LOS ANGELES – A single look at the gut microbiome of patients with Alzheimer’s disease (AD) suggests an interaction between anti-inflammatory gut bacteria and long-term exposure to an investigational sigma 1 receptor agonist.
Dr. Christopher Missling
After up to 148 weeks treatment with Anavex 2-73, patients with stable or improved functional scores showed significantly higher levels of both Ruminococcaceae and Porphyromonadaceae, compared with patients who had declining function. Both bacterial families produce butyrate, an anti-inflammatory short-chain fatty acid.
Conversely, poor response was associated with a low level of Verrucomicrobia, a mucin-degrading phylum thought to be important in gut homeostasis. These bacteria live mainly in the intestinal mucosa – the physical interface between the microbiome and the rest of the body.
The data, presented at the Alzheimer’s Association International Conference, represent the first microbiome measurements reported in a clinical trial of an investigational Alzheimer’s therapy. Because they come from a single sample taken from a small group in an extension study, without a baseline comparator, it’s impossible to know what these associations mean. But the findings are enough to nudge Anavex Life Sciences into adding microbiome changes to its new study of Anavex 2-73, according to Christopher Missling, PhD, president and chief executive officer of the company.
The study, ramping up now, aims to recruit 450 patients with mild AD. They will be randomized to high-dose or mid-dose Anavex 2-73 for 48 weeks. The primary outcomes are measures of cognition and function. Stool sampling at baseline and at the end of the study will be included as well, Dr. Missling said in an interview.
Anavex 2-73 is a sigma-1 receptor agonist. A chaperone protein, sigma-1 is activated in response to acute and chronic cellular stressors, several which are important in neurodegeneration. The sigma-1 receptor is found on neurons and glia in many areas of the central nervous system. It modulates several processes implicated in neurodegenerative diseases, including glutamate and calcium activity, reaction to oxidative stress, and mitochondrial function. There is some evidence that sigma-1 receptor activation can induce neuronal regrowth and functional recovery after stroke. It also appears to play a role in helping cells clear misfolded proteins – a pathway that makes it an attractive drug target in Alzheimer’s disease, as well as other neurodegenerative diseases with aberrant proteins, such as Parkinson’s and Huntington’s diseases.
Anavex 2-73’s phase 2 development started with a 5-week crossover trial of 32 patients. This was followed by a 52-week, open-label extension trial of 10, 20, 30, and 50 mg/day orally, in which each patient was titrated to the maximum tolerated dose. The main endpoints were change on the Mini Mental State Exam and change on the Alzheimer’s Disease Cooperative Study-activities of daily living (ADCS-ADL) scale.
At 57 weeks, six patients had improved on the Mini Mental State Exam score: four with high plasma levels and two with low plasma levels, correlating to the dosage obtained. On the functional measure of activities of daily living, nine patients had improved, including five with high plasma levels, three with moderate levels, and one with a low level. One patient, with a moderate level, remained stable. The remaining 14 patients declined.
The company then enrolled 21 of the cohort in a 208-week extension trial, primarily because of patient request, Dr. Missling said. “They know they are doing better. Their families know they’re doing better. They did not want to give this up.”
Last fall, the company released 148-week functional and cognitive data confirming the initial findings: Patients with higher plasma levels (correlating with higher doses) declined about 2 points on the ADCS-ADL scale, compared with a mean decline of about 25 points among those with lower blood levels – an 88% difference in favor of treatment. Cognition scores showed a similar pattern, with the high-concentration group declining 64% less than the low-concentration group.
Sixteen patients consented to stool sampling. A sophisticated computer algorithm characterized the microbiome of each, measuring the relative abundance of phyla. Microbiome analysis wasn’t included as an endpoint in the original study design because, at that time, the idea of a connection between AD and the gut microbiome was barely on the research radar.
Things shifted dramatically in 2017, with a seminal paper finding that germ-free mice inoculated with stool from Parkinson’s patients developed Parkinson’s symptoms. This study was widely heralded as a breakthrough in the field – the first time any neurodegenerative disease had been conclusively linked to dysregulations in the human microbiome.
Last year, Vo Van Giau, PhD, of Gachon University, South Korea, and his colleagues published an extensive review of the data suggesting a similar link with Alzheimer’s disease.
Dr. Giau and his coauthors laid out a potential pathogenic pathway for this interaction.
“The microbiota is closely related to neurological dysfunction and plays a significant role in neuroinflammation through the secretion of proinflammatory cytokines. Changes in the homeostatic state of the microbiota lead to increased intestinal permeability, which may promote the translocation of bacteria and endotoxins across the epithelial barrier, inducing an immunological response associated with the production of proinflammatory cytokines. The activation of both enteric neurons and glial cells may result in various neurological disorders,” including Alzheimer’s, he wrote.
Dr. Missling said this paper, and smaller studies appearing at Alzheimer’s meetings, prompted the company to add the stool sampling as a follow-up measure.
“It’s something of great interest, we think, and deserves to be investigated.”
SOURCE: Missling C et al. AAIC 2019, Abstract 32260.