Energy-restricted high-fat diets only partially improve markers of systemic and adipose tissue inflammation

Effects of chronic high fat diet on mediobasal hypothalamic satiety neuron function in POMC-Cre mice

OBJECTIVE

The prevalence of obesity has increased over the past three decades. Proopiomelanocortin (POMC) neurons in the hypothalamic arcuate nucleus (ARC) play a vital role in induction of satiety. Chronic consumption of high-fat diet is known to reduce hypothalamic neuronal sensitivity to hormones like leptin, thus contributing to the development and persistence of obesity. The functional and morphological effects of a high-calorie diet on POMC neurons and how these effects contribute to the development and maintenance of the obese phenotype are not fully understood. For this purpose, POMC-Cre transgenic mice model was exposed to high-fat diet (HFD) and at the end of a 3- and 6-month period, electrophysiological and morphological changes, and the role of POMC neurons in homeostatic nutrition and their response to leptin were thoroughly investigated.

METHODS

Effects of HFD on POMC-satiety neurons in transgenic mice models exposed to chronic high-fat diet were investigated using electrophysiological (patch-clamp), chemogenetic and Cre recombinase advanced technological methods. Leptin, glucose and lipid profiles were determined and analyzed.

RESULTS

In mice exposed to a high-fat diet for 6 months, no significant changes in POMC dendritic spine number or projection density from POMC neurons to the paraventricular hypothalamus (PVN), lateral hypothalamus (LH), and bed nucleus stria terminalis (BNST) were observed. It was revealed that leptin hormone did not change the electrophysiological activities of POMC neurons in mice fed with HFD for 6 months. In addition, chemogenetic stimulation of POMC neurons increased HFD consumption. In the 3-month HFD-fed group, POMC activation induced an orexigenic response in mice, whereas switching to a standard diet was found to abolish orexigenic behavior in POMC mice.

CONCLUSIONS

Chronic high fat consumption disrupts the regulation of POMC neuron activation by leptin. Altered POMC neuron activation abolished the neuron's characteristic behavioral anorexigenic response. Change in nutritional content contributes to the reorganization of developing maladaptations.

Dietary Macronutrients and Circulating Nonesterified Fatty Acids: A Secondary Analysis of the OMNI Heart Crossover Trial

BACKGROUND

Nonesterified fatty acids (NEFAs) play key roles in the pathophysiology of diabetes and cardiovascular disease.

OBJECTIVES

We sought to determine whether macronutrient content differences affect NEFA concentrations in a randomized crossover trial.

METHODS

Total NEFAs were measured from postintervention specimens of participants in the OMNI Heart trial (Optimal Macronutrient Intake Trial to Prevent Heart Disease). OMNI Heart compared 3 healthful diets to evaluate their effect on systolic blood pressure and serum LDL cholesterol: carbohydrate-rich diet (58% carbohydrate); protein-rich diet (25% protein), about half from plant sources; and a diet rich in unsaturated fatty acids (21% unsaturated fat), predominantly monounsaturated. The trial included 164 participants who consumed the 3 diets, each for 6 wk. Data were analyzed from the 156 participants with unthawed serum available from the week 6 visit for all diet periods. We used ANCOVA and generalized estimating equations (GEEs) to compare serum NEFA concentrations across the 3 diet periods.

RESULTS

The mean ± SD age of study participants was 52.9 ± 10.6 y and mean BMI was 30.3 ± 6.1 kg/m2. Fifty-five percent of participants were women and 55% were African American. Comparisons of adjusted mean serum NEFA concentrations after each diet intervention identified no statistically significant differences (58% carbohydrate: 0.144 ± 0.083 mEq/L; 25% protein: 0.143 ± 0.076 mEq/L; 21% unsaturated fat: 0.143 ± 0.084 mEq/L; ANCOVA, P = 0.99). Likewise, we observed no significant serum NEFA concentration difference by diet in adjusted GEE models. In adjusted models, serum NEFA concentrations were positively associated, as anticipated, with female sex and higher BMI.

CONCLUSIONS

In this randomized crossover trial, we observed nearly identical serum NEFA concentrations after each of 3 healthful diets, regardless of macronutrient content.

The Influence of Obesity and Weight Loss on the Bioregulation of Innate/Inflammatory Responses: Macrophages and Immunometabolism

Obesity is characterized by low-grade inflammation and more susceptibility to infection, particularly viral infections, as clearly demonstrated in COVID-19. In this context, immunometabolism and metabolic flexibility of macrophages play an important role. Since inflammation is an inherent part of the innate response, strategies for decreasing the inflammatory response must avoid immunocompromise the innate defenses against pathogen challenges. The concept “bioregulation of inflammatory/innate responses” was coined in the context of the effects of exercise on these responses, implying a reduction in excessive inflammatory response, together with the preservation or stimulation of the innate response, with good transitions between pro- and anti-inflammatory macrophages adapted to each individual’s inflammatory set-point in inflammatory diseases, particularly in obesity. The question now is whether these responses can be obtained in the context of weight loss by dietary interventions (low-fat diet or abandonment of the high-fat diet) in the absence of exercise, which can be especially relevant for obese individuals with difficulties exercising such as those suffering from persistent COVID-19. Results from recent studies are controversial and do not point to a clear anti-inflammatory effect of these dietary interventions, particularly in the adipose tissue. Further research focusing on the innate response is also necessary.

Caloric Restriction Prevents Metabolic Dysfunction and the Changes in Hypothalamic Neuropeptides Associated with Obesity Independently of Dietary Fat Content in Rats

Energy restriction is a first therapy in the treatment of obesity, but the underlying biological mechanisms have not been completely clarified. We analyzed the effects of restriction of high-fat diet (HFD) on weight loss, circulating gut hormone levels and expression of hypothalamic neuropeptides. Ten-week-old male Wistar rats (n = 40) were randomly distributed into four groups: two fed ad libitum a normal diet (ND) (N group) or a HFD (H group) and two subjected to a 25% caloric restriction of ND (NR group) or HFD (HR group) for 9 weeks. A 25% restriction of HFD over 9 weeks leads to a 36% weight loss with regard to the group fed HFD ad libitum accompanied by normal values in adiposity index and food efficiency ratio (FER). This restriction also carried the normalization of NPY, AgRP and POMC hypothalamic mRNA expression, without changes in CART. Caloric restriction did not succeed in improving glucose homeostasis but reduced HFD-induced hyperinsulinemia. In conclusion, 25% restriction of HFD reduced adiposity and improved metabolism in experimental obesity, without changes in glycemia. Restriction of the HFD triggered the normalization of hypothalamic NPY, AgRP and POMC expression, as well as ghrelin and leptin levels.

High Fat Rodent Models of Type 2 Diabetes: From Rodent to Human

Poor dietary habits contribute to increased incidences of obesity and related co-morbidities, such as type 2 diabetes (T2D). The biological, genetic, and pathological implications of T2D, are commonly investigated using animal models induced by a dietary intervention. In spite of significant research contributions, animal models have limitations regarding the translation to human pathology, which leads to questioning their clinical relevance. Important considerations include diet-specific effects on whole organism energy balance and glucose and insulin homeostasis, as well as tissue-specific changes in insulin and glucose tolerance. This review will examine the T2D-like phenotype in rodents resulting from common diet-induced models and their relevance to the human disease state. Emphasis will be placed on the disparity in percentages and type of dietary fat, the duration of intervention, and whole organism and tissue-specific changes in rodents. An evaluation of these models will help to identify a diet-induced rodent model with the greatest clinical relevance to the human T2D pathology. We propose that a 45% high-fat diet composed of approximately one-third saturated fats and two-thirds unsaturated fats may provide a diet composition that aligns closely to average Western diet macronutrient composition, and induces metabolic alterations mirrored by clinical populations.

Fortifying diet with rapeseed oil instead of butterfat attenuates the progression of diet-induced non-alcoholic fatty liver disease (NAFLD) and impairment of glucose tolerance

BACKGROUND

Absolute dietary fat intake but even more so fatty acid pattern is discussed to be critical in the development of non-alcoholic fatty liver disease (NAFLD). Here, we determined if switching a butterfat enriched diet to a rapeseed oil (RO) enriched diet affects progression of an existing NAFLD and glucose intolerance in mice.

METHODS

For eight weeks, female C57Bl/6J mice were either fed a liquid control (C) or a butterfat-, fructose- and cholesterol-rich diet (BFC, 25E% butterfat) to induce early signs of steatohepatitis and glucose intolerance in mice. For additional five weeks mice received either BFC or C or a fat-, fructose- and cholesterol-rich and control diet, in which butterfat was replaced with RO (ROFC and CRO). Markers of glucose metabolism, liver damage and intestinal barrier were assessed.

RESULTS

Exchanging butterfat with RO attenuated the progression of BFC diet-induced NAFLD and glucose intolerance. Beneficial effects of RO were associated with lower portal endotoxin levels and an attenuation of the induction of the toll-like receptor-4-dependent signaling cascades in liver. Peroxisome proliferator-activated receptor γ activity was induced in small intestine of ROFC-fed mice.

CONCLUSION

Taken together, exchanging butterfat with RO attenuated the progression of diet-induced steatohepatitis and glucose intolerance in mice.

Weight Regain in Formerly Obese Mice Hastens Development of Hepatic Steatosis Due to Impaired Adipose Tissue Function

OBJECTIVE

Weight regain after weight loss is common, and there is evidence to suggest negative effects on health because of weight cycling. This study sought to investigate the impact of weight regain in formerly obese mice on adipose tissue architecture and stromal cell function.

METHODS

A diet-switch model was employed for obesity induction, weight loss, and weight regain in mice. Flow cytometry quantified adipose tissue leukocytes in adipose tissue. Liver and adipose tissue depots were compared to determine tissue-specific effects of weight cycling.

RESULTS

Epididymal white adipose tissue of formerly obese mice failed to expand in response to repeat exposure to high-fat diet and retained elevated numbers of macrophages and T cells. Weight regain was associated with disproportionally elevated liver mass, hepatic triglyceride content, serum insulin concentration, and serum transaminase concentration. These effects occurred despite an extended 6-month weight loss cycle and they demonstrate that formerly obese mice maintain durable alterations in their physiological response to weight regain. Conditioned media from epididymal adipose tissue of formerly obese mice inhibited adipogenesis of 3T3-L1 preadipocytes, suggesting a potential mechanism to explain failed epididymal adipose tissue expansion during weight regain.

CONCLUSIONS

Metabolic abnormalities related to defects in adipose tissue expansion and ongoing dysfunction manifest in formerly obese mice during weight regain.

The Impact of Glucose-Based or Lipid-Based Total Parenteral Nutrition on the Free Fatty Acids Profile in Critically Ill Patients

Introduction: Our study aim was to assess how the macronutrient intake during total parenteral nutrition (TPN) modulates plasma total free fatty acids (FFAs) levels and individual fatty acids in critically ill patients. Method: Adult patients aged 18–80, admitted to the intensive care unit (ICU), who were indicated for TPN, with an expected duration of more than three days, were included in the study. Isoenergetic and isonitrogenous TPN solutions were given with a major non-protein energy source, which was glucose (group G) or glucose and lipid emulsions (Smof lipid; group L). Blood samples were collected on days 0, 1, 3, 6, 9, 14, and 28. Results: A significant decrease (p < 0.001) in total FFAs occurred in both groups with a bigger decrease in group G (p < 0.001) from day 0 (0.41 ± 0.19 mmol∙L⁻¹) to day 28 (0.10 ± 0.07 mmol∙L⁻¹). Increased palmitooleic acid and decreased linoleic and docosahexaenoic acids, with a trend of increased mead acid to arachidonic acid ratio, on day 28 were observed in group G in comparison with group L. Group G had an insignificant increase in leptin with no differences in the concentrations of vitamin E, triacylglycerides, and plasminogen activator inhibitor-1. Conclusion: Decreased plasma FFA in critically ill patients who receive TPN may result from increased insulin sensitivity with a better effect in group G, owing to higher insulin and glucose dosing and no lipid emulsions. It is advisable to include a lipid emulsion at the latest from three weeks of TPN to prevent essential fatty acid deficiency.

Maternal metabolic, immune, and microbial systems in late pregnancy vary with malnutrition in mice

Malnutrition is a global threat to pregnancy health and impacts offspring development. Establishing an optimal pregnancy environment requires the coordination of maternal metabolic and immune pathways, which converge at the gut. Diet, metabolic, and immune dysfunctions have been associated with gut dysbiosis in the nonpregnant individual. In pregnancy, these states are associated with poor pregnancy outcomes and offspring development. However, the impact of malnutrition on maternal gut microbes, and their relationships with maternal metabolic and immune status, has been largely underexplored. To determine the impact of undernutrition and overnutrition on maternal metabolic status, inflammation, and the microbiome, and whether relationships exist between these systems, pregnant mice were fed either a normal, calorically restricted (CR), or a high fat (HF) diet. In late pregnancy, maternal inflammatory and metabolic biomarkers were measured and the cecal microbiome was characterized. Microbial richness was reduced in HF mothers although they did not gain more weight than controls. First trimester weight gain was associated with differences in the microbiome. Microbial abundance was associated with altered plasma and gut inflammatory phenotypes and peripheral leptin levels. Taxa potentially protective against elevated maternal leptin, without the requirement of a CR diet, were identified. Suboptimal dietary conditions common during pregnancy adversely impact maternal metabolic and immune status and the microbiome. HF nutrition exerts the greatest pressures on maternal microbial dynamics and inflammation. Key gut bacteria may mediate local and peripheral inflammatory events in response to maternal nutrient and metabolic status, with implications for maternal and offspring health.

Free Fatty Acids' Level and Nutrition in Critically Ill Patients and Association with Outcomes: A Prospective Sub-Study of PermiT Trial

OBJECTIVES

The objectives of this study were to evaluate the clinical and nutritional correlates of high free fatty acids (FFAs) level in critically ill patients and the association with outcomes, and to study the effect of short-term caloric restriction (permissive underfeeding) on FFAs level during critical illness.

PATIENTS/METHOD

In this pre-planned sub-study of the PermiT (Permissive Underfeeding vs. Target Enteral Feeding in Adult Critically Ill Patients) trial, we included critically ill patients who were expected to stay for ≥14 days in the intensive care unit. We measured FFAs level on day 1, 3, 5, 7, and 14 of enrollment. Of 70 enrolled patients, 23 (32.8%) patients had high FFAs level (baseline FFAs level >0.45 mmol/L in females and >0.6 mmol/L in males).

RESULTS

Patients with high FFAs level were significantly older and more likely to be females and diabetics and they had lower ratio of partial pressure of oxygen to the fraction of inspired oxygen, higher creatinine, and higher total cholesterol levels than those with normal FFAs level. During the study period, patients with high FFAs level had higher blood glucose and required more insulin. On multivariable logistic regression analysis, the predictors of high baseline FFAs level were diabetes (adjusted odds ratio (aOR): 5.36; 95% confidence interval (CI): 1.56, 18.43, p = 0.008) and baseline cholesterol level (aOR, 4.29; 95% CI: 11.64, 11.19, p = 0.003). Serial levels of FFAs did not differ with time between permissive underfeeding and standard feeding groups. FFAs level was not associated with 90-day mortality (aOR: 0.49; 95% CI: 0.09, 2.60, p = 0.40).

CONCLUSION

We conclude that high FFAs level in critically ill patients is associated with features of metabolic syndrome and is not affected by short-term permissive underfeeding.

An integrative transcriptomic approach to identify depot differences in genes and microRNAs in adipose tissues from high fat fed mice

Obesity contributes to metabolic disorders such as diabetes and cardiovascular disease. Characterization of differences between the main adipose tissue depots, white (WAT) [including subcutaneous (SAT) and visceral adipose tissue (VAT)] and brown adipose tissue (BAT) helps to identify their roles in obesity. Thus, we studied depot-specific differences in whole transcriptome and miRNA profiles of SAT, VAT and BAT from high fat diet (HFD/45% of calories from fat) fed mice using RNA sequencing and small RNA-Seq. Using quantitative real-time polymerase chain reaction, we validated depot-specific differences in endoplasmic reticulum (ER) stress related genes and miRNAs using mice fed a HFD vs. low fat diet (LFD/10% of calories from fat). According to the transcriptomic analysis, lipogenesis, adipogenesis, inflammation, endoplasmic reticulum (ER) stress and unfolded protein response (UPR) were higher in VAT compared to BAT, whereas energy expenditure, fatty acid oxidation and oxidative phosphorylation were higher in BAT than in VAT of the HFD fed mice. In contrast to BAT, ER stress marker genes were significantly upregulated in VAT of HFD fed mice than the LFD fed mice. For the first time, we report depot specific differences in ER stress related miRNAs including; downregulation of miR-125b-5p, upregulation miR-143-3p, and miR-222-3p in VAT following HFD and upregulation of miR-30c-2-3p only in BAT following a HFD in mice than the LFD mice. In conclusion, HFD differentially regulates miRNAs and genes in different adipose depots with significant induction of genes related to lipogenesis, adipogenesis, inflammation, ER stress, and UPR in WAT compared to BAT.

Regulation and Functions of the Renin-Angiotensin System in White and Brown Adipose Tissue

The renin angiotensin system (RAS) is a major regulator of blood pressure, fluid, and electrolyte homeostasis. RAS precursor angiotensinogen (Agt) is cleaved into angiotensin I (Ang I) and II (Ang II) by renin and angiotensin converting enzyme (ACE), respectively. Major effects of Ang II, the main bioactive peptide of this system, is mediated by G protein coupled receptors, Angiotensin Type 1 (AGTR1, AT1R) and Type 2 (AGTR2, AT2R) receptors. Further, the discovery of additional RAS peptides such as Ang 1-7 generated by the action of another enzyme ACE2 identified novel functions of this complex system. In addition to the systemic RAS, several local RAS exist in organs such as the brain, kidney, pancreas, and adipose tissue. The expression and regulation of various components of RAS in adipose tissue prompted extensive research into the role of adipose RAS in metabolic diseases. Indeed, animal studies have shown that adipose-derived Agt contributes to circulating RAS, kidney, and blood pressure regulation. Further, mice overexpressing Agt have high blood pressure and increased adiposity characterized by inflammation, adipocyte hypertrophy, and insulin resistance, which can be reversed at least in part by RAS inhibition. These findings highlight the importance of this system in energy homeostasis, especially in the context of obesity. This overview article discusses the depot-specific functions of adipose RAS, genetic and pharmacological manipulations of RAS, and its applications to adipogenesis, thermogenesis, and overall energy homeostasis. © 2017 American Physiological Society. Compr Physiol 7:1137-1150, 2017.

Weight Changes and Metabolic Outcomes in Calorie-Restricted Obese Mice Fed High-Fat Diets Containing Corn or Flaxseed Oil: Physiological Role of Sugar Replacement with Polyphenol-Rich Grape

OBJECTIVE

Because diet components are important during dieting in obesity treatment, we examined possible beneficial effects of substituting corn oil and sugar with flaxseed oil and grape in calorie-restricted high-fat diets on weight changes as well as improvement in some metabolic markers and related gene expression.

METHODS

Seventy-five C57BL/6J male mice were given free access to a high-fat (36% of energy from fat) diet containing corn oil plus sugar (CO + S). After 11 weeks, 15 mice were sacrificed and another 60 were divided among 4 high-fat diet groups with 30% calorie restriction (CR) for the next 12 weeks. The diets contained corn oil (CO) or flaxseed oil (FO) with sugar (S) or grape (G).

RESULTS

Despite CR, a weight loss trend was observed only during the first 4 weeks in all groups. CR did not significantly increase SIRT1 gene expression. Higher liver weight was observed in mice consuming FO (p < 0.05). Proliferator-activated receptor gamma (PPARγ) expression decreased in FO + G-CR significantly and even with a reduction of adiposity and higher adiponectin levels, fasting blood sugar (FBS) was significantly higher than in CO + G-CR. Grape intake increased Peroxisome proliferator-activated receptor gamma coactivator 1-alpha (PGC-1α) expression and decreased insulin resistance in CO + G-CR.

CONCLUSIONS

Sugar replacement with polyphenol-rich grape along with CR improved glucose homeostasis, and substituting corn oil with flaxseed oil in obese mice reduced fat mass, but even with no change in adiponectin levels it could not decrease insulin resistance. However, none of the food item combinations facilitated weight reduction in the long-term CR. Therefore, regardless of the total calorie intake, different diet components and fat contents may have unexpected effects on metabolic regulation.

Plasminogen Activator Inhibitor-1 is Regulated Through Dietary Fat Intake and Heritability: Studies in Twins

In different pathophysiological conditions plasminogen activator inhibitor-1 (PAI-1) plasma concentrations are elevated. As dietary patterns are considered to influence PAI-1 concentration, we aimed to determine active PAI-1 plasma concentrations and mRNA expression in adipose tissue before and after consumption of a high-fat diet (HFD) and the impact of additive genetic effects herein in humans. For 6 weeks, 46 healthy, non-obese pairs of twins (aged 18–70) received a normal nutritionally balanced diet (ND) followed by an isocaloric HFD for 6 weeks. Active PAI-1 plasma levels and PAI-1 mRNA expression in subcutaneous adipose tissue were assessed after the ND and after 1 and 6 weeks of HFD. Active PAI-1 plasma concentrations and PAI-1 mRNA expression in adipose tissue were significantly increased after both 1 and 6 weeks of HFD when compared to concentrations determined after ND (p< .05), with increases of active PAI-1 being independent of gender, age, or changes of BMI and intrahepatic fat content, respectively. However, analysis of covariance suggests that serum insulin concentration significantly affected the increase of active PAI-1 plasma concentrations. Furthermore, the increase of active PAI-1 plasma concentrations after 6 weeks of HFD was highly heritable (47%). In contrast, changes in PAI-1 mRNA expression in fatty tissue in response to HFD showed no heritability and were independent of all tested covariates. In summary, our data suggest that even an isocaloric exchange of macronutrients — for example, a switch to a fat-rich diet — affects PAI-1 concentrations in humans and that this is highly heritable.

Macrophage Proliferation Sustains Adipose Tissue Inflammation in Formerly Obese Mice

Obesity causes dramatic proinflammatory changes in the adipose tissue immune environment, but relatively little is known regarding how this inflammation responds to weight loss (WL). To understand the mechanisms by which meta-inflammation resolves during WL, we examined adipose tissue leukocytes in mice after withdrawal of a high-fat diet. After 8 weeks of WL, mice achieved similar weights and glucose tolerance values as age-matched lean controls but showed abnormal insulin tolerance. Despite fat mass normalization, total and CD11c⁺ adipose tissue macrophage (ATM) content remained elevated in WL mice for up to 6 months and was associated with persistent fibrosis in adipose tissue. ATMs in formerly obese mice demonstrated a proinflammatory profile, including elevated expression of interferon-γ, tumor necrosis factor-α, and interleukin-1β. T-cell-deficient Rag1^-/- mice showed a degree of ATM persistence similar to that in WT mice, but with reduced inflammatory gene expression. ATM proliferation was identified as the predominant mechanism by which ATMs are retained in adipose tissue with WL. Our study suggests that WL does not completely resolve obesity-induced ATM activation, which may contribute to the persistent adipose tissue damage and reduced insulin sensitivity observed in formerly obese mice.

Skeletal muscle inflammation and insulin resistance in obesity

Obesity is associated with chronic inflammation, which contributes to insulin resistance and type 2 diabetes mellitus. Under normal conditions, skeletal muscle is responsible for the majority of insulin-stimulated whole-body glucose disposal; thus, dysregulation of skeletal muscle metabolism can strongly influence whole-body glucose homeostasis and insulin sensitivity. Increasing evidence suggests that inflammation occurs in skeletal muscle in obesity and is mainly manifested by increased immune cell infiltration and proinflammatory activation in intermyocellular and perimuscular adipose tissue. By secreting proinflammatory molecules, immune cells may induce myocyte inflammation, adversely regulate myocyte metabolism, and contribute to insulin resistance via paracrine effects. Increased influx of fatty acids and inflammatory molecules from other tissues, particularly visceral adipose tissue, can also induce muscle inflammation and negatively regulate myocyte metabolism, leading to insulin resistance.

Restriction on an energy-dense diet improves markers of metabolic health and cellular aging in mice through decreasing hepatic mTOR activity

Dietary restriction (DR) on a normal low-fat diet improves metabolic health and may prolong life span. However, it is still uncertain whether restriction of an energy-dense, high-fat diet would also be beneficial and mitigate age-related processes. In the present study, we determined biomarkers of metabolic health, energy metabolism, and cellular aging in obesity-prone mice subjected to 30% DR on a high-fat diet for 6 months. Dietary-restricted mice had significantly lower body weights, less adipose tissue, lower energy expenditure, and altered substrate oxidation compared to their ad libitum-fed counterparts. Hepatic major urinary proteins (Mup) expression, which is linked to glucose and energy metabolism, and biomarkers of metabolic health, including insulin, glucose, cholesterol, and leptin/adiponectin ratio, were likewise reduced in high-fat, dietary-restricted mice. Hallmarks of cellular senescence such as Lamp2a and Hsc70 that mediate chaperone-mediated autophagy were induced and mechanistic target of rapamycin (mTOR) signaling mitigated upon high-fat DR. In contrast to DR applied in low-fat diets, anti-oxidant gene expression, proteasome activity, as well as 5'-adenosine monophosphate-activated protein kinase (AMPK) activation were not changed, suggesting that high-fat DR may attenuate some processes associated with cellular aging without the induction of cellular stress response or energy deprivation.

High-Fat Diets Containing Different Amounts of n3 and n6 Polyunsaturated Fatty Acids Modulate Inflammatory Cytokine Production in Mice

Dysregulation of adipokines is a hallmark of obesity. Polyunsaturated fatty acids in fish oil may exert anti-inflammatory effects on adipose tissue mitigating the dysregulation of adipokines thereby preventing obesity. This study investigated the effects of high-fat diets containing different amounts of n3 polyunsaturated fatty acids (PUFA) on adiposity and adipokine production in mice. Mice were fed a low-fat or a high-fat diet with 16 or 45 % of energy from corn oil (low n3 PUFA) in comparison with a high-fat diet containing soybean or high-oleic sunflower oil (adequate n3 PUFA) or flaxseed or fish oil (high n3 PUFA) for 11 weeks. High-fat diets, regardless of types of oils, significantly increased body fat mass and body weights compared to the low-fat diet. Adipose fatty acid composition and contents reflected dietary fatty acid profiles. The high-fat fish oil diet significantly increased adiponectin and reduced leptin concentrations in both plasma and adipose tissue; it did not elevate plasma insulin concentration compared to the high-fat corn oil diet. All high-fat diets elevated concentrations of plasminogen activator inhibitor-1 (PAI-1) and monocyte chemoattractant protein-1 (MCP-1) but lowered resistin concentrations in both plasma and adipose tissue. In conclusion, fish oil may be beneficial in improving insulin sensitivity by upregulation of adiponectin and downregulation of leptin production; n3 and n6 PUFA do not play a role at the dietary levels tested in reducing adiposity and production of pro-inflammatory cytokines (leptin, PAI-1, MCP-1 and resistin) and anti-inflammatory cytokine adiponectin.

High-fat diet decreases energy expenditure and expression of genes controlling lipid metabolism, mitochondrial function and skeletal system development in the adipose tissue, along with increased expression of extracellular matrix remodelling- and inflammation-related genes

The aim of the present study was to identify the genes differentially expressed in the visceral adipose tissue in a well-characterised mouse model of high-fat diet (HFD)-induced obesity. Male C57BL/6J mice (n 20) were fed either HFD (189 % of energy from fat) or low-fat diet (LFD, 42 % of energy from fat) for 16 weeks. HFD-fed mice exhibited obesity, insulin resistance, dyslipidaemia and adipose collagen accumulation, along with higher levels of plasma leptin, resistin and plasminogen activator inhibitor type 1, although there were no significant differences in plasma cytokine levels. Energy intake was similar in the two diet groups owing to lower food intake in the HFD group; however, energy expenditure was also lower in the HFD group than in the LFD group. Microarray analysis revealed that genes related to lipolysis, fatty acid metabolism, mitochondrial energy transduction, oxidation-reduction, insulin sensitivity and skeletal system development were down-regulated in HFD-fed mice, and genes associated with extracellular matrix (ECM) components, ECM remodelling and inflammation were up-regulated. The top ten up- or down-regulated genes include Acsm3, mt-Nd6, Fam13a, Cyp2e1, Rgs1 and Gpnmb, whose roles in the deterioration of obesity-associated adipose tissue are poorly understood. In conclusion, the genes identified here provide new therapeutic opportunities for prevention and treatment of diet-induced obesity.

Aortic cholesterol accumulation correlates with systemic inflammation but not hepatic and gonadal adipose tissue inflammation in low-density lipoprotein receptor null mice

Inflammation is a major contributor to the development of atherosclerotic plaque, yet the involvement of liver and visceral adipose tissue inflammatory status in atherosclerotic lesion development has yet to be fully elucidated. We hypothesized that an atherogenic diet would increase inflammatory response and lipid accumulation in the liver and gonadal adipose tissue (GAT) and would correlate with systemic inflammation and aortic lesion formation in low-density lipoprotein (LDL) receptor null (LDLr-/-) mice. For 32 weeks, LDLr-/- mice (n = 10/group) were fed either an atherogenic (high saturated fat and cholesterol) or control (low fat and cholesterol) diet. Hepatic and GAT lipid content and expression of inflammatory factors were measured using standard procedures. Compared with the control diet, the atherogenic diet significantly increased hepatic triglyceride and total cholesterol (TC), primarily esterified cholesterol, and GAT triglyceride content. These changes were accompanied by increased expression of acyl-CoA synthetase long-chain family member 5, CD36, ATP-binding cassette, subfamily A, member 1 and scavenger receptor B class 1, and they decreased the expression of cytochrome P450, family 7 and subfamily a, polypeptide 1 in GAT. Aortic TC content was positively associated with hepatic TC, triglyceride, and GAT triglyceride contents as well as plasma interleukin 6 and monocyte chemoattractant protein-1 concentrations. Although when compared with the control diet, the atherogenic diet increased hepatic tumor necrosis factor α production, they were not associated with aortic TC content. These data suggest that the LDLr-/- mice responded to the atherogenic diet by increasing lipid accumulation in the liver and GAT, which may have increased inflammatory response. Aortic TC content was positively associated with systemic inflammation but not hepatic and GAT inflammatory status.

Adipose tissue metabolism and inflammation are differently affected by weight loss in obese mice due to either a high-fat diet restriction or change to a low-fat diet

Restriction of a high-fat diet (HFD) and a change to a low-fat diet (LFD) are two interventions that were shown to promote weight loss and improve parameters of metabolic health in obesity. Examination of the biochemical and molecular responses of white adipose tissue (WAT) to these interventions has not been performed so far. Here, male C57BL/6JOlaHsd mice, harboring an intact nicotinamide nucleotide transhydrogenase gene, were fed a purified 40 energy% HFD for 14 weeks to induce obesity. Afterward, mice were divided into three dietary groups: HFD (maintained on HFD), LFD (changed to LFD with identical ingredients), and HFD-CR (restricted to 70 % of the HFD). The effects of the interventions were examined after 5 weeks. Beneficial effects were seen for both HFD-CR and LFD (compared to HFD) regarding physiological parameters (body weight and fat mass) and metabolic parameters, including circulating insulin and leptin levels. Macrophage infiltration in WAT was reduced by both interventions, although more effectively by HFD-CR. Strikingly, molecular parameters in WAT differed between HFD-CR and LFD, with increased activation of mitochondrial carbohydrate and fat metabolism in HFD-CR mice. Our results confirm that restriction of the amount of dietary intake and reduction in the dietary energy content are both effective in inducing weight loss. The larger decrease in WAT inflammation and increase in mitochondrial carbohydrate metabolism may be due to a larger degree of energy restriction in HFD-CR, but could also be due to superior effectiveness of dietary restriction in weight loss strategies.

Modulation of adipose tissue inflammation by bioactive food compounds

Adipose tissue has an important endocrine function in the regulation of whole-body metabolism. Obesity leads to a chronic low-grade inflammation of the adipose tissue, which disrupts this endocrine function and results in metabolic derangements, such as type-2 diabetes. Dietary bioactive compounds, such as polyphenols and certain fatty acids, are known to suppress both systemic and adipose tissue inflammation and have the potential to improve these obesity-associated metabolic disorders. Mechanistically, polyphenolic compounds including non-flavonoids, such as curcumin and resveratrol, and flavonoids, such as catechins (tea-polyphenols), quercetin and isoflavones, suppress nuclear factor-κB (NF-κB) and mitogen-activated protein (MAP) kinases (MAPK) pathways while activating the 5' adenosine monophosphate-activated protein kinase (AMPK) pathway in adipose tissue. Dietary polyunsaturated fatty acids, such as eicosapentaenoic acid (EPA), docosahexaenoic acid (DHA), conjugated linoleic acid (CLA) and monounsaturated fatty acids (MUFA), such as oleic acid, also impart anti-inflammatory effects through several mechanisms. These include activation of AMPK and peroxisome proliferator-activated receptor gamma (PPAR-γ), as well as suppression of toll-like receptors (TLRs) and NF-κB pathway. This review discusses the major molecular mechanisms of dietary polyphenols and fatty acids, alone or in combination, which are responsible for adipose tissue-associated anti-inflammatory effects.

Lasting effects on body weight and mammary gland gene expression in female mice upon early life exposure to n-3 but not n-6 high-fat diets

Exposure to an imbalance of nutrients prior to conception and during critical developmental periods can have lasting consequences on physiological processes resulting in chronic diseases later in life. Developmental programming has been shown to involve structural and functional changes in important tissues. The aim of the present study was to investigate whether early life diet has a programming effect on the mammary gland. Wild-type mice were exposed from 2 weeks prior to conception to 6 weeks of age to a regular low-fat diet, or to high-fat diets based on either corn oil or flaxseed oil. At 6 weeks of age, all mice were shifted to the regular low-fat diet until termination at 10 weeks of age. Early life exposure to a high-fat diet, either high in n-6 (corn oil) or in n-3 (flaxseed oil) polyunsaturated fatty acids, did not affect birth weight, but resulted in an increased body weight at 10 weeks of age. Transcriptome analyses of the fourth abdominal mammary gland revealed differentially expressed genes between the different treatment groups. Exposure to high-fat diet based on flaxseed oil, but not on corn oil, resulted in regulation of pathways involved in energy metabolism, immune response and inflammation. Our findings suggest that diet during early life indeed has a lasting effect on the mammary gland and significantly influences postnatal body weight gain, metabolic status, and signaling networks in the mammary gland of female offspring.

Eicosanoids in metabolic syndrome

Chronic persistent inflammation plays a significant role in disease pathology of cancer, cardiovascular disease, and metabolic syndrome (MetS). MetS is a constellation of diseases that include obesity, diabetes, hypertension, dyslipidemia, hypertriglyceridemia, and hypercholesterolemia. Nonalcoholic fatty liver disease (NAFLD) is associated with many of the MetS diseases. These metabolic derangements trigger a persistent inflammatory cascade, which includes production of lipid autacoids (eicosanoids) that recruit immune cells to the site of injury and subsequent expression of cytokines and chemokines that amplify the inflammatory response. In acute inflammation, the transcellular synthesis of antiinflammatory eicosanoids resolve inflammation, while persistent activation of the autacoid-cytokine-chemokine cascade in metabolic disease leads to chronic inflammation and accompanying tissue pathology. Many drugs targeting the eicosanoid pathways have been shown to be effective in the treatment of MetS, suggesting a common linkage between inflammation, MetS and drug metabolism. The cross-talk between inflammation and MetS seems apparent because of the growing evidence linking immune cell activation and metabolic disorders such as insulin resistance, dyslipidemia, and hypertriglyceridemia. Thus modulation of lipid metabolism through either dietary adjustment or selective drugs may become a new paradigm in the treatment of metabolic disorders. This review focuses on the mechanisms linking eicosanoid metabolism to persistent inflammation and altered lipid and carbohydrate metabolism in MetS.

n-3 and n-6 polyunsaturated fatty acids differentially regulate adipose angiotensinogen and other inflammatory adipokines in part via NF-κB-dependent mechanisms

Excessive secretion of proinflammatory adipokines has been linked to metabolic disorders. We have previously documented anti-inflammatory effects of n-3 polyunsaturated fatty acids (n-3 PUFAs) in adipose tissue; however, the mechanisms by which these fatty acids regulate adipokine secretion remain unclear. Here, we determined differential effects of eicosapentaenoic acid (EPA, n-3 PUFA) vs. arachidonic acid (AA, n-6 PUFA) on expression and secretion of angiotensinogen (Agt), interleukin 6 (IL-6) and monocyte chemotactic protein (MCP-1) in 3T3-L1 adipocytes. While both PUFAs increased intracellular Agt protein and mRNA expression, Agt secretion into culture media was increased only by AA treatment, which in turn was prevented by co-treatment with EPA. At various AA/EPA ratios, increasing AA concentrations significantly increased secretion of the above three adipokines, whereas increasing EPA dose-dependently, while lowering AA, decreased their secretion. Moreover, IL-6 and MCP-1 were more significantly reduced by EPA treatment compared to Agt (IL-6>MCP>Agt). Next, we tested whether nuclear factor-κB (NF-κB), a major proinflammatory transcription factor, was involved in regulation of these adipokines by PUFAs. EPA significantly inhibited NF-κB activation compared to control or AA treatments. Moreover, EPA attenuated tumor necrosis factor-α-induced MCP-1 and further reduced its secretion in the presence of an NF-κB inhibitor. Taken together, we reported here novel beneficial effects of EPA in adipocytes. We demonstrated direct anti-inflammatory effects of EPA, which are at least in part due to the inhibitory effects of this n-3 PUFA on the NF-κB pathway in adipocytes. In conclusion, these studies further support beneficial effects of n-3 PUFAs in adipocyte inflammation and metabolic disorders.

Unconventional microarray design reveals the response to obesity is largely tissue specific: analysis of common and divergent responses to diet-induced obesity in insulin-sensitive tissues

Obesity is a chronic condition involving the excessive accumulation of adipose tissue that adversely affects all systems in the body. The aim of the present study was to employ an unbiased, genome-wide assessment of transcript abundance in order to identify common gene expression pathways within insulin-sensitive tissues in response to dietary-induced diabetes. Following 20 weeks of chow or high-fat feeding (60% kcal), age-matched mice underwent a euglycemic-hyperinsulinemic clamp to assess insulin sensitivity. High-fat-fed animals were obese and highly insulin resistant, disposing of ∼75% less glucose compared with their chow-fed counterparts. Tissues were collected, and gene expression was examined by microarray in 4 tissues known to exhibit obesity-related metabolic disturbances: white adipose tissue, skeletal muscle, liver, and heart. A total of 463 genes were differentially expressed between diets. Analysis of individual tissues showed skeletal muscle to exhibit the largest number of differentially expressed genes (191) in response to high-fat feeding, followed by adipose tissue (169), liver (115), and heart (65). Analyses revealed that the response of individual genes to obesity is distinct and largely tissue specific, with less than 10% of transcripts being shared among tissues. Although transcripts are largely tissue specific, a systems approach shows numerous commonly activated pathways, including those involved in signal transduction, inflammation, oxidative stress, substrate transport, and metabolism. This suggests a coordinated attempt by tissues to limit metabolic perturbations occurring in early-stage obesity. Many identified genes were associated with a variety of disorders, thereby serving as potential links between obesity and its related health risks.

The renin-angiotensin system: a link between obesity, inflammation and insulin resistance

The renin-angiotensin system (RAS) is classically known for its role in regulation of blood pressure, fluid and electrolyte balance. Recently, several local RASs in organs such as brain, heart, pancreas and adipose tissue have also been identified. Evidence from clinical trials suggests that in addition to anti-hypertensive effects, pharmacological inhibition of RAS also provides protection against the development of type-2 diabetes. Moreover, animal models with targeted inactivation of RAS genes exhibit improved insulin sensitivity and are protected from high-fat diet-induced obesity and insulin resistance. Because there is evidence for RAS overactivation in obesity, it is possible that RAS is a link between obesity and insulin resistance. This review summarizes the evidence and mechanistic insights on the associations between RAS, obesity and insulin resistance, with special emphasis on the role of adipose tissue RAS in the pathogenesis of metabolic derangements in obesity.

Overproduction of angiotensinogen from adipose tissue induces adipose inflammation, glucose intolerance, and insulin resistance

Although obesity is associated with overactivation of the white adipose tissue (WAT) renin-angiotensin system (RAS), a causal link between the latter and systemic insulin resistance is not established. We tested the hypothesis that overexpression of angiotensinogen (Agt) from WAT causes systemic insulin resistance via modulation of adipose inflammation. Glucose tolerance, systemic insulin sensitivity, and WAT inflammatory markers were analyzed in mice overexpressing Agt in the WAT (aP2-Agt mice). Proteomic studies and in vitro studies using 3T3-L1 adipocytes were performed to build a mechanistic framework. Male aP2-Agt mice exhibited glucose intolerance, insulin resistance, and lower insulin-stimulated glucose uptake by the skeletal muscle. The difference in glucose tolerance between genotypes was normalized by high-fat (HF) feeding, and was significantly improved by treatment with angiotensin-converting enzyme (ACE) inhibitor captopril. aP2-Agt mice also had higher monocyte chemotactic protein-1 (MCP-1) and lower interleukin-10 (IL-10) in the WAT, indicating adipose inflammation. Proteomic studies in WAT showed that they also had higher monoglyceride lipase (MGL) and glycerol-3-phosphate dehydrogenase levels. Treatment with angiotensin II (Ang II) increased MCP-1 and resistin secretion from adipocytes, which was prevented by cotreating with inhibitors of the nuclear factor-κB (NF-κB) pathway or nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. In conclusion, we show for the first time that adipose RAS overactivation causes glucose intolerance and systemic insulin resistance. The mechanisms appear to be via reduced skeletal muscle glucose uptake, at least in part due to Ang II-induced, NADPH oxidase and NFκB-dependent increases in WAT inflammation.

Immunity as a link between obesity and insulin resistance

Obesity is a major public health problem in the United States and worldwide. Further, obesity is causally linked to the pathogenesis of insulin resistance, metabolic syndrome and type-2 diabetes (T2D). A chronic low-grade inflammation occurring in adipose tissue is at least in part responsible for the obesity-induced insulin resistance. This adipose tissue inflammation is characterized by changes in immune cell populations giving rise to altered adipo/cytokine profiles, which in turn induces skeletal muscle and hepatic insulin resistance. Detailed molecular mechanisms of insulin resistance, adipose tissue inflammation and the implications of these findings on therapeutic strategies are discussed in this review.

Differential effect of weight loss with low-fat diet or high-fat diet restriction on inflammation in the liver and adipose tissue of mice with diet-induced obesity

OBJECTIVE

We studied the effects of weight loss induced by either a low-fat normal diet (ND) or restriction of high-fat diet (HFD) on hepatic steatosis, inflammation in the liver and adipose tissue (AT), and blood monocytes of obese mice.

METHODS

In mice with HFD-induced obesity, weight loss was achieved by switching from HFD to ND and maintaining on ND ad libitum or by restricting HFD intake to match body weight of mice with ND-induced weight loss. After diet interventions for 4 weeks, hepatic steatosis, hepatic and AT inflammation, and blood CD11c(+) monocytes were examined.

RESULTS

At 4 weeks after switching diets, body weight was reduced by 23% from baseline. To achieve the same reduced body weight required restricting calorie intake from HFD. Weight loss with either ND or HFD restriction decreased body fat mass and ameliorated liver steatosis; both effects were greater with ND-induced weight loss than HFD restriction-induced weight loss. Weight loss with ND but not HFD restriction normalized blood CD11c(+) monocytes and attenuated hepatic inflammation assessed by chemokine and CD11c expression. In contrast, weight loss with HFD restriction significantly reduced chemokine levels and CD11c(+) cells in AT compared to obese controls, and tended to reduce AT chemokines and CD11c(+) cells more than ND-induced weight loss.

CONCLUSION

In mice with diet-induced obesity, weight loss with ND was superior in alleviating hepatic inflammation and steatosis, whereas weight loss with HFD calorie restriction provided greater amelioration of AT inflammation.

(n-3) Fatty acids alleviate adipose tissue inflammation and insulin resistance: mechanistic insights

Obesity is associated with the metabolic syndrome, a significant risk factor for developing type 2 diabetes and cardiovascular diseases. Chronic low-grade inflammation occurring in the adipose tissue of obese individuals is causally linked to the pathogenesis of insulin resistance and the metabolic syndrome. Although the exact trigger of this inflammatory process is unknown, adipose tissue hypoxia, endoplasmic reticular stress, and saturated fatty acid-mediated activation of innate immune processes have been identified as important processes in these disorders. Furthermore, macrophages and T lymphocytes have important roles in orchestrating this immune process. Although energy restriction leading to weight loss is the primary dietary intervention to reverse these obesity-associated metabolic disorders, other interventions targeted at alleviating adipose tissue inflammation have not been explored in detail. In this regard, (n-3) PUFA of marine origin both prevent and reverse high-fat-diet-induced adipose tissue inflammation and insulin resistance in rodents. We provide an update on the pathogenesis of adipose tissue inflammation and insulin resistance in obesity and discuss potential mechanisms by which (n-3) PUFA prevent and reverse these changes and the implications in human health.

Dietary restriction of mice on a high-fat diet induces substrate efficiency and improves metabolic health

High energy intake and, specifically, high dietary fat intake challenge the mammalian metabolism and correlate with many metabolic disorders such as obesity and diabetes. However, dietary restriction (DR) is known to prevent the development of metabolic disorders. The current western diets are highly enriched in fat, and it is as yet unclear whether DR on a certain high-fat (HF) diet elicits similar beneficial effects on health. In this research, we report that HF-DR improves metabolic health of mice compared with mice receiving the same diet on an ad libitum basis (HF-AL). Already after five weeks of restriction, the serum levels of cholesterol and leptin were significantly decreased in HF-DR mice, whereas their glucose sensitivity and serum adiponectin levels were increased. The body weight and measured serum parameters remained stable in the following 7 weeks of restriction, implying metabolic adaptation. To understand the molecular events associated with this adaptation, we analyzed gene expression in white adipose tissue (WAT) with whole genome microarrays. HF-DR strongly influenced gene expression in WAT; in total, 8643 genes were differentially expressed between both groups of mice, with a major role for genes involved in lipid metabolism and mitochondrial functioning. This was confirmed by quantitative real-time reverse transcription-PCR and substantiated by increase in mitochondrial density in WAT of HF-DR mice. These results provide new insights in the metabolic flexibility of dietary restricted animals and suggest the development of substrate efficiency.