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The external appearance of urinary calcium oxalate (CaOx) crystals suggests that they are solid, homogeneous structures, despite their known association with proteins. Our aim was to determine whether proteins comprising the organic matrix of CaOx crystals are superficial or intracrystalline in order to clarify the role of urinary proteins in the formation of kidney stones. CaOx crystals were precipitated from centrifuged and filtered, or ultrafiltered, healthy human urine. They were then treated with dilute NaOH to remove bound proteins, partially demineralized with EDTA, or fractured and subjected to limited proteolysis before examination by low-resolution scanning electron microscopy or field emission scanning electron microscopy. Crystals precipitated from centrifuged and filtered urine had a complex interior network of protein distributed throughout the mineral phase, which appeared to comprise closely packed subcrystalline particles stacked in an orderly array among an amorphous organic matrix. This ultrastructure was not evident in crystals deposited in the absence of macromolecules, which were completely solid. This is the first direct evidence that crystals generated from cell-free systems contain significant amounts of protein distributed throughout a complex internal cribriform ultrastructure. Combined with mineral erosion in the acidic lysosomal environment, proteins inside CaOx crystals would render them susceptible to attack by urinary and intracellular renal proteases and facilitate their further dissolution or disruption into small particles and ions for removal by exocytosis. The findings also have broader ramifications for industry and the materials sciences, as well as the development and resorption of crystals in biomineralization systems throughout nature., (Copyright 2001 Academic Press.)

The ultimate aim of our research is to understand the role of macromolecules in the formation of human kidney stones, particularly their interactions with calcium oxalate (CaOx) crystals. The invariable association of stones with proteins raises the possibility that proteins play a role in their formation, similar to the role of proteins in healthy biomineralization. Do these proteins induce mineralization? Are they merely a response to the disease process? Or are they protective molecules that were overwhelmed by mineral supersaturation? A protein of particular interest is fragment 1 (F1) of prothrombin. We have shown that mRNA for prothrombin is present in the kidney. Because the F1 fragment of prothrombin present in urine is slightly different from that found in the blood, we refer to this protein as "urinary prothrombin fragment 1" (UPTF1). Available evidence suggests that the kidney manufactures the protein for protection against stone disease and that the protein has a directive role in stone formation. We now have evidence that proteins are interred within CaOx crystals precipitated from human urine, where it is distributed in continuous channels. These proteins could facilitate crystal deconstruction and removal after attachment to the renal epithelium and endocytosis. We suspect that the formation of CaOx crystals in the urine is a normal process designed to permit harmless disposal of an excess of calcium, oxalate, or both. The incorporation of proteins provides a second line of defense against stone formation by enabling the destruction and removal of retained crystals. Understanding the basic molecular strategies by which plants produce protein-containing CaOx crystals may provide insight into human CaOx stone formation.

The evidence invariably cited to support the suspicion that urinary urate is a predisposing factor in calcium oxalate (CaOx) stone formation is critically reviewed. Analysis of the relevant literature shows that speculation is based on the clinical impression that CaOx stone-formers appear to excrete more urate than do normal subjects, and that allopurinol reduces the rate of CaOx stone recurrences. On balance, this is sufficient to suggest that a high urinary excretion of urate promotes CaOx stone formation. However, in the past, evidence to disclose the mechanism by which urate could exert this effect has been largely shrouded in confusion and controversy. The evidence for two theories that have dominated thinking in this area are reviewed and new findings are reported that indicate that neither can account for the purported effect of urate. It is concluded that dissolved urate in urine, at normal physiological pH values, directly provokes CaOx crystal nucleation by the phenomenon of salting-out. The possibility that urate promotes CaOx stone formation is further strengthened by its ability to increase significantly the amount of CaOx precipitated from solution and to cause the aggregation of individual crystals into large clusters. Future avenues of investigation that should assist in the formulation of diagnostic and therapeutic guidelines are presented.

The inhibitory activity of whole urines from 32 healthy subjects and 50 calcium oxalate renal stone formers was assessed in terms of their ability to withstand increasing quantities of oxalate before undergoing spontaneous nucleation of calcium oxalate, and their response to a standard 30-mumol challenge of oxalate above their measured metastable limits. The concentrations of calcium (p less than 0.05), oxalate (p less than 0.05), urate (p less than 0.01) and glycosaminoglycans (p less than 0.005) were significantly lower in the stone formers than in the controls and were associated with a significantly higher 24-h urinary volume (p less than 0.001). The majority of urine samples precipitated envelope crystals of calcium oxalate dihydrate, while the remainder precipitated the monohydrate. A significantly (p less than 0.02) greater proportion of the urines from stone formers than from controls deposited calcium oxalate monohydrate, and this was attributed to a lower concentration of calcium in these urines. The minimum amounts of oxalate necessary to induce crystal nucleation did not differ between the two groups, but when the measured metastable limits were expressed as the product of the total (i.e. endogenous + that added to induce nucleation) concentrations of oxalate and calcium at which precipitation occurred, then these limits were significantly lower (p less than 0.05) in the stone formers than in the healthy subjects. However, when the metastable limits of a subgroup of stone formers and controls matched for 24-h urinary volume and calcium and urate concentrations were compared, no differences between the groups could be discerned.(ABSTRACT TRUNCATED AT 250 WORDS)

The inhibitory effect of urine from 64 male stone-formers and from 42 normal men on the growth and aggregation of calcium oxalate crystals was measured. The degree of inhibition of each urine specimen was related to the endogenous concentrations of glycosaminoglycans, uric acid, and creatinine, and to the ratio of glycosaminoglycan to uric acid concentrations. No significant difference between the two groups of subjects with regard to the effect of urine on crystal growth or aggregation was found. Inhibitory activity was found to be significantly correlated with the urinary concentration of glycosaminoglycans, creatinine and uric acid, but not to the ratio of glycosaminoglycan/uric acid concentrations. It was concluded that urinary inhibitory activity depends only partly on the endogenous concentration of glycosaminoglycans and that the inhibitory activity of these compounds in vitro does not depend on the associated level of uric acid in the urine.

A review of the urographic findings in 200 patients with renal colic due to urolithiasis demonstrated radiological evidence of medullary sponge kidney in 34, an incidence of 17%. In the majority, the diagnosis was readily made and the changes were bilateral and extensive. This relatively high incidence suggests that medullary sponge kidney may be a contributing factor in a population already predisposed to calculus formation because of other factors such as diet and dehydration.

In 416 patients with renal and ureteric calculi other than large staghorns we found that when it was possible to identify the calyx of origin of the stones, the lower poles were involved in 36-6% of males and 40-4% of females. In the follow up of the 115 lower poles originally containing stones the recurrence rate was 17% in those who were merely observed, 56% in those treated by pyelo- or nephrolithotomy, and zero in those treated by partial neprectomy. But when these cases were looked at more closely it was found that recurrences were virtually confined to lower poles which had originally harboured more than one stone, while in those with single stones to start with, the recurrence rate was not significantly different in either of these three groups. Partial nephrectomy should therefore be reserved for selected cases where the stones are originally multiple, or where the lower pole has been severely damaged. It is not necessary for small and single calyceal calculi.

The effects of pyrophosphate, citrate, magnesium, heparin and chondroitin sulphate on the growth and aggregation of calcium oxalate crystals were measured at concentrations likely to be found in 1% urine. The degrees of inhibition of growth and of aggregation caused by these compounds were related to the effects of normal 1% urine on these processes. It was concluded that chondroitin sulphate is responsible for the major portion of the inhibitory effect of urine on crystal aggregation, but that the effect on crystal growth is probably due to the additive or synergistic effects of a number of urinary constituents.

Saline bladder washouts were obtained from 31 normal patients undergoing routine cystoscopy. A urine control was prepared by diluting a urine sample to the same creatinine concentration as the bladder washout. The inhibitory activities of the samples were then measured in a calcium oxalate seeded crystallization system. Washouts from the first 9 patients inhibited crystal aggregation more strongly than did the controls. This was attributable to microscopic blood contamination, since in the following 22 subjects, in whom contamination was excluded by the use of sensitive haemoglobin test strips, no increase in inhibition of aggregation was seen. The inhibition of calcium oxalate crystal growth by the washouts was consistently greater than that by the urine controls (p less than 0.05). This suggests that the bladder mucosa is a source of inhibitor(s) of crystal growth but not crystal aggregation.

Stones smaller than 5 mm in diameter seldom need any operation other than the use of the stone-basket. Stones larger than 10 mm in diameter usually need an operation, are more often accompanied by infection, and have a higher recurrence rate. The size of the stone is unrelated to the level of urinary calcium or to body surface area. In planning the follow-up of patients with calculi the size of the first stone is a useful guide.