Fish oil supplementation ameliorates fructose-induced hypertriglyceridemia and insulin resistance in adult male rhesus macaques

Circulating levels of adropin and diabetes: a systematic review and meta-analysis of observational studies

OBJECTIVE

Adropin, a newly identified regulatory protein has garnered attention given its potential role in metabolism regulation, especially glucose metabolism and insulin resistance. However, studies on the association between adropin and type 2 diabetes mellitus (T2DM) are equivocal. The aim of this study is to assess the association between serum adropin levels and T2DM using a systematic review and meta-analysis of observational studies.

METHODS

PubMed, Scopus, ISI Web of science, and Google Scholar were searched, up to August 2022, for studies that reported the association between serum levels of adropin in adults with T2DM compared to a control group without diabetes. A random-effect model was used to compute the pooled weighted mean difference (WMD) with 95% confidence intervals (CI).

RESULTS

Meta-analysis of 15 studies (n = 2813 participants) revealed that the serum adropin concentrations were significantly lower in patients with T2DM compared with the control group (WMD= -0.60 ng/mL, 95% CI: -0.70 to -0.49; I² = 99.5%). Subgroup analysis also found lower concentration of adropin in patients with T2DM who were otherwise healthy compared to a control group (n = 9; WMD=-0.04 ng/ml, 95% CI= -0.06 to -0.01, p = 0.002; I² = 96.4).

CONCLUSIONS

Our study showed adropin levels are lower in patients with diabetes compared to a control group without diabetes. However, the limitations of observational studies challenge the validity of the results, and further investigations are needed to confirm the veracity of these findings and additionally explore possible mechanisms.

The Influence of Diet on Metabolism and Health Across the Lifespan in Nonhuman Primates

The macro and micronutrient composition and the overall quantity of the diet are important predictors of physical and psychological health and, as a consequence, behavior. Translational preclinical models are critical to identifying the mechanisms underlying these relationships. Nonhuman primate models are particularly instrumental to this line of research as they exhibit considerable genetic, social, and physiological similarities, as well as similarities in their developmental trajectories to humans. This review aims to discuss recent contributions to the field of diet and metabolism and health using nonhuman primate models. The influence of diet composition on health and physiology across the lifespan will be the primary focus, including recent work examining the impact of maternal diet programming of offspring physiologic and behavioral developmental outcomes.

Hepatocyte expression of the micropeptide adropin regulates the liver fasting response and is enhanced by caloric restriction

The micropeptide adropin encoded by the clock-controlled energy homeostasis-associated gene is implicated in the regulation of glucose metabolism. However, its links to rhythms of nutrient intake, energy balance, and metabolic control remain poorly defined. Using surveys of Gene Expression Omnibus data sets, we confirm that fasting suppresses liver adropin expression in lean C57BL/6J (B6) mice. However, circadian rhythm data are inconsistent. In lean mice, caloric restriction (CR) induces bouts of compulsive binge feeding separated by prolonged fasting intervals, increasing NAD-dependent deacetylase sirtuin-1 signaling important for glucose and lipid metabolism regulation. CR up-regulates adropin expression and induces rhythms correlating with cellular stress-response pathways. Furthermore, adropin expression correlates positively with phosphoenolpyruvate carboxokinase-1 (Pck1) expression, suggesting a link with gluconeogenesis. Our previous data suggest that adropin suppresses gluconeogenesis in hepatocytes. Liver-specific adropin knockout (LAdrKO) mice exhibit increased glucose excursions following pyruvate injections, indicating increased gluconeogenesis. Gluconeogenesis is also increased in primary cultured hepatocytes derived from LAdrKO mice. Analysis of circulating insulin levels and liver expression of fasting-responsive cAMP-dependent protein kinase A (PKA) signaling pathways also suggests enhanced responses in LAdrKO mice during a glucagon tolerance test (250 µg/kg intraperitoneally). Fasting-associated changes in PKA signaling are attenuated in transgenic mice constitutively expressing adropin and in fasting mice treated acutely with adropin peptide. In summary, hepatic adropin expression is regulated by nutrient- and clock-dependent extrahepatic signals. CR induces pronounced postprandial peaks in hepatic adropin expression. Rhythms of hepatic adropin expression appear to link energy balance and cellular stress to the intracellular signal transduction pathways that drive the liver fasting response.

Maternal fats and pregnancy complications: Implications for long-term health

Pregnancy imposes increased nutritional requirements for the well being of the mother and fetus. Maternal lipid metabolism is critical for fetal development and long-term health of the offspring as it plays a key role in energy storage, tissue growth and cell signaling. Maternal fat composition is considered as a modifiable risk for abnormal lipid metabolism and glucose tolerance during pregnancy. Data derived from observational studies demonstrate that higher intake of saturated fats during pregnancy is associated with pregnancy complications (preeclampsia, gestational diabetes mellitus and preterm delivery) and poor birth outcomes (intra uterine growth retardation and large for gestational age babies). On the other hand, prenatal long chain polyunsaturated fatty acids status is shown to improve birth outome. In this article, we discuss the role of maternal lipids during pregnancy on fetal growth and development and its consequences on the health of the offspring.

Setting fire to fat

Adropin is a liver-secreted peptide that is crucial for metabolic health. However, the molecular functions and clinical significance of adropin have not been adequately explored. Butler et al. now investigate adropin expression profiles and links to cardiometabolic disease risk in two nonhuman primate models, increasing our translational and mechanistic understanding of this fascinating hormone.

Diets with low n-6:n-3 PUFA ratio protects rats from fructose-induced dyslipidemia and associated hepatic changes: Comparison between 18:3 n-3 and long-chain n-3 PUFA

In the present study, we investigated the impact of substituting alpha-linolenic acid (ALA) or long-chain n-3 PUFA (eicosapentaenoic acid and docosahexaenoic acid) for linoleic acid and hence decreasing n-6:n-3 PUFA ratio on high-fructose diet-induced hypertriglyceridemia and associated hepatic changes. Weanling male Wistar rats were divided into four groups and fed with starch-diet (n-6:n-3 PUFA ratio 215:1) and high-fructose diets with different n-6:n-3 PUFA ratio (215:1, 2:1 with ALA and 5:1 with long-chain n-3 PUFA) for twenty-four weeks. Substitution of linoleic acid with ALA (n-6:n-3 PUFA ratio of 2) or long-chain n-3 PUFA (n-6:n-3 PUFA ratio of 5) protected the rats from fructose-induced dyslipidemia, hepatic oxidative stress and corrected lipogenic and proinflammatory gene expression. Both ALA and long-chain n-3 PUFA supplementation also reversed the fructose-induced upregulation of 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) gene, which is involved in the generation of active glucocorticoids in tissues. Although both ALA and LC n-3 PUFA prevented fructose-induced dyslipidemia to a similar extent, compared to ALA, LC n-3 PUFA is more effective in preventing hepatic oxidative stress and inflammation.

Role of angiopoietin-like protein 3 in sugar-induced dyslipidemia in rhesus macaques: suppression by fish oil or RNAi

Angiopoietin-like protein 3 (ANGPTL3) inhibits lipid clearance and is a promising target for managing cardiovascular disease. Here we investigated the effects of a high-sugar (high-fructose) diet on circulating ANGPTL3 concentrations in rhesus macaques. Plasma ANGPTL3 concentrations increased ∼30% to 40% after 1 and 3 months of a high-fructose diet (both P < 0.001 vs. baseline). During fructose-induced metabolic dysregulation, plasma ANGPTL3 concentrations were positively correlated with circulating indices of insulin resistance [assessed with fasting insulin and the homeostatic model assessment of insulin resistance (HOMA-IR)], hypertriglyceridemia, adiposity (assessed as leptin), and systemic inflammation [C-reactive peptide (CRP)] and negatively correlated with plasma levels of the insulin-sensitizing hormone adropin. Multiple regression analyses identified a strong association between circulating APOC3 and ANGPTL3 concentrations. Higher baseline plasma levels of both ANGPTL3 and APOC3 were associated with an increased risk for fructose-induced insulin resistance. Fish oil previously shown to prevent insulin resistance and hypertriglyceridemia in this model prevented increases of ANGPTL3 without affecting systemic inflammation (increased plasma CRP and interleukin-6 concentrations). ANGPTL3 RNAi lowered plasma concentrations of ANGPTL3, triglycerides (TGs), VLDL-C, APOC3, and APOE. These decreases were consistent with a reduced risk of atherosclerosis. In summary, dietary sugar-induced increases of circulating ANGPTL3 concentrations after metabolic dysregulation correlated positively with leptin levels, HOMA-IR, and dyslipidemia. Targeting ANGPTL3 expression with RNAi inhibited dyslipidemia by lowering plasma TGs, VLDL-C, APOC3, and APOE levels in rhesus macaques.

Prevention of Potential Adverse Metabolic Effects of a Supplementation with Omega-3 Fatty Acids Using a Genetic Score Approach

INTRODUCTION

The consumption of long-chain omega-3 polyunsaturated fatty acids (n-3 PUFA) has been reported to have beneficial health effects, notably, by reducing plasma triglyceride levels. Nonetheless, a concomitant decrease in insulin sensitivity has also been observed, but is highly variable among subjects. Herein, we aimed to determine the importance of the genetic background in the interindividual variability of the insulin sensitivity response following an n-3 PUFA supplementation.

METHODS

A total of 210 participants completed a 6-week n-3 PUFA supplementation with 5 g/day of fish oil (providing 1.9-2.2 g of eicosapentaenoic acid + 1.1 g of docosahexaenoic acid). Insulin resistance was estimated by the homeostatic model assessment (HOMA-IR), and participants were further classified as high-risk or low-risk depending on their HOMA-IR change following the n-3 PUFA supplementation, as compared to pre-supplementation values. Genome-wide genotyping data were obtained for 138 participants using HumanOmni-5-Quad BeadChips containing 4,301,331 single nucleotide polymorphisms. A genome-wide association analysis (GWAS) was carried out between high-risk and low-risk participants. The population study was split into training (60%) and testing (40%) datasets to assess the predictive accuracy of a genetic risk score (GRS) constructed by summing the number of risk alleles.

RESULTS

Following the n-3 PUFA supplementation, 32 participants had increased HOMA-IR as compared to initial values and were classified as high risk (23.2%), whereas remaining subjects were classified as low risk (n = 106, 76.8%). A total of 8 loci had frequency differences between high-risk and low-risk participants at a suggestive GWAS association threshold (p value <1 × 10-5). After applying 10-fold cross validation, the GRS showed a significant association with the risk of increased HOMA-IR in the testing dataset (OR = 3.16 [95% CI, 1.85-7.14]), with a predictive accuracy of 0.85, and explained 40% of variation in HOMA-IR change.

CONCLUSIONS

These results suggest that the genetic background has a relevant role in the interindividual variability observed in the insulin sensitivity response following an n-3 PUFA supplementation. Subjects being at risk of insulin sensitivity lowering following an n-3 PUFA supplementation may be identified using genetic-based precision nutrition approaches.

Acute suppression of insulin resistance-associated hepatic miR-29 in vivo improves glycemic control in adult mice

MicroRNAs (miRNAs) are important posttranscriptional regulators of metabolism and energy homeostasis. Dysregulation of certain miRNAs in the liver has been shown to contribute to the pathogenesis of Type 2 diabetes (T2D), in part by impairing hepatic insulin sensitivity. By small RNA-sequencing analysis, we identified seven hepatic miRNAs (including miR-29b) that are consistently aberrantly expressed across five different rodent models of metabolic dysfunction that share the feature of insulin resistance (IR). We also showed that hepatic miR-29b exhibits persistent dysregulation during disease progression in a rat model of diabetes, UCD-T2DM. Furthermore, we observed that hepatic levels of miR-29 family members are attenuated by interventions known to improve IR in rodent and rhesus macaque models. To examine the function of the miR-29 family in modulating insulin sensitivity, we used locked nucleic acid (LNA) technology and demonstrated that acute in vivo suppression of the miR-29 family in adult mice leads to significant reduction of fasting blood glucose (in both chow-fed lean and high-fat diet-fed obese mice) and improvement in insulin sensitivity (in chow-fed lean mice). We carried out whole transcriptome studies and uncovered candidate mechanisms, including regulation of DNA methyltransferase 3a (Dnmt3a) and the hormone-encoding gene Energy homeostasis associated (Enho). In sum, we showed that IR/T2D is linked to dysregulation of hepatic miR-29b across numerous models and that acute suppression of the miR-29 family in adult mice leads to improved glycemic control. Future studies should investigate the therapeutic utility of miR-29 suppression in different metabolic disease states.Enho; insulin resistance; liver; microRNA-29 (miR-29); UCD-T2DM.

Low plasma adropin concentrations increase risks of weight gain and metabolic dysregulation in response to a high-sugar diet in male nonhuman primates

Mouse studies linking adropin, a peptide hormone encoded by the energy homeostasis-associated (ENHO) gene, to biological clocks and to glucose and lipid metabolism suggest a potential therapeutic target for managing diseases of metabolism. However, adropin's roles in human metabolism are unclear. In silico expression profiling in a nonhuman primate diurnal transcriptome atlas (GSE98965) revealed a dynamic and diurnal pattern of ENHO expression. ENHO expression is abundant in brain, including ventromedial and lateral hypothalamic nuclei regulating appetite and autonomic function. Lower ENHO expression is present in liver, lung, kidney, ileum, and some endocrine glands. Hepatic ENHO expression associates with genes involved in glucose and lipid metabolism. Unsupervised hierarchical clustering identified 426 genes co-regulated with ENHO in liver, ileum, kidney medulla, and lung. Gene Ontology analysis of this cluster revealed enrichment for epigenetic silencing by histone H3K27 trimethylation and biological processes related to neural function. Dietary intervention experiments with 59 adult male rhesus macaques indicated low plasma adropin concentrations were positively correlated with fasting glucose, plasma leptin, and apolipoprotein C3 (APOC3) concentrations. During consumption of a high-sugar (fructose) diet, which induced 10% weight gain, animals with low adropin had larger increases of plasma leptin and more severe hyperglycemia. Declining adropin concentrations were correlated with increases of plasma APOC3 and triglycerides. In summary, peripheral ENHO expression associates with pathways related to epigenetic and neural functions, and carbohydrate and lipid metabolism, suggesting co-regulation in nonhuman primates. Low circulating adropin predicts increased weight gain and metabolic dysregulation during consumption of a high-sugar diet.

Fructose-induced hypertriglyceridemia in rhesus macaques is attenuated with fish oil or ApoC3 RNA interference

Dyslipidemia and insulin resistance are significant adverse outcomes of consuming high-sugar diets. Conversely, dietary fish oil (FO) reduces plasma lipids. Diet-induced dyslipidemia in a rhesus model better approximates the pathophysiology of human metabolic syndrome (MetS) than rodent models. Here, we investigated relationships between metabolic parameters and hypertriglyceridemia in rhesus macaques consuming a high-fructose diet (n = 59) and determined the effects of FO supplementation or RNA interference (RNAi) on plasma ApoC3 and triglyceride (TG) concentrations. Fructose supplementation increased body weight, fasting insulin, leptin, TGs, and large VLDL particles and reduced adiponectin concentrations (all P < 0.001). In multiple regression analyses, increased plasma ApoC3 was the most consistent and significant variable related to diet-induced hypertriglyceridemia. FO supplementation, which attenuated increases of plasma TG and ApoC3 concentrations, reversed fructose-induced shifts of lipoprotein particle size toward IDL and VLDL, a likely mechanism contributing to beneficial metabolic effects, and reduced hepatic expression of genes regulated by the SREBP pathway, particularly acetyl-CoA carboxylase. Furthermore, RNAi-mediated ApoC3 inhibition lowered plasma TG concentrations in animals with diet-induced hypertriglyceridemia. In summary, ApoC3 is an important independent correlate of TG-rich lipoprotein concentrations in rhesus macaques consuming a high-fructose diet. ApoC3 is a promising therapeutic target for hypertriglyceridemia in patients with MetS and diabetes.

Docosahexaenoic Acid at 0.4% of Dietary Weight Enhances Lean Mass in Young Female Sprague-Dawley Rats

BACKGROUND

Docosahexaenoic acid (DHA; 22:6n-3) is an n-3 (ω-3) fatty acid known for beneficial effects on body composition.

OBJECTIVE

The objective of the study was to test the dose response of lean and fat mass to DHA in healthy growing female rats.

METHODS

Female Sprague-Dawley rats (7 wk at baseline; n = 12/diet) were randomly assigned to receive a control (AIN-93M; 60 g soybean oil/kg diet) or experimental diet for 10 wk. Experimental diets contained 0.1%, 0.4%, 0.8%, or 1.2% DHA (wt:wt of total diet). Imaging for whole-body and abdominal composition was conducted using dual-energy X-ray absorptiometry and microcomputed tomography, respectively, at weeks 0, 5, and 10. Fatty acid profiles of several tissues were analyzed using gas chromatography. Serum leptin, C-reactive protein, and plasma insulin-like growth factor I concentrations were measured at each time point using immunoassays. Data were tested using Pearson's correlations and mixed-model ANOVA.

RESULTS

No differences were observed in weight at baseline or food intake throughout the study. Overall, a 6% increase (P < 0.05) in whole-body and abdominal lean mass was observed in the 0.4%-DHA diet group compared with the control diet group. Moreover, the abdominal visceral fat mass was 31.4% lower in rats in the 0.4%-DHA than in the 1.2%-DHA diet group (P < 0.001). Rats in the 1.2%-DHA diet group showed greater percent differences in whole-body (32.5% and 40.6% higher) and in abdominal (33.9% and 49.4% higher) fat mass relative to the 0.1%- and 0.4%-DHA diet groups, respectively (P < 0.01). Accordingly, serum leptin concentration was lower in the 0.1%-DHA (38.2%) and 0.4%-DHA (43.8%) diet groups (P < 0.01) than in the 1.2%-DHA diet group and positively related to whole-body fat mass (r = 0.91, P < 0.0001).

CONCLUSION

Dietary DHA at 0.4% of dietary weight effectively enhances lean mass and proportionally reduces fat mass in growing female rats.

Nitro-fatty acids: New drug candidates for chronic inflammatory and fibrotic diseases

Nitrated oleic acid (NO₂-OA) was first identified in 2003, and after the characterization of its formation and thiol reactivity, it was used as a prototypical molecule to investigate the physiological actions of endogenous nitrated fatty acids (NO₂-FA). Based on in vitro observations showing significant activation of cytoprotective and anti-inflammatory signaling responses by NO₂-FA, experiments were designed to determine their pharmacological potential. Supported by strong intellectual protection and favorable pharmacokinetic and pharmacodynamic data, 10-NO₂-OA (CXA-10) underwent pharmaceutical development as a drug to treat fibrotic and inflammatory diseases. NO₂-FA are at the intersection of three unconventional drug candidate classes that include 1) fatty acids, 2) metabolic intermediates and 3) electrophilic molecules. These three groups use different scaffolds for drug development, are characterized by broad activities and are individually gaining traction as alternatives to mono-target drug therapies. In particular, NO₂-FA share key characteristics with currently approved pharmacological agents regarding reactivity, distribution, and mechanism of action. This review first presents the characteristics, liabilities, and opportunities that these different drug candidate classes display, and then discusses these issues in the context of current progress in the preclinical and clinical development of NO₂-FA as drugs. Lessons learned from the novel approaches presented herein were considered early on during development to structurally define and improve NO₂-FA and their disease targets.

Fructose and sugar: A major mediator of non-alcoholic fatty liver disease

Non-alcoholic fatty liver disease (NAFLD) is the hepatic manifestation of metabolic syndrome; its rising prevalence parallels the rise in obesity and diabetes. Historically thought to result from overnutrition and a sedentary lifestyle, recent evidence suggests that diets high in sugar (from sucrose and/or high-fructose corn syrup [HFCS]) not only increase the risk of NAFLD, but also non-alcoholic steatohepatitis (NASH). Herein, we review the experimental and clinical evidence that fructose precipitates fat accumulation in the liver, due to both increased lipogenesis and impaired fat oxidation. Recent evidence suggests that the predisposition to fatty liver is linked to the metabolism of fructose by fructokinase C, which results in ATP consumption, nucleotide turnover and uric acid generation that mediate fat accumulation. Alterations to gut permeability, the microbiome, and associated endotoxemia contribute to the risk of NAFLD and NASH. Early clinical studies suggest that reducing sugary beverages and total fructose intake, especially from added sugars, may have a significant benefit on reducing hepatic fat accumulation. We suggest larger, more definitive trials to determine if lowering sugar/HFCS intake, and/or blocking uric acid generation, may help reduce NAFLD and its downstream complications of cirrhosis and chronic liver disease.

Animal models of obesity and diabetes mellitus

More than one-third of the worldwide population is overweight or obese and therefore at risk of developing type 2 diabetes mellitus. In order to mitigate this pandemic, safer and more potent therapeutics are urgently required. This necessitates the continued use of animal models to discover, validate and optimize novel therapeutics for their safe use in humans. In order to improve the transition from bench to bedside, researchers must not only carefully select the appropriate model but also draw the right conclusions. In this Review, we consolidate the key information on the currently available animal models of obesity and diabetes and highlight the advantages, limitations and important caveats of each of these models.

Adropin: An endocrine link between the biological clock and cholesterol homeostasis

Objective

Identify determinants of plasma adropin concentrations, a secreted peptide translated from the Energy Homeostasis Associated (ENHO) gene linked to metabolic control and vascular function.

Methods

Associations between plasma adropin concentrations, demographics (sex, age, BMI) and circulating biomarkers of lipid and glucose metabolism were assessed in plasma obtained after an overnight fast in humans. The regulation of adropin expression was then assessed in silico, in cultured human cells, and in animal models.

Results

In humans, plasma adropin concentrations are inversely related to atherogenic LDL-cholesterol (LDL-C) levels in men (n = 349), but not in women (n = 401). Analysis of hepatic Enho expression in male mice suggests control by the biological clock. Expression is rhythmic, peaking during maximal food consumption in the dark correlating with transcriptional activation by RORα/γ. The nadir in the light phase coincides with the rest phase and repression by Rev-erb. Plasma adropin concentrations in nonhuman primates (rhesus monkeys) also exhibit peaks coinciding with feeding times (07:00 h, 15:00 h). The ROR inverse agonists SR1001 and the 7-oxygenated sterols 7-β-hydroxysterol and 7-ketocholesterol, or the Rev-erb agonist SR9009, suppress ENHO expression in cultured human HepG2 cells. Consumption of high-cholesterol diets suppress expression of the adropin transcript in mouse liver. However, adropin over expression does not prevent hypercholesterolemia resulting from a high cholesterol diet and/or LDL receptor mutations.

Conclusions

In humans, associations between plasma adropin concentrations and LDL-C suggest a link with hepatic lipid metabolism. Mouse studies suggest that the relationship between adropin and cholesterol metabolism is unidirectional, and predominantly involves suppression of adropin expression by cholesterol and 7-oxygenated sterols. Sensing of fatty acids, cholesterol and oxysterols by the RORα/γ ligand-binding domain suggests a plausible functional link between adropin expression and cellular lipid metabolism. Furthermore, the nuclear receptors RORα/γ and Rev-erb may couple adropin synthesis with circadian rhythms in carbohydrate and lipid metabolism.

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In male humans, plasma adropin concentrations are inversely related to low-density circulating cholesterol (LDL-C) levels.

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Adropin expression is regulated by core elements of the biological clock (RORA/G, Rev-Erb).

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Sterol-sensing by the ROR ligand-binding domain provides a plausible link between adropin expression and lipid metabolism.

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In mouse liver, adropin expression is rhythmic and suppressed by exogenous (dietary) cholesterol.

Use and Importance of Nonhuman Primates in Metabolic Disease Research: Current State of the Field

Obesity and its multiple metabolic sequelae, including type 2 diabetes, cardiovascular disease, and fatty liver disease, are becoming increasingly widespread in both the developed and developing world. There is an urgent need to identify new approaches for the prevention and treatment of these costly and prevalent metabolic conditions. Accomplishing this will require the use of appropriate animal models for preclinical and translational investigations in metabolic disease research. Although studies in rodent models are often useful for target/pathway identification and testing hypotheses, there are important differences in metabolic physiology between rodents and primates, and experimental findings in rodent models have often failed to be successfully translated into new, clinically useful therapeutic modalities in humans. Nonhuman primates represent a valuable and physiologically relevant model that serve as a critical translational bridge between basic studies performed in rodent models and clinical studies in humans. The purpose of this review is to evaluate the evidence, including a number of specific examples, in support of the use of nonhuman primate models in metabolic disease research, as well as some of the disadvantages and limitations involved in the use of nonhuman primates. The evidence taken as a whole indicates that nonhuman primates are and will remain an indispensable resource for evaluating the efficacy and safety of novel therapeutic strategies targeting clinically important metabolic diseases, including dyslipidemia and atherosclerosis, type 2 diabetes, hepatic steatosis, steatohepatitis, and hepatic fibrosis, and potentially the cognitive decline and dementia associated with metabolic dysfunction, prior to taking these therapies into clinical trials in humans.

Dietary fish oil differentially ameliorates high-fructose diet-induced hepatic steatosis and hyperlipidemia in mice depending on time of feeding

Chrononutrition is the science of nutrition based on chronobiology. Numerous epidemiological studies have shown that fish oil (FO) reduces the risk of cardiovascular events through various actions such as lowering triglycerides. The present study aimed to determine the time of day when the hypertriglyceridemia-decreasing ability of FO is optimal in mice. A high-fructose diet (HFrD) that induces hyperlipidemia in mice was replaced with the same diet containing 4% FO (HFrD-4% FO) at different times of the day for 2 weeks as described below. Mice were fed with HFrD alone (CTRL) or with HFrD containing 4% FO for 12 h around the time of activity onset [breakfast (BF)-FO] or offset [dinner (DN)-FO]. Plasma and liver concentrations of triglycerides and total cholesterol were reduced in BF-FO but not in DN-FO mice compared with CTRL mice. The temporal expression of genes associated with fatty acid synthesis such as Fasn, Acaca, Scd1 and Acly in the liver was significantly suppressed in both BF-FO and DN-FO mice. Expression levels of Scd1 in epididymal adipose tissue were significantly suppressed only in the BF-FO mice. Plasma concentrations of docosahexaenoic acid and eicosapentaenoic acid were far more increased in BF-FO than in DN-FO mice. Significantly more of these n-3 polyunsaturated fatty acids (PUFAs) were excreted in the feces of DN-FO than of BF-FO mice. These findings suggest that dietary FO exerts more hypolipidemic activity at the time of breakfast than dinner because the intestinal absorption of n-3 PUFAs is more effective at that time.

Impact of Fish Oil Supplementation and Interruption of Fructose Ingestion on Glucose and Lipid Homeostasis of Rats Drinking Different Concentrations of Fructose

Background. Continuous fructose consumption may cause elevation of circulating triacylglycerol. However, how much of this alteration is reverted after the removal of fructose intake is not known. We explored this question and compared the efficacy of this approach with fish oil supplementation. Methods. Male Wistar rats were divided into the following groups: control (C), fructose (F) (water intake with 10% or 30% fructose for 9 weeks), fish oil (FO), and fructose/fish oil (FFO). Fish oil was supplemented only for the last 33 days of fructose ingestion. Half of the F group remained for additional 8 weeks without fructose ingestion (FR). Results. Fructose ingestion reduced food intake to compensate for the increased energy obtained through water ingestion, independent of fructose concentration. Fish oil supplementation exerted no impact on these parameters, but the removal of fructose from water recovered both ingestion behaviors. Plasma triacylglycerol augmented significantly during the second and third weeks (both fructose groups). Fish oil supplementation did not attenuate the elevation in triacylglycerol caused by fructose intake, but the interruption of sugar consumption normalized this parameter. Conclusion. Elevation in triacylglyceridemia may be recovered by removing fructose from diet, suggesting that it is never too late to repair improper dietary habits.

Eicosapentaenoic acid (EPA) vs. Docosahexaenoic acid (DHA): Effects in epididymal white adipose tissue of mice fed a high-fructose diet

BACKGROUND

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) have been demonstrated to be beneficial for many diseases, including those associated with the metabolic syndrome (e.g. insulin resistance and hypertension). Nevertheless, not only their actions are not entirely understood, but also their only effects were not yet elucidated. Therefore, we aimed to compare the effects of EPA and DHA, alone or in combination, on the epididymal white adipose tissue (WAT) metabolism in mice fed a high-fructose diet.

METHODS

3-mo-old C57Bl/6 mice were fed a control diet (C) or a high-fructose diet (HFru). After three weeks on the diets, the HFru group was subdivided into four new groups for another five weeks: HFru, HFru+EPA, HFru+DHA, and HFru-EPA+DHA (n=10/group). Besides evaluating biometric and metabolic parameters of the animals, we measured the adipocyte area and performed molecular analyses (inflammation and lipolysis) in the epididymal WAT.

RESULTS

The HFru group showed adipocyte hypertrophy, inflammation, and uncontrolled lipolysis. The treated animals showed a reversion of adipocyte hypertrophy, inhibition of inflammation with activation of anti-inflammatory mediators, and regularization of lipolysis. Overall, the beneficial effects were more marked with DHA than EPA.

CONCLUSION

Although the whole-body metabolic effects were similar between EPA and DHA, DHA appeared to be the central actor in WAT metabolism, modulating pro and anti-inflammatory pathways and alleviating adipocytes abnormalities. Therefore, when considering fructose-induced adverse effects in WAT, the most prominent actions were observed with DHA.

Maternal plasma polyunsaturated fatty acid levels during pregnancy and childhood lipid and insulin levels

BACKGROUND AND AIMS

Maternal polyunsaturated fatty acid (PUFA) levels are associated with cord blood lipid and insulin levels. Not much is known about the influence of maternal PUFAs during pregnancy on long-term offspring lipid and insulin metabolism. We examined the associations of maternal plasma n-3 and n-6 PUFA levels during pregnancy with childhood lipid and insulin levels.

METHODS AND RESULTS

In a population-based prospective cohort study, among 3230 mothers and their children, we measured maternal second trimester n-3 and n-6 PUFA plasma levels. At the median age of 6.0 years (95% range, 5.6-7.9), we measured childhood total-cholesterol, high-density lipoprotein (HDL)-cholesterol, low-density lipoprotein (LDL)-cholesterol, triglyceride, insulin and c-peptide levels. Higher maternal total n-3 PUFA levels, and specifically DHA levels, were associated with higher childhood total-cholesterol, HDL-cholesterol and insulin levels (p-values <0.05), but not with LDL-cholesterol and triglycerides. Maternal total n-6 PUFA levels were not associated with childhood outcomes, but higher levels of the individual n-6 PUFAs, EDA and DGLA were associated with a lower childhood HDL-cholesterol, and higher AA levels with higher childhood total-cholesterol and HDL-cholesterol levels (all p-values <0.05). A higher maternal n-6/n-3 PUFA ratio was only associated with lower childhood HDL-cholesterol and insulin levels (p-values <0.05). These associations were not explained by childhood body mass index.

CONCLUSIONS

Higher maternal total n-3 PUFAs and specifically DHA levels during pregnancy are associated with higher childhood total-cholesterol, HDL-cholesterol and insulin levels. Only individual maternal n-6 PUFAs, not total maternal n-6 PUFA levels, tended to be associated with childhood lipid and insulin levels.

Adropin- A Novel Biomarker of Heart Disease: A Systematic Review Article

BACKGROUND

Heart disease is one of the most common chronic disease and leading cause of morbidity and mortality worldwide. Adropin, a newly identified protein, is important for energy homeostasis and maintaining insulin sensitivity, and has been referred to as a novel regulator of endothelial cells. Endothelial dysfunction is a key early event in atherogenesis and onset of HD. Therefore, this review gives a systematic overview of studies investigating plasma adropin level in patient with heart disease.

METHODS

Data carried out in PubMed, Scopus, Web of Science, Embase, Google scholar and MEDLINE, from the earliest available online indexing year through 2015. The search restricted to studies conducted in humans. The keyword search was adropin to apply in title, abstract and keywords. References lists of all original published articles were scanned to find additional eligible studies.

RESULTS

Heart failure (HF), coronary atherosclerosis acute myocardial infarction and Cardiac Syndrome X (CSX) were type of heart disease acknowledged in this study. Majority of evidences introduced low adropin as an independent risk factor of heart disease. In a case-control study, the plasma level of adropin increased with the severity of HF.

CONCLUSION

Adropinmay be a potential serum biomarker for early diagnosis of HD.

Dietary omega-3 but not omega-6 fatty acids down-regulate maternal dyslipidemia induced oxidative stress: A three generation study in rats

BACKGROUND

Maternal nutrition modulates fetal metabolic programming and development later. Maternal dyslipidemia effects on oxidative stress (OS) in offsprings and its modulation by dietary fatty acids over generations remains to be elucidated. The objective of present study was to assess the long-term (three generations) effect of omega-3 fatty acids on OS under dyslipidemia.

METHODS

Weanling female Wistar rats were fed with control diet (7% lard), high fat diet (35% lard, HFL), high fat with fish oil (21% fish oil + 14% lard, HFF), high fat with canola oil (21% canola oil + 14% lard, HFC) and high fat with sunflower oil (21% sunflower oil + 14% lard, HFS). Following 60 days feeding, the female rats were mated with sexually matured males (fed normal chow diet) and continued with the above diet regimen during pregnancy and lactation. The pups after lactation were continued with their maternal diet for 60 days and subjected to mating and feeding trial as above for two generations. Serum lipid profiles, OS markers (lipid peroxidation, nitric oxide release and protein carbonyl) and antioxidant defence enzymes (catalase, SOD, glutathione peroxidase and glutathione transferase) were assessed in serum, liver and uterus of rats fed on experimental and control diets for three generations.

RESULTS

Feeding HFL diet increased blood lipids, OS and lowered the antioxidant enzymes activity in serum, liver and uterus (p < 0.05). The reduction in the antioxidant enzymes in HFL group were higher in third followed by second generation compared to first generation (p < 0.05). Omega-3 fatty acids prevented the dyslipidemia induced loss of antioxidant enzyme activities in serum, liver and uterus.

CONCLUSIONS

Our data show for the first time that offsprings born to dyslipidemic mothers' exhibit diminished enzymatic antioxidant defence and its progressive reduction in future generation, and dietary omega-3 fatty acids restore the enzymatic antioxidant defence in offsprings and suppress the markers of OS.

Insulin-Sensitizing Effects of Omega-3 Fatty Acids: Lost in Translation?

Omega-3 polyunsaturated fatty acids (n-3 PUFA) of marine origin, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), have been long studied for their therapeutic potential in the context of type 2 diabetes, insulin resistance, and glucose homeostasis. Glaring discordance between observations in animal and human studies precludes, to date, any practical application of n-3 PUFA as nutritional therapeutics against insulin resistance in humans. Our objective in this review is to summarize current knowledge and provide an up-to-date commentary on the therapeutic value of EPA and DHA supplementation for improving insulin sensitivity in humans. We also sought to discuss potential mechanisms of n-3 PUFA action in target tissues, in specific skeletal muscle, based on our recent work, as well as in liver and adipose tissue. We conducted a literature search to include all preclinical and clinical studies performed within the last two years and to comment on representative studies published earlier. Recent studies support a growing consensus that there are beneficial effects of n-3 PUFA on insulin sensitivity in rodents. Observational studies in humans are encouraging, however, the vast majority of human intervention studies fail to demonstrate the benefit of n-3 PUFA in type 2 diabetes or insulin-resistant non-diabetic people. Nevertheless, there are still several unanswered questions regarding the potential impact of n-3 PUFA on metabolic function in humans.

Systems Nutrigenomics Reveals Brain Gene Networks Linking Metabolic and Brain Disorders

Nutrition plays a significant role in the increasing prevalence of metabolic and brain disorders. Here we employ systems nutrigenomics to scrutinize the genomic bases of nutrient–host interaction underlying disease predisposition or therapeutic potential. We conducted transcriptome and epigenome sequencing of hypothalamus (metabolic control) and hippocampus (cognitive processing) from a rodent model of fructose consumption, and identified significant reprogramming of DNA methylation, transcript abundance, alternative splicing, and gene networks governing cell metabolism, cell communication, inflammation, and neuronal signaling. These signals converged with genetic causal risks of metabolic, neurological, and psychiatric disorders revealed in humans. Gene network modeling uncovered the extracellular matrix genes Bgn and Fmod as main orchestrators of the effects of fructose, as validated using two knockout mouse models. We further demonstrate that an omega-3 fatty acid, DHA, reverses the genomic and network perturbations elicited by fructose, providing molecular support for nutritional interventions to counteract diet-induced metabolic and brain disorders. Our integrative approach complementing rodent and human studies supports the applicability of nutrigenomics principles to predict disease susceptibility and to guide personalized medicine.

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Fructose promotes transcriptomic and epigenomic reprogramming to perturb brain networks linking metabolism and brain function.

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The extracellular matrix genes Bgn and Fmod emerge as key regulators of gene networks responsive to fructose.

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The omega-3 fatty acid DHA reverses fructose-induced genomic and network reprogramming.

Meng et al. report fructose as a powerful inducer of genomic and epigenomic variability with the capacity to reorganize gene networks critical for central metabolic regulation and neuronal processes in the brain; conversely, an omega-3 fatty acid, DHA, has the potential to normalize the genomic impact of fructose. Our findings help explain the pathogenic actions of fructose on prevalent metabolic and brain disorders and provide proof-of-concept for nutritional remedies supported by nutrigenomics evidence. Our integrative approach complementing rodent and human studies supports the applicability of nutrigenomics principles to predict disease susceptibility and to guide personalized medicine.

Comparative anti-inflammatory and lipid-normalizing effects of metformin and omega-3 fatty acids through modulation of transcription factors in diabetic rats

BACKGROUND

Emerging evidence suggests beneficial effects of omega-3 fatty acids on diabetic complications. The present study compared the progressive effects of metformin and flax/fish oil on lipid metabolism, inflammatory markers, and liver and renal function test markers in streptozotocin-nicotinamide-induced diabetic rats.

METHODS

Streptozotocin-induced diabetic rats were randomized into control and four diabetic groups: streptozotocin (STZ), metformin (200 mg/kg body weight (b.w)/day (D)), flax and fish oil (500 mg/kg b.w/D).

RESULTS

Metformin and flax and fish oil exhibited increased expression of transcription factor peroxisome proliferator-activated receptor γ while the treatment downregulated sterol regulatory element-binding protein 1 and nuclear factor kβ as compared to those of the STZ group. Apart from modulation of transcription factor expression, the expression of fatty acid synthase, long chain acyl CoA synthase, and malonyl-CoA-acyl carrier protein transacylase was lowered by flax/fish oil treatment. Serum cholesterol, triglycerides, and VLDL were also significantly reduced in the treatment groups as compared to those in the STZ group. Although pathological abnormalities were seen in the liver and kidneys of rats on metformin, no significant changes in liver/renal function markers were observed at day 15 and day 30 of the treatment groups. Flax/fish oil had protective effects toward pathological abnormalities in the liver and kidney. Flax/fish oil improved lipid profile and alkaline phosphatase at day 30 as compared to that at day 15.

CONCLUSIONS

The present study demonstrates potential beneficial effects of metformin and flax/fish oil intervention in improving serum lipid profile by regulating the expression of transcription factors and genes involved in lipid metabolism in diabetic rats. In addition, these interventions also lowered the expression of atherogenic cytokines. The protective effects of flax/fish oil are worth investigating in human subjects on metformin monotherapy.

A combined supplementation of vitamin B12and omega-3 fatty acids across two generations improves cardiometabolic variables in rats

Our earlier studies indicate that micronutrients (vitamin B₁₂, folic acid) and omega-3 fatty acids especially docosahexaenoic acid (DHA) are interlinked in one carbon cycle.

Differential Responses of Plasma Adropin Concentrations To Dietary Glucose or Fructose Consumption In Humans

Adropin is a peptide hormone encoded by the Energy Homeostasis Associated (ENHO) gene whose physiological role in humans remains incompletely defined. Here we investigated the impact of dietary interventions that affect systemic glucose and lipid metabolism on plasma adropin concentrations in humans. Consumption of glucose or fructose as 25% of daily energy requirements (E) differentially affected plasma adropin concentrations (P < 0.005) irrespective of duration, sex or age. Glucose consumption reduced plasma adropin from 3.55 ± 0.26 to 3.28 ± 0.23 ng/ml (N = 42). Fructose consumption increased plasma adropin from 3.63 ± 0.29 to 3.93 ± 0.34 ng/ml (N = 45). Consumption of high fructose corn syrup (HFCS) as 25% E had no effect (3.43 ± 0.32 versus 3.39 ± 0.24 ng/ml, N = 26). Overall, the effect of glucose, HFCS and fructose on circulating adropin concentrations were similar to those observed on postprandial plasma triglyceride concentrations. Furthermore, increases in plasma adropin levels with fructose intake were most robust in individuals exhibiting hypertriglyceridemia. Individuals with low plasma adropin concentrations also exhibited rapid increases in plasma levels following consumption of breakfasts supplemented with lipids. These are the first results linking plasma adropin levels with dietary sugar intake in humans, with the impact of fructose consumption linked to systemic triglyceride metabolism. In addition, dietary fat intake may also increase circulating adropin concentrations.

Aerobic exercise training-induced changes in serum adropin level are associated with reduced arterial stiffness in middle-aged and older adults

Aging-induced arterial stiffening is reduced by aerobic exercise training, and elevated production of nitric oxide (NO) participates in this effect. Adropin is a regulator of endothelial NO synthase and NO release, and circulating adropin level decreases with age. However, the effect of habitual aerobic exercise on circulating adropin levels in healthy middle-aged and older adults remains unclear. We sought to determine whether serum adropin level is associated with exercise training-induced changes in arterial stiffness. First, in a cross-sectional study, we investigated the association between serum adropin level and both arterial stiffness and cardiorespiratory fitness in 80 healthy middle-aged and older subjects (65.6 ± 0.9 yr). Second, in an intervention study, we examined the effects of 8-wk aerobic exercise training on serum adropin level and arterial stiffness in 40 healthy middle-aged and older subjects (67.3 ± 1.0 yr) divided into two groups: aerobic exercise training and sedentary controls. In the cross-sectional study, serum adropin level was negatively correlated with carotid β-stiffness (r = -0.437, P < 0.001) and positively correlated with plasma NOx level (r = 0.493, P < 0.001) and cardiorespiratory fitness (r = 0.457, P < 0.001). Serum adropin levels were elevated after the 8-wk aerobic exercise training intervention, and training-induced changes in serum adropin level were correlated with training-induced changes in carotid β-stiffness (r = -0.399, P < 0.05) and plasma NOx level (r = 0.623, P < 0.001). Thus the increase in adropin may participate in the exercise-induced reduction of arterial stiffness.

Vitamin B12 and omega-3 fatty acids together regulate lipid metabolism in Wistar rats

Our recent study indicates that maternal vitamin B12 and omega-3 fatty acid status influence plasma and erythrocyte fatty acid profile in dams. The present study examines the effects of prenatal and postnatal vitamin B12 and omega-3 fatty acid status on lipid metabolism in the offspring. Pregnant dams were divided into five groups: Control; Vitamin B12 deficient (BD); Vitamin B12 supplemented (BS); Vitamin B12 deficient group supplemented with omega-3 fatty acids (BDO); Vitamin B12 supplemented group with omega-3 fatty acids (BSO). The offspring were continued on the same diets till 3 month of age. Vitamin B12 deficiency increased cholesterol levels (p<0.01) but reduced docosahexaenoic acid (DHA) (p<0.05), liver mRNA levels of acetyl CoA carboxylase-1 (ACC-1) (p<0.05) and carnitine palmitoyltransferase-1 (CPT-1) (p<0.01) in the offspring. Omega-3 fatty acid supplementation to this group normalized cholesterol but not mRNA levels of ACC-1 and CPT-1. Vitamin B12 supplementation normalized the levels cholesterol to that of control but increased plasma triglyceride (p<0.01) and reduced liver mRNA levels of adiponectin, ACC-1, and CPT-1 (p<0.01 for all). Supplementation of both vitamin B12 and omega-3 fatty acid normalized triglyceride and mRNA levels of all the above genes. Prenatal and postnatal vitamin B12 and omega-3 fatty acids together play a crucial role in regulating the genes involved in lipid metabolism in adult offspring.

Maternal omega-3 fatty acids and micronutrients modulate fetal lipid metabolism: A review

It is well established that alterations in the mother's diet or metabolism during pregnancy has long-term adverse effects on the lipid metabolism in the offspring. There is growing interest in the role of specific nutrients especially omega-3 fatty acids in the pathophysiology of lipid disorders. A series of studies carried out in humans and rodents in our department have consistently suggested a link between omega-3 fatty acids especially docosahexaenoic acid and micronutrients (vitamin B12 and folic acid) in the one carbon metabolic cycle and its effect on the fatty acid metabolism, hepatic transcription factors and DNA methylation patterns. However the association of maternal intake or metabolism of these nutrients with fetal lipid metabolism is relatively less explored. In this review, we provide insights into the role of maternal omega-3 fatty acids and vitamin B12 and their influence on fetal lipid metabolism through various mechanisms which influence phosphatidylethanolamine-N-methyltransferase activity, peroxisome proliferator activated receptor, adiponectin signaling pathway and epigenetic process like chromatin methylation. This will help understand the possible mechanisms involved in fetal lipid metabolism and may provide important clues for the prevention of lipid disorders in the offspring.

A dose-response study of consuming high-fructose corn syrup-sweetened beverages on lipid/lipoprotein risk factors for cardiovascular disease in young adults

BACKGROUND

National Health and Nutrition Examination Survey data show an increased risk of cardiovascular disease (CVD) mortality with an increased intake of added sugar.

OBJECTIVE

We determined the dose-response effects of consuming beverages sweetened with high-fructose corn syrup (HFCS) at zero, low, medium, and high proportions of energy requirements (Ereq) on circulating lipid/lipoprotein risk factors for CVD and uric acid in adults [age: 18-40 y; body mass index (in kg/m(2)): 18-35].

DESIGN

We conducted a parallel-arm, nonrandomized, double-blinded intervention study in which adults participated in 3.5 inpatient days of baseline testing at the University of California Davis Clinical and Translational Science Center's Clinical Research Center. Participants then consumed beverages sweetened with HFCS at 0% (aspartame sweetened, n = 23), 10% (n = 18), 17.5% (n = 16), or 25% (n = 28) of Ereq during 13 outpatient days and during 3.5 inpatient days of intervention testing at the research center. We conducted 24-h serial blood collections during the baseline and intervention testing periods.

RESULTS

Consuming beverages containing 10%, 17.5%, or 25% Ereq from HFCS produced significant linear dose-response increases of lipid/lipoprotein risk factors for CVD and uric acid: postprandial triglyceride (0%: 0 ± 4; 10%: 22 ± 8; 17.5%: 25 ± 5: 25%: 37 ± 5 mg/dL, mean of Δ ± SE, P < 0.0001 effect of HFCS-dose), fasting LDL cholesterol (0%: -1.0 ± 3.1; 10%: 7.4 ± 3.2; 17.5%: 8.2 ± 3.1; 25%: 15.9 ± 3.1 mg/dL, P < 0.0001), and 24-h mean uric acid concentrations (0%: -0.13 ± 0.07; 10%: 0.15 ± 0.06; 17.5%: 0.30 ± 0.07; 25%: 0.59 ± 0.09 mg/dL, P < 0.0001). Compared with beverages containing 0% HFCS, all 3 doses of HFCS-containing beverages increased concentrations of postprandial triglyceride, and the 2 higher doses increased fasting and/or postprandial concentrations of non-HDL cholesterol, LDL cholesterol, apolipoprotein B, apolipoprotein CIII, and uric acid.

CONCLUSIONS

Consuming beverages containing 10%, 17.5%, or 25% Ereq from HFCS produced dose-dependent increases in circulating lipid/lipoprotein risk factors for CVD and uric acid within 2 wk. These results provide mechanistic support for the epidemiologic evidence that the risk of cardiovascular mortality is positively associated with consumption of increasing amounts of added sugars. This trial was registered at clinicaltrials.gov as NCT01103921.

Fish oil decreases hepatic lipogenic genes in rats fasted and refed on a high fructose diet

Fasting and then refeeding on a high-carbohydrate diet increases serum and hepatic triacylglycerol (TAG) concentrations compared to standard diets. Fructose is a lipogenic monosaccharide which stimulates de novo fatty acid synthesis. Omega-3 (n-3) fatty acids stimulate hepatic β-oxidation, partitioning fatty acids away from TAG synthesis. This study investigated whether dietary n-3 fatty acids from fish oil (FO) improve the hepatic lipid metabolic response seen in rats fasted and then refed on a high-fructose diet. During the post-prandial (fed) period, rats fed a FO rich diet showed an increase in hepatic peroxisome proliferator-activated receptor α (PPAR-α) gene expression and decreased expression of carbohydrate responsive element binding protein (ChREBP), fatty acid synthase (FAS) and microsomal triglyceride transfer protein (MTTP). Feeding a FO rich diet for 7 days prior to 48 h of fasting resulted in lower hepatic TAG, lower PPAR-α expression and maintenance of hepatic n-3 fatty acid content. Refeeding on a high fructose diet promoted an increase in hepatic and serum TAG and in hepatic PPAR-α, ChREBP and MTTP expression. FO did not prevent the increase in serum and hepatic TAG after fructose refeeding, but did decrease hepatic expression of lipogenic genes and increased the n-3 fatty acid content of the liver. n-3 Fatty acids can modify some components of the hepatic lipid metabolic response to later feeding with a high fructose diet.

The impact of the Bellagio Report on healthy agriculture, healthy nutrition, healthy people: scientific and policy aspects and the International Network of Centers for Genetics, Nutrition and Fitness for Health

The Bellagio Report on Healthy Agriculture, Healthy Nutrition, Healthy People was the result of a meeting held at the Rockefeller Foundation Bellagio Center in the fall of 2012. The meeting was science based but policy oriented. The Bellagio Report concluded that: (1) sugar consumption, especially in the form of high-energy fructose in soft drinks, poses a major and insidious health threat, particularly for children; (2) current diets in most populations, albeit with regional differences, are deficient in omega-3 fatty acids but too high in omega-6 fatty acid intake, and (3) not all calories are the same since calories from different sources (i.e. glucose or fructose or omega-6 or omega-3 fatty acids) have different metabolic and neurohormonal effects. This paper summarizes the scientific progress and policy actions that have occurred in these three areas. Genetic variation in populations and gene-nutrient interactions are fundamental concepts that need to be taken into consideration in growth and development and in the prevention and management of chronic noncommunicable diseases since there is enormous variation in both the frequency of genetic variants and dietary composition worldwide. Furthermore, this paper updates the Bellagio Report in terms of the scientific and policy aspects, both of which have expanded over the past 2 years, and describes the progress made in establishing an International Network of Centers for Genetics, Nutrition and Fitness for Health.

Therapeutic effects of adropin on glucose tolerance and substrate utilization in diet-induced obese mice with insulin resistance

Objective

The peptide hormone adropin regulates fuel selection preferences in skeletal muscle under fed and fasted conditions. Here, we investigated whether adropin treatment can ameliorate the dysregulation of fuel substrate metabolism, and improve aspects of glucose homeostasis in diet-induced obesity (DIO) with insulin resistance.

Methods

DIO C57BL/6 mice maintained on a 60% kcal fat diet received five intraperitoneal (i.p.) injections of the bioactive peptide adropin^34-76 (450 nmol/kg/i.p.). Following treatment, glucose tolerance and whole body insulin sensitivity were assessed and indirect calorimetry was employed to analyze whole body substrate oxidation preferences. Biochemical assays performed in skeletal muscle samples analyzed insulin signaling action and substrate oxidation.

Results

Adropin treatment improved glucose tolerance, enhanced insulin action and augmented metabolic flexibility towards glucose utilization. In muscle, adropin treatment increased insulin-induced Akt phosphorylation and cell-surface expression of GLUT4 suggesting sensitization of insulin signaling pathways. Reduced incomplete fatty acid oxidation and increased CoA/acetyl-CoA ratio suggested improved mitochondrial function. The underlying mechanisms appear to involve suppressions of carnitine palmitoyltransferase-1B (CPT-1B) and CD36, two key enzymes in fatty acid utilization. Adropin treatment activated pyruvate dehydrogenase (PDH), a rate-limiting enzyme in glucose oxidation, and downregulated PDH kinase-4 (PDK-4) that inhibits PDH. Along with these changes, adropin treatment downregulated peroxisome proliferator-activated receptor-gamma coactivator-1α that regulates expression of Cpt1b, Cd36 and Pdk4.

Conclusions

Adropin treatment of DIO mice enhances glucose tolerance, ameliorates insulin resistance and promotes preferential use of carbohydrate over fat in fuel selection. Skeletal muscle is a key organ in mediating adropin's whole-body effects, sensitizing insulin signaling pathways and altering fuel selection preference to favor glucose while suppressing fat oxidation.

Chronic oxytocin administration inhibits food intake, increases energy expenditure, and produces weight loss in fructose-fed obese rhesus monkeys

Despite compelling evidence that oxytocin (OT) is effective in reducing body weight (BW) in diet-induced obese (DIO) rodents, studies of the effects of OT in humans and rhesus monkeys have primarily focused on noningestive behaviors. The goal of this study was to translate findings in DIO rodents to a preclinical translational model of DIO. We tested the hypothesis that increased OT signaling would reduce BW in DIO rhesus monkeys by inhibiting food intake and increasing energy expenditure (EE). Male DIO rhesus monkeys from the California National Primate Research Center were adapted to a 12-h fast and maintained on chow and a daily 15% fructose-sweetened beverage. Monkeys received 2× daily subcutaneous vehicle injections over 1 wk. We subsequently identified doses of OT (0.2 and 0.4 mg/kg) that reduced food intake and BW in the absence of nausea or diarrhea. Chronic administration of OT for 4 wk (0.2 mg/kg for 2 wk; 0.4 mg/kg for 2 wk) reduced BW relative to vehicle by 3.3 ± 0.4% (≈0.6 kg; P < 0.05). Moreover, the low dose of OT suppressed 12-h chow intake by 26 ± 7% (P < 0.05). The higher dose of OT reduced 12-h chow intake by 27 ± 5% (P < 0.05) and 8-h fructose-sweetened beverage intake by 18 ± 8% (P < 0.05). OT increased EE during the dark cycle by 14 ± 3% (P < 0.05) and was associated with elevations of free fatty acids and glycerol and reductions in triglycerides suggesting increased lipolysis. Together, these data suggest that OT reduces BW in DIO rhesus monkeys through decreased food intake as well as increased EE and lipolysis.

SREBF1 gene variations modulate insulin sensitivity in response to a fish oil supplementation

BACKGROUND

An important inter-individual variability in the response of insulin sensitivity following a fish oil supplementation has been observed. The objective was to examine the associations between single nucleotide polymorphisms (SNPs) within sterol regulatory element binding transcription factor 1 (SREBF1) gene and the response of insulin sensitivity to a fish oil supplementation.

METHODS

Participants (n = 210) were recruited in the greater Quebec City area and followed a 6-week fish oil supplementation protocol (5 g/day: 1.9-2.2 g EPA; 1.1 g DHA). Insulin sensitivity was assessed by the quantitative insulin sensitivity check index (QUICKI). Three tag SNPs (tSNPs) within SREBF1 gene were genotyped according to TAQMAN methodology.

RESULTS

Three tSNPs (rs12953299, rs4925118 and rs4925115) covered 100% of the known genetic variability within SREBF1 gene. None of the three tSNPs was associated with either baseline fasting insulin concentrations (rs12953299, rs4925118 and rs4925115) (p = 0.29, p = 0.20 and p = 0.70, respectively) or QUICKI (p = 0.20, p = 0.18 and p = 0.76, respectively). The three tSNPs (rs12953299, rs4925118 and rs4925115) were associated with differences in the response of plasma insulin levels (p = 0.01, p = 0.005 and p = 0.004, respectively) and rs12953299 as well as rs4925115 were associated with the insulin sensitivity response (p = 0.009 and p = 0.01, respectively) to the fish oil supplementation, independently of the effects of age, sex and BMI.

CONCLUSIONS

The genetic variability within SREBF1 gene has an impact on the insulin sensitivity in response to a fish oil supplementation.

TRIAL REGISTRATION

clinicaltrials.gov: NCT01343342.

Three new players in energy regulation: preptin, adropin and irisin

Homeostasis of energy is regulated by genetic factors, food intake, and energy expenditure. When energy input is greater than expenditure, the balance is positive, which can lead to weight gain and obesity. When the balance is negative, weight is lost. Regulation of this homeostasis is multi-factorial, involving many orexigenic (appetite-stimulating) and anorexigenic (appetite-suppressing) peptide hormones. Peripheral tissues are now known to be involved in weight regulation and research on its endocrine characteristics proceeds apace. Preptin with 34 amino acids (MW 3948 Da), adropin with 43 amino acids and a molecular weight of (4999 Da), and irisin with 112 amino acids (12587 Da), are three newly discovered peptides critical for regulating energy metabolism. Preptin is synthesized primarily in pancreatic beta cells, and adropin mainly in the liver and brain, and many peripheral tissues. Irisin, however, is synthesized principally in the heart muscle, along with peripheral tissues, including salivary glands, kidney and liver. The prime functions of preptin and adropin include regulating carbohydrate, lipid and protein metabolisms by moderating glucose-mediated insulin release. Irisin is an anti-obesitic and anti-diabetic hormone regulating adipose tissue metabolism and glucose homeostasis by converting white to brown adipose tissue. This review offers a historical account of these discovery and function of these peptides, including their structure, and physiological and biochemical properties. Their roles in energy regulation will be discussed. Their measurement in biological fluids will be considered, which will lead to further discussion of their possible clinical value.