Activated Protein C Found to Affect Damaged Motor Neurons in ALS, Slowing Symptoms in Mouse Model of Disease
ARTICLE IN BRIEF
Investigators have evidence that a therapy already in the pipeline as a treatment for sepsis can help an ALS mouse live 25 percent longer, move around better, and show a marked decrease in muscle wasting.
Many experimental medicines have had enough success in slowing symptoms in mouse models of amyotrophic lateral sclerosis (ALS) that they have been pushed into clinical trials. They have all failed to have similar benefits on patients.
Now, investigators have evidence that a therapy already in the pipeline as a treatment for sepsis can help an ALS mouse live 25 percent longer, move around better, and show a marked decrease in muscle wasting. The agent is an enzyme called activated protein C, or APC, given by injection. Its potent activity as an anti-inflammatory led to its approval for severe sepsis in 2001.
In the laboratory, Berislav Zlokovic, MD, PhD, director of the Center for Neurodegenerative & Vascular Brain Disorders and professor of neurology and neurosurgery at the University of Rochester Medical Center, found that APC works directly on neurons and may serve as a potent way to protect neurons under siege. Dr. Zlokovic's work has extended to stroke and more recently ALS. He discovered that APC also protects the integrity of the blood-brain barrier.
This latest finding, published online Oct. 19 ahead of the print Journal of Clinical Investigation, supports the idea that APC has an impact on the damaged motor neurons in ALS.
APC is not without its risks and one of the major side effects is bleeding. Scientists have been working on developing mutant strains of the enzyme that has the neuronal protection properties with reduced anticoagulation activities. The Rochester team worked in collaboration with John Griffin, PhD, of the Scripps Institute in La Jolla.
APC has been reported to benefit the brain following acute injuries such as stroke, but had never been tested in an animal model of ALS. Dr. Zlokovic said there is growing evidence that there are a lot of microbleeds in ALS, suggesting that the blood-brain barrier is compromised during the attack against the motor neurons.
According to the investigators, APC inhibited SOD1 (superoxide dismutase 1) synthesis by preventing transcription of the protein. SOD1 causes toxicity to different cell types, including inflammatory cells (microglia) that pump out molecules in response to injury. They studied spinal cords of SOD1 mice following daily exposure to APC a week after the first symptoms, and found that microglia were down, inflammation was delayed, and the disease progression was slowed. The scientists gave peripheral injections of the substance. The target was microglia and the blood-brain barrier (known at the spinal cord as spinal cord barrier), not motor neurons. APC crossed the spinal cord barrier. It prevented the progression of disease.
The medicine increased the lifespan and pushed back the duration of the asymptomatic phase of the disease. “They lived much, much longer,” he said of the animals.
“It all made sense,” said Dr. Zlokovic. “APC down-regulates several transcription factors.”
Last year, the Rochester team worked with Don Cleveland, PhD, professor of medicine, neuroscience and cellular and molecular medicine at the University of California-San Diego, on the effects of the SOD1 mutation on the blood-brain barrier. In a 2008 paper in Nature Neuroscience, they reported that ALS-causing SOD1 mutants generate vascular changes before there is degeneration of the motor neurons.
Leaks in the spinal cord could allow entry of toxic substances from the blood, including iron, a byproduct of hemoglobin, Dr. Zlokovic explained.
Now, the scientists are trying to figure out the best analog that will have a potent effect on brain without the risk of bleeding. They are also studying the role of the microbleeds and how it might contribute to injury of the motor neurons.
“I remain very optimistic. This is a new approach and it is a natural molecule,” said Dr. Zlokovic. APC's risk of bleeding does not make it a good candidate for its prolonged use in ALS, he added. That is why he has been working on developing analogs.
Dr. Zlokovic is the scientific founder of three start-up biotech companies that focus on identifying AD vascular genes and small molecules to block this neurovascular dysfunction. One of his companies, ZZ Biotech, is developing APC analogs for stroke and other neurological conditions. The company also is following the direction of many pharmaceutical companies searching for medicines that clear amyloid beta from the brain.
MORE RESEARCH NEEDED
Stanley Appel, MD, chairman of the neurology department and co-director of the Methodist Neurological Institute in Houston, called it “an exciting finding” but cautions that more work needs to be done before it is known whether APC would work in patients with ALS. For one thing, others need to confirm the findings. And scientists have to identify the best APC analog to test in patients.
ALS scientists are hampered by a limited number of animal models for ALS. Most models involve a mutation in the gene for SOD1- based on mutations identified in families with a genetic form of the disease, he said, adding that most sporadic cases do not involve SOD1.
That said, Dr. Appel said that it is now becoming clear that there are probably many cells that are damaged in the degenerative disease process, not just motor neurons. He said that endothelial cells are among the cells that are at play in ALS. And the work showing involvement in a leaky blood-brain barrier is impressive, and could open the field to new ways to treat ALS.
“ALS may be a motor neuron disease but it is true that many cells are affected by this disease,” said Dr. Appel. “It takes a village.”
He said that APC's ability to delay microglial activation and extend the lives of the animals is hopeful. But he added that neuropathologists continue to debate whether there is evidence that the blood-brain barrier is leaky in ALS patients. “Maybe we aren't looking with the right tools.” Dr. Appel added.
Microbleeds are showing up in many areas of neurology, including Alzheimer disease, stroke, and ALS. There is growing evidence that these tiny blood products identified in tissue or in macrophages stay around and may also lead to more subtle cognitive problems short of dementia. A report earlier this year in Archives of Neurology by the Rotterdam Scan Study group showed that almost 18 percent of the community-residing population between 60- and 70 years old have evidence of these microbleeds that show up on sensitive MRI devices. By age 80, 38 percent of those studied had microbleeds.
They are roadposts that point the way to some problem, said Steven M. Greenberg, MD, director of hemorrhagic stroke research at Massachusetts General Hospital and professor of neurology at Harvard Medical School. But no one is sure exactly whether the microbleeds lead directly to disease.