Uric acid: an old actor for a new role

concentrations. These factors (including high uric acid) have been mentioned in one or more definitions of the metabolic syndrome [7]. Recently, much attention has been paid to the metabolic syndrome due to its possible role as a risk factor for the development of type 2 diabetes and cardiovascular disease. The worldwide increase in the prevalence of obesity and diabetes is a reason not only for the increasing prevalence of the metabolic syndrome but also of hyperuricaemia. Hyperinsulinaemia and insulin resistance lead to elevated serum uric acid levels through both direct and indirect mechanisms, which include increased urate production as well as decreased renal urate excretion (probably due to the stimulating effect of insulin on urate reabsorption in the renal proximal tubule). Hypertension, use of some drugs (in particular diuretics) and renal disease are also associated to increased uric acid concentrations. The link between uric acid and the progression of vascular disease has been examined not only in epidemiological studies but also with experimental investigations [8]. The possible mechanisms involved in this causal relationship are: uric acid may induce a thickening of the glomerular afferent arteriole, activation of the renin-angiotensin system, and hence hypertension; uric acid may contribute to endothelial dysfunction by inducing anti-proliferative effects on endothelium and impairing nitric oxide production; uric acid stimulates human vascular smooth muscle cell proliferation and synthesis of C-reactive protein; uric acid may increase platelet adhesiveness and platelet lysis (a platelet dysfunction may be linked to endothelial dysfunction); hyperuricaemia could promote thrombus formation; uric acid may have a role in oxidative stress and in the formation of free radicals; uric acid may enhance oxygenation of low-density lipoprotein cholesterol and lipid peroxidation. An independent link between uric acid and endothelial function has been reported in patients with uncomplicated, Intern Emerg Med (2007) 2:1–2 DOI 10.1007/s11739-007-0001-6