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In our Perspectives article (The case for uric acid- lowering treatment in patients with hyperuricaemia and CKD. Nat. Rev. Nephrol.15, 767–775; 2019)1 we proposed that individuals with hyperuricaemia and chronic kidney disease (CKD) with wors-ening kidney function should be consid-ered for urate- lowering therapy (ULT) to 422 | July 2020 | volume 16 CorrespondenCewww.nature.com/nrneph slow progression of CKD1. When review-ing the literature, we argued that a trial was only interpretable if the control group showed clinically meaningful worsening of kidney function, which we defined as a reduction in estimated glomerular filtration rate (eGFR) of at least 4–5 ml/min/1.73 m2.

We aimed to investigate the effects of chronic fluid restriction and hydration with a sweetened beverage (SB) in rats from weaning until adolescence, in a posterior acute kidney injury (AKI) event induced by ischemia-reperfusion (I/R). We followed 5 groups of weaning rats: control group (C); two groups with 22 h/day fluid restriction, a group hydrated for two hours with water (-W) and a group hydrated with SB; one group receiving SB ad libitum all day (+SB); and one group in which water consumption was increased using a gel diet. The rats that reached adolescence were submitted to I/R. Fluid restriction and/or SB hydration induced mild renal alterations that were significantly accentuated in the -SB group and resulted in worse outcomes after I/R-induced AKI that resulted in a catastrophic fall in creatinine clearance and diffuse acute tubular necrosis. In summary, low tap water intakes, as well as SB intake in infancy, prompt kidney worse outcomes in a later event of AKI during adolescence and both insults magnify kidney damage. Studies on hydration habits in children are recommended to disclose the potentially harmful effects that those behavioral patterns might carry to future renal health.

The potential cause–effect relationship between uric acid plasma concentrations and HDL functionality remains elusive. Therefore, this study aimed to explore the effect of oxonic acid (OA)-induced hyperuricemia on the HDL size distribution, lipid content of HDL subclasses, and apo AI turnover, as well as HDL functionality in New Zealand white rabbits. Experimental animals received OA 750 mg/kg/day by oral gavage during 21 days. The HDL-apo AI fractional catabolic rate (FCR) was determined by exogenous labeling with 125I, and HDL subclasses were determined by sequential ultracentrifugation and PAGE. Paraoxonase-1 activity (PON-1) and the effect of HDL on relaxation of aorta rings in vitro were determined as an indication of HDL functionality. Oxonic acid induced a sixfold increase of uricemia (0.84 ± 0.06 vs. 5.24 ± 0.12 mg/dL, P

Controversy exists with regard to the causal role of hyperuricemia in chronic kidney disease. Vascular stiffness may be the link that explains the relation between hyperuricemia and kidney disease. Hyperuricemia is associated with a number of effects on the vascular endothelium and vascular smooth muscle cells, including an increase in oxidative stress, production of vasoconstrictors, and changes on the structural properties of the large artery wall. Observational evidence in large epidemiological cross-sectional studies suggests that there is an independent association between uric acid and arterial stiffness. The limited evidence from cohort studies or clinical trials does not support treatment of hyperuricemia to reduce vascular stiffness in order to prevent kidney disease. Nevertheless, vascular stiffness may be a valid, reproducible, and useful surrogate endpoint. At this point there seems to be sufficient evidence to warrant larger clinical trials to determine whether lowering uric acid concentrations would be useful for prevention or treatment of vascular stiffness and, subsequently, of cardiovascular and kidney diseases. Video Journal Club ‘Cappuccino with Claudio Ronco' at http://www.karger.com/?doi=452726.

Chronic vasopressin secretion induced by recurrent mild heat stress exposure is significantly enhanced by limited rehydration with a fructose-containing beverage both in rodents and in humans. Moreover, this effect has been associated with upregulation of the polyol&ndash, fructokinase pathway and increased renal oxidative stress. Previously, we have shown that pharmacological inhibition of both V1a and V2 vasopressin receptors with conivaptan improved such renal alterations. The aim of this study was to evaluate the independent contributions of V1a and V2 receptors to the renal damage caused by mild heat stress and limited rehydration with a fructose-containing beverage. Osmotic minipumps were used to deliver either relcovaptan (0.64 mg/day) or tolvaptan (0.25 mg/day) in male Wistar rats for two weeks. Corresponding dilution vehicles were used as controls. To induce dehydration, rats were exposed to mild heat stress (37 &deg, C for 1 h, Monday to Friday). All groups received a 10% fructose solution as a rehydration fluid for 2 h after mild heat stress. For the remainder of the day and on weekends, rats received tap water. The independent blockade of either the V1a or the V2 receptor prevented renal damage, reduced oxidative stress, and decreased plasma cortisol and systemic inflammation. However, the beneficial effects were regulated by different mechanisms. Tolvaptan inhibited polyol&ndash, fructokinase pathway overactivation, while relcovaptan prevented upregulation of the renin&ndash, angiotensin system and SGK1 expression. These data suggest that both V1a and V2 receptors participate in renal damage caused by heat stress-induced dehydration when fructose-containing beverages are used as rehydration fluids.

In modern societies, high fructose intake from sugar-sweetened beverages has contributed to obesity development. In the diet, sucrose and high fructose corn syrup are the main sources of fructose and can be metabolized in the intestine and transported into the systemic circulation. The liver can metabolize around 70% of fructose intake, while the remaining is metabolized by other tissues. Several tissues including adipose tissue express the main fructose transporter GLUT5. In vivo, chronic fructose intake promotes white adipose tissue accumulation through activating adipogenesis. In vitro experiments have also demonstrated that fructose alone induces adipogenesis by several mechanisms, including (1) triglycerides and very-low-density lipoprotein (VLDL) production by fructose metabolism, (2) the stimulation of glucocorticoid activation by increasing 11β-HSD1 activity, and (3) the promotion of reactive oxygen species (ROS) production through uric acid, NOX and XOR expression, mTORC1 signaling and Ang II induction. Moreover, it has been observed that fructose induces adipogenesis through increased ACE2 expression, which promotes high Ang-(1-7) levels, and through the inhibition of the thermogenic program by regulating Sirt1 and UCP1. Finally, microRNAs may also be involved in regulating adipogenesis in high fructose intake conditions. In this paper, we propose further directions for research in fructose participation in adipogenesis.

Hyperuricaemia is common among patients with chronic kidney disease (CKD), and increases in severity with the deterioration of kidney function. Although existing guidelines for CKD management do not recommend testing for or treatment of hyperuricaemia in the absence of a diagnosis of gout or urate nephrolithiasis, an emerging body of evidence supports a direct causal relationship between serum urate levels and the development of CKD. Here, we review randomized clinical trials that have evaluated the effect of urate-lowering therapy (ULT) on the rate of CKD progression. Among trials in which individuals in the control arm experienced progressive deterioration of kidney function (which we define as ≥4 ml/min/1.73 m² over the course of the study — typically 6 months to 2 years), treatment with ULT conferred consistent clinical benefits. In contrast, among trials where clinical progression was not observed in the control arm, treatment with ULT was ineffective, but this finding should not be used as an argument against the use of uric acid-lowering therapy. Although additional studies are needed to identify threshold values of serum urate for treatment initiation and to confirm optimal target levels, we believe that sufficient evidence exists to recommend routine measurement of serum urate levels in patients with CKD and consider initiation of ULT among those who are hyperuricaemic with evidence of deteriorating renal function, unless specific contraindications exist. This Perspectives article considers why clinical trials of urate-lowering therapy (ULT) have shown inconsistent renoprotective effects in patients with chronic kidney disease, and suggests that sufficient evidence exists to support the use of routine screening for hyperuricaemia and initiation of ULT in selected patients.

Background: In subjects without a history of coronary heart disease (CHD), type 2 diabetes mellitus (T2DM) is associated with carotid artery plaques (CAP), which is a better marker than high carotid intima-media thickness (hCIMT) for predicting first or recurrent cardiovascular events. Objective: The objective of this study is to analyze the association of T2DM with CAP and hCIMT in premature CHD patients. Methods: Premature CHD was considered before the age of 55 years in men and before 65 in women. T2DM was defined according to the American Diabetes Association criteria. CAP was defined as a focal structure encroaching the arterial lumen by at least 50% of the surrounding IMT value or with a thickness > 1.5 mm. Results: Among 1196 patients (CHD duration 1.5 years [interquartile range: 0.4-5.6]), 37.2% had T2DM, and 97.8% were on antihypertensive, 94.4% on lipid-lowering, and 97.3% on anti-aggregate treatment. hCIMT prevalence was similar in patients with or without T2DM, whereas CAP prevalence was higher among T2DM patients (17.7% vs. 30.9%; p < 0.001). T2DM showed association with CAP, independently of CHD evolution and glycemic control (odds ratio: 1.57; 95% confidence interval: 1.09-2.26). Conclusions: T2DM has an independent association with CAP. Early detection of recurrent cardiovascular events, with CAP identification, could be useful to prevent complications in patients with CHD. (REV INVEST CLIN. 2018;70:301-9)

Asymptomatic hyperuricemia was regarded as a marker and considered secondary to some pathological conditions such as hypertension. During the last 16 years, a vast amount of experimental work has shown that uric acid can cause intracellular alterations that lead to cardiovascular, renal, and metabolic disease. Epidemiological and clinical studies support this notion in specific populations. However, the clinical studies done so far are of such a small number that it is difficult to reach a consensus in regard to the benefit of treating asymptomatic hyperuricemia.Mild hyperuricemia in rodents induces hypertension associated to renal microvascular disease, tubulointerstitial inflammation, vasoconstriction, and glomerular hypertension. The cellular mechanisms that lead to those outcomes require an increase in intracellular concentrations of uric acid inducing oxidative stress that then activates the synthesis and secretion of proinflammatory factors and vasoconstrictive substances, and diminishes the bioavailability of nitric oxide produced by eNOS. Uric acid also induces proliferation, senescence, and fat accumulation or inhibits insulin secretion, depending on the cell type. Extracellular uric acid can act as an antioxidant; however, when it crystallizes it also induces the activation of prooxidant and proinflammatory pathways resulting in renal lesion. Key Messages: Experimental evidence shows that uric acid is a true mediator for cardiovascular, renal, and metabolic diseases. However, there is still need for greater and well-controlled intervention studies in humans to define whether treating asymptomatic hyperuricemia is worthwhile or not.

Hyperuricemia is common in subjects with obesity, metabolic syndrome, and type 2 diabetes. For many years, hyperuricemia was attributed to the effects of insulin resistance to reduce urinary excretion of uric acid, and it was believed that uric acid may not have any causal role in the metabolic syndrome. However, in recent years, hyperuricemia has been found to independently predict the development of diabetes. Experimental studies have also shown that hyperuricemia may mediate insulin resistance, fatty liver, and dyslipidemia in both fructose-dependent and fructose-independent models of metabolic syndrome. The mechanism for uric acid-induced insulin resistance appears to be mediated by the development of mitochondrial oxidative stress and impairment of insulin-dependent stimulation of nitric oxide in endothelial cells. Pilot studies in humans have reported a potential benefit of lowering serum uric acid on insulin resistance. Large clinical trials are recommended. If uric acid is shown to be a mediator of incident type 2 diabetes in humans, then lowering serum uric acid would represent a simple and inexpensive way to help prevent the development of diabetes and to slow the epidemic.

Hyperuricemia is common in subjects with obesity, metabolic syndrome, and type 2 diabetes. For many years, hyperuricemia was attributed to the effects of insulin resistance to reduce urinary excretion of uric acid, and it was believed that uric acid may not have any causal role in the metabolic syndrome. However, in recent years, hyperuricemia has been found to independently predict the development of diabetes. Experimental studies have also shown that hyperuricemia may mediate insulin resistance, fatty liver, and dyslipidemia in both fructose-dependent and fructose-independent models of metabolic syndrome. The mechanism for uric acid-induced insulin resistance appears to be mediated by the development of mitochondrial oxidative stress and impairment of insulin-dependent stimulation of nitric oxide in endothelial cells. Pilot studies in humans have reported a potential benefit of lowering serum uric acid on insulin resistance. Large clinical trials are recommended. If uric acid is shown to be a mediator of incident type 2 diabetes in humans, then lowering serum uric acid would represent a simple and inexpensive way to help prevent the development of diabetes and to slow the epidemic.

Background Asymptomatic hyperuricemia was regarded as a marker and considered secondary to some pathological conditions such as hypertension. During the last 16 years, a vast amount of experimental work has shown that uric acid can cause intracellular alterations that lead to cardiovascular, renal, and metabolic disease. Epidemiological and clinical studies support this notion in specific populations. However, the clinical studies done so far are of such a small number that it is difficult to reach a consensus in regard to the benefit of treating asymptomatic hyperuricemia. Summary Mild hyperuricemia in rodents induces hypertension associated to renal microvascular disease, tubulointerstitial inflammation, vasoconstriction, and glomerular hypertension. The cellular mechanisms that lead to those outcomes require an increase in intracellular concentrations of uric acid inducing oxidative stress that then activates the synthesis and secretion of proinflammatory factors and vasoconstrictive substances, and diminishes the bioavailability of nitric oxide produced by eNOS. Uric acid also induces proliferation, senescence, and fat accumulation or inhibits insulin secretion, depending on the cell type. Extracellular uric acid can act as an antioxidant; however, when it crystallizes it also induces the activation of prooxidant and proinflammatory pathways resulting in renal lesion. Key Messages: Experimental evidence shows that uric acid is a true mediator for cardiovascular, renal, and metabolic diseases. However, there is still need for greater and well-controlled intervention studies in humans to define whether treating asymptomatic hyperuricemia is worthwhile or not.

Fructose and sodium intake have been associated with hypertension and metabolic syndrome. Although various mechanisms are involved, fructose causes hypertension partly through rising intracellular and serum uric acid. To date, there are no studies in adults that have evaluated the impact of low fructose diets and allopurinol on prehypertensive and overweight subjects. The objective of this study was to compare the effect of low fructose diet and allopurinol or placebo on blood pressure (BP) and metabolic syndrome components The study was a controlled clinical trial and consisted of two phases; in the first phase of intervention (4 weeks), patients were randomized to either low fructose diet (34 patients) or control diet (38 patients). In the second phase of intervention (weeks 4-8), the same groups continued with the same diet prescriptions but were further randomized to receive placebo or allopurinol (300 mg/d). Clinic and 24-hour ambulatory BP, anthropometric measures, and laboratory data were determined at baseline, weeks 4 and 8. Seventy-two patients were included in the trial. At the end of the dietary phase, both diet groups significantly reduced their BP, but there were no between-group differences. Compared to placebo, at the end of follow-up, subjects in the allopurinol group had a lower clinic systolic blood pressure and this was significant within- and between-group comparisons. The percentage of dippers was higher in the allopurinol group, and weight was reduced significantly despite the absence of caloric restriction Allopurinol was associated with a significant reduction in clinic BP, an increase in the percentage of dippers, and significant weight loss. Larger studies with longer follow-up are needed to confirm our findings.

We investigated whether short term high fructose intake may induce early hepatic dysfunction in rats and to test whether allopurinol treatment may have beneficial effects. Twenty male Sprague-Dawley rats received 20% fructose in drinking water (10 treated with allopurinol and 10 received vehicle) and 10 control rats received tap water. After 14 days, the hepatic response to an acute fructose load was evaluated, and in fasted animals, respirometry studies in freshly isolated mitochondria were performed. In fasting rats, we did not find differences in systemic or hepatic uric acid and triglyceride concentrations among the groups, but mitochondrial respiratory control rate was significantly decreased by high fructose feeding and correlated with a reduced expression of Complex I, as well as decreased aconitase-2 activity. On the other hand, in fructose fed rats, an acute fructose load increased systemic and hepatic uric acid, triglycerides and oxidative stress. Fructose feeding was also associated with fructokinase and xanthine oxidase overexpression and increased liver de novo lipogenesis program (fatty acid synthase (FAS) and cell death-inducing DFFA-like effector C (CIDEC) overexpression, ATP citrate lyase (ACL) and acetyl coA carboxylase (ACC) overactivity and decreased AMP-activated protein kinase (AMPk) and endothelial nitric oxide synthase (eNOS) activation). Allopurinol treatment prevented hepatic and systemic alterations. These data suggest that early treatment with xanthine oxidase inhibitors might provide a therapeutic advantage by delaying or even halting the progression of non-alcoholic fatty liver disease (NAFLD).

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. Recent studies show that fructose-induced uric acid generation causes mitochondrial oxidative stress that stimulates fat accumulation independent of excessive caloric intake. These studies challenge the long-standing dogma that “a calorie is just a calorie” and suggest that the metabolic effects of food may matter as much as its energy content. The discovery that fructose-mediated generation of uric acid may have a causal role in diabetes and obesity provides new insights into pathogenesis and therapies for this important disease.

To investigate the participation of purinergic P2 receptors in the regulation of renal function in ANG II-dependent hypertension, renal and glomerular hemodynamics were evaluated in chronic ANG II-infused (14 days) and Sham rats during acute blockade of P2 receptors with PPADS. In addition, P2X1 and P2Y1 protein and mRNA expression were compared in ANG II-infused and Sham rats. Chronic ANG II-infused rats exhibited increased afferent and efferent arteriolar resistances and reductions in glomerular blood flow, glomerular filtration rate (GFR), single-nephron GFR (SNGFR), and glomerular ultrafiltration coefficient. PPADS restored afferent and efferent resistances as well as glomerular blood flow and SNGFR, but did not ameliorate the elevated arterial blood pressure. In Sham rats, PPADS increased afferent and efferent arteriolar resistances and reduced GFR and SNGFR. Since purinergic blockade may influence nitric oxide (NO) release, we evaluated the role of NO in the response to PPADS. Acute blockade with Nω-nitro-l-arginine methyl ester (l-NAME) reversed the vasodilatory effects of PPADS and reduced urinary nitrate excretion (NO2−/NO3−) in ANG II-infused rats, indicating a NO-mediated vasodilation during PPADS treatment. In Sham rats, PPADS induced renal vasoconstriction which was not modified by l-NAME, suggesting blockade of a P2X receptor subtype linked to the NO pathway; the response was similar to that obtained with l-NAME alone. P2X1 receptor expression in the renal cortex was increased by chronic ANG II infusion, but there were no changes in P2Y1 receptor abundance. These findings indicate that there is an enhanced P2 receptor-mediated vasoconstriction of afferent and efferent arterioles in chronic ANG II-infused rats, which contributes to the increased renal vascular resistance observed in ANG II-dependent hypertension.

Hyperuricemia is highly prevalent and especially common in subjects with metabolic, cardiovascular and renal diseases. In chronic kidney disease, hyperuricemia is extremely common, and uric acid (UA) excretion relies on gut uricolysis by gut microbiota. Current therapy for lowering serum UA includes drugs that may produce undesired secondary effects. Therefore, this pilot study was designed to evaluate the potential of two probiotic supplements to reduce systemic uric acid concentrations. Secondary objectives were to assess whether the hypouricemic effect related to a therapeutic benefit on the hyperuricemia-induced renal damage and hypertension. Analysis of fecal microbiota was also performed. Groups of 6 rats each were followed for 5 weeks and allocated in the following treatment groups: C = Control; HU-ND = Oxonic acid-induced hyperuricemia (HU) +regular diet; HU-P = HU+placebo; HU-F1 = HU+ probiotics formula 1 and HU-F2 = HU+ probiotics formula 2. We confirmed that oxonic acid-induced hyperuricemia produced hypertension and renal functional and structural changes, along with modest changes in the overall composition of fecal microbiota. Both probiotic-containing diets prevented HU, elevated UA urinary excretion and intrarenal UA accumulation induced by oxonic acid. The hypouricemic effect conferred by probiotic supplementation also prevented the renal changes and hypertension caused by hyperuricemia. However, probiotic treatment did not restore the fecal microbiota. In conclusion, we demonstrated for the first time the ability of probiotics containing uricolytic bacteria to lower serum uric acid in hyperuricemic animals with beneficial consequences on blood pressure and renal disease. As probiotics supplements are innocuous for human health, we recommend clinical studies to test if probiotic supplements could benefit hyperuricemic individuals.

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. We further suggest that there is a complex interplay between fructose, uric acid and vitamin C, with fructose and uric acid stimulating the foraging response and vitamin C countering this response. Finally, we suggest that the mutations in ascorbate synthesis and uricase that characterized early primate evolution were likely in response to the need to stimulate the foraging "survival" response and might have inadvertently had a role in accelerating the development of bipedal locomotion and intellectual development. Unfortunately, due to marked changes in the diet, resulting in dramatic increases in fructose- and purine-rich foods, these identical genotypic changes may be largely responsible for the epidemic of obesity, diabetes and cardiovascular disease in today's society.

Since its first identification in the late 1800s, a variety of etiologies for essential hypertension have been proposed. In this paper we review the primary proposed hypotheses in the context of both the time in which they were proposed as well as the subsequent studies performed over the years. From these various insights, we propose a current paradigm to explain the renal mechanisms underlying the hypertension epidemic today. Specifically, we propose that hypertension is initiated by agents that cause systemic and intrarenal vasoconstriction. Over time intrarenal injury develops with microvascular disease, interstitial T cell and macrophage recruitment with the induction of an autoimmune response, with local angiotensin II formation and oxidant generation. These changes maintain intrarenal vasoconstriction and hypoxia with a change in local vasoconstrictor-vasodilator balance favoring sodium retention. Both genetic and congenital (nephron number) mechanisms have profound influence on this pathway. As blood pressure rises, renal ischemia is ameliorated and sodium balance restored completely (in salt-resistant) or partially (in salt-sensitive) hypertension, but at the expense of a rightward shift in the pressure natriuresis curve and persistent hypertension.

Uric acid might often be regarded as a simple marker of renal disease. Although it is well known that hyperuricemia causes gout which is associated with renal insufficiency and cardiovascular disease, one might think that it could attribute to the intrarenal urate crystal, but not to uric acid per se. In order to clarify the role of uric acid in the kidney, we hypothesized that uric acid causes renal disease. To generate mild hyperuricemia without intrarenal crystal in rats, we used low doses of an uricase inhibitor (2% oxonic acid). Hyperuricemia induced systemic hypertension, glomerular hypertrophy/hypertension, afferent arteriolar sclerosis, and macrophage infiltration in normal rat kidney. In progressive renal disease, such as cyclosporine nephropathy and remnant kidney in rat, uric acid accelerated the progression of renal disease. Thus, we concluded that uric acid is not a simple marker, but a cause of renal disease.

Rheumatologists commonly recommend low purine diets to gouty subjects based on studies linking the purine contents of food to increased risk for gout1. However, most rheumatologists, as well as physicians in general, do not know that one of the basic 5 human tastes is for purine-rich foods, a taste known as umami (oo-mah-mee). We present evidence of this revelation and why this may have occurred. Historically, an elevation in serum urate was considered benign except for carrying an increased risk for gout. Recently, soluble urate has been found to have myriad biologic effects, including raising blood pressure, increasing hepatic fat stores, and inducing insulin resistance2,3. Indeed, the uricase mutation that occurred in the mid-Miocene likely provided a survival advantage to our ancestors during a period of famine that occurred during that time in Europe4. If uric acid has an important role in human survival, then it is logical that there should be a taste receptor that would encourage the ingestion of foods that raise serum urate. In addition to the classic tastes of sour, bitter, sweet, and salt, there is a fifth basic taste, umami. Umami is the “savory” flavor and was first identified in traditional Japanese foods such as kombu (sea kelp), where it was found to result from the presence of free glutamate. The umami receptor in the taste buds is complex, and consists of the metabotropic glutamate receptor-4, the G-protein-coupled heterodimer of taste receptor type 1 member 1 (TAS1R1), and taste receptor type 1 receptor3 … Address correspondence to Dr. R.J. Johnson, Division of Kidney Diseases and Hypertension, University of Colorado Denver, Aurora, Colorado 80045, USA. E-mail: richard.johnson{at}ucdenver.edu

Primary hypertension is increasingly common and is associated with significant morbidity. Here, we review the history of its discovery and rise during the last century with an emphasis on studies trying to identify its cause. Early studies identified a defect in sodium excretion by the kidney as being central to the pathogenesis. Recent studies have focused on a variety of genetic, congenital (fetal programming), and acquired mechanisms for causing the defect in natriuresis. Certain risk factors are apparent, including genetic polymorphisms that regulate sodium excretion, a congenital reduction in nephron number, obesity and hyperleptinemia, an elevated sympathetic nervous system, diet (salt and fructose), and metabolic (hyperuricemia) mechanisms. The kidney shows evidence for renal arteriolar vasoconstriction, an intrarenal inflammatory response, local oxidative stress, and intrarenal activation of the renin-angiotensin system. Recent studies suggest that intrarenal T cells have an important role in causing hypertension to be persistent, likely due to the induction of a local autoimmune response to neoantigens such as heat shock protein 70 and protein aggregates formed by isoketals resulting from lipid peroxidation. Salt retention due to impairment in pressure-diuresis leads to the release of cardiotonic steroids and central nervous system effects that cause systemic vasoconstriction and a rise in blood pressure. Some recent studies suggest that salt may increase blood pressure not simply by effects on extracellular volume but rather as a consequence of hyperosmolarity. These new insights could lead to new approaches for the prevention and treatment of this important disease.

From the Division of Pediatric Nephrology, University of Alabama at Birmingham, Birmingham, AL; Division of Nephrology, National Heart Institute, Instituto Nacional de Cardiologia–Ignacio Chavez, Mexico City, Mexico; Division of Renal Diseases and Hypertension, University of Colorado Aurora, Aurora, CO; and Laboratory of Renal Physiopathology, Instituto Nacional de Cardiologia–Ignacio Chavez, Mexico City, Mexico

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. In vitro studies were performed in rat insulinoma cells (RIN-m5F) exposed to uric acid, and markers of inflammation were assessed. Rats fed a 40% sucrose diet developed accelerated features of metabolic syndrome with up-regulation of fructose-dependent transporter Glut5 and fructokinase. Fatty liver and low-grade pancreatic inflammation also occurred. Uric acid was found to stimulate inflammatory mediators and oxidative stress in islet cells in vitro. Sucrose, at concentrations ingested by a subset of Americans, can accelerate metabolic syndrome, fatty liver, and type 2 diabetes mellitus in male breeder rats; and the effects are independent of excess energy intake.

Dietary fructose intake is increasing. It is increasing primarily from added sugars, including sucrose and high fructose corn syrup, and correlates epidemiologically with the rising prevalence of metabolic syndrome and hypertension worldwide. The administration of fructose to animals and humans increases BP and the development of metabolic syndrome. These changes occur independently of caloric intake because of the effect of fructose on ATP depletion and uric acid generation. Fructose ingestion may also be a risk factor for kidney disease that includes glomerular hypertension, renal inflammation, and tubulointerstitial injury in animals. We suggest excessive fructose intake should be considered an environmental toxin with major health implications.

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.