PPARδ activation in human myotubes increases mitochondrial fatty acid oxidative capacity and reduces glucose utilization by a switch in substrate preference

The role of peroxisome proliferator-activated receptor δ (PPARδ) activation on global gene expression and mitochondrial fuel utilization were investigated in human myotubes. Only 21 genes were up-regulated and 3 genes were down-regulated after activation by the PPARδ agonist GW501516. Pathway analysis showed up-regulated mitochondrial fatty acid oxidation, TCA cycle and cholesterol biosynthesis. GW501516 increased oleic acid oxidation and mitochondrial oxidative capacity by 2-fold. Glucose uptake and oxidation were reduced, but total substrate oxidation was not affected, indicating a fuel switch from glucose to fatty acid. Cholesterol biosynthesis was increased, but lipid biosynthesis and mitochondrial content were not affected. This study confirmed that the principal effect of PPARδ activation was to increase mitochondrial fatty acid oxidative capacity. Our results further suggest that PPARδ activation reduced glucose utilization through a switch in mitochondrial substrate preference by up-regulating pyruvate dehydrogenase kinase isozyme 4 and genes involved in lipid metabolism and fatty acid oxidation.

Increased plasma citrulline in mice marks diet-induced obesity and may predict the development of the metabolic syndrome

In humans, plasma amino acid concentrations of branched-chain amino acids (BCAA) and aromatic amino acids (AAA) increase in states of obesity, insulin resistance and diabetes. We here assessed whether these putative biomarkers can also be identified in two different obesity and diabetic mouse models. C57BL/6 mice with diet-induced obesity (DIO) mimic the metabolic impairments of obesity in humans characterized by hyperglycemia, hyperinsulinemia and hepatic triglyceride accumulation. Mice treated with streptozotocin (STZ) to induce insulin deficiency were used as a type 1 diabetes model. Plasma amino acid profiling of two high fat (HF) feeding trials revealed that citrulline and ornithine concentrations are elevated in obese mice, while systemic arginine bioavailability (ratio of plasma arginine to ornithine + citrulline) is reduced. In skeletal muscle, HF feeding induced a reduction of arginine levels while citrulline levels were elevated. However, arginine or citrulline remained unchanged in their key metabolic organs, intestine and kidney. Moreover, the intestinal conversion of labeled arginine to ornithine and citrulline in vitro remained unaffected by HF feeding excluding the intestine as prime site of these alterations. In liver, citrulline is mainly derived from ornithine in the urea cycle and DIO mice displayed reduced hepatic ornithine levels. Since both amino acids share an antiport mechanism for mitochondrial import and export, elevated plasma citrulline may indicate impaired hepatic amino acid handling in DIO mice. In the insulin deficient mice, plasma citrulline and ornithine levels also increased and additionally these animals displayed elevated BCAA and AAA levels like insulin resistant and diabetic patients. Therefore, type 1 diabetic mice but not DIO mice show the “diabetic fingerprint” of plasma amino acid changes observed in humans. Additionally, citrulline may serve as an early indicator of the obesity-dependent metabolic impairments.

Dietary heme induces acute oxidative stress, but delayed cytotoxicity and compensatory hyperproliferation in mouse colon

Red meat consumption is associated with an increased colon cancer risk. Heme, present in red meat, injures the colon surface epithelium by generating cytotoxic and oxidative stress. Recently, we found that this surface injury is compensated by hyperproliferation and hyperplasia of crypt cells, which was induced by a changed surface to crypt signaling. It is unknown whether this changed signaling is caused by cytotoxic stress and/or oxidative stress, as these processes were never studied separately. The aim of this study was to determine the possible differential effects of dietary heme on these luminal stressors and their impact on the colonic mucosa after 2, 4, 7 and 14 days of heme feeding. Mice received a purified, humanized, control diet or the diet supplemented with 0.2 µmol heme/g. Oxidative and cytotoxic stress were measured in fecal water. Proliferation was determined by Ki67-immunohistochemistry and mucosal responses by whole-genome transcriptomics. After heme ingestion, there was an acute increase in reactive oxygen species (ROS) leading to increased levels of lipid peroxidation products. Mucosal gene expression showed an acute antioxidant response, but no change in cell turnover. After day 4, cytotoxicity of the colonic contents was increased and this coincided with differential signaling and hyperproliferation, indicating that cytotoxicity was the causal factor. Simultaneously, several oncogenes were activated, whereas the tumor suppressor p53 was inhibited. In conclusion, luminal cytotoxicity, but not ROS, caused differential surface to crypt signaling resulting in mucosal hyperproliferation and the differential expression of oncogenes and tumor suppressor genes.

Structural, functional and molecular analysis of the effects of aging in the small intestine and colon of C57BL/6J mice

BACKGROUND

By regulating digestion and absorption of nutrients and providing a barrier against the external environment the intestine provides a crucial contribution to the maintenance of health. To what extent aging-related changes in the intestinal system contribute to the functional decline associated with aging is still under debate.

METHODS

Young (4 M) and old (21 M) male C57BL/6J mice were fed a control low-fat (10E%) or a high-fat diet (45E%) for 2 weeks. During the intervention gross energy intake and energy excretion in the feces were measured. After sacrifice the small and large intestine were isolated and the small intestine was divided in three equal parts. Swiss rolls were prepared of each of the isolated segments for histological analysis and the luminal content was isolated to examine alterations in the microflora with 16S rRNA Q-PCR. Furthermore, mucosal scrapings were isolated from each segment to determine differential gene expression by microarray analysis and global DNA methylation by pyrosequencing.

RESULTS

Digestible energy intake was similar between the two age groups on both the control and the high-fat diet. Microarray analysis on RNA from intestinal scrapings showed no marked changes in expression of genes involved in metabolic processes. Decreased expression of Cubilin was observed in the intestine of 21-month-old mice, which might contribute to aging-induced vitamin B12 deficiency. Furthermore, microarray data analysis revealed enhanced expression of a large number of genes involved in immune response and inflammation in the colon, but not in the small intestine of the 21-month-old mice. Aging-induced global hypomethylation was observed in the colon and the distal part of the small intestine, but not in the first two sections of the small intestine.

CONCLUSION

In 21-month old mice the most pronounced effects of aging were observed in the colon, whereas very few changes were observed in the small intestine.

Combined deficiency of iron and (n-3) fatty acids in male rats disrupts brain monoamine metabolism and produces greater memory deficits than iron deficiency or (n-3) fatty acid deficiency alone

Deficiencies of iron (Fe) (ID) and (n-3) fatty acids (FA) [(n-3)FAD] may impair brain development and function through shared mechanisms. However, little is known about the potential interactions between these 2 common deficiencies. We studied the effects of ID and (n-3)FAD, alone and in combination, on brain monoamine pathways (by measuring monoamines and related gene expression) and spatial working and reference memory (by Morris water maze testing). Using a 2 × 2 design, male rats were fed an ID, (n-3)FAD, ID+(n-3)FAD, or control diet for 5 wk postweaning (postnatal d 21-56) after (n-3)FAD had been induced over 2 generations. The (n-3)FAD and ID diets decreased brain (n-3) FA by 70-76% and Fe by 20-32%, respectively. ID and (n-3)FAD significantly increased dopamine (DA) concentrations in the olfactory bulb (OB) and striatum, with an additive 1- to 2-fold increase in ID+(n-3)FAD rats compared with controls (P < 0.05). ID decreased serotonin (5-HT) levels in OB, with a significant decrease in ID+(n-3)FAD rats. Furthermore, norepinephrine concentrations were increased 2-fold in the frontal cortex (FC) of (n-3)FAD rats (P < 0.05). Dopa decarboxylase was downregulated in the hippocampus of ID and ID+(n-3)FAD rats (fold-change = -1.33; P < 0.05). ID and (n-3)FAD significantly impaired working memory performance and the impairment positively correlated with DA concentrations in FC (r = 0.39; P = 0.026). Reference memory was impaired in the ID+(n-3)FAD rats (P < 0.05) and was negatively associated with 5-HT in FC (r = -0.42; P = 0.018). These results suggest that the combined deficiencies of Fe and (n-3) FA disrupt brain monoamine metabolism and produce greater deficits in reference memory than ID or (n-3)FAD alone.

In male rats with concurrent iron and (n-3) fatty acid deficiency, provision of either iron or (n-3) fatty acids alone alters monoamine metabolism and exacerbates the cognitive deficits associated with combined deficiency

Concurrent deficiencies of iron (Fe) (ID) and (n-3) fatty acids [(n-3)FAD)] in rats can alter brain monoamine pathways and impair learning and memory. We examined whether repletion with Fe and DHA/EPA, alone and in combination, corrects the deficits in brain monoamine activity (by measuring monoamines and related gene expression) and spatial working and reference memory [by Morris water maze (MWM) testing] associated with deficiency. Using a 2 × 2 design, male rats with concurrent ID and (n-3)FAD [ID+(n-3)FAD] were fed an Fe+DHA/EPA, Fe+(n-3)FAD, ID+DHA/EPA, or ID+(n-3)FAD diet for 5 wk [postnatal d 56-91]. Biochemical measures and MWM performance after repletion were compared to age-matched control rats. The provision of Fe in combination with DHA/EPA synergistically increased Fe concentrations in the olfactory bulb (OB) (Fe x DHA/EPA interaction). Similarly, provision of DHA/EPA in combination with Fe resulted in higher brain DHA concentrations than provision of DHA alone in the frontal cortex (FC) and OB (P < 0.05). Dopamine (DA) receptor D1 was upregulated in the hippocampus of Fe+DHA/EPA rats (fold-change = 1.25; P < 0.05) and there were significant Fe x DHA/EPA interactions on serotonin (5-HT) in the OB and on the DA metabolite dihydroxyphenylacetic acid in the FC and striatum. Working memory performance was impaired in ID+DHA/EPA rats compared with controls (P < 0.05). In the reference memory task, Fe+DHA/EPA improved learning behavior, but Fe or DHA/EPA alone did not. These findings suggest that feeding either Fe or DHA/EPA alone to adult rats with both ID and (n-3)FAD affects the DA and 5-HT pathways differently than combined repletion and exacerbates the cognitive deficits associated with combined deficiency.

PUFAs acutely affect triacylglycerol-derived skeletal muscle fatty acid uptake and increase postprandial insulin sensitivity

BACKGROUND

Dietary fat quality may influence skeletal muscle lipid processing and fat accumulation, thereby modulating insulin sensitivity.

OBJECTIVE

The objective was to examine the acute effects of meals with various fatty acid (FA) compositions on skeletal muscle FA processing and postprandial insulin sensitivity in obese, insulin-resistant men.

DESIGN

In a single-blind, randomized, crossover study, 10 insulin-resistant men consumed 3 high-fat mixed meals (2.6 MJ), which were high in SFAs, MUFAs, or PUFAs. Fasting and postprandial skeletal muscle FA processing was examined by measuring differences in arteriovenous concentrations across the forearm muscle. [²H₂]Palmitate was infused intravenously to label endogenous triacylglycerol and FFAs in the circulation, and [U-¹³C]palmitate was added to the meal to label chylomicron-triacylglycerol. Skeletal muscle biopsy samples were taken to assess intramuscular lipid metabolism and gene expression.

RESULTS

Insulin and glucose responses (AUC) after the SFA meal were significantly higher than those after the PUFA meal (P = 0.006 and 0.033, respectively). Uptake of triacylglycerol-derived FAs was lower in the postprandial phase after the PUFA meal than after the other meals (AUC₆₀₋₂₄₀; P = 0.02). The fractional synthetic rate of the triacylglycerol, diacylglycerol, and phospholipid pool was higher after the MUFA meal than after the SFA meal. PUFA induced less transcriptional downregulation of oxidative pathways than did the other meals.

CONCLUSION

PUFAs reduced triacylglycerol-derived skeletal muscle FA uptake, which was accompanied by higher postprandial insulin sensitivity, a more transcriptional oxidative phenotype, and altered intramyocellular lipid partitioning and may therefore be protective against the development of insulin resistance.

Detailed transcriptomics analysis of the effect of dietary fatty acids on gene expression in the heart

Fatty acids comprise the primary energy source for the heart and are mainly taken up via hydrolysis of circulating triglyceride-rich lipoproteins. While most of the fatty acids entering the cardiomyocyte are oxidized, a small portion is involved in altering gene transcription to modulate cardiometabolic functions. So far, no in vivo model has been developed enabling study of the transcriptional effects of specific fatty acids in the intact heart. In the present study, mice were given a single oral dose of synthetic triglycerides composed of one single fatty acid. Hearts were collected 6 h thereafter and used for whole genome gene expression profiling. Experiments were conducted in wild-type and peroxisome proliferator-activated receptor (PPAR)α-/- mice to allow exploration of the specific contribution of PPARα. It was found that: 1) C18:3 had the most pronounced effect on cardiac gene expression. 2) The largest similarity in gene regulation was observed between C18:2 and C18:3. Large similarity was also observed between PPARα agonist Wy14643 and C22:6. 3) Many genes were regulated by one particular treatment only. Genes regulated by one particular treatment showed large functional divergence. 4) The majority of genes responding to fatty acid treatment were regulated in a PPARα-dependent manner, emphasizing the importance of PPARα in mediating transcriptional regulation by fatty acids in the heart. 5) Several genes were robustly regulated by all or many of the fatty acids studied, mostly representing well-described targets of PPARs (e.g., Acot1, Angptl4, Ucp3) but also including Zbtb16/PLZF, a transcription factor crucial for natural killer T cell function. 6) Deletion and activation of PPARα had a major effect on expression of numerous genes involved in metabolism and immunity. Our analysis demonstrates the marked impact of dietary fatty acids on gene regulation in the heart via PPARα.

Comparative transcriptomic and metabolomic analysis of fenofibrate and fish oil treatments in mice

Elevated circulating triglycerides, which are considered a risk factor for cardiovascular disease, can be targeted by treatment with fenofibrate or fish oil. To gain insight into underlying mechanisms, we carried out a comparative transcriptomics and metabolomics analysis of the effect of 2 wk treatment with fenofibrate and fish oil in mice. Plasma triglycerides were significantly decreased by fenofibrate (−49.1%) and fish oil (−21.8%), whereas plasma cholesterol was increased by fenofibrate (+29.9%) and decreased by fish oil (−32.8%). Levels of various phospholipid species were specifically decreased by fish oil, while levels of Krebs cycle intermediates were increased specifically by fenofibrate. Plasma levels of many amino acids were altered by fenofibrate and to a lesser extent by fish oil. Both fenofibrate and fish oil upregulated genes involved in fatty acid metabolism and downregulated genes involved in blood coagulation and fibrinolysis. Significant overlap in gene regulation by fenofibrate and fish oil was observed, reflecting their property as high or low affinity agonist for peroxisome proliferator-activated receptor-α, respectively. Fenofibrate specifically downregulated genes involved in complement cascade and inflammatory response. Fish oil specifically downregulated genes involved in cholesterol and fatty acid biosynthesis and upregulated genes involved in amino acid and arachidonic acid metabolism. Taken together, the data indicate that despite being similarly potent toward modulating plasma free fatty acids, cholesterol, and triglyceride levels, fish oil causes modest changes in gene expression likely via activation of multiple mechanistic pathways, whereas fenofibrate causes pronounced gene expression changes via a single pathway, reflecting the key difference between nutritional and pharmacological intervention.

Detection of prokaryotic mRNA signifies microbial viability and promotes immunity

Live vaccines have long been known to trigger far more vigorous immune responses than their killed counterparts. This has been attributed to the ability of live microorganisms to replicate and express specialized virulence factors that facilitate invasion and infection of their hosts. However, protective immunization can often be achieved with a single injection of live, but not dead, attenuated microorganisms stripped of their virulence factors. Pathogen-associated molecular patterns (PAMPs), which are detected by the immune system, are present in both live and killed vaccines, indicating that certain poorly characterized aspects of live microorganisms, not incorporated in dead vaccines, are particularly effective at inducing protective immunity. Here we show that the mammalian innate immune system can directly sense microbial viability through detection of a special class of viability-associated PAMPs (vita-PAMPs). We identify prokaryotic messenger RNA as a vita-PAMP present only in viable bacteria, the recognition of which elicits a unique innate response and a robust adaptive antibody response. Notably, the innate response evoked by viability and prokaryotic mRNA was thus far considered to be reserved for pathogenic bacteria, but we show that even non-pathogenic bacteria in sterile tissues can trigger similar responses, provided that they are alive. Thus, the immune system actively gauges the infectious risk by searching PAMPs for signatures of microbial life and thus infectivity. Detection of vita-PAMPs triggers a state of alert not warranted for dead bacteria. Vaccine formulations that incorporate vita-PAMPs could thus combine the superior protection of live vaccines with the safety of dead vaccines.

Dose-dependent effects of dietary fat on development of obesity in relation to intestinal differential gene expression in C57BL/6J mice

Excessive intake of dietary fat is known to be a contributing factor in the development of obesity. In this study, we determined the dose-dependent effects of dietary fat on the development of this metabolic condition with a focus on changes in gene expression in the small intestine. C57BL/6J mice were fed diets with either 10, 20, 30 or 45 energy% (E%) derived from fat for four weeks (n = 10 mice/diet). We found a significant higher weight gain in mice fed the 30E% and 45E% fat diet compared to mice on the control diet. These data indicate that the main shift towards an obese phenotype lies between a 20E% and 30E% dietary fat intake. Analysis of differential gene expression in the small intestine showed a fat-dose dependent gradient in differentially expressed genes, with the highest numbers in mice fed the 45E% fat diet. The main shift in fat-induced differential gene expression was found between the 30E% and 45E% fat diet. Furthermore, approximately 70% of the differentially expressed genes were changed in a fat-dose dependent manner. Many of these genes were involved in lipid metabolism-related processes and were already differentially expressed on a 30E% fat diet. Taken together, we conclude that up to 20E% of dietary fat, the small intestine has an effective ‘buffer capacity’ for fat handling. From 30E% of dietary fat, a switch towards an obese phenotype is triggered. We further speculate that especially fat-dose dependently changed lipid metabolism-related genes are involved in development of obesity.

Alterations in hepatic one-carbon metabolism and related pathways following a high-fat dietary intervention

Obesity frequently leads to insulin resistance and the development of hepatic steatosis. To characterize the molecular changes that promote hepatic steatosis, transcriptomics, proteomics, and metabolomics technologies were applied to liver samples from C57BL/6J mice obtained from two independent intervention trials. After 12 wk of high-fat feeding the animals became obese, hyperglycemic, and insulin resistant, had elevated levels of blood cholesterol and VLDL, and developed hepatic steatosis. Nutrigenomic analysis revealed alterations of key metabolites and enzyme transcript levels of hepatic one-carbon metabolism and related pathways. The hepatic oxidative capacity and the lipid milieu were significantly altered, which may play a key role in the development of insulin resistance. Additionally, high choline levels were observed after the high-fat diet. Previous studies have linked choline levels with insulin resistance and hepatic steatosis in conjunction with changes of certain metabolites and enzyme levels of one-carbon metabolism. The present results suggest that the coupling of high levels of choline and low levels of methionine plays an important role in the development of insulin resistance and liver steatosis. In conclusion, the complexities of the alterations induced by high-fat feeding are multifactorial, indicating that the interplay between several metabolic pathways is responsible for the pathological consequences.

Adipose tissue dysfunction signals progression of hepatic steatosis towards nonalcoholic steatohepatitis in C57BL/6 mice

OBJECTIVE

Nonalcoholic fatty liver disease (NAFLD) is linked to obesity and diabetes, suggesting an important role of adipose tissue in the pathogenesis of NAFLD. Here, we aimed to investigate the interaction between adipose tissue and liver in NAFLD and identify potential early plasma markers that predict nonalcoholic steatohepatitis (NASH).

RESEARCH DESIGN AND METHODS

C57Bl/6 mice were chronically fed a high-fat diet to induce NAFLD and compared with mice fed a low-fat diet. Extensive histological and phenotypical analyses coupled with a time course study of plasma proteins using multiplex assay were performed.

RESULTS

Mice exhibited pronounced heterogeneity in liver histological scoring, leading to classification into four subgroups: low-fat low (LFL) responders displaying normal liver morphology, low-fat high (LFH) responders showing benign hepatic steatosis, high-fat low (HFL) responders displaying pre-NASH with macrovesicular lipid droplets, and high fat high (HFH) responders exhibiting overt NASH characterized by ballooning of hepatocytes, presence of Mallory bodies, and activated inflammatory cells. Compared with HFL responders, HFH mice gained weight more rapidly and exhibited adipose tissue dysfunction characterized by decreased final fat mass, enhanced macrophage infiltration and inflammation, and adipose tissue remodeling. Plasma haptoglobin, IL-1β, TIMP-1, adiponectin, and leptin were significantly changed in HFH mice. Multivariate analysis indicated that in addition to leptin, plasma CRP, haptoglobin, eotaxin, and MIP-1α early in the intervention were positively associated with liver triglycerides. Intermediate prognostic markers of liver triglycerides included IL-18, IL-1β, MIP-1γ, and MIP-2, whereas insulin, TIMP-1, granulocyte chemotactic protein 2, and myeloperoxidase emerged as late markers.

CONCLUSIONS

Our data support the existence of a tight relationship between adipose tissue dysfunction and NASH pathogenesis and point to several novel potential predictive biomarkers for NASH.

An 8-week high-fat diet induces obesity and insulin resistance with small changes in the muscle transcriptome of C57BL/6J mice

BACKGROUND

Skeletal muscle is responsible for most of the insulin-stimulated glucose uptake and metabolism. Therefore, it plays an important role in the development of insulin resistance, one of the characteristics of the metabolic syndrome (MS). As the prevalence of the MS is increasing, there is an urgent need for more effective intervention strategies.

METHODS

C57BL/6J mice were fed an 8-week low-fat diet (10 kcal%; LFD) or high-fat diet (45 kcal%; HFD). Microarray analysis was performed by using two comparisons: (1) 8-week HFD transcriptome versus 8-week LFD transcriptome and (2) transcriptome of mice sacrificed at the start of the intervention versus 8-week LFD transcriptome and 8-week HFD transcriptome, respectively.

RESULTS

Although an 8-week HFD induced obesity and impaired insulin sensitivity, HFD-responsive changes in the muscle transcriptome were relatively small (<1.3-fold). In fact, 8-weeks of aging induced more pronounced changes than an HFD. One comparison revealed the transcriptional downregulation of the mito- gen-activated protein kinase cascade, whereas both comparisons showed the upregulation of fatty acid oxidation, demonstrating that the two comparison strategies are confirmative as well as complementary.

CONCLUSION

We suggest using complementary analysis strategies in the genome-wide search for gene expression changes induced by mild interventions, such as an HFD.

Induction of Cardiac Angptl4 by Dietary Fatty Acids Is Mediated by Peroxisome Proliferator-Activated Receptor β/δ and Protects Against Fatty Acid–Induced Oxidative Stress

Rationale : Although dietary fatty acids are a major fuel for the heart, little is known about the direct effects of dietary fatty acids on gene regulation in the intact heart.

Objective : To study the effect of dietary fatty acids on cardiac gene expression and explore the functional consequences.

Methods and Results : Oral administration of synthetic triglycerides composed of one single fatty acid altered cardiac expression of numerous genes, many of which are involved in the oxidative stress response. The gene most significantly and consistently upregulated by dietary fatty acids encoded Angiopoietin-like protein (Angptl)4, a circulating inhibitor of lipoprotein lipase expressed by cardiomyocytes. Induction of Angptl4 by the fatty acid linolenic acid was specifically abolished in peroxisome proliferator-activated receptor (PPAR)β/δ −/− and not PPARα −/− mice and was blunted on siRNA-mediated PPARβ/δ knockdown in cultured cardiomyocytes. Consistent with these data, linolenic acid stimulated binding of PPARβ/δ but not PPARα to the Angptl4 gene. Upregulation of Angptl4 resulted in decreased cardiac uptake of plasma triglyceride-derived fatty acids and decreased fatty acid-induced oxidative stress and lipid peroxidation. In contrast, Angptl4 deletion led to enhanced oxidative stress in the heart, both after an acute oral fat load and after prolonged high fat feeding.

Conclusions : Stimulation of cardiac Angptl4 gene expression by dietary fatty acids and via PPARβ/δ is part of a feedback mechanism aimed at protecting the heart against lipid overload and consequently fatty acid–induced oxidative stress.

Metabolic switching of human myotubes is improved by n-3 fatty acids

The aim of the present study was to examine whether pretreatment with different fatty acids, as well as the liver X receptor (LXR) agonist T0901317, could modify metabolic switching of human myotubes. The n-3 FA eicosapentaenoic acid (EPA) increased suppressibility, the ability of glucose to suppress FA oxidation. Substrate-regulated flexibility, the ability to increase FA oxidation when changing from a high glucose, low fatty acid condition ("fed") to a high fatty acid, low glucose ("fasted") condition, was increased by EPA and other n-3 FAs. Adaptability, the capacity to increase FA oxidation with increasing FA availability, was enhanced after pretreatment with EPA, linoleic acid (LA), and palmitic acid (PA). T0901317 counteracted the effect of EPA on suppressibility and adaptability, but it did not affect these parameters alone. EPA per se accumulated less, however, EPA, LA, oleic acid, and T0901317 treatment increased the number of lipid droplets (LD) in myotubes. LD volume and intensity, as well as mitochondrial mass, were independent of FA pretreatment. Microarray analysis showed that EPA regulated more genes than the other FAs and that specific pathways involved in carbohydrate metabolism were induced only by EPA. The present study suggests a favorable effect of n-3 FAs on skeletal muscle metabolic switching and glucose utilization.

The embryonic genes Dkk3, Hoxd8, Hoxd9 and Tbx1 identify muscle types in a diet-independent and fiber-type unrelated way

BACKGROUND

The mouse skeletal muscle is composed of four distinct fiber types that differ in contractile function, number of mitochondria and metabolism. Every muscle type has a specific composition and distribution of the four fiber types. To find novel genes involved in specifying muscle types, we used microarray analysis to compare the gastrocnemius with the quadriceps from mice fed a low fat diet (LFD) or high fat diet (HFD) for 8 weeks. Additional qPCR analysis were performed in the gastrocnemius, quadriceps and soleus muscle from mice fed an LFD or HFD for 20 weeks.

RESULTS

In mice fed the 8-week LFD 162 genes were differentially expressed in the gastrocnemius vs. the quadriceps. Genes with the strongest differences in expression were markers for oxidative fiber types (e.g. Tnni1) and genes which are known to be involved in embryogenesis (Dkk3, Hoxd8,Hoxd9 and Tbx1). Also Dkk2, Hoxa5, Hoxa10, Hoxc9, Hoxc10, Hoxc6 and Tbx15 were detectably, but not differentially expressed in adult muscle tissue. Expression of differentially expressed genes was not influenced by an 8-week or 20-week HFD. Comparing gastrocnemius, quadriceps and soleus, expression of Hoxd8 and Hoxd9 was not related with expression of markers for the four different fiber types. We found that the expression of both Hoxd8 and Hoxd9 was much higher in the gastrocnemius than in the quadriceps or soleus, whereas the expression of Dkk3 was high in quadriceps, but low in both gastrocnemius and soleus. Finally, expression of Tbx1 was high in quadriceps, intermediate in soleus and low in gastrocnemius.

CONCLUSIONS

We found that genes from the Dkk family, Hox family and Tbx family are detectably expressed in adult mouse muscle. Interestingly, expression of Dkk3, Hoxd8, Hoxd9 and Tbx1 was highly different between gastrocnemius, quadriceps and soleus. In fact, every muscle type showed a unique combination of expression of these four genes which was not influenced by diet. Altogether, we conclude that genes important for embryogenesis identify mouse muscle types in a diet-independent and fiber type-unrelated manner.

Transcriptional profiling reveals divergent roles of PPARα and PPARβ/δ in regulation of gene expression in mouse liver

Little is known about the role of the transcription factor peroxisome proliferator-activated receptor (PPAR) β/δ in liver. Here we set out to better elucidate the function of PPARβ/δ in liver by comparing the effect of PPARα and PPARβ/δ deletion using whole genome transcriptional profiling and analysis of plasma and liver metabolites. In fed state, the number of genes altered by PPARα and PPARβ/δ deletion was similar, whereas in fasted state the effect of PPARα deletion was much more pronounced, consistent with the pattern of gene expression of PPARα and PPARβ/δ. Minor overlap was found between PPARα- and PPARβ/δ-dependent gene regulation in liver. Pathways upregulated by PPARβ/δ deletion were connected to innate immunity and inflammation. Pathways downregulated by PPARβ/δ deletion included lipoprotein metabolism and various pathways related to glucose utilization, which correlated with elevated plasma glucose and triglycerides and reduced plasma cholesterol in PPARβ/δ−/− mice. Downregulated genes that may underlie these metabolic alterations included Pklr, Fbp1, Apoa4, Vldlr, Lipg, and Pcsk9, which may represent novel PPARβ/δ target genes. In contrast to PPARα−/− mice, no changes in plasma free fatty acid, plasma β-hydroxybutyrate, liver triglycerides, and liver glycogen were observed in PPARβ/δ−/− mice. Our data indicate that PPARβ/δ governs glucose utilization and lipoprotein metabolism and has an important anti-inflammatory role in liver. Overall, our analysis reveals divergent roles of PPARα and PPARβ/δ in regulation of gene expression in mouse liver.

LXR{beta} is the dominant LXR subtype in skeletal muscle regulating lipogenesis and cholesterol efflux

Liver X receptors (LXRs) are important regulators of cholesterol, lipid, and glucose metabolism and have been extensively studied in liver, macrophages, and adipose tissue. However, their role in skeletal muscle is poorly studied and the functional role of each of the LXRalpha and LXRbeta subtypes in skeletal muscle is at present unknown. To study the importance of each of the receptor subtypes, myotube cultures derived from wild-type (WT) and LXRalpha and LXRbeta knockout (KO) mice were established. The present study showed that treatment with the LXR agonist T0901317 increased lipogenesis and apoA1-dependent cholesterol efflux in LXRalpha KO and WT myotubes but not in LXRbeta KO cells. The functional studies were confirmed by T0901317-induced increase in mRNA levels of LXR target genes involved in lipid and cholesterol metabolism in myotubes established from WT and LXRalpha KO mice, whereas only minor changes were observed for these genes in myotubes from LXRbeta KO mice. Gene expression analysis using microarrays showed that very few genes other than the classical, well-known LXR target genes were regulated by LXR in skeletal muscle. The present study also showed that basal glucose uptake was increased in LXRbeta KO myotubes compared with WT myotubes, suggesting a role for LXRbeta in glucose metabolism in skeletal muscle. In conclusion, LXRbeta seems to be the main LXR subtype regulating lipogenesis and cholesterol efflux in skeletal muscle.

Absorption, distribution, and biliary excretion of cafestol, a potent cholesterol-elevating compound in unfiltered coffees, in mice

Cafestol is a diterpene present in unfiltered coffees. It is the most potent cholesterol-elevating compound present in the human diet. However, the precise mechanisms underlying this effect are still unclear. In contrast, cafestol is also known as a hepatoprotective compound, which is likely to be related to the induction of glutathione biosynthesis and conjugation. In the present study, we investigated whole-body distribution, biliary excretion, and portal bioavailability of cafestol in mice. First, dissection was used to study distribution. Five hours after an oral dose with (3)H-labeled cafestol, most activity was found in small intestine, liver, and bile. These results were confirmed by quantitative whole-body autoradiography in a time course study, which also showed elimination of all radioactivity within 48 h after administration. Next, radiolabeled cafestol was dosed intravenously to bile duct-cannulated mice. Five hours after the dose 20% of the radioactivity was found in bile. Bile contained several metabolites but no parent compound. After intestinal administration of radioactive cafestol to portal vein-cannulated mice, cafestol was shown to be rapidly absorbed into the portal vein as the parent compound, a glucuronide, and an unidentified metabolite. From the presence of a glucuronide in bile that can be deconjugated by a bacterial enzyme and the prolonged absorption of parent compound from the gastrointestinal tract, we hypothesized that cafestol undergoes enterohepatic cycling. Together with our earlier observation that epoxidation of the furan ring occurs in liver, these findings merit further research on the process of accumulation of this coffee ingredient in liver and intestinal tract.

The role of epoxidation and electrophile-responsive element-regulated gene transcription in the potentially beneficial and harmful effects of the coffee components cafestol and kahweol

Cafestol and kahweol are diterpene compounds present in unfiltered coffees. Cafestol is known as the most potent cholesterol-raising agent that may be present in the human diet. Remarkably, the mechanisms behind this effect have only been partly resolved so far. Even less is known about the metabolic fate of cafestol and kahweol. From the structure of cafestol, carrying a furan moiety, we hypothesized that epoxidation may not only be an important biotransformation route but that this also plays a role in its effects found. In bile duct-cannulated mice, dosed with cafestol, we were able to demonstrate the presence of epoxy-glutathione (GSH) conjugates, GSH conjugates and glucuronide conjugates. In addition, it was shown that cafestol was able to induce an electrophile-responsive element (EpRE). Using a murine hepatoma cell line with a luciferase reporter gene under control of an EpRE from the human NQO1 regulatory region, we also found that metabolic activation by CYP450 enzymes is needed for EpRE induction. Furthermore, raising intracellular GSH resulted in a decrease in EpRE-mediated gene induction, whereas lowering intracellular GSH levels increased EpRE-mediated gene induction. In conclusion, evidence suggests that cafestol induces EpRE, apparently via a bioactivation process that possibly involves epoxidation of the furan ring. The epoxides themselves appear subject to conjugation with GSH. The effects on EpRE can also explain the induction of GSH which seems to be involved in the reported beneficial effects of cafestol, for example, when administered with aflatoxin B1 or other toxic or carcinogenic compounds.

c-Met confers protection against chronic liver tissue damage and fibrosis progression after bile duct ligation in mice

BACKGROUND & AIMS

The hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (c-Met) system is an essential inducer of hepatocyte growth and proliferation. Although a fundamental role for the HGF receptor c-Met has been shown in acute liver regeneration, its cell-specific role in hepatocytes during chronic liver injury and fibrosis progression has not been determined.

METHODS

Hepatocyte-specific c-Met knockout mice (c-Met(Delta hepa)) using the Cre-loxP system were studied in a bile duct ligation (BDL) model. Microarray analyses were performed to define HGF/c-Met-dependent gene expression.

RESULTS

Two strategies for c-Met deletion in hepatocytes to generate hepatocyte-specific c-Met knockout mice were tested. Early deletion during embryonic development was lethal, whereas post-natal Cre expression was successful, leading to the generation of viable c-Met(Delta hepa) mice. BDL in these mice resulted in extensive necrosis and lower proliferation rates of hepatocytes. Gene array analysis of c-Met(Delta hepa) mice revealed a significant reduction of anti-apoptotic genes in c-Met-deleted hepatocytes. These findings could be tested functionally because c-Met(Delta hepa) mice showed a stronger apoptotic response after BDL and Jo-2 stimulation. The phenotype was associated with increased expression of proinflammatory cytokines (tumor necrosis factor-alpha and interleukin-6) and an enhanced recruitment of neutrophils. Activation of these mechanisms triggered a stronger profibrogenic response as evidenced by increased transforming growth factor-beta(1), alpha-smooth muscle actin, collagen-1alpha messenger RNA expression, and enhanced collagen-fiber staining in c-Met(Delta hepa) mice.

CONCLUSIONS

Our results show that deletion of c-Met in hepatocytes leads to more liver cell damage and fibrosis in a chronic cholestatic liver injury model because c-Met triggers survival signals important for hepatocyte recovery.

The cholesterol-raising factor from coffee beans, cafestol, as an agonist ligand for the farnesoid and pregnane X receptors

Cafestol, a diterpene present in unfiltered coffee brews such as Scandinavian boiled, Turkish, and cafetière coffee, is the most potent cholesterol-elevating compound known in the human diet. Several genes involved in cholesterol homeostasis have previously been shown to be targets of cafestol, including cholesterol 7alpha-hydroxylase (CYP7A1), the rate-limiting enzyme in bile acid biosynthesis. We have examined the mechanism by which cafestol elevates serum lipid levels. Changes in several lipid parameters were observed in cafestol-treated APOE3Leiden mice, including a significant increase in serum triglyceride levels. Microarray analysis of these mice identified alterations in hepatic expression of genes involved in lipid metabolism and detoxification, many of which are regulated by the nuclear hormone receptors farnesoid X receptor (FXR) and pregnane X receptor (PXR). Further studies demonstrate that cafestol is an agonist ligand for FXR and PXR, and that cafestol down-regulates expression of the bile acid homeostatic genes CYP7A1, sterol 12alpha-hydroxylase, and Na(+)-taurocholate cotransporting polypeptide in the liver of wild-type but not FXR null mice. Cafestol did not affect genes known to be up-regulated by FXR in the liver of wild-type mice, but did increase expression of the positive FXR-target genes intestinal bile acid-binding protein and fibroblast growth factor 15 (FGF15) in the intestine. Because FGF15 has recently been shown to function in an enterohepatic regulatory pathway to repress liver expression of bile acid homeostatic genes, its direct induction in the gut may account for indirect effects of cafestol on liver gene expression. PXR-dependent gene regulation of cytochrome P450 3A11 and other targets by cafestol was also only seen in the intestine. Using a double FXR/PXR knockout mouse model, we found that both receptors contribute to the cafestol-dependent induction of intestinal FGF15 gene expression. In conclusion, cafestol acts as an agonist ligand for both FXR and PXR, and this may contribute to its impact on cholesterol homeostasis.

[Negligible amounts of cholesterol-raising diterpenes in coffee made with coffee pads in comparison with unfiltered coffee]

OBJECTIVE

To determine the amounts of the serum-cholesterol raising diterpenes cafestol and kahweol in coffee made with coffee pads and the Senseo coffee machine as opposed to filtered and unfiltered coffee.

DESIGN

Observational.

METHOD

In five cities in the Netherlands coffee was purchased in three major supermarkets resulting in a total of 30 samples of coffee pads. The levels of cafestol and kahweol were determined by gas chromatography. As controls, the diterpene levels in filtered and unfiltered coffee were also measured.

RESULTS

Coffee prepared using coffee pads contained on average 0.76 mg/l cafestol (95% CI: 0.69-0.82) and 0.85 mg/l kahweol (95% CI: 0.77-0.94). Filtered coffee contained 0.76 mg/l cafestol (95% CI: 0.63-0.88) and 0.81 mg/l kahweol (95% CI: 0.63-0.99). Unfiltered coffee contained 72.5 mg/l cafestol (95% CI: 48.5-96.4) and 71.5 mg/l kahweol (95% CI: 45.0-98.1).

CONCLUSION

Coffee prepared using coffee pads and the Senseo coffee machine contained minute levels of diterpenes comparable to those of filtered coffee. Its effect on serum-cholesterol levels is therefore likely to be negligible.

Coffee oil consumption increases plasma levels of 7alpha-hydroxy-4-cholesten-3-one in humans

Unfiltered coffee brews such as French press and espresso contain a lipid from coffee beans named cafestol that raises serum cholesterol in humans. Cafestol decreases the expression and activity of cholesterol 7alpha-hydroxylase, the rate-limiting enzyme in the classical pathway of bile acid synthesis, in cultured rat hepatocytes and livers of APOE3Leiden mice. Inhibition of bile acid synthesis has been suggested to be responsible for the cholesterol-raising effect of cafestol. Therefore, we assessed whether cafestol decreases the activity of cholesterol 7alpha-hydroxylase in humans. Because liver biopsies were not feasible, we measured plasma levels of 7alpha-hydroxy-4-cholesten-3-one, a marker for the activity of cholesterol 7alpha-hydroxylase in the liver. Plasma 7alpha-hydroxy-4-cholesten-3-one was measured in 2 separate periods in which healthy volunteers consumed coffee oil containing cafestol (69 mg/d) for 5 wk. Plasma levels of 7alpha-hydroxy-4-cholesten-3-one increased by 47 +/- 13% (mean +/- SEM, n = 38, P = 0.001) in the first period and by 23 +/- 10% (n = 31, P = 0.03) in the second treatment period. Serum cholesterol was raised by 23 +/- 2% (P < 0.001) in the first period and by 18 +/- 2% (P < 0.001) in the second period. We corrected individual 7alpha-hydroxy-4-cholesten-3-one levels for serum cholesterol levels, because coffee oil increases serum cholesterol and 7alpha-hydroxy-4-cholesten-3-one is probably present in the lipoprotein fraction of serum. After correction, the increase in 7alpha-hydroxy-4-cholesten-3-one was 24 +/- 11% (P = 0.04) in the first period and there was no effect in period 2. Our study showed that coffee oil did not decrease, and actually increased, plasma levels of 7alpha-hydroxy-4-cholesten-3-one in humans in 2 separate treatment periods. Therefore, this study does not support the hypothesis that cafestol decreases bile acid synthesis in humans.

Coffee bean extracts rich and poor in kahweol both give rise to elevation of liver enzymes in healthy volunteers

Background

Coffee oil potently raises serum cholesterol levels in humans. The diterpenes cafestol and kahweol are responsible for this elevation. Coffee oil also causes elevation of liver enzyme levels in serum. It has been suggested that cafestol is mainly responsible for the effect on serum cholesterol levels and that kahweol is mainly responsible for the effect on liver enzyme levels. The objective of this study was to investigate whether coffee oil that only contains a minute amount of kahweol indeed does not cause elevation of liver enzyme levels.

Methods

The response of serum alanine aminotransferase (ALAT) and aspartate aminotransferase (ASAT) to Robusta coffee oil (62 mg/day cafestol, 1.6 mg/day kahweol) was measured in 18 healthy volunteers.

Results

After nine days one subject was taken off Robusta oil treatment due to an ALAT level of 3.6 times the upper limit of normal (ULN). Another two subjects stopped treatment due to other reasons. After 16 days another two subjects were taken off Robusta oil treatment. One of those subjects had levels of 5.8 ULN for ALAT and 2.0 ULN for ASAT; the other subject had an ALAT level of 12.4 ULN and an ASAT level of 4.7 ULN. It was then decided to terminate the study. The median response of subjects to Robusta oil after 16 days was 0.27 ULN (n = 15, 25^th,75^th percentile: 0.09;0.53) for ALAT and 0.06 ULN (25^th,75^th percentile -0.06;0.22) for ASAT.

Conclusions

We conclude that the effect on liver enzyme levels of coffee oil containing hardly any kahweol is similar to that of coffee oil containing high amounts of kahweol. Therefore it is unlikely that kahweol is the component of coffee oil that is responsible for the effect. Furthermore, we conclude that otherwise unexplained elevation of liver enzyme levels observed in patients might be caused by a switch from consumption of filtered coffee to unfiltered coffee.

Reproducibility of the serum lipid response to coffee oil in healthy volunteers

Background

Humans and animals show a certain consistency in the response of their serum lipids to fat-modified diets. This may indicate a genetic basis underlying this response. Coffee oil might be used as a model substance to investigate which genes determine differences in the serum lipid response. Before carrying out such studies our objective was to investigate to what extent the effect of coffee oil on serum lipid concentrations is reproducible within subjects.

Methods

The serum lipid response of 32 healthy volunteers was measured twice in separate five-week periods in which coffee oil was administered (69 mg cafestol / day).

Results

Total cholesterol levels increased by 24% in period 1 (range:0;52%) and 18% in period 2 (1;48%), LDL cholesterol by 29 % (-9;71%) and 20% (-12;57%), triglycerides by 66% (16;175%) and 58% (-13;202%), and HDL cholesterol did not change significantly: The range of the HDL response was -19;25% in period 1 and -20;33% in period 2.

The correlation between the two responses was 0.20 (95%CI -0.16, 0.51) for total cholesterol, 0.16 (95%CI -0.20, 0.48) for LDL, 0.67 (95%CI 0.42, 0.83) for HDL, and 0.77 (95%CI 0.56, 0.88) for triglycerides.

Conclusions

The responses of total and LDL cholesterol to coffee oil were poorly reproducible within subjects. The responses of HDL and triglycerides, however, appeared to be highly reproducible. Therefore, investigating the genetic sources of the variation in the serum-lipid response to coffee oil is more promising for HDL and triglycerides.