Urate Reabsorption Research Articles

The Dual Actions ofPaederia scandensExtract as a Hypouricemic Agent: Xanthine Oxidase Inhibitory Activity and Uricosuric Effect

Hyperuricemia is associated with a number of pathological conditions, such as gout. Lowering of elevated uric acid levels in the blood could be achieved by xanthine oxidase inhibitors and inhibitors of renal urate reabsorption. Some natural compounds isolated from herbs used in traditional Chinese medicine have been previously demonstrated to act as xanthine oxidase inhibitors. In the present investigation, Paederia scandens (Lour.) Merrill (Rubiaceae) extract (PSE; 4.5, 2.25, and 1.125 g/kg) orally for 14 days was demonstrated to possess in vivo potent hypouricemic activity in hyperuricemic rats pretreated with potassium oxonate. In addition, PSE was also demonstrated to be an inhibitor of xanthine oxidase. Lineweaver-Burk analysis of the enzyme kinetics indicated that the inhibition of PSE was of a mixed type. Using an oxonate-induced hyperuricemic rat model, PSE was indeed shown to exhibit uricosuric action in vivo, which could explain, at least in part, the observed hypouricemic effect of PSE in these rats. The potential application of this compound in the treatment of conditions associated with hyperuricemia is discussed.

Identification of a New Urate and High Affinity Nicotinate Transporter, hOAT10 (SLC22A13)

The orphan transporter hORCTL3 (human organic cation transporter like 3; SLC22A13) is highly expressed in kidneys and to a weaker extent in brain, heart, and intestine. hORCTL3-expressing Xenopus laevis oocytes showed uptake of [(3)H]nicotinate, [(3)H]p-aminohippurate, and [(14)C]urate. Hence, hORCTL3 is an organic anion transporter, and we renamed it hOAT10. [(3)H]Nicotinate transport by hOAT10 into X. laevis oocytes and into Caco-2 cells was saturable with Michaelis constants (K(m)) of 22 and 44 microm, respectively, suggesting that hOAT10 may be the molecular equivalent of the postulated high affinity nicotinate transporter in kidneys and intestine. The pH dependence of hOAT10 suggests p-aminohippurate(-)/OH(-), urate(-)/OH(-), and nicotinate(-)/OH(-) exchange as possible transport modes. Urate inhibited [(3)H]nicotinate transport by hOAT10 with an IC(50) value of 759 microm, assuming that hOAT10 represents a low affinity urate transporter. hOAT10-mediated [(14)C]urate uptake was elevated by an exchange with l -lactate, pyrazinoate, and nicotinate. Surprisingly, we have detected urate(-)/glutathione exchange by hOAT10, consistent with an involvement of hOAT10 in the renal glutathione cycle. Uricosurics, diuretics, and cyclosporine A showed substantial interactions with hOAT10, of which cyclosporine A enhanced [(14)C]urate uptake, providing the first molecular evidence for cyclosporine A-induced hyperuricemia.

Multiple organic anion transporters contribute to net renal excretion of uric acid

Excretion of uric acid, a compound of considerable medical importance, is largely determined by the balance between renal secretion and reabsorption. The latter process has been suggested to be principally mediated by urate transporter 1 (URAT1; slc22a12), but the role of various putative urate transporters has been much debated. We have characterized urate handling in mice null for RST, the murine ortholog of URAT1, as well as in those null for the related organic anion transporters Oat1 and Oat3. Expression of mRNA of other putative urate transporters (UAT, MRP2, MRP4, Oatv1) was unaffected in the knockouts, as were general indexes of renal function (glomerular filtration rate, fractional excretion of fluid and electrolytes). While mass spectrometric analyses of urine and plasma revealed significantly diminished renal reabsorption of urate in RST-null mice, the bulk of reabsorption, surprisingly, was preserved. Oat1- and Oat3-null mice manifested decreased secretion rather than reabsorption, indicating that these related transporters transport urate in the "opposite" direction to RST. Moreover, metabolomic analyses revealed significant alteration in the concentration of several molecules in the plasma and urine of RST knockouts, some of which may represent additional substrates of RST. The results suggest that RST, Oat1, and Oat3 each contribute to urate handling, but, at least in mice, the bulk of reabsorption is mediated by a transporter(s) that remains to be identified. We discuss the data in the context of recent human genetic studies that suggest that the magnitude of the contribution of URAT1 to urate reabsorption might vary with ethnic background.

Regulation of Tissue-Specific Expression of the Human and Mouse Urate Transporter 1 Gene by Hepatocyte Nuclear Factor 1 α/β and DNA Methylation

Expression of Urate transporter 1 (URAT1/SLC22A12) is restricted to the proximal tubules in the kidney, where it is responsible for the tubular reabsorption of urate. To elucidate the mechanism underlying its tissue-specific expression, the transcriptional regulation of the hURAT1 and mUrat1 genes was investigated. Hepatocyte nuclear factor 1 alpha (HNF1alpha) and HNF1beta positively regulate minimal promoter activity of the URAT1 gene as shown by reporter gene assays. Electrophoretic mobility shift assays revealed binding of HNF1alpha and/or HNF1beta to the HNF1 motif in the hURAT1 promoter. Furthermore, the mRNA expression of Urat1 is reduced in the kidneys of Hnf1alpha-null mice compared with wild-type mice, confirming the indispensable role of HNF1alpha in the constitutive expression of URAT1 genes. It was also shown that the proximal promoter region of mUrat1 was hypermethylated in the liver and kidney medulla, whereas this region was relatively hypomethylated in the kidney cortex. These methylation profiles are in a good agreement with the proximal tubule-restricted expression of mUrat1 in the kidney cortex. Taken together, these results strongly suggest that tissue-specific expression of the URAT1 genes is coordinately regulated by the transcriptional activation by HNF1alpha/HNF1beta heterodimer and repression by DNA methylation.

Outcome of kidney transplantation in familial juvenile hyperuricaemic nephropathy

Familial juvenile hyperuricaemic nephropathy (FJHN) and medullary cystic kidney disease (MCKD) are rare autosomal-dominant disorders, both characterized by early hyperuricaemia due to reduced urinary excretion of urate and the development of chronic interstitial nephropathy, most often leading to end-stage renal failure (ESRF) in adulthood. Although a history of gout is more frequently reported in FJHN and corticomedullary renal cysts more frequently found in MCKD, both phenotypes overlap [1]. Two loci for MCKD (MCKD1 and MCKD2) were localized to chromosome 1q21 and 16p12, respectively [2,3]. A locus for FJHN was mapped to chromosome 16p11.2, in a region overlapping with the MCKD2 locus, raising the hypothesis that FJHN and MCKD2 were two facets of the same disease [4]. This was demonstrated by the identification of mutations in the UMOD gene encoding uromodulin (or Tamm-Horsfall protein) in three families with FJHN and one with MCKD2 [5]. Several groups soon confirmed the role of the UMOD gene as the cause of FJHN, with a cluster of mutations in exons 4 and 5 (reviewed in [1]). The cause of the onset and progression of chronic interstitial nephritis in UMOD-related disorders remains a moot point. Uromodulin is a kidney-specific protein produced in the thick ascending limb (TAL) of the loop of Henle and excreted in the urine [1]. Mutant uromodulin has been shown to accumulate in the endoplasmic reticulum of TAL cells, with only wildtype uromodulin found in the urine of affected patients [6,7]. Intratubular accumulated uromodulin is thought to induce cell death and interstitial fibrosis, through unidentified mechanisms. If this is true, the transplantation of a normal kidney producing only wild-type uromodulin should cure the disease, without fear of recurrence. The earliest manifestation of the disease is a decreased fractional urinary excretion of urate (FEur), expressed as a function of age and sex. The most likely explanation for this abnormality is an increased reabsorption of urate in the proximal tubule along with sodium, the latter thought to be a compensation for the decreased sodium uptake in the TAL related to the uromodulin defect [1]. This abnormality should be reversed after kidney transplantation. There is so far no data in the literature on the results of kidney transplantation in this condition. This prompts us to report on the outcome of kidney transplantation in six patients with FJHN due to a documented mutation in the UMOD gene, with emphasis on the post-transplant renal handling of uric acid.

Morin (3,5,7,2′,4′-Pentahydroxyflavone) Exhibits Potent Inhibitory Actions on Urate Transport by the Human Urate Anion Transporter (hURAT1) Expressed in Human Embryonic Kidney Cells

In allopurinol-allergic patients, uricosuric agents are often used in the treatment of hyperuricemia. The existing uricosuric agents are not without problems and the availability of better and safer alternatives is highly desirable. Our previous study (J Pharmacol Exp Ther (2006) 316:169-175) has demonstrated that morin (3,5,7,2',4'-pentahydroxyflavone), which occurs in the twigs of Morus alba L. documented in traditional Chinese medicinal literature for treatment of conditions akin to gout, is a potent inhibitor of urate uptake in rat renal brush-border membrane vesicles. It is also effective in lowering uric acid level in a hyperuricemic rat model in vivo. Whether morin is an equally effective uricosuric agent in human requires verification. The human urate anion transporter (hURAT1) has recently been cloned and identified to be the organic anion transporter that mediates renal urate reabsorption in the human kidney. In the present investigation, human embryonic kidney cells were transfected with hURAT1 and the expression was validated by reverse transcription-polymerase chain reaction and subcellular distribution of the exogenously introduced transporter by confocal microscopy. The inhibitory actions of morin on human renal urate reabsorption were demonstrated using this system. The IC50 value of the inhibition by morin was determined to be 2.0 microM, compared with 50 microM for probenecid, 100 microM for sulfinpyrazone, and 0.3 microM for benzbromarone. Kinetic analysis of the uptake inhibition by morin indicates that this compound is a competitive inhibitor of urate uptake on the human urate transporter with a K(i) value of 5.74 microM.

Gout and Hyperuricemia: Recent Advances and a Systematic Review

Gout is an increasingly common rheumatic disease. Global studies have found an increase in mean serum urate in both genders during the past four decades. Furthermore, there has been a resurgence of interest in hyperuricemia as an independent and potential modifiable cardiovascular risk factor. This work discusses recent advances in the epidemiology, pathogenesis, clinical manifestations, and treatment of gout and hyperuricemia. Humans have an uricase silencing mutation together with effective renal tubule urate reabsorption, thus resulted in a high urate levels. From evolutionary point of view, hyperuricemia should be biologically relevant. However, the exact role of uric acid as an end product of purine metabolism in human remains unclear. It is important to point out that many gout patients are not been adequately managed and highlighting the burden of gout and hyperuricemia. Recent advances in understanding of the molecular mechanisms of renal urate handling may help in developing better uricosuric agents in the future. Though it remains uncertain whether hyperuricemia is an independent risk factor for cardiovascular disease, a diagnosis of hyperuricemia or gout should prompt a search for cardiovascular risk factors. If data supporting treatment of hyperuricemia to prevent cardiovascular or renal disease become available in the future, such data will significantly change the way we treat asymptomatic hyperuricemia. However, well-designed randomized controlled study is necessary to clarify this. From evidence-based point of view, the current treatment practices of patients with gout, including long-term prevention of gout recurrence, are largely empirical. For example, the long-term effect of allopurinol or uricosuric agents on renal function and their relative safety is still unknown and requires examination via a well designed, randomized controlled study.

C/ebpδ Null Mouse as a Model for the Double Knock-out of slc5a8 and slc5a12 in Kidney

slc5a8 and slc5a12 represent the high affinity and low affinity Na+/lactate co-transporters, respectively, in the kidney. Here we show that these transporters are expressed in the apical membrane of the proximal tubular cells in mouse kidney, indicating that these transporters are likely to mediate the first step in the renal reabsorption of lactate. Interestingly, the renal expression of both transporters is almost completely ablated in mice homozygous for the deletion of the transcription factor c/ebpdelta. This effect is tissue-specific since the expression of the transporters is not affected in non-renal tissues. The functional role of C/EBPdelta in the expression of SLC5A8 and SLC5A12 is demonstrable in HEK293 cells in reporter assays using gene-specific promoters. The ablation of the transporters in the kidney is accompanied by a marked increase in urinary excretion of lactate as well as a decrease in blood levels of lactate in c/ebpdelta-/- mice. These data provide evidence for an obligatory role for slc5a8 and slc5a12 in the renal absorption of lactate. In addition, we show that urinary excretion of urate is significantly elevated in c/ebpdelta-/- mice even though the expression of URAT1, the transporter responsible for the apical membrane uptake of urate in renal proximal tubule, is not altered. These data provide in vivo evidence for the functional coupling between lactate reabsorption and urate reabsorption in the kidney. Thus, the fortuitous double knock-out of slc5a8 and slc5a12 in kidney in c/ebpdelta-/- mice reveals the physiologic role of these transporters in the renal handling of lactate and urate.

New developments in clinically relevant mechanisms and treatment of hyperuricemia

The prevalence of gout has increased markedly in the United States in the past two decades, and new treatments for hyperuricemia are being developed. Recent molecular identification of urate transporter-1 (URAT1) as the central mediator of renal urate reabsorption has provided novel understanding of the pathogenesis of hyperuricemia, and the target site for current and possibly future primary uricosuric agents. Recent studies have also highlighted uricosuric effects of several drugs (losartan, atorvastatin, fenofibrate) that are prescribed for primary indications other than hyperuricemia. The niche of these agents in current management of hyperuricemia is discussed. We also review the ongoing development of recombinant uricase preparations and of novel xanthine oxidase inhibitors exemplified by febuxostat. These agents should provide novel options for patients with chronic, refractory gout and hyperuricemia, particularly in association with allopurinol hypersensitivity and renal insufficiency.

Association of the human urate transporter 1 with reduced renal uric acid excretion and hyperuricemia in a German Caucasian population

Human urate transporter 1 (hURAT1) is a member of the organic anion transporter family (SLC22A12) that mainly regulates tubular urate reabsorption. Loss-of-function mutations result in idiopathic hypouricemia. The present case-control study was designed to analyze whether hURAT1 might also be a candidate gene for hyperuricemia with primary reduced renal urate excretion. DNA samples from 389 individuals with reduced fractional excretion of uric acid (FEUA) (< or =6.5%) and from 263 controls (FEUA >6.5%) were sequenced. Genotype frequencies between groups were compared by Cochran-Armitage trend test. Significantly different genotype distributions could be demonstrated for the -788 T >A (promoter; P = 0.014), the C258T (exon 1; P = 0.006), and the C426T (exon 2; P = 0.0002) polymorphisms, but not for the T1309C (exon 8) and the +18 C >T (intron 9) polymorphisms. The strongest association with reduced FEUA was observed for the C426T polymorphism, with odds ratios (ORs) of 1.59 and 2.54 (P = 0.0002) for the CT and TT genotypes, respectively. Adjusted values for FEUA in the C426T genotype, were significantly reduced decreasing to 7.3%, 6.7%, and 6.3% in individuals with the CC, CT, and TT genotypes, respectively (P = 0.004). Haplotypes were constructed from the -788 T >A, C258T, and C426T polymorphisms. Individuals carrying at least 1 ACT haplotype (n = 349) had a significantly higher risk for reduced FEUA than individuals without any ACT haplotype (n = 303) (OR 1.39, P = 0.041). These results indicate that polymorphisms in the N-terminus of the hURAT1 gene were significantly associated with reduced renal uric acid excretion. The main regulating factor seems to be located close to the C426T polymorphism or is in strong linkage disequilibrium.

The Dual Actions of Morin (3,5,7,2′,4′-Pentahydroxyflavone) as a Hypouricemic Agent: Uricosuric Effect and Xanthine Oxidase Inhibitory Activity

Hyperuricemia is associated with a number of pathological conditions such as gout. Lowering of elevated uric acid level in the blood could be achieved by xanthine oxidase inhibitors and inhibitors of renal urate reabsorption. Some natural compounds isolated from herbs used in traditional Chinese medicine have been previously demonstrated to possess xanthine oxidase inhibitory activities. In the present investigation, morin (3,5,7,2',4'-pentahydroxyflavone), which occurs in the twigs of Morus alba L. documented in traditional Chinese medicinal literature to treat conditions akin to gout, was demonstrated to exert potent inhibitory action on urate uptake in rat renal brush-border membrane vesicles, indicating that this compound acts on the kidney to inhibit urate reabsorption. Lineweaver-Burk transformation of the inhibition kinetics data demonstrated that the inhibition of urate uptake was of a competitive type, with a K(i) value of 17.4 microM. In addition, morin was also demonstrated to be an inhibitor of xanthine oxidase. Lineweaver-Burk analysis of the enzyme kinetics indicated that the mode of inhibition was of a mixed type, with K(i) and K(ies) values being 7.9 and 35.1 microM, respectively. Using an oxonate-induced hyperuricemic rat model, morin was indeed shown to exhibit an in vivo uricosuric action, which could explain, in part at least, the observed hypouricemic effect of morin in these rats. The potential application of this compound in the treatment of conditions associated with hyperuricemia was discussed.

The Multivalent PDZ Domain-containing Protein PDZK1 Regulates Transport Activity of Renal Urate-Anion Exchanger URAT1 via Its C Terminus

The urate-anion exchanger URAT1 is a member of the organic anion transporter (OAT) family that regulates blood urate level in humans and is targeted by uricosuric and antiuricosuric agents. URAT1 is expressed only in the kidney, where it is thought to participate in tubular urate reabsorption. We found that the multivalent PDZ (PSD-95, Drosophila discs-large protein, Zonula occludens protein 1) domain-containing protein, PDZK1 interacts with URAT1 in a yeast two-hybrid screen. Such an interaction requires the PDZ motif of URAT1 in its extreme intracellular C-terminal region and the first, second, and fourth PDZ domains of PDZK1 as identified by yeast two-hybrid assay, in vitro binding assay and surface plasmon resonance analysis (K(D) = 1.97-514 nM). Coimmunoprecipitation studies revealed that the wild-type URAT1, but not its mutant lacking the PDZ-motif, directly interacts with PDZK1. Colocalization of URAT1 and PDZK1 was observed at the apical membrane of renal proximal tubular cells. The association of URAT1 with PDZK1 enhanced urate transport activities in HEK293 cells (1.4-fold), and the deletion of the URAT1 C-terminal PDZ motif abolished this effect. The augmentation of the transport activity was accompanied by a significant increase in the V(max) of urate transport via URAT1 and was associated with the increased surface expression level of URAT1 protein from HEK293 cells stably expressing URAT1 transfected with PDZK1. Taken together, the present study indicates the novel role of PDZK1 in regulating the functional activity of URAT1-mediated urate transport in the apical membrane of renal proximal tubules.

The W258X mutation in SLC22A12 is the predominant cause of Japanese renal hypouricemia.

Recently, a urate transporter, hURAT1 (human uric acid transporter 1) encoded by SLC22A12, was isolated from the human kidney. hURAT1 is presumed to play the central role in reabsorption of urate from glomerular filtrate. In the present study, we analyzed SLC22A12 in seven unrelated Japanese patients with renal hypouricemia whose serum level of urate was less than 1.0 mg/dl, and their family members. We performed direct DNA sequencing of the exon and exon-intron boundaries of SLC22A12 using genomic DNA. Six of the seven patients (86%) possess mutations in SLC22A12. In five patients, a homozygous G to A transition at nucleotide 774 within exon 4 of SLC22A12, which forms a stop codon (TGA) at codon 258 (TGG), was identified (W258X). In one patient, the C to T transition within exon 3, which changes threonine at codon 217 to methionine (T217 M), and the W258X mutation were found (compound heterozygote). Thus, among 12 mutational alleles in six patients, 11 were the W258 X mutation (92%). Family members with the heterozygous W258X mutation (carriers) show relatively low levels of serum urate. The present study demonstrates that homozygous W258X mutation is the predominant genetic cause of idiopathic renal hypouricemia in Japanese patients.

Drug-induced Fanconi's syndrome

Fanconi's syndrome (FS) was first described by Lignac in 1924. Associated with numerous varieties of inherited and acquired conditions, FS is characterized by a generalized transport defect in the proximal tubules, leading to renal losses of glucose, phosphate, calcium, uric acid, amino acids, bicarbonates, and other organic compounds. Cardinal symptoms of the syndrome are hyperaminoaciduria, glucosuria in the face of a normal serum glucose level, and phosphate wasting. Other symptoms may be associated, such as defects in bicarbonate reabsorption; renal acidification; urate reabsorption; urinary concentration; potassium conservation; reabsorption of sodium, calcium, and low-molecular-weight proteins; and secretion of p-aminohippuric acid. Acquired renal tubular defects resulting in FS also have been described in association with many exogenous agents, whether administered or accidentally ingested. This review concentrates on drug-induced FS. Am J Kidney Dis 41:292-309.

Molecular identification of a renal urate anion exchanger that regulates blood urate levels.

Urate, a naturally occurring product of purine metabolism, is a scavenger of biological oxidants implicated in numerous disease processes, as demonstrated by its capacity of neuroprotection. It is present at higher levels in human blood (200 500 microM) than in other mammals, because humans have an effective renal urate reabsorption system, despite their evolutionary loss of hepatic uricase by mutational silencing. The molecular basis for urate handling in the human kidney remains unclear because of difficulties in understanding diverse urate transport systems and species differences. Here we identify the long-hypothesized urate transporter in the human kidney (URAT1, encoded by SLC22A12), a urate anion exchanger regulating blood urate levels and targeted by uricosuric and antiuricosuric agents (which affect excretion of uric acid). Moreover, we provide evidence that patients with idiopathic renal hypouricaemia (lack of blood uric acid) have defects in SLC22A12. Identification of URAT1 should provide insights into the nature of urate homeostasis, as well as lead to the development of better agents against hyperuricaemia, a disadvantage concomitant with human evolution.

Abstracts from the 3rd international conference for advances in osteopathic research [ICAOR], Melbourne 2002

Summary: Uric acid, the end product of purine metabolism, plays a key role in the pathogenesis of gout and other disease processes. The circulating serum uric acid concentration is governed by the relative balance of hepatic production, intestinal secretion, and renal tubular reabsorption and secretion. An elegant synergy between genome-wide association studies and transport physiology has led to the identification and characterization of the major transporters involved with urate reabsorption and secretion, in both kidney and intestine. This development, combined with continued analysis of population-level genetic data, has yielded an increasingly refined mechanistic understanding of uric acid homeostasis as well as greater understanding of the genetic and acquired influences on serum uric acid concentration. The continued delineation of novel and established regulatory pathways that regulate uric acid homeostasis promises to lead to a more complete understanding of uric acid–associated diseases and to identify new targets for treatment.

Management of Hypertension and Dyslipidaemia in Patients Presenting with Hyperuricaemia: Case Histories

A number of studies have shown that hyperuricaemia is associated with an increased incidence of coronary heart disease. It has been proposed that the elevated serum uric acid levels are linked to other risk factors, such as hypertension, dyslipidaemia and diabetes. Hyperuricaemia is commonly encountered in patients with essential hypertension and is considered as a risk factor for morbidity and mortality associated with hypertension. In addition, lipid abnormalities (mainly hypertriglyceridaemia) are also found more frequently in hypertensive patients than in normotensives. There is evidence that the angiotensin II receptor antagonist, losartan, increases urate excretion by reducing reabsorption of urate in the renal proximal tubule. It is also known that fibric acid derivatives (fibrates) have several beneficial actions in addition to their lipid-lowering capacity. Fenofibrate administration is associated with a uric acid lowering effect. In this respect, we present two patients with hypertension and dyslipidaemia together with elevated serum uric acid levels. We also discuss (in the format of questions and answers) the pathophysiological mechanisms underlying the association of serum uric acid with cardiovascular disease, and we review the relevant literature to justify an evidence-based decision to choose an antihypetensive agent (losartan) or a lipid-lowering drug (fenofibrate) with an additional hypouricaemic effect.

Effect of anti-inflammatory bowel disease drug, E3040, on urate transport in rat renal brush border membrane vesicles

To confirm the assumption that 6-hydroxy-5,7-dimethyl-2-methylamino-4-(3-pyridylmethyl)benzothiazole (E3040) acts on urate reabsorption by inhibiting urate–anion exchange at the luminal membrane of renal tubules, we investigated the inhibitory effect of E3040 and its two conjugated metabolites on hydroxyl ion (OH −) gradient-dependent urate uptake into brush border membrane vesicles from rat renal cortex and compared it with other uricosuric agents. The order of potency was AA193 (5-chloro-7,8-dihydro-3-phenylfuro[2,3- g]-1,2-benzisoxazole-7-carboxylic acid)>benzbromarone>E3040>probenecid>E3040 sulfate>E3040 glucuronide. Furthermore, kinetic analysis revealed that E3040 may be a competitive inhibitor of the OH − gradient-dependent uptake of urate into brush border membrane vesicles.

Management of Hypertension and Dyslipidaemia in Patients Presenting with Hyperuricaemia: Case Histories

SummaryA number of studies have shown that hyperuricaemia is associated with an increased incidence of coronary heart disease. It has been proposed that the elevated serum uric acid levels are linked to other risk factors, such as hypertension, dyslipidaemia and diabetes. Hyperuricaemia is commonly encountered in patients with essential hypertension and is considered as a risk factor for morbidity and mortality associated with hypertension. In addition, lipid abnormalities (mainly hypertriglyceridaemia) are also found more frequently in hypertensive patients than in normotensives. There is evidence that the angiotensin II receptor antagonist, losartan, increases urate excretion by reducing reabsorption of urate in the renal proximal tubule. It is also known that fibric acid derivatives (fibrates) have several beneficial actions in addition to their lipidlowering capacity. Fenofibrate administration is associated with a uric acid lowering effect. In this respect, we present two patients with hypertension and dyslipidaemia together with elevated serum uric acid levels. We also discuss (in the format of questions and answers) the pathophysiological mechanisms underlying the association of serum uric acid with cardiovascular disease, and we review the relevant literature to justify an evidence-based decision to choose an antihypetensive agent (losartan) or a lipidlowering drug (fenofibrate) with an additional hypouricaemic effect.

Serum uric acid levels and microalbuminuria in mild hypertensive patients.

A low proportion of mild hypertensive patients, recently diagnosed in a primary care setting are microalbuminuric. These patients show a higher serum urate than normoalbuminuric hypertensive patients. The higher serum urate levels in microalbuminuric hypertensive patients may be due to insulin resistance and hyperinsulinemia, which may enhance renal urate reabsorption.