Researchers at the Purdue School of Veterinary Medicine (West Lafayette, IN, USA) first converted chitin--one of the most common sugars found in crustacean shells--into chitosan. The researchers then isolated a segment of guinea pig spinal cord, compressed a section, applied the modified chitin, and then added a fluorescent dye that could only enter the cells through damaged membranes. If the chitosan repaired the crushed membranes then the spinal cord tissue would be unstained, but if the chitosan had failed, the spinal cord neurons would be flooded with the fluorescent dye. Viewing a section of the spinal cord under the microscope, the researchers were amazed to see that the spinal cord was completely dark; none of the dye had entered the nerve cells. The chitosan had effectively repaired the damaged cell membranes.
Next, the researchers tested whether a dose of chitosan could prevent large molecules from leaking out of damaged spinal cord cells. Testing for the presence of the colossal enzyme lactate dehydrogenase (LDH), the researchers observed that levels of LDH leakage from chitosan treated spinal cord were lower than from undamaged spinal cords. Not only had the sugar repaired membranes at the compression site, it had also done so at other sites, where the cell membranes were broken due to handling. When they further tested for the presence of harmful reactive oxygen species (ROS, released when adenosine triphosphate (ATP) generating mitochondria are damaged) they found that ROS levels also fell after applying chitosan to the damaged tissue, indicating that chitosan probably repairs mitochondrial membranes as well as the nerve cell membranes.
In a further test, the researchers measured the brain's response to nerve signals generated in the hind leg of a guinea pig, and found that the signals were unable to reach the brain through a damaged spinal cord. However, 30 minutes after injecting chitosan into the rodents, the nerve signals returned to the animals' brains. The study was published in the April 16, 2010, issue of the Journal of Experimental Biology.
"This is not like a drug which may work in some species and not in others; this is a mechanical effect,” said lead author professor of developmental anatomy Richard Borgens, Ph.D. "The sugar molecules migrate to the nerve injury target and repair the injured area, not the undamaged area.”
Chitosan is a biocompatible, biodegradable linear polysaccharide composed of randomly distributed β-(1-4)-linked D-glucosamine (deacetylated units) and N-acetyl-D-glucosamine (acetylated units). Chitosan is produced commercially by deacetylation of chitin, which is the structural element in the exoskeleton of crustaceans (crabs, shrimp, etc.) and cell walls of fungi. Chitosan is also a bioadhesive, which readily binds to negatively charged surfaces such as mucosal membranes, and enhances the transport of polar drugs across epithelial surfaces.
Related Links:
Purdue School of Veterinary Medicine
