Development of protein extraction method from urinary calculus and identification of protein in calculus extract

Summary Correct extraction of proteins contained within the calculi of urolithiasis patients is important to correctly identify these diverse proteins. Based on protein extraction solutions previously reported, we developed an efficient method to extract protein from the urinary calculus and confirmed the presence of the following proteins in the extract: albumin (Alb), Tamm-Horsfall protein (THP), and IgG, which are all major proteins in urine, and α1-antitrypsin, which is a marker of inflammation. Using this extraction method, we further reveal for the first time that cystatin C, a marker of tubular injury, is also present in the urinary calculus. We observed an abundance of Alb, THP, and IgG proteins in the calculus; in addition, each of these proteins exhibited a variety of molecular weights by western blot, possibly indicating protein polymerization within the calculus material. Overall, these improved methods can contribute to determining urinary stone formation mechanisms.