The proinsulin content of commercial bovine insulin formulations

The proinsulin-like immunoreactivity (PLI) content of traditional and highly purified bovine insulin preparations sold by three insulin manufacturers in the UK has been estimated by radioimmunoassay. We report the PLI content of 22 batches of traditional insulin products and 32 of highly purified insulin, marketed between March 1980 and March 1983. Estimates of the PLI content of traditional insulins ranged from 2290 to 48400 parts per million (ppm). In contrast the estimated PLI content of the highly purified insulins varied between less than 1 ppm and 1160 ppm, although more recent batches prepared by current methodology contained less than 10 ppm of PLI. We conclude that highly purified bovine insulin on sale in the UK may now be expected to contain less than 10 ppm of proinsulin-like immunoreactivity.