Antimicrobial Peptides (AMPs) in the Pathogenesis of Alzheimer's Disease: Implications for Diagnosis and Treatment

Salivary Antimicrobial Peptide in Patients With Dementia Before and After Clinical Oral Rehabilitation Programme: A Randomised Controlled Trial

BACKGROUND

Emerging evidence suggests a link between salivary metabolite changes and neurodegenerative dementia, with antimicrobial peptides (AMPs) implicated in its pathogenesis.

OBJECTIVE

We investigated the effects of a clinical oral rehabilitation programme tailored for dementia patients on salivary flow rate, AMP levels and oral health-related quality of life (OHRQoL).

METHODS

Eligible patients were randomly assigned to either the experimental group (EG; n = 28) or the control group (CG; n = 27). Both groups received a leaflet on oral health. In addition, the EG received an oral care intervention that included individual lessons on oral muscle exercises and oral self-care practices. Saliva samples and OHRQoL data were collected at baseline and follow-up visits. Generalised estimating equation models were used to analyse the changes over time.

RESULTS

At the 3-month follow-up, EG showed significantly lower histatin 5 (HTN-5) levels (β = -0.08; effect size [ES] = 0.72) than CG. At 6 months, EG exhibited improved salivary flow rate (β = 0.89; ES = 0.89) and OHRQoL (β = 6.99; ES = 1.31) compared to CG. Changes in salivary flow rate (β = 4.03), HTN-5 level (β = -0.78) and beta-defensin 2 level (BD-2) (β = -0.91) at 3 months predicted improved OHRQoL at 6 months (all p < 0.05).

CONCLUSIONS

Our clinical oral rehabilitation programme reduced the level of salivary HTN-5, increased salivary flow rate and enhanced OHRQoL in dementia patients. Furthermore, changes in salivary flow rate, HTN-5 level and BD-2 level were associated with improvements in patients' OHRQoL.

Detection of Amyloid-β Peptides in Gingival Crevicular Fluid and Its Effect on Oral Pathogens

Periodontitis is the most common oral inflammatory disease, contributing to the onset and progression of Alzheimer's disease. However, a full investigation has not been performed on the expression level of amyloid-β (Aβ) peptides in gingival crevicular fluid (GCF) and its effects on oral pathogens. This study aimed to analyze the expression level of Aβ peptides in GCF of patients with periodontitis and the effects of Aβ peptides against common oral pathogens. GCF samples were collected from patients with periodontitis (n = 15) and periodontally healthy people (n = 10). The antimicrobial effects of Aβ peptides were evaluated on four common oral pathogenic strains using an MTT assay, crystal violet staining, fluorescence microscope, and transmission electron microscope. The protein levels of Aβ40 and Aβ42 were upregulated in the GCF of periodontitis group compared with the healthy group. Both Aβ40 and Aβ42 exhibited antimicrobial effects on Porphyromonas gingivalis, Aggregatibacter actinomycetemcomitans, and Lactobacillus acidophilus in both planktonic and biofilm conditions. Further, only Aβ40 showed an antimicrobial effect on the Fusobacterium nucleatum. The results of this study demonstrate that Aβ peptides in GCF may be a relevant indicator of periodontitis status. Besides, the antimicrobial peptides derived from Aβ peptides have great potential in periodontal therapy.

Interplay between Antimicrobial Peptides and Amyloid Proteins in Host Defense and Disease Modulation

The biological properties of antimicrobial peptides (AMPs) and amyloid proteins and their cross-talks have gained increasing attention due to their potential implications in both host defense mechanisms and amyloid-related diseases. However, complex interactions, molecular mechanisms, and physiological applications are not fully understood. The interplay between antimicrobial peptides and amyloid proteins is crucial for uncovering new insights into immune defense and disease mechanisms, bridging critical gaps in understanding infectious and neurodegenerative diseases. This review provides an overview of the cross-talk between AMPs and amyloids, highlighting their intricate interplay, mechanisms of action, and potential therapeutic implications. The dual roles of AMPs, which not only serve as key components of the innate immune system, combating microbial infections, but also exhibit modulatory effects on amyloid formation and toxicity, are discussed. The diverse mechanisms employed by AMPs to modulate amyloid aggregation, fibril formation, and toxicity are also discussed. Additionally, we explore emerging evidence suggesting that amyloid proteins may possess antimicrobial properties, adding a new dimension to the intricate relationship between AMPs and amyloids. This review underscores the importance of understanding the cross-talk between AMPs and amyloids to better understand the molecular processes underlying infectious diseases and amyloid-related disorders and to aid in the development of therapeutic avenues to treat them.

Unveiling the atlas of associations between 1,400 plasma metabolites and 24 tumors: Mendelian randomization analyses

Background

Association between plasma metabolites and pan-cancer remains controversial. Herein, we performed a two-sample Mendelian randomization (MR) analysis to verify whether there is a causal relationship between the two and to point the way for cancer metabolism research.

Methods

In our research, we downloaded 1,400 plasma metabolites from a large genome-wide association study (GWAS). We also obtained GWAS summary statistics for 24 types of cancers from the publicly available GWAS database, totaling 5,003,410 European individuals. We mainly used the fixed/random-effects inverse variance-weighted (IVW) method for two-sample MR analysis.

Results

In a combined sample of 291,202 cancer cases and 4,712,208 controls, a total of 55 plasma metabolites were identified as causally associated with nine types of cancer as a result of our MR analysis [P<0.05, false discovery rate (FDR) <0.2], including methionine sulfone, gamma-glutamylcitrulline, alliin, tetradecanedioate, hexadecanedioate, glutarate, ceramide, linolenoylcarnitine, hydroxypalmitoyl sphingomyelin, 1-palmitoyl-2-linoleoyl-glycerylphosphorylcholine (1-palmitoyl-2-linoleoyl-GPC), 3-acetylphenol sulfate, retinol (vitamin a) to linoleoyl-arachidonoyl-glycerol (18:2 to 20:4) ratio, etc. Reverse MR analysis revealed a causal relationship between lung cancer and the only plasma metabolite, 1-palmitoyl-2-linoleoyl-GPC (P<0.05, FDR <0.2).

Conclusions

Our study provides a comprehensive atlas of cancer-related plasma metabolites, offering possible targets for cancer detection, as well as a reference for future research on tumorigenesis mechanisms and therapeutic targets.

Cognition and Oral Health: Association Between Alzheimer's Disease and Periodontitis

A relationship between poor oral health conditions and cognitive decline has been clinically observed. A bidirectional association between periodontitis and Alzheimer's disease has been repeatedly identified in clinical and pre-clinical studies. This association is supported by four major overlapped pathways and mechanisms, including the microbiota-gut-brain axis via the vagus nerve pathway, periodontopathogen-involved neuroinflammation via the trigeminal nerve pathway, proinflammatory cytokines, and trained immunity. Partly linked with periodontitis, increased levels of proinflammatory cytokines and decreased levels of anti-inflammatory cytokines can exacerbate the abnormal accumulation of amyloid beta plaques and hyperphosphorylation of tau protein. Periodontitis is considered an important environmental factor involved in Alzheimer's disease development. This review discusses the bidirectional relationship between Alzheimer's disease and periodontitis, focusing on the association between cognitive decline and poor oral health conditions. Thus, oral health intervention strategies have been proposed as potential therapeutic methods for the prevention and management of Alzheimer's disease. [ Psychiatr Ann . 2024;54(8):e230–e234.]

A comprehensive review on the progress and challenges of tetrahydroisoquinoline derivatives as a promising therapeutic agent to treat Alzheimer's disease

Alzheimer's disease (AD) is the most common and irreversible neurodegenerative disorder worldwide. While the precise mechanism behind this rapid progression and multifaceted disease remains unknown, the numerous drawbacks of the available therapies are prevalent, necessitating effective alternative treatment methods. In view of the rising demand for effective AD treatment, numerous reports have shown that tetrahydroisoquinoline (THIQ) is a valuable scaffold in various clinical medicinal molecules and has a promising potential as a therapeutic agent in treating AD due to its significant neuroprotective, anti-inflammatory, and antioxidative properties via several mechanisms that target the altered signaling pathways. Therefore, this review comprehensively outlines the potential application of THIQ derivatives in AD treatment and the challenges in imparting the action of these prospective therapeutic agents. The review emphasizes a number of THIQ derivatives, including Dauricine, jatrorrhizine, 1MeTIQ, and THICAPA, that have been incorporated in AD studies in recent years. Subsequently, a dedicated section of the review briefly discusses the emerging potential benefits of multi-target therapeutics, which lie in their ability to be integrated with alternative therapeutics. Eventually, this review elaborates on the rising challenges and future recommendations for the development of therapeutic drug agents to treat AD effectively. In essence, the valuable research insights of THIQ derivatives presented in this comprehensive review would serve as an integral reference for future studies to develop potent therapeutic drugs for AD research.

Alzheimer's disease and herpes viruses: Current events and perspectives

Alzheimer's disease (AD) is a real and current scientific and societal challenge. Alzheimer's disease is characterised by a neurodegenerative neuroinflammatory process, but the etiopathogenetic mechanisms are still unclear. The possible infectious aetiology and potential involvement of Herpes viruses as triggers for the formation of extracellular deposits of amyloid beta (Aβ) peptide (amyloid plaques) and intraneuronal aggregates of hyperphosphorylated and misfold could be a possible explanation. In fact, the possible genetic interference of Herpes viruses with the genome of the host neuronal cell or the stimulation of the infection to a continuous immune response with a consequent chronic inflammation could constitute those mechanisms underlying the development of AD, with possible implications in the understanding and management of the disease. Herpes viruses could be significantly involved in the pathogenesis of AD and in particular, their ability to reactivate in particular conditions such as immunocompromise and immunosenescence, could explain the neurological damage characteristic of AD. Our review aims to evaluate the state of the art of knowledge and perspectives regarding the potential relationship between Herpes viruses and AD, in order to be able to identify the possible etiopathogenetic mechanisms and the possible therapeutic implications.

Therapeutics for neurodegenerative diseases by targeting the gut microbiome: from bench to bedside

The aetiologies and origins of neurodegenerative diseases, such as Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and Huntington's disease (HD), are complex and multifaceted. A growing body of evidence suggests that the gut microbiome plays crucial roles in the development and progression of neurodegenerative diseases. Clinicians have come to realize that therapeutics targeting the gut microbiome have the potential to halt the progression of neurodegenerative diseases. This narrative review examines the alterations in the gut microbiome in AD, PD, ALS and HD, highlighting the close relationship between the gut microbiome and the brain in neurodegenerative diseases. Processes that mediate the gut microbiome-brain communication in neurodegenerative diseases, including the immunological, vagus nerve and circulatory pathways, are evaluated. Furthermore, we summarize potential therapeutics for neurodegenerative diseases that modify the gut microbiome and its metabolites, including diets, probiotics and prebiotics, microbial metabolites, antibacterials and faecal microbiome transplantation. Finally, current challenges and future directions are discussed.

Pangenomics: A new era in the field of neurodegenerative diseases

A pangenome is composed of all the genetic variability of a group of individuals, and its application to the study of neurodegenerative diseases may provide valuable insights into the underlying aspects of genetic heterogenetiy for these complex ailments, including gene expression, epigenetics, and translation mechanisms. Furthermore, a reference pangenome allows for the identification of previously undetected structural commonalities and differences among individuals, which may help in the diagnosis of a disease, support the prediction of what will happen over time (prognosis) and aid in developing novel treatments in the perspective of personalized medicine. Therefore, in the present review, the application of the pangenome concept to the study of neurodegenerative diseases will be discussed and analyzed for its potential to enable an improvement in diagnosis and prognosis for these illnesses, leading to the development of tailored treatments for individual patients from the knowledge of the genomic composition of a whole population.

Alzheimer's disease as a viral disease: Revisiting the infectious hypothesis

Alzheimer's disease (AD) represents the most frequent type of dementia in elderly people. Two major forms of the disease exist: sporadic - the causes of which have not yet been fully understood - and familial - inherited within families from generation to generation, with a clear autosomal dominant transmission of mutations in Presenilin 1 (PSEN1), 2 (PSEN2) or Amyloid Precursors Protein (APP) genes. The main hallmark of AD consists of extracellular deposits of amyloid-beta (Aβ) peptide and intracellular deposits of the hyperphosphorylated form of the tau protein. An ever-growing body of research supports the viral infectious hypothesis of sporadic forms of AD. In particular, it has been shown that several herpes viruses (i.e., HHV-1, HHV-2, HHV-3 or varicella zoster virus, HHV-4 or Epstein Barr virus, HHV-5 or cytomegalovirus, HHV-6A and B, HHV-7), flaviviruses (i.e., Zika virus, Dengue fever virus, Japanese encephalitis virus) as well as Human Immunodeficiency Virus (HIV), hepatitis viruses (HAV, HBV, HCV, HDV, HEV), SARS-CoV2, Ljungan virus (LV), Influenza A virus and Borna disease virus, could increase the risk of AD. Here, we summarized and discussed these results. Based on these findings, significant issues for future studies are also put forward.

3-[[(3S)-1,2,3,4-Tetrahydroisoquinoline-3-Carbonyl]Amino]Propanoic Acid (THICAPA) Is Protective Against Aβ42-Induced Toxicity In Vitro and in an Alzheimer's Disease Drosophila

Alzheimer's disease (AD) is the most prevalent type of dementia globally. The accumulation of amyloid-beta (Aβ) extracellular senile plaques in the brain is one of the hallmark mechanisms found in AD. Aβ42 is the most damaging and aggressively aggregating Aβ isomer produced in the brain. Although Aβ42 has been extensively researched as a crucial peptide connected to the development of the characteristic amyloid fibrils in AD, the specifics of its pathophysiology are still unknown. Therefore, the main objective was to identify novel compounds that could potentially mitigate the negative effects of Aβ42. 3-[[(3S)-1,2,3,4-Tetrahydroisoquinoline-3-carbonyl]amino]propanoic acid (THICAPA) was identified as a ligand for Aβ42 and for reducing fibrillary Aβ42 aggregation. THICAPA also improved cell viability when administered to PC12 neuronal cells that were exposed to Aβ42. Additionally, this compound diminished Aβ42 toxicity in the current AD Drosophila model by rescuing the rough eye phenotype, prolonging the life span, and enhancing motor functions. Through next-generation RNA-sequencing, immune response pathways were downregulated in response to THICAPA treatment. Thus, this study suggests THICAPA as a possible disease-modifying treatment for AD.

Proteolytically Stable ααγ-Hybrid Peptides Inhibit the Aggregation and Cytotoxicity of Aβ42

The recent approval of antibody-based therapy for targeting the clearance of amyloid plaques fuels the research in designing small molecules and peptide inhibitors to target the aggregation of Aβ-peptides. Here, we report that the 15-residue ααγ-hybrid peptide not only inhibits the aggregation of soluble Aβ42 into fibrils but also disintegrates the aggregated Aβ42 fibrils into smaller assemblies. Further, the hybrid peptide completely rescues neuronal cells from the toxicity of Aβ42 at equimolar concentrations. The shorter 10- and 12-mer peptides showed weak aggregation inhibition activity, while the fully hydrophobic 15-mer ααγ-hybrid peptide analogue showed no aggregation inhibition activity. Further, the 15-mer ααγ-hybrid peptide showed resistance against trypsin digestion and also nontoxic to the neuronal cells. The CD revealed that the peptide upon interaction induces a helix-type conformation in the Aβ42. This is in sharp contrast to the β-sheet conformation of Aβ42 upon incubation. The two-dimensional-NMR (2D-NMR) analysis revealed a large perturbation in the chemical shifts of residues at the N-terminus. The presence of 15-mer peptide at an equimolar concentration of Aβ42 showed less tendency for aggregation and also exhibited nontoxicity to the neuronal cells. The results reported here may be useful in designing new therapeutics for Alzheimer's disease.

Clinical evidence of human pathogens implicated in Alzheimer's disease pathology and the therapeutic efficacy of antimicrobials: an overview

A wealth of pre-clinical reports and data derived from human subjects and brain autopsies suggest that microbial infections are relevant to Alzheimer's disease (AD). This has inspired the hypothesis that microbial infections increase the risk or even trigger the onset of AD. Multiple models have been developed to explain the increase in pathogenic microbes in AD patients. Although this hypothesis is well accepted in the field, it is not yet clear whether microbial neuroinvasion is a cause of AD or a consequence of the pathological changes experienced by the demented brain. Along the same line, the gut microbiome has also been proposed as a modulator of AD. In this review, we focus on human-based evidence demonstrating the elevated abundance of microbes and microbe-derived molecules in AD hosts as well as their interactions with AD hallmarks. Further, the direct-purpose and potential off-target effects underpinning the efficacy of anti-microbial treatments in AD are also addressed.

Associations of Serum Antimicrobial Peptide LL-37 with Longitudinal Cognitive Decline and Neurodegeneration Among Older Adults with Memory Complaints

BACKGROUND

A potential role of the antimicrobial peptide LL-37, which is upregulated after infection, in the pathogenesis of Alzheimer's disease (AD) was identified. However, the clinical relevance of LL-37 in AD is not clear yet.

OBJECTIVE

This study aims to investigate the association of circulating LL-37 with longitudinal cognitive decline and neurodegeneration among older adults with memory complaints.

METHODS

This cohort study recruited 357 older adults with memory complaints. Participants were followed-up for two years and the cognitive functions were assessed using the Mini-Mental State Examination (MMSE). Serum LL-37, pTau181, and tTau levels were determined at baseline. Associations of baseline LL-37 with longitudinal cognitive decline and change of neurodegenerative biomarkers were analyzed.

RESULTS

No difference was found in the slope of longitudinal cognitive decline during follow-up between the low and high LL-37 group, adjusting for age, sex, education, body mass index, APOE ɛ4 carrier status, comorbidities, and baseline MMSE scores (difference in slope: 0.226, 95% CI: -0.169 to 0.621). Higher LL-37 levels were associated with longitudinal cognitive decline, as indicated by a decrease of MMSE scores of 3 points or above during follow-up (RR = 2.11, 95% CI: 1.32 to 3.38). The high LL-37 group had larger slopes of the increase in neurofilament light (difference in slope: 3.759, 95% CI: 2.367 to 5.152) and pTau181 (difference in slope: 0.325, 95% CI: 0.151 to 0.499) than the low LL-37 group.

CONCLUSION

These findings support an association of the antimicrobial peptide LL-37 with AD from a clinical perspective.

Calabria as a Genetic Isolate: A Model for the Study of Neurodegenerative Diseases

Although originally multi-ethnic in its structure, nowadays the Calabria region of southern Italy represents an area with low genetic heterogeneity and a high level of consanguinity that allows rare mutations to be maintained due to the founder effect. A complex research methodology—ranging from clinical activity to the genealogical reconstruction of families/populations across the centuries, the creation of databases, and molecular/genetic research—was modelled on the characteristics of the Calabrian population for more than three decades. This methodology allowed the identification of several novel genetic mutations or variants associated with neurodegenerative diseases. In addition, a higher prevalence of several hereditary neurodegenerative diseases has been reported in this population, such as Alzheimer’s disease, frontotemporal dementia, Parkinson’s disease, Niemann–Pick type C disease, spinocerebellar ataxia, Creutzfeldt–Jakob disease, and Gerstmann–Straussler–Scheinker disease. Here, we summarize and discuss the results of research data supporting the view that Calabria could be considered as a genetic isolate and could represent a model, a sort of outdoor laboratory—similar to very few places in the world—useful for the advancement of knowledge on neurodegenerative diseases.