Rodent models of diet-induced obesity and sedentary lifestyle

The "lipotoxic footprint" of cardiac maladaptation in diet-induced obesity is poorly defined. We investigated how manipulation of dietary lipid and carbohydrate influenced potential lipotoxic species in the failing heart. In Wistar rats, contractile dysfunction develops at 48 weeks on a high-fat/high-carbohydrate "Western" diet, but not on low-fat/high-carbohydrate or high-fat diets. Cardiac content of the lipotoxic candidates--diacylglycerol, ceramide, lipid peroxide, and long-chain acyl-CoA species--was measured at different time points by high-performance liquid chromatography and biochemical assays, as was lipogenic capacity in the heart and liver by qRT-PCR and radiometric assays. Changes in membranes fluidity were also monitored using fluorescence polarization. We report that Western feeding induced a 40% decrease in myocardial palmitoleoyl-CoA content and a similar decrease in the unsaturated-to-saturated fatty acid ratio. These changes were associated with impaired cardiac mitochondrial membrane fluidity. At the same time, hepatic lipogenic capacity was increased in animals fed Western diet (+270% fatty acid elongase activity compared with high-fat diet), while fatty acid desaturase activity decreased over time. Our findings suggest that dysregulation of lipogenesis is a significant component of heart failure in diet-induced obesity.

Metabolic disorders such as obesity and type 2 diabetes (T2D) coincide with an increased expression of pro-inflammatory factors. The NLRP3 inflammasome is a complex that activates the pro-inflammatory cytokine IL-1β. (NOD-like receptor protein 3). Some nutrients, such as fatty acids, influence inflammatory processes. For example, in clinical studies, higher trans-palmitoyl acid (TP) concentrations coincide with lower adiposity and lower risk of developing T2D. This study aims to evaluate the effect of TP on NLRP3 expression in a rodent model of diet-induced obesity (DIO). C57BL/6J mice were fed ad libitum with a control or a high-fat diet (HFD), added with or without TP (3 g/kg diet), for 11 weeks. IL-1β was quantified in serum, and NLRP3-related gene expression was explored in epididymal adipose tissue. Despite increased weight gain in both high-fat groups, the high-fat TP group gained less weight than the high-fat group. In addition, NLRP3 and caspase-1 expression was higher in the HFD groups, but no differences were observed between the HFD and the HFD TP groups. Serum IL-1β levels were not different among groups. Diet supplementation with TP prevents weight gain and has a neutral influence over NLRP3 expression and IL-1β concentration in a DIO mice model.

Obesity is defined as increased adiposity, which leads to metabolic disease. The growth of adipose tissue depends on its capacity to expand through hyperplasia or hypertrophy, in order to buffer energy surplus. Also, during the establishment of obesity, adipose tissue expansion reflects adipose lipid metabolism (lipogenesis and/or lipolysis). It is well known that dietary factors can modify lipid metabolism promoting or preventing the development of metabolic abnormalities that concur with obesity. Trans-palmitoleic acid (TP), a biomarker of dairy consumption, has been associated with reduced adiposity in clinical studies. Thus, we aimed to evaluate the effect of TP over adiposity and lipid metabolism-related genes in a rodent model of diet-induced obesity (DIO). To fulfil this aim, we fed C57BL/6 mice with a Control or a High-Fat diet, added with or without TP (3 g/kg diet), during 11 weeks. Body weight and food intake were monitored, fat pads were weighted, histology of visceral adipose tissue was analysed and lipid metabolism-related gene expression was explored by qPCR. Results show that TP consumption prevented weight gain induced by high-fat diet, reduced visceral adipose tissue weight and adipocyte size, while increasing the expression of lipolytic molecules. In conclusion, we show for the first time that TP influences adipose tissue metabolism, specifically lipolysis, resulting in decreased adiposity and reduced adipocyte size in a DIO mice model.

Trans-palmitoleic acid prevents weight gain, but does not modify glucose homeostasis in a rodent model of diet-induced obesity

Objective: Lipoic Acid Synthase (LASY) was recently shown to play a critical role in inflammation, mitochondrial function and insulin resistance. In this study using a pharmacological inducer of LASY as a tool, we studied the effects of LASY induction in vivo in rodent models of obesity and type 2 diabetes. Methods: We identified a small molecule that increases LASY mRNA and lipoic acid levels in vitro. Effect of the inducer (compound 1) on body weight, food intake, energy expenditure and metabolic parameters was studied in rodent models of genetic and diet-induced obesity. Results: Compound 1 was identified as a transcriptional inducer of LASY. In vitro, compound 1 increased LASY mRNA expression, mitochondrial lipoic acid levels and improved mitochondrial function in cultured skeletal muscle cells. LASY mRNA and lipoic acid levels were significantly increased in skeletal muscle and adipose tissue of animals treated with compound 1. In genetic and diet-induced rodent models of obesity, treatment with compound 1 significantly reduced body weight gain and fat mass without changes in food intake. Whole-animal calorimetry revealed that compound 1-treated animals had a significant increase in energy expenditure over vehicle control. Compound 1 treatment was also accompanied by improvements in plasma metabolic parameters and increase in lean mass. Conclusion: Our data suggests that the benefical effects of compound 1 are mediated by increase in mitochondrial lipoic acid levels, although general effects on mitochondrial function cannot be ruled out. These results establish the in vivo relevance of LASY induction and show the potential of a peripheral mediated approach for achieving many of the desired effects in treating obesity. Future studies focusing on the mechanism(s) by which compound 1 exerts its beneficial effects will help to reveal if these benefits are specific to LASY induction or are due to non-specific effects on mitochondrial function.

Adipocyte death has been reported in both obese humans and rodents. However, its role in metabolic disorders, including insulin resistance, hepatic steatosis, and inflammation associated with obesity has not been studied. We now show using real-time reverse transcription-PCR arrays that adipose tissue of obese mice display a pro-apoptotic phenotype. Moreover, caspase activation and adipocyte apoptosis were markedly increased in adipose tissue from both mice with diet-induced obesity and obese humans. These changes were associated with activation of both the extrinsic, death receptor-mediated, and intrinsic, mitochondrial-mediated pathways of apoptosis. Genetic inactivation of Bid, a key pro-apoptotic molecule that serves as a link between these two cell death pathways, significantly reduced caspase activation, adipocyte apoptosis, prevented adipose tissue macrophage infiltration, and protected against the development of systemic insulin resistance and hepatic steatosis independent of body weight. These data strongly suggest that adipocyte apoptosis is a key initial event that contributes to macrophage infiltration into adipose tissue, insulin resistance, and hepatic steatosis associated with obesity in both mice and humans. Inhibition of adipocyte apoptosis may be a new therapeutic strategy for the treatment of obesity-associated metabolic complications.

Obesity has reached epidemic proportions worldwide and reports estimate that American children consume up to 25% of calories from snacks. Several animal models of obesity exist, but studies are lacking that compare high-fat diets (HFD) traditionally used in rodent models of diet-induced obesity (DIO) to diets consisting of food regularly consumed by humans, including high-salt, high-fat, low-fiber, energy dense foods such as cookies, chips, and processed meats. To investigate the obesogenic and inflammatory consequences of a cafeteria diet (CAF) compared to a lard-based 45% HFD in rodent models, male Wistar rats were fed HFD, CAF or chow control diets for 15 weeks. Body weight increased dramatically and remained significantly elevated in CAF-fed rats compared to all other diets. Glucose- and insulin-tolerance tests revealed that hyperinsulinemia, hyperglycemia, and glucose intolerance were exaggerated in the CAF-fed rats compared to controls and HFD-fed rats. It is well-established that macrophages infiltrate metabolic tissues at the onset of weight gain and directly contribute to inflammation, insulin resistance, and obesity. Although both high fat diets resulted in increased adiposity and hepatosteatosis, CAF-fed rats displayed remarkable inflammation in white fat, brown fat and liver compared to HFD and controls. In sum, the CAF provided a robust model of human metabolic syndrome compared to traditional lard-based HFD, creating a phenotype of exaggerated obesity with glucose intolerance and inflammation. This model provides a unique platform to study the biochemical, genomic and physiological mechanisms of obesity and obesity-related disease states that are pandemic in western civilization today.

The C57BL/6 mouse strain fed a high‐fat diet (HFD) with ~60% of kcals from fat (lard) is an established rodent model of diet‐induced obesity. To determine if there is an ideal start age or diet composition which enhances development of obesity phenotypes, two HFD patterns were initiated at 3, 6, or 9 weeks of age. The HFD varied in fat (F, amount and type) and sucrose (S), abbreviated as follows in percent energy: 45F30S (milkfat) and 60F10S (lard). The HFD fed mice were compared to mice fed a purified low‐fat control (17F7S). Body weight and food disappearance were assessed once weekly in the nine groups of mice (n=15–16/group). Half of the mice underwent a glucose tolerance test at 17 weeks of age and had serial DEXA measurements performed at 9, 15, and 19 weeks of age. Within 3–4 weeks, mice started on the HFD were significantly heavier than controls irrespective of the age the diet was started. Upon initiation of HFD at 6 or 9 weeks, mice rapidly increased their rate of weight gain and attained similar weight compared to 3 week HFD mice with the exception of 9 week 60F10S which failed to catch‐up by 19 weeks. Calculated energy intake was greatest in the first week following HFD initiation. Intake tended to be higher throughout the remainder of feeding in all HFD groups. DEXA measurements at 9 weeks of age revealed animals fed HFD for 3 or 6 weeks showed similar percent fat that was approximately double controls (17 vs 32%). By 15 and 19 weeks of age all HFD groups showed a doubling of percent fat compared to controls (22 vs 44%‐15 wk and 25 vs 46%‐19 wk). Independent of start age, GTT at 17 weeks revealed HFD fed mice were glucose intolerant compared to control animals with a 60% increase in glucose area under the curve. In summary, these two HFD diet patterns produced similar obesity phenotypes. The age at which these HFD were initiated did not impact the percent fat or glucose tolerance measured after 8–14 weeks of feeding.

The contribution of high fructose corn syrup (HFCS) to metabolic disorder and obesity, independent of high fat, energy-rich diets, is controversial. While high-fat diets are widely accepted as a rodent model of diet-induced obesity (DIO) and metabolic disorder, the value of HFCS alone as a rodent model of DIO is unclear. Impaired dopamine function is associated with obesity and high fat diet, but the effect of HFCS on the dopamine system has not been investigated. The objective of this study was to test the effect of HFCS on weight gain, glucose regulation, and evoked dopamine release using fast-scan cyclic voltammetry. Mice (C57BL/6) received either water or 10% HFCS solution in combination with ad libitum chow for 15 weeks. HFCS consumption with chow diet did not induce weight gain compared to water, chow-only controls but did induce glucose dysregulation and reduced evoked dopamine release in the dorsolateral striatum. These data show that HFCS can contribute to metabolic disorder and altered dopamine function independent of weight gain and high-fat diets.

Sex differences in rodent models of diet-induced obesity are still poorly documented, particularly regarding how central mechanisms vary between sexes in response to an obesogenic diet. Here, we wanted to determine whether obese phenotype and hypothalamic response to a high-fat diet (HFD) differed between male and female C57Bl/6J mice. Mice were exposed to either a 60% HFD or a standard diet first for both a long- (14 weeks) and shorter-periods of time (3, 7, 14 and 28 days). Analysis of the expression profile of key neuronal, glial and inflammatory hypothalamic markers was performed using RT-qPCR. In addition, astrocytic and microglial morphology was examined in the arcuate nucleus. Monitoring of body weight and composition revealed that body weight and fat mass gain appeared earlier and was more pronounced in male mice. After 14 weeks of HFD exposure, normalized increase of body weight reached similar levels between male and female mice. Overall, both sexes under HFD displayed a decrease of orexigenic neuropeptides expression while an increase in Pomc gene expression was observed only in female mice. In addition, changes in the expression of hypothalamic inflammatory markers were relatively modest. We also reported that the glial cell markers expression and morphology were affected by HFD in a sex- and time dependent manner, suggesting a more pronounced glial cell activation in female mice. Taken together, these data show that male and female mice responded differently to HFD exposure, both on short- and long-term and suggest that a strong inflammatory hypothalamic profile is not systematically present in diet-induced obesity models. Nevertheless, in addition to these present data, the underlying mechanisms should be deciphered in further investigations.

Berries and other anthocyanin-rich treatments have prevented weight gain and adiposity in rodent models of diet-induced obesity. Their efficacy may be explained by modulation of energy substrate utilization. However, this effect has never been translated to humans. The objective of this study was to evaluate the effects of berry intake on energy substrate use and glucoregulation in volunteers consuming a high-fat diet. Twenty-seven overweight or obese men were enrolled in a randomized, placebo-controlled crossover study with two treatment periods. Subjects were fed an investigator controlled, high-fat (40% of energy from fat) diet which contained either 600 g/day blackberries (BB, 1500 mg/day flavonoids) or a calorie and carbohydrate matched amount of gelatin (GEL, flavonoid-free control) for seven days prior to a meal-based glucose tolerance test (MTT) in combination with a 24 h stay in a room-sized indirect calorimeter. The washout period that separated the treatment periods was also seven days. The BB treatment resulted in a significant reduction in average 24 h respiratory quotient (RQ) (0.810 vs. 0.817, BB vs. GEL, p = 0.040), indicating increased fat oxidation. RQ during the MTT was significantly lower with the BB treatment (0.84) compared to GEL control (0.85), p = 0.004. A 4 h time isolation during dinner showed similar treatment effects, where RQ was reduced and fat oxidation increased with BB (0.818 vs. 0.836, 28 vs. 25 g, respectively; BB vs. GEL treatments). The glucose AUC was not different between the BB and GEL treatments during the MTT (3488 vs. 4070 mg·min/dL, respectively, p = 0.12). However, the insulin AUC was significantly lower with the BB compared to the GEL control (6485 vs. 8245 µU·min/mL, p = 0.0002), and HOMA-IR improved with BB (p = 0.0318). Blackberry consumption may promote increased fat oxidation and improved insulin sensitivity in overweight or obese males fed a high fat diet.

Role of human pregnane X receptor in high fat diet-induced obesity in pre-menopausal female mice

Nicotinamide improves glucose metabolism and affects the hepatic NAD-sirtuin pathway in a rodent model of obesity and type 2 diabetes

Maternal obesity is an adverse factor that affects the intrauterine environment during critical periods of fetal developmental causing adverse lifelong effects on offspring health. Several different interventions have been performed in animal models of obesity to ameliorate maternal conditions and consequently reduce the adverse effects on offspring. Our aim was to critically review studies involving murine models of obesity induced by high fat diet (HFD), assessing maternal outcomes during pregnancy and the related offspring conditions. We carried out a computerized literature search of PubMed and Medline. We identified eight studies that fulfilled the inclusion criteria and have performed interventions in pregnancy with natural, synthetized compounds, and lifestyle modifications. Metabolic profile and lipid metabolism were improved by inositols, resveratrol, germinated brown rice (GBR), and exercise in the mother. The offspring whose mother received resveratrol, adiponectin, GBR, and exercise, showed an improvement in leptin, triglycerides, adiponectin levels, and a decrease in insulin resistance. These experimental studies demonstrate that several interventions in pregnant rodents improve the metabolic profile of both the mother and the offspring. Clinical research could now explore the efficacy and safety of such interventions, interrupting the vicious circle that an obese mother generates a child prone to develop metabolic (and cardiovascular) disease in adult life.

The gut plays a significant role in the development of obesity, notably through peptide signaling to the brain. However, few studies have investigated intestinal function per se in a rodent model of diet-induced obesity (DIO). Our aim was to investigate intestinal secretomotor function and glucose transport in DIO and diet-resistant (DR) rat jejunum. Male outbred Sprague-Dawley rats were maintained on a medium high fat diet for 9-10 weeks and split into DIO and DR groups based on weight gain. Mucosal-submucosal preparations of the proximal jejunum were mounted in Ussing chambers and voltage-clamped at 0 mV. Glucose (10 mmol L(-1)), 2-deoxy-D-glucose (10 mmol L(-1)), and leptin (10 nmol L(-1)) were added to the luminal side of the tissue and veratridine (30 micromol L(-1)), bethanechol (100 micromol L(-1)), and forskolin (10 micromol L(-1)) were added to the basolateral side of the tissue. Secretomotor responses were significantly decreased in DIO jejunum compared to DR tissues. Glucose-stimulated increases in I(sc) in DR animals, that were sensitive to leptin inhibition, were significantly reduced in DIO rats. Decreased sodium glucose transporter-1 mediated glucose transport was accompanied by a concomitant increase in the expression of jejunal glucose transporter-2. These data suggest that submucosal nerve function is compromised in DIO rats and electrogenic glucose transport is significantly decreased. The latter may represent an adaptive response to limit nutrient absorption in the jejunum from DIO rats. However, the loss of secretomotor control may lead to an altered host defense with a resultant change in intestinal flora contributing to the maintenance of obesity.