Insulin is a peptide hormone produced by the pancreas that acts as a key to allow glucose, or sugar, to move from the bloodstream into cells where it is used for energy. When the body fails to produce enough insulin or cannot properly use the insulin it makes, a condition known as diabetes develops. For over a century, the treatment for this condition has required the external administration of this hormone to manage blood glucose levels. The challenge became finding a reliable, large-scale source of a substance originally produced only in tiny amounts within the human body.
The History of Animal Insulin Treatment
The breakthrough discovery of insulin in the 1920s transformed diabetes from a rapidly fatal diagnosis into a manageable chronic condition. Researchers quickly realized that the pancreatic extracts they had isolated could save lives, but they immediately faced the challenge of mass production. The initial crude extracts were derived from the pancreases of animals, with manufacturers turning to the livestock industry to meet the sudden, massive demand.
Cattle (bovine) and pigs (porcine) became the primary sources because their insulin hormones are structurally similar to the human version. This biological proximity meant the animal-derived hormone could effectively function within the human body to regulate blood sugar. Porcine insulin was chemically closer to human insulin, differing by only a single amino acid, while bovine insulin differed by three. This slight difference made pig insulin the preferred therapeutic option for many patients due to better compatibility and fewer adverse reactions.
The Porcine Source and Extraction Process
The insulin used to treat millions of people came from the pancreases of pigs processed in slaughterhouses. Insulin is naturally produced in clusters of cells within the pancreas called the Islets of Langerhans, and it was this tissue that needed to be harvested. The pancreas itself is a relatively small organ, meaning that a large quantity of them was required for commercial production.
The process involved collecting thousands of porcine pancreases, which were a readily available byproduct of the meatpacking industry. To obtain a usable amount of the hormone, the collected pancreases were ground up into a slurry. This raw material then underwent a complex series of chemical treatments and purification steps to isolate the insulin from the surrounding pancreatic tissue and digestive enzymes. Even with improved purification techniques developed in the 1970s, the yield remained low, sometimes requiring the glands from over 23,000 animals to produce enough insulin to treat just 750 patients for one year.
The Rise of Recombinant Human Insulin
The reliance on animal organs for insulin production ended with the scientific advancement known as recombinant DNA technology. This genetic engineering technique allowed scientists to produce human insulin that is chemically identical to the hormone naturally made in the body. The process begins by isolating the human gene that contains the instructions for making insulin.
This human insulin gene is then inserted into the genetic material of fast-growing microorganisms, typically a common bacterium like Escherichia coli or Saccharomyces cerevisiae yeast. The modified bacteria or yeast are then grown in large, sterile fermentation tanks. As these microorganisms multiply, they execute the instructions from the inserted human gene, effectively becoming microscopic insulin factories that produce vast quantities of human insulin.
The resulting biosynthetic insulin is then harvested from the fermentation vats and purified to pharmaceutical grade. This technological shift offered several immediate advantages, including an unlimited supply no longer dependent on the livestock industry. Furthermore, the resulting product was true human insulin, which significantly reduced the allergic reactions and immune responses sometimes seen with the animal-derived versions. This highly efficient genetic method now forms the basis for the world’s supply of insulin and its modern-day analogs.