Johns Hopkins researchers have discovered that plant-derived compounds known for their ability to protect tissue also appear to block the activity of an enzyme that triggers inflammation in joints. Their findings, based on experiments with human cells in a lab, could lead to new arthritis treatments and better methods of making artificial cartilage.
The discovery was detailed in a paper published in the Sept. 27 edition of Proceedings of the National Academy of Sciences.
The findings came to light while the researchers were studying the wildly different ways in which cells in human blood vessels and joints respond to pressure gradients generated from liquid moving along their surface, a force called shear stress. In cells that line blood vessels, the reaction to shear stress is beneficial: the boosting of phase 2 enzymes that may protect the cells from cancer-causing chemicals and other toxic agents. Yet in joints, the response to high shear stress is potentially harmful: an increase in the levels of COX-2 enzyme, which triggers inflammation and pain, and suppresses the activity of phase 2 enzymes, ultimately causing the death of chondrocytic cells. Healthy chondrocytes are responsible for the smooth functioning of joints. When chondrocytes stop functioning properly, the result can be arthritis.
The divergent responses to shear stress prompted a series of experiments in a Johns Hopkins lab supervised by Konstantinos Konstantopoulos, associate professor of chemical and biomolecular engineering and Agarwal-Masson Faculty Scholar. His team knew that strenuous exercise or heavy exertion of muscles can cause joints to increase the levels of harmful COX-2 enzyme. What would happen, the researchers wondered, if the vulnerable chondrocyte cells in human joints were first exposed to the beneficial phase 2 enzymes?
To find out, the researchers obtained compounds that boost the activity of helpful phase 2 enzymes. They added these phase 2 inducers to a dish containing the chondrocyte cells that are crucial to maintaining healthy joints. After 24 hours, the cells were subjected to a stress test designed to mimic aspects of strenuous exercise on a joint as well as the hydrodynamic environment in a bioreactor designed to generate artificial cartilage.
The results were surprising. "The beneficial phase 2 enzymes somehow seemed to prevent the activation of the inflammatory COX-2 enzyme," said Zachary R. Healy, a doctoral student in Konstantopoulos' lab and lead author of the journal paper. "The phase 2 enzymes inhibited the inflammation and the apoptosis -- the cellular suicide we'd observed."
Some prescription drugs like Vioxx keep COX-2 enzyme at bay by temporarily blocking its ability to send the biochemical signals that set off pain and inflammation. When the medication is stopped, however, the stockpiled COX-2 enzyme can resume its damaging ways. Unlike these traditional pain killers, Healy said, the phase 2 enzyme inducers seemed to stop the increasing activity of COX-2 enzyme.
"That means these compounds could be useful as a preventive measure, perhaps before strenuous exercise," Healy said. "This has the potential for stopping pain and inflammation before they start."