BACKGROUND/AIMS-While the rise in non-alcoholic fatty liver disease (NAFLD) parallels the increase in obesity and diabetes, a significant increase in dietary fructose consumption in industrialized countries has also occurred. The increased consumption of high fructose corn syrup, primarily in the form of soft-drinks, is linked with complications of the insulin resistance syndrome. Furthermore, the hepatic metabolism of fructose favors de novo lipogenesis and ATP depletion. We hypothesize that increased fructose consumption contributes to the development of NAFLD.

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. At a similar concentration to that observed in peripheral blood after a meal, fructose induced production of monocyte chemotactic protein 1 (MCP-1) and reactive oxygen species in HK-2 cells. Knockdown of KHK by stable transfection with small hairpin RNA demonstrated that these processes were KHK dependent. Several antioxidants, including specific inhibitors of NADPH oxidase and XOR, prevented MCP-1 secretion. We detected XOR mRNA in HK-2 cells and confirmed its activity by identifying uric acid by mass spectrometry. Fructose increased intracellular uric acid, and uric acid induced production of MCP-1 as well. In summary, postprandial concentrations of fructose stimulate redox-and urate-dependent inflammatory mediators in proximal tubular cells.

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. Three groups of 14 male Sprague-Dawley rats were pair fed a specialized diet containing 60% fructose (FRU) or 60% dextrose (DEX) or standard rat chow (CON). After the animals were fed their assigned diet for 6 wk, five-sixths nephrectomy was performed, and the assigned diet was continued for 11 wk. Proteinuria was significantly increased and creatinine clearance was decreased in the FRU group compared with the CON and DEX groups, and blood urea nitrogen was higher in the FRU group than in the CON and DEX groups. Kidneys from the FRU group were markedly larger than kidneys from the CON and DEX groups. Glomerular sclerosis, tubular atrophy, tubular dilatation, and cellular infiltration appeared markedly worse in kidneys from the FRU group than in kidneys from the DEX and CON groups. Monocyte chemoattractant protein-1 (MCP-1) was measured in renal tissue homogenate and found to be increased in the FRU group. In vitro studies were conducted to determine the mechanism for increased renal MCP-1, and fructose stimulation of proximal tubular cells resulted in production of MCP-1. In conclusion, consumption of a high-fructose diet greatly accelerates progression of chronic kidney disease in the rat remnant kidney model. metabolic syndrome; high-fructose corn syrup; monocyte chemoattractant protein-1

Serum uric acid (SUA) levels discriminating across the different strata of cardiovascular risk is still unknown. By utilizing a large population-based database, we assessed the threshold of SUA that increases the risk of total mortality and cardiovascular mortality (CVM). The URRAH study (Uric Acid Right for Heart Health) is a multicentre retrospective, observational study, which collected data from several large population-based longitudinal studies in Italy and subjects recruited in the hypertension clinics of the Italian Society of Hypertension. Total mortality was defined as mortality for any cause, CVM as death due to fatal myocardial infarction, stroke, sudden cardiac death, or heart failure. A total of 22 714 subjects were included in the analysis. Multivariate Cox regression analyses identified an independent association between SUA and total mortality (hazard ratio, 1.53 [95% CI, 1.21–1.93]) or CVM (hazard ratio, 2.08 [95% CI, 1.146–2.97]; P <0.001). Cutoff values of SUA able to discriminate total mortality (4.7 mg/dL [95% CI, 4.3–5.1 mg/dL]) and CVM status (5.6 mg/dL [95% CI, 4.99–6.21 mg/dL]) were identified. The information on SUA levels provided a significant net reclassification improvement of 0.26 and of 0.27 over the Heart Score risk chart for total mortality and CVM, respectively ( P <0.001). Sex-specific cutoff values for total mortality and CVM were also identified and validated. In conclusion, SUA levels increasing the risk of total mortality and CVM are significantly lower than those used for the definition of hyperuricemia in clinical practice. Our data provide evidence of a cardiovascular SUA threshold that might contribute in clinical practice to improve identification of patients at higher risk of CVM.

Metabolic syndrome, characterized by truncal obesity, hypertriglyceridemia, elevated BP, and insulin resistance, is recognized increasingly as a major risk factor for kidney disease and also is a common feature of patients who are on dialysis. One feature that is common to patients with metabolic syndrome is an elevated uric acid. Although often considered to be secondary to hyperinsulinemia, recent evidence supports a primary role for uric acid in mediating this syndrome. Specifically, fructose, which rapidly can cause metabolic syndrome in rats, also raises uric acid, and lowering uric acid in fructose-fed rats prevents features of the metabolic syndrome. Uric acid also can accelerate renal disease in experimental animals and epidemiologically is associated with progressive renal disease in humans. It is proposed that fructose-and purine-rich foods that have in common the raising of uric acid may have a role in the epidemic of metabolic syndrome and renal disease that is occurring throughout the world.J Am Soc Nephrol 17: S165-S168, . doi: 10.1681 T he metabolic syndrome is defined as a syndrome of truncal obesity, insulin resistance, elevated BP, hypertriglyceridemia, and hyperuricemia (Table 1) (1-4). The prevalence of metabolic syndrome has been increasing at an alarming rate throughout the world. In the United States, the current prevalence is estimated to be 27% (29% in women and 25.2% in men) (5); in Europe, it is 15.7% in men and 14.2% in women (6); and in China it is 13.7% (9.8% in men and 17.8% in women) (7).The presence of metabolic syndrome is strongly associated with the development of diabetes (8), hypertension (9), cardiovascular disease (10), and all-cause mortality (11). However, recent studies have emphasized that metabolic syndrome also is both associated with and a risk for the development of chronic kidney disease (CKD). For example, in a recent study, the metabolic syndrome was found to be strongly correlated with CKD (defined as GFR Ͻ60 ml/min) and microalbuminuria, and the risk increased progressively with the number of criteria constituting the syndrome (12). In another study of Native Americans without diabetes, a positive relationship was identified between microalbuminuria and features of the metabolic syndrome (13).The mechanism(s) by which metabolic syndrome might accelerate renal disease remains unclear. One possibility relates to the presence of obesity itself. Obesity has been found to be an independent risk factor for CKD (12,14), and treating obesity might stabilize renal function (15) or reverse early hemodynamic abnormalities and glomerular dysfunction (16). Obesity has been associated with a type of focal segmental glomerulosclerosis (FSGS) called "obesity-related glomerulopathy" (17).Hall et al. (18) proposed that lipid deposition in the inner medulla increases intrarenal pressure, leading to decreased tubular flow, which results in increased sodium reabsorption in Henle loop, volume expansion, and the development of systemic hypertension. Obesity also increases the risk...

Epidemiologic studies have linked fructose intake with the metabolic syndrome, and it was recently reported that fructose induces an inflammatory response in the rat kidney. Here, we examined whether fructose directly stimulates endothelial inflammatory processes by upregulating the inflammatory molecule intercellular adhesion molecule-1 (ICAM-1). When human aortic endothelial cells were stimulated with physiologic concentrations of fructose, ICAM-1 mRNA and protein expression increased in a time-and dosage-dependent manner, which was independent of NF-B activation. Fructose reduced endothelial nitric oxide (NO) levels and caused a transient reduction in endothelial NO synthase expression. The administration of an NO donor inhibited fructose-induced ICAM-1 expression, whereas blocking NO synthase enhanced it, suggesting that NO inhibits endothelial ICAM-1 expression. Furthermore, fructose resulted in decreased intracellular ATP; administration of exogenous ATP blocked fructose-induced ICAM-1 expression and increased NO levels. Consistent with the in vitro studies, dietary intake of fructose at physiologic dosages increased both serum ICAM-1 concentration and endothelial ICAM-1 expression in the rat kidney. These data suggest that fructose induces inflammatory changes in vascular cells at physiologic concentrations.

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The level of serum uric acid in human has been increasing over the last decades, and correlates with an increase prevalence of renal disease and metabolic syndrome. Understanding the role of uric acid in these conditions may provide clues for preventing the current epidemic of renal disease. Controversy still remains if hyperuricemia is simply a consequence or a cause of renal disease although epidemiological studies have attempted to resolve this issue. In this review, we discuss the clinical and experimental evidence for a causal role of hyperuricemia in renal diseases and potential relationships of hyperuricemia with metabolic syndrome.