Ixion Biotechnology, Inc.

The long-term placement of biomaterials within the urinary tract is limited by the development of encrustation. In a noninfected urinary environment, encrustation often results from the deposition of calcium oxalate on the biomaterial surface. There is an association between the absence of Oxalobacter formigenes, a commensal colonic bacterium capable of degrading oxalate, and calcium oxalate stone formation. This pilot study was designed to evaluate several oxalate-degrading enzymes produced by O. formigenes as a potential biomaterial coating to reduce urinary tract encrustation.

Circular silicone disks of 6-mm diameter were incubated for 48 hours in oxalylcoenzyme A decarboxylase (OXC), formyl-coenzyme A transferase (FRC), and coenzyme A, while control disks were incubated in distilled water. The adsorption of OXC and FRC was assessed using enhanced chemiluminescence (ECL) and atomic force microscopy (AFM). Coated and uncoated disks (20 of each) were implanted in the bladders of 40 female New Zealand White rabbits. After 30 days, the disks were recovered, and the degree of encrustation on the polymer surface was evaluated utilizing dry weight measurement, calcium atomic absorption spectroscopy (AAS), and scanning electron microscopy/energy-dispersive X-ray analysis (SEM/EDX).

Both ECL and AFM demonstrated coating of the silicone disks with OXC and FRC. The mean dry weights of the coated and control disks following explantation were 0.591 +/- 0.438 g and 0.747 +/- 0.428 g, respectively (P = 0.307). The mean weight of calcium on the coated and control disks, as determined by AAS, was 154.1 +/- 96.25 mg and 258 +/- 181.35 mg, respectively (P = 0.008).

The use of oxalate-degrading enzymes from O. formigenes to coat urinary biomaterials represents a novel paradigm to reduce biomaterial-related encrustation. Coating of silicone with oxalate-degrading enzymes from O. formigenes results in a modest reduction in encrustation with no apparent toxicity. Further studies are warranted.

Oxalate degradation by the anaerobic bacterium Oxalobacter formigenes is important for human health, helping to prevent hyperoxaluria and disorders such as the development of kidney stones. Oxalate-degrading activity cannot be detected in the gut flora of some individuals, possibly because Oxalobacter is susceptible to commonly used antimicrobials. Here, clarithromycin, doxycycline, and some other antibiotics inhibited oxalate degradation by two human strains of O. formigenes . These strains varied in their response to gut environmental factors, including exposure to gastric acidity and bile salts. O. formigenes strains established oxalate breakdown in fermentors which were preinoculated with fecal bacteria from individuals lacking oxalate-degrading activity. Reducing the concentration of oxalate in the medium reduced the numbers of O. formigenes bacteria. Oxalate degradation was established and maintained at dilution rates comparable to colonic transit times in healthy individuals. A single oral ingestion of O. formigenes by adult volunteers was, for the first time, shown to result in (i) reduced urinary oxalate excretion following administration of an oxalate load, (ii) the recovery of oxalate-degrading activity in feces, and (iii) prolonged retention of colonization.