Urinary macromolecules are promoters of calcium oxalate nucleation in human urine: turbidimetric studies

Calcium oxalate crystallization in untreated urine, centrifuged and filtered urine and ultrafiltered urine

Centrifuged and filtered urine is often used to evaluate in vitro the crystallization processes of calcium oxalate (CaOx), but even such simple manipulations can alter the composition of the urine, as regards its protein and lipid concentrations. In urine samples taken from 17 normal male adults, we evaluated CaOx crystallization by simultaneously using three different types of urine: untreated (U), centrifuged at 2000 rpm (800

Solid-state 13 C and 31 P NMR analysis of urinary stones

PURPOSE

We investigated the applicability of solid-state nuclear magnetic resonance (NMR) spectroscopy to obtain information about the structure and composition of renal calculi.

MATERIALS AND METHODS

Various types urinary and bladder stones as well as a variety of presumed constituents were investigated using 13C and 31P magic-angle spinning (MAS) solid-state NMR. Different experimental methods were applied to differentiate resonances from crystalline/amorphous (immobile/mobile) as well as protonated/non-protonated moieties. The NMR spectra were analyzed using multiple-component numerical simulations and iterative fitting to identify and quantify the major amorphous or crystalline organic and inorganic components.

RESULTS

By comparison of the NMR spectra for the various renal calculi with those obtained under similar conditions for various presumed components, it is demonstrated possible to unambiguously distinguish and quantify the major amorphous or crystalline organic and inorganic components. The components are identified in terms of their isotropic and anisotropic chemical shielding parameters, protonation or proximity of protons, and the degree of crystallinity/mobility. For the calculi investigated we have detected and quantified calcium oxalate, uric acid, struvite, and calcium phosphates that closely resemble brushite and calcium hydroxyapatite.

CONCLUSIONS

Using 13C and 31P MAS NMR spectroscopy we have been able to account for 60 to 85% (by weight) of the constituents in the calculi investigated. The ability to identify and quantify both crystalline and amorphous components makes solid-state NMR an interesting new method for the compositional analysis of renal calculi.