José Luis Cantero

INTRODUCTION: Accumulating evidence suggests that amyloid‐β (Aβ) preferentially deposits in poorly myelinated cortical regions and may interfere with remyelination. We hypothesized that this vulnerability would manifest as altered Aβ–myelin coupling in preclinical Alzheimer's disease (AD). METHODS: We assessed spatial coupling between amyloid positron emission tomography (PET) and myelin content estimated from T1w/T2w ratio maps in 151 cognitively unimpaired older adults. Associations with preclinical AD, blood‐based biomarkers, resting‐state functional connectivity (rs‐FC), and subjective memory complaints (SMC) were examined. RESULTS: Compared with controls, Aβ ⁺ individuals exhibited increased positive and negative Aβ–myelin coupling in late‐ and early‐myelinating regions, respectively, likely reflecting compensatory remyelination versus progressive myelin loss, along with disrupted rs‐FC and greater SMC. Serum glial fibrillary acidic protein (GFAP) and plasma phosphorylated tau at threonine 181 (pTau‐181) showed differential, region‐specific associations with Aβ–myelin coupling, with GFAP partially mediating tau‐related effects. Exploratory stratification suggested distinct biomarker profiles linked to the direction of coupling dominance, potentially reflecting different preclinical AD phases. DISCUSSION: Aβ–myelin coupling may represent a sensitive, stage‐dependent marker of early AD–related cortical pathology.

Lipidomics offers potential for the early detection of Alzheimer’s disease (AD) and for elucidating the molecular mechanisms driving the progression from mild cognitive impairment (MCI) to AD. In this study, we investigated and validated the association between 139 cerebrospinal fluid (CSF) lipids and MCI-to-AD conversion. We included 400 MCI participants from the Ace Alzheimer Center Barcelona (ACE) cohort, all free of type 2 diabetes, comprising both ATN+ and ATN− individuals. After a median follow-up of 2.1 years, 142 participants progressed to AD dementia. We identified a multi-lipid signature of 11 lipids (including phosphatidylcholines, lysophosphatidylcholines, triglycerides, phosphatidylethanolamines, lysophosphatidylethanolamines and phosphatidylinositols) in CSF, which was associated with increased AD progression (HR = 1.85, 95% CI: 1.53–2.27). This signature was validated in paired plasma samples, a less invasive biofluid (HR = 1.26, 95% CI: 1.04–1.52) and in plasma samples from an external cohort of 189 participants (149 with subjective cognitive decline, 40 with MCI; β = 0.261, 95% CI: 0.022–0.500), demonstrating moderate-to-high predictive accuracy for MCI-to-AD progression. Counterfactual-based mediation analysis revealed that plasma phosphorylated tau-181 mediated up to 47% of the association between the lipid signature and AD dementia, highlighting glycerophospholipid metabolism as a key pathway. Exploratory Mendelian randomisation analyses suggested a potential causal association of lipid signature and AD, with two instrumental single-nucleotide polymorphisms mapped to loci implicated in neurodevelopmental and metabolic regulation (RBFOX1 and CDKAL1). In conclusion, our findings support the growing evidence of lipid metabolism dysregulation as an early marker of AD and identify plasma lipids reflecting CSF profiles that may be promising prognostic markers for AD dementia.

A significant body of evidence suggests that mitochondrial dysfunction plays a key role in the development and progression of Alzheimer’s disease (AD). However, the absence of peripheral biomarkers for mitochondrial dysfunction limits its clinical applicability. Mitochondrial DNA (mtDNA) copy number, a proxy for mitochondrial function, has shown promise in detecting early stages of AD and predicting AD risk in cerebrospinal fluid (CSF) and blood, respectively. Surprisingly, recent studies have identified mtDNA molecules in human saliva, but their relationship with AD remains unexplored. Here, we investigated potential associations between salivary mtDNA copy number and cortical amyloid-β (Aβ) load measured with PET, and blood AD markers measured with ultrasensitive single molecule array (SIMOA) assays, in cognitively normal older adults. We found that salivary mtDNA copy number was positively correlated with cortical Aβ burden and plasma levels of tau phosphorylated at threonine 181 (pTau-181), and negatively correlated with general cognitive ability. It is worth noting that salivary mtDNA was not significantly associated with other blood-based AD biomarkers, including Aβ_1-40, Aβ_1-42, neurofilament-light chain (NfL), or glial fibrillary acidic protein (GFAP). Additionally, plasma pTau-181 levels moderated the association between salivary mtDNA and Aβ accumulation in the inferior temporal lobe, while Aβ load in the occipital cortex mediated the association between plasma pTau-181 and salivary mtDNA. Together, these findings represent the first evidence linking salivary mtDNA to well-established AD biomarkers in normal aging, suggesting that salivary mtDNA may serve as a potential non-invasive biomarker for identifying individuals at risk for developing AD in the general population.

Background: Substantial evidence supports the relationship between peripheral insulin resistance (IR) and the development of Alzheimer’s disease (AD)-dementia. However, the mechanisms explaining these associations are only partly understood. We aimed to identify a metabolic signature of IR associated with the progression from mild cognitive impairment (MCI) to AD-dementia. Methods: This is a case-control study on 400 MCI subjects, free of type 2 diabetes, within the ACE cohort, including individuals ATN + and ATN−. After a median of 2.1 years of follow-up, 142 subjects converted to AD-dementia. IR was assessed using the homeostasis model assessment for insulin resistance (HOMA-IR). A targeted multiplatform approach profiled over 600 plasma metabolites. Elastic net penalized linear regression with 10-fold cross-validation was employed to select those metabolites associated with HOMA-IR. The prediction ability of the signature was assessed using support vector machine and performance metrics. The metabolic signature was associated with AD-dementia risk using a multivariable Cox regression model. Using counterfactual-based mediation analysis, we investigated the mediation role of the metabolic signature between HOMA-IR and AD-dementia. The metabolic pathways in which the metabolites were involved were identified using MetaboAnalyst. Results: The metabolic signature comprised 18 metabolites correlated with HOMA-IR. After adjustments by confounders, the signature was associated with increased AD-dementia risk (HR = 1.234; 95% CI = 1.019–1.494; p < .05). The metabolic signature mediated 35% of the total effect of HOMA-IR on AD-dementia risk. Significant metabolic pathways were related to glycerophospholipid and tyrosine metabolism. Conclusions: We have identified a blood-based metabolic signature that reflects IR and may enhance our understanding of the biological mechanisms through which IR affects AD-dementia.

Hearing loss constitutes a major disability that hinders communication and quality of life. Recent evidence has uncovered its impact on cognitive decline, thus highlighting its multifactorial dimension and the outstanding need for creating multimodal hearing datasets that further cover clinical data across different health domains. The aim of this study is to develop a multi-collaborative database to systematically collect and analyze interdisciplinary data for audiological research, including auditory thresholds, speech tests, auditory evoked potentials, cognitive and quality-of-life tests, and medical images, among others. The database has been implemented in the Otorhinolaryngology Service of the Virgen Macarena University Hospital in Seville, integrated in the Intranet of the Andalusian Health Service, connected to the electronic patients’ medical records. This database relies on open-source software and complies with national and international guidelines on data protection. A specific registry module has been designed to automatically import auditory thresholds and auditory evoked potentials from clinical devices into the platform. A mobile app has also been implemented to collect questionnaires from patients remotely. A demo web version of the platform is freely available to the audiology community. The multimodal platform developed paves the way towards a multi-collaborative and unified framework for audiology research in Spain. Nevertheless, support from clinicians and healthcare stakeholders remains critical to develop more evidence and high-quality multimodal open datasets in hearing research.

Background: Mounting data suggests that herpes simplex virus type 1 (HSV-1) is involved in the pathogenesis of AD, possibly instigating amyloid-beta (Aβ) accumulation decades before the onset of clinical symptoms. However, human in vivo evidence linking HSV-1 infection to AD pathology is lacking in normal aging, which may contribute to the elucidation of the role of HSV-1 infection as a potential AD risk factor.Methods: To shed light into this question, serum anti-HSV IgG levels were correlated with¹⁸F-Florbetaben-PET binding to Aβ deposits and blood markers of neurodegeneration (pTau181 and neurofilament light chain) in cognitively normal older adults. Additionally, we investigated whether associations between anti-HSV IgG and AD markers were more evident in APOE4 carriers.Results: We showed that increased anti-HSV IgG levels are associated with higher Aβ load in fronto-temporal regions of cognitively normal older adults. Remarkably, these cortical regions exhibited abnormal patterns of resting state-functional connectivity (rs-FC) only in those individuals showing the highest levels of anti-HSV IgG. We further found that positive relationships between anti-HSV IgG levels and Aβ load, particularly in the anterior cingulate cortex, are moderated by the APOE4 genotype, the strongest genetic risk factor for AD. Importantly, anti-HSV IgG levels were unrelated to either subclinical cognitive deficits or to blood markers of neurodegeneration.Conclusions: All together, these results suggest that HSV infection is selectively related to cortical Aβ deposition in normal aging, supporting the inclusion of cognitively normal older adults in prospective trials of antimicrobial therapy aimed at decreasing the AD risk in the aging population.

Salivary extracellular vesicles (EVs) represent an attractive source of biomarkers due to the accessibility of saliva and its non-invasive sampling methods. However, the lack of comparative studies assessing the efficacy of different EV isolation techniques hampers the use of salivary EVs in clinical settings. Moreover, the effects of age on salivary EVs are largely unknown, hindering the identification of salivary EV-associated biomarkers across the lifespan. To address these questions, we compared salivary EV concentration, size mode, protein concentration, and purity using eight EV isolation techniques before and after magnetic bead immunocapture with antibodies against CD9, CD63, and CD81. The effects of age on salivary EVs obtained with each isolation technique were further investigated. Results showed higher expression of CD63 on isolated salivary EVs compared to the expression of CD81 and flotillin-1. Overall, magnetic bead immunocapture was more efficient in recovering salivary EVs with Norgen’s Saliva Exosome Purification Kit and ExoQuick-TC ULTRA at the cost of EV yield. Regardless of age, Invitrogen Total Exosome Isolation Solution showed the highest level of protein concentration, whereas Izon qEVOriginal-70nm columns revealed the highest purity. This study provides the first comprehensive comparison of salivary EVs in younger and older adults using different EV isolation techniques, which represents a step forward for assessing salivary EVs as a source of potential biomarkers of tissue-specific diseases throughout the life cycle.

Amyloid-beta (Aβ) aggregates and myelin breakdown are among the earliest detrimental effects of Alzheimer’s disease (AD), likely inducing abnormal patterns of neuronal communication within cortical networks. However, human in vivo evidence linking Aβ burden, intracortical myelin, and cortical synchronization is lacking in cognitively normal older individuals. Here, we addressed this question combining ¹⁸F-Florbetaben-PET imaging, cortical T1-weigthed/T2-weighted (T1w/T2w) ratio maps, and resting-state functional connectivity (rs-FC) in cognitively unimpaired older adults. Results showed that global Aβ burden was both positively and negatively associated with the T1w/T2w ratio in different cortical territories. Affected cortical regions were further associated with abnormal patterns of rs-FC and with subclinical cognitive deficits. Finally, causal mediation analysis revealed that the negative impact of T1w/T2w ratio in left posterior cingulate cortex on processing speed was driven by Aβ burden. Collectively, these findings provide novel insights into the relationship between initial Aβ plaques and intracortical myelin before the onset of cognitive decline, which may contribute to monitor the efficacy of novel disease-modifying strategies in normal elderly individuals at risk for cognitive impairment.

Background: Non-modifiable risk factors of Alzheimer’s disease (AD) have lifelong effects on cortical integrity that could be mitigated if identified at early stages. However, it remains unknown whether cortical microstructure is affected in older individuals with non-modifiable AD risk factors and whether altered cortical tissue integrity produces abnormalities in brain functional networks in this AD-risk population.Methods: Using relative T1w/T2w (rT1w/T2w) ratio maps, we have compared tissue integrity of normal-appearing cortical GM between controls and cognitively normal older adults with either APOE4 (N= 50), with a first-degree family history (FH) of AD (N= 52), or with the co-occurrence of both AD risk factors (APOE4+FH) (N= 35). Additionally, individuals with only one risk factor (APOE4 or FH) were combined into one group (N= 102) and compared with controls. The same number of controls matched in age, sex, and years of education was employed for each of these comparisons. Group differences in resting state functional connectivity (rs-FC) patterns were also investigated, using as FC seeds those cortical regions showing significant changes in rT1w/T2w ratios.Results: Overall, individuals with non-modifiable AD risk factors exhibited significant variations in rT1w/T2w ratios compared to controls, being APOE4 and APOE4+FH at opposite ends of a continuum. The co-occurrence of APOE4 and FH was further accompanied by altered patterns of rs-FC.Conclusions: These findings may have practical implications for early detection of cortical abnormalities in older populations with APOE4 and/or FH of AD and open new avenues to monitor changes in cortical tissue integrity associated with non-modifiable AD risk factors.

Evidence suggests that lightly myelinated cortical regions are vulnerable to aging and Alzheimer’s disease (AD). However, it remains unknown whether plasma markers of amyloid and neurodegeneration are related to deficits in intracortical myelin content, and whether this relationship, in turn, is associated with altered patterns of resting-state functional connectivity (rs-FC). To shed light into these questions, plasma levels of amyloid-β fragment 1–42 (Aβ_1–42) and neurofilament light chain (NfL) were measured using ultra-sensitive single-molecule array (Simoa) assays, and the intracortical myelin content was estimated with the ratio T1-weigthed/T2-weighted (T1w/T2w) in 133 cognitively normal older adults. We assessed: (i) whether plasma Aβ_1–42 and/or NfL levels were associated with intracortical myelin content at different cortical depths and (ii) whether cortical regions showing myelin reductions also exhibited altered rs-FC patterns. Surface-based multiple regression analyses revealed that lower plasma Aβ_1–42 and higher plasma NfL were associated with lower myelin content in temporo-parietal-occipital regions and the insular cortex, respectively. Whereas the association with Aβ_1–42 decreased with depth, the NfL-myelin relationship was most evident in the innermost layer. Older individuals with higher plasma NfL levels also exhibited altered rs-FC between the insula and medial orbitofrontal cortex. Together, these findings establish a link between plasma markers of amyloid/neurodegeneration and intracortical myelin content in cognitively normal older adults, and support the role of plasma NfL in boosting aberrant FC patterns of the insular cortex, a central brain hub highly vulnerable to aging and neurodegeneration.