Calcium oxalate crystallisation kinetics and the effects of calcium and gamma-carboxyglutamic acid.
gamma-carboxyglutamic acid (GLA) is an amino acid with a high affinity for calcium. It is found in urine both as the free amino acid and incorporated into proteins such as osteocalcin. Free and bound GLA have been reported to be found at higher concentrations in the urine of stone formers than controls. We have investigated the effect of GLA and calcium, at physiological levels, on the crystallisation of calcium oxalate using a mixed suspension mixed product removal continuous crystalliser. GLA caused very significant changes in the crystallisation kinetics, but the effect was dependent on the calcium concentration. At 4 mM calcium, GLA decreased the growth rate and increased the nucleation rate; at 12 mM the reverse occurred. At all concentrations of calcium tested, GLA caused a significantly increased crystal mass to be produced. Our evidence supports the hypothesis that GLA modifies calcium oxalate crystallisation and could be a promoter of stone formation in vivo, particularly at moderately elevated levels of calcium excretion.
Nishio
S
S
Department of Urology, University Hospital of South Manchester.
Kavanagh
J P
JP
Faragher
E B
EB
Garside
J
J
Blacklock
N J
NJ
D015055:1-Carboxyglutamic Acid / Q000737:chemistry*; D002118:Calcium / Q000737:chemistry*; D002129:Calcium Oxalate / Q000737:chemistry*; D003460:Crystallization; D014556:Urine
D002129:Calcium Oxalate; D015055:1-Carboxyglutamic Acid; D002118:Calcium