Mechanisms of fructose-induced hypertriglyceridaemia in the rat. Activation of hepatic pyruvate dehydrogenase through inhibition of pyruvate dehydrogenase kinase

The effects of high fructose fruits and honey on the serum level of metabolic factors and nonalcoholic fatty liver disease

Introduction

The effect of the natural sources of fructose such as high fructose fruits and honey on the risk of fatty liver is still challenging. This study aimed to compare the effect of fructose, high fructose fruits, and honey on the metabolic factors and non-alcoholic fatty liver disease (NAFLD).

Methods

Forty-four rats were divided into four groups including normal diet group, high fructose group (HF), high fructose fruits group (HFF), and honey group (HO). After 120 days of intervention, the levels of insulin resistance, hepatic enzyme, and lipid profile were measured. Also, the expression levels of the acetyl-coA carboxylase (ACC), sterol regulatory element-binding protein 1c (SREBP-1c), Interleukin 6 (IL-6), and transforming growth factor-beta (TGF-β) genes were assessed. In addition, a histopathologic assessment was performed on liver tissues.

Results

Insulin resistance (IR) increased significantly in the HF, HFF, and HO groups (All P < 0.05). The levels of liver enzymes was significantly increased only in the group receiving the HF regimen (P < 0.01). A significant decrease in total cholesterol and HDL-C (high density lipoprotein cholesterol) levels was found in HO group compared to the control group (P < 0.05). The expression levels of ACC and SREBP-1c genes in HF, HFF, and HO groups were significantly higher than the control group (All P < 0.05). The HF group had a greater increase in the level of gene expression of IL-6 and TGF-β (All P < 0.05). Histopathological assessment did not find any changes in fatty liver formation and inflammatory damage.

Conclusion

Consumption of fructose-rich honey and fruits improved the status of inflammatory markers and liver enzymes compared with the industrial fructose-rich products.

Effect of fructose instead of glucose or sucrose on cardiometabolic markers: a systematic review and meta-analysis of isoenergetic intervention trials

CONTEXT

Free, or added, sugars are considered important determinants in the pandemics of obesity and associated chronic diseases, and fructose has emerged as the sugar of main concern.

OBJECTIVE

The aim of this review was to assess the evidence of the effects of isoenergetic replacement of fructose or high-fructose corn syrup (HFCS) for glucose or sucrose on cardiometabolic markers in controlled dietary intervention trials.

DATA SOURCES

The electronic databases PubMed/MEDLINE, the Cochrane Library, and Embase were searched from 1980 to May 5, 2020.

STUDY SELECTION

Studies were eligible if they measured at least one of the following outcomes: total cholesterol, low- and high-density lipoprotein cholesterol, triacylglycerols, apolipoprotein A1, apolipoprotein B, systolic blood pressure, diastolic blood pressure, fasting glucose, and body weight.

DATA EXTRACTION

For each outcome, the mean values and the corresponding measure of dispersion were extracted after the intervention or control diet.

DATA ANALYSIS

Fixed-effects and random-effects models were used to pool study-specific estimates. Between-study heterogeneity was assessed by the χ2 test and the I2 statistic and publication bias by the Egger test and funnel plots.

RESULTS

Twenty-five studies involving 1744 volunteers were identified. No significant effects were found when fructose or HFCS was substituted for glucose, except for a slight decrease in diastolic blood pressure when fructose was substituted for glucose. Similarly, no effects were found when fructose or HFCS was substituted for sucrose, except for a small increase, of uncertain clinical significance, of apolipoprotein B when HFCS was substituted for sucrose.

CONCLUSIONS

Isoenergetic substitution of fructose or HFCS for glucose or sucrose has no significant effect on most of the cardiometabolic markers investigated; however, some results were affected by residual between-study heterogeneity and studies with high or unclear risk of bias.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration number CRD42016042930.

Substitution of high-dose sucrose with fructose in high-fat diets resulted in higher plasma concentrations of aspartic acid, cystine, glutamic acid, ornithine and phenylalanine, and higher urine concentrations of arginine and citrulline

High fructose intake has been shown to increase circulating alanine transaminase in humans, which could reflect damage to the liver by fructose but could also be linked to higher level of transamination of amino acids in liver. Therefore, we hypothesized that a diet with high content of fructose would affect the amino acid composition in rat plasma and urine differently from a diet with high sucrose content. Because high intake of sucrose and fructose is often accompanied with high intake of saturated fat in the Western-style diet, we wanted to compare the effects of high fructose/sucrose in diets with normal or high content of coconut oil on individual free amino acids plasma and urine. Male Wistar rats were fed diets with normal (10 wt%) or high (40 wt%) content of sucrose or fructose, with normal or high fat content (7 or 22 wt%) and 20 wt% protein (casein). Rats fed high-fructose high-fat diet had higher plasma concentrations of aspartic acid, cystine, glutamic acid, ornithine, and phenylalanine and higher urine concentrations of arginine and citrulline when compared to rats fed high-sucrose high-fat diet. Substituting normal content of sucrose with fructose in the diets had little impact on amino acids in plasma and urine. Serum concentrations of alanine transaminase, aspartate transaminase, and creatinine, and urine cystatin C and T cell immunoglobulin mucin-1 concentrations were comparable between the groups and within normal ranges. To conclude, substituting high-dose sucrose with high-dose fructose in high-fat diets affected amino acid compositions in plasma and urine.

The Beneficial Effects of Stingless Bee Honey from Heterotrigona itama against Metabolic Changes in Rats Fed with High-Carbohydrate and High-Fat Diet

Metabolic syndrome (MetS) is a group of conditions including central obesity, hyperglycemia, dyslipidemia, and hypertension that increases the risk for cardiometabolic diseases. Kelulut honey (KH) produced by stingless honey bees has stronger antioxidant properties compared to other honey types and may be a functional food against MetS. This study aimed to determine the efficacy of KH in preventing metabolic changes in rats with MetS induced by high-carbohydrate and high-fat (HCHF) diet. Male Wistar rats were randomly assigned to the control (C), HCHF diet-induced MetS (S), and MetS supplemented with KH (K) groups. The K group was given KH (1 g/kg/day) for eight weeks. Compared to the control, the S group had significant higher omental fat mass, serum triglyceride, systolic blood pressure, diastolic blood pressures, adipocyte area, and adipocyte perimeter (p < 0.05). KH supplementation significantly prevented these MetS-induced changes at week 16 (p < 0.05). Several compounds, including 4-hydroxyphenyl acetic acid, coumaric and caffeic acids, had been detected via liquid chromatography-mass spectrometry analysis that might contribute to the reversal of these changes. The beneficial effects of KH against MetS-induced rats provide the basis for future KH research to investigate its potential use in humans and its molecular mechanisms in alleviating the disease.

Acute fructose intake suppresses fasting-induced hepatic gluconeogenesis through the AKT-FoxO1 pathway

Excessive intake of fructose increases lipogenesis in the liver, leading to hepatic lipid accumulation and development of fatty liver disease. Metabolic alterations in the liver due to fructose intake have been reported in many studies, but the effect of fructose administration on hepatic gluconeogenesis is not fully understood. The aim of this study was to evaluate the acute effects of fructose administration on fasting-induced hepatic gluconeogenesis. C57BL/6J mice were administered fructose solution after 14 h of fasting and plasma insulin, glucose, free fatty acids, and ketone bodies were analysed. We also measured phosphorylated AKT and forkhead box O (FoxO) 1 protein levels and gene expression related to gluconeogenesis in the liver. Furthermore, we measured glucose production from pyruvate after fructose administration. Glucose-administered mice were used as controls. Fructose administration enhanced phosphorylation of AKT in the liver, without increase of blood insulin levels. Blood free fatty acids and ketone bodies concentrations were as high as those in the fasting group after fructose administration, suggesting that insulin-induced inhibition of lipolysis did not occur in mice administered with fructose. Fructose also enhanced phosphorylation of FoxO1 and suppressed gluconeogenic gene expression, glucose-6-phosphatase activity, and glucose production from pyruvate. The present study suggests that acute fructose administration suppresses fasting-induced hepatic gluconeogenesis in an insulin-independent manner.

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Fructose administration does not increase blood glucose and insulin levels.

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Fructose administration suppressed fasting-induced hepatic gluconeogenic gene expression and G6Pase activity.

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Fructose accelerates FoxO1 phosphorylation through the AKT-FoxO1 pathway.

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We propose that fructose intake suppresses fasting-induced hepatic gluconeogenesis in an insulin-independent manner.

Copper-Fructose Interactions: A Novel Mechanism in the Pathogenesis of NAFLD

Compelling epidemiologic data support the critical role of dietary fructose in the epidemic of obesity, metabolic syndrome and nonalcoholic fatty liver disease (NAFLD). The metabolic effects of fructose on the development of metabolic syndrome and NAFLD are not completely understood. High fructose intake impairs copper status, and copper-fructose interactions have been well documented in rats. Altered copper-fructose metabolism leads to exacerbated experimental metabolic syndrome and NAFLD. A growing body of evidence has demonstrated that copper levels are low in NAFLD patients. Moreover, hepatic and serum copper levels are inversely correlated with the severity of NAFLD. Thus, high fructose consumption and low copper availability are considered two important risk factors in NAFLD. However, the causal effect of copper-fructose interactions as well as the effects of fructose intake on copper status remain to be evaluated in humans. The aim of this review is to summarize the role of copper-fructose interactions in the pathogenesis of the metabolic syndrome and discuss the potential underlying mechanisms. This review will shed light on the role of copper homeostasis and high fructose intake and point to copper-fructose interactions as novel mechanisms in the fructose induced NAFLD.

Dietary sugars, exercise and hepatic carbohydrate metabolism

The present paper reviews the physiological responses of human liver carbohydrate metabolism to physical activity and ingestion of dietary sugars. The liver represents a central link in human carbohydrate metabolism and a mechanistic crux point for the effects of dietary sugars on athletic performance and metabolic health. As a corollary, knowledge regarding physiological responses to sugar ingestion has potential application to either improve endurance performance in athletes, or target metabolic diseases in people who are overweight, obese and/or sedentary. For example, exercise increases whole-body glycogen utilisation, and the breakdown of liver glycogen to maintain blood glucose concentrations becomes increasingly important as exercise intensity increases. Accordingly, prolonged exercise at moderate-to-high exercise intensity results in depletion of liver glycogen stores unless carbohydrate is ingested during exercise. The exercise-induced glycogen deficit can increase insulin sensitivity and blood glucose control, and may result in less hepatic lipid synthesis. Therefore, the induction and maintenance of a glycogen deficit with exercise could be a specific target to improve metabolic health and could be achieved by carbohydrate (sugar) restriction before, during and/or after exercise. Conversely, for athletes, maintaining and restoring these glycogen stores is a priority when competing in events requiring repeated exertion with limited recovery. With this in mind, evidence consistently demonstrates that fructose-containing sugars accelerate post-exercise liver glycogen repletion and could reduce recovery time by as much as half that seen with ingestion of glucose (polymers)-only. Therefore, athletes aiming for rapid recovery in multi-stage events should consider ingesting fructose-containing sugars to accelerate recovery.

Fructose and prostate cancer: toward an integrated view of cancer cell metabolism

Activation of glucose transporter-1 (Glut-1) gene expression is a molecular feature of cancer cells that increases glucose uptake and metabolism. Increased glucose uptake is the basis for the clinical localization of primary tumors using positron emission tomography (PET) and 2-deoxy-2-[18F]-fluoro-D-glucose (FDG) as a radiotracer. However, previous studies have demonstrated that a considerable number of cancers, which include prostate cancer (CaP), express low to undetectable levels of Glut-1 and that FDG-PET has limited clinical applicability in CaP. This observation could be explained by a low metabolic activity of CaP cells that may be overcome using different hexoses, such as fructose, as the preferred energy source. However, these hypotheses have not been examined critically in CaP. This review article summarizes what is currently known about transport and metabolism of hexoses, and more specifically fructose, in CaP and provides experimental evidences indicating that CaP cells may have increased capacity to transport and metabolize fructose in vitro and in vivo. Moreover, this review highlights recent findings that allow better understanding of how metabolism of fructose may regulate cancer cell proliferation and how fructose uptake and metabolism, through the de novo lipogenesis pathway, may provide new opportunities for CaP early diagnosis, staging, and treatment.

Dietary fat stimulates development of NAFLD more potently than dietary fructose in Sprague-Dawley rats

BACKGROUND

In humans and animal models, excessive intake of dietary fat, fructose and cholesterol has been linked to the development of non-alcoholic fatty liver disease (NAFLD). However, the individual roles of the dietary components remain unclear. To investigate this further, we compared the effects of a high-fat diet, a high-fructose diet and a combination diet with added cholesterol on the development of NAFLD in rats.

METHODS

Forty male Sprague-Dawley rats were randomized into four groups receiving either a control-diet (Control: 10% fat); a high-fat diet (HFD: 60% fat, 20% carbohydrate), a high-fructose diet [HFr: 10% fat, 70% carbohydrate (mainly fructose)] or a high-fat/high-fructose/high-cholesterol-diet (NASH: 40% fat, 40% carbohydrate (mainly fructose), 2% cholesterol) for 16 weeks.

RESULTS

After 16 weeks, liver histology revealed extensive steatosis and inflammation in both NASH- and HFD-fed rats, while hepatic changes in HFr-rats were much more subtle. These findings were corroborated by significantly elevated hepatic triglyceride content in both NASH- (p < 0.01) and HFD-fed rats (p < 0.0001), elevated hepatic cholesterol levels in NASH-fed rats (p < 0.0001), but no changes in HFr-fed rats, compared to Control. On the contrary, only HFr-fed rats developed dyslipidemia as characterized by higher levels of plasma triglycerides compared to all other groups (p < 0.0001). Hepatic dysfunction and inflammation was confirmed in HFD-fed rats by elevated levels of hepatic MCP-1 (p < 0.0001), TNF-alpha (p < 0.001) and plasma β-hydroxybutyrate (p < 0.0001), and in NASH-fed rats by elevated levels of hepatic MCP-1 (p < 0.01), increased hepatic macrophage infiltration (p < 0.001), and higher plasma levels of alanine aminotransferase (p < 0.0001) aspartate aminotransferase (p < 0.05), haptoglobin (p < 0.001) and TIMP-1 (p < 0.01) compared to Control.

CONCLUSION

These findings show that dietary fat and cholesterol are the primary drivers of NAFLD development and progression in rats, while fructose mostly exerts its effect on the circulating lipid pool.

An In Vivo Magnetic Resonance Spectroscopy Study of the Effects of Caloric and Non-Caloric Sweeteners on Liver Lipid Metabolism in Rats

We aimed to elucidate the effects of caloric and non-caloric sweeteners on liver lipid metabolism in rats using in vivo magnetic resonance spectroscopy (MRS) and to determine their roles in the development of liver steatosis. Wistar rats received normal chow and either normal drinking water, or solutions containing 13% (w/v) glucose, 13% fructose, or 0.4% aspartame. After 7 weeks, in vivo hepatic dietary lipid uptake and de novo lipogenesis were assessed with proton-observed, carbon-13-edited MRS combined with ¹³C-labeled lipids and ¹³C-labeled glucose, respectively. The molecular basis of alterations in hepatic liver metabolism was analyzed in detail ex vivo using immunoblotting and targeted quantitative proteomics. Both glucose and fructose feeding increased adiposity, but only fructose induced hepatic lipid accumulation. In vivo MRS showed that this was not caused by increased hepatic uptake of dietary lipids, but could be attributed to an increase in de novo lipogenesis. Stimulation of lipogenesis by fructose was confirmed by a strong upregulation of lipogenic enzymes, which was more potent than with glucose. The non-caloric sweetener aspartame did not significantly affect liver lipid content or metabolism. In conclusion, liquid fructose more severely affected liver lipid metabolism in rats than glucose, while aspartame had no effect.

The role of insufficient copper in lipid synthesis and fatty-liver disease

The essential transition metal copper is important in lipid metabolism, redox balance, iron mobilization, and many other critical processes in eukaryotic organisms. Genetic diseases where copper homeostasis is disrupted, including Menkes disease and Wilson disease, indicate the importance of copper balance to human health. The severe consequences of insufficient copper supply are illustrated by Menkes disease, caused by mutation in the X-linked ATP7A gene encoding a protein that transports copper from intestinal epithelia into the bloodstream and across the blood-brain barrier. Inadequate copper supply to the body due to poor diet quality or malabsorption can disrupt several molecular level pathways and processes. Though much of the copper distribution machinery has been described and consequences of disrupted copper handling have been characterized in human disease as well as animal models, physiological consequences of sub-optimal copper due to poor nutrition or malabsorption have not been extensively studied. Recent work indicates that insufficient copper may be important in a number of common diseases including obesity, ischemic heart disease, and metabolic syndrome. Specifically, marginal copper deficiency (CuD) has been reported as a potential etiologic factor in diseases characterized by disrupted lipid metabolism such as non-alcoholic fatty-liver disease (NAFLD). In this review, we discuss the available data suggesting that a significant portion of the North American population may consume insufficient copper, the potential mechanisms by which CuD may promote lipid biosynthesis, and the interaction between CuD and dietary fructose in the etiology of NAFLD. © 2016 IUBMB Life, 69(4):263-270, 2017.

Nutritional and Lipid Modulation of PCSK9: Effects on Cardiometabolic Risk Factors

Proprotein convertase subtilisin/kexin type 9 (PCSK9) is a serine protease involved in the regulation of LDL receptor (LDLR) expression and apolipoprotein B lipoprotein cholesterol metabolism. Hepatic PCSK9 protein expression, activity, and secretion have been shown to affect cholesterol homeostasis. An upregulation of hepatic PSCK9 protein leads to increased LDLR degradation, resulting in decreased uptake of apoB lipoproteins and a consequent increase in the plasma concentration of these lipoproteins, including LDL and chylomicron remnants. Hence, PCSK9 has become a novel target for lipid-lowering therapies. The aim of this review is to outline current findings on the metabolic and dietary regulation of PCSK9 and effects on cholesterol, apoB lipoprotein metabolism, and cardiovascular disease (CVD) risk. PCSK9 gene and protein expression have been shown to be regulated by metabolic status and the diurnal pattern. In the fasting state, plasma PCSK9 is reduced via modulation of the nuclear transcriptional factors, including sterol regulatory element-binding protein (SREBP) 1c, SREBP2, and hepatocyte nuclear factor 1α. Plasma PCSK9 concentrations are also known to be positively associated with plasma insulin and homeostasis model assessment of insulin resistance, and appear to be regulated by SREBP1c independently of glucose status. Plasma PCSK9 concentrations are stable in response to high-fat or high-protein diets in healthy individuals; however, this response may differ in altered metabolic conditions. Dietary n-3 polyunsaturated fatty acids have been shown to reduce plasma PCSK9 concentration and hepatic PCSK9 mRNA expression, consistent with their lipid-lowering effects, whereas dietary fructose appears to upregulate PCSK9 mRNA expression and plasma PCSK9 concentrations. Further studies are needed to elucidate the mechanisms of how dietary components regulate PCSK9 and effects on cholesterol and apoB lipoprotein metabolism, as well as to delineate the clinical impact of diet on PCSK9 in terms of CVD risk.

Curcumin inhibits hyperlipidemia and hepatic fat accumulation in high-fructose-fed male Wistar rats

CONTEXT

Curcumin, an active principal of Curcuma longa Linn. (Zingiberaceae), has potent antioxidant and anti-inflammatory properties.

OBJECTIVES

This study investigated the effects of curcumin on hyperlipidemia and hepatic steatosis in high-fructose-fed Wistar rats.

MATERIALS AND METHODS

Forty male Wistar rats were divided into four groups with 10 rats in each. Two groups were fed with standard rodent diet and the other two with 60% high-fructose diet for 10 weeks. Curcumin (200 mg/kg body weight) was administered along with the diets simultaneously to each of the aforementioned diet groups. After 10 weeks of experiment, blood samples were collected from tail vein. Liver, adipose and epididymal tissues were collected after sacrifice of the animals and stored for further analyses.

RESULTS

Administration of curcumin reduced body weight (280.6 ± 7.4 g), liver weight (2.5 ± 0.2 g/100 g BW), adipose weight (1.4 ± 0.3 g/100 g BW), plasma levels of TAG (86.1 ± 13.5 mg/dL), VLDL-C (17.2 ± 2.7 mg/dL), lipid ratios and increased HDL-C (28.4 ± 4.5 mg/dL) in fructose-fed rats. Curcumin supplementation significantly lowered TAG content and decreased the protein expression of LXR-α (43%) and SREBP1c (59%) in the liver. Furthermore, curcumin suppressed the expression of lipogenic enzymes, ACLY (95%), ACC (50%) and FAS (77%) in rats fed with high-fructose diet. No significant change was found in the expression of PPAR-α.

DISCUSSION AND CONCLUSION

Curcumin prevented the high-fructose induced hyperlipidemia and hepatic steatosis.

The Sweet Path to Metabolic Demise: Fructose and Lipid Synthesis

Epidemiological studies link fructose consumption with metabolic disease, an association attributable in part to fructose-mediated lipogenesis. The mechanisms governing fructose-induced lipogenesis and disease remain debated. Acutely, fructose increases de novo lipogenesis through the efficient and uninhibited action of ketohexokinase and aldolase B which yields substrates for fatty-acid synthesis. Chronic fructose consumption further enhances the capacity for hepatic fructose metabolism by activating several key transcription factors (i.e., SREBP1c and ChREBP) which augment the expression of lipogenic enzymes, increasing lipogenesis and further compounding hypertriglyceridemia and hepatic steatosis. Hepatic insulin resistance develops from diacylglycerol-PKCɛ-mediated impairment of insulin signaling and possibly additional mechanisms. Initiatives that decrease fructose consumption and therapies that block fructose-mediated lipogenesis will be necessary to avert future metabolic pandemics.

Fructose Metabolism and Relation to Atherosclerosis, Type 2 Diabetes, and Obesity

A high intake of sugars has been linked to diet-induced health problems. The fructose content in sugars consumed may also affect health, although the extent to which fructose has a particularly significant negative impact on health remains controversial. The aim of this narrative review is to describe the body's fructose management and to discuss the role of fructose as a risk factor for atherosclerosis, type 2 diabetes, and obesity. Despite some positive effects of fructose, such as high relative sweetness, high thermogenic effect, and low glycaemic index, a high intake of fructose, particularly when combined with glucose, can, to a larger extent than a similar glucose intake, lead to metabolic changes in the liver. Increased de novo lipogenesis (DNL), and thus altered blood lipid profile, seems to be the most prominent change. More studies with realistic consumption levels of fructose are needed, but current literature does not indicate that a normal consumption of fructose (approximately 50–60 g/day) increases the risk of atherosclerosis, type 2 diabetes, or obesity more than consumption of other sugars. However, a high intake of fructose, particularly if combined with a high energy intake in the form of glucose/starch, may have negative health effects via DNL.

Dietary docosahexaenoic acid and eicosapentaenoic acid influence liver triacylglycerol and insulin resistance in rats fed a high-fructose diet

This study aimed to examine the benefits of different amounts of omega-3 (n-3) polyunsaturated fatty acids from fish oil (FO) on lipid metabolism, insulin resistance and gene expression in rats fed a high-fructose diet. Male Wistar rats were separated into two groups: Control (C, n = 6) and Fructose (Fr, n = 32), the latter receiving a diet containing 63% by weight fructose for 60 days. After this period, 24 animals from Fr group were allocated to three groups: FrFO2 (n = 8) receiving 63% fructose and 2% FO plus 5% soybean oil; FrFO5 (n = 8) receiving 63% fructose and 5% FO plus 2% soybean oil; and FrFO7 (n = 8) receiving 63% fructose and 7% FO. Animals were fed these diets for 30 days. Fructose led to an increase in liver weight, hepatic and serum triacylglycerol, serum alanine aminotransferase and HOMA1-IR index. These alterations were reversed by 5% and 7% FO. FO had a dose-dependent effect on expression of genes related to hepatic β-oxidation (increased) and hepatic lipogenesis (decreased). The group receiving the highest FO amount had increased markers of oxidative stress. It is concluded that n-3 fatty acids may be able to reverse the adverse metabolic effects induced by a high fructose diet.

Antihyperlipidemic Activity of Aloe succotrina in Rats: Possibly Mediated by Inhibition of HMG-CoA Reductase

The present study was designed to investigate antihyperlipidemic activity of dried pulp of Aloe succotrina leaves in Wistar albino rats. Hyperlipidemia was induced in rats by feeding them high fat diet (HFD) or D-fructose (25% w/v) for 4 successive weeks. From 15th to 28th day, dried pulp (100 and 200 mg/kg, p.o) and atorvastatin (10 mg/kg, p.o.) per se were administered 2 h prior to feeding rats with HFD or fructose. Aloe succotrina did not significantly decrease the body weight of rats. The dried pulp and atorvastatin per se significantly decreased relative liver weight but did not significantly affect relative heart weight. HFD or fructose significantly increased serum total cholesterol, triglycerides, LDL-c, and VLDL, and decreased HDL-c; significantly increased liver MDA and decreased GSH levels. The dried pulp (200 mg/kg p.o.) significantly reversed high fat diet-induced and fructose-induced hyperlipidemia and atherogenic index. Aloe succotrina significantly decreased HMG Co-A reductase activity. Antihyperlipidemic effect of the dried pulp was comparable to atorvastatin. Thus, Aloe succotrina produced significant antihyperlipidemic activity in both HFD and fructose-induced hyperlipidemic rats, possibly through normalization of serum lipid profile, HMG-CoA reductase inhibitory activity, and amelioration of oxidative stress in liver.

The effects of phentolamine on fructose-fed rats

Metabolic syndrome (MS) is a combination of medical disorders that increase the risk of developing cardiovascular disease and diabetes. MS is associated with obesity, increased blood pressure, hyperlipidemia, and hyperglycemia. This study was designed to investigate the pharmacological profile of phentolamine, a nonselective α adrenergic receptor antagonist, in the prevention of increased blood pressure in fructose-fed rats. Phentolamine prevented the fructose-induced increase in systolic blood pressure without affecting insulin sensitivity and major metabolic parameters. The levels of plasma noradrenaline and angiotensin II, 2 proposed contributors to the development of fructose-induced elevated blood pressure, were examined. Neither noradrenaline nor angiotensin II levels were affected by phentolamine treatment. Since overproduction of nitric oxide has been shown to lead to an elevation in peroxynitrite, the role of oxidative stress, a proposed mechanism of fructose-induced elevated blood pressure and insulin resistance, was examined by measuring plasma levels of total nitrate/nitrite. Plasma nitrate/nitrite was significantly elevated in all fructose-fed animals, regardless of treatment with phentolamine. Another proposed contributor toward fructose-induced MS is an elevation in uric acid levels. In this experiment, plasma levels of uric acid were found to be increased by dietary fructose and were unaffected by phentolamine treatment.

Effects of Bixa orellana L. seeds on hyperlipidemia

Bixa orellana L., urucum, or urucu, a native tropical tree of Central and South American rain forests is used to treat various diseases in popular medicine. In Ceará, Northeast of Brazil, the seeds of urucum have been used for the treatment of high lipid blood levels. The present study investigated the effects of the aqueous extract from Bixa orellana seeds (AEBO) in mice with hyperlipidemia induced by tyloxapol, fructose and ethanol. In hyperlipidemia induced by Triton WR1339, 400 and 800 mg/kg AEBO reduced triglycerides (TG) serum levels at 24 h and 48 h. In the study of hypertriglyceridemia induced by fructose, AEBO in doses of 400 mg/kg and 800 mg/kg reduced TG levels by 48.2% and 48.7%, respectively. Finally, the ethanol experimental model with 400 mg/kg AEBO promoted a reduction of 33.6% of TG levels, while the 800 mg/kg concentration reduced hypertriglyceridemia in 62.2%. In conclusion, the aqueous extract of the seeds of Bixa orellana was capable of reversing the hypertriglyceridemia induced by Triton, fructose and ethanol, demonstrating a hypolipidemic effect. However, further studies are necessary to discover the precise mechanism of action.

The role of fructose-enriched diets in mechanisms of nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) currently affects 20%-30% of adults and 10% of children in industrialized countries, and its prevalence is increasing worldwide. Although NAFLD is a benign form of liver dysfunction, it can proceed to a more serious condition, nonalcoholic steatohepatitis (NASH), which may lead to liver cirrhosis and hepatocellular carcinoma. NAFLD is accompanied by obesity, metabolic syndrome and diabetes mellitus, and evidence suggests that fructose, a major caloric sweetener in the diet, plays a significant role in its pathogenesis. Inflammatory progression to NASH is proposed to occur by a two-hit process. The first "hit" is hepatic fat accumulation owing to increased hepatic de novo lipogenesis, inhibition of fatty acid beta oxidation, impaired triglyceride clearance and decreased very-low-density lipoprotein export. The mechanisms of the second "hit" are still largely unknown, but recent studies suggest several possibilities, including inflammation caused by oxidative stress associated with lipid peroxidation, cytokine activation, nitric oxide and reactive oxygen species, and endogenous toxins of fructose metabolites.

High-fructose feeding impacts on the adrenergic control of renal haemodynamics in the rat

The present study explored the hypothesis that a prolonged 8 weeks exposure to a high fructose intake suppresses adrenergic and angiotensin II (Ang II)-mediated vasoconstriction and is associated with a higher contribution of α1D-adrenoceptors. A total of thirty-two Sprague–Dawley rats received either 20 % fructose solution (FFR) or tap water (control, C) to drink ad libitum for 8 weeks. Metabolic and haemodynamic parameters were assessed weekly. The renal cortical vasoconstrictor responses to noradrenaline (NA), phenylephrine (PE), methoxamine (ME) and Ang II were determined in the presence and absence of BMY7378 (α1D-adrenoceptor antagonist). FFR had increased blood pressure, plasma levels of glucose, TAG and insulin. FFR expressed reduced renal vascular responses to adrenergic agonists and Ang II (NA: 50 %, PE: 50 %, ME, 65 %, Ang II: 54 %). Furthermore in the C group, the magnitude of the renal cortical vasoconstriction to all agonists was blunted in the presence of the low or high dose of BMY7378 (NA: 30 and 31 %, PE: 23 and 33 %, ME: 19 and 44 %, Ang II: 53 and 77 %), respectively, while in the FFR, vasoconstriction was enhanced to adrenergic agonists and reduced to Ang II (NA: 8 and 83 %, PE: 55 %, ME, 2 and 177 %, Ang II: 61 and 31 %). Chronic high fructose intake blunts vascular sensitivity to adrenergic agonists and Ang II. Moreover, blocking of the α1D-adrenoceptor subtype results in enhancement of renal vasoconstriction to adrenergic agonists, suggesting an inhibitory action of α1D-adrenoceptors in the FFR. α1D-Adrenoceptors buffer the AT1-receptor response in the renal vasculature of normal rats and fructose feeding suppressed this interaction.

High dietary fructose intake: Sweet or bitter life?

Epidemiological data show that the consumption of added sugars as ingredients in processed or prepared foods and caloric beverages has dramatically increased. Fructose and fructose-based sweeteners are the most commonly added sugars and high-fructose corn syrup (HFCS-55: 55% fructose, 42% glucose and 3% higher saccharides) accounts for over 40% of all added caloric sweeteners. Concerns regarding the health risk of added sugar follow the demonstration that the consumption of foods and beverages high in sugars is associated with an increased prevalence of obesity, insulin resistance, dyslipidemia and, more recently, ischemic heart and kidney diseases. The molecular mechanism(s) underlying the detrimental effects of sugar are not completely understood and their elucidation is critical to provide new insights on the health risk of fructose-based sweeteners. A better understanding of the key role of fructose overconsumption in the development of metabolic disorders may contribute to planning new strategies for preventing deleterious dietary behaviors from becoming established and, thus, curbing the rise in the number of insulin-resistant, obese and diabetic populations worldwide.

Hypolipidemic and Antiobesity-Like Activity of Standardised Extract of Hypericum perforatum L. in Rats

Hypericum perforatum is known to have diverse medicinal uses for centuries. The antidepressant activity of Hypericum perforatum is widely accepted and proved in both animal and clinical studies. Present study was undertaken to investigate the effect of Hypericum perforatum in a battery of animal models for metabolic disorder. Hypericum is tested for hypolipidemic activity in normal rats, antiobesity activity in high-fat-diet induced obese rats, and fructose-fed rats. Hypericum was orally administered as suspension in 0.3% carboxymethyl cellulose at the doses of 100 and 200 mg/kg body weight for 15 consecutive days. Hypericum significantly lowered total cholesterol and low-density cholesterol in normal rats. Hypericum significantly inhibited weight gain in high-fat-fed rats. In fructose-fed rats, Hypericum normalised the dyslipidemia induced by fructose feeding and improved the insulin sensitivity. Taken together, Hypericum could be the antidepressant therapy of choice for patients suffering from comorbid diabetes and obesity.

Fructose induced lipogenesis: from sugar to fat to insulin resistance

Increasing consumption of sugars is one of the contributing factors to the obesity epidemic. Both cane sugar and high-fructose corn syrup contain glucose and fructose. Fructose, in contrast to glucose, is known to potently stimulate lipogenesis, but the mechanisms responsible are not yet fully known. This paper reviews several possible pathways that might be involved, such as activation of pyruvate dehydrogenase, and transcriptional activation of sterol regulatory element binding protein 1c by key regulators such as peroxisome proliferator activated receptor-γ co-activator 1β and the splice variant of X-box binding protein 1. Together, these pathways might establish a feed forward cycle that can rapidly increase hepatic lipogenesis. As a result, dietary fructose might promote the development of nonalcoholic fatty liver disease, which in and of itself, can result in hepatic insulin resistance, a key feature of type 2 diabetes mellitus.

Chronic consumption of fructose rich soft drinks alters tissue lipids of rats

BACKGROUND

Fructose-based diets are apparently related to the occurrence of several metabolic dysfunctions, but the effects of the consumption of high amounts of fructose on body tissues have not been well described. The aim of this study was to analyze the general characteristics and the lipid content of different tissues of rats after chronic ingestion of a fructose rich soft drink.

METHODS

Forty-five Wistar rats were used. The rats were divided into three groups (n = 15) and allowed to consume water (C), light Coca Cola (R) (L) or regular Coca Cola(R) (R) as the sole source of liquids for eight weeks.

RESULTS

The R group presented significantly higher daily liquid intake and significantly lower food intake than the C and L groups. Moreover, relative to the C and L groups, the R group showed higher triglyceride concentrations in the serum and liver. However, the L group animals presented lower values of serum triglycerides and cholesterol than controls.

CONCLUSIONS

Based on the results, it can be concluded that daily ingestion of a large amount of fructose- rich soft drink resulted in unfavorable alterations to the lipid profile of the rats.

Attenuated alpha-adrenoceptor-mediated arterial and venous constrictions in rat models of diabetes

Diabetes is associated with metabolic and vascular abnormalities. We investigated if arterial and venous constrictions are impaired in rat models of diabetes. Wistar rats (5 weeks old) were fed a normal or high-fructose diet (60% of caloric intake). On Day 14, half of the animals in each diet regimen were given streptozotocin (60 mg/kg, i.v.). On Day 35, plasma insulin and triglyceride were measured, and on Day 42, insulin sensitivity (via hyperinsulinemic euglycemic clamp), and pressor as well as mean circulatory filling pressure (index of venous tone) responses to noradrenaline were determined. The rats treated with streptozotocin or fructose-streptozotocin were hyperglycemic, hypoinsulinemic and insulin resistant, and they also had reduced potency (increased ED(50)) of pressor response and reduced venoconstriction to noradrenaline compared to the two groups not given streptozotocin. Plasma triglyceride was unchanged in streptozotocin-treated rats, moderately increased in fructose-fed rats, and markedly increased in fructose-streptozotocin-treated rats. Hyperglycemia, insulin resistance and alpha-adrenoceptor-mediated venous contractile dysfunction were more pronounced in the group given fructose-streptozotocin than that given streptozotocin alone. The presence of marked hypertriglyceridemia, insulin resistance and vascular dysfunction makes the fructose-streptozotocin-treated rats a suitable model for study of metabolic and vascular abnormalities in advanced type 2 diabetes.

Metabolic effects of fructose and the worldwide increase in obesity

While virtually absent in our diet a few hundred years ago, fructose has now become a major constituent of our modern diet. Our main sources of fructose are sucrose from beet or cane, high fructose corn syrup, fruits, and honey. Fructose has the same chemical formula as glucose (C(6)H(12)O(6)), but its metabolism differs markedly from that of glucose due to its almost complete hepatic extraction and rapid hepatic conversion into glucose, glycogen, lactate, and fat. Fructose was initially thought to be advisable for patients with diabetes due to its low glycemic index. However, chronically high consumption of fructose in rodents leads to hepatic and extrahepatic insulin resistance, obesity, type 2 diabetes mellitus, and high blood pressure. The evidence is less compelling in humans, but high fructose intake has indeed been shown to cause dyslipidemia and to impair hepatic insulin sensitivity. Hepatic de novo lipogenesis and lipotoxicity, oxidative stress, and hyperuricemia have all been proposed as mechanisms responsible for these adverse metabolic effects of fructose. Although there is compelling evidence that very high fructose intake can have deleterious metabolic effects in humans as in rodents, the role of fructose in the development of the current epidemic of metabolic disorders remains controversial. Epidemiological studies show growing evidence that consumption of sweetened beverages (containing either sucrose or a mixture of glucose and fructose) is associated with a high energy intake, increased body weight, and the occurrence of metabolic and cardiovascular disorders. There is, however, no unequivocal evidence that fructose intake at moderate doses is directly related with adverse metabolic effects. There has also been much concern that consumption of free fructose, as provided in high fructose corn syrup, may cause more adverse effects than consumption of fructose consumed with sucrose. There is, however, no direct evidence for more serious metabolic consequences of high fructose corn syrup versus sucrose consumption.

Antidyslipidaemic activity of Glycyrrhiza glabra in high fructose diet induced dsyslipidaemic Syrian golden hamsters

The root of Glycyrrhiza glabra is a traditional medicine used mainly for the treatment of peptic ulcer, hepatitis C, pulmonary and skin diseases, although clinical and experimental studies suggest that it has several other useful pharmacological properties such as antiinflammatory, antiviral, antimicrobial, antioxidative, anticancer activities, immunomodulatory, hepatoprotective and cardioprotective effects. Glycyrrhizinic acid, a major component of licorice, has antiulcer effect by raising the local concentration of prostaglandins that promote mucous secretion and cell proliferation in the stomach. Glycyrrhizin shows hepatoprotective effect by preventing changes in cell membrane permeability, inhibiting phospholipase A(2) (PLA(2)) and increasing survival rate of hepatocytes. Glabridin has effect in melanogenesis and inflammation by inhibiting the tyrosinase activity of melanocytes. α-glycyhrritinic acid exhibits anti-inflammatory activity by inhibiting glucocorticoid metabolism. In present study ethanolic (95%) extract of root of Glycyrrhiza glabra and its fractions were investigated for its antidyslipidaemic activity on HFD induced dyslipidaemic hamsters. Ethanolic extract and its ethyl acetate soluble, water soluble and hexane soluble fractions decreased serum level of total cholesterol by 25.9, 38.0, 39.0 and 26.3%, respectively. On the other hand ethanolic extract, ethyl acetate soluble, water soluble and hexane soluble fraction increased the serum HDL-cholesterol level by 14.8, 34.3, 27.3 and 17.2%, respectively. Ethanolic extract, ethyl acetate fraction, aqueous fraction and hexane fraction decreased triglyceride level by 31.3, 37.2, 41.2 and 28.9%, respectively. The reduction in LDL-cholesterol level by ethanolic extract, ethyl acetate soluble fraction and water soluble fraction were 43.9, 31.0, 33.4 and 24.6%, respectively.

A high fructose diet impairs spatial memory in male rats

Over the past three decades there has been a substantial increase in the amount of fructose consumed by North Americans. Recent evidence from rodents indicates that hippocampal insulin signaling facilitates memory and excessive fructose consumption produces hippocampal insulin resistance. Based on this evidence, the present study tested the hypothesis that a high fructose diet would impair hippocampal-dependent memory. Adult male Sprague-Dawley rats (postnatal day 61) were fed either a control (0% fructose) or high fructose diet (60% of calories). Food intake and body mass were measured regularly. After 19 weeks, the rats were given 3 days of training (8 trials/day) in a spatial version of the water maze task, and retention performance was probed 48 h later. The high fructose diet did not affect acquisition of the task, but did impair performance on the retention test. Specifically, rats fed a high fructose diet displayed significantly longer latencies to reach the area where the platform had been located, made significantly fewer approaches to that area, and spent significantly less time in the target quadrant than did control diet rats. There was no difference in swim speed between the two groups. The retention deficits correlated significantly with fructose-induced elevations of plasma triglyceride concentrations. Consequently, the impaired spatial water maze retention performance seen with the high fructose diet may have been attributable, at least in part, to fructose-induced increases in plasma triglycerides.

Endocrine and metabolic effects of consuming fructose- and glucose-sweetened beverages with meals in obese men and women: influence of insulin resistance on plasma triglyceride responses

CONTEXT

Compared with glucose-sweetened beverages, consumption of fructose-sweetened beverages with meals elevates postprandial plasma triglycerides and lowers 24-h insulin and leptin profiles in normal-weight women. The effects of fructose, compared with glucose, ingestion on metabolic profiles in obese subjects has not been studied.

OBJECTIVE

The objective of the study was to compare the effects of fructose- and glucose-sweetened beverages consumed with meals on hormones and metabolic substrates in obese subjects.

DESIGN AND SETTING

The study had a within-subject design conducted in the clinical and translational research center.

PARTICIPANTS

Participants included 17 obese men (n = 9) and women (n = 8), with a body mass index greater than 30 kg/m(2).

INTERVENTIONS

Subjects were studied under two conditions involving ingestion of mixed nutrient meals with either glucose-sweetened beverages or fructose-sweetened beverages. The beverages provided 30% of total kilocalories. Blood samples were collected over 24 h.

MAIN OUTCOME MEASURES

Area under the curve (24 h AUC) for glucose, lactate, insulin, leptin, ghrelin, uric acid, triglycerides (TGs), and free fatty acids was measured.

RESULTS

Compared with glucose-sweetened beverages, fructose consumption was associated with lower AUCs for insulin (1052.6 +/- 135.1 vs. 549.2 +/- 79.7 muU/ml per 23 h, P < 0.001) and leptin (151.9 +/- 22.7 vs. 107.0 +/- 15.0 ng/ml per 24 h, P < 0.03) and increased AUC for TG (242.3 +/- 96.8 vs. 704.3 +/- 124.4 mg/dl per 24 h, P < 0.0001). Insulin-resistant subjects exhibited larger 24-h TG profiles (P < 0.03).

CONCLUSIONS

In obese subjects, consumption of fructose-sweetened beverages with meals was associated with less insulin secretion, blunted diurnal leptin profiles, and increased postprandial TG concentrations compared with glucose consumption. Increases of TGs were augmented in obese subjects with insulin resistance, suggesting that fructose consumption may exacerbate an already adverse metabolic profile present in many obese subjects.

Fructose modifies the hormonal response and modulates lipid metabolism during aerobic exercise after glucose supplementation

The metabolic response when aerobic exercise is performed after the ingestion of glucose plus fructose is unclear. In the present study, we administered two beverages containing GluF (glucose+fructose) or Glu (glucose alone) in a randomized cross-over design to 20 healthy aerobically trained volunteers to compare the hormonal and lipid responses provoked during aerobic exercise and the recovery phase. After ingesting the beverages and a 15-min resting period, volunteers performed 30 min of moderate aerobic exercise. Urinary and blood samples were taken at baseline (t(-15)), during the exercise (t(0), t(15) and t(30)) and during the recovery phase (t(45), t(75) and t(105)). Plasma insulin concentrations were higher halfway through the exercise period and during acute recuperation (t(15) and t(75); P<0.05) following ingestion of GluF than after Glu alone, without any differences between the effects of either intervention on plasma glucose concentrations. Towards the end of the exercise period, urinary catecholamine concentrations were lower following GluF (t(45); P<0.05). Plasma triacylglycerol (triglyceride) concentrations were higher after the ingestion of GluF compared with Glu (t(15), t(30), t(45) and t(105); P<0.05). Furthermore, with GluF, we observed higher levels of lipoperoxides (t(15), t(30), t(45) and t(105); P<0.05) and oxidized LDL (low-density lipoprotein; t(30); P<0.05) compared with after the ingestion of Glu alone. In conclusion, hormonal and lipid alterations are provoked during aerobic exercise and recovery by the addition of a dose of fructose to the pre-exercise ingestion of glucose.

Consumption of fructose-sweetened beverages for 10 weeks increases postprandial triacylglycerol and apolipoprotein-B concentrations in overweight and obese women

Fructose consumption in the USA has increased over the past three decades. During this time, obesity, insulin resistance and the metabolic syndrome have also increased in prevalence. While diets high in fructose have been shown to promote insulin resistance and increase TAG concentrations in animals, there are insufficient data available regarding the long-term metabolic effects of fructose consumption in humans. The objective of the present study was to investigate the metabolic effects of 10-week consumption of fructose-sweetened beverages in human subjects under energy-balanced conditions in a controlled research setting. Following a 4-week weight-maintaining complex carbohydrate diet, seven overweight or obese (BMI 26.8-33.3 kg/m2) postmenopausal women were fed an isoenergetic intervention diet, which included a fructose-sweetened beverage with each meal, for 10 weeks. The intervention diet provided 15 % of energy from protein, 30 % from fat and 55 % from carbohydrate (30 % complex carbohydrate, 25 % fructose). Fasting and postprandial glucose, insulin, TAG and apoB concentrations were measured. Fructose consumption increased fasting glucose concentrations and decreased meal-associated glucose and insulin responses (P = 0.0002, P = 0.007 and P = 0.013, respectively). Moreover, after 10 weeks of fructose consumption, 14 h postprandial TAG profiles were significantly increased, with the area under the curve at 10 weeks being 141 % higher than at baseline (P = 0.04). Fructose also increased fasting apoB concentrations by 19 % (P = 0.043 v. baseline). In summary, consumption of fructose-sweetened beverages increased postprandial TAG and fasting apoB concentrations, and the present results suggest that long-term consumption of diets high in fructose could lead to an increased risk of CVD.

Consumption of fructose-sweetened beverages for 10 weeks increases postprandial triacylglycerol and apolipoprotein-B concentrations in overweight and obese women

Fructose consumption in the USA has increased over the past three decades. During this time, obesity, insulin resistance and the metabolic syndrome have also increased in prevalence. While diets high in fructose have been shown to promote insulin resistance and increase TAG concentrations in animals, there are insufficient data available regarding the long-term metabolic effects of fructose consumption in humans. The objective of the present study was to investigate the metabolic effects of 10-week consumption of fructose-sweetened beverages in human subjects under energy-balanced conditions in a controlled research setting. Following a 4-week weight-maintaining complex carbohydrate diet, seven overweight or obese (BMI 26.8-33.3 kg/m2) postmenopausal women were fed an isoenergetic intervention diet, which included a fructose-sweetened beverage with each meal, for 10 weeks. The intervention diet provided 15 % of energy from protein, 30 % from fat and 55 % from carbohydrate (30 % complex carbohydrate, 25 % fructose). Fasting and postprandial glucose, insulin, TAG and apoB concentrations were measured. Fructose consumption increased fasting glucose concentrations and decreased meal-associated glucose and insulin responses (P = 0.0002, P = 0.007 and P = 0.013, respectively). Moreover, after 10 weeks of fructose consumption, 14 h postprandial TAG profiles were significantly increased, with the area under the curve at 10 weeks being 141 % higher than at baseline (P = 0.04). Fructose also increased fasting apoB concentrations by 19 % (P = 0.043 v. baseline). In summary, consumption of fructose-sweetened beverages increased postprandial TAG and fasting apoB concentrations, and the present results suggest that long-term consumption of diets high in fructose could lead to an increased risk of CVD.

Substitution of drinking water by fructose solution induces hyperinsulinemia and hyperglycemia in hamsters

PURPOSE

To test the possibility of obtaining a practical and stable model of hyperinsulinemia and hyperglycemia in hamsters, substituting the drinking water by 10% or 20% fructose solutions for a period of 2, 4, or 6 months.

METHODS

Male hamsters were divided into 3 main groups, further divided in 3 subgroups: Two months: Group Ia control (n = 51) received filtered water, Group Ib (n = 49) received 10% fructose solution instead of water, Group Ic (n=8) received 20% fructose solution instead of water. Four months: Group IIa control (n=8), Group IIb 10% fructose (n = 7), Group IIc 20% fructose (FIIc, n = 7). Six months: Group IIIa control (n = 6), Group IIIb 10% Fructose (n = 6), Group IIIc 20% Fructose (n = 5). All groups were fed with the same laboratory diet. The animals were weighed every 2 weeks during the study period. On the final day of each experiment (61st, 121st, and 181st day after the beginning of the study, respectively), the animals were weighed and anesthetized for blood collection to determine plasma glucose and insulin after at least a 12-h fast. Ten animals of group Ia and 10 of group Ib were evaluated to determine changes in macromolecular permeability induced by ischemia/reperfusion as measured in the cheek pouch microcirculation.

RESULTS

Compared to controls, the animals that drank the 10% or 20% fructose solution had significantly greater weight gain (P < .001), fasting plasma glucose (P < .001) Reperfusion, after 30 min ischemia, resulted in an immediate but reversible increase in postcapillary leakage (L) of 89.0 +/- 2.0 L/cm(2) (group Ia - controls), and 116.5 +/- 4.8 L/cm(2) (group Ib 10% fructose), P < .001. These results suggest that chronic administration of either 10% or 20% fructose solutions could be used to experimentally induce a stable hamster model of hyperinsulinemia and hyperglycemia.

CONCLUSION

The model might facilitate the study of basic mechanisms of hyperglycemia and hyperinsulinemia affecting the microvasculature as demonstrated by the findings regarding ischemia/reperfusion after only 2 months of treatment.

A 4-wk high-fructose diet alters lipid metabolism without affecting insulin sensitivity or ectopic lipids in healthy humans

BACKGROUND

High fructose consumption is suspected to be causally linked to the epidemics of obesity and metabolic disorders. In rodents, fructose leads to insulin resistance and ectopic lipid deposition. In humans, the effects of fructose on insulin sensitivity remain debated, whereas its effect on ectopic lipids has never been investigated.

OBJECTIVE

We assessed the effect of moderate fructose supplementation on insulin sensitivity (IS) and ectopic lipids in healthy male volunteers (n = 7).

DESIGN

IS, intrahepatocellular lipids (IHCL), and intramyocellular lipids (IMCL) were measured before and after 1 and 4 wk of a high-fructose diet containing 1.5 g fructose . kg body wt(-1) . d(-1). Adipose tissue IS was evaluated from nonesterified fatty acid suppression, hepatic IS from suppression of hepatic glucose output (6,6-2H2-glucose), and muscle IS from the whole-body glucose disposal rate during a 2-step hyperinsulinemic euglycemic clamp. IHCL and IMCL were measured by 1H magnetic resonance spectroscopy.

RESULTS

Fructose caused significant (P < 0.05) increases in fasting plasma concentrations of triacylglycerol (36%), VLDL-triacylglycerol (72%), lactate (49%), glucose (5.5%), and leptin (48%) without any significant changes in body weight, IHCL, IMCL, or IS. IHCL were negatively correlated with triacylglycerol after 4 wk of the high-fructose diet (r = -0.78, P < 0.05).

CONCLUSION

Moderate fructose supplementation over 4 wk increases plasma triacylglycerol and glucose concentrations without causing ectopic lipid deposition or insulin resistance in healthy humans.

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.

Dietary fructose: implications for dysregulation of energy homeostasis and lipid/carbohydrate metabolism

Fructose intake and the prevalence of obesity have both increased over the past two to three decades. Compared with glucose, the hepatic metabolism of fructose favors lipogenesis, which may contribute to hyperlipidemia and obesity. Fructose does not increase insulin and leptin or suppress ghrelin, which suggests an endocrine mechanism by which it induces a positive energy balance. This review examines the available data on the effects of dietary fructose on energy homeostasis and lipid/carbohydrate metabolism. Recent publications, studies in human subjects, and areas in which additional research is needed are emphasized.

Fibrates inhibit aldose reductase activity in the forward and reverse reactions

Fibrates such as bezafibrate, gemfibrozil, clofibric acid, ciprofibrate and fenofibrate, are ligands for peroxisome proliferator-activated receptor alpha (PPARalpha), and are used as therapeutic agents in the treatment of hyperlipidemia. Synthesis and accumulation of sorbitol in cells due to aldose reductase (AR) activity is implicated in secondary diabetic complications. In pursuit of finding a lead compound identification to design an effective AR inhibitor employing fragment-based design-like approach, we found that this class of compounds and their nearest neighbors could inhibit AR. Bezafibrate and gemfibrozil displayed a mixed non-competitive inhibition pattern in the glyceraldehyde reduction activity and pure non-competitive inhibition pattern in the benzyl alcohol oxidation activity of AR. Clofibric acid, ciprofibrate and fenofibrate showed pure non-competitive inhibition patterns in the forward reaction. In the reverse reaction, clofibric acid displayed a non-competitive inhibition pattern while ciprofibrate and fenofibrate displayed competitive inhibition patterns. This finding reveals for the first time a novel attribute of the fibrates in the regulation of AR activity and may be useful as lead compounds to control the function of AR in the progression and treatment of secondary diabetic complications in addition to other clinical conditions. Alternatively, these findings demonstrate that AR plays a significant role in the fibrate metabolism under various scenarios.

Fructose, insulin resistance, and metabolic dyslipidemia

Obesity and type 2 diabetes are occurring at epidemic rates in the United States and many parts of the world. The "obesity epidemic" appears to have emerged largely from changes in our diet and reduced physical activity. An important but not well-appreciated dietary change has been the substantial increase in the amount of dietary fructose consumption from high intake of sucrose and high fructose corn syrup, a common sweetener used in the food industry. A high flux of fructose to the liver, the main organ capable of metabolizing this simple carbohydrate, perturbs glucose metabolism and glucose uptake pathways, and leads to a significantly enhanced rate of de novo lipogenesis and triglyceride (TG) synthesis, driven by the high flux of glycerol and acyl portions of TG molecules from fructose catabolism. These metabolic disturbances appear to underlie the induction of insulin resistance commonly observed with high fructose feeding in both humans and animal models. Fructose-induced insulin resistant states are commonly characterized by a profound metabolic dyslipidemia, which appears to result from hepatic and intestinal overproduction of atherogenic lipoprotein particles. Thus, emerging evidence from recent epidemiological and biochemical studies clearly suggests that the high dietary intake of fructose has rapidly become an important causative factor in the development of the metabolic syndrome. There is an urgent need for increased public awareness of the risks associated with high fructose consumption and greater efforts should be made to curb the supplementation of packaged foods with high fructose additives. The present review will discuss the trends in fructose consumption, the metabolic consequences of increased fructose intake, and the molecular mechanisms leading to fructose-induced lipogenesis, insulin resistance and metabolic dyslipidemia.

Olmesartan Medoxomil, an Angiotensin II Receptor Blocker Ameliorates Insulin Resistance and Decreases Triglyceride Production in Fructose-Fed Rats

Although angiotensin II receptor blockers (ARBs) have been recommended as a first line of anti-hypertensive agents in patients with diabetes, it remains unclear whether ARBs have a favorable effect on insulin action and triglyceride (TG) metabolism, both of which are impaired in type 2 diabetes. In this study we addressed this issue by investigating how a newly developed ARB, olmesartan medoxomil, influenced insulin sensitivity and TG metabolism in fructose-fed rats, a representative animal model of insulin resistance. Olmesartan was administrated as a 0.01% drinking solution ad libitum to rats either fed normal chow or fructose-enriched chow (60%) for 21 days. Olmesartan treatment markedly decreased both systolic and diastolic blood pressure in both chow-fed and fructose-fed animals. The area under the curve of insulin (AUCI) was substantially greater in fructose-fed rats in the intravenous glucose tolerance test, and olmesartan treatment significantly reduced the AUCI. Olmesartan significantly improved the insulin sensitivity index in fructose-fed rats assessed by Bergman's minimal model without affecting insulin-independent glucose disposal. Olmesartan significantly decreased plasma TG and non-esterified fatty acid levels in fructose-fed rats without affecting lipoprotein lipase mass. The TG secretion rate determined by the triton WR1339 technique was two-fold higher in fructose-fed rats, but olmesartan restored the TG secretion to a normal rate. Olmesartan did not affect plasma parameters, insulin sensitivity or TG metabolism in chow-fed rats. Olmesartan ameliorates insulin resistance and overproduction of TG in fructose-fed rats, and these effects appear to be independent of its hypotensive action.