Plasma Abeta levels do not reflect brain Abeta levels

Area of Science:

• Neurology
• Biochemistry
• Gerontology

Background:

• Alzheimer disease (AD) is characterized by cerebral amyloid beta protein (Abeta) accumulation.
• Abeta is detectable in cerebrospinal fluid and plasma.
• The utility of plasma Abeta as an AD risk marker is debated due to unknown correlations with neuropathologic levels.

Purpose of the Study:

• To investigate the relationship between plasma Abeta levels and brain Abeta burden in individuals with and without dementia.
• To determine if plasma Abeta40 and Abeta42 correlate with neuropathologic and biochemical measures of amyloid in the brain.

Main Methods:

• Comparison of plasma Abeta40 and Abeta42 levels with brain biochemical and pathologic Abeta levels.
• Analysis conducted on 25 individuals (17 AD, 3 control, 5 non-AD dementia) with blood collected a median of 1 year before death.
• Statistical adjustments for age and post-mortem interval were applied.

Main Results:

• Plasma Abeta40 and Abeta42 levels showed no association with any brain Abeta measures.
• No correlation was observed even after adjusting for age and post-mortem interval.
• APOE epsilon4 allele may influence the relationship between plasma Abeta42 and brain Abeta42.

Conclusions:

• Plasma Abeta40 and Abeta42 are not robust correlates of brain amyloid burden in Alzheimer disease.
• The APOE genotype's potential modifying effect on plasma-brain Abeta relationships warrants further investigation.