How Is Insulin Made? From Pancreas Glands to Engineered Bacteria
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For sixty years insulin was extracted from the pancreases of slaughtered cattle and pigs, at a rate of tens of thousands of animals for a single patient's lifetime supply. Then in 1978 a gene was inserted into bacteria and they started making a human protein. It was the first commercial product of genetic engineering, and the process that produced it is now how most protein medicines are made.
What insulin is and does
Insulin is a small protein hormone of fifty-one amino acids, made in the beta cells of the pancreas and released when blood glucose rises after a meal. Its function is to instruct cells, principally in muscle, fat and liver, to take up glucose from the blood and store it, which lowers blood glucose and stores energy. Without it, glucose accumulates in the blood while cells starve, and the body switches to breaking down fat, producing ketones that acidify the blood, which is the mechanism of diabetic ketoacidosis. Type one diabetes is the autoimmune destruction of the beta cells, leaving no insulin at all, and before treatment existed it was fatal within months, managed only by starvation diets that bought a little time. Type two diabetes involves resistance to insulin's signal along with declining production, and is treated with insulin when other measures no longer maintain control. The structure of insulin, two chains joined by sulphur bridges, was determined by Frederick Sanger, work that won the first of his two Nobel prizes.
The animal era
The discovery in Toronto in 1921 and 1922 by Frederick Banting, Charles Best, James Collip and John Macleod was a matter of extraction and purification rather than synthesis: pancreatic extract, prepared in a way that preserved the hormone, was injected into a dying teenager and reversed his condition. Collip's purification work was essential and is frequently underweighted in the popular account. The discoverers sold the patent to the University of Toronto for a nominal sum, on the stated principle that it should not be exploited for profit. Industrial production then followed, with pancreases collected from abattoirs and processed at enormous scale, and the animal origin brought real limitations. Porcine insulin differs from human by one amino acid and bovine by three, which is close enough to work and different enough to provoke immune reactions and injection-site problems in some patients. Supply was tied to meat production, and rising diabetes prevalence raised a genuine prospect of shortage, which is part of what drove the search for an alternative.
The recombinant process
Manufacturing now uses genetically modified microorganisms, and the sequence is the template for the whole biotechnology industry:
- •The human insulin gene sequence is synthesised and inserted into a plasmid, a small circular piece of DNA, along with control sequences telling the host when to express it
- •The plasmid is introduced into a host, either the bacterium Escherichia coli or the yeast Saccharomyces cerevisiae, each with different advantages in folding and secretion
- •A single verified colony is expanded through progressively larger cultures into fermentation vessels of tens of thousands of litres, with tightly controlled temperature, oxygen, pH and feeding
- •The cells produce a precursor, since insulin's two chains must be correctly joined, so the protein is typically made as a single chain that is afterwards cut and folded enzymatically
- •Purification runs through several chromatography steps to reach the extremely high purity a repeatedly injected protein requires
- •The product is crystallised, formulated with zinc and preservatives, filled into vials or cartridges under sterile conditions, and tested for identity, potency, purity and endotoxin
Analogues and the price problem
Once the gene could be written, it could be altered, and modern insulins are mostly analogues with deliberately changed amino acids that adjust how quickly the molecule disperses from the injection site. Rapid-acting analogues resist clumping into hexamers and therefore act within minutes, suiting mealtime dosing, while long-acting ones are designed to precipitate or bind albumin and release over many hours, giving a flat background level. That flexibility improved control substantially. The economics have been widely criticised, since insulin has been available for a century and the list price in some markets, particularly the United States, rose several-fold over two decades, leading to documented rationing with fatal consequences. The reasons offered include patent thickets around delivery devices and formulations, a concentrated manufacturer market, and rebate structures between manufacturers, insurers and intermediaries that raise list prices without raising net ones. Biosimilar competition and policy caps have begun to reduce prices, which is a recent and incomplete change to a situation that sits oddly beside the founders selling the patent for a dollar.
The takeaway
Insulin is a fifty-one amino acid protein that tells cells to take up glucose, and it was extracted from animal pancreases from 1922 until recombinant production began in 1978, the first commercial product of genetic engineering. Manufacturing inserts the gene into bacteria or yeast, grows them in large fermenters, cuts and folds the precursor and purifies it through chromatography. Modern analogues alter amino acids to speed or slow absorption, and pricing has drawn heavy criticism given the original patent was sold for a nominal sum.