Hyperuricemia and gout

Hyperuricemia as a Risk Factor for Atrial Fibrillation Due to Soluble and Crystalized Uric Acid

Among the several independent risk factors for atrial fibrillation (AF), hyperuricemia has been widely accepted as associated with the incidence of paroxysmal or persistent AF, as well as with the risk of AF in patients undergoing cardiovascular surgery. The electrophysiological mechanism of AF involves electrical remodeling of the arrhythmogenic substrate and abnormal automaticity as trigger. Both electrical and structural remodeling mediated by oxidative stress derived from either xanthine oxidoreductase (XOR), soluble uric acid (UA) or monosodium urate (MSU) crystals might be plausible explanations for the association of AF with hyperuricemia. XOR generates reactive oxygen species (ROS) that lead to atrial structural remodeling via inflammation. Soluble UA accumulates intracellularly through UA transporters (UAT), shortening the atrial action potential via enhanced expression and activity of Kv1.5 channel proteins. Intracellular accumulation of soluble UA generates ROS in atrial myocytes via nicotinamide adenine dinucleotide phosphate oxidase, which phosphorylates ERK/Akt and heat shock factor 1 (HSF1), thereby increasing transcription and translation of Hsp70, which stabilizes Kv1.5. In macrophages, MSU activates the NLRP3 inflammasome and proteolytic processing mediated by caspase-1 with enhanced interleukin (IL)-1β and IL-18 secretion. Use of an XOR inhibitor, antioxidants, a UAT inhibitor such as a uricosuric agent, and an NLRP3 inflammasome inhibitor, might become a potential strategy to reduce the risk of hyperuricemia-induced AF, and control serum UA level.

Imaging features of crystal-induced arthropathy

Crystal-induced arthropathies constitute a spectrum of inflammatory arthritides that is induced by cellular reaction to crystal deposition in and around joints. A variety of microcrystals may be deposited and can induce an inflammatory response. The three most common types of crystal-induced arthropathy are gout, calcium pyrophosphate dihydrate deposition disease, and calcium hydroxyapatite deposition disease. Each has a characteristic clinical presentation, crystal type that may be aspirated from affected tissues, and radiographic appearance. Each of these entities may occur as a primary abnormality or secondary to an underlying disorder. Sometimes these diseases may coexist in the same joint or individual. Imaging frequently plays a crucial role in the diagnosis of crystal-induced arthropathies and may help to monitor disease progression and treatment response.

Cutaneous deposition diseases. Part II

Part II of the cutaneous deposition disorders focuses on cutaneous calcification and ossification, alkaptonuria and ochronosis, and gout. These disorders have in common the deposition of materials in the dermis or subcutis and often involve metabolic defects in hormonal and enzymatic regulation. The pathogenesis, clinical findings, and treatment of these diseases are discussed. Both the histologic and ultrastructural findings are reviewed.

Effect of diltiazem on plasma concentrations of oxypurines and uric acid

To determine the clinical effect of diltiazem on the metabolism of adenosine, and its importance in ischemic heart disease, arterial plasma concentrations of the purine metabolites were determined in 21 healthy volunteers (10 female and 11 male) and 19 patients with effort angina (8 female and 11 male) before, during, and immediately after standard treadmill exercise tests conducted before and after they had taken 60 mg diltiazem (Cardizem; Hoechst Marion Roussel, Laval, QC, Canada) four times a day for 1 week. The results showed that the cardiac patients had significantly lower mean plasma concentrations of uric acid (46.82 +/- 25.51 versus 95.47 +/- 35.41 micrograms/ml, p 0.05), inosine (0.25 +/- 0.19 versus 0.84 +/- 0.17 microgram/ml, p < 0.05), and hypoxanthine (0.28 +/- 0.35 versus 0.50 +/- 0.27 microgram/ml, p < 0.05). Diltiazem decreased the mean resting plasma concentrations of uric acid in patients (uric acid 43.47 +/- 22.26 versus 46.82 +/- 25.51 micrograms/ml, p < 0.05) and healthy volunteers (uric acid 85.68 +/- 26.71 versus 95.47 +/- 35.41 micrograms/ml, p < 0.05). There was no statistically significant change in the plasma concentrations of the purine metabolites during exercise (p < 0.05). Female subjects had significantly lower plasma concentrations of uric acid than males (patients, 34.87 +/- 26.93 versus 55.78 +/- 21.25 micrograms/ml; healthy volunteers, 84.79 +/- 32.07 versus 104.22 +/- 37.05 micrograms/ml; p < 0.05 for both). Results of the study suggest that normal therapeutic doses of diltiazem may modulate the metabolism of adenosine and that some of the purine metabolites may be useful markers for specific types of ischemic heart disease.

Effect of insulin on uric acid excretion in humans

Although hyperuricemia is a frequent finding in insulin-resistant states, insulin's effect on renal uric acid (UA) handling is not known. In 20 healthy volunteers, diastolic blood pressure, body weight, and fasting plasma insulin were positively (and age was negatively) related to fasting plasma UA concentrations, together accounting for 53% of their variability. During an insulin clamp, urine flow was lower than during fasting conditions (1.01 +/- 0.12 vs. 1.56 +/- 0.32 ml/min, P = 0.04), whereas creatinine clearance was unchanged (129 +/- 7 and 131 +/- 9 ml/min, P = not significant). Hyperinsulinemia did not alter serum UA concentrations (303 +/- 13 vs. 304 +/- 12 microM) but caused a significant decrease in urinary UA excretion [whether expressed as absolute excretion rate (1.66 +/- 0.21 vs. 2.12 +/- 0.23 mumol/min, P = 0.03), clearance rate (5.6 +/- 0.8 vs. 7.3 +/- 0.8 ml/min, P = 0.03), or fractional excretion (4.48 +/- 0.80 ml/min vs. 6.06 +/- 0.64%, P < 0.03)]. Hyperinsulinemia was also associated with a 30% (P < 0.001) fall in urine Na excretion. Fractional UA excretion was related to Na fractional excretion under basal conditions (r = 0.59, P < 0.01) and during the insulin period (r = 0.53, P < 0.02). Furthermore, the insulin-induced changes in fractional UA and Na excretion correlated with one another (r = 0.66, P < 0.001). Physiological hyperinsulinemia acutely reduces urinary UA and Na excretion in a coupled fashion.

Permanent stained preparations of synovial fluid for detection of calcium compounds using alizarin red S

Permanent preparations of air dried synovial fluids were prepared by staining calcium compounds with alizarin red S stain; each slide was coverslipped with Permount. Variables studied were: (a) concentration of the solution of alizarin red S, (b) pH of staining solution, (c) time of incubation in staining solution and aqueous and ethanolic content of staining solution. The staining effect of each solution was tested on calcium pyrophosphate dihydrate, calcium oxalate, apatite and monosodium urate (MSU). Of all the solutions, best results were obtained with 0.25% alizarin red S in 50% ethanol at pH 7.0 for 30 min. With this solution, the calcium-containing compounds were well stained. MSU did not stain and still preserved negative birefringence on polarization. Fixation of smears with ethanol served a double purpose: It fixed the slides without dissolving or removing MSU or the calcium compounds, yet it did dissolve five corticosteroids commonly used for intra-articular injection which may interfere with interpretation of compensated polarized light microscopy of synovial fluids.

Renal sonography in long standing Lesch-Nyhan syndrome

The Lesch-Nyhan syndrome is an x-linked defect of purine metabolism resulting in its classical form in major neurodevelopmental abnormality, hyperuricaemia, and hyperuricosuria. Uric acid calculi and crystalluria are common. Allopurinol is the main method of reducing serum and urinary uric acid levels, but results in xanthinuria and oxypurinoluria, both of which may cause crystal nephropathy and calculi. The variable ultrasonic appearances of multiple calculi and increased medullary echogenicity in four cases of long-standing treated disease and the nature of the renal disorder, which is at least partially iatrogenic, are described.

Acute uric acid nephropathy

Uric acid, as the end-product of purine metabolism in humans, presents a clinical problem because of its relative insolubility, particularly in the acid environment of the distal nephron of the kidney. As a result, states of enhanced purine catabolism increase the urate load on the kidney, leading to intrarenal precipitation. Major causes of increased purine metabolism are malignancies with rapid cell turnover, such as leukemias and lymphomas, and the added acceleration of cell lysis that occurs with chemotherapy and radiation. Serum urate levels rise rapidly, and acute renal failure occurs as a consequence of tubular deposition of urate and uric acid. The keys to the diagnosis of acute uric acid nephropathy are the appropriate clinical setting of increased cell lysis, oliguria, marked hyperuricemia, and hyperuricosuria. A urinary uric acid-to-creatinine ratio greater than 1 helps to distinguish acute uric acid nephropathy from other catabolic forms of acute renal failure in which serum urate is elevated. Preventive treatment involves pharmacologic xanthine oxidase inhibition with allopurinol and alkaline diuresis. Occasionally, acute renal failure occurs despite allopurinol because of the tubular precipitation of the precursor metabolites, such as xanthine, which accumulate with xanthine oxidase inhibition. Dialysis therapy may be required both to correct azotemia and to reduce the body burden of urate. Hemodialysis is preferred because it can achieve greater clearance than other dialysis modes.

Gout in the heart transplant recipient: physiologic puzzle and therapeutic challenge

PURPOSE

Hyperuricemia and gouty arthritis have been associated with cyclosporine use in renal transplant recipients. Patients requiring heart or heart-lung transplantation may have additional risk factors for the development of gout, yet it has not previously been described in this population. We share herein our clinical experience with gouty arthritis in six heart transplant recipients.

PATIENTS AND METHODS

During a one-year period, six hospitalized male heart transplant patients were seen in consultation for gouty arthritis. Five were subsequently followed for gout as outpatients; the sixth died within six months. Management included trials of nonsteroidal anti-inflammatory drugs (NSAIDs), colchicine, allopurinol, and intra-articular steroid injections, as well as attempts to minimize cyclosporine nephrotoxicity.

RESULTS

Three patients had gout in remission at time of transplant surgery, and three others developed gout for the first time two to 45 months after transplantation. Following transplant surgery, both pre-existing and new-onset gout appeared to exhibit an accelerated course, with unusually rapid development of chronic polyarticular disease and tophi in four of the five patients followed for more than six months. Peak serum uric acid levels ranged from 11.0 mg/dL to 16.5 mg/dL. NSAIDs produced reversible renal insufficiency in four patients. Gout-related infections occurred in three patients, one of whom died.

CONCLUSION

Acute gouty arthritis may occur in the heart transplant recipient despite concomitant use of immunosuppressive drugs. Cyclosporine, with its attendant hypertension and nephrotoxicity, appears to be the major risk factor for hyperuricemia in this setting, leading to the accelerated development of tophi and chronic polyarthritis. Management is complicated by the patients' renal insufficiency and propensity to infection, as well as by interaction with transplant-related medications. Prevention of hyperuricemia by minimizing cyclosporine nephrotoxicity appears to be the best management strategy, with judicious use of allopurinol for those patients in whom this preventive approach fails.

Renal excretion of hypoxanthine and xanthine in primary gout

PURPOSE

The renal excretion of uric acid is usually diminished in primary gout with respect to increased serum urate levels. To determine whether the renal excretion of uric acid precursors, hypoxanthine and xanthine, is also abnormal in primary gout, the concentrations of these purines were measured in plasma and 24-hour urine samples in normal subjects, in patients with primary gout and uric acid underexcretion, and in patients with enzyme deficiencies that are known to result in over-production of uric acid.

SUBJECTS AND METHODS

Three groups of subjects were studied: Group I consisted of 10 ambulatory healthy normal men; Group II consisted of 15 patients in whom primary gout was diagnosed; and Group III consisted of 10 patients with various enzyme defects known to produce an excessive synthesis of uric acid. In each subject, plasma and 24-hour urinary uric acid, hypoxanthine, xanthine, and creatinine concentrations were measured and the mean of three consecutive determinations was used. The fractional excretion of purine compounds was calculated from a formula. Hypoxanthine phosphoribosyltransferase, adenine phosphoribosyltransferase, and hemoglobin were also measured in each subject.

RESULTS

Plasma hypoxanthine and xanthine were increased in the two groups of patients compared with the control subjects. Urinary hypoxanthine and xanthine levels were reduced in gouty patients compared with control subjects, whereas levels were increased in patients with uric acid overproduction. A positive correlation was found between the renal clearances of uric acid, hypoxanthine, and xanthine.

CONCLUSION

The results indicate that the renal excretion of hypoxanthine and xanthine is severely impaired in most patients with primary gout.