Development of Mucin Analogues to Inhibit the Growth of Calcium Oxalate Kidney Stones

Abstract

Kidney stones disease (KSD) is infamous for the morbidity it renders to an afflicted individual by causing intense pain through abrasions the urinary tract during stone passage and/or by causing increased fluid pressure caused by outflow blockage. Symptomatic kidney stones are typically treated through lithotripsy, in which stones are broken into fragments which are small enough for active retrieval or spontaneous passage. However, many individuals experience incomplete passage and some fragments remain in the kidney indefinitely. These residual stone fragments (RSF) serve as nuclei for further stone growth and cause KSD recurrence. RSFs can grow through two mechanisms: 1) calcium and other ionic stone precursors can directly crystalize on the surface of a fragment, and 2) small urinary crystallites become coated in an adhesive layer of urinary protein and adhere to the RSF. While dietary changes and a variety of medications have been shown to be effective at inhibiting this growth, and ultimately disease recurrence, a lack of patient compliance severely limits the efficacy of these approaches. In this work, we designed an analogue of mucins, biological surface coatings employed by the body as surface protectants and lubricants, to adsorb to the surface of RSFs and inhibit both mechanisms of stone growth. To do so, we performed phage display to identify peptides which bind to kidney stones. We designed genes for these peptides and expressed them as fusion peptides with elastin-like polypeptides to facilitate expression. We also used a calcium depletion assay to probe their ability to inhibit growth of kidney stone. The peptides discovered by phage display were unable to inhibit growth of RSFs through calcium adsorption. Instead, we used oligoanionic binders to synthesize analogue mucins composed of elastin-like polypeptides and synthetic polymers. We characterized these mucin analogues at each step using a combination of NMR, IR, and GPC when appropriate. Stone-targeted mucin analogues successfully inhibited the growth of calcium oxalate monohydrate stone models. Finally, to monitor adsorption of these mucin analogues to model kidney stones, we functionalized sensors with calcium oxalate monohydrate using polyacrylate as an adhesive layer. In sum, this work explores the ability to synthesize mucin analogues to inhibit recurrent kidney stone disease and have potential to shift the paradigm of kidney stone treatment.