Nanoparticles show great promise as diagnostic tools and drug delivery agents. The tiny particles, which scientists can modify with drugs, dyes or targeting molecules, can travel in the circulation and squeeze through small spaces into cells and tissues. But until now, most nanoparticles had to be injected into the bloodstream because they weren't absorbed well orally. Now, researchers reporting in ACS Nano have modified nanoparticles to improve their uptake in the gastrointestinal tract.
When it comes to daily medication, most people would rather take a pill than an injection. So scientists have tried to design nanoparticles that, when taken orally, are readily absorbed through the intestine and into the bloodstream, instead of being excreted from the body. But so far they have had little success. You Han Bae and his colleagues wondered if they could get polystyrene nanoparticles to "hitch a ride" with bile acids --- small molecules that help move digested fats from the intestine into special cells called enterocytes, where fats are processed before entering the circulation.
The researchers attached 24 copies of a bile acid to each 100-nm nanoparticle, as well as a red fluorescent compound for easy visualization. When the team fed the modified nanoparticles to rats, about 47 percent of the particles made it into the blood. This was much improved from the 7 percent seen for nanoparticles lacking bile acids. Larger nanoparticles were not taken up as well as smaller ones, however. Bae and coworkers also showed preliminary evidence that bile acids on the nanoparticles interact with a bile acid transporter found on the surface of enterocytes, which might help the nanoparticles move through the cells and into the circulation.