In vitro release performance and analgesic activity of endomorphin-1 loaded nanoparticles.

Endomorphin-1 normally has a short half-live in blood and brain and has difficulty in penetrating the blood-brain barrier when given intravenously. To transport endomorphin-1 across the blood-brain barrier, the peptide was adsorbed onto the surface of butylcyanoacrylate nanoparticles and coated with polysorbate 80. The release properties of the drug in vitro were demonstrated. The central analgesic effect of the drug was measured by tail flick test. The results of the in vitro release study show that there is a burst release effect at first and a slow and continuous release then followed. A longer analgesic effect was shown when the nanoparticles coated with polysorbate 80 were intravenously injected into mice than with the other groups including endomorphin-1, nanoparticles uncoated with polysorbate 80, and a simple mixture of the three components (drug, nanoparticles, and surfactant) mixed directly. The results showed that the way we used to promote endomorphin-1 penetration of the blood-brain barrier was useful. These results suggested that nanoparticles coated with polysorbate 80 were useful for delivery of EM-1 loaded nanoparticles to target the brain.