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Lasers highlight – and destroy – bad proteins

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Hank Hogan,

Researchers here have developed a scheme for studying amyloid fibers that could prove useful in treating Alzheimer’s, Parkinson’s, Huntington’s and other neurodegenerative diseases. These ailments all have amyloids, fibrous protein masses that share specific structural traits and that are present in a score of diseases.

The new observational technique might become the basis for therapy because it can do more than simply visualize the fibers, noted research leader and Osaka University biophysics professor Yuji Goto. “Our results suggest that it may be possible to selectively break down amyloid fibrils.”

The researchers stumbled upon this result while doing real-time observation of the growth of individual fibrils. They were performing these studies using an amyloid-specific fluorescent dye – thioflavin T – and were applying the technique to fibrils associated with dialysis-related amyloidosis, a common and serious complication in patients receiving long-term hemodialysis. It is known that an increase in the concentration of a particular protein is the most important risk factor for amyloidosis, but exactly how the fibers form is still a mystery.

The investigators examined the process using the dye and total internal reflection fluorescence microscopy based on an Olympus inverted microscope. After exciting the amyloid-bound thioflavin T at 442 nm with a HeCd laser from Kimmon Electric Co. Ltd. of Tokyo, they filtered the signal and captured the resulting fluorescence image with a digital camera from Olympus.

A new monitoring technique based on total internal reflection fluorescence microscopy highlights amyloid fibrils. Researchers then use the same laser to destroy the fibrils, thus demonstrating a potential treatment for Alzheimer’s and other neurodegenerative diseases. Image courtesy of Yuji Goto, Osaka University.

They made fibrils in solution, imaging their growth and extracting quantitative data about that growth. However, they found that the irradiation needed for observation – if done at a high enough intensity and for a long enough time – inhibited the growth and even destroyed the fibrils. Various tests convinced them that this effect was caused by the photochemical production of active oxygen.

Goto and his colleagues noted in a paper published in the January 2009 issue of the Journal of Biological Chemistry that the mechanism behind this fibril destruction is similar to that behind photodynamic therapy, which uses light to produce active oxygen and free radicals that kill cancer cells. The active oxygen produced during the laser-induced fibril destruction could damage other, nearby healthy structures, but Goto said the possibility of such side effects is minimal because of the nature of the interaction.

“We only excite thioflavin T specifically bound to amyloid deposits. This is an important and clever point of our method: specific destruction of amyloid fibrils by taking advantage of amyloid-specific dye,” he said.

He added that research into this area has only just begun and that more effective dyes are a possibility. The technique also could prove more important as an observational tool for individual fibril growth than as the basis for treatment. To help settle that question, the researchers are looking for clinical collaborators, according to Goto. “We are very much interested in examining the practical applicability of our approach.”

Feb 2009
Amyloid fibersamyloidsBasic ScienceBiophotonicsfibrous protein massesMicroscopyneurodegenerative diseasesNews & Features

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