Fructose-rich diet-induced abdominal adipose tissue endocrine dysfunction in normal male rats

The impact of dietary fructose on gut permeability, microbiota, abdominal adiposity, insulin signaling and reproductive function

The excessive intake of fructose in the regular human diet could be related to global increases in metabolic disorders. Sugar-sweetened soft drinks, mostly consumed by children, adolescents, and young adults, are the main source of added fructose. Dietary high-fructose can increase intestinal permeability and circulatory endotoxin by changing the gut barrier function and microbial composition. Excess fructose transports to the liver and then triggers inflammation as well as de novo lipogenesis leading to hepatic steatosis. Fructose also induces fat deposition in adipose tissue by stimulating the expression of lipogenic genes, thus causing abdominal adiposity. Activation of the inflammatory pathway by fructose in target tissues is thought to contribute to the suppression of the insulin signaling pathway producing systemic insulin resistance. Moreover, there is some evidence that high intake of fructose negatively affects both male and female reproductive systems and may lead to infertility. This review addresses dietary high-fructose-induced deteriorations that are obvious, especially in gut permeability, microbiota, abdominal fat accumulation, insulin signaling, and reproductive function. The recognition of the detrimental effects of fructose and the development of relevant new public health policies are necessary in order to prevent diet-related metabolic disorders.

Effects of Natural Alternative Sweeteners on Metabolic Diseases

The rising prevalence of obesity and diabetes is a significant health concern both in globally and is now regarded as a worldwide epidemic. Added sugars like sucrose and high-fructose corn syrup (HFCS) are a major concern due to their link with an increased incidence of diet-induced obesity and diabetes. The purpose of this review is to provide insight into the effects of natural sweeteners as alternatives to sucrose and HFCS, which are known to have negative impacts on metabolic diseases and to promote further research on sugar consumption with a focus on improving metabolic health. The collective evidences suggest that natural alternative sweeteners have positive impacts on various markers associated with obesity and diabetes, including body weight gain, hepatic fat accumulation, abnormal blood glucose or lipid homeostasis, and insulin resistance. Taken together, natural alternative sweeteners can be useful substitutes to decrease the risk of obesity and diabetes compared with sucrose and HFCS.

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.

Circadian Rhythm in Adipose Tissue: Novel Antioxidant Target for Metabolic and Cardiovascular Diseases

Obesity is a major risk factor for most metabolic and cardiovascular disorders. Adipose tissue is an important endocrine organ that modulates metabolic and cardiovascular health by secreting signaling molecules. Oxidative stress is a common mechanism associated with metabolic and cardiovascular complications including obesity, type 2 diabetes, and hypertension. Oxidative stress can cause adipose tissue dysfunction. Accumulating data from both humans and experimental animal models suggest that adipose tissue function and oxidative stress have an innate connection with the intrinsic biological clock. Circadian clock orchestrates biological processes in adjusting to daily environmental changes according to internal or external cues. Recent studies have identified the genes and molecular pathways exhibiting circadian expression patterns in adipose tissue. Disruption of the circadian rhythmicity has been suggested to augment oxidative stress and aberrate adipose tissue function and metabolism. Therefore, circadian machinery in the adipose tissue may be a novel therapeutic target for the prevention and treatment of metabolic and cardiovascular diseases. In this review, we summarize recent findings on circadian rhythm and oxidative stress in adipose tissue, dissect the key components that play a role in regulating the clock rhythm, oxidative stress and adipose tissue function, and discuss the potential use of antioxidant treatment on metabolic and cardiovascular diseases by targeting the adipose clock.

Foods with Potential Prooxidant and Antioxidant Effects Involved in Parkinson's Disease

Oxidative stress plays a fundamental role in the pathogenesis of Parkinson's disease (PD). Oxidative stress appears to be responsible for the gradual dysfunction that manifests via numerous cellular pathways throughout PD progression. This review will describe the prooxidant effect of excessive consumption of processed food. Processed meat can affect health due to its high sodium content, advanced lipid oxidation end-products, cholesterol, and free fatty acids. During cooking, lipids can react with proteins to form advanced end-products of lipid oxidation. Excessive consumption of different types of carbohydrates is a risk factor for PD. The antioxidant effects of some foods in the regular diet provide an inconclusive interpretation of the environment's mechanisms with the modulation of oxidation stress-induced PD. Some antioxidant molecules are known whose primary mechanism is the neuroprotective effect. The melatonin mechanism consists of neutralizing reactive oxygen species (ROS) and inducing antioxidant enzyme's expression and activity. N-acetylcysteine protects against the development of PD by restoring levels of brain glutathione. The balanced administration of vitamin B3, ascorbic acid, vitamin D and the intake of caffeine every day seem beneficial for brain health in PD. Excessive chocolate intake could have adverse effects in PD patients. The findings reported to date do not provide clear benefits for a possible efficient therapeutic intervention by consuming the nutrients that are consumed regularly.

Fructose Consumption During Pregnancy Influences Milk Lipid Composition and Offspring Lipid Profiles in Guinea Pigs

Excess dietary fructose is a major public health concern (1-4). Evidence shows increased fructose intake can cause insulin resistance, hepatic de novo lipogenesis, hypertriglyceridemia, obesity and non-alcoholic fatty liver disease (NAFLD) (5-9). However, little is known about the effects of fructose during pregnancy and its influence on offspring development and predisposition to later-life disease. To determine whether moderately increased maternal fructose intake could have health consequences on offspring, we have investigated the effects of 10% w/v fructose water intake during preconception and pregnancy. Female Dunkin Hartley guinea pigs were fed a control diet (CD) or fructose diet (FD;10% kcal from fructose) ad-libitum 60 days prior to mating and throughout gestation. Offspring were culled at weaning, day 21 (d21). Compared to CD dams, FD dams had altered glucose metabolism and increased milk free fatty acid content. Matsuda-DeFronzo insulin sensitivity index (M-ISI) from OGTT plasma showed no significant difference in whole-body insulin sensitivity between FD and CD dams 60 days post-dietary intervention and during midgestation. Fetal exposure to increased maternal fructose resulted in offspring with significantly altered serum free fatty acids at days 0, 7, 14, and 21 [including pentadecanoic acid (15:0), dma16:0, margaric acid (17:0) palmitoleic acid, total omega-7 and total saturates], increased levels of uric acid and triglycerides were also observed at d21. We have demonstrated that increased fructose intake during pregnancy can cause significant changes in maternal metabolic function and milk composition, which alters offspring metabolism. Taken together, these changes in pregnancy outcomes and feto-maternal condition may underlie their offspring's predisposition to metabolic dysfunction during later-life.

Browning is activated in the subcutaneous white adipose tissue of mice metabolically challenged with a high-fructose diet submitted to high-intensity interval training

Fructose may induce an endocrine dysfunction in adipose tissue in rodents. Browning is identified by deposits of beige adipocytes in subcutaneous white adipose tissue (sWAT). We study the effects of the high-intensity interval training (HIIT) on the formation of beige adipocytes in the sWAT of mice fed a high-fructose diet. Sixty male mice (3 months old; C57BL/6) were fed two diets for 18 weeks (n=30 each): control diet (C) or high-fructose diet (F). At the 10th week, for an additional 8-week period, the groups were (n=15 each) nontrained (NT) or trained (HIIT): C-NT, C-HIIT, F-NT and F-HIIT. We evaluated body mass, energy expenditure and molecular analyses for browning and thermogenic markers in sWAT. The HIIT groups showed significantly lower body mass and increased energy expenditure. The consumption of fructose was linked with an increased sWAT mass. However, HIIT caused a reduction of sWAT mass compared to the NT groups. Energy intake was parallel in the groups, regardless of the diet type and HIIT. Fructose was related to higher glucose and insulin levels and hypertrophied sWAT adipocytes, but HIIT decreased both glucose and insulin levels and led to the appearance of brown fat-like adipocytes dispersed in sWAT with higher expression of browning markers. Also, fructose reduced the sWAT markers of mitochondrial biogenesis and beta-oxidation, which were enhanced by HIIT. In conclusion, HIIT might stimulate the sWAT browning in mice fed a high-fructose diet associated with beneficial changes in mitochondrial biogenesis and beta-oxidation markers, contributing to a whole-body metabolic improvement.

Alpha-lipoic acid and its protective role in fructose induced endocrine-metabolic disturbances

In recent decades a worldwide increase has been reported in the consumption of unhealthy high calorie diets associated with marked changes in meal nutrient composition, such as a higher intake of refined carbohydrates, which leads to the speculatation that changes in food habits have contributed to the current epidemic of obesity and type 2 diabetes. Among these refined carbohydrates, fructose has been deeply investigated and murine models of high fructose diet have emerged as useful tools to study dietary-induced insulin resistance, impaired glucose tolerance, dyslipidemia and alterations in glucose metabolism. Since oxidative stress has been demonstrated to play a key pathogenic role in the alterations described above, several lines of research have focused on the possible preventive effects of antioxidant/redox state regulation therapy, among which alpha-lipoic acid has been extensively investigated. The following references discussed support the fact that co-administration of alpha-lipoic acid normalized the changes generated by fructose rich diets, thereby making this compound a good therapeutic tool, also administered as a food supplement, to prevent endocrine-metabolic disturbances triggered by high fructose associated with obesity and type 2 diabetes at an early stage of development (prediabetes).

High-fructose diet initiated during adolescence does not affect basolateral amygdala excitability or affective-like behavior in Sprague Dawley rats

Patients with type-2 diabetes, obesity, and metabolic syndrome have a significantly increased risk of developing depression. Dysregulated metabolism may contribute to the etiology of depression by affecting neuronal activity in key limbic areas. The basolateral amygdala (BLA) acts as a critical emotional valence detector in the brain's limbic circuit, and shows hyperactivity and abnormal glucose metabolism in depressed patients. Furthermore, administering a periadolescent high-fructose diet (HFrD; a model of metabolic syndrome) to male Wistar rats increases anxiety- and depressive-like behavior. Repeated shock stress in Sprague Dawley rats similarly increases anxiety-like behavior and increases BLA excitability. We therefore investigated whether a metabolic stressor (HFrD) would have similar effects as shock stress on BLA excitability in Sprague Dawley rats. We found that a HFrD did not affect the intrinsic excitability of BLA neurons. Fructose-fed Sprague Dawley rats had elevated body fat mass, but did not show increases in metabolic efficiency and fasting blood glucose relative to control. Finally unlike Wistar rats, fructose-fed Sprague Dawley rats did not show increased anxiety- and depressive-like behavior. These results suggest that genetic differences between rat strains may affect susceptibility to a metabolic insult. Collectively, these data show that a periadolescent HFrD disrupts metabolism, but does not change affective behavior or BLA excitability in Sprague Dawley rats.

Impaired endocrine-metabolic homeostasis: underlying mechanism of its induction by unbalanced diet

To characterize the intrinsic mechanism by which sucrose induces β-cell dysfunction. Normal rats received for 3 weeks a standard diet supplemented with 10% sucrose in the drinking water (high sucrose (HS)) with/out an antioxidant agent (R/S α-lipoic acid). We measured plasma glucose, insulin, triglyceride, leptin, and lipid peroxidation levels; homeostasis model assessment (HOMA)-insulin resistance (HOMA-IR) and HOMA for β-cell function (HOMA-β) indexes were also determined. Insulin secretion, β-cell apoptosis, intracellular insulin and leptin mediators, and oxidative stress (OS) markers were also measured in islets isolated from each experimental group. HS rats had increased plasma triglyceride, insulin, leptin, and lipid peroxidation (OS marker) levels associated with an insulin-resistant state. Their islets developed an initial compensatory increase in glucose-induced insulin secretion and mRNA and protein levels of β-cell apoptotic markers. They also showed a significant decrease in mRNA and protein levels of insulin and leptin signaling pathway mediators. Uncoupling protein 2 (UCP2), peroxisome proliferator-activated receptor (PPAR)-α and -δ mRNA and protein levels were increased whereas mRNA levels of Sirtuin-1 (Sirt-1), glutathione peroxidase, and catalase were significantly lower in these animals. Development of all these endocrine-metabolic abnormalities was prevented by co-administration of R/S α-lipoic acid together with sucrose. OS may be actively involved in the mechanism by which unbalanced/unhealthy diet induces β-cell dysfunction. Since metabolic-endocrine dysfunctions recorded in HS rats resembled those measured in human pre-diabetes, knowledge of its molecular mechanism could help to develop appropriate strategies to prevent the progression of this metabolic state toward type 2 diabetes (T2D).

Nutrients and Oxidative Stress: Friend or Foe?

There are different types of nutritionally mediated oxidative stress sources that trigger inflammation. Much information indicates that high intakes of macronutrients can promote oxidative stress and subsequently contribute to inflammation via nuclear factor-kappa B- (NF-κB-) mediated cell signaling pathways. Dietary carbohydrates, animal-based proteins, and fats are important to highlight here because they may contribute to the long-term consequences of nutritionally mediated inflammation. Oxidative stress is a central player of metabolic ailments associated with high-carbohydrate and animal-based protein diets and excessive fat consumption. Obesity has become an epidemic and represents the major risk factor for several chronic diseases, including diabetes, cardiovascular disease (CVD), and cancer. However, the molecular mechanisms of nutritionally mediated oxidative stress are complex and poorly understood. Therefore, this review aimed to explore how dietary choices exacerbate or dampen the oxidative stress and inflammation. We also discussed the implications of oxidative stress in the adipocyte and glucose metabolism and obesity-associated noncommunicable diseases (NCDs). Taken together, a better understanding of the role of oxidative stress in obesity and the development of obesity-related NCDs would provide a useful approach. This is because oxidative stress can be mediated by both extrinsic and intrinsic factors, hence providing a plausible means for the prevention of metabolic disorders.

Vanadyl Sulfate Effects on Systemic Profiles of Metabolic Syndrome in Old Rats with Fructose-Induced Obesity

BACKGROUND

Currently, energy obtained from hypercaloric diets has been part of the obesity and type 2 diabetes mellitus (T2DM) epidemics from childhood to old age. Treatment alternatives have been sought from plants, minerals, and trace elements with metabolic effects. Vanadyl sulfate (VS) has been investigated as a hypoglycemic compound in animal and human studies showing effective insulin-mimetic properties. This characteristic encompasses several molecules that have beneficial pleiotropic effects. The aim was to determine the antiobesity, hypoglycemic, and hypolipidemic effects of VS on fructose-induced metabolic syndrome in aged rats.

MATERIAL AND METHODS

Five groups of male Wistar rats were made, each with six rats: two groups with normal diet (ND) and three with high-fructose diet (HFD). The first ND group was treated with saline solution (SS), the second with VS; treatment for HFD groups was in the first group with SS, second with VS, and third with metformin. Weight, body mass index (BMI), blood glucose, and lipidic profile were measured; water, food, fructose and energy consumption were also determined. All parameters were compared among groups.

RESULTS AND DISCUSSION

Although obese rats treated with VS presented anorexia, oligodipsia, and a marked weight loss in the first two weeks. They recovered food and water intake in the third week with a slow recovery of some weight weeks later. VS normalized blood glucose level and decreased triglyceride and insulin levels in obese rats. These results suggest that vanadyl sulfate shows antiobesity, hypoglycemic, and hypolipidemic properties in old obese rats and could be useful as an alternative, additional, and potent preventive treatment for obesity and T2DM control in elderly obese and poorly controlled diabetic patients.

CONCLUSION

VS could play an important role in the treatment of metabolic syndrome, contributing to a decrease in obesity and T2DM, through different ways, such as euglycemia, satiety, weight loss, and lipid profile optimization, among others. However, more research is needed to confirm this suggestion.

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

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

Renin inhibition improves metabolic syndrome, and reduces angiotensin II levels and oxidative stress in visceral fat tissues in fructose-fed rats

Renin–angiotensin system in visceral fat plays a crucial role in the pathogenesis of metabolic syndrome in fructose-fed rats. However, the effects of renin inhibition on visceral adiposity in metabolic syndrome are not fully investigated. We investigated the effects of renin inhibition on visceral adiposity in fructose-fed rats. Male Wistar–Kyoto rats were divided into 4 groups for 8-week experiments: Group Con (standard chow diet), Group Fru (high-fructose diet; 60% fructose), Group FruA (high-fructose diet and concurrent aliskiren treatment; 100 mg/kg body weight [BW] per day), and Group FruB (high-fructose diet and subsequent, i.e. 4 weeks after initiating high-fructose feeding, aliskiren treatment; 100 mg/kg BW per day). The high-fructose diet induced metabolic syndrome, increased visceral fat weights and adipocyte sizes, and augmented angiotensin II (Ang II), NADPH oxidase (NOX) isoforms expressions, oxidative stress, and dysregulated production of adipocytokines from visceral adipose tissues. Concurrent and subsequent aliskiren administration ameliorated metabolic syndrome, dysregulated adipocytokines, and visceral adiposity in high fructose-fed hypertensive rats, and was associated with reducing Ang II levels, NOX isoforms expressions and oxidative stress in visceral fat tissues. Therefore, this study demonstrates renin inhibition could improve metabolic syndrome, and reduce Ang II levels and oxidative stress in visceral fat tissue in fructose-fed rats, and suggests that visceral adipose Ang II plays a crucial role in the pathogenesis of metabolic syndrome in fructose-fed rats.

Quercetin attenuates high fructose feeding-induced atherosclerosis by suppressing inflammation and apoptosis via ROS-regulated PI3K/AKT signaling pathway

Quercetin is a dietary flavonoid compound extracted from various plants, such as apple and onions. Previous studies have revealed its anti-inflammatory, anti-cancer, antioxidant and anti-apoptotic activities. This study investigated the ability of quercetin to inhibit high fructose feeding- or LPS-induced atherosclerosis through regulating oxidative stress, apoptosis and inflammation response in vivo and in vitro experiments. 50 and 100mg/kg quercetin were used in our study, showing significant inhibitory role in high fructose-induced atherosclerosis via reducing reactive oxygen species (ROS) levels, Caspase-3 activation, inflammatory cytokines releasing, the number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive cells and collagen contents as well as modulating apoptosis- and inflammation-related proteins expression. We also explored the protective effects of quercetin on atherosclerosis by phosphatidylinositide 3-kinases (PI3K)/Protein kinase B (AKT)-associated Bcl-2/Caspase-3 and nuclear factor kappa B (NF-κB) signal pathways activation, promoting AKT and Bcl-2 expression and reducing Caspase-3 and NF-κB activation. Quercetin reduced the atherosclerotic plaque size in vivo in high fructose feeding-induced mice assessed by oil red O. Also, in vitro experiments, quercetin displayed inhibitory role in LPS-induced ROS production, inflammatory response and apoptosis, which were linked with PI3K/AKT-regulated Caspase-3 and NF-κB activation. In conclusion, our results showed that quercetin inhibited atherosclerotic plaque development in high fructose feeding mice via PI3K/AKT activation regulated by ROS.

Different Anti-Contractile Function and Nitric Oxide Production of Thoracic and Abdominal Perivascular Adipose Tissues

Divergent phenotypes between the perivascular adipose tissue (PVAT) surrounding the abdominal and the thoracic aorta might be implicated in regional aortic differences, such as susceptibility to atherosclerosis. Although PVAT of the thoracic aorta exhibits anti-contractile function, the role of PVAT in the regulation of the vascular tone of the abdominal aorta is not well defined. In the present study, we compared the anti-contractile function, nitric oxide (NO) availability, and reactive oxygen species (ROS) formation in PVAT and vessel walls of abdominal and thoracic aorta. Abdominal and thoracic aortic tissue from male Wistar rats were used to perform functional and molecular experiments. PVAT reduced the contraction evoked by phenylephrine in the absence and presence of endothelium in the thoracic aorta, whereas this anti-contractile effect was not observed in the abdominal aorta. Abdominal PVAT exhibited a reduction in endothelial NO synthase (eNOS) expression compared with thoracic PVAT, without differences in eNOS expression in the vessel walls. In agreement with this result, NO production evaluated in situ using 4,5-diaminofluorescein was less pronounced in abdominal compared with thoracic aortic PVAT, whereas no significant difference was observed for endothelial NO production. Moreover, NOS inhibition with L-NAME enhanced the phenylephrine-induced contraction in endothelial-denuded rings with PVAT from thoracic but not abdominal aorta. ROS formation and lipid peroxidation products evaluated through the quantification of hydroethidine fluorescence and 4-hydroxynonenal adducts, respectively, were similar between PVAT and vessel walls from the abdominal and thoracic aorta. Extracellular superoxide dismutase (SOD) expression was similar between the vessel walls and PVAT of the abdominal and thoracic aorta. However, Mn-SOD levels were reduced, while CuZn-SOD levels were increased in abdominal PVAT compared with thoracic aortic PVAT. In conclusion, our results demonstrate that the anti-contractile function of PVAT is lost in the abdominal portion of the aorta through a reduction in eNOS-derived NO production compared with the thoracic aorta. Although relative SOD isoforms are different along the aorta, ROS formation, and lipid peroxidation seem to be similar. These findings highlight the specific regional roles of PVAT depots in the control of vascular function that can drive differences in susceptibility to vascular injury.

Long-Term Fructose Intake Increases Adipogenic Potential: Evidence of Direct Effects of Fructose on Adipocyte Precursor Cells

We have previously addressed that fructose rich diet (FRD) intake for three weeks increases the adipogenic potential of stromal vascular fraction cells from the retroperitoneal adipose tissue (RPAT). We have now evaluated the effect of prolonged FRD intake (eight weeks) on metabolic parameters, number of adipocyte precursor cells (APCs) and in vitro adipogenic potential from control (CTR) and FRD adult male rats. Additionally, we have examined the direct fructose effects on the adipogenic capacity of normal APCs. FRD fed rats had increased plasma levels of insulin, triglyceride and leptin, and RPAT mass and adipocyte size. FACS studies showed higher APCs number and adipogenic potential in FRD RPAT pads; data is supported by high mRNA levels of competency markers: PPARγ2 and Zfp423. Complementary in vitro experiments indicate that fructose-exposed normal APCs displayed an overall increased adipogenic capacity. We conclude that the RPAT mass expansion observed in eight week-FRD fed rats depends on combined accelerated adipogenesis and adipocyte hypertrophy, partially due to a direct effect of fructose on APCs.

High Risk of Metabolic and Adipose Tissue Dysfunctions in Adult Male Progeny, Due to Prenatal and Adulthood Malnutrition Induced by Fructose Rich Diet

The aim of this work was to determine the effect of a fructose rich diet (FRD) consumed by the pregnant mother on the endocrine-metabolic and in vivo and in vitro adipose tissue (AT) functions of the male offspring in adulthood. At 60 days of age, rats born to FRD-fed mothers (F) showed impaired glucose tolerance after glucose overload and high circulating levels of leptin (LEP). Despite the diminished mass of retroperitoneal AT, this tissue was characterized by enhanced LEP gene expression, and hypertrophic adipocytes secreting in vitro larger amounts of LEP. Analyses of stromal vascular fraction composition by flow cytometry revealed a reduced number of adipocyte precursor cells. Additionally, 60 day-old control (C) and F male rats were subjected to control diet (CC and FC animals) or FRD (CF and FF rats) for three weeks. FF animals were heavier and consumed more calories. Their metabolic-endocrine parameters were aggravated; they developed severe hyperglycemia, hypertriglyceridemia, hyperleptinemia and augmented AT mass with hypertrophic adipocytes. Our study highlights that manipulation of maternal diet induced an offspring phenotype mainly imprinted with a severely unhealthy adipogenic process with undesirable endocrine-metabolic consequences, putting them at high risk for developing a diabetic state.

Dietary Fructose Activates Insulin Signaling and Inflammation in Adipose Tissue: Modulatory Role of Resveratrol

The effects of high-fructose diet on adipose tissue insulin signaling and inflammatory process have been poorly documented. In this study, we examined the influences of long-term fructose intake and resveratrol supplementation on the expression of genes involved in insulin signaling and the levels of inflammatory cytokines and sex hormones in the white adipose tissues of male and female rats. Consumption of high-fructose diet for 24 weeks increased the expression of genes involved in insulin signaling including IR, IRS-1, IRS-2, Akt, PI3K, eNOS, mTOR, and PPARγ, despite induction of proinflammatory markers, iNOS, TNFα, IL-1β, IL-18, MDA, and ALT, as well as anti-inflammatory factors, IL-10 and Nrf2 in adipose tissues from males and females. Total and free testosterone concentrations of adipose tissues were impaired in males but increased in females, although there were no changes in their blood levels. Resveratrol supplementation markedly restored the levels of MDA, IL6, IL-10, and IL-18, as well as iNOS, Nrf2, and PI3K mRNA, in adipose tissues of both genders. Dietary fructose activates both insulin signaling and inflammatory pathway in the adipose tissues of male and female rats proposing no correlation between the tissue insulin signaling and inflammation. Resveratrol has partly modulatory effects on fructose-induced changes.

Ryanodine receptor phosphorylation by CaMKII promotes spontaneous Ca(2+) release events in a rodent model of early stage diabetes: The arrhythmogenic substrate

BACKGROUND

Heart failure and arrhythmias occur more frequently in patients with type 2 diabetes (T2DM) than in the general population. T2DM is preceded by a prediabetic condition marked by elevated reactive oxygen species (ROS) and subclinical cardiovascular defects. Although multifunctional Ca2+ calmodulin-dependent protein kinase II (CaMKII) is ROS-activated and CaMKII hyperactivity promotes cardiac diseases, a link between prediabetes and CaMKII in the heart is unprecedented.

OBJECTIVES

To prove the hypothesis that increased ROS and CaMKII activity contribute to heart failure and arrhythmogenic mechanisms in early stage diabetes.

METHODS-RESULTS

Echocardiography, electrocardiography, biochemical and intracellular Ca2+ (Ca2+i) determinations were performed in fructose-rich diet-induced impaired glucose tolerance, a prediabetes model, in rodents. Fructose-rich diet rats showed decreased contractility and hypertrophy associated with increased CaMKII activity, ROS production, oxidized CaMKII and enhanced CaMKII-dependent ryanodine receptor (RyR2) phosphorylation compared to rats fed with control diet. Isolated cardiomyocytes from fructose-rich diet showed increased spontaneous Ca2+i release events associated with spontaneous contractions, which were prevented by KN-93, a CaMKII inhibitor, or addition of Tempol, a ROS scavenger, to the diet. Moreover, fructose-rich diet myocytes showed increased diastolic Ca2+ during the burst of spontaneous Ca2+i release events. Mice treated with Tempol or with sarcoplasmic reticulum-targeted CaMKII-inhibition by transgenic expression of the CaMKII inhibitory peptide AIP, were protected from fructose-rich diet-induced spontaneous Ca2+i release events, spontaneous contractions and arrhythmogenesis in vivo, despite ROS increases.

CONCLUSIONS

RyR2 phosphorylation by ROS-activated CaMKII, contributes to impaired glucose tolerance-induced arrhythmogenic mechanisms, suggesting that CaMKII inhibition could prevent prediabetic cardiovascular complications and/or evolution.

Catechin and quercetin attenuate adipose inflammation in fructose-fed rats and 3T3-L1 adipocytes

SCOPE

This study evaluated the capacity of dietary catechin (C), quercetin (Q), and the combination of both (CQ), to attenuate adipose inflammation triggered by high fructose (HFr) consumption in rats and by tumor necrosis factor alpha (TNF-α) in 3T3-L1 adipocytes.

METHODS AND RESULTS

In rats, HFr consumption for 6 wk caused dyslipidemia, insulin resistance, reduced plasma adiponectin, adiposity, and adipose tissue inflammation. Dietary supplementation with 20 mg/kg/day of C, Q, and CQ improved all these parameters. In 3T3-L1 adipocytes, C and Q attenuated TNF-α-induced elevated protein carbonyls, increased proinflammatory cytokine expression (MCP-1, resistin), and decreased adiponectin. The protective effects of C and Q on adipose inflammation are in part associated with their capacity to (i) decrease the activation of the mitogen-activated kinases (MAPKs) JNK and p38; and (ii) prevent the downregulation of PPAR-γ. In summary, C and Q, and to a larger extent the combination of both, attenuated adipose proinflammatory signaling cascades and regulated the balance of molecules that improve (adiponectin) or impair (TNF-α, MCP-1, resistin) insulin sensitivity.

CONCLUSION

Together, these findings suggest that dietary Q and C may have potential benefits in mitigating MetS-associated adipose inflammation, oxidative stress, and insulin resistance.

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.

Alterations in neutrophil production and function at an early stage in the high-fructose rat model of metabolic syndrome

BACKGROUND

Although neutrophils are crucially involved in inflammation, they have received only little attention in metabolic syndrome (MetS). We hypothesized that neutrophil infiltration into adipose tissue (AT) may occur at an early stage of MetS, in association with modulation of major functions of neutrophils and of their bone marrow production.

METHODS

Fifty-six male Sprague-Dawley rats were fed regular (control rats (CRs)) or high-fructose (60%; fructose-fed rats (FFRs)) diets. After 6 weeks, metabolic parameters were measured. Distribution of neutrophils into AT was investigated by immunohistochemistry. Function of circulating neutrophils (activation, reactive oxygen species production, phagocytosis, and apoptosis) was determined by flow cytometry. Granulopoiesis was evaluated by measuring the number and survival characteristics of neutrophil progenitors using bone marrow culture assays and flow cytometry.

RESULTS

Compared with the CR group, the FFR group developed MetS (i.e., arterial hypertension, hypertriglyceridemia, fasting hyperglycemia, and greater intra-abdominal AT volume) and presented higher neutrophil infiltration into AT. At resting state, no significant difference for circulating neutrophil functions was observed between the 2 groups. In contrast, circulating neutrophils from the FFR group exhibited higher responses to phorbol-12-myristate-13-acetate for all studied functions, compared with the CR group, suggesting that early MetS induces neutrophil priming. In parallel, a diminished clonal capacity and an increased apoptosis in bone marrow-derived granulocyte progenitors and neutrophil precursors were observed in the FFR group compared with the CR group.

CONCLUSIONS

These results provide evidence of an increased infiltration into intra-abdominal AT and modified production, function, and phenotype of neutrophils at an early stage of high-fructose diet-induced MetS.

Detection of impaired cognitive function in rat with hepatosteatosis model and improving effect of GLP-1 analogs (exenatide) on cognitive function in hepatosteatosis

The aims of the study were to evaluate (1) detection of cognitive function changing in rat with hepatosteatosis model and (2) evaluate the effect of GLP-1 analog (exenatide) on cognitive function in hepatosteatosis. In the study group, 30% fructose was given in nutrition water to perform hepatosteatosis for 8 weeks to 18 male rats. Six male rats were chosen as control group and had normal nutrition. Fructose nutrition group were stratified into 3 groups. In first group (n = 6), intracerebroventricular (ICV) infusion of exenatide (n = 6) was given. ICV infusion of NaCl (n = 6) was given to second group. And also, the third group had no treatment. And also, rats were evaluated for passive avoidance learning (PAL) and liver histopathology. Mean levels of latency time were statistically significantly decreased in rats with hepatosteatosis than those of normal rats (P < 0.00001). However, mean level of latency time in rats with hepatosteatosis treated with ICV exenatide was statistically significantly increased than that of rats treated with ICV NaCl (P < 0.001). Memory performance falls off in rats with hepatosteatosis feeding on fructose (decreased latency time). However, GLP-1 ameliorates cognitive functions (increased latency time) in rats with hepatosteatosis and releated metabolic syndrome.

Effect of fructooligosaccharides fraction from Psacalium decompositum on inflammation and dyslipidemia in rats with fructose-induced obesity

Psacalium decompositum, commonly known as "Matarique," is a medicinal plant used in Mexico for diabetes mellitus empirical therapy. Previous studies have shown that the fructooligosaccharides (FOS) present in the roots of this plant exhibit a notable hypoglycemic effect in animal models; this effect might be associated with the attenuation of the inflammatory process and other metabolic disorders. In this study, we examined the effects of FOS fraction administration in a fructose-fed rat model for obesity. Phytochemical chromatographic studies (high performance thin layer chromatography and nuclear magnetic resonance) were performed to verify isolation of FOS. 24 male Wistar rats were maintained for 12 weeks on a diet of 20% HFCS in drinking water and chow. Glucose, cholesterol, triglycerides and liver transaminases levels were measured monthly, after administering FOS fraction intragastrically (150 mg/kg/day for 12 weeks), while the levels of inflammatory cytokines were only quantified at the end of the treatments. Rats treated with FOS fraction decreased body weight, cholesterol, triglycerides, and significantly reduced IL-6, IFN-γ, MCP-1, IL-1β and VEGF levels (p < 0.05). These results suggest that P. decompositum has anti-inflammatory and hypolipidemic properties that might be used as an alternative treatment for the control of obesity.

Lipoic acid prevents fructose-induced changes in liver carbohydrate metabolism: role of oxidative stress

BACKGROUND

Fructose administration rapidly induces oxidative stress that triggers compensatory hepatic metabolic changes. We evaluated the effect of an antioxidant, R/S-α-lipoic acid on fructose-induced oxidative stress and carbohydrate metabolism changes.

METHODS

Wistar rats were fed a standard commercial diet, the same diet plus 10% fructose in drinking water, or injected with R/S-α-lipoic acid (35mg/kg, i.p.) (control+L and fructose+L). Three weeks thereafter, blood samples were drawn to measure glucose, triglycerides, insulin, and the homeostasis model assessment-insulin resistance (HOMA-IR) and Matsuda indices. In the liver, we measured gene expression, protein content and activity of several enzymes, and metabolite concentration.

RESULTS

Comparable body weight changes and calorie intake were recorded in all groups after the treatments. Fructose fed rats had hyperinsulinemia, hypertriglyceridemia, higher HOMA-IR and lower Matsuda indices compared to control animals. Fructose fed rats showed increased fructokinase gene expression, protein content and activity, glucokinase and glucose-6-phosphatase gene expression and activity, glycogen storage, glucose-6-phosphate dehydrogenase mRNA and enzyme activity, NAD(P)H oxidase subunits (gp91(phox) and p22(phox)) gene expression and protein concentration and phosphofructokinase-2 protein content than control rats. All these changes were prevented by R/S-α-lipoic acid co-administration.

CONCLUSIONS

Fructose induces hepatic metabolic changes that presumably begin with increased fructose phosphorylation by fructokinase, followed by adaptive changes that attempt to switch the substrate flow from mitochondrial metabolism to energy storage. These changes can be effectively prevented by R/S-α-lipoic acid co-administration.

GENERAL SIGNIFICANCE

Control of oxidative stress could be a useful strategy to prevent the transition from impaired glucose tolerance to type 2 diabetes.

Islet cannabinoid receptors: cellular distribution and biological function

OBJECTIVES

This study aimed to determine the cellular distribution of islet cannabinoid receptors (CBs) and their involvement in the development of metabolic and hormonal changes in rats fed a fructose-rich diet (F).

METHODS

In normal rat islets, we determined CBs (immunofluorescence and retrotranscription-polymerase chain reaction) and glucose-stimulated insulin secretion (GSIS) of isolated islets incubated with the CB1 antagonist rimonabant (R) and/or different CBs agonists. In 3-week F-fed rats, we determined the in vivo effect of R on serum glucose, triglyceride, and insulin levels; homeostasis model assessment for insulin resistance, GSIS, and CBs and insulin receptor substrate gene expression levels (real-time polymerase chain reaction).

RESULTS

Cannabinoid receptors appeared exclusively in islet α cells. Whereas different CB agonists enhanced GSIS in normal rat islets, R did not affect it. F rats had higher serum triglyceride and insulin levels and homeostasis model assessment for insulin resistance than control rats; these alterations were prevented by R coadministration. Although R did not correct the increased GSIS observed in F islets, it modulated CBs and insulin receptor substrate gene expression.

CONCLUSIONS

Islet CBs would exert an important modulatory role in metabolic homeostasis. Administration of R and F affected islet CB expression and prevented the development of F-induced metabolic impairment. Selective islet CB1 blockers could be useful to prevent/treat the alterations induced by the intake of unbalanced/unhealthy diets.

Antioxidant treatment prevents the development of fructose-induced abdominal adipose tissue dysfunction

In the present study, we tested the effect of OS (oxidative stress) inhibition in rats fed on an FRD [fructose-rich diet; 10% (w/v) in drinking water] for 3 weeks. Normal adult male rats received a standard CD (commercial diet) or an FRD without or with an inhibitor of NADPH oxidase, APO (apocynin; 5 mM in drinking water; CD-APO and FRD-APO). We thereafter measured plasma OS and metabolic-endocrine markers, AAT (abdominal adipose tissue) mass and cell size, FA (fatty acid) composition (content and release), OS status, LEP (leptin) and IRS (insulin receptor substrate)-1/IRS-2 mRNAs, ROS (reactive oxygen species) production, NADPH oxidase activity and LEP release by isolated AAT adipocytes. FRD-fed rats had larger AAT mass without changes in body weight, and higher plasma levels of TAG (triacylglycerol), FAs, TBARS (thiobarbituric acid-reactive substance) and LEP. Although no significant changes in glucose and insulin plasma levels were observed in these animals, their HOMA-IR (homoeostasis model assessment of insulin resistance) values were significantly higher than those of CD. The AAT from FRD-fed rats had larger adipocytes, higher saturated FA content, higher NADPH oxidase activity, greater ROS production, a distorted FA content/release pattern, lower insulin sensitivity together with higher and lower mRNA content of LEP and IRS-1-/2 respectively, and released a larger amount of LEP. The development of all the clinical, OS, metabolic, endocrine and molecular changes induced by the FRD were significantly prevented by APO co-administration. The fact that APO treatment prevented both changes in NADPH oxidase activity and the development of all the FRD-induced AAT dysfunctions in normal rats strongly suggests that OS plays an important role in the FRD-induced MS (metabolic syndrome) phenotype.

Apocynin administration prevents the changes induced by a fructose-rich diet on rat liver metabolism and the antioxidant system

In the present study, we investigated the role of NADPH oxidase in F (fructose)-rich-diet-induced hepatic OS (oxidative stress) and metabolic changes, and their prevention by apocynin co-administration. Wistar rats were fed for 21 days on (i) a control diet, (ii) a control diet plus 10% F in the drinking water, (iii) a control diet with apocynin in the drinking water (CA) and (iv) F plus apocynin in the drinking water (FA). Glycaemia, triglyceridaemia, NEFAs (non-esterified fatty acids) and insulinaemia were determined. In the liver, we measured (i) NADPH oxidase activity, and gene and protein expression; (ii) protein carbonyl groups, GSH and TBARSs (thiobarbituric acid-reactive substances); (iii) catalase, CuZn-SOD (superoxide dismutase) and Mn-SOD expression; (iv) liver glycogen and lipid content; (v) GK (glucokinase), G6Pase (glucose-6-phosphatase) and G6PDH (glucose-6-phosphate dehydrogenase) activities; (vi) FAS (fatty acid synthase), GPAT (glycerol-3-phosphate acyltransferase), G6Pase and G6PDH, IL-1β (interleukin-1β), PAI-1 (plasminogen-activator inhibitor-1) and TNFα (tumour necrosis factor α) gene expression; and (vii) IκBα (inhibitor of nuclear factor κB α) protein expression. F-fed animals had high serum TAG (triacylglycerol), NEFA and insulin levels, high liver NADPH oxidase activity/expression, increased OS markers, reduced antioxidant enzyme expression, and increased glycogen, TAG storage and GK, G6Pase and G6PDH activities. They also had high G6Pase, G6PDH, FAS, GPAT, TNFα and IL-1β gene expression and decreased IκBα expression. Co-administration of apocynin to F-fed rats prevented the development of most of these abnormalities. In conclusion, NADPH oxidase plays a key role in F-induced hepatic OS production and probably also in the mechanism of liver steatosis, suggesting its potential usefulness for the prevention/treatment of T2DM (Type 2 diabetes mellitus).

Lipoic acid prevents liver metabolic changes induced by administration of a fructose-rich diet

BACKGROUND

To evaluate whether co-administration of R/S-α-lipoic acid can prevent the development of oxidative stress and metabolic changes induced by a fructose-rich diet (F).

METHODS

We assessed glycemia in the fasting state and during an oral glucose tolerance test, triglyceridemia and insulinemia in rats fed with standard diet (control) and fructose without or with R/S-α-lipoic acid. Insulin resistance and hepatic insulin sensitivity were also calculated. In liver, we measured reduced glutathione, protein carbonyl groups, antioxidant capacity by ABTS assay, antioxidant enzymes (catalase and superoxide dismutase 1 and 2), uncoupling protein 2, PPARδ and PPARγ protein expressions, SREBP-1c, fatty acid synthase and glycerol-3-phosphate acyltransferase-1 gene expression, and glucokinase activity.

RESULTS

R/S-α-lipoic acid co-administration to F-fed rats a) prevented hyperinsulinemia, hypertriglyceridemia and insulin resistance, b) improved hepatic insulin sensitivity and glucose tolerance, c) decreased liver oxidative stress and increased antioxidant capacity and antioxidant enzymes expression, d) decreased uncoupling protein 2 and PPARδ protein expression and increased PPARγ levels, e) restored the basal gene expression of PPARδ, SREBP-1c and the lipogenic genes fatty acid synthase and glycerol-3-phosphate acyltransferase, and f) decreased the fructose-mediated enhancement of glucokinase activity.

CONCLUSIONS

Our results suggest that fructose-induced oxidative stress is an early phenomenon associated with compensatory hepatic metabolic mechanisms, and that treatment with an antioxidant prevented the development of such changes.

GENERAL SIGNIFICANCE

This knowledge would help to better understand the mechanisms involved in liver adaptation to fructose-induced oxidative stress and to develop effective strategies to prevent and treat, at early stages, obesity and type 2 diabetes mellitus.

Effect of pioglitazone on the fructose-induced abdominal adipose tissue dysfunction

Aim. To test the potential role of PPARγ in the endocrine abdominal tissue dysfunction induced by feeding normal rats with a fructose rich diet (FRD) during three weeks. Methodology. Adult normal male rats received a standard commercial diet (CD) or FRD, (10% in drinking water) without or with pioglitazone (PIO) (i.p. 0.25 mg/Kg BW/day; CD-PIO and FRD-PIO). Thereafter, we measured circulating metabolic, endocrine, and oxidative stress (OS) markers, abdominal adipose tissue (AAT) mass, leptin (LEP) and plasminogen activator inhibitor-1 (PAI-1) tissue content/expression, and leptin release by isolated adipocytes incubated with different concentrations of insulin. Results. Plasma glucose, insulin, triglyceride, TBARS, LEP, and PAI-1 levels were higher in FRD rats; PIO coadministration fully prevented all these increments. AAT adipocytes from FRD rats were larger, secreted a higher amount of LEP, and displayed decreased sensitivity to insulin stimulation; these effects were significantly ameliorated by PIO. Whereas AAT LEP and PAI-1 (mRNA) concentrations increased significantly in FRD rats, those of insulin-receptor-substrate- (IRS-) 1 and IRS-2 were reduced. PIO coadministration prevented FRD effects on LEP, PAI-1, and IRS-2 (fully) and IRS-1 (partially) mRNAs in AAT. Conclusion. PPARγ would play a relevant role in the development of the FRD-induced metabolic-endocrine dysfunction.

Fructose rich diet-induced high plasminogen activator inhibitor-1 (PAI-1) production in the adult female rat: protective effect of progesterone

The effect of progesterone (P4) on fructose rich diet (FRD) intake-induced metabolic, endocrine and parametrial adipose tissue (PMAT) dysfunctions was studied in the adult female rat. Sixty day-old rats were i.m. treated with oil alone (control, CT) or containing P4 (12 mg/kg). Rats ate Purina chow-diet ad libitum throughout the entire experiment and, between 100 and 120 days of age drank ad libitum tap water alone (normal diet; CT-ND and P4-ND) or containing fructose (10% w/v; CT-FRD and P4-FRD). At age 120 days, animals were subjected to a glucose tolerance test or decapitated. Plasma concentrations of various biomarkers and PMAT gene abundance were monitored. P4-ND (vs. CT-ND) rats showed elevated circulating levels of lipids. CT-FRD rats displayed high (vs. CT-ND) plasma concentrations of lipids, leptin, adiponectin and plasminogen activator inhibitor-1 (PAI-1). Lipidemia and adiponectinemia were high (vs. P4-ND) in P4-FRD rats. Although P4 failed to prevent FRD-induced hyperleptinemia, it was fully protective on FRD-enhanced plasma PAI-1 levels. PMAT leptin and adiponectin mRNAs were high in CT-FRD and P4-FRD rats. While FRD enhanced PMAT PAI-1 mRNA abundance in CT rats, this effect was absent in P4 rats. Our study supports that a preceding P4-enriched milieu prevented the enhanced prothrombotic risk induced by FRD-elicited high PAI-1 production.

Oral metformin treatment prevents enhanced insulin demand and placental dysfunction in the pregnant rat fed a fructose-rich diet

The intake of a fructose-rich diet (FRD) in the normal female rat induces features similar to those observed in the human metabolic syndrome phenotype. We studied the impact of FRD administration to mothers on pregnancy outcome. On gestational day (Gd) zero rats were assigned to either group: ad libitum drinking tap water alone (normal diet, ND) or containing fructose (10% w/vol; FRD) through pregnancy; all rats were fed a Purina chow diet ad libitum ND and FRD rats were daily cotreated or not with metformin (60 mg/Kg/day oral; ND + MF and FRD + MF) and submitted to a high glucose load test on Gd 14. Additionally, placentas from different groups were studied on Gd 20. Data indicated that: (1) although FRD rats well tolerated glucose overload, their circulating levels of insulin were significantly higher than in ND rats; (2) the mesometrial triangle blood vessel area was significantly lower in placentas from FRD than ND dams; (3) the detrimental effects of FRD administration to mothers were ameliorated by metformin cotreatment. Our study suggests that excessive intake of fructose during pregnancy enhanced the risk for developing gestational diabetes and subsequent preeclampsia, and that metformin prevented the poor pregnancy outcome induced by FRD.

Changes in glucose tolerance and leptin responsiveness of rats offered a choice of lard, sucrose, and chow

Rats offered chow, lard, and 30% sucrose solution (choice) rapidly become obese. We tested metabolic disturbances in rats offered choice, chow+lard, or chow+30% sucrose solution [chow+liquid sucrose (LS)] and compared them with rats fed a composite 60% kcal fat, 7% sucrose diet [high-fat diet (HFD)], or a 10% kcal fat, 35% sucrose diet [low-fat diet (LFD)]. Choice rats had the highest energy intake, but HFD rats gained the most weight. After 23 days carcass fat was the same for choice, HFD, chow+lard, and chow+LS groups. Glucose clearance was the same for all groups during an intraperitoneal glucose tolerance test (GTT) on day 12, but fasting insulin was increased in choice, LFD fed, and chow+LS rats. By contrast, only choice and chow+LS rats were resistant to an intraperitoneal injection of 2 mg leptin/kg on day 17. In experiment 2 choice rats were insulin insensitive during an intraperitoneal GTT, but this was corrected in an oral GTT due to GLP-1 release. UCP-1 protein was increased in brown fat and inguinal white fat in choice rats, and this was associated with a significant increase in energy expenditure of choice rats during the dark period whether expenditure was expressed on a per animal or a metabolic body size basis. The increase in expenditure obviously was not great enough to prevent development of obesity. Further studies are required to determine the mechanistic basis of the rapid onset of leptin resistance in choice rats and how consumption of sucrose solution drives this process.

Nutritional and hormonal modulation of adiponectin and its receptors adipoR1 and adipoR2

Adiponectin is the most abundant plasma protein synthesized mostly by adipose tissue and is an insulin-sensitive hormone, playing a central role in glucose and lipid metabolism. Adiponectin effects are mediated via two receptors, adipoR1 and adipoR2. Several hormones and diet components that are involved in insulin resistance may impair insulin sensitivity at least in part by decreasing adiponectin and adiponectin receptors. Adiponectin expression and serum levels are associated with the amount and type of fatty acids and carbohydrate consumed. Other food items, such as vitamins, alcohol, sodium, green tea, and coffee, have been reported to modify adiponectin levels. Several hormones, including testosterone, estrogen, prolactin, glucocorticoids, catecholamines, and growth hormone, have been shown to inhibit adiponectin production, but the studies are still controversial. Even so, adiponectin is a potential therapeutic target in the treatment of diabetes mellitus and other diseases associated with hypoadiponectinemia.

An extract of chokeberry attenuates weight gain and modulates insulin, adipogenic and inflammatory signalling pathways in epididymal adipose tissue of rats fed a fructose-rich diet

Chokeberries are a rich source of anthocyanins, which may contribute to the prevention of obesity and the metabolic syndrome. The aim of the present study was to determine if an extract from chokeberries would reduce weight gain in rats fed a fructose-rich diet (FRD) and to explore the potential mechanisms related to insulin signalling, adipogenesis and inflammatory-related pathways. Wistar rats were fed a FRD for 6 weeks to induce insulin resistance, with or without chokeberry extract (CBE) added to the drinking-water (100 and 200 mg/kg body weight, daily: CBE100 and CBE200). Both doses of CBE consumption lowered epididymal fat, blood glucose, TAG, cholesterol and LDL-cholesterol. CBE consumption also elevated plasma adiponectin levels and inhibited plasma TNF-α and IL6, compared with the control group. There were increases in the mRNA expression for Irs1, Irs2, Pi3k, Glut1, Glut4 and Gys1, and decreases in mRNA levels of Gsk3β. The protein and gene expression of adiponectin and Pparγ mRNA levels were up-regulated and Fabp4, Fas and Lpl mRNA levels were inhibited. The levels of gene expression of inflammatory cytokines, such as Il1β, Il6 and Tnfα were lowered, and protein and gene expression of ZFP36 (zinc finger protein) were enhanced in the epididymal adipose tissue of the rats that consumed the CBE200 extract. In summary, these results suggest that the CBE decreased risk factors related to insulin resistance by modulating multiple pathways associated with insulin signalling, adipogenesis and inflammation.

Rat liver uncoupling protein 2: changes induced by a fructose-rich diet

AIM

To evaluate the role of uncoupling protein 2 (UCP2) and peroxisome proliferator-activated receptors (PPARs) in the response of liver to glycoxidative stress triggered by administration of a fructose-rich diet (FRD).

MAIN METHODS

We assessed blood glucose in the fasting state and after a glucose load (glucose-oxidase method), serum triglyceride (enzymatic measurement), insulin (radioimmunoassay), alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels (colorimetric kits) in control and FRD animals. In liver, we measured UCP2, PPARα, PPARδ and PPARγ gene (real-time PCR) and protein (Western blot) expression, fatty acid synthase (FAS) and glycerol-3-phosphate acyltransferase (GPAT) gene expression, as well as triglyceride content.

KEY FINDINGS

Blood glucose, serum insulin and triglyceride levels, homeostasis model assessment of insulin resistance (HOMA-IR) indexes and impaired glucose tolerance were higher in FRD rats. Whereas UCP2 and PPARδ gene and protein expression increased in these animals; PPARγ levels were lower and those of PPARα remained unchanged. FRD also increased the mRNA expression of PPARδ target genes FAS and GPAT.

SIGNIFICANCE

Our results suggest that a) the increased UCP2 gene and protein expression measured in FRD rats could be part of a compensatory mechanism to reduce reactive oxygen species production induced by the fructose overload, and b) PPARs expression participates actively in the regulation of UCP2 expression, and under the metabolic condition tested, PPARδ played a key role. This knowledge would help to better understand the mechanisms involved in liver adaptation to fructose-induced glycoxidative stress, and to develop appropriate prevention strategies in obesity and type 2 diabetes.

The relation between dietary fructose, dietary fat and leptin responsiveness in rats

Others reported that rats fed a high-fructose diet for 6 months were leptin resistant. We tested peripheral and/or central leptin responses in rats fed fructose for shorter time periods. Rats fed a diet containing 60% energy (% kcal) fructose and 10% kcal fat diet for 21 days had the same serum triglycerides (TG), gained less weight than controls, decreased their food intake and weight gain in response to central injections of 0.5 or 1.0 ug leptin, but were resistant to an i.p. injection of 2.0 mg leptin/kg. An i.p. injection of 1 mg leptin/kg increased phosphorylation of hypothalamic signal transducer and activator of transcription 3 (PSTAT3) implying resistance was not a failure of leptin to cross the blood brain barrier. The effects of dietary fructose were compared with those of dietary fat. Rats fed a 10%kcal fructose and 30%kcal fat diet for 39 days were leptin resistant whereas rats fed a 40%kcal fructose and 30%kcal fat diet responded to i.p. leptin. Another monosaccharide, glucose, replicated the effects of fructose in the 30% kcal fat diet. Surprisingly, none of the rats showed a reliable response to third ventricle leptin and peripheral leptin failed to stimulate hypothalamic PSTAT3 although it did increase PSTAT3 in the brainstem of rats fed the 40%kcal fructose or glucose diets. Thus a high-fructose, low-fat diet induces peripheral leptin resistance in less than 4 weeks, but high dietary concentrations of fructose or glucose prevent peripheral leptin resistance in rats fed a high-fat diet.

A high fructose diet does not affect amphetamine self-administration or spatial water maze learning and memory in female rats

High energy diets can have a detrimental effect on brain plasticity. For example, a high fructose diet impairs spatial memory in male rats. The aim of the present study was to determine whether a high fructose diet impairs another form of learning and memory: drug reinforcement learning. Female Sprague-Dawley rats were fed a high fructose diet (60%) from weaning at postnatal day (PND) 21, then allowed to acquire lever-pressing maintained by intravenous (i.v.) amphetamine at PND 68, 109, or 165. Acquisition was tested on a fixed ratio one (FR1) schedule of reinforcement (0.025 mg/kg/infusion, 1h daily sessions, 10 sessions over 14 days), followed by testing for reinforcing efficacy on a progressive ratio (PR) schedule (0.025, 0.01, and 0.1mg/kg/infusion), 14 days of abstinence, and within-session extinction and reinstatement tests. Subsequently, water maze acquisition and retention were tested in these subjects as well as a separate cohort tested in the water maze only. The diet had no effect on acquisition, reinforcing efficacy, extinction, or reinstatement of amphetamine seeking. Nor did the diet alter any measures of spatial memory. The high fructose diet did decrease body mass and increase relative liver and spleen mass, but did not affect plasma triglyceride concentrations consistently. Together with prior research on males, these results suggest that the metabolism of fructose and the effects of a high fructose diet on learning and memory may be sex-dependent.

Effect of red wine on adipocytokine expression and vascular alterations in fructose-fed rats

BACKGROUND

Imbalance in adipocytokines secretion is related to the development of metabolic syndrome (MS). In addition, moderate consumption of red wine (RW) decreases the risk of cardiovascular disease. The aim of this study was to evaluate the effects of moderate consumption of RW or ethanol (E) on adiponectin and resistin expression, and vascular alterations in fructose-fed rats (FFRs) as an experimental model of MS.

METHODS

Thirty-day-old male Wistar rats were assigned to control (C), F (10% fructose in drinking water), F+E (4.5 ml/kg), and F+RW (35 ml/kg of Malbec RW containing 4.5 ml/kg E). E and RW were administered during the last 4 weeks of a 10-week period.

RESULTS

RW administration to F rats was able to significantly decrease insulin resistance, mesenteric adipose tissue weight, and systolic blood pressure (SBP) compared to F group. F+E only reduced the SBP (P < 0.05 vs. F). F+RW also reduced aortic NAD(P)H-oxidase activity, NAD(P)H subunits Nox4 expression in mesenteric tissue, plasma thiobarbituric acid reactive substances (TBARS), and recovered plasma total antioxidant activity (TAA) compared to F and F+E groups (P < 0.05). Adiponectin expression decreased, whereas resistin, vascular cell adhesion molecules-1 (VCAM-1), and nuclear factor-κB (NF-κB) expression and vascular remodeling in mesenteric arteries were higher in F than in C group (P < 0.05). Only RW was able to partially reverse the aforementioned alterations.

CONCLUSION

In this study, Malbec RW, but not alcohol alone, improved the balance of adipocytokines and attenuated the oxidative stress and vascular inflammation in a model of MS, suggesting that nonalcohol components of RW are responsible for the beneficial effects.

Pharmacological and non-pharmacological interventions to influence adipose tissue function

Obesity is associated with metabolic derangements such as insulin resistance, inflammation and hypercoagulobility which can all be understood as consequences of adipose tissue dysfunction. The potential role for adipose tissue derived cytokines and adipokines in the development of vascular disease and diabetes may produce a clinical need to influence adipose tissue function. Various pharmacological and non-pharmacological interventions affect plasma cytokine and adipokine levels. The effects of these interventions depend on weight loss per se, changes in fat distribution without weight loss and/or direct effects on adipose tissue inflammation.

Weight loss, as a result of diet, pharmacology and surgery, positively influences plasma adipokines and systemic inflammation. Several classes of drugs influence systemic inflammation directly through their anti-inflammatory actions. PPAR-γ agonism positively influences adipose tissue inflammation in several classes of intervention such as the thiazolidinediones and perhaps salicylates, CB1-antagonists and angiotensin II receptor blockers. Furthermore, within drug classes there are differential effects of individual pharmacologic agents on adipose tissue function.

It can be concluded that several commonly used pharmacological and non-pharmacological interventions have unintended influences on adipose tissue function. Improving adipose tissue function may contribute to reducing the risk of vascular diseases and the development of type 2 diabetes.

Sitagliptin prevents the development of metabolic and hormonal disturbances, increased β-cell apoptosis and liver steatosis induced by a fructose-rich diet in normal rats

The aim of the present study was to test the effect of sitagliptin and exendin-4 upon metabolic alterations, β-cell mass decrease and hepatic steatosis induced by F (fructose) in rats. Normal adult male Wistar rats received a standard commercial diet without (C) or with 10% (w/v) F in the drinking water (F) for 3 weeks; animals from each group were randomly divided into three subgroups: untreated (C and F) and simultaneously receiving either sitagliptin (CS and FS; 115.2 mg/day per rat) or exendin-4 (CE and FE; 0.35 nmol/kg of body weight, intraperitoneally). Water and food intake, oral glucose tolerance, plasma glucose, triacylglycerol (triglyceride), insulin and fructosamine concentration, HOMA-IR [HOMA (homoeostasis model assessment) for insulin resistance], HOMA-β (HOMA for β-cell function) and liver triacylglycerol content were measured. Pancreas immunomorphometric analyses were also performed. IGT (impaired glucose tolerance), plasma triacylglycerol, fructosamine and insulin levels, HOMA-IR and HOMA-β indexes, and liver triacylglycerol content were significantly higher in F rats. Islet β-cell mass was significantly lower in these rats, due to an increase in the percentage of apoptosis. The administration of exendin-4 and sitagliptin to F animals prevented the development of all the metabolic disturbances and the changes in β-cell mass and fatty liver. Thus these compounds, useful in treating Type 2 diabetes, would also prevent/delay the progression of early metabolic and tissue markers of this disease.

Early alterations in vascular contractility associated to changes in fatty acid composition and oxidative stress markers in perivascular adipose tissue

Aim

To test the early effect of fructose-induced changes in fatty acid composition and oxidative stress markers in perivascular adipose tissue (PVAT) upon vascular contractility.

Methods

Adult male Wistar rats were fed a commercial diet without (CD) or with 10% fructose (FRD) in the drinking water for 3 weeks. We measured plasma metabolic parameters, lipid composition and oxidative stress markers in aortic PVAT. Vascular contractility was measured in aortic rings sequentially, stimulated with serotonin (5-HT) and high K⁺-induced depolarization using intact and thereafter PVAT-deprived rings.

Results

Comparable body weights were recorded in both groups. FRD rats had increased plasma triglyceride and fructosamine levels. Their PVAT had an increased saturated to mono- or poly-unsaturated fatty acid ratio, a significant decrease in total superoxide dismutase and glutathione peroxidase activities and in the total content of glutathione. Conversely, lipid peroxidation (TBARS), nitric oxide content, and gluthathione reductase activity were significantly higher, indicating an increase in oxidative stress. In aortic rings, removal of PVAT increased serotonin-induced contractions, but the effect was significantly lower in rings from FRD rats. This effect was no longer observed when the two contractions were performed in PVAT-deprived rings. PVAT did not affect the contractions triggered by high K⁺-induced depolarization either in CD or FRD rats.

Conclusions

FRD induces multiple metabolic and endocrine systemic alterations which also alter PVAT and the vascular relaxant properties of this tissue. The changes in PVAT would affect its paracrine modulation of vascular function.

Increased male offspring's risk of metabolic-neuroendocrine dysfunction and overweight after fructose-rich diet intake by the lactating mother

An adverse endogenous environment during early life predisposes the organism to develop metabolic disorders. We evaluated the impact of intake of an iso-caloric fructose rich diet (FRD) by lactating mothers (LM) on several metabolic functions of their male offspring. On postnatal d 1, ad libitum eating, lactating Sprague-Dawley rats received either 10% F (wt/vol; FRD-LM) or tap water (controls, CTR-LM) to drink throughout lactation. Weaned male offspring were fed ad libitum a normal diet, and body weight (BW) and food intake were registered until experimentation (60 d of age). Basal circulating levels of metabolic markers were evaluated. Both iv glucose tolerance and hypothalamic leptin sensitivity tests were performed. The hypothalamus was dissected for isolation of total RNA and Western blot analysis. Retroperitoneal (RP) adipose tissue was dissected and either kept frozen for gene analysis or digested to isolate adipocytes or for histological studies. FRD rats showed increased BW and decreased hypothalamic sensitivity to exogenous leptin, enhanced food intake (between 49-60 d), and decreased hypothalamic expression of several anorexigenic signals. FRD rats developed increased insulin and leptin peripheral levels and decreased adiponectinemia; although FRD rats normally tolerated glucose excess, it was associated with enhanced insulin secretion. FRD RP adipocytes were enlarged and spontaneously released high leptin, although they were less sensitive to insulin-induced leptin release. Accordingly, RP fat leptin gene expression was high in FRD rats. Excessive fructose consumption by lactating mothers resulted in deep neuroendocrine-metabolic disorders of their male offspring, probably enhancing the susceptibility to develop overweight/obesity during adult life.