March 14, 2006
Rodent Sight Restored With Self Assembling Peptides

Self-assembling peptides were used to guide nerves to restore partial sight in rodents.

Rodents blinded by a severed tract in their brains' visual system had their sight partially restored within weeks, thanks to a tiny biodegradable scaffold invented by MIT bioengineers and neuroscientists.

This technique, which involves giving brain cells an internal matrix on which to regrow, just as ivy grows on a trellis, may one day help patients with traumatic brain injuries, spinal cord injuries and stroke.

The study, which will appear in the online early edition of the Proceedings of the National Academy of Sciences (PNAS) the week of March 13-17, is the first that uses nanotechnology to repair and heal the brain and restore function of a damaged brain region.

"If we can reconnect parts of the brain that were disconnected by a stroke, then we may be able to restore speech to an individual who is able to understand what is said but has lost the ability to speak," said co-author Rutledge G. Ellis-Behnke, research scientist in the MIT Department of Brain and Cognitive Sciences. "This is not about restoring 100 percent of damaged brain cells, but 20 percent or even less may be enough to restore function, and that is our goal."

Spinal cord injuries, serious stroke and severe traumatic brain injuries affect more than 5 million Americans at a total cost of $65 billion a year in treatment.

Biotech will eventually lead to massive savings aind increased productivity as many disabling diseases and disorders become curable.

Self-assembling peptides (amino acids in polymers) were key to this achievement.

Shuguang Zhang, associate director of the CBE and one of the study's co-authors, has been working on self-assembling peptides for a variety of applications since he discovered them by accident in 1991. Zhang found that placing certain peptides in a salt solution causes them to assemble into thin sheets of 99 percent water and 1 percent peptides. These sheets form a mesh or scaffold of tiny interwoven fibers. Neurons are able to grow through the nanofiber mesh, which is similar to that which normally exists in the extracellular space that holds tissues together.

The process does not involve growing new neurons, but creates an environment conducive for existing cells to regrow their long branchlike projections called axons, through which neurons form synaptic connections to communicate with other neurons. These projections were able to bridge the gap created when the neural pathway was cut and restore enough communication among cells to give the animals back useful vision within around six weeks. The researchers were surprised to find that adult brains responded as robustly as the younger animals' brains, which typically are more adaptable.

The injected peptides self-assemble when they come into contact with fluid that bathes the brain.

When the clear fluid containing the self-assembling peptides is injected into the area of the cut, it flows into gaps and starts to work as soon as it comes into contact with the fluid that bathes the brain. After serving as a matrix for new cell growth, the peptides' nanofibers break down into harmless products that are eventually excreted in urine or used for tissue repair.

The MIT researchers' synthetic biological material is better than currently available biomaterials because it forms a network of nanofibers similar in scale to the brain's own matrix for cell growth; it can be broken down into natural amino acids that may even be beneficial to surrounding tissue; it is free of chemical and biological contaminants that may show up in animal-derived products such as collagen; and it appears to be immunologically inert, avoiding the problem of rejection by surrounding tissue, the authors wrote.

The researchers are testing the self-assembling peptides on spinal cord injuries and hope to launch trials in primates and eventually humans.

Some day severe spinal cord injuries will not condemn people to spend the remainder of their lives in wheelchairs.

This result is another example showing that the ability to manipulate things on a small scale enables big advances over previous achievements.

Schneider estimates that 30,000 axons had reconnected, compared with only around 30 in previous experiments using other approaches, such as nerve growth factors. The team speculates that the similarity between the size of the fibres and the features on neural material is what encourages the axons to bridge the gap. The scaffold appears to eventually break down harmlessly.

Bioengineering is taking off. Some advances such as the one above are measured in orders of magnitude differences as compared to what was possible previously. This is why I'm optimistic that reversal of the aging process is within a few decades reach.

Share |      Randall Parker, 2006 March 14 10:31 PM  Biotech Tissue Engineering

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