Adiponectin resistance and proinflammatory changes in the visceral adipose tissue induced by fructose consumption via ketohexokinase-dependent pathway.

An epidemic of obesity and type 2 diabetes is linked with the increase in consumption of fructose-containing sugars, such as sucrose and high-fructose corn syrup. In mammalian cells, fructose is metabolized predominantly via phosphorylation to fructose-1 phosphate by ketohexokinase (KHK) or by alternative pathways. Here we demonstrate that a KHK-dependent pathway mediates insulin resistance and inflammatory changes in the visceral fat in response to high fructose.

Endogenous fructose production and fructokinase activation mediate renal injury in diabetic nephropathy.

Diabetes is associated with activation of the polyol pathway, in which glucose is converted to sorbitol by aldose reductase. Previous studies focused on the role of sorbitol in mediating diabetic complications. However, in the proximal tubule, sorbitol can be converted to fructose, which is then metabolized largely by fructokinase, also known as ketohexokinase, leading to ATP depletion, proinflammatory cytokine expression, and oxidative stress.

Uric acid-dependent inhibition of AMP kinase induces hepatic glucose production in diabetes and starvation: evolutionary implications of the uricase loss in hominids.

Reduced AMP kinase (AMPK) activity has been shown to play a key deleterious role in increased hepatic gluconeogenesis in diabetes, but the mechanism whereby this occurs remains unclear. In this article, we document that another AMP-dependent enzyme, AMP deaminase (AMPD) is activated in the liver of diabetic mice, which parallels with a significant reduction in AMPK activity and a significant increase in intracellular glucose accumulation in human HepG2 cells. AMPD activation is induced by a reduction in intracellular phosphate levels, which is characteristic of insulin resistance and diabetic states.

Sugar, uric acid, and the etiology of diabetes and obesity.

The intake of added sugars, such as from table sugar (sucrose) and high-fructose corn syrup has increased dramatically in the last hundred years and correlates closely with the rise in obesity, metabolic syndrome, and diabetes. Fructose is a major component of added sugars and is distinct from other sugars in its ability to cause intracellular ATP depletion, nucleotide turnover, and the generation of uric acid. In this article, we revisit the hypothesis that it is this unique aspect of fructose metabolism that accounts for why fructose intake increases the risk for metabolic syndrome.

Endogenous fructose production and metabolism in the liver contributes to the development of metabolic syndrome.

Carbohydrates with high glycaemic index are proposed to promote the development of obesity, insulin resistance and fatty liver, but the mechanism by which this occurs remains unknown. High serum glucose concentrations are known to induce the polyol pathway and increase fructose generation in the liver. Here we show that this hepatic, endogenously produced fructose causes systemic metabolic changes.

High-fat and high-sucrose (western) diet induces steatohepatitis that is dependent on fructokinase.

Unlabelled: Fructose intake from added sugars has been implicated as a cause of nonalcoholic fatty liver disease. Here we tested the hypothesis that fructose may interact with a high-fat diet to induce fatty liver, and to determine if this was dependent on a key enzyme in fructose metabolism, fructokinase. Wild-type or fructokinase knockout mice were fed a low-fat (11%), high-fat (36%), or high-fat (36%) and high-sucrose (30%) diet for 15 weeks.

Uric acid stimulates fructokinase and accelerates fructose metabolism in the development of fatty liver.

Excessive dietary fructose intake may have an important role in the current epidemics of fatty liver, obesity and diabetes as its intake parallels the development of these syndromes and because it can induce features of metabolic syndrome. The effects of fructose to induce fatty liver, hypertriglyceridemia and insulin resistance, however, vary dramatically among individuals. The first step in fructose metabolism is mediated by fructokinase (KHK), which phosphorylates fructose to fructose-1-phosphate; intracellular uric acid is also generated as a consequence of the transient ATP depletion that occurs during this reaction.

Uric acid induces hepatic steatosis by generation of mitochondrial oxidative stress: potential role in fructose-dependent and -independent fatty liver.

Background: Uric acid is an independent risk factor in fructose-induced fatty liver, but whether it is a marker or a cause remains unknown.

Results: Hepatocytes exposed to uric acid developed mitochondrial dysfunction and increased de novo lipogenesis, and its blockade prevented fructose-induced lipogenesis.

Conclusion: Rather than a consequence, uric acid induces fatty liver

Significance: Hyperuricemic people are more prone to develop fructose-induced fatty liver.

Opposing effects of fructokinase C and A isoforms on fructose-induced metabolic syndrome in mice.

Fructose intake from added sugars correlates with the epidemic rise in obesity, metabolic syndrome, and nonalcoholic fatty liver disease. Fructose intake also causes features of metabolic syndrome in laboratory animals and humans. The first enzyme in fructose metabolism is fructokinase, which exists as two isoforms, A and C.

Sucrose induces fatty liver and pancreatic inflammation in male breeder rats independent of excess energy intake.

Fructose induces metabolic syndrome in rats; but studies have been criticized for using high concentrations of fructose that are not physiologic, for using only pure fructose, and for not controlling for energy intake. We tested the hypothesis that a 40% sucrose diet (containing 20% fructose) might induce features of metabolic syndrome in male breeder rats independent of excess energy intake. Male Sprague-Dawley breeder rats were pair fed 40% sucrose or isocaloric starch diet for 4 months and evaluated for metabolic syndrome and diabetes.

Hyperuricemia as a mediator of the proinflammatory endocrine imbalance in the adipose tissue in a murine model of the metabolic syndrome.

Objective: Hyperuricemia is strongly associated with obesity and metabolic syndrome and can predict visceral obesity and insulin resistance. Previously, we showed that soluble uric acid directly stimulated the redox-dependent proinflammatory signaling in adipocytes. In this study we demonstrate the role of hyperuricemia in the production of key adipokines.

Combination of captopril and allopurinol retards fructose-induced metabolic syndrome.

Background: Both ACE inhibitors and allopurinol have been shown to partially prevent metabolic syndrome induced by fructose. We tested the hypothesis that combined therapy might be more effective at blocking the metabolic syndrome induced with fructose.

Methods: Male Sprague-Dawley rats were fed a high fructose diet with or without allopurinol, captopril, or the combination for 20 weeks.

Comparison of free fructose and glucose to sucrose in the ability to cause fatty liver.

Background: There is evidence that disaccharide sucrose produce a greater increase in serum fructose and triglycerides (TGs) than the effect produced by their equivalent monosaccharides, suggesting that long-term exposure to sucrose or fructose + glucose could potentially result in different effects.

Aim Of The Study: We studied the chronic effects of a combination of free fructose and glucose relative to sucrose on rat liver.

Methods: Rats were fed either a combination of 30% fructose and 30% glucose (FG) or 60% sucrose (S).

A sensitive and specific liquid chromatography-tandem mass spectrometry method for the determination of intracellular and extracellular uric acid.

Uric acid (UA) is known to be a major biological antioxidant in plasma. However, there is a strong correlation between UA levels and cardiovascular risk. Recent studies suggest that in the intracellular environment, UA can become a prooxidant that causes endothelial dysfunction.

Ketohexokinase-dependent metabolism of fructose induces proinflammatory mediators in proximal tubular cells.

Increased consumption of fructose may play an important role in the epidemic of metabolic syndrome and may presage the development of diabetes, cardiovascular disease, and chronic kidney disease. Once in the cell, fructose is phosphorylated by ketohexokinase (KHK), leading to consumption of ATP, formation of AMP, and generation of uric acid through xanthine oxidoreductase (XOR). This study aimed to examine the direct effects of fructose in human kidney proximal tubular cells (HK-2) and whether they are mediated by the fructose metabolism via KHK.

Hypothesis: could excessive fructose intake and uric acid cause type 2 diabetes?

We propose that excessive fructose intake (>50 g/d) may be one of the underlying etiologies of metabolic syndrome and type 2 diabetes. The primary sources of fructose are sugar (sucrose) and high fructose corn syrup. First, fructose intake correlates closely with the rate of diabetes worldwide.

Role of oxidative stress in the renal abnormalities induced by experimental hyperuricemia.

Endothelial dysfunction is a characteristic feature during the renal damage induced by mild hyperuricemia. The mechanism by which uric acid reduces the bioavailability of intrarenal nitric oxide is not known. We tested the hypothesis that oxidative stress might contribute to the endothelial dysfunction and glomerular hemodynamic changes that occur with hyperuricemia.

Lessons from comparative physiology: could uric acid represent a physiologic alarm signal gone awry in western society?

Uric acid has historically been viewed as a purine metabolic waste product excreted by the kidney and gut that is relatively unimportant other than its penchant to crystallize in joints to cause the disease gout. In recent years, however, there has been the realization that uric acid is not biologically inert but may have a wide range of actions, including being both a pro- and anti-oxidant, a neurostimulant, and an inducer of inflammation and activator of the innate immune response. In this paper, we present the hypothesis that uric acid has a key role in the foraging response associated with starvation and fasting.

Uric acid: the oxidant-antioxidant paradox.

Uric acid, despite being a major antioxidant in the human plasma, both correlates and predicts development of obesity, hypertension, and cardiovascular disease, conditions associated with oxidative stress. While one explanation for this paradox could be that a rise in uric acid represents an attempted protective response by the host, we review the evidence that uric acid may function either as an antioxidant (primarily in plasma) or pro-oxidant (primarily within the cell). We suggest that it is the pro-oxidative effects of uric acid that occur in cardiovascular disease and may have a contributory role in the pathogenesis of these conditions.

The planetary biology of ascorbate and uric acid and their relationship with the epidemic of obesity and cardiovascular disease.

Humans have relatively low plasma ascorbate levels and high serum uric acid levels compared to most mammals due to the presence of genetic mutations in l-gulonolactone oxidase and uricase, respectively. We review the major hypotheses for why these mutations may have occurred. In particular, we suggest that both mutations may have provided a survival advantage to early primates by helping maintain blood pressure during periods of dietary change and environmental stress.

Could uric acid have a role in acute renal failure?

Acute renal failure (ARF), induced by either toxins or ischemia, is associated with significant morbidity. The pathogenesis of ARF is complex and is characterized by renal vasoconstriction and oxidative stress in association with tubular and microvascular injury and interstitial inflammation. In many situations, ARF is associated with a rise in serum uric acid as a result of both increased generation and decreased excretion.

Fructose, but not dextrose, accelerates the progression of chronic kidney disease.

The metabolic syndrome has recently been recognized as a risk factor for kidney disease, but the mechanisms mediating this risk remain unclear. High fructose consumption by animals produces a model of the metabolic syndrome with hypertension, hyperlipidemia, and insulin resistance. The present study was conducted to test the hypothesis that consumption of a high-fructose diet could accelerate the progression of chronic kidney disease.