Sequential analysis of kidney stone formation in the Aprt knockout mouse

Background. We have previously shown that, as in human adenine phosphoribos yltransferase (APRT) deficiency, Aprt knockout mice form 2,8-dihydroxyadeni ne (DHA) renal stones. The disease develops earlier and is more severe in m ale than in female mice. To examine the biological bases for these differen ces, the area occupied by DHA crystals was quantified in kidney sections fr om male and female mice (strain 129) aged one day to eight months and this parameter was correlated with changes in renal histopathology. Aprt heteroz ygous and wild-type mice were used as controls. Methods. Following anesthesia, the left kidney was removed and immediately frozen in dry ice. Unstained cryosections were examined by polarized light to determine total area of birefringent particles. The right kidney was per fused and embedded in plastic, and stained sections were viewed by light mi croscopy to examine the histopathology and to determine the location of the birefringent particles. A pathological score was assigned to the histologi cal findings. The scores from the right kidney were compared with crystal/p article area in the left kidney, and the data were analyzed using two-way a nalysis of variance. The chemical composition of the particles was determin ed by x-ray diffraction analysis. Several stone fragments from the bladder were also examined by scanning electron microscopy (SEM). Results. Crystals were detected in kidney sections from one-to two-day-old Aprt knockout mice. The crystal burden remained low in both sexes throughou t the study except in males at the 120- to 240-day period. Furthermore, the re was a substantial degree of renal pathology, primarily seen as interstit ial fibrosis, in those males with a very high level of stone formation. The crystalline material was identified as 6-amino-2,8(3,9)-purine dione, a ta utomeric form of DHA. SEM indicated that the crystals were spherical, with a diameter of 10 to 20 mum. Tissue staining and fixation procedures dramati cally reduced the amount of birefringent material in kidney sections. Aprt heterozygotes of both sexes had low levels of crystalline material in the k idneys and no pathology. Birefringent material or pathological changes were not seen in kidneys from wild-type mice. Conclusions. Both male and female Aprt knockout mice accumulate DHA. Howeve r, the area occupied by DHA crystals was significantly greater in 120- to 2 40-day-old males compared with the females of similar age. Also, substantia l renal pathology was detected in kidneys of male mice that had very high l evels of stone material.