Plasma phospholipid arachidonic acid content and calcium metabolism in idiopathic calcium nephrolithiasis

Background. Reports of an increase in plasma and erythrocyte phospholipid arachidonic acid content and in urinary prostaglandin E-2 (PGE(2)) excretion in patients with idiopathic calcium nephrolithiasis suggested their crucial role in the pathogenesis of hypercalciuria, a well-known risk factor for lithogenesis. Methods. To confirm this hypothesis, 15 healthy subjects and 20 nephrolithiasis patients were evaluated for plasma phospholipid polyunsaturated fatty acid content and PGE(2) concentration, serum parathyroid hormone, 25 hydroxyvitamin D-3, 1,25-dihydroxyvitamin D-3, and bone-specific alkaline phosphatase levels, as well as urinary excretion of calcium, biochemical markers of bone resorption (hydroxyproline and crossLaps), and intestinal calcium absorption. Furthermore, the effect of a 30-day fish-oil diet supplementation on the previously mentioned parameters was investigated in the patients. Results. At baseline, patients compared with controls showed higher levels of plasma phospholipid arachidonic acid content (P = 0.002). PGE(2) (P = 0.0004), serum 25-vitamin D-3 (P = 0.001), and 1,25-vitamin D-3 (P = 0.001), urinary excretion of calcium (P = 0.001), hydroxyproline (P = 0.007), and crossLaps (P = 0.019), as well as intestinal calcium absorption (P = 0.03 at 60 min). Fish oil supplementation induced a reduction in the plasma phospholipid arachidonic acid level (P < 0.0001), and except for serum concentrations of 25-vitamin D-3, normalized baseline blood and urinary parameters, including intestinal calcium absorption. A close correlation between plasma PGE, and serum 1,25-vitamin D-3 (P = 0.004) and between phospholipid arachidonic acid and intestinal calcium absorption (P = 0.0002) and calciuria (P = 0.007) was observed, as well as between urine excretion of crossLaps and hydroxyproline (P < 0.0001), crossLaps and calcium (P < 0.0001), and hydroxyproline and calcium (P < 0.0001). Conclusions. These findings indicate that the phospholipid arachidonic acid content anomaly could represent the primary event responsible for the mosaic of metabolic and clinical alterations that are distinctive features of renal stone formers, and suggest that a common pathogenetic mechanism might account for the several forms of hypercalciuria detected in idiopathic calcium nephrolithiasis.