in new findings that may provide a prevention target.
Investigators found one of the clusters includes small high-density lipoprotein (HDL) metabolites associated with vascular dementia, while another cluster involves ketone bodies and citrate that are primarily associated with Alzheimer’s disease.
Ketone bodies, or ketones, are three related compounds – acetone, acetoacetic acid, and beta-hydroxybutyric acid (BHB) – produced by the liver during fat metabolism. Citrate is a salt or ester of citric acid.
Dr. Cornelia van Duijn
These metabolite clusters are not only linked to the future development of dementia but also correlate with early pathology in those under age 60 years, said study investigator Cornelia M. van Duijn, PhD, professor of epidemiology at Nuffield Department of Population Health, Oxford (England) University.
“These metabolites flag early and late pathology and may be relevant as targets for prevention of dementia,” she noted.
The findings were presented at the 2021 Alzheimer’s Association International Conference.
Weight loss before dementia explained?
For the study, investigators included 125,000 patients from the UK Biobank, which includes 51,031 who were over age 60 at baseline. Of these, 1,188 developed dementia during a follow-up of about 10 years; 553 were diagnosed with Alzheimer’s disease and 298 with vascular dementia.
Researchers used a platform that covers 249 metabolic measures, including small molecules, fatty acids, and lipoprotein lipids.
They estimated risk associated with these metabolites, adjusting for age, sex, body mass index, technical variables, ethnicity, smoking, alcohol, education, metabolic and neuropsychiatric medication, and APOE4 genotypes.
Of the 249 metabolites, 47 (19%) were associated with dementia risk in those over age 60, after adjustment.
The investigators examined effect estimates for associations of metabolites with both Alzheimer’s disease and vascular dementia over age 60 versus hippocampal volume under age 60. They found a “very strong, very significant” association for Alzheimer’s disease, and a “marginally significant” association for vascular dementia, said Dr. van Duijn.
This would be expected, as there is a much stronger correlation between hippocampal and Alzheimer’s disease versus vascular dementia, she added.
“We not only see that the metabolites predict dementia, but also early pathology. This makes these findings rather interesting for targeting prevention,” she said. An analysis of total brain volume showed “very strong, very similar, very significant associations” for both Alzheimer’s disease and vascular dementia,” added Dr. van Duijn.
The researchers found a major shift in various metabolites involved in energy metabolism in the 10-year period before the diagnosis of Alzheimer’s disease. These changes include low levels of branched-chain amino acids and omega-3 fatty acids and high levels of glucose, citrate, acetone, beta-hydroxybutyrate, and acetate. “This finding is in line with that in APOE models that show reduced energy metabolism over age in the brain,” said Dr. van Duijn.
She added that high levels of some of these metabolites are associated with low body weight before dementia onset, which may explain the weight loss seen in patients before developing the disease. “Our hypothesis is that the liver is burning the fat reserves of the patients in order to provide the brain with fuel,” she explained.