INTER-ALPHA-INHIBITOR IN URINE AND CALCIUM-OXALATE URINARY CRYSTALS

Objective To determine which chains of inter-alpha-inhibitor (I alpha I) are present in urine and whether they are also found in calcium oxa late (CaOx) crystals generated in human urine. Materials and methods F resh urine specimens were collected from five five women and live men with no previous history of stone disease, An aliquot of each urine wa s retained for analysis, the remainder treated With a standard load of oxalate and the CaOx crystals precipitated from each specimen deminer alized with ethylenediamine tetracetic acid, The resulting organic ext racts from crystals and their corresponding urine samples were subject ed to sodium dodecyl sulphate gel electrophoresis analysis and Western blotting using a commercial polyclonal antibody to I alpha I. Results Heavy chain 1 (H1) and 2 (H2) of I alpha I were commonly found in eve ry urine sample, and in the CaOx crystals precipitated from those urin e samples. Several protein bands were visible in urine samples from bo th sexes in the molecular mass range 25-70 kDa, which may be bikunin o r its fragments. As well as H1 and H2, the crystals from both sexes co ntained a protein band at approximate to 33 kDa. In many cases there a ppeared tu be no direct relationship between the proteins detected ill the crystals and the urine samples from which they were derived, whic h probably reflects the well known instability of I alpha I and the oc currence of a range of bikunin fragments in urine, Conclusion These re sults show for the first time that HI and H2 are present in human urin e and urinary CaOx crystals, that the bikunin chain of I alpha I is no t the only part of the molecule capable of participating in CaOx cryst allization in urine, and in theory at least, in the regulation of crys tallization events in stone formation, It is also apparent that signif icant fragmentation of I alpha I occurs both in vivo and in vitro, and this must be considered in any study attempting to elucidate the infl uence of this protein in the formation of CaOx stones.