Hepatic Peroxisome Proliferation Research Articles

Gckr depletion leads to growth retardation and diet-dependent visceral obesity in red crucian carp (Carassius auratus red var.)

There exists a notable contrast in the carbohydrate utilization capacity between fish and mammals. In mammals, the glucokinase regulatory protein (GCKR) is known to exert inhibitory effects on glycolysis by binding to glucokinase (GCK), but its role in fish remains unexplored. In this study, the function of gckr in red crucian carp (Carassius auratus red var.), hereafter referred to as RCC, was investigated through its knockout. Under normal dietary conditions, the growth rate of gckr knockout RCC was significantly lower compared to wild-type (WT) RCC reared in the same environment. Subsequent analysis found that gckr knockout RCC exhibited significantly higher serum glucose levels at 1 h post-feeding or glucose injection (hpi), while the difference was abolished at 3 h. Therefore, the metabolic characteristics at 1 and 3 hpi were evaluated between WT and gckr knockout RCC. The results revealed that gckr knockout led to impaired insulin signaling and glycolysis, as evidenced by a reduction in serum insulin level, hepatic insulin receptor a and pyruvate kinase expression, GCK contents, and pyruvate levels at 1 hpi. Additionally, gckr knockout resulted in compromised gluconeogenesis, as indicated by a significant decrease in hepatic expression of fructose-1,6-bisphosphatase 1 and glucose-6-phosphatase at 1 hpi, while it did not affect glycogen accumulation after glucose injection. Regarding lipid metabolism, gckr knockout caused a transient decrease in triglyceride level and reduced expression of fatty acid synthase after glucose injection. Moreover, decreased hepatic peroxisome proliferator activated receptor alpha (ppara) transcripts and proteins were observed in gckr knockout RCC at 1 dpi, indicating a reduced capacity for β-oxidation due to Gckr deficiency. Interestingly, when fed a high-lipid diet, gckr knockout resulted in a significant increase in visceral mass with higher triglyceride level, accompanied by attenuated PPARα signaling. Taken together, this study provides evidence that Gckr-mediated maintenance of Gck contributes to the facilitation of postprandial glycolysis, gluconeogenesis, lipogenesis, and fatty acid β-oxidation in RCC. This study further suggests that enhancing glycolysis may promote growth and liver health in fish under high lipid dietary conditions.

The role of mouse and human peroxisome proliferator-activated receptor-α in modulating the hepatic effects of perfluorooctane sulfonate in mice

Perfluorooctane sulfonate (PFOS) is a stable environmental contaminant that can activate peroxisome proliferator-activated receptor alpha (PPARα). In the present work, the specific role of mouse and human PPARα in mediating the hepatic effects of PFOS was examined in short-term studies using wild type, Ppara-null and PPARA-humanized mice. Mice fed 0.006 % PFOS for seven days (∼10 mg/kg/day), or 0.003 % PFOS for twenty-eight days (∼5 mg/kg/day), exhibited higher liver and serum PFOS concentrations compared to controls. Relative liver weights were also higher following exposure to dietary PFOS in all three genotypes as compared vehicle fed control groups. Histopathological examination of liver sections from mice treated for twenty-eight days with 0.003 % PFOS revealed a phenotype consistent with peroxisome proliferation, in wild-type and PPARA-humanized mice that was not observed in Ppara-null mice. With both exposures, expression of the PPARα target genes, Acox1, Cyp4a10, was significantly increased in wild type mice but not in Ppara-null or PPARA-humanized mice. By contrast, expression of the constitutive androstane receptor (CAR) target gene, Cyp2b10, and the pregnane X receptor (PXR) target gene, Cyp3a11, were higher in response to PFOS administration in all three genotypes compared to controls for both exposure periods. These results indicate that mouse PPARα can be activated in the liver by PFOS causing increased expression of Acox1, Cyp4a10 and histopathological changes in the liver. While histopathological analyses indicated the presence of mouse PPARα-dependent hepatic peroxisome proliferation in wild-type (a response associated with activation of PPARα) and a similar phenotype in PPARA-humanized mice, the lack of increased Acox1 and Cyp4a10 mRNA by PFOS in PPARA-humanized mice indicates that the human PPARα was not as responsive to PFOS as mouse PPARα with this dose regimen. Moreover, results indicate that hepatomegaly caused by PFOS does not require mouse or human PPARα and could be due to effects induced by activation of CAR and/or PXR.

Endocrine disruptor responses in African sharptooth catfish (Clarias gariepinus) exposed to di-(2-ethylhexyl)-phthalate

In the present study, we have investigated the endocrine disruptive effects of waterborne di-(2-ethylhexyl) phthalate (DEHP: 0 (control), 10, 100, 200 and 400 μg/L) on juvenile Clarias gariepinus by analyzing transcript patterns for hepatic vitellogenin (vtg), estrogen receptor-α (er-α), aromatase (cyp19a1b) and peroxisome proliferator activated receptor-α (ppar-α) using quantitative real-time PCR after 3, 7 and 14 days exposure period. In addition, we analyzed CYP19 and PPAR protein levels using enzyme-linked immunosorbent assay (ELISA), while cellular testosterone (T) and 17β-estradiol (E2) levels were measured using enzyme immune assay (EIA). Tissue burden of DEHP was measured in the liver using gas chromatography-mass spectroscopy (GC–MS). We observed apparent concentration- and time-dependent increases of vtg, er-α, cyp19a1b transcripts, E2 and T levels after exposure to DEHP. A biphasic pattern of effect was observed for ppar-α, showing a concentration-dependent increase that peaked at 100 μg/L and thereafter, an apparent concentration-dependent decrease at 200 and 400 μg/L at all exposure days. Given that the post-differentiation changes of gonads in C. gariepinus corresponded with the 14-day sampling period, we separated the analyzed data into sexes after histological examination of the gonads, showing that females responded stronger, compared to males, to DEHP exposure at all exposure concentrations. Oocyte atresia, intersex (ovotestis) and karyoplasmic clumping were observed in females while male fish showed distortion and degeneration of seminiferous tubules and condensation of tubular cells in the 400 μg/L exposure group after 14 days. Corresponding canonical analysis (CCA) of all analyzed variables revealed a positive relationship between analyzed biological variables with increasing DEHP concentrations. Overall, molecular, biochemical and physiological responses presented in the present study indicate that exposure of C. gariepinus to waterborne DEHP produced endocrine disruptive responses with potential consequences for overt reproduction, development, physiology and general health of fish populations inhabiting phthalate contaminated aquatic environments. These responses represent valuable and effective biomarkers of exposure and effects, that can be adopted for screening the presence of EDCs in Nigeria and other developing countries.

Danshen protects against early-stage alcoholic liver disease in mice via inducing PPARα activation and subsequent 4-HNE degradation.

Alcoholic liver disease (ALD) is a type of chronic liver disease caused by long-term heavy ethanol consumption. Danshen is one of the most commonly used substances in traditional Chinese medicine and has been widely used for the treatment of various diseases, and most frequently, the ALD. The current study aims to determine the potential beneficial effect of Danshen administration on ALD and to clarify the underlying molecular mechanisms. Danshen administration improved liver pathologies of ALD, attenuated alcohol-induced increment of hepatic 4-Hydroxynonenal (4-HNE) formation, and prevented hepatic Peroxisome proliferators activated receptor alpha (PPARα) suppression in response to chronic alcohol consumption. Cell culture studies revealed that both hepatoprotective effect and increased intracellular 4-HNE clearance instigated by Danshen supplementation are PPARα-dependent. In conclusion, Danshen administration can protect against ALD via inducing PPARα activation and subsequent 4-HNE degradation.

Beraprost sodium, a prostacyclin analogue, reduces fructose-induced hepatocellular steatosis in mice and in vitro via the microRNA-200a and SIRT1 signaling pathway

PurposeTo determine whether beraprost sodium, a prostacyclin analogue, could reduce hepatic lipid accumulation induced by fructose in mice and cultured human hepatocytes, and to investigate the expression of microRNAs and the sirtuin 1 (SIRT1) pathway. MethodsMale C57BL/6JNju mice were divided into three groups and fed one of the following diets: a normal diet, a high fructose diet, or a high fructose diet with beraprost sodium treatment. In addition, human-derived HepG2 cells were cultured and treated with fructose (25mmol/L) with or without beraprost sodium (10μmol/L) for 24h, and transfected with small interfering RNA (siRNA) against SIRT1, miR-200a mimic, or miR-200a inhibitor for 48h. The miRNA microarray analysis was performed on the HepG2 cells, and the expression profiles of miRNAs were analyzed using Gene Cluster 3.0 and verified using qPCR. ResultsBeraprost sodium treatment attenuated hepatic steatosis, induced the transcription of genes involved in lipid metabolism in C57BL/6 mice (P<0.05), and increased the expression of hepatic SIRT1 and peroxisome proliferator activated receptor α (PPARα) in the cells treated with fructose. These effects were blocked in HepG2 cells after transfection with siRNA against SIRT1. MiR-200a was highly expressed during fructose treatment and was down regulated by beraprost sodium (P<0.05). A luciferase assay showed that miR-200a regulated SIRT1 by binding to the 3′ UTR. Overexpression of miR-200a inhibited expression of hepatic SIRT1. ConclusionsOur study demonstrated that SIRT1 pathway mediated the effects of beraprost sodium on attenuation of hepatic lipid disorders induced by fructose and revealed the primary role of miR-200a in the regulation of hepatic SIRT1 by beraprost sodium. Our findings suggested that SIRT1 might be a therapeutic target of fructose-related metabolism disorders.

PEGylated Curcumin Derivative Attenuates Hepatic Steatosis via CREB/PPAR-γ/CD36 Pathway

Curcumin has the potential to cure dyslipidemia and nonalcoholic fatty liver disease (NAFLD). However, its therapeutic effects are curbed by poor bioavailability. Our previous work has shown that modification of curcumin with polyethylene glycol (PEG) improves blood concentration and tissue distribution. This study sought to investigate the role of a novel PEGylated curcumin derivative (Curc-mPEG454) in regulating hepatic lipid metabolism and to elucidate the underlying molecular mechanism in a high-fat-diet- (HFD-) fed C57BL/6J mouse model. Mice were fed either a control chow diet (D12450B), an HFD (D12492) as the NAFLD model, or an HFD with Curc-mPEG454 administered by intraperitoneal injection at 50 mg/kg or 100 mg/kg for 16 weeks. We found that Curc-mPEG454 significantly lowered the body weight and serum triglyceride (TG) levels and reduced liver lipid accumulation in HFD-induced NAFLD mice. It was also shown that Curc-mPEG454 suppressed the HFD-induced upregulated expression of CD36 and hepatic peroxisome proliferator activated receptor-γ (PPAR-γ), a positive regulator of CD36. Moreover, Curc-mPEG454 dramatically activated cAMP response element-binding (CREB) protein, which negatively controls hepatic PPAR-γ expression. These findings suggest that Curc-mPEG454 reverses HFD-induced hepatic steatosis via the activation of CREB inhibition of the hepatic PPAR-γ/CD36 pathway, which may be an effective therapeutic for high-fat-diet-induced NAFLD.

A lard-rich high-fat diet increases hepatic peroxisome proliferator–activated receptors in endotoxemic rats

BackgroundDiets high in saturated fatty acids activate chronic inflammation. We previously reported that, in even acute inflammation caused by lipopolysaccharide (LPS), liver injury was exacerbated in rats fed a lard-rich diet. Peroxisome proliferator–activated receptors (PPARs) are related to inflammation and are also key regulators of lipid metabolism. In this study, we examined effects of high-fat diet on liver injury and hepatic lipid metabolism during endotoxemia, measuring hepatic PPARs and other markers. Materials and methodsMale Wistar rats were fed a high-fat diet (HFD, 60 kcal% fat) or control diet (CD, 10 kcal% fat) for 4 or 12 wk, injected with LPS and sacrificed at 0, 1.5, or 6 h. Analyses included plasma aspartate transaminase (AST) and alanine transaminase (ALT) levels, messenger RNA (mRNA) and protein levels of hepatic PPARα and PPARγ, and mRNA levels of enzymes related to fatty acid oxidation and synthesis. ResultsEndotoxemic rats on HFD for 12 wk, but not 4 wk, had higher mRNA and protein levels for hepatic PPARs, than did those on CD (P < 0.01-0.05). Similarly, these rats had increased mRNA expression of hepatic fatty acid oxidation- and synthesis-related enzymes (P < 0.01-0.05). Rats injected with LPS had more severe liver injury, indicated by plasma AST/ALT, if on the HFD for 12 wk, compared with for 4 wk. ConclusionsConsumption of a lard-rich diet for 12 wk worsened liver injury and increased hepatic PPARα and PPARγ expression in endotoxemic rats.

Diosmin attenuates radiation-induced hepatic fibrosis by boosting PPAR-γ expression and hampering miR-17-5p-activated canonical Wnt-β-catenin signaling.

Liver fibrosis is one of the major complications from upper right quadrant radiotherapy. MicroRNA-17-5p (miR-17-5p) is hypothesized to act as a regulator of hepatic stellate cell (HSCs) activation by activation of the canonical Wnt-β-catenin pathway. Diosmin (Dios), a citrus bioflavonoid, is known to possess potent antioxidant, anti-inflammatory, and anti-apoptotic properties. To explore the molecular mechanisms that underlie radiation-induced liver fibrosis, and to evaluate the possible influence of Dios on the miR-17-5p-Wnt-β-catenin signaling axis during fibrogenesis provoked by irradiation (IRR) in rats. Also, the effect of Dios on hepatic peroxisome proliferator activated receptor-γ (PPAR-γ) expression as a regulator for HSC activation was considered. We administered 100 mg·(kg body mass)-1·day-1 (per oral) of Dios were administered to IRR-exposed rats (overall dose of 12 Gy on 6 fractions of 2 Gy each) for 6 successive weeks. Data analysis revealed that Dios treatment mitigated oxidative stress, enhanced antioxidant defenses, alleviated hepatic inflammatory responses, abrogated pro-fibrogenic cytokines, and stimulated PPAR-γ expression. Dios treatment repressed the miR-17-5p activated Wnt-β-catenin signaling induced by IRR. Moreover, Dios treatment restored the normal hepatic architecture and reversed pathological alterations induced by IRR. We hypothesize that the stimulation of PPAR-γ expression and interference with miR-17-5p activated Wnt-β-catenin signaling mediates the antifibrotic properties of Dios.

High-fructose corn syrup-55 consumption alters hepatic lipid metabolism and promotes triglyceride accumulation

High-fructose corn syrup-55 (HFCS-55) has been suggested to be more lipogenic than sucrose, which increases the risk for nonalcoholic fatty liver disease (NAFLD) and dyslipidemia. The study objectives were to determine the effects of drinking different sugar-sweetened solutions on hepatic gene expression in relation to liver fatty acid composition and risk of NAFLD. Female rats were randomly assigned (n=7 rats/group) to drink water or water sweetened with 13% (w/v) HFCS-55, sucrose or fructose for 8 weeks. Rats drinking HFCS-55 solution had the highest (P=.03) hepatic total lipid and triglyceride content and histological evidence of fat infiltration. Rats drinking HFCS-55 solution had the highest hepatic de novo lipogenesis indicated by the up-regulation of stearoyl-CoA desaturase-1 and the highest (P<.001) oleic acid (18:1n-9) content. This was accompanied by reduced β-oxidation indicated by down-regulation of hepatic peroxisome proliferator–activated receptor α. Disposal of excess lipids by export of triglyceride-rich lipoprotein from the liver was increased as shown by up-regulation of gene expression of microsomal triglyceride transfer protein in rats drinking sucrose, but not HFCS-55 solution. The observed lipogenic effects were attributed to the slightly higher fructose content of HFCS-55 solution in the absence of differences in macronutrient and total caloric intake between rats drinking HFCS-55 and sucrose solution. Results from gene expression and fatty acid composition analysis showed that, in a hypercaloric state, some types of sugars are more detrimental to the liver. Based on these preclinical study results, excess consumption of caloric sweetened beverage, particularly HFCS-sweetened beverages, should be limited.

CREBH Couples Circadian Clock With Hepatic Lipid Metabolism.

The circadian clock orchestrates diverse physiological processes critical for health and disease. CREB, hepatocyte specific (CREBH) is a liver-enriched, endoplasmic reticulum (ER)–tethered transcription factor known to regulate the hepatic acute phase response and energy homeostasis under stress conditions. We demonstrate that CREBH is regulated by the circadian clock and functions as a circadian regulator of hepatic lipid metabolism. Proteolytic activation of CREBH in the liver exhibits typical circadian rhythmicity controlled by the core clock oscillator BMAL1 and AKT/glycogen synthase kinase 3β (GSK3β) signaling pathway. GSK3β-mediated phosphorylation of CREBH modulates the association between CREBH and the coat protein complex II transport vesicle and thus controls the ER-to-Golgi transport and subsequent proteolytic cleavage of CREBH in a circadian manner. Functionally, CREBH regulates circadian expression of the key genes involved in triglyceride (TG) and fatty acid (FA) metabolism and is required to maintain circadian amplitudes of blood TG and FA in mice. During the circadian cycle, CREBH rhythmically regulates and interacts with the hepatic nuclear receptors peroxisome proliferator–activated receptor α and liver X receptor α as well as with the circadian oscillation activator DBP and the repressor E4BP4 to modulate CREBH transcriptional activities. In conclusion, these studies reveal that CREBH functions as a circadian-regulated liver transcriptional regulator that integrates energy metabolism with circadian rhythm.

Dietary saturated fatty acids reduce hepatic lipid accumulation but induce fibrotic change in alcohol-fed rats.

In this study, we evaluated the influence of an ethanol-containing diet with high saturated fatty acids (SFAs) on alcoholic liver disease (ALD) in rats. Male Wistar rats weighing about 160 g were divided into four groups: an ethanol (E) group fed an ethanol-containing liquid diet with 36% total calories as fat (corn oil, olive oil and safflower oil); a control (C) group pair-fed an isoenergetic diet without ethanol; an ethanol with saturated fat (EHS) group fed an ethanol-containing diet which contained 40% total calories as fat (90% lard); and a control with saturated fat (CHS) group fed an isoenergetic diet without ethanol, which contained 40% total calories as fat. After 8 weeks of treatment, the liver weight and plasma aspartate aminotransferase (AST) activities in E and EHS groups were significantly higher than those of C group. Significantly higher scores of inflammation, necrosis, and fatty changes were found in E group, whereas significantly higher scores of necrosis, bile duct hyperplasia, and fibrosis were found in EHS group. Although significantly lower plasma adiponectin concentrations were observed in both E and EHS groups, compared to C group, plasma adiponectin in EHS group was significantly higher than that in E group. There was no change in hepatic peroxisome proliferator activated receptor (PPAR)-α expression between E and C groups, and rats in EHS group showed a significantly elevated level compared to the other groups. A lower hepatic sirtuins (SIRT)-1 level was found in E group, but it did not reach statistical significance. Moreover, the highest plasma TGF-β1 level was found in EHS group. Compared to C group, the hepatic reduced glutathione/oxidized glutathione ratio and thiobarbituric acid (TBA)-reactive substance level were significantly increased in E and EHS groups; however, there was no significant difference between E and EHS groups. Significantly increased hepatic CYP2E1 expression was observed in both E and EHS groups, while at the same time, hepatic CYP2E1 in EHS group was the highest among all groups. The hepatic tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-6, and IL-10 concentrations in the E group were significantly higher than those in C group, whereas the hepatic IL-6 and IL-10 concentrations in ES group were significantly lower than those of E group. These results suggested that dietary saturated fats may inhibit hepatic fat accumulation and induce hepatic fibrosis in rats under chronic alcohol intake.

Cellular target recognition of perfluoroalkyl acids: In vitro evaluation of inhibitory effects on lysine decarboxylase

Perfluoroalkyl acids (PFAAs) have been shown to bind with hepatic peroxisome proliferator receptor α, estrogen receptors and human serum albumin and subsequently cause some toxic effects. Lysine decarboxylase (LDC) plays an important role in cell growth and developmental processes. In this study, the inhibitory effect of 16 PFAAs, including 13 perfluorinated carboxylic acids (PFCAs) and 3 perfluorinated sulfonic acids (PFSAs), on lysine decarboxylase (LDC) activity was investigated. The inhibition constants obtained in fluorescence enzyme assays fall in the range of 2.960μM to 290.8μM for targeted PFCAs, and 41.22μM to 67.44μM for targeted PFSAs. The inhibitory effect of PFCAs increased significantly with carbon chain (7–18 carbons), whereas the short chain PFCAs (less than 7 carbons) did not show any effect. Circular dichroism results showed that PFAA binding induced significant protein secondary structural changes. Molecular docking revealed that the inhibitory effect could be rationalized well by the cleft binding mode as well as the size, substituent group and hydrophobic characteristics of the PFAAs. At non-cytotoxic concentrations, three selected PFAAs inhibited LDC activity in HepG2 cells, and subsequently resulted in the decreased cadaverine level in the exposed cells, suggesting that LDC may be a possible target of PFAAs for their in vivo toxic effects.

Derivation of an Oral Reference Dose (RfD) for the Nonphthalate Alternative Plasticizer 1,2-Cyclohexane Dicarboxylic Acid, Di-Isononyl Ester (DINCH)

1,2-Cyclohexanedicarboxylic acid, 1,2-diisononylester (DINCH), a polyvinyl chloride plasticizer, has food, beverage, and medical device applications that may result in general population exposure. Although no apparent toxicity information in humans was identified, there is a substantial data set in lab animals to serve as the basis of hazard identification for DINCH. Target tissues associated with repeated dietary DINCH exposure in lab animals included liver, kidney, and thyroid and mammary glands. In contrast to some phthalate ester plasticizers, DINCH did not show evidence of hepatic peroxisomal proliferation, testicular toxicity, or liver tumors in rats. Liver and thyroid effects associated with DINCH exposure were attributed to compensatory thyroid stimulation secondary to prolonged metabolic enzyme induction. The toxicological significance of mammary fibroadenomas in female rats is unclear, given that this common benign and spontaneously occurring tumor type is unique to rats. The weight of evidence suggests DINCH is not genotoxic and the proposed mode of action (MOA) for thyroid gland lesions was considered to have a threshold. No adverse reproductive effects were seen in a two-generation study. An oral reference dose (RfD) of 0.7 mg/kg-d was derived from a human equivalent BMDL10 of 21 mg/kg-d for thyroid hypertrophy/hyperplasia seen in adult F1 rats also exposed in utero. The total uncertainty factor of 30x was comprised of intraspecies (10×) and database (3×) factors. An interspecies extrapolation factor was not applied since rodents are more sensitive than humans with respect to the proposed indirect MOA for thyroid gland lesions.

Increased plasma corticosterone contributes to the development of alcoholic fatty liver in mice.

Ethanol ingestion increases endogenous glucocorticoid levels in both humans and rodents. The present study aimed to define a mechanistic link between the increased glucocorticoids and alcoholic fatty liver in mice. Plasma corticosterone levels were not affected in mice on a 2-wk ethanol diet regimen but significantly increased upon 4 wk of ethanol ingestion. Accordingly, hepatic triglyceride levels were not altered after 2 wk of ethanol ingestion but were elevated at 4 wk. Based on the observation that 2 wk of ethanol ingestion did not significantly increase endogenous corticosterone levels, we administered exogenous glucocorticoids along with the 2-wk ethanol treatment to determine whether the elevated glucocorticoid contributes to the development of alcoholic fatty liver. Mice were subjected to ethanol feeding for 2 wk with or without dexamethasone administration. Hepatic triglyceride contents were not affected by either ethanol or dexamethasone alone but were significantly increased by administration of both. Microarray and protein level analyses revealed two distinct changes in hepatic lipid metabolism in mice administered with both ethanol and dexamethasone: accelerated triglyceride synthesis by diacylglycerol O-acyltransferase 2 and suppressed fatty acid β-oxidation by long-chain acyl-CoA synthetase 1, carnitine palmitoyltransferase 1a, and acyl-CoA oxidase 1. A reduction of hepatic peroxisome proliferation activator receptor-α (PPAR-α) was associated with coadministration of ethanol and dexamethasone. These findings suggest that increased glucocorticoid levels may contribute to the development of alcoholic fatty liver, at least partially, through hepatic PPAR-α inactivation.

Glucose Transporter-8 (GLUT8) Mediates Glucose Intolerance and Dyslipidemia in High-Fructose Diet-Fed Male Mice

Members of the glucose transporter (GLUT) family of membrane-spanning hexose transporters are subjects of intensive investigation for their potential as modifiable targets to treat or prevent obesity, metabolic syndrome, and type 2 diabetes mellitus. Mounting evidence suggests that the ubiquitously expressed class III dual-specificity glucose and fructose transporter, GLUT8, has important metabolic homeostatic functions. We therefore tested the hypothesis that GLUT8 mediates the deleterious metabolic effects of chronic high-fructose diet exposure. Here we demonstrate resistance to high-fructose diet-induced glucose intolerance and dyslipidemia concomitant with enhanced oxygen consumption and thermogenesis in GLUT8-deficient male mice. Independent of diet, significantly lower systolic blood pressure both at baseline and after high-fructose diet feeding was also observed by tail-cuff plethysmography in GLUT8-deficient mice vs wild-type controls. Resistance to fructose-induced metabolic dysregulation occurred in the context of enhanced hepatic peroxisome proliferator antigen receptor-γ (PPARγ) protein abundance, whereas in vivo hepatic adenoviral GLUT8 overexpression suppressed hepatic PPARγ expression. Taken together, these findings suggest that GLUT8 blockade prevents fructose-induced metabolic dysregulation, potentially by enhancing hepatic fatty acid metabolism through PPARγ and its downstream targets. We thus establish GLUT8 as a promising target in the prevention of diet-induced obesity, metabolic syndrome, and type 2 diabetes mellitus in males.

Differential induction of cytochrome P450 isoforms and peroxisomal proliferation by cyfluthrin in male Wistar rats

Cyfluthrin effects on in vivo drug metabolizing enzymes were evaluated using the oxidative substrate antipyrine. Antipyrine pharmacokinetics in plasma and urinary excretion of its major metabolites with and without cyfluthrin oral treatment (20mg/kg/day for 6 days) were investigated in rats. Cyfluthrin increased the apparent intrinsic clearance and decreased the antipyrine half-life at β phase. Cyfluthrin also increased the clearance of the antipyrine metabolites, norantipyrine, 4-hydroxyantipyrine and 3-hydroxymethylantipyrine and the formation rate constants for each of the three metabolites measured in urine. These results suggest that cyfluthrin affects hepatic cytochrome P450 (CYP) system. In order to confirm, a second experiment was carried out. We evaluated the effects of repeated exposure to cyfluthrin on hepatic and renal CYP2E, CYP1A and CYP4A subfamilies and peroxisomal proliferation in rats following oral administration (10 and 20mg/kg/day for 6 days). At the highest dose, cyfluthrin increased renal and hepatic O-deethylation of ethoxyresorufin and O-demethylation of methoxyresorufin, metabolism mediated by the CYP1A subfamily. Liver and kidney were susceptible to cyfluthrin-dependent induction of 12- and 11-hydroxylation of lauric acid, suggesting CYP4A subfamily induction. Also cyfluthrin increased the β-oxidation of palmitoyl-coenzyme A and carnitine acetyltransferase activity, supporting cyfluthrin as a peroxisome proliferator. In conclusion, the demonstration that cyfluthrin induced hepatic CYP1A, CYP4A subfamilies and peroxisomal proliferation raises the possibility of cyfluthrin could produce changes in oxidative stress.

Diesel and biodiesels induce hepatic palmitoyl‐coa oxidase enzymatic activity through different molecular mechanisms in rats

Induction of palmitoyl-CoA oxidase enzymatic activity in rat liver suggests that ingestion of diesel and biodiesels can cause mild hepatic peroxisomal proliferation. Surprisingly, quantification by immunochemistry of the enzyme itself (ACOX1) revealed that palmitoyl-CoA oxidase enzymatic activity correlates with ACOX1 protein level following exposure to diesel, but not following exposure to biodiesels. Quantification of CYP4A1, another biomarker of peroxisomal proliferation, further indicates that contrary to diesel, the effects of biodiesels appear to be independent of this pathway. There are two ACOX1 protein isoforms that exhibit different enzymatic activities depending on the substrate. The results of our enzymatic assays performed on substrates presenting different carbon chain lengths (octanoyl-CoA and palmitoyl-CoA) are compatible with the hypothesis of a differential regulation of the ACOX1 isoforms by diesel and biodiesels. Further studies will be required to precisely determine the molecular mechanisms by which diesel and biodiesels induce palmitoyl-CoA oxidase activity in rat liver.

Ciprofibrate regulation of rat hepatic bilirubin glucuronidation and UDP-glucuronosyltransferases expression

Synthetic fibrates are hypolipidemic drugs known to stimulate hepatic peroxisome proliferation and bilirubin glucuronidation. This study was designed to estimate the effects of ciprofibrate simultaneously on rat hepatic bilirubin glucuronoconjugation and on hepatic expression of UGT1A1, UGT1A2 and UGT1A5, all of which belong to the bilirubin cluster. Hepatic bilirubin glucuronidation activity and UDP-glucuronosyltransferase expression (RT-PCR and Western blotting) were measured after a single-dose ciprofibrate treatment (5mg/kg by gastric intubation) in 36-h time course experiments. Ciprofibrate regulation of PPARα and UGT1A5 mRNA expression was also investigated in rat hepatocytes. Bilirubin conjugation activity was induced by ciprofibrate, reaching a maximum level (2.4×) 24h after the treatment. UGT1A1 and UGT1A5 mRNA expression was induced 1.5 times by ciprofibrate, with UGT1A5 reaching the basal level of UGT1A1. Although UGT1A2 mRNA was induced approximately threefold by ciprofibrate, its expression level remained low in comparison with basal or induced levels of UGT1A1 and UGT1A5 mRNA. In the 36-h time course experiment, bilirubin conjugation activity as well as UGT1A5 and PPARα mRNA expression presented a biphasic induction profile. Although a similar level of induction was observed in primary cultured hepatocyte experiments, such biphasic variation was not observed for both UGT1A5 and PPARα, and the induction of UGT1A5 mRNA expression by ciprofibrate required de novo protein synthesis. A single dose of ciprofibrate significantly induces rat liver bilirubin conjugation as well as UGT1A1, UGT1A5 and PPARα expression. The induction mechanism may involve PPARα, at least regarding UGT1A5 regulation.

Myricetin Increases Hepatic Peroxisome Proliferator-Activated ReceptorαProtein Expression and Decreases Plasma Lipids and Adiposity in Rats

The aim of this study was to investigate the antiobesity and antihyperlipidaemic effects of myricetin. Myricetin exhibited a significant concentration-dependent decrease in the intracellular accumulation of triglyceride in 3T3-L1 adipocytes. The high-fat diet (HFD)-fed rats were dosed orally with myricetin or fenofibrate, once daily for eight weeks. Myricetin (300 mg kg−1 per day) displayed similar characteristics to fenofibrate (100 mg kg−1 per day) in reducing lowered body weight (BW) gain, visceral fat-pad weights and plasma lipid levels of HFD-fed rats. Myricetin also reduced the hepatic triglyceride and cholesterol contents, as well as lowered hepatic lipid droplets accumulation and epididymal adipocyte size in HFD-fed rats. Myricetin and fenofibrate reversed the HFD-induced down-regulation of the hepatic peroxisome proliferator activated receptor (PPAR)α. HFD-induced decreases of the hepatic protein level of acyl-CoA oxidase and cytochrome P450 isoform 4A1 were up-regulated by myricetin and fenofibrate. The elevated expressions of hepatic sterol regulatory element binding proteins (SREBPs) of HFD-fed rats were lowered by myricetin and fenofibrate. These results suggest that myricetin suppressed BW gain and body fat accumulation by increasing the fatty acid oxidation, which was likely mediated via up-regulation of PPARα and down-regulation of SREBP expressions in the liver of HFD-fed rats.

Regulation of Obesity and Lipid Disorders by Extracts from Angelica acutiloba Root in High‐fat Diet‐induced Obese Rats

The aim of this study was to investigate the antiobesity and antihyperlipidemic effects of Angelica acutiloba root (Japanese Dong Quai). High-fat diet (HFD)-induced obese rats were treated orally with the polyphenolic-rich extract of Angelica acutiloba root (AARE) once daily for 8 weeks. The AARE (300 mg/kg per day) supplementation significantly lowered body weight gain, visceral fat-pad weights and plasma lipid levels, as well as the coronary artery risk index and the atherogenic index of HFD-fed rats. The AARE caused dose related reductions in the hepatic triglyceride and cholesterol contents, as well as lowered hepatic lipid droplet accumulation and epididymal adipocyte size in the HFD-fed rats. The AARE reversed the HFD-induced down-regulation of the hepatic peroxisome proliferator activated receptor-α (PPARα). The HFD-induced decreases of the hepatic protein level of acyl-CoA oxidase (ACO), and the cytochrome P450 isoform 4A1 (CYP4A1) was up-regulated by AARE. The elevated expressions of hepatic sterol regulatory element binding proteins (SREBPs) of HFD-fed rats were lowered by AARE. These results suggest that AARE attenuated visceral fat accumulation and improved hyperlipidemia in HFD-induced obesity by increasing lipid metabolism through the down-regulation of SREBPs and enhanced the expression of ACO and CYP4A1 in the liver, which was likely mediated by up-regulation of the expression of hepatic PPARα.