Liver carbohydrate and lipid metabolism of insulin-deficient mice is altered by trans-10, cis-12 conjugated linoleic acid

Differential expression of gluconeogenic enzymes in early- and late-stage diabetes: the effect of Citrullus colocynthis (L.) Schrad. Seed extract on hyperglycemia and hyperlipidemia in Wistar-Albino rats model

Background

The medicinal plant Citrullus colocynthis (L.) Schrad. (C. colocynthis) may benefit patients at different phases of diabetes by attuning to contrasting situations. Our primary objective was to find the mechanism(s) behind the antidiabetic/anti-hyperlipidemic effects of C.colocynthis seed aqueous extract (CCAE) in two different stages of type 2 diabetes (T2D) in rats.

Methods

Fasting blood sugar (FBS) levels, body weights, and the degree of impaired glucose tolerance (IGT) were measured in healthy nondiabetic control rats (Con), as well as rats with early and late stages of T2D, denoted as ET2D and LT2D, respectively. CCAE was intraperitoneally (IP) injected for 28 days. In the end, the hepatic mRNA expression levels of the following genes were determined by RT-PCR: glucose-6-phosphatase (G6Pase), phosphoenolpyruvate carboxykinase (PEPCK), insulin-dependent sterol regulatory element-binding protein-1c (SREBP-1c), acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), peroxisome proliferator-activated receptor alpha (PPARα), and carnitine palmitoyltransferase I (CPT1). The liver was examined by hematoxylin and eosin (H&E) and Oil-Red O staining. CCAE was partially analyzed by HPLC-DAD.

Results

ET2D and LT2D were characterized by differentially elevated FBS, deteriorated bodyweight, and significant IGT compared to Con. Hepatosteatoses of varying morphologies and higher hepatic expression of G6Pase than PRPCK in ET2D versus the opposite in LT2D further confirmed the divergent nature of metabolic aberrations. At the end of 28 days, the high levels of FBS, alkaline phosphatase (ALP), triglyceride (TG), urea, hepatic protein carbonyl content (PCC), and alanine and aspartate aminotransferases (AST and ALT, respectively) persisted in untreated LT2D. CCAE ameliorated oxidative stress and upregulated PPARα expression in diabetic groups and Con; it downregulated CPT1 expression in the LT2D group. CCAE’s ability to lower FBS and serum and hepatic TG in both ET2D and LT2D indicated its ability to act via different mechanisms. Ferulic acid (Fer A) and rutin hydrate (RH) were detected in CCAE.

Conclusion

CCAE lowered the FBS in ET2D via inhibiting the hepatic G6Pase expression (glycogenolysis). In LT2D, CCAE abated sugar levels by diverting PEPCK activity, preferably towards glyceroneogenesis than gluconeogenesis. The preserved triglyceride/fatty acid (TG/FA) cycle, the upregulated PPARα, and the downregulated CPT1 gene expressions reduced serum and hepatic TG.

Simultaneous Inhibition of Peripheral CB1R and iNOS Mitigates Obesity-Related Dyslipidemia Through Distinct Mechanisms

Diabetic dyslipidemia, characterized by increased plasma triglycerides and decreased HDL cholesterol levels, is a major factor contributing to nonalcoholic steatohepatitis and cardiovascular risk in type 2 diabetes. Activation of the cannabinoid-1 receptor (CB1R) and activation of inducible nitric oxide synthase (iNOS) are associated with nonalcoholic steatohepatitis progression. Here, we tested whether dual-targeting inhibition of hepatic CB1R and iNOS improves diabetic dyslipidemia in mice with diet-induced obesity (DIO mice). DIO mice were treated for 14 days with (S)-MRI-1867, a peripherally restricted hybrid inhibitor of CB1R and iNOS. (R)-MRI-1867, the CB1R-inactive stereoisomer that retains iNOS inhibitory activity, and JD-5037, a peripherally restricted CB1R antagonist, were used to assess the relative contribution of the two targets to the effects of (S)-MRI-1867. (S)-MRI-1867 reduced hepatic steatosis and the rate of hepatic VLDL secretion, upregulated hepatic LDLR expression, and reduced the circulating levels of proprotein convertase subtilisin/kexin type 9 (PCSK9). The decrease in VLDL secretion could be attributed to CB1R blockade, while the reduction of PCSK9 levels and the related increase in LDLR resulted from iNOS inhibition via an mTOR complex 1-dependent mechanism. In conclusion, this approach based on the concomitant inhibition of CB1R and iNOS represents a promising therapeutic strategy for the treatment of dyslipidemia.

Tissue-dependent effects of cis-9,trans-11- and trans-10,cis-12-CLA isomers on glucose and lipid metabolism in adult male mice

Mixtures of the two major conjugated linoleic acid (CLA) isomers trans-10,cis-12-CLA and cis-9,trans-11-CLA are used as over the counter supplements for weight loss. Because of the reported adverse effects of CLA on insulin sensitivity in some mouse studies, we sought to compare the impact of dietary t10c12-CLA and c9t11-CLA on liver, adipose tissue, and systemic metabolism of adult lean mice. We fed 8 week-old C57Bl/6J male mice with low fat diets (10.5% Kcal from fat) containing 0.8% t10c12-CLA or c9t11-CLA for 9 or 38 days. Diets containing c9t11-CLA had minimal impact on the endpoints studied. However, 7 days after starting the t10c12-CLA diet, we observed a dramatic reduction in fat mass measured by NMR spectroscopy, which interestingly rebounded by 38 days. This rebound was apparently due to a massive accumulation of lipids in the liver, because adipose tissue depots were visually undetectable. Hepatic steatosis and the disappearance of adipose tissue after t10c12-CLA feeding was associated with elevated plasma insulin levels and insulin resistance, compared to mice fed a control diet or c9t11-CLA diet. Unexpectedly, despite being insulin resistant, mice fed t10c12-CLA had normal levels of blood glucose, without signs of impaired glucose clearance. Hepatic gene expression and fatty acid composition suggested enhanced hepatic de novo lipogenesis without an increase in expression of gluconeogenic genes. These data indicate that dietary t10c12-CLA may alter hepatic glucose and lipid metabolism indirectly, in response to the loss of adipose tissue in mice fed a low fat diet.

Conjugated linoleic acid does not affect digestion and absorption of fat and starch-a randomized, double-blinded, placebo-controlled parallel study

OBJECTIVE

Conjugated linoleic acid (CLA) is known as a potent agent for altering body weight and composition. However, its effect on the process of digestion is still unknown. The aim of this study has been to elucidate the effect of a 3-month supplementation with CLA on starch and fat digestion and absorption in humans.

APPROACH

The study included 74 obese and overweight adults who were randomized to receive 3.0 g of CLA or sunflower oil as placebo daily for 3 months. Digestion and absorption of fat and starch was assessed using non-invasive breath tests with a stable ¹³C isotope (cumulative percentage dose recovery, CPDR) before and after the supplementation period. To exclude the effect of oxidation, in addition total energy expenditure (TTE) was measured by a ¹³C bicarbonate breath test.

RESULTS

The changes in CPDR values (∆CPDR median 〈interquartile range〉) were no different between subjects from the CLA group and the placebo group (fat: -0.2 〈-9.1-4.1〉 versus 0.6 〈-7.0-8.0〉, p < 0.4796; starch: -1.3 〈-9.5-2.4〉 versus -1.0 〈-5.1-1.7〉, p < 0.5520, respectively). The incidence of negative and positive values of ∆CPDR was no different between groups [for fat: 53.1% versus 46.7%, RR 1.138, (95% CI 0.689-1.882) and for starch: 67.7% versus 56.7%, RR 1.195, (95% CI 0.804-1.777)]. The changes in TTE did not differ between the CLA and the placebo group (respectively 1 〈48; 267〉 versus -8 〈-120;93〉 kcal; p < 0.2728).

CONCLUSION

Supplementation with CLA for 3 months did not affect fat and starch digestion assessed by ¹³C mixed triglyceride breath test and ¹³C starch breath test.

Characterization of hepatic fatty acids in mice with reduced liver fat by ultra-short echo time (1)H-MRS at 14.1 T in vivo

Alterations in the hepatic lipid content (HLC) and fatty acid composition are associated with disruptions in whole body metabolism, both in humans and in rodent models, and can be non-invasively assessed by (1)H-MRS in vivo. We used (1)H-MRS to characterize the hepatic fatty-acyl chains of healthy mice and to follow changes caused by streptozotocin (STZ) injection. Using STEAM at 14.1 T with an ultra-short TE of 2.8 ms, confounding effects from T2 relaxation and J-coupling were avoided, allowing for accurate estimations of the contribution of unsaturated (UFA), saturated (SFA), mono-unsaturated (MUFA) and poly-unsaturated (PUFA) fatty-acyl chains, number of double bonds, PU bonds and mean chain length. Compared with in vivo (1) H-MRS, high resolution NMR performed in vitro in hepatic lipid extracts reported longer fatty-acyl chains (18 versus 15 carbons) with a lower contribution from UFA (61 ± 1% versus 80 ± 5%) but a higher number of PU bonds per UFA (1.39 ± 0.03 versus 0.58 ± 0.08), driven by the presence of membrane species in the extracts. STZ injection caused a decrease of HLC (from 1.7 ± 0.3% to 0.7 ± 0.1%), an increase in the contribution of SFA (from 21 ± 2% to 45 ± 6%) and a reduction of the mean length (from 15 to 13 carbons) of cytosolic fatty-acyl chains. In addition, SFAs were also likely to have increased in membrane lipids of STZ-induced diabetic mice, along with a decrease of the mean chain length. These studies show the applicability of (1)H-MRS in vivo to monitor changes in the composition of the hepatic fatty-acyl chains in mice even when they exhibit reduced HLC, pointing to the value of this methodology to evaluate lipid-lowering interventions in the scope of metabolic disorders.

Epigenetic mechanisms contribute to the expression of immune related genes in the livers of dairy cows fed a high concentrate diet

Purpose

Epigenetic modifications critically regulate the expression of immune-related genes in response to inflammatory stimuli. It has been extensively reported that a high concentrate (HC) diet can trigger systemic inflammation in dairy cows, yet it is unclear whether epigenetic regulation is involved in the expression of immune genes in the livers of dairy cows. This study aimed to investigate the impact of epigenetic modifications on the expression of immune-related genes.

Experimental Design

In eight mid-lactating cows, we installed a rumen cannula and catheters of the portal and hepatic veins. Cows were randomly assigned to either the treatment group fed a high concentrate (HC) diet (60% concentrate + 40% forage, n = 4) or a control group fed a low concentrate (LC) diet (40% concentrate + 60% forage, n = 4).

Results

After 10 weeks of feeding, the rumen pH was reduced, and levels of lipopolysaccharide (LPS) in the rumen, and portal and hepatic veins were notably increased in the HC group compared with the LC group. The expression levels of detected immune response-related genes, including Toll-like receptor 4 (TLR4), cytokines, chemokines, and acute phase proteins, were significantly up-regulated in the livers of cows fed a HC diet. Chromatin loosening at the promoter region of four candidate immune-related genes (TLR4, LPS-binding protein, haptoglobin, and serum amyloid A3) was elicited, and was strongly correlated with enhanced expression of these genes in the HC group. Demethylation at the promoter region of all four candidate immune-related genes was accompanied by chromatin decompaction.

Conclusion

After HC diet feeding, LPS derived from the digestive tract translocated to the liver via the portal vein, enhancing hepatic immune gene expression. The up-regulation of these immune genes was mediated by epigenetic mechanisms, which involve chromatin remodeling and DNA methylation. Our findings suggest that modulating epigenetic mechanisms could provide novel ways to treat systemic inflammatory responses elicited by the feeding of a HC diet.

Dietary trans-10, cis-12-conjugated linoleic acid alters fatty acid metabolism and microbiota composition in mice

The main aim of the present study was to investigate the effects of dietary trans-10, cis-12-conjugated linoleic acid (t10c12-CLA) on intestinal microbiota composition and SCFA production. C57BL/6 mice (n 8 per group) were fed a standard diet either supplemented with t10c12-CLA (0·5 %, w/w) (intervention) or with no supplementation (control), daily for 8 weeks. Metabolic markers (serum glucose, leptin, insulin and TAG, and liver TAG) were assessed by ELISA commercial kits, tissue long-chain fatty acids and caecal SCFA by GC, and microbial composition by 16S rRNA pyrosequencing. Dietary t10c12-CLA significantly decreased visceral fat mass (P< 0·001), but did not affect body weight (intervention), when compared with no supplementation (control). Additionally, lipid mass and composition were affected by t10c12-CLA intake. Caecal acetate, propionate and isobutyrate concentrations were higher (P< 0·05) in the t10c12-CLA-supplemented group than in the control group. The analysis of the microbiota composition following 8 weeks of t10c12-CLA supplementation revealed lower proportions of Firmicutes (P= 0·003) and higher proportions of Bacteroidetes (P= 0·027) compared with no supplementation. Furthermore, t10c12-CLA supplementation for 8 weeks significantly altered the gut microbiota composition, harbouring higher proportions of Bacteroidetes, including Porphyromonadaceae bacteria previously linked with negative effects on lipid metabolism and induction of hepatic steatosis. These results indicate that the mechanism of dietary t10c12-CLA on lipid metabolism in mice may be, at least, partially mediated by alterations in gut microbiota composition and functionality.

Lipolysis, and not hepatic lipogenesis, is the primary modulator of triglyceride levels in streptozotocin-induced diabetic mice

OBJECTIVE

Diabetic hypertriglyceridemia is thought to be primarily driven by increased hepatic de novo lipogenesis. However, experiments in animal models indicated that insulin deficiency should decrease hepatic de novo lipogenesis and reduce plasma triglyceride levels.

APPROACH AND RESULTS

To address the discrepancy between human data and genetically altered mouse models, we investigated whether insulin-deficient diabetic mice had triglyceride changes that resemble those in diabetic humans. Streptozotocin-induced insulin deficiency increased plasma triglyceride levels in mice. Contrary to the mouse models with impaired hepatic insulin receptor signaling, insulin deficiency did not reduce hepatic triglyceride secretion and de novo lipogenesis-related gene expression. Diabetic mice had a marked decrease in postprandial triglycerides clearance, which was associated with decreased lipoprotein lipase and peroxisome proliferator-activated receptor α mRNA levels in peripheral tissues and decreased lipoprotein lipase activity in skeletal muscle, heart, and brown adipose tissue. Diabetic heterozygous lipoprotein lipase knockout mice had markedly elevated fasting plasma triglyceride levels and prolonged postprandial triglycerides clearance.

CONCLUSIONS

Insulin deficiency causes hypertriglyceridemia by decreasing peripheral lipolysis and not by an increase in hepatic triglycerides production and secretion.

Approach to assessing determinants of glucose homeostasis in the conscious mouse

Obesity and type 2 diabetes lessen the quality of life of those afflicted and place considerable burden on the healthcare system. Furthermore, the detrimental impact of these pathologies is expected to persist or even worsen. Diabetes is characterized by impaired insulin action and glucose homeostasis. This has led to a rapid increase in the number of mouse models of metabolic disease being used in the basic sciences to assist in facilitating a greater understanding of the metabolic dysregulation associated with obesity and diabetes, the identification of therapeutic targets, and the discovery of effective treatments. This review briefly describes the most frequently utilized models of metabolic disease. A presentation of standard methods and technologies on the horizon for assessing metabolic phenotypes in mice, with particular emphasis on glucose handling and energy balance, is provided. The article also addresses issues related to study design, selection and execution of metabolic tests of glucose metabolism, the presentation of data, and interpretation of results.

Rosiglitazone, a PPAR-γ agonist, fails to attenuate CLA-induced milk fat depression and hepatic lipid accumulation in lactating mice

Our objective was to investigate the combination of rosiglitazone (ROSI) and conjugated linoleic acid (CLA) on mammary and hepatic lipogenesis in lactating C57Bl/6 J mice. Twenty-four lactating mice were randomly assigned to one of four treatments applied from postpartum day 6 to day 10. Treatments included: (1) control diet, (2) control plus 1.5 % dietary CLA (CLA) substituted for soybean oil, (3) control plus daily intra-peritoneal (IP) rosiglitazone injections (10 mg/kg body weight) (ROSI), and (4) CLA plus ROSI (CLA-ROSI). Dam food intake and milk fat concentration were depressed with CLA. However, no effects were observed with ROSI. The CLA-induced milk fat depression was due to reduced expression for mammary lipogenic genes involved in de-novo fatty acid (FA) synthesis, FA uptake and desaturation, and triacyglycerol synthesis. Liver weight (g/100 g body weight) was increased by CLA due to an increase in lipid accumulation triggering a compensatory reduction in mRNA abundance of hepatic lipogenic enzymes, including acetyl-CoA carboxylase I and stearoyl-CoA desaturase I. On the contrary, no effects were observed with ROSI on hepatic and mammary lipogenic gene and enzyme expression. Overall, feeding CLA to lactating mice induced milk fat depression and increased hepatic lipid accumulation, probably due to the presence of trans-10, cis-12 CLA isomer, while ROSI failed to significantly attenuate both hepatic steatosis and reduction in milk fat content.

Adenovirus-mediated overexpression of Tcfe3 ameliorates hyperglycaemia in a mouse model of diabetes by upregulating glucokinase in the liver

AIMS/HYPOTHESIS

Transcription factor E3 (TFE3) has been shown to increase insulin sensitivity by activating insulin-signalling pathways. However, the role of TFE3 in glucose homeostasis is not fully understood. Here, we explored the possible therapeutic potential of TFE3 for the control of hyperglycaemia using a streptozotocin-induced mouse model of diabetes.

METHODS

We achieved overabundance of TFE3 in streptozotocin mice by administering an adenovirus (Ad) or adeno-associated virus serotype 2 (AAV2). We also performed an oral glucose tolerance test (OGTT) and insulin tolerance test (ITT). To explore molecular mechanisms of blood glucose control by TFE3, transcriptional studies on the regulation of genes involved in hepatic glucose metabolism were performed using quantitative real-time PCR and chromatin immunoprecipitation assay. The binding site of TFE3 in the liver Gck gene promoter was identified using deletion and site-specific mutation studies.

RESULTS

Overabundance of TFE3 resulted in reduced hyperglycaemia as shown by the OGTT and ITT in streptozotocin-treated mice. We observed that TFE3 can upregulate Gck in a state of insulin deficiency. However, glucose-6-phosphatase and cytosolic phosphoenolpyruvate carboxykinase mRNA levels were decreased by Ad-mediated overexpression of Tcfe3. Biochemical studies revealed that the anti-hyperglycaemic effect of TFE3 is due to the upregulation of Gck. In primary cultured hepatocytes, TFE3 increased expression of Gck mRNA. Conversely, small interfering RNA-mediated knockdown of TFE3 resulted in a decrease in Gck mRNA.

CONCLUSIONS/INTERPRETATION

This study demonstrates that TFE3 counteracts hyperglycaemia in streptozotocin-treated mice. This effect could be due to the upregulation of Gck by binding of TFE3 to its cognitive promoter region.

Antagonism of peripheral hepatic cannabinoid receptor-1 improves liver lipid metabolism in mice: evidence from cultured explants

It is well established that inactivation of the central endocannabinoid system (ECS) through antagonism of cannabinoid receptor 1 (CB1R) reduces food intake and improves several pathological features associated with obesity, such as dyslipidemia and liver steatosis. Nevertheless, recent data indicate that inactivation of peripheral CB1R could also be directly involved in the control of lipid metabolism independently of central CB1R. To further investigate this notion, we tested the direct effect of the specific CB1R antagonist, SR141716, on hepatic carbohydrate and lipid metabolism using cultured liver slices. CB1R messenger RNA expression was strongly decreased by SR141716, whereas it was increased by the CB1R agonist, arachidonic acid N-hydroxyethylamide (AEA), indicating the effectiveness of treatments in modulating ECS activity in liver explants both from lean or ob/ob mice. The measurement of O(2) consumption revealed that SR141716 increased carbohydrate or fatty acid utilization, according to the cellular hormonal environment. In line with this, SR141716 stimulated ß-oxidation activity, and the role of CB1R in regulating this pathway was particularly emphasized when ECS was hyperactivated by AEA and in ob/ob tissue. SR141716 also improved carbohydrate and lipid metabolism, blunting the AEA-induced increase in gene expression of proteins related to lipogenesis. In addition, we showed that SR141716 induced cholesterol de novo synthesis and high-density lipoprotein uptake, revealing a relationship between CB1R and cholesterol metabolism.

CONCLUSION

These data suggest that blocking hepatic CB1R improves both carbohydrate and lipid metabolism and confirm that peripheral CB1R should be considered as a promising target to reduce cardiometabolic risk in obesity.

Interrelated effects of dihomo-γ-linolenic and arachidonic acids, and sesamin on hepatic fatty acid synthesis and oxidation in rats

Interrelated effects of dihomo-γ-linolenic acid (DGLA) and arachidonic acid (ARA), and sesamin, a sesame lignan, on hepatic fatty acid synthesis and oxidation were examined in rats. Rats were fed experimental diets supplemented with 0 or 2 g/kg sesamin (1:1 mixture of sesamin and episesamin), containing 100 g/kg of maize oil or fungal oil rich in DGLA or ARA for 16 d. Among the groups fed sesamin-free diets, oils rich in DGLA or ARA, especially the latter, compared with maize oil strongly reduced the activity and mRNA levels of various lipogenic enzymes. Sesamin, irrespective of the type of fat, reduced the parameters of lipogenic enzymes except for malic enzyme. The type of dietary fat was rather irrelevant in affecting hepatic fatty acid oxidation among rats fed the sesamin-free diets. Sesamin increased the activities of enzymes involved in fatty acid oxidation in all groups of rats given different fats. The extent of the increase depended on the dietary fat type, and the values became much higher with a diet containing sesamin and oil rich in ARA in combination than with a diet containing lignan and maize oil. Analyses of mRNA levels revealed that the combination of sesamin and oil rich in ARA compared with the combination of lignan and maize oil markedly increased the gene expression of various peroxisomal fatty acid oxidation enzymes but not mitochondrial enzymes. The enhancement of sesamin action on hepatic fatty acid oxidation was also confirmed with oil rich in DGLA but to a lesser extent.

Apolipoprotein E4 exaggerates diabetic dyslipidemia and atherosclerosis in mice lacking the LDL receptor

OBJECTIVE

We investigated the differential roles of apolipoprotein E (apoE) isoforms in modulating diabetic dyslipidemia-a potential cause of the increased cardiovascular disease risk of patients with diabetes.

RESEARCH DESIGN AND METHODS

Diabetes was induced using streptozotocin (STZ) in human apoE3 (E3) or human apoE4 (E4) mice deficient in the LDL receptor (LDLR(-/-)).

RESULTS

Diabetic E3LDLR(-/-) and E4LDLR(-/-) mice have indistinguishable levels of plasma glucose and insulin. Despite this, diabetes increased VLDL triglycerides and LDL cholesterol in E4LDLR(-/-) mice twice as much as in E3LDLR(-/-) mice. Diabetic E4LDLR(-/-) mice had similar lipoprotein fractional catabolic rates compared with diabetic E3LDLR(-/-) mice but had larger hepatic fat stores and increased VLDL secretion. Diabetic E4LDLR(-/-) mice demonstrated a decreased reliance on lipid as an energy source based on indirect calorimetry. Lower phosphorylated acetyl-CoA carboxylase content and higher gene expression of fatty acid synthase in the liver indicated reduced fatty acid oxidation and increased fatty acid synthesis. E4LDLR(-/-) primary hepatocytes cultured in high glucose accumulated more intracellular lipid than E3LDLR(-/-) hepatocytes concomitant with a 60% reduction in fatty acid oxidation. Finally, the exaggerated dyslipidemia in diabetic E4LDLR(-/-) mice was accompanied by a dramatic increase in atherosclerosis.

CONCLUSIONS

ApoE4 causes severe dyslipidemia and atherosclerosis independent of its interaction with LDLR in a model of STZ-induced diabetes. ApoE4-expressing livers have reduced fatty acid oxidation, which contributes to the accumulation of tissue and plasma lipids.

Dietary conjugated linoleic Acid and hepatic steatosis: species-specific effects on liver and adipose lipid metabolism and gene expression

Objective. To summarize the recent studies on effect of conjugated linoleic acid (CLA) on hepatic steatosis and hepatic and adipose lipid metabolism highlighting the potential regulatory mechanisms. Methods. Sixty-four published experiments were summarized in which trans-10, cis-12 CLA was fed either alone or in combination with other CLA isomers to mice, rats, hamsters, and humans were compared. Summary and Conclusions. Dietary trans-10, cis-12 CLA induces a severe hepatic steatosis in mice with a more muted response in other species. Regardless of species, when hepatic steatosis was present, a concurrent decrease in body adiposity was observed, suggesting that hepatic lipid accumulation is a result of uptake of mobilized fatty acids (FA) from adipose tissue and the liver's inability to sufficiently increase FA oxidation and export of synthesized triglycerides. The potential role of liver FA composition, insulin secretion and sensitivity, adipokine, and inflammatory responses are discussed as potential mechanisms behind CLA-induced hepatic steatosis.

CLA-enriched diet containing t10,c12-CLA alters bile acid homeostasis and increases the risk of cholelithiasis in mice

Mice fed a mixture of CLA containing t10,c12-CLA lose fat mass and develop hyperinsulinemia and hepatic steatosis due to an accumulation of TG and cholesterol. Because cholesterol is the precursor in bile acid (BA) synthesis, we investigated whether t10,c12-CLA alters BA metabolism. In Expt. 1, female C57Bl/6J mice were fed a standard diet for 28 d supplemented with a CLA mixture (1 g/100 g) or not (controls). In Expt. 2, the feeding period was reduced to 4, 6, and 10 d. In Expt. 3, mice were fed a diet supplemented with linoleic acid, c9,t11-CLA, or t10,c12-CLA (0.4 g/100 g) for 28 d. In Expt. 1, the BA pool size was greater in CLA-fed mice than in controls and the entero-hepatic circulation of BA was altered due to greater BA synthesis and ileal reclamation. This resulted from higher hepatic cholesterol 7α-hydroxylase (CYP7A1) and ileal apical sodium BA transporter expressions in CLA-fed mice. Furthermore, hepatic Na(+)/taurocholate co-transporting polypeptide (NTCP) (-52%) and bile salt export pump (BSEP) (-77%) protein levels were lower in CLA-fed mice than in controls, leading to a greater accumulation of BA in the plasma (+500%); also, the cholesterol saturation index and the concentration of hydrophobic BA in the bile were greater in CLA-fed mice, changes associated with the presence of cholesterol crystals. Expt. 2 suggests that CLA-mediated changes were caused by hyperinsulinemia, which occurred after 6 d of the CLA diet before NTCP and BSEP mRNA downregulation (10 d). Expt. 3 demonstrated that only t10,c12-CLA altered NTCP and BSEP mRNA levels. In conclusion, t10,c12-CLA alters BA homeostasis and increases the risk of cholelithiasis in mice.

Catalytic production of conjugated fatty acids and oils

The reactive double bonds in conjugated vegetable oils are of high interest in industry. Traditionally, conjugated vegetable oils are added to paints, varnishes, and inks to improve their drying properties, while recently there is an increased interest in their use in the production of bioplastics. Besides the industrial applications, also food manufactures are interested in conjugated vegetable oils due to their various positive health effects. While the isomer type is less important for their industrial purposes, the beneficial health effects are mainly associated with the c9,t11, t10,c12 and t9,t11 CLA isomers. The production of CLA-enriched oils as additives in functional foods thus requires a high CLA isomer selectivity. Currently, CLAs are produced by conjugation of oils high in linoleic acid, for example soybean and safflower oil, using homogeneous bases. Although high CLA productivities and very high isomer selectivities are obtained, this process faces many ecological drawbacks. Moreover, CLA-enriched oils can not be produced directly with the homogeneous bases. Literature reports describe many catalytic processes to conjugate linoleic acid, linoleic acid methyl ester, and vegetable oils rich in linoleic acid: biocatalysts, for example enzymes and cells; metal catalysts, for example homogeneous metal complexes and heterogeneous catalysts; and photocatalysts. This Review discusses state-of-the-art catalytic processes in comparison with some new catalytic production routes. For each category of catalytic process, the CLA productivities and the CLA isomer selectivity are compared. Heterogeneous catalysis seems the most attractive approach for CLA production due to its easy recovery process, provided that the competing hydrogenation reaction is limited and the CLA production rate competes with the current homogeneous base catalysis. The most important criteria to obtain high CLA productivity and isomer selectivity are (1) absence of a hydrogen donor, (2) absence of catalyst acidity, (3) high metal dispersion, and (4) highly accessible pore architecture.

CB1 antagonism exerts specific molecular effects on visceral and subcutaneous fat and reverses liver steatosis in diet-induced obese mice

OBJECTIVE

The beneficial effects of the inactivation of endocannabinoid system (ECS) by administration of antagonists of the cannabinoid receptor (CB) 1 on several pathological features associated with obesity is well demonstrated, but the relative contribution of central versus peripheral mechanisms is unclear. We examined the impact of CB1 antagonism on liver and adipose tissue lipid metabolism in a mouse model of diet-induced obesity.

RESEARCH DESIGN AND METHODS

Mice were fed either with a standard diet or a high-sucrose high-fat (HSHF) diet for 19 weeks and then treated with the CB1-specific antagonist SR141716 (10 mg x kg(-1) x day(-1)) for 6 weeks.

RESULTS

Treatment with SR141716 reduced fat mass, insulin levels, and liver triglycerides primarily increased by HSHF feeding. Serum adiponectin levels were restored after being reduced in HSHF mice. Gene expression of scavenger receptor class B type I and hepatic lipase was induced by CB1 blockade and associated with an increase in HDL-cholesteryl ether uptake. Concomitantly, the expression of CB1, which was strongly increased in the liver and adipose tissue of HSHF mice, was totally normalized by the treatment. Interestingly, in visceral but not subcutaneous fat, genes involved in transport, synthesis, oxidation, and release of fatty acids were upregulated by HSHF feeding, while this effect was counteracted by CB1 antagonism.

CONCLUSIONS

A reduction in the CB1-mediated ECS activity in visceral fat is associated with a normalization of adipocyte metabolism, which may be a determining factor in the reversion of liver steatosis induced by treatment with SR141716.