Plasma apolipoprotein E levels in longitudinally followed patients with mild cognitive impairment and Alzheimer's disease.

BACKGROUND: Low levels of plasma apolipoprotein E (apoE) and presence of the APOE ε4 allele are associated with an increased risk of Alzheimer's disease (AD). Although the increased risk of AD in APOE ε4-carriers is well-established, the protein levels have received limited attention. METHODS: We here report the total plasma apoE and apoE isoform levels at baseline from a longitudinally (24 months) followed cohort including controls (n = 39), patients with stable amnestic mild cognitive impairment during 24 months follow up (MCI-MCI, n = 30), patients with amnestic MCI (aMCI) that during follow-up were clinically diagnosed with AD with dementia (ADD) (MCI-ADD, n = 28), and patients with AD with dementia (ADD) at baseline (ADD, n = 28). We furthermore assessed associations between plasma apoE levels with cerebrospinal fluid (CSF) AD biomarkers and α-synuclein, as well as both CSF and plasma neurofilament light chain (NfL), YKL-40 and kallikrein 6. RESULTS: Irrespective of clinical diagnosis, the highest versus the lowest apoE levels were found in APOE Îµ2/ε3 versus APOE Îµ4/ε4 subjects, with the most prominent differences exhibited in females. Total plasma apoE levels were 32% and 21% higher in the controls versus MCI-ADD and ADD patients, respectively. Interestingly, MCI-ADD patients exhibited a 30% reduction in plasma apoE compared to MCI-MCI patients. This decrease appeared to be associated with brain amyloid-ß (Aß42) pathology regardless of disease status as assessed using the Amyloid, Tau, and Neurodegeneration (A/T/N) classification. In addition to the association between low plasma apoE and low levels of CSF Aß42, lower apoE levels were also related to higher levels of CSF total tau (t-tau) and tau phosphorylated at Threonine 181 residue (p-tau) and NfL as well as a worse performance on the mini-mental-state-examination. In MCI-ADD patients, low levels of plasma apoE were associated with higher levels of CSF α-synuclein and kallikrein 6. No significant correlations between plasma apoE and the astrocytic inflammatory marker YKL40 were observed. CONCLUSIONS: Our results demonstrate important associations between low plasma apoE levels, Aß pathology, and progression from aMCI to a clinical ADD diagnosis.

The Amyloid, Tau, and Neurodegeneration (A/T/N) Classification Applied to a Clinical Research Cohort with Long-Term Follow-Up.

BACKGROUND: The unbiased amyloid, tau, and neurodegeneration (A/T/N) classification is designed to characterize individuals in the Alzheimer continuum and is currently little explored in clinical cohorts. OBJECTIVE: A retrospective comparison of the A/T/N classification system with the results of a two-year clinical study, with extended follow-up up to 10 years after inclusion. METHODS: Patients (n = 102) clinically diagnosed as Alzheimer's disease (AD) with dementia or amnestic mild cognitive impairment (MCI), and 61 cognitively healthy control individuals were included. Baseline cerebrospinal fluid core biomarkers for AD (Aß42, phosphorylated tau, and total tau) were applied to the A/T/N classification using the final clinical diagnosis at extended follow-up as the gold standard. RESULTS: A + T + N+ was a strong predictor for AD dementia, even among cognitively healthy individuals. Amnestic MCI was heterogenous, considering both clinical outcome and distribution within A/T/N. Some individuals with amnestic MCI progressed to clinical AD dementia within all four major A/T/N groups. The highest proportion of progression was among triple positive cases, but progression was also common in individuals with suspected non-Alzheimer pathophysiology (A-T + N+), and those with triple negative status. A-T-N- individuals who were cognitively healthy overwhelmingly remained cognitively intact over time, but in amnestic MCI the clinical outcome was heterogenous, including AD dementia, other dementias, and recovery. CONCLUSION: The A/T/N framework accentuates biomarkers over clinical status. However, when selecting individuals for research, a combination of the two may be necessary since the prognostic value of the A/T/N framework depends on clinical status.

Plasma Apolipoprotein E Monomer and Dimer Profile and Relevance to Alzheimer's Disease.

The APOEɛ4 gene variant is the strongest genetic risk factor for Alzheimer's disease (AD), whereas APOEɛ3 conventionally is considered as 'risk neutral' although APOEɛ3-carriers also develop AD. Previous studies have shown that the apolipoprotein E3 (apoE3) isoform occurs as monomers, homodimers and heterodimers with apolipoprotein A-II in human body fluids and brain tissue, but the relevance of a plasma apoE3 monomer/dimer profile to AD is unknown. Here we assessed the distribution of monomers, homodimers and heterodimers in plasma from control subjects and patients with mild cognitive impairment (MCI) and AD with either a homozygous APOEɛ3 (n = 31 control subjects, and n = 14 MCI versus n = 5 AD patients) or APOEɛ4 genotype (n = 1 control subject, n = 21 MCI and n = 7 AD patients). Total plasma apoE levels were lower in APOEɛ4-carriers and overall correlated significantly to CSF Aß42, p(Thr181)-tau and t-tau levels. Apolipoprotein E dimers were only observed in the APOEɛ3-carriers and associated with total plasma apoE levels, negatively correlated to apoE monomers, but were unrelated to plasma homocysteine levels. Importantly, the APOEɛ3-carrying AD patients versus controls exhibited a significant decrease in apoE homodimers (17.8±9.6% versus 26.7±6.3%, p = 0.025) paralleled by an increase in apoE monomers (67.8±18.3% versus 48.5±11.2%, p = 0.008). In the controls, apoE monomers and heterodimers were significantly associated with plasma triglycerides; the apoE heterodimers were also associated with levels of high-density lipoprotein cholesterol. The physiological relevance of apoE dimer formation needs to be further investigated, though the distribution of apoE in monomers and dimers appears to be of relevance to AD in APOEɛ3 subjects.

The relevance of cerebrospinal fluid α-synuclein levels to sporadic and familial Alzheimer's disease.

Accumulating evidence demonstrating higher cerebrospinal fluid (CSF) α-synuclein (αSyn) levels and αSyn pathology in the brains of Alzheimer's disease (AD) patients suggests that αSyn is involved in the pathophysiology of AD. To investigate whether αSyn could be related to specific aspects of the pathophysiology present in both sporadic and familial disease, we quantified CSF levels of αSyn and assessed links to various disease parameters in a longitudinally followed cohort (n = 136) including patients with sporadic mild cognitive impairment (MCI) and AD, and in a cross-sectional sample from the Dominantly Inherited Alzheimer's Network (n = 142) including participants carrying autosomal dominant AD (ADAD) gene mutations and their non-mutation carrying family members.Our results show that sporadic MCI patients that developed AD over a period of two years exhibited higher baseline αSyn levels (p = 0.03), which inversely correlated to their Mini-Mental State Examination scores, compared to cognitively normal controls (p = 0.02). In the same patients, there was a dose-dependent positive association between CSF αSyn and the APOEε4 allele. Further, CSF αSyn levels were higher in symptomatic ADAD mutation carriers versus non-mutation carriers (p = 0.03), and positively correlated to the estimated years from symptom onset (p = 0.05) across all mutation carriers. In asymptomatic (Clinical Dementia Rating < 0.5) PET amyloid-positive ADAD mutation carriers CSF αSyn was positively correlated to 11C-Pittsburgh Compound-B (PiB) retention in several brain regions including the posterior cingulate, superior temporal and frontal cortical areas. Importantly, APOEε4-positive ADAD mutation carriers exhibited an association between CSF αSyn levels and mean cortical PiB retention (p = 0.032). In both the sporadic AD and ADAD cohorts we found several associations predominantly between CSF levels of αSyn, tau and amyloid-ß1-40.Our results suggest that higher CSF αSyn levels are linked to AD pathophysiology at the early stages of disease development and to the onset of cognitive symptoms in both sporadic and autosomal dominant AD. We conclude that APOEε4 may promote the processes driven by αSyn, which in turn may reflect on molecular mechanisms linked to the asymptomatic build-up of amyloid plaque burden in brain regions involved in the early stages of AD development.

Assessment of kallikrein 6 as a cross-sectional and longitudinal biomarker for Alzheimer's disease.

BACKGROUND: Kallikrein 6 (KLK6) is known to be an age-related protease expressed at high levels in the central nervous system. It was previously shown to be involved in proteolysis of extracellular proteins implicated in neurodegenerative diseases such as Alzheimer's disease (AD), prompting validation of KLK6 as a potential biomarker of disease. However, analyses of both plasma and cerebrospinal fluid (CSF) levels of KLK6 in patients with AD have been inconclusive. We present a detailed analysis of KLK6 in plasma and CSF in two separate cohorts in a cross-sectional and a longitudinal clinical setting. METHODS: The cross-sectional cohort included control subjects without dementia and patients with AD, and the longitudinal cohort included patients with MCI and patients with AD followed over a 2-year period. Plasma and CSF levels of KLK6 were quantified by use of a previously developed and validated enzyme-linked immunosorbent assay. Statistical analyses were performed to compare KLK6 levels between diagnostic groups and to identify potential associations between KLK6 level, age, apolipoprotein E (APOE) genotype, total apoE level and the classical CSF AD biomarkers. RESULTS: In the cross-sectional setting, KLK6 levels in plasma but not in CSF were significantly higher in the AD group than in control subjects. CSF but not plasma KLK6 levels were positively correlated with age in both the cross-sectional and longitudinal settings. In both cohorts, the CSF KLK6 levels were significantly and positively correlated with the CSF levels of core AD biomarkers. Total plasma and CSF apoE levels were positively associated with KLK6 in the cross-sectional study. Finally, during the 2-year monitoring period of the longitudinal cohort, CSF KLK6 levels increased with disease progression over time in the investigated patient groups. CONCLUSIONS: In two separate cohorts we have confirmed the previously reported correlation between age and CSF levels of KLK6. Increased plasma KLK6 levels in patients with AD with a more advanced disease stage suggest KLK6 as a potential biomarker in patients with AD with more severe dementia. Significant correlations between KLK6 levels and core CSF AD biomarkers suggest molecular links between KLK6 and AD-related pathological processes.

Cerebrospinal Fluid Aß43 Is Reduced in Early-Onset Compared to Late-Onset Alzheimer's Disease, But Has Similar Diagnostic Accuracy to Aß42.

Background: Amyloid beta 1-43 (Aß43) may be a useful additional biomarker for diagnosing Alzheimer's disease (AD). We have investigated cerebrospinal fluid (CSF) levels of Aß43 in patients with early-onset AD in contrast to levels in late-onset AD. For comparison, in addition to the 'core' biomarkers, several other analytes were also determined [YKL-40, neurofilament light (NF-L), glial fibrillary acidic protein (GFAP), and progranulin]. Material and Methods: Cerebrospinal fluid samples were obtained from patients with early-onset AD (age ≤ 62, n = 66), late-onset AD (age ≥ 68, n = 25), and groups of cognitively intact individuals (age ≤ 62, n = 41, age ≥ 68, n = 39). Core CSF AD biomarkers [amyloid beta 1-42 (Aß42), total tau, phosphorylated tau] were analyzed, as well as levels of Aß43 and other analytes, using commercially available enzyme-linked immunosorbent assays. Results: Cerebrospinal fluid Aß43 was significantly reduced in early-onset AD compared to late-onset AD (14.8 ± 7.3 vs. 21.8 ± 9.4 pg/ml, respectively), whereas the levels of Aß42 in the two AD groups were not significantly different (474.9 ± 142.0 vs. 539.6 ± 159.9 pg/ml, respectively). Aß43 and all core biomarkers were significantly altered in patients with AD compared to corresponding controls. NF-L was significantly increased in early-onset AD compared to younger controls, an effect not found between the older groups. Relationships between the Aß peptides and tau proteins, YKL-40, NF-L, GFAP and progranulin were also investigated without finding marked associations. However, age-associated increases in levels of tau proteins, YKL-40, NF-L and GFAP were found with respect to age in healthy controls. Results for these other analytes were similar to previously published data. Aß43 did not improve diagnostic accuracy in either AD group compared to Aß42. DISCUSSION: Cerebrospinal fluid Aß43, but not Aß42 levels, varied significantly with age in patients with AD. If CSF levels of Aß peptides reflect amyloid deposition in brain, the possibility arises that there is a difference between Aß43 and Aß42 deposition in younger compared to older brain. However, the level of Aß43 in CSF shows no improvement over Aß42 regarding diagnostic accuracy.

Alpha-synuclein measured in cerebrospinal fluid from patients with Alzheimer's disease, mild cognitive impairment, or healthy controls: a two year follow-up study.

BACKGROUND: α-Synuclein has been proposed as a potential biomarker for Alzheimer's disease (AD) and amnestic mild cognitive impairment (aMCI). However, results from α-synuclein measurements in cerebrospinal fluid (CSF) have been inconclusive, and to our knowledge, longitudinal studies of changes prior to the AD diagnosis have not been investigated. METHODS: Levels of α-synuclein at baseline and after one and two years were measured in CSF, by enzyme-linked immunosorbent assay. Twenty-six patients with early AD (AD-AD), 48 patients with aMCI, subdivided as 23 that developed AD during follow-up (MCI-AD), and 25 that did not (MCI-MCI), and 25 healthy control individuals, were included. One-way ANOVA was applied to compare mean α-synuclein baseline values between all four study groups, and a linear mixed model was used to compare mean change over time between the three patient groups. Linear associations between α-synuclein and amyloid-ß 1-42 (Aß42), amyloid-ß 1-40 (Aß40), total tau and phosphorylated tau were also examined. RESULTS: A large variation in individual α-synuclein CSF levels was observed, particularly in the MCI-AD group. No significant differences were found in mean α-synuclein levels between all the study groups at baseline. When using a linear mixed model, no significant differences were found at follow-up for estimated mean changes between the patient groups. MCI-AD patients with short duration of symptoms prior to inclusion in the study (≤2 years) had considerably higher mean CSF α-synuclein levels compared to patients with a longer symptom duration (802.2 vs. 442.8 pg/mL, p = 0.01). No such difference was seen in the MCI-MCI or AD-AD groups. Significant linear associations (p < 0.0005) between α-synuclein and Aß40, total tau and phosphorylated tau were found. CONCLUSION: The observed difference in mean CSF α-synuclein level according to duration of symptoms in the MCI-AD group, may be an indication of changes related to disease progression. However, the lack of significant differences between groups, as well as the large individual variation in CSF levels of α-synuclein in the present study, suggest that α-synuclein is not a useful biomarker for AD.

Cerebrospinal Fluid Levels of Amyloid Beta 1-43 in Patients with Amnestic Mild Cognitive Impairment or Early Alzheimer's Disease: A 2-Year Follow-Up Study.

INTRODUCTION: Biomarkers that will reliably predict the onset of Alzheimer's disease (AD) are urgently needed. Although cerebrospinal fluid (CSF) amyloid beta 1-42 (Aß42), total tau, and phosphorylated tau can be used to complement the clinical diagnosis of AD, amnestic mild cognitive impairment (aMCI), the prodromal phase of AD, is heterogeneous. Biomarkers should be able to determine which patients with aMCI are at greatest risk of AD. Histological studies and animal models indicate that amyloid beta 1-43 (Aß43) aggregates early, and may play a role in the pathological process of AD. We have examined levels of CSF Aß43 in a 2-year longitudinal study of aMCI and early AD. MATERIALS AND METHODS: Cerebrospinal fluid was collected at baseline, and after one and 2 years from patients with AD (n = 19), and patients with aMCI (n = 42). Of these, 21 progressed to AD during the 2 years of study, whereas 21 did not. Controls (n = 32) were lumbar punctured at baseline only. CSF analyses of Aß43, Aß42, and total tau were carried out with ELISA. RESULTS: At baseline, CSF Aß43, CSF Aß42 and ratios with total tau could be used to separate controls from all three patient groups. CSF Aß43, but not Aß42, could separate patients with aMCI who progressed to AD during the 2 years of follow-up, from those that did not. The CSF total tau/Aß43 ratio had a slightly but significantly larger area under the receiver operating characteristic curve when compared to the CSF total tau/Aß42 ratio. CSF Aß43 levels, but not Aß42 levels, decreased from baseline to 2 years in the AD group. DISCUSSION AND CONCLUSION: CSF Aß43 was demonstrated to be significantly reduced in patients already by the time that aMCI or AD was diagnosed, compared to controls, and this change must have occurred during the preclinical period. Since our results suggested that CSF Aß43 distinguishes between subgroups of patients with aMCI better than CSF Aß42, it may prove to be a useful additional biomarker for identifying aMCI patients at greatest risk of AD.

Association of Butyrylcholinesterase-K Allele and Apolipoprotein E ɛ4 Allele with Cognitive Decline in Dementia with Lewy Bodies and Alzheimer's Disease.

BACKGROUND: A common polymorphism of the butyrylcholinesterase gene, the K-variant (BCHE-K) is associated with reduced butyrylcholinesterase (BuChE) activity. Insufficient studies exist regarding the frequency and role of BCHE-K in dementias. OBJECTIVE: To determine the association of BCHE-K and APOEɛ4 with diagnosis and rate of cognitive decline in dementia with Lewy bodies (DLB) and Alzheimer's disease (AD) patients. METHODS: Genomic DNA from 368 subjects (108 AD, 174 DLB, and 86 controls) from two routine clinical cohort studies in Norway; DemVest and TrønderBrain, were genotyped for BCHE-K and APOEɛ4. The mild dementia DemVest subjects received annual Mini-Mental State Examination assessments for five years. RESULTS: BCHE-K frequency was lower in DLB (33.9% ; p <  0.01) than in control subjects (51.2%), and was numerically lower in AD as well (38.9% ; p = 0.11). More rapid cognitive decline was associated with the APOEɛ4 genotype, but not with the BCHE-K genotype. In an exploratory analysis of patients who completed all five follow-up visits, there was greater cognitive decline in BCHE-K carriers in the presence of the APOEɛ4 allele than in the absence of these polymorphisms. CONCLUSION: BCHE-K is associated with a reduced risk for AD and DLB whereas APOEɛ4 is associated with more rapid cognitive decline. The greater cognitive decline in individuals with both APOEɛ4 and BCHE-K alleles require prospective confirmation in well-controlled trials.

Effect of Tween-20 on Core Biomarkers Measured in Cerebrospinal Fluid from Patients with Alzheimer's Disease, Mild Cognitive Impairment, or Healthy Control Individuals.

BACKGROUND: There is substantial variation caused by preanalytical procedures in the measurement of cerebrospinal fluid (CSF) biomarkers for Alzheimer's disease (AD) reported in the literature. OBJECTIVE: Determine whether the detergent Tween-20 improves diagnostic accuracy. METHODS: CSF proteins (Aß42, Aß40, total tau, and phosphorylated tau) were measured by standard ELISA, in uncentrifuged CSF with or without 0.05% Tween-20 from patients with AD or amnestic mild cognitive impairment, and healthy elderly controls. In the main study, collection tubes containing Tween-20 (Sarstedt 15 mL) were filled with 5 mL CSF to ensure consistent detergent concentration across subsequent aliquots into Corning 2 mL tubes. These latter were also the primary collection vessel for samples without Tween-20. The effect of centrifugation, and extra tube transfer of samples with Tween-20 were also examined. RESULTS: 0.05% Tween-20 significantly increased mean measured CSF concentration of Aß42 (30% ), Aß40 (23% ), and total tau (4% ), but not phosphorylated tau. Generally, these increases were similar in all groups, although for Aß42, the mean percentage increase with Tween-20 was slightly larger for AD. Areas under receiver-operator characteristic curves were similar whether Tween-20 was present or not. Centrifuged CSF without Tween-20 significantly reduced the measured concentration of Aß42 versus non-centrifuged samples, a difference not seen when detergent was added. Similar CSF Aß42 levels were found whether Tween-20 was added at collection in an extra tube or directly to the main collection tube. CONCLUSION: Addition of Tween-20 to CSF did not improve differentiation of patients from controls.

Apolipoprotein E ε2 genotype delays onset of dementia with Lewy bodies in a Norwegian cohort.

BACKGROUND: Results conflict concerning the relevance of APOE alleles on the development of dementia with Lewy bodies (DLB), though they are well established in connection with Alzheimer's disease (AD). The role of APOE alleles in a Norwegian cohort of patients with DLB was therefore examined compared with patients with AD and healthy control individuals. METHODS: The study included 156 patients with DLB diagnosed according to the consensus criteria guidelines, 519 patients diagnosed with AD according to the National Institute of Neurological and Communicative Diseases and Stroke/Alzheimer's Disease and Related Disorders Association (NINCDS/ARDRA) criteria and 643 healthy elderly volunteers. Patients were recruited through hospitals, outpatient clinics, nursing homes or from local care authorities in central and south-western parts of Norway. Healthy individuals were recruited from caregivers and societies for retired people. RESULTS: Subjects carrying an APOE ε2 allele had a reduced risk for developing DLB (OR 0.4, CI 0.3 to 0.8, p=0.004), and the onset of disease was delayed by 4 years (p=0.01, Mann-Whitney U test). Conversely, the APOE ε4 allele increased the risk for development of DLB (OR 5.9, CI 2.7 to 13.0, p<0.0005 for homozygotes). Similar results were found for patients with AD regarding the effect of APOE ε2, though the protective effect appeared to be slightly less pronounced than in DLB. This study is one of the largest regarding DLB and APOE to date. CONCLUSION: The results indicate that APOE ε2, a protective factor in AD, has a clear beneficial effect on the development of DLB also.