INHIBITION OF GROWTH AND AGGREGATION OF CALCIUM-OXALATE CRYSTALS IN-VITRO - A COMPARISON OF 4 HUMAN PROTEINS

The aim of this study was to compare directly, in the absence of inter fering contaminants, the inhibitory effects of Tamm-Horsfall glycoprot ein (THG), human serum albumin (HSA), alpha(1)-microglobulin and proth rombin fragment 1 (PTF1) on calcium oxalate crystallization. These pro teins have been detected in urinary calculi, and with the exception of THG in calcium oxalate crystals generated from undiluted human urine. THG was isolated from the urine of healthy men, while PTF1 was purifi ed from Prothrombinex-HT, a human blood concentrate; HSA and alpha(1)- microglobulin were obtained from commercial sources. The effects of th ese proteins were determined, separately, at the same final concentrat ion (32 nM) on calcium oxalate crystallization in a seeded, inorganic reaction system, using Coulter Counter and [C-14]oxalate analysis. Ana lysis of [C-14]oxalate data showed that THG, HSA and alpha(1)-microglo bulin had no measurable effect on deposition of calcium oxalate. Howev er, PTF1 significantly inhibited mineral deposition by 19.6%. The aver age size of the particles precipitated was reduced from the control va lue of 8.6 mu m to 7.3, 5.9, 5.6 and 4.0 mu m in the presence of alpha (1)-microglobulin, HSA, THG and PTF1 respectively. These findings were confirmed by scanning electron microscopy, which also revealed that t he smaller particles deposited in the presence of the proteins resulte d from reduced crystal aggregation rather than a decrease in the size of the individual crystals. It was concluded that, on a molar basis, P TF1 is a more potent inhibitor of calcium oxalate crystal aggregation than THG, HSA and alpha(1)-microglobulin. Moreover, unlike those prote ins it significantly inhibits the deposition of calcium oxalate. These findings have implications for the putative role of urinary proteins in the formation of calcium oxalate stones.