Alzheimer's disease (AD), a progressive
neurodegenerative disease, is characterized by the accumulation of
senile plaques, neurofibrillary tangles, and loss of synapses and neurons in the brain. The pathophysiological process of AD begins with a long asymptomatic phase, which provides a potential opportunity for early therapeutic intervention. Therefore, it is crucial to define putative
biomarkers via reliable and validated methods for early diagnosis of AD. Here, we characterized candidate
biomarkers by discovery proteomics analysis of cerebrospinal fluid (CSF), revealing that 732 and 704
proteins with more than one unique
peptide were identified in healthy controls and preclinical AD patients, respectively. Among them, 79 and 98
proteins were significantly altered in preclinical AD for women and men, respectively, many of which have been demonstrated with consistent regulation pattern in patients with
mild cognitive impairment or AD
dementia. In-house developed 5-plex isotopic
N,N-dimethyl leucine (iDiLeu) tags were further utilized to verify candidate
biomarkers, neurosecretory
protein VGF (VGF) and
apolipoprotein E (
apoE). By labeling
peptide standards with different iDiLeu tags, a four-point internal calibration curve was constructed to allow for determination of the absolute amount of target analytes in CSF through a single liquid chromatography-mass spectrometry run.