Insulin is a hormone naturally produced by the pancreas, playing a central role in regulating blood sugar levels. For individuals with diabetes, the body either does not produce enough insulin or cannot effectively use the insulin it makes, leading to elevated blood glucose. Administering external insulin becomes a life-saving treatment for many people managing this condition. The development of methods to reliably produce this medication has been a significant challenge in medical history.
The Historical Need for Human Insulin
Before molecular cloning, insulin for diabetes treatment was primarily sourced from animal pancreases, such as pigs and cows. This method faced challenges in meeting global demand. Producing one pound of insulin required processing thousands of pounds of animal pancreases, leading to a limited supply.
Beyond scarcity, animal-derived insulin often contained impurities due to purification difficulties. Slight structural differences between animal and human insulin could provoke adverse immunological responses, including allergic reactions or insulin resistance. Ethical or cultural beliefs also posed barriers to using animal-derived products.
Steps in Producing Insulin by Molecular Cloning
Producing human insulin through molecular cloning begins by obtaining its genetic blueprint. Scientists either isolate the human messenger RNA (mRNA) for insulin and synthesize a complementary DNA (cDNA) molecule, or they chemically synthesize the DNA sequences corresponding to the insulin A and B chains.
Next, these genetic instructions are inserted into small, circular DNA molecules called plasmids, which are naturally found in bacteria. Plasmids serve as “vectors” or carriers, enabling the transfer of foreign DNA into a host cell. Specific enzymes, known as restriction enzymes, act as “molecular scissors,” cutting both the human insulin gene sequence and the plasmid at precise locations, creating complementary “sticky ends.”
Another enzyme, DNA ligase, functions as “molecular glue,” joining the human insulin gene into the opened plasmid, forming a recombinant plasmid. These newly engineered recombinant plasmids are then introduced into host bacteria, typically Escherichia coli (E. coli), through a process called transformation.
The modified bacteria are cultivated in large fermentation tanks, where they multiply rapidly. As they grow, they read the inserted human insulin gene and begin to produce human insulin. The final stages involve isolating the human insulin from the bacterial cultures, followed by extensive purification steps to ensure a high-quality product suitable for medical use.
The Revolution in Diabetes Treatment
The successful production of human insulin by molecular cloning brought about a profound transformation in diabetes management. This breakthrough allowed for the creation of an abundant and consistent supply of human-identical insulin, ensuring its widespread availability for patients globally. The high purity of recombinant human insulin significantly reduced the incidence of allergic reactions and immune responses that were common with animal-derived insulin.
This new method also eliminated concerns about the potential transmission of animal diseases, enhancing the safety profile of insulin therapy. The approval of human insulin produced by recombinant DNA technology in 1982 marked a historic moment in biotechnology. The success with insulin also laid the groundwork for developing numerous other life-saving recombinant proteins and advanced biopharmaceutical technologies, fundamentally changing how many diseases are treated.