Increased urinary excretion of lipids by patients with kidney stones

Objective. To test the hypothesis that patients with calcific kidney stones (stone formers) excrete more lipids and cell membranes in their urine than do normal individuals. Patients, subjects and methods. Lipids were isolated from the urine of patients with calcific stones (four women and six men, age range 28-69 years) and from normal subjects (three men and three women, age range 31-54 years). Different phospholipids, neutral lipids and glycolipids were identified using thin layer chromatography and individual lipids were characterized by several assays after scraping the spots from the plates, or by densitometry. Results. Stone formers excreted more lipids and acidic phospholipids than did normal individuals; the urinary excretion of glycolipid, cholesterol and cholesterol esters was also increased. Conclusions. The greater excretion of lipids may reflect the increased turnover of cells in the tubular epithelium and sloughing of cells into the urine in response to a challenge by oxalate and calcium oxalate crystals. Acidic phospholipids from cellular membranes of the sloughed epithelial cells may be involved in crystal nucleation and retention within the kidneys and thus the initial development of stone nidus and the continued growth thereafter.