Hippuric Acid as a Modifier of Calcium Oxalate Crystallisation

Prevalence and chemical composition of uroliths in fattening pigs in Belgium

The present study investigated the prevalence of uroliths in fattening pigs and assessed the composition of these urinary tract concrements. In total, 2,432 urinary bladders were sampled in the slaughterhouse and checked for abnormal content. Urinary samples were analysed microscopically, and samples of the urinary bladder wall were tested for histological signs of inflammation. The composition of the concrements was examined by infrared spectrophotometry. Macroscopic and microscopic abnormalities were detected in 8.4% and 52.8% of the samples respectively. Magnesium ammonium phosphate (struvite), calcium oxalate dihydrate (COD), calcium carbonate (calcite), calcium oxalate monohydrate (COM) and amorphous crystals were detected. Analysis of stones showed COD in all samples in different proportions. The calcium content of examined stones was always considerable (up to 34%), in contrast to the magnesium content which represented max 1.9%. Struvite was found in one third of the samples, but was never part of stones and grit. COD crystals were the second most common microscopic crystal. These COD crystals and some COD stones had a rectangular shape, and therefore, they can be harmful to the bladder mucosa. In conclusion, uroliths are present in a large proportion of male fattening pigs, and consequently, urinary concrements pose a life-threatening risk for urethra obstruction in male pigs. Further research is warranted to identify potential risk factors for urolithiasis and microscopic crystals.

Impact of various modifiers on calcium oxalate crystallization

OBJECTIVE

This work focuses on the behavior of in vitro calcium oxalate crystallization. The effects of several compounds on the kinetics of calcium oxalate crystallization were examined.

METHODS

Rates of nucleation and aggregation of calcium oxalate crystals were derived from 30-min time-course measurements of optic density at 620 nm after mixing solutions containing calcium chloride and sodium oxalate at 37 degrees C, pH 5.7. The maximum increase of optic density with time, termed S(N), mainly reflects maximum rate of formation of new particles and thus crystal nucleation. After equilibrium has been reached, optic density decreases. No new particles were formed due to crystal aggregation. S(A) (the maximum slope of decrease of optic density at 620 nm with time, representing crystal aggregation) is derived from the maximum decrease in optic density.

RESULTS

Among the modifiers studied, citrate decreased both S(N) and S(A) (P < 0.001). Magnesium was also found to inhibit the rate of nucleation and crystal aggregation, but it appeared in a non-concentrated manner. Nucleation and aggregation inhibition ratios were related inversely to concentration of albumin (P < 0.001).

CONCLUSION

The growth and agglomeration of calcium oxalate crystals are differently modulated by various compounds. The treatments aiming at inhibiting crystallization of calcium oxalate can be better defined by these findings. And new treatment modalities can be developed.