Involvement of guanylin and GC-C in rat mesenteric macrophages in resistance to a high-fat diet

A high-fat diet (HFD) is a well-known contributing factor in the development of obesity. Most rats fed HFDs become obese. Those that avoid obesity when fed HFDs are considered diet resistant (DR). We performed a microarray screen to identify genes specific to the mesenteric fat of DR rats and revealed high expression of guanylin and guanylyl cyclase C (GC-C) in some subjects. Our histologic studies revealed that the cellular source of guanylin and GC-C is macrophages. Therefore, we developed double-transgenic (Tg) rats overexpressing guanylin and GC-C in macrophages and found that they were resistant to the effects of HFDs. In the mesenteric fat of HFD-fed Tg rats, Fas and perilipin mRNAs were downregulated, and those of genes involved in fatty acid oxidation were upregulated, compared with the levels in HFD-fed wild-type rats. In vitro studies demonstrated that lipid accumulation was markedly inhibited in adipocytes cocultured with macrophages expressing guanylin and GC-C and that this inhibition was reduced after treatment with guanylin- and GC-C-specific siRNAs. Our results suggest that the macrophagic guanylin-GC-C system contributes to the altered expression of genes involved in lipid metabolism, leading to resistance to obesity.     

Attenuation by a Vigna nakashimae extract of nonalcoholic fatty liver disease in high-fat diet-fed mice

A Vigna nakashimae (VN) extract has been shown to have antidiabetic and anti-obesity effects. However, the mechanism underlying the effect of a VN extract on hepatic inflammation and endoplasmic reticulum (ER) stress remains unclear. In the present study, we investigated how a VN extract protects against the development of non-alcoholic fatty liver disease (NAFLD). A VN extract for 12 weeks reduced the body weight, serum metabolic parameters, cytokines, and hepatic steatosis in high-fat diet (HFD)-fed mice. A VN extract decreased HFD-induced hepatic acetyl CoA carboxylase and glucose transporter 4 expressions. In addition to the levels of high-mobility group box 1 and receptor for advanced glycation, the hepatic expression of ATF4 and caspase-3 was also reduced by a VN extract. Thus, these data indicate that a chronic VN extract prevented NAFLD through multiple mechanisms, including inflammation, ER stress, and apoptosis in the liver.     

Prevention of DNA damage by l-carnitine induced by metabolites accumulated in maple syrup urine disease in human peripheral leukocytes in vitro

Maple syrup urine disease (MSUD) is an inherited aminoacidopathy caused by a deficiency in branched-chain α-keto acid dehydrogenase complex activity that leads to the accumulation of the branched-chain amino acids (BCAAs) leucine (Leu), isoleucine, and valine and their respective α-keto-acids, α-ketoisocaproic acid (KIC), α keto-β-methylvaleric acid, and α-ketoisovaleric acid. The major clinical features presented by MSUD patients include ketoacidosis, failure to thrive, poor feeding, apnea, ataxia, seizures, coma, psychomotor delay, and mental retardation; however, the pathophysiology of this disease is poorly understood. MSUD treatment consists of a low protein diet supplemented with a mixture containing micronutrients and essential amino acids but excluding BCAAs. Studies have shown that oxidative stress may be involved in the neuropathology of MSUD, with the existence of lipid and protein oxidative damage in affected patients. In recent years, studies have demonstrated the antioxidant role of l-carnitine (l-Car), which plays a central function in cellular energy metabolism and for which MSUD patients have a deficiency. In this work, we investigated the in vitro effect of Leu and KIC in the presence or absence of l-Car on DNA damage in peripheral whole blood leukocytes using the alkaline comet assay with silver staining and visual scoring. Leu and KIC resulted in a DNA damage index that was significantly higher than that of the control group, and l-Car was able to significantly prevent this damage, mainly that due to KIC.     

High‐fat diet induced alteration in lipid enzymes and inflammation in cardiac and brain tissues: Assessment of the effects of Atorvastatin‐loaded nanoparticles

Treatment with Lipitor is associated with several adverse impacts. Here we investigated the effects of low Lipitor nanoparticles (atorvastatin calcium nanopartilcle [AC‐NP]), with size less than 100 , on enzymes of lipid metabolism and inflammation in cardiac, hepatic, and brain tissues of hypercholestremic adult male rats. Adult male rats were divided into five experimental groups. In group 1, the intact control (normal pellet diet), animals were fed a normal control diet; the other four groups were fed a high‐fat diet (HFD) for 6 weeks. After 6 weeks, groups from 2 to 5 were assigned as a positive control (HFD), HFD + Lipitor, HFD + AC‐NP‐R1, or HFD + AC‐NP‐R2. Different treatments were administrated orally for two regimen periods (R1 daily and R2 once every 3 days). The treatment was conducted for two consecutive weeks. The HFD group faced a significant elevation in 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA), associated with a significant reduction in low‐density lipoprotein receptor (LDL‐R) along with cholesterol 7 α‐hydroxylase enzyme in hepatic tissues, compared with the control group. Also, the HFD group induced hepatic, cardiac, and brain inflammation, evidenced by increased hepatic oxidative stress markers and cardiac homocysteine, together with elevated proinflammatory cytokines interleukin‐1β (IL‐1β) and IL‐6 levels in brain tissue, compared with the control group. Different AC‐NP treatments significantly augmented both mRNA LDL‐R and mRNA 7α‐hydroxylase expression in hepatic tissues, associated with significant depletion in mRNA HMG‐CoA expression, compared with HFD + Lipitor. The inflammation symptoms were ameliorated by the AC‐NP treatments, compared to HFD + Lipitor. Lipitor encapsulation in NP formulation results in increased efficiency and reduced dose‐related adverse effects known to be associated with the Lipitor chronic administration.     

Berberine reduces methylation of the MTTP promoter and alleviates fatty liver induced by a high-fat diet in rats

High-calorie food leads to nonalcoholic fatty liver disease (NAFLD) through dysregulation of genes involved in lipid metabolism, but the precise mechanism remains unclear. DNA methylation represents one of the mechanisms that contributes to dysregulation of gene expression via interaction with environmental factors. Berberine can alleviate fatty liver in db/db and ob/ob mice. Here, we investigated whether DNA methylation is involved in the pathogenesis of NAFLD induced by a high-fat diet (HFD) and whether berberine improves NAFLD through influencing the methylation status of promoters of key genes. HFD markedly decreased the mRNA levels encoding CPT-1α, MTTP, and LDLR in the liver. In parallel, DNA methylation levels in the MTTP promoter of rats with NAFLD were elevated in the liver. Interestingly, berberine reversed the downregulated expression of these genes and selectively inhibited HFD-induced increase in the methylation of MTTP. Consistently, berberine increased hepatic triglyceride (TG) export and ameliorated HFD-induced fatty liver. Furthermore, a close negative correlation was observed between the MTTP expression and its DNA methylation (at sites −113 and −20). These data indicate that DNA methylation of the MTTP promoter likely contributes to its downregulation during HFD-induced NAFLD and, further, that berberine can partially counteract the HFD-elicited dysregulation of MTTP by reversing the methylation state of its promoter, leading to reduced hepatic fat content.     

Curcumin‐galactomannosides mitigate alcohol‐induced liver damage by inhibiting oxidative stress,hepatic inflammation,and enhance bioavailability on TLR4/MMP events compared to curcumin

Alcoholic liver diseases are classified as one of the major reasons for worldwide morbidity and mortality. Curcuminoids exhibit a wide range of pharmacological activities that are beneficial for health, including hepatoprotective effects, but its clinical significance is limited due to poor oral bioavailability. In the present study, a novel formulation of curcumin as curcumin‐galactomannosides (CGM) with enhanced oral bioavailability alleviated alcohol‐induced liver damage in wistar rats with an increased potency compared to the unformulated natural curcuminoids (CM). Ethanol administration significantly elevated liver toxicity markers, lipid peroxidation and inflammatory markers with a simultaneous reduction in antioxidant defenses. Supplementation of CGM reversed all of the pathological effects of alcohol administration, almost close to the normal level, when compared with CM. Histopathology of liver tissue also confirmed the better protective effect of CGM, indicating the enhancement in antioxidant and anti‐inflammatory effects as a function of bioavailability.     

Ilex paraguariensis extract ameliorates obesity induced by high-fat diet: potential role of AMPK in the visceral adipose tissue

The aim of present study was to investigate the anti-obesity effect of Ilex paraguariensis extract and its molecular mechanism in rats rendered obese by a high-fat diet (HFD). I. paraguariensis extract supplementation significantly lowered body weight, visceral fat-pad weights, blood and hepatic lipid, glucose, insulin, and leptin levels of rats administered HFD. Feeding I. paraguariensis extract reversed the HFD-induced downregulation of the epididymal adipose tissue genes implicated in adipogenesis or thermogenesis, such as peroxisome proliferators’ activated receptor γ2, adipocyte fatty acid binding protein, sterol-regulatory-element-binding protein-1c, fatty acid synthase, HMG-CoA reductase, uncoupling protein 2, and uncoupling protein 3. Dietary supplementation with I. paraguariensis extract protected rats from the HFD-induced decreases in the phospho-AMP-activated protein kinase (AMPK)/AMPK and phospho-acetyl-CoA carboxylase (ACC)/ACC protein ratio related to fatty acid oxidation in the edipidymal adipose tissue. The present study reports that the I. paraguariensis extract can have a protective effect against a HFD-induced obesity in rats through an enhanced expression of uncoupling proteins and elevated AMPK phosphorylation in the visceral adipose tissue.     

SphK1 mediates hepatic inflammation in a mouse model of NASH induced by high saturated fat feeding and initiates proinflammatory signaling in hepatocytes

Steatohepatitis occurs in up to 20% of patients with fatty liver disease and leads to its primary disease outcomes, including fibrosis, cirrhosis, and increased risk of hepatocellular carcinoma. Mechanisms that mediate this inflammation are of major interest. We previously showed that overload of saturated fatty acids, such as that which occurs with metabolic syndrome, induced sphingosine kinase 1 (SphK1), an enzyme that generates sphingosine-1-phosphate (S1P). While data suggest beneficial roles for S1P in some contexts, we hypothesized that it may promote hepatic inflammation in the context of obesity. Consistent with this, we observed 2-fold elevation of this enzyme in livers from humans with nonalcoholic fatty liver disease and also in mice with high saturated fat feeding, which recapitulated the human disease. Mice exhibited activation of NFκB, elevated cytokine production, and immune cell infiltration. Importantly, SphK1-null mice were protected from these outcomes. Studies in cultured cells demonstrated saturated fatty acid induction of SphK1 message, protein, and activity, and also a requirement of the enzyme for NFκB signaling and increased mRNA encoding TNFα and MCP1. Moreover, saturated fat-induced NFκB signaling and elevation of TNFα and MCP1 mRNA in HepG2 cells was blocked by targeted knockdown of S1P receptor 1, supporting a role for this lipid signaling pathway in inflammation in nonalcoholic fatty liver disease.     

Binding free energy differences in a TCR-peptide-MHC complex induced by a peptide mutation: a simulation analysis

Recognition by the T-cell receptor (TCR) of immunogenic peptides presented by class I major histocompatibility complexes (MHCs) is the determining event in the specific cellular immune response against virus-infected cells or tumor cells. It is of great interest, therefore, to elucidate the molecular principles upon which the selectivity of a TCR is based. These principles can in turn be used to design therapeutic approaches, such as peptide-based immunotherapies of cancer. In this study, free energy simulation methods are used to analyze the binding free energy difference of a particular TCR (A6) for a wild-type peptide (Tax) and a mutant peptide (Tax P6A), both presented in HLA A2. The computed free energy difference is 2.9 kcal/mol, in good agreement with the experimental value. This makes possible the use of the simulation results for obtaining an understanding of the origin of the free energy difference which was not available from the experimental results. A free energy component analysis makes possible the decomposition of the free energy difference between the binding of the wild-type and mutant peptide into its components. Of particular interest is the fact that better solvation of the mutant peptide when bound to the MHC molecule is an important contribution to the greater affinity of the TCR for the latter. The results make possible identification of the residues of the TCR which are important for the selectivity. This provides an understanding of the molecular principles that govern the recognition. The possibility of using free energy simulations in designing peptide derivatives for cancer immunotherapy is briefly discussed.     

Searching for genetic factors of fatty liver in SMXA-5 mice by quantitative trait loci analysis under a high-fat diet

Fatty liver is strongly associated with the metabolic syndrome characterized by obesity, insulin resistance, and type 2 diabetes, but the genetic basis and functional mechanisms linking fatty liver with the metabolic syndrome are largely unknown. The SMXA-5 mouse is one of the SMXA recombinant inbred substrains established from SM/J and A/J strains and is a model for polygenic type 2 diabetes, characterized by moderately impaired glucose tolerance, hyperinsulinemia, and mild obesity. SMXA-5 mice also developed fatty liver, and a high-fat diet markedly worsened this trait, although SM/J and A/J mice are resistant to fatty liver development under a high-fat diet. To dissect loci for fatty liver in the A/J regions of the SMXA-5 genome, we attempted quantitative trait loci (QTLs) analysis in (SM/JxSMXA-5)F2 intercross mice fed a high-fat diet. We mapped a major QTL for relative liver weight and liver lipid content near D12Mit270 on chromosome 12 and designated this QTL Fl1sa. The A/J allele at this locus contributes to the increase in these traits. We confirmed the effect of Fl1sa on lipid accumulation in liver using the A/J-Chr12(SM) consomic strain, which showed significantly less accumulation than A/J mice. This suggests that the SM/J and A/J strains, neither of which develops fatty liver, possess loci causing fatty liver and that the coexistence of these loci causes fatty liver in SMXA-5 mice.     

Effects of a plant product consisting of green tea and curcuma extract on milk production and the expression of hepatic genes involved in endoplasmic stress response and inflammation in dairy cows

During the periparturient phase, cows are typically in an inflammation-like condition, and it has been proposed that inflammation associated with the induction of stress of the endoplasmic reticulum (ER) in the liver contributes to the development of fatty liver syndrome and ketosis. In the present study, the hypothesis that supplementation of dairy cows with a plant product consisting of green tea (95%) and curcuma extract (5%) rich in polyphenols attenuates inflammation and ER stress in the liver during early lactation was investigated. Twenty-seven cows were assigned to two groups, either a control group (n = 14) or a treatment group (n = 13). Both groups of cows received a total mixed ration, and the ration of the treatment group was supplemented with 0.175 g of the plant product per kg dry matter from week 3 prepartum to week 9 postpartum. Dry matter intake and energy balance during week 2 to week 9 postpartum were not different between the two groups. However, cows supplemented with the plant product had a greater amount of energy-corrected milk during week 2 to week 9 postpartum and lower concentrations of triacylglycerols and cholesterol in the liver in week 1 and week 3 postpartum than cows of the control group (p < 0.05). Cows supplemented with the plant product showed a trend towards a reduced mRNA concentration of haptoglobin (p < 0.10), while relative mRNA concentrations of eight genes of the unfolded protein response considered in the liver were not different between the two groups of cows. Relative hepatic mRNA concentration of fibroblast growth factor, a stress hormone induced by various stress conditions, was reduced at week 1 and week 3 postpartum in cows supplemented with the plant product (p < 0.05). Overall, the data of this study suggest that – although there were only minor effects on the occurrence of ER stress and inflammation – a supplementation of polyphenols might be useful to improve milk yield and prevent fatty liver syndrome in dairy cows.     

Influence of feeding a fish oil-containing diet to young,lean, adult dogs: effects on lipid metabolites,postprandial glycaemia and body weight

The aim of this study was to determine the effect of feeding a fish oil (FO)-containing diet on lipid and protein metabolism, postprandial glycaemia and body weight in young, lean, adult dogs. Eight female Beagles were randomly assigned to one of two isonitrogenous and isoenergetic diets, Control or FO, in a crossover design. At the beginning of the experiment and at 30 and 60 d, a baseline blood sample was collected and the dogs then were fed their daily ration. Nitrogen balance began at 07:00 h on day 63 of each experimental period and ended at 07:00 h on day 69. On day 66 of each period, a single dose (7.5 mg/kg) of ¹⁵N-glycine was administered orally to each dog via gelatin capsule. Postprandial glycaemia did not differ between treatments or among sampling days within treatment. Cholesterol concentration was increased (p < 0.05) on the Control treatment throughout the experiment when compared to values of day 0. Dogs fed the FO treatment had higher plasma triglyceride and ghrelin concentrations than those fed the Control treatment. Body weight and food intake did not differ between dietary treatments. Faecal excretion was increased (p < 0.05) in the FO treatment. Dry matter digestibility was decreased (p < 0.05) and fat digestibility tended (p < 0.10) to decrease in the FO treatment. Overall, feeding a FO-containing diet showed a protective effect against the rise of plasma cholesterol and it increased plasma ghrelin concentration. However, FO supplementation did not appear to affect protein metabolism or postprandial glycaemia in adult lean dogs.     

Constitutive activation of LXR in macrophages regulates metabolic and inflammatory gene expression: identification of ARL7 as a direct target

Ligand activation of liver X receptors (LXRs) has been shown to impact both lipid metabolism and inflammation. One complicating factor in studies utilizing synthetic LXR agonists is the potential for pharmacologic and receptor-independent effects. Here, we describe an LXR gain-of-function system that does not depend on the addition of exogenous ligand. We generated transgenic mice expressing a constitutively active VP16-LXRα protein from the aP2 promoter. These mice exhibit increased LXR signaling selectively in adipose and macrophages. Analysis of gene expression in primary macrophages derived from two independent VP16-LXRα transgenic lines confirmed the ability of LXR to drive expression of genes involved in cholesterol efflux and fatty acid synthesis. Moreover, VP16-LXRα expression also suppressed the induction of inflammatory genes by lipopolysaccharide to a comparable degree as synthetic agonist. We further utilized VP16-LXRα-expressing macrophages to identify and validate new targets for LXRs, including the gene encoding ADP-ribosylation factor-like 7 (ARL7). ARL7 has previously been shown to transport cholesterol to the membrane for ABCA1-associated removal and thus may be integral to the LXR-dependent efflux pathway. We show that the ARL7 promoter contains a functional LXRE and can be transactivated by LXRs in a sequence-specific manner, indicating that ARL7 is a direct target of LXR. These findings provide further support for an important role of LXRs in the coordinated regulation of lipid metabolic and inflammatory gene programs in macrophages.     

Effect of a negative energy balance induced by feed restriction in lactating sows on hepatic lipid metabolism,milk production and development of litters

In rodents, forced activation of hepatic peroxisome proliferator-activated receptor α (PPARα) by administration of exogenous PPARα activators during lactation leads to a reduction of milk triacylglycerol (TAG) production. Herein, we investigated whether a negative energy balance (NEB) induced by feed restriction (about 18% lower feed and energy intake) during lactation by increasing the release of fatty acids, which act as PPARα agonists, causes a disruption of hepatic lipid metabolism and thereby impairs milk TAG production in sows. Nutrient and energy content of the milk on day 20 of lactation and gains of litters during the first 14 d and the whole 21 d suckling period did not differ between Control and feed-restricted sows. The mRNA concentrations of several sterol regulatory element-binding protein target genes involved in lipid synthesis in the liver and the plasma concentration of TAG were reduced in the feed-restricted sows, whereas the mRNA concentrations of PPARα target genes involved in fatty acid oxidation in liver and skeletal muscle were not different between groups. In conclusion, it was shown that an NEB during lactation does not adversely affect milk composition and gains of litters, despite inhibiting hepatic expression of genes involved in lipid synthesis and reducing plasma TAG concentration. The finding that PPARα target genes involved in fatty acid utilisation in liver and muscle of sows are not induced by the NEB during lactation may explain that fatty acid availability in the mammary gland is sufficient to maintain milk TAG production and to allow normal litter gain.     

Growth of a pupal ectoparasitoid, Diapetimorphaintroita, on an artificial diet: stimulation of growth rate by a lipid extract from host pupae

An artificial diet used to rear the ectoparasitoid,Diapetimorpha introita, was supplemented withlipids extracted from pupae of the host, Spodoptera frugiperda (J. E. Smith). The diet alsowas sequentially supplemented with four fatty acids(arachidonic, linoleic, -linolenic and oleic),flax oil and Lipid Concentrate^® which is used in cellculture. Pupae were homogenized and extracted withchloroform:methanol (2:1 v/v) and after drying downthe chloroform and methanol phases separately, theresidues from each solvent phase were evaluated in theartificial diet. Growth-promoting activity wasobserved in the chloroform phase containing lipids. Diet supplemented with lipid stored at –80 °C, andinsects reared on diet with fresh 1× and 2× extractsdeveloped significantly faster than those reared onthe artificial diet but slower than those reared onhost pupae. The fresh 1× and the 2× extracts alsoenhanced the average weight of the males and females,respectively. Storing the lipids at –20 °C resultedin a loss of activity. A lipid extract from Galleria mellonella pupae increased the averageweight of male and females but did not increase theirdevelopmental rate. Adult emergence was not improvedby any of the dietary additives. None of thecommercial lipid treatments significantly reduceddevelopmental time; however, the -linolenicacid-supplemented diet significantly increased theaverage weight of females. TLC analyses of the lipidextract from S. frugiperda revealed lipidsrepresenting four classes of neutral lipids in theextract: triolein, cholesterol, diacylglycerol, andphospholipid. Data from this study indicate thatoptimization and successful utilization of anartificial diet to rear D. introita depends onidentification of host factors required by theparasitic for growth and development.     

乳酸菌胆盐水解酶和共轭脂肪酸产生及对宿主脂代谢影响的研究进展

乳酸菌是一类影响宿主脂代谢的人体肠道益生菌。乳酸菌对脂代谢的影响作用与其产生胆盐水解酶(bile salt hydrolase,EC3.5.1.24,BSH)及共轭转化多不饱和脂肪酸(polyunsaturated fatty acids,PUFAs)关系密切。菌株差异、菌群分布和饮食差异是影响BSH及共轭脂肪酸产生的重要因素。本文重点阐述了两类物质对宿主脂代谢的影响机制,以期为后续研究提供借鉴。BSH能够降解肝脏分泌的胆汁酸(bile acids,BAs),降低脂类物质的吸收。BAs的降解产物胆汁酸脱氧胆酸(deoxycholic acid,DCA)和石胆酸(lithocholic acid,LCA)能够通过机体信号通路法尼类X受体(farnesoid X receptor,FXR)、小异二聚体伴侣(small heterodimer partner,SHP)及肝脏X受体(liver X receptor,LXR)等信号通路进行调控,促进胆固醇转运及向BAs转化。此外,BSH还能够通过下调固醇调节元件结合蛋白1c (sterol regulatory element binding protein 1c,SREBP-1c)、上调5ʹ-腺苷单磷酸激活蛋白激酶α(5ʹ-AMP activated protein kinase,AMPKα)和过氧化物酶体增殖物激活受体α (peroxisome proliferator-activated receptor α,PPARα)抑制脂质合成,促进脂质的分解。PUFAs可被乳酸菌转化产生共轭脂肪酸,如共轭亚油酸(conjugated linoleic acid,CLA)和共轭亚麻酸(conjugated linolenic acid,CLNA),CLA/CLNA能够促进机体产生瘦素(leptin,LP),抑制食欲、促进能量消耗;CLA/CLNA还可以通过激活PPARα进行调控,促进人体脂质的氧化分解。乳酸菌通过以上多种途径共同作用调节宿主的脂代谢,对深入理解乳酸菌调控脂代谢机制及临床应用有着重要意义。