Recombinant human insulin is a commercial hormone used to treat patients suffering from diabetes. Insulin, which is normally produced in the pancreas, serves to regulate blood sugar. It functions by allowing sugar in the blood to pass into the cells of the body so the cells can use it for energy. If a patient is diabetic and cannot produce insulin, levels of sugar in the blood will become elevated, which could cause serious health problems. Insulin must then be injected daily to maintain a constant level of blood sugar.
Insulin can be extracted from pigs or cows and be purified for use in humans. Bovine insulin from cows differs from human insulin by three amino acids, while porcine insulin from pigs only differs from human insulin by one amino acid. Some diabetic patients may develop an allergic reaction to insulin from animals if the body recognizes it as foreign. Recombinant human insulin produced in the laboratory is identical to the hormone produced naturally and typically does not cause an allergic reaction.
Recombinant deoxyribonucleic acid (DNA) technology has allowed researchers to move away from animal-extracted insulin and develop a technique for making recombinant human insulin. Insulin is made up of two chains of amino acids that are linked together to make a small protein molecule. Recombinant human insulin is synthesized by inserting the DNA from each insulin chain separately into the DNA of weakened non-infectious strains of the bacteria Escherichia coli — more commonly known as E. coli.
The bacteria then undergo many cycles of cell division and can produce many copies of each of the insulin chains. Individual chains of the insulin molecule are extracted from the bacteria and purified. The two chains that make up the complete insulin molecule are then mixed and allowed to bind to each other.
Recombinant human insulin can also be cultured in yeast cells. Yeast cells can secrete the complete insulin molecule containing both chains already bound together. This is an improvement over E.coli production because it eliminates the extra step of mixing two chains together.
Once the complete recombinant human insulin molecule has been purified, other structural changes can be made to enhance the function of the molecule. Substituting one amino acid in a certain position within the molecule can result in an insulin preparation that is either rapid-acting or long-acting. These are referred to as insulin analogues, and they can remain active for different lengths of time in the body. This gives the physician and the patient flexibility in designing an insulin treatment protocol based on lifestyle.