Two unhealthy dietary habits featuring a high fat content and a sucrose-containing beverage intake, alone or in combination, on inducing metabolic syndrome in Wistar rats and C57BL/6J mice

Sucrose overconsumption impairs AgRP neuron dynamics and promotes palatable food intake

Rapid gut-brain communication is critical to maintain energy balance and is disrupted in diet-induced obesity. In particular, the role of carbohydrate overconsumption in the regulation of interoceptive circuits in vivo requires further investigation. Here, we report that an obesogenic high-sucrose diet (HSD) selectively blunts silencing of hunger-promoting agouti-related protein (AgRP) neurons following intragastric delivery of glucose, whereas we previously showed that overconsumption of a high-fat diet (HFD) selectively attenuates lipid-induced neural silencing. By contrast, both HSD and HFD reversibly dampen rapid AgRP neuron inhibition following chow presentation and promote intake of more palatable foods. Our findings reveal that excess sugar and fat pathologically modulate feeding circuit activity in both macronutrient-dependent and -independent ways and thus may additively exacerbate obesity.

Chronic consumption of imbalance diets high in sucrose or fat induces abdominal obesity with different pattern of metabolic disturbances and lost in Langerhans cells population

AIM

Obesity is a worldwide health issue, associated with development of type 2 Diabetes Mellitus. The aim of this study is to analyze the effect of consumption of two hypercaloric diets on metabolic disturbance and beta cells damage.

MAIN METHODS

Male Wistar rats were subjected to twelve months consumption of three diets: a Control balanced diet (CTD, carbohydrates 58 %, proteins 29 %, lipids 13 %) and two hypercaloric diets, high in sucrose (HSD, carbohydrates 68 %, proteins 22 %, lipids 10 %) or high in fat (HFD, carbohydrates 31 %, proteins 14 %, lipids 55 %). Serum levels of glucose, triglycerides and free fatty acids were measured after zoometric parameters determination. Antioxidant enzymes activity and oxidative stress-marker were measured in pancreas tissue among histological analysis of Langerhans islets.

KEY FINDINGS

Although diets were hypercaloric, the amount of food consumed by rats decreased, resulting in an equal caloric consumption. The HSD induced hypertriglyceridemia and hyperglycemia with higher levels in free fatty acids (FFA, lipotoxicity); whereas HFD did not increased neither the triglycerides nor FFA, nevertheless the loss of islets' cell was larger. Both diets induced obesity with hyperglycemia and significant reduction in Langerhans islets size.

SIGNIFICANCE

Our results demonstrate that consumption of HSD induces more significant metabolic disturbances that HFD, although both generated pancreas damage; as well hypercaloric diet consumption is not indispensable to becoming obese; the chronic consumption of unbalanced diets (rich in carbohydrates or lipids) may lead to abdominal obesity with metabolic and functional disturbances, although the total amount of calories are similar.

High sugar but not high fat diet consumption induces hepatic metabolic disruption and up-regulation of mitochondrial fission-associated protein Drp1 in a model of moderate obesity

Identification of new modifications and the association with diet patterns are essential for the prevention of non-alcoholic fatty liver disease (NAFLD). To address this problem, we feed rats with high caloric diets based on high sucrose (HSD) and high fat (HFD) and analysed metabolic and mitochondrial alterations. Both diets induce moderated obesity and fat accumulation in the liver after 8, 10 and 12 months of diet. The HSD induces both hyperleptinemia and hyperinsulinemia, as well as up-regulation of transcription factors SRBEP1 and PPARγ along slight increase nitrosylation of proteins and increased mitochondrial fission. In contrast, HFD induced hyperleptinemia without changes in neither insulin levels nor oxidative stress, SREBP1, PPARγ, or mitochondrial dynamics. In conclusion, chronic consumption of high sucrose content diets induces more pathological and metabolic alteration in liver in comparison with consumption of high-fat content diets, although both induces obesity and liver steatosis in these animal models.

Chronic intake of high dietary sucrose induces sexually dimorphic metabolic adaptations in mouse liver and adipose tissue

Almost all effective treatments for non-alcoholic fatty liver disease (NAFLD) involve reduction of adiposity, which suggests the metabolic axis between liver and adipose tissue is essential to NAFLD development. Since excessive dietary sugar intake may be an initiating factor for NAFLD, we have characterized the metabolic effects of liquid sucrose intake at concentrations relevant to typical human consumption in mice. We report that sucrose intake induces sexually dimorphic effects in liver, adipose tissue, and the microbiome; differences concordant with steatosis severity. We show that when steatosis is decoupled from impairments in insulin responsiveness, sex is a moderating factor that influences sucrose-driven lipid storage and the contribution of de novo fatty acid synthesis to the overall hepatic triglyceride pool. Our findings provide physiologic insight into how sex influences the regulation of adipose-liver crosstalk and highlight the importance of extrahepatic metabolism in the pathogenesis of diet-induced steatosis and NAFLD.

β-Lapachone, an NQO1 activator, alleviates diabetic cardiomyopathy by regulating antioxidant ability and mitochondrial function

BACKGROUND

Diabetic cardiomyopathy (DC) is one of the major lethal complications in patients with diabetes mellitus (DM); however, no specific strategy for preventing or treating DC has been identified.

PURPOSE

This study aimed to investigate the effects of β-lapachone (Lap), a natural compound that increases antioxidant activity in various tissues, on DC and explore the underlying mechanisms.

STUDY DESIGN AND METHODS

As an in vivo model, C57BL/6 mice were fed with the high-fat diet (HF) for 10 weeks to induce type 2 DM. Mice were fed Lap with the HF or after 5 weeks of HF treatment to investigate the protective effects of Lap against DC.

RESULTS

In the two in vivo models, Lap decreased heart weight, increased heart function, reduced oxidative stress, and elevated mitochondrial content under the HF. In the in vitro model, palmitic acid (PA) was used to mimic the effects of an HF on the differentiated-cardiomyoblast cell line H9c2. The results demonstrated that Lap reduced PA-induced ROS production by increasing the expression of antioxidant regulators and enzymes, inhibiting inflammation, increasing mitochondrial activity, and thus reducing cell damage. Via the use of specific inhibitors and siRNA, the protective effects of Lap were determined to be mediated mainly by NQO1, Sirt1 and mitochondrial activity.

CONCLUSION

Heart damage in DM is usually caused by excessive oxidative stress. This study showed that Lap can protect the heart from DC by upregulating antioxidant ability and mitochondrial activity in cardiomyocytes. Lap has the potential to serve as a novel therapeutic agent for both the prevention and treatment of DC.

The Effect of Dietary Fat and Sucrose on Cognitive Functioning in Mice Lacking Insulin Signaling in Neuropeptide Y Neurons

Obesogenic diets can produce hippocampal insulin resistance and impairments to hippocampal-dependent cognition. This study investigated the effect of disrupted insulin signaling in Neuropeptide Y (NPY) neurons on diet-induced deficits in hippocampal-dependent memory. Wild-type mice and mice that had a targeted knockout of insulin receptors on NPY cells (IR^lox/lox;NPY^Cre/+) were given ad libitum access to a high-fat diet (high fat; HF), 10% sucrose solution (high sugar; HS), both high-fat diet and sucrose solution (high fat, high sugar; HFHS), or a normal fat control chow for 12 weeks. Mice were tested in the Morris Water Maze (MWM), a hippocampal-dependent spatial memory task. Glucose homeostasis was assessed via a glucose tolerance test. Independent of genotype, consumption of HF, but not HS, diet increased energy intake, body weight, and plasma leptin, and impaired glucose tolerance. Disrupted insulin signaling in NPY cells and dietary interventions did not significantly affect the ability of mice to learn the location of the platform in the MWM. However, for IR^lox/lox control mice, consumption of HF, but not HS, diet resulted in reduced time spent in the target quadrant during the probe trial, suggesting a hippocampal-dependent memory deficit. IR^lox/lox;NPY^Cre/+ mice had poor performance in the probe trial regardless of diet, suggesting a floor effect. This study did not find adverse effects of chronic sucrose intake on metabolic outcomes or hippocampal-dependent memory. These data also suggest that the effects of HF diet on hippocampal-dependent memory may be dependent on insulin signaling in hippocampal NPY cells.

Gut Microbiome Composition and Metabolic Status Are Differently Affected by Early Exposure to Unhealthy Diets in a Rat Model

Childhood is a critical stage of development during which diet can have profound influence on the microbiota–host interactions, leading to potentially lifelong impacts. This study aimed to investigate whether the consumption of cafeteria diet (CAFD) and sugary drinks during early rat life alters the structure of the gut microbial community and the metabolic activity. Four-week-old male Wistar rats (n = 27) were fed a standard chow diet with ad libitum access to water (CD) or to sucrose solution (HSD), and a third group was fed with CAFD and a sucrose solution for 14 weeks. HSD and CAFD consumption induced alterations in Firmicutes to Bacteroidetes ratio, Proteobacteria, and Verrucomicrobia. HSD increased the abundance of Barnesiella, whereas CAFD induced a depletion of Saccharibacteria. CAFD increased total white adipose tissue (WAT) weight (p < 0.0005) compared to CD. When CAFD was compared to HSD, a significant difference was found only for retroperitoneal WAT (p < 0.0005). Unhealthy diet-fed groups presented higher glucose (p < 0.0005), total cholesterol and creatinine serum levels (p < 0.005) compared to the CD rats. Early-life consumption of HSD, and of CAFD even more so, can have long-lasting negative effects on metabolic function. The gut microbiota communities were distinctively perturbed by diet composition.

Vitamin A deficiency indicating as low expression of LRAT may be a novel biomarker of primary hypertension

AIMS

Vitamin A (VA) deficiency triggers many diseases and is a worldwide nutrition problem. The Retinol acyltransferase (LRAT) is an indicator of VA storage function, and the relationship between LRAT and blood pressure level and the regulation mechanism will be elucidated.

METHODS

160 children aged 6-12 years were included, and the serum VA and, the transcription levels of LRAT and RARs, were measured. Spontaneously hypertensive rats (SHRs) and WKY rats were treated with VA deficiency (VAD) or normal (VAN) fodder for 20 weeks. LRAT, retinoic acid, renin angiotensin system (RAS) biomarkers, and the structure and function of the heart for SHRs were measured.

RESULTS

The serum retinol and serum retinol/BMI levels were lower in children in the low LRAT group (LRAT<P₅₀) compared with the high LRAT group (LRAT≥P₅₀)(0.82 μmol/L vs. 0.94 μmol/L, 0.04 vs. 0.05, all P < .01). Moreover, SBP, DBP, and Ang Ⅱ were lower in the low LRAT group (all P < .01). Compared with VAN-treated SHRs, LRAT, retinoic acid receptor alpha (RARα), ACE2, and Ang (1-7) protein expression levels were decreased, while ACE and AT1R expression levels were increased in VAD SHRs. Notably, heart weight (HW), left ventricle weight, the HW-to-body weight ratio and the left ventricle weight-to-body weight ratio were significantly increased in VAD SHRs compared with those in VAN SHRs (P < .01). Cardiomyocyte hypertrophy and ventricular fibrosis were significantly increased in VAD SHRs compared with those in VAN SHRs (both P < .01).

CONCLUSIONS

LRAT may be an important biomarker of vitamin A deficiency in target organs and may regulate BP by affecting RAS biomarkers.

An antidiabetic nutraceutical combination of red yeast rice (Monascus purpureus), bitter gourd (Momordica charantia), and chromium alleviates dedifferentiation of pancreatic β cells in db/db mice

Antidiabetic properties of red yeast rice, bitter gourd, and chromium have gained scientific support. This study aimed to test whether a nutraceutical combination of these 3 materials prevented dedifferentiation of pancreatic β cells. Male db/db mice (8 weeks of age) were allocated into four groups (DB, DB/L, DB/M, and DB/H; n = 8-10) and fed a high-fat diet containing 0%, 0.2%, 0.4%, or 1% nutraceutical, respectively, whereas wild-type mice receiving a standard diet served as a healthy control (C; n = 10). The nutraceutical contained 10 mg/g monacolin K, 165 µg/g chromium, and 300 mg/g bitter gourd. After 8-weeks dietary treatment, diabetic syndromes (including hyperglycemia, hyperphagia, excessive drinking, polyuria, glucosuria, albuminuria, and glucose intolerance), were improved by the nutraceutical in a dose-dependent fashion. Decreased insulin and increased glucagon in serum and pancreatic islets in db/db mice were abolished in the DB/H group. Furthermore, supplementation curtailed dedifferentiation of β cells, as evidenced by decreasing the dedifferentiation marker (Aldh1a3) and increasing β-cell-enriched genes and transcription factors (Ins1, Ins2, FOXO1, and NKX6.1), as well as nuclear localization of NKX6.1 in pancreatic islets when compared to the DB group. We concluded that this nutraceutical, a combination of Monascus purpureus, Momordica charantia, and chromium, could be used as an adjunct for type 2 diabetes treatment and delay disease progression by sustaining β-cell function.

Diet-induced rodent models of obesity-related metabolic disorders-A guide to a translational perspective

Diet is a critical element determining human health and diseases, and unbalanced food habits are major risk factors for the development of obesity and related metabolic disorders. Despite technological and pharmacological advances, as well as intensification of awareness campaigns, the prevalence of metabolic disorders worldwide is still increasing. Thus, novel therapeutic approaches with increased efficacy are urgently required, which often depends on cellular and molecular investigations using robust animal models. In the absence of perfect rodent models, those induced by excessive consumption of fat and sugars better replicate the key aspects that are the root causes of human metabolic diseases. However, the results obtained using these models cannot be directly compared, particularly because of the use of different dietary protocols, and animal species and strains, among other confounding factors. This review article revisits diet-induced models of obesity and related metabolic disorders, namely, metabolic syndrome, prediabetes, diabetes and nonalcoholic fatty liver disease. A critical analysis focused on the main pathophysiological features of rodent models, as opposed to the criteria defined for humans, is provided as a practical guide with a translational perspective for the establishment of animal models of obesity-related metabolic diseases.

Differential effect of high-fat, high-sucrose and combined high-fat/high-sucrose diets consumption on fat accumulation, serum leptin and cardiac hypertrophy in rats

The consumption of high calorie-content diets is the first cause of obesity, probably the main health issue worldwide; however, the experimental evidences for evaluating the differential metabolic modifications of high-sucrose or high-fat diets are scare. We evaluated the metabolic outcomes of the obesity induced by the chronic consumption of high-sucrose (HS), high-fat (HF) or combined diets (HSHF), among the effect on the development of cardiac hypertrophy in Wistar rats. Rats from the HS, HF, and HSHS groups developed moderate obesity. Only the HS group showed increased triglycerides levels after four months. Increased leptin levels were observed in HS and HF groups without changes on cardiac hypertrophy; on the opposing, HSHF group presented hypertrophy without the changes in serum leptin. The three experimental groups showed a decreased expression of leptin receptors ObR-b. In our results, the kind of diet for the induction of obesity is relevant for the outcome of the pathological profile.

Long-term sucrose solution consumption causes metabolic alterations and affects hepatic oxidative stress in Wistar rats

As the number of overweight and obese people has risen in recent years, there has been a parallel increase in the number of people with metabolic syndrome, diabetes and non-alcoholic fatty liver disease. The consumption of artificially sweetened beverages contributes to these epidemics. This study investigated the long-term effects of ingestion of a 40% sucrose solution on serum and hepatic parameters in male Wistar rats (Rattus norvegicus). After 180 days, the glycemic response, lipid profile and hepatic oxidative stress were compared to those of rats maintained on water. Sucrose ingestion led to higher body weight, increased fat deposits, reduced voluntary food intake and reduced feeding efficiency. Rats that received sucrose solution showed early signs of glucose intolerance and insulin resistance, such as hyperinsulinemia. Serum triacylglycerol (TG), very-low density lipoprotein (VLDL), cholesterol, ALT and AST levels increased after sucrose consumption. Elevated malondialdehyde and superoxide dismutase (SOD) levels and reduced glutathione levels characterize the hepatic oxidative stress due to sucrose ingestion. Liver sample histology showed vacuolar traces and increased fibrotic tissue. Our data showed the harmful effects of chronic consumption of sucrose solution, which can cause alterations that are found frequently in obesity, glucose intolerance and non-alcoholic hepatic disease, characteristics of metabolic syndrome.

Electric stimulation of ears accelerates body weight loss mediated by high-fat to low-fat diet switch accompanied by increased white adipose tissue browning in C57BL/6 J mice

Background

Weight reduction frequently occurs in patients receiving vagus nerve stimulation (VNS) therapy. Therefore, we hypothesized that during dietary intervention for weight loss, auricular electric stimulation (AES), an alternative of VNS, accelerates weight loss by increasing white adipose tissue (WAT) browning and increases energy expenditure.

Methods

C57BL/6J male mice were fed a high-fat diet for 5 wk. to induce obesity, then switched to a low-fat diet for 5 wk. and allocated into 3 groups to receive 2 Hz electric stimulation on ears, electrode clamps only, or nothing (AES, Sham and Ctrl, respectively).

Results

Switching to a low-fat diet reduced body weight progressively in all 3 groups, with the greatest reduction in the AES group. In accordance with a mild decrease in feed intake, hypothalamus mRNA levels of Npy, AgRP tended to be reduced, while Pomc tended to be increased by AES. Mice in the AES group had the highest concentrations of norepinephrine in serum and inguinal WAT, and expression levels of uncoupling protein-1 (UCP-1) and tyrosine hydroxylase in inguinal WAT. Furthermore, their subcutaneous adipocytes had multilocular and UCP-1⁺ characteristics, along with a smaller cell size.

Conclusion

AES, by increasing WAT browning, could be used in conjunction with a low-fat diet to augment weight loss in addition to suppressing appetite.

Dietary fish oil ameliorates adipose tissue dysfunction in insulin-resistant rats fed a sucrose-rich diet improving oxidative stress, peroxisome proliferator-activated receptor γ and uncoupling protein 2

This work aims to assess the possible beneficial effects of dietary fish oil (FO) on the pre-existing adipose tissue dysfunction through the improvement or reversion of the mechanisms underlying oxidative stress and pro-inflammatory cytokines in dyslipemic insulin-resistant rats. Wistar rats were fed a sucrose rich diet (SRD) for 6 months. After that half of the animals continued with the SRD until month 8 while in the other half corn oil was replaced by FO for 2 months (SRD + FO). A reference group consumed a control diet all the time. In an epididymal fat pad, we analyzed antioxidant and oxidant enzyme activities, ROS content, glutathione redox state, the protein level of peroxisome proliferator-activated receptor gamma (PPARγ) and the expression and protein levels of uncoupling protein 2 (UCP2) as well as oxidative stress biomarkers and TNF-α and IL-6 plasma levels. Besides these, insulin sensitivity and the composition of fatty acid phospholipids of adipose tissue were measured. Compared with the SRD the SRD + FO fed group showed a decrease of fat pad weight and the antioxidant and oxidant enzyme activities and ROS content returned to control values along with normal plasma TNF-α and IL-6 levels. FO normalized both the decrease of PPARγ protein and the increase of protein and expression of UCP2. Furthermore, FO increased the n-3/n-6 fatty acid ratio in the adipose tissue phospholipids and normalized dyslipidemia and insulin resistance. Finally, these findings reinforce the view that dietary FO may exert a beneficial effect in ameliorating the dyslipidemia and insulin resistance in this animal model.

Metabolic dysregulation accelerates injury-induced joint degeneration, driven by local inflammation; an in vivo rat study

Evidence is growing for the existence of an obesity-related phenotype of osteoarthritis in which low-grade inflammation and a disturbed metabolic profile play a role. The contribution of an obesity-induced metabolic dysbalance to the progression of the features of osteoarthritis upon mechanically induced cartilage damage was studied in a rat in vivo model. Forty Wistar rats were randomly allocated 1:1 to a standard diet or a high-fat diet. After 12 weeks, in 14 out of 20 rats in each group, cartilage was mechanically damaged in the right knee joint. The remaining six animals in each group served as controls. After a subsequent 12 weeks, serum was collected for metabolic state, subchondral bone changes assessed by μCT imaging, osteoarthritis severity determined by histology, and macrophage presence assessed by CD68 staining. The high-fat diet increased statistically all relevant metabolic parameters, resulting in a dysmetabolic state and subsequent synovial inflammation, whereas cartilage degeneration was hardly influenced. The high-fat condition in combination with mechanical cartilage damage resulted in a clear statistically significant progression of the osteoarthritic features, with increased synovitis and multiple large osteophytes. Both the synovium and osteophytes contained numerous CD68 positive cells. It is concluded that a metabolic dysbalance due to a high-fat diet increases joint inflammation without cartilage degeneration. The dysmetabolic state clearly accelerates progression of osteoarthritis upon surgically induced cartilage damage supported by inflammatory responses as demonstrated by histology and increased CD68 expressing cells localized on the synovial membrane and osteophytes. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:881-890, 2018.

Sex differences in the neuroendocrine control of metabolism and the implication of astrocytes

Males and females have distinct propensities to develop obesity and its related comorbidities, partially due to gonadal steroids. There are sex differences in hypothalamic neuronal circuits, as well as in astrocytes, that participate in metabolic control and the development of obesity-associated complications. Astrocytes are involved in nutrient transport and metabolism, glucose sensing, synaptic remodeling and modulation of neuronal signaling. They express receptors for metabolic hormones and mediate effects of these metabolic signals on neurons, with astrogliosis occurring in response to high fat diet and excess weight gain. However, most studies of obesity have focused on males. Recent reports indicate that male and female astrocytes respond differently to metabolic signals and this could be involved in the differential response to high fat diet and the onset of obesity-associated pathologies. Here we focus on the sex differences in response to obesogenic paradigms and the possible role of hypothalamic astrocytes in this phenomenon.

Oxidative Stress as a Mechanism Involved in Kidney Damage After Subchronic Exposure to Vanadium Inhalation and Oral Sweetened Beverages in a Mouse Model

Kidney diseases have notably increased in the last few years. This is partially explained by the increase in metabolic syndrome, diabetes, and systemic blood hypertension. However, there is a segment of the population that has neither of the previous risk factors, yet suffers kidney damage. Exposure to atmospheric pollutants has been suggested as a possible risk factor. Air-suspended particles carry on their surface a variety of fuel combustion-related residues such as metals, and vanadium is one of these. Vanadium might produce oxidative stress resulting in the damage of some organs such as the kidney. Additionally, in countries like Mexico, the ingestion of sweetened beverages is a major issue; whether these beverages alone are responsible for direct kidney damage or whether their ingestion promotes the progression of an existing renal damage generates controversy. In this study, we report the combined effect of vanadium inhalation and sweetened beverages ingestion in a mouse model. Forty CD-1 male mice were distributed in 4 groups: control, vanadium inhalation, 30% sucrose in drinking water, and vanadium inhalation plus sucrose 30% in drinking water. Our results support that vanadium inhalation and the ingestion of 30% sucrose induce functional and histological kidney damage and an increase in oxidative stress biomarkers, which were higher in the combined effect of vanadium plus 30% sucrose. The results also support that the ingestion of 30% sucrose alone without hyperglycemia also produces kidney damage.

Electrophysiological basis of metabolic-syndrome-induced cardiac dysfunction

Myocardial contractility is controlled by intracellular Ca2+ cycling with the contribution of sarcoplasmic reticulum (SR). In this study, we aimed to investigate the role of altered SR function in defective regulation of intracellular Ca2+ levels in rats with metabolic syndrome (MetS) induced by a 16-week high-sucrose drinking-water diet. Electric-field stimulated transient intracellular Ca2+ changes in MetS cardiomyocytes exhibited significantly reduced amplitude (∼30%) and prolonged time courses (2-fold), as well as depressed SR Ca2+ loading (∼55%) with increased basal Ca2+ level. Consistent with these data, altered ryanodine receptor (RyR2) function and SERCA2a activity were found in MetS cardiomyocytes through Ca2+ spark measurements and caffeine application assay in a state in which sodium calcium exchanger was inhibited. Furthermore, tetracaine application assay results and hyperphosphorylated level of RyR2 also support the “leaky RyR2” hypothesis. Moreover, altered phosphorylation levels of phospholamban (PLN) support the depressed SERCA2a-activity thesis and these alterations in the phosphorylation of Ca2+-handling proteins are correlated with altered protein kinase and phosphatase activity in MetS cardiomyocytes. In conclusion, MetS-rat heart exhibits altered Ca2+ signaling largely due to altered SR function via changes in RyR2 and SERCA2a activity. These results point to RyR2 and SERCA2a as potential pharmacological targets for restoring intracellular Ca2+ homeostasis and, thereby, combatting dysfunction in MetS-rat heart.

High-fat but not sucrose intake is essential for induction of dyslipidemia and non-alcoholic steatohepatitis in guinea pigs

Background

Non-alcoholic fatty liver disease (NAFLD) and dyslipidemia are closely related. Diet plays an important role in the progression of these diseases, but the role of specific dietary components is not completely understood. Therefore, we investigated the role of dietary sucrose and fat/cholesterol on the development of dyslipidemia and NAFLD.

Methods

Seventy female guinea pigs were block-randomized (based on weight) into five groups and fed a normal chow diet (control: 4 % fat), a very high-sucrose diet (vHS: 4 % fat, 25 % sucrose), a high-fat diet (HF: 20 % fat, 0.35 % cholesterol), a high-fat/high-sucrose diet (HFHS: 20 % fat, 15 % sucrose, 0.35 % cholesterol) or a high-fat/very high-sucrose diet (HFvHS: 20 % fat, 25 % sucrose, 0.35 % cholesterol) for 16 and 25 weeks.

Results

All three high-fat diets induced dyslipidemia with increased concentrations of plasma cholesterol (p < 0.0001), LDL-C (p < 0.0001) and VLDL-C (p < 0.05) compared to control and vHS. Contrary to this, plasma triglycerides were increased in control and vHS compared to high-fat fed animals (p < 0.01), while circulating levels of free fatty acids were even between groups. Histological evaluation of liver sections revealed non-alcoholic steatohepatitis (NASH) with progressive inflammation and bridging fibrosis in high-fat fed animals. Accordingly, hepatic triglycerides (p < 0.05) and cholesterol (p < 0.0001) was increased alongside elevated levels of alanine and aspartate aminotransferase (p < 0.01) compared to control and vHS.

Conclusion

Collectively, our results suggest that intake of fat and cholesterol, but not sucrose, are the main factors driving the development and progression of dyslipidemia and NAFLD/NASH.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-016-0110-1) contains supplementary material, which is available to authorized users.

Short Exposure to a High-Sucrose Diet and the First 'Hit' of Nonalcoholic Fatty Liver Disease in Mice

High-sucrose and high-fat diets induce deregulation in the metabolism of lipids and carbohydrates. This study aimed to detect the initial consequences on lipogenesis, gluconeogenesis and insulin signaling in the livers of rodents fed high-fat and/or high-sucrose diets for a short period of time. Male mice received a standard chow (SC), high-fat (HF), high-sucrose (HSu) or high-fat, high-sucrose (HFHSu) diet for 4 weeks. At euthanasia, blood was collected and the liver was removed for histomorphometrical and molecular analysis. The HF, HSu and HFHSu groups presented glucose intolerance, hepatomegaly, liver steatosis and lipid profile alteration when compared to the SC group (p < 0.0005). Additionally, there was an elevation in protein levels involved in lipogenesis (SREBP-1c), gluconeogenesis (PEPCK and G6Pase) and insulin signaling (IRS-1 and Akt) in the livers from the experimental groups compared to the SC group (p < 0.0005). Thus, we conclude that a short-term HF and/or HSu diet promotes glucose intolerance and liver damage in adult male mice. Surprisingly, the short exposure to excess sucrose in the diet promoted glucose intolerance and liver damage even in the absence of an increase in body mass or changes in serum insulin, cholesterol and triacylglycerol levels.

Time course of adipose tissue dysfunction associated with antioxidant defense, inflammatory cytokines and oxidative stress in dyslipemic insulin resistant rats

Time course of adipose tissue dysfunction in dyslipemic insulin resistant rats.

Nutrigenomics of body weight regulation: a rationale for careful dissection of individual contributors

Body weight stability may imply active regulation towards a certain physiological condition, a body weight setpoint. This interpretation is ill at odds with the world-wide increase in overweight and obesity. Until now, a body weight setpoint has remained elusive and the setpoint theory did not provide practical clues for body weight reduction interventions. For this an alternative theoretical model is necessary, which is available as the settling point model. The settling point model postulates that there is little active regulation towards a predefined body weight, but that body weight settles based on the resultant of a number of contributors, represented by the individual's genetic predisposition, in interaction with environmental and socioeconomic factors, such as diet and lifestyle. This review refines the settling point model and argues that by taking body weight regulation from a settling point perspective, the road will be opened to careful dissection of the various contributors to establishment of body weight and its regulation. This is both necessary and useful. Nutrigenomic technologies may help to delineate contributors to body weight settling. Understanding how and to which extent the different contributors influence body weight will allow the design of weight loss and weight maintenance interventions, which hopefully are more successful than those that are currently available.

Cognitive and behavioural effects of sugar consumption in rodents. A review

The pronounced global rise in sugar consumption in recent years has been driven largely by increased consumption of sugar-sweetened beverages. Although high sugar intakes are recognised to increase the risk of obesity and related metabolic disturbances, less is known about how sugar might also impair cognition and learned behaviour. This review considers the effects of sugar in rodents on measures of learning and memory, reward processing, anxiety and mood. The parallels between sugar consumption and addictive behaviours are also discussed. The available evidence clearly indicates that sugar consumption can induce cognitive dysfunction. Deficits have been found most consistently on tasks measuring spatial learning and memory. Younger animals appear to be particularly sensitive to the effects of sugar on reward processing, yet results vary according to what reward-related behaviour is assessed. Sugar does not appear to produce long-term effects on anxiety or mood. Importantly, cognitive impairments have been found when intake approximates levels of sugar consumption in people and without changes to weight gain. There remain several caveats when extrapolating from animal models to putative effects of sugar on cognitive function in people. These issues are discussed in conjunction with potential underlying neural mechanisms and directions for future research.

Metabolic syndrome remodels electrical activity of the sinoatrial node and produces arrhythmias in rats

In the last ten years, the incidences of metabolic syndrome and supraventricular arrhythmias have greatly increased. The metabolic syndrome is a cluster of alterations, which include obesity, hypertension, hypertriglyceridemia, glucose intolerance and insulin resistance, that increase the risk of developing, among others, atrial and nodal arrhythmias.

The aim of this study is to demonstrate that metabolic syndrome induces electrical remodeling of the sinus node and produces arrhythmias. We induced metabolic syndrome in 2-month-old male Wistar rats by administering 20% sucrose in the drinking water. Eight weeks later, the rats were anesthetized and the electrocardiogram was recorded, revealing the presence of arrhythmias only in treated rats. Using conventional microelectrode and voltage clamp techniques, we analyzed the electrical activity of the sinoatrial node.

We observed that in the sinoatrial node of “metabolic syndrome rats”, compared to controls, the spontaneous firing of all cells decreased, while the slope of the diastolic depolarization increased only in latent pacemaker cells. Accordingly, the pacemaker currents I_f and I_st increased. Furthermore, histological analysis showed a large amount of fat surrounding nodal cardiomyocytes and a rise in the sympathetic innervation. Finally, Poincaré plot denoted irregularity in the R-R and P-P ECG intervals, in agreement with the variability of nodal firing potential recorded in metabolic syndrome rats.

We conclude that metabolic syndrome produces a dysfunction SA node by disrupting normal architecture and the electrical activity, which could explain the onset of arrhythmias in rats.

Low-volume exercise can prevent sucrose-induced weight gain but has limited impact on metabolic measures in rats

PURPOSE

Rats given sugar-sweetened drinks can develop glucose intolerance, insulin resistance and dyslipidaemia. The aim of this study was to investigate whether such metabolic disruptions and also possible weight gain induced by chronic sucrose consumption could be attenuated by low-volume exercise.

METHODS

Using a 2 × 2 factorial design, rats were given free access for 57 days to either a 10% sucrose solution (Suc and SucEx) or water only (Con and ConEx), while exercise rats (SucEx and ConEx) received 20-min treadmill training every 3 days. Caloric intake and body weight were measured throughout this dietary intervention. Oral glucose tolerance tests were performed on days 29 and 54. Plasma insulin, triglycerides and leptin were also measured, together with post-mortem measures of retroperitoneal fat pads and liver triglycerides.

RESULTS

In groups given sucrose, exercise reduced calorie consumption, reduced weight gain and decreased leptin relative to non-exercised controls. Exercise was found to improve glucose tolerance and insulin action at day 29, but not day 54.

CONCLUSIONS

Low-volume exercise can be effective in preventing weight gain in sucrose-fed rats, probably via reduction of subcutaneous fat, but prevention of the glucose intolerance and dyslipidaemia produced by sucrose consumption may be transient.

Way back for fructose and liver metabolism: Bench side to molecular insights

The World Health Organization recommends that the daily intake of added sugars should make up no more than 10% of total energy. The consumption of sugar-sweetened beverages is the main source of added sugars. Fructose, together with glucose, as a component of high fructose corn syrups or as a component of the sucrose molecule, is one of the main sweeteners present in this kind of beverages. Data from prospective and intervention studies clearly point to high fructose consumption, mainly in the form of sweetened beverages, as a risk factor for several metabolic diseases in humans. The incidence of hypertension, nonalcoholic fatty liver disease (NAFLD), dyslipidemia (mainly hypertriglyceridemia), insulin resistance, type 2 diabetes mellitus, obesity, and the cluster of many of these pathologies in the form of metabolic syndrome is higher in human population segments that show high intake of fructose. Adolescent and young adults from low-income families are especially at risk. We recently reviewed evidence from experimental animals and human data that confirms the deleterious effect of fructose on lipid and glucose metabolism. In this present review we update the information generated in the past 2 years about high consumption of fructose-enriched beverages and the occurrence of metabolic disturbances, especially NAFLD, type 2 diabetes mellitus, and metabolic syndrome. We have explored recent data from observational and experimental human studies, as well as experimental data from animal and cell models. Finally, using information generated in our laboratory and others, we provide a view of the molecular mechanisms that may be specifically involved in the development of liver lipid and glucose metabolic alterations after fructose consumption in liquid form.

Early endocrine and molecular changes in metabolic syndrome models

The twenty-first century arrived in the middle of a global epidemic of metabolic syndrome (MS) and type 2 diabetes mellitus (DM2). It is generally accepted that an excess of nutrients linked to a low physical activity triggers the problem. However, the molecular features that interact to develop the MS are not clear. In an effort to understand and control them, they have been extensively studied, but this goal has not been achieved yet. Nonhuman animal models have been used to explore diet and genetic factors in which experimental conditions are controlled. For example, only one factor in the diet, such as fats or carbohydrates can be modified to better understand a single change that would be impossible in humans. Most of the studies have been done in rodents. However, it is difficult to directly compare them, because experiments are different in more than one variable; genetic strains, amount, and the type of fat used in the diet and sex. Thus, the only possible criteria of comparison are the relevance of the observed changes. We review different animal models and add some original observations on short-term changes in metabolism and beta cells in our own model of adult Wistar rats that are not especially prone to get fat or develop DM2, treated with 20% sucrose in drinking water. One early change observed in pancreatic beta cells is the increase in GLUT2 expression that is located to the membrane of the cells. This change could partially explain the presence of insulin hypersecretion and hyperinsulinemia in these rats. Understanding early changes that lead to MS and in time to pancreatic islet exhaustion is an important biomedical problem that may contribute to learn how to prevent or even reverse MS, before developing DM2.

The manner in which calories are restricted impacts mammary tumor cancer prevention

Although treatments for breast cancer have improved and long-term survival after diagnosis is now common, prevention of the disease is the ultimate goal. Weight loss or weight maintenance is one approach that has been recommended to reduce the risk of breast cancer, particularly for peri/postmenopausal women. This approach is supported by decades of data indicating that calorie restriction prevents spontaneous and chemically induced mammary tumor development in rodents. In most cases, calorie restriction was implemented by a consistent daily reduction of calories, i.e. chronic calorie restriction (CCR). There have also been several studies where periods of reduced caloric intake were followed by periods of refeeding, i.e. intermittent calorie restriction (ICR), resulting in the prevention of spontaneous mammary tumorigenesis. In most of the early studies, there were no direct comparisons of CCR to ICR. One study using moderate calorie restriction in a chemically induced breast cancer rat model found a slight increase in mammary tumor incidence compared with ad libitum fed and CCR rats. However, recently, it has been demonstrated in several transgenic mouse models of breast cancer that ICR consistently provided a greater degree of protection than CCR. This review will provide a detailed comparison of ICR and CCR for breast cancer prevention. It will also examine potential mechanisms of action that may include periods of reduced IGF-I and leptin as well as an increase in the adiponectin:leptin ratio. Application of this approach to at-risk women may provide an approach to lower the risk of breast cancer in overweight/obese women.

Effect of chronic and intermittent calorie restriction on serum adiponectin and leptin and mammary tumorigenesis

The effect of chronic (CCR) and intermittent (ICR) caloric restriction on serum adiponectin and leptin levels was investigated in relation to mammary tumorigenesis. 10-wks old MMTV-TGF-α female mice were assigned to ad libitum fed (AL; AIN-93M diet), ICR (3-week 50% caloric restriction, AIN-93M-mod diet, 2× protein, fat, vitamins, and minerals followed by 3-wks 100% AL consumption of AIN-93M), and CCR (calorie and nutrient intake matched for each 6-wks ICR cycle, ∼ 75% of AL) groups. Mice were sacrificed at 79 (end of restriction) or 82 (end of refeeding) wks of age. Serum was obtained in cycles 1, 3, 5, 8, 11, and terminal. Mammary tumor incidence was 71.0%, 35.4%, and 9.1% for AL, CCR, and ICR mice, respectively. Serum adiponectin levels were similar among groups with no impact of either CCR or ICR. Serum leptin level rose in AL mice with increasing age but was significantly reduced by long-term CCR and ICR. The ICR protocol was also associated with an elevated adiponectin/leptin ratio. In addition, ICR-restricted mice had increased mammary tissue AdipoR1 expression and decreased leptin and ObRb expression compared with AL mice. Mammary fat pads from tumor-free ICR-mice had higher adiponectin expression than AL and CCR mice whereas all tumor-bearing mice had weak adiponectin signal in mammary fat pad. Although we did not show an association of either adiponectin or leptin with individual mice in relation to mammary tumorigenesis, we did find that reduced serum leptin and elevated adiponectin/leptin ratio were associated with the protective effect of intermittent calorie restriction.

The metabolic benefits of Polygonum hypoleucum Ohwi in HepG2 cells and Wistar rats under lipogenic stress

Inhibition of acetyl-CoA carboxylase (ACC) is one approach used for treating metabolic syndrome. Using partially purified ACC to screen herbs commonly used in Taiwanese folk medicine, we previously showed that an ethanol extract of Polygonum hypoleucum Ohwi (EP) had potent ACC inhibitory activity and partially alleviated metabolic disorders induced by a high fat diet. Since ACC plays a crucial role in de novo lipogenesis, the favorable effects of EP on metabolism were tested under lipogenic conditions in the present study. On incubating high glucose (30 mM)-stimulated HepG2 cells with EP (72.5 or 145 microg/mL), ACC and fatty acid synthase activity, triacylglycerol content, and microsomal triacylglycerol transfer protein mRNA levels were all significantly reduced (P < 0.05, vs vehicle). When EP was given at low, medium, and high dosages (94, 188, and 470 mg/kg) to sucrose water-treated Wistar rats for four weeks, alleviation of symptoms associated with metabolic syndrome, including obesity, insulin resistance, hypertriglyceridemia, and hypertension, accompanied by hepatic ACC inactivation, was seen in the low dosage group. Four compounds (emodin, emodin-8-O-beta-D-glucopyranoside, (+)-catechin, and (-)-epicatechin) isolated from EP were identified as ACC inhibitors. These results confirm that P. hypoleucum Ohwi, acting partly through ACC inhibition, has favorable effects in alleviating metabolic disturbances occurring under lipogenic conditions.