High-Throughput in vitro Gel-Based Plate Assay to Screen for Calcium Oxalate Stone Inhibitors

Abstract

<b><i>Objective:</i></b> Kidney stones are a common medical condition that is increasing in prevalence worldwide. Approximately, ∼80% of urinary calculi are composed of calcium oxalate (CaOx). There is a growing interest toward identifying therapeutic compounds that can inhibit the formation of CaOx crystals. However, some chemicals (e.g., antibiotics and bacterial metabolites) may directly promote crystallization. Current knowledge is limited regarding crystal promoters and inhibitors. Thus, we have developed an in vitro gel-based diffusion model to screen for substances that directly influence CaOx crystal formation. <b><i>Materials and Methods:</i></b> We used double diffusion of sodium oxalate and calcium chloride-loaded paper disks along an agar medium to facilitate the controlled formation of monohydrate and dihydrate CaOx crystals. A third disk was used for the perpendicular diffusion of a test substance to assess its influence on CaOx crystal formation. <b><i>Results:</i></b> We confirmed that citrates and magnesium are effective inhibitors of CaOx crystals. We also demonstrated that 2 strains of uropathogenic <i>Escherichia coli</i> are able to promote crystal formation. While the other tested uropathogens and most antibiotics did not change crystal formation, ampicillin was able to reduce crystallization. <b><i>Conclusion:</i></b> We have developed an inexpensive and high-throughput model to evaluate substances that influence CaOx crystallization.

Vitamins as regulators of calcium-containing kidney stones — new perspectives on the role of the gut microbiome

“…The formation of renal calculi is not completely understood, but is predicted to proceed along the path of crystal nucleation, growth, aggregation and fixation within the kidney, where the crystal can further grow into a macroscopic stone 16 . The presence of stone-forming substrates or inhibitors at any point in this process can promote or hamper crystal formation 17 . Randall’s plaques or plugs — which are calcium phosphate deposits found in the papillary interstitium or collecting ducts, respectively — are hypothesized to serve as a nidus for crystal attachment and subsequent stone development 18 .…”