Amyloid-β load predicts medial temporal lobe dysfunction in Alzheimer dementia

Glucose Metabolism of Hippocampal Subfields in Medial Temporal Lobe Epilepsy

PURPOSE

Reduced glucose metabolism in the hippocampus is commonly observed in cases of medial temporal lobe epilepsy (MTLE) with hippocampal sclerosis (HS). Glucose metabolism among the various hippocampal subfields has not been thoroughly investigated.

PATIENTS AND METHODS

This study examined 29 patients (18 females; 15-58 years) diagnosed with HS who underwent surgery for drug-resistant epilepsy. FreeSurfer 7.1.1 was used in the processing of MRI data and 18 F-FDG PET scans to derive volumetric data and the FDG SUVr in the whole hippocampus and hippocampal subfields, including the CA1, CA2-4, granule cell and molecular layer of the dentate gyrus (GC-ML-DG), and subiculum. Asymmetries in the volume and SUVr between the 2 sides from the subfields of the hippocampus were defined in terms of an asymmetry index. Comparisons of the asymmetry index among these regions were performed. The correlations between asymmetry index values and postoperative outcomes and presurgical neuropsychological test results were also evaluated.

RESULT

The CA1, CA2-4, subiculum, GC-ML-DG, and whole hippocampus presented reductions in volume and hypometabolism ipsilateral to MTLE. Asymmetries in volume and SUVr were significantly less pronounced in the CA1 and subiculum than in the CA2-4 or GC-ML-DG. Postoperative seizure outcomes were not correlated with the asymmetry index for volume or SUVr in any hippocampal subfield. In cases of left MTLE, scores of immediate logical memory and delayed logical memory were positively correlated with the asymmetry index for SUVr in the following subfields: CA1 ( R = 0.829, P = 0.021; R = 0.770, P = 0.043), CA2-4 ( R = 0.825, P = 0.022; R = 0.894, P = 0.007), subiculum ( R = 0.882, P = 0.009; R = 0.853, P = 0.015), GC-ML-DG ( R = 0.850, P = 0.015; R = 0.796, P = 0.032), and whole hippocampus ( R = 0.841, P = 0.018; R = 0.822, P = 0.023). In cases of right MTLE, the scores for delayed face memory were positively correlated with the asymmetry index for SUVr in the subiculum ( R = 0.935, P = 0.006).

CONCLUSIONS

In cases of HS, changes in glucose metabolism levels varied among the hippocampal subfields. Asymmetries in glucose metabolism among the CA-1, CA2-4, subiculum, and GC-ML-DG subregions were correlated with scores for verbal memory among patients with left MTLE. Asymmetric glucose metabolism in the subiculum was also correlated with visual memory scores among patients with right MTLE.

The use of individual-based FDG-PET volume of interest in predicting conversion from mild cognitive impairment to dementia

BACKGROUND

Based on a longitudinal cohort design, the aim of this study was to investigate whether individual-based 18F fluorodeoxyglucose positron emission tomography (18F-FDG-PET) regional signals can predict dementia conversion in patients with mild cognitive impairment (MCI).

METHODS

We included 44 MCI converters (MCI-C), 38 non-converters (MCI-NC), 42 patients with Alzheimer's disease with dementia, and 40 cognitively normal controls. Data from annual cognitive measurements, 3D T1 magnetic resonance imaging (MRI) scans, and 18F-FDG-PET scans were used for outcome analysis. An individual-based FDG-PET approach was applied using seven volumes of interest (VOIs), Z transformed using a normal FDG-PET template. Hypometabolism was defined as a Z score < -2 of regional standard uptake value ratio. For the longitudinal cognitive test scores, generalized estimating equations were used. A linear mixed-effects model was used to compare the temporal impact of cortical hypometabolism and cortical thickness degeneration.

RESULTS

The clinical follow-up period was 6.6 ± 3.8 years (range 3.1 to 16.0 years). The trend of cognitive decline could differentiate MCI-C from MCI-NC after 3 years of follow-up. In the baseline 18F-FDG-PET scan of the patients with MCI, medial temporal lobe (MTL; 94.7% sensitivity, 80.5% specificity) and posterior cingulate cortex (PCC; 89.5% sensitivity, 73.1% specificity) hypometabolism predicted conversion with high accuracy. 18F-FDG-PET hypometabolism preceded dementia conversion at an interval of 3.70 ± 1.68 years and was earlier than volumetric changes, with the exception of the MTL.

CONCLUSIONS

Our finding supports the use of individual-based 18F-FDG-PET analysis to predict MCI conversion to dementia. Reduced FDG-PET metabolism in the MTL and PCC were strongly associated with future cognitive decline in the MCI-C group. Changes in 18F-FDG-PET occurred 1 to 8 years prior to conversion to dementia. Progressive hypometabolism in the PCC, precuneus and lateral temporal lobe, but not MTL, preceded MRI findings at the MCI stage.

Kisspeptin-13 prevented the electrophysiological alterations induced by Amyloid-Beta pathology in rat: Possible involvement of stromal interaction molecules and pCREB

Alzheimer's disease (AD) is a progressive neurological disease that slowly causing memory impairments with no effective treatment. We have recently reported that kisspeptin-13 (KP-13) ameliorates Aβ toxicity-induced memory deficit in rats. Here, the possible cellular impact of kisspeptin receptor activation in a rat model of the early stage AD was assessed using whole-cell patch-clamp recording from CA1 pyramidal neurons and molecular approaches. Compared to neurons from the control group, cells from the Aβ-treated group displayed spontaneous and evoked hyperexcitability with lower spike frequency adaptation. These cells had also a lower sag ratio in response to hyperpolarizing prepulse current delivered before a depolarizing current injection. Neurons from the Aβ-treated group exhibited short spike onset latency, lower rheobase and short utilization time compared with those in the control group. Furthermore, phase plot analysis of action potential showed that Aβ treatment affected the action potential features. These electrophysiological changes induced by Aβ were associated with increased expression of stromal interaction molecules (STIMs), particularly (STIM2) and decreased pCREB/CREB ratio. Treatment with KP-13 following Aβ injection into the entorhinal cortex, however, prevented the excitatory effect of Aβ on spontaneous and evoked neuronal activity, increased the latency of onset, enhanced the sag ratio, increased the rheobase and utilization time, and prevented the changes induced Aβ on spike parameters. In addition, the KP-13 application after Aβ treatment reduced the expression of STIMs and increased the pCREB/CREB ratio compared to those receiving Aβ treatment alone. In summary, these results provide evidence that activation of kisspeptin receptor may be effective against pathology of Aβ.

Regional amyloid correlates of cognitive performance in ageing and mild cognitive impairment

Beta-amyloid deposition is one of the earliest pathological markers associated with Alzheimer's disease. Mild cognitive impairment in the setting of beta-amyloid deposition is considered to represent a preclinical manifestation of Alzheimer's disease. In vivo imaging studies are unique in their potential to advance our understanding of the role of beta-amyloid deposition in cognitive deficits in Alzheimer's disease and in mild cognitive impairment. Previous work has shown an association between global cortical measures of beta-amyloid deposition ('amyloid positivity') in mild cognitive impairment with greater cognitive deficits and greater risk of progression to Alzheimer's disease. The focus of the present study was to examine the relationship between the regional distribution of beta-amyloid deposition and specific cognitive deficits in people with mild cognitive impairment and cognitively normal elderly individuals. Forty-seven participants with multi-domain, amnestic mild cognitive impairment (43% female, aged 57-82 years) and 37 healthy, cognitively normal comparison subjects (42% female, aged 55-82 years) underwent clinical and neuropsychological assessments and high-resolution positron emission tomography with the radiotracer 11C-labelled Pittsburgh compound B to measure beta-amyloid deposition. Brain-behaviour partial least-squares analysis was conducted to identify spatial patterns of beta-amyloid deposition that correlated with the performance on neuropsychological assessments. Partial least-squares analysis identified a single significant (P < 0.001) latent variable which accounted for 80% of the covariance between demographic and cognitive measures and beta-amyloid deposition. Performance in immediate verbal recall (R = -0.46 ± 0.07, P < 0.001), delayed verbal recall (R = -0.39 ± 0.09, P < 0.001), immediate visual-spatial recall (R = -0.39 ± 0.08, P < 0.001), delayed visual-spatial recall (R = -0.45 ± 0.08, P < 0.001) and semantic fluency (R = -0.33 ± 0.11, P = 0.002) but not phonemic fluency (R = -0.05 ± 0.12, P < 0.705) negatively covaried with beta-amyloid deposition in the identified regions. Partial least-squares analysis of the same cognitive measures with grey matter volumes showed similar associations in overlapping brain regions. These findings suggest that the regional distribution of beta-amyloid deposition and grey matter volumetric decreases is associated with deficits in executive function and memory in mild cognitive impairment. Longitudinal analysis of these relationships may advance our understanding of the role of beta-amyloid deposition in relation to grey matter volumetric decreases in cognitive decline.

Applications of amyloid, tau, and neuroinflammation PET imaging to Alzheimer's disease and mild cognitive impairment

Alzheimer's disease (AD) is a devastating and progressive neurodegenerative disease for which there is no cure. Mild cognitive impairment (MCI) is considered a prodromal stage of the disease. Molecular imaging with positron emission tomography (PET) allows for the in vivo visualisation and tracking of pathophysiological changes in AD and MCI. PET is a very promising methodology for differential diagnosis and novel targets of PET imaging might also serve as biomarkers for disease-modifying therapeutic interventions. This review provides an overview of the current status and applications of in vivo molecular imaging of AD pathology, specifically amyloid, tau, and microglial activation. PET imaging studies were included and evaluated as potential biomarkers and for monitoring disease progression. Although the majority of radiotracers showed the ability to discriminate AD and MCI patients from healthy controls, they had various limitations that prevent the recommendation of a single technique or tracer as an optimal biomarker. Newer research examining amyloid, tau, and microglial PET imaging in combination suggest an alternative approach in studying the disease process.

Plasma Aβ42/40 ratio alone or combined with FDG-PET can accurately predict amyloid-PET positivity: a cross-sectional analysis from the AB255 Study

BACKGROUND

To facilitate population screening and clinical trials of disease-modifying therapies for Alzheimer's disease, supportive biomarker information is necessary. This study was aimed to investigate the association of plasma amyloid-beta (Aβ) levels with the presence of pathological accumulation of Aβ in the brain measured by amyloid-PET. Both plasma Aβ42/40 ratio alone or combined with an FDG-PET-based biomarker of neurodegeneration were assessed as potential AD biomarkers.

METHODS

We included 39 cognitively normal subjects and 20 patients with mild cognitive impairment from the AB255 Study who had undergone PiB-PET scans. Total Aβ40 and Aβ42 levels in plasma (TP42/40) were quantified using ABtest kits. Subjects were dichotomized as Aβ-PET positive or negative, and the ability of TP42/40 to detect Aβ-PET positivity was assessed by logistic regression and receiver operating characteristic analyses. Combination of plasma Aβ biomarkers and FDG-PET was further assessed as an improvement for brain amyloidosis detection and diagnosis classification.

RESULTS

Eighteen (30.5%) subjects were Aβ-PET positive. TP42/40 ratio alone identified Aβ-PET status with an area under the curve (AUC) of 0.881 (95% confidence interval [CI] = 0.779-0.982). Discriminating performance of TP42/40 to detect Aβ-PET-positive subjects yielded sensitivity and specificity values at Youden's cutoff of 77.8% and 87.5%, respectively, with a positive predictive value of 0.732 and negative predictive value of 0.900. All these parameters improved after adjusting the model for significant covariates. Applying TP42/40 as the first screening tool in a sequential diagnostic work-up would reduce the number of Aβ-PET scans by 64%. Combination of both FDG-PET scores and plasma Aβ biomarkers was found to be the most accurate Aβ-PET predictor, with an AUC of 0.965 (95% CI = 0.913-0.100).

CONCLUSIONS

Plasma TP42/40 ratio showed a relevant and significant potential as a screening tool to identify brain Aβ positivity in preclinical and prodromal stages of Alzheimer's disease.

New multifunctional AChE inhibitor drug prototypes protect against Aβ-induced memory deficit

Alzheimer's disease (AD) is the most incident neurodegenerative disorder, characterized by accumulation of extracellular amyloid-β (Aβ), intracellular neurofibrillary tangles, and cognitive impairment. The current available treatments are mainly based on the use of reversible acetylcholinesterase (AChE) inhibitors, which only ameliorate the cognitive deficits. However, it is important to develop disease-modifying drugs with neuroprotective effects in order to hamper the progression of the disease. Here, we describe the effect of four promising new drugs with additional protective characteristics on AD-associated memory changes. C57Bl/6 mice treated with the compounds received an intra-hippocampal injection of Aβ1-40 and were submitted to the novel object recognition test, to evaluate memory recovery. All the compounds prevented memory loss. Compounds PQM-56 (4c) and PQM-67 (4g) showed the best profile of memory recovery, representing potential drug candidates for AD treatment.

Irritable Bowel Syndrome Is Associated with an Increased Risk of Dementia: A Nationwide Population-Based Study

Purpose

Abnormal interaction in the brain–gut axis has emerged as one of the relevant pathophysiological mechanisms for the development of irritable bowel syndrome (IBS). Moreover, the brain–gut axis has recently been demonstrated to be crucial for the maintenance of cognitive performance. Therefore, we assessed the risk of dementia following diagnosis of IBS.

Methods

Using the Taiwan National Health Insurance Research Database (NHIRD) to obtain medical claims data from 2000 to 2011, we employed a random sampling method to enroll32 298 adult patients with IBS and frequency-matched them according to sex, age, and baseline year with 129 192 patients without IBS.

Results

The patients with IBS exhibited an increased risk of dementia [adjusted hazard ratio (aHR) = 1.26, 95% confidence interval (CI) = 1.17–1.35]after adjustment for age, sex, diabetes, hypertension, stroke, coronary artery disease (CAD), head injury, depression, and epilepsy, and the overall incidence of dementia for the cohorts with and without IBS was 4.86 and 3.41 per 1000 person-years, respectively. IBS was associated with an increased risk of dementia in patients older than 50 years in both male and female, and in those with comorbidity or without comorbidity. After adjustment for age, sex, and comorbidity, patients with IBS were also more likely to develop either non- Alzheimer’s disease (AD) dementia (aHR = 1.24, 95% CI = 1.15–1.33) or AD (aHR = 1.76, 95% CI = 1.28–2.43).

Conclusions

IBS is associated with an increased risk of dementia, and this effect is obvious only in patients who are ≥50 years old.

Asymmetries of amyloid-β burden and neuronal dysfunction are positively correlated in Alzheimer's disease

Clinical Alzheimer's disease affects both cerebral hemispheres to a similar degree in clinically typical cases. However, in atypical variants like logopenic progressive aphasia, neurodegeneration often presents asymmetrically. Yet, no in vivo imaging study has investigated whether lateralized neurodegeneration corresponds to lateralized amyloid-β burden. Therefore, using combined (11)C-Pittsburgh compound B and (18)F-fluorodeoxyglucose positron emission tomography, we explored whether asymmetric amyloid-β deposition in Alzheimer's disease is associated with asymmetric hypometabolism and clinical symptoms. From our database of patients who underwent positron emission tomography with both (11)C-Pittsburgh compound B and (18)F-fluorodeoxyglucose (n = 132), we included all amyloid-positive patients with prodromal or mild-to-moderate Alzheimer's disease (n = 69). The relationship between (11)C-Pittsburgh compound B binding potential and (18)F-fluorodeoxyglucose uptake was assessed in atlas-based regions of interest covering the entire cerebral cortex. Lateralizations of amyloid-β and hypometabolism were tested for associations with each other and with type and severity of cognitive symptoms. Positive correlations between asymmetries of Pittsburgh compound B binding potential and hypometabolism were detected in 6 of 25 regions (angular gyrus, middle frontal gyrus, middle occipital gyrus, superior parietal gyrus, inferior and middle temporal gyrus), i.e. hypometabolism was more pronounced on the side of greater amyloid-β deposition (range: r = 0.41 to 0.53, all P < 0.001). Stronger leftward asymmetry of amyloid-β deposition was associated with more severe language impairment (P < 0.05), and stronger rightward asymmetry with more severe visuospatial impairment (at trend level, P = 0.073). Similarly, patients with predominance of language deficits showed more left-lateralized amyloid-β burden and hypometabolism than patients with predominant visuospatial impairment and vice versa in several cortical regions. Associations between amyloid-β deposition and hypometabolism or cognitive impairment were predominantly observed in brain regions with high amyloid-β load. The relationship between asymmetries of amyloid-β deposition and hypometabolism in cortical regions with high amyloid-β load is in line with the detrimental effect of amyloid-β burden on neuronal function. Asymmetries were also concordant with lateralized cognitive symptoms, indicating their clinical relevance.

Alterations in CA1 pyramidal neuronal intrinsic excitability mediated by Ih channel currents in a rat model of amyloid beta pathology

Amyloid beta (Aβ) accumulation plays an important role in the pathogenesis of Alzheimer's disease (AD) by changing the neuronal excitability. However, the cellular mechanisms by which accumulation of Aβ affects intrinsic neuronal properties are not well understood. The effect of bilateral intra-frontal cortex Aβ (1-42) peptide injection on the intrinsic excitability of hippocampal CA1 pyramidal neurons with particular focus on the contribution of hyperpolarization-activated (Ih) channel currents was examined using whole-cell patch-clamp recording. Passive avoidance memory impairment and morphological changes in rats receiving intra-frontal Aβ treatment were observed, which was associated with significant changes both in passive and active intrinsic electrical membrane properties of CA1 pyramidal neurons. Electrophysiological recording showed a significant decrease in neuronal excitability associated with an augmentation in the first spike after-hyperpolarization (AHP) amplitude. In addition, the depolarizing sag voltage was altered in neurons recorded from Aβ-treated group. In voltage-clamp condition, a hyperpolarizing activated inward current sensitive to ZD7288 and capsaicin was significantly increased in neurons from Aβ-treated rats. The Ih current density was increased and the activation curve was shifted toward less negative potential in the Aβ-treated group as compared to control group. The enhancing effect of Aβ treatment on Ih current was confirmed by showing upregulation of the mRNA of HCN1 channel in the CA1 pyramidal layer of hippocampi. These findings suggest the contribution of Ih and possibly TRPV1 channel currents to the changes induced by Aβ treatment in the intrinsic membrane properties, which, in turn, may provide therapeutic targets for treatment of AD.

Brain amyloid-β burden is associated with disruption of intrinsic functional connectivity within the medial temporal lobe in cognitively normal elderly

The medial temporal lobe is implicated as a key brain region involved in the pathogenesis of Alzheimer's disease (AD) and consequent memory loss. Tau tangle aggregation in this region may develop concurrently with cortical Aβ deposition in preclinical AD, but the pathological relationship between tau and Aβ remains unclear. We used task-free fMRI with a focus on the medical temporal lobe, together with Aβ PET imaging, in cognitively normal elderly human participants. We found that cortical Aβ load was related to disrupted intrinsic functional connectivity of the perirhinal cortex, which is typically the first brain region affected by tauopathies in AD. There was no concurrent association of cortical Aβ load with cognitive performance or brain atrophy. These findings suggest that dysfunction in the medial temporal lobe may represent a very early sign of preclinical AD and may predict future memory loss.

Low plasma ApoE levels are associated with smaller hippocampal size in the Alzheimer's disease neuroimaging initiative cohort

Apolipoprotein E (APOE) genotype is the strongest known genetic risk factor for sporadic Alzheimer's disease (AD), but the utility of plasma ApoE levels for assessing the severity of underlying neurodegenerative changes remains uncertain. Here, we examined cross-sectional associations between plasma ApoE levels and volumetric magnetic resonance imaging indices of the hippocampus from 541 participants [57 with normal cognition (NC), 375 with mild cognitive impairment (MCI), and 109 with mild AD] who were enrolled in the Alzheimer's Disease Neuroimaging Initiative. Across the NC and MCI groups, lower plasma ApoE levels were significantly correlated with smaller hippocampal size, as measured by either hippocampal volume or hippocampal radial distance. These associations were driven primarily by findings from carriers of an APOE ε4 allele and are consistent with prior reports that lower plasma ApoE levels correlate with greater global cortical Pittsburgh Compound B retention. In this high-risk group, plasma ApoE levels may represent a peripheral marker of underlying AD neuropathology in nondemented elderly individuals.

Chronic functional bowel syndrome enhances gut-brain axis dysfunction, neuroinflammation, cognitive impairment, and vulnerability to dementia

The irritable bowel syndrome (IBS) is a common chronic functional gastrointestinal disorder world wide that lasts for decades. The human gut harbors a diverse population of microbial organisms which is symbiotic and important for well being. However, studies on conventional, germ-free, and obese animals have shown that alteration in normal commensal gut microbiota and an increase in pathogenic microbiota-termed "dysbiosis", impact gut function, homeostasis, and health. Diarrhea, constipation, visceral hypersensitivity, and abdominal pain arise in IBS from the gut-induced dysfunctional metabolic, immune, and neuro-immune communication. Dysbiosis in IBS is associated with gut inflammation. Gut-related inflammation is pivotal in promoting endotoxemia, systemic inflammation, and neuroinflammation. A significant proportion of IBS patients chronically consume alcohol, non-steroidal anti-inflammatories, and fatty diet; they may also suffer from co-morbid respiratory, neuromuscular, psychological, sleep, and neurological disorders. The above pathophysiological substrate is underpinned by dysbiosis, and dysfunctional bidirectional "Gut-Brain Axis" pathways. Pathogenic gut microbiota-related systemic inflammation (due to increased lipopolysaccharide and pro-inflammatory cytokines, and barrier dysfunction), may trigger neuroinflammation enhancing dysfunctional brain regions including hippocampus and cerebellum. These as well as dysfunctional vago-vagal gut-brain axis may promote cognitive impairment. Indeed, inflammation is characteristic of a broad spectrum of neurodegenerative diseases that manifest demntia. It is argued that an awareness of pathophysiological impact of IBS and implementation of appropriate therapeutic measures may prevent cognitive impairment and minimize vulnerability to dementia.

Cholinergic modulation of event-related oscillations (ERO)

The cholinergic system in the brain modulates patterns of activity involved in general arousal, attention processing, memory and consciousness. In the present study we determined the effects of selective cholinergic lesions of the medial septum area (MS) or nucleus basalis magnocellularis (NBM) on amplitude and phase characteristics of event related oscillations (EROs). A time-frequency based representation was used to determine ERO energy, phase synchronization across trials, recorded within a structure (phase lock index, PLI), and phase synchronization across trials, recorded between brain structures (phase difference lock index, PDLI), in the frontal cortex (Fctx), dorsal hippocampus (DHPC) and central amygdala (Amyg). Lesions in MS produced: (1) decreases in ERO energy in delta, theta, alpha, beta and gamma frequencies in Amyg, (2) reductions in gamma ERO energy and PLI in Fctx, (3) decreases in PDLI between the Fctx-Amyg in the theta, alpha, beta and gamma frequencies, and (4) decreases in PDLI between the DHPC-Amyg and Fctx-DHPC in the theta frequency bands. Lesions in NBM resulted in: (1) increased ERO energy in delta and theta frequency bands in Fctx, (2) reduced gamma ERO energy in Fctx and Amyg, (3) reductions in PLI in the theta, beta and gamma frequency ranges in Fctx, (4) reductions in gamma PLI in DHPC and (5) reduced beta PLI in Amyg. These studies suggest that the MS cholinergic system can alter phase synchronization between brain areas whereas the NBM cholinergic system modifies phase synchronization/phase resetting within a brain area.