Role of the peroxisome proliferator-activated receptor in cytochrome P450 4A gene regulation

The fatty acid omega hydroxylase genes (CYP4 family) in the progression of metabolic dysfunction-associated steatotic liver disease (MASLD): An RNA sequence database analysis and review

Fatty acid omega hydroxylase P450s consist of enzymes that hydroxylate various chain-length saturated and unsaturated fatty acids (FAs) and bioactive eicosanoid lipids. The human cytochrome P450 gene 4 family (CYP4) consists of 12 members that are associated with several human diseases. However, their role in the progression of metabolic dysfunction-associated fatty liver disease (MASLD) remains largely unknown. It has long been thought that the induction of CYP4 family P450 during fasting and starvation prevents FA-related lipotoxicity through FA metabolism to dicarboxylic acids that are chain-shortened in peroxisomes and then transported to the mitochondria for complete oxidation. Several studies have revealed that peroxisome succinate transported to the mitochondria is used for gluconeogenesis during fasting and starvation, and recent evidence suggests that peroxisome acetate can be utilized for lipogenesis and lipid droplet formation as well as epigenetic modification of gene transcription. In addition, omega hydroxylation of the bioactive eicosanoid arachidonic acid to 20-Hydroxyeicosatetraenoic acid (20-HETE) is essential for activating the GPR75 receptor, leading to vasoconstriction and cell proliferation. Several mouse models of diet-induced MASLD have revealed the induction of selective CYP4A members and the suppression of CYP4F during steatosis and steatohepatitis, suggesting a critical metabolic role in the progression of fatty liver disease. Thus, to further investigate the functional roles of CYP4 genes, we analyzed the differential gene expression of 12 members of CYP4 gene family in datasets from the Gene Expression Omnibus (GEO) from patients with steatosis, steatohepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. We also observed the differential expression of various CYP4 genes in the progression of MASLD, indicating that different CYP4 members may have unique functional roles in the metabolism of specific FAs and eicosanoids at various stages of fatty liver disease. These results suggest that targeting selective members of the CYP4A family is a viable therapeutic approach for treating and managing MASLD.

Alteration of CYP4A11 expression in renal cell carcinoma: diagnostic and prognostic implications

Background: Cytochrome P-450 4A11 (CYP4A11) and peroxisome proliferator-activated receptor-α (PPARα) are expressed at high levels in renal proximal tubules, and upregulation of CYP4A11 protein levels is known to be influenced by PPAR agonists. The goal of this study was to evaluate the clinicopathological role of CYP4A11 expression in renal cell carcinoma (RCC).

Methods: We performed immunohistochemical analysis of CYP4A11, CYP4A22 and PPARα and correlated the results with the clinicopathological features of RCC (n=139). Reverse transcription digital droplet polymerase chain reaction (RT-ddPCR) against CYP4A11 and CYP4A22 was also performed.

Results: CYP4A11 mRNA expression levels were higher in non-neoplastic kidney tissues than in matched tumor tissues in 12 matched pairs of freshly frozen primary clear-cell RCC (ccRCC) and nontumor tissue (p=0.002). Immunohistochemical staining showed that CYP4A11 expression was significantly lower in ccRCC than in non-ccRCCs, including papillary, chromophobe, and unclassified RCCs (p<0.001). CYP4A11 expression was associated with PPARα expression, males and high nuclear histologic grades (p=0.001, p=0.018 and p<0.001). Univariate and multivariate analyses revealed that CYP4A11 expression was correlated with short overall survival (p=0.007 and p=0.010).

Conclusion: These findings suggest that CYP4A11 expression is a potential poor prognostic factor of RCC. The considerable decrease in CYP4A11 expression is a predictive diagnostic factor of ccRCC, and CYP4A11 metabolism in ccRCC might be different from that in non-ccRCCs.

Perfluorinated Alkyl Acids in Hawaiian Cetaceans and Potential Biomarkers of Effect: Peroxisome Proliferator-Activated Receptor Alpha and Cytochrome P450 4A

Perfluorinated alkyl acids (PFAAs) are persistent in marine biota and are toxic to many species, including marine mammals. We measured the concentrations of 15 PFAAs in liver and kidney samples of 16 species of stranded cetaceans from Hawai'i and other tropical North Pacific regions utilizing high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). Eleven PFAAs in liver and nine PFAAs in kidney were detected, including substantial perfluorooctanesulfonate (PFOS) and perfluoroundecanoic acid (PFUnA). Regression models indicated that phylogenetic family and age class significantly influenced concentrations of certain PFAAs. PFAAs can activate transcription factor peroxisome proliferator-activated receptor alpha (PPARα), which induces transcription of cytochrome P450 4A (CYP4A). Relative expression of PPARα and CYP4A mRNA was quantified using real-time PCR (qPCR) and CYP4A protein expression, using Western blot and then compared to PFAA concentrations in liver and kidney. Concentrations of four PFAA congeners, summation of perfluoroalkyl carboxylic acids (ΣPFCAs), and ΣPFAAs correlated significantly with PPARα mRNA expression and CYP4A protein expression in kidney, suggesting either may be biomarkers of PFAA exposure in cetaceans. This is the first study to quantify PFAAs in marine mammals from this region and the first observation of a direct relationship between PFAA exposure and PPARα and CYP4A expression in cetaceans.

Cytochrome P450 4A11 expression in tumor cells: A favorable prognostic factor for hepatocellular carcinoma patients

BACKGROUND AND AIM

Elevated cytochrome p450 (CYP) 4A gene expression has been linked to the aggravation of various cancers and affects various regulated metabolites. In hepatocellular carcinoma (HCC), the clinicopathological value of CYP4A has not yet been explored, although CYP4A is expressed at high levels in the liver. The goal of this study was to evaluate the clinicopathological value of CYP4A11 expression in HCC.

METHODS

We performed immunohistochemical analysis of CYP4A11 and correlated the results with clinicopathological features of HCC (n = 155). Western blotting and reverse transcription-polymerase chain reaction against CYP4A11 and CYP4A22 were also performed for 15 and 20 pairs of fresh-frozen primary HCC and non-neoplastic liver tissue, respectively. Moreover, we analyzed the underlying mechanism by comparing the high and low CYP4A11 mRNA expression groups using gene set enrichment analysis.

RESULTS

CYP4A11 expression level was higher in non-neoplastic hepatocytes than those in HCC cells (P < 0.001), and CYP4A11 expression positively correlated with favorable prognostic factors, including tumor size, histological grade, and pathological tumor stage (P = 0.007, P = 0.005, and P = 0.007). Multivariate analysis revealed that CYP4A11 expression was an independent prognostic factor of overall and disease-free survival (P = 0.002 and P = 0.033). Based on gene set enrichment analysis, high CYP4A11 mRNA expression negatively correlated with the expression of cell cycle-related genes.

CONCLUSION

These findings support the notion that CYP4A11 expression is a favorable prognostic factor of HCC and suggest potential predictive diagnostic and prognostic roles of CYP4A11 expression in HCC.

Regulation of cytochrome P450 gene expression by ketamine: a review

INTRODUCTION

Although used as an anesthetic drug for decades, ketamine appears to have garnered renewed interest due to its potential therapeutic uses in pain therapy, neurology, and psychiatry. Ketamine undergoes extensive oxidative metabolism by cytochrome P450 (CYP) enzymes. Considerable efforts have been expended to elucidate the ketamine-induced regulation of CYP gene expression. The safety profile of chronic ketamine administration is still unclear. Understanding how ketamine regulates CYP gene expression is clinically meaningful. Areas covered: In this article, the authors provide a brief review of clinical applications of ketamine and its metabolism by CYP enzymes. We discuss the effects of ketamine on the regulation of CYP gene expression, exploring aspects of cytoskeletal remodeling, mitochondrial functions, and calcium homeostasis. Expert opinion: Ketamine may inhibit CYP gene expression through inhibiting calcium signaling, decreasing ATP levels, producing excessive reactive oxygen species, and subsequently perturbing cytoskeletal dynamics. Further research is still needed to avoid possible ketamine-drug interactions during long-term use in the clinic.

Generation and Characterization of a CYP2C11-Null Rat Model by Using the CRISPR/Cas9 Method

CYP2C11 is involved in the metabolism of many drugs in rats. To assess the roles of CYP2C11 in physiology and drug metabolism, a CYP2C11-null rat model was generated using the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9method. A 2-base pair insertion was added to exon 6 of CYP2C11 in Sprague-Dawley rats. CYP2C11 was not detected by western blotting in liver microsomes of CYP2C11-null rats. No off-target effects were found at 11 predicted sites of the knockout model. The CYP2C11-null rats were viable and had no obvious abnormalities, with the exception of reduced fertility. Puberty in CYP2C11-null rats appeared to be delayed by ∼20 days, and the average litter size fell by 43%. Tolbutamide was used as a probe in this drug metabolism study. In the liver microsomes of CYP2C11-null rats, the V_max and intrinsicclearance values decreased by 22% and 47%, respectively, compared with those of wild-type rats. The K_m values increased by 47% compared with that of wild types. However, our pharmacokinetics study showed no major differences in any parameters between the two strains, in both males and females. In conclusion, a CYP2C11-null rat model was successfully generated and is a valuable tool to study the in vivo function of CYP2C11.

Fatty acid metabolism in fish species as a biomarker for environmental monitoring

Pollution by Organic Contaminants (OC) in aquatic environments is a relevant issue at the global scale. Lipids comprised of Fatty Acids (FA) play many important roles in the physiology and life history of fishes. Toxic effects of OC are partly dependent on its bioaccumulation in the lipids of aquatic organisms due its physicochemical properties. Therefore, there is an increasing interest to investigate the gene expression as well as the presence and activity of proteins involved in FA metabolism. The attention on Peroxisome Proliferation Activate Receptors (PPARs) also prevails in fish species exposed to OC and in the transport, biosynthesis and β-oxidation of FA. Several studies have been conducted under controlled conditions to evaluate these biological aspects of fish species exposed to OC, as fibrates, endocrine disrupting compounds, perfluoroalkyl acids, flame retardants, metals and mixtures of organic compounds associated with a polluted area. However, only fibrates, which are agonists of PPARs, induce biological responses suitable to be considered as biomarkers of exposure to these pollutants. According to the documented findings on this topic, it is unlikely that these physiological aspects are suitable to be employed as biomarkers with some noticeable exceptions, which depend on experimental design. This emphasises the need to investigate the responses in fish treated with mixtures of OC and in wild fish species from polluted areas to validate or refute the suitability of these biomarkers for environmental or fish health monitoring.

Transient postnatal fluoxetine decreases brain concentrations of 20-HETE and 15-epi-LXA4, arachidonic acid metabolites in adult mice

BACKGROUND

Transient postnatal exposure of rodents to the selective serotonin (5-HT) reuptake inhibitor (SSRI) fluoxetine alters behavior and brain 5-HT neurotransmission during adulthood, and also reduces brain arachidonic (ARA) metabolic consumption and protein level of the ARA metabolizing enzyme, cytochrome P4504A (CYP4A).

HYPOTHESIS

Brain 20-hydroxyeicosatetraenoic acid (20-HETE), converted by CYP4A from ARA, will be reduced in adult mice treated transiently and postnatally with fluoxetine.

METHODS

Male mice pups were injected i.p. daily with fluoxetine (10mg/kg) or saline during P4-P21. At P90 their brain was high-energy microwaved and analyzed for 20-HETE and six other ARA metabolites by enzyme immunoassay.

RESULTS

Postnatal fluoxetine vs. saline significantly decreased brain concentrations of 20-HETE (-70.3%) and 15-epi-lipoxin A4 (-60%) in adult mice, but did not change other eicosanoid concentrations.

CONCLUSIONS

Behavioral changes in adult mice treated postnatally with fluoxetine may be related to reduced brain ARA metabolism involving CYP4A and 20-HETE formation.

Plasticizer endocrine disruption: Highlighting developmental and reproductive effects in mammals and non-mammalian aquatic species

Due to their versatility, robustness, and low production costs, plastics are used in a wide variety of applications. Plasticizers are mixed with polymers to increase flexibility of plastics. However, plasticizers are not covalently bound to plastics, and thus leach from products into the environment. Several studies have reported that two common plasticizers, bisphenol A (BPA) and phthalates, induce adverse health effects in vertebrates; however few studies have addressed their toxicity to non-mammalian species. The aim of this review is to compare the effects of plasticizers in animals, with a focus on aquatic species. In summary, we identified three main chains of events that occur in animals exposed to BPA and phthalates. Firstly, plasticizers affect development by altering both the thyroid hormone and growth hormone axes. Secondly, these chemicals interfere with reproduction by decreasing cholesterol transport through the mitochondrial membrane, leading to reduced steroidogenesis. Lastly, exposure to plasticizers leads to the activation of peroxisome proliferator-activated receptors, the increase of fatty acid oxidation, and the reduction in the ability to cope with the augmented oxidative stress leading to reproductive organ malformations, reproductive defects, and decreased fertility.

Cytochrome P450 ω-Hydroxylases in Inflammation and Cancer

Cytochrome P450-dependent ω-hydroxylation is a prototypic metabolic reaction of CYP4 family members that is important for the elimination and bioactivation of not only therapeutic drugs, but also endogenous compounds, principally fatty acids. Eicosanoids, derived from arachidonic acid, are key substrates in the latter category. Human CYP4 enzymes, mainly CYP4A11, CYP4F2, and CYP4F3B, hydroxylate arachidonic acid at the omega position to form 20-HETE, which has important effects in tumor progression and on angiogenesis and blood pressure regulation in the vasculature and kidney. CYP4F3A in myeloid tissue catalyzes the ω-hydroxylation of leukotriene B4 to 20-hydroxy leukotriene B4, an inactivation process that is critical for the regulation of the inflammatory response. Here, we review the enzymology, tissue distribution, and substrate selectivity of human CYP4 ω-hydroxylases and their roles as catalysts for the formation and termination of the biological effects of key eicosanoid metabolites in inflammation and cancer progression.

Altered inflammatory responses to Citrobacter rodentium infection, but not bacterial lipopolysaccharide, in mice lacking the Cyp4a10 or Cyp4a14 genes

Murine hepatic Cyp4a mRNAs are markedly downregulated during inflammation. Here, we investigated the roles of Cyp4a10 and Cyp4a14 in the response to infection with C. rodentium. Absence of either Cyp4a gene attenuated or abrogated the changes in spleen weight, colon crypt length, hepatic cytokine, and acute phase protein mRNAs, and serum acute phase proteins and cytokines caused by infection. Cyp4a10(-/-) mice on a low-salt diet had a similar hepatic acute phase response as those mice on a high-salt diet, suggesting that hypertension associated with this genotype is not the cause of their altered inflammatory response. In contrast, wild-type, Cyp4a10(-/-), and Cyp4a14(-/-) mice showed similar responses to injected LPS. These results implicate Cyp4a10 and Cyp4a14 in the regulation of the host inflammatory response to enteropathogenic bacterial infection but not to acute aseptic inflammation. Understanding the mechanism of this role may lead to novel therapeutic approaches in some inflammatory diseases.

Integrated proteomic and miRNA transcriptional analysis reveals the hepatotoxicity mechanism of PFNA exposure in mice

Perfluoroalkyl chemicals (PFASs) are a class of highly stable man-made compounds, and their toxicological impacts are currently of worldwide concern. Administration of perfluorononanoic acid (PFNA), a perfluorocarboxylic acid (PFCA) with a nine carbon backbone, resulted in dose-dependent hepatomegaly in mice (0, 0.2, 1, and 5 mg/kg body weight, once a day for 14 days) and an increase in hepatic triglycerides (TG) and total cholesterol (TCHO) in the median dose group as well as serum transaminases in the high dose group. Using isobaric tags for relative and absolute quantitation (iTRAQ), we identified 108 (80 up-regulated, 28 down-regulated) and 342 hepatic proteins (179 up-regulated, 163 down-regulated) that exhibited statistically significant changes (at least a 1.2-fold alteration and P < 0.05) in the 1 and 5 mg/kg/d PFNA treatment groups, respectively. Sixty-six proteins (54 up-regulated, 12 down-regulated) significantly changed in both of the two treatment groups. Among these 54 up-regulated proteins, most were proteins related to the lipid metabolism process (31 proteins). The mRNA analysis results further suggested that PFNA exposure not only resulted in a fatty acid oxidation effect but also activated mouse liver genes involved in fatty acid and cholesterol synthesis. Additionally, three (2 down-regulated, 1 up-regulated) and 30 (14 down-regulated, 16 up-regulated) microRNAs (miRNAs) exhibited at least a 2-fold alteration (P < 0.05) in the 1 and 5 mg/kg/d PFNA treatment groups, respectively, Three miRNAs (up-regulated: miR-34a; down-regulated: miR-362-3p and miR-338-3p) significantly changed in both of the two treatment groups. The repression effect of miR-34a on fucosyltransferase 8 (Fut8) and lactate dehydrogenase (Ldha) was confirmed by luciferase activity assay and Western blot analysis. The results implied that PFNA exerted a hepatic effect, at least partially, by miRNAs mediated post-translational protein repression.

Metabolic interactions between vitamin A and conjugated linoleic acid

Lipid-soluble molecules share several aspects of their physiology due to their common adaptations to a hydrophilic environment, and may interact to regulate their action in a tissue-specific manner. Dietary conjugated linoleic acid (CLA) is a fatty acid with a conjugated diene structure that is found in low concentrations in ruminant products and available as a nutritional supplement. CLA has been shown to increase tissue levels of retinol (vitamin A alcohol) and its sole specific circulating carrier protein retinol-binding protein (RBP or RBP4). However, the precise mechanism of this action has not been elucidated yet. Here, we provide a summary of the current knowledge in this specific area of research and speculate that retinol and CLA may compete for catabolic pathways modulated by the activity of PPAR-α and RXR heterodimer. We also present preliminary data that may position PPAR-α at the crossroads between the metabolism of lipids and vitamin A.

Peroxisome proliferator-activated receptor agonists in a battle against the aging kidney

As aging is a complex phenomenon characterized by intraindividual and interindividual diversities in the maintenance of the homeostatic condition of cells and tissues, changes in renal function are not uniform and depend on associated diseases and environmental factors. Multiple studies have investigated the possible underlying mechanisms of age-related decline in kidney function. Evolutionary, molecular, cellular and systemic theories have been postulated to explain the primary disease independent age-related changes and adaptive responses. As peroxisome proliferator-activated receptors (PPARs) are involved in a broad spectrum of biological processes, PPAR activation might have an effect on the prevention of cell senescence. In this review, we will focus on the experimental and clinical evidence of PPAR agonists in a battle against the aging kidney.

An epidemiologic and genomic investigation into the obesity paradox in renal cell carcinoma

BACKGROUND

Obesity increases risk for clear-cell renal cell carcinoma (ccRCC), yet obese patients appear to experience longer survival than nonobese patients. We examined body mass index (BMI) in relation to stage, grade, and cancer-specific mortality (CSM) while considering detection bias, nutritional status, and molecular tumor features.

METHODS

Data were available from 2119 ccRCC patients who underwent renal mass surgery at Memorial Sloan-Kettering Cancer Center between 1995 and 2012. Logistic regression models produced associations between BMI and advanced disease. Multivariable competing risks regression models estimated associations between BMI and CSM. Somatic mutation, copy number, methylation, and expression data were examined by BMI among a subset of 126 patients who participated in the Cancer Genome Atlas Project for ccRCC using the Kruskal-Wallis or Fisher exact tests. All statistical tests were two-sided.

RESULTS

Obese and overweight patients were less likely to present with advanced-stage disease compared with normal-weight patients (odds ratio [OR] = 0.61, 95% confidence interval [CI] = 0.48 to 0.79 vs OR = 0.65, 95% CI = 0.51 to 0.83, respectively). Higher BMI was associated with reduced CSM in univariable analyses (P < .005). It remained statistically significant after adjustment for comorbidities and albumin level, but it became non-statistically significant after adjusting for stage and grade (P > .10). Genome-wide interrogation by BMI suggested differences in gene expression of metabolic and fatty acid genes, including fatty acid synthase (FASN), consistent with the obesity paradox.

CONCLUSIONS

Our findings suggest that although BMI is not an independent prognostic factor for CSM after controlling for stage and grade, tumors developing in an obesogenic environment may be more indolent.

Effects of 4-nonylphenol on hepatic gene expression of peroxisome proliferator-activated receptors and cytochrome P450 isoforms (CYP1A1 and CYP3A4) in juvenile sole (Solea solea)

The objective of the present study was to investigate the modulatory effects of the xenoestrogen 4-nonylphenol (4-NP) on hepatic peroxisome proliferator-activated receptor (PPAR) α and β gene expression patterns in relation to the detoxification pathways mediated by cytochrome P450 isoforms (CYP1A1 and CYP3A4). Waterborne 4-NP-induced effects were compared with those of 10(-8)M 17β-estradiol (E2) by using in vivo dose-response experiments carried out with juvenile sole (Solea solea). Compared to the controls, significantly higher levels of PPARα mRNAs were found in fish treated with E2 or 4-NP (10(-6)M) 3 d after exposure; the highest dose of 4-NP also caused up-regulation of retinoid X receptor α (RXRα) transcript levels. On the contrary, PPARβ gene expression was not modulated by E2 or 4-NP. Our data show that 4-NP-induced PPARα mRNA levels coincide with suppression of CYP1A1 and CYP3A4 expression similarly to E2. The results from these in vivo studies suggest the presence of cross-talk between nuclear receptor-mediated signaling pathways and PPARα that may result in modulation of CYP450 isoforms expression following 4-NP treatment in sole liver.

Medium chain triglycerides dose-dependently prevent liver pathology in a rat model of non-alcoholic fatty liver disease

Metabolic syndrome is often accompanied by development of hepatic steatosis and less frequently by non-alcoholic fatty liver disease (NAFLD) leading to non-alcoholic steatohepatitis (NASH). Replacement of corn oil with medium chain triacylglycerols (MCT) in the diets of alcohol-fed rats has been shown to protect against steatosis and alcoholic liver injury. The current study was designed to determine if a similar beneficial effect of MCT occurs in a rat model of NAFLD. Groups of male rats were isocalorically overfed diets containing 10%, 35% or 70% total energy as corn oil or a 70% fat diet in which corn oil was replaced with increasing concentrations of saturated fat (18:82, beef tallow:MCT oil) from 20% to 65% for 21 days using total enteral nutrition (TEN). As dietary content of corn oil increased, hepatic steatosis and serum alanine amino transferases were elevated (P < 0.05). This was accompanied by greater expression of cytochrome P450 enzyme CYP2E1 (P < 0.05) and higher concentrations of polyunsaturated 18:2 and 20:4 fatty acids (FA) in the hepatic lipid fractions (P < 0.05). Keeping the total dietary fat at 70%, but increasing the proportion of MCT-enriched saturated fat resulted in a dose-dependent reduction in steatosis and necrosis without affecting CYP2E1 induction. There was no incorporation of C8-C10 FAs into liver lipids, but increasing the ratio of MCT to corn oil: reduced liver lipid 18:2 and 20:4 concentrations; reduced membrane susceptibility to radical attack; stimulated FA β- and ω-oxidation as a result of activation of peroxisomal proliferator activated receptor (PPAR)α, and appeared to increase mitochondrial respiration through complex III. These data suggest that replacing unsaturated fats like corn oil with MCT oil in the diet could be utilized as a potential treatment for NAFLD.

Direct transcriptional regulation of human hepatic cytochrome P450 3A4 (CYP3A4) by peroxisome proliferator-activated receptor alpha (PPARα)

The nuclear receptor peroxisome proliferator-activated receptor (PPAR)α is known primarily as a regulator of fatty acid metabolism, energy balance, and inflammation, but evidence suggests a wider role in regulating the biotransformation of drugs and other lipophilic chemicals. We investigated whether PPARα directly regulates the transcription of cytochrome P450 3A4, the major human drug-metabolizing enzyme. Using chromatin immunoprecipitation in human primary hepatocytes as well as electrophoretic mobility shift and luciferase reporter-gene assays, we identified three functional PPARα-binding regions (PBR-I, -II, and -III) within ∼12 kb of the CYP3A4 upstream sequence. Furthermore, a humanized CYP3A4/3A7 mouse model showed in vivo induction of CYP3A4 mRNA and protein by [4-chloro-6-(2,3-xylidino)-2-pyrimidinylthio]acetic acid (WY14,643) in liver but not in intestine, whereas hepatic occupancy of PBRs by PPARα was ligand independent. Using lentiviral gene knock-down and treatment with WY14,643 in primary human hepatocytes, PPARα was further shown to affect the expression of a distinct set of CYPs, including 1A1, 1A2, 2B6, 2C8, 3A4, and 7A1, but not 2C9, 2C19, 2D6, or 2E1. Interestingly, the common phospholipid 1-palmitoyl-2-oleoyl-sn-glycerol-3-phosphocholine (16:0/18:1-PC), previously proposed to reflect nutritional status and shown to be a specific endogenous ligand of PPARα, induced CYP3A4 (up to 4-fold) and other biotransformation genes in hepatocytes with similar selectivity and potency as WY14,643. These data establish PPARα as a direct transcriptional regulator of hepatic CYP3A4. This finding warrants investigation of both known and newly developed PPARα-targeted drugs for their drug-drug interaction potential. Furthermore, our data suggest that nutritional status can influence drug biotransformation capacity via endogenous phospholipid signaling.

CYP4 enzymes as potential drug targets: focus on enzyme multiplicity, inducers and inhibitors, and therapeutic modulation of 20-hydroxyeicosatetraenoic acid (20-HETE) synthase and fatty acid ω-hydroxylase activities

The Cytochrome P450 4 (CYP4) family of enzymes in humans is comprised of thirteen isozymes that typically catalyze the ω-oxidation of endogenous fatty acids and eicosanoids. Several CYP4 enzymes can biosynthesize 20- hydroxyeicosatetraenoic acid, or 20-HETE, an important signaling eicosanoid involved in regulation of vascular tone and kidney reabsorption. Additionally, accumulation of certain fatty acids is a hallmark of the rare genetic disorders, Refsum disease and X-ALD. Therefore, modulation of CYP4 enzyme activity, either by inhibition or induction, is a potential strategy for drug discovery. Here we review the substrate specificities, sites of expression, genetic regulation, and inhibition by exogenous chemicals of the human CYP4 enzymes, and discuss the targeting of CYP4 enzymes in the development of new treatments for hypertension, stroke, certain cancers and the fatty acid-linked orphan diseases.

PPAR-alpha cloning, expression, and characterization

Peroxisome proliferator-activated receptor α (PPARα) is a member of the nuclear/steroid receptor gene superfamily that also comprises β, δ, and γ isoforms. PPARα is a ligand-activated transcription factor that plays an important role in the regulation of many genes involved in key metabolic processes. Today, PPARα has been cloned from mammalian, marsupial, and a number of marine species and its expression has been found to be relatively tissue- and species-specific. Here, we describe the methods for cloning of PPARα genes by RT-PCR and RACE approaches and related protocols for studying the expression of cloned PPARα cDNAs in mammalian cell systems.

Fructose-rich diet leads to reduced aerobic capacity and to liver injury in rats

The main purpose of this research was to investigate the alterations in the aerobic capacity and appearance of metabolic alterations in Wistar rats fed on fructose-rich diet. We separated twenty-eight rats into two groups according to diet: a control group (C) (balanced diet) and a fructose-rich diet group (F). The animals were fed these diets for 60 d (d 120 to 180). We performed insulin, glucose as well as a minimum lactate test, at d 120 and 180. At the end of the experiment, sixteen animals were euthanized, and the following main variables were analysed: aerobic capacity, the serum aspartate aminotransferase (AST) to alanine aminotransferase (ALT) ratio, serum and liver triglyceride concentrations, serum and liver thiobarbituric acid reactive substance (TBARS) concentrations, serum and liver catalase and superoxide dismutase (SOD) activity and haematoxylin-eosin histology (HE) in hepatocytes. The remaining twelve animals were submitted to an analysis of their hepatic lipogenic rate. The animals fed a fructose-rich diet exhibited a reduction in aerobic capacity, glucose tolerance and insulin sensitivity and increased concentrations of triglycerides and TBARS in the liver. Catalase and SOD activities were reduced in the livers of the fructose-fed animals. In addition, the serum AST/ALT ratio was higher than that of the C group, which indicates hepatic damage, and the damage was confirmed by histology. In conclusion, the fructose-rich diet caused significant liver damage and a reduction in insulin sensitivity in the animals, which could lead to deleterious metabolic effects.

Nuclear receptors in the multidrug resistance through the regulation of drug-metabolizing enzymes and drug transporters

Chemotherapy is one of the three most common treatment modalities for cancer. However, its efficacy is limited by multidrug resistant cancer cells. Drug metabolizing enzymes (DMEs) and efflux transporters promote the metabolism, elimination, and detoxification of chemotherapeutic agents. Consequently, elevated levels of DMEs and efflux transporters reduce the therapeutic effectiveness of chemotherapeutics and, often, lead to treatment failure. Nuclear receptors, especially pregnane X receptor (PXR, NR1I2) and constitutive androstane activated receptor (CAR, NR1I3), are increasingly recognized for their role in xenobiotic metabolism and clearance as well as their role in the development of multidrug resistance (MDR) during chemotherapy. Promiscuous xenobiotic receptors, including PXR and CAR, govern the inducible expressions of a broad spectrum of target genes that encode phase I DMEs, phase II DMEs, and efflux transporters. Recent studies conducted by a number of groups, including ours, have revealed that PXR and CAR play pivotal roles in the development of MDR in various human carcinomas, including prostate, colon, ovarian, and esophageal squamous cell carcinomas. Accordingly, PXR/CAR expression levels and/or activation statuses may predict prognosis and identify the risk of drug resistance in patients subjected to chemotherapy. Further, PXR/CAR antagonists, when used in combination with existing chemotherapeutics that activate PXR/CAR, are feasible and promising options that could be utilized to overcome or, at least, attenuate MDR in cancer cells.

Coordinated regulation of hepatic phase I and II drug-metabolizing genes and transporters using AhR-, CAR-, PXR-, PPARα-, and Nrf2-null mice

The transcription factors aryl hydrocarbon receptor (AhR), constitutive androstane receptor (CAR), pregnane X receptor (PXR), peroxisome proliferator-activated receptor α (PPARα), and nuclear factor erythroid 2-related factor 2 (Nrf2) regulate genes encoding drug-metabolizing enzymes and transporters in livers of mice after chemical activation. However, the specificity of their transcriptional regulation has not been determined systematically in vivo. The purpose of this study was to identify genes encoding drug-metabolizing enzymes and transporters altered by chemical activators in a transcription factor-dependent manner using wild-type and transcription factor-null mice. Chemical activators were administered intraperitoneally to mice once daily for 4 days. Livers were collected 24 h after the final dose, and total RNA was isolated for mRNA quantification of cytochromes P450, NAD(P)H quinone oxidoreductase 1 (Nqo1), aldehyde dehydrogenases (Aldhs), glutathione transferases (Gsts), sulfotransferases (Sults), UDP-glucuronosyltransferases (Ugts), organic anion-transporting polypeptides (Oatps), and multidrug resistance-associated proteins (Mrps). Pharmacological activation of each transcription factor leads to mRNA induction of drug metabolic and transport genes in livers of male and female wild-type mice, but no change in null mice: AhR (Cyp1a2, Nqo1, Aldh7a1, Ugt1a1, Ugt1a6, Ugt1a9, Ugt2b35, Sult5a1, Gstm3, and Mrp4), CAR (Cyp2b10, Aldh1a1, Aldh1a7, Ugt1a1, Ugt2b34, Sult1e1, Sult3a1, Sult5a1, Papps2, Gstt1, Gsta1, Gsta4, Gstm1-4, and Mrp2-4), PXR (Cyp3a11, Ugt1a1, Ugt1a5, Ugt1a9, Gsta1, Gstm1-m3, Oatp1a4, and Mrp3), PPARα (Cyp4a14, Aldh1a1, mGst3, Gstm4, and Mrp4), and Nrf2 (Nqo1, Aldh1a1, Gsta1, Gsta4, Gstm1-m4, mGst3, and Mrp3-4). Taken together, these data reveal transcription factor specificity and overlap in regulating hepatic drug disposition genes by chemical activators. Coordinated regulation of phase I, phase II, and transport genes by activators of transcription factors can have implications in development of pharmaceuticals as well as risk assessment of environmental contaminants.

The renoprotective actions of peroxisome proliferator-activated receptors agonists in diabetes

Pharmaceutical agonists of peroxisome proliferator-activated receptors (PPARs) are widely used in the management of type 2 diabetes, chiefly as lipid-lowering agents and oral hypoglycaemic agents. Although most of the focus has been placed on their cardiovascular effects, both positive and negative, these agents also have significant renoprotective actions in the diabetic kidney. Over and above action on metabolic control and effects on blood pressure, PPAR agonists also appear to have independent effects on a number of critical pathways that are implicated in the development and progression of diabetic kidney disease, including oxidative stress, inflammation, hypertrophy, and podocyte function. This review will examine these direct and indirect actions of PPAR agonists in the diabetic kidney and explore recent findings of clinical trials of PPAR agonists in patients with diabetes.

Role of oxidative stress in the pathogenesis of nonalcoholic steatohepatitis

The worldwide rising prevalence of obesity and insulin resistance is associated with a parallel increase in nonalcoholic fatty liver disease (NAFLD). NAFLD is characterized by excess accumulation of triglyceride in the hepatocyte due to increased inflow of free fatty acids and/or de novo lipogenesis caused by various drugs and multiple defects in energy metabolism. Accumulation of lipids in the hepatocyte impairs the oxidative capacity of the mitochondria, increasing the reduced state of the electron transport chain (ETC) complexes and stimulating peroxisomal and microsomal pathways of fat oxidation. The consequent increased generation of reactive oxygen species (ROS) and reactive aldehydic derivatives causes oxidative stress and cell death, via ATP, NAD, and glutathione depletion and DNA, lipid, and protein damage. Oxidative stress also triggers production of inflammatory cytokines, causing inflammation and a fibrogenic response. This ultimately results in the development of nonalcoholic steatohepatitis (NASH), which can result in end-stage liver disease. The current therapeutic strategies for NASH treatment are mostly directed toward correction of the risk factors. Stimulation of mitochondrial function may also prevent NASH development, protecting the cell against the increased flux of reduced substrates to the ETC and ROS generation.

Peroxisome proliferator-activated receptor alpha target genes

The peroxisome proliferator-activated receptor alpha (PPARα) is a ligand-activated transcription factor involved in the regulation of a variety of processes, ranging from inflammation and immunity to nutrient metabolism and energy homeostasis. PPARα serves as a molecular target for hypolipidemic fibrates drugs which bind the receptor with high affinity. Furthermore, PPARα binds and is activated by numerous fatty acids and fatty acid-derived compounds. PPARα governs biological processes by altering the expression of a large number of target genes. Accordingly, the specific role of PPARα is directly related to the biological function of its target genes. Here, we present an overview of the involvement of PPARα in lipid metabolism and other pathways through a detailed analysis of the different known or putative PPARα target genes. The emphasis is on gene regulation by PPARα in liver although many of the results likely apply to other organs and tissues as well.

Pharmacological and non-pharmacological treatment of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) comprises a disease spectrum ranging from simple steatosis and steatohepatitis to cirrhosis. Based on its strongest risk factors namely visceral obesity and insulin resistance, NAFLD is thought to be the hepatic manifestation of the metabolic syndrome and is considered to be the most common liver disorder in Western countries. Pathophysiological mechanisms include an enlarged pool of fatty acids, subclinical inflammation, oxidative stress and imbalances of various adipocytokines such as adiponectin. Accordingly, targets for therapeutic interventions are miscellaneous: amelioration of obesity by pharmacological, surgical or lifestyle intervention has been evaluated with success in numerous, but not all studies. Some efficacy was reported for metformin and short-term glitazone treatment. In a large recently reported trial, vitamin E supplementation improved biochemical and histological markers in subjects with non-alcoholic steatohepatitis. Blockade of the endocannabinoid system has been proposed to be a promising target in NAFLD; however, very recently the cannabinoid receptor blocker rimonabant has been withdrawn because of central nervous system toxicity. Cytoprotective therapies and statins have been mainly ineffective in NAFLD. New but so far insufficiently studied therapeutic approaches include inhibitors of the renin-angiotensin system as well as incretin mimetics respectively.

On the general mechanism of selective induction of cytochrome P450 enzymes by chemicals: some theoretical considerations

IMPORTANCE OF THE FIELD

The CYP isoforms that are selectively induced following exposure to structurally-diverse chemicals often are the ones capable of metabolizing these chemicals. However, the molecular mechanism underlying this apparent functional coupling is not understood at present.

AREAS COVERED IN THIS REVIEW

Three hypotheses are developed to explain the complex process of selective chemical induction of CYPs: i) each inducible CYP may have a corresponding intracellular receptor that interacts with the inducer chemical and mediates the selective induction of this CYP; ii) each inducible CYP and its corresponding receptor may share highly similar steric structures for their substrate/inducer-binding sites and iii) each chemically-inducible CYP gene may have distinct genomic response element(s) that interact selectively with the corresponding receptor.

WHAT THE READER WILL GAIN

The readers are introduced to a novel theoretical framework that offers a plausible mechanistic explanation at the molecular level concerning the complex process of how an organism selectively activates the biosynthesis of certain CYP isoform(s) that can effectively metabolize a chemical to which the organism is exposed.

TAKE HOME MESSAGE

The theoretical framework developed herein seeks to ignite additional critical thinking on this important research subject as well as to promote experimental testing of the proposed theories in the future. Undoubtedly, these studies will enhance the understanding of the molecular mechanisms for the selective induction of CYP enzymes by chemicals.

Oxidative stress induced by high-glucose diet in liver of C57BL/6J mice and its underlying mechanism

High glycemic index diet can induce multiple diseases. Many research indicated that oxidative stress played important role in many pathological conditions. However, the impact of gene expression and dietary habit on oxidation process are still less clear. We used high-glucose diet to feed C57BL/6J mice for 4 weeks, measured the redox status, physiological and biochemical changes related to diabetes and consequence of metabolic syndrome (nonalcoholic fatty liver, cardiovascular disease), and detected the expressions of 14,446 genes in liver of C57BL/6J mice with DNA microarray. The results showed high-glucose diet induced elevated fatty acid accumulation in liver, insulin resistance index and higher weight in C57BL/6J mice, which indicated high-glucose diet caused to the initiation and development of diabetes and consequence of metabolic syndrome. The results also showed high-glucose diet induced oxidative stress in liver of C57BL/6J mice, which might the cause of initiation and development of diabetes and consequence of metabolic syndrome. Microarray analysis found expressions of genes related to thiol redox, fatty acid oxidation in peroxisome and cytochrome P450 were significantly changed, indicating system in which non-enzyme antioxidant capacity was impaired and sources from which reactive oxygen species (ROS) generated, which revealed the molecular mechanism of oxidative stress induced by high-glucose diet. We validated our microarray findings by conducting real-time RT-PCR assays on selected genes.

Xenobiotic, bile acid, and cholesterol transporters: function and regulation

Transporters influence the disposition of chemicals within the body by participating in absorption, distribution, and elimination. Transporters of the solute carrier family (SLC) comprise a variety of proteins, including organic cation transporters (OCT) 1 to 3, organic cation/carnitine transporters (OCTN) 1 to 3, organic anion transporters (OAT) 1 to 7, various organic anion transporting polypeptide isoforms, sodium taurocholate cotransporting polypeptide, apical sodium-dependent bile acid transporter, peptide transporters (PEPT) 1 and 2, concentrative nucleoside transporters (CNT) 1 to 3, equilibrative nucleoside transporter (ENT) 1 to 3, and multidrug and toxin extrusion transporters (MATE) 1 and 2, which mediate the uptake (except MATEs) of organic anions and cations as well as peptides and nucleosides. Efflux transporters of the ATP-binding cassette superfamily, such as ATP-binding cassette transporter A1 (ABCA1), multidrug resistance proteins (MDR) 1 and 2, bile salt export pump, multidrug resistance-associated proteins (MRP) 1 to 9, breast cancer resistance protein, and ATP-binding cassette subfamily G members 5 and 8, are responsible for the unidirectional export of endogenous and exogenous substances. Other efflux transporters [ATPase copper-transporting beta polypeptide (ATP7B) and ATPase class I type 8B member 1 (ATP8B1) as well as organic solute transporters (OST) alpha and beta] also play major roles in the transport of some endogenous chemicals across biological membranes. This review article provides a comprehensive overview of these transporters (both rodent and human) with regard to tissue distribution, subcellular localization, and substrate preferences. Because uptake and efflux transporters are expressed in multiple cell types, the roles of transporters in a variety of tissues, including the liver, kidneys, intestine, brain, heart, placenta, mammary glands, immune cells, and testes are discussed. Attention is also placed upon a variety of regulatory factors that influence transporter expression and function, including transcriptional activation and post-translational modifications as well as subcellular trafficking. Sex differences, ontogeny, and pharmacological and toxicological regulation of transporters are also addressed. Transporters are important transmembrane proteins that mediate the cellular entry and exit of a wide range of substrates throughout the body and thereby play important roles in human physiology, pharmacology, pathology, and toxicology.

The cytochrome P450 CYP86A22 is a fatty acyl-CoA omega-hydroxylase essential for Estolide synthesis in the stigma of Petunia hybrida

The stigmatic estolide is a lipid-based polyester constituting the major component of exudate in solanaceous plants. Although the exudate is believed to play important roles in the pollination process, the biosynthetic pathway of stigmatic estolide, including genes encoding the key enzymes, remains unknown. Here we report the cloning and characterization of the cytochrome P450 gene CYP86A22, which encodes a fatty acyl-CoA omega-hydroxylase involved in estolide biosynthesis in the stigma of Petunia hybrida. A CYP86A22 cDNA was isolated from a developing stigma cDNA library, and the corresponding gene was shown to express predominantly in the developing stigma. Among six P450 genes isolated from this library, only CYP86A22 was implicated in omega-hydroxylation following RNA interference (RNAi)-mediated suppression. Unlike wild-type plants in which omega-hydroxy fatty acids (mainly in the form of 18-hydroxy oleic acid and 18-hydroxy linoleic acid) compose 96% of total stigma fatty acids, the omega-hydroxy fatty acids were essentially absent in the stigmas from 18 of 46 CYP86A22-RNAi transgenic plants and had varying levels of suppression in the remaining 28 plants. Furthermore, lipids in the 18 CYP86A22-RNAi stigmas were predominantly triacylglycerols and diacylglycerols instead of the estolides, which characterize the wild-type stigma. Analyses of recombinant CYP86A22 conclusively demonstrated that this P450 is a omega-hydroxylase with a substrate preference for both saturated and unsaturated acyl-CoAs rather than free fatty acids. We conclude that the cytochrome P450 enzyme CYP86A22 is the key fatty acyl-CoA omega-hydroxylase essential for the production of omega-hydroxy fatty acids and the biosynthesis of triacylglycerol-/diacylglycerol-based estolide polyesters in the petunia stigma.

Mouse carnitine-acylcarnitine translocase (CACT) is transcriptionally regulated by PPARalpha and PPARdelta in liver cells

BACKGROUND

Hepatic PPARalpha acts as the primary mediator of the adaptive response to fasting by upregulation of a number of genes involved in fatty acid catabolism. Whether carnitine-acylcarnitine translocase (CACT), which mediates the import of acylcarnitines into the mitochondrial matrix for subsequent beta-oxidation of fatty acid moieties, is also regulated by PPARalpha in the liver has not yet been investigated.

METHODS AND RESULTS

Herein, we observed that hepatic mRNA abundance of CACT was increased by both, fasting and treatment with PPARalpha agonist WY-14,643 in wild-type mice but not PPARalpha-knockout mice (P<0.05). Cell culture experiments revealed that CACT mRNA abundance was higher in liver cells treated with either WY-14,643 or PPARdelta agonist GW0742, but not with PPARgamma agonist troglitazone (TGZ) than in control cells (P<0.05). In addition, reporter assays revealed activation of mouse CACT promoter by WY-14,643 and GW0742, but not TGZ. Moreover, deletion and mutation analyses of CACT promoter and 5'-UTR revealed one functional PPRE in the 5'-UTR of mouse CACT.

GENERAL SIGNIFICANCE

CACT is upregulated by PPARalpha and PPARdelta, probably by binding to a functional PPRE at position +45 to +57 relative to the transcription start site. The upregulation of CACT by PPARalpha and PPARdelta, which are both important for the regulation of fatty acid oxidation in tissues during fasting, may increase the import of acylcarnitine into the mitochondrial matrix during fasting.

Opposing roles of peroxisome proliferator-activated receptor alpha and growth hormone in the regulation of CYP4A11 expression in a transgenic mouse model

CYP4A11 transgenic mice (CYP4A11 Tg) were generated to examine in vivo regulation of the human CYP4A11 gene. Expression of CYP4A11 in mice yields liver and kidney P450 4A11 levels similar to those found in the corresponding human tissues and leads to an increased microsomal capacity for omega-hydroxylation of lauric acid. Fasted CYP4A11 Tg mice exhibit 2-3-fold increases in hepatic CYP4A11 mRNA and protein, and this response is absent in peroxisome proliferator-activated receptor alpha (PPARalpha) null mice. Dietary administration of either of the PPARalpha agonists, fenofibrate or clofibric acid, increases hepatic and renal CYP4A11 levels by 2-3-fold, and these responses were also abrogated in PPARalpha null mice. Basal liver CYP4A11 levels are reduced differentially in PPARalpha-/- females (>95%) and males (<50%) compared with PPARalpha-/+ mice. Quantitative and temporal differences in growth hormone secretion are known to alter hepatic lipid metabolism and to underlie sexually dimorphic gene expression, respectively. Continuous infusion of low levels of growth hormone reduced CYP4A11 expression by 50% in PPARalpha-proficient male and female transgenic mice. A larger decrease was observed for the expression of CYP4A11 in PPARalpha-/- CYP4A11 Tg male mice to levels similar to that of female PPARalpha-deficient mice. These results suggest that PPARalpha contributes to the maintenance of basal CYP4A11 expression and mediates CYP4A11 induction in response to fibrates or fasting. In contrast, increased exposure to growth hormone down-regulates CYP4A11 expression in liver.

Hypolipidemic effects of silymarin are not mediated by the peroxisome proliferator-activated receptor alpha

Silymarin is widely used in supportive therapy of liver diseases. It has been shown lately that silymarin has beneficial effects on some risk factors of atherosclerosis owing to its hypolipidemic properties. PPARalpha plays a key role in lipid metabolism and homeostasis as its target genes are involved in catabolism of fatty acids by beta-oxidation (e.g. acyl-CoA oxidase) and by omega-oxidation (e.g. cytochrome P4504A). Here we studied the possibility that hypolipidemic effects of silymarin may be mediated by PPARalpha. Rats fed with a high-cholesterol diet with either silymarin or fenofibrate (as a positive control both for PPARalpha expression as well as for lipid determination) were used. The effects of silymarin on expression of PPARalpha both at the mRNA (including selected target genes) as well as the protein level were determined. In parallel, the levels of cholesterol and triacylglycerols were determined. Our results confirmed the hypolipidemic effects of silymarin and demonstrated that these effects are probably not mediated by PPARalpha because of unchanged mRNA levels of PPARalpha target genes. Furthermore, this work shows for the first time that cholesterol itself inhibits expression of CYP4A mRNA.

Effects of ertiprotafib on hepatic cytochrome P450 and peroxisomal enzymes in rats and dogs, and in rat and human primary hepatocytes

Ertiprotafib (ERTI) significantly increased liver weights in male and female rats, and moderately increased liver weights in male dogs after treatment for 28 days. The present study tested the hypotheses that the organ weight increases were associated with peroxisome proliferation in rats and induction of hepatic enzymes in rats and dogs, and would have limited impacts on humans. At a dosage of 200 mg kg-1 day-1, CYP4A was induced by tenfold in male rats and 2.4-fold in female rats. In male rats, CYP2B was induced by 1.2-fold and CYP3A was induced by 1.7-fold. Palmitoyl CoA oxidase was induced by 5.1-fold in male rats and 2.9-fold in female rats; carnitine acetyltransferase was induced by 10.4-fold in male rats and 5.2-fold in female rats. CYP3A, CYP4A and peroxisomal enzymes were not induced in dogs at 150/200 mg kg-1 day-1. ERTI at 50 microM markedly induced the mRNA level of CYP4A by up to fivefold in rat hepatocytes, but not in human primary hepatocytes. In conclusion, the liver weight increases observed in rats treated with ERTI appears to be due to rodent-specific peroxisome proliferation and the substantial induction of CYP4A1. ERTI is not a potent P450 inducer in dogs or in human hepatocytes. Therefore, ERTI is not expected to exert any significant effects on hepatic drug-metabolizing enzymes in humans.

Biomarker induction in tropical fish species on the Northwest Shelf of Australia by produced formation water

Normal operation of oil well platforms results in the discharge of produced formation water (PFW). The expression of CYP1A, CYP2M1- and 2K1-like proteins was examined for use as possible biomarkers of PFW exposure. A pilot study on the Northwest Shelf of Australia had indicated that PFW contamination possibly contributes to induction of CYP1A-like proteins in Gold-Spotted Trevally (Carangoides fulvoguttatus). The pilot study samples were re-examined for CYP1A, and, in addition, CYP2K1/2M1-like proteins. In a subsequent caged fish study in the same location a second species, Stripey seaperch (Lutjanus carponotatus), caught at a clean site, were distributed to three caging sites in a PFW gradient from the Harriet A production platform: A (near-field), B (far-field) and C (a non-impacted reference site). Fish were sampled at time (T) T = 0, T = 3 and T = 10 days. Significant increases of CYP1A, one CYP2K1- and two CYP2M1-like proteins were noted at Site A at T = 10d. For another CYP2K1-like protein, a significant increase was observed at Site A only at T = 3d. These results support a previous study indicating that CYP1A protein is sensitive to PFW exposure. Importantly, statistically significant environmental induction of both CYP2M1- and CYP2K1-like proteins in tropical fish due to PFW exposure had not previously been described and induction of enzymes in the CYP2 family suggest new biomarkers for PFW. In addition, the novel response of one CYP2K-like protein requires further verification, but offers promise for improved monitoring of sub-lethal responses in marine organisms.

Genomic structure and regulation of the rat hepatic CYP4F1 gene by peroxisome proliferators

The rat hepatic gene CYP4F1 encodes a fatty acid omega hydroxylase P450 that metabolizes proinflammatory eicosanoids and long-chain fatty acids. We have completely sequenced the CYP4F1 gene (Accession Nos. AF200361 and AF181083), identified multiple transcription start sites, and characterized a strong core promoter region, -760/116, induced by retinoic acids and peroxisome proliferators in rat hepatoma McA-RH7777 cells. Three peroxisome proliferator responsive elements (PPRE) bind both PPARalpha/RXRalpha and HNF4alpha. Co-transfection of McA-RH7777 cells with the -760/116 reporter construct and PPARalpha/RXRalpha or HNF4alpha showed that HNF4alpha activated while PPARalpha/RXRalpha inhibited CYP4F1 promoter activity. Treating cells with Wy14,643 reversed all initial effects, indicating co-regulation of CYP4F1 gene transcription by PPARalpha/RXRalpha and HNF4alpha. Chromatin immunoprecipitation analysis of cells treated with Wy14,643 showed association of PPARalpha/RXRalpha with the active transcription of the CYP4F1 gene while in clofibrate treated rats HNF4alpha binds during gene repression, suggesting differential regulation of the CYP4F1 gene in vivo and in cell lines.

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.

Hepatic nuclear receptor PPARalpha in the koala (Phascolarctos cinereus): cloning and molecular characterisation

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear/steroid receptor gene superfamily that plays an essential role in fatty acid metabolism. PPARalpha modulates the expression of genes encoding peroxisomal fatty acid beta-oxidation enzymes and microsomal fatty acid hydroxylases CYP4As. We have previously reported that the obligate Eucalyptus feeder koala (Phascolarctos cinereus) exhibits a higher hepatic CYP4A activity and an absence of peroxisomal palmitoyl-CoA oxidation as compared to non-Eucalyptus feeders human, rat or wallaby. Here we describe the cloning, expression and molecular characterisation of koala hepatic PPARalpha. A full-length PPARalpha cDNA of size 1515 bp was cloned by reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (RACE). The koala PPARalpha cDNA encodes a protein of 468 amino acids. Transfection of the koala PPARalpha cDNA into Cos-7 cells resulted in the expression of a protein recognised by a rabbit anti-human PPARalpha polyclonal antibody. PPARalpha immunoreactive bands of the same molecular mass were detected in nuclear extracts of koala livers. The results of this study demonstrate the presence of koala hepatic PPARalpha which shares several common features with other published PPARalphas; however, it exhibits important differences in both the DNA and ligand binding domains.

Energizing miRNA research: a review of the role of miRNAs in lipid metabolism, with a prediction that miR-103/107 regulates human metabolic pathways

MicroRNAs (miRNAs) are powerful regulators of gene expression. Although first discovered in worm larvae, miRNAs play fundamental biological roles-including in humans-well beyond development. MiRNAs participate in the regulation of metabolism (including lipid metabolism) for all animal species studied. A review of the fascinating and fast-growing literature on miRNA regulation of metabolism can be parsed into three main categories: (1) adipocyte biochemistry and cell fate determination; (2) regulation of metabolic biochemistry in invertebrates; and (3) regulation of metabolic biochemistry in mammals. Most research into the 'function' of a given miRNA in metabolic pathways has concentrated on a given miRNA acting upon a particular 'target' mRNA. Whereas in some biological contexts the effects of a given miRNA:mRNA pair may predominate, this might not be the case generally. In order to provide an example of how a single miRNA could regulate multiple 'target' mRNAs or even entire human metabolic pathways, we include a discussion of metabolic pathways that are predicted to be regulated by the miRNA paralogs, miR-103 and miR-107. These miRNAs, which exist in vertebrate genomes within introns of the pantothenate kinase (PANK) genes, are predicted by bioinformatics to affect multiple mRNA targets in pathways that involve cellular Acetyl-CoA and lipid levels. Significantly, PANK enzymes also affect these pathways, so the miRNA and 'host' gene may act synergistically. These predictions require experimental verification. In conclusion, a review of the literature on miRNA regulation of metabolism leads us believe that the future will provide researchers with many additional energizing revelations.

An antioxidant effect by acyclic retinoid suppresses liver tumor in mice

The mechanisms of prevention of the development of liver cancer by NIK-333, an acyclic retinoid (ACR), were investigated. The transgenic mice expressing the dominant negative form of retinoic acid receptor alpha (RARE mice), that produce reactive oxygen species and lead to development of liver tumor were used. The effect of NIK-333 on hepatocarcinogenesis in RARE mice was studied. The RARE mice were examined after feeding 0.03% and 0.06% NIK-333 diets at 12 months of age. In the mice fed 0.06% NIK-333 diet, tumor incidence was greatly suppressed, compared to that of wild type mice (0/9 versus 5/9, P<0.05), but not in the mice fed 0.03% NIK-333 diet. In addition, expression of cytochrome p450 4a14 and acyl-CoA oxidase was normalized, and the percentages of positive cells for 8-hydroxy-2'-deoxyguanosine, 4-hydroxy-2-nonenal and proliferating cell nuclear antigen were decreased. Furthermore, expression of beta-catenin and cyclin D1 was also depressed. These data suggest that NIK-333 suppressed liver tumor in association with repression of oxidative stress.

Catalytic characterization and cytokine mediated regulation of cytochrome P450 4Fs in rat hepatocytes

Cytochrome P450 (CYP) 4F mediated leukotriene B(4) (LTB(4)) metabolism modulates inflammation during injury and infection. Here we show that in addition to LTB(4), the recombinant rat CYP4Fs catalyze omega-hydroxylations of lipoxin A(4), and hydroxyeicosatetraeonic acids. CYP4F gene regulation studies in primary hepatocytes reveal that pro-inflammatory cytokines interleukin (IL) -1beta, IL-6 and tumor necrosis factor (TNF) -alpha produce a general inductive response whereas IL-10, an anti-inflammatory cytokine, suppresses CYP4F expression. The molecular mechanism behind IL-6 related induction of CYP4F4 and 4F5 is partially signal transducer and activator of transcription 3 (STAT3) dependent. When hepatocytes are subjected to high concentrations of LTB(4) or prostaglandin E(2), lipid mediators of inflammation, only an increase in CYP4F5 mRNA expression is observed. Collectively, the results from isozyme activity and substrate driven CYP4F induction do not support the notion that an autoregulatory pathway could control the excessive concentrations of LTB(4) during an inflammatory challenge to hepatocytes.

Regulation of the rat CYP4A2 gene promoter by c-Jun and octamer binding protein-1

The physiologically important cytochrome P450 (CYP) 4A2 arachidonic acid omega-hydroxylase gene is widely expressed in rat tissues. Although the induction of CYPs 4A by peroxisome proliferators and dietary lipids is established there is minimal information on the factors that control constitutive expression. To address this issue we cloned 1.4 kb of the CYP4A2 5'-upstream region and identified several DNA elements that resembled the activator protein-1 (AP-1) consensus sequence. Using a series of 5'-truncated reporter constructs a 42 bp region was detected that was responsive to the AP-1 factor c-Jun, which is important in basal gene regulation. The roles of two putative AP-1 elements at -47/-41 and -31/-25 were tested, with the former emerging from studies with mutagenised constructs as the functionally important site. These findings were supported by electromobility shift assay (EMSA) studies that indicated the interaction of the -47/-41 element with c-Jun. The -31/-25 element mediated the suppression of CYP4A2 transactivation by octamer binding protein-1 (oct-1). Thus, mutagenesis of this element relieved the modulatory effect of oct-1 on c-Jun-mediated transactivation. In EMSAs, the binding of nuclear proteins to the -31/-25 element was competed by an oct-1 consensus sequence and supershifted by an anti-oct-1 antibody. Overexpression of c-Jun in rat liver-derived H4IIE cells increased CYP4A2 mRNA to approximately 2-fold of control, but oct-1 overexpression was without significant effect. From chromatin immunoprecipitation assays both c-Jun and oct-1 bound to the CYP4A2 5'-upstream sequence in H4IIE cells. These findings implicate c-Jun and oct-1 as potentially important constitutive factors that modulate the transactivation of the CYP4A2 gene promoter.