Peroxisome proliferator-activated receptor alpha plays a vital role in inducing a detoxification system against plant compounds with crosstalk with other xenobiotic nuclear receptors

Concentration-dependent effects of chlorpyrifos oxon on peroxisome proliferator-activated receptor signaling in MCF-7 cells

Chlorpyrifos oxon (CPO) is the active metabolite of the organophosphorus pesticide, chlorpyrifos. CPO is a potent inhibitor of acetylcholinesterase (AChE) and other serine hydrolases including fatty acid amide hydrolase (FAAH). AChE is critical in regulating cholinergic signaling while FAAH catalyzes the inactivation of fatty acid signaling lipids including the endocannabinoid (eCB) N-arachidonylethanolamine (anandamide, AEA) and eCB-like metabolites (e.g., oleoylethanolamide, OEA). AEA and OEA are both peroxisome proliferator-activated receptor (PPAR) agonists that regulate numerous genes involved in lipid metabolism and energy homeostasis. We used the MCF-7 human breast cancer cell line, which expresses AChE, FAAH and PPAR alpha and gamma subtypes, to evaluate the potential effects of CPO on PPAR-related gene expression in an in vitro human cell system. CPO elicited relatively similar concentration-dependent inhibition of both AChE and FAAH. Marked concentration- and time-dependent changes in the expression of four selected PPAR-related genes, LXRα, ACOX1, ABCG2 and AGPAT2, were noted. These findings suggest chlorpyrifos may influence lipid metabolism through blocking the degradation of eCBs or eCB-like metabolites and in turn affecting PPAR receptor activation. The results highlight the potential for non-cholinesterase actions of this common insecticide metabolite through disruption of PPAR signaling including effects on lipid metabolism, immune function and inflammation.

Increased risk of acute liver failure by pain killer drugs in NAFLD: Focus on nuclear receptors and their coactivators

Non-alcoholic fatty liver disease (NAFLD) is a global condition characterized by an accumulation of lipids in the hepatocytes. NAFLD ranges from simple steatosis, a reversible and relatively benign condition, to fibrosis with non-alcoholic steatohepatitis (NASH), potentially leading to cirrhosis and hepatocarcinoma. NAFLD can increase the susceptibility to severe liver injury with eventual acute liver failure induced by specific hepatotoxic drugs, including acetaminophen (APAP), which is commonly used as analgesic and antipyretic. Although several animal models have been used to clarify the predisposing role of hepatic steatosis to APAP intoxication, the exact mechanism is still not clear. Here, we shed a light into the association between NAFLD and APAP toxicity by examining the peculiar role of nuclear receptor peroxisome proliferator-activated receptor α (PPARα) and coactivator peroxisome proliferator-activated receptor gamma coactivator 1-β (PGC-1β) in driving fatty acid metabolism, inflammation and mitochondria redox balance. The knowledge of the mechanism that exposes patients with NAFLD to higher risk of acute liver failure by pain killer drug is the first step to eventually claim for a reduction of the maximal diurnal dose of APAP for subjects with liver steatosis.

Xenobiotic Receptors and Their Mates in Atopic Dermatitis

Atopic dermatitis (AD) is the most common inflammatory skin disease worldwide. It is a chronic, relapsing and pruritic skin disorder which results from epidermal barrier abnormalities and immune dysregulation, both modulated by environmental factors. AD is strongly associated with asthma and allergic rhinitis in the so-called 'atopic march.' Xenobiotic receptors and their mates are ligand-activated transcription factors expressed in the skin where they control cellular detoxification pathways. Moreover, they regulate the expression of genes in pathways involved in AD in epithelial cells and immune cells. Activation or overexpression of xenobiotic receptors in the skin can be deleterious or beneficial, depending on context, ligand and activation duration. Moreover, their impact on skin might be amplified by crosstalk among xenobiotic receptors and their mates. Because they are activated by a broad range of endogenous molecules, drugs and pollutants owing to their promiscuous ligand affinity, they have recently crystalized the attention of researchers, including in dermatology and especially in the AD field. This review examines the putative roles of these receptors in AD by critically evaluating the conditions under which the proteins and their ligands have been studied. This information should provide new insights into AD pathogenesis and ways to develop new therapeutic interventions.

[Lessons Learned after 25 Years of Studies on the Physiological Roles of the Peroxisome Proliferator-activated Receptor]

The peroxisome proliferator-activated receptor (PPAR) was discovered a quarter of a century ago. PPAR was soon recognized as a general transcriptional regulator of lipid homeostasis, and several hypolipidemic and antidiabetic agents were shown to be effective ligands for it. Since then, many attempts to develop more potent drugs have been made worldwide, but most were unsuccessful due to serious side effects. It appears that the PPAR boom has ended. This review summarizes the short history of PPAR studies, including our own results, and discusses the lessons learned from the rise and fall of studies in this field for next-generation basic studies and drug development research.

Potential approaches to ameliorate hepatic fat accumulation seen with MTP inhibition

Microsomal triglyceride transfer protein (MTP) is one of the promising targets for the therapy of dyslipidemia and MTP inhibition can lead to robust plasma low-density lipoprotein cholesterol (LDL-C) reduction. Lomitapide, a small-molecule MTP inhibitor, was recently approved by the US FDA as an additional treatment for homozygous familial hypercholesterolemia (hoFH). However, liver-related side effects, including hepatic fat accumulation and transaminase elevations, are the main safety concerns associated with MTP inhibitors. Here, we review recent knowledge on the mechanisms underlying liver toxicity of MTP inhibitors. The contribution of altered levels of intracellular triglycerides, cholesteryl esters, and free cholesterols toward cellular dysfunction is specifically addressed. On this basis, therapies targeted to attenuate cellular lipid accumulation, to reduce risk factors for non-alcoholic fatty liver disease (NAFLD) (i.e., insulin resistance and oxidative stress) and to specifically inhibit intestinal MTP may be useful for ameliorating liver damage induced by MTP inhibitors. In particular, weight loss through lifestyle interventions is expected to be the most effective and safest way to minimize the undesirable side effects. Specific dietary supplementation might also have protective effects against hepatosteatosis. Despite that, to date, few clinical data support these therapeutic options in MTP inhibition-related liver damage, such proposed approaches may be further explored in the future for their use in preventing unwanted effects of MTP inhibitors.

Chronopharmacokinetics of drugs in toxicological aspects: A short review for pharmacy practitioners

A rough 24-hour cycle driven endogenously in biochemical, physiological or behavioral processes is called circadian rhythm. Chronobiology is the study of biological temporal rhythms. For decades, we know that the biological rhythm and the drug metabolism are also affected from daylight and chronopharmacology became recognized by scientists in the early 1970s. Its lateral branch chronocopharmacokinetics is the study of rhythmic, predictable-in-time differences in the pharmacokinetics of drugs. Chronopharmacokinetic studies are performed at every step of the biotransformation i.e., absorption, distribution, metabolism and excretion. Feeding schedules, sex and phenotype must be taken into consideration while applying pharmacotherapy to increase the efficiency and to decrease side effects. The impact of drugs on circadian rhythm should be not neglected. On the other hand, new special drug delivery systems can be used to synchronize drug concentrations according to circadian rhythms. “Chronopharmaceuticals” can identify the proper dosing time and this amelioration will lead to improved progress and diffusion of pharmacotherapy. Chronopharmaceuticals coupled with nanotechnology could be the future of drug delivery systems, and lead to safer and more efficient disease therapy in the future. In this review, we will discuss the pharmacokinetic effects of circadian rhythm and its toxicological outcomes. Besides, we will try to give some practical points for clinical pharmacist/pharmacy practitioners, concerning chronopharmacokinetics.

Severe hypoxia exerts parallel and cell-specific regulation of gene expression and alternative splicing in human mesenchymal stem cells

BACKGROUND

The endosteum of the bone marrow provides a specialized hypoxic niche that may serve to preserve the integrity, pluripotency, longevity and stemness of resident mesenchymal stem cells (MSCs). To explore the molecular genetic consequences of such a niche we subjected human (h) MSCs to a pO2 of 4 mmHg and analyzed global gene expression and alternative splicing (AS) by genome-exon microarray and RT-qPCR, and phenotype by western blot and immunostaining.

RESULTS

Out of 446 genes differentially regulated by >2.5-fold, down-regulated genes outnumbered up-regulated genes by 243:203. Exon analyses revealed 60 hypoxia-regulated AS events with splice indices (SI) >1.0 from 53 genes and a correlation between high SI and degree of transcript regulation. Parallel analyses of a publicly available AS study on human umbilical vein endothelial cells (HUVECs) showed that there was a strong cell-specific component with only 11 genes commonly regulated in hMSCs and HUVECs and 17 common differentially spliced genes. Only 3 genes were differentially responsive to hypoxia at the gene (>2.0) and AS levels in both cell types. Functional assignments revealed unique profiles of gene expression with complex regulation of differentiation, extracellular matrix, intermediate filament and metabolic marker genes. Antioxidant genes, striated muscle genes and insulin/IGF-1 signaling intermediates were down-regulated. There was a coordinate induction of 9 out of 12 acidic keratins that along with other epithelial and cell adhesion markers implies a partial mesenchymal to epithelial transition.

CONCLUSIONS

We conclude that severe hypoxia confers a quiescent phenotype in hMSCs that is reflected by both the transcriptome profile and gene-specific changes of splicosome actions. The results reveal that severe hypoxia imposes markedly different patterns of gene regulation of MSCs compared with more moderate hypoxia. This is the first study to report hypoxia-regulation of AS in stem/progenitor cells and the first molecular genetic characterization of MSC in a hypoxia-induced quiescent immobile state.

Regulation of energy metabolism by long-chain fatty acids

In mammals, excess energy is stored primarily as triglycerides, which are mobilized when energy demands arise. This review mainly focuses on the role of long chain fatty acids (LCFAs) in regulating energy metabolism as ligands of peroxisome proliferator-activated receptors (PPARs). PPAR-alpha expressed primarily in liver is essential for metabolic adaptation to starvation by inducing genes for beta-oxidation and ketogenesis and by downregulating energy expenditure through fibroblast growth factor 21. PPAR-delta is highly expressed in skeletal muscle and induces genes for LCFA oxidation during fasting and endurance exercise. PPAR-delta also regulates glucose metabolism and mitochondrial biogenesis by inducing FOXO1 and PGC1-alpha. Genes targeted by PPAR-gamma in adipocytes suggest that PPAR-gamma senses incoming non-esterified LCFAs and induces the pathways to store LCFAs as triglycerides. Adiponectin, another important target of PPAR-gamma may act as a spacer between adipocytes to maintain their metabolic activity and insulin sensitivity. Another topic of this review is effects of skin LCFAs on energy metabolism. Specific LCFAs are required for the synthesis of skin lipids, which are essential for water barrier and thermal insulation functions of the skin. Disturbance of skin lipid metabolism often causes apparent resistance to developing obesity at the expense of normal skin function.

The use of transcriptomics to unveil the role of nutrients in Mammalian liver

Liver is the organ primarily responding to diet, and it is crucial in determining plasma carbohydrate, protein, and lipid levels. In addition, it is mainly responsible for transformation of xenobiotics. For these reasons, it has been a target of transcriptomic analyses. In this review, we have covered the works dealing with the response of mammalian liver to different nutritional stimuli such as fasting/feeding, caloric restriction, dietary carbohydrate, cholesterol, fat, protein, bile acid, salt, vitamin, and oligoelement contents. Quality of fats or proteins has been equally addressed, and has the influence of minor dietary components. Other compounds, not purely nutritional as those represented by alcohol and food additives, have been included due to their relevance in processed food. The influence has been studied not only on mRNA but also on miRNA. The wide scope of the technology clearly reflects that any simple intervention has profound changes in many metabolic parameters and that there is a synergy in response when more compounds are included in the intervention. Standardized arrays to systematically test the same genes in all studies and analyzing data to establish patterns of response are required, particularly for RNA sequencing. Moreover, RNA is a valuable, easy-screening ally but always requires further confirmation.

PPARα as a Transcriptional Regulator for Detoxification of Plant Diet-Derived Unfavorable Compounds

Plants contain potentially toxic compounds for animals and animals have developed physiological strategies to detoxify the ingested toxins during evolution. Feeding mice with various plant seeds and grains showed unexpected result that only sesame killed PPARα-null mice but not wild-type mice at all. A detailed analysis of this observation revealed that PPARα is involved in the metabolism of toxic compounds from plants as well as endobiotic substrates by inducing phase I and phase II detoxification enzymes. PPARα plays a vital role in direct or indirect activation of the relevant genes via the complex network among other xenobiotic nuclear receptors. Thus, PPARα plays its wider and more extensive role in energy metabolism from natural food intake to fat storage than previously thought.

Physiologic roles of hepatic lipid droplets and involvement of peroxisome proliferator-activated receptor alpha in their dynamism

The liver is not a storage site of excess energy as triacylglycerides but a major site of carbohydrate storage, playing a vital role in glucose homeostasis, and the hepatic lipid droplets (LDs) should have a distinct physiologic role from those in lipid-storing tissues. Most studies so far have been limited to characterization of the LDs in cultured cells or of the liver of animals maintained on a normal laboratory diet, and little is known about the properties of the LDs in the liver responding to dietary excess, irregular fats, and potentially toxic compounds contained in a natural food diet. We started to characterize the hepatic LDs in wild-type and peroxisome proliferator-activated receptor alpha (PPARalpha)-null mice fed various natural diets by identifying the liver-enriched LD-associated proteins and the changes in lipid compositions. Based on the currently available data, we propose the hypothesis that hepatic LDs play vital protective roles against diet-derived excess fatty acids and potentially toxic hydrophobic compounds by temporarily storing them as neutral lipids or compounds until completion of the remodeling of fatty acids and detoxification of the compounds in a PPARalpha-dependent manner.

Identification and characterization of the ER/lipid droplet-targeting sequence in 17beta-hydroxysteroid dehydrogenase type 11

17beta-Hydroxysteroid dehydrogenase type 11 (17betaHSD11) is mostly localized on the endoplasmic reticulum (ER) membrane under normal conditions and redistributes to lipid droplets (LDs) when the formation of LDs is induced. In this study, confocal microscopy analyses of the subcellular localization of the mutated 17betaHSD11 proteins in cells with or without LDs revealed that both an N-terminal hydrophobic sequence and an adjacent sequence that has a weak homology with the PAT motif are independently necessary and both parts together (28 amino acid residues in total) are sufficient for the dual localization of 17betaHSD11. Mutation analyses suggest that the PAT-like motif in 17betaHSD11 will not be functionally similar to the canonical PAT motif. Hsp60 was identified as a possibly interacting protein with the PAT-like motif, and biochemical and microscopic analyses suggest that Hsp60 may be partly, but not necessarily involved in recognition of the PAT-like part of the targeting sequence of 17betaHSD11.

Characterization of human DHRS4: an inducible short-chain dehydrogenase/reductase enzyme with 3beta-hydroxysteroid dehydrogenase activity

Human DHRS4 is a peroxisomal member of the short-chain dehydrogenase/reductase superfamily, but its enzymatic properties, except for displaying NADP(H)-dependent retinol dehydrogenase/reductase activity, are unknown. We show that the human enzyme, a tetramer composed of 27kDa subunits, is inactivated at low temperature without dissociation into subunits. The cold inactivation was prevented by a mutation of Thr177 with the corresponding residue, Asn, in cold-stable pig DHRS4, where this residue is hydrogen-bonded to Asn165 in a substrate-binding loop of other subunit. Human DHRS4 reduced various aromatic ketones and alpha-dicarbonyl compounds including cytotoxic 9,10-phenanthrenequinone. The overexpression of the peroxisomal enzyme in cultured cells did not increase the cytotoxicity of 9,10-phenanthrenequinone. While its activity towards all-trans-retinal was low, human DHRS4 efficiently reduced 3-keto-C(19)/C(21)-steroids into 3beta-hydroxysteroids. The stereospecific conversion to 3beta-hydroxysteroids was observed in endothelial cells transfected with vectors expressing the enzyme. The mRNA for the enzyme was ubiquitously expressed in human tissues and several cancer cells, and the enzyme in HepG2 cells was induced by peroxisome-proliferator-activated receptor alpha ligands. The results suggest a novel mechanism of cold inactivation and role of the inducible human DHRS4 in 3beta-hydroxysteroid synthesis and xenobiotic carbonyl metabolism.

17beta-Hydroxysteroid dehydrogenase type 13 is a liver-specific lipid droplet-associated protein

17beta-Hydroxysteroid dehydrogenase (17betaHSD) type 13 is identified as a new lipid droplet-associated protein. 17betaHSD type 13 has an N-terminal sequence similar to that of 17betaHSD type 11, and both sequences function as an endoplasmic reticulum and lipid droplet-targeting signal. Localization of native 17betaHSD type 13 on the lipid droplets was confirmed by subcellular fractionation and Western blotting. In contrast to 17betaHSD type 11, however, expression of 17betaHSD type 13 is largely restricted to the liver and is not enhanced by peroxisome proliferator-activated receptor alpha and its ligand. Instead the expression level of 17betaHSD type 13 in the receptor-null mice was increased several-fold. 17betaHSD type 13 may have a distinct physiological role as a lipid droplet-associated protein in the liver.

Alpha-methylacyl-CoA racemase--an 'obscure' metabolic enzyme takes centre stage

Branched-chain lipids are important components of the human diet and are used as drug molecules, e.g. ibuprofen. Owing to the presence of methyl groups on their carbon chains, they cannot be metabolized in mitochondria, and instead are processed and degraded in peroxisomes. Several different oxidative degradation pathways for these lipids are known, including alpha-oxidation, beta-oxidation, and omega-oxidation. Dietary branched-chain lipids (especially phytanic acid) have attracted much attention in recent years, due to their link with prostate, breast, colon and other cancers as well as their role in neurological disease. A central role in all the metabolic pathways is played by alpha-methylacyl-CoA racemase (AMACR), which regulates metabolism of these lipids and drugs. AMACR catalyses the chiral inversion of a diverse number of 2-methyl acids (as their CoA esters), and regulates the entry of branched-chain lipids into the peroxisomal and mitochondrial beta-oxidation pathways. This review brings together advances in the different disciplines, and considers new research in both the metabolism of branched-chain lipids and their role in cancer, with particular emphasis on the crucial role played by AMACR. These recent advances enable new preventative and treatment strategies for cancer.

PPARalpha agonists positively and negatively regulate the expression of several nutrient/drug transporters in mouse small intestine

A systematic analysis to examine the effects of peroxisome proliferator-activated receptor (PPAR)alpha agonists on the expression levels of all the nutrient/drug plasma-membrane transporters in the mouse small intestine was performed. Transporter mRNAs that were induced or repressed by two independent PPARalpha-specific agonists were identified by a genome-wide microarray method, and the changes were confirmed by real-time PCR using RNA isolated from the intestines and livers of wild-type and PPARalpha-null mice. Expression levels of seven nutrient/drug transporters (Abcd3, Octn2/Slc22a5, FATP2/Slc27a2, Slc22a21, Mct13/Slc16a13, Slc23a1 and Bcrp/Abcg2) in the intestine were up-regulated and the expression level of one (Mrp1/Abcc1) was down-regulated by PPARalpha; although the previously report that the H(+)/peptide co-transporter 1 (Pept1) is up-regulated by PPARalpha was not replicated in our study. We propose that the transport processes can be coordinately regulated with intracellular metabolism by nutrient nuclear receptors.

Regulated expression by PPARalpha and unique localization of 17beta-hydroxysteroid dehydrogenase type 11 protein in mouse intestine and liver

17beta-Hydroxysteroid dehydrogenase type 11 (17beta-HSD11) is a member of the short-chain dehydrogenase/reductase family involved in the activation and inactivation of sex steroid hormones. We recently identified 17beta-HSD11 as a gene that is efficiently regulated by peroxisome proliferator-activated receptor-alpha PPARalpha in the intestine and the liver [Motojima K (2004) Eur J Biochem271, 4141-4146]. In this study, we characterized 17beta-HSD11 at the protein level to obtain information about its physiologic role in the intestine and liver. For this purpose, specific antibodies against 17beta-HSD11 were obtained. Western blotting analysis showed that administration of a peroxisome proliferator-activated receptor-alpha agonist induced 17beta-HSD11 protein in the jejunum but not in the colon, and to a much higher extent than in the liver of mice. A subcellular localization study using Chinese hamster ovary cells and green fluorescent protein-tagged 17beta-HSD11 showed that it was mostly localized in the endoplasmic reticulum under normal conditions, whereas it was concentrated on lipid droplets when they were induced. A pulse-chase experiment suggested that 17beta-HSD11 was redistributed to the lipid droplets via the endoplasmic reticulum. Immunohistochemical analysis using tissue sections showed that 17beta-HSD11 was induced mostly in intestinal epithelia and hepatocytes, with heterogeneous localization both in the cytoplasm and in vesicular structures. A subcellular fractionation study of liver homogenates confirmed that 17beta-HSD11 was localized mostly in the endoplasmic reticulum when mice were fed a normal diet, but was distributed in both the endoplasmic reticulum and the lipid droplets of which formation was induced by feeding a diet containing a proliferator-activated receptor-alpha agonist. Taken together, these data indicate that 17beta-HSD11 localizes both in the endoplasmic reticulum and in lipid droplets, depending on physiologic conditions, and that lipid droplet 17beta-HSD11 is not merely an endoplasmic reticulum contaminant or a nonphysiologically associated protein in the cultured cells, but a bona fide protein component of the membranes of both intracellular compartments.

Dual subcellular localization in the endoplasmic reticulum and peroxisomes and a vital role in protecting against oxidative stress of fatty aldehyde dehydrogenase are achieved by alternative splicing

Fatty aldehyde dehydrogenase (FALDH, ALDH3A2) is thought to be involved in the degradation of phytanic acid, a saturated branched chain fatty acid derived from chlorophyll. However, the identity, subcellular distribution, and physiological roles of FALDH are unclear because several variants produced by alternative splicing are present in varying amounts at different subcellular locations. Subcellular fractionation experiments do not provide a clear-cut conclusion because of the incomplete separation of organelles. We established human cell lines heterologously expressing mouse FALDH from each cDNA without tagging under the control of an inducible promoter and detected the variant FALDH proteins using a mouse FALDH-specific antibody. One variant, FALDH-V, was exclusively detected in peroxisomal membranes. Human FALDH-V with an amino-terminal Myc sequence also localized to peroxisomes. The most dominant form, FALDH-N, and other variants examined, however, were distributed in the endoplasmic reticulum. A gas chromatography-mass spectrometry-based analysis of metabolites in FALDH-expressing cells incubated with phytol or phytanic acid showed that FALDH-V, not FALDH-N, is the key aldehyde dehydrogenase in the degradation pathway and that it protects peroxisomes from oxidative stress. In contrast, both FALDHs had a protective effect against oxidative stress induced by a model aldehyde for lipid peroxidation, dodecanal. These results suggest that FALDH variants are produced by alternative splicing and share an important role in protecting against oxidative stress in an organelle-specific manner.

Crosstalk between xenobiotics metabolism and circadian clock

Many aspects of physiology and behavior in organisms from bacteria to man are subjected to circadian regulation. Indeed, the major function of the circadian clock consists in the adaptation of physiology to daily environmental change and the accompanying stresses such as exposition to UV-light and food-contained toxic compounds. In this way, most aspects of xenobiotic detoxification are subjected to circadian regulation. These phenomena are now considered as the molecular basis for the time-dependence of drug toxicities and efficacy. However, there is now evidences that these toxic compounds can, in turn, regulate circadian gene expression and thus influence circadian rhythms. As food seems to be the major regulator of peripheral clock, the possibility that food-contained toxic compounds participate in the entrainment of the clock will be discussed.

Inhibition of Atherosclerosis in Low-Density Lipoprotein Receptor-Negative Mice by Sesame Oil

Diet has profound effects on the development of atherosclerosis. Fatty acid composition, antioxidants, and other components such as lignans have major effects on the atherosclerotic process. Sesame oil has both mono- and polyunsaturated fatty acid constituents in equal proportions. In addition, it also has high levels of numerous antioxidants and inducers of peroxisome proliferator-activated receptor. The objective of this study was to determine the anti-atherosclerotic effects of sesame oil. In this study, male low-density lipoprotein (LDL) receptor (LDLR) -/- mice were fed atherogenic diet or atherogenic diet reformulated with the same level of sesame oil (sesame oil diet). Plasma lipids and atherosclerotic lesions were quantified after 3 months of feeding. Sesame oil-containing diet significantly reduced the atherosclerotic lesion formation and plasma cholesterol, triglyceride, and LDL cholesterol levels in LDLR -/- mice. These findings suggest that sesame oil could inhibit atherosclerosis lesion formation effectively, perhaps because of the synergistic actions of fatty acid and nonsaponifiable components.

A temporal study on the histopathological, biochemical and molecular responses of CCl(4)-induced hepatotoxicity in Cyp2e1-null mice

Previous study using Cyp2e1-null mice showed that Cyp2e1 is required in CCl(4)-induced liver injury at 24h, what remains unclear are the temporal changes in liver damage and the spectrum of genes involved in this process. We investigated the time-dependent liver changes that occurred at morphological, histopathological, biochemical and molecular levels in both Cyp2e1(+/+) and Cyp2e1(-/-) mice after treating with either corn oil or CCl(4) (1 ml/kg) for 2, 6, 12, 24 and 48 h. A pale orange colored liver, indicative of fatty infiltration, was observed in Cyp2e1(+/+) mice treated with CCl(4) for 24 and 48 h, while the Cyp2e1(+/+) mice treated with corn oil and Cyp2e1(-/-) mice treated with either corn oil or CCl(4) showed normal reddish brown colored liver. Ballooned hepatocytes with multiple vacuoles in their cytoplasm were observed in the livers of Cyp2e1(+/+) mice 24 and 48 h after treating with CCl(4). The levels of serum alanine aminotransferase and aspartate aminotransferase, markers for liver injury, were significantly higher at 12h, peaked at 24h and gradually decreased at 48 h after CCl(4) intoxication. In contrast, this kind of damage was not apparent in the Cyp2e1(-/-) mice treated with CCl(4). Altered expressions of genes related to liver cirrhosis, apoptosis, oxidative stress, xenobiotic detoxification, lipid metabolism, chemsensory signaling or tumorigenesis, structural organization, regeneration and inflammatory response were identified, and the time-dependent changes in expression of these genes were varied. Overall, the present study provides insights into the mechanism of CCl(4)-induced hepatotoxicity in animal models.