Insulin genes obtained from human cells are inserted into bacteria, which then produce the hormone, explains Dr. Erika Gebel of Diabetes Forecast for the American Diabetes Association. Enzymes are used to break down the bacteria to release the insulin, which is then purified, crystallized, dried and packed.
Insulin was previously manufactured from pig and cow pancreases, explains Gebel. The process was extremely inefficient. For instance, to produce 8 ounces of insulin, more than 2 tons of pig pancreases were needed. Genentech was the first company to produce insulin from genetically modified Escherichia coli bacteria. Genentech makes insulin in partnership with a company known as Lilly.
At Lilly, E. coli bacteria are grown in large tanks called fermentors that contain a nutritious liquid. After several days, a chemical known as an inducer is added to the liquid to stimulate the bacteria to produce insulin. Harvesting starts a few hours after the inducer is added. The bacteria are separated from the nutritious fluid using a centrifuge and bathed in an enzyme that breaks down cell membranes. This releases the raw insulin, which is imprisoned within the bacterial cell walls. The insulin is purified and mixed with zinc, causing it to crystallize. The crystals are dried, packed and shipped to customers around the globe. The dried mixture needs to be rehydrated before use, notes Gebel.