Grohe Bernd, Chan Brian P H, Sørensen Esben S, Lajoie Gilles, Goldberg Harvey A, Hunter Graeme K
Department of Dentistry, Schulich School of Medicine and Dentistry, University of Western Ontario, London, ON, N6A 5C1, Canada.
Urol Res. 2011 Oct;39(5):327-38. doi: 10.1007/s00240-010-0360-8. Epub 2011 Jan 14.
Osteopontin (OPN) is one of a group of proteins found in urine that are believed to limit the formation of kidney stones. In the present study, we investigate the roles of phosphate and carboxylate groups in the OPN-mediated modulation of calcium oxalate (CaOx), the principal mineral phase found in kidney stones. To this end, crystallization was induced by addition of CaOx solution to ultrafiltered human urine containing either human kidney OPN (kOPN; 7 consecutive carboxylates, 8 phosphates) or synthesized peptides corresponding to residues 65-80 (pSHDHMDDDDDDDDDGD; pOPAR) or 220-235 (pSHEpSTEQSDAIDpSAEK; P3) of rat bone OPN. Sequence 65-80 was also synthesized without the phosphate group (OPAR). Effects on calcium oxalate monohydrate (COM) and dihydrate (COD) formation were studied by scanning electron microscopy. We found that controls form large, partly intergrown COM platelets; COD was never observed. Adding any of the polyelectrolytes was sufficient to prevent intergrowth of COM platelets entirely, inhibiting formation of these platelets strongly, and inducing formation of the COD phase. Strongest effects on COM formation were found for pOPAR and OPAR followed by kOPN and then P3, showing that acidity and hydrophilicity are crucial in polyelectrolyte-affected COM crystallization. At higher concentrations, OPAR also inhibited COD formation, while P3, kOPN and, in particular, pOPAR promoted COD, a difference explainable by the variations of carboxylate and phosphate groups present in the molecules. Thus, we conclude that carboxylate groups play a primary role in inhibiting COM formation, but phosphate and carboxylate groups are both important in initiating and promoting COD formation.
骨桥蛋白（OPN）是尿液中发现的一组蛋白质之一，据信它们可限制肾结石的形成。在本研究中，我们研究了磷酸基团和羧酸基团在OPN介导的草酸钙（CaOx）调节中的作用，草酸钙是肾结石中主要的矿物相。为此，通过向含有人类肾脏OPN（kOPN；7个连续的羧酸盐，8个磷酸盐）或与大鼠骨OPN的65-80位残基（pSHDHMDDDDDDDDDGD；pOPAR）或220-235位残基（pSHEpSTEQSDAIDpSAEK；P3）相对应的合成肽的超滤人尿中添加CaOx溶液来诱导结晶。65-80序列也在没有磷酸基团的情况下合成（OPAR）。通过扫描电子显微镜研究了对一水草酸钙（COM）和二水草酸钙（COD）形成的影响。我们发现对照组形成大的、部分共生的COM片状晶体；从未观察到COD。添加任何一种聚电解质都足以完全防止COM片状晶体的共生，强烈抑制这些片状晶体的形成，并诱导COD相的形成。对COM形成影响最强的是pOPAR和OPAR，其次是kOPN，然后是P3，这表明酸度和亲水性在聚电解质影响的COM结晶中至关重要。在较高浓度下，OPAR也抑制COD的形成，而P3、kOPN，特别是pOPAR促进COD的形成，这种差异可以通过分子中存在的羧酸盐和磷酸基团的变化来解释。因此，我们得出结论，羧酸盐基团在抑制COM形成中起主要作用，但磷酸基团和羧酸盐基团在启动和促进COD形成中都很重要。
