Nanoparticle Treatment May Prove Useful for Treating Retinal Degenerative Diseases
January 23, 2012 - A new treatment using tiny nanoparticles to carry drug into the cells of the retina may one day help protect the vision of people with retinitis pigmentosa (RP) and age-related macular degeneration (AMD).
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A dendrimer is a tiny branching molecule that can carry other substances, like drugs, within its branches. Image created by Rik van der Lingen, 2006. |
In animal studies, American scientists, led by Dr. Raymond Iezzi of the Mayo clinic, used nanoparticles called dendrimers to carry drug into specific cells in the retina. The treatment targets microglia cells, trash-collecting immune cells that rush into damaged areas of the retina to gobble up damaged cells and other debris.
In diseases such as RP and AMD, these cells may become part of the problem - by causing ongoing inflammation and by destroying photoreceptor cells that show any impairment, even those cells that may still be capable of vision. Although debate remains about the role of microglia cells in RP and AMD, some experts believe that deactivating the responding microglia might help to protect vision. This study supports that view.
The study was done in rats with a retinal degenerative disease. A few molecules of an anti-inflammatory steroid drug called fluocinolone acetonide were attached to the fern-like projections on each dendrimer nanoparticle and the nanoparticles were injected into the eye.
"Surprisingly, the activated microglia in the degenerating retina appeared to eat the dendrimers selectively, and retain them for at least a month," says Dr. Rangaramanujam Kannan, another study scientist. Within the microglia the drug is slowly released from the dendrimer.
"We've developed an intracellular, sustained-release drug delivery system," says Dr. Iezzi. He explains more about the study in this YouTube interview.
The drug deactivated the microglia and delayed retinal damage for the month following the injection. Treated rats had better electroretinogram (ERG) readings and thicker retinas than did untreated rats. Both outcomes suggest that the treatment was protecting vital visual cells.
In the past two years, other pre-clinical testing has been done using fluocinolone acetonide to treat retinal degeneration. These studies embedded a tiny drug-containing capsule with the eye. Scientists hope that the new nanoparticle approach may prove superior, because microglial cells normally gobble up tiny particles where other retinal cells do not. Thus the drug is targetted directly to the microglial cells and released within them, while other parts of the eye are protected from drug toxicity.
This study was published in the January issue of the journal Biomaterials.