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

PROTECTIVE ROLE OF CELLS AND SPORES OF SHOUCHELLA CLAUSII SF174 AGAINST FRUCTOSE-INDUCED GUT DYSFUNCTIONS IN SMALL AND LARGE INTESTINE

The oral administration of probiotics is nowadays recognized as a strategy to treat or prevent the consequences of unhealthy dietary habits. Here we analyze and compare the effects of the oral administration of vegetative cells or spores of Shouchella clausii SF174 in counteracting gut dysfunctions induced by 6 weeks of high fructose intake in a rat model. Gut microbiota composition, tight junction proteins, markers of inflammation and redox homeostasis were evaluated in ileum and colon in rats fed fructose rich diet and supplemented with cells or spores of Shouchella clausii SF174. Our results show that both spores and cells of SF174 were effective in preventing the fructose-induced metabolic damage to the gut, namely establishment of "leaky gut", inflammation and oxidative damage, thus preserving gut function. Our results also suggest that vegetative cells and germination-derived cells metabolize part of the ingested fructose at the ileum level.

Akebia Saponin D prevents axonal loss against TNF-induced optic nerve damage with autophagy modulation

Akebia Saponin D (ASD), a triterpenoid saponin, was shown to have protective effects in certain neuronal cells. The purpose of the present study was to investigate the possibility of ASD to prevent tumor necrosis factor (TNF)-induced axonal loss and the ASD modulation of the biologic process of autophagy in optic nerves. Rats were given intravitreal administration of TNF, simultaneous administration of 2, 20, or 200 pmol ASD and TNF, or ASD alone. LC3-II and p62 expression, which is a marker of autophagic flux, and phosphorylated p38 (p-p38) expression in optic nerves were examined by immunoblot analysis. Morphometric analysis revealed a significant ameliorated effect of ASD against TNF-induced optic nerve damage. p62 was significantly increased in the optic nerve in TNF-treated eyes, but this increase was totally prevented by ASD. The ASD alone injection showed significant reduction of p62 levels compared with the PBS-treated control eyes. LC3-II was significantly increased by ASD treatment in the TNF-injected eyes. p-p38 was significantly increased in the optic nerve in TNF-treated eyes, but this increase was completely prevented by ASD. The protective effects of ASD may be associated with enhanced autophagy activation and inhibition of p-p38.

Nutrients, Genetic Factors, and Their Interaction in Non-Alcoholic Fatty Liver Disease and Cardiovascular Disease

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease in Western countries and expose patients to increased risk of hepatic and cardiovascular (CV) morbidity and mortality. Both environmental factors and genetic predisposition contribute to the risk. An inappropriate diet, rich in refined carbohydrates, especially fructose, and saturated fats, and poor in fibers, polyunsaturated fats, and vitamins is one of the main key factors, as well as the polymorphism of patatin-like phospholipase domain containing 3 (PNPLA3 gene) for NAFLD and the apolipoproteins and the peroxisome proliferator-activated receptor (PPAR) family for the cardiovascular damage. Beyond genetic influence, also epigenetics modifications are responsible for various clinical manifestations of both hepatic and CV disease. Interestingly, data are accumulating on the interplay between diet and genetic and epigenetic modifications, modulating pathogenetic pathways in NAFLD and CV disease. We report the main evidence from literature on the influence of both macro and micronutrients in NAFLD and CV damage and the role of genetics either alone or combined with diet in increasing the risk of developing both diseases. Understanding the interaction between metabolic alterations, genetics and diet are essential to treat the diseases and tailoring nutritional therapy to control NAFLD and CV risk.

Effects of a Low Dose of Caffeine Alone or as Part of a Green Coffee Extract, in a Rat Dietary Model of Lean Non-Alcoholic Fatty Liver Disease without Inflammation

Non-alcoholic fatty liver disease is a highly prevalent condition without specific pharmacological treatment, characterized in the initial stages by hepatic steatosis. It was suggested that lipid infiltration in the liver might be reduced by caffeine through anti-inflammatory, antioxidative, and fatty acid metabolism-related mechanisms. We investigated the effects of caffeine (CAF) and green coffee extract (GCE) on hepatic lipids in lean female rats with steatosis. For three months, female Sprague-Dawley rats were fed a standard diet or a cocoa butter-based high-fat diet plus 10% liquid fructose. In the last month, the high-fat diet was supplemented or not with CAF or a GCE, providing 5 mg/kg of CAF. Plasma lipid levels and the hepatic expression of molecules involved in lipid metabolism were determined. Lipidomic analysis was performed in liver samples. The diet caused hepatic steatosis without obesity, inflammation, endoplasmic reticulum stress, or hepatic insulin resistance. Neither CAF nor GCE alleviated hepatic steatosis, but GCE-treated rats showed lower hepatic triglyceride levels compared to the CAF group. The GCE effects could be related to reductions of hepatic (i) mTOR phosphorylation, leading to higher nuclear lipin-1 levels and limiting lipogenic gene expression; (ii) diacylglycerol levels; (iii) hexosylceramide/ceramide ratios; and (iv) very-low-density lipoprotein receptor expression. In conclusion, a low dose of CAF did not reduce hepatic steatosis in lean female rats, but the same dose provided as a green coffee extract led to lower liver triglyceride levels.

Diet and liver cancer risk: a narrative review of epidemiological evidence

Primary liver cancer is the third leading cause of cancer-related death worldwide. Most patients are diagnosed at late stages with poor prognosis; thus, identification of modifiable risk factors for primary prevention of liver cancer is urgently needed. The well-established risk factors of liver cancer include chronic infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), heavy alcohol consumption, metabolic diseases such as obesity and diabetes, and aflatoxin exposure. However, a large proportion of cancer cases worldwide cannot be explained by current known risk factors. Dietary factors have been suspected as important, but dietary aetiology of liver cancer remains poorly understood. In this review, we summarised and evaluated the observational studies of diet including single nutrients, food and food groups, as well as dietary patterns with the risk of developing liver cancer. Although there are large knowledge gaps between diet and liver cancer risk, current epidemiological evidence supports an important role of diet in liver cancer development. For example, exposure to aflatoxin, heavy alcohol drinking and possibly dairy product (not including yogurt) intake increase, while intake of coffee, fish and tea, light-to-moderate alcohol drinking and several healthy dietary patterns (e.g. Alternative Healthy Eating Index) may decrease liver cancer risk. Future studies with large sample size and accurate diet measurement are warranted and need to consider issues such as the possible aetiological heterogeneity between liver cancer subtypes, the influence of chronic HBV or HCV infection, the high-risk populations (e.g. cirrhosis) and a potential interplay with host gut microbiota or genetic variations.

mTOR is a Key Protein Involved in the Metabolic Effects of Simple Sugars

One of the most important threats to global human health is the increasing incidences of metabolic pathologies (including obesity, type 2 diabetes and non-alcoholic fatty liver disease), which is paralleled by increasing consumptions of hypercaloric diets enriched in simple sugars. The challenge is to identify the metabolic pathways affected by the excessive consumption of these dietary components when they are consumed in excess, to unravel the molecular mechanisms leading to metabolic pathologies and identify novel therapeutic targets to manage them. Mechanistic (mammalian) target of rapamycin (mTOR) has emerged as one of the key molecular nodes that integrate extracellular signals, such as energy status and nutrient availability, to trigger cell responses that could lead to the above-mentioned diseases through the regulation of lipid and glucose metabolism. By activating mTOR signalling, excessive consumption of simple sugars (such as fructose and glucose), could modulate hepatic gluconeogenesis, lipogenesis and fatty acid uptake and catabolism and thus lipid deposition in the liver. In the present review we will discuss some of the most recent studies showing the central role of mTOR in the metabolic effects of excessive simple sugar consumption.

Pterostilbene Decreases Cardiac Oxidative Stress and Inflammation via Activation of AMPK/Nrf2/HO-1 Pathway in Fructose-Fed Diabetic Rats

PURPOSE

Oxidative stress has a pivotal role in the pathogenesis of diabetes-associated cardiovascular problems, which has remained a primary cause of the increased morbidity and mortality in diabetic patients. It is of paramount importance to prevent the diabetes-associated cardiac complications by reducing oxidative stress with the help of nutritional or pharmacological agents. Pterostilbene (PT), the primary antioxidant in blueberries, has recently gained attention for its promising health benefits in metabolic and cardiac diseases. However, the mechanism whereby PT reduces diabetic cardiac complications is currently unknown.

METHODS

Sprague-Dawley rats were fed with 65% fructose diet with or without PT (20 mg kg^-1 day^-1) for 8 weeks. Heart rate and blood pressure were measured by tail-cuff apparatus. Real-time PCR and western blot experiments were executed to quantify the expression levels of mRNA and protein, respectively.

RESULTS

Fructose-fed rats demonstrated cardiac hypertrophy, hypertension, enhanced myocardial oxidative stress, inflammation and increased NF-κB expression. Administration of PT significantly decreased cardiac hypertrophy, hypertension, oxidative stress, inflammation, NF-κB expression and NLRP3 inflammasome. We demonstrated that PT improved mitochondrial biogenesis as evidenced by increased protein expression of PGC-1α, complex III and complex V in fructose-fed diabetic rats. Further, PT increased protein expressions of AMPK, Nrf2, HO-1 in cardiac tissues, which may account for the prevention of cardiac oxidative stress and inflammation in fructose-fed rats.

CONCLUSIONS

Collectively, PT reduced cardiac oxidative stress and inflammation in diabetic rats through stimulation of AMPK/Nrf2/HO-1 signalling.

Perigestational high folic acid: impact on offspring's peripheral metabolic response

Perigestational excess folic acid programmed offspring to increased weight gain, but also to adipocyte hypertrophy, associated with Lpl upregulation, and to hyperglycemia, possibly due to VAT and skeletal muscle Glut4 downregulation.

Resveratrol regulates blood pressure by enhancing AMPK signaling to downregulate a Rac1-derived NADPH oxidase in the central nervous system

Resveratrol is a polyphenol with pleiotropic effects against oxidative damage that has been widely implicated in lowering hypertension risk. The purpose of this study was to determine whether improve nitric oxide (NO) release in the brain, either through the activation of AMP-activated protein kinase (AMPK) or reduced Ras-related C3 botulinum toxin substrate 1 (Rac1)-induced reactive oxygen species (ROS) generation, thereby reducing blood pressure (BP) in rats with fructose-induced hypertension. The rats were fed with 10% fructose or Crestor (rosuvastatin; 1.5 mg·kg−1·day−1) and resveratrol (10 mg·kg−1·day−1) treatment for 1 wk, then the systolic blood pressure of the rats was measured by tail-cuff method. Endogenous in vivo superoxide radical production in the nucleus tractus solitarii (NTS) was determined with dihydroethidium. Immunoblotting analyses were used to quantify protein expression levels. Oral resveratrol treatment for 1 wk decreased BP and increased NO production in the NTS of fructose-fed rats but not in the control Wistar-Kyoto rats. The effect of Crestor is opposite that of resveratrol. Fructose induced hypertension by inactivating AMPK, which in turn enhanced the generation of ROS and reduced manganese superoxide dismutase by increasing the activity of Rac1-induced NADPH oxidase, abolishing the activity of the extracellular signal-regulated kinases 1 and 2 (ERK1/2) and ribosomal protein S6 kinase (RSK) and neuronal nitric oxide synthase (nNOS) phosphorylation signaling pathway in the brain. However, resveratrol had the opposite effect in the fructose-fed rats. Overall, we show that the resveratrol decreased BP better than Crestor, abolished ROS generation, and enhanced the ERK1/2-RSK-nNOS pathway by activating AMPK to downregulate Rac1-induced NADPH oxidase levels in the NTS during oxidative stress–associated hypertension.

NEW & NOTEWORTHY 1) Evidence showed that the Ras-related C3 botulinum toxin substrate 1 (Rac1) augmented by Crestor (rosuvastatin) did not result in a significant change in blood pressure (BP) in fructose-induced hypertension. 2) Fructose induced hypertension by inactivating AMP-activated protein kinase (AMPK), which in turn enhanced the generation of reactive oxygen species (ROS) and reduced manganese superoxide dismutase in the brain. 3) Resveratrol decreased BP better than Crestor, abolished ROS generation, and enhanced the ERK1/2-ribosomal protein S6 kinase-neuronal nitric oxide synthase pathway by activating AMPK to negatively regulate Rac1-induced NADPH oxidase levels in the nucleus tractus solitarii during oxidative stress–associated hypertension.

Phenotypic Alteration of Hepatocytes in Non-Alcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) has been recognized as the most common liver disorder in developed countries. NAFLD progresses from fat accumulation in hepatocytes to steatohepatitis to further stages of fibrosis and cirrhosis. Simple steatosis, i.e. fat deposition in the liver, is considered benign and gives way to non-alcoholic steatohepatitis (NASH) with a higher probability of progressing to cirrhosis, and liver-related mortality. Evidence has been found that this progression has been associated with marked alterations in hepatocyte histology and a shift in marker expression of healthy hepatocytes including increased expression of peroxisome proliferator-activated receptor gamma (PPARγ), adipocyte protein (aP2), CD36, interleukin-6 (IL-6), interleukin-18 (IL-18) and adiponectin. This progression shares much in common with the obesity phenotype, which involves a transformation of adipocytes from small, healthy cells to large, dysfunctional ones that contribute to redox imbalance and the progression of metabolic syndrome. Further, activation of Src/ERK signaling via the sodium potassium adenosine triphosphatase (Na/K-ATPase) α-1 subunit in impaired hepatocytes may contribute to redox imbalance, exacerbating the progression of NAFLD. This review hypothesizes that an adipogenic transformation of hepatocytes propagates redox imbalance and that the processes occurring in adipogenesis become activated in fat-laden hepatocytes in liver, thereby driving progression to NAFLD. Further, this review discusses therapeutic interventions to reverse NAFLD including the thiazolidinediones (TZDs) and a variety of antioxidant species. The peptide, pNaKtide, which is an antagonist of Na/K-ATPase signaling, is also proposed as a potential pharmacologic option for reducing reactive oxygen species (ROS) and reversing NAFLD by inhibiting the Na/K-ATPase-modulated ROS amplification loop.

Isocaloric Dietary Changes and Non-Alcoholic Fatty Liver Disease in High Cardiometabolic Risk Individuals

Non-alcoholic fatty liver disease (NAFLD) incorporates an extensive spectrum of histologic liver abnormalities, varying from simple triglyceride accumulation in hepatocytes non-alcoholic fatty liver (NAFL) to non-alcoholic steatohepatitis (NASH), and it is the most frequent chronic liver disease in the industrialized world. Beyond liver related complications such as cirrhosis and hepatocellular carcinoma, NAFLD is also an emerging risk factor for type 2 diabetes and cardiovascular disease. Currently, lifestyle intervention including strategies to reduce body weight and to increase regular physical activity represents the mainstay of NAFLD management. Total caloric intake plays a very important role in both the development and the treatment of NAFLD; however, apart from the caloric restriction alone, modifying the quality of the diet and modulating either the macro- or micronutrient composition can also markedly affect the clinical evolution of NAFLD, offering a more realistic and feasible treatment alternative. The aim of the present review is to summarize currently available evidence from randomized controlled trials on the effects of different nutrients including carbohydrates, lipids, protein and other dietary components, in isocaloric conditions, on NAFLD in people at high cardiometabolic risk. We also describe the plausible mechanisms by which different dietary components could modulate liver fat content.

Longitudinal Associations of High-Fructose Diet with Cardiovascular Events and Potential Risk Factors: Tehran Lipid and Glucose Study

The relationship between fructose and cardiovascular disease (CVD) remains controversial. In this study, we aimed to assess possible association of dietary intakes of fructose with the risk of CVD events in a prospective population-based study. Participants without CVD (n = 2369) were recruited from the Tehran Lipid and Glucose Study and followed a mean of 6.7 years. Dietary data were collected using a validated 168 item semi-quantitative food frequency questionnaire. Dietary total fructose (TF) intake was calculated by sum of natural fructose (NF) in fruits and vegetables and added fructose (AF) in commercial foods. Multivariate Cox proportional hazard regression models, adjusted for potential confounders, were used to estimate the risk of CVD across tertiles of dietary fructose. Linear regression models were used to indicate association of fructose intakes with changes of CVD risk factors over the study period. The mean age of participants (43.5% men) was 38.1 ± 13.3 years at baseline. During an average of 6.7 ± 1.4 years of follow-up, 79 participants experienced CVD outcomes. The mean daily intake of TF was 6.4 ± 3.7% of total energy (3.6 ± 2.0 from AF and 2.7 ± 1.8 from NF). Higher consumption of TF (≥7.4% vs. <4.5% of total energy) was accompanied with an increased risk of CVD (HR = 1.81, 95% CI = 1.04–3.15); higher energy intake from AF was also related to incidence of CVD (HR = 1.80, 95% CI = 1.04–3.12), whereas NF was not associated with the risk of CVD outcomes. Both AF and TF were also related to changes of systolic and diastolic blood pressures, waist circumference, serum insulin and creatinine levels, as well as HDL-C. Our data provides further evidence regarding undesirable effects of fructose intake in relation to risk of CVD events.

Aegle marmelos differentially affects hepatic markers of glycolysis, insulin signalling pathway, hypoxia, and inflammation in HepG2 cells grown in fructose versus glucose-rich environment

Fructose consumption is responsible for the onset of insulin resistance (IR), and metabolic syndrome. It possesses no functional utility in body and its detrimental effects on hepatic metabolic milieu are beyond those produced by glucose. The need of the hour is to identify fructose-induced IR as an unique pathological state to be managed differentially. The effect of aqueous leaf extract of Aegle marmelos (AM) on hepatic markers of insulin resistance using HepG2 cells cultured in either fructose or glucose-rich environment is investigated. Human hepatocellular carcinoma cells (HepG2) were grown under standard conditions in either-DMEM without glucose (NC), DMEM with high glucose 25 mM (Glu), DMEM-glucose+0.55 mM fructose (FC1), DMEM-glucose+1 mM fructose (FC2) or DMEM-glucose+1 mM fructose+0.1 µM insulin (FC3). The cells were treated with either AM, rutin, quercetin, metformin or pioglitazone and assessed for levels of hexokinase, phosphofructokinase (PFK), aldehyde dehydrogenase, phosphatidylinositol kinase (PI3K), signal transducer and activator of transcription-3 (STAT-3), mitochondrial target of rapamycin (mTOR), hypoxia-induced factor (HIF-1α), vascular endothelial growth factor (VEGF) and tumour necrosis factor (TNF-α). Summarily, when results from fructose- and glucose-rich environment were compared, then (1) IR was more pronounced in former; (2) AM performed better in former; (3) metformin and pioglitazone were equivocal in either; (4) rutin and quercetin showed deviant effects from AM; and lastly (5) effects of rutin were closer to AM than quercetin. We hypothesize that AM ameliorates fructose-induced IR through a mechanism which is distinct from standard drugs and not shared by individual phytoconstituents in toto.

Adverse effects of fructose on cardiometabolic risk factors and hepatic lipid metabolism in subjects with abdominal obesity

BACKGROUND

Overconsumption of dietary sugars, fructose in particular, is linked to cardiovascular risk factors such as type 2 diabetes, obesity, dyslipidemia and nonalcoholic fatty liver disease. However, clinical studies have to date not clarified whether these adverse cardiometabolic effects are induced directly by dietary sugars, or whether they are secondary to weight gain.

OBJECTIVES

To assess the effects of fructose (75 g day^-1 ), served with their habitual diet over 12 weeks, on liver fat content and other cardiometabolic risk factors in a large cohort (n = 71) of abdominally obese men.

METHODS

We analysed changes in body composition, dietary intake, an extensive panel of cardiometabolic risk markers, hepatic de novo lipogenesis (DNL), liver fat content and postprandial lipid responses after a standardized oral fat tolerance test (OFTT).

RESULTS

Fructose consumption had modest adverse effects on cardiometabolic risk factors. However, fructose consumption significantly increased liver fat content and hepatic DNL and decreased β-hydroxybutyrate (a measure of β-oxidation). The individual changes in liver fat were highly variable in subjects matched for the same level of weight change. The increase in liver fat content was significantly more pronounced than the weight gain. The increase in DNL correlated positively with triglyceride area under the curve responses after an OFTT.

CONCLUSION

Our data demonstrated adverse effects of moderate fructose consumption for 12 weeks on multiple cardiometabolic risk factors in particular on liver fat content despite only relative low increases in weight and waist circumference. Our study also indicates that there are remarkable individual differences in susceptibility to visceral adiposity/liver fat after real-world daily consumption of fructose-sweetened beverages over 12 weeks.

(p-ClPhSe)2 stimulates carbohydrate metabolism and reverses the metabolic alterations induced by high fructose load in rats

The modern life leads to excess consumption of food rich in fructose; however, the long-term changes in carbohydrate and lipid metabolism could lead to metabolic dysfunction in humans. The present study evaluated the in vitro insulin-mimetic action of p-chloro-diphenyl diselenide (p-ClPhSe)₂. The second aim of this study was to investigate if (p-ClPhSe)₂ reverses metabolic dysfunction induced by fructose load in Wistar rats. The insulin-mimetic action of (p-ClPhSe)₂ at concentrations of 50 and 100 μM was determined in slices of rat skeletal muscle. (p-ClPhSe)₂ at a concentration of 50 μM stimulated the glucose uptake by 40% in skeletal muscle. A dose-response curve revealed that (p-ClPhSe)₂ at a dose of 25 mg/kg reduced (∼20%) glycemia in rats treated with fructose (5 g/kg, i.g.). The administration of fructose impaired the liver homeostasis and (p-ClPhSe)₂ (25 mg/kg) protected against the increase (∼25%) in the G-6-Pase and isocitrate dehydrogenase activities and reduced the triglyceride content (∼25%) in the liver. (p-ClPhSe)₂ regulated the liver homeostasis by stimulating hexokinase activity (∼27%), regulating the TCA cycle activity (increased the ATP and citrate synthase activity (∼15%)) and increasing the glycogen levels (∼67%). In conclusion, (p-ClPhSe)₂ stimulated carbohydrate metabolism and reversed metabolic dysfunction in rats fed with fructose.

Liquid fructose in Western-diet-fed mice impairs liver insulin signaling and causes cholesterol and triglyceride loading without changing calorie intake and body weight

BACKGROUND/OBJECTIVES

Liquid fructose associates with prevalence of type 2 diabetes mellitus and obesity. Intervention studies suggest that metabolically unfit individuals are more responsive than healthy individuals to liquid fructose. We determined whether mice consuming an obesogenic Western diet were more responsive than chow-fed mice to the alterations induced by liquid fructose supplementation (LFS).

METHODS

C57BL/6N mice were fed chow or Western diet±ad libitum 15% fructose solution for 12 weeks. Food and liquid intake and body weight were monitored. Plasma analytes and liver lipids, histology and the expression of genes related to lipid handling, endoplasmic reticulum stress, inflammation and insulin signaling were analyzed.

RESULTS

Western diet increased energy intake, visceral adipose tissue (vWAT), body weight, plasma and liver triglycerides and cholesterol, and inflammatory markers in vWAT vs. chow-fed mice. LFS did not change energy intake, vWAT or body weight. LFS significantly increased plasma and liver triglycerides and cholesterol levels only in Western-diet-fed mice. These changes associated with a potentiation of the increased liver expression of PPARγ and CD36 that was observed in Western-fed mice and related to the increased liver mTOR phosphorylation induced by LFS. Furthermore, LFS in Western-diet-fed mice induced the largest reduction in liver IRS2 protein and a significant decrease in whole-body insulin sensitivity.

CONCLUSIONS

LFS in mice, in a background of an unhealthy diet that already induces fatty liver visceral fat accretion and obesity, increases liver lipid burden, hinders hepatic insulin signaling and diminishes whole-body insulin sensitivity without changing energy intake.

Resveratrol Inhibition of Rac1-Derived Reactive Oxygen Species by AMPK Decreases Blood Pressure in a Fructose-Induced Rat Model of Hypertension

Recent studies have reported that the activation of AMP-activated protein kinase (AMPK) suppressed oxidative stress. The aim of this study was to examine whether the activation of AMPK in the brain decreased Rac1-induced ROS generation, thereby reducing blood pressure (BP) in rats with fructose-induced hypertension. The inhibition of ROS by treatment with an AMPK activator (oral resveratrol, 10 mg/kg/day) for 1 week decreased the BP and increased the NO production in the rostral ventrolateral medulla (RVLM) of fructose-fed rats but not in control Wistar-Kyoto (WKY) rats. In addition, resveratrol treatment abolished the Rac1-induced increases in the activity of the NADPH oxidase subunits p22-phox and reduced the activity of SOD2, while treatment with an AMPK inhibitor (compound C, 40 μM/day) had the opposite effect, in the fructose-fed rats. Interestingly, the activation of AMPK abolished Rac1 activation and decreased BP by inducing the activities of extracellular signal-regulated kinases 1 and 2 (ERK1/2) and ribosomal protein S6 kinase (RSK) and nNOS phosphorylation in the fructose-fed rats. We conclude that the activation of AMPK decreased BP, abolished ROS generation, and enhanced ERK1/2-RSK-nNOS pathway activity by negatively regulating Racl-induced NADPH oxidase levels in the RVLM during oxidative stress–associated hypertension.

Fructose induces mitochondrial dysfunction and triggers apoptosis in skeletal muscle cells by provoking oxidative stress

Mitochondrial dysfunction in skeletal muscle has been implicated in the development of insulin resistance, a major characteristic of type 2 diabetes. There is evidence that oxidative stress results from the increased production of reactive oxygen species and reactive nitrogen species leads to mitochondrial dysfunction, tissue damage, insulin resistance, and other complications observed in type 2 diabetes. It has been suggested that intake of high fructose contributes to insulin resistance and other metabolic disturbances. However, there is limited information about the direct effect of fructose on the mitochondrial function of skeletal muscle, the major metabolic determinant of whole body insulin activity. Here, we assessed the effect of fructose exposure on mitochondria-mediated mechanisms in skeletal muscle cells. Exposure of L6 myotubes to high fructose stimulated the production of mitochondrial reactive oxygen species and nitric oxide (NO), and the expression of inducible NO synthase. Fructose-induced oxidative stress was associated with increased translocation of nuclear factor erythroid 2-related factor-2 to the nucleus, decreases in mitochondrial DNA content and mitochondrial dysfunctions, as evidenced by decreased activities of citrate synthase and mitochondrial dehydrogenases, loss of mitochondrial membrane potential, decreased activity of the mitochondrial respiratory complexes, and impaired mitochondrial energy metabolism. Furthermore, positive Annexin-propidium iodide staining and altered expression of Bcl-2 family members and caspases in L6 myotubes indicated that the cells progressively became apoptotic upon fructose exposure. Taken together, these findings suggest that exposure of skeletal muscle cells to fructose induced oxidative stress that decreased mitochondrial DNA content and triggered mitochondrial dysfunction, which caused apoptosis.

Health effects of fructose and fructose-containing caloric sweeteners: where do we stand 10 years after the initial whistle blowings?

Suspicion that fructose-containing caloric sweeteners (FCCS) may play a causal role in the development of metabolic diseases has elicited intense basic and clinical research over the past 10 years. Prospective cohort studies converge to indicate that FCCS, and more specifically sugar-sweetened beverages (SSBs), consumption is associated with weight gain over time. Intervention studies in which FCCS or SSB consumption is altered while food intake is otherwise left ad libitum indicate that increased FCCS generally increases total energy intake and body weight, while FCCS reduction decreases body weight gain. Clinical trials assessing the effects of SSB reduction as a sole intervention however fail to observe clinically significant weight loss. Many mechanistic studies indicate that excess FCCS can cause potential adverse metabolic effects. Whether this is associated with a long-term risk remains unknown. Scientific evidence that excess FCCS intake causes more deleterious effects to health than excess of other macronutrients is presently lacking. However, the large consumption of FCCS in the population makes it one out of several targets for the treatment and prevention of metabolic diseases.

Fructose Mediated Non-Alcoholic Fatty Liver Is Attenuated by HO-1-SIRT1 Module in Murine Hepatocytes and Mice Fed a High Fructose Diet

Background

Oxidative stress underlies the etiopathogenesis of nonalcoholic fatty liver disease (NAFLD), obesity and cardiovascular disease (CVD). Heme Oxygenase-1 (HO-1) is a potent endogenous antioxidant gene that plays a key role in decreasing oxidative stress. Sirtuin1 (SIRT1) belongs to the family of NAD-dependent de-acyetylases and is modulated by cellular redox.

Hypothesis

We hypothesize that fructose-induced obesity creates an inflammatory and oxidative environment conducive to the development of NAFLD and metabolic syndrome. The aim of this study is to determine whether HO-1 acts through SIRT1 to form a functional module within hepatocytes to attenuate steatohepatitis, hepatic fibrosis and cardiovascular dysfunction.

Methods and Results

We examined the effect of fructose, on hepatocyte lipid accumulation and fibrosis in murine hepatocytes and in mice fed a high fructose diet in the presence and absence of CoPP, an inducer of HO-1, and SnMP, an inhibitor of HO activity. Fructose increased oxidative stress markers and decreased HO-1 and SIRT1 levels in hepatocytes (p<0.05). Further fructose supplementation increased FAS, PPARα, pAMPK and triglycerides levels; CoPP negated this increase. Concurrent treatment with CoPP and SIRT1 siRNA in hepatocytes increased FAS, PPARα, pAMPK and triglycerides levels suggesting that HO-1 is upstream of SIRT1 and suppression of SIRT1 attenuates the beneficial effects of HO-1. A high fructose diet increased insulin resistance, blood pressure, markers of oxidative stress and lipogenesis along with fibrotic markers in mice (p<0.05). Increased levels of HO-1 increased SIRT1 levels and ameliorated fructose-mediated lipid accumulation and fibrosis in liver along with decreasing vascular dysfunction (p<0.05 vs. fructose). These beneficial effects of CoPP were reversed by SnMP.

Conclusion

Taken together, our study demonstrates, for the first time, that HO-1 induction attenuates fructose-induced hepatic lipid deposition, prevents the development of hepatic fibrosis and abates NAFLD-associated vascular dysfunction; effects that are mediated by activation of SIRT1 gene expression.

Resveratrol decreases fructose-induced oxidative stress, mediated by NADPH oxidase via an AMPK-dependent mechanism

BACKGROUND AND PURPOSE

Oxidative stress is an important pathogenic factor in the development of hypertension. Resveratrol, the main antioxidant in red wine, improves NO bioavailability and prevents cardiovascular disease. The aim of this study was to examine whether resveratrol decreases the generation of reactive oxygen species (ROS), thereby reducing BP in rats with fructose-induced hypertension.

EXPERIMENTAL APPROACH

Rats were fed 10% fructose with or without resveratrol (10 mg·kg(-1) ·day(-1) ) for 1 week or for 4 weeks with resveratrol treatment beginning at week 2; systolic BP (SBP) was measured by tail-cuff method. Endogenous in vivo O2 (-) production in the nucleus tractus solitarii (NTS) was determined with dihydroethidium. Real-time PCR and immunoblotting analyses were used to quantify RNA and protein expression levels.

KEY RESULTS

In fructose-fed rats, ROS levels in the NTS were higher, whereas the NO level was significantly decreased. Also, RNA and protein levels of NADPH oxidase subunits (p67, p22-phox) were elevated, superoxide dismutase 2 (SOD2) reduced and AMP-activated PK (AMPK) T172 phosphorylation levels in the NTS were lower in fructose-fed rats. Treatment with the AMPK activator resveratrol decreased levels of NADPH oxidase subunits and ROS, and increased NO and SOD2 levels in the NTS of fructose-fed rats. Administration of resveratrol, in combination with fructose at week 0 and later at week 2, significantly reduced the SBP of fructose-fed rats.

CONCLUSIONS AND IMPLICATIONS

Collectively, resveratrol decreased BP through the phosphorylation of AMPK, Akt and neuronal NOS in fructose-fed rats. These novel findings suggest that resveratrol may be a potential pharmacological candidate for the treatment of hypertension.

Simple sugar intake and hepatocellular carcinoma: epidemiological and mechanistic insight

Sugar intake has dramatically increased during the last few decades. Specifically, there has been a clear trend towards higher consumption of fructose and high fructose corn syrup, which are the most common added sugars in processed food, soft drinks and other sweetened beverages. Although still controversial, this rising trend in simple sugar consumption has been positively associated with weight gain and obesity, insulin resistance and type 2 diabetes mellitus and non-alcoholic fatty liver disease. Interestingly, all of these metabolic alterations have also been related to the development of hepatocellular carcinoma. The purpose of this review is to discuss the evidence coming from epidemiological studies and data from animal models relating the consumption of simple sugars, and specifically fructose, with an increased risk of hepatocellular carcinoma and to gain insight into the putative molecular mechanisms involved.

AAV8-mediated Sirt1 gene transfer to the liver prevents high carbohydrate diet-induced nonalcoholic fatty liver disease

Nonalcoholic fatty liver disease (NAFLD) is the most common hepatic disease worldwide, and evidence suggests that it promotes insulin resistance and type 2 diabetes. Caloric restriction (CR) is the only available strategy for NAFLD treatment. The protein deacetylase Sirtuin1 (SIRT1), which is activated by CR, increases catabolic metabolism and decreases lipogenesis and inflammation, both involved in the development of NAFLD. Here we show that adeno-associated viral vectors of serotype 8 (AAV8)-mediated liver-specific Sirt1 gene transfer prevents the development of NAFLD induced by a high carbohydrate (HC) diet. Long-term hepatic SIRT1 overexpression led to upregulation of key hepatic genes involved in β-oxidation, prevented HC diet-induced lipid accumulation and reduced liver inflammation. AAV8-Sirt1-treated mice showed improved insulin sensitivity, increased oxidative capacity in skeletal muscle and reduced white adipose tissue inflammation. Moreover, HC feeding induced leptin resistance, which was also attenuated in AAV8-Sirt1-treated mice. Therefore, AAV-mediated gene transfer to overexpress SIRT1 specifically in the liver may represent a new gene therapy strategy to counteract NAFLD and related diseases such as type 2 diabetes.

Impact of sugar-sweetened beverages on blood pressure

The impact of sugar-sweetened beverages (SSBs) on blood pressure (BP) has been debated, with some evidence suggesting that their increased intake is related to higher risk of developing hypertension. We conducted a systematic review exploring the relation between consumption of SSB and BP. A comprehensive search in 5 electronic databases along with a bibliography search was performed. The keywords "sugar sweetened beverages," "sugary drinks," "added sugars," "blood pressure," and "hypertension" were indexed in all combinations. Studies were included that reported the effects of intake of SSBs on BP. We excluded studies with <100 subjects and those involving subjects aged <12 years. Of 605 potentially relevant studies, a total of 12 studies (409,707 participants) met our inclusion criteria; 6 were cross sectional studies, whereas the rest were prospective cohort studies. All 12 studies showed positive relation between increased SSB intake and hypertension; however, statistical significance was reported in 10 of these studies. Of the 12 studies, 5 reported an increase in mean BP whereas 7 reported an increase in the incidence of high BP. In conclusion, our systematic review shows that the consumption of SSBs is associated with higher BP, leading to increased incidence of hypertension. Restriction on SSB consumption should be incorporated in the recommendations of lifestyle modifications for the treatment of hypertension. Interventions to reduce intake of SSBs should be an integral part of public health strategy to reduce the incidence of hypertension.

How Much Weight Loss is Effective on Nonalcoholic Fatty Liver Disease?

BACKGROUND

Nonalcoholic fatty liver disease (NAFLD) is the most common liver disease worldwide with no specific treatment. Weight loss is the most effective therapeutic strategy in its management; however, there is no consensus on its specifics. Thus, this study was conducted to evaluate the effects of weight loss on liver enzymes, markers of inflammation, oxidative stress and CK18-M30 (cytokeratin 18) as a biomarker of hepatocellular apoptosis.

OBJECTIVES

To study the effect of weight reduction diet as an exclusive treatment for NAFLD.

PATIENTS AND METHODS

Forty four patients with NAFLD received a diet including a 500 to 1000 kcal per day intake reduction as30% fat, 15% protein, and 55% carbohydrate for six months. Anthropometric parameters, alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma glutamyl transferase (GGT), lipid profile, malondialdehyde (MDA), TNF-α, IL-6, CK18-M30 were measured at baseline and at the end of the study. At the end of follow up, patients were classified as adherent or nonadherent to treatment according to a weight loss of ≥ 5%, or < 5% of initial body weight, respectively.

RESULTS

Twenty five patients were classified as adherent group and nineteen as nonadherent group (9.7% vs. 1.9% total body weight loss after 6 months, respectively). After 6 months, changes in adherent and nonadherent groups were as follows: reduction in body weight from 93.7 ± 15.8 kg to 84.2 ± 13.4 kg vs. 94 ± 16.6 kg to 92.2 ± 16.2 kg (P < 0.05), BMI from 32.7 ± 3.9 to 29.5 ± 3.2 vs.31.8 ± 5.4 to 31.1 ± 5.3 (P < 0.001), and waist circumference from 105.1 ± 12.6 cm to 97.4 ± 9.8 cm vs.106.8 ± 14.2 cm to 103.7 ± 14 cm (P < 0.001), respectively. Diastolic blood pressure was significantly decreased in adherent group (from 80.2 ± 5.1 mmHg to 76.9 ± 5 mmHg; P < 0.001). Also, total cholesterol, LDL, triglyceride, ALT, AST, GGT and CK18-M30 levels were significantly decreased in the adherent group compared to nonadherent group (P < 0.05).

CONCLUSIONS

This intervention offers a practical approach for treatment of patients with NAFLD with diet therapy.

Fructation in vivo: detrimental and protective effects of fructose

There is compelling evidence that long-term intake of excessive fructose can have deleterious side effects in different experimental models. However, the role of fructose in vivo remains controversial, since acute temporary application of fructose is found to protect yeast as well as animal tissues against exogenous oxidative stress. This review suggests the involvement of reactive carbonyl and oxygen species in both the cytotoxic and defensive effects of fructose. Potential mechanisms of the generation of reactive species by fructose in the nonenzymatic reactions, their implication in the detrimental and protective effects of fructose are discussed.

Adverse metabolic effects of dietary fructose: results from the recent epidemiological, clinical, and mechanistic studies

PURPOSE OF REVIEW

The effects of dietary sugar on risk factors and the processes associated with metabolic disease remain a controversial topic, with recent reviews of the available evidence arriving at widely discrepant conclusions.

RECENT FINDINGS

There are many recently published epidemiological studies that provide evidence that sugar consumption is associated with metabolic disease. Three recent clinical studies, which investigated the effects of consuming relevant doses of sucrose or high-fructose corn syrup along with ad libitum diets, provide evidence that consumption of these sugars increase the risk factors for cardiovascular disease and metabolic syndrome. Mechanistic studies suggest that these effects result from the rapid hepatic metabolism of fructose catalyzed by fructokinase C, which generates substrate for de novo lipogenesis and leads to increased uric acid levels. Recent clinical studies investigating the effects of consuming less sugar, via educational interventions or by substitution of sugar-sweetened beverages for noncalorically sweetened beverages, provide evidence that such strategies have beneficial effects on risk factors for metabolic disease or on BMI in children.

SUMMARY

The accumulating epidemiological evidence, direct clinical evidence, and the evidence suggesting plausible mechanisms support a role for sugar in the epidemics of metabolic syndrome, cardiovascular disease, and type 2 diabetes.

Fructose: a key factor in the development of metabolic syndrome and hypertension

Diabetes mellitus and the metabolic syndrome are becoming leading causes of death in the world. Identifying the etiology of diabetes is key to prevention. Despite the similarity in their structures, fructose and glucose are metabolized in different ways. Uric acid, a byproduct of uncontrolled fructose metabolism is known risk factor for hypertension. In the liver, fructose bypasses the two highly regulated steps in glycolysis, glucokinase and phosphofructokinase, both of which are inhibited by increasing concentrations of their byproducts. Fructose is metabolized by fructokinase (KHK). KHK has no negative feedback system, and ATP is used for phosphorylation. This results in intracellular phosphate depletion and the rapid generation of uric acid due to activation of AMP deaminase. Uric acid, a byproduct of this reaction, has been linked to endothelial dysfunction, insulin resistance, and hypertension. We present possible mechanisms by which fructose causes insulin resistance and suggest actions based on this association that have therapeutic implications.