Regulation of mouse liver microsomal esterases by clofibrate and sexual hormones

Emerging role of carboxylesterases in nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is increasingly recognized as a global public health problem. Carboxylesterases (CESs), as potential influencing factors of NAFLD, are very important to improve clinical outcomes. This review aims to deeply understand the role of CESs in the progression of NAFLD and proposes that CESs can be used as potential targets for NAFLD treatment. We first introduced CESs and analyzed the relationship between CESs and hepatic lipid metabolism and inflammation. Then, we further reviewed the regulation of nuclear receptors on CESs, including PXR, CAR, PPARα, HNF4α and FXR, which may influence the progression of NAFLD. Finally, we evaluated the advantages and disadvantages of existing NAFLD animal models and summarized the application of CES-related animal models in NAFLD research. In general, this review provides an overview of the relationship between CESs and NAFLD and discusses the role and potential value of CESs in the treatment and prevention of NAFLD.

Hepatic carboxylesterases are differentially regulated in PPARα-null mice treated with perfluorooctanoic acid

Hepatic carboxylesterases (Ces) catalyze the metabolism of drugs, environmental toxicants, and endogenous lipids and are known to be regulated by multiple nuclear receptors. Perfluorooctanoic acid (PFOA) is a synthetic fluorochemical that has been associated with dyslipidemia in exposed populations. In liver, PFOA can activate nuclear receptors such as PPARα, and alter the metabolism and excretion of chemicals. Here, we sought to test the ability of PFOA to modulate Ces expression and activity in the presence and absence of the PPARα receptor. For this purpose, male C57BL/6 NCrl mice were administered PFOA (1 or 3 mg/kg, po, 7 days) and livers collected for assessment of Ces expression and activity. PFOA increased Ces1 and 2 protein and activity. Notably, PFOA increased Ces1d, 1e, 1f, 1 g, 2c, and 2e mRNAs between 1.5- and 2.5-fold, while it decreased Ces1c and 2b. Activation of PPARα by PFOA was confirmed by up-regulation of Cyp4a14 mRNA. In a separate study of PFOA-treated wild-type (WT) and PPARα-null mice, induction of Ces 1e and 1f mRNA and in turn, Ces1 protein, was PPARα-dependent. Interestingly, in PPARα-null mice, Ces1c, 1d, 1 g, 2a, 2b, and 2e mRNAs and Ces2 protein were up-regulated by PFOA which contributed to sustained up-regulation of Ces activity, although to a lower extent than observed in WT mice. Activation of the CAR and PXR receptors likely accounted for up-regulation of select Ces1 and 2 subtypes in PPARα-null mice. In conclusion, the environmental contaminant PFOA modulates the expression and function of hepatic Ces enzymes, in part through PPARα.

Carboxylesterases are uniquely expressed among tissues and regulated by nuclear hormone receptors in the mouse

Carboxylesterases (CES) are a well recognized, yet incompletely characterized family of proteins that catalyze neutral lipid hydrolysis. Some CES have well-defined roles in xenobiotic clearance, pharmacologic prodrug activation, and narcotic detoxification. In addition, emerging evidence suggests other CES may have roles in lipid metabolism. Humans have six CES genes, whereas mice have 20 Ces genes grouped into five isoenzyme classes. Perhaps due to the high sequence similarity shared by the mouse Ces genes, the tissue-specific distribution of expression for these enzymes has not been fully addressed. Therefore, we performed studies to provide a comprehensive tissue distribution analysis of mouse Ces mRNAs. These data demonstrated that while the mouse Ces family 1 is highly expressed in liver and family 2 in intestine, many Ces genes have a wide and unique tissue distribution defined by relative mRNA levels. Furthermore, evaluating Ces gene expression in response to pharmacologic activation of lipid- and xenobiotic-sensing nuclear hormone receptors showed differential regulation. Finally, specific shifts in Ces gene expression were seen in peritoneal macrophages following lipopolysaccharide treatment and in a steatotic liver model induced by high-fat feeding, two model systems relevant to disease. Overall these data show that each mouse Ces gene has its own distinctive tissue expression pattern and suggest that some CES may have tissue-specific roles in lipid metabolism and xenobiotic clearance.

Potential adverse effects of oseltamivir in rats: males are more vulnerable than females

Oseltamivir is the most widely used antiviral drug for the treatment and prophylaxis of influenza. However, not much is known about its adverse effects. The potential side effects were investigated in male and female rats (140-170 g). Oseltamivir was administered at 2.2 mg·kg(-1)·day(-1) for 5 days. For both genders, treatment with oseltamivir resulted in significant reductions in the hepatic activities of glutathione reductase, glutathione peroxidase, and glutathione S-transferase. Also for both genders, oseltamivir produced modest reductions in the hepatic activities of UDP-glucuronosyltransferase, quinone oxidoreductase, thioredoxin reductase, CYP1A1/2, and CYP3A, as well as hepatic glutathione content. For both genders, neither the kidney functions nor protein profile was affected by oseltamivir. Oseltamivir also caused significant elevation in serum levels of both triacylglycerols and LDL-cholesterol and in the activity of γ-glutamyl transpeptidase, in both genders. For male animals only, oseltamivir treatment elevated the serum level of total cholesterol as well as the activity of serum alanine aminotransferase, and reduced the hepatic activities of superoxide dismutase and catalase. Oseltamivir caused oxidative stress and acute toxicity in the liver, and disrupted the cholesterol and lipid metabolism but was less likely to cause serious drug interactions. There was a sexual differentiation in these adverse effects, with adverse effects being more evident in male rats.

Regulation of triacylglycerol hydrolase expression by dietary fatty acids and peroxisomal proliferator-activated receptors

Triacylglycerol hydrolase (TGH) is an enzyme that catalyzes the lipolysis of intracellular stored triacylglycerol (TG). Peroxisomal proliferator-activated receptors (PPAR) regulate a multitude of genes involved in lipid homeostasis. Polyunsaturated fatty acids (PUFA) are PPAR ligands and fatty acids are produced via TGH activity, so we studied whether dietary fats and PPAR agonists could regulate TGH expression. In 3T3-L1 adipocytes, TGH expression was increased 10-fold upon differentiation, compared to pre-adipocytes. 3T3-L1 cells incubated with a PPARgamma agonist during the differentiation process resulted in a 5-fold increase in TGH expression compared to control cells. Evidence for direct regulation of TGH expression by PPARgamma could not be demonstrated as TGH expression was not affected by a 24-h incubation of mature 3T3-L1 adipocytes with the PPARgamma agonist. Feeding mice diets enriched in fatty acids for 3 weeks did not affect hepatic TGH expression, though a 3-week diet enriched in fatty acids and cholesterol increased hepatic TGH expression 2-fold. Two weeks of clofibrate feeding did not significantly affect hepatic TGH expression or microsomal lipolytic activities in wild-type or PPARalpha-null mice, indicating that PPARalpha does not regulate hepatic TGH expression. Therefore, TGH expression does not appear to be directly regulated by PPARs or fatty acids in the liver or adipocytes.

Gene Expression Analysis of Peroxisome Proliferators- and Phenytoin-Induced Hepatotoxicity Using cDNA Microarray

The recent DNA microarray technology enables us to understand a large number of gene expression profiling. The technology has potential possibility to comprehend mechanism of multiple genes were related to compounds which have toxicity in biological system. So, the toxicogenomics through this technology may be very powerful for understanding the effect of unknown toxic mechanisms in biological system. We have studied that the effect of compounds related to hepatotoxin in vivo system using DNA microarray and classified chemicals which have been well characterized. We have studied three compounds; 2 peroxisome proliferators: Clofibrate (ethyl-p-chlorophenoxyisobutyrate), gemfibrozil (5-2[2,5-dimethyl-phenoxy]2-2-dimethyl-pentanonic), and an antiepileptic drug: phenytoin (5,5-diphenylhydantoin). Male Sprague-Dawely VAF(+) albino rats of 5-6 weeks old were treated with each compound for 24 hr and 2 weeks. 4.8 K cDNA microarray in house has been used for gene expression profiling. We found that the clustering of gene expression had similarity like as the toxic phenotype of compounds.

Altered expression of the carboxylesterases ES-4 and ES-10 by peroxisome proliferator chemicals

The nonspecific carboxylesterases (EC.3.1.1.1) are a large group of enzymes that play important roles in the metabolism of foreign xenobiotics and endogenous lipids, including activators of the peroxisome proliferator-activated receptor alpha, a nuclear receptor that is the central mediator of peroxisome proliferator (PP) effects in the rodent liver. A number of reports have demonstrated that PP exposure leads to alterations in levels of carboxylesterases in the liver. In this study, we determined by Western blot analysis whether exposure to diverse PP results in alteration of expression of two highly expressed microsomal carboxylesterases. Chronic exposure to the PP WY-14,643 (WY) and gemfibrozil (GEM), but not di-n-butyl phthalate (DBP), led to decreases in ES-4 in male rat livers. ES-4 was increased in female rat livers treated with GEM. WY exposure led to decreases in ES-10 in male and female rat livers. ES-10 was increased in female rats treated with DBP. Compared with other end points that are altered within days after PP exposure, the downregulation of ES-4 and ES-10 by WY was considerably slower, occurring between 1 and 5 weeks of exposure. Decreased expression of ES-4 was observed at doses of WY or GEM as low as 10 or 8000 ppm, respectively, whereas decreased expression of ES-10 was more resistant to changes by any PP occurring only with WY at doses as low as 50 ppm. After chronic exposure to WY or diethylhexyl phthalate in wild-type mice, kidney, but not liver, expression of ES-4 and ES-10 was downregulated. These decreases in kidney ES expression were not observed in PPARalpha-null mice lacking a functional PPARalpha gene, demonstrating the importance of this transcription factor in these changes. These studies demonstrate that ES protein expression is under complex control by PP that is sex- and compound-dependent. These results lend support to the hypothesis that PP exposure leads to a reprogramming of expression of enzymes important in the metabolism of PPARalpha activators.

Major clofibrate effects on liver and plasma lipids are independent of changes in polyunsaturated fatty acid composition induced by dietary fat

The effects of clofibrate on the content and composition of liver and plasma lipids was studied in mice fed for 4 wk on diets enriched in n-6 or n-3 polyunsaturated fatty acids (PUFA) from sunflower oil (SO) or fish oil (FO), respectively; both oils were fed at 9% of the diet (dry weight basis). Only FO was hypolipidemic. Both oil regimes led to slightly increased concentrations of phospholipids (PL) and triacylglycerols (TG) in liver as compared with a standard chow diet containing 2% fat. Clofibrate promoted hypolipidemia only in animals fed SO. Its main effect was to enlarge the liver, such growth increasing the amounts of major glycerophospholipids while depleting the TG. SO and FO consumption changed the proportion of n-6 or n-3 PUFA in liver and plasma lipids in opposite ways. After clofibrate action, the PUFA of liver PL were preserved better than in the absence of oil supplementation. However, most of the drug-induced changes (e.g., increased 18:1n-9 and 20:3n-6, decreased 22:6/20:5 ratios) occurred irrespective of lipids being rich in n-6 or n-3 PUFA. The concentration of sphingomyelin (SM), a minor liver lipid that virtually lacks PUFA, increased with the dietary oils, decreased with clofibrate, and changed its fatty acid composition in both situations. Thus, oil-increased SM had more 22:0 and 24:0 than clofibrate-decreased SM, which was significantly richer in 22:1 and 24:1.

The mutagenic activity of unpolymerized resin monomers in Salmonella typhimurium and V79 cells

Dimethacrylate derivatives are used as monomers to polymerize dental composite materials and for a great variety of other industrial resins. Occupational exposure is likely in various ways because of the many areas of methacrylate application. Here, the mutagenicity of the monomers, bisphenol A-diglycidyl dimethacrylate (Bis-GMA), urethane dimethacrylate (UDMA), triethylene glycol dimethacrylate (TEGDMA), Bisphenol A (BPA), glycidyl methacrylate (GMA), methyl methacrylate (MMA), and 2-hydroxyethyl methacrylate (HEMA) was studied in a bacterial (Ames test) and a mammalian gene mutation assay (V79/HPRT assay). Mutagenicity was determined in different Salmonella typhimurium strains (TA97a, TA98, TA100, TA102) and in V79 cells in the presence and in the absence of a metabolically active microsomal fraction from rat liver (S9). No mutagenic effects were observed with Bis-GMA and UDMA, methyl methacrylate, 2-hydroxyethyl methacrylate and bisphenol A. Glycidyl methacrylate (GMA) was mutagenic in a dose-dependent manner in three Salmonella tester strains. The number of mutants was increased by a factor of 2 to 3 with strains TA97a and TA102 in the absence of S9. Moreover, the numbers of mutants induced in S. typhimurium TA100 were about 8-fold higher than in solvent controls. GMA also induced an increase of mutants in V79 cells in the absence of S9. However, GMA was inactivated by microsomal enzymes. Triethylenglycol dimethacrylate (TEGDMA) was not mutagenic in any S. typhimurium. In contrast, the compound induced a dose-dependent rise in mutant frequencies in V79 cell cultures. It is concluded that TEGDMA acted through a clastogenic mechanism which is not detected by Ames tester strains.