A team at Kumamoto University, led by Associate Professor Shingo Ito, has now developed a promising solution. Their approach uses a cyclic peptide that can pass through the small intestine, known as the DNP peptide. This platform allows insulin to be delivered orally in a way that was not previously possible.

Two Effective Strategies for Intestinal Absorption

To make this work, the researchers designed two different methods to help insulin cross the intestinal barrier:

• Mixing method (interaction-based): The team combined a modified "D-DNP-V peptide" with zinc-stabilized insulin hexamers. When given orally to several diabetes models, including chemically induced (STZ mice) and genetic (Kuma mice) models, this mixture quickly brought blood sugar levels down to normal. Stable glucose control was maintained with once-daily dosing for three consecutive days.
• Conjugation method (covalent-based): Using click chemistry, the researchers attached the DNP peptide directly to insulin, creating a "DNP-insulin conjugate." This version lowered blood sugar just as effectively as the mixing method, confirming that the peptide actively helps transport insulin through the intestine.

Lower Doses Make Oral Insulin More Practical

One of the biggest obstacles for oral insulin has been the need for extremely high doses, sometimes more than ten times higher than injections. This new platform significantly reduces that requirement. It achieved a pharmacological bioavailability of about 33-41% compared to subcutaneous injection. That level of efficiency suggests oral insulin could become far more practical for real-world use.

Future Potential for Diabetes Treatment

"Insulin injections remain a daily burden for many patients," said Associate Professor Shingo Ito. "Our peptide-based platform offers a new route to deliver insulin orally and may be applicable to long-acting insulin formulations and other injectable biologics."

The findings were published in the journal Molecular Pharmaceutics. The researchers are now moving forward with additional studies, including testing in larger animal models and systems that replicate the human intestine, as they work toward eventual clinical applications.