December 10, 2009

Minimizing Spinal Injury

An experimental approach using micelles to prevent the spread of nerve damage shows promise.

Researchers at Purdue University have been able to limit the damage from spinal injury to rats by treating the injury quickly. The treatment involves injection of a polymer that fuses with damaged nerve cell membranes, sealing any holes and preventing the damage from spreading.

Animals treated with the polymer shortly after injury regained use of all four limbs, while untreated animals did not.

The inflammation caused by a spinal injury often has a cascading effect, leading to death of many more nerve cells than were originally damaged. This all starts when the outer membrane of some of the nerve cells gets damaged.

Soap and detergents are the best known micelle-formers. They dissolve in water and can also combine with oily dirt, which normally avoids water, bringing the dirt along into the water.

The material inside of a cell is very different from what lies outside. The cell membrane surrounds the cell and keeps what's inside from mixing with what's outside. When holes are made in the cell membrane, there no longer is an inside and an outside. What was once outside the cell is now free to come in. This quickly kills the cell, and a dead cell can cause neighboring cells to die, turning a tiny injury into a much larger one.

Everyone knows that oil and water don't mix, and this fact is part of the problem facing researchers trying to find a way to seal off nerve damage. Membranes are largely lipid (fat), while their surroundings are watery. Any injected agent that can fuse with and repair a membrane must be similar in structure to the membrane and also has to make its way through a watery environment (the blood) to the injury site. So the agent has to be both water−loving and oil−loving at the same time.

This is a job for micelles.

Micelles are structures that can interact with both oil and water. A micelle can form when a substance has both oil soluble and water soluble parts. Soap and detergents are the best known micelle−formers. They dissolve in water and can also combine with oily dirt, which normally avoids water, bringing the dirt along into the water.

Synthetic micelles have been used in the past as drug delivery systems, a way of getting a drug past the cell membrane's lipid barrier and into the cells. Here, the researchers created a synthetic polymer which has an outer water−loving head and an inner fat−loving core. When injected, this combination allows the polymer to migrate through the blood to the damaged nerve cells and then to seal up any holes in their membranes.

The researchers' approach to spinal injury is similar to that used in heart attack victims, where the quick administration of clot−busting drugs helps limit further damage to the heart. They are planning future studies to find out how soon after the initial injury the polymer needs to be injected to effectively halt nerve damage.

The study was published online by Nature Nanotechnology on November 8, 2009.

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