treatment increased cholesterol levels to 1.95-fold mainly due to the increase in high-density lipoprotein (HDL) cholesterol. The observed changes in HDL are associated with the upregulation of genes involved in phospholipid biosynthesis and lipid hydrolysis, as well as phospholipid transfer protein. Significant upregulation was observed in genes involved in fatty acid transport and β-oxidation, but not in those of fatty acid and cholesterol biosynthesis, Krebs cycle and gluconeogenesis. Fenofibrate changed significantly the expression of seven transcription factors. The estrogen receptor-related gamma gene was upregulated 2.36-fold and had a significant positive correlation with genes of lipid and lipoprotein metabolism and mitochondrial functions, indicating an important role of this orphan receptor in mediating the fenofibrate-induced activation of a specific subset of its target genes.

Nuclear receptors: the controlling force in drug metabolism of the liver?

The body is in a constant battle to achieve homeostasis; indeed, the robustness with which it can respond to moves away from homeostasis is a vital part in the survival of the organism as a whole. There thus exists a need for a network of sensors that are able to capture, interpret, and respond to alterations in chemical levels that move the body away from homeostasis and this applies to both endogenous and exogenous chemicals. With respect to external chemicals (xenobiotics), this xenosensing is often carried out through specific interactions with cellular receptors. The phenomenon of 'xenosensing' has attracted much interest of late, whereby xenobiotics interact with receptors resulting in the activation of a battery of genes mediating oxidative drug metabolism, conjugation, and transport, thereby enhancing the elimination of the xenobiotic by the organism. However, this beneficial response is counterbalanced by the increasingly recognized role of nuclear receptors in mediating drug-drug interactions via enzyme induction or the production of toxicity through interaction with endogenous pathways. This review will focus on the role of nuclear receptors in mediating these effects, and how such knowledge will contribute to a mechanism-based risk assessment for xenobiotics.

Untargeted metabolomic profiling as an evaluative tool of fenofibrate-induced toxicology in Fischer 344 male rats

Peroxisome proliferator-activated receptor-alpha (PPARalpha) agonists such as fenofibrate are used to treat dyslipidemia. Although fenofibrate is considered safe in humans, it is known to cause hepatocarcinogenesis in rodents. To evaluate untargeted metabolic profiling as a tool for gaining insight into the underlying pharmacology and hepatotoxicology, Fischer 344 male rats were dosed with 300 mg/kg/day of fenofibrate for 14 days and the urine and plasma were analyzed on days 2 and 14. A combination of liquid and gas chromatography mass spectrometry returned the profiles of 486 plasma and 932 urinary metabolites. Aside from known pharmacological effects, such as accelerated fatty acid beta-oxidation and reduced plasma cholesterol, new observations on the drug's impact on cellular metabolism were generated. Reductions in TCA cycle intermediates and biochemical evidence of lactic acidosis demonstrated that energy metabolism homeostasis was altered. Perturbation of the glutathione biosynthesis and elevation of oxidative stress markers were observed. Furthermore, tryptophan metabolism was up-regulated, resulting in accumulation of tryptophan metabolites associated with reactive oxygen species generation, suggesting the possibility of oxidative stress as a mechanism of nongenotoxic carcinogenesis. Finally, several metabolites related to liver function, kidney function, cell damage, and cell proliferation were altered by fenofibrate-induced toxicity at this dose.

Gene expression profiling in the liver and lung of perfluorooctane sulfonate-exposed mouse fetuses: comparison to changes induced by exposure to perfluorooctanoic acid

Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) are environmental contaminants found in the tissues of humans and wildlife. They are activators of peroxisome proliferator-activated receptor-alpha (PPAR alpha) and exhibit hepatocarcinogenic potential in rats. PFOS and PFOA are also developmental toxicants in rodents and PFOS has been shown to induce pulmonary deficits in rat offspring. Pregnant CD-1 mice were dosed with 0, 5, or 10mg/kg PFOS from gestation days 1-17. Transcript profiling was conducted on the fetal liver and lung. Results were contrasted to data derived from a previous PFOA study. PFOS-dependent changes were primarily related to activation of PPAR alpha. No remarkable differences were found between PFOS and PFOA. Given that PPAR alpha signaling is required for neonatal mortality in PFOA-treated mice but not those exposed to PFOS, the neonatal mortality observed for PFOS may reflect functional deficits related to the physical properties of the chemical rather than to transcript alterations.

Molecular characterization of novel and selective peroxisome proliferator-activated receptor alpha agonists with robust hypolipidemic activity in vivo

The nuclear receptor peroxisome proliferator-activated receptor alpha (PPARalpha) is recognized as the primary target of the fibrate class of hypolipidemic drugs and mediates lipid lowering in part by activating a transcriptional cascade that induces genes involved in the catabolism of lipids. We report here the characterization of three novel PPARalpha agonists with therapeutic potential for treating dyslipidemia. These structurally related compounds display potent and selective binding to human PPARalpha and support robust recruitment of coactivator peptides in vitro. These compounds markedly potentiate chimeric transcription systems in cell-based assays and strikingly lower serum triglycerides in vivo. The transcription networks induced by these selective PPARalpha agonists were assessed by transcriptional profiling of mouse liver after short- and long-term treatment. The induction of several known PPARalpha target genes involved with fatty acid metabolism were observed, reflecting the expected pharmacology associated with PPARalpha activation. We also noted the down-regulation of a number of genes related to immune cell function, the acute phase response, and glucose metabolism, suggesting that these compounds may have anti-inflammatory action in the mammalian liver. Whereas these compounds are efficacious in acute preclinical models, extended safety studies and further clinical testing will be required before the full therapeutic promise of a selective PPARalpha agonist is realized.

PPARalpha agonists inhibit nitric oxide production by enhancing iNOS degradation in LPS-treated macrophages

BACKGROUND AND PURPOSE

Nitric oxide (NO) production through the inducible nitric oxide synthase (iNOS) pathway is increased in response to pro-inflammatory cytokines and bacterial products. In inflammation, NO has pro-inflammatory and regulatory effects. Peroxisome proliferator-activated receptors (PPARs), members of the nuclear steroid receptor superfamily, regulate not only metabolic but also inflammatory processes. The aim of the present study was to investigate the role of PPARalpha in the regulation of NO production and iNOS expression in activated macrophages.

EXPERIMENTAL APPROACH

The effects of PPARalpha agonists were investigated on iNOS mRNA and protein expression, on NO production and on the activation of transcription factors NF-kappaB and STAT1 in J774 murine macrophages exposed to bacterial lipopolysaccharide (LPS).

KEY RESULTS

PPARalpha agonists GW7647 and WY14643 reduced LPS-induced NO production in a dose-dependent manner as measured by the accumulation of nitrite into the culture medium. However, PPARalpha agonists did not alter LPS-induced iNOS mRNA expression or activation of NF-kappaB or STAT1 which are important transcription factors for iNOS. Nevertheless, iNOS protein levels were reduced by PPARalpha agonists in a time-dependent manner. The reduction was markedly greater after 24 h incubation than after 8 h incubation. Treatment with the proteasome inhibitors, lactacystin or MG132, reversed the decrease in iNOS protein levels caused by PPARalpha agonists.

CONCLUSIONS AND IMPLICATIONS

The results suggest that PPARalpha agonists reduce LPS-induced iNOS expression and NO production in macrophages by enhancing iNOS protein degradation through the proteasome pathway. The results offer an additional mechanism underlying the anti-inflammatory effects of PPARalpha agonists.

Genomic profiling in nuclear receptor-mediated toxicity

Nuclear receptors (NRs) are attractive drug targets due to their role in regulation of a wide range of physiologic responses. In addition to providing therapeutic value, many pharmaceutical agents along with environmental chemicals are ligands for NRs and can cause adverse health effects that are directly related to activation of NRs. Identifying the molecular events that produce a toxic response may be confounded by the fact that there is a significant overlap in the biological processes that NRs regulate. Microarrays and other methods for gene expression profiling have served as useful, sensitive tools for discerning the mechanisms by which therapeutics and environmental chemicals invoke toxic effects. The capability to probe thousands of genes simultaneously has made genomics a prime technology for identifying drug targets, biomarkers of exposure/toxicity and key players in the mechanisms of disease. The complex intertwining networks regulated by NRs are hard to probe comprehensively without global approaches and genomics has become a key technology that facilitates our understanding of NR-dependent and -independent events. The future of drug discovery, design and optimization, and risk assessment of chemical toxicants that activate NRs will inevitably involve genomic profiling. This review will focus on genomics studies related to PPAR, CAR, PXR, RXR, LXR, FXR, and AHR.

Gene expression profiling in the lung and liver of PFOA-exposed mouse fetuses

Perfluorooctanoic acid (PFOA) is a stable perfluoroalkyl acid used to synthesize fluoropolymers during the manufacture of a wide variety of products. Concerns have been raised over the potential health effects of PFOA because it is persistent in the environment and can be detected in blood and other tissues of many animal species, including humans. PFOA has also been shown to induce growth deficits and mortality in murine neonates. To better understand the mechanism of PFOA induced developmental toxicity, lung and liver gene expression profiling was conducted in PFOA-exposed full-term mouse fetuses. Thirty timed-pregnant CD-1 mice were orally dosed from gestation days 1-17 with either 0, 1, 3, 5, or 10mg/(kgday) PFOA in water. At term, fetal lung and liver were collected, total RNA prepared, and samples pooled from three fetuses per litter. Five biological replicates consisting of individual litter samples were then evaluated for each treatment group using Affymetrix mouse 430_2 microarrays. The expression of genes related to fatty acid catabolism was altered in both the fetal liver and lung. In the fetal liver, the effects of PFOA were robust and also included genes associated with lipid transport, ketogenesis, glucose metabolism, lipoprotein metabolism, cholesterol biosynthesis, steroid metabolism, bile acid biosynthesis, phospholipid metabolism, retinol metabolism, proteosome activation, and inflammation. These changes are consistent with transactivation of PPARalpha, although, with regard to bile acid biosynthesis and glucose metabolism, non-PPARalpha related effects were suggested as well. Additional studies will be needed to more thoroughly address the role of PPARalpha, and other nuclear receptors, in PFOA mediated developmental toxicity.

The PPAR alpha-humanized mouse: a model to investigate species differences in liver toxicity mediated by PPAR alpha

To determine the impact of the species difference between rodents and humans in response to peroxisome proliferators (PPs) mediated by peroxisome proliferator-activated receptor (PPAR)alpha, PPAR alpha-humanized transgenic mice were generated using a P1 phage artificial chromosome (PAC) genomic clone bred onto a ppar alpha-null mouse background, designated hPPAR alpha PAC. In hPPAR alpha PAC mice, the human PPAR alpha gene is expressed in tissues with high fatty acid catabolism and induced upon fasting, similar to mouse PPAR alpha in wild-type (Wt) mice. Upon treatment with the PP fenofibrate, hPPAR alpha PAC mice exhibited responses similar to Wt mice, including peroxisome proliferation, lowering of serum triglycerides, and induction of PPAR alpha target genes encoding enzymes involved in fatty acid metabolism in liver, kidney, and heart, suggesting that human PPAR alpha (hPPAR alpha) functions in the same manner as mouse PPAR alpha in regulating fatty acid metabolism and lowering serum triglycerides. However, in contrast to Wt mice, treatment of hPPAR alpha PAC mice with fenofibrate did not cause significant hepatomegaly and hepatocyte proliferation, thus indicating that the mechanisms by which PPAR alpha affects lipid metabolism are distinct from the hepatocyte proliferation response, the latter of which is only induced by mouse PPAR alpha. In addition, a differential regulation of several genes, including the oncogenic let-7C miRNA by PPs, was observed between Wt and hPPAR alpha PAC mice that may contribute to the inherent difference between mouse and human PPAR alpha in activation of hepatocellular proliferation. The hPPAR alpha PAC mouse model provides an in vivo platform to investigate the species difference mediated by PPAR alpha and an ideal model for human risk assessment PPs exposure.

The PPAR alpha-humanized mouse: a model to investigate species differences in liver toxicity mediated by PPAR alpha. Toxicol Sci. 2008;101:132-139. [PMID: 17690133 DOI: 10.1093toxsci/kfm206]

To determine the impact of the species difference between rodents and humans in response to peroxisome proliferators (PPs) mediated by peroxisome proliferator-activated receptor (PPAR)alpha, PPAR alpha-humanized transgenic mice were generated using a P1 phage artificial chromosome (PAC) genomic clone bred onto a ppar alpha-null mouse background, designated hPPAR alpha PAC. In hPPAR alpha PAC mice, the human PPAR alpha gene is expressed in tissues with high fatty acid catabolism and induced upon fasting, similar to mouse PPAR alpha in wild-type (Wt) mice. Upon treatment with the PP fenofibrate, hPPAR alpha PAC mice exhibited responses similar to Wt mice, including peroxisome proliferation, lowering of serum triglycerides, and induction of PPAR alpha target genes encoding enzymes involved in fatty acid metabolism in liver, kidney, and heart, suggesting that human PPAR alpha (hPPAR alpha) functions in the same manner as mouse PPAR alpha in regulating fatty acid metabolism and lowering serum triglycerides. However, in contrast to Wt mice, treatment of hPPAR alpha PAC mice with fenofibrate did not cause significant hepatomegaly and hepatocyte proliferation, thus indicating that the mechanisms by which PPAR alpha affects lipid metabolism are distinct from the hepatocyte proliferation response, the latter of which is only induced by mouse PPAR alpha. In addition, a differential regulation of several genes, including the oncogenic let-7C miRNA by PPs, was observed between Wt and hPPAR alpha PAC mice that may contribute to the inherent difference between mouse and human PPAR alpha in activation of hepatocellular proliferation. The hPPAR alpha PAC mouse model provides an in vivo platform to investigate the species difference mediated by PPAR alpha and an ideal model for human risk assessment PPs exposure.

Subchronic toxicity and toxicogenomic evaluation of tamoxifen citrate + bexarotene in female rats

Tamoxifen (TAM) is a nonsteroidal antiestrogen that prevents estrogen receptor-positive breast cancer in rodents and humans. Bexarotene (BEX), a selective agonist for retinoid X receptors, inhibits mammary carcinogenesis in rodents. The present study was conducted to support the preclinical development of TAM (tamoxifen citrate) + BEX for use in breast cancer chemoprevention, and to investigate the influence of these agents on hepatic gene expression. Female CD rats (20 per group) received daily oral (gavage) exposure to TAM (0 or 60 microg/kg/day) and/or BEX (0, 5, 15, or 45 mg/kg/day) for a minimum of 90 days. BEX induced mild, dose-related anemia and dose-related increases in serum alkaline phosphatase, cholesterol, triglycerides, and calcium levels, and increased platelet counts. TAM had no biologically significant effect on any clinical pathology parameter and did not alter the effects of BEX on these endpoints. Microscopic alterations induced by BEX included epidermal hyperplasia, hyperkeratosis (stomach), and cytoplasmic clearing (liver). Microscopic changes in TAM-treated rats were limited to mucous cell hypertrophy in the cervix and vagina. The toxicity of administration of the combination of TAM + BEX can generally be predicted on the basis of the toxicity of each drug as a single agent. BEX induced dose-related alterations in the expression of several genes involved in steroid, drug, and/or fatty acid metabolism; TAM did not alter these effects of BEX. Differential expression of genes involved in drug and lipid metabolism may underlie the observed effects of BEX on cholesterol and triglyceride levels and its effects on liver histology.

Temporal dynamics of gene expression in the lung in a baboon model of E. coli sepsis

Background

Bacterial invasion during sepsis induces disregulated systemic responses that could lead to fatal lung failure. The purpose of this study was to relate the temporal dynamics of gene expression to the pathophysiological changes in the lung during the first and second stages of E. coli sepsis in baboons.

Results

Using human oligonucleotide microarrays, we have explored the temporal changes of gene expression in the lung of baboons challenged with sublethal doses of E. coli. Temporal expression pattern and biological significance of the differentially expressed genes were explored using clustering and pathway analysis software. Expression of selected genes was validated by real-time PCR. Cytokine levels in tissue and plasma were assayed by multiplex ELISA. Changes in lung ultrastructure were visualized by electron microscopy. We found that genes involved in primary inflammation, innate immune response, and apoptosis peaked at 2 hrs. Inflammatory and immune response genes that function in the stimulation of monocytes, natural killer and T-cells, and in the modulation of cell adhesion peaked at 8 hrs, while genes involved in wound healing and functional recovery were upregulated at 24 hrs.

Conclusion

The analysis of gene expression modulation in response to sepsis provides the baseline information that is crucial for the understanding of the pathophysiology of systemic inflammation and may facilitate the development of future approaches for sepsis therapy.

Hypolipidemic Mechanisms of Ananas comosus L. Leaves in Mice: Different From Fibrates but Similar to Statins

In this study, we investigated hypolipidemic mechanisms of the ethanolic extract of Ananas comosus L. leaves (AC) in mice and then determined its activities in related enzymes. The results showed that AC (0.40 g/kg) significantly inhibited the increase in serum triglycerides by 40% in fructose-fed mice. In mice induced by alloxan and high-fat diets, serum total cholesterol remained at a high level (180 - 220 mg/dl) within 7 days of removing high-fat diets but reached normal level (120 - 140 mg/dl) after AC (0.40 g/kg per day) treatment. Also, AC (0.40 and 0.80 g/kg) significantly inhibited serum lipids from the increase in Triton WR-1339-induced hyperlipidemic mice. AC (0.01 - 100 microg/ml) selectively activated lipoprotein lipase (LPL) activity by 200% - 400% and significantly inhibited 3-hydroxyl-methyl glutaryl coenzyme A (HMGCoA) reductase activity by 20% - 49% in vitro. Furthermore, 2 months of fenofibrate (0.20 g/kg) administration particularly increased mice liver weights (0.0760 +/- 0.0110 g/g) while AC (0.40 g/kg) had no effect (0.0403 +/- 0.0047). Taken together, these results suggest that AC will be a new potential natural product for the treatment of hyperlipidemia that exerts its actions through mechanisms of inhibiting HMGCoA reductase and activating LPL activities. Its action mechanisms differentiate from those with fibrates but may be partly similar to those with statins. It is hopeful that AC may serve as the adjuvant for fibrates.