Caselli, Richard J.

Abstract Brains of 42 COVID-19 decedents and 107 non-COVID-19 controls were studied. RT-PCR screening of 16 regions from 20 COVID-19 autopsies found SARS-CoV-2 E gene viral sequences in 7 regions (2.5% of 320 samples), concentrated in 4/20 subjects (20%). Additional screening of olfactory bulb (OB), amygdala (AMY) and entorhinal area for E, N1, N2, RNA-dependent RNA polymerase, and S gene sequences detected one or more of these in OB in 8/21 subjects (38%). It is uncertain whether these RNA sequences represent viable virus. Significant histopathology was limited to 2/42 cases (4.8%), one with a large acute cerebral infarct and one with hemorrhagic encephalitis. Case-control RNAseq in OB and AMY found more than 5000 and 700 differentially expressed genes, respectively, unrelated to RT-PCR results; these involved immune response, neuronal constituents, and olfactory/taste receptor genes. Olfactory marker protein-1 reduction indicated COVID-19-related loss of OB olfactory mucosa afferents. Iba-1-immunoreactive microglia had reduced area fractions in cerebellar cortex and AMY, and cytokine arrays showed generalized downregulation in AMY and upregulation in blood serum in COVID-19 cases. Although OB is a major brain portal for SARS-CoV-2, COVID-19 brain changes are more likely due to blood-borne immune mediators and trans-synaptic gene expression changes arising from OB deafferentation.

BackgroundAdvanced diffusion‐based MRI biomarkers may provide insight into microstructural and perfusion changes associated with neurodegeneration and cognitive decline.PurposeTo assess longitudinal microstructural and perfusion changes using apparent diffusion coefficient (ADC) and intravoxel incoherent motion diffusion‐weighted imaging (IVIM‐DWI) parameters in cognitively impaired (CI) and healthy control (HC) groups.Study TypeProspective/longitudinal.PopulationTwelve CI patients (75% female) and 13 HC subjects (69% female).Field Strength/Sequence3 T; Spin‐Echo‐IVIM‐DWI.AssessmentTwo MRI scans were performed with a 12‐month interval. ADC and IVIM‐DWI metrics (diffusion coefficient [D] and perfusion fraction [f]) were generated from monoexponential and biexponential fits, respectively. Additionally, voxel‐based correlations were evaluated between change in Montreal Cognitive Assessment (ΔMoCA) and baseline imaging parameters.Statistical TestsAnalysis of covariance with sex and age as covariates was performed for main effects of group and time (false discovery rate [FDR] corrected) with post hoc comparisons using Bonferroni correction. Partial‐η2 and Hedges' g were used for effect‐size analysis. Spearman's correlations (FDR corrected) were used for the relationship between ΔMoCA score and imaging. P < 0.05 was considered statistically significant.ResultsSignificant differences were found for the main effects of group (HC vs. CI) and time. For group effects, higher ADC, IVIM‐D, and IVIM‐f were observed in the CI group compared to HC (ADC: 1.23 ± 0.08.10−3 vs. 1.09 ± 0.07.10−3 mm2/sec; IVIM‐D: 0.82 ± 0.01.10−3 vs. 0.73 ± 0.01.10−3 mm2/sec; and IVIM‐f: 0.317 ± 0.008 vs. 0.253 ± 0.009). Significantly higher ADC, IVIM‐D, and IVIM‐f values were observed in the CI group after 12 months (ADC: 1.45 ± 0.05.10−3 vs. 1.50 ± 0.07.10−3 mm2/sec; IVIM‐D: 0.87 ± 0.01.10−3 vs. 0.94 ± 0.02.10−3 mm2/sec; and IVIM‐f: 0.303 ± 0.007 vs. 0.332 ± 0.008), but not in the HC group at large effect size. ADC, IVIM‐D, and IVIM‐f negatively correlated with ΔMoCA score (ρ = −0.49, −0.51, and −0.50, respectively).Data ConclusionThese findings demonstrate that longitudinal differences between CI and HC cohorts can be measured using IVIM‐based metrics.Level of Evidence2Technical Efficacy Stage2

AbstractBackgroundAPOE4 gene dose, the number of apolipoprotein E ‐ɛ4 (APOE4) ɛ4 alleles in a person’s genotype, is associated with higher Alzheimer’s disease (AD) risk and younger median age at dementia onset. We previously found relationships between PET, plasma, and CSF measurements of amyloid‐β (Aβ) pathophysiology in APOE4 gene dose. Here, we characterize the core AD CSF biomarkers (Aβ42/40, pTau181, tTau), the neurodegeneration marker neurofilament light chain (NfL) and the glial biomarkers soluble TREM2 (sTREM2), and glial fibrillary acidic protein (GFAP) measurements in age‐matched 48‐70 year‐old cognitively unimpaired (CU) APOE4 homozygotes (HMs), heterozygotes (HTs) and non‐carriers (NCs) from the Arizona cohort.MethodCSF biomarker measurements were performed at the University of Gothenburg using Lumipulse and ELISA immunoassays. CSF biomarker measurements were characterized and compared using linear‐tend ANOVAs in 12 HMs, 17 HTs, and 20 NCs who were CU, 48‐70 years old and did not differ significantly in their age, sex, or educational level.ResultAs expected, CSF Aβ42/40 ratios were inversely associated with APOE4 gene dose (linear trend, HM<HT<NC, p<0.05), and tTau/Aβ42 and pTau181/Aβ42 ratios were directly associated with APOE4 gene dose (HM>HT>NC p<0.05). Non‐significant trends suggested that CSF sTREM2 and sTREM2/pTau181 measurements were inversely associated with APOE4 gene dose (HM<HT≤NC, (0.05<p≤0.06). We failed to detect significant differences or linear trends in CSF pTau181, tTau, GFAP, or NfL measurements among these small subject groups.ConclusionAPOE4 gene dose is associated with measures of CSF Aβ42/40 and Aβ‐related tau pathophysiology, reflecting higher Aβ plaque burden in CU subjects close to their estimated ages at clinical onset. Additional studies are needed to clarify relationships between different Aβ, tau, neurodegenerative, inflammatory, and other CSF, or blood‐based biomarkers, and APOE4 gene dose in larger subject groups and at other ages.

Background: Altered cerebral glucose metabolism, especially prominent in APOE ɛ4 carriers, occurs years prior to symptoms in Alzheimer’s disease (AD). We recently found an association between a higher ratio of plasma apolipoprotein E4 (apoE4) over apoE3, and cerebral glucose hypometabolism in cognitively healthy APOE ɛ3/ɛ4 subjects. Plasma apoE does not cross the blood-brain barrier, hence we speculate that apoE is linked to peripheral glucose metabolism which is known to affect glucose metabolism in the brain. Objective: Explore potential associations between levels of plasma insulin and glucose with previously acquired plasma apoE, cerebral metabolic rate of glucose (CMRgl), gray matter volume, and neuropsychological test scores. Methods: Plasma insulin and glucose levels were determined by ELISA and a glucose oxidase assay whereas apoE levels were earlier quantified by mass-spectrometry in 128 cognitively healthy APOE ɛ3/ɛ4 subjects. Twenty-five study subjects had previously undergone FDG-PET and structural MRI. Results: Lower plasma apoE3 associated with higher plasma glucose but not insulin in male subjects and subjects with a body mass index above 25. Negative correlations were found between plasma glucose and CMRgl in the left prefrontal and bilateral occipital regions. These associations may have functional implications since glucose levels in turn were negatively associated with neuropsychological test scores. Conclusion: Plasma apoE3 but not apoE4 may be involved in insulin-independent processes governing plasma glucose levels. Higher plasma glucose, which negatively affects brain glucose metabolism, was associated with lower plasma apoE levels in APOE ɛ3/ɛ4 subjects. High plasma glucose and low apoE levels may be a hazardous combination leading to an increased risk of AD.

Background: Besides their other roles, brain imaging and other biomarkers of Alzheimer’s disease (AD) have the potential to inform a cognitively unimpaired (CU) person’s likelihood of progression to mild cognitive impairment (MCI) and benefit subject selection when evaluating promising prevention therapies. We previously described that among baseline FDG-PET and MRI measures known to be preferentially affected in the preclinical and clinical stages of AD, hippocampal volume was the best predictor of incident MCI within 2 years (79%sensitivity/78%specificity), using standard automated MRI volumetric algorithmic programs, binary logistic regression, and leave-one-out procedures. Objective: To improve the same prediction by using different hippocampal features and machine learning methods, cross-validated via two independent and prospective cohorts (Arizona and ADNI). Methods: Patch-based sparse coding algorithms were applied to hippocampal surface features of baseline TI-MRIs from 78 CU adults who subsequently progressed to amnestic MCI in approximately 2 years (“progressors”) and 80 matched adults who remained CU for at least 4 years (“nonprogressors”). Nonprogressors and progressors were matched for age, sex, education, and apolipoprotein E4 allele dose. We did not include amyloid or tau biomarkers in defining MCI. Results: We achieved 92%prediction accuracy in the Arizona cohort, 92%prediction accuracy in the ADNI cohort, and 90%prediction accuracy when combining the two demographically distinct cohorts, as compared to 79%(Arizona) and 72%(ADNI) prediction accuracy using hippocampal volume. Conclusion: Surface multivariate morphometry and sparse coding, applied to individual MRIs, may accurately predict imminent progression to MCI even in the absence of other AD biomarkers.

Background: Whether brain-derived neurotrophic factor (BDNF) Met carriage impacts the risk or progression of Alzheimer’s disease (AD) is unknown. Objective: To evaluate the interaction of BDNF Met and APOE4 carriage on cerebral metabolic rate for glucose (CMRgl), amyloid burden, hippocampus volume, and cognitive decline among cognitively unimpaired (CU) adults enrolled in the Arizona APOE cohort study. Methods: 114 CU adults (mean age 56.85 years, 38% male) with longitudinal FDG PET, magnetic resonance imaging, and cognitive measures were BDNF and APOE genotyped. A subgroup of 58 individuals also had Pittsburgh B (PiB) PET imaging. We examined baseline CMRgl, PiB PET amyloid burden, CMRgl, and hippocampus volume change over time, and rate of change in cognition over an average of 15 years. Results: Among APOE4 carriers, BDNF Met carriers had significantly increased amyloid deposition and accelerated CMRgl decline in regions typically affected by AD, but without accompanying acceleration of cognitive decline or hippocampal volume changes and with higher baseline frontal CMRgl and slower frontal decline relative to the Val/Val group. The BDNF effects were not found among APOE4 non-carriers. Conclusion: Our preliminary studies suggest that there is a weak interaction between BDNF Met and APOE4 on amyloid-β plaque burden and longitudinal PET measurements of AD-related CMRgl decline in cognitively unimpaired late-middle-aged and older adults, but with no apparent effect upon rate of cognitive decline. We suggest that cognitive effects of BDNF variants may be mitigated by compensatory increases in frontal brain activity—findings that would need to be confirmed in larger studies.

BackgroundAlzheimer's disease (AD) is a progressive neurodegenerative disease that affects aging populations. Current MRI techniques are often limited in their sensitivity to underlying neuropathological changes.PurposeTo characterize differences in voxel‐based morphometry (VBM), apparent diffusion coefficient (ADC), and intravoxel incoherent motion diffusion‐weighted imaging (IVIM‐DWI) metrics in aging populations. Additionally, to investigate the connection between cognitive assessments and neuroimaging metrics.Study TypeProspective/cross‐sectional.PopulationIn all, 49 subjects, including 13 with AD dementia, 12 with mild cognitive impairment (MCI), and 24 healthy controls (HC).Field Strength/Sequence3T/magnetization‐prepared rapid acquisition gradient echo (MP‐RAGE) and IVIM‐DWIAssessmentAll participants completed a cognitive screening battery prior to MRI. IVIM‐DWI maps (pure diffusion coefficient [D], pseudodiffusion coefficient [D*], and perfusion fraction [f]) were generated from a biexponential fit of diffusion MRI data. VBM was performed on the standard T1‐weighted MP‐RAGE structural images. Group‐wise templates were used to compare across groups.Statistical TestsAnalysis of covariance (ANCOVA) with gender and age as covariates (familywise error [FWE] corrected, post‐hoc comparisons using Bonferroni correction) for group comparisons. Partial‐η2 and Hedges' g were used for effect‐size analysis. Spearman's correlations (false discovery rate [FDR]‐corrected) for the relationship between cognitive scores and imaging.ResultsClusters of significant group‐wise differences were found mainly in the temporal lobe, hippocampus, and amygdala using all VBM and IVIM methods (P < 0.05 FWE). While VBM showed significant changes between MCI and AD groups and between HC and AD groups, no significant clusters were observed between HC and MCI using VBM. ADC and IVIM‐D demonstrated significant changes, at P < 0.05 FWE, between HC and MCI, notably in the amygdala and hippocampus. Several voxel‐based correlations were observed between neuroimaging metrics and cognitive tests within the cognitively impaired groups (P < 0.05 FDR).Data ConclusionThese findings suggest that IVIM‐DWI metrics may be earlier biomarkers for AD‐related changes than VBM. The use of these techniques may provide novel insight into subvoxel neurodegenerative processes.Level of Evidence2Technical Efficacy Stage2 J. MAGN. RESON. IMAGING 2020;52:1811–1826.

AbstractObjectiveTo reassess the role of amyloid beta (Aβ) and the amyloid precursor protein (APP) system in the pathogenesis of Alzheimer's disease (AD).BackgroundAPP is a cell adhesion molecule that has been highly conserved over the course of phylogeny that has critical roles in brain development, synaptic plasticity, and the brain's intrinsic immune system. The amyloid cascade hypothesis describes a relatively linear, deterministic sequence of events triggered by a gain of Aβ peptide fragment toxicity that results in neurodegeneration and cognitive loss, yet well designed immunotherapy and beta secretase inhibitor trials that have successfully targeted Aβ have failed to have any consistent effects on the steady decline of cognition.New/updated hypothesisMutations of the APP and presenilin genes not only alter the ratio of longer to shorter Aβ fragments (resulting in a gain of Aβ toxicity), but also disrupt the normal homeostatic roles of their respective proteins. The evolutionary history, physiological importance, and complexity of the APP and presenilin systems, as well as other critical components including tau and apolipoprotein E (APOE) imply that altered function of such systems could have severe consequences that include but need not be limited to a gain of Aβ toxicity and would more generally result in altered homeostasis of APP‐related functions.Major challenges addressed by our hypothesisChallenges that a loss of APP homeostasis addresses better than the more limited gain of Aβ toxicity model include the topographic mismatches between Aβ and tau pathology, the profile and chronology of cognitive and biomarker changes that precede the clinical expression of mild cognitive impairment and dementia, and the disappointments of Aβ targeted therapeutics among others.Linkage to other major theoriesThe importance of APP, α‐ and β‐secretases, the presenilins and γ‐secretase, as well as tau was recognized by the authors of the amyloid cascade hypothesis, and has since led multiple investigators to propose alternative, more balanced hypotheses including reduced homeostasis and frank loss‐of‐function of key components that include but go beyond the currently envisioned linear model of Aβ toxicity.