The quantification of phosphorylated tau in biofluids, either cerebrospinal fluid (CSF) or plasma, has shown great promise in detecting Alzheimer’s disease (AD) pathophysiology. Tau phosphorylated at threonine 231 (p-tau231) is one such biomarker in CSF but its usefulness as a blood biomarker is currently unknown. Here, we developed an ultrasensitive Single molecule array (Simoa) for the quantification of plasma p-tau231 which was validated in four independent cohorts (n = 588) in different settings, including the full AD continuum and non-AD neurodegenerative disorders. Plasma p-tau231 was able to identify patients with AD and differentiate them from amyloid-β negative cognitively unimpaired (CU) older adults with high accuracy (AUC = 0.92–0.94). Plasma p-tau231 also distinguished AD patients from patients with non-AD neurodegenerative disorders (AUC = 0.93), as well as from amyloid-β negative MCI patients (AUC = 0.89). In a neuropathology cohort, plasma p-tau231 in samples taken on avergae 4.2 years prior to post-mortem very accurately identified AD neuropathology in comparison to non-AD neurodegenerative disorders (AUC = 0.99), this is despite all patients being given an AD dementia diagnosis during life. Plasma p-tau231 was highly correlated with CSF p-tau231, tau pathology as assessed by [18F]MK-6240 positron emission tomography (PET), and brain amyloidosis by [18F]AZD469 PET. Remarkably, the inflection point of plasma p-tau231, increasing as a function of continuous [18F]AZD469 amyloid-β PET standardized uptake value ratio, was shown to be earlier than standard thresholds of amyloid-β PET positivity and the increase of plasma p-tau181. Furthermore, plasma p-tau231 was significantly increased in amyloid-β PET quartiles 2–4, whereas CSF p-tau217 and plasma p-tau181 increased only at quartiles 3–4 and 4, respectively. Finally, plasma p-tau231 differentiated individuals across the entire Braak stage spectrum, including Braak staging from Braak 0 through Braak I–II, which was not observed for plasma p-tau181. To conclude, this novel plasma p-tau231 assay identifies the clinical stages of AD and neuropathology equally well as plasma p-tau181, but increases earlier, already with subtle amyloid-β deposition, prior to the threshold for amyloid-β PET positivity has been attained, and also in response to early brain tau deposition. Thus, plasma p-tau231 is a promising novel biomarker of emerging AD pathology with the potential to facilitate clinical trials to identify vulnerable populations below PET threshold of amyloid-β positivity or apparent entorhinal tau deposition.

Whilst cerebrospinal fluid (CSF) and positron emission tomography (PET) biomarkers for amyloid-β (Aβ) and tau pathologies are accurate for the diagnosis of Alzheimer's disease (AD), their broad implementation in clinical and trial settings are restricted by high cost and limited accessibility. Plasma phosphorylated-tau181 (p-tau181) is a promising blood-based biomarker that is specific for AD, correlates with cerebral Aβ and tau pathology, and predicts future cognitive decline. In this study, we report the performance of p-tau181 in >1,000 individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI), including cognitively unimpaired (CU), mild cognitive impairment (MCI) and AD dementia patients characterized by Aβ PET. We confirmed that plasma p-tau181 is increased at the preclinical stage of Alzheimer and further increases in MCI and AD dementia. Individuals clinically classified as AD dementia but having negative Aβ PET scans did not show increased plasma p-tau181. Despite being a multicenter study, plasma p-tau181 demonstrated high diagnostic accuracy to identify AD dementia (AUC=85.3%; 95% CI, 81.4%-89.2%), as well as to distinguish between Aβ-and Aβ+ individuals along the Alzheimer's continuum (AUC=76.9%; 95% CI, 74.0%-79.8%). Higher baseline concentrations of plasma p-tau181 accurately predicted future dementia and performed comparably to the baseline prediction of CSF p-tau181. Longitudinal measurements of plasma p-tau181 revealed low intra-individual variability, which could be of potential benefit in disease-modifying trials seeking a measurable response to a therapeutic target. This study adds significant weight to the growing body of evidence in the use of plasma p-tau181 as a non-invasive diagnostic and prognostic tool for AD, regardless of clinical stage, which would be of great benefit in clinical practice and a large cost-saving in clinical trial recruitment.a Continuous variables are given as mean (SD) b Aβ status defined by Aβ PET. * p<0.05 compared with the Aβ+ AD group # p<0.05 compared with the Aβ-CU group Continuous variables were compared with one-way ANOVA followed by Tukey's post-hoc test. Categorical variables were compared with Chi test

IMPORTANCEPlasma phosphorylated tau at threonine 181 (p-tau181) has been proposed as an easily accessible biomarker for the detection of Alzheimer disease (AD) pathology, but its ability to monitor disease progression in AD remains unclear.OBJECTIVE To study the potential of longitudinal plasma p-tau181 measures for assessing neurodegeneration progression and cognitive decline in AD in comparison to plasma neurofilament light chain (NfL), a disease-nonspecific marker of neuronal injury.

Tau phosphorylated at threonine 181 (p-tau181) measured in blood plasma has recently been proposed as an accessible, scalable, and highly specific biomarker for Alzheimer’s disease. Longitudinal studies, however, investigating the temporal dynamics of this novel biomarker are lacking. It is therefore unclear when in the disease process plasma p-tau181 increases above physiological levels and how it relates to the spatiotemporal progression of Alzheimer’s disease characteristic pathologies. We aimed to establish the natural time course of plasma p-tau181 across the sporadic Alzheimer’s disease spectrum in comparison to those of established imaging and fluid-derived biomarkers of Alzheimer’s disease. We examined longitudinal data from a large prospective cohort of elderly individuals enrolled in the Alzheimer’s Disease Neuroimaging Initiative (ADNI) (n = 1067) covering a wide clinical spectrum from normal cognition to dementia, and with measures of plasma p-tau181 and an 18F-florbetapir amyloid-β PET scan at baseline. A subset of participants (n = 864) also had measures of amyloid-β1–42 and p-tau181 levels in CSF, and another subset (n = 298) had undergone an 18F-flortaucipir tau PET scan 6 years later. We performed brain-wide analyses to investigate the associations of plasma p-tau181 baseline levels and longitudinal change with progression of regional amyloid-β pathology and tau burden 6 years later, and estimated the time course of changes in plasma p-tau181 and other Alzheimer’s disease biomarkers using a previously developed method for the construction of long-term biomarker temporal trajectories using shorter-term longitudinal data. Smoothing splines demonstrated that earliest plasma p-tau181 changes occurred even before amyloid-β markers reached abnormal levels, with greater rates of change correlating with increased amyloid-β pathology. Voxel-wise PET analyses yielded relatively weak, yet significant, associations of plasma p-tau181 with amyloid-β pathology in early accumulating brain regions in cognitively healthy individuals, while the strongest associations with amyloid-β were observed in late accumulating regions in patients with mild cognitive impairment. Cross-sectional and particularly longitudinal measures of plasma p-tau181 were associated with widespread cortical tau aggregation 6 years later, covering temporoparietal regions typical for neurofibrillary tangle distribution in Alzheimer’s disease. Finally, we estimated that plasma p-tau181 reaches abnormal levels ∼6.5 and 5.7 years after CSF and PET measures of amyloid-β, respectively, following similar dynamics as CSF p-tau181. Our findings suggest that plasma p-tau181 increases are associated with the presence of widespread cortical amyloid-β pathology and with prospective Alzheimer’s disease typical tau aggregation, providing clear implications for the use of this novel blood biomarker as a diagnostic and screening tool for Alzheimer’s disease.

Alzheimer's disease is characterized by the accumulation and deposition of plaques of ␤-amyloid (A␤) peptide in the brain. Given its pivotal role, new therapies targeting A␤ are in demand. We rationally designed liposomes targeting the brain and promoting the disaggregation of A␤ assemblies and evaluated their efficiency in reducing the A␤ burden in Alzheimer's disease mouse models. Liposomes were bifunctionalized with a peptide derived from the apolipoprotein-E receptor-binding domain for blood-brain barrier targeting and with phosphatidic acid for A␤ binding. Bifunctionalized liposomes display the unique ability to hinder the formation of, and disaggregate, A␤ assemblies in vitro (EM experiments). Administration of bifunctionalized liposomes to APP/presenilin 1 transgenic mice (aged 10 months) for 3 weeks (three injections per week) decreased total brain-insoluble A␤ 1-42 (Ϫ33%), assessed by ELISA, and the number and total area of plaques (Ϫ34%) detected histologically. Also, brain A␤ oligomers were reduced (Ϫ70.5%), as assessed by SDS-PAGE. Plaque reduction was confirmed in APP23 transgenic mice (aged 15 months) either histologically or by PET imaging with [ 11 C]Pittsburgh compound B (PIB). The reduction of brain A␤ was associated with its increase in liver (ϩ18%) and spleen (ϩ20%). Notably, the novel-object recognition test showed that the treatment ameliorated mouse impaired memory. Finally, liposomes reached the brain in an intact form, as determined by confocal microscopy experiments with fluorescently labeled liposomes. These data suggest that bifunctionalized liposomes destabilize brain A␤ aggregates and promote peptide removal across the blood-brain barrier and its peripheral clearance. This all-in-one multitask therapeutic device can be considered as a candidate for the treatment of Alzheimer's disease.

Whilst cerebrospinal fluid (CSF) and positron emission tomography (PET) biomarkers for amyloid-beta and tau pathologies are accurate for the diagnosis of Alzheimer's disease (AD), their broad implementation in clinical and trial settings are restricted by high cost and limited accessibility. Plasma phosphorylated-tau181 (p-tau181) is a promising blood-based biomarker that is specific for AD, correlates with cerebral amyloid-beta and tau pathology, and predicts future cognitive decline. In this study, we report the performance of p-tau181 in >1,000 individuals from the Alzheimer's Disease Neuroimaging Initiative (ADNI), including cognitively unimpaired (CU), mild cognitive impairment (MCI) and AD dementia patients characterized by amyloid-beta PET. We confirmed that plasma p-tau181 is increased at the preclinical stage of Alzheimer and further increases in MCI and AD dementia. Individuals clinically classified as AD dementia but having negative amyloid-beta PET scans did not show increased plasma p-tau181. Despite being a multicenter study, plasma p-tau181 demonstrated high diagnostic accuracy to identify AD dementia (AUC=85.3%; 95% CI, 81.4%-89.2%), as well as to distinguish between amyloid-beta-negative and amyloid-beta-positive individuals along the Alzheimer's continuum (AUC=76.9%; 95% CI, 74.0%-79.8%). Higher baseline concentrations of plasma p-tau181 accurately predicted future dementia and performed comparably to the baseline prediction of CSF p-tau181. Longitudinal measurements of plasma p-tau181 revealed low intra-individual variability, which could be of potential benefit in disease-modifying trials seeking a measurable response to a therapeutic target. This study adds significant weight to the growing body of evidence in the use of plasma p-tau181 as a non-invasive diagnostic and prognostic tool for AD, regardless of clinical stage, which would be of great benefit in clinical practice and a large cost-saving in clinical trial recruitment.

Introduction We tested how tube types (ethylenediaminetetraacetic acid [EDTA], serum, lithium heparin [LiHep], and citrate) and freeze–thaw cycles affect levels of blood biomarkers for Alzheimer's disease (AD) pathophysiology, glial activation, and neuronal injury. Methods Amyloid beta (Aβ)42, Aβ40, phosphorylated tau181 (p‐tau181), glial fibrillary acidic protein, total tau (t‐tau), neurofilament light, and phosphorylated neurofilament heavy protein were measured using single molecule arrays. Results LiHep demonstrated the highest mean value for all biomarkers. Tube types were highly correlated for most biomarkers (r > 0.95) but gave significantly different absolute concentrations. Weaker correlations between tube types were found for Aβ42/40 (r = 0.63–0.86) and serum t‐tau (r = 0.46–0.64). Freeze–thaw cycles highly influenced levels of serum Aβ and t‐tau (P < .0001), and minor decreases in EDTA Aβ40 and EDTA p‐tau181 were found after freeze–thaw cycle 4 (P < .05). Discussion The same tube type should be used in research studies on blood biomarkers. Individual concentration cut‐offs are needed for each tube type in all tested biomarkers despite being highly correlated. Serum should be avoided for Aβ42, Aβ40, and t‐tau. Freeze–thaw cycles > 3 should be avoided for p‐tau181.

Follow-up of b-amyloid (Ab) deposition in transgenic mouse models of Alzheimer disease (AD) would be a valuable translational tool in the preclinical evaluation of potential antiamyloid therapies. This study aimed to evaluate the ability of the clinically used PET tracer 11 C-Pittsburgh compound B ( 11 C-PIB) to detect changes over time in Ab deposition in the brains of living mice representing the APP23, Tg2576, and APP swe -PS1 dE9 transgenic mouse models of AD. Methods: Mice from each transgenic strain were imaged with 60-min dynamic PET scans at 729, 12, 15, and 18222 mo of age. Regional 11 C-PIB retention was quantitated as distribution volume ratios using Logan graphical analysis with cerebellar reference input, as radioactivity uptake ratios between the frontal cortex (FC) and the cerebellum (CB) during the 60-min scan, and as bound-tofree ratios in the late washout phase (40260 min). Ex vivo autoradiography experiments were performed after the final imaging session to validate 11 C-PIB binding to Ab deposits. Additionally, the presence of Ab deposits was evaluated in vitro using staining with thioflavin-S and Ab 1-40 , Ab 1-16 , and Ab N3(pE) immunohistochemistry. Results: Neocortical 11 C-PIB retention was markedly increased in old APP23 mice with large thioflavin-S-positive Ab deposits. At 12 mo, the Logan distribution volume ratio for the FC was 1.03 and 0.93 (n 5 2), increasing to 1.38 6 0.03 (n 5 3) and 1.34 (n 5 1) at 18 and 21 mo of age, respectively. An increase was also observed in bound-to-free ratios for the FC between young (7-to 12-mo-old) and old (15-to 22-mo-old) APP23 mice. Binding of 11 C-PIB to Ab-rich cortical regions was also evident in ex vivo autoradiograms of APP23 brain sections. In contrast, no increases in 11 C-PIB retention were observed in aging Tg2576 or APP swe -PS1 dE9 mice in vivo, although in the latter, extensive Ab deposition was already observed at 9 mo of age with immunohistochemistry. Conclusion: The results suggest that 11 C-PIB binding to Ab deposits in transgenic mouse brain is highly dependent on the AD model and the structure of its Ab plaques. Longitudinal in vivo 11 C-PIB uptake studies are possible in APP23 mice.