Study links gum bacteria to Alzheimer’s

Stephen Dominy and colleagues at Cortexyme and several academic institutions reported in a January 23, 2019 Science Advances paper that they found the oral bacterium *Porphyromonas gingivalis* in the brains of people with Alzheimer’s disease. The paper also described toxic bacterial enzymes called gingipains in postmortem brain tissue and said their levels tracked with tau and ubiquitin pathology. In mice, the researchers said oral infection led to brain colonization and higher production of Aβ1-42, a component of amyloid plaques. The findings helped push an experimental gingipain inhibitor, atuzaginstat, into human testing, though the paper did not show that the bacterium causes Alzheimer’s in people. ### What exactly did the 2019 study find in human brains? The January 2019 study said *P. gingivalis*, a bacterium best known as a driver of chronic periodontitis, was identified in Alzheimer’s disease brains. The researchers also detected gingipains, proteases made by the bacterium, in brain samples from people with Alzheimer’s. More than 90% of postmortem Alzheimer’s brains in the study showed gingipain antigen, according to a follow-up paper by some of the same researchers and a review of the field. (science.org) The Science Advances paper said gingipain levels correlated with tau and ubiquitin pathology, linking the bacterial signal to proteins already associated with neurodegeneration. ### Why did the mouse experiments draw attention? (science.org) In mice, the Science Advances paper said oral infection with *P. gingivalis* produced brain colonization and increased Aβ1-42 production. Aβ1-42 is a form of amyloid-beta that is found in amyloid plaques, one of the hallmarks seen in Alzheimer’s disease brains. The same paper said small-molecule gingipain inhibitors reduced bacterial load, lowered neuroinflammation and rescued neurons from gingipain-related toxicity in the animal experiments. (pmc.ncbi.nlm.nih.gov) Alzforum, summarizing the study and outside commentary, said the work revived interest in the idea that infection and inflammation may contribute to at least some Alzheimer’s cases. (science.org) ### Did the researchers say this proves gum disease causes Alzheimer’s? The authors did not present the study as proof of causation in humans. A later review in the Journal of Alzheimer’s Disease said epidemiological studies had identified an association between periodontitis and Alzheimer’s disease, but that the nature of the relationship remained unclear. Alzforum’s coverage of the 2019 paper quoted outside researchers saying the case for *P. gingivalis* as a contributor to Alzheimer’s progression was compelling, while also saying it was unlikely to be the only bacterium or only cause involved. (science.org) That is a narrower claim than saying gum disease directly causes Alzheimer’s. (pmc.ncbi.nlm.nih.gov) ### What was the therapy the paper pointed toward? Cortexyme’s proposed follow-up therapy was atuzaginstat, also known as COR388, a gingipain inhibitor designed to block the bacterium’s toxic enzymes. Alzforum reported in January 2019 that the company had completed Phase 1 testing and planned a Phase 2/3 study in people with mild to moderate Alzheimer’s disease. (alzforum.org) The GAIN trial was later described in a February 2021 SEC filing as a randomized, double-blind, placebo-controlled Phase 2/3 study evaluating the drug’s efficacy, safety and tolerability in mild to moderate Alzheimer’s disease. That filing confirms the “large human trials” step the original paper argued should follow the lab findings. ### How should readers treat the claim now? (alzforum.org) The 2019 paper remains one of the best-known studies linking *P. gingivalis* to Alzheimer’s pathology, but later reviews describe the evidence as an association with mechanistic support rather than settled proof of human causation. Reviews published since then say the hypothesis is biologically plausible and supported by animal and tissue data, while also noting that Alzheimer’s disease is multifactorial. (sec.gov) The next concrete step after the paper was not another mouse experiment but human drug testing. The GAIN trial of atuzaginstat, identified in company SEC filings and Alzheimer’s treatment databases, became the named clinical milestone tied to this line of research. (sec.gov) (pmc.ncbi.nlm.nih.gov)