Changes in renal urate handling after prolonged thiazide treatment

A 12-Week, Multicenter, Randomized, Double-Blind, Placebo-Controlled Clinical Trial for Evaluation of the Efficacy and Safety of DKB114 on Reduction of Uric Acid in Serum

This study sought to investigate the antihyperuricemia efficacy and safety of DKB114 (a mixture of Chrysanthemum indicum Linn flower extract and Cinnamomum cassia extract) to evaluate its potential as a dietary supplement ingredient. This clinical trial was a randomized, 12-week, double-blind, placebo-controlled study. A total of 80 subjects (40 subjects with an intake of DKB114 and 40 subjects with that of placebo) who had asymptomatic hyperuricemia (7.0–9.0 mg/dL with serum uric acid) was randomly assigned. No significant difference between the DKB114 and placebo groups was observed in the amount of uric acid in serum after six weeks of intake. However, after 12 weeks of intake, the uric acid level in serum of subjects in the DKB114 group decreased by 0.58 ± 0.86 mg/dL and was 7.37 ± 0.92 mg/dL, whereas that in the placebo group decreased by 0.02 ± 0.93 mg/dL and was 7.67 ± 0.89 mg/dL, a significant difference (p = 0.0229). In the analysis of C-reactive protein (CRP) change, after 12 weeks of administration, the DKB114 group showed an increase of 0.05 ± 0.27 mg/dL (p = 0.3187), while the placebo group showed an increase of 0.10 ± 0.21 mg/dL (p = 0.0324), a statistically significant difference (p = 0.0443). In the analysis of amount of change in apoprotein B, after 12 weeks of administration, the DKB114 group decreased by 4.75 ± 16.69 mg/dL (p = 0.1175), and the placebo group increased by 3.13 ± 12.64 mg/dL (p = 0.2187), a statistically significant difference between the administration groups (p = 0.0189). In the clinical pathology test, vital signs and weight measurement, and electrocardiogram test conducted for safety evaluation, no clinically significant difference was found between the ingestion groups, confirming the safety of DKB114. Therefore, it may have potential as a treatment for hyperuricemia and gout. We suggest that DKB114 as a beneficial and safe food ingredient for individuals with high serum uric acid. Trial registration (CRIS.NIH. go. Kr): KCT0002840.

Individualising the dose of allopurinol in patients with gout

AIMS

The aims of the study were to: 1) determine if a plasma oxypurinol concentration-response relationship or an allopurinol dose-response relationship best predicts the dose requirements of allopurinol in the treatment of gout; and 2) to construct a nomogram for calculating the optimum maintenance dose of allopurinol to achieve target serum urate (SU) concentrations.

METHODS

A nonlinear regression analysis was used to examine the plasma oxypurinol concentration- and allopurinol dose-response relationships with serum urate. In 81 patients (205 samples), creatinine clearance (CL_CR ), concomitant diuretic use and SU concentrations before (U_P ) and during (U_T ) treatment were monitored across a range of allopurinol doses (D, 50-700 mg daily). Plasma concentrations of oxypurinol (C) were measured in 47 patients (98 samples). Models (n = 47 patients) and predictions from each relationship were compared using F-tests, r² values and paired t-tests. The best model was used to construct a nomogram.

RESULTS

The final plasma oxypurinol concentration-response relationship (U_T  = U_P  - C*(U_P  - U_R )/(ID₅₀  + C), r²  = 0.64) and allopurinol dose-response relationship (U_T  = U_P  - D^* (U_P  - U_R )/(ID₅₀  + D), r²  = 0.60) did not include CL_CR or diuretic use as covariates. There was no difference (P = 0.87) between the predicted SU concentrations derived from the oxypurinol concentration- and allopurinol dose-response relationships. The nomogram constructed using the allopurinol dose-response relationship for all recruited patients (n = 81 patients) required pretreatment SU as the predictor of allopurinol maintenance dose.

CONCLUSIONS

Plasma oxypurinol concentrations, CL_CR and diuretic status are not required to predict the maintenance dose of allopurinol. Using the nomogram, the maintenance dose of allopurinol estimated to reach target concentrations can be predicted from U_P .

Chronic gout in the elderly

Gout is the most common cause of inflammatory arthritis in men over 40 years old; it is a debilitating disease and, if untreated, can result in a chronic progressive disease, including tophaceous gout. In the elderly it represents a special issue, with notable clinical and therapeutic differences from the classical form with a systemic involvement. The burden of the disease increases particularly in the very old people, in whom arthritis, impaired gait and eyesight problems may enhance the related disability. Chronic gout moreover could aggravate heart and kidney disease and increase overall mortality and organ-related damage. Early diagnosis and appropriate treatment are important goals for the clinician that should to rely on the cooperation of specialists working together through the methodology of comprehensive geriatric assessment. The aim of the present review was to analyze chronic gout in old people in terms of epidemiology, pathophysiology, risk factors, clinical approach, and current treatment.

Fractional clearance of urate: validation of measurement in spot-urine samples in healthy subjects and gouty patients

INTRODUCTION

Hyperuricemia is the greatest risk factor for gout and is caused by an overproduction and/or inefficient renal clearance of urate. The fractional renal clearance of urate (FCU, renal clearance of urate/renal clearance of creatinine) has been proposed as a tool to identify subjects who manifest inefficient clearance of urate. The aim of the present studies was to validate the measurement of FCU by using spot-urine samples as a reliable indicator of the efficiency of the kidney to remove urate and to explore its distribution in healthy subjects and gouty patients.

METHODS

Timed (spot, 2-hour, 4-hour, 6-hour, 12-hour, and 24-hour) urine collections were used to derive FCU in 12 healthy subjects. FCUs from spot-urine samples were then determined in 13 healthy subjects twice a day, repeated on 3 nonconsecutive days. The effect of allopurinol, probenecid, and the combination on FCU was explored in 11 healthy subjects. FCU was determined in 36 patients with gout being treated with allopurinol. The distribution of FCU was examined in 118 healthy subjects and compared with that from the 36 patients with gout.

RESULTS

No substantive or statistically significant differences were observed between the FCUs derived from spot and 24-hour urine collections. Coefficients of variation (CVs) were both 28%. No significant variation in the spot FCU was obtained either within or between days, with mean intrasubject CV of 16.4%. FCU increased with probenecid (P < 0.05), whereas allopurinol did not change the FCU in healthy or gouty subjects. FCUs of patients with gout were lower than the FCUs of healthy subjects (4.8% versus 6.9%; P < 0.0001).

CONCLUSIONS

The present studies indicate that the spot-FCU is a convenient, valid, and reliable indicator of the efficiency of the kidney in removing urate from the blood and thus from tissues. Spot-FCU determinations may provide useful correlates in studies investigating molecular mechanisms underpinning the observed range of efficiencies of the kidneys in clearing urate from the blood.

TRIAL REGISTRATION

ACTRN12611000743965.

The serum urate-lowering impact of weight loss among men with a high cardiovascular risk profile: the Multiple Risk Factor Intervention Trial

OBJECTIVES

To evaluate the person-level impact of weight loss on serum urate levels among men with a high cardiovascular risk profile.

METHODS

We analysed 12,379 men (mean serum urate level=407 μmol/l) from the Multiple Risk Factor Intervention Trial, using data prospectively collected at baseline and annually over a 7-year period (78,881 visits). Our endpoint was normouricaemia, defined by serum urate levels≤360 μmol/l, a widely accepted therapeutic target. Person-level effects were estimated using conditional logistic regression models to adjust for time-varying covariates (age, congestive heart failure, hypertension, diuretic use, renal function, alcohol intake and dietary factors).

RESULTS

There was a graded relation between weight loss and achieving normouricaemia (P-value for trend<0.001). Compared with no weight change (-0.9 to 0.9 kg), the multivariate odds ratios of achieving normouricaemia for a weight loss of 1-4.9, 5-9.9 and ≥10 kg were 1.43 (95% CI: 1.33, 1.54), 2.17 (1.95, 2.40) and 3.90 (3.31, 4.61), respectively. The corresponding serum urate level changes were -7, -19 and -37 μmol/l (-0.12, -0.31 and -0.62 mg/dl). Similar levels of associations persisted among subgroups stratified by demographics, presence of gout, hypertension, diuretic use, renal insufficiency, alcohol intake, trial group assignment and adiposity categories (all P-values for trend<0.001).

CONCLUSIONS

Weight reduction could help achieve a widely accepted therapeutic urate target level (≤360 μmol/l) among men with a high cardiovascular risk profile. Although the urate-lowering effect appeared weaker than that of urate-lowering drugs, other associated health benefits would make weight reduction important, particularly in this population.

Extracellular matrix changes regulate calcium crystal formation in articular cartilage

PURPOSE OF REVIEW

The pathologic matrix mineralization seen in calcium pyrophosphate dihydrate and basic calcium phosphate deposition diseases identifies a subset of osteoarthritis patients with an unusual joint distribution and rapid progression of disease. Several factors contribute to pathologic matrix mineralization, including changes in the extracellular matrix of articular cartilage. The factors contributing to extracellular matrix changes that promote crystal formation are important and not well understood. Better characterization of these factors will enhance the understanding of the pathogenesis of pathologic matrix mineralization and may identify potential targets for novel therapeutic interventions.

RECENT FINDINGS

Histologic studies of cartilage from patients affected by calcium crystal arthritis show changes in the pericellular matrix of articular chondrocytes. The amounts and types of collagens, proteoglycans, and calcium-binding proteins are altered. The mechanisms by which these changes occur remain poorly understood. Recent work, however, has implicated alterations in the chondrocyte phenotype and post-translational matrix-modulating enzymes such as the transglutaminases.

SUMMARY

Changes in extracellular matrix are associated with the pathologic matrix mineralization seen in calcium pyrophosphate dihydrate and basic calcium phosphate crystal deposition diseases. The literature on growth plate cartilage provides observations and mechanisms through which extracellular matrix contributes to normal matrix mineralization, and has served as a model on which to base studies in articular cartilage. More studies are warranted to enhance the understanding of how changes in extracellular matrix contribute to crystal deposition diseases.

Can idiopathic tinnitus be caused by hyperuricemia?

It is hypothesized that heretofore medically untreatable idiopathic tinnitus of intermittent intensity may be related to hyperuricemia. A number of pathogenic features common to both are given. Hyperuricemia is treatable.

Hyperuricemia as a clue for central diabetes insipidus (lack of V1 effect) in the differential diagnosis of polydipsia

PURPOSE

In the differential diagnosis of patients with polyuria-polydipsia one must distinguish usually between primary polydipsia (PP) and central diabetes insipidus (CDI). The first situation is a state of volume expansion and the second of volume contraction. We evaluate whether serum uric acid determination could help to differentiate between the two conditions.

PATIENTS AND METHODS

We analyzed the score of 13 consecutive patients with CDI, 7 patients with PP, and 7 patients with nephrogenic diabetes insipidus (NDI). Serum uric acid concentration was available during normonatremia without treatment with 1-desamino-8-D-arginine vasopressin (dDAVP), during mild dehydration and during treatment with dDAVP. In 8 of these patients plasma renin activity (PRA), urate, urea and creatinine clearances were also available. These data were also obtained in the patients with NDI. In 1 patient with CDI, we studied the effect on urate clearance of dDAVP, which stimulates exclusively the V2 receptors, and of triglycyl-lysine-vasopressin (TGLV), a potent V1-receptor agonist.

RESULTS

Normonatremic polydypsic patients with CDI presented an increase in uric acid concentration (7.1 +/- 2.2 mg/dL), whereas in the PP group the value was decreased (3 +/- 0.75 mg/dL; P <0.001). All the normonatremic PP presented a serum uric acid concentration lower than 5 mg/dL, whereas all the normonatremic CDI patients, exept 1, presented a value higher than 5 mg/dL. In both groups blood urea concentration was decreased as a consequence of high renal clearances. The hyperuricemia of CDI was related to low uric acid clearances. Patients with hypernatremia and NDI presented a lower increase in serum uric acid concentration than those with similar levels of hypernatremia and CDI (NDI: 5.7 +/- 0.8 mg/dL and CDI: 7.9 +/- 2.3 mg/dL; P <0.05) and the NDI patients presented an urate clearance corrected for creatinine clearance which was significantly higher than in CDI (9% +/- 3% and 4% +/- 1.1%; P <0.01). When the patients with CDI were treated with dDAVP and normalyzed their PRA (0.9 +/- 0.4 ng/mL/h) we observed still mild hyperuricemia compared to controls (5.5 +/- 1.4 mg/dL and 4.3 +/- 0.9 mg/dL; P <0.01) and a low fractional excretion of filtered uric acid (6.5% +/- 1.7% compared to 8.2% +/- 2% in controls; P <0.05). Acute administration of dDAVP, stimulating the V2 receptors, in one patient with CDI, had no effect on urate clerance, while TGLV, which stimulates the V1 receptor, increased urate clearance.

CONCLUSION

The presence of an serum uric acid concentration higher than 5 mg/dL in polyuric polydipsic patients is highly suggestive of CDI. Even when these patients are treated with dDAVP many of them remain hyperuricemic, and this seems to be the consequence of a lack of V1 receptor stimulation.

Thiazide diuretics and the initiation of anti-gout therapy

While physiologic and epidemiologic evidence link diuretic therapy with hyperuricemia, no previous study has quantified the risk for initiation of treatment specific for hyperuricemia or gout among elderly patients taking thiazide diuretics. We performed a retrospective cohort study of 9249 enrollees aged 65 or older in the New Jersey Medicaid program who were newly started on an antihypertensive medication from November 1981 through February 1989 and who had no prior use of anti-gout therapy (allopurinol, colchicine, or a uricosutic) during the preceding one-year period. We used Cox proportional hazards analysis to determine the risk for the initiation of anti-gout therapy in patients using various antihypertensive treatment regimens relative to no antihypertensive exposure. Patient follow-up extended for up to two years. Antihypertensive exposure was characterized over the entire period of follow-up according to the following categories: thiazide diuretic therapy alone; non-thiazide antihypertensive therapy; thiazide diuretic therapy in combination with any non-thiazide antihypertensive agent(s); and no antihypertensive use. Antihypertensive exposure was entered into the model as a time-varying covariate. Estimates of risk were adjusted for age, sex, race, nursing home residence, number of prescriptions filled, intensity of physician use, hospitalization history, and year of antihypertensive treatment initiation. The adjusted relative risk for the initiation of anti-gout therapy was 1.00 (95% CI, 0.65-1.53) for non-thiazide antihypertensive therapy alone, 1.99 (95%, CI, 1.21-3.26) for thiazide diuretic therapy, and 2.29 (95% CI, 1.55-3.37) for thiazide diuretic therapy in combination with any non-thiazide agent(s). Risk for anti-gout therapy was significantly increased for thiazide doses of > or = 25 mg/day (in hydrochlorothiazide equivalents); no significant increase in risk was seen for lower doses. We conclude that use of thiazide diuretics in doses of 25 mg/day or higher is associated with a significantly increased risk for initiation of anti-gout therapy. Such treatment may reflect the occurrence of clinical sequelae of diuretic-induced hyperuricemia or the inappropriate treatment of asymptomatic hyperuricemia.

Racial differences in the incidence of gout. The role of hypertension

OBJECTIVE

To estimate the incidence of and examine risk factors for the development of gout in black and white male physicians.

METHODS

Data from 2 cohorts of former medical students, 352 black men in the Meharry Cohort Study and 571 white men in the Johns Hopkins Precursors Study, were analyzed. Cases of gout were identified by self-report. Baseline variables and incident hypertension were examined as risk factors for the development of gout in both cohorts.

RESULTS

The incidence of gout was 3.11 and 1.82 per 1,000 person-years in the black men and the white men, respectively (P < 0.05); the cumulative incidence was 10.9% and 5.8%, respectively (P = 0.04). The relative risk (RR) for gout among the black men was 1.69 (95% confidence interval [95% CI] 1.02-2.80). This excess risk persisted after adjustment for baseline systolic blood pressure (adjusted RR = 1.96 [95% CI 1.14-3.38]). Incident hypertension was independently associated with the development of gout in univariate analysis (RR = 3.78 [95% CI 2.18-6.58]); when this variable was included as a time-dependent covariate in a Cox model, the excess risk for gout in black men was reduced and no longer significant (adjusted RR = 1.30 [95% CI 0.77-2.19]).

CONCLUSION

The approximately 2-fold excess risk for gout among black men is explained, in part, by a greater risk of incident hypertension.

Uricosuric and diuretic activities of DR-3438 in dogs and rabbits

The purpose of this study was to evaluate the uricosuric and diuretic properties of the new diuretic agent DR-3438. In the conventional clearance studies in urate-loaded dogs, intravenous injection of DR-3438 (3-30 mg/kg) resulted in dose-related increases in fractional excretion of urate (FEua), urine flow and sodium excretion. At doses causing similar natriuresis, tienilic acid (50 mg/kg, i.v.) markedly increased the FEua value, whereas indacrinone (1 mg/kg, i.v.) had no significant effect on it. Trichloromethiazide (1 mg/kg, i.v.) and furosemide (0.3 mg/kg, i.v.) tended to decrease the FEua. Thus, the uricosuric activity of DR-3438 (30 mg/kg) was 0.6-fold that of tienilic acid and 3.4-fold that of indacrinone. In contrast, in urate-loaded rabbits that exhibit net tubular secretion of urate, intravenous DR-3438 (30 mg/kg) produced a significant decrease in FEua. Stop-flow studies in dogs revealed that DR-3438 (30 mg/kg) blocks both urate reabsorption and p-aminohippurate secretion in the proximal segment of the nephron and strongly inhibits reabsorption of water, sodium and potassium in the distal segments. These results suggest that DR-3438 exerts uricosuric activity through blocking urate transport in the proximal tubules and diuretic and saluretic activities by inhibiting water and sodium reabsorption in the distal segment of the nephron.

Serum uric acid and the renin-angiotensin system in hypertension

To study whether the renin-angiotensin system is related to hyperuricemia in hypertension, the serum concentration of uric acid was determined in 96 patients with various types of hypertension and various degrees of plasma renin activity (PRA). In malignant hypertension, both PRA and the serum uric acid level were higher than in essential hypertension; but in primary aldosteronism or desoxycorticosterone-excess hypertension, they were lower than in the essential type. In renovascular hypertension, PRA was higher than in essential hypertension, but the serum uric acid levels were similar. There were no differences in PRA and serum uric acid concentration between Cushing's syndrome and essential hypertension. The serum uric acid level in high-renin essential hypertension was higher than in either the normal-renin or the low-renin type. There was a significant correlation between serum uric acid concentration and PRA in the basal state, and between the change in PRA and the change in serum uric acid induced by administration of furosemide. Apparently the close correlation between the renin-angiotensin system and the concentration of serum uric acid is related to changes in extracellular fluid volume, although an intrarenal effect of angiotensin II cannot be excluded.

The effect of ascorbic acid on uric acid excretion with a commentary on the renal handling of ascorbic acid

Under spontaneous conditions in man and dog, very little ascorbic acid is excreted in urine. Ascorbic acid clearance (C ascorbic acid) is promptly augmented when plasma ascorbic acid is increased by intravenous injection. No net tubular secretion of ascorbic acid is demonstrable in either man or dog when plasma ascorbic acid is elevated to levels as high as 12 mg/100 ml in man, and 28 mg/100 ml in the dog. Nevertheless, both in men and the Dalmatian dog, when the glomerular filtration rate (GFR) is decreased, excreted ascorbic acid in relation to the amount filtered is exaggerated so that C ascorbic acid:GFR approaches unity. It is possible that secreted ascorbic acid is masked under ordinary circumstances, with a more significant contribution of secreted ascorbic acid to total urinary ascorbic acid becoming apparent under conditions of low GFR. In man, when the plasma ascorbic acid level is raised to above 6 mg/100 ml, C urate:GFR rises from control value of 0.081 +/- 0.020, to 0.116 +/- 0.026. In both mongrel and Dalmatian dogs an effect of ascorbic acid on urate excretion is not conclusively shown. The uricosuric effect of ascorbic acid in man may be due to competition with uric acid for renal tubular reabsorptive transport. The difference in the metabolism of ascorbic acid in the dog as compared to man may help account for the inconsistent effect of ascorbic acid on uric acid excretion in the dog.

Renal transport of urate during diuretic-induced hypouricemia

The effect of two weeks administration of a uricosuric diuretic (SKF-62698) on renal urate handling has been examined in 11 normal men. Plasma urate concentrations had declined by more than 60 per cent after two weeks. Urate excretion per unit of glomerular filtration rate and urate clearance (Curate) per unit of glomerular filtration rate were increased after the administration of SKF-62698. The importance of intact tubular secretion of urate in producing these changes was assessed by administering pyrazinamide, an agent that curtails urate secretion, to each participant. The decrements in urate excretion and clearance produced by pyrazinamide both increased significantly, whereas the residual urate excretion rates and clearances not suppressible by pyrazinamide were only minimally altered by SKF-62698 treatment. These results suggest that the excretion of secreted urate was enhanced by prolonged administration of SKF-62698, probably secondary to the inhibition of postsecretory urate reabsorption. In addition, because the nonsuppressible urate excretion did not decline despite a 63 per cent reduction in the plasma urate, it is likely that the reabsorption of filtered urate also was impaired by SKF-62698.