Developing an oral insulin preparation
A new delivery system for administering insulin orally
was reported on 26 August at a meeting of the American Chemical Society
in Chicago.
Researchers from Purdue University, West Lafayette,
Indiana, have developed a particle that remains stable in acid conditions
but when exposed to less acid conditions, opens up to release protein
loaded inside. It is hoped that this will allow insulin to pass through
the stomach and be released into the small intestine intact.
The particle is a polymer network that contains
acid groups. At low pH values, the acid groups are protonated and the
polymer is in a collapsed conformation trapping insulin inside. When the
pH is raised, deprotonation of the acid groups occurs and this causes
the polymer network to swell allowing insulin to diffuse through it. Experiments
showed that little insulin was released at pH 3.2 but that more was released
at pH 7.4.
“This system is a favourable candidate for oral
insulin delivery because the material would trap the insulin inside the
network at the low pH of the stomach and protect it from degradation by
the harsh conditions present in the stomach.
“In the upper small intestine where the network
opens because of the higher pH, it releases the insulin for absorption
into the body,” the researchers say.
In addition, when the particles expand, they use
chemical “tethers” to attach to the mucosal surface of the intestine.
This keeps the particles anchored for long enough to release insulin in
the small intestine. Without the tethers, the particles would not remain
in the small intestine long enough for the insulin to be absorbed, the
researchers say.
The researchers add that the particles are washed
out naturally by the body’s digestive system and that experiments showed
that the particles are not toxic to the intestinal cells.
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