Researchers at Johns Hopkins have discovered how to
block a molecular switch that triggers brain damage caused
by the lack of oxygen during a stroke.
The Johns Hopkins study, conducted on mice, is
believed to be the first to demonstrate that a protein on
the surface of nerve cells, called the EP1 receptor, is the
switch, and that a specific compound, known as ONO-8713,
turns it off.
The finding holds promise for the development of
effective alternatives to anti-inflammatory drugs called
COX inhibitors, which have potentially lethal side effects
that limit their use, said Sylvain Doré, an
associate professor in the departments of
Anesthesiology and Critical Care Medicine and of
Neuroscience at the School of Medicine. Doré is
senior author of the paper, published in the January issue
of Toxicological Sciences.
"Our work has shifted the focus from drugs that
inhibit COX-2 to drugs that block the EP1 receptor,"
Receptors are protein-docking sites on cells into
which "signaling" molecules such as nerve chemicals or
hormones insert themselves. This binding activates the
receptor, which transfers the signal into the cell to
produce a specific response.
COX inhibitors block the ability of the enzyme
cyclooxygenase-2 (COX-2) to make prostaglandin E2 (PGE2), a
hormonelike substance long linked to inflammation and other
effects. The John Hopkins study results suggest that PGE2
causes brain damage following stroke by binding to the EP1
receptor on nerve cells. Therefore, blocking PGE2 activity
directly rather than inhibiting COX-2 could reduce brain
damage in individuals who have a stroke while avoiding the
side effects of COX-2 inhibitors, the investigators say.
Previous work by others had shown that certain events
that interrupt oxygen flow to the brain, such as cerebral
ischemia (stroke) and seizures, also cause excessive
activation of so-called NMDA receptors by the nerve
chemical glutamate. Other work had suggested that
activation of NMDA receptors by glutamate causes an
increase in the production of COX-2, which then produces
"A lot of the previous findings kept bringing us back
to PGE2 and its receptors," Doré said, "so we
investigated whether it's possible to block the EP1
receptor so PGE2 couldn't trigger toxic effects."
Doré's team first injected either the EP1
blocker ONO-8713 or the EP1 stimulator ONO-DI-004 into the
ventricles (fluid-filled areas of the brain) of mice. A
group of control mice received an injection of the solvent
used to carry the drugs. The investigators then injected
each mouse with NMDA, a drug that stimulates the NMDA
receptor. Excessive stimulation of these receptors by NMDA,
such as during stroke, leads to nerve cell damage.
In mice that had first received the EP1 stimulator
ONO-DI-004, the area of brain damage was more than 28
percent greater than in control animals. The volume of
damage in mice treated first with the EP1 blocker ONO-8713
was only about 71 percent that of controls.
"ONO-8713 significantly reduced brain damage in our
mouse models following activation of a nervous-system
response known to cause brain damage in humans during
stroke," Doré said.
The team next showed that in mice lacking the gene for
the EP1 receptor, the volume of brain damage caused by
stimulation of the NMDA receptor was only about 75 percent
that of mice with the EP1 gene. This suggested that a
significant part of the damage caused by activation of the
NMDA receptor depends on the EP1 receptor. In addition,
when the researchers injected the EP1-blocking drug
ONO-8713 in mice lacking the gene for the EP1 receptor, the
drug did not provide any additional protection. This
suggested that ONO-8713 can exert its effect only by
binding to the EP1 receptor, Doré said.
"These findings demonstrate the critical role played
by the EP1 receptor in brain damage caused by stroke," he
said. "And they show that ONO-8713 works specifically at
Finally, the scientists showed that stimulation of EP1
receptors triggers the damage caused when blood flow is
suddenly restored after a stroke. The team blocked blood
flow in one of the main arteries feeding specific areas of
the brain in mice lacking the gene for the EP1 receptor and
then restored blood flow after 90 minutes. The area of
brain damage (infarct size) in the mice lacking the EP1
gene was only about 57 percent of that seen in normal mice
that underwent the same treatment. This provided additional
evidence that brain damage caused by ischemia depends in
large part on the stimulation of EP1 receptors, the
"Our results strongly suggest that given the side
effects associated with COX inhibitors, we should focus our
efforts on developing drugs that block the EP1 receptor
instead of inhibiting COX-2 activity," Doré said.
Doré has applied for a patent covering the
prevention and/or treatment of neurodegenerative diseases
by administering agents that block the EP1 receptor.
Additional contributing authors of the paper are
postdoctoral fellows Abdullah Shafique Ahmad and Sofiyan
Saleem and research fellow Muzamil Ahmad, all of the
Department of Anesthesiology and Critical Care Medicine.
This work was supported in part by the National
Institutes of Health and a postdoctoral fellowship from the
Mid-Atlantic American Heart and Stroke Association.