University of Louisville researcher has strong evidence connecting P. gingivalis and Alzheimer’s pathogenesis.
In animal models, oral Pg infection led to brain colonization and increased production of amyloid beta (Aβ), a component of the amyloid plaques commonly associated with AD.
Gum disease is also associated with heart disease and stroke.
The study team also found the organism’s toxic enzymes, or gingipains, in the neurons of patients with AD. Gingipains are secreted and transported to outer bacterial membrane surfaces and have been shown to mediate the toxicity of Pg in a variety of cells. The team correlated the gingipain levels with pathology related to two markers: tau, a protein needed for normal neuronal function, and ubiquitin, a small protein tag that marks damaged proteins.
Seeking to block Pg-driven neurotoxicity, Cortexyme set out to design a series of small molecule therapies targeting Pg gingipains. In preclinical experiments detailed in the paper, researchers demonstrated that by inhibiting the compound COR388, there was reduced bacterial load of an established Pg brain infection, blocked Aβ42 production, reduced neuroinflammation and protected neurons in the hippocampus – the part of the brain that mediates memory and frequently atrophies early in the development of AD.
In October 2018, Cortexyme announced results from its Phase 1b clinical trial of COR388 at the 11th Clinical Trials in Alzheimer’s Disease Conference. COR388 showed positive trends across several cognitive tests in patients suffering from AD, and Cortexyme plans to initiate a Phase 2 and 3 clinical trial of COR388 in mild to moderate AD in 2019.
The team swabbed the gums of healthy mice with P. gingivalis every other day for 6 weeks to establish an infection. They later detected the bacteria in the animals’ brains, along with dying neurons and higher than normal levels of β-amyloid protein. In a lab dish, the gingipains—whose job is to chop up proteins—damaged tau, a regularly occurring brain protein that forms tangles in people with Alzheimer’s. In the brain, this protein damage may spur the formation of tangles.
Porphyromonas gingivalis, the keystone pathogen in chronic periodontitis, was identified in the brain of Alzheimer’s disease patients. Toxic proteases from the bacterium called gingipains were also identified in the brain of Alzheimer’s patients, and levels correlated with tau and ubiquitin pathology. Oral P. gingivalis infection in mice resulted in brain colonization and increased production of Aβ1–42, a component of amyloid plaques. Further, gingipains were neurotoxic in vivo and in vitro, exerting detrimental effects on tau, a protein needed for normal neuronal function. To block this neurotoxicity, we designed and synthesized small-molecule inhibitors targeting gingipains. Gingipain inhibition reduced the bacterial load of an established P. gingivalis brain infection, blocked Aβ1–42 production, reduced neuroinflammation, and rescued neurons in the hippocampus. These data suggest that gingipain inhibitors could be valuable for treating P. gingivalis brain colonization and neurodegeneration in Alzheimer’s disease.