Insulin is a peptide hormone produced by the beta cells within the pancreatic islets, serving as the body’s primary regulator of blood glucose levels. Its main function is to promote the absorption of glucose from the bloodstream into the liver, fat, and muscle cells, preventing the damaging effects of high blood sugar. For individuals with diabetes, whose bodies either do not produce insulin or cannot use it effectively, an external source of the hormone is required for survival. Before modern biotechnology, this life-saving substance was sourced directly from the pancreases of slaughtered animals, with pigs becoming a significant source for mass therapeutic use.
How Pig Insulin Became the First Treatment
The history of insulin as a treatment began in 1921 when a team of researchers at the University of Toronto, including Frederick Banting and Charles Best, successfully isolated an extract from a dog’s pancreas. Prior to this discovery, a diagnosis of Type 1 diabetes was a virtual death sentence. Within a year, the first human patient, a 14-year-old boy, was treated with the purified extract, demonstrating its life-saving potential.
The pharmaceutical industry quickly recognized the need for mass production, necessitating a transition from small-scale laboratory extraction to industrial harvesting. Pancreases from pigs and cattle, readily available byproducts of the meatpacking industry, became the most practical source for the global supply. Porcine insulin was favored due to its close molecular resemblance to the human hormone, establishing itself as the standard treatment worldwide for the next six decades.
The Key Biological Difference from Human Insulin
The effectiveness of porcine insulin is rooted in its near-perfect molecular match to human insulin. Human insulin is composed of two polypeptide chains, an A-chain and a B-chain, which are linked together by disulfide bonds and total 51 amino acids. Porcine insulin shares this structure, but it differs by only a single amino acid residue at the C-terminus of the B-chain.
At position B30, human insulin features the amino acid threonine, while the pig version contains alanine. This minor substitution was well-tolerated by the human body. However, the immune system sometimes recognized this slight variation as a foreign protein, leading to allergic reactions, local skin irritation, or the development of immunological resistance that reduced the therapy’s effectiveness.
Extracting Insulin from Animal Sources
The process of producing animal-sourced insulin required an immense industrial scale. Estimates suggest that the pancreatic glands from roughly 30 animals were needed to supply a single diabetic patient for an entire year. The manufacturing process, which began immediately after the animals were slaughtered, was a complex series of chemical extractions and purifications.
The initial step involved homogenizing the harvested pancreases using an acid-ethanol solution to extract the crude insulin. This extract was then subjected to a rigorous purification process designed to remove contaminating proteins and lipids. Technicians adjusted the mixture’s acidity and temperature to exploit the hormone’s isoelectric point, causing the insulin to selectively precipitate out of the solution.
Further purification was achieved through precipitation with high concentrations of salts, such as sodium chloride, to separate the crude insulin from other polypeptides. The final product was never perfectly pure, and the residual contaminants contributed to the allergic and immunological issues experienced by some patients.
The Technological Shift to Modern Insulin
The limitations of animal-sourced insulin—the supply constraint and the risk of allergic reactions—drove research toward a synthetic alternative. This goal was achieved with recombinant DNA technology in the late 1970s, which revolutionized insulin production. Scientists successfully isolated the human insulin gene and inserted it into the genome of a bacterium, typically Escherichia coli.
The bacteria were then cultured in large fermentation tanks, where they acted as tiny factories, producing large quantities of the human insulin protein. The early method involved synthesizing the A and B chains separately in two different bacterial cultures. These chains were then chemically extracted and joined in vitro using disulfide bonds to form the complete, active human insulin molecule.
This genetically engineered product, first approved in the early 1980s, was chemically identical to the insulin produced by the human pancreas. The new method provided an unlimited, consistent supply with higher purity and lower cost. Though highly purified porcine insulin remains available in certain markets for specific patient needs, synthetic human insulin is now the global standard of care.