[Metabolic syndrome and nephrolithiasis].

Recent epidemiological studies revealed an association of obesity, diabetes mellitus, hypertension and metabolic syndrome (MetS) with kidney stone disease. We examined how these disorders cause kidney stones. A clinical study on 467 patients with nephrolithiasis at our institution revealed that clustering of MetS traits increased the risk of uric acid stone formation by decreasing urinary pH. A subsequent study analyzing detailed data from 30,448 patients enrolled in the 6th Nationwide Survey on Urolithiasis in Japan showed that clustering of MetS traits were associated with an increased severity of the kidney stone disease and elevated urinary excretion of calcium, uric acid and oxalate. Finally, the OLETF rats, an animal model of MetS, showed lower urinary pH, decreased citrate excretion, and increased uric acid and calcium excretion. In addition, the administration of pioglitazone, an agent that improves insulin resistance, significantly increased the urinary pH. These results indicate that MetS causes changes in urinary constituents, leading to an increased risk of both uric acid and calcium oxalate stone formation. We suggest that kidney stone disease should be considered as a component of MetS and that the improvement in insulin resistance by means of diet and lifestyle changes and medical therapy might help to prevent this disorder.