Although the first written descriptions of gout date back over 4000 years, it wasn’t until the mid nineteenth century that excess uric acid in the blood leading to needle-like urate deposits in joint spaces was recognised to be the cause of this painful condition. Nowadays, gout is the most common cause of inflammatory joint disease in older men, most commonly affecting men between the ages of 30 and 60. Uric acid is the end product of purine metabolism and most current treatments for gout inhibit xanthine oxidase, the enzyme responsible for oxidising xanthine to uric acid. On June 16th, Savient Pharmaceuticals announced that an FDA advisory committee had recommended that Krystexxa™ (pegloticase), a PEGylated form of recombinant porcine uricase, be granted marketing approval by the FDA for the treatment of chronic refractory gout.
Although uricase (urate oxidase) is present in many species, the gene is non-functional in humans so that uric acid is the endpoint of purine catabolism. Most other non-primates are able to convert uric acid to the more soluble allantoin, which is more easily excreted by the kidneys. A recombinant uricase, Elitek® (rasburicase) is already used to treat some patients undergoing cancer chemotherapy where tumour lysis is expected to lead to elevated levels of plasma uric acid.