Apolipoprotein D levels are elevated in prefrontal cortex of subjects with Alzheimer's disease: No relation to apolipoprotein E expression or genotype

Background: Apolipoprotein E (apoE) has been implicated in the pathology of AD ever since inheritance of the ε4 allele was shown to be an important risk factor for the development of AD. Apolipoprotein D (apoD) is elevated in association with several central nervous system disorders, including Alzheimer's disease (AD), and has been proposed to be an especially robust marker for brain regions specifically affected by particular neuropathologies. Progressive cognitive decline is the core clinical feature of AD and is associated with disturbances in the prefrontal cortex. Methods: We measured apoD levels in prefrontal cortex samples obtained postmortem from 20 autopsy-confirmed AD subjects and 40 control subjects. Results: Enzyme-linked immunosorbent assay analysis revealed a significant increase in apoD expression in AD subjects compared with control subjects (.218 ± .029 μg/mg protein vs. .117 ± .011 μg/mg protein; p = .0003). There was no significant difference in apoD expression between early-onset and late-onset Alzheimer's subjects. Apolipoprotein D expression levels were not correlated with apoE levels, nor were they correlated with inheritance of the APOE ε4 allele. Conclusions: These findings suggest that apoD may be related to the cognitive decline observed in AD patients and that apoD and apoE likely play different roles in the pathogenesis of AD.