Insulin is a naturally occurring peptide hormone that regulates blood glucose levels within the body. When the body cannot produce this hormone effectively, such as in diabetes, treatments that replace or supplement insulin are necessary. For decades, the only viable treatment was insulin extracted from the pancreases of animals, primarily cows and pigs. This reliance on animal sourcing has now been entirely replaced by laboratory-produced versions.
The Historical Reliance on Animal Sources
The discovery of insulin treatment in the early 1920s transformed diabetes from a rapid death sentence into a manageable chronic condition. This success created an immense demand for the hormone, which was met by sourcing it from the meat processing industry. Pancreases from cattle (bovine) and swine (porcine) were collected from slaughterhouses and processed to extract the insulin.
Large-scale production required collecting millions of animal glands to create the injectable medicine. Early extracts, such as those used in the first successful human trial in 1922, were often impure and caused pain or swelling at the injection site. Over the following decades, pharmaceutical companies developed new purification techniques to improve the quality of the animal-derived products. By the 1970s, highly purified pork insulin became available, but the fundamental reliance on the meat industry supply chain remained.
Limitations of Animal-Derived Treatments
The discontinuation of animal insulin was prompted by biological, logistical, and economic limitations that modern technology overcame. A primary issue was the slight difference in the amino acid structure between animal and human insulin. Porcine insulin differs by one amino acid, while bovine insulin differs by three, which caused problems for some patients.
These structural variations often triggered immunological issues, leading to the formation of anti-insulin antibodies. This immune response could manifest as allergic reactions or lead to insulin resistance, making blood sugar control difficult. Furthermore, achieving absolute purity remained a challenge, and remaining impurities sometimes contributed to side effects.
Another limitation was the unsustainable supply chain required to meet the growing global need for diabetes management. By the early 1980s, extracting one pound of pure insulin required glands from approximately 23,500 animals. This reliance on the slaughter industry presented a fear of shortages, as insulin demand quickly outpaced the logistical capacity to process the necessary animal pancreases.
The Technological Breakthrough of Biosynthesis
Supply and safety issues were resolved by shifting from extraction to laboratory synthesis, powered by recombinant DNA technology. This genetic engineering approach allowed scientists to create human insulin structurally identical to the hormone produced by the body. The process begins by isolating or synthesizing the human insulin gene, which contains the blueprint for the hormone’s two polypeptide chains.
This human gene is then inserted into a bacterial DNA plasmid using specific enzymes. The resulting recombinant plasmid is introduced into a host organism, typically a fast-replicating microbe like Escherichia coli bacteria or yeast. The transformed microbes are grown in large fermentation tanks, where they use the human gene to mass-produce the insulin protein.
Biosynthetic human insulin, first marketed as Humulin in 1982, solved the historical problems of purity and supply. Since the product is chemically identical to human insulin, it significantly reduces the risk of allergic or immune reactions. The process also provides a virtually limitless, scalable source of insulin independent of the meat industry.
Current Standards: Human Insulin and Analogs
The advent of biosynthesis enabled the creation of two modern categories of insulin products: human insulin and insulin analogs. Biosynthetic human insulin is a direct, laboratory-made copy of the natural hormone, available in forms like regular (short-acting) and NPH (intermediate-acting) insulin. Regular human insulin begins to act within 15 to 30 minutes, peaking in action within one to three hours after injection.
Insulin analogs are a subgroup of human insulin genetically modified to alter their action profile for therapeutic benefit. This molecular alteration changes how the insulin is absorbed, making it either very rapid-acting or very long-acting. Rapid-acting analogs, such as lispro or aspart, have a faster onset and offset of action compared to regular human insulin, allowing for greater flexibility in meal timing.
Long-acting basal analogs, such as glargine or detemir, offer a consistent, peakless action profile that can last up to 24 hours. This reduces the risk of nocturnal hypoglycemia compared to older intermediate-acting insulins. These modern products offer better predictability and control, allowing patients to more closely mimic the body’s natural release of insulin. While human insulin remains a cost-effective option, the clinical advantages of analogs have made them the standard of care for many individuals with type 1 diabetes.