Effects of chondroitin sulphate, human serum albumin and Tamm-Horsfall mucoprotein on calcium oxalate crystallization in undiluted human urine.

The effects of physiological concentrations of chondroitin sulphate, human serum albumin and Tamm-Horsfall mucoprotein on the crystallization of calcium oxalate in undiluted, ultrafiltered human urine were investigated using particle size analysis and scanning electron microscopy. Neither the amount of oxalate required to induce detectable calcium oxalate crystal nucleation nor crystal morphology was affected by the presence of any of these macromolecules. Chondroitin sulphate had no effect on the amount of crystalline material deposited or on the size of the particles precipitated in response to a standard oxalate load. Human serum albumin slightly reduced the size of the crystal aggregates and caused a small increase in the amount of crystal matter precipitated. By contrast, Tamm-Horsfall mucoprotein significantly inhibited crystal aggregation and markedly increased the volume of matter deposited, although this could not be attributed to a promotion of solute precipitation. It was concluded that chondroitin sulphate, human serum albumin and Tamm-Horsfall mucoprotein cannot account for the inhibitory effects of macromolecules with a relative mass greater than 10 kDa in spun and filtered urine. Nonetheless, Tamm-Horsfall mucoprotein is likely to inhibit crystal aggregation in whole urine in vivo and may therefore be instrumental in preventing calcium oxalate stone formation.

Urinary risk factors in calcium oxalate stone disease: comparison of men and women.

The daily excretion of calcium, oxalate, uric acid and glycosaminoglycans, the 24-h urinary pH and volume, and the inhibitory effects of the urines on calcium oxalate crystal growth and aggregation, were measured in 44 normal women, 41 normal men, 32 female stone formers and 63 male stone formers. No significant differences could be found between the normal men and women, the male and female stone formers, or between the patients and their normal controls with regard to the excretion of oxalate and glycosaminoglycans, and the urinary pH. The normal women exhibited significantly lower urinary volumes and excreted less calcium per day than did the other subject groups. The excretion of calcium by the female stone formers was indistinguishable from that of both groups of men. The male and female stone formers did not differ from their corresponding control groups with regard to the excretion of urate, but both groups of male subjects had significantly higher daily urate excretions than did either female category. This was attributed to the greater body weights of the men. There were no discernible differences between any of the subject groups with regard to the inhibitory effects of their urines on calcium oxalate crystal growth, but urines from both groups of female subjects demonstrated a significantly greater inhibitory influence on crystal aggregation than did those of the men. It would appear that the relatively low incidence of uninfected calcium oxalate urolithiasis in women compared with men may be attributable to (a) a lower daily calcium excretion and (b) a higher inhibitory activity of their urines towards crystal aggregation.

Macromolecules inhibit calcium oxalate crystal growth and aggregation in whole human urine.

Removal of macromolecules with Mr greater than 10,000 had no discernible effect on the detectable nucleation of calcium oxalate crystals from undiluted human urine, but promoted the deposition of crystalline material and markedly increased the degree of aggregation of the precipitated crystals. Calcium oxalate crystals and crystal aggregates precipitated from ultrafiltered urine were, on average, 68% larger than those deposited from whole urine. These findings suggest that urinary macromolecules play a key role in preventing calcium oxalate kidney stone disease by inhibiting the formation of large crystal aggregates and thereby reducing the probability of particle retention in the kidney tubules.

The effect of crystalline monosodium urate on the crystallisation of calcium oxalate in whole human urine.

Samples of undiluted urine from normal men were preincubated with crystalline monosodium urate and their metastable limits and responses to a standard oxalate challenge were compared with results obtained from control samples preincubated without urate. Preincubation with urate had no significant effect on the metastable limits of the urines, the morphology, size, or growth rates of calcium oxalate crystals precipitated from the urines, or on the total amount of calcium oxalate deposited in a given time. It was concluded that particulate monosodium urate is unlikely to influence calcium oxalate stone formation by binding to and attenuating the potency of urinary inhibitors.

Inhibitory activity of whole urine: a comparison of urines from stone formers and healthy subjects.

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)

A method for studying inhibitory activity in whole urine.

A method has been developed for inducing and quantifying calcium oxalate crystallisation in whole human urine. The propensity of a given urine to induce crystal formation was described in two ways: its ability to resist spontaneous nucleation of calcium oxalate crystals was assessed by titrating 20 mls of the urine with increasing quantities of sodium oxalate (0-150 mumol) to determine its practical metastable limit. This limit was inversely related to the endogenous calcium concentration; its capacity to inhibit crystal growth was quantified by determining the rate of growth of calcium oxalate crystals precipitated in response to a fixed oxalate load (30 mumol) above its metastable limit. The crystals produced were predominantly calcium oxalate dihydrate and were morphologically identical to those occurring naturally in urine. Citrate had no effect on the metastable limits of 3 urines examined, but markedly inhibited crystal growth. Pyrophosphate had a similar effect on crystal growth, and in addition, raised the metastable limit of one of the urine samples.

Variation in the composition of breast milk during the first 5 weeks of lactation: implications for the feeding of preterm infants.

Milk samples were collected from 10 mothers by a standardised technique with complete expression of both breasts at each feed for 24 hours. Samples were obtained at 8 intervals during the first 36 days of lactation. Analyses were performed for trichloroacetic acid-precipitable protein, total protein, lactose, triglycerides, phospholipids, cholesterol, energy, sodium, potassium, calcium, magnesium, zinc, copper, pH, and osmolality. The results give a comprehensive picture of the development of milk composition from transitional to mature milk. The most striking feature of the results was the high degree of variation observed both between samples from the same mother and between samples from different mothers on the same day of lactation.