Cerebrospinal Fluid Profile of Lipid Mediators in Alzheimer's Disease

Abstract

Alzheimer's disease (AD) develops into dementia over a period of several years, during which subjective cognitive impairment (SCI) and mild cognitive impairment (MCI) can be used as intermediary diagnoses of increasing severity. Chronic neuroinflammation resulting from insufficient resolution is involved in the pathogenesis of AD and is associated with cognitive impairment. Specialized pro-resolving lipid mediators (LMs) that promote the resolution of inflammation may be valuable markers in AD diagnosis and as therapeutic targets. Liquid chromatography-tandem mass spectrometry was used to analyze pro-resolving and pro-inflammatory LMs in cerebrospinal fluid (CSF) from patients with cognitive impairment ranging from subjective impairment to a diagnosis of AD and correlated to cognition, CSF tau, and β-amyloid. Resolvin (Rv) D4, RvD1, neuroprotectin D1 (NPD1), maresin 1 (MaR1), and RvE4 were lower in AD and/or MCI compared to SCI. The pro-inflammatory LTB₄ and 15-HETE were higher in AD and MCI, respectively, while PGD2, PGE2, and PGF2a were decreased in AD, compared to SCI. RvD4 was also negatively correlated to AD tangle biomarkers, and positive correlations to cognitive test scores were observed for both pro-resolving LMs and their precursor fatty acids. In this exploratory study of the lipidome in CSF of AD, MCI, and SCI, the results indicate a shift in the LM profile from pro-resolving to pro-inflammatory in progression to AD, suggesting that it may be of use as a biomarker when followed by confirmation by replication studies.

Keywords: Biomarker; Cognitive tests; Gender; Inflammation; Resolution; Subjective cognitive impairment; Tau; β-amyloid.

Fig. 1

Study flow-chart. Cerebrospinal fluid (CSF) samples were obtained from a cohort of 136 patients subjected to clinical, radiography, and laboratory examinations for the diagnosis of subjective cognitive impairment (SCI) (n = 53), mild cognitive impairment (MCI) (n = 43), and Alzheimer's disease (AD) (n = 40)

Fig. 2

Pro-resolving LMs are reduced in CSF from MCI and AD patients, while pro-inflammatory LMs show a mixed pattern. Lipid mediators (LMs) were assessed in the cerebrospinal fluid (CSF) samples from patients with Alzheimer’s disease (AD) (n = 40), mild cognitive impairment (MCI) (n = 43), or subjective cognitive impairment (SCI) (n = 53), using liquid chromatography–tandem mass spectrometry (LC-MS/MS). The levels of resolvin (Rv) D4 (D4) and neuroprotectin D1 (NPD1) were reduced in CSF from AD and MCI compared to SCI, while the levels of the pro-inflammatory LM leukotriene B4 (LTB4) levels were higher in AD. The levels of maresin 1 (MaR1) and RvE4 were significantly lower in MCI patients compared to SCI. The levels of the intermediate precursor for RvD4, NPD1, and MaR1, 17-hydroxy docosahexaenoic acid (17-HDHA), were higher in AD than in MCI, and the levels of the intermediate precursor 15-hydroxyeicosatetraenoic acid (15-HETE) were lower in SCI compared to MCI and AD. The levels of prostaglandin (PG) D₂ were lower in CSF from MCI patients compared with SCI, and the PGE₂ levels were lower in AD and MCI patients compared to SCI. Comparisons between groups were performed by Kruskal–Wallis ANOVA with Dunn’s multiple comparisons post hoc test (*P < 0.05, **P < 0.005, ***P < 0.001, ****P < 0.0001)

Fig. 3

Pro-resolving LMs are reduced in CSF from MCI and AD patients in an age-matched sub-cohort. Lipid mediators (LMs) were assessed in the cerebrospinal fluid (CSF) samples from patients with Alzheimer’s disease (AD) (n = 15), mild cognitive impairment (MCI) (n = 17), or subjective cognitive impairment (SCI) (n = 21), using liquid chromatography–tandem mass spectrometry (LC-MS/MS). The reduced levels of resolvin (Rv) D4 in AD and MCI compared to SCI are confirmed in this smaller age-matched sub-cohort. Also, the reduced levels of RvE4 and prostaglandin (PG) E2 in MCI compared to SCI are confirmed, whereas there is no difference between AD and SCI for PGE2 in the age-matched cohort. Similarly, the increased levels of the intermediate precursor 15-hydroxyeicosatetraenoic acid (15-HETE) in MCI compared to SCI are confirmed, but not the difference between AD and SCI. The other alterations seen in the total cohort do not reach statistical significance in the age-matched cohort, but two additional changes were observed, i.e., reduced levels of RvD1 in AD compared to SCI and of PGF2a in AD and MCI compared to SCI. Comparisons between groups were performed by Kruskal–Wallis ANOVA with Dunn’s multiple comparisons post hoc test (*P < 0.05, **P < 0.005)

Fig. 4

Low levels of bioactive LMs correlate with low test scores for cognitive function. The levels of lipid mediators (LMs) in cerebrospinal fluid (CSF) samples from the total cohort of patients with Alzheimer’s disease (AD) (n = 40), mild cognitive impairment (MCI) (n = 43), or subjective cognitive impairment (SCI) (n = 53) were correlated to the mini-mental state examination (MMSE) test scores and the r-value according to Spearman rank-order test is given together with the P-value. Resolvin (Rv) D1 and RvD4 show positive correlation to the MMSE scores in the SCI group and when analyzing all three diagnostic groups together (Supplementary Table 2a). The omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) and the intermediate precursor 14-hydroxy-docosahexaenoic acid (14-HDHA) are positively correlated to the MMSE scores in the AD group. Also, levels of the omega-6 fatty acid arachidonic acid (AA) are positively correlated to the MMSE scores in the AD group

Fig. 5

Correlations of bioactive LMs with cognitive function in an age-matched sub-cohort. The levels of lipid mediators (LMs) in cerebrospinal fluid (CSF) samples from the age-matched cohort of patients with Alzheimer’s disease (AD) (n = 15), mild cognitive impairment (MCI) (n = 17), or subjective cognitive impairment (SCI) (n = 21) were correlated to the mini-mental state examination (MMSE) test scores and the r-value according to Spearman rank-order test is given together with the P-value. Resolvin (Rv) D4 shows positive correlation to the MMSE scores in the SCI group and when analyzing all three diagnostic groups together (Supplementary Table 4a). Unlike in the entire cohort, the levels of RvD1 did not correlate, but a positive correlation is observed in the MCI group between LTB4 and MMSE scores (r = 0.52, P < 0.05). The omega-3 fatty acid docosahexaenoic acid (DHA) and the intermediate precursor 14-hydroxy-docosahexaenoic acid (14-HDHA) are positively correlated to the MMSE scores in the AD group, whereas the eicosapentaenoic acid (EPA) is not. The levels of the omega-6 fatty acid arachidonic acid (AA) are also positively correlated to the MMSE scores in the AD group

Fig. 6

Correlations of bioactive LMs with tau protein in an age-matched sub-cohort. The levels of lipid mediators (LMs) in cerebrospinal fluid (CSF) samples from the age-matched cohort of patients with Alzheimer’s disease (AD) (n = 15), mild cognitive impairment (MCI) (n = 17), or subjective cognitive impairment (SCI) (n = 21) were correlated to the CSF levels of total tau (t-tau) or phosphorylated tau (p-tau) and the r-value according to Spearman rank-order test is given together with the P-value (see Supplementary Table 4c, d). In the AD group, resolvin (Rv) D1 shows a negative correlation to the p-tau levels and when analyzing all three diagnostic groups together, whereas prostaglandin (PG) D2 levels correlated positively to the levels of p-tau. The levels of the omega-3 fatty acids docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) correlated negatively to t-tau levels