The influence of trace elements on urinary stone formation

J. R. GUERRA-LÓPEZ; J. A. GÜIDA; R. GARCÍA; C. O. DELLA VÉDOVA; R. GODDARD; G. PUNTE

Aguas de Lindoia, S, Brasil

Congreso; Annual Meeting of the Brazilian Society of Biochemistry and Molecular Biology (SBBq; 2008

Urinary calculi are the symptom of a number of health disorders, which lead to the formation of precipitated solids in the urinary tract. Knowledge of their composition is an important, and sometimes the only, tool to identify disorders origin. The mineral constituents of urinary calculi can be divided in two major groups: organic and inorganic compounds. From these, calcium oxalate, calcium phosphate and uric acid are the principal ones. The significance and role of trace elements have been the subject of many investigations. However, few studies have established relationships between metals presence and stones components. In the present work, the effects of trace elements on urinary stone formation are debated from the results obtained of in vitro studied and the characterization of urinary calculi stone. The mineral composition of 20 renal stones was analyzed by powder x ray diffraction (XRD), Infrared spectroscopy (IR) and X-ray Fluorecence. All stones were collected from patients treated at different hospitals of La Plata and Lujan cities, Argentina. The kinetic experiments were conducted as described in previous works. Aliquots of phosphates synthesized were dispensed into a water bath at 37 ºC. At timed intervals, samples were removed from the bath filtrated and dried at 100 ºC for 24 hours. The composition of the products was checked by determination of Ca, Ni, P and Zn content. Ca, Zn and Ni were determined by atomic absorption spectrometry and phosphorus was determined spectrophotometrically. Mineral standards of ACP, CaHap, MgNH4PO4·H2O were prepared according to different methods reported in the literature and analyzed by FTIR and Drx as the rest of samples studied. Different trace metals have been identified in the stone; the more abundant were Zn, Ni, Sr and Fe. According to M. Dauton et al., the trace elements were detected principally in calcium phosphate stones. However, it should be noted the levels of Ni2+ in the analyzed samples and the absence of this mineral in other reports. Furthermore, the effects of two of these cations on the formation of mineral stones were also studied in in-vitro systems. Different types of calcium phosphate phases (dicalcium phosphate dehydrated (DCPD), hydroxyapatite (CaHap),betha-tricalcium phosphate (betha –TCP) and MNH4PO4·H2O (M = Ni, Zn) were precipitated from solutions contained increasing concentration of zinc (Zn) or nickel (Ni) cations. In the cases of calcium phosphate synthesized in presence of nickel ions, the formation of dicalcium phosphate dehydrated and amorphous compounds were promoted depending of pH and temperature. On the other hand, the presence of zinc in solution affected the type and amount of calcium phosphate phase formed in a different way. Zn at lower concentration promoted the formation of Zn-substituted tricalcium phosphate betha –TCP and at higher concentration promoted the formation of a mixture of phases or CaHap depending on the pH and temperature. The chemical and structural analyses of synthetic and biological apatites have been shown to easily incorporate heavy metal. However, it should be noticed that in both materials zinc incorporation is greater than that of Ni. In both cases, the incorporation of these cations takes place at Ca(2) site of the stoichiometric CaHap. This assumption is principally based on the noticeable modifications observed in the signals coming from the OH- groups, which belong to the coordination sphere of calcium ions at Ca(2) site. Ca2+ substitution at this site by a small ion such as Ni2+ allows water to replace and/or bond to OH- ions and induces changes in the vibrational spectra and a loss of crystallinity that increases with Ni2+ or Zn2+ content. The chemicals analysis of different calculi evidence the presence of trace metal in their structure, the elements founds in most appreciable concentration were Zn, Ni, Sr and Fe. This result was most evident in phosphate stone. From the combined results of the techniques employed we have determined that the presence of Ni2+ and Zn2+ ions affected the type and amounts of calcium phosphate phases formed. The present results suggest that the presence of trace elements may modify the formation of urinary calcium phosphate stone.