A study using genetically engineered mice and human cell and tissue samples has added to evidence that higher levels of inflammatory chemicals involved in fat metabolism occur in people with the neuromuscular disorder amyotrophic lateral sclerosis (ALS). The study, which focused on genetic pathways involved in how spinal motor cells process fats, found that compared with people without ALS, individuals with the disorder have about 2.5-fold higher levels of arachidonic acid, a lipid commonly found in the fatty parts of meat and fish, which plays a role in promoting inflammatory processes needed to repair wounds or tissue damage.
The researchers, headed by Gabsang Lee, DVM, PhD, associate professor of neurology at the Johns Hopkins University School of Medicine, and member of the Institute for Cell Engineering at Johns Hopkins Medicine, used caffeic acid—an anti-inflammatory compound found naturally in coffee, tea, tomatoes, and wine—to tamp down the arachidonic acid pathway in mice bred to develop the biological hallmarks of ALS. They found that treated animals demonstrated reduced muscle-weakening symptoms, and experienced a 20–25% increase in grip strength, along with 2–3 weeks’ extended survival.
The team cautions against people with ALS treating themselves with caffeic acid, which they noted is sold as an unregulated dietary supplement. The investigators suggest that more studies are needed to determine safe levels of caffeic acid supplements, with some reports having indicated potentially harmful side effects, including cancers and gut problems. The researchers also noted that experts warn that arachidonic acid—also sold in alleged muscle enhancement powders—in inappropriate and untested amounts can be toxic, triggering brain cells to die off.
Lee and colleagues reported on their study in Nature Neuroscience, in a paper titled, “Multi-omics analysis of selectively vulnerable motor neuron subtypes implicates altered lipid metabolism in ALS.” Lee has filed provisional patents for technology related to the potential use of the arachidonic acid pathway to treat ALS.
ALS is a disorder in which motor neurons degenerate, the causes of which remain unclear, the authors noted. Progressive loss of spinal motor neurons (sMNs) is a hallmark of ALS, and results in progressive paralysis and eventually death. Some 30,000 people in the United States have ALS, according to the researchers. About 10% of ALS cases are inherited, and more than 20 genes are now known to cause familial ALS (fALS). “However, 90% of ALS cases are sporadic (sALS) and caused by unknown factors,” the team continued. There is no known curative treatment.
The new study builds on the established observation that although patients with ALS lose most of their muscle control because of damaged spinal motor neurons, generally they can still control their eye movements, which are guided by ocular neurons, Lee pointed out. “Ocular motor neurons (oMNs) are functionally intact in most individuals with ALS,” the team noted. “While motor neuron subtypes in the spinal cord, hindbrain, and cortex are gradually impaired or lost during ALS progression leading to disability of voluntary movement, oMNs in the midbrain remain relatively unaffected until the final stages.”
To explore any potentially important genetic differences between disease-free ocular neurons and spinal motor neurons, Lee’s team studied stem cell lines they cultivated from an individual with ALS. Looking at the genetic pathways actively making proteins, the scientists found more activity in genes that control lipid metabolism—the process in which cells process fat.
Lee then sent to colleagues at the University of Southern California samples of ocular neurons and spinal motor neurons from 17 people with ALS who were treated at the Johns Hopkins Hospital, and six sample sets of people without the condition. The researchers confirmed that the spinal motor neurons and ocular neurons of the people with ALS contained completely different amounts and types of lipids, when compared with people without the condition. “ … we applied comparative multi-omics analysis of human induced pluripotent stem cell-derived sMNs and ocular motor neurons to identify shared metabolic perturbations in inherited and sporadic ALS sMNs, revealing dysregulation in lipid metabolism and its related genes,” they wrote. “Targeted metabolomics studies confirmed such findings in sMNs of 17 ALS (SOD1, C9ORF72, TDP43 (TARDBP) and sporadic) human induced pluripotent stem cell lines, identifying elevated levels of arachidonic acid.”
Further analysis carried out to identify which lipid pathways were most altered between cells of people with ALS and cells of people without the disease showed that one pathway, arachidonic acid, stood out. Arachidonic acid is an omega-6 fatty acid that controls the body’s inflammatory response, and has been linked to Alzheimer’s and Parkinson’s diseases. Two decades ago, researchers found higher than expected amounts of the enzyme in neuromuscular tissue of people with ALS.
Lee noted that lipid pathways have been highly studied because they are critical parts of the cell membrane that enable the flow of molecules in and out of cells. Cell membranes often break when there is inflammation, and the body must tightly regulate arachidonic acid, or inflammation can run amok and send signals to the immune system to destroy neural tissue.
To further test the potential role of arachidonic acid in ALS, the investigators performed experiments to reverse its effects. First, they fed caffeic acid to fruit flies genetically engineered to develop ALS-type symptoms. They found that flies fed caffeic acid were able to move around more, climb up the test tube more often, and lived longer than flies that did not receive the compound.
The scientists then conducted similar experiments with caffeic acid in mice bred to develop ALS. They found that those receiving the compound lived two to three weeks longer than mice that weren’t fed the compound. The authors concluded, “Taken together, our data demonstrate that substantially dysregulated lipid metabolism pathways are common in 17 different ALS hiPSC-derived sMN cultures, and pharmacological modulation of AA metabolism shows protective effects in an in vitro human sMN model and Drosophila model and SOD1G93A mouse models.”
Although the new evidence may one day point to potential new therapeutic strategies for ALS, Lee said that questions do remain. “We don’t know yet why ocular and spinal neurons differ in lipid metabolism or what percentage of ALS patients have alterations in the arachidonic acid pathway,” he said. Nevertheless, the team stated, “The current study provides a new framework for disease modeling by comparing affected and non-affected cell types from a disease hiPSC line, leading to the unraveling of metabolic aberrations in ALS sMNs and identification of potential drug candidates.”