How 2 common viruses can cause Alzheimer’s disease?

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Are two common viruses responsible for the onset of Alzheimer’s disease? Image Source: Bloomberg Creative / Getty Images.
  • A new study has found that two very common viruses that most people carry can interact to cause Alzheimer’s disease.
  • Vaccines against one of the viruses appear to reduce the risk of developing Alzheimer’s disease.
  • Research suggests that other common viruses may fuel the development of the debilitating state.

A study by researchers at Tufts University in Medford, Massachusetts reports that a combination of very common viruses may be the leading cause of Alzheimer’s disease (AD).

The virus responsible for chickenpox and shingles can activate the dormant herpes virus that is closely associated with AD in an active state.

The varicella zoster virus (VZV) is the virus that causes the chickenpox – or Chickenpox – in childhood and can cause shingles – shingles – later in life.

Correspondent author of the study, prof. Tufts’ David Kaplan said Medical news today that “[m]over 95% of adults contracted chickenpox in childhood and adolescence ”. The virus remains in the body afterwards.

Co-author Dr. Ruth Itzhaki, visiting professor at the University of Oxford and Professor Emeritus of the University of Manchester, said MNT that “age and weakening of the immune system with age, and immunosuppression” are factors that can awaken VZV as shingles in an adult.

Before the new study, ‘VZV was related to AD, but the link was unclear and the mechanisms were not understood,’ said Dr Itzhaki.

The study found that when VZV activates as shingles, it reactivates while dormant herpes simplex type 1 virus (HSV-1). In 2021, Dr. Itzhaki published a compilation significant study research collection showing the relationship between activated HSV-1 and AD.

HSV-1 is also extremely common, with 50% to 80% of American adults carrying the virus. Although the oral or genital forms of VZV are active, it can cause painful blisters at the site of infection.

Dr. Itzhaki noted:

“It is now known that infectious diseases are generally associated with a risk of AD, and our results explain this for shingles. We are currently investigating whether this is the case for some other infections. If so, that would explain the main risk posed by infectious diseases. ‘

“If we change paradigms,” said Prof. Kaplan, “to focus our efforts more on preventive treatment strategies for these microbial species before they have a chance to wreak havoc, we can do a better job of preventing this disease.”

The study appears in Alzheimer’s Disease Journal.

“Thirty years of evidence from my lab, and then from many others, suggests that HSV-1 is the leading cause of AD, although the disease is obviously multifactorial,” Dr. Itzhaki told us.

According to prof. Kaplan, “a number of factors have been reported that reactivate HSV-1 from a latent state, including stresses and disease states.” Dr. Itzhaki added “stress, immunosuppression, UV light and menstruation” as possible triggers.

Dr. Tharick Pascoal, assistant professor of psychiatry and neurology at the University of Pittsburgh School of Medicine, who was not involved in the study, commented on the results.

“This study adds to the evidence that suggests HSV-1 may lead to neuritis, which is associated with an increased risk of developing Alzheimer’s disease,” he noted.

“Interestingly,” he added, “this study suggests that this occurs independently of amyloid and tau deposition, which may support the notion that there are independent neurinflammatory pathways leading to AD or that the presence of inflammation reduces brain reserve, making patients more susceptible.” to the development of AD ”.

“If the latter is true,” said Dr. Pascoal, “we can imagine that various viruses may increase the risk of AD, including COVID-19.”

The study authors noted that there was evidence that both HSV-1 and VZV could become activated after COVID-19.

Professor Kaplan said MNT believes that his study “also shows how the 3D tissue model can be used to explain such interactions and synergies using relatively rapid methods”. Much AD research uses animal models.

To test the effect of active VZV on inactive HSV-1, prof. Kaplan and his colleagues created brain-like environments embedded in six-millimeter donut-shaped sponges made of silk protein and collagen.

Nerve stem cells – some of which developed into functional neurons and some became supportive glial cells in the brain – were delivered to the sponges.

When scientists introduced VZV into brain tissue, they found that although the neurons became infected, there was no trigger for the development of the AD characteristic amyloid plaques or tau protein tangles. More importantly, the functionality of the neurons also remained intact.

However, when they introduced VZV into dormant HSV-1 neurons, HSV-1 was reactivated, there was an increased increase in amyloid and tau protein, and electrical signals from the neurons began to slow down, as in AD.

Scientists have put a lot of effort into developing vaccines for HSV-1, but so far no effective vaccine exists. Some have suggested that mRNA vaccines could provide a more productive way forward.

Dr. Pascoal suggested there might be cause for hope, saying, “I think during the COVID pandemic we learned a lot about mRNA vaccines in a very short time.”

“I am optimistic that we will have effective mRNA-based vaccines for a variety of purposes in the coming years, using the knowledge gained from COVID-19,” he told us.

Dr. Heather M. Snyder, Alzheimer’s Association’s vice president for medical and scientific relations, and not involved in the research, however, expressed some caution.

“Any potential therapy must be evaluated in a number of rigorous human studies. Several antiviral studies are ongoing, including one funded by the Alzheimer’s Association through our Part the Cloud initiative, ‘she noted.

Meanwhile, while there is no vaccine for HSV-1, there are vaccines for shingles. The idea that stopping VZV can help people avoid AD is supported by: previous researchincluding Dr. Itzhaki’s own.

Obtaining a shingles vaccine was found to be indeed associated with a reduced risk of AD.

Meanwhile, Dr. Snyder said: “As we age, there are things that research says are good for our body and brain – engaging in physical activity, eating a balanced diet, and keeping your brain active and engaged. Find out more about reducing the risk of cognitive decline and dementia at the Alzheimer’s Association website.

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