Hyperuricosuria and increased tubular secretion of urate in sickle cell anemia

Haemoglobinopathies and the rheumatologist

The haemoglobinopathies are a relatively common, heterogeneous group of inherited conditions that are the result of either a quantitative abnormality (e.g. thalassaemia) or structural [e.g. sickle cell anaemia (SCA)] of the globin part of the haemoglobin molecule. Musculoskeletal (MSK) complications are common in patients with haemoglobinopathies and may affect the whole of the MSK system, in addition to bone, which is the primary site of the disease. Typical MSK complications include painful vaso-occlusive disease and osteomyelitis in SCA and reduced BMD in thalassaemia. Patients may also develop a number of related (e.g. gout) or unrelated rheumatic diseases (e.g. inflammatory arthritis and autoimmune CTDs). Treatment of MSK conditions in patients with haemoglobinopathies may be challenging (e.g. bone marrow suppression from disease-modifying agents) and in particular in SCA, steroid therapy (by any route) may precipitate potentially severe vaso-occlusive complications. Rheumatologists need to be aware of the range of MSK complications, treatment challenges and the need for such patients to be managed as part of a dedicated multidisciplinary team alongside haematology.

[Kidney and hemoglobinopathy]

Sickle-cell disease (SCD), one of the most common severe monogenic disorders into the world, is associated with an increased frequency of chronic kidney disease. SCD is caused by a point mutation in the gene encoding β globin gene which leads to the formation of hemoglobin S that polymerises after deoxygenation. HbS polymerisation is associated with erythrocyte rigidity and vaso-occlusive episodes that play a central role into SCD pathogenesis. The spectrum of renal diseases during SCD is broad and includes various renal manifestations which become more apparent with increasing age. Underlying pathophysiological processes involved in sickle cell nephropathy are multifactorial but endothelial dysfunction related to chronic hemolysis is a key factor contributing to renal involvement. Our review focuses on the pathogenesis and on the spectrum of renal manifestations occurring in SCD patients.

[Hyperuricemia in sickle cell disease in France]

PURPOSE

Hyperuricemia has been reported to be a common feature of sickle cell disease occurring between 32 to 41% of the patients, in studies conducted during the 1970's. Since then, this notion has been rarely challenged. The objective of this study was to assess the prevalence of hyperuricemia and gout in adult patients with sickle cell disease in France.

METHODS

Between May 2007 and March 2009, serum and urinary urate concentration, creatininemia and hemogram were prospectively assessed in all consecutive sickle cell patients, followed in our sickle cell disease centre. All subjects were in a clinically steady state. Clinical acute gout history was also recorded.

RESULTS

Sixty-five patients (mean age 31±10.3 years) were investigated. Mean uric acid serum level was 281.6±74μmol/L. Hyperuricemia was evidenced in six patients only (9.2%) (95% IC: 3.5-19.0). None of the patient had a medical history of acute gout. Patients in the higher serum uric acid tertile concentration had higher serum creatinine level (62.3±17.1μmol/L vs 51.5±12.6μmol/L, P<0.01), lower fractional excretion of urate (4.5% vs 6.8%, P<0.03) and higher reticulocyte count (median 219500/mm(3) vs 144000/mm(3), P=0.08) compared to the other patients.

CONCLUSION

Hyperuricemia and gout are not a clinical problem in sickle cell disease in our country. Nevertheless, our findings indicate that kidney function has to be fully explored if serum uric acid level is elevated or significantly deteriorates during follow-up. Serum uric acid level could be an early marker of renal dysfunction in sickle cell disease patients.

Uric Acid Nephrolithiasis: A Systemic Metabolic Disorder

Uric acid nephrolithiasis is characteristically a manifestation of a systemic metabolic disorder. It has a prevalence of about 10% among all stone formers, the third most common type of kidney stone in the industrialized world. Uric acid stones form primarily due to an unduly acid urine; less deciding factors are hyperuricosuria and a low urine volume. The vast majority of uric acid stone formers have the metabolic syndrome, and not infrequently, clinical gout is present as well. A universal finding is a low baseline urine pH plus insufficient production of urinary ammonium buffer. Persons with gastrointestinal disorders, in particular chronic diarrhea or ostomies, and patients with malignancies with a large tumor mass and high cell turnover comprise a less common but nevertheless important subset. Pure uric acid stones are radiolucent but well visualized on renal ultrasound. A 24 h urine collection for stone risk analysis provides essential insight into the pathophysiology of stone formation and may guide therapy. Management includes a liberal fluid intake and dietary modification. Potassium citrate to alkalinize the urine to a goal pH between 6 and 6.5 is essential, as undissociated uric acid deprotonates into its much more soluble urate form.

Urate homeostasis in polycystic kidney disease: comparison with chronic glomerulonephritic kidney

Autosomal dominant polycystic kidney disease (ADPKD) might affect urate homeostasis and clearance. Renal tubular urate transport was studied by means of probenecid (PB) and pyrazinamide (PZA) tests in individuals with ADPKD and normal renal function as well as various degrees of renal failure (49 patients). Comparisons were made between polycystic and chronic glomerulonephritic kidney (CGNK), as well as with controls (men with normal renal function). Patients with ADPKD and normal renal function showed plasma urate levels within normal range and normal renal urate handling. In contrast higher plasma urate levels comparing to controls were found in patients with CGNK and normal renal function. During the evolution of renal failure ADPKD patients showed lower urate plasma levels and higher renal clearance as well as, fractional urate excretion, comparing to CGNK patients with the same degree of renal failure. In conclusion patients with ADPKD and normal renal function have normal urate handling and plasma urate levels within normal range. With increasing severity of disease and during evolution of renal failure CGNK patients showed higher urate plasma levels and lower clearances comparing to ADPKD patients. When renal disease becomes more advanced there was no difference in renal urate handling between ADPKD and CGNK patients.

Single kidney function: early and late changes in urate transport after nephrectomy

Renal urate transport was studied by means of pyrazinamide (PZA) and probenecid (PB): (a) before and at 2, 6, 24 weeks (24 patients), (b) 1 to 30 years after uninephrectomy in 27 and 12 patients with Ccr greater than 80 and 30 to 70 ml/min, respectively. Uninephrectomy was followed by important tubular urate transport modifications during at least two weeks, which lead to a marked uricosuria as indicated by significant increase in FEur (mean value +/- SD, 0.228 +/- 0.059 vs. 0.097 +/- 0.014 and 0.099 +/- 0.019 in normals and chronically diseased solitary kidneys). Reduced response to PZA and PB suggests a diminished reabsorptive capacity for urate mainly at the presecretory site which persisted after FENa normalization. Tubular compensations were presumably complete at six weeks, since pattern of urate transport returned to normal with an almost complete reabsorption of filtered urate load (99%) and a percentage of postsecretory reabsorption (80%) very close to those seen in normal subjects with a pair of kidneys. The adjustment in urate excretion in solitary kidneys was achieved by a significant increase of secreted urate as compared with 50% of pre-uninephrectomy values. Thus, increased urate secretion by the remaining intact organ is sufficient to maintain urate balance with a normal serum level.

Abnormal urate transport in patients with intracranial disease

Based on our demonstration of a high incidence of hypouricemia, tubular urate transport abnormality, and cerebral atrophy in patients with acquired immunodeficiency syndrome (AIDS), we performed prospective renal clearance studies in 29 consecutive neurosurgical patients with intracranial diseases of multiple etiologies to test our hypothesis that patients with intracranial disorders had defective tubular urate transport. Similar studies were performed in 21 age-matched controls. None of the subjects had serum creatinine greater than 123.8 mumol/L (1.4 mg/dL), sickle cell or liver diseases, or received intravenous fluid or uricosuric drugs at the time of study. Seven patients had no surgical procedures, 12 were studied after a neurosurgical procedure, and 10 had preoperative and postoperative studies. Ten had more than one postoperative study. Twelve had 24-hour urine collections. We found that 18 of 29 patients had elevated fractional excretion (FE) of urate greater than 10%. There was no difference in preoperative and postoperative FE urate by nonpaired t test for all patients and by paired t test in the 10 patients who had preoperative and postoperative studies performed. Seven patients had hypouricemia, defined as serum urate less than or equal to 0.18 mmol/L (3 mg/dL). Only one had hyponatremia (serum sodium less than 130 mmol/L). Urate excretion averaged 3.6 +/- 0.32 mmol (603 +/- 52.7 mg)/24 h, suggesting that the hypouricemia was not due to decreased urate production. None of the medications or surgical procedures could be considered to have caused the urate transport abnormality, nor was it associated with any specific intracranial location or type of disease.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nonsteroidal antiinflammatory drugs on renal function in sickle cell anemia

Renal hemodynamics and solute and water handling were evaluated in 19 sickle cell patients and 8 matched normal subjects during water diuresis, before and after acute oral administration of a nonsteroidal antiinflammatory drug (NSAID). Baseline GFR and RPF were higher in the patients compared to the normals. In contrast to normals, indomethacin and sulindac induced a 16% and 14% decrease in GFR, respectively. Indomethacin resulted in a slight increase in UOsm in normals, but a substantially greater rise in the patients. Following indomethacin a greater fall in FENa, fractional solute delivery to the diluting segment of the nephron [(CH2O + CNa + K)/GFR], fractional solute reabsorption in the diluting segment [CH2O/GFR] and the fraction of distally delivered solute reabsorbed [CH2O/(CH2O + CNa + K)] was observed in the sickle cell patients than in the normal subjects. A similar trend, but of significantly lesser magnitude than that induced by indomethacin, was observed following sulindac in the sickle cell patient. The data imply that the supranormal GFR observed in the sickle cell patients was prostaglandin-mediated. The effects of NSAID's on renal solute and water handling in the sickle cell patients are compatible with a prostaglandin-dependent decreased salt reabsorption in the medullary thick ascending limb of Henle, together with a hyperfunctioning proximal tubule. The data also imply an additional indomethacin-sensitive antinatriuretic effect in the diluting segment in these patients. Moreover, the results suggest that in sickle cell anemia sulindac may not have a "renal sparing" advantage over other NSAID's.

Serum uric acid in renovascular hypertension: reduction following surgical correction

Mild hyperuricemia in patients with essential hypertension reflects early renal vascular involvement. This report describes a retrospective analysis of 28 patients with unilateral renal arterial disease and hypertension who underwent surgical treatment. Following surgical repair of the arterial lesion: systolic pressure decreased from 188 +/- 25 to 146 +/- 21 mm Hg (p less than 0.001); diastolic pressure decreased from 108 +/- 4 to 87 +/- 6 mm Hg (p less than 0.001), and serum uric acid and creatinine concentrations decreased from 7.0 +/- 1.1 to 6.1 +/- 1.4 mg/dL and from 1.3 +/- 0.3 to 1.0 +/- 0.3 (p less than 0.02 and p less than 0.03, respectively). The reduced serum potassium levels, reflecting hyperaldosteronism, increased after surgical treatment (p less than 0.003). The 28 patients were classified in three groups according to previous therapy: group I (14 patients) had been treated with a centrally active adrenergic agonist or a beta adrenergic receptor blocking agent; group II (7 patients) had been treated with a diuretic, and group III (7 patients) had never received antihypertensive therapy. Serum uric acid concentrations were similar in each of the three groups and decreased significantly in each group after correction of the renal artery stenosis. These data strengthen our previous observations and further suggest that serum uric acid concentration may be useful as an index of renal vascular involvement in hypertension.

Renal function in children undergoing cardiac operations

Because we sometimes observed large amounts of uric acid crystals in the urine of infants and children after open-heart operations and since renal insufficiency from any cause can be a serious complication of cardiac procedures, 8 acyanotic and 5 cyanotic children were studied prospectively by comparing several preoperative and postoperative measures of renal function. There were no significant differences between the acyanotic and cyanotic groups in terms of age, time on cardiopulmonary bypass, or other preoperative variables. Postoperatively, children in both groups had a wide range of free water clearances (CH2O), with some values in the range reported to be diagnostic of renal insufficiency in adults. Since none of these children had renal insufficiency by other criteria, CH2O may not be as reliable an indicator of renal insufficiency in children. The major difference between the cyanotic and acyanotic groups was seen in postoperative serum uric acid levels (SUA); the mean SUA levels in the acyanotic and cyanotic groups were 5.3 +/- 0.5 mg/dl (+/- standard error of the mean) and 10.4 +/- 1.7 mg/dl (range, 8.0 to 15.5 mg/dl), respectively. Since the hyperuricemia in the cyanotic children could not be related to increased exogenous administration or decreased renal excretion, it is probably caused by increased endogenous production and may be related to the resolution of the cyanotic state.

Gout and hyperuricemia associated with sickle-cell anemia

Since the initial description, in 1958, of gouty arthritis occurring in association with SCA, more than 12 cases have been reported. The high proportion of women and the relatively young ages are noteworthy. Since 1968, studies of patients with SCA have shown a high prevalence of hyperuricemia, beginning during childhood. The initial event in the development of hyperuricemia presumably is increased synthesis of nucleic acids occurring as part of the erythropoietic response to hemolysis. Catabolism of the nucleic acids generates urate. Increased production of UA normally is compensated for by increased urinary excretion of UA. This response occurs in patients with SCA, but during the third decade of life hyperuricosuria can be reduced, probably by damage to the renal tubules caused by infarction and hypoxia resulting from sickling. Impairment of the compensatory renal response leads to more severe and sustained hyperuricemia, and gouty arthritis may then develop. A number of questions about hyperuricemia and gout in SCA remain unanswered. The prevalence of gout among patients with SCA, both in general and in relation to age and sex, has not been determined. The relationships between specific aspects of SCA and of hyperuricemia and gout need to be determined. These include any effect of sickle cell crises on SUA and attacks of gout, and correlation of abnormalities in renal handling of urate with other indices of tubular function and with the pathologic anatomy of the kidney. Finally, it is important to learn whether hyperuricemia and hyperuricosuria contribute to the renal manifestations of SCA; if so, allopurinol might be useful in the prevention and treatment of the renal disease.

Secondary gout in hemoglobinopathies: report of two cases and review of the literature

Although patients with hemolytic hemoglobinopathies characteristically are over-producers of urate, and hyperuricemia is frequently recognized, clinical gout has rarely been reported in such patients. Our evaluation of 2 premenopausal women with gout led to the diagnosis of previously unrecognized hemoglobinopathies (SC disease and CC disease). Investigation of these 2 patients and review of the reported cases of gout in patients with hemoglobin S or C disorders suggest that relatively minor abnormalities of renal function in these patients may lead to early development of significant hyperuricemia. With increasing lifespan of patients with hemolytic hemoglobinopathies and the likelihood of increased occurrence of renal function abnormalities, it is anticipated that gout will more frequently be responsible for joint symptoms in such patients.