Systemic Inflammation and Multimodal Biomarkers in Amnestic Mild Cognitive Impairment and Alzheimer’s Disease

Multitrajectories of Frailty and Depression With Cognitive Function: Findings From the Health and Retirement Longitudinal Study

BACKGROUND

Little is known about the joint associations between trajectories of frailty and depression with cognitive function. This study aims to explore the multitrajectories of frailty and depression and their joint impact on cognition.

METHODS

A total of 8600 participants from the Health and Retirement Study (HRS) (1996-2018) were analysed using a group-based trajectory model for 10-year multitrajectories. Participants were classified into five groups based on their trajectories. Multivariable linear mixed models and Cox proportional hazards models were utilized.

RESULTS

Compared with Group 1 (stable robust and nondepressed), Groups 2 ('worsening prefrailty without depression,' β = -0.022 SD/year), 3 ('stable prefrailty with escalating depressive symptoms,' β = -0.016 SD/year), 4 ('increasing frailty alongside worsening depressive symptoms,' β = -0.034 SD/year) and 5 ('high and escalating frailty with persistent depression,' β = -0.055 SD/year) exhibited accelerated cognitive decline. Dementia risk was significantly higher in G2 (HR = 1.26, 95% CI: 1.08-1.48), G3 (HR = 1.54, 95% CI: 1.31-1.80), G4 (HR = 1.81, 95% CI: 1.54-2.14) and G5 (HR = 1.86, 95% CI: 1.48-2.33) compared with G1.

CONCLUSIONS

Worsening frailty and depression accelerate cognitive decline and risk of dementia, underscoring the need to address both conditions to mitigate cognition.

"Let's talk about sex, inflammaging, and cognition, baby": A meta-analysis and meta-regression of 106 case-control studies on mild cognitive impairment and Alzheimer's disease

Background

Chronic inflammation is recognised as an important component of Alzheimer's disease (AD), yet its relationship with cognitive decline, sex-differences, and age is not well understood. This study investigated the relationship between inflammatory markers, cognition, sex, and age in individuals with mild cognitive impairment (MCI) and AD.

Methods

A systematic review was performed to identify case-control studies which measured cognitive function and inflammatory markers in serum, plasma, and cerebrospinal fluid in individuals with MCI or AD compared with healthy control (HC) participants. Meta-analysis was performed with Hedges' g calculated in a random effects model. Meta-regression was conducted using age, sex, and mini-mental status exam (MMSE) values.

Results

A total of 106 studies without a high risk of bias were included in the meta-analysis including 18,145 individuals: 5625 AD participants, 3907 MCI participants, and 8613 HC participants. Combined serum and plasma meta-analysis found that IL1β, IL6, IL8, IL18, CRP, and hsCRP were significantly raised in individuals with AD compared to HC. In CSF, YKL40, and MCP-1 were raised in AD compared to HC. YKL40 was also raised in MCI compared to HC. Meta-regression analysis highlighted several novel findings: MMSE was negatively correlated with IL6 and positively correlated with IL1α in AD, while in MCI studies, MMSE was negatively correlated with IL8 and TNFα. Meta-regression also revealed sex-specific differences in levels of IL1α, IL4, IL6, IL18, hsCRP, MCP-1, and YKL-40 across AD and MCI studies, and age was found to account for heterogeneity of CRP, MCP-1, and IL4 in MCI and AD.

Conclusion

Elevated levels of IL6 and YKL40 may reflect microglial inflammatory activity in both MCI and AD. Systemic inflammation may interact with the central nervous system, as poor cognitive function in individuals with AD and MCI was associated with higher levels of serum and plasma proinflammatory cytokines IL6 and TNFα. Moreover, variations of systemic inflammation between males and females may be modulated by sex-specific hormonal changes, such as declining oestrogen levels in females throughout the menopause transition. Longitudinal studies sampling a range of biospecimen types are needed to elucidate the nuances of the relationship between inflammation and cognition in individuals with MCI and AD, and understand how systemic and central inflammation differentially impact cognitive function.

Association between frailty index and cognitive dysfunction in older adults: insights from the 2011-2014 NHANES data

Background

As the population ages, the occurrence of cognitive decline and dementia is continuously increasing. Frailty is a prevalent problem among older adults. Epidemiologic studies have shown a comorbidity between frailty and cognitive impairment. However, their relationship remains unclear. The frailty index is an important indicator for measuring frailty. This study aims to investigate the relationship between frailty index and cognitive dysfunction in older adults aged 60 years and older in the United States from the 2011-2014 National Health and Nutrition Examination Survey (NHANES).

Methods

Community-dwelling older adults aged 60 years or older from 2011 to 2014 were extracted from the NHANES database. The frailty index was calculated using the formula: frailty index = total number of deficits present/total number of deficits measured. The Animal Fluency (AF), the Digit Symbol Substitution Test (DSST), the Consortium to Establish a Registry for Alzheimer's disease Delayed Recall (CERAD-DR), and Word Learning (CERAD-WL) were used to evaluate cognitive dysfunction. Firstly, weighted logistic regression analysis was used to explore the relationship between frailty index and cognitive dysfunction. Secondly, the influence of covariates on the frailty index was evaluated by subgroup analysis and interaction. Finally, the non-linear relationship is discussed by using the restricted cubic spline regression model.

Results

Our study included a total of 2,574 patients, weighted logistic regression analysis, after adjusting for all covariates, showed that the frailty index was associated with every test score. The interaction showed that covariates had no significant effect on this association in AF. The association between the frailty index and AF in the restricted cubic spline regression model is non-linear. As the frailty index increased, the risk of AF reduction increased, suggesting a higher risk of cognitive dysfunction.

Conclusion

In general, a high frailty index appears to be associated with an increased risk of cognitive dysfunction in the elderly. Consequently, protecting against cognitive decline necessitates making geriatric frailty prevention and treatment top priorities.

Diagnostic accuracy of interleukin-6, interleukin-10 and tumor necrosis factor alpha cytokine levels in patients with mild cognitive impairment: systematic review and meta-analysis

There is growing evidence suggesting an association between neurodegeneration and inflammation playing a role in the pathogenesis of age-associated diseases, including Alzheimer's disease (AD) and Mild Cognitive Impairment (MCI).

Objective

A systematic review and meta-analysis were performed to verify evidence on the diagnostic accuracy parameters of the inflammatory cytokines interleukin-6 (IL-6), interleukin-10 (IL-10) and tumor necrosis factor alpha (TNF-α).

Methods

A search of Medical Literature Analysis and Retrieval System Online (Medline), Scientific Electronic Library Online (SciELO), Web of Science and Science Direct databases was performed and nine observational studies associated with peripheral inflammatory biomarkers in MCI were identified. Mean (±standard deviation - SD) concentrations of these biomarkers and values of true positives, true negatives, false positives and false negatives for MCI and healthy controls (HC) were extracted from these studies.

Results

Significantly higher levels of IL-10 were observed in subjects in the MCI group and Mini-Mental State Examination (MMSE) scores were lower compared to HC. For the other investigations, no differences were found between the groups. Our meta-analysis for the TNF-α biomarker revealed high heterogeneity between studies in terms of sensitivity and specificity.

Conclusion

These findings do not support the involvement of inflammatory biomarkers for detection of MCI, although significant heterogeneity was observed. More studies are needed to evaluate the role of these cytokines in MCI, as well as in other stages of cognitive decline and all-cause dementias.

Assessing causal relationship between circulating cytokines and age-related neurodegenerative diseases: a bidirectional two-sample Mendelian randomization analysis

Numerous studies have reported that circulating cytokines (CCs) are linked to age-related neurodegenerative diseases (ANDDs); however, there is a lack of systematic investigation for the causal association. A two-sample bidirectional Mendelian Randomisation (MR) method was utilized to evaluate the causal effect. We applied genetic variants correlated with concentrations of CCs from a genome-wide association study meta-analysis (n = 8293) as instrumental variables. Summary data of three major ANDDs [Alzheimer's disease (AD), Parkinson's disease (PD), and Amyotrophic lateral sclerosis (ALS)] were identified from the IEU OpenGWAS platform (n = 627, 266). Inverse-variance weighted method is the main approach to analyse causal effect, and MR results are verified by several sensitivity and pleiotropy analyses. In directional MR, it suggested that several CCs were nominally correlated with the risk of ANDDs, with a causal odds ratio (OR) of Interleukin (IL)-5 of 0.909 for AD; OR of IL-2 of 1.169 for PD; and OR of Beta nerve growth factor of 1.142 for ALS). In reverse MR, there were some suggestively causal effects of ANDDs on CCs (AD on increased Basic fibroblast growth factor and IL-12 and decreased Stem cell growth factor beta; PD on decreased Monokine induced by interferon-gamma; ALS on decreased Basic fibroblast growth factor and IL-17). The findings were stable across sensitivity and pleiotropy analyses. However, after Bonferroni correction, there is no statistically significant association between CCs and ANDDs. Through the genetic epidemiological approach, our study assessed the role and presented possible causal associations between CCs and ANDDs. Further studies are warranted to verify the causal associations.

[Association between oral health and cognitive decline in older Chileans]

OBJECTIVE

To identify the association between oral health and suspected cognitive impairment in older adults in Chile.

METHOD

Cross-sectional study including 1826 people ≥60 years who participated in the National Health Survey of Chile, 2016-2017. Oral health was evaluated by the number of teeth, presence of caries, use of dental prostheses, self-reported oral health, and pain and/or discomfort in the oral cavity. Cognitive impairment was assessed using the Mini-Mental State Examination (MMSE). The association was evaluated by logistic and linear regression, adjusted for sociodemographic and lifestyle variables.

RESULTS

Compared with people without suspicion of cognitive impairment, people with suspected impairment had five fewer teeth (13.4 vs. 8.5 teeth), a much higher difference in women than in men, and a higher frequency of oral pain. Edentulism and fewer teeth were associated with a higher likelihood of suspected cognitive impairment, associations that were not maintained in adjusted models. Oral pain was associated with a higher likelihood of suspected impairment even in the most adjusted model (odds ratio: 1.99; 95% confidence interval [95%CI]: 1.09-3.63). In linear models, an increase of 2% (95%CI: 0.01-0.05) in the MMSE score was observed for each additional tooth.

CONCLUSIONS

Poor oral health, particularly tooth loss and the presence of pain, was associated with cognitive impairment in older adults in Chile.

The pollutome-connectome axis: a putative mechanism to explain pollution effects on neurodegeneration

The study of pollutant effects is extremely important to address the epochal challenges we are facing, where world populations are increasingly moving from rural to urban centers, revolutionizing our world into an urban world. These transformations will exacerbate pollution, thus highlighting the necessity to unravel its effect on human health. Epidemiological studies have reported that pollution increases the risk of neurological diseases, with growing evidence on the risk of neurodegenerative disorders. Air pollution and water pollutants are the main chemicals driving this risk. These chemicals can promote inflammation, acting in synergy with genotype vulnerability. However, the biological underpinnings of this association are unknown. In this review, we focus on the link between pollution and brain network connectivity at the macro-scale level. We provide an updated overview of epidemiological findings and studies investigating brain network changes associated with pollution exposure, and discuss the mechanistic insights of pollution-induced brain changes through neural networks. We explain, in detail, the pollutome-connectome axis that might provide the functional substrate for pollution-induced processes leading to cognitive impairment and neurodegeneration. We describe this model within the framework of two pollutants, air pollution, a widely recognized threat, and polyfluoroalkyl substances, a large class of synthetic chemicals which are currently emerging as new neurotoxic source.

Whole-brain DTI parameters associated with tau protein and hippocampal volume in Alzheimer's disease

The causes of the neurodegenerative processes in Alzheimer's disease (AD) are not completely known. Recent studies have shown that white matter (WM) damage could be more severe and widespread than whole-brain cortical atrophy and that such damage may appear even before the damage to the gray matter (GM). In AD, Amyloid-beta (Aβ₄₂ ) and tau proteins could directly affect WM, spreading across brain networks. Since hippocampal atrophy is common in the early phase of disease, it is reasonable to expect that hippocampal volume (HV) might be also related to WM integrity. Our study aimed to evaluate the integrity of the whole-brain WM, through diffusion tensor imaging (DTI) parameters, in mild AD and amnestic mild cognitive impairment (aMCI) due to AD (with Aβ₄₂ alteration in cerebrospinal fluid [CSF]) in relation to controls; and possible correlations between those measures and the CSF levels of Aβ₄₂ , phosphorylated tau protein (p-Tau) and total tau (t-Tau). We found a widespread WM alteration in the groups, and we also observed correlations between p-Tau and t-Tau with tracts directly linked to mesial temporal lobe (MTL) structures (fornix and hippocampal cingulum). However, linear regressions showed that the HV better explained the variation found in the DTI measures (with weak to moderate effect sizes, explaining from 9% to 31%) than did CSF proteins. In conclusion, we found widespread alterations in WM integrity, particularly in regions commonly affected by the disease in our group of early-stage disease and patients with Alzheimer's disease. Nonetheless, in the statistical models, the HV better predicted the integrity of the MTL tracts than the biomarkers in CSF.

Relationships between Inflammation and Age-Related Neurocognitive Changes

The relationship between inflammation and age-related neurocognitive changes is significant, which may relate to the age-related immune dysfunctions characterized by the senescence of immune cells and elevated inflammatory markers in the peripheral circulation and the central nervous system. In this review, we discuss the potential mechanisms, including the development of vascular inflammation, neuroinflammation, organelle dysfunctions, abnormal cholesterol metabolism, and glymphatic dysfunctions as well as the role that the key molecules play in the immune-cognition interplay. We propose potential therapeutic pharmacological and behavioral strategies for ameliorating age-related neurocognitive changes associated with inflammation. Further research to decipher the multidimensional roles of chronic inflammation in normal and pathological aging processes will help unfold the pathophysiological mechanisms underpinning neurocognitive disorders. The insight gained will lay the path for developing cost-effective preventative measures and the buffering or delaying of age-related neurocognitive decline.

Early Prediction of a Pre-Symptomatic Neurodegeneration Disorder by Measuring Macrophage Inhibitory Factor Level in Diabetic Patients

BACKGROUND

The relationship between diabetes mellitus and neurodegenerative disorders has been of great interest. Macrophage migration inhibitory factor (MIF) is a pro-inflammatory cytokine in which a variety of signaling cascades are activated through it. MIF has been involved in the pathogenesis of several diseases and can predict early pre-symptomatic stages of neurodegeneration in diabetic patients.

OBJECTIVE

To investigate whether serum MIF could predict brain neurodegeneration at the early pre-symptomatic stages in diabetic patients.

METHODS

We examined adults with type 2 diabetes mellitus and compared with normal control adults using a short form of the IQCODE and biochemical examination, including assessment of HA1C, fasting blood glucose, lipid profile, and MIF which was measured by ELISA technique. Correlations between parameters were studied. Computational PathLinker bioinformatic tool was used to search for potential pathway reconstructions for the insulin/amyloid-β/MIF signaling.

RESULTS

We demonstrated that MIF level was increased in the serum at the early pre-symptomatic stages of neurodegenerative disorder in diabetic patients. In addition, network analysis demonstrates that insulin receptor substrate 1 can ameliorate amyloid-β protein precursor through COP9 signalosome complex subunit 5 that enhances MIF elevation.

CONCLUSION

Diagnosis processes could not be used as routine examinations for still pre-symptomatic neurodegenerative disorders. This may be due to the time constraints and the heavy dependence on the physician's experience. Therefore, serum MIF level could predict brain neurodegeneration at the early pre-symptomatic stages in diabetic patients which may support its potential utility as a clinically useful biomarker.

Progress in the correlation of postoperative cognitive dysfunction and Alzheimer's disease and the potential therapeutic drug exploration

Postoperative cognitive dysfunction (POCD) is a decrease in mental capacity that can occur days to weeks after a medical procedure and may become permanent and rarely lasts for a longer period of time. With the continuous development of research, various viewpoints in academic circles have undergone subtle changes, and the role of anesthesia depth and anesthesia type seems to be gradually weakened; Alzheimer's disease (AD) is a latent and progressive neurodegenerative disease in the elderly. The protein hypothesis and the synaptic hypothesis are well-known reasons. These changes will also lead to the occurrence of an inflammatory cascade. The exact etiology and pathogenesis need to be studied. The reasonable biological mechanism affecting brain protein deposition, neuroinflammation, and acetylcholine-like effect has a certain relationship between AD and POCD. Whereas there is still further uncertainty about the mechanism and treatment, and it is elusive whether POCD is a link in the continuous progress of AD or a separate entity, which has doubts about the diagnosis and treatment of the disease. Therefore, this review is based on the current common clinical characteristics of AD and POCD, and pathophysiological research, to search for their common points and explore the direction and new strategies for future treatment.

Serum Amyloidogenic Nanoplaques and Cytokines in Alzheimer's Disease: Pilot Study in a Small Naturalistic Memory Clinic Cohort

Background:

Neuroinflammation is a central component of Alzheimer’s disease (AD) and correlates closely with amyloid pathology. Markers of inflammation such as cytokines, and amyloidogenic aggregates, so-called nanoplaques, are both promising biomarker candidates for AD. We have previously shown that there is a relationship between the levels of nanoplaques and cytokines in cerebrospinal fluid, but it is unknown whether this association extends to serum.

Objective:

Investigate in a naturalistic memory clinic cohort whether the associations between nanoplaques and cytokines in the cerebrospinal fluid extends to serum.

Methods:

We collected serum from 49 patients assessed for cognitive complaints at the Oslo University Hospital Memory Clinic (15 with clinical AD). We assessed the levels of serum nanoplaques with the novel Thioflavin-T fluorescence correlation spectroscopy (ThT-FCS) assay. Serum levels of nine cytokines (eotaxin-1, granulocyte colony-stimulating factor [G-CSF], interleukin [IL]-6, IL-7, IL-8, monocyte chemoattractant protein-1 (MCP-1), gamma induced protein 10 (IP-10), macrophage inflammatory protein [MIP]-1α, and MIP-1β) were quantified with a multiplex assay and read on a Luminex IS 200 instrument.

Results:

Serum nanoplaques were not increased in clinical AD patients compared to non-AD memory clinic patients and nanoplaques were not associated with any cytokines. The cytokines IL-8 and G-CSF were increased in patients with clinical AD compared to non-AD patients.

Conclusion:

In this small pilot study, serum nanoplaques were not associated with serum cytokines. Nanoplaque levels could not be used to separate clinical AD patients from non-AD patients in this unselected memory clinic cohort.

Role of the mtDNA Mutations and Mitophagy in Inflammaging

Ageing is an unavoidable multi-factorial process, characterised by a gradual decrease in physiological functionality and increasing vulnerability of the organism to environmental factors and pathogens, ending, eventually, in death. One of the most elaborated ageing theories implies a direct connection between ROS-mediated mtDNA damage and mutations. In this review, we focus on the role of mitochondrial metabolism, mitochondria generated ROS, mitochondrial dynamics and mitophagy in normal ageing and pathological conditions, such as inflammation. Also, a chronic form of inflammation, which could change the long-term status of the immune system in an age-dependent way, is discussed. Finally, the role of inflammaging in the most common neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, is also discussed.

Alterations in T-Cell Transcription Factors and Cytokine Gene Expression in Late-Onset Alzheimer's Disease

BACKGROUND

Late-onset Alzheimer's disease (LOAD) is associated with many environmental and genetic factors. The effect of systemic inflammation on the pathogenesis of neurodegenerative diseases such as AD has been strongly suggested. T helper cells (Th) are one of the important components of the immune system and can easily infiltrate the brain in pathological conditions. The development of each Th-subset depends on the production of unique cytokines and their main regulator.

OBJECTIVE

This study aimed to compare the mRNA levels of Th-related genes derived from peripheral blood mononuclear cells of LOAD patients with control. Also, the identification of the most important Th1/Th2 genes and downstream pathways that may be involved in the pathogenesis of AD was followed by computational approaches.

METHODS

This study invloved 30 patients with LOAD and 30 non-demented controls. The relative expression of T-cell cytokines (IFN-γ, TNF-α, IL-4, and IL-5) and transcription factors (T-bet and GATA-3) were assessed using real-time PCR. Additionally, protein-protein interaction (PPI) was investigated by gene network construction.

RESULTS

A significant decrease at T-bet, IFN-γ, TNF-α, and GATA-3 mRNA levels was detected in the LOAD group, compared to the controls. However, there was no significant difference in IL-4 or IL-5 mRNA levels. Network analysis revealed a list of the highly connected protein (hubs) related to mitogen-activated protein kinase (MAPK) signaling and Th17 cell differentiation pathways.

CONCLUSION

The findings point to a molecular dysregulation in Th-related genes, which can promising in the early diagnosis or targeted interventions of AD. Furthermore, the PPI analysis showed that upstream off-target stimulation may involve MAPK cascade activation and Th17 axis induction.

Association between dementia and hepatitis B and C virus infection

ABSTRACT

Several viral infections are known to increase the risk of dementia through brain cell damage and systemic infection. The association between hepatitis B and C virus (HBV and HCV) infections and dementia was evaluated using a national sample cohort from South Korea. Using the national cohort study from the Korean National Health Insurance Service, we extracted data for patients with HBV or HCV infection and for matched control participants. The controls were matched to the patients according to age, sex, income, region of residence, and past medical histories. The incidence of HCV infection was higher in the dementia group (1.0% [113/11,228]) than in the control group (0.8% [364/44,912], P = .043). However, there was no difference in the incidence of HBV infection in the dementia and control groups. The adjusted odds ratio (OR) for HCV infection was 1.25 (95% confidence interval [CI] = 1.01-1.54, P = .043) in the dementia group. According to the subgroup analysis by sex, the adjusted ORs for HCV infection were 1.04 (95% CI = 072-1.49, P = .851) in men and 1.38 (95% CI = 1.06-1.79, P = .016) in women. We concluded that the incidence of HCV infection was higher (with a higher OR) in women with dementia than in matched control participants in South Korea.

Neurological impairment caused by Schistosoma mansoni systemic infection exhibits early features of idiopathic neurodegenerative disease

Schistosomiasis, a neglected tropical disease caused by trematodes of the Schistosoma genus, affects over 250 million people around the world. This disease has been associated with learning and memory deficits in children, whereas reduced attention levels, impaired work capacity, and cognitive deficits have been observed in adults. Strongly correlated with poverty and lack of basic sanitary conditions, this chronic endemic infection is common in Africa, South America, and parts of Asia and contributes to inhibition of social development and low quality of life in affected areas. Nonetheless, studies on the mechanisms involved in the neurological impairment caused by schistosomiasis are scarce. Here, we used a murine model of infection with Schistosoma mansoni in which parasites do not invade the central nervous system to evaluate the consequences of systemic infection on neurologic function. We observed that systemic infection with S. mansoni led to astrocyte and microglia activation, expression of oxidative stress-induced transcription factor Nrf2, oxidative damage, Tau phosphorylation, and amyloid-β peptide accumulation in the prefrontal cortex of infected animals. We also found impairment in spatial learning and memory as evaluated by the Morris water maze task. Administration of anthelmintic (praziquantel) and antioxidant (N-acetylcysteine plus deferoxamine) treatments was effective in inhibiting most of these phenotypes, and the combination of both treatments had a synergistic effect to prevent such changes. These data demonstrate new perspectives toward the understanding of the pathology and possible therapeutic approaches to counteract long-term effects of systemic schistosomiasis on brain function.

Tripchlorolide attenuates β-amyloid generation by inducing NEP activity in N2a/APP695 cells

Background and purpose

Alzheimer’s disease (AD) is a neurodegeneration disease. The previous work from our research group demonstrated the neuroprotective effects of tripchlorolide (T4) in AD animal models.

Materials and methods

Neprilysin (NEP) is known as an important physiological amyloid-β protein (Aβ) peptide-degrading enzyme in the brain due to its apparent rate-limiting function. In this study, we explored the effect of NEP on AD model N2a/APP695 cells. Western blots and enzyme-linked immunosorbent assays were performed to assess the expression of proteins, while quantitative real-time polymerase chain reaction assays were used to evaluate RNA levels. Cell vitality was detected by the MTT assay, and reactive oxygen species (ROS) levels were assessed using a ROS activity assay kit.

Results

We discovered that T4 was able to enhance the enzyme activity of NEP. T4 administration decreased the protein levels of the soluble amyloid precursor protein. In further experiments, we found that by using thiorphan the secretion of Aβ, oxidative stress, nitrosative stress, and inflammatory factors, which were suppressed by T4, were reversed. Due to its ability to attenuate Aβ generation and to protect neurons against the neurotoxicity of Aβ, T4 may be a potential therapy in the regulation of Aβ-related pathology in AD by affecting NEP activity.

Conclusion

Tripchlorolide attenuates Aβ generation by inducing NEP activity in N2a/APP695 cells.

Differences in structural and functional default mode network connectivity in amyloid positive mild cognitive impairment: a longitudinal study

PURPOSE

Default mode network (DMN) has emerged as a potential biomarker of Alzheimer's disease (AD); however, it is not clear whether it can differentiate amnestic mild cognitive impairment with altered amyloid (aMCI-Aβ +) who will evolve to AD. We evaluated if structural and functional connectivity (FC), hippocampal volumes (HV), and cerebrospinal fluid biomarkers (CSF-Aβ₄₂, p-Tau, and t-Tau) can differentiate aMCI-Aβ + converters from non-converters.

METHODS

Forty-eight individuals (18 normal controls and 30 aMCI subjects in the AD continuum - with altered Aβ₄₂ in the CSF) were followed up for an average of 13 months. We used MultiAtlas, UF²C, and Freesurfer software to evaluate diffusion tensor imaging, FC, and HV, respectively, INNOTEST® kits to measure CSF proteins, and neuropsychological tests. Besides, we performed different MANOVAs with further univariate analyses to differentiate groups.

RESULTS

During follow-up, 8/30 aMCI-Aβ + converted (26.6%) to AD dementia. There were no differences in multivariate analysis between groups in CSF biomarkers (p = 0.092) or at DMN functional connectivity (p = 0.814). aMCI-Aβ + converters had smaller right HV than controls (p = 0.013), and greater right cingulum parahippocampal bundle radial diffusivity than controls (p < 0.001) and non-converters (p = 0.036).

CONCLUSION

In this exploratory study, structural, but not functional, DMN connectivity alterations may differentiate aMCI-Aβ + subjects who converted to AD dementia.

Inflammatory pathways in Alzheimer's disease mediated by gut microbiota

In the past decade, numerous studies have demonstrated the close relationship between gut microbiota and the occurrence and development of Alzheimer's disease (AD). However, the specific mechanism is still unclear. Both the neuroinflammation and systemic inflammation serve as the key hubs to accelerate the process of AD by promoting pathology and damaging neuron. What's more, the gut microbiota is also crucial for the regulation of inflammation. Therefore, this review focused on the role of gut microbiota in AD through inflammatory pathways. Firstly, this review summarized the relationship and interaction among gut microbiota, inflammation, and AD. Secondly, the direct and indirect regulatory effects of gut microbiota on AD through inflammatory pathways were described. These effects were mainly mediated by the component of the gut microbiota (lipopolysaccharides (LPS) and amyloid peptides), the metabolites of bacteria (short-chain fatty acids, branched amino acids, and neurotransmitters) and functional by-products (bile acids). In addition, potential treatments (fecal microbiota transplantation, antibiotics, probiotics, prebiotics, and dietary interventions) for AD were also discussed through these mechanisms. Finally, according to the current research status, the key problems to be solved in the future studies were proposed.

Brain morphology is differentially impacted by peripheral cytokines in schizophrenia-spectrum disorder

Deficits in brain morphology are one of the most widely replicated neuropathological features in schizophrenia-spectrum disorder (SSD), although their biological underpinnings remain unclear. Despite the existence of hypotheses by which peripheral inflammation may impact brain structure, few studies have examined this relationship in SSD. This study aimed to establish the relationship between peripheral markers of inflammation and brain morphology and determine whether such relationships differed across healthy controls and individuals with first episode psychosis (FEP) and chronic schizophrenia. A panel of 13 pro- and anti-inflammatory cytokines were quantified from serum in 175 participants [n = 84 Healthy Controls (HC), n = 40 FEP, n = 51 Chronic SCZ]. We first performed a series of permutation tests to identify the cytokines most consistently associated with brain structural regions. Using moderation analysis, we then determined the extent to which individual variation in select cytokines, and their interaction with diagnostic status, predicted variation in brain structure. We found significant interactions between cytokine level and diagnosis on brain structure. Diagnostic status significantly moderated the relationship of IFNγ, IL4, IL5 and IL13 with frontal thickness, and of IFNγ and IL5 and total cortical volume. Specifically, frontal thickness was positively associated with IFNγ, IL4, IL5 and IL13 cytokine levels in the healthy control group, whereas pro-inflammatory cytokines IFNγ and IL5 were associated with lower total cortical volume in the FEP group. Our findings suggest that while there were no relationships detected in chronic schizophrenia, the relationship between peripheral inflammatory markers and select brain regions are differentially impacted in FEP and healthy controls. Longitudinal investigations are required to determine whether the relationship between brain structure and peripheral inflammation changes over time.

Peripheral inflammatory biomarkers predict the deposition and progression of amyloid-β in cognitively unimpaired older adults

INTRODUCTION

Systemic inflammation has been increasingly implicated in the pathogenesis of Alzheimer's disease (AD), yet the mechanistic and temporal specificity of this relationship is poorly understood. We aimed to characterize the cross-sectional and longitudinal associations between peripheral inflammatory biomarkers, cognition, and Aβ deposition in oldest-old cognitively unimpaired (CU) adults.

METHODS

A large sample of 139 CU older adults (mean age (range) = 85.4 (82-95)) underwent neuropsychological testing, Pittsburgh compound-B (PiB)-PET imaging and structural MRI. Hierarchical regression models examined associations between circulating inflammatory biomarkers (Interleukin-6 (IL-6), soluble Tumor Necrosis Factor receptors 1 and 2 (sTNFr1 and sTNFr2), soluble cluster of differentiation 14 (sCD14), C-reactive protein (CRP)), cognition, and global and regional Aβ deposition at baseline and over follow-up. Indices of preclinical disease, including pathologic Aβ status and hippocampal volume, were incorporated to assess conditional associations.

RESULTS

At baseline evaluation, higher concentrations of IL-6 and sTNFr2 were associated with greater global Aβ burden in those with lower hippocampal volume. In longitudinal models, IL-6 predicted subsequent conversion to MCI and both IL-6 and CRP predicted greater change in global and regional Aβ deposition specifically among participants PiB-positive at baseline. These relationships withstood adjustment for demographic factors, anti-hypertensive medication use, history of diabetes, heart disease, APOE ε4 carrier status, and white matter lesions.

DISCUSSION

In a large prospective sample of CU adults aged 80 and over, peripheral inflammatory biomarkers were associated with and predictive of the progression of Aβ deposition. This was specific to those with biomarker evidence of preclinical AD at baseline, supporting recent evidence of disease-state-dependent differences in inflammatory expression profiles. Chronic, low-level systemic inflammation may exacerbate the deposition of Aβ pathology among those with emerging disease processes, and place individuals at a higher risk of developing clinically significant cognitive impairment.

Higher CSF sTNFR1-related proteins associate with better prognosis in very early Alzheimer's disease

Neuroinflammation is associated with Alzheimer's disease, but the application of cerebrospinal fluid measures of inflammatory proteins may be limited by overlapping pathways and relationships between them. In this work, we measure 15 cerebrospinal proteins related to microglial and T-cell functions, and show them to reproducibly form functionally-related groups within and across diagnostic categories in 382 participants from the Alzheimer's Disease Neuro-imaging Initiative as well participants from two independent cohorts. We further show higher levels of proteins related to soluble tumor necrosis factor receptor 1 are associated with reduced risk of conversion to dementia in the multi-centered (p = 0.027) and independent (p = 0.038) cohorts of people with mild cognitive impairment due to predicted Alzheimer's disease, while higher soluble TREM2 levels associated with slower decline in the dementia stage of Alzheimer's disease. These inflammatory proteins thus provide prognostic information independent of established Alzheimer's markers.

Neuroimaging Research on Dementia in Brazil in the Last Decade: Scientometric Analysis, Challenges, and Peculiarities

The last years have evinced a remarkable growth in neuroimaging studies around the world. All these studies have contributed to a better understanding of the cerebral outcomes of dementia, even in the earliest phases. In low- and middle-income countries, studies involving structural and functional neuroimaging are challenging due to low investments and heterogeneous populations. Outstanding the importance of diagnosing mild cognitive impairment and dementia, the purpose of this paper is to offer an overview of neuroimaging dementia research in Brazil. The review includes a brief scientometric analysis of quantitative information about the development of this field over the past 10 years. Besides, discusses some peculiarities and challenges that have limited neuroimaging dementia research in this big and heterogeneous country of Latin America. We systematically reviewed existing neuroimaging literature with Brazilian authors that presented outcomes related to a dementia syndrome, published from 2010 to 2020. Briefly, the main neuroimaging methods used were morphometrics, followed by fMRI, and DTI. The major diseases analyzed were Alzheimer's disease, mild cognitive impairment, and vascular dementia, respectively. Moreover, research activity in Brazil has been restricted almost entirely to a few centers in the Southeast region, and funding could be the main driver for publications. There was relative stability concerning the number of publications per year, the citation impact has historically been below the world average, and the author's gender inequalities are not relevant in this specific field. Neuroimaging research in Brazil is far from being developed and widespread across the country. Fortunately, increasingly collaborations with foreign partnerships contribute to the impact of Brazil's domestic research. Although the challenges, neuroimaging researches performed in the native population regarding regional peculiarities and adversities are of pivotal importance.

Palmitate Is Increased in the Cerebrospinal Fluid of Humans with Obesity and Induces Memory Impairment in Mice via Pro-inflammatory TNF-α

Obesity has been associated with cognitive decline, atrophy of brain regions related to learning and memory, and higher risk of developing dementia. However, the molecular mechanisms underlying these neurological alterations are still largely unknown. Here, we investigate the effects of palmitate, a saturated fatty acid present at high amounts in fat-rich diets, in the brain. Palmitate is increased in the cerebrospinal fluid (CSF) of overweight and obese patients with amnestic mild cognitive impairment. In mice, intracerebroventricular infusion of palmitate impairs synaptic plasticity and memory. Palmitate induces astroglial and microglial activation in the mouse hippocampus, and its deleterious impact is mediated by microglia-derived tumor necrosis factor alpha (TNF-α) signaling. Our results establish that obesity is associated with increases in CSF palmitate. By defining a pro-inflammatory mechanism by which abnormal levels of palmitate in the brain impair memory, the results further suggest that anti-inflammatory strategies may attenuate memory impairment in obesity.

Inflammation is correlated with abnormal functional connectivity in unmedicated bipolar depression: an independent component analysis study of resting-state fMRI

BACKGROUND

Inflammation might play a role in bipolar disorder (BD), but it remains unclear the relationship between inflammation and brain structural and functional abnormalities in patients with BD. In this study, we focused on the alterations of functional connectivity (FC), peripheral pro-inflammatory cytokines and their correlations to investigate the role of inflammation in FC in BD depression.

METHODS

In this study, 42 unmedicated patients with BD II depression and 62 healthy controls (HCs) were enrolled. Resting-state-functional magnetic resonance imaging was performed in all participants and independent component analysis was used. Serum levels of Interleukin-6 (IL-6) and Interleukin-8 (IL-8) were measured in all participants. Correlation between FC values and IL-6 and IL-8 levels in BD was calculated.

RESULTS

Compared with the HCs, BD II patients showed decreased FC in the left orbitofrontal cortex (OFC) implicating the limbic network and the right precentral gyrus implicating the somatomotor network. BD II showed increased IL-6 (p = 0.039), IL-8 (p = 0.002) levels. Moreover, abnormal FC in the right precentral gyrus were inversely correlated with the IL-8 (r = -0.458, p = 0.004) levels in BD II. No significant correlation was found between FC in the left OFC and cytokines levels.

CONCLUSIONS

Our findings that serum IL-8 levels are associated with impaired FC in the right precentral gyrus in BD II patients suggest that inflammation might play a crucial role in brain functional abnormalities in BD.

Microglial response to experimental periodontitis in a murine model of Alzheimer's disease

Periodontal disease (PD) has been suggested to be a risk factor for Alzheimer's disease (AD). We tested the impact of ligature-induced PD on 5xFAD mice and WT littermates. At baseline, 5xFAD mice presented significant alveolar bone loss compared to WT mice. After the induction of PD, both WT and 5xFAD mice experienced alveolar bone loss. PD increased the level of Iba1-immunostained microglia in WT mice. In 5xFAD mice, PD increased the level of insoluble Aβ42. The increased level in Iba1 immunostaining that parallels the accumulation of Aβ in 5xFAD mice was not affected by PD except for a decrease in the dentate gyrus. Analysis of double-label fluorescent images showed a decline in Iba1 in the proximity of Aβ plaques in 5xFAD mice with PD compared to those without PD suggesting a PD-induced decrease in plaque-associated microglia (PAM). PD reduced IL-6, MCP-1, GM-CSF, and IFN-γ in brains of WT mice and reduced IL-10 in 5xFAD mice. The data demonstrated that PD increases neuroinflammation in WT mice and disrupts the neuroinflammatory response in 5xFAD mice and suggest that microglia is central to the association between PD and AD.

Peptic ulcer does not increase the risk of dementia: A nested case control study using a national sample cohort

Studies have shown that peptic ulcer disease (PUD) increases the risk of dementia via the mechanism of systemic inflammation. We examined the association between PUD and the risk of dementia using a population-based national sample cohort from South Korea.Using the national cohort study from the Korean National Health Insurance Service, we extracted data for patients with dementia (n = 11,434) and for 1:4 matched control participants (n = 45,736) and then analyzed the previous histories of PUD from 2002 to 2013 using conditional logistic regression analyses. The controls were matched to the patients according to age, sex, income, region of residence, and past medical history. Subgroup analyses were performed based on age and sex.There was no statistically significant difference in the incidence of PUD between the dementia and control groups (18.0% vs 17.4%, P = .107). The adjusted odds ratio (OR) for PUD was 0.92 (95% confidence interval [CI] = 0.88-0.97, P = .002). In the subgroup analysis based on age, the adjusted ORs for PUD were 0.93 (95% CI = 0.88-0.99) in the <80-year-old group and 0.90 (95% CI = 0.82-1.00) in the ≥80-year-old group (each P < .05). In the subgroup analysis based on sex, the adjusted ORs for PUD were 0.89 (95% CI = 0.81-0.97; P < .05) in men and 0.94 (95% CI = 0.89-1.00; P = .06) in women.PUD does not increase the risk of dementia at any age or in either sex after adjusting for age and the history of hypertension, diabetes mellitus, dyslipidemia, ischemic heart disease, stroke, and depression.

Dysfunction of the Blood-Brain Barrier-A Key Step in Neurodegeneration and Dementia

The vascular endothelium in the brain is an essential part of the blood-brain-barrier (BBB) because of its very tight structure to secure a functional and molecular separation of the brain from the rest of the body and to protect neurons from pathogens and toxins. Impaired transport of metabolites across the BBB due to its increasing dysfunction affects brain health and cognitive functioning, thus providing a starting point of neurodegenerative diseases. The term “cerebral metabolic syndrome” is proposed to highlight the importance of lifestyle factors in neurodegeneration and to describe the impact of increasing BBB dysfunction on neurodegeneration and dementia, especially in elderly patients. If untreated, the cerebral metabolic syndrome may evolve into dementia. Due to the high energy demand of the brain, impaired glucose transport across the BBB via glucose transporters as GLUT1 renders the brain increasingly susceptible to neurodegeneration. Apoptotic processes are further supported by the lack of essential metabolites of the phosphocholine synthesis. In Alzheimer’s disease (AD), inflammatory and infectious processes at the BBB increase the dysfunction and might be pace-making events. At this point, the potentially highly relevant role of the thrombocytic amyloid precursor protein (APP) in endothelial inflammation of the BBB is discussed. Chronic inflammatory processes of the BBB transmitted to an increasing number of brain areas might cause a lasting build-up of spreading, pore-forming β-amyloid fragments explaining the dramatic progression of the disease. In the view of the essential requirement of an early diagnosis to investigate and implement causal therapeutic strategies against dementia, brain imaging methods are of great importance. Therefore, status and opportunities in the field of diagnostic imaging of the living human brain will be portrayed, comprising diverse techniques such as positron emissions tomography (PET) and functional magnetic resonance imaging (fMRI) to uncover the patterns of atrophy, protein deposits, hypometabolism, and molecular as well as functional alterations in AD.

Periodontal disease as a possible cause for Alzheimer's disease

Approximately 47 million people worldwide have been diagnosed with dementia, 60%-80% of whom have dementia of the Alzheimer's disease type. Unfortunately, there is no cure in sight. Defining modifiable risk factors for Alzheimer's disease may have a significant impact on its prevalence. An increasing body of evidence suggests that chronic inflammation and microbial dysbiosis are risk factors for Alzheimer's disease. Periodontal disease is a chronic inflammatory disease that develops in response to response to microbial dysbiosis. Many studies have shown an association between periodontal disease and Alzheimer's disease. The intent of this paper was to review the existing literature and determine, using the Bradford Hill criteria, whether periodontal disease is causally related to Alzheimer's disease.

Early Diagnosis and Targeted Treatment Strategy for Improved Therapeutic Outcomes in Alzheimer's Disease

There have been repeated failures of clinical studies in the development of new efficacious treatments for Alzheimer's disease. This may be due to the fact that Alzheimer's disease is a heterogeneous disorder caused by person-to-person differences in genetic background, epigenetic profiles, environmental triggers, or the presence of other diseases. Furthermore, most Alzheimer's disease patients are diagnosed in the middle to late stages of the illness, when irreversible damage to the brain has already occurred. With this in mind, a strategy is presented involving identification and implementation of biomarker tests for diagnosis during the prodromal or early stages of the disease. In addition, it is proposed that targeting specific components of the amyloid deposition, tau oligomerization and neuroinflammation pathways may lead to improved outcomes in clinical studies.

GW9508 ameliorates cognitive impairment via the cAMP-CREB and JNK pathways in APPswe/PS1dE9 mouse model of Alzheimer's disease

GPR40 was utilized as the drug target to the treatment of diabetes, but the function and mechanisms ameliorating the Alzheimer's disease (AD) remain unknown. In present study, the typical APP/PS1 mouse model was applied to explore the function and mechanism of GPR40 in AD. GPR40 agonist GW9508 and antagonist GW1100 were respectively given by i.c.v. injection to activate/inhibit the GPR40 in the brain of APP/PS1 mice which illustrated the function and mechanism of GPR40 in ameliorating AD symptoms. Morris water maze test, step-through test, Y-maze spontaneous alternation test, open field test and new object recognition test were used to test the cognitive function and memory ability of mice, while molecular biology experiments such as Western blot, immunofluorescence, JC-1 were used to detect the corresponding changes of signal pathways. The results revealed that treatment with GW9508 could significantly ameliorate cognitive deficits of APP/PS1 mice, upregulate the expression levels of cAMP, p-CREB and neurotrophic factors in vivo, while GW9508 also ameliorate Aβ_1-42-induced neuron damage and downregulate the expression levels of pathological protein such as p-JNK, JNK and apoptosis-related proteins such as IL-6, IL-1β, TNF-α and caspase-3 in vitro. Meanwhile, high-content screening also showed that GW9508 promoted the cellular differentiation of SH-SY5Y cells, while GW1100 reversed the effects of GW9508. These results suggested that GPR40 was an underlying therapeutic target for the treatment of AD and GPR40 agonist could be explored as the emerging AD therapeutic drug.

Neuroimmune interactions in Alzheimer's disease-New frontier with old challenges?

The perceived role of the immune system in neurodegenerative diseases has undergone drastic changes over time. Initially considered as a passive bystander, then condemned as a mediator of neurodegeneration and now established as an important player in the pathogenetic cascade, neuroimmune interactions have come a long way to arrive center stage in Alzheimer's disease research. Despite major breakthroughs in recent years, basic questions remain unanswered as conflicting data describe immune overactivation, inadequate response or exhaustion of the immune system in neurodegenerative diseases. Furthermore, difficulties in translating in vitro and in vivo studies in model systems to the complex human disease condition with multiple overlapping pathologies and the long disease duration in patients suffering from neurodegenerative diseases have hampered progress. Development of novel, advanced model systems, as well as new technologies to interrogate existing disease models and valuable collections of human tissue samples, including brain tissue in parallel with improved imaging and biomarker technologies are guiding the way to better understand the role of the immune system in Alzheimer's disease with hopes for more effective interventions in the future.

Early Detection and Treatment of Patients with Alzheimer's Disease: Future Perspectives

Alzheimer's disease affects approximately 6% of people over the age of 65 years. It is characterized as chronic degeneration of cortical neurons, with loss of memory, cognition and executive functions. As the disease progresses, it is accompanied by accumulation of amyloid plaques and neurofibrillary tangles in key areas of the brain, leading to a loss of neurogenesis and synaptic plasticity in the hippocampus, along with changes in the levels of essential neurotransmitters such as acetylcholine and glutamate. Individuals with concomitant diseases such as depression, diabetes and cardiovascular disorders have a higher risk of developing Alzheimer's disease, and those who have a healthier diet and partake in regular exercise and intellectual stimulation have a lower risk of developing the disorder. This chapter describes the advances made in early diagnosis of Alzheimer's disease as this could help to improve outcomes for the patients by facilitating earlier treatment.

Impact of reduced P-glycoprotein function on digoxin concentrations in patients with dementia

AIMS

Patients with Alzheimer's disease (AD), the most common form of dementia, have reduced P-glycoprotein (P-gp) function at the blood-brain barrier. However, the effect of AD on P-gp function in peripheral organs, and the impact on medication efficacy and toxicity is unknown. In this study, clinical chart review and physiologically based pharmacokinetic (PBPK) modelling were employed to determine whether disease-associated changes in P-gp could be assessed from clinically measured digoxin concentrations in patients without and with dementia.

METHODS

A retrospective chart review was conducted to compare digoxin dose and concentrations between cohorts. A PBPK model was developed to simulate changes in digoxin concentrations at single and multiple 62.5 and 125 μg/d doses due to reduced P-gp function in peripheral organs.

RESULTS

Digoxin concentrations were similar between the nondementia (n = 75) and dementia (n = 72) cohorts (mean ± standard deviation; 0.64 ± 0.31 and 0.60 ± 0.34 ng/mL, respectively; -0.06 to 0.15, 95% confidence interval of difference). PBPK simulations showed that reduced P-gp function resulted in a significant increase in digoxin exposure (AUC), but not in C_max . For example, when a 2-fold reduction in P-gp function was simulated in older people following multiple 125 μg/d digoxin doses, the AUC over the last dosing interval was increased compared to baseline (24.29 ± 3.94 vs 17.04 ± 3.46 ng/mL*h; 4.52 to 9.98); however, C_max was similar (1.38 ± 0.20 vs 0.99 ± 0.18 ng/mL; -2.33 to 3.13).

CONCLUSION

Clinically measured digoxin concentrations were not statistically different in patients with dementia. Based on PBPK simulations, digoxin AUC may need to be evaluated to adequately assess the impact of reduced P-gp function in peripheral organs.

Microbiome-Derived Lipopolysaccharide (LPS) Selectively Inhibits Neurofilament Light Chain (NF-L) Gene Expression in Human Neuronal-Glial (HNG) Cells in Primary Culture

The remarkable co-localization of highly pro-inflammatory lipopolysaccharide (LPS) with sporadic Alzheimer's disease (AD)-affected neuronal nuclei suggests that there may be some novel pathogenic contribution of this heat stable neurotoxin to neuronal activity and neuron-specific gene expression. In this communication we show for the first time: (i) the association and envelopment of sporadic AD neuronal nuclei with LPS in multiple AD neocortical tissue samples; and (ii) a selective repression in the output of neuron-specific neurofilament light (NF-L) chain messenger RNA (mRNA), perhaps as a consequence of this association. The down-regulation of NF-L mRNA and protein is a characteristic attribute of AD brain and accompanies neuronal atrophy and an associated loss of neuronal architecture with synaptic deficits. To study this phenomenon further, human neuronal-glial (HNG) cells in primary culture were incubated with LPS, and DNA arrays, Northern, Western, and ELISA analyses were used to quantify transcription patterns for the three member neuron-specific intermediate filament-gene family NF-H, NF-M, and NF-L. As in sporadic AD limbic-regions, down-regulated transcription products for the NF-L intermediate filament protein was significant. These results support our novel hypothesis: (i) that internally sourced, microbiome-derived neurotoxins such as LPS contribute to a progressive disruption in the read-out of neuron-specific genetic-information; (ii) that the presence of LPS-enveloped neuronal nuclei is associated with a down-regulation in NF-L expression, a key neuron-specific cytoskeletal component; and (iii) this may have a bearing on progressive neuronal atrophy, loss of synaptic-contact and disruption of neuronal architecture, all of which are characteristic pathological features of sporadic-AD brain. This is the first report that provides evidence for a neuron-specific effect of a human GI-tract microbiome-derived neurotoxin on decreased NF-L abundance in both sporadic AD temporal lobe neocortex in vivo and in LPS-stressed HNG cells in vitro.

Microbiome-Mediated Upregulation of MicroRNA-146a in Sporadic Alzheimer's Disease

The first indication of a potential mechanistic link between the pathobiology of the human gastrointestinal (GI)-tract microbiome and its contribution to the pathogenetic mechanisms of sporadic Alzheimer's disease (AD) came a scant 4 years ago (1). Ongoing research continues to strengthen the hypothesis that neurotoxic microbial-derived components of the GI tract microbiome can cross aging GI tract and blood-brain barriers and contribute to progressive proinflammatory neurodegeneration, as exemplified by the AD-process. Of central interest in these recent investigations are the pathological roles played by human GI tract resident Gram-negative anaerobic bacteria and neurotropic viruses-two prominent divisions of GI tract microbiome-derived microbiota-which harbor considerable pathogenic potential. It is noteworthy that the first two well-studied microbiota-the GI tract abundant Gram-negative bacteria Bacteroides fragilis and the neurotropic herpes simplex virus-1 both share a final common pathway of NF-κB (p50/p65) activation and microRNA-146a induction with ensuing pathogenic stimulation of innate-immune and neuroinflammatory pathways. These appear to strongly contribute to the inflammation-mediated amyloidogenic neuropathology of AD. This communication: (i) will review recent research contributions that have expanded our understanding of the nature of the translocation of microbiome-derived neurotoxins-across biophysiological barriers; (ii) will assess multiple-recent investigations of the induction of the proinflammatory pathogenic microRNA-146a by these two prominent classes of human microbiota; and (iii) will discuss the role of molecular neurobiology and mechanistic contribution of polymicrobial infections to AD-type neuropathological change.