Biologic Inhibition of Lipid Metabolism
In addition to pharmacologic treatment, genetic mutations affect CPT1 function. The Hutterites, an ethnoreligious group in Canada, have a mutation in CPT1A that almost completely blocks the molecule’s activity. Similarly, the Inuit have a mutation in CPT1A that reduces its activity to approximately 22%. The prevalence of MS is one in 1,100 among the Hutterites and one in 50,000 among the Inuit, compared with one in 350 in the Canadian population. These observations suggest that gene therapy could be another way to block CPT1.
Dr. Nieland’s group collaborated with the Netherlands Cancer Institute to develop mouse strains with two distinct mutations in CPT1A. The first mutation mimics that found among the Hutterites, and the other mimics that found among the Inuit. In a preliminary study, the investigators induced EAE in three wild-type mice and two mice with the CPT1A mutation similar to that of the Inuit. The mice were 10 weeks old at the time of immunization.
At 24 days, disease score was lower in the CPT1A mutant mice, compared with the wild-type mice. Furthermore, body weight was higher in the mutant mice, compared with the wild-type mice. The investigators also measured the mice’s grip strength at Day 2 and Day 24. Grip strength decreased in the wild-type mice but remained the same in the mutant mice. At Day 24, grip strength was significantly higher among mutant mice than among wild-type mice.
“These results indicate an interaction of the lipid metabolism in the brain and in the immune system, which supports our hypothesis regarding MS pathology,” said Anne Skøttrup Mørkholt, a doctoral student at Aalborg University, who collaborated with Dr. Nieland on these animal studies. “MS is not a disease of the immune system, but a systemic disease with dysregulation of multiple components.”
Anne Skøttrup Mørkholt
Lipid Metabolism in Other Neurologic Diseases
Data suggest that lipid metabolism may contribute to other neurologic diseases such as amyotrophic lateral sclerosis (ALS) as well. Huang et al found a correlation between serum triglyceride levels and the development of ALS. Dupuis et al observed upregulated lipid metabolism and downregulated glucose metabolism in SOD1 mouse models of the disease, as did subsequent researchers. In addition, a 2015 study by Palamiuc et al found that CPT1B was significantly increased in the muscle tissue of SOD1 mice.
To investigate whether suppressing lipid metabolism affected ALS, Dr. Nieland’s group examined a SOD1 mouse model of the disease. The mice developed symptoms at Day 70 and were randomized at Day 100 to etomoxir or placebo. Etomoxir was associated with less weight loss and better neurologic score, compared with placebo. Etomoxir also was associated with better performance on the wire hanging and rotarod tests, compared with placebo. “It seems like etomoxir was able to slow down the disease progression,” said Michael Sloth Trabjerg, MD, a doctoral student at Aalborg University.
Michael Sloth Trabjerg, MD
Because research has found increased beta oxidation and decreased glucose metabolism in Parkinson’s disease, Dr. Nieland’s group studied the effect of CPT1 inhibition in a rotenone mouse model of the disease. They induced the disease in the mice for 32 days before randomizing them to placebo or etomoxir. For all mice, treatment alternated between rotenone on one day and placebo or etomoxir on the next day. The investigators observed significantly better sensorimotor performance among treated mice, compared with controls, on Day 47 and Day 56. At Day 60, mice who received etomoxir had significantly more muscle strength and longer latency to fall on the rotarod test, compared with mice that received placebo. These data are being prepared for publication.
The data suggest that dysregulated glucose metabolism and increased lipid metabolism play a role in ALS and Parkinson’s disease. “CPT1 seems to be a prominent target for moderating these diseases,” said Dr. Trabjerg.