Plausible mechanism of melamine-related urinary calculi formation in children: a model description

To explore melamine-related urinary calculi (MRUC) formation mechanism.

Twenty-four MRUC and 19 adult urinary stones (serving as controls) were included. Stone calcium, uric acid, creatinine, creatine, melamine, and cyanuric acid levels were measured quantitatively using flame atomic absorption spectrum and high-performance liquid chromatography, respectively. The structure of extractions from MRUC and controls, artificial melamine-cyanurate assemblies, chromatographic-grade uric acid, creatine, and creatinine were investigated by transmission electron microscope.

Creatinine and creatine levels in MRUC were significant higher than those in controls (P = .000., 008). There were positive correlations between MRUC creatinine level and creatine and uric acid levels (r = .854, 0.846, P = .002, 001). However, no relationship was found between MRUC-children's blood biochemical indexes and stone indexes (P > .05). Compared with noncalcium oxalate-containing MRUC, calcium oxalate-containing MRUC had more melamine and cyanuric acid but without significance (P = .497). No relationship was found between MRUC calcium level and melamine and cyanurate levels (P = .481). Networks only observed in extractions from MRUC core area were very similar to those in artificial melamine-cyanurate assemblies. The single molecule size of creatine, creatinine, and uric acid was less than the mesh observed both in MRUC and artificial melamine-cyanurate assemblies.

This study primarily illustrates existence of networks in MRUC. Smaller molecules in urine, especially acidic molecules, are probably trapped in the mesh within renal tubule provided by melamine-cyanurate assemblies networks based on its molecule sievelike effect and alkaline nature, which induces nucleation in MRUC formation.