Therapeutic bubble tea: Preventing the formation of uremic toxins with hydrogel immobilized microbes

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Abstract of the funded parent award or project. Dialysis is the leading therapy when kidneys lose their capacity to remove toxins from the blood. However, dialysis cannot replicate all the functions of healthy kidneys and as a result, patients with advanced chronic kidney disease (CKD) and end-stage kidney disease (ESKD) receiving dialysis continue to experience high rates of residual symptomatology, cardiovascular complications, and mortality. It is increasingly recognized that byproducts of gut microbial metabolism, such as the protein-bound uremic toxins (PBUTs) indoxyl sulfate and para-cresol sulfate, are not effectively removed because they bind tightly to plasma albumin and remain on the blood side of dialysis membranes. The plasma concentrations of gut derived PBUTs has repeatedly been related to cardiovascular morbidity, cognitive decline, and mortality in patients with chronic kidney disease (CKD) and end stage renal disease (ESKD). However, multiple attempts to modify the intestinal microbiome in kidney failure with the use of pre- and pro-biotics have not demonstrated significant clinical benefit to date. In response to this critical unmet need, we propose a radically different (high risk high reward) approach to preventing uremic toxicity from PBUTs based on bioengineering principles and civil and environmental engineering strategies, which have had demonstrated success in drug delivery and wastewater treatment. Our innovation targets the degradation of PBUT precursors (indole and p-cresol) in the gut to prevent sulfonation in the liver to their toxic forms by using bacteria immobilized in hydrogel particles, which can be ingested similar to a bubble tea. Rather than attempting to alter the underlying microbiome, the hydrogel bubbles will provide a protective environment for their cargo to target the colon (primary site of formation and absorption of indole and p-cresol) and will allow the introduced bacteria to exit the digestive system after treatment, hence avoiding a disturbance of the human microbiome. The overarching goal of this application is to leverage these field-leading engineering tools, in order to develop a novel ‘needle free’ technology that ultimately can improve the wellbeing of patients with advanced CKD and ESKD by reducing uremic toxicity. Our strategy is to combine expertise in microbiology, bioreactor technology, mathematical modelling, uremic toxicity, intestinal function, and polymer chemistry in order to prevent formation of PBUTs, rather than trying to eliminate them from the bloodstream. Our approach will utilize polymer and hydrogel engineering to tailor gel beads. The gels will contain immobilized bacteria that will degrade indole and p-cresol to non-toxic, beneficial or probiotic components. The gels will function as protective barrier for the bacteria in the acidic stomach but will allow diffusion of indole and p-cresol into the bead interior once they reach the pH-neutral small and large intestine hence unlocking maximal activity for biological PBUT removal. Kinetic data will be used to run mathematical models to predict bacterial distribution in the beads to direct bioreactor experiments. The bioreactors will simulate the trip through the gut and will mirror the conditions (such as pH, oxygen, nutrients) and transit times of the stomach, small and large intestine. We propose the following specific aims: Specific Aim 1: Enrich a community or pure cultures of microorganisms from environmental sources which are capable of converting indole and p-cresol both aerobically and anaerobically, and to describe their kinetics and identity, and determine intermediate products. Specific Aim 2: Utilize polymer science and hydrogel engineering to design tailored hydrogel beads which enclose uremic toxin degrading microorganisms, and retain structural and functional integrity for passage through the gut, while preserving the functionality of their cargo. Specific Aim 3: Achieve in vitro uremic toxin degradation in a scaled-up gut-like column bioreactor, to inform a patient specific daily bubble tea dose and formulation.