Because of its ability to inhibit the growth of calcium oxalate monohydrate (COM) crystals, citrate plays an important role in preventing the formation of kidney stones. To determine the mechanism of inhibition, we studied the citrate-COM interaction using a combination of microscopic and simulation techniques. Using scanning confocal interference microscopy, we found that addition of citrate preferentially inhibits crystal growth in <100> and, to a lesser extent, <001> directions, suggesting that citrate adsorbs to the faces of COM in the order {100} > {121} > {010}. Scanning electron microscopy showed that the resulting crystals are plate shaped, with large {100} faces and rounded ends. Molecular-dynamics simulations predicted, however, that citrate interacts with the faces of COM in a different order, i.e. {100} > {010} > {121}. Our simulations showed that citrate molecules align with the rows of Ca2+ ions on the {010} face but do not form close contacts, presumably because of electrostatic repulsion by the carboxylate groups that project from the Ca2+-rich plane. We propose that this weak interaction is responsible for citrate’s limited inhibition of COM growth in <010> directions. Overall, these findings indicate that electrostatic interactions with the Ca2+-rich faces of COM crystals are responsible for the growth-modulating properties of citrate.

Keywords:
Calcium oxalate monohydrate, Citrate, Molecular dynamics, Kidney stones, Biomineralization
1.
Grohe, B., J. O’Young, A. Ionescu, G. Lajoie, K.A. Rogers, M. Karttunen, H.A. Goldberg, G.K. Hunter (2007) Control of calcium oxalate crystal growth by face-specific adsorption of an osteopontin phosphopeptide. J Am Chem Soc 129: 14946–14951.
2.
Grohe, B., A. Taller, P.L. Vincent, L.D. Tieu, K.A. Rogers, A. Heiss, E.S. Sorensen, S. Mittler, H.A. Goldberg, G.K. Hunter (2009) Crystallization of calcium oxalates is controlled by molecular hydrophilicity and specific polyanion-crystal interactions. Langmuir 25: 11635–11646.
3.
Guerra, A., T. Meschi, F. Allegri, B. Prati, A. Nouvenne, E. Fiaccadori, L. Borghi (2006) Concentrated urine and diluted urine: the effects of citrate and magnesium on the crystallization of calcium oxalate induced in vitro by an oxalate load. Urol Res 34: 359–364.
4.
Hallson, P.C., G.A. Rose, S. Sulaiman (1983) Raising urinary citrate lowers calcium oxalate and calcium phosphate crystal formation in whole urine. Urol Int 38: 179–181.
5.
Hess, B., S. Jordi, L. Zipperle, E. Ettinger, R. Giovanoli (2000) Citrate determines calcium oxalate crystallization kinetics and crystal morphology-studies in the presence of Tamm-Horsfall protein of a healthy subject and a severely recurrent calcium stone former. Nephrol Dial Transplant 15: 366–374.
6.
Heywood, B.R., N.H.C. Sparks, R.P. Shellis, S. Weiner, S. Mann (1990) Ultrastructure, morphology, and crystal growth of biogenic and synthetic apatites. Connect Tissue Res 25: 103–119.
7.
Hunter, G.K., B. Grohe, S. Jeffrey, J. O’Young, E.S. Sorensen, H.A. Goldberg (2009) Role of phosphate groups in inhibition of calcium oxalate crystal growth by osteopontin. Cells Tissues Organs 189: 44–50.
8.
Hunter, G.K., J. O’Young, B. Grohe, M. Karttunen, H.A. Goldberg (2010) The flexible polyelectrolyte hypothesis of protein-biomineral interaction. Langmuir 26;18639–18646.
9.
Jung, T., X. Sheng, C.K. Choi, W.S. Kim, J.A. Wesson, M.D. Ward (2004) Probing crystallization of calcium oxalate monohydrate and the role of macromolecule additives with in situ atomic force microscopy. Langmuir 20: 8587–8596.
10.
Kok, D.J., S.E. Papapoulos, O.L. Bijvoet (1986) Excessive crystal agglomeration with low citrate excretion in recurrent stone-formers. Lancet 1: 1056–1058.
11.
Kumar, V., J.C. Lieske (2006) Protein regulation of intrarenal crystallization. Curr Opin Nephrol Hypertens 15: 374–380.
12.
Langdon, A., G.R. Wignall, K. Rogers, E.S. Sorensen, J. Denstedt, B. Grohe, H.A. Goldberg, G.K. Hunter (2009) Kinetics of calcium oxalate crystal growth in the presence of osteopontin isoforms: an analysis by scanning confocal interference microscopy. Calcif Tissue Int 84: 240–248.
13.
Mattle, D., B. Hess (2005) Preventive treatment of nephrolithiasis with alkali citrate – a critical review. Urol Res 33: 73–79.
14.
Pak, C.Y. (1991) Citrate and renal calculi: new insights and future directions. Am J Kidney Dis 17: 420–425.
15.
Qiu, S.R., A. Wierzbicki, C.A. Orme, A.M. Cody, J.R. Hoyer, G.H. Nancollas, S. Zepeda, J.J. De Yoreo (2004) Molecular modulation of calcium oxalate crystallization by osteopontin and citrate. Proc Natl Acad Sci USA 101: 1811–1815.
16.
Rodgers, A., S. Allie-Hamdulay, G. Jackson (2006) Therapeutic action of citrate in urolithiasis explained by chemical speciation: increase in pH is the determinant factor. Nephrol Dial Transplant 21: 361–369.
17.
Ryall, R.L., R.M. Harnett, V.R. Marshall (1981) The effect of urine, pyrophosphate, citrate, magnesium and glycosaminoglycans on the growth and aggregation of calcium oxalate crystals in vitro. Clin Chim Acta 112: 349–356.
18.
Sakhaee, K., J.R. Poindexter, C.S. Griffith, C.Y. Pak (2004) Stone forming risk of calcium citrate supplementation in healthy postmenopausal women. J Urol 172: 958–961.
19.
Sheng, X., T. Jung, J.A. Wesson, M.D. Ward (2005) Adhesion at calcium oxalate crystal surfaces and the effect of urinary constituents. Proc Natl Acad Sci USA 102: 267–272.
20.
Shirane, Y.K., S. Kagawa (1993) Scanning electron microscopic study of the effect of citrate and pyrophosphate on calcium oxalate crystal morphology. Journal of Urology 150: 1980–1983.
21.
Taller, A., B. Grohe, K. Rogers, H.A. Goldberg, G.K. Hunter (2007) Specific adsorption of osteopontin and synthetic polypeptides to calcium oxalate monohydrate crystals. Biophys J 93: 1768–1777.
22.
Tazzoli, V., C. Domenghetti (1980) The crystal structures of whewellite and weddellite: re-examination and comparison. Am Mineralogist 65: 327–334.
23.
Weast, R.C., M.J. Astle, W.H. Beyer (eds) (1988) Handbook of Chemistry and Physics, ed 69. Boca Raton, CRC Press.
24.
Weaver, M.L., S.R. Qiu, J.R. Hoyer, W.H. Casey, G.H. Nancollas, J.J. De Yoreo (2006) Improved model for inhibition of pathological mineralization based on citrate-calcium oxalate monohydrate interaction. Chemphyschem 7: 2081–2084.
25.
Zerwekh, J.E., C.V. Odvina, L.A. Wuermser, C.Y. Pak (2007) Reduction of renal stone risk by potassium-magnesium citrate during 5 weeks of bed rest. J Urol 177: 2179–2184.
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2011
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