Comparison of mechanisms involved in impaired vascular reactivity between high sucrose and high fat diets in rats

Obesity-related vascular dysfunction persists after weight loss and is associated with decreased vascular glucagon-like peptide (GLP-1) receptor in female rats

Obesity-related cardiovascular complications are a major health problem worldwide. Overconsumption of the Western diet is a well-known culprit for the development of obesity. While short-term weight loss through switching from a Western diet to a normal diet is known to promote metabolic improvement, its short-term effects on vascular parameters are not well-characterized. Glucagon-like peptide 1 (GLP-1), an incretin with vasculo-protective properties, is decreased in plasma from obese patients. We hypothesize that obesity causes persistent vascular dysfunction in association with downregulation of vascular GLP-1R. Female Wistar rats were randomized into three groups: lean received a chow diet for 28 weeks, obese received a Western diet for 28 weeks, and reverse obese received a Western diet for 18 weeks followed by 12 weeks of standard chow diet. The obese group exhibited increased body weight and body mass index, while the reverse obese group lost weight. Weight loss failed to reverse impaired vasodilation and high systolic blood pressure in obese rats. Strikingly, our results show that obese rats exhibit decreased serum levels of GLP-1 accompanied by decreased vascular GLP-1R expression. Weight loss recovered GLP-1 serum levels, however GLP-1R expression remained downregulated. Decreased Akt phosphorylation was observed in the obese and reverse obese group, suggesting that GLP-1/Akt signaling is persistently downregulated. Our results support that GLP-1 signaling is associated with obesity-related vascular dysfunction in females and short-term weight loss does not guarantee recovery of vascular function. This study suggests that GLP-1R may be a potential target for therapeutic intervention in obesity-related hypertension in females.

Zucker Diabetic Sprague Dawley rat (ZDSD): type 2 diabetes translational research model

New Findings

What is the topic of this review?

The Zucker Diabetic‐Sprague Dawley (ZDSD) rat is in the early adoption phase of use by researchers in the fields of diabetes, including prediabetes, obesity and metabolic syndrome. It is essential that physiology researchers choose preclinical models that model human type 2 diabetes appropriately and are aware of the limitations on experimental design.

What advances does it highlight?

Our review of the scientific literature finds that although sex, age and diets contribute to variability, the ZDSD phenotype and disease progression model the characteristics of humans who have prediabetes and diabetes, including co‐morbidities.

Abstract

Type 2 diabetes (T2D) is a prevalent disease and a significant concern for global population health. For persons with T2D, clinical treatments target not only the characteristics of hyperglycaemia and insulin resistance, but also co‐morbidities, such as obesity, cardiovascular and renal disease, neuropathies and skeletal bone conditions. The Zucker Diabetic‐Sprague Dawley (ZDSD) rat is a rodent model developed for experimental studies of T2D. We reviewed the scientific literature to highlight the characteristics of T2D development and the associated phenotypes, such as metabolic syndrome, cardiovascular complications and bone and skeletal pathologies in ZDSD rats. We found that ZDSD phenotype characteristics are independent of leptin receptor signalling. The ZDSD rat develops prediabetes, then progresses to overt diabetes that is accelerated by introduction of a timed high‐fat diet. In male ZDSD rats, glycated haemoglobin (HbA1c) increases at a constant rate from 7 to >30 weeks of age. Diabetic ZDSD rats are moderately hypertensive compared with other rat strains. Diabetes in ZDSD rats leads to endothelial dysfunction in specific vasculatures, impaired wound healing, decreased systolic and diastolic cardiac function, neuropathy and nephropathy. Changes to bone composition and the skeleton increase the risk of bone fractures. Zucker Diabetic‐Sprague Dawley rats have not yet achieved widespread use by researchers. We highlight sex‐related differences in the ZDSD phenotype and gaps in knowledge for future studies. Overall, scientific data support the premise that the phenotype and disease progression in ZDSD rats models the characteristics in humans. We conclude that ZDSD rats are an advantageous model to advance understanding and discovery of treatments for T2D through preclinical research.

Different effects of high-fat and high-sucrose diets on the physiology of perivascular adipose tissues of the thoracic and abdominal aorta

Vascular diseases such as atherosclerosis and aneurysms are associated with diet. Perivascular adipose tissue (PVAT) was reportedly involved in the regulation of vascular functions. It is suggested that imbalanced diets can cause PVAT inflammation and dysfunction as well as impaired vascular function. However, the association between diets and PVAT are not clearly understood. Here, we showed that a high-fat and a high-sucrose diet affected PVAT at different sites. A high-fat diet induced increased number of large-sized lipid droplets and increased CD (Cluster of differentiation) 68+ macrophage- and monocyte chemotactic protein (MCP)-1-positive areas in the abdominal aortic PVAT (aPVAT). In addition, a high-fat diet caused decreased collagen fibre-positive area and increased CD68+ macrophage- and MCP-1-positive areas in the abdominal aorta. In contrast, a high-sucrose diet induced increased number of large-sized lipid droplets, increased CD68+ macrophage- and MCP-1-positive areas, and decreased UCP-1 positive area in the thoracic aortic PVAT (tPVAT). A high-sucrose diet caused decreased collagen fibre-positive area and increased CD68+ macrophage- and MCP-1-positive areas in the thoracic aorta. These results could be attributed to the different adipocyte populations in the tPVAT and aPVAT. Our results provide pathological evidence to improve our understanding of the relationship between diet and vascular diseases.

Short-term high fat diet alters genes associated with metabolic and vascular dysfunction during adolescence in rats: a pilot study

Background

Diet-induced metabolic dysfunction precedes multiple disease states including diabetes, heart disease, and vascular dysfunction. The critical role of the vasculature in disease progression is established, yet the details of how gene expression changes in early cardiovascular disease remain an enigma. The objective of the current pilot project was to evaluate whether a quantitative assessment of gene expression within the aorta of six-week old healthy male Sprague-Dawley rats compared to those exhibiting symptoms of metabolic dysfunction could reveal potential mediators of vascular dysfunction.

Methods

RNA was extracted from the aorta of eight rats from a larger experiment; four animals fed a high-fat diet (HFD) known to induce symptoms of metabolic dysfunction (hypertension, increased adiposity, fasting hyperglycemia) and four age-matched healthy animals fed a standard chow diet (CHOW). The bioinformatic workflow included Gene Ontology (GO) biological process enrichment and network analyses.

Results

The resulting network contained genes relevant to physiological processes including fat and protein metabolism, oxygen transport, hormone regulation, vascular regulation, thermoregulation, and circadian rhythm. The majority of differentially regulated genes were downregulated, including several associated with circadian clock function. In contrast, leptin and 3-hydroxy-3-methylglutaryl-CoA synthase 2 (Hmgcs2) were notably upregulated. Leptin is involved in several major energy balance signaling pathways and Hmgcs2 is a mitochondrial enzyme that catalyzes the first reaction of ketogenesis.

Conclusion

Together, these data describe changes in gene expression within the aortic wall of HFD rats with early metabolic dysfunction and highlight potential pathways and signaling intermediates that may impact the development of early vascular dysfunction.

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.

A novel organic mineral complex prevented high fat diet-induced hyperglycemia, endotoxemia, liver injury and endothelial dysfunction in young male Sprague-Dawley rats

The prevalence of metabolic syndrome (MetSyn) has risen 35% since 2012 and over two-thirds of Americans exhibit features characterizing this condition (obesity, dyslipidemia, hyperglycemia, insulin resistance and/or endothelial dysfunction). The aim of this study was to evaluate the effects of a novel dietary supplemental organic mineral complex (OMC) on these risk factors in a rodent model of MetSyn. Six-week old male Sprague-Dawley rats were fed either standard chow or a high-fat diet (HFD) composed of 60% kcal from fat for 10 weeks. Rats were also treated with OMC in their drinking water at either 0 mg/mL (control), 0.6 mg/mL, or 3.0 mg/mL. The HFD-treated rats exhibited significantly increased body mass (p<0.05), epididymal fat pad mass (p<0.001), waist circumference (p = 0.010), in addition to elevations in plasma endotoxins (p<0.001), ALT activity (p<0.001), fasting serum glucose (p = 0.025) and insulin concentrations (p = 0.009). OMC did not affect body weight or adiposity induced by the HFD. At the higher dose OMC significantly blunted HFD-induced hyperglycemia (p = 0.021), whereas both low and high doses of OMC prevented HFD-induced endotoxemia (p = 0.002 and <0.001, respectively) and hepatocyte injury (ALT activity, p<0.01). Despite evidence of oxidative stress (elevated urinary H2O2 p = 0.032) in HFD-fed rats, OMC exhibited no demonstrable antioxidative effect. Consistent with prior studies, mesenteric arteries from HFD rats had more uncoupled eNOS (p = 0.006) and iNOS protein expression (p = 0.027) in addition to impaired endothelium-dependent vasodilation that was abrogated by the high dose of OMC (p<0.05). This effect of OMC may be attributed to the high nitrate content of the supplement. These findings suggest that the OMC supplement, particularly at the higher dose, ameliorated several risk factors associated with MetSyn via a non-antioxidant-dependent mechanism.

The Postprandial Appearance of Features of Cardiometabolic Risk: Acute Induction and Prevention by Nutrients and Other Dietary Substances

The purpose of this review is to provide an overview of diets, food, and food components that affect postprandial inflammation, endothelial function, and oxidative stress, which are related to cardiometabolic risk. A high-energy meal, rich in saturated fat and sugars, induces the transient appearance of a series of metabolic, signaling and physiological dysregulations or dysfunctions, including oxidative stress, low-grade inflammation, and endothelial dysfunction, which are directly related to the amplitude of postprandial plasma triglycerides and glucose. Low-grade inflammation and endothelial dysfunction are also known to cluster together with insulin resistance, a third risk factor for cardiovascular diseases (CVD) and type-II diabetes, thus making a considerable contribution to cardiometabolic risk. Because of the marked relevance of the postprandial model to nutritional pathophysiology, many studies have investigated whether adding various nutrients and other substances to such a challenge meal might mitigate the onset of these adverse effects. Some foods (e.g., nuts, berries, and citrus), nutrients (e.g., l-arginine), and other substances (various polyphenols) have been widely studied. Reports of favorable effects in the postprandial state have concerned plasma markers for systemic or vascular pro-inflammatory conditions, the activation of inflammatory pathways in plasma monocytes, vascular endothelial function (mostly assessed using physiological criteria), and postprandial oxidative stress. Although the literature is fragmented, this topic warrants further study using multiple endpoints and markers to investigate whether the interesting candidates identified might prevent or limit the postprandial appearance of critical features of cardiometabolic risk.

Six-Week High-Fat Diet Alters the Gut Microbiome and Promotes Cecal Inflammation, Endotoxin Production, and Simple Steatosis without Obesity in Male Rats

Energy-dense foods can alter gut microbial diversity. However, the physiological effects of diet-induced microbial changes on the development of nonalcoholic fatty liver disease (NAFLD) remain debatable. We hypothesized that high-fat intake for 6 weeks would promote intestinal dysbiosis by increasing gram-positive bacteria, inducing the intestinal production of proinflammatory cytokines and subsequent hepatic lipid infiltration in young male rats. Six-week old male Sprague-Dawley rats were divided into two groups and fed either a standard rodent chow or a 60% high-fat diet (HFD) for 6 weeks. Chromogenic endotoxin quantification assays indicate an increase in lipopolysaccharide concentration in the plasma of HFD rats (p = 0.032). Additionally, Western blot analyses of the cecum showed significantly greater protein expression of the transcription factor, nuclear factor kappa B (NF-kB), (p = 0.037) and the proinflammatory cytokine, interleukin-1β (IL-1β), (p = 0.042) in rats fed HFD. Linear discriminate analysis of effect size (LEfSe) showed greater abundance of Firmicutes and Actinobacteria in the samples collected from the cecum of HFD rats compared to chow. Consistent with the development of steatosis, the Oil-Red-O-stained area was increased in liver sections from HFD rats. Hepatic triacylglycerol concentrations (p < 0.001) and plasma alanine aminotransferase (p < 0.001) were significantly increased in HFD-fed animals compared to chow. These findings show that a short duration of high-fat consumption can have profound deleterious effects on gastrointestinal health and the inflammatory state of these young male Sprague-Dawley rats.

Short-term weight loss reverses obesity-induced microvascular endothelial dysfunction

Obesity is one of the major risk factors for cardiovascular diseases and its prevalence is increasing in all age groups, with the biggest impact observed in middle-aged and older adults. A critical mechanism by which obesity promotes vascular pathologies in these patients involves impairment of endothelial function. While endothelial dysfunction in large vessels promotes atherogenesis, obesity-induced microvascular endothelial dysfunction impairs organ perfusion and thereby is causally related to the pathogenesis of ischemic heart disease, chronic kidney disease, intermittent claudication, exercise intolerance, and exacerbates cognitive decline in aging. Reduction of weight via calorie-based diet and exercise in animal models of obesity results in significant improvement of endothelial function both in large vessels and in the microcirculation, primarily due to attenuation of oxidative stress and inflammation. Clinical data on the protective effects of weight loss on endothelial function is limited to studies of flow-mediated dilation assessed in brachial arteries. Currently, there is no guideline on testing the effects of different weight management strategies on microvascular endothelial function in obese patients. Here, we provide proof-of-concept that weight loss-induced improvement of microvascular endothelial function can be reliably assessed in the setting of a geriatric outpatient clinic using a fast, reproducible, non-invasive method: laser speckle contrast imaging-based measurement of endothelium-dependent microvascular responses during post-occlusive reactive hyperemia tests. Our study also provides initial evidence that short-term weight loss induced by consumption of a low-carbohydrate low-calorie diet can reverse microvascular endothelial dysfunction associated with obesity.

Long-term diet-induced hypertension in rats is associated with reduced expression and function of small artery SKCa, IKCa, and Kir2.1 channels

Abdominal obesity and/or a high intake of fructose may cause hypertension. K+ channels, Na/K-ATPase, and voltage-gated Ca2+ channels are crucial determinants of resistance artery tone and thus the control of blood pressure. Limited information is available on the role of K+ transporters in long-term diet-induced hypertension in rats. We hypothesized that a 28-week diet rich in fat, fructose, or both, will lead to changes in K+ transporter expression and function, which is associated with increased blood pressure and decreased arterial function. Male Sprague–Dawley (SD) rats received a diet containing normal chow (Control), high-fat chow (High Fat), high-fructose in drinking water (High Fructose), or a combination of high-fat and high-fructose diet (High Fat/Fruc) for 28 weeks from the age of 4 weeks. Measurements included body weight (BW), systolic blood pressure (SBP), mRNA expression of vascular K+ transporters, and vessel myography in small mesenteric arteries (SMAs). BW was increased in the High Fat and High Fat/Fruc groups, and SBP was increased in the High Fat/Fruc group. mRNA expression of small conductance calcium-activated K+ channel (SKCa), intermediate conductance calcium-activated K+ (IKCa), and Kir2.1 inward rectifier K+ channels were reduced in the High Fat/Fruc group. Reduced endothelium-derived hyperpolarization (EDH)-type relaxation to acetylcholine (ACh) was seen in the High Fat and High Fat/Fruc groups. Ba2+-sensitive dilatation to extracellular K+ was impaired in all the experimental diet groups. In conclusion, reduced expression and function of SKCa, IKCa, and Kir2.1 channels are associated with elevated blood pressure in rats fed a long-term High Fat/Fruc. Rats fed a 28-week High Fat/Fruc provide a relevant model of diet-induced hypertension.

Aspartame intake is associated with greater glucose intolerance in individuals with obesity

This study examined whether sucrose, fructose, aspartame, and saccharin influences the association between obesity and glucose tolerance in 2856 adults from the NHANES III survey. Aspartame intake significantly influenced the association between body mass index (BMI) and glucose tolerance (interaction: P = 0.004), wherein only those reporting aspartame intake had a steeper positive association between BMI and glucose tolerance than those reporting no aspartame intake. Therefore, consumption of aspartame is associated with greater obesity-related impairments in glucose tolerance.

Genistein supplementation prevents weight gain but promotes oxidative stress and inflammation in the vasculature of female obese ob/ob mice

Obesity, a state of chronic low-grade inflammation, is strongly associated with the development of hypertension and diabetes. Superoxide, a free radical elevated in obese individuals, promotes hypertension through scavenging the endogenous vasodilator nitric oxide. The hypothesis was a genistein-enriched diet would promote weight loss and reduce oxidative stress and inflammation in the vasculature of intact female ob/ob mice. Aortas and mesenteric arteries were isolated from female ob/ob mice fed genistein-free (0mg genistein/kg diet; n=6), standard chow (200-300mg genistein/kg diet; n=11) or genistein-enriched (600mg genistein/kg diet; n=9) diets for 4weeks. Sections of isolated vessels were labeled with the superoxide indicator dihydroethidium and fluorescence was measured by confocal microscopy. Protein expression of the inflammatory marker inducible nitric oxide synthase (iNOS) was measured in the perivascular adipose tissue (PVAT) surrounding each vessel and plasma concentrations of superoxide dismutase (SOD) were quantified. Genistein-enriched diet promoted less weight gain compared to animals fed standard chow (P=.008). Standard chow promoted increased superoxide in the aorta (P=.030) and mesenteric arteries (P=.024) compared to a diet devoid of genistein. At all tested concentrations, genistein significantly increased iNOS expression in mesenteric artery PVAT (vs. standard chow, P<.001; vs. genistein-enriched, P=.002) and tended to increase iNOS within the aortic PVAT (standard chow, P=.075) compared to the genistein-free group. Plasma SOD activity was significantly downregulated in genistein-enriched animals as compared to those fed a genistein-free diet (P=.028). In summary, although genistein prevents weight gain, it promotes vascular oxidative stress and inflammation in obese ovarian-intact female mice.

A high-fat diet decreases GABA concentration in the frontal cortex and hippocampus of rats

BACKGROUND

It has been proposed that the γ-aminobutyric acid (GABA) plays a key role in the regulation of food intake and body weight by controlling the excitability, plasticity and the synchronization of neuronal activity in the frontal cortex (FC). It has been also proposed that the high-fat diet (HFD) could disturb the metabolism of glutamate and consequently the GABA levels, but the mechanism is not yet clearly understood. Therefore, the aim of this study was to investigate the effect of a HFD on the GABA levels in the FC and hippocampus of rats.

RESULTS

The HFD significantly increased weight gain and blood glucose levels, whereas decreased the GABA levels in the FC and hippocampus compared with standard diet-fed rats.

CONCLUSIONS

HFD decreases GABA levels in the FC and hippocampus of rat, which likely disrupts the GABAergic inhibitory processes, underlying feeding behavior.

Short-Term High Fat Intake Does Not Significantly Alter Markers of Renal Function or Inflammation in Young Male Sprague-Dawley Rats

Chronic high fat feeding is correlated with diabetes and kidney disease. However, the impact of short-term high fat diets (HFD) is not well-understood. Six weeks of HFD result in indices of metabolic syndrome (increased adiposity, hyperglycemia, hyperinsulinemia, hyperlipidemia, hyperleptinemia, and impaired endothelium-dependent vasodilation) compared to rats fed on standard chow. The hypothesis was that short-term HFD would induce early signs of renal disease. Young male Sprague-Dawley rats were fed either HFD (60% fat) or standard chow (5% fat) for six weeks. Morphology was determined by measuring changes in renal mass and microstructure. Kidney function was measured by analyzing urinary protein, creatinine, and hydrogen peroxide (H₂O₂) concentrations, as well as plasma cystatin C concentrations. Renal damage was measured through assessment of urinary oxDNA/RNA concentrations as well as renal lipid peroxidation, tumor necrosis factor alpha (TNFα), and interleukin 6 (IL-6). Despite HFD significantly increasing adiposity and renal mass, there was no evidence of early stage kidney disease as measured by changes in urinary and plasma biomarkers as well as histology. These findings suggest that moderate hyperglycemia and inflammation produced by short-term HFD are not sufficient to damage kidneys or that the ketogenic HFD may have protective effects within the kidneys.

A model of metabolic syndrome and related diseases with intestinal endotoxemia in rats fed a high fat and high sucrose diet

AIM

We sought develop and characterize a diet-induced model of metabolic syndrome and its related diseases.

METHODS

The experimental animals (Spague-Dawley rats) were randomly divided into two groups, and each group was fed a different feed for 48 weeks as follows: 1) standard control diet (SC), and 2) a high sucrose and high fat diet (HSHF). The blood, small intestine, liver, pancreas, and adipose tissues were sampled for analysis and characterization.

RESULTS

Typical metabolic syndrome (MS), non-alcoholic fatty liver disease (NAFLD), and type II diabetes (T2DM) were common in the HSHF group after a 48 week feeding period. The rats fed HSHF exhibited signs of obesity, dyslipidemia, hyperglycaemia, glucose intolerance, and insulin resistance (IR). At the same time, these animals had significantly increased levels of circulating LPS, TNFα, and IL-6 and increased ALP in their intestinal tissue homogenates. These animals also showed a significant reduction in the expression of occluding protein. The HSHF rats showed fatty degeneration, inflammation, fibrosis, cirrhosis, and lipid accumulation when their liver pathologies were examined. The HSHF rats also displayed increased islet diameters from 12 to 24 weeks, while reduced islet diameters occurred from 36 to 48 weeks with inflammatory cell infiltration and islet fat deposition. The morphometry of adipocytes in HSHF rats showed hypertrophy and inflammatory cell infiltration. HSHF CD68 analysis showed macrophage infiltration and significant increases in fat and pancreas size. HSHF Tunel analysis showed significant increases in liver and pancreas cell apoptosis.

CONCLUSIONS

This work demonstrated the following: 1) a characteristic rat model of metabolic syndrome (MS) can be induced by a high sucrose and high fat diet, 2) this model can be used to research metabolic syndrome and its related diseases, such as NAFLD and T2DM, and 3) intestinal endotoxemia (IETM) may play an important role in the pathogenesis of MS and related diseases, such as NAFLD and T2DM.

Glycine restores glutathione and protects against oxidative stress in vascular tissue from sucrose-fed rats

The attenuation of oxidative stress could be an important mechanism whereby the incidence of vascular complications in the MS (metabolic syndrome) may be diminished. The present study was undertaken to investigate the mechanism by which glycine, supplemented to the diet of SF (sucrose-fed) rats, modulates glutathione biosynthesis and protects against oxidative stress and altered endothelium-dependent relaxation in isolated aorta. Glycine reduced O2•- (superoxide anion radical) release in the presence of NADPH, and decreased protein carbonyl and lipid peroxidation. This effect of glycine could be because of the increased amount of glutathione synthetase, which may be responsible for increased glutathione (GSH) content in vascular tissue from SF rats. Moreover, glycine increased the amount of Cu,Zn-SOD (copper/zinc superoxide dismutase) and eNOS (endothelial NO synthase) in aorta from SF animals. Finally, it improved the relaxation response to ACh (acetylcholine) found impaired in aortic rings from SF rats. In the presence of NAC (N-acetylcysteine), a precursor of GSH, an improved ACh-mediated aortic relaxation of aortic rings from SF rats was observed, whereas BSO (buthionine sulfoximine), an inhibitor of glutathione biosynthesis, inhibited the relaxing effect of NAC in aortas from both control and SF rats. This experiment emphasizes the role of GSH in endothelial function in SF rats. The present data suggest that glycine rectifies vascular reactivity by increasing the biosynthesis of glutathione. Glutathione protects vascular tissue against oxidative stress, and enhances the availability of NO, which exerts its relaxing effect, thus contributing to the reduction of high BP (blood pressure) in the SF rats.

Energy restriction ameliorates metabolic syndrome-induced cavernous tissue structural modifications in aged rats

High-fat (HF) diet regular intake along life highly contributes to vascular dysfunction and to an increment in prevalence of metabolic syndrome (MetS) and erectile dysfunction (ED), a surrogate symptom of occult vascular disease, in the elderly. However, little is known about the effects of energy restriction (ER) alone/or after an HF-feeding period. We show here that in male Sprague-Dawley rats, 16 months of HF-diet consumption led to an increase in body adiposity, blood pressure, lipidemia, C-reactive protein, and insulin resistance and to hypoadiponectinemia, conditions that cluster in MetS. In addition, this treatment strongly favored collagen deposition in cavernous tissue and myocardium. Conversely, for the same time period, the ingestion of 75 % of ad libitum energy intake by controls (ER) extensively counteracted these outcomes. The impact of 6-month ER after 10-month HF period was also analyzed, and despite the decrease in body weight, adiposity, blood pressure, lipidemia, and C-reactive protein and improvement of insulin sensitivity, no differences were observed either in adiponectin blood levels or in retroperitoneal fat pad mass. Moreover, this treatment led to a reduction in cavernous tissue collagen deposition, but not in the myocardium, and evidenced differential mobilization of adipose tissue accretions. The data show the ability of HF diet to cause MetS and produce unwanted effects on myocardium and corpora vascular structure. They also indicate that these consequences are preventable upon ER diet starting early, but not later, in life.

Cafeteria diet-induced obesity plus chronic stress alter serum leptin levels

Obesity is a disease that has become a serious public health issue worldwide, and chronic stressors, which are a problem for modern society, cause neuroendocrine changes with alterations in food intake. Obesity and chronic stress are associated with the development of cardiovascular diseases and metabolic disorders. In this study, a rat model was used to evaluate the effects of a hypercaloric diet plus chronic restraint stress on the serum leptin and lipids levels and on the weight of specific adipose tissue (mesenteric, MAT; subcutaneous, SAT and visceral, VAT). Wistar rats were divided into the following 4 groups: standard chow (C), hypercaloric diet (HD), stress plus standard chow (S), and stress plus hypercaloric diet (SHD). The animals in the stress groups were subjected to chronic stress (placed inside a 25 cm × 7 cm plastic tube for 1h per day, 5 days per week for 6 weeks). The following parameters were evaluated: the weight of the liver, adrenal glands and specific adipose tissue; the delta weight; the Lee index; and the serum levels of leptin, corticosterone, glucose, total cholesterol, and triglycerides. The hypercaloric diet induced obesity in rats, increasing the Lee index, weight, leptin, triglycerides, and cholesterol levels. The stress decreased weight gain even in animals fed a hypercaloric diet but did not prevent a significant increase in the Lee index. However, an interaction between the independent factors (hypercaloric diet and stress) was observed, which is demonstrated by the increased serum leptin levels in the animals exposed to both protocols.

Impaired myogenic tone in mesenteric arteries from overweight rats

Background

Rats fed high fat (HFD) or high sucrose (HSD) diets develop increased adiposity as well as impaired vasodilatory responsiveness stemming from oxidative stress. Moreover, HFD rats become hypertensive compared to either control (Chow) or HSD fed rats, suggesting elevated vascular tone. We hypothesized that rats with increased adiposity and oxidative stress demonstrate augmented pressure-induced vasoconstriction (i.e. myogenic tone) that could account for the hypertensive state.

Methods

Male Sprague-Dawley rats were fed Chow, HFD or HSD for 6 weeks. The effects of oxidative stress and endogenous nitric oxide on myogenic responses were examined in small mesenteric arteries by exposing the arteries to incremental intraluminal pressure steps in the presence of antioxidants or an inhibitor of nitric oxide synthase, LNNA (100 μM).

Results

Contrary to the hypothesis, rats fed either HSD or HFD had significantly impaired myogenic responses despite similar vascular morphology and passive diameter responses to increasing pressures. Vascular smooth muscle (VSM) calcium levels were normal in HFD arteries suggesting that diminished calcium sensitivity was responsible for the impaired myogenic response. In contrast, VSM calcium levels were reduced in HSD arteries but were increased with pre-exposure of arteries to the antioxidants tiron (10 mM) and catalase (1200 U/mL), also resulting in enhanced myogenic tone. These findings show that oxidative stress impairs myogenic tone in arteries from HSD rats by decreasing VSM calcium. Similarly, VSM calcium responses were increased in arteries from HFD rats following treatment with tiron and catalase, but this did not result in improved myogenic tone. Nitric oxide is involved in the impaired myogenic response in HFD, but not HSD, rats since inhibition with LNNA resulted in maximal myogenic responses at lower intraluminal pressures and VSM calcium levels, further implicating reduced calcium sensitivity in the impaired response.

Conclusion

The impaired myogenic responses observed in isolated arteries from HSD and HFD rats are attributed to changes in VSM calcium signaling.

High fat feeding impairs endothelin-1 mediated vasoconstriction through increased iNOS-derived nitric oxide

Rats fed a high fat diet develop increased adiposity and oxidative stress leading to impaired vasodilation. The purpose of the present study was to examine the effects of high fat-induced increases in adiposity and oxidative stress on vasoconstrictor reactivity of isolated mesenteric arteries. We hypothesized that rats with more adiposity would develop oxidative stress-potentiated increases in iNOS-derived nitric oxide leading to diminished vasoconstriction. Male Sprague-Dawley rats were fed either a control (Chow) or high fat diet for 6 weeks. The roles of oxidative stress and iNOS in the impaired vasoconstrictor responses to endothelin-1 were characterized in small mesenteric arteries. Rats fed the HFD developed significantly more adiposity compared to Chow rats. Plasma levels of nitric oxide and the inflammatory factor tumor necrosis factor α were significantly higher in high fat fed rats compared to Chow rats (nitric oxide: 95.36±19.3 vs. 38.96±6.7 μM; tumor necrosis factor α: 598±111.4 vs. 292±71.8 pg/ml, respectively). Despite exhibiting elevated systolic blood pressure compared to Chow rats (153.5±2.4 vs. 137.5±2.7 mm Hg), endothelin-1 mediated vasoconstriction was impaired in isolated mesenteric arteries from high fat fed rats but was normalized by individual or combined inhibition of nitric oxide synthase, iNOS, or oxidative stress. Therefore, oxidative stress and iNOS are involved in the attenuation of endothelin-1 mediated vasoconstriction observed in isolated mesenteric arteries from high fat fed rats.

Naturally high plasma glucose levels in mourning doves (Zenaida macroura) do not lead to high levels of reactive oxygen species in the vasculature

Plasma glucose (P(Glu)) concentrations in birds are 1.5-2 times higher than those of mammals of similar body mass. In mammals, sustained elevations of P(Glu) lead to oxidative stress and free radical-mediated scavenging of endogenous vasodilators (e.g., nitric oxide), contributing to elevated blood pressure. Despite the relatively high P(Glu) levels in birds, they appear resistant to the development of oxidative stress in tissues such as the heart, brain and kidneys. To our knowledge no information exists on oxidative stress susceptibility in the resistance vasculature of birds. Therefore, we compared endogenous antioxidant mechanisms in the resistance vasculature of mourning doves (MODO; Zenaida macroura) and rats (Rattus norvegicus). Reactive oxygen species (ROS) were assessed with the fluorescent indicator 7'-dichlorodihydrofluorescein diacetate, acetyl ester in mesenteric arteries from rats and wild-caught MODO. Despite having significantly higher P(Glu) than rats, there were no significant differences in ROS levels between mesenteric arteries from rats or doves. Although superoxide dismutase and catalase activities were lower in the plasma, total antioxidant capacity, uric acid, vitamin E (α-tocopherol), and carotenoids (lutein and zeaxanthin) were significantly higher in MODO than in rats. Thus, compared to rats, MODO have multiple circulating antioxidants that may prevent the development of oxidative stress in the vasculature.

Rodent models for metabolic syndrome research

Rodents are widely used to mimic human diseases to improve understanding of the causes and progression of disease symptoms and to test potential therapeutic interventions. Chronic diseases such as obesity, diabetes and hypertension, together known as the metabolic syndrome, are causing increasing morbidity and mortality. To control these diseases, research in rodent models that closely mimic the changes in humans is essential. This review will examine the adequacy of the many rodent models of metabolic syndrome to mimic the causes and progression of the disease in humans. The primary criterion will be whether a rodent model initiates all of the signs, especially obesity, diabetes, hypertension and dysfunction of the heart, blood vessels, liver and kidney, primarily by diet since these are the diet-induced signs in humans with metabolic syndrome. We conclude that the model that comes closest to fulfilling this criterion is the high carbohydrate, high fat-fed male rodent.

Increased adiposity does not exacerbate impaired vasodilation in rats exposed to eucapnic intermittent hypoxia

BACKGROUND

Although there often is a clinical co-incidence of increased adiposity and obstructive sleep apnea, each factor is independently associated with elevated oxidative stress.

OBJECTIVE

We hypothesized that overweight rats exposed to simulated sleep apnea would develop exacerbated oxidative stress leading to impaired endothelium-dependent vasodilation.

METHODS

Rats were fed either a chow or high-fat diet (HFD; 60% kcal from fat) for 6 weeks. During the final 14 days of each diet, animals were exposed to either air or eucapnic intermittent hypoxia (E-IH) to simulate sleep apnea.

RESULTS

Rats exposed to either E-IH or HFD alone showed increases of 161 and 176%, respectively, in oxidative stress (measured as thiobarbituric acid-reactive substances) compared to chow + air controls. However, oxidative stress was lower following combined HFD + E-IH treatment (132% of chow + air controls) compared to each individual treatment. All three treatment groups, chow + E-IH, HFD + air and HFD + E-IH, had increased blood pressure (144.5 ± 4.4, 148.2 ± 5.6, and 136.2 ± 2.0 mm Hg, respectively, vs. chow + air: 123 ± 2.0 mm Hg) and attenuated acetylcholine (ACh)-mediated vasodilation (78.3, 72.7, and 78.2% of the chow + air response at the highest dose of ACh) compared to chow + air controls. Combined HFD and E-IH treatment did not further impair vasodilation compared to chow + E-IH alone. Vasodilatory responses were normalized by the antioxidant EUK-134 in each treatment group.

CONCLUSIONS

Increased adiposity and simulated sleep apnea impair endothelium- dependent vasodilation through enhanced generation of reactive oxygen species (ROS). However, the combined treatment does not exacerbate either ROS generation or vascular dysfunction observed with HFD or E-IH alone.