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

Establishment of a Steatosis Model in LMH Cells, Chicken Embryo Hepatocytes, and Liver Tissues Based on a Mixture of Sodium Oleate and Palmitic Acid

Research on hepatic steatosis in animal husbandry has been a prominent area of study. Developing an appropriate in vitro cellular steatosis model is crucial for comprehensively investigating the mechanisms involved in liver lipid deposition in poultry and for identifying potential interventions to address abnormalities in lipid metabolism. The research on the methods of in vitro liver steatosis in chickens, particularly the effects of different fat mixtures, is still lacking. In this study, LMH cells were utilized to investigate the effects of OA, SO, PA, SP, and their pairwise combinations on steatosis development, with the aim of identifying the optimal conditions for inducing steatosis. Analysis of triglyceride (TG) content in LMH cells revealed that OA and SP had limited efficacy in increasing TG content, while a combination of SO and PA in a 1:2 ratio exhibited the highest TG content. Moreover, Oil Red O staining results in LMH cells demonstrated that the combination treatment had a more pronounced induction effect compared to 0.375 mM SO. Additionally, RNA-seq analysis showed that 0.375 mM SO significantly influenced the expression of genes associated with fatty acid metabolism compared to the control group, whereas the combination of SO and PA led to an enrichment of key GO terms associated with programmed cell death. These findings suggest that varying conditions of cellular steatosis could lead to distinct disruptions in gene expression. The optimal conditions for inducing steatosis in LMH cells were also tested on chicken embryonic liver cells and embryos. TG detection and Oil Red O staining assays showed that the combination of SO and PA successfully induced steatosis. However, the gene expression pattern differed from that of LMH cells. This study lays the foundations for further investigations into avian hepatic steatosis.

MASLD/MASH and type 2 diabetes: Two sides of the same coin? From single PPAR to pan-PPAR agonists

Type 2 diabetes (T2D) and metabolic dysfunction-associated steatotic liver disease (MASLD), mainly related to nutrition and lack of physical activity, are both very common conditions, share several disease pathways and clinical manifestations, and increasingly co-occur with disease progression. Insulin resistance is an upstream node in the biology of both conditions and triggers liver parenchymal injury, inflammation and fibrosis. Peroxisome proliferator-activated receptor (PPAR) nuclear transcription factors are master regulators of energy homeostasis - insulin signaling in liver, adipose and skeletal muscle tissue - and affect immune and fibrogenesis pathways. Among distinct yet overlapping effects, PPARα regulates lipid metabolism and energy expenditure, PPARβ/δ has anti-inflammatory effects and increases glucose uptake by skeletal muscle, while PPARγ improves insulin sensitivity and exerts direct antifibrotic effects on hepatic stellate cells. Together PPARs thus represent pharmacological targets across the entire biology of MASH. Single PPAR agonists are approved for hypertriglyceridemia (PPARα) and T2D (PPARγ), but these, as well as dual PPAR agonists, have shown mixed results as anti-MASH treatments in clinical trials. Agonists of all three PPAR isoforms have the potential to improve the full disease spectrum from insulin resistance to fibrosis, and correspondingly to improve cardiometabolic and hepatic health, as has been shown (phase II data) with the pan-PPAR agonist lanifibranor.

Treating NASH by targeting peroxisome proliferator-activated receptors

The pathophysiology of non-alcoholic steatohepatitis (NASH) encompasses a complex set of intra- and extrahepatic driving mechanisms, involving numerous metabolic, inflammatory, vascular and fibrogenic pathways. The peroxisome proliferator-activated receptors (PPARs) α, β/δ and γ belong to the nuclear receptor family of ligand-activated transcription factors. Activated PPARs modulate target tissue transcriptomic profiles, enabling the body's adaptation to changing nutritional, metabolic and inflammatory environments. PPARs hence regulate several pathways involved in NASH pathogenesis. Whereas single PPAR agonists exert robust anti-NASH activity in several preclinical models, their clinical effects on histological endpoints of NASH resolution and fibrosis regression appear more modest. Simultaneous activation of several PPAR isotypes across different organs and within-organ cell types, resulting in pleiotropic actions, enhances the therapeutic potential of PPAR agonists as pharmacological agents for NASH and NASH-related hepatic and extrahepatic morbidity, with some compounds having already shown clinical efficacy on histological endpoints.

Omega-3 fatty acids and individual variability in plasma triglyceride response: A mini-review

Cardiovascular disease (CVD) is a leading cause of death worldwide. Supplementation with the marine omega-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) is associated with lower CVD risk. However, results from randomized controlled trials that examine the effect of omega-3 supplementation on CVD risk are inconsistent. This risk-reducing effect may be mediated by reducing inflammation, oxidative stress and serum triglyceride (TG) levels. However, not all individuals respond by reducing TG levels after omega-3 supplementation. This inter-individual variability in TG response to omega-3 supplementation is not fully understood. Hence, we aim to review the evidence for how interactions between omega-3 fatty acid supplementation and genetic variants, epigenetic and gene expression profiling, gut microbiota and habitual intake of omega-3 fatty acids can explain why the TG response differs between individuals. This may contribute to understanding the current controversies and play a role in defining future personalized guidelines to prevent CVD.

Omega-3 polyunsaturated fatty acids ameliorate PM2.5 exposure induced lung injury in mice through remodeling the gut microbiota and modulating the lung metabolism

Short-term or long-term exposure to fine particulate matter (PM2.5) is related to increased incidences of respiratory diseases. This study aimed to investigate the influences of omega-3 polyunsaturated fatty acids (ω-3 PUFAs) supplementation on oxidative stress, inflammation, lung metabolic profile, and gut microbiota in PM2.5-induced lung injury mice. Mice were divided into four groups (n = 15, per group): two unsupplemented groups, control group and PM2.5 group, and two supplemented groups with ω-3 PUFAs, ω-3 PUFAs group, and ω-3 PUFAs + PM2.5 group. Mice in the supplemented groups were placed on an ω-3 PUFAs-enriched diet (ω-3 PUFAs, 21 g/kg). During the 5th to 6th week of dietary supplementation, mice were exposed to PM2.5 by intra-tracheal instillation. ω-3 PUFAs ameliorate lung histopathological injury, reduce inflammatory responses and oxidative stress, affect lung metabolite profile, and modulate gut microbiota in PM2.5-induced lung injury mice. Thus, supplementary ω-3 PUFAs showed effectiveness in attenuation of PM2.5-induced lung injury, indicating that the interventions exhibited preventive and therapeutic potential.

Pharmacometabolomics for the Study of Lipid-Lowering Therapies: Opportunities and Challenges

Lipid-lowering therapies are widely used to prevent the development of atherosclerotic cardiovascular disease (ASCVD) and related mortality worldwide. "Omics" technologies have been successfully applied in recent decades to investigate the mechanisms of action of these drugs, their pleiotropic effects, and their side effects, aiming to identify novel targets for future personalized medicine with an improvement of the efficacy and safety associated with the treatment. Pharmacometabolomics is a branch of metabolomics that is focused on the study of drug effects on metabolic pathways that are implicated in the variation of response to the treatment considering also the influences from a specific disease, environment, and concomitant pharmacological therapies. In this review, we summarized the most significant metabolomic studies on the effects of lipid-lowering therapies, including the most commonly used statins and fibrates to novel drugs or nutraceutical approaches. The integration of pharmacometabolomics data with the information obtained from the other "omics" approaches could help in the comprehension of the biological mechanisms underlying the use of lipid-lowering drugs in view of defining a precision medicine to improve the efficacy and reduce the side effects associated with the treatment.

Exposure to low-dose perfluorooctanoic acid promotes hepatic steatosis and disrupts the hepatic transcriptome in mice

OBJECTIVE

Perfluoroalkyl substances (PFAS) are man-made chemicals with demonstrated endocrine-disrupting properties. Exposure to perfluorooctanoic acid (PFOA) has been linked to disturbed metabolism via the liver, although the exact mechanism is not clear. Moreover, information on the metabolic effects of the new PFAS alternative GenX is limited. We examined whether exposure to low-dose PFOA and GenX induces metabolic disturbances in mice, including NAFLD, dyslipidemia, and glucose tolerance, and studied the involvement of PPARα.

METHODS

Male C57BL/6J wildtype and PPARα^-/- mice were given 0.05 or 0.3 mg/kg body weight/day PFOA, or 0.3 mg/kg body weight/day GenX while being fed a high-fat diet for 20 weeks. Glucose and insulin tolerance tests were performed after 18 and 19 weeks. Plasma metabolite levels were measured next to a detailed assessment of the liver phenotype, including lipid content and RNA sequencing.

RESULTS

Exposure to high-dose PFOA decreased body weight and increased liver weight in wildtype and PPARα^-/- mice. High-dose but not low-dose PFOA reduced plasma triglycerides and cholesterol, which for triglycerides was dependent on PPARα. PFOA and GenX increased hepatic triglycerides in a PPARα-dependent manner. RNA sequencing showed that the effects of GenX on hepatic gene expression were entirely dependent on PPARα, while the effects of PFOA were mostly dependent on PPARα. In the absence of PPARα, the involvement of PXR and CAR became more prominent.

CONCLUSION

Overall, we show that long-term and low-dose exposure to PFOA and GenX disrupts hepatic lipid metabolism in mice. Whereas the effects of PFOA are mediated by multiple nuclear receptors, the effects of GenX are entirely mediated by PPARα. Our data underscore the potential of PFAS to disrupt metabolism by altering signaling pathways in the liver.

Review article: vascular effects of PPARs in the context of NASH

BACKGROUND

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors known to regulate glucose and fatty acid metabolism, inflammation, endothelial function and fibrosis. PPAR isoforms have been extensively studied in metabolic diseases, including type 2 diabetes and cardiovascular diseases. Recent data extend the key role of PPARs to liver diseases coursing with vascular dysfunction, including nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH).

AIM

This review summarises and discusses the pathobiological role of PPARs in cardiovascular diseases with a special focus on their impact and therapeutic potential in NAFLD and NASH.

RESULTS AND CONCLUSIONS

PPARs may be attractive for the treatment of NASH due to their liver-specific effects but also because of their efficacy in improving cardiovascular outcomes, which may later impact liver disease. Assessment of cardiovascular disease in the context of NASH trials is, therefore, of the utmost importance, both from a safety and efficacy perspective.

Untargeted metabolomics identifies the potential role of monocarboxylate transporter 6 (MCT6/SLC16A5) in lipid and amino acid metabolism pathways

Monocarboxylate transporter 6 (MCT6; SLC16A5) is an orphan transporter protein with expression in multiple tissues. The endogenous function of MCT6 related to human health and disease remains unknown. Our previous transcriptomic and proteomic analyses in Mct6 knockout (KO) mice suggested that MCT6 may play a role in lipid and glucose homeostasis, but additional evidence is required. Thus, the objective of this study was to further explore the impact of MCT6 on metabolic function using untargeted metabolomic analysis in Mct6 KO mice. The plasma from male and female mice and livers from male mice were submitted for global metabolomics analysis to assess the relative changes in endogenous small molecules across the liver and systemic circulation associated with absence of Mct6. More than 782 compounds were detected with 101 and 51 metabolites significantly changed in plasma of male and female mice, respectively, and 100 metabolites significantly changed in the livers of male mice (p < .05). Significant perturbations in lipid metabolism were annotated in the plasma and liver metabolome, with additional alterations in the amino acid metabolism pathway in plasma samples from male and female mice. Elevated lipid diacylglycerol and altered fatty acid metabolite concentrations were found in liver and plasma samples of male Mct6 KO mice. Significant reduction of N-terminal acetylated amino acids was found in plasma samples of male and female Mct6 KO mice. In summary, the present study confirmed the significant role of MCT6 in lipid and amino acid homeostasis, suggesting its contribution in metabolic diseases.

Comparative Analysis of the Effects of Fish Oil and Fenofibrate on Plasma Metabolomic Profiles in Overweight and Obese Individuals

SCOPE

The drug fenofibrate and dietary fish oils can effectively lower circulating triglyceride (TG) concentrations. However, a detailed comparative analysis of the effects on the plasma metabolome is missing.

METHODS AND RESULTS

Twenty overweight and obese subjects participate in a double-blind, cross-over intervention trial and receive in a random order 3.7 g day-1 n-3 fatty acids, 200 mg fenofibrate, or placebo treatment for 6 weeks. Four hundred twenty plasma metabolites are measured via gas chromatography-mass spectrometry (GC-MS) and liquid chromatography-mass spectrometry (LC-MS). Among the treatments, 237 metabolites are significantly different, of which 22 metabolites change in the same direction by fish oil and fenofibrate, including a decrease in several saturated TG-species. Fenofibrate additionally changes 33 metabolites, including a decrease in total cholesterol, and total lysophosphatidylcholine (LPC), whereas 54 metabolites are changed by fish oil, including an increase in unsaturated TG-, LPC-, phosphatidylcholine-, and cholesterol ester-species. All q < 0.05.

CONCLUSION

Fenofibrate and fish oil reduce several saturated TG-species markedly. These reductions have been associated with a decreased risk for developing cardiovascular disease (CVD). Interestingly, fish oil consumption increases several unsaturated lipid species, which have also been associated with a reduced CVD risk. Altogether, this points towards the power of fish oil to change the plasma lipid metabolome in a potentially beneficial way.

Multi-omics integration strategies for animal epigenetic studies - A review

Genome-wide studies provide considerable insights into the genetic background of animals; however, the inheritance of several heritable factors cannot be elucidated. Epigenetics explains these heritabilities, including those of genes influenced by environmental factors. Knowledge of the mechanisms underlying epigenetics enables understanding the processes of gene regulation through interactions with the environment. Recently developed next-generation sequencing (NGS) technologies help understand the interactional changes in epigenetic mechanisms. There are large sets of NGS data available; however, the integrative data analysis approaches still have limitations with regard to reliably interpreting the epigenetic changes. This review focuses on the epigenetic mechanisms and profiling methods and multi-omics integration methods that can provide comprehensive biological insights in animal genetic studies.

Transcriptomic analyses of livers from mice exposed to 1,4-dioxane for up to 90 days to assess potential mode(s) of action underlying liver tumor development

1,4-Dioxane is a volatile organic compound with industrial and commercial applications as a solvent and in the manufacture of other chemicals. 1,4-Dioxane has been demonstrated to induce liver tumors in chronic rodent bioassays conducted at very high doses. The available evidence for 1,4-dioxane-induced liver tumors in rodents aligns with a threshold-dependent mode of action (MOA), with the underlying mechanism being less clear in the mouse than in rats. To gain a better understanding of the underlying molecular mechanisms related to liver tumor development in mice orally exposed to 1,4-dioxane, transcriptomics analysis was conducted on liver tissue collected from a 90-day drinking water study in female B6D2F₁/Crl mice (Lafranconi et al., 2020). Using tissue samples from female mice exposed to 1,4-dioxane in the drinking water at concentrations of 0, 40, 200, 600, 2,000 or 6,000 ppm for 7, 28, and 90 days, transcriptomic analyses demonstrate minimal treatment effects on global gene expression at concentrations below 600 ppm. At higher concentrations, genes involved in phase II metabolism and mitotic cell cycle checkpoints were significantly upregulated. There was an overall lack of enrichment of genes related to DNA damage response. The increase in mitotic signaling is most prevalent in the livers of mice exposed to 1,4-dioxane at the highest concentrations for 90 days. This finding aligns with phenotypic changes reported by Lafranconi et al. (2020) after 90-days of exposure to 6,000 ppm 1,4-dioxane in the same tissues. The transcriptomics analysis further supports overarching study findings demonstrating a non-mutagenic, threshold-based, mitogenic MOA for 1,4-dioxane-induced liver tumors.

Restoration of mRNA Expression of Solute Carrier Proteins in Liver of Diet-Induced Obese Mice by Metformin

Metformin (MET), the most common medicine for type 2 diabetes (T2DM), improves insulin sensitivity by targeting the liver, intestine and other organs. Its impact on expression of the solute carrier (Slc) transporter genes have not been reported in the mechanism of insulin sensitization. In this study, we examined Slc gene expression in the liver and colon of diet-induced obese (DIO) mice treated with MET by transcriptomic analysis. There were 939 differentially expressed genes (DEGs) in the liver of DIO mice vs lean mice, which included 34 Slc genes. MET altered 489 DEGs in the liver of DIO mice, in which 23 were Slc genes. Expression of 20 MET-responsive Slc DEGs was confirmed by qRT-PCR, in which 15 Slc genes were altered in DIO mice and their expressions were restored by MET, including Slc2a10, Slc2a13, Slc5a9, Slc6a14, Slc7a9, Slc9a2, Slc9a3, Slc13a2, Slc15a2, Slc26a3, Slc34a2, Slc37a1, Slc44a4, Slc51b and Slc52a3. While, there were only 97 DEGs in the colon of DIO mice with 5 Slc genes, whose expression was not restored by MET. The data suggest that more genes were altered in the liver over the colon by the high fat diet (HFD). There were 20 Slc genes with alteration confirmed in the liver of DIO mice and 15 of them were restored by MET, which was associated with improvement of insulin sensitivity and obesity. The restoration may improve the uptake of glucose, amino acids, mannose, fructose, 1,5-anhydro-D-glucitol and bumetanide in hepatocytes of the liver of DIO mice. The study provides new insight into the mechanism of metformin action in insulin sensitization and obesity.

An Optimized Dual Extraction Method for the Simultaneous and Accurate Analysis of Polar Metabolites and Lipids Carried out on Single Biological Samples

The functional understanding of metabolic changes requires both a significant investigation into metabolic pathways, as enabled by global metabolomics and lipidomics approaches, and the comprehensive and accurate exploration of specific key pathways. To answer this pivotal challenge, we propose an optimized approach, which combines an efficient sample preparation, aiming to reduce the variability, with a biphasic extraction method, where both the aqueous and organic phases of the same sample are used for mass spectrometry analyses. We demonstrated that this double extraction protocol allows working with one single sample without decreasing the metabolome and lipidome coverage. It enables the targeted analysis of 40 polar metabolites and 82 lipids, together with the absolute quantification of 32 polar metabolites, providing comprehensive coverage and quantitative measurement of the metabolites involved in central carbon energy pathways. With this method, we evidenced modulations of several lipids, amino acids, and energy metabolites in HepaRG cells exposed to fenofibrate, a model hepatic toxicant, and metabolic modulator. This new protocol is particularly relevant for experiments involving limited amounts of biological material and for functional metabolic explorations and is thus of particular interest for studies aiming to decipher the effects and modes of action of metabolic disrupting compounds.

Eicosapentaenoic acid-enriched phospholipids suppressed lipid accumulation by specific inhibition of lipid droplet-associated protein FSP27 in mice

BACKGROUND

Sea cucumber is a rich source of eicosapentaenoic acid in the form of eicosapentaenoic acid-enriched phospholipids (EPA-PL). It is known to be efficacious in preventing obesity. However, few studies have focused on the role of EPA-PL in inhibiting lipid accumulation by lipid droplets (LDs). This study first investigated the effect of EPA-PL from sea cucumber on the formation of LDs and the underlying mechanism in C57BL/6J mice. The mice were randomly divided into two groups and treated for 8 weeks or 3, 7, and 14 days with either (i) a high-sucrose diet (model group), (ii) a high-sucrose diet plus 2% EPA-PL (EPA-PL group).

RESULTS

Eight-week EPA-PL supplementation significantly reduced lipid accumulation and LD size in liver and white adipose tissue (WAT), which was accompanied by the decreased expression of LDs-associated protein FSP27. A 3-day EPA-PL treatment suppressed the mRNA expression of Fsp27. The mRNA level of Fsp27 reached its 'normal level' after withdrawing EPA-PL for 7 days, suggesting that EPA-PL might serve as a rapid regulator of FSP27. Furthermore, EPA-PL increased the expression of lipolysis genes Hsl and Atgl accompanied by the regulation of Pparγ in WAT.

CONCLUSIONS

Dietary EPA-PL from sea cucumber (Cucumaria frondosa) protected against lipid accumulation by regulating LDs-associated protein FSP27, which might provide novel evidence for the anti-obesity action of EPA-PL. © 2020 Society of Chemical Industry.

Monocarboxylate Transporter 6-Mediated Interactions with Prostaglandin F2α: In Vitro and In Vivo Evidence Utilizing a Knockout Mouse Model

Monocarboxylate transporter 6 (MCT6; SLC16A5) is a recently studied drug transporter that currently has no annotated endogenous function. Currently, only a handful of compounds have been characterized as substrates for MCT6 (e.g., bumetanide, nateglinide, probenecid, and prostaglandin F_2α (PGF2α)). The objective of our research was to characterize the MCT6-specific transporter kinetic parameters and MCT6-specific in vitro and in vivo interactions of PGF2α. Murine and human MCT6-mediated transport of PGF2α was assessed in MCT6-transfected oocytes. Additionally, endogenous PGF2α and a primary PGF2α metabolite (PGFM) were measured in plasma and urine in Mct6 knockout (Mct6^−/−) and wild-type (Mct6^+/+) mice. Results demonstrated that the affinity was approximately 40.1 and 246 µM respectively, for mouse and human, at pH 7.4. In vivo, plasma PGF2α concentrations in Mct6^−/− mice were significantly decreased, compared to Mct6^+/+ mice (3.3-fold). Mct6^-/- mice demonstrated a significant increase in urinary PGF2α concentrations (1.7-fold). A similar trend was observed with plasma PGFM concentrations. However, overnight fasting resulted in significantly increased plasma PGF2α concentrations, suggesting a diet-dependent role of Mct6 regulation on the homeostasis of systemic PGF2α. Overall, these results are the first to suggest the potential regulatory role of MCT6 in PGF2α homeostasis, and potentially other PGs, in distribution and metabolism.

Short-term treatment with a peroxisome proliferator-activated receptor α agonist influences plasma one-carbon metabolites and B-vitamin status in rats

INTRODUCTION

Peroxisome proliferator-activated receptors (PPARs) have been suggested to be involved in the regulation of one-carbon metabolism. Previously we have reported effects on plasma concentrations of metabolites along these pathways as well as markers of B-vitamin status in rats following treatment with a pan-PPAR agonist. Here we aimed to investigate the effect on these metabolites after specific activation of the PPARα and PPARγ subtypes.

METHODS

For a period of 12 days, Male Wistar rats (n = 20) were randomly allocated to receive treatment with the PPARα agonist WY-14.643 (n = 6), the PPARγ agonist rosiglitazone (n = 6) or placebo (n = 8). The animals were sacrificed under fasting conditions, and plasma concentration of metabolites were determined. Group differences were assessed by one-way ANOVA, and planned comparisons were performed for both active treatment groups towards the control group.

RESULTS

Treatment with a PPARα agonist was associated with increased plasma concentrations of most biomarkers, with the most pronounced differences observed for betaine, dimethylglycine, glycine, nicotinamide, methylnicotinamide, pyridoxal and methylmalonic acid. Lower levels were observed for flavin mononucleotide. Fewer associations were observed after treatment with a PPARγ agonist, and the most notable was increased plasma serine.

CONCLUSION

Treatment with a PPARα agonist influenced plasma concentration of one-carbon metabolites and markers of B-vitamin status. This confirms previous findings, suggesting specific involvement of PPARα in the regulation of these metabolic pathways as well as the status of closely related B-vitamins.

Characterization and Proteomic-Transcriptomic Investigation of Monocarboxylate Transporter 6 Knockout Mice: Evidence of a Potential Role in Glucose and Lipid Metabolism

Monocarboxylate transporter 6 [(MCT6), SLC16A5] is an orphan transporter with no known endogenous substrates or physiological role. Previous in vitro and in vivo experiments investigated MCT6 substrate/inhibitor specificity in Xenopus laevis oocytes; however, these data remain limited. Transcriptomic changes in the livers of mice undergoing different dieting schemes have suggested that Mct6 plays a role in glucose and lipid metabolism. The objectives of this study were 1) to develop a novel knockout (KO) mouse model (Mct6^-/-) using CRISPR/Cas9 technology, 2) to characterize the KO animal model by examining physiological and biochemical parameters, and 3) to understand the physiological role of MCT6 in vivo through global proteomic and liver transcriptomic profiling. mRNA tissue analysis demonstrated knockout of Mct6, which showed greater than 90% knockdown of Mct6 (Slc16a5) gene expression in all major tissues analyzed when normalized to Mct6^+/+ mice. Proteomic analyses identified greater than 4000 unique proteins in kidney, liver, and colon tissues, among which 51, 38, and 241 proteins were significantly altered, respectively (for each tissue), between Mct6^+/+ and Mct6^-/- mice. Additionally, Mct6^-/- mice demonstrated significant changes in 199 genes in the liver compared with Mct6^+/+ mice. In silico biological pathway analyses revealed significant changes in proteins and genes involved in glucose and lipid metabolism-associated pathways. This study is the first to provide evidence for an association of Mct6 in the regulation of glucose and lipid metabolism. SIGNIFICANCE STATEMENT: This paper focuses on elucidating the innate biological role of an orphan transporter in vivo, which has not been investigated thus far. Using efficient and high-throughput technologies, such as CRISPR/Cas9 gene editing, liquid chromatography-tandem mass spectrometry-based proteomic and RNA-sequencing transcriptomic analyses, our laboratory provides the first existence and characterization of a Mct6 knockout mouse model. The evidence gathered in this paper, as well as other laboratories, support the importance of MCT6 in regulating a variety of glucose and lipid metabolic pathways, which may indicate its significance in metabolic diseases.

P465L-PPARγ mutation confers partial resistance to the hypolipidaemic action of fibrates

AIMS

Familial partial lipodystrophic syndrome 3 (FPLD3) is associated with mutations in the transcription factor PPARγ. One of these mutations, the P467L, confers a dominant negative effect. We and others have previously investigated the pathophysiology associated with this mutation using a humanized mouse model that recapitulates most of the clinical symptoms observed in patients who have been phenotyped under different experimental conditions. One of the key clinical manifestations observed, both in humans and mouse models, is the ectopic accumulation of fat in the liver. With this study we aim to dissect the molecular mechanisms that contribute to the excessive accumulation of lipids in the liver and characterize the negative effect of this PPARγ mutation on the activity of PPARα in vivo when activated by fibrates.

MATERIAL AND METHODS

P465L-PPAR mutant and wild-type mice were divided into 8 experimental groups, 4 different conditions per genotype. Briefly, mice were fed a chow diet or a high-fat diet (HFD 45% Kcal from fat) for a period of 28 days and treated with WY14643 or vehicle for five days before culling. At the end of the experiment, tissues and plasma were collected. We performed extensive gene expression, fatty acid composition and histological analysis in the livers. The serum collected was used to measure several metabolites and to perform basic lipoprotein profile.

RESULTS

P465L mice showed increased levels of insulin and free fatty acids (FFA) as well as increased liver steatosis. They also exhibit decreased levels of very low density lipoproteins (VLDL) when fed an HFD. We also provide evidence of impaired expression of a number of well-established PPARα target genes in the P465L mutant livers.

CONCLUSION

Our data demonstrate that P465L confers partial resistance to the hypolipidemic action of fibrates. These results show that the fatty liver phenotype observed in P465L mutant mice is not only the consequence of dysfunctional adipose tissue, but also involves defective liver metabolism. All in all, the deleterious effects of P465L-PPARγ mutation may be magnified by their collateral negative effect on PPARα function.

The whole transcriptome effects of the PPARα agonist fenofibrate on livers of hepatocyte humanized mice

Background

The role of PPARα in gene regulation in mouse liver is well characterized. However, less is known about the role of PPARα in human liver. The aim of the present study was to better characterize the impact of PPARα activation on gene regulation in human liver. To that end, chimeric mice containing hepatocyte humanized livers were given an oral dose of 300 mg/kg fenofibrate daily for 4 days. Livers were collected and analyzed by hematoxilin and eosin staining, qPCR, and transcriptomics. Transcriptomics data were compared with existing datasets on PPARα activation in normal mouse liver, human primary hepatocytes, and human precision cut liver slices.

Results

Of the different human liver models, the gene expression profile of hepatocyte humanized livers most closely resembled actual human liver. In the hepatocyte humanized mouse livers, the human hepatocytes exhibited excessive lipid accumulation. Fenofibrate increased the size of the mouse but not human hepatocytes, and tended to reduce steatosis in the human hepatocytes. Quantitative PCR indicated that induction of PPARα targets by fenofibrate was less pronounced in the human hepatocytes than in the residual mouse hepatocytes. Transcriptomics analysis indicated that, after filtering, a total of 282 genes was significantly different between fenofibrate- and control-treated mice (P < 0.01). 123 genes were significantly lower and 159 genes significantly higher in the fenofibrate-treated mice, including many established PPARα targets such as FABP1, HADHB, HADHA, VNN1, PLIN2, ACADVL and HMGCS2. According to gene set enrichment analysis, fenofibrate upregulated interferon/cytokine signaling-related pathways in hepatocyte humanized liver, but downregulated these pathways in normal mouse liver. Also, fenofibrate downregulated pathways related to DNA synthesis in hepatocyte humanized liver but not in normal mouse liver.

Conclusion

The results support the major role of PPARα in regulating hepatic lipid metabolism, and underscore the more modest effect of PPARα activation on gene regulation in human liver compared to mouse liver. The data suggest that PPARα may have a suppressive effect on DNA synthesis in human liver, and a stimulatory effect on interferon/cytokine signalling.

Nutrient-sensing nuclear receptors PPARα and FXR control liver energy balance

The nuclear receptors PPARα (encoded by NR1C1) and farnesoid X receptor (FXR, encoded by NR1H4) are activated in the liver in the fasted and fed state, respectively. PPARα activation induces fatty acid oxidation, while FXR controls bile acid homeostasis, but both nuclear receptors also regulate numerous other metabolic pathways relevant to liver energy balance. Here we review evidence that they function coordinately to control key nutrient pathways, including fatty acid oxidation and gluconeogenesis in the fasted state and lipogenesis and glycolysis in the fed state. We have also recently reported that these receptors have mutually antagonistic impacts on autophagy, which is induced by PPARα but suppressed by FXR. Secretion of multiple blood proteins is a major drain on liver energy and nutrient resources, and we present preliminary evidence that the liver secretome may be directly suppressed by PPARα, but induced by FXR. Finally, previous studies demonstrated a striking deficiency in bile acid levels in malnourished mice that is consistent with results in malnourished children. We present evidence that hepatic targets of PPARα and FXR are dysregulated in chronic undernutrition. We conclude that PPARα and FXR function coordinately to integrate liver energy balance.

Monocarboxylate Transporters: Therapeutic Targets and Prognostic Factors in Disease

Solute carrier (SLC) transporters represent 52 families of membrane transport proteins that function in endogenous compound homeostasis and xenobiotic disposition, and have been exploited in drug delivery and therapeutic targeting strategies. In particular, the SLC16 family that encodes for the 14 isoforms of the monocarboxylate transporter (MCT) family plays a significant role in the absorption, tissue distribution, and clearance of both endogenous and exogenous compounds. MCTs are required for the transport of essential cell nutrients and for cellular metabolic and pH regulation. Recent publications have indicated their novel roles in disease, and thus their potential as biomarkers and new therapeutic targets in disease are under investigation. More research into MCT isoform function, specificity, expression, and regulation will allow researchers to exploit the potential utility of MCTs in the clinic as therapeutic targets and prognostic factors of disease.

Changes in plasma metabolites and glucose homeostasis during omega-3 polyunsaturated fatty acid supplementation in women with polycystic ovary syndrome

Background

Both fish (FO) and flaxseed oils (FLX) are n-3 polyunsaturated fatty acids (PUFA). Fish oil contains long chain while FLX contains essential n-3 PUFA. We demonstrated that FO altered insulin secretion and resistance in polycystic ovary syndrome (PCOS) women but FLX did not. Surprisingly, the effects of FO were similar to those of the n-6 PUFA-rich soybean oil (SBO). Since increased branched chain (BCAA) and aromatic amino acids (AA) affect insulin secretion and resistance, we investigated whether FO, FLX and /or SBO affect plasma metabolites, especially AA.

Methods and findings

In this six-week, randomized, 3-parallel arm, double-blinded study, 54 women received 3.5 g/day FO, FLX or SBO. In 51 completers (17 from each arm), fasting plasma metabolites were measured at the beginning and at the end.

As compared to FLX, FO and SBO increased insulin response and resistance as well as several BCAA and aromatic AA. Pathway analysis indicated that FO exerted the largest biochemical impact, affecting AA degradation and biosynthesis, amine, polyamine degradation and alanine, glycine, l-carnitine biosynthesis and TCA cycle, while FLX had minimal impact affecting only alanine biosynthesis and l-cysteine degradation.

Conclusion

Effects of FO and SBO on plasma AA were similar and differed significantly from those of the FLX. The primary target of dietary PUFA is not known. Dietary PUFA may influence insulin secretion and resistance directly and alter plasma AA indirectly. Alternatively, as a novel concept, dietary PUFA may directly affect AA metabolism and the changes in insulin secretion and resistance may be secondary.

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Increased serum branched chain amino acids (BCAA) and aromatic amino acids are associated with insulin resistance and type 2 diabetes.

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Although both fish oil (FO) and flaxseed oil (FLX) are n-3 PUFA, FO contains the long chain, while FLX contains the essential n-3 PUFA.

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We compared the effects of different PUFAs on plasma metabolites in women with insulin resistance.

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Fish oil, but not FLX, increased plasma BCAA, and insulin resistance and secretion, indicating differential effects of essential vs. long chain n-3 PUFA.

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It is possible that effects of FO on insulin resistance and secretion may have been indirect, through its actions on BCAA metabolism.

Fenofibrate unexpectedly induces cardiac hypertrophy in mice lacking MuRF1

The muscle-specific ubiquitin ligase muscle ring finger-1 (MuRF1) is critical in regulating both pathological and physiological cardiac hypertrophy in vivo. Previous work from our group has identified MuRF1's ability to inhibit serum response factor and insulin-like growth factor-1 signaling pathways (via targeted inhibition of cJun as underlying mechanisms). More recently, we have identified that MuRF1 inhibits fatty acid metabolism by targeting peroxisome proliferator-activated receptor alpha (PPARα) for nuclear export via mono-ubiquitination. Since MuRF1-/- mice have an estimated fivefold increase in PPARα activity, we sought to determine how challenge with the PPARα agonist fenofibrate, a PPARα ligand, would affect the heart physiologically. In as little as 3 weeks, feeding with fenofibrate/chow (0.05% wt/wt) induced unexpected pathological cardiac hypertrophy not present in age-matched sibling wild-type (MuRF1+/+) mice, identified by echocardiography, cardiomyocyte cross-sectional area, and increased beta-myosin heavy chain, brain natriuretic peptide, and skeletal muscle α-actin mRNA. In addition to pathological hypertrophy, MuRF1-/- mice had an unexpected differential expression in genes associated with the pleiotropic effects of fenofibrate involved in the extracellular matrix, protease inhibition, hemostasis, and the sarcomere. At both 3 and 8 weeks of fenofibrate treatment, the differentially expressed MuRF1-/- genes most commonly had SREBP-1 and E2F1/E2F promoter regions by TRANSFAC analysis (54 and 50 genes, respectively, of the 111 of the genes >4 and <-4 log fold change; P ≤ .0004). These studies identify MuRF1's unexpected regulation of fenofibrate's pleiotropic effects and bridges, for the first time, MuRF1's regulation of PPARα, cardiac hypertrophy, and hemostasis.

Transcriptomic and metabolomic data integration

Many studies now produce parallel data sets from different omics technologies; however, the task of interpreting the acquired data in an integrated fashion is not trivial. This review covers those methods that have been used over the past decade to statistically integrate and interpret metabolomics and transcriptomic data sets. It defines four categories of approaches, correlation-based integration, concatenation-based integration, multivariate-based integration and pathway-based integration, into which all existing statistical methods fit. It also explores the choices in study design for generating samples for analysis by these omics technologies and the impact that these technical decisions have on the subsequent data analysis options.

Ketone Body Therapy Protects From Lipotoxicity and Acute Liver Failure Upon Pparα Deficiency

Acute liver failure (ALF) is a severe and rapid liver injury, often occurring without any preexisting liver disease, which may precipitate multiorgan failure and death. ALF is often associated with impaired β-oxidation and increased oxidative stress (OS), characterized by elevated levels of hepatic reactive oxygen species (ROS) and lipid peroxidation (LPO) products. Peroxisome proliferator-activated receptor (PPAR)α has been shown to confer hepatoprotection in acute and chronic liver injury, at least in part, related to its ability to control peroxisomal and mitochondrial β-oxidation. To study the pathophysiological role of PPARα in hepatic response to high OS, we induced a pronounced LPO by treating wild-type and Pparα-deficient mice with high doses of fish oil (FO), containing n-3 polyunsaturated fatty acids. FO feeding of Pparα-deficient mice, in contrast to control sunflower oil, surprisingly induced coma and death due to ALF as indicated by elevated serum alanine aminotransferase, aspartate aminotransferase, ammonia, and a liver-specific increase of ROS and LPO-derived malondialdehyde. Reconstitution of PPARα specifically in the liver using adeno-associated serotype 8 virus-PPARα in Pparα-deficient mice restored β-oxidation and ketogenesis and protected mice from FO-induced lipotoxicity and death. Interestingly, administration of the ketone body β-hydroxybutyrate prevented FO-induced ALF in Pparα-deficient mice, and normalized liver ROS and malondialdehyde levels. Therefore, PPARα protects the liver from FO-induced OS through its regulatory actions on ketone body levels. β-Hydroxybutyrate treatment could thus be an option to prevent LPO-induced liver damage.

Molecular mechanism of PPARα action and its impact on lipid metabolism, inflammation and fibrosis in non-alcoholic fatty liver disease

Peroxisome proliferator-activated receptor α (PPARα) is a ligand-activated transcription factor belonging, together with PPARγ and PPARβ/δ, to the NR1C nuclear receptor subfamily. Many PPARα target genes are involved in fatty acid metabolism in tissues with high oxidative rates such as muscle, heart and liver. PPARα activation, in combination with PPARβ/δ agonism, improves steatosis, inflammation and fibrosis in pre-clinical models of non-alcoholic fatty liver disease, identifying a new potential therapeutic area. In this review, we discuss the transcriptional activation and repression mechanisms by PPARα, the spectrum of target genes and chromatin-binding maps from recent genome-wide studies, paying particular attention to PPARα-regulation of hepatic fatty acid and plasma lipoprotein metabolism during nutritional transition, and of the inflammatory response. The role of PPARα, together with other PPARs, in non-alcoholic steatohepatitis will be discussed in light of available pre-clinical and clinical data.

Influence of fenofibrate treatment on triacylglycerides, diacylglycerides and fatty acids in fructose fed rats

Fenofibrate (FF) lowers plasma triglycerides via PPARα activation. Here, we analyzed lipidomic changes upon FF treatment of fructose fed rats. Three groups with 6 animals each were defined as control, fructose-fed and fructose-fed/FF treated. Male Wistar Unilever Rats were subjected to 10% fructose-feeding for 20 days. On day 14, fenofibrate treatment (100 mg/kg p.o.) was initiated and maintained for 7 days. Lipid species in serum were analyzed using mass spectrometry (ESI-MS/MS; LC-FT-MS, GC-MS) on days 0, 14 and 20 in all three groups. In addition, lipid levels in liver and intestine were determined. Short-chain TAGs increased in serum and liver upon fructose-feeding, while almost all TAG-species decreased under FF treatment. Long-chain unsaturated DAG-levels (36:1, 36:2, 36:4, 38:3, 38:4, 38:5) increased upon FF treatment in rat liver and decreased in rat serum. FAs, especially short-chain FAs (12:0, 14:0, 16:0) increased during fructose-challenge. VLDL secretion increased upon fructose-feeding and together with FA-levels decreased to control levels during FF treatment. Fructose challenge of de novo fatty acid synthesis through fatty acid synthase (FAS) may enhance the release of FAs ≤ 16:0 chain length, a process reversed by FF-mediated PPARα-activation.

ABCD2 alters peroxisome proliferator-activated receptor α signaling in vitro, but does not impair responses to fenofibrate therapy in a mouse model of diet-induced obesity

Fenofibrate is a peroxisome proliferator-activated receptor (PPAR) α ligand that has been widely used as a lipid-lowering agent in the treatment of hypertriglyceridemia. ABCD2 (D2) is a peroxisomal long-chain acyl-CoA transporter that is highly induced by fenofibrate in the livers of mice. To determine whether D2 is a modifier of fibrate responses, wild-type and D2-deficient mice were treated with fenofibrate for 14 days. The absence of D2 altered expression of gene clusters associated with lipid metabolism, including PPARα signaling. Using 3T3-L1 adipocytes, which express high levels of D2, we confirmed that knockdown of D2 modified genomic responses to fibrate treatment. We next evaluated the impact of D2 on effects of fibrates in a mouse model of diet-induced obesity. Fenofibrate treatment opposed the development of obesity, hypertriglyceridemia, and insulin resistance. However, these effects were unaffected by D2 genotype. We concluded that D2 can modulate genomic responses to fibrates, but that these effects are not sufficiently robust to alter the effects of fibrates on diet-induced obesity phenotypes.

PPARα-independent actions of omega-3 PUFAs contribute to their beneficial effects on adiposity and glucose homeostasis

Excess dietary lipid generally leads to fat deposition and impaired glucose homeostasis, but consumption of fish oil (FO) alleviates many of these detrimental effects. The beneficial effects of FO are thought to be mediated largely via activation of the nuclear receptor peroxisomal-proliferator-activated receptor α (PPARα) by omega-3 polyunsaturated fatty acids and the resulting upregulation of lipid catabolism. However, pharmacological and genetic PPARα manipulations have yielded variable results. We have compared the metabolic effects of FO supplementation and the synthetic PPARα agonist Wy-14,643 (WY) in mice fed a lard-based high-fat diet. In contrast to FO, WY treatment resulted in little protection against diet-induced obesity and glucose intolerance, despite upregulating many lipid metabolic pathways. These differences were likely due to differential effects on hepatic lipid synthesis, with FO decreasing and WY amplifying hepatic lipid accumulation. Our results highlight that the beneficial metabolic effects of FO are likely mediated through multiple independent pathways.

Fish oil and krill oil supplementations differentially regulate lipid catabolic and synthetic pathways in mice

Background

Marine derived oils are rich in long-chain polyunsaturated omega-3 fatty acids, in particular eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), which have long been associated with health promoting effects such as reduced plasma lipid levels and anti-inflammatory effects. Krill oil (KO) is a novel marine oil on the market and is also rich in EPA and DHA, but the fatty acids are incorporated mainly into phospholipids (PLs) rather than triacylglycerols (TAG). This study compares the effects of fish oil (FO) and KO on gene regulation that influences plasma and liver lipids in a high fat diet mouse model.

Methods

Male C57BL/6J mice were fed either a high-fat diet (HF) containing 24% (wt/wt) fat (21.3% lard and 2.3% soy oil), or the HF diet supplemented with FO (15.7% lard, 2.3% soy oil and 5.8% FO) or KO (15.6% lard, 2.3% soy oil and 5.7% KO) for 6 weeks. Total levels of cholesterol, TAG, PLs, and fatty acid composition were measured in plasma and liver. Gene regulation was investigated using quantitative PCR in liver and intestinal epithelium.

Results

Plasma cholesterol (esterified and unesterified), TAG and PLs were significantly decreased with FO. Analysis of the plasma lipoprotein particles indicated that the lipid lowering effect by FO is at least in part due to decreased very low density lipoprotein (VLDL) content in plasma with subsequent liver lipid accumulation. KO lowered plasma non-esterified fatty acids (NEFA) with a minor effect on fatty acid accumulation in the liver. In spite of a lower omega-3 fatty acid content in the KO supplemented diet, plasma and liver PLs omega-3 levels were similar in the two groups, indicating a higher bioavailability of omega-3 fatty acids from KO. KO more efficiently decreased arachidonic acid and its elongation/desaturation products in plasma and liver. FO mainly increased the expression of several genes involved in fatty acid metabolism, while KO specifically decreased the expression of genes involved in the early steps of isoprenoid/cholesterol and lipid synthesis.

Conclusions

The data show that both FO and KO promote lowering of plasma lipids and regulate lipid homeostasis, but with different efficiency and partially via different mechanisms.

Fibrates and fish oil, but not corn oil, up-regulate the expression of the cholesteryl ester transfer protein (CETP) gene

Cholesteryl ester transfer protein (CETP) is a plasma protein that reduces high density lipoprotein (HDL)-cholesterol (chol) levels and may increase atherosclerosis risk. n-3 and n-6 polyunsaturated fatty acids (PUFAs) are natural ligands, and fibrates are synthetic ligands for peroxisome proliferator activated receptor-alpha (PPARα), a transcription factor that modulates lipid metabolism. In this study, we investigated the effects of PUFA oils and fibrates on CETP expression. Hypertriglyceridemic CETP transgenic mice were treated with gemfibrozil, fenofibrate, bezafibrate or vehicle (control), and normolipidemic CETP transgenic mice were treated with fenofibrate or with fish oil (FO; n-3 PUFA rich), corn oil (CO, n-6 PUFA rich) or saline. Compared with the control treatment, only fenofibrate significantly diminished triglyceridemia (50%), whereas all fibrates decreased the HDL-chol level. Elevation of the CETP liver mRNA levels and plasma activity was observed in the fenofibrate (53%) and gemfibrozil (75%) groups. Compared with saline, FO reduced the plasma levels of nonesterified fatty acid (26%), total chol (15%) and HDL-chol (20%). Neither of the oil treatments affected the plasma triglyceride levels. Compared with saline, FO increased the plasma adiponectin level and reduced plasma leptin levels, whereas CO increased the leptin levels. FO, but not CO, significantly increased the plasma CETP mass (90%) and activity (23%) as well as increased the liver level of CETP mRNA (28%). In conclusion, fibrates and FO, but not CO, up-regulated CETP expression at both the mRNA and protein levels. We propose that these effects are mediated by the activation of PPARα, which acts on a putative PPAR response element in the CETP gene.

Integrated physiology and systems biology of PPARα

The Peroxisome Proliferator Activated Receptor alpha (PPARα) is a transcription factor that plays a major role in metabolic regulation. This review addresses the functional role of PPARα in intermediary metabolism and provides a detailed overview of metabolic genes targeted by PPARα, with a focus on liver. A distinction is made between the impact of PPARα on metabolism upon physiological, pharmacological, and nutritional activation. Low and high throughput gene expression analyses have allowed the creation of a comprehensive map illustrating the role of PPARα as master regulator of lipid metabolism via regulation of numerous genes. The map puts PPARα at the center of a regulatory hub impacting fatty acid uptake, fatty acid activation, intracellular fatty acid binding, mitochondrial and peroxisomal fatty acid oxidation, ketogenesis, triglyceride turnover, lipid droplet biology, gluconeogenesis, and bile synthesis/secretion. In addition, PPARα governs the expression of several secreted proteins that exert local and endocrine functions.

Mechanisms of amiodarone and valproic acid induced liver steatosis in mouse in vivo act as a template for other hepatotoxicity models

Liver injury is the leading cause of drug-induced toxicity. For the evaluation of a chemical compound to induce toxicity, in this case steatosis or fatty liver, it is imperative to identify markers reflective of mechanisms and processes induced upon exposure, as these will be the earliest changes reflective of disease. Therefore, an in vivo mouse toxicogenomics study was completed to identify common pathways, nuclear receptor (NR) binding sites, and genes regulated by three known human steatosis-inducing compounds, amiodarone (AMD), valproic acid (VPA), and tetracycline (TET). Over 1, 4, and 11 days of treatment, AMD induced changes in clinical chemistry parameters and histopathology consistent with steatosis. Common processes and NR binding sites involved in lipid, retinol, and drug metabolism were found for AMD and VPA, but not for TET, which showed no response. Interestingly, the pattern of enrichment of these common pathways and NR binding sites over time was unique to each compound. Eleven biomarkers of steatosis were identified as dose responsive and time sensitive to toxicity for AMD and VPA. Finally, this in vivo mouse study was compared to an AMD rat in vivo, an AMD mouse primary hepatocyte, and a VPA human primary hepatocyte study to identify concordance for steatosis. We conclude that concordance is found on the process level independent of species, model or dose*time point.

Mode of action framework analysis for receptor-mediated toxicity: The peroxisome proliferator-activated receptor alpha (PPARα) as a case study

Several therapeutic agents and industrial chemicals induce liver tumors in rodents through the activation of the peroxisome proliferator-activated receptor alpha (PPARα). The cellular and molecular events by which PPARα activators induce rodent hepatocarcinogenesis has been extensively studied and elucidated. This review summarizes the weight of evidence relevant to the hypothesized mode of action (MOA) for PPARα activator-induced rodent hepatocarcinogenesis and identifies gaps in our knowledge of this MOA. Chemical-specific and mechanistic data support concordance of temporal and dose-response relationships for the key events associated with many PPARα activators including a phthalate ester plasticizer di(2-ethylhexyl) phthalate (DEHP) and the drug gemfibrozil. While biologically plausible in humans, the hypothesized key events in the rodent MOA, for PPARα activators, are unlikely to induce liver tumors in humans because of toxicodynamic and biological differences in responses. This conclusion is based on minimal or no effects observed on growth pathways, hepatocellular proliferation and liver tumors in humans and/or species (including hamsters, guinea pigs and cynomolgous monkeys) that are more appropriate human surrogates than mice and rats at overlapping dose levels. Overall, the panel concluded that significant quantitative differences in PPARα activator-induced effects related to liver cancer formation exist between rodents and humans. On the basis of these quantitative differences, most of the workgroup felt that the rodent MOA is "not relevant to humans" with the remaining members concluding that the MOA is "unlikely to be relevant to humans". The two groups differed in their level of confidence based on perceived limitations of the quantitative and mechanistic knowledge of the species differences, which for some panel members strongly supports but cannot preclude the absence of effects under unlikely exposure scenarios.

Nutritional lipidomics: molecular metabolism, analytics, and diagnostics

The field of lipidomics is providing nutritional science a more comprehensive view of lipid intermediates. Lipidomics research takes advantage of the increase in accuracy and sensitivity of mass detection of MS with new bioinformatics toolsets to characterize the structures and abundances of complex lipids. Yet, translating lipidomics to practice via nutritional interventions is still in its infancy. No single instrumentation platform is able to solve the varying analytical challenges of the different molecular lipid species. Biochemical pathways of lipid metabolism remain incomplete and the tools to map lipid compositional data to pathways are still being assembled. Biology itself is dauntingly complex and simply separating biological structures remains a key challenge to lipidomics. Nonetheless, the strategy of combining tandem analytical methods to perform the sensitive, high-throughput, quantitative, and comprehensive analysis of lipid metabolites of very large numbers of molecules is poised to drive the field forward rapidly. Among the next steps for nutrition to understand the changes in structures, compositions, and function of lipid biomolecules in response to diet is to describe their distribution within discrete functional compartments lipoproteins. Additionally, lipidomics must tackle the task of assigning the functions of lipids as signaling molecules, nutrient sensors, and intermediates of metabolic pathways.

Fish oil and the pan-PPAR agonist tetradecylthioacetic acid affect the amino acid and carnitine metabolism in rats

Peroxisome proliferator-activated receptors (PPARs) are important in the regulation of lipid and glucose metabolism. Recent studies have shown that PPARα-activation by WY 14,643 regulates the metabolism of amino acids. We investigated the effect of PPAR activation on plasma amino acid levels using two PPARα activators with different ligand binding properties, tetradecylthioacetic acid (TTA) and fish oil, where the pan-PPAR agonist TTA is a more potent ligand than omega-3 polyunsaturated fatty acids. In addition, plasma L-carnitine esters were investigated to reflect cellular fatty acid catabolism. Male Wistar rats (Rattus norvegicus) were fed a high-fat (25% w/w) diet including TTA (0.375%, w/w), fish oil (10%, w/w) or a combination of both. The rats were fed for 50 weeks, and although TTA and fish oil had hypotriglyceridemic effects in these animals, only TTA lowered the body weight gain compared to high fat control animals. Distinct dietary effects of fish oil and TTA were observed on plasma amino acid composition. Administration of TTA led to increased plasma levels of the majority of amino acids, except arginine and lysine, which were reduced. Fish oil however, increased plasma levels of only a few amino acids, and the combination showed an intermediate or TTA-dominated effect. On the other hand, TTA and fish oil additively reduced plasma levels of the L-carnitine precursor γ-butyrobetaine, as well as the carnitine esters acetylcarnitine, propionylcarnitine, valeryl/isovalerylcarnitine, and octanoylcarnitine. These data suggest that while both fish oil and TTA affect lipid metabolism, strong PPARα activation is required to obtain effects on amino acid plasma levels. TTA and fish oil may influence amino acid metabolism through different metabolic mechanisms.