California Pacific Currents 2003
Three ALS Researchers in Pursuit of New Clues, Better Therapies
Amyotrophic lateral sclerosis (ALS), sometimes called Lou Gehrig’s disease, involves a rapid degeneration of the neurons that control voluntary muscles. As these motor neurons in the brain and spinal cord die, the associated muscles waste away and patients weaken, eventually losing the ability to move their arms and legs. Speaking, eating, and breathing also become difficult. Unfortunately, most of the 5,000 patients who are diagnosed with ALS every year in the US will die from respiratory failure within three to five years of noticing symptoms.
Two Prime Suspects
For decades, researchers have hunted in vain for the underlying cause of this devastating disease. One prime suspect in ALS pathophysiology is excitotoxicity, or overstimulation of motor neurons by a chemical messenger called glutamate. An overload of glutamate can damage and kill neurons. Evidence of excitotoxicity has been found in tissue samples from ALS patients. In one of the first successes in ALS therapy, a drug called riluzole is thought to slow disease pro-gression at least in part by blocking glutamate.
Another suspected cause of ALS is oxidative stress. All cells require oxygen-rich free radicals to carry out their normal activities. However, these highly reactive molecules, which are part of the body’s normal metabolism, must be handled carefully—like gasoline in a can. Any spillage or excess normally is “sponged up” by special enzymes before causing cell damage. But about 10 years ago, researchers discovered that some patients with rare inherited forms of ALS had faulty genes for a key antioxidative enzyme called SOD1, which normally soaks up the free radicals. Patients with SOD1 mutations were rare, but the clue was still important. In response, researchers genetically engineered a mouse with the SOD1 mutation that reliably develops ALS; this SOD1 mouse now provides the best animal model for testing new treatments. Over the past two decades, several other theories of ALS pathophysiology have been proposed. These include copper toxicity, protein aggregation, mitochondrial dysfunction, inflammation, autoimmune system abnormalities, alterations in nerve growth factors, viral infection, and programmed cell death (apoptosis). Despite the growing list of suspected ALS causes, real progress in ALS therapy has been slow.
Seeking New Connections
After decades of searching in vain for “the ALS cause,” researchers have recently begun to understand that there is likely no single factor that leads to the development of ALS. Instead, based on emerging evidence, ALS and other common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, are now seen as disorders with multiple causes that will likely require combination therapies.
Like bright floodlights cast over a nighttime crime scene, the new tools of molecular biology are beginning to allow researchers to trace the footprints between the many scattered clues related to ALS. For the first time, neuroscientists are defining the distinct roles of the ALS perpetrators, the accomplices, and the innocent bystan-ders. In sorting out these connections, they are beginning to sketch the variety of alternative pathways that might lead to ALS. Three scientists at California Pacific Medical Center’s Forbes Norris MDA/ALS Research Center are at the forefront of this new understanding of the complex pathophysiologic origins of ALS.
Nancy M. Lee, PhD, Senior Scientist at California Pacific Medical Center Research Institute since 1995, is applying her vast experience in neuro-peptide receptor research (she is an expert in opioid analgesia and tolerance) to define the events that first switch on the ALS disease process. By focusing on distinct, early-stage changes—instead of the complex cascade of cell changes that occur later—Dr. Lee hopes to target these processes with treatment that can halt or reverse progression of the disease. To catch the first signs of disease onset, she scans for early abnormalities in gene expression. Using sophisticated tests, her group has already discovered genes (e.g., for oxidative stress, glutamate metabolism, and immuno-surveillance) that are activated early in the SOD1 mouse model.
“We have found that many of these genes were altered in animals where symptoms had appeared,” says Dr. Lee, “but only a handful of these genes were also altered in animals prior to the development of symptoms.” By targeting those molecular pathologies that appear very early in the ALS disease process, Dr. Lee hopes to find therapies that will prevent, or at least slow, the deterioration in bodily function that now relentlessly afflicts ALS patients.
“Our goal is to help ALS patients lead independent, productive lives,” comments Dr. Lee. “Even in the absence of an immediate cure, preventing progression of the disease beyond the point where patients can no longer take care of themselves would represent an enormous medical breakthrough.”
Jian Liu, PhD, is the newest addition to the California Pacific team of ALS researchers. As a Research Institute associate scientist, Dr. Liu is investigating how mitochondrial abnormalities contribute to ALS. Mitochondria are the “mini-furnaces” within human cells that take in carbon-based fuel and combine it with oxygen to produce ready-to-use energy for the cell. Faulty mitochondria have now been implicated in several neurodegenerative disorders. Dr. Liu’s previous work at the University of California, San Diego, showed that the mitochondria in the spinal cord neurons of patients, or mice, with ALS were especially susceptible to damage when a mutant SOD1 gene was present.
“We found that a common feature shared by the ALS mice is the selective association of mutant SOD1 genes with spinal cord mitochondria that is accompanied by abnormal changes in proteins. We confirmed this in ALS patients with two different SOD1 mutations.”
Apparently, the motor neurons are especially vulnerable to any glitches in the energy-generating process. Whenever the mitochondria begin to misfire, the whole cellular environment of the neuron is upset by “spilled” forms of oxygen that can be highly destructive. Eventually, the energy-starved cell overloads on glutamate and calcium and then dies. Thus, in addition to their key role in generating energy, the mitochondria also appear to be critical gatekeepers in overall cell survival and death. In her work at California Pacific, Dr. Liu and her colleagues are trying to identify the abnormal mitochondrial proteins that occur in spinal cord neurons. They are also trying to figure out how mitochondrial dysfunctions are linked to ALS-related changes in oxidative stress, SOD1 function, and “downstream” ALS mechanisms.
From the Lab Bench to the Clinic
While Drs. Lee and Liu are hunting for new clues and gathering evidence for various fundamental mechanisms of disease, Mary E. Abood, PhD, and her colleagues are investigating a potential therapy: they are studying the effectiveness of cannabinoids, the active ingredients in marijuana, to counteract the key neurodegenerative changes of ALS. A research scientist at California Pacific since 1999, Dr. Abood has already demonstrated that both plant-derived and synthetic tetrahydrocannabinol (THC) can modestly reduce the rate of decline in motor function in the SOD1 mouse model. Receptors for the cannabinoids are widely distributed in the normal nervous system and account not only for the recreational effects of the cannabinoids but also for reduction of nausea, pain, and intraocular pressure.
“In general,” says Dr. Abood, “THC was neuroprotective against two major types of insults to the neuron: excitotoxicity and oxidative stress. But the most exciting part of our study was that THC slowed progression of disease not only in animals who started healthy but also in those who started treatment after they had signs of disease.”
“This is a situation that is closer to the real-life clinical situation,” she points out, “because ALS patients are only diagnosed after symptoms develop.”
Such sensitivity to real-world clinical issues permeates all research at California Pacific. But it is especially prominent in the work of Dr. Abood, who has already seen her basic research results translated into a small study of THC in ALS patients. Her ALS study used Marinol® pills, which contain a synthetic version of THC and are already approved for treating chemotherapy-related nausea and vomiting and for stimulating weight gain in patients with AIDS. This pilot study was coordinated by Deborah F. Gelinas, MD, of the Comprehensive Clinical Care Team of the Forbes Norris MDA/ALS Center. Although the preliminary results in terms of symptom relief were encouraging, Dr. Abood is quick to stress that this initial study was designed mainly to test the tolerance of THC in ALS patients. Also, she remains acutely aware that more than 25 large clinical trials based on a wide range of once-promising ALS therapies have failed.
“Lots of things work well in mice but not in human patients,” she emphasizes. By finding a class of agents that is active in animal models even after disease onset, she hopes to reverse that string of negative results. Her group is also involved in the discovery and testing of THC variants that might be especially effective in ALS patients. “As a molecular biologist and a pharmacologist,” says Dr. Abood, “I’ve always had an interest in taking a drug from start to finish, from the lab bench to the clinic. That’s one big reason I came to California Pacific.”
A Crossroads of Scientists, Clinicians, and Patients
The interactions of Dr. Abood and her fellow ALS researchers with patients and clinicians ensure a high level of cooperation and, ultimately, a better chance of real progress toward improved and practical ALS therapies. Fortunately, the opportunities for such interactions are plentiful at California Pacific. The Forbes Norris MDA/ALS Research Center here is one of the largest ALS clinical research centers in the United States. It was also the first of six US centers designated by the Muscular Dystrophy Association for the treatment of ALS and related neuromuscular disorders.
“Our neuroscientists have locked arms with the clinical scientists to search for the cause and cure of ALS,” notes Robert G. Miller, MD, director of the Forbes Norris MDA/ALS Center. “Our patients have given generously with their donations of tissues and fluids to support this research. Our whole team is inspired by our patients to crack this disease wide open.”
Indeed, the California Pacific research teams are reminded every day of the ultimate goal of their efforts. According to Dr. Liu, “the proximity of our labs to the ALS patients who suffer from the disease and who have no cure at the moment adds further urgency to our search for new treatments.”