Hyperuricemia in health and disease

Implications of disorders of purine metabolism for the kidney and the urinary tract

The spectrum of kidney and urinary tract disorders related to purines comprises acute hyperuricosuric nephropathy, chronic urate nephropathy and urolithiasis. Two factors in the development of acute hyperuricosuric nephropathy are increased uric acid concentration and low pH in the tubular fluid. Chronic urate nephropathy still possess several problems: incidence (although this seems to be decreasing, presumably owing to effective prevention), the source of interstitial urate, the cause of the interstitial deposition of urate, and the role of urate deposits in the pathogenesis of the interstitial nephropathy. The relation of the experimental nephropathy to the pathogenesis of chronic urate nephropathy in the human is not yet clear but a model is proposed according to which interstitial urate derives from two sources: hyperuricaemic plasma and hyperuricosuric tubular fluid. Urolithiasis related to purines leads to uric acid-urate stones, xanthine stones, 2,8-dihydroxyadenine stones, iatrogenic xanthine and oxipurinol stones, and possibly calcium stones. Pathogenetic factors in uric acid lithiasis are hyperuricosuria (whether due to an inborn enzyme abnormality or of unknown aetiology) and low urinary pH; oliguria is a contributory factor. There remain several open questions about uric acid lithiasis: incidence, the shift of its location from lower to upper urinary tract, the interplay of pathogenetic factors, and the role of compounds which inhibit crystallization.

Determination of urate in undiluted whole blood by enzyme electrode

An amperometric enzyme electrode is described for the assay of urate in undiluted, unstirred whole blood. The electrode used Aspergillus flavus uricase (EC.1.7.3.3) cross-linked to bovine serum albumin by means of glutaraldehyde, sandwiched between a dimethyldichlorosilane-treated microporous polycarbonate membrane and an inner cellulosic H2O2-selective membrane. The resulting device had a low pH dependence, was capable of repeated use in blood, and gave an acceptable correlation with a standard spectrophotometric method. Electrode steady state and dynamic response were found to be dependent upon the amount of enzyme loading, and could be further optimised by the incorporation of catalase in the enzyme layer.

Exercise and uric Acid: implication in cardiovascular disease

The association of elevated serum uric acid (SUA) concentration (hyperuricemia) with gout has been known for many years, but more recently hyperuricemia has been observed to be associated with many of the known major risk factors for coronary heart disease (hypertension, stress, hypercholesterolemia) with much greater frequency than in the general population. Several epidemiological studies have indicated a beneficial relationship between physical activity, risk factor modification, and susceptibility to coronary heart disease. Physical activity has been shown to modify not only the major identified risk factors but SUA levels as well. Whereas acute exercise lasting between one-half and three hours elevates SUA in proportion to intensity of exercise, chronic exercise lowers SUA levels. Mechanisms for these changes are discussed as well as implications in relation to coronary disease.J Orthop Sports Phys Ther 1984;6(1):34-39.

Gout

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Proceedings of a symposium on crystal-related arthropathies. 22 October and 23 October, 1982, Bristol Polytechnic, Bristol

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Enantiomers of indacrinone: a new approach to producing an isouricemic diuretic

Racemic indacrinone is a potent loop diuretic with transient uricosuric properties in certain nonhuman primates and in man. After chronic treatment, hyperuricemia develops presumably because of enhanced proximal tubular urate reabsorption secondary to extracellular fluid volume contraction. The natriuretic and uricosuric activities are associated with both enantiomers, but the (-)-enantiomer is significantly more potent as a natriuretic agent than the (+). Acutely, in Cebus monkeys, both enantiomers appear to have similar uricosuric activity. The difference in the natriuretic potency between the two enantiomers provides the possibility of altering the enantiomer ratio from its naturally occurring 1:1 ratio to another combination which would enhance the uricosuric action [more (+) relative to (-)] while preserving the potent natriuretic action of the (-). In healthy volunteers, a 1:4 ratio [(-):(+)] was isouricemic after 7 days of treatment and a 1:8 mixture lowered mean serum urate by 13%. Presumably, the desired ratio of (-):(+) will be in the range 1:4-1:9. Further enhancement of the diuretic profile of this compound may be obtained by adding sufficient amiloride to produce isokalemia.

Uric acid in childhood essential hypertension

Serum uric acid concentrations and the fractional excretion of uric acid were determined in 31 children from 3 1/2 to 18 years of age with essential hypertension. While on an unrestricted sodium intake, elevated serum values of uric acid were found in 13 of 31 (42%) of the children. After ingesting a low-sodium diet (200 mg/day) for three days, mean serum uric acid values increased by 0.7 mg/dl (P less than 0.001). There was a significant inverse correlation between the serum uric acid concentrations and fractional excretion of uric acid during the normal and low-sodium diet. This study indicates that the major factor leading to hyperuricemia in our hypertensive patients was a decrease in urate clearance. Insofar as hyperuricemia may represent a cardiovascular risk factor, this abnormality already exists in a significant fraction of hypertensive children and adolescents.

High uric acid as an indicator of cardiovascular disease. Independence from obesity

In three groups of patients, we investigated the hypothesis that body weight is not the factor underlying the relation between hyperuricemia and cardiovascular disease. Among 111 subjects with asymptomatic hyperuricemia followed for 108 months, atherosclerotic heart disease (ASHD) developed in six; their mean was 77.4 kg (172 pounds) compared with 79.7 kg (177 pounds) in the remainder; in 25 of the 111 patients hypertension developed; their mean weight was not significantly higher than that of the remainder. Among 156 patients with established gout followed for 133 months, clinical atherosclerosis developed in 25 after a mean of 95 months; their mean weight was 78.3 kg (174 pounds) contrasted with 79.7 kg (177 pounds) in those 81 of the remaining patients who had a weight recorded with 75 +/- 12 months after their initial attack of gout. Among 1,356 men aaged 60 to 69 years who had their serum uric acid recorded in 1967, subsequent deaths from cardiovascular disease showed a stepwise increase when deaths were arranged according to the serum uric acid levels but not when they were arranged according to body weight. Hyperuricemia thus predicts future cardiovascular disease independently of body weight.