Specific Cerebrospinal Fluid SerpinA1 Isoform Pattern in Alzheimer's Disease

Abstract

SerpinA1 (α1-antitrypsin) is a soluble glycoprotein, the cerebrospinal fluid (CSF) isoforms of which showed disease-specific changes in neurodegenerative disorders that are still unexplored in Alz-heimer’s disease (AD). By means of capillary isoelectric focusing immunoassay, we investigated six serpinA1 isoforms in CSF samples of controls (n = 29), AD-MCI (n = 29), AD-dem (n = 26) and Lewy body disease (LBD, n = 59) patients and correlated the findings with CSF AD core biomarkers (Aβ42/40 ratio, p-tau, t-tau). Four CSF serpinA1 isoforms were differently expressed in AD patients compared to controls and LBD patients, especially isoforms 2 and 4. AD-specific changes were found since the MCI stage and significantly correlated with decreased Aβ42/40 (p < 0.05) and in-creased p-tau and t-tau levels in CSF (p < 0.001). Analysis of serpinA1 isoform provided good di-agnostic accuracy in discriminating AD patients versus controls (AUC = 0.80) and versus LBD patients (AUC = 0.92), with best results in patients in the dementia stage (AUC = 0.97). SerpinA1 isoform expression is altered in AD patients, suggesting a common, albeit disease-specific, in-volvement of serpinA1 in most neurodegenerative disorders.

Keywords: Alzheimer’s disease; CIEF immunoassay; biomarker; cerebrospinal fluid; serpinA1.

Figure 1

Typical CIEF electropherograms of serpinA1 isoforms. Exemplary CIEF electropherograms of (A) control subjects (six distinct peaks in the pH range of 4.3–4.7), (B) patients with Alzheimer’s disease with dementia (AD-dem) (with a relative decrease in isoform 2 and an increase in peak 4) and (C) patients with Parkinson’s disease with dementia (PDD). The grey color indicates the area under each peak. Signal intensity is reported in chemiluminescence units (CUs). pI: isoelectric point; exposure time: 120 s.

Figure 2

SerpinA1 isoform expression in AD, controls and LBD. (A) Comparison of total absolute peak areas among diagnostic groups (AD: Alzheimer’s disease, n = 55; Controls, n = 29; LBD: Lewy body disorders, n = 59), expressed in chemiluminescence units (CUs). (B–H) Relative expression of isoforms 0–6, reported as a percentage (normalized area *10⁻²). Box plots indicate median value, interquartile range and range of values. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001.

Figure 3

Relative expression of serpinA1 isoforms 0, 1, 2 and 4 among diagnostic subgroups. (A–D) Comparison of the relative expression of serpinA1 isoforms in controls, AD-MCI, AD-dem, PD, PD-MCI, PDD and DLB. Box plots indicate median value, interquartile range and range of values. * p < 0.05, ** p < 0.01, *** p < 0.001, **** p < 0.0001. Abbreviations. AD-dem: Alzheimer’s disease with dementia; AD-MCI: Alzheimer’s disease with mild cognitive impairment; DLB: dementia with Lewy bodies; PD: Parkinson’s disease; PDD: Parkinson’s disease with dementia; PD-MCI: Parkinson’s disease with mild cognitive impairment.

Figure 4

Receiver operating characteristic analysis. ROC curves relative to expression of isoforms 0, 1, 2 and 4 for discrimination of (A) AD vs. controls, (B) AD vs. LBD, (C) AD-dem vs. PDD/DLB and (D) AD-MCI vs. PD-MCI. Abbreviations. AD: Alzheimer’s disease; AD-dem: Alzheimer’s disease with dementia; AD-MCI: Alzheimer’s disease with mild cognitive impairment; AUC: area under the curve; DLB: dementia with Lewy bodies; LBD: Lewy body disease; PDD: Parkinson’s disease with dementia; PD-MCI: Parkinson’s disease with mild cognitive impairment; ROC: receiver operating characteristic.