Research
A novel Aβ isoform pattern in CSF reflects γ-secretase inhibition in Alzheimer disease
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* Corresponding author: Erik Portelius erik.portelius@neuro.gu.se
1 Department of Psychiatry and Neurochemistry, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at the University of Gothenburg, Molndal, SE-431 80, Sweden
2 Translational Medicine, Eli Lilly and Company, Lilly Corporate Headquarters, Indianapolis, IN 46285, USA
3 Global Alzheimer's Disease Research Team, Eli Lilly and Company, Lilly Corporate Headquarters, Indianapolis, IN 46285, USA
Alzheimer's Research & Therapy 2010, 2:7 doi:10.1186/alzrt30
Published: 29 March 2010Abstract
Introduction
LY450139 (semagacestat) inhibits γ-secretase, a key enzyme for generation of amyloid β (Aβ), the peptide deposited in plaques in Alzheimer disease (AD). Previous data have shown that LY450139 lowers plasma Aβ, but has no clear effect on Aβ1-40 or Aβ1-42 levels in cerebrospinal fluid (CSF). By using targeted proteomics techniques, we recently identified several shorter Aβ isoforms, such as Aβ1-16, that in experimental settings increase during γ-secretase inhibitor treatment, and thus may serve as sensitive biochemical indices of the treatment effect. Here, we test the hypothesis that these shorter Aβ isoforms may be biomarkers of γ-secretase inhibitor treatment in clinical trials.
Methods
In a phase II clinical trial, 35 individuals with mild to moderate AD were randomized to placebo (n = 10) or LY450139 (100 mg (n = 15) or 140 mg (n = 10)) and underwent lumbar puncture at baseline and after 14 weeks of treatment. The CSF Aβ isoform pattern was analyzed with immunoprecipitation combined with MALDI-TOF mass spectrometry.
Results
The CSF levels of Aβ1-14, Aβ1-15, and Aβ1-16 showed a dose-dependent increase by 57% and 74%, 21% and 35%, and 30% and 67%, respectively in the 100-mg and 140-mg treatment groups. Aβ1-40 and Aβ1-42 were unaffected by treatment.
Conclusions
CSF Aβ1-14, Aβ1-15, and Aβ1-16 increase during γ-secretase inhibitor treatment in AD, even at doses that do not affect Aβ1-42 or Aβ1-40, probably because of increased substrate availability of the C99 APP stub (APP β-CTF) induced by γ-secretase inhibition. These Aβ isoforms may be novel sensitive biomarkers to monitor the biochemical effect in clinical trials.
Trial registration
Clinical Trials.gov NCT00244322