Affiliations: [a] Division of Alzheimer Neurobiology Center, Karolinska Institutet, Department of Neurobiology, Care Sciences and Society, Stockholm, Sweden | [b] Department of Geriatric Medicine, Karolinska University Hospital Huddinge, Stockholm, Sweden
Correspondence:
[*]
Correspondence to: Taher Darreh-Shori, PhD, Karolinska Institutet, Department of Neurobiology, Care Sciences and Society, Division of Alzheimer Neurobiology, Novum Floor 4th, 141 86 Stockholm, Sweden. Tel.: +46 8 585 863 12; Fax: +46 8 585 854 70; E-mail: Taher.Darreh-Shori@ki.se.
Abstract: Butyrylcholinesterase K (BCHE-K) is associated with increased risk of developing Alzheimer's disease (AD) in apolipoprotein ε (APOE4) carriers, while among APOE4 non-carriers BCHE-K appears to be protective. Nonetheless, pure pharmacogenetic reports have provided conflicting results. To provide insights about these controversies, we combined BCHE-K pharmacogenetic observations in AD patients (n = 179) with proteomic and enzymatic analysis of plasma, cerebrospinal fluid (CSF), or both samples. We found that BCHE-K genotype was overrepresented among the AD patients (χ2 = 14.21, p < 0.0001). Plasma BuChE activity was gene dose-dependently 20–50% less among K-carriers (p < 0.001). CSF BuChE activity did not show such robust K-gene dosage-dependency, because K homozygotes (n = 9) had 30–40% less activity compared to both non-carriers (n = 78, p < 0.01) and heterozygotes (n = 42, p < 0.09). CSF ApoE protein expression was also altered by presence of K-allele (p < 0.001, n = 129). Mutually, APOE4 altered phenotypic display of BuChE variants in CSF (p < 0.01, n = 129). In absence of APOE4, CSF BuChE activity was essentially indistinguishable among K-carriers (n = 16) and non-carriers (n = 17, p < 0.8) although the K-carriers had 24–39% less circulating BuChE protein. In contrast in presence of APOE4, the K-carriers (n = 35) had K allele dose-dependently a BuChE phenotype with 14–46% reduced activity compared to K non-carriers (p < 0.001, n = 59), despite an essentially identical BChE concentration in CSF (1 ± 4%, p < 0.8). Pattern of the patients' cognitive performance in MMSE closely resembled the APOE4-derived phenotypic display of BuChE variants. APOE4-dependent outcome of BCHE-K genotype as AD risk factor arises through a differential phenotypic modulation of BuChE. Future pharmacogenetic studies should include assessment of the subjects' true phenotypic display of BuChE.
Keywords: Acetylcholinesterase, Alzheimer's disease, apolipoprotein ε4 genotype, cutyrylcholinesterase K variant, central cholinergic system, pharmacogenetic
