Salivary and Kidney Stones: Insights into Pathologic Biomineralization
Salivary stones affect 1-2 percent of individuals in the United States and are typically composed of calcium apatite, similar to Randall&[prime]s plaque and phosphate renal calculi. We seek to correlate ultrastructural features, mineral density profiles, and energy dispersive X-ray (EDX) spectroscopy maps between sialoliths, Randall&[prime]s plaque (in the form of phosphate stems on oxalate stones), and phosphate renal calculi.
After obtaining institutional approval, intact submandibular salivary stones (n=5), calcium phosphate kidney stones (n=5), and calcium oxalate stones with an identifiable stem (n=5) were compared using light and scanning electron microscopy techniques (SEM), and X-ray micro-computed tomography (Micro-XCT) techniques. EDX maps and ultrastructural features were correlated to mineral density profiles for all stones.
Sialoliths and phosphate kidney stones visualized by light microscopy and micro-XCT demonstrated a layer-by-layer apposition (Figure 1, A, D, G). EDX confirmed a predominant composition of calcium and phosphorus for stone stems, sialoliths, and phosphate stones (Figure 2, A, C, E). Mineral density profiles were trimodal (low, medium and high) for all stone types (Figure 2, upper B, D, F) and ultrastructural features were similar across stone types at each density region: plate-like formations observed in lower mineral density zones, spherulitic particles of medium mineral density, and packed spheres of higher mineral density. Patterns of elemental Ca and P intensities by EDX correlated with mineral density profiles (Figure 2, lower B, D, F).
Calcium phosphate dispersion in urine and saliva appears to follow a common hierarchical archetype resulting in either nephroliths or sialoliths: spherulitic particles agglomerating into stratified structures. These pathologic biominerals varied in density but had similar elemental composition (Ca and P) indicating that the mechanistic process for biomineralization could be similar between these disparate secretory (salivary) and excretory (kidney) systems.
Funding: NIH: NIDDK/P20DK100863 (to MLS), R21 DK109912 (SPH, MLS), and NIDCR/R01DE022032 (to SPH)