Cardiac lipids and antioxidant status in high fructose rats and the effect of alpha-lipoic acid

Spexin alleviates hypertension, hyperuricaemia, dyslipidemia and insulin resistance in high fructose diet induced metabolic syndrome in rats via enhancing PPAR-ɣ and AMPK and inhibiting IL-6 and TNF-α

Spexin is a novel peptide implicated in obesity and energy homeostasis. The objective of the current study was to evaluate the effect of spexin on blood pressure, insulin resistance, and dyslipidemia in rats with metabolic syndrome (MS) induced by high-fructose diet (HFD) and the possible underlying mechanism. Forty adult male rats were randomly assigned into four equal groups; Control, Spexin, HFD and HFD + spexin. Induction of the MS with HFD was associated with increased body mass index, elevated blood pressure, blood glucose, insulin, uric acid, advanced glycation end products and insulin resistance, interlekin-6, tumour necrosis factor-alpha together with dyslipidemia, low-serum spexin, peroxisome proliferator-activated receptors-gamma (PPAR-ɣ) and adenosine monophosphate-activated protein kinase (AMPK). Spexin attenuated MS-induced deleterious effects which can be attributed to activation of PPAR-ɣ and AMPK as well as inhibiting inflammation. These findings indicate that spexin could be a beneficial complementary agent for metabolic syndrome treatment.

Low-Intensity Exercise Affects Cardiac Fatty Acid Oxidation by Increasing the Nuclear Content of PPARα, FOXO1, and Lipin1 in Fructose-Fed Rats

Background and Aim: Excessive fructose consumption along with a sedentary lifestyle provokes metabolic disorders and cardiovascular diseases. Fructose overload causes cardiac insulin resistance and increases reliance on fatty acid (FA) uptake and catabolism. The cardiometabolic benefits of exercise training have long been appreciated. The goal of the presented study is to shed a new light to the preventive role of exercise training on cardiac lipid metabolism in fructose-fed rats. Methods: Male Wistar rats were divided into control (C), sedentary fructose (F), and exercised fructose (EF) groups. Fructose was given as a 10% fructose solution in drinking water for 9 weeks. Low-intensity exercise training was applied for 9 weeks. The protein expression and subcellular localization of Lipin1, peroxisome proliferator-activated receptor α (PPARα), and peroxisome proliferator-activated receptor-γ coactivator 1 α (PGC1) were analyzed in the heart using Western blot. Cardiac forkhead box transcription factor 1 (FOXO1) and sirtuin 1 (SIRT1) protein levels were also evaluated. Gene expression of long-chain acyl-CoA dehydrogenase was analyzed by quantitative polymerase chain reaction. Results: Exercise training has augmented the expression of main regulators of FA oxidation in the heart and achieves its effect by increasing the nuclear content of PPARα, Lipin1, and FOXO1 compared with the fructose group (P = 0.0422, P = 0.000045, P = 0.00958, respectively). In addition, Lipin1, FOXO1, and SIRT1 were increased in nuclear extract after exercise compared with the control group (P = 0.000043, P = 0.0417, P = 0.0329, respectively). In cardiac lysate, low-intensity exercise caused significantly increased protein level of PPARα, PGC1, FOXO1, and SIRT1 compared with control (P = 0.0377, P = 0.0275, P = 0.0096, P = 0.0282, respectively) and PGC1 level compared with the fructose group (P = 0.0417). Conclusion: The obtained results imply that the heart with a metabolic burden additionally relies on FA as an energy substrate after low-intensity running.

Guidelines on Models of Diabetic Heart Disease

Diabetes is a major risk factor for cardiovascular diseases, including diabetic cardiomyopathy, atherosclerosis, myocardial infarction, and heart failure. As cardiovascular disease represents the number one cause of death in people with diabetes, there has been a major emphasis on understanding the mechanisms by which diabetes promotes cardiovascular disease, and how antidiabetic therapies impact diabetic heart disease. With a wide array of models to study diabetes (both type 1 and type 2), the field has made major progress in answering these questions. However, each model has its own inherent limitations. Therefore, the purpose of this guidelines document is to provide the field with information on which aspects of cardiovascular disease in the human diabetic population are most accurately reproduced by the available models. This review aims to emphasize the advantages and disadvantages of each model, and to highlight the practical challenges and technical considerations involved. We will review the preclinical animal models of diabetes (based on their method of induction), appraise models of diabetes-related atherosclerosis and heart failure, and discuss in vitro models of diabetic heart disease. These guidelines will allow researchers to select the appropriate model of diabetic heart disease, depending on the specific research question being addressed.

Effects of alpha lipoic acid on metabolic syndrome: A comprehensive review

Metabolic syndrome (MetS) is a multifactorial disease with medical conditions such as hypertension, diabetes, obesity, dyslipidemia, and insulin resistance. Alpha-lipoic acid (α-LA) possesses various pharmacological effects, including antidiabetic, antiobesity, hypotensive, and hypolipidemia actions. It exhibits reactive oxygen species scavenger properties against oxidation and age-related inflammation and refines MetS components. Also, α-LA activates the 5' adenosine monophosphate-activated protein kinase and inhibits the NFκb. It can decrease cholesterol biosynthesis, fatty acid β-oxidation, and vascular stiffness. α-LA decreases lipogenesis, cholesterol biosynthesis, low-density lipoprotein and very low-density lipoprotein levels, and atherosclerosis. Moreover, α-LA increases insulin secretion, glucose transport, and insulin sensitivity. These changes occur via PI3K/Akt activation. On the other hand, α-LA treats central obesity by increasing adiponectin levels and mitochondrial biogenesis and can reduce food intake mainly by SIRT1 stimulation. In this review, the most relevant articles have been discussed to determine the effects of α-LA on different components of MetS with a special focus on different molecular mechanisms behind these effects. This review exhibits the potential properties of α-LA in managing MetS; however, high-quality studies are needed to confirm the clinical efficacy of α-LA.

The protective effect of alpha lipoic acid (ALA) on social interaction memory, but not passive avoidance in sleep-deprived rats

Sleep is involved in maintaining energy, regulating heat, and recovering tissues. Furthermore, proper cognitive functions need sufficient sleep. Many studies have revealed the impairment effect of sleep deprivation (SD) on cognitive functions including learning and memory. Alpha lipoic acid (ALA) is a potent free radical scavenger, biological antioxidant, and neuroprotective agent. Furthermore, ALA improves learning and memory performance, decreases oxidative stress, and enhances antioxidant biomarkers. In this study, we aimed to investigate the effect of ALA on social interaction and passive avoidance memories in sleep-deprived rats. Total sleep deprivation (TSD) apparatus was used to induce SD (for 24 h). Three-chamber paradigm test and shuttle box apparatus were used to evaluate social interaction and passive avoidance memory, respectively. Rats' locomotor apparatus was used to assess locomotion. ALA was administered intraperitoneally at doses of 17 and 35 mg/kg for 3 consecutive days. The results showed SD impaired both types of memories. ALA at the dose of 35 mg/kg restored social interaction memory in sleep-deprived rats; while, at the dose of 17 mg/kg attenuated impairment effect of SD. Moreover, ALA at the dose of 35 mg/kg impaired passive avoidance memory in sham-SD rats and at both doses did not rescue passive avoidance memory in sleep-deprived rats. In conclusion, ALA showed impairment effect on passive avoidance memory, while improved social interaction memory in sleep-deprived rats.

Cardioprotective effect of Phyllanthus amarus against high fructose diet induced myocardial and aortic stress in rat model

Increased number of population with heart stroke/attack is attributed to sedentary lifestyle and consumption of high-sugar diets, especially fructose. The objective of this study is to investigate the cardio-protective activity of aqueous extract of Phyllanthus amarus (PAAE) against high-fructose (HF) diet induced cardiac damage in Wistar rats. Male Wistar rats were randomly assigned into five groups of six animals each: Control (C), Control treated with PAAE (C+PAAE), High fructose diet fed (F), High fructose diet fed treated with PAAE (F+PAAE) and High fructose diet fed treated with Pioglitazone (F+Pio). PAAE was orally administered at a dosage of 200mg/kg body weight/day to C+PAAE and F+PAAE group rats for 60days. Pioglitazone (10mg/kg body weight/day) was used to compare the efficacy of PAAE. After 60days, heart and aorta samples were collected for biochemical and histological analysis. Co-administration of PAAE along with HF-diet for 60days prevented the increase in levels of cardiac and aortic lipids i.e., total lipids, triglycerides, total cholesterol and free fatty acids and decreased phospholipids. Further, enhanced activities of cardiac aldose reductase (15.3%) and sorbital dehydrogenase (6.9%) and decreased activity of creatine kinase (35.6%) in group-F were also prevented by PAAE treatment with the recovery of 126% for AR, 122% for SDH and 118% for CK. PAAE treatment showed protection from HF-diet induced increase in stress markers (LPO and PO), decreased non-enzymatic (GSH and Vit-C) and enzymatic (GR, GPx, GST, SOD, and CAT) antioxidants in the heart and aorta. Histopathological examination of the heart and aorta indicated that PAAE/Pio treatment reduced fat deposition and necrosis. The present study clearly indicates the cardio protection efficacy of PAAE against HF-diet induced oxidative stress in rats.

Similarities and interactions between the ageing process and high chronic intake of added sugars

In our societies, the proportions of elderly people and of obese individuals are increasing. Both factors are associated with high health-related costs. During obesity, many authors suggest that it is a high chronic intake of added sugars (HCIAS) that triggers the shift towards pathology. However, the majority of studies were performed in young subjects and only a few were interested in the interaction with the ageing process. Our purpose was to discuss the metabolic effects of HCIAS, compare with the effects of ageing, and evaluate how deleterious the combined action of HCIAS and ageing could be. This effect of HCIAS seems mediated by fructose, targeting the liver first, which may lead to all subsequent metabolic alterations. The first basic alterations induced by fructose are increased oxidative stress, protein glycation, inflammation, dyslipidaemia and insulin resistance. These alterations are also present during the ageing process, and are closely related to each other, one leading to the other. These basic alterations are also involved in more complex syndromes, which are also favoured by HCIAS, and present during ageing. These include non-alcoholic fatty liver disease, hypertension, neurodegenerative diseases, sarcopenia and osteoporosis. Cumulative effects of ageing and HCIAS have been seldom tested and may not always be strictly additive. Data also suggest that some of the metabolic alterations that are more prevalent during ageing could be related more with nutritional habits than to intrinsic ageing. In conclusion, it is clear that HCIAS interacts with the ageing process, accelerates the accumulation of metabolic alterations, and that it should be avoided.

The Role of Reactive Oxygen Species in β-Adrenergic Signaling in Cardiomyocytes from Mice with the Metabolic Syndrome

The metabolic syndrome is associated with prolonged stress and hyperactivity of the sympathetic nervous system and afflicted subjects are prone to develop cardiovascular disease. Under normal conditions, the cardiomyocyte response to acute β-adrenergic stimulation partly depends on increased production of reactive oxygen species (ROS). Here we investigated the interplay between beta-adrenergic signaling, ROS and cardiac contractility using freshly isolated cardiomyocytes and whole hearts from two mouse models with the metabolic syndrome (high-fat diet and ob/ob mice). We hypothesized that cardiomyocytes of mice with the metabolic syndrome would experience excessive ROS levels that trigger cellular dysfunctions. Fluorescent dyes and confocal microscopy were used to assess mitochondrial ROS production, cellular Ca2+ handling and contractile function in freshly isolated adult cardiomyocytes. Immunofluorescence, western blot and enzyme assay were used to study protein biochemistry. Unexpectedly, our results point towards decreased cardiac ROS signaling in a stable, chronic phase of the metabolic syndrome because: β-adrenergic-induced increases in the amplitude of intracellular Ca2+ signals were insensitive to antioxidant treatment; mitochondrial ROS production showed decreased basal rate and smaller response to β-adrenergic stimulation. Moreover, control hearts and hearts with the metabolic syndrome showed similar basal levels of ROS-mediated protein modification, but only control hearts showed increases after β-adrenergic stimulation. In conclusion, in contrast to the situation in control hearts, the cardiomyocyte response to acute β-adrenergic stimulation does not involve increased mitochondrial ROS production in a stable, chronic phase of the metabolic syndrome. This can be seen as a beneficial adaptation to prevent excessive ROS levels.

Potential link between excess added sugar intake and ectopic fat: a systematic review of randomized controlled trials

CONTEXT

The effect of added sugar intake on ectopic fat accumulation is a subject of debate.

OBJECTIVE

A systematic review and meta-analysis of randomized controlled trials (RCTs) was conducted to examine the potential effect of added sugar intake on ectopic fat depots.

DATA SOURCES

MEDLINE, CAB Abstracts, CAB Global Health, and EBM (Evidence-Based Medicine) Reviews - Cochrane Central Register of Controlled Trials databases were searched for studies published from 1973 to September 2014.

DATA EXTRACTION

RCTs with a minimum of 6 days' duration of added sugar exposure in the intervention group were selected. The dosage of added sugar intake as a percentage of total energy was extracted or calculated. Means and standard deviations of pre- and post-test measurements or changes in ectopic fat depots were collected.

DATA SYNTHESIS

Fourteen RCTs were included. Most of the studies had a medium to high risk of bias. Meta-analysis showed that, compared with eucaloric controls, subjects who consumed added sugar under hypercaloric conditions likely increased ectopic fat, particularly in the liver (pooled standardized mean difference = 0.9 [95%CI, 0.6-1.2], n = 6) and muscles (pooled SMD = 0.6 [95%CI, 0.2-1.0], n = 4). No significant difference was observed in liver fat, visceral adipose tissue, or muscle fat when isocaloric intakes of different sources of added sugars were compared.

CONCLUSIONS

Data from a limited number of RCTs suggest that excess added sugar intake under hypercaloric diet conditions likely increases ectopic fat depots, particularly in the liver and in muscle fat. There are insufficient data to compare the effect of different sources of added sugars on ectopic fat deposition or to compare intake of added sugar with intakes of other macronutrients. Future well-designed RCTs with sufficient power and duration are needed to address the role of sugars on ectopic fat deposition.

Functional foods as potential therapeutic options for metabolic syndrome

Obesity as part of metabolic syndrome is a major lifestyle disorder throughout the world. Current drug treatments for obesity produce small and usually unsustainable decreases in body weight with the risk of major adverse effects. Surgery has been the only treatment producing successful long-term weight loss. As a different but complementary approach, lifestyle modification including the use of functional foods could produce a reliable decrease in obesity with decreased comorbidities. Functional foods may include fruits such as berries, vegetables, fibre-enriched grains and beverages such as tea and coffee. Although health improvements continue to be reported for these functional foods in rodent studies, further evidence showing the translation of these results into humans is required. Thus, the concept that these fruits and vegetables will act as functional foods in humans to reduce obesity and thereby improve health remains intuitive and possible rather than proven.

Ursodeoxycholic acid ameliorates fructose-induced metabolic syndrome in rats

The metabolic syndrome (MS) is characterized by insulin resistance, dyslipidemia and hypertension. It is associated with increased risk of cardiovascular diseases and type-2 diabetes. Consumption of fructose is linked to increased prevalence of MS. Ursodeoxycholic acid (UDCA) is a steroid bile acid with antioxidant, anti-inflammatory activities and has been shown to improve insulin resistance. The current study aims to investigate the effect of UDCA (150 mg/kg) on MS induced in rats by fructose administration (10%) in drinking water for 12 weeks. The effects of UDCA were compared to fenofibrate (100 mg/kg), an agonist of PPAR-α receptors. Treatment with UDCA or fenofibrate started from the 6^th week after fructose administration once daily. Fructose administration resulted in significant increase in body weight, elevations of blood glucose, serum insulin, cholesterol, triglycerides, advanced glycation end products (AGEs), uric acid levels, insulin resistance index and blood pressure compared to control rats. Moreover, fructose increased oxidative stress in aortic tissues indicated by significant increases of malondialdehyde (MDA), expression of iNOS and reduction of reduced glutathione (GSH) content. These disturbances were associated with decreased eNOS expression, increased infiltration of leukocytes and loss of aortic vascular elasticity. Treatment with UDCA successfully ameliorated the deleterious effects of fructose. The protective effect of UDCA could be attributed to its ability to decrease uric acid level, improve insulin resistance and diminish oxidative stress in vascular tissues. These results might support possible clinical application of UDCA in MS patients especially those present with liver diseases, taking into account its tolerability and safety. However, further investigations on human subjects are needed before the clinical application of UDCA for this indication.

Dietary and nutraceutical approach to type 2 diabetes

Nutritional medical treatment is the first step to achieve adequate glycemic control and prevent diabetic complications. Lifestyle changes include moderate weight loss (7%) and regular physical activity (150 min/week). The appropriate diet composition is < 30% total fat, < 10% saturated fats, > 15 g/1000 kcal fiber, half soluble, 45-60% of carbohydrates with amoderate intake of sugar (50 g/day) and protein intake of 15-20% of the total calories a day. Patients need to limit the intake of saturated fats to < 7% of the daily calorie intake. Monounsaturated fatty acids such as olive oil and other vegetable oils are recommended. L-carnitine, α-lipoic acid, berberine and ω-3 fatty acids can be useful supplements.

Gender differences in the expression and cellular localization of lipin 1 in the hearts of fructose-fed rats

To give new insight to alterations of cardiac lipid metabolism accompanied by a fructose-rich diet (FRD), rats of both sexes were exposed to 10 % fructose in drinking water during 9 weeks. The protein level and subcellular localization of the main regulators of cardiac lipid metabolism, such as lipin 1, peroxisome proliferator-activated receptor α (PPARα), peroxisome proliferator-activated receptor γ coactivator-1 α (PGC-1α), carnitine palmitoyltransferase I (CPTI), and CD36 were studied. Caloric intake in fructose-fed rats (FFR) of both sexes was increased. Circulating triacylglyceroles (TAG) and non-esterified fatty acids were increased in male FFR, while females increased visceral adiposity and blood TAG. Total expression of lipin 1 in cardiac cell lysate and its cytosolic and microsomal level were increased in the hearts of male FFR. PPARα and PGC-1α content were decreased in the nuclear extract. In addition, cardiac deposition of TAG in male FFR was elevated, as well as inhibitory phosphorylation of insulin receptor substrate 1 (IRS-1). In contrast, in female FFR, lipin 1 level was increased in nuclear extract only, while overall CPTI expression and phosphorylation of IRS-1 at serine 307 were decreased. The results of our study suggest that fructose diet causes gender-dependent alterations in cardiac lipid metabolism. Potentially detrimental effects of FRD seem to be limited to male rats. Most of the observed changes might be a consequence of elevated expression and altered localization of lipin 1. Increased inhibitory phosphorylation of IRS-1 is possible link between cardiac lipid metabolism and insulin resistance in FFR.

Chronic intermittent hypobaric hypoxia prevents cardiac dysfunction through enhancing antioxidation in fructose-fed rats

High-fructose intake induces metabolic syndrome and cardiac dysfunction. Chronic intermittent hypobaric hypoxia (CIHH) preserves cardiac function during ischemia. We hypothesized that CIHH restores the impaired cardiac function in fructose-fed rats. Sprague-Dawley rats were randomly subject to treatment with fructose (10% fructose in drinking water for 6 weeks), CIHH (simulated 5000 m altitude, 6 h/day for 6 weeks in a hypobaric chamber), and CIHH plus fructose groups. In addition to an increase in blood pressure, fructose feeding caused elevated serum levels of glucose, fasting insulin and insulin C peptide, triglyceride, cholesterol, and mass ratio of heart to body. CIHH treatment decreased the arterial blood pressure, serum levels of biochemical markers, and cardiac hypertrophy in fructose-fed rats. Furthermore, CIHH treatment improved the recovery of left ventricular function after ischemia-reperfusion procedure (30 min global no-flow ischemia followed by 60 min of reperfusion) in rats with or without fructose feeding. In addition, CIHH treatment caused a significant increase in superoxide dismutase (SOD) activity and decrease in malondialdehyde level in cardiac myocardium experiencing ischemia-reperfusion in control and fructose-fed rats. Collectively, these data suggest that CIHH improve impaired cardiac function in fructose-fed rats through enhancing antioxidation in the myocardium.

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).

Administration of rosmarinic acid reduces cardiopathology and blood pressure through inhibition of p22phox NADPH oxidase in fructose-fed hypertensive rats

Rosmarinic acid (RA), a caffeic acid ester, has insulin-sensitizing and antioxidant effects in high fructose-fed model of insulin resistance (IR). This study investigated whether RA supplementation prevents cardiac abnormalities and hypertension in fructose-fed rats (FFR). Rats fed with fructose diet (60 g/100 g) for 60 days exhibited metabolic abnormalities and rise in plasma and cardiac lipids and whole body IR. The levels of cardiac antioxidants and plasma ferric reducing antioxidant power were significantly reduced in FFR concomitant with increased levels of lipid peroxidation and protein oxidation products. A significant rise in troponin T, creatine kinase-MB, aspartate transaminase, and lactate dehydrogenase in plasma of FFR was noted. RA supplementation to FFR (10 mg/kg from the 16th day) significantly improved insulin sensitivity, reduced lipid levels, oxidative damage, and the expression of p22phox subunit of nicotinamide adenine dinucleotide phosphate reduced oxidase, and prevented cardiac hypertrophy. Fructose-induced rise in blood pressure was also lowered by RA through decrease in endothelin-1 and angiotensin-converting enzyme activity and increase in nitric oxide levels. Histology revealed a reduction in myocardial damage in RA-supplemented FFR. These findings suggest that RA acts as a vasoactive substance and a cardioprotector through its antioxidant property. Thus, RA may be useful in reducing the cardiovascular risk associated with IR.

Aliskiren prevents and ameliorates metabolic syndrome in fructose-fed rats

INTRODUCTION

The renin-angiotensin system plays a major role in the pathogenesis of metabolic syndrome. The objective of this study was to examine the effects of aliskiren, a direct renin inhibitor, on the metabolic syndrome of fructose-fed rats.

MATERIAL AND METHODS

Male Sprague-Dawley rats were divided into 4 groups (n = 6 for each group). Group Con: rats were fed a standard chow diet for 8 weeks, group Fru: rats were fed a high fructose diet (60% fructose) for 8 weeks, group FruA: rats were fed a high fructose diet and were co-infused with aliskiren (100 mg/kg/day), and group FruB: rats were treated as group Fru, but aliskiren was administered 4 weeks later. Systolic blood pressure (SBP), homeostasis model assessment-insulin resistance (HOMA-IR), and blood profiles were measured.

RESULTS

By the end of week 4 and 8 of a high fructose diet, SBP had increased significantly from 111 ±5 to 142 ±4 and 139 ±5 mmHg (p < 0.05), respectively. A high fructose diet significantly increased HOMA-IR from baseline (6.15 ±1.59) to 21.25 ±2.08 and 21.28 ±3.1 (p < 0.05) at week 4 and 8, respectively, and significantly induced metabolic syndrome. Concurrent aliskiren treatment prevented the development of hypertension and metabolic syndrome in fructose-fed rats. When fructose-induced hypertension was established, subsequent aliskiren treatment for 4 weeks reversed the elevated SBP and ameliorated metabolic syndrome. There were no significant differences in food, water intake, urine flow or body weight gain among groups.

CONCLUSIONS

Aliskiren not only prevents but also ameliorates metabolic syndrome in fructose-fed rats.

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.

Effect of galangin supplementation on oxidative damage and inflammatory changes in fructose-fed rat liver

The study examined the effects of galangin (GA) on oxidative stress, inflammatory cytokine levels and nuclear factor-kappa B (NF-κB) activation in fructose-fed rat liver. Adult male albino Wistar rats were divided into 4 groups. Groups 1 and 4 received the control diet containing starch as the source of carbohydrate while groups 2 and 3 were fed a diet containing fructose. Groups 3 and 4 additionally received GA (100μg/kg, p.o) from the 15th day. At the end of 60 days, the levels of plasma glucose, insulin and triglycerides, insulin sensitivity indices and oxidative stress markers in the liver were determined. Cytokines of interest were assayed by ELISA and RT-PCR and NF-κB p65 nuclear translocation by Western blot and RT-PCR. Compared to control diet-fed animals, fructose-fed animals developed hyperglycemia, hyperinsulinemia, hypertriglyceridemia and insulin resistance (IR) (all p<0.01). GA prevented the rise in plasma glucose, insulin and triglycerides and improved insulin sensitivity. Tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels in plasma and the mRNA and protein levels of TNF-α and transforming growth factor-β1(TGF-β(1)) in liver were significantly higher in fructose-fed rats than control rats. However, treatment with GA downregulated the expression of these cytokines. Translocation of NF-κB into the nucleus was also increased in fructose diet-fed animals, which was prevented by GA. These results suggest that GA prevents oxidative damage and has a downregulatory effect on the inflammatory pathway in liver of fructose-fed rats.

Dose-dependent effect of galangin on fructose-mediated insulin resistance and oxidative events in rat kidney

Galangin is an antioxidant flavonol present in high concentrations in the rhizome of Alpinia galanga. We investigated the effect of galangin on whole-body insulin resistance and kidney oxidative stress in a fructose-induced rat model of metabolic syndrome. Male albino Wistar rats were divided into 6 groups containing six animals each. Groups I and VI received a starch-based control diet, while groups II, III, IV and V were fed a high fructose diet (60 g/100 g). Groups III, IV and V additionally received galangin (50, 100 and 200 μg/kg body weight, respectively) while group VI received 200 μg galangin/kg body weight. At the end of 60 days, fructose-fed rats exhibited insulin resistance, increased levels of peroxidation end products and diminished antioxidant status. galangin, dose-dependently normalized blood glucose and insulin levels. The minimum effective dose was 100 μg galangin/kg body weight. At this dose, galangin also prevented the development of insulin resistance and the exaggerated the response to oral glucose challenge. The oxidant-antioxidant balance was maintained by galangin. Micro-albuminuria and tubular and glomerular changes observed in fructose-treated rats were significantly prevented by galangin (100 μg/kg body weight). These findings imply that galangin potentiates insulin sensitivity and antioxidant capacity and reduces renal damage in this dietary model of metabolic syndrome.

Elevated dietary sugar and the heart: experimental models and myocardial remodeling

A dramatic rise in the prevalence of insulin resistance has been paralleled by increasing dietary consumption of sugar. The use of added sweeteners containing fructose (sucrose and high-fructose corn syrup) has increased by 25% over the past 3 decades. High fructose intake has the potential to adversely influence systemic and cellular metabolism via insulin resistance and glycolytic dysregulation. As a tissue that is both insulin sensitive and glycolysis dependent, the heart may be especially vulnerable to fructose over-consumption. In this review, experimental studies of elevated dietary sugar intake are evaluated, including sucrose and fructose dietary manipulation models. The possible role of the GLUT5 transporter as a mediator of cardiomyocyte fructose uptake is considered. The impact of dietary sucrose and fructose on cardiac insulin-dependent signaling in the context of perturbed systemic metabolic response is detailed. Myocardial dysfunction, modified growth, and oxidative stress responses associated with high dietary sugar intake are discussed. Finally, the involvement of the renin-angiotensin system in mediating fructose cardiopathology is considered. This review highlights the importance of obtaining new mechanistic data that can contribute to a more developed understanding of how high sugar intake directly contributes to structural and functional cardiomyopathy.

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.

Changes induced by a fructose-rich diet on hepatic metabolism and the antioxidant system

AIMS

The effect of a three-week fructose-rich diet (FRD) upon gene expression, protein and activity levels of liver antioxidant system and carbohydrate metabolism was studied.

MAIN METHODS

Serum glucose (fasting and after a glucose load), triglyceride and insulin levels of normal male Wistar rats were measured. In liver, we measured gene/protein expression and enzyme activity of catalase (CAT), copper-zinc-superoxide dismutase (CuZnSOD) and glutathione peroxidase (GSHPx); reduced glutathione (GSH); protein carbonyl content; thiobarbituric acid reactive substances (TBARS) content and microsomal membrane susceptibility to lipid peroxidation; glucokinase (GK), glucose-6-phosphatase (G-6-Pase) and glucose-6-phosphate dehydrogenase (G-6-PDH) activity; and glycogen, pyruvate, lactate and triglyceride content.

KEY FINDINGS

Similar body weights and caloric intake were recorded in both groups. FRD rats had higher serum glucose, insulin and triglyceride levels, molar insulin:glucose ratio, HOMA-IR values and impaired glucose tolerance, whereas CAT, CuZnSOD and GSHPx relative gene expression levels were significantly lower. CAT and CuZnSOD protein expression, CAT activity and GSH content were also lower, while protein carbonyl content was higher. No differences were recorded in CuZnSOD, MnSOD and GSHPx activity, TBARS content and membrane susceptibility to lipid peroxidation. Glycogen, lactate and triglyceride content and GK, G-6-Pase and G-6-PDH activity were significantly higher in FRD rats.

SIGNIFICANCE

In the presence of oxidative stress, the liver exhibits changes in the carbohydrate and lipid metabolic pathways that would decrease reactive oxygen species production and their deleterious effect, thus inducing little impact on specific antioxidant mechanisms. This knowledge could facilitate the design and implementation of strategies to prevent oxidative stress-induced liver damage.

Glycoxidative stress-induced damage on lipid profile in a fructose-enriched diet model of insulin resistance in rats

OBJECTIVE

To study alterations in plasma lipid profile and oxidative damage to lipoprotein fractions (LF) and their fatty acids during an early insulin-resistant and increased oxidative state developed by a fructose-rich diet (FRD).

METHODS AND RESULTS

Wistar rats were fed a commercial diet with (FRD) or without (CD) 10% fructose in the drinking water. After 3 weeks, plasma glucose, triglyceride (TG), insulin (I), fructosamine (F), free fatty acids (FFA) and lipid profile (total cholesterol [TC] and HDL-C, LDL-C and VLDL-C sub-fractions) were determined. The insulin sensitivity HOMA index was assessed. FRD-fed rats had higher plasma TG, I, and F levels; increased HOMA; decreased HDL-C and LDL-C; augmented VLDL-C and TC/HDL-C, and TG/HDL-C atherogenic risk scores. LF of FRD rats had increased oxidative damage on the fatty acyl profile and in copper-induced lipoperoxidation.

CONCLUSIONS

Fructose feeding early increases the atherogenic risk inducing an insulin resistant-glycoxidative state that affects plasma lipid profiles.

Genistein improves liver function and attenuates non-alcoholic fatty liver disease in a rat model of insulin resistance

BACKGROUND

The high fructose-fed rat is widely used as a model of insulin resistance. Genistein, a soy isoflavone, has been shown to improve insulin sensitivity in this model. The present study investigated whether genistein could prevent fatty liver disease in this model.

METHODS

Male Wistar rats were fed a diet containing starch (control) or 60% fructose (insulin-resistant model). Fifteen days later, rats in each dietary group were divided into two groups and were treated with either genistein (1 mg/kg per day) in dimethylsulfoxide (DMSO) or 30% DMSO alone. After 60 days, markers of liver injury, oxidative stress, interleukin (IL)-6, tumor necrosis factor (TNF)-α, lipids, lipoprotein profile, nitrite, and nitrosothiol in the plasma and liver were quantified. Liver sections were examined for 3-nitrotyrosine (3-NT) expression and pathological lesions.

RESULTS

Fructose-fed rats displayed hyperlipidemia, significant changes in plasma lipoprotein profile, and increases in IL-6 and TNF-α levels compared with control. In addition, the accumulation of lipids, liver injury, a decline in liver function, inactivation of the glyoxalase system, depletion of antioxidants, and increased 3-NT expression were observed in the fructose-fed group. Administration of genistein to fructose-fed rats significantly reduced these biochemical and histological abnormalities.

CONCLUSIONS

Genistein activates the antioxidant profile, decreases IL-6 and TNF-α concentrations, prevents oxidative damage, and ameliorates fatty liver in insulin-resistant rats.

Safety evaluation of alpha-lipoic acid (ALA)

The safety of the antioxidant alpha-lipoic acid (racemic form) (ALA), also called thioctic acid (CAS RN 1077-28-7) was assessed in acute and subchronic toxicity studies as well as in in vitro and in vivo mutagenicity/genotoxicity studies. ALA was not acutely toxic to rats (LD(50)>2000mg/kg bw, OECD method 425). Administration of 31.6 or 61.9mg ALA/kg bw/day for 4 weeks to male/female Wistar rats did not show any adverse effects. Specifically, there was no significant difference between control and treated animals at 31.6 or 61.9mg ALA/kg bw with regard to body weight gain, feed consumption, animal behaviour, or haematological and clinical chemistry parameters. Only the high-dose of 121mg ALA/kg bw was associated with slight alterations in liver enzymes as well as histopathological effects on the liver and mammary gland. ALA did not possess any mutagenic activity in the Ames assays conducted with various bacterial strains of Salmonella typhimurium. Moreover, there was no evidence of genotoxic activity in a mouse micronucleus assay. The results of these studies support the safety of ALA. The no-observed-adverse-effect level (NOAEL) is considered to be 61.9mg/kg bw/day.

Metabolic effects of fructose

PURPOSE OF REVIEW

Fructose is consumed in significant amounts in Western diets. An increase in fructose consumption over the past 10-20 years has been linked with a rise in obesity and metabolic disorders. Fructose/sucrose produces deleterious metabolic effects in animal models. This raises concern regarding the short-term and long-term effects of fructose and its risk in humans.

RECENT FINDINGS

In rodents, fructose stimulates lipogenesis and leads to hepatic and extrahepatic insulin resistance, dyslipidaemia and high blood pressure. Insulin resistance appears to be related to ectopic lipid deposition. In humans, short-term fructose feeding increases de-novo lipogenesis and blood triglycerides and causes hepatic insulin resistance. There is presently no evidence for fructose-induced muscle insulin resistance in humans. The cellular mechanisms underlying the metabolic effects of fructose involve production of reactive oxygen species, activation of cellular stress pathways and possibly an increase in uric acid synthesis.

SUMMARY

Consuming large amounts of fructose can lead to the development of a complete metabolic syndrome in rodents. In humans, fructose consumed in moderate to high quantities in the diet increases plasma triglycerides and alters hepatic glucose homeostasis, but does not appear to cause muscle insulin resistance or high blood pressure in the short term. Further human studies are required to delineate the effects of fructose in humans.