Insulin: Biology, Production, and Emerging Therapies

Background

Insulin is a peptide hormone that regulates blood glucose and is essential for cellular energy metabolism. It is secreted by β‑cells in the pancreas’s islets of Langerhans. Basal secretion maintains fasting glucose, while postprandial surges respond to elevated glucose levels.

After food intake, glucose rises in the bloodstream, triggering β‑cells to release insulin. Insulin binds to receptors on cell membranes, initiating a cascade that transports glucose and amino acids into cells for energy production. Without insulin, glucose accumulates in the blood and cells are starved of energy, leading to symptoms such as fatigue, blurred vision, tingling, increased thirst, and slow wound healing.

Chronic insulin deficiency can cause the body to metabolize fat, producing ketones that, if unchecked, lead to diabetic ketoacidosis and coma.

Diabetes Types and Insulin Therapy

Type I diabetes (juvenile‑onset) is characterized by absolute insulin deficiency; patients typically inject rapid‑acting insulin 3–4 times daily, with dosages adjusted by glucose meter readings.

Type II diabetes involves relative insulin deficiency or resistance. Many patients manage with lifestyle changes and oral agents, but insulin injections—usually once or twice daily—may be required as the disease progresses.

Insulin products vary by onset, peak, and duration. According to the American Diabetes Association:

• Rapid‑acting: onset 15 min, peak 30–90 min, duration ~5 h.
• Short‑acting: onset 30 min, peak 2–4 h, duration 4–8 h.
• Intermediate‑acting: onset 2–6 h, peak 4–14 h, duration 14–20 h.
• Long‑acting: onset 6–14 h, minimal peak, duration 20–24 h.

Historical Milestones

In 1921, Frederick Banting and Charles Best purified insulin from a dog’s pancreas, marking the first successful treatment for Type I diabetes. Subsequent breakthroughs included the use of protamine for slower‑release insulin (1936), development of intermediate‑acting formulations (1950), and the introduction of analogs that mimic natural insulin patterns (1970s).

Early insulin production relied on extraction from bovine and porcine pancreases. The 1980s saw a revolution with recombinant DNA technology: in 1982, Eli Lilly released the first human insulin produced in genetically engineered bacteria, eliminating animal contaminants and disease transmission risks. Today, over 95 % of insulin worldwide is human or analog.

Raw Materials and Production

Human insulin is produced in recombinant Escherichia coli or yeast. The process starts with synthesizing the insulin gene—two chains (A‑chain: 21 amino acids; B‑chain: 30 amino acids)—or the proinsulin precursor. The gene is inserted into plasmids, which are then introduced into host bacteria via transfection.

Bacterial cultures grow in large fermenters, reproducing every ~20 min. After harvesting, cells are lysed, and insulin chains are extracted, purified through chromatography (ion‑exchange, reverse‑phase HPLC, gel filtration), and assembled by forming disulfide bonds.

For analogs, the gene sequence is slightly altered to improve pharmacokinetics (e.g., glargine for prolonged action). Additives such as zinc oxide may be included to modulate absorption rates.

Quality Control and Regulatory Standards

Manufactured insulin undergoes rigorous testing: high‑performance liquid chromatography for purity, X‑ray crystallography, gel filtration, and amino‑acid sequencing confirm structure. Packaging integrity is verified, and all products must meet NIH guidelines and receive FDA approval.

Future Delivery Systems

Innovations aim to improve convenience and mimic endogenous insulin release:

• Insulin pens—compact, prefilled cartridges that deliver a single dose.
• Jet injectors—pressure‑driven devices that deliver insulin without a needle.
• Insulin pumps—wearable devices that continuously infuse basal insulin and provide bolus doses before meals.
• Inhaled insulin—fine particles that reach the deep lung for rapid absorption.
• Buccal (cheek) sprays—absorb insulin through the inner cheek mucosa.
• Transdermal patches—use ultrasound or microneedles to increase skin permeability.

Long‑term goals include stem‑cell therapies that restore pancreatic β‑cells and gene editing approaches to correct insulin gene mutations, potentially eliminating the need for exogenous insulin.

Where to Learn More

Books

• Clark, David P., and Lonnie D. Russell. Molecular Biology Made Simple and Fun, 2nd ed. Vienna, IL: Cache River Press, 2000.
• Considine, Douglas M., ed. Van Nostrand’s Scientific Encyclopedia, 8th ed. New York: International Thomson Publishing, 1995.

Periodicals

Dinsmoor, Robert S. “Insulin: A Never‑ending Evolution.” Countdown (Spring 2001).

Web Resources

• Diabetes Digest Web Page (15 Nov 2001)
• Discovery of Insulin Web Page (16 Nov 2001)
• Eli Lilly Diabetes Web Page (16 Nov 2001)
• Novo Nordisk Diabetes Web Page (15 Nov 2001)

Additional Reference

Eli Lilly Corporation. Humulin and Humalog Development, CD‑ROM, 2001.