Natural Abundance ⁴³Ca NMR as a Tool for Exploring Calcium Biomineralization: Renal Stone Formation and Growth

Renal stone diseases are a global health issue with little effective therapeutic recourse aside from surgery and shock-wave lithotripsy, primarily because the fundamental chemical mechanisms behind calcium biomineralization are poorly understood. In this work, we show that natural abundance 43 Ca NMR at 21.1 T is an effective means to probe the molecular-level Ca 2+ structure in oxalate-based kidney stones. We find that the 43 Ca NMR resonance of an authentic oxalate-based kidney stone cannot be explained by a single pure phase of any common Ca 2+ -bearing stone mineral. Combined with XRD results, our findings suggest an altered calcium oxalate monohydrate-like Ca 2+ coordination environment for some fraction of Ca 2+ in our sample. The evidence is consistent with existing literature hypothesizing that nonoxalate organic material interacts directly with Ca 2+ at stone surfaces and is the primary driver of renal stone aggregation and growth. Our findings show that 43 Ca NMR spectroscopy may provide unique and crucial insight into the fundamental chemistry of kidney stone formation, growth, and the role organic molecules play in these processes.