EVIDENCE that the condition is caused by a bacterium involved in gum disease could prove a game-changer in tackling one of medicine’s biggest mysteries, and lead to effective treatments or even a vaccine.
Alzheimer’s constitutes some 70 per cent of these cases , yet we don’t know what causes it. The condition, which results in progressive loss of memory and cognitive function, usually over a decade or so, is devastating both to those who have it and to their loved ones.
The condition often involves the accumulation of two types of proteins – called amyloid and tau – in the brain. As these are among the earliest physical signs of the disease, the leading hypothesis since 1984 has been that the condition is caused by the defective control of these proteins, especially amyloid, which accumulates to form large, sticky plaques in the brain.
The bulk of research into understanding and treating Alzheimer’s has centred on this “amyloid hypothesis”. Huge sums of money have been invested in experiments involving mice genetically modified to produce amyloid, and in developing drugs that block or destroy amyloid proteins, or sometimes degraded tangles of tau.
Hope for treatments
The speed at which damage accumulates is a key factor in the disease. Although many people harbour P. gingivalis in their mouths, only some develop Alzheimer’s. Because it can be decades before Alzheimer’s symptoms appear, whether a person develops the condition could come down to how much damage occurs before they die of other causes.
Some have begun to question the amyloid hypothesis. The lack of results has been compounded by the discovery that people – including some in their 90s with exceptional memories – can have brain plaques and tangles without having dementia. In a review of the research to date last year, Bryce Vissel at the University of Technology Sydney, Australia, concluded that there isn’t sufficient data to suggest that “amyloid has a central or unique role in Alzheimer’s”.
Bacteria in the brain
In 2016, researchers discovered that amyloid seems to function as a sticky defence against bacteria. They found that the protein can act as an anti-microbial compound that kills bacteria, and when they injected bacteria into the brains of mice engineered to make Alzheimer’s proteins, plaques developed round bacterial cells overnight.
Multiple teams have been researching Porphyromonas gingivalis, the main bacterium involved in gum disease, which is a known risk factor for Alzheimer’s. So far, teams have found that P. gingivalis invades and inflames brain regions affected by Alzheimer’s; that gum infections can worsen symptoms in mice genetically engineered to have Alzheimer’s; and that it can cause Alzheimer’s-like brain inflammation, neural damage and amyloid plaques in healthy mice. -Internet
