Alzheimer's disease and infections, where we stand and where we go

Focus of endothelial glycocalyx dysfunction in ischemic stroke and Alzheimer's disease: Possible intervention strategies

The integrity of the endothelial glycocalyx (eGCX), a mixture of carbohydrates attached to proteins expressed on the surface of blood vessel endothelial cells (EC), is critical for the maintenance of homeostasis of the cardiovascular system and all systems of the human body, the endothelium being the critical component of the stroma of all tissues. Consequently, dysfunction of eGCX results in a dysfunctional cardiovascular wall and severe downstream cardiovascular events, which contribute to the onset of cardio- and cerebrovascular diseases and neurodegenerative disorders, as well as other age-related diseases (ARDs). The key role of eGCX dysfunction in the onset of ARDs is examined here, with a focus on the most prevalent neurological diseases: ischemic stroke and Alzheimer's disease. Furthermore, the advantages and limitations of some treatment strategies for anti-eGCX dysfunction are described, ranging from experimental drug therapies, which need to be better tested and explored not only in animal models but also in humans, as well as reprogramming, the use of nutraceuticals, which are emerging as regenerative and new approaches. The promotion of these strategies is essential to keep eGCX and endothelium healthy, as is the development of intravital (e.g., intravascular) tools to estimate eGCX health status and treatment efficacy, which could lead to advanced solutions to address ARDs.

Neuroinflammation and Neurodegenerative Diseases: How Much Do We Still Not Know?

The term "neuroinflammation" defines the typical inflammatory response of the brain closely related to the onset of many neurodegenerative diseases (NDs). Neuroinflammation is well known, but its mechanisms and pathways are not entirely comprehended. Some progresses have been achieved through many efforts and research. Consequently, new cellular and molecular mechanisms, diverse and conventional, are emerging. In listing some of those that will be the subject of our description and discussion, essential are the important roles of peripheral and infiltrated monocytes and clonotypic cells, alterations in the gut-brain axis, dysregulation of the apelinergic system, alterations in the endothelial glycocalyx of the endothelial component of neuronal vascular units, variations in expression of some genes and levels of the encoding molecules by the action of microRNAs (miRNAs), or other epigenetic factors and distinctive transcriptional factors, as well as the role of autophagy, ferroptosis, sex differences, and modifications in the circadian cycle. Such mechanisms can add significantly to understanding the complex etiological puzzle of neuroinflammation and ND. In addition, they could represent biomarkers and targets of ND, which is increasing in the elderly.

Microbial Infections Are a Risk Factor for Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, comprise a family of disorders characterized by progressive loss of nervous system function. Neuroinflammation is increasingly recognized to be associated with many neurodegenerative diseases but whether it is a cause or consequence of the disease process is unclear. Of growing interest is the role of microbial infections in inciting degenerative neuroinflammatory responses and genetic factors that may regulate those responses. Microbial infections cause inflammation within the central nervous system through activation of brain-resident immune cells and infiltration of peripheral immune cells. These responses are necessary to protect the brain from lethal infections but may also induce neuropathological changes that lead to neurodegeneration. This review discusses the molecular and cellular mechanisms through which microbial infections may increase susceptibility to neurodegenerative diseases. Elucidating these mechanisms is critical for developing targeted therapeutic approaches that prevent the onset and slow the progression of neurodegenerative diseases.

Broader Insights into Understanding Tumor Necrosis Factor and Neurodegenerative Disease Pathogenesis Infer New Therapeutic Approaches

Proinflammatory cytokines such as tumor necrosis factor (TNF), with its now appreciated key roles in neurophysiology as well as neuropathophysiology, are sufficiently well-documented to be useful tools for enquiry into the natural history of neurodegenerative diseases. We review the broader literature on TNF to rationalize why abruptly-acquired neurodegenerative states do not exhibit the remorseless clinical progression seen in those states with gradual onsets. We propose that the three typically non-worsening neurodegenerative syndromes, post-stroke, post-traumatic brain injury (TBI), and post cardiac arrest, usually become and remain static because of excess cerebral TNF induced by the initial dramatic peak keeping microglia chronically activated through an autocrine loop of microglial activation through excess cerebral TNF. The existence of this autocrine loop rationalizes post-damage repair with perispinal etanercept and proposes a treatment for cerebral aspects of COVID-19 chronicity. Another insufficiently considered aspect of cerebral proinflammatory cytokines is the fitness of the endogenous cerebral anti-TNF system provided by norepinephrine (NE), generated and distributed throughout the brain from the locus coeruleus (LC). We propose that an intact LC, and therefore an intact NE-mediated endogenous anti-cerebral TNF system, plus the DAMP (damage or danger-associated molecular pattern) input having diminished, is what allows post-stroke, post-TBI, and post cardiac arrest patients a strong long-term survival advantage over Alzheimer's disease and Parkinson's disease sufferers. In contrast, Alzheimer's disease and Parkinson's disease patients remorselessly worsen, being handicapped by sustained, accumulating, DAMP and PAMP (pathogen-associated molecular patterns) input, as well as loss of the LC-origin, NE-mediated, endogenous anti-cerebral TNF system. Adrenergic receptor agonists may counter this.

Oral Health Status in Subjects with Amnestic Mild Cognitive Impairment and Alzheimer's Disease: Data from the Zabút Aging Project

Background:

The relationship between Alzheimer’s disease (AD) and periodontitis has been recently investigated with heterogenous results.

Objective:

This study aims to evaluate the oral health status and its relationship with cognitive impairment of participants, enrolled in the Zabút Aging Project, a community-based cohort study performed in a rural community in Sicily, Italy.

Methods:

A case-control study (20 subjects with AD, 20 with amnestic mild cognitive impairment [aMCI], and 20 controls) was conducted. The protocol included a comprehensive medical and cognitive-behavioral examination. Full-mouth evaluation, microbial analysis of subgingival plaque samples (by RT-PCR analysis), and oral health-related quality of life (OHR-QoL) were evaluated.

Results:

The decayed, missing, and filled teeth (DMFT) total score of AD subjects was significantly higher than aMCI (p = 0.009) and controls (p = 0.001). Furthermore, the “M” component of DMFT (i.e., the number of missing teeth) was significantly higher in AD than in aMCI (p < 0.001) and controls (p < 0.001). A Poisson regression model revealed that age (p < 0.001), male gender (p = 0.001), and AD (p = 0.001) were positively correlated with DMFT. Concerning oral microbial load, the presence of Fusobacterium nucleatum was significantly higher in AD than in controls (p = 0.02), and a higher load of Treponema denticola was found in aMCI than with AD (p = 0.004). OHR-QoL scores did not differ among the groups.

Conclusion:

The current research suggests that AD is associated with chronic periodontitis, which is capable of determining tooth loss due to the pathogenicity of Fusobacterium nucleatum. These data remain to be confirmed in larger population-based cohorts.

Crosstalk between neurokinin receptor signaling and neuroinflammation in neurological disorders

The neurokinin 1 receptor with the natural substrate substance P is one of the intensely studied receptors among the neurokinin receptors. The intracellular signaling mechanism uses G protein-coupled transduction regulating various physiological processes from nausea to Alzheimer's disease. The neurokinin 1 receptor plays a significant role in neuroinflammation-mediated alterations in neural circuitry. Neurokinin 1 receptor antagonists are selective, potent and exhibited efficacy in animal models of nervous system disorders. Evolving data now strengthen the viewpoint of brain substance P/neurokinin 1 receptor axis-mediated action in neural circuit dysfunction. Thus, a deep-rooted analysis of disease mechanism in which the neurokinin 1 receptor is involved is necessary for augmenting disease models which encourage the pharmaceutical industry to intensify the research pipeline. This review is an attempt to outline the concept of neurokinin 1 receptor signaling interlinked to the brain innate immune system. We also uncover the mechanisms of the neurokinin 1 receptor involved in neurological disorder and various methods of modulating the neurokinin 1 receptor, which may result in therapeutic action.

Association of immunoglobulin GM allotypes with longevity in long-living individuals from Southern Italy

Background

The aim of this study was to analyse the role of GM allotypes, i.e. the hereditary antigenic determinants expressed on immunoglobulin polypeptide chains, in the attainment of longevity. The role played by immunoglobulin allotypes in the control of immune responses is well known as well as the role of an efficient immune response in longevity achievement. So, it is conceivable that particular GM allotypes may contribute to the generation of an efficient immune response that supports successful ageing, hence longevity.

Methods

In order to show if GM allotypes play a role in the achievement of longevity, we typed the DNA of 95 Long-living individuals (LLIs) and 96 young control individuals (YCs) from South Italy for GM3/17 and GM23+/− alleles.

Results

To demonstrate the role of GM allotypes in the attainment of longevity we compared genotype and allele frequencies of GM allotypes between LLIs and YCs. A global chi-square test (3 × 2) shows that the distribution of genotypes at the GM 3/17 locus is highly significantly different in LLIs from that observed in YCs (p < 0.0001). The 2 × 2 chi-square test shows that the carriers of the GM3 allele contribute to this highly significant difference. Accordingly, GM3 allele is significantly overrepresented in LLIs. No significant differences were instead observed regarding GM23 allele.

Conclusion

These preliminary results show that GM3 allotype is significantly overrepresented in LLIs. To best of our knowledge, this is the first study performed to assess the role of GM allotypes in longevity. So, it should be necessary to verify the data in a larger sample of individuals to confirm GM role in the attainment of longevity.

Pumping the Brakes: Neurotrophic Factors for the Prevention of Cognitive Impairment and Dementia after Traumatic Brain Injury

Traumatic brain injury (TBI) is the leading cause of disability and death worldwide, affecting as many as 54,000,000-60,000,000 people annually. TBI is associated with significant impairments in brain function, impacting cognitive, emotional, behavioral, and physical functioning. Although much previous research has focused on the impairment immediately following injury, TBI may have much longer-lasting consequences, including neuropsychiatric disorders and cognitive impairment. TBI, even mild brain injury, has also been recognized as a significant risk factor for the later development of dementia and Alzheimer's disease. Although the link between TBI and dementia is currently unknown, several proposed mechanisms have been put forward, including alterations in glucose metabolism, excitotoxicity, calcium influx, mitochondrial dysfunction, oxidative stress, and neuroinflammation. A treatment for the devastating long-term consequences of TBI is desperately needed. Unfortunately, however, no such treatment is currently available, making this a major area of unmet medical need. Increasing the level of neurotrophic factor expression in key brain areas may be one potential therapeutic strategy. Of the neurotrophic factors, granulocyte-colony stimulating factor (G-CSF) may be particularly effective for preventing the emergence of long-term complications of TBI, including dementia, because of its ability to reduce apoptosis, stimulate neurogenesis, and increase neuroplasticity.

Persistent infections, immune-senescence and Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia. Classical hallmarks of AD such as amyloid deposition and neurofibrillary tangles do not completely explain AD pathogenesis. Recent investigations proposed Aβ peptide as an anti-microbial factor. Our previous works suggested that the concomitant presence of single nucleotide polymorphisms (SNPs) from AD genetic studies might impair antiviral defenses and increase the individual susceptibility to herpes virus infection. Viruses of herpes family by inducing frequent cycles of reactivation and latency constantly challenge the immune response and drive the accumulation of memory T cells. However, the immune system is not able to completely eradicate these viruses. The continuous antigen stimulation activates chronic inflammatory responses that may progressively induce neurodegenerative mechanisms in genetically susceptible elderly. The aim of this paper is to suggest new perspectives in clinical pathogenesis of AD with potential prevention and new medical treatment of the age associated cognitive decline.

Variants in Antiviral Genes are Risk Factors for Cognitive Decline and Dementia

A gene association study of factors regulating antiviral response such as interferon (IFN)-λ3, also known as IL-28B, mediator complex (Med) 23, and interferon regulatory factor (IRF) 7 with cognitive deterioration and Alzheimer's disease (AD) was performed. Differences in the TT genotype distribution of IL-28B single nucleotide polymorphism (SNP) between AD patients and controls were found. The GG genotype of Med23 gene appeared to influence the progression of the disease, being more frequent in the APOE ɛ4 negative elderly that developed AD during the five year follow-up. Leukocyte positivity for Epstein Barr virus (EBV) and human herpes virus (HHV)-6 DNA was analyzed. Med23 GG genotype correlated with the positivity to HHV-6 DNA. EBV and HHV-6 plasma IgG levels were also investigated and EBV IgG levels were increased in AD with the IRF7 GG genotype. A differential genetic background in genes regulating anti-virus responses was associated with an increased risk of cognitive decline and AD. EBV and HHV-6 appeared to be risk factors for AD in genetically susceptible elderly.