New leads on treating dementia and Alzheimer's
A new research study by scientists in Australia
and the US provides an explanation for why clinical trials of drugs reducing
proteins in the brain that were thought to cause dementia and Alzheimer's have
failed. The study has opened the way for potential new treatments with existing
drugs. Published online in the journal Human Molecular Genetics, the
researchers assembled evidence from a wide range of human studies and animal
models of dementia-related diseases to show that inflammation is a major cause,
not just a consequence.
They show that many genes linked with dementia regulate our
susceptibility and response to inflammatory damage.
"For decades, scientists have thought that dementia and
Alzheimer's Disease are caused by protein aggregates forming in the brain. But
recent clinical trials of drugs that reduce the aggregates have failed,"
says project leader Professor Robert Richards, from the University of
Adelaide's School of Biological Sciences. He is working in collaboration with
the University's Adelaide Medical School and the National Institutes of Health,
in the US.
Inflammation has long been known to increase as dementia-related
diseases progress, but only now is it identified as the cause. Previously it
was thought to act simply to clean up tissue damage caused by the protein
aggregates.
"We know that inflammation has different phases - early
on it can be protective against a threat by actively degrading it, but if the
threat is not removed, then persistent inflammation actually causes cell death,"
says Professor Richards.
The new work turns previous thinking around. The genetic
linkages imply that the inflammation comes first - and the tissue damage
second.
"Many genes linked with dementia operate at the level of
controlling cellular inflammation. Both internal and external triggers interact
with these genes to play a part. Inflammation is the point through which many
triggers converge," says Professor Richards.
He likens the brain inflammation to a virus infection. "Inflammation
is a very effective defence against foreign agents like viruses. But as we get
older and accumulate mutations, our cells can make proteins and DNA products
that mimic viruses, and these build up in the system," he says.
"Normally, our cells bar-code their own products to tell
them apart from foreign agents. When these bar-codes aren't in place, our cells
can't properly distinguish 'self' and 'non-self' trigger molecules. The result
is inflammation that escalates and spreads - hence the term autoinflammatory
disease."
Certain types of gene mutation cause these systems to fail earlier
or more often and can increase as we age - possibly accounting for age-related
increased risk of developing dementia.
The good news is that by reducing some elements of inflammation,
it may be possible to reduce dementia symptoms.
"With this new understanding of the disease, we now need
to test existing anti-inflammatory drugs for their effectiveness in treating
dementia," he says.
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