Reappraisal of the pathogenesis and consequences of hyperuricemia in hypertension, cardiovascular disease, and renal disease

Interactions between vitamins C and E in human subjects

Despite convincing in vitro evidence, a vitamin C-E interaction has not been confirmed in vivo. This study was designed to examine the effects of supplementation with either vitamin C or E on their respective plasma concentrations, other antioxidants, lipids and some haemostatic variables. Fasting blood was collected before and after intervention from thirty healthy adults in a double-blinded crossover study. Baselines for measured variables were established after 2 weeks of placebo supplementation, followed by daily supplementation with 73.5 mg RRR-alpha-tocopherol acetate or 500 mg ascorbic acid, and placebo, for 6 weeks. A 2 month washout preceded supplement crossover. Mean values showed that plasma lipid standardised alpha-tocopherol increased with ascorbic acid supplementation: from 4.09 (sem 0.51) to 4.53 (sem 0.66) micromol/mmol total cholesterol plus triacylglycerol (P < 0.05), and plasma ascorbic acid increased from 62.8 (sem 14.9) to 101.3 (sem 22. 2) micromol/l (P < 0.005). Supplementation with (RRR)-alpha-tocopherol acetate increased plasma alpha-tocopherol from 26.8 (sem 3.9) to 32.2 (sem 3.8) micromol/l (P < 0.05), and lipid-standardised alpha-tocopherol from 4.12 (sem 0.48) to 5.38 (sem 0.52) micromol/mmol (P < 0.001). Mean plasma ascorbic acid also increased with vitamin E supplementation, from 64.4 (sem 13.3) to 76. 4 (sem 18.4) micromol/l (P < 0.05). Plasma ferric reducing (antioxidant) power and glutathione peroxidase (U/g haemoglobin) increased in both groups, while urate, total cholesterol and triacylglycerol levels decreased (P < 0.05 throughout). Results are supportive of an in vivo interaction between vitamins C and E.

Gout and other crystal-associated arthropathies

Intra-articular crystals (monosodium urate monohydrate, calcium pyrophosphate dihydrate, basic calcium phosphates) can cause acute and chronic inflammation and joint damage. Identification of the crystals by polarized microscopy is the key step in diagnosis but improved reliability of synovial examination is required. Treatment of disorders associated with gout or calcium pyrophosphate deposition may reduce non-joint morbidity and assist treatment of the arthritis. Various forms of anti-inflammatory therapy work for acute crystal-induced arthritis; prompt commencement is usually more important than which option is used. In gout, recurrent attacks are usual, but hypouricaemic therapy is almost never urgent, is life-long, and is too often negated by poor compliance. In most patients, allopurinol or any of the potent uricosuric drugs will allow maintenance of normouricaemia but renal failure, renal calculi, transplantation, and allopurinol allergy narrow the options and complicate management.

Gout update: from lab to the clinic and back

Reviews and opinion articles stressing the need for better reproducibility of crystal identification in synovial fluid continue to be published. The possibility of definitive diagnosis of gout by crystal identification during intercritical periods appears now established. The problems associated with the use of allopurinol have also received some attention, as well as the strategies of dealing with allopurinol hypersensitivity. Gout in transplanted patients is reviewed, with special attention to the difficulties related to its treatment; various therapeutic options for this group are reviewed. The use of benzbromarone to reduce uricemia appears to be especially appropriate for this group of patients, in whom allopurinol is problematic. Finally, the pathogenetic mechanisms of the disease, and the relation between urate crystals and inflammation are reviewed.

Function of murine adenosine deaminase in the gastrointestinal tract

Adenosine deaminase (ADA) deficiency in humans leads to a combined immunodeficiency characterized by severe T and B cell lymphopenia. ADA-deficient humans also display defective development of gut-associated lymphoid tissues (GALT). They lack lymphoid cells, and the Peyer's patches are without germinal centers. In mice, ADA-deficient fetuses die perinatally due to liver damage, but they also exhibit pathology in the thymus, spleen, and the small intestine. The GI phenotype associated with ADA-deficient humans prompted us to examine the effect of ADA-deficiency on mouse small intestine tissue. The work presented here focuses on understanding the physiological role of ADA in the GI tract, using ADA-deficient mice rescued from perinatal lethality by restoring Ada expression to trophoblast cells. Histologically and immunologically, the GALT was compromised at all sites in ADA-/- mice, with the most dramatic changes seen in the Peyer's patches. Profound disturbances in purine metabolism were detected in all the gastrointestinal tissues. In particular, adenosine and deoxyadenosine, the ADA substrates, increased markedly while the product inosine decreased. The activity of S-adenosylhomocysteine hydrolase decreased throughout the GI tract, indicating a possible disruption of cellular transmethylation and activation of apoptotic pathways. There were also disturbances in the purine metabolic pathway with a decrease in the production of downstream nucleosides hypoxanthine and xanthine.

Hypertriglyceridaemia and hyperuricaemia are risk factors for progression of IgA nephropathy

BACKGROUND

The prognosis of IgA nephropathy (IgAN) is variable and about 10-20% of patients progress to end-stage renal disease (ESRD) in 10 years. Hypertension, proteinuria and renal insufficiency at the time of diagnosis are risk factors associated with poor prognosis. Lipid abnormalities may have a role in the progression of glomerulonephritides, and glomerulosclerosis and atherosclerosis may have similar pathophysiological mechanisms. We therefore evaluated factors associated with cardiovascular diseases, especially hypercholesterolaemia, hypertriglyceridaemia, and hyperuricaemia, as predictors of the progression of IgAN.

METHODS

A total of 223 patients with IgAN (141 men, 82 women; median age 41 years, range 8-78 years) were studied. The following parameters were recorded at the time of renal biopsy: presence of hypertension or diabetes, smoking habits, body mass index (BMI), serum creatinine, total and HDL-cholesterol, triglycerides, and urate and 24-h urinary protein excretion. The patients were followed up for 0.2-17 years (median 10 years) with respect to progression of renal disease defined as elevation of serum creatinine above 125 micromol/l in men or 105 micromol/l in women, and over 20% elevation from baseline.

RESULTS

Forty-one patients (18%) showed progression. Hypertriglyceridaemia and hyperuricaemia were significantly more common at the time of renal biopsy in patients with progressive than in those with stable disease. In patients with normal renal function at the time of diagnosis initial hypertriglyceridaemia, hyperuricaemia, hypertension and proteinuria were independent risk factors for progression of IgAN in the Cox regression hazard model.

CONCLUSIONS

Our results show that hypertriglyceridaemia and hyperuricaemia at the time of diagnosis are important, previously underestimated predictors of poor outcome in IgAN, although causality between these factors and progression cannot be inferred from the present study.

Hyperuricemia and renal insufficiency associated with malignant disease: urate oxidase as an efficient therapy?

Hyperuricemia is a common finding in patients with malignant diseases. Chemotherapy can induce life-threatening tumor lysis syndrome with severe hyperuricemia, other metabolic abnormalities, and acute renal failure. Intrarenal precipitation of uric acid contributes to renal insufficiency in this situation. Allopurinol, by preventing the conversion of hypoxanthine and xanthine to uric acid, has been long considered the standard pharmacological approach to hyperuricemia and prevention of tumor lysis syndrome. However, allopurinol itself may facilitate precipitation of xanthine crystals and has little influence on already-formed uric acid crystals deposited in the kidney. Urate oxidase further oxidizes uric acid to the highly water-soluble allantoin in mammals, except humans, who lack this enzyme. We report four cases of hyperuricemia (initial serum uric acid concentrations, 14.0 to 25.0 mg/dL) associated with malignant diseases treated with exogenous urate oxidase. Two of the patients showed full-blown tumor lysis syndrome. A single urate oxidase infusion (1,000 U) readily reduced serum uric acid levels in all patients. Furthermore, renal insufficiency, determined by serum creatinine concentrations, improved in three of the four patients. No adverse effects were observed. Currently, a recombinant urate oxidase is undergoing clinical testing and may make this efficient therapy more widely available. We believe that treatment with urate oxidase is a safe and efficient therapy for patients with cancer-associated hyperuricemia and may be effective even in individuals with only moderately elevated serum uric acid concentrations.