Role of Microbes in the Development of Alzheimer's Disease: State of the Art - An International Symposium Presented at the 2017 IAGG Congress in San Francisco

Exercised-enriched blood plasma rescues hippocampal impairments and cognitive deficits in an Alzheimer's disease model

Alzheimer's disease (AD) is a progressive neurodegenerative disorder, and moderate exercise holds promise in ameliorating the ongoing neurodegeneration and cognitive decline. Here, we investigated whether exercise-enriched blood plasm could yield a beneficial therapeutic effect on AD pathologies and cognitive decline in transgenic AD (P301S) mice. In this investigation, a cohort of 2-month-old C57BL/6 mice were granted continuous access to either a running wheel or a fixed wheel for 6 weeks. After that, their plasmas were extracted and subsequently injected intravenously into 4.5-month-old P301S mice biweekly over a 6-week period. A comprehensive methodology was then employed, integrating behavioral tests, pathology assessments, and biochemical analyses to unveil the potential anti-dementia implications of exercise-enriched blood plasma in P301S mice. Upon systemic administration, the findings revealed a noteworthy attenuation of hippocampus-dependent behavioral impairments in P301S mice. Conversely, blood plasma from sedentary counterparts exhibited no discernible impact. These effects were intricately associated with the mitigation of neuroinflammation, the augmentation of hippocampal adult neurogenesis, and a reduction of synaptic impairments following the administration of exercise-enriched blood plasma. These findings advance the proposition that administering exercise-enriched blood plasma may serve as an effective prophylactic measure against AD, opening avenues for further exploration and potential therapeutic interventions.

Associations of infections and vaccines with Alzheimer's disease point to a role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been associated with Alzheimer's disease (AD) and related traits in various studies. This suggests that compromised immunity, rather than specific microbes, may play a role in AD by increasing an individual's vulnerability to various infections, which could contribute to neurodegeneration. If true, then vaccines that have heterologous effects on immunity, extending beyond protection against the targeted disease, may hold a potential for AD prevention.

METHODS

We evaluated the associations of common adult infections (herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses), and vaccinations against shingles and pneumonia, with the risks of AD and other dementias in a pseudorandomized sample of the Health and Retirement Study (HRS).

RESULTS

Shingles, pneumonia and mycoses, diagnosed between ages 65 and 75, were all associated with significantly increased risk of AD later in life, by 16 %-42 %. Pneumococcal and shingles vaccines administered between ages 65-75 were both associated with a significantly lower risk of AD, by 15 %-21 %. These effects became less pronounced when AD was combined with other dementias.

DISCUSSION

Our findings suggest that both the pneumococcal polysaccharide vaccine and the live attenuated zoster vaccine can offer significant protection against AD. It remains to be determined if non-live shingles vaccine has a similar beneficial effect on AD. This study also found significant associations of various infections with the risk of AD, but not with the risks of other dementias. This indicates that vulnerability to infections may play a more significant role in AD than in other types of dementia, which warrants further investigation.

New approaches for understanding the potential role of microbes in Alzheimer's disease

Alzheimer's disease (AD) involves a complex pathological process that evolves over years, and its etiology is understood as a classic example of gene-environment interaction. The notion that exposure to microbial organisms may play some role in AD pathology has been proposed and debated for decades. New evidence from model organisms and -omic studies, as well as epidemiological data from the recent COVID-19 pandemic and widespread use of vaccines, offers new insights into the "germ hypothesis" of AD. To review new evidence and identify key research questions, the Duke/University of North Carolina (Duke/UNC) Alzheimer's Disease Research Center hosted a virtual symposium and workshop: "New Approaches for Understanding the Potential Role of Microbes in Alzheimer's disease." Discussion centered around the antimicrobial protection hypothesis of amyloid accumulation, and other mechanisms by which microbes could influence AD pathology including immune cell activation, changes in blood-brain barrier, or direct neurotoxicity. This summary of proceedings reviews the content presented in the symposium and provides a summary of major topics and key questions discussed in the workshop.

Associations of infections and vaccines with Alzheimer's disease point to a major role of compromised immunity rather than specific pathogen in AD

INTRODUCTION

Diverse pathogens (viral, bacterial, fungal) have been linked to Alzheimer's disease (AD) indicating a possibility that the culprit may be compromised immunity rather than particular microbe. If true, then vaccines with broad beneficial effects on immunity might be protective against AD.

METHODS

We estimated associations of common adult infections, including herpes simplex, zoster (shingles), pneumonia, and recurrent mycoses, as well as vaccinations against shingles and pneumonia, with the risk of AD in a pseudorandomized sample of the Health and Retirement Study.

RESULTS

Shingles, pneumonia, and mycoses diagnosed between ages 65-75, were all associated with higher risk of AD later in life, by 16%-42%. Pneumococcal and shingles vaccines received between ages 65-75 both lowered the risk of AD, by 15%-21%.

DISCUSSION

Our results support the idea that the connection between AD and infections involves compromised immunity rather than specific pathogen. We discuss mechanisms by which the declining immune surveillance may promote AD, and the role of biological aging in it. Repurposing of vaccines with broad beneficial effects on immunity could be a reasonable approach to AD prevention. Pneumococcal and zoster vaccines are promising candidates for such repurposing.

Neuroinflammation in Alzheimer's Disease: A Potential Role of Nose-Picking in Pathogen Entry via the Olfactory System?

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized by progressive cognitive decline and memory impairment. Many possible factors might contribute to the development of AD, including amyloid peptide and tau deposition, but more recent evidence suggests that neuroinflammation may also play an-at least partial-role in its pathogenesis. In recent years, emerging research has explored the possible involvement of external, invading pathogens in starting or accelerating the neuroinflammatory processes in AD. In this narrative review, we advance the hypothesis that neuroinflammation in AD might be partially caused by viral, bacterial, and fungal pathogens entering the brain through the nose and the olfactory system. The olfactory system represents a plausible route for pathogen entry, given its direct anatomical connection to the brain and its involvement in the early stages of AD. We discuss the potential mechanisms through which pathogens may exploit the olfactory pathway to initiate neuroinflammation, one of them being accidental exposure of the olfactory mucosa to hands contaminated with soil and feces when picking one's nose.

Apolipoprotein E and viral infection: Risks and Mechanisms

Apolipoprotein E (ApoE) is a multifunctional protein critical for lipid metabolism and cholesterol homeostasis. In addition to being a well known genetic determinant of both neurodegenerative and cardiovascular diseases, ApoE is frequently involved in various viral infection-related diseases. Human ApoE protein is functionally polymorphic with three isoforms, namely, ApoE2, ApoE3, and ApoE4, with markedly altered protein structures and functions. ApoE4 is associated with increased susceptibility to infection with herpes simplex virus type-1 and HIV. Conversely, ApoE4 protects against hepatitis C virus and hepatitis B virus infection. With the outbreak of coronavirus disease 2019, ApoE4 has been shown to determine the incidence and progression of severe acute respiratory syndrome coronavirus 2 infection. These findings clearly indicate the critical role of ApoE in viral infection. Furthermore, ApoE polymorphism has various or even opposite effects in these infection processes, which are partly related to the structural features that distinguish the different ApoE statuses. In the current review, we summarize the emerging relationship between ApoE and viral infection, discuss the potential mechanisms, and identify future directions that may help to advance our understanding of the link between ApoE and viral infection.

The elusive role of herpesviruses in Alzheimer's disease: current evidence and future directions

Alzheimer's disease (AD) is the most common cause of dementia. While pathologic hallmarks, such as extracellular beta-amyloid plaques, are well-characterized in affected individuals, the pathogenesis that causes plaque formation and eventual cognitive decline is not well understood. A recent resurgence of the decades-old "infectious hypothesis" has garnered increased attention on the potential role that microbes may play in AD. In this theory, it is thought that pathogens such as viruses may act as seeds for beta-amyloid aggregation, ultimately leading to plaques. Interest in the infectious hypothesis has also spurred further investigation into additional characteristics of viral infection that may play a role in AD progression, such as neuroinflammation, latency, and viral DNA integration. While a flurry of research in this area has been recently published, with herpesviruses being of particular interest, the role of pathogens in AD remains controversial. In this review, the insights gained thus far into the possible role of herpesviruses in AD are summarized. The challenges and potential future directions of herpesvirus research in AD and dementia are also discussed.

Recent Advances in Microbiota-Associated Metabolites in Heart Failure

Heart failure is a risk factor for adverse events such as sudden cardiac arrest, liver and kidney failure and death. The gut microbiota and its metabolites are directly linked to the pathogenesis of heart failure. As emerging studies have increased in the literature on the role of specific gut microbiota metabolites in heart failure development, this review highlights and summarizes the current evidence and underlying mechanisms associated with the pathogenesis of heart failure. We found that gut microbiota-derived metabolites such as short chain fatty acids, bile acids, branched-chain amino acids, tryptophan and indole derivatives as well as trimethylamine-derived metabolite, trimethylamine N-oxide, play critical roles in promoting heart failure through various mechanisms. Mainly, they modulate complex signaling pathways such as nuclear factor kappa-light-chain-enhancer of activated B cells, Bcl-2 interacting protein 3, NLR Family Pyrin Domain Containing inflammasome, and Protein kinase RNA-like endoplasmic reticulum kinase. We have also highlighted the beneficial role of other gut metabolites in heart failure and other cardiovascular and metabolic diseases.

Viruses - a major cause of amyloid deposition in the brain

INTRODUCTION

Clinically, Alzheimer's disease (AD) is a syndrome with a spectrum of various cognitive disorders. There is a complete dissociation between the pathology and the clinical presentation. Therefore, we need a disruptive new approach to be able to prevent and treat AD.

AREAS COVERED

In this review, the authors extensively discuss the evidence why the amyloid beta is not the pathological cause of AD which makes therefore the amyloid hypothesis not sustainable anymore. They review the experimental evidence underlying the role of microbes, especially that of viruses, as a trigger/cause for the production of amyloid beta leading to the establishment of a chronic neuroinflammation as the mediator manifesting decades later by AD as a clinical spectrum. In this context, the emergence and consequences of the infection/antimicrobial protection hypothesis are described. The epidemiological and clinical data supporting this hypothesis are also analyzed.

EXPERT OPINION

For decades, we have known that viruses are involved in the pathogenesis of AD. This discovery was ignored and discarded for a long time. Now we should accept this fact, which is not a hypothesis anymore, and stimulate the research community to come up with new ideas, new treatments, and new concepts.

Dementia, infections and vaccines: 30 years of controversy

This paper reports the proceedings of a virtual meeting convened by the European Interdisciplinary Council on Ageing (EICA), to discuss the involvement of infectious disorders in the pathogenesis of dementia and neurological disorders leading to dementia. We recap how our view of the infectious etiology of dementia has changed over the last 30 years in light of emerging evidence, and we present evidence in support of the implication of infection in dementia, notably Alzheimer's disease (AD). The bacteria and viruses thought to be responsible for neuroinflammation and neurological damage are reviewed. We then review the genetic basis for neuroinflammation and dementia, highlighting the genes that are currently the focus of investigation as potential targets for therapy. Next, we describe the antimicrobial hypothesis of dementia, notably the intriguing possibility that amyloid beta may itself possess antimicrobial properties. We further describe the clinical relevance of the gut-brain axis in dementia, the mechanisms by which infection can move from the intestine to the brain, and recent findings regarding dysbiosis patterns in patients with AD. We review the involvement of specific pathogens in neurological disorders, i.e. SARS-CoV-2, human immunodeficiency virus (HIV), herpes simplex virus type 1 (HSV1), and influenza. Finally, we look at the role of vaccination to prevent dementia. In conclusion, there is a large body of evidence supporting the involvement of various infectious pathogens in the pathogenesis of dementia, but large-scale studies with long-term follow-up are needed to elucidate the role that infection may play, especially before subclinical or clinical disease is present.

An Insight into Cellular and Molecular Mechanisms Underlying the Pathogenesis of Neurodegeneration in Alzheimer's Disease

Alzheimer's disease (AD) is the most prominent neurodegenerative disorder in the aging population. It is characterized by cognitive decline, gradual neurodegeneration, and the development of amyloid-β (Aβ)-plaques and neurofibrillary tangles, which constitute hyperphosphorylated tau. The early stages of neurodegeneration in AD include the loss of neurons, followed by synaptic impairment. Since the discovery of AD, substantial factual research has surfaced that outlines the disease's causes, molecular mechanisms, and prospective therapeutics, but a successful cure for the disease has not yet been discovered. This may be attributed to the complicated pathogenesis of AD, the absence of a well-defined molecular mechanism, and the constrained diagnostic resources and treatment options. To address the aforementioned challenges, extensive disease modeling is essential to fully comprehend the underlying mechanisms of AD, making it easier to design and develop effective treatment strategies. Emerging evidence over the past few decades supports the critical role of Aβ and tau in AD pathogenesis and the participation of glial cells in different molecular and cellular pathways. This review extensively discusses the current understanding concerning Aβ- and tau-associated molecular mechanisms and glial dysfunction in AD. Moreover, the critical risk factors associated with AD including genetics, aging, environmental variables, lifestyle habits, medical conditions, viral/bacterial infections, and psychiatric factors have been summarized. The present study will entice researchers to more thoroughly comprehend and explore the current status of the molecular mechanism of AD, which may assist in AD drug development in the forthcoming era.

Predicting Key Genes and Therapeutic Molecular Modelling to Explain the Association between Porphyromonas gingivalis (P. gingivalis) and Alzheimer’s Disease (AD)

The association between Porphyromonas gingivalis (P. gingivalis) and Alzheimer’s disease (AD) remains unclear. The major aim of this study was to elucidate the role of genes and molecular targets in P. gingivalis-associated AD. Two Gene Expression Omnibus (GEO) datasets, GSE5281 for AD (n = 84 Alzheimer’s, n = 74 control) and GSE9723 (n = 4 P. gingivalis, n = 4 control), were downloaded from the GEO database. Differentially expressed genes (DEGs) were obtained, and genes common to both diseases were drawn. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) analysis was performed from the top 100 genes (50 upregulated and 50 downregulated genes). We then proceeded with CMap analysis to screen for possible small drug molecules targeting these genes. Subsequently, we performed molecular dynamics simulations. A total of 10 common genes (CALD1, HES1, ID3, PLK2, PPP2R2D, RASGRF1, SUN1, VPS33B, WTH3DI/RAB6A, and ZFP36L1) were identified with a p-value < 0.05. The PPI network of the top 100 genes showed UCHL1, SST, CHGB, CALY, and INA to be common in the MCC, DMNC, and MNC domains. Out of the 10 common genes identified, only 1 was mapped in CMap. We found three candidate small drug molecules to be a fit for PLK2, namely PubChem ID: 24971422, 11364421, and 49792852. We then performed molecular docking of PLK2 with PubChem ID: 24971422, 11364421, and 49792852. The best target, 11364421, was used to conduct the molecular dynamics simulations. The results of this study unravel novel genes to P. gingivalis-associated AD that warrant further validation.

Role of Gut Microbiota in Neurological Disorders and Its Therapeutic Significance

In humans, the gut microbiota (GM) are known to play a significant role in the metabolism of nutrients and drugs, immunomodulation, and pathogen defense by inhabiting the gastrointestinal tract (GIT). The role of the GM in the gut-brain axis (GBA) has been documented for different regulatory mechanisms and associated pathways and it shows different behaviors with individualized bacteria. In addition, the GM are known as susceptibility factor for neurological disorders in the central nervous system (CNS), regulating disease progression and being amenable to intervention. Bidirectional transmission between the brain and the GM occurs in the GBA, implying that it performs a significant role in neurocrine, endocrine, and immune-mediated signaling pathways. The GM regulates multiple neurological disorders by supplementing them with prebiotics, probiotics, postbiotics, synbiotics, fecal transplantations, and/or antibiotics. A well-balanced diet is critically important for establishing healthy GM, which can alter the enteric nervous system (ENS) and regulate multiple neurological disorders. Here, we have discussed the function of the GM in the GBA from the gut to the brain and the brain to the gut, the pathways associated with neurology that interacts with the GM, and the various neurological disorders associated with the GM. Furthermore, we have highlighted the recent advances and future prospects of the GBA, which may require addressing research concerns about GM and associated neurological disorders.

Virus-Like Cytosolic and Cell-Free Oxidatively Damaged Nucleic Acids Likely Drive Inflammation, Synapse Degeneration, and Neuron Death in Alzheimer's Disease

Oxidative stress, inflammation, and amyloid-β are Alzheimer's disease (AD) hallmarks that cause each other and other AD hallmarks. Most amyloid-β-lowering, antioxidant, anti-inflammatory, and antimicrobial AD clinical trials failed; none stopped or reversed AD. Although signs suggest an infectious etiology, no pathogen accumulated consistently in AD patients. Neuropathology, neuronal cell culture, rodent, genome-wide association, epidemiological, biomarker, and clinical studies, plus analysis using Hill causality criteria and revised Koch's postulates, indicate that the virus-like oxidative damage-associated molecular-pattern (DAMP) cytosolic and cell-free nucleic acids accumulated in AD patients' brains likely drive neuroinflammation, synaptotoxicity, and neurotoxicity. Cytosolic oxidatively-damaged mitochondrial DNA accumulated outside mitochondria dose-dependently in preclinical AD and AD patients' hippocampal neurons, and in AD patients' neocortical neurons but not cerebellar neurons or glia. In oxidatively-stressed neural cells and rodents' brains, cytosolic oxidatively-damaged mitochondrial DNA accumulated and increased antiviral and inflammatory proteins, including cleaved caspase-1, interleukin-1β, and interferon-β. Cytosolic double-stranded RNA and DNA are DAMPs that induce antiviral interferons and/or inflammatory proteins by oligomerizing with various innate-immune pattern-recognition receptors, e.g., cyclic GMP-AMP synthase and the nucleotide-binding-oligomerization-domain-like-receptor-pyrin-domain-containing-3 inflammasome. In oxidatively-stressed neural cells, cytosolic oxidatively-damaged mitochondrial DNA caused synaptotoxicity and neurotoxicity. Depleting mitochondrial DNA prevented these effects. Additionally, cell-free nucleic acids accumulated in AD patients' blood, extracellular vesicles, and senile plaques. Injecting cell-free nucleic acids bound to albumin oligomers into wild-type mice's hippocampi triggered antiviral interferon-β secretion; interferon-β injection caused synapse degeneration. Deoxyribonuclease-I treatment appeared to improve a severe-AD patient's Mini-Mental Status Exam by 15 points. Preclinical and clinical studies of deoxyribonuclease-I and a ribonuclease for AD should be prioritized.

Vaccination Against Pneumonia May Provide Genotype-Specific Protection Against Alzheimer's Disease

Vaccine repurposing that considers individual genotype may aid personalized prevention of Alzheimer's disease (AD). In this retrospective cohort study, we used Cardiovascular Health Study data to estimate associations of pneumococcal polysaccharide vaccine and flu shots received between ages 65-75 with AD onset at age 75 or older, taking into account rs6859 polymorphism in NECTIN2 gene (AD risk factor). Pneumococcal vaccine, and total count of vaccinations against pneumonia and flu, were associated with lower odds of AD in carriers of rs6859 A allele, but not in non-carriers. We conclude that pneumococcal polysaccharide vaccine is a promising candidate for genotype-tailored AD prevention.

High resolution 16S rRNA gene Next Generation Sequencing study of brain areas associated with Alzheimer's and Parkinson's disease

Introduction

Alzheimer's (AD) and Parkinson's disease (PD) are neurodegenerative conditions characterized by incremental deposition of β-amyloid (Aβ) and α-synuclein in AD and PD brain, respectively, in relatively conserved patterns. Both are associated with neuroinflammation, with a proposed microbial component for disease initiation and/or progression. Notably, Aβ and α-synuclein have been shown to possess antimicrobial properties. There is evidence for bacterial presence within the brain, including the oral pathobiont Porphyromonas gingivalis, with cognitive impairment and brain pathology being linked to periodontal (gum) disease and gut dysbiosis.

Methods

Here, we use high resolution 16S rRNA PCR-based Next Generation Sequencing (16SNGS) to characterize bacterial composition in brain areas associated with the early, intermediate and late-stage of the diseases.

Results and discussion

This study reveals the widespread presence of bacteria in areas of the brain associated with AD and PD pathology, with distinctly different bacterial profiles in blood and brain. Brain area profiles were overall somewhat similar, predominantly oral, with some bacteria subgingival and oronasal in origin, and relatively comparable profiles in AD and PD brain. However, brain areas associated with early disease development, such as the locus coeruleus, were substantially different in bacterial DNA content compared to areas affected later in disease etiology.

Benefit and safety of antibiotics for Alzheimer's disease: Protocol for a systematic review and meta-analysis

BACKGROUND

Alzheimer's disease (AD) is an age-related degenerative change of the central nervous system, the cause of which remains unclear. Recent studies have found that brain inflammation caused by microbial infections may be one of the etiologies of AD, and antibiotics as novel treatments may be beneficial for delaying the development of AD. Several prospective studies have investigated the effects of different antibiotics on Alzheimer's disease. However, no systematic review or meta-analysis has evaluated the benefits and safety of antibiotics in AD patients.

METHODS

This study will analyze randomized controlled trials and observational studies published from database inception to December 31, 2022, and included direct or indirect evidence. Studies will be retrieved by searching PubMed, Scopus, Web of Science, Cochrane Central Register of Controlled Clinical Trials, CNKI, and Wan Fang databases. The outcomes of this study included the Alzheimer's Disease Assessment Scale cognitive subscale (ADAS-cog), Montreal Cognitive Assessment (MoCA), Standardized Mini-Mental State Examination (SMMSE), Clinical Dementia Rating (CDR), Frontal Functioning Scale (FAB), Dysfunctional Behavior Rating Instrument (DBRI), Activities of Daily Living (ADLs) Index, and Geriatric Depression Scale (GDS). The risk of bias will be assessed using the Cochrane risk-of-bias assessment instrument for randomized controlled trials. A random-effect/fixed-effects model will be used to summarize the estimates of the mean difference/risk ratio using a 95% confidence interval.

RESULTS

This study will analyze the benefits and safety of antibiotics in patients with AD.

CONCLUSION

The results of this analysis will provide evidence to evaluate the benefits and safety of antibiotics in the treatment of AD.

Non-Pharmacological Therapeutic Options for the Treatment of Alzheimer’s Disease

Alzheimer’s disease is a growing global crisis in need of urgent diagnostic and therapeutic strategies. The current treatment strategy mostly involves immunotherapeutic medications that have had little success in halting disease progress. Hypotheses for pathogenesis and development of AD have been expanded to implicate both organ systems as well as cellular reactions. Non-pharmacologic interventions ranging from minimally to deeply invasive have attempted to address these diverse contributors to AD. In this review, we aim to delineate mechanisms underlying such interventions while attempting to provide explanatory links between the observed differences in disease states and postulated metabolic or structural mechanisms of change. The techniques discussed are not an exhaustive list of non-pharmacological interventions against AD but provide a foundation to facilitate a deeper understanding of the area of study.

Toll-Like Receptor 4: A Promising Therapeutic Target for Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disease that primarily manifests as memory deficits and cognitive impairment and has created health challenges for patients and society. In AD, amyloid β-protein (Aβ) induces Toll-like receptor 4 (TLR4) activation in microglia. Activation of TLR4 induces downstream signaling pathways and promotes the generation of proinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), and interleukin-1β (IL-1β), which also trigger the activation of astrocytes and influence amyloid-dependent neuronal death. Therefore, TLR4 may be an important molecular target for treating AD by regulating neuroinflammation. Moreover, TLR4 regulates apoptosis, autophagy, and gut microbiota and is closely related to AD. This article reviews the role of TLR4 in the pathogenesis of AD and a range of potential therapies targeting TLR4 for AD. Elucidating the regulatory mechanism of TLR4 in AD may provide valuable clues for developing new therapeutic strategies for AD.

Back to the Future: The Role of Infections in Psychopathology. Focus on OCD

OBJECTIVE

Recently, there has been a resurgence of interest in the relationship between infections and psychopathology, given the increasing data on the neurotropism and neurological/psychiatric morbidity of the SARS-COV2 virus, responsible for the current worldwide pandemic. Although the majority of observations were those obtained in mood and schizophrenic disorders, a few data are also available on the presence of bacterial or viral infections in patients suffering from obsessive-compulsive disorder (OCD). Therefore, given the limited information, the present paper aimed at reviewing the most updated evidence of infections in neuropsychiatric disorders and their possible mechanisms of actions, with a narrow focus on microbes in OCD.

METHOD

This paper is a narrative review. The databases of PubMed, Scopus, Embase, PsycINFO and Google Scholar were accessed to research and collect English language papers published between 1 January 1980 and 31 December 2021. The data on PANDAS/PANS and those observed during severe brain infections were excluded.

RESULTS

Several pathogens have been associated with an increased risk to develop a broad spectrum of neuropsychiatric conditions, such as schizophrenia, mood disorders, autism, attention-deficit/hyperactivity disorder, anorexia nervosa, and post-traumatic stress disorder. Some evidence supported a possible role of infections also in the pathophysiology of OCD. Infections from Herpes simplex virus 1, Borna disease virus, Group A-Beta Hemolytic Streptococcus, Borrelia spp., and Toxoplasma gondii were actually found in patients with OCD. Although different mechanisms have been hypothesized, all would converge to trigger functional/structural alterations of specific circuits or immune processes, with cascade dysfunctions of several other systems.

CONCLUSIONS

Based on the current evidence, a possible contribution of different types of microbes has been proposed for different neuropsychiatric disorders including OCD. However, the currently available literature is meager and heterogeneous in terms of sample characteristics and methods used. Therefore, further studies are needed to better understand the impact of infectious agents in neuropsychiatric disorders. Our opinion is that deeper insights in this field might contribute to a better definition of biological underpinnings of specific clinical pictures, as well as to promote psychiatric precision medicine, with treatments based on altered pathological pathways of single patients. This might be particularly relevant in OCD, a disorder with a high proportion of patients who are resistant or do not respond to conventional therapeutic strategies.

Does Dementia Have a Microbial Cause?

The potential contribution of pathogenic microbes to dementia-inducing disease is a subject of considerable importance. Alzheimer’s disease (AD) is a neurocognitive disease that slowly destroys brain function, leading to cognitive decline and behavioral and psychiatric disorders. The histopathology of AD is associated with neuronal loss and progressive synaptic dysfunction, accompanied by the deposition of amyloid-β (Aβ) peptide in the form of parenchymal plaques and abnormal aggregated tau protein in the form of neurofibrillary tangles. Observational, epidemiological, experimental, and pathological studies have generated evidence for the complexity and possible polymicrobial causality in dementia-inducing diseases. The AD pathogen hypothesis states that pathogens and microbes act as triggers, interacting with genetic factors to initiate the accumulation of Aβ, hyperphosphorylated tau protein (p-tau), and inflammation in the brain. Evidence indicates that Borrelia sp., HSV-1, VZV (HHV-2), HHV-6/7, oral pathogens, Chlamydophila pneumoniae, and Candida albicans can infect the central nervous system (CNS), evade the immune system, and consequently prevail in the AD brain. Researchers have made significant progress in understanding the multifactorial and overlapping factors that are thought to take part in the etiopathogenesis of dementia; however, the cause of AD remains unclear.

Lactoferrin as Immune-Enhancement Strategy for SARS-CoV-2 Infection in Alzheimer's Disease Patients

Coronavirus 2 (SARS-CoV2) (COVID-19) causes severe acute respiratory syndrome. Severe illness of COVID-19 largely occurs in older people and recent evidence indicates that demented patients have higher risk for COVID-19. Additionally, COVID-19 further enhances the vulnerability of older adults with cognitive damage. A balance between the immune and inflammatory response is necessary to control the infection. Thus, antimicrobial and anti-inflammatory drugs are hopeful therapeutic agents for the treatment of COVID-19. Accumulating evidence suggests that lactoferrin (Lf) is active against SARS-CoV-2, likely due to its potent antiviral and anti-inflammatory actions that ultimately improves immune system responses. Remarkably, salivary Lf levels are significantly reduced in different Alzheimer's disease (AD) stages, which may reflect AD-related immunological disturbances, leading to reduced defense mechanisms against viral pathogens and an increase of the COVID-19 susceptibility. Overall, there is an urgent necessity to protect AD patients against COVID-19, decreasing the risk of viral infections. In this context, we propose bovine Lf (bLf) as a promising preventive therapeutic tool to minimize COVID-19 risk in patients with dementia or AD.

Synthetic amyloid beta does not induce a robust transcriptional response in innate immune cell culture systems

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease that impacts nearly 400 million people worldwide. The accumulation of amyloid beta (Aβ) in the brain has historically been associated with AD, and recent evidence suggests that neuroinflammation plays a central role in its origin and progression. These observations have given rise to the theory that Aβ is the primary trigger of AD, and induces proinflammatory activation of immune brain cells (i.e., microglia), which culminates in neuronal damage and cognitive decline. To test this hypothesis, many in vitro systems have been established to study Aβ-mediated activation of innate immune cells. Nevertheless, the transcriptional resemblance of these models to the microglia in the AD brain has never been comprehensively studied on a genome-wide scale.

METHODS

We used bulk RNA-seq to assess the transcriptional differences between in vitro cell types used to model neuroinflammation in AD, including several established, primary and iPSC-derived immune cell lines (macrophages, microglia and astrocytes) and their similarities to primary cells in the AD brain. We then analyzed the transcriptional response of these innate immune cells to synthetic Aβ or LPS and INFγ.

RESULTS

We found that human induced pluripotent stem cell (hIPSC)-derived microglia (IMGL) are the in vitro cell model that best resembles primary microglia. Surprisingly, synthetic Aβ does not trigger a robust transcriptional response in any of the cellular models analyzed, despite testing a wide variety of Aβ formulations, concentrations, and treatment conditions. Finally, we found that bacterial LPS and INFγ activate microglia and induce transcriptional changes that resemble many, but not all, aspects of the transcriptomic profiles of disease associated microglia (DAM) present in the AD brain.

CONCLUSIONS

These results suggest that synthetic Aβ treatment of innate immune cell cultures does not recapitulate transcriptional profiles observed in microglia from AD brains. In contrast, treating IMGL with LPS and INFγ induces transcriptional changes similar to those observed in microglia detected in AD brains.

Association between microbiological risk factors and neurodegenerative disorders: An umbrella review of systematic reviews and meta-analyses

The role of microbiological factors in the development of neurodegenerative diseases is attracting increasing attention, while the relationship remains debated. This study aimed to comprehensively summarize and evaluate the associations between microbiological factors and the risk of neurodegenerative disorders with an umbrella review. PubMed, Embase, and the Cochrane library were used to search for papers from the earliest to March 2021 for identifying meta-analyses and systematic reviews that examined associations between microbiological factors and neurodegenerative diseases. AMSTAR2 tool was employed to evaluate the methodical quality of systematic reviews and meta-analyses. The effect size and 95% confidence interval (95% CI) were recalculated with a random effect model after the overlap was recognized by the corrected covered area (CCA) method. The heterogeneity of each meta-analysis was measured by the I ² statistic and 95% prediction interval (95% PI). Additionally, publication bias and the quality of evidence were evaluated for all 37 unique associations. Only 4 associations had above the medium level of evidence, and the rest associations presented a low level of evidence. Among them, helicobacter pylori (HP), infection, and bacteria are associated with Parkinson's disease (PD), and the other one verifies that periodontal disease is a risk factor for all types of dementia. Following the evidence of our study, eradication of HP and aggressive treatment of periodontitis are beneficial for the prevention of PD and dementia, respectively. This umbrella review provides comprehensive quality-grade evidence on the relationship between microbial factors and neurodegenerative disease. Regardless of much evidence linking microbial factors to neurodegenerative diseases, these associations are not necessarily causal, and the evidence level is generally low. Thus, more effective studies are required.

SYSTEMATIC REVIEW REGISTRATION

https://www.crd.york.ac.uk/PROSPERO/#searchadvanced, PROSPERO, identifier: CRD42021239512.

Lipopolysaccharide, Identified Using an Antibody and by PAS Staining, Is Associated With Corpora amylacea and White Matter Injury in Alzheimer's Disease and Aging Brain

Corpora amylacea (CA) increase in number and size with aging. Their origins and functions remain unknown. Previously, we found that Alzheimer's disease (AD) brains have more CA in the periventricular white matter (PVWM) compared to aging controls. In addition, CA is associated with neurodegeneration as indicated by colocalization of degraded myelin basic protein (dMBP) with periodic acid-Schiff (PAS), a CA marker. We also found that bacterial lipopolysaccharide is present in aging brains, with more LPS in AD compared with controls. Periodic acid-Schiff staining is used to identify CA by virtue of their high polysaccharide content. Despite the growing knowledge of CA as a contributor to AD pathology, the molecules that contribute to the polysaccharides in CA are not known. Notably, lipopolysaccharides (LPS) are important cell-surface polysaccharides found in all Gram-negative bacteria. However, it is unknown whether PAS could detect LPS, whether the LPS found in aging brains contribute to the polysaccharide found in CA, and whether LPS associate with myelin injury. In this study, we found that aging brains had a myelin deficit zone (MDZ) adjacent to the ventricles in PVWM. The MDZ contained vesicles, most of which were CA. LPS and dMBP levels were higher in AD than in control brains. LPS was colocalized with dMBP in the vesicles/CA, linking white matter injury with a bacterial pro-inflammatory molecule. The vesicles also contained oxidized fibers, C-reactive protein, NG2, and GALC, markers of oligodendrocyte precursor cells (OPCs) and oligodendrocyte cells (OLs), respectively. The vesicles/CA were surrounded by dense astrocyte processes in control and AD brains. LPS was co-localized with CA by double staining of PAS with LPS in aging brains. The relationship of LPS with PAS staining was confirmed by PAS staining of purified LPS on nitrocellulose membranes. These findings reveal that LPS is one of the polysaccharides found in CA which can be stained with PAS. In addition, vesicles/CA are associated with oxidized and damaged myelin. The LPS in these vesicles/CA may have contributed to this oxidative myelin damage and may have contributed to oxidative stress to OPCs and OLs which could impair the ability to repair damaged myelin in AD and control brains.

Do Periodontal Pathogens or Associated Virulence Factors Have a Deleterious Effect on the Blood-Brain Barrier, Contributing to Alzheimer's Disease?

The central nervous system (CNS) is protected by a highly selective barrier, the blood-brain barrier (BBB), that regulates the exchange and homeostasis of bloodborne molecules, excluding xenobiotics. This barrier forms the first line of defense by prohibiting pathogens from crossing to the CNS. Aging and chronic exposure of the BBB to pathogens renders it permeable, and this may give rise to pathology in the CNS such as Alzheimer's disease (AD). Researchers have linked pathogens associated with periodontitis to neuroinflammation and AD-like pathology in vivo and in vitro. Although the presence of periodontitis-associated bacteria has been linked to AD in several clinical studies as DNA and virulence factors were confirmed in brain samples of human AD subjects, the mechanism by which the bacteria traverse to the brain and potentially influences neuropathology is unknown. In this review, we present current knowledge about the association between periodontitis and AD, the mechanism whereby periodontal pathogens might provoke neuroinflammation and how periodontal pathogens could affect the BBB. We suggest future studies, with emphasis on the use of human in vitro models of cells associated with the BBB to unravel the pathway of entry for these bacteria to the CNS and to reveal the molecular and cellular pathways involved in initiating the AD-like pathology. In conclusion, evidence demonstrate that bacteria associated with periodontitis and their virulence factors are capable of inflecting damage to the BBB and have a role in giving rise to pathology similar to that found in AD.

[Mechanisms underlying chronic fatigue, a symptom too often overlooked II- From deregulated immunity to neuroinflammation and its consequences]

Hypothalamus stimulation by inflammatory and / or stress signals can trigger activation of the HPA (hypothalamic-pituitary-adrenal) axis, which includes the hypothalamus, pituitary and adrenal gland. Acute activation of the HPA axis is fundamental for the fight or flight response. It allows a maximal energy mobilization available for an effort, whilst erasing fatigue. On the contrary, the chronic activation of this axis decreases muscle efficiency and leads to chronic fatigue. In this second part of our review will be discussed several strategic points that need to be considered for attempting to understand and treat together inflammation and chronic fatigue.

Lack of Convincing Evidence that Borrelia burgdorferi Infection Causes Either Alzheimer's Disease or Lewy Body Dementia

The role that microorganisms might have in the development of Alzheimer's disease is a topic of considerable interest. In this article we discuss whether there is credible evidence that Lyme disease is a cause of Alzheimer's disease and critically review a recent publication claiming that Borrelia burgdorferi sensu stricto infection, the primary cause of Lyme disease in the United States, may cause Lewy body dementia. We conclude that no convincing evidence exists that Lyme disease is a cause of either Alzheimer's disease or Lewy body dementia.

Impact of herpes zoster vaccination on incident dementia: A retrospective study in two patient cohorts

Background

Herpes zoster (HZ) infection increases dementia risk, but it is not known if herpes zoster vaccination is associated with lower risk for dementia. We determined if HZ vaccination, compared to no HZ vaccination, is associated with lower risk for incident dementia.

Methods and findings

Data was obtained from Veterans Health Affairs (VHA) medical records (10/1/2008–9/30/2019) with replication in MarketScan® commercial and Medicare claims (1/1/2009-12/31/2018). Eligible patients were ≥65 years of age and free of dementia for two years prior to baseline (VHA n = 136,016; MarketScan n = 172,790). Two index periods (either start of 2011 or 2012) were defined, where patients either had or did not have a HZ vaccination. Confounding was controlled with propensity scores and inverse probability of treatment weighting. Competing risk (VHA) and Cox proportional hazard (MarketScan) models estimated the association between HZ vaccination and incident dementia in all patients and in age (65–69, 70–74, ≥75) and race (White, Black, Other) sub-groups. Sensitivity analysis measured the association between HZ vaccination and incident Alzheimer’s dementia (AD). HZ vaccination at index versus no HZ vaccination throughout follow-up. VHA patients mean age was 75.7 (SD±7.4) years, 4.0% were female, 91.2% white and 20.2% had HZ vaccination. MarketScan patients mean age was 69.9 (SD±5.7) years, 65.0% were female and 14.2% had HZ vaccination. In both cohorts, HZ vaccination compared with no vaccination, was significantly associated with lower dementia risk (VHA HR = 0.69; 95%CI: 0.67–0.72; MarketScan HR = 0.65; 95%CI:0.57–0.74). HZ vaccination was not related to dementia risk in MarketScan patients aged 65–69 years. No difference in HZ vaccination to dementia effects were found by race. HZ vaccination was associated with lower risk for AD.

Conclusions

HZ vaccination is associated with reduced risk of dementia. Vaccination may provide nonspecific neuroprotection by training the immune system to limit damaging inflammation, or specific neuroprotection that prevents viral cytopathic effects.

Low cerebrospinal fluid Amyloid-βeta 1-42 in patients with tuberculous meningitis

BACKGROUND

Tuberculous meningitis (TBM) is an important disease leading to morbidity, disability and mortality that primarily affects children and immune-depressed patients. Specific neuromarkers predicting outcomes, severity and inflammatory response are still lacking. In recent years an increasing number of evidences show a possible role for infective agents in developing neurodegenerative diseases.

METHODS

We retrospectively included 13 HIV-negative patients presenting with TBM and we compared them with two control groups: one of patients with a confirmed diagnosis of AD, and one of those with syphilis where lumbar punctures excluded central nervous system involvement. Lumbar punctures were performed for clinical reasons and CSF biomarkers were routinely available: we analyzed blood brain barrier permeability (CSF to serum albumin ratio, "CSAR"), intrathecal IgG synthesis, (CSF to serum IgG ratio), inflammation (neopterin), amyloid deposition (Aβ1-42), neuronal damage (T-tau, P-tau, 14.3.3) and astrocytosis (S-100 β).

RESULTS

TBM patients were 83 % male and 67 % Caucasian with a median age of 51 years (24.5-63.5 IQR). Apart from altered CSAR (median value 18.4, 17.1-30.9 IQR), neopterin (14.3 ng/ml, 9.7-18.8) and IgG ratios (15.4, 7.9-24.9), patients showed very low levels of Aβ1-42 in their CSF (348.5 pg/mL,125-532.2), even lower compared to AD and controls [603 pg/mL (IQR 528-797) and 978 (IQR 789-1178)]. Protein 14.3.3 tested altered in 38.5 % cases. T-tau, P-tau and S100Beta were in the range of normality. Altered low level of Aβ1-42 correlated over time with classical TBM findings and altered neuromarkers.

CONCLUSIONS

CSF Biomarkers from patients with TBM were compatible with inflammation, blood brain barrier damage and impairment in amyloid-beta metabolism. Amyloid-beta could be tested as a prognostic markers, backing the routine use of available neuromarkers. To our knowledge this is the first case showing such low levels of Aβ1-42 in TBM; its accumulation, drove by neuroinflammation related to infections, can be central in understanding neurodegenerative diseases.

Association between Cognitive Function and Depression with Human T-Cell Lymphotropic Virus 1 Seropositivity and Serointensity in UK Adults

Several viral, bacterial, and parasitic diseases have been associated with cognitive function and neuropsychiatric outcomes in humans, including human T-cell lymphotropic virus 1 (HTLV-1). In this study, we sought to further generalize previously reported associations of cognitive function and depression with HTLV-1 seropositivity and serointensity using a community-based sample of adults aged approximately 40 to 70 years (mean = 55.3 years) from the United Kingdom. In this sample, the results of adjusted linear regression models showed no associations of HTLV-1 seropositivity or serointensity with reasoning, pairs-matching, or reaction-time cognitive tasks or with depression. In addition, neither age, sex, educational attainment, nor income moderated associations of HTLV-1 seropositivity or serointensity with cognitive function or depression. In this middle-aged to older middle-aged adult community sample, HTLV-1 seropositivity and serointensity do not appear to be associated with reasoning, pairs-matching, and reaction-time tasks or with depression.

Interspecific interactions that affect ageing: Age-distorters manipulate host ageing to their own evolutionary benefits

Genetic causes for ageing are traditionally investigated within a species. Yet, the lifecycles of many organisms intersect. Additional evolutionary and genetic causes of ageing, external to a focal species/organism, may thus be overlooked. Here, we introduce the phrase and concept of age-distorters and its evidence. Age-distorters carry ageing interfering genes, used to manipulate the biological age of other entities upon which the reproduction of age-distorters relies, e.g. age-distorters bias the reproduction/maintenance trade-offs of cells/organisms for their own evolutionary interests. Candidate age-distorters include viruses, parasites and symbionts, operating through specific, genetically encoded interferences resulting from co-evolution and arms race between manipulative non-kins and manipulable species. This interference results in organismal ageing when age-distorters prompt manipulated organisms to favor their reproduction at the expense of their maintenance, turning these hosts into expanded disposable soma. By relying on reproduction/maintenance trade-offs affecting disposable entities, which are left ageing to the reproductive benefit of other physically connected lineages with conflicting evolutionary interests, the concept of age-distorters expands the logic of the Disposable Soma theory beyond species with fixed germen/soma distinctions. Moreover, acknowledging age-distorters as external sources of mutation accumulation and antagonistic pleiotropic genes expands the scope of the mutation accumulation and of the antagonistic pleiotropy theories.

Warm, Sweetened Milk at the Twilight of Immunity - Alzheimer's Disease - Inflammaging, Insulin Resistance, M. paratuberculosis and Immunosenescence

This article prosecutes a case against the zoonotic pathogen Mycobacterium avium ss. paratuberculosis (MAP) as a precipitant of Alzheimer’s disease (AD). Like the other major neurodegenerative diseases AD is, at its core, a proteinopathy. Aggregated extracellular amyloid protein plaques and intracellular tau protein tangles are the recognized protein pathologies of AD. Autophagy is the cellular housekeeping process that manages protein quality control and recycling, cellular metabolism, and pathogen elimination. Impaired autophagy and cerebral insulin resistance are invariant features of AD. With a backdrop of age-related low-grade inflammation (inflammaging) and heightened immune risk (immunosenescence), infection with MAP subverts glucose metabolism and further exhausts an already exhausted autophagic capacity. Increasingly, a variety of agents have been found to favorably impact AD; they are agents that promote autophagy and reduce insulin resistance. The potpourri of these therapeutic agents: mTOR inhibitors, SIRT1 activators and vaccines are seemingly random until one recognizes that all these agents also suppress intracellular mycobacterial infection. The zoonotic mycobacterial MAP causes a common fatal enteritis in ruminant animals. Humans are exposed to MAP from contaminated food products and from the environment. The enteritis in animals is called paratuberculosis or Johne’s disease; in humans, it is the putative cause of Crohn’s disease. Beyond Crohn’s, MAP is associated with an increasing number of inflammatory and autoimmune diseases: sarcoidosis, Blau syndrome, autoimmune diabetes, autoimmune thyroiditis, multiple sclerosis, and rheumatoid arthritis. Moreover, MAP has been associated with Parkinson’s disease. India is one county that has extensively studied the human bio-load of MAP; 30% of more than 28,000 tested individuals were found to harbor, or to have harbored, MAP. This article asserts an unfolding realization that MAP infection of humans 1) is widespread in its presence, 2) is wide-ranging in its zoonosis and 3) provides a plausible link connecting MAP to AD.

Matrix metalloproteinase 14 regulates HSV-1 infection in neuroblastoma cells

Growing evidence supports that chronic or latent infection of the central nervous system might be implicated in Alzheimer's disease (AD). Among them, Herpes simplex virus type 1 (HSV-1) has emerged as a major factor in the etiology of the disease. Our group is devoted to the study of the relationship among HSV-1, oxidative stress (OS) and neurodegeneration. We have found that HSV-1 induces the main neuropathological hallmarks of AD, including the accumulation of intracellular amyloid beta (Aβ), hyperphosphorylated tau protein and autophagic vesicles, that OS exacerbates these effects, and that matrix metalloproteinase 14 (MMP-14) participates in the alterations induced by OS. In this work, we focused on the role of MMP-14 in the degenerative markers raised by HSV-1 infection. Interestingly, we found that MMP-14 blockage is a potent inhibitor of HSV-1 infection efficiency, that also reduces the degeneration markers, accumulation of Aβ and hyperphosphorylated tau, induced by the virus. Our results point to MMP-14 as a potent antiviral target to control HSV-1 infection and its associated neurodegenerative effects.

Lipopolysaccharide-Induced Exosomal miR-146a Is Involved in Altered Expression of Alzheimer's Risk Genes Via Suppression of TLR4 Signaling

Repeated exposure to toll-like receptor 4 (TLR4) ligands, such as lipopolysaccharide (LPS), reduces responses of monocytes/macrophages to LPS (LPS/endotoxin tolerance). Microglial exposure to Aβ deposits, a TLR4 ligand, may cause "Aβ/LPS tolerance," leading to decreased Aβ clearance. We demonstrated that microglial activation by LPS is diminished in Aβ deposit-bearing 12-month-old model mice of Alzheimer's disease (AD), compared with non-AD mice and Aβ deposit-free 2-month-old AD mice. Because miR-146a plays a predominant role in inducing TLR tolerance in macrophages and because miR-146a in extracellular vesicles (EVs) shed by inflammatory macrophages increases in circulation, we investigated potential roles of miR-146a and inflammatory EVs in inducing TLR tolerance in microglia and in altering expression of inflammatory AD risk genes. We found that miR-146a upregulation induces TLR tolerance and alters expression of inflammatory AD risk genes in response to LPS treatment in BV2 microglia. LPS brain injection altered expression of the AD risk genes in 12-month-old AD mice but not in non-AD littermates. EVs from inflammatory macrophages polarize BV2 microglia to M1 phenotype and induce TLR tolerance. Microglia exposed to Aβ in the brain show reduced cytokine responses to systemic inflammation due to peripheral LPS injection, indicating TLR/Aβ tolerance in microglia. Our results suggest that increased miR-146a induces microglial Aβ/LPS tolerance and that circulating EVs shed by inflammatory macrophages contribute to microglial Aβ/LPS tolerance, leading to reduced Aβ clearance. Our study also suggests that altered expression of inflammatory AD risk genes may contribute to AD development via the same molecular mechanism underlying LPS tolerance.

The Microbiota-Gut-Brain Axis and Alzheimer Disease. From Dysbiosis to Neurodegeneration: Focus on the Central Nervous System Glial Cells

The microbiota-gut system can be thought of as a single unit that interacts with the brain via the "two-way" microbiota-gut-brain axis. Through this axis, a constant interplay mediated by the several products originating from the microbiota guarantees the physiological development and shaping of the gut and the brain. In the present review will be described the modalities through which the microbiota and gut control each other, and the main microbiota products conditioning both local and brain homeostasis. Much evidence has accumulated over the past decade in favor of a significant association between dysbiosis, neuroinflammation and neurodegeneration. Presently, the pathogenetic mechanisms triggered by molecules produced by the altered microbiota, also responsible for the onset and evolution of Alzheimer disease, will be described. Our attention will be focused on the role of astrocytes and microglia. Numerous studies have progressively demonstrated how these glial cells are important to ensure an adequate environment for neuronal activity in healthy conditions. Furthermore, it is becoming evident how both cell types can mediate the onset of neuroinflammation and lead to neurodegeneration when subjected to pathological stimuli. Based on this information, the role of the major microbiota products in shifting the activation profiles of astrocytes and microglia from a healthy to a diseased state will be discussed, focusing on Alzheimer disease pathogenesis.

Hypothesis: Does the Apparent Protective Action of Green Valley's Drug GV971 Against Cognitive Decline Result from Antiviral Action Against Herpes Simplex Virus Type 1 in Brain?

There has been much interest in the clinical trial of GV972 for treatment of Alzheimer's disease in that the data have indicated that the compound is protective against cognitive decline. This effect has been attributed to a remodelling of the gut microbiota. I suggest that the effect might be caused by an antiviral action of GV971 against herpes simplex virus type 1 in brain, which many studies have strongly implicated as having a major role in Alzheimer's disease. The antiviral action of GV971 is proposed on the basis that it is an acidic polysaccharide consisting of linear sodium oligomannurarate molecules of a range of sizes, derived from brown algae. Marine-derived polysaccharides are well known for possessing various bioactivities, including antiviral and antibacterial properties.

Self-Assembling, Ultrashort Peptide Gels as Antimicrobial Biomaterials

Supramolecular antimicrobial hydrogels based on peptides are attractive soft materials for the treatment of infections, considering their ease of preparation and benign fate in biological settings and in the environment. In particular, stimuli-responsive systems that can be assembled/disassembled ad hoc could offer the opportunity to switch on/off their bioactivity as needed. Besides, the shorter is the peptide, the lower its cost of production. However, a structure-to-function relationship is yet to be defined and reported activities are generally not yet competitive relative to traditional antibiotics. Inspiration for their design can be found in host defense peptides (HDPs), which can self-assemble to exert their function. This article reviews research developments in this emerging area, and it examines features, differences and similarities between antimicrobial and amyloid peptides to open the avenue towards the next generation of supramolecular antimicrobial peptides as innovative therapeutic materials.

Pharmacological Strategies to Improve Dendritic Spines in Alzheimer's Disease

To deeply understand late onset Alzheimer's disease (LOAD), it may be necessary to change the concept that it is a disease exclusively driven by aging processes. The onset of LOAD could be associated with a previous peripheral stress at the level of the gut (changes in the gut microbiota), obesity (metabolic stress), and infections, among other systemic/environmental stressors. The onset of LOAD, then, may result from the generation of mild peripheral inflammatory processes involving cytokine production associated with peripheral stressors that in a second step enter the brain and spread out the process causing a neuroinflammatory brain disease. This hypothesis could explain the potential efficacy of Sodium Oligomannate (GV-971), a mixture of acidic linear oligosaccharides that have shown to remodel gut microbiota and slowdown LOAD. However, regardless of the origin of the disease, the end goal of LOAD-related preventative or disease modifying therapies is to preserve dendritic spines and synaptic plasticity that underlay and support healthy cognition. Here we discuss how systemic/environmental stressors impact pathways associated with the regulation of spine morphogenesis and synaptic maintenance, including insulin receptor and the brain derived neurotrophic factor signaling. Spine structure remodeling is a plausible mechanism to maintain synapses and provide cognitive resilience in LOAD patients. Importantly, we also propose a combination of drugs targeting such stressors that may be able to modify the course of LOAD by acting on preventing dendritic spines and synapsis loss.

Comprehensive Review on Alzheimer's Disease: Causes and Treatment

Alzheimer’s disease (AD) is a disorder that causes degeneration of the cells in the brain and it is the main cause of dementia, which is characterized by a decline in thinking and independence in personal daily activities. AD is considered a multifactorial disease: two main hypotheses were proposed as a cause for AD, cholinergic and amyloid hypotheses. Additionally, several risk factors such as increasing age, genetic factors, head injuries, vascular diseases, infections, and environmental factors play a role in the disease. Currently, there are only two classes of approved drugs to treat AD, including inhibitors to cholinesterase enzyme and antagonists to N-methyl d-aspartate (NMDA), which are effective only in treating the symptoms of AD, but do not cure or prevent the disease. Nowadays, the research is focusing on understanding AD pathology by targeting several mechanisms, such as abnormal tau protein metabolism, β-amyloid, inflammatory response, and cholinergic and free radical damage, aiming to develop successful treatments that are capable of stopping or modifying the course of AD. This review discusses currently available drugs and future theories for the development of new therapies for AD, such as disease-modifying therapeutics (DMT), chaperones, and natural compounds.

Association of microbiota-derived propionic acid and Alzheimer's disease; bioinformatics analysis

PURPOSE

Microbiota-derived metabolites could alter the brain tissue toward the neurodegeneration disease. This study aims to select the genes associated with Propionic acid (PPA) and compromise Alzheimer's disease (AD) to find the possible roles of PPA in AD pathogenesis.

METHODS

Microbiota-derived metabolites could alter the brain tissue toward the neurodegeneration disease. This study aims to select the genes associated with Propionic acid (PPA) and compromise Alzheimer's disease (AD) to find the possible roles of PPA in AD pathogenesis.

RESULTS

Amongst all genes associated with PPA and AD, 284 genes to be shared by searching databases and were subjected to further analysis. AD-PPA genes mainly involved in cancer, bacterial and virus infection, and neurological and non-neurological diseases. Gene Ontology and pathway analysis covered the most AD hallmark, such as amyloid formation, apoptosis, proliferation, inflammation, and immune system. Network analysis revealed hub and bottleneck genes. MCODE analysis also indicated the seed genes represented in the significant subnetworks. ICAM1 and CCND1 were the hub, bottleneck, and seed genes.

CONCLUSIONS

PPA interacted genes implicated in AD act through pathways initiate neuronal cell death. In sum up, AD-PPA shared genes exhibited evidence that supports the idea PPA secreted from bacteria could alter brain physiology toward the emerging AD signs. This idea needs to confirm by more future investigation in animal models.

A Perspective on Roles Played by Immunosenescence in the Pathobiology of Alzheimer's Disease

Alzheimer's disease (AD) is a chronic progressive neurodegenerative disorder. Aging is the most significant risk factor for late-onset AD. The age-associated changes in the immune system are termed immunosenescence. A close connection between immunosenescence and AD is increasingly recognized. This article provides an overview of immunosenescence and evidence for its role in the pathogenesis of AD and possible mechanisms as well as the outlook for drug development.

Evidence for aggregation-independent, PrPC-mediated Aβ cellular internalization

Evidence linking amyloid beta (Aβ) cellular uptake and toxicity has burgeoned, and mechanisms underlying this association are subjects of active research. Two major, interconnected questions are whether Aβ uptake is aggregation-dependent and whether it is sequence-specific. We recently reported that the neuronal uptake of Aβ depends significantly on peptide chirality, suggesting that the process is predominantly receptor-mediated. Over the past decade, the cellular prion protein (PrP^C) has emerged as an important mediator of Aβ-induced toxicity and of neuronal Aβ internalization. Here, we report that the soluble, nonfibrillizing Aβ (1-30) peptide recapitulates full-length Aβ stereoselective cellular uptake, allowing us to decouple aggregation from cellular, receptor-mediated internalization. Moreover, we found that Aβ (1-30) uptake is also dependent on PrP^C expression. NMR-based molecular-level characterization identified the docking site on PrP^C that underlies the stereoselective binding of Aβ (1-30). Our findings therefore identify a specific sequence within Aβ that is responsible for the recognition of the peptide by PrP^C, as well as PrP^C-dependent cellular uptake. Further uptake stereodifferentiation in PrP^C-free cells points toward additional receptor-mediated interactions as likely contributors for Aβ cellular internalization. Taken together, our results highlight the potential of targeting cellular surface receptors to inhibit Aβ cellular uptake as an alternative route for future therapeutic development for Alzheimer's disease.

Toxoplasma gondii seropositivity and serointensity and cognitive function in adults

Infecting approximately one-third of the world's human population, Toxoplasma gondii has been associated with cognitive function. Here, we sought to further characterize the association between Toxoplasma gondii and cognitive function in a community sample of adults aged approximately 40 to70 years. Using adjusted linear regression models, we found associations of Toxoplasma gondii seropositivity with worse reasoning (b = -.192, p < .05) and matrix pattern completion (b = -.681, p < .01), of higher anti-Toxoplasma gondii p22 antibody levels with worse reasoning (b = -.078, p < .01) and slower Trails (numeric) performance (b = 5.962, p < .05), of higher anti-Toxoplasma gondii sag1 levels with worse reasoning (b = -.081, p < .05) and worse matrix pattern completion (b = -.217, p < .05), and of higher mean of the anti-Toxoplasma gondii p22 and sag1 levels with worse reasoning (b = -.112, p < .05), slower Trails (numeric) performance (b = 9.195, p < .05), and worse matrix pattern completion (b = -.245, p < .05). Neither age nor educational attainment moderated associations between the measures of Toxoplasma gondii seropositivity or serointensity. Sex, however, moderated the association between the sag1 titer and digit-symbol substitution and the association between the mean of the p22 and sag1 levels and digit-symbol substitution, and income moderated the association between Toxoplasma gondii seropositivity and numeric memory and the association between the p22 level and symbol-digit substitution. Based on the available neuropsychological tasks in this study, Toxoplasma gondii seropositivity and serointensity were associated with some aspects of poorer executive function in adults.

Alzheimer's disease as a systems network disorder: chronic stress/dyshomeostasis, innate immunity, and genetics

Ineffective results of clinical trials of over 200 anti-Alzheimer's drug candidates, with a 99.6% attrition rate, suggest that the current paradigm of Alzheimer's disease (AD) may be incomplete, necessitating exploration of alternative and complementary frameworks.Using algorithms for hypothesis independent search and expert-assisted synthesis of heterogeneous data, we attempted to reconcile multimodal clinical profiles of early-stage AD patients and accumulated research data within a parsimonious framework. Results of our analysis suggest that Alzheimer's may not be a brain disease but a progressive system-level network disorder, which is driven by chronic network stress and dyshomeostasis. The latter can be caused by various endogenous and exogenous factors, such as chronic inflammatory conditions, infections, vascular dysfunction, head trauma, environmental toxicity, and immune disorders. Whether originating in the brain or on the periphery, chronic stress, toxicity, and inflammation are communicated to the central nervous system (CNS) via humoral and neural routes, preferentially targeting high-centrality regulatory nodes and circuits of the nervous system, and eventually manifesting as a neurodegenerative CNS disease.In this report, we outline an alternative perspective on AD as a systems network disorder and discuss biochemical and genetic evidence suggesting the central role of chronic tissue injury/dyshomeostasis, innate immune reactivity, and inflammation in the etiopathobiology of Alzheimer's disease.

DNA Encapsidation and Capsid Assembly Are Underexploited Antiviral Targets for the Treatment of Herpesviruses

Although there are effective nucleoside analogs to treat HSV, VZV, and HCMV disease, herpesvirus infections continue to contribute to significant morbidity and mortality. Acyclovir is the drug of choice for HSV encephalopathy, yet there is an estimated 6-19% mortality rate with half of the survivors experiencing moderate to severe chronic neurological deficits. For VZV, current treatments are inadequate to prevent acute and persistent pain due to zoster. Treatment of HCMV with GCV requires close monitoring particularly in patients with impaired renal function and there are no approved treatments for congenital HCMV infections. New therapeutic options to control cytomegalovirus reactivation in bone marrow and stem cell transplant patients are needed to improve patient outcome. No successful chemotherapeutic options are available for EBV, HHV-6, 7, and 8. Drug resistance is a concern for HCMV, HSV, and VZV since approved drugs share common mechanisms of action. Targeting DNA encapsidation or capsid assembly provide additional options for the development of non-nucleoside, small molecule anti-herpesviral drugs.

Association between periodontitis and Alzheimer's disease and its impact on the self-perceived oral health status: a case-control study

PURPOSE

To test the hypothesis that periodontitis is associated with AD and search whether periodontal and other variables would negatively impact the oral health-related quality of life (OHRQoL) perception.

MATERIALS AND METHODS

Oral examinations and interview on self-perceived oral health status (Geriatric Oral Health Assessment Index (GOHAI) questionnaire (higher score corresponds to better perceived oral status)) were carried out and socio-demographic data were collected from outpatients with mild to moderate AD (cases, n = 50) and from their age- and sex-matched family caregivers (controls, n = 52). Full-mouth periodontal examination was performed. Significance of differences between groups was sought by chi-square, Student's t, or the Mann-Whitney test. The association between the variables periodontitis, probing depth (PD) ≥ 5 mm, and clinical attachment loss (CAL) ≥ 5 mm with the variable group was tested in binary logistic regression models (LRMs). LRMs were used to test the association of oral findings, demographics, and group with GOHAI.

RESULTS

Cases had fewer teeth and greater CAL than controls. Cases had a superior percentage of sites with plaque, calculus, and bleeding on probing than controls. Cases had greater GOHAI scores than controls. Periodontitis was a variable most likely associated with AD (OR = 11.08, p < 0.001). None of the oral findings or demographics, but group, was associated with GOHAI (OR = 14.45, p < 0.001).

CONCLUSION

Periodontitis is associated with AD, but not with patients' OHRQoL.

CLINICAL RELEVANCE

Health care professionals must be aware that AD patients should have a periodic thorough oral examination and preventive intervention aiming at their welfare and maintenance of a pain-free functional dentition.

Icariin sustains the proliferation and differentiation of Aβ25-35-treated hippocampal neural stem cells via the BDNF-TrkB-ERK/Akt signaling pathway

OBJECTIVES

Icariin (ICA) can be potentially used to treat Alzheimer's disease (AD), but the mechanism was not clear. The current study explored the effects of ICA on hippocampal neural stem cells, aiming to provide a comprehensive basis for its clinical application.

METHODS

Hippocampal neural stem cells were isolated from newborn rats and their differentiation ability was evaluated by performing immunofluorescence staining. Next, Aβ cell model was constructed by treating the cells with Aβ_25-35, and then the model was further treated by ICA or shBDNF or the two in combination. The viability and differentiation of the cells were, respectively, analyzed by 3-(4, 5-Dimethylthiazol-2-yl)-2, 5-Diphenyltetrazolium Bromide (MTT) and flow cytometry. The expression of BDNF-TrkB-ERK/Akt signaling pathway was assessed by quantitative real-time polymerase chain reaction (qRT-PCR) or Western blot (WB).

RESULTS

The hippocampal neural stem cells can differentiate into neurons and astrocytes. ICA effectively promoted the viability and differentiation of Aβ cell models. The expression levels of BDNF and TrkB in Aβ cell models were obviously decreased, which were noticeably increased by ICA. Moreover, BDNF knockdown further inhibited the viability and differentiation of Aβ model cells, which could be reversed by ICA. BDNF knockdown not only suppressed the expressions of BDNF and TrkB in Aβ cell models but also effectively prevented the phosphorylation of ERK/Akt; however, these phenomena were significantly alleviated by ICA treatment.

DISCUSSION

ICA promoted the proliferation and differentiation of Aβ_25-35-treated hippocampal neural stem cells through BDNF-TrkB-ERK/Akt signaling pathway. The current findings might contribute to the treatment of AD.