Initial characterization of Chlamydophila (Chlamydia) pneumoniae cultured from the late-onset Alzheimer brain

MAD-microbial (origin of) Alzheimer's disease hypothesis: from infection and the antimicrobial response to disruption of key copper-based systems

Microbes have been suspected to cause Alzheimer's disease since at least 1908, but this has generally remained unpopular in comparison to the amyloid hypothesis and the dominance of Aβ and Tau. However, evidence has been accumulating to suggest that these earlier theories are but a manifestation of a common cause that can trigger and interact with all the major molecular players recognized in AD. Aβ, Tau and ApoE, in particular appear to be molecules with normal homeostatic functions but also with alternative antimicrobial functions. Their alternative functions confer the non-immune specialized neuron with some innate intracellular defenses that appear to be re-appropriated from their normal functions in times of need. Indeed, signs of infection of the neurons by biofilm-forming microbial colonies, in synergy with herpes viruses, are evident from the clinical and preclinical studies we discuss. Furthermore, we attempt to provide a mechanistic understanding of the AD landscape by discussing the antimicrobial effect of Aβ, Tau and ApoE and Lactoferrin in AD, and a possible mechanistic link with deficiency of vital copper-based systems. In particular, we focus on mitochondrial oxidative respiration via complex 4 and ceruloplasmin for iron homeostasis, and how this is similar and possibly central to neurodegenerative diseases in general. In the case of AD, we provide evidence for the microbial Alzheimer's disease (MAD) theory, namely that AD could in fact be caused by a long-term microbial exposure or even long-term infection of the neurons themselves that results in a costly prolonged antimicrobial response that disrupts copper-based systems that govern neurotransmission, iron homeostasis and respiration. Finally, we discuss potential treatment modalities based on this holistic understanding of AD that incorporates the many separate and seemingly conflicting theories. If the MAD theory is correct, then the reduction of microbial exposure through use of broad antimicrobial and anti-inflammatory treatments could potentially alleviate AD although this requires further clinical investigation.

Regional Differences in Microbial Infiltration of Brain Tissue from Alzheimer's Disease Patients and Control Individuals

Alzheimer's disease (AD) is characterized by cognitive decline and neuropathology including amyloid beta (Aβ) plaques and neurofibrillary tangles (tau). Factors initiating or driving these pathologies remain unclear, though microbes have been increasingly implicated. Our data and others' findings indicate that microbes may be common constituents of the brain. It is notable that Aβ and tau have antimicrobial properties, suggesting a response to microbes in the brain. We used 16S rRNA sequencing to compare major bacterial phyla in post-mortem tissues from individuals exhibiting a range of neuropathology and cognitive status in two brain regions variably affected in AD. Our data indicate that strong regional differences exist, driven in part by the varied presence of Proteobacteria and Firmicutes. We confirmed our data using ELISA of bacterial lipopolysaccharide (LPS) and lipoteichoic acid in the same brain tissue. We identified a potential association between the composition of phyla and the presence of neuropathology but not cognitive status. Declining cognition and increasing pathology correlated closely with serum LPS, but not brain levels of LPS, although brain LPS showed a strong negative correlation with cerebral amyloid angiopathy. Collectively, our data suggest a region-specific heterogeneity of microbial populations in brain tissue potentially associated with neurodegenerative pathology.

Chlamydia pneumoniae in Alzheimer's disease pathology

While recent advances in diagnostics and therapeutics offer promising new approaches for Alzheimer's disease (AD) diagnosis and treatment, there is still an unmet need for an effective remedy, suggesting new avenues of research are required. Besides many plausible etiologies for AD pathogenesis, mounting evidence supports a possible role for microbial infections. Various microbes have been identified in the postmortem brain tissues of human AD patients. Among bacterial pathogens in AD, Chlamydia pneumoniae (Cp) has been well characterized in human AD brains and is a leading candidate for an infectious involvement. However, no definitive studies have been performed proving or disproving Cp's role as a causative or accelerating agent in AD pathology and cognitive decline. In this review, we discuss recent updates for the role of Cp in human AD brains as well as experimental models of AD. Furthermore, based on the current literature, we have compiled a list of potential mechanistic pathways which may connect Cp with AD pathology.

Infectious origin of Alzheimer’s disease: Amyloid beta as a component of brain antimicrobial immunity

The amyloid cascade hypothesis, focusing on pathological proteins aggregation, has so far failed to uncover the root cause of Alzheimer’s disease (AD), or to provide an effective therapy. This traditional paradigm essentially explains a mechanism involved in the development of sporadic AD rather than its cause. The failure of an overwhelming majority of clinical studies (99.6%) demonstrates that a breakthrough in therapy would be difficult if not impossible without understanding the etiology of AD. It becomes more and more apparent that the AD pathology might originate from brain infection. In this review, we discuss a potential role of bacteria, viruses, fungi, and eukaryotic parasites as triggers of AD pathology. We show evidence from the current literature that amyloid beta, traditionally viewed as pathological, actually acts as an antimicrobial peptide, protecting the brain against pathogens. However, in case of a prolonged or excessive activation of a senescent immune system, amyloid beta accumulation and aggregation becomes damaging and supports runaway neurodegenerative processes in AD. This is paralleled by the recent study by Alam and colleagues (2022) who showed that alpha-synuclein, the protein accumulating in synucleinopathies, also plays a critical physiological role in immune reactions and inflammation, showing an unforeseen link between the 2 unrelated classes of neurodegenerative disorders. The multiplication of the amyloid precursor protein gene, recently described by Lee and collegues (2018), and possible reactivation of human endogenous retroviruses by pathogens fits well into the same picture. We discuss these new findings from the viewpoint of the infection hypothesis of AD and offer suggestions for future research.

More than a century after its discovery, Alzheimer’s disease (AD) remains incurable and mysterious. The dominant hypothesis of amyloid cascade has succeeded in explaining the key pathological mechanism, but not its trigger. Amyloid beta has been traditionally considered a pathological peptide, and its physiological functions remain poorly known. These knowledge gaps have contributed to repeated failures of clinical studies. The emerging infectious hypothesis of AD considers central nervous system (CNS) infection the primary trigger of sporadic AD. A closely connected hypothesis claims that amyloid beta is an antimicrobial peptide. In this review, we discuss the available evidence for the involvement of infections in AD, coming from epidemiological studies, post mortem analyses of brain tissue, and experiments in vitro and in vivo. We argue there is no unique “Alzheimer’s germ,” instead, AD is a general reaction of the CNS to chronic infections, in the milieu of an aged immune system. The pathology may become self-sustained even without continuous presence of microbes in the brain. Importantly, the infectious hypothesis leads to testable predictions. Targeting amyloid beta should be ineffective, unless the triggering pathogen and inflammatory response are addressed as well. Meticulous control of selected infections might be the best near-term strategy for AD prevention.

Circulating Chlamydia Trachomatis Antigens in Subjects With Alzheimer's Disease

BACKGROUND/AIM

Chlamydia pneumoniae (C. pneumoniae) is implicated in the pathogenesis of Alzheimer's disease (AD). Chlamydial elementary and reticulate bodies have been identified in tissues from afflicted AD brain regions by electron and immunoelectron microscopy, whereas similar tests of non-AD brains were negative for the bacterium. Studies in mice have shown that C. pneumoniae can rapidly penetrate the central nervous system by entering glia and causing beta amyloid deposition via the nerves between the nasal cavity and the brain, which serve as invasion pathways.

MATERIALS AND METHODS

We used data from the UK Biobank (UKBB) to assess the relationship of chlamydia and AD. Circulating C. pneumoniae antigen measurements were not available, but UKBB data field 23037 held measurements of PorB antigen for Chlamydia trachomatis (C. trachomatis). We used C. trachomatis as a surrogate for C. pneumoniae since serum cross-reactivity to C. trachomatis and C. pneumoniae antigens occurs in patients with documented infection and in healthy children as revealed by microimmunofluorescence and immunoblotting techniques. Single nucleotide polymorphism (SNP) data for rs429358 and rs7412 were used to impute ApoE genotypes.

RESULTS

PorB antigen levels for C. trachomatis were significantly higher in subjects with AD (p=0.007). PorB antigen levels were not related to ApoE genotype (e3e3, e3e4, e4e4) p=0.783. To control for the effects of age, sex, educational level, and apoE genotype, logistic regression analysis was performed. AD was the dependent variable. Independent variables were sqrt PorB antigen for C. trachomatis, age, sex, educational level, apoE genotype. AD odds ratio (OR) increased 1.156 for each unit increase of sqrt PorB antigen for C. trachomatis and the effect was significant (p=0.004).

CONCLUSION

PorB antigens for C. trachomatis being significantly higher in subjects with AD, corroborates previous studies demonstrating that C. pneumoniae inflammation appears to play a role in AD development. AD may result from the reactivation of embryologic processes and pathways silenced at birth. A trigger for the reactivation may be bacterial or viral infections. Further studies are warranted.

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.

Gram-negative bacteria and their lipopolysaccharides in Alzheimer's disease: pathologic roles and therapeutic implications

Alzheimer's disease (AD) is the most serious age-related neurodegenerative disease and causes destructive and irreversible cognitive decline. Failures in the development of therapeutics targeting amyloid-β (Aβ) and tau, principal proteins inducing pathology in AD, suggest a paradigm shift towards the development of new therapeutic targets. The gram-negative bacteria and lipopolysaccharides (LPS) are attractive new targets for AD treatment. Surprisingly, an altered distribution of gram-negative bacteria and their LPS has been reported in AD patients. Moreover, gram-negative bacteria and their LPS have been shown to affect a variety of AD-related pathologies, such as Aβ homeostasis, tau pathology, neuroinflammation, and neurodegeneration. Moreover, therapeutic approaches targeting gram-negative bacteria or gram-negative bacterial molecules have significantly alleviated AD-related pathology and cognitive dysfunction. Despite multiple evidence showing that the gram-negative bacteria and their LPS play a crucial role in AD pathogenesis, the pathogenic mechanisms of gram-negative bacteria and their LPS have not been clarified. Here, we summarize the roles and pathomechanisms of gram-negative bacteria and LPS in AD. Furthermore, we discuss the possibility of using gram-negative bacteria and gram-negative bacterial molecules as novel therapeutic targets and new pathological characteristics for AD.

Perspectives on the Intracellular Bacterium Chlamydia pneumoniae in Late-Onset Dementia

Purpose of Review

Chronic diseases remain a daunting challenge for clinicians and researchers alike. While difficult to completely understand, most chronic diseases, including late-onset dementias, are thought to arise as an interplay between host genetic factors and environmental insults. One of the most diverse and ubiquitous environmental insults centers on infectious agents. Associations of infectious agents with late-onset dementia have taken on heightened importance, including our investigations of infection by the intracellular respiratory bacterium, Chlamydia pneumoniae (Cpn), in late-onset dementia of the Alzheimer’s type.

Recent Findings

Over the last two decades, the relationship of this infection to pathogenesis in late-onset dementia has become much clearer. This clarity has resulted from applying contemporary molecular genetic, biochemical, immunochemical, and cell culture techniques to analysis of human brains, animal models, and relevant in vitro cell culture systems. Data from these studies, taken in aggregate form, now can be applied to evaluation of proof of concept for causation of this infection with late-onset disease. In this evaluation, modifications to the original Koch postulates can be useful for elucidating causation.

Summary

All such relevant studies are outlined and summarized in this review, and they demonstrate the utility of applying modified Koch postulates to the etiology of late-onset dementia of the Alzheimer’s type. Regardless, it is clear that even with strong observational evidence, in combination with application of modifications of Koch’s postulates, we will not be able to conclusively state that Cpn infection is causative for disease pathogenesis in late-onset dementia. Moreover, this conclusion obtains as well for the putative causation of this condition by other pathogens, including herpes simplex virus type 1, Borrelia burgdorferi, and Porphyromonas gingivalis.

Naked-Eye Enumeration of Single Chlamydia pneumoniae Based on Light Scattering of Gold Nanoparticle Probe

Chlamydia pneumoniae is a spherical zoonotic pathogen with a diameter of ∼200 nm, which can lead to a wide range of acute and chronic diseases in human body. Early and reliable on-site detection of C. pneumoniae is the key step to control the spread of the pathogen. However, the lack of a current technology with advantages of rapidity, ultrasensitivity, and convenience limits the implementation of traditional techniques for on-site detection of C. pneumoniae. Herein, we developed a naked-eye counting of C. pneumoniae based on the light scattering properties of gold nanoparticle (GNP) under dark-field microscopy (termed "GNP-labeled dark-field counting strategy"). The recognition of single C. pneumoniae by anti-C. pneumoniae antibodies-functionalized GNP probes with size of 15 nm leads to the formation of wreath-like structure due to the strong scattered light resulted from hundreds of GNP probes binding on one C. pneumoniae under dark-field microscopy. Hundreds of GNP probes can bind to the surface of C. pneumoniae due to the high stability and specificity of the nucleic acid immuno-GNP probes, which generates by the hybridization of DNA-modified GNP with DNA-functionalized antibodies. The limit of detection (LOD) of the GNP-labeled dark-field counting strategy for C. pneumoniae detection in spiked samples or real samples is down to four C. pneumoniae per microliter, which is about 4 times more sensitive than that of quantitative polymerase chain reaction (qPCR). Together with the advantages of the strong light scattering characteristic of aggregated GNPs under dark-field microscopy and the specific identification of functionalized GNP probes, we can detect C. pneumoniae in less than 30 min using a cheap and portable microscope even if the sample contains only a few targets of interest and other species at high concentration. The GNP-labeled dark-field counting strategy meets the demands of rapid detection, low cost, easy to operate, and on-site detection, which paves the way for early and on-site detection of infectious pathogens.

An agent-based model to investigate microbial initiation of Alzheimer's via the olfactory system

BACKGROUND

Alzheimer's disease (AD) is a degenerative brain disease. A novel agent-based modelling framework was developed in NetLogo 3D to provide fundamental insights into the potential mechanisms by which a microbe (eg. Chlamydia pneumoniae) may play a role in late-onset AD. The objective of our initial model is to simulate one possible spatial and temporal pathway of bacterial propagation via the olfactory system, which may then lead to AD symptoms. The model maps the bacteria infecting cells from the nasal cavity and the olfactory epithelium, through the olfactory bulb and into the olfactory cortex and hippocampus regions of the brain.

RESULTS

Based on the set of biological rules, simulated randomized infection by the microbe led to the formation of beta-amyloid (Aβ) plaque and neurofibrillary (NF) tangles as well as caused immune responses. Our initial simulations demonstrated that breathing in C. pneumoniae can result in infection propagation and significant buildup of Aβ plaque and NF tangles in the olfactory cortex and hippocampus. Our model also indicated how mucosal and neural immunity can play a significant role in the pathway considered. Lower immunities, correlated with elderly individuals, had quicker and more Aβ plaque and NF tangle formation counts. In contrast, higher immunities, correlated with younger individuals, demonstrated little to no such formation.

CONCLUSION

The modelling framework provides an organized visual representation of how AD progression may occur via the olfactory system to better understand disease pathogenesis. The model confirms current conclusions in available research but can be easily adjusted to match future evidence and be used by researchers for their own individual purposes. The goal of our initial model is to ultimately guide further hypothesis refinement and experimental testing to better understand the dynamic system interactions present in the etiology and pathogenesis of AD.

Assessment of evidence for or against contributions of Chlamydia pneumoniae infections to Alzheimer's disease etiology

Alzheimer's disease, the most common form of dementia, was first formally described in 1907 yet its etiology has remained elusive. Recent proposals that Aβ peptide may be part of the brain immune response have revived longstanding contention about the possibility of causal relationships between brain pathogens and Alzheimer's disease. Research has focused on infectious pathogens that may colonize the brain such as herpes simplex type I. Some researchers have proposed the respiratory bacteria Chlamydia pneumoniae may also be implicated in Alzheimer's disease, however this remains controversial. This review aims to provide a balanced overview of the current evidence and its limitations and future approaches that may resolve controversies. We discuss the evidence from in vitro, animal and human studies proposed to implicate Chlamydia pneumoniae in Alzheimer's disease and other neurological conditions, the potential mechanisms by which the bacterium may contribute to pathogenesis and limitations of previous studies that may explain the inconsistencies in the literature.

Astrocytes infected with Chlamydia pneumoniae demonstrate altered expression and activity of secretases involved in the generation of β-amyloid found in Alzheimer disease

Background

Epidemiologic studies strongly suggest that the pathophysiology of late-onset Alzheimer disease (AD) versus early-onset AD has environmental rather than genetic causes, thus revealing potentially novel therapeutic targets to limit disease progression. Several studies supporting the “pathogen hypothesis” of AD demonstrate a strong association between pathogens and the production of β-amyloid, the pathologic hallmark of AD. Although the mechanism of pathogen-induced neurodegeneration of AD remains unclear, astrocytes, a key player of the CNS innate immune response and producer/metabolizer of β-amyloid, have been implicated. We hypothesized that Chlamydia pneumoniae infection of human astrocytes alters the expression of the amyloid precursor protein (APP)-processing secretases, ADAM10, BACE1, and PSEN1, to promote β-amyloid formation. Utilizing immunofluorescent microscopy, molecular, and biochemical approaches, these studies explore the role of an intracellular respiratory pathogen, Chlamydia pneumoniae, as an environmental trigger for AD pathology. Human astrocytoma cells in vitro were infected with Chlamydia pneumoniae over the course of 6–72 h. The gene and protein expression, as well as the enzymatic activity of non-amyloidogenic (ADAM10), and pro-amyloidogenic (BACE1 and PSEN1) secretases were qualitatively and quantitatively assessed. In addition, the formation of toxic amyloid products as an outcome of pro-amyloidogenic APP processing was evaluated through various modalities.

Results

Chlamydia pneumoniae infection of human astrocytoma cells promoted the transcriptional upregulation of numerous genes implicated in host neuroinflammation, lipid homeostasis, microtubule function, and APP processing. Relative to that of uninfected astrocytes, BACE1 and PSEN1 protein levels were enhanced by nearly twofold at 48–72 h post-Chlamydia pneumoniae infection. The processing of APP in Chlamydia pneumoniae-infected astrocytes favors the pro-amyloidogenic pathway, as demonstrated by an increase in enzymatic activity of BACE1, while that of ADAM10 was decreased. Fluorescence intensity of β-amyloid and ELISA-quantified levels of soluble-APP by products revealed temporally similar increases, confirming a BACE1/PSEN1-mediated processing of APP.

Conclusions

Our findings suggest that Chlamydia pneumoniae infection of human astrocytes promotes the pro-amyloidogenic pathway of APP processing through the upregulation of expression and activity of β-secretase, upregulated expression of γ-secretase, and decreased activity of α-secretase. These effects of astrocyte infection provide evidence for a direct link between Chlamydia pneumoniae and AD pathology.

Electronic supplementary material

The online version of this article (10.1186/s12868-019-0489-5) contains supplementary material, which is available to authorized users.

Chlamydia pneumoniae: An Etiologic Agent for Late-Onset Dementia

The disease known as late-onset Alzheimer's disease is a neurodegenerative condition recognized as the single most commonform of senile dementia. The condition is sporadic and has been attributed to neuronal damage and loss, both of which have been linked to the accumulation of protein deposits in the brain. Significant progress has been made over the past two decades regarding our overall understanding of the apparently pathogenic entities that arise in the affected brain, both for early-onset disease, which constitutes approximately 5% of all cases, as well as late-onset disease, which constitutes the remainder of cases. Observable neuropathology includes: neurofibrillary tangles, neuropil threads, neuritic senile plaques and often deposits of amyloid around the cerebrovasculature. Although many studies have provided a relatively detailed knowledge of these putatively pathogenic entities, understanding of the events that initiate and support the biological processes generating them and the subsequent observable neuropathology and neurodegeneration remain limited. This is especially true in the case of late-onset disease. Although early-onset Alzheimer's disease has been shown conclusively to have genetic roots, the detailed etiologic initiation of late-onset disease without such genetic origins has remained elusive. Over the last 15 years, current and ongoing work has implicated infection in the etiology and pathogenesis of late-onset dementia. Infectious agents reported to be associated with disease initiation are various, including several viruses and pathogenic bacterial species. We have reported extensively regarding an association between late-onset disease and infection with the intracellular bacterial pathogen Chlamydia pneumoniae. In this article, we review previously published data and recent results that support involvement of this unusual respiratory pathogen in disease induction and development. We further suggest several areas for future research that should elucidate details relating to those processes, and we argue for a change in the designation of the disease based on increased understanding of its clinical attributes.

The human microglial HMC3 cell line: where do we stand? A systematic literature review

Microglia, unique myeloid cells residing in the brain parenchyma, represent the first line of immune defense within the central nervous system. In addition to their immune functions, microglial cells play an important role in other cerebral processes, including the regulation of synaptic architecture and neurogenesis. Chronic microglial activation is regarded as detrimental, and it is considered a pathogenic mechanism common to several neurological disorders. Microglial activation and function have been extensively studied in rodent experimental models, whereas the characterization of human cells has been limited due to the restricted availability of primary sources of human microglia. To overcome this problem, human immortalized microglial cell lines have been developed. The human microglial clone 3 cell line, HMC3, was established in 1995, through SV40-dependent immortalization of human embryonic microglial cells. It has been recently authenticated by the American Type Culture Collection (ATCC®) and distributed under the name of HMC3 (ATCC®CRL-3304). The HMC3 cells have been used in six research studies, two of which also indicated by ATCC® as reference articles. However, a more accurate literature revision suggests that clone 3 was initially distributed under the name of CHME3. In this regard, several studies have been published, thus contributing to a more extensive characterization of this cell line. Remarkably, the same cell line has been used in different laboratories with other denominations, i.e., CHME-5 cells and C13-NJ cells. In view of the fact that "being now authenticated by ATCC®" may imply a wider distribution of the cells, we aimed at reviewing data obtained with the human microglia cell line clone 3, making the readers aware of this complicated nomenclature. In addition, we also included original data, generated in our laboratory with the HMC3 (ATCC®CRL-3304) cells, providing information on the current state of the culture together with supplementary details on the culturing procedures to obtain and maintain viable cells.

The Physiological Roles of Amyloid-β Peptide Hint at New Ways to Treat Alzheimer's Disease

Amyloid-ß (Aß) is best known as the misfolded peptide that is involved in the pathogenesis of Alzheimer's disease (AD), and it is currently the primary therapeutic target in attempts to arrest the course of this disease. This notoriety has overshadowed evidence that Aß serves several important physiological functions. Aß is present throughout the lifespan, it has been found in all vertebrates examined thus far, and its molecular sequence shows a high degree of conservation. These features are typical of a factor that contributes significantly to biological fitness, and this suggestion has been supported by evidence of functions that are beneficial for the brain. The putative roles of Aß include protecting the body from infections, repairing leaks in the blood-brain barrier, promoting recovery from injury, and regulating synaptic function. Evidence for these beneficial roles comes from in vitro and in vivo studies, which have shown that the cellular production of Aß rapidly increases in response to a physiological challenge and often diminishes upon recovery. These roles are further supported by the adverse outcomes of clinical trials that have attempted to deplete Aß in order to treat AD. We suggest that anti-Aß therapies will produce fewer adverse effects if the known triggers of Aß deposition (e.g., pathogens, hypertension, and diabetes) are addressed first.

Chlamydia pneumoniae Infection and Inflammatory Diseases

Chlamydia pneumoniae, an obligate intracellular bacterial pathogen, has long been investigated as a potential developmental or exacerbating factor in various pathologies. Its unique lifestyle and ability to disseminate throughout the host while persisting in relative safety from the immune response has placed this obligate intracellular pathogen in the crosshairs as a potentially mitigating factor in chronic inflammatory diseases. Many animal model and human correlative studies have been performed to confirm or deny a role for C. pneumoniae infection in these disorders. In some cases, antibiotic clinical trials were conducted to prove a link between bacterial infections and atherosclerosis. In this review, we detail the latest information regarding the potential role that C. pneumoniae infection may have in chronic inflammatory diseases.

Phylogenetic analysis of human Chlamydia pneumoniae strains reveals a distinct Australian indigenous clade that predates European exploration of the continent

Background

The obligate intracellular bacterium Chlamydia pneumoniae is a common respiratory pathogen, which has been found in a range of hosts including humans, marsupials and amphibians. Whole genome comparisons of human C. pneumoniae have previously highlighted a highly conserved nucleotide sequence, with minor but key polymorphisms and additional coding capacity when human and animal strains are compared.

Results

In this study, we sequenced three Australian human C. pneumoniae strains, two of which were isolated from patients in remote indigenous communities, and compared them to all available C. pneumoniae genomes. Our study demonstrated a phylogenetically distinct human C. pneumoniae clade containing the two indigenous Australian strains, with estimates that the most recent common ancestor of these strains predates the arrival of European settlers to Australia. We describe several polymorphisms characteristic to these strains, some of which are similar in sequence to animal C. pneumoniae strains, as well as evidence to suggest that several recombination events have shaped these distinct strains.

Conclusions

Our study reveals a greater sequence diversity amongst both human and animal C. pneumoniae strains, and suggests that a wider range of strains may be circulating in the human population than current sampling indicates.

Can oral infection be a risk factor for Alzheimer's disease?

Alzheimer's disease (AD) is a scourge of longevity that will drain enormous resources from public health budgets in the future. Currently, there is no diagnostic biomarker and/or treatment for this most common form of dementia in humans. AD can be of early familial-onset or sporadic with a late-onset. Apart from the two main hallmarks, amyloid-beta and neurofibrillary tangles, inflammation is a characteristic feature of AD neuropathology. Inflammation may be caused by a local central nervous system insult and/or by peripheral infections. Numerous microorganisms are suspected in AD brains ranging from bacteria (mainly oral and non-oral Treponema species), viruses (herpes simplex type I), and yeasts (Candida species). A causal relationship between periodontal pathogens and non-oral Treponema species of bacteria has been proposed via the amyloid-beta and inflammatory links. Periodontitis constitutes a peripheral oral infection that can provide the brain with intact bacteria and virulence factors and inflammatory mediators due to daily, transient bacteremias. If and when genetic risk factors meet environmental risk factors in the brain, disease is expressed, in which neurocognition may be impacted, leading to the development of dementia. To achieve the goal of finding a diagnostic biomarker and possible prophylactic treatment for AD, there is an initial need to solve the etiological puzzle contributing to its pathogenesis. This review therefore addresses oral infection as the plausible etiology of late-onset AD (LOAD).

Dendrimer-enabled transformation of Chlamydia trachomatis

Lack of a system for genetic manipulation of Chlamydia trachomatis has been a key challenge to advancing understanding the molecular genetic basis of virulence for this bacterial pathogen. We developed a non-viral, dendrimer-enabled system for transformation of this organism and used it to characterize the effects of inserting the common 7.5 kbp chlamydial plasmid into strain L2(25667R), a C. trachomatis isolate lacking it. The plasmid was cloned in pUC19 and the clone complexed to polyamidoamine dendrimers, producing ∼83 nm spherical particles. Nearly confluent McCoy cell cultures were infected with L2(25667R) and reference strain L2(434). At 16 h post-infection, medium was replaced with dendrimer-plasmid complexes in medium lacking additives (L2(25667R)) or with additive-free medium alone (L2(434)). Three h later complexes/buffer were removed, and medium was replaced; cultures were harvested at various times post-transformation for analyses. Real time PCR and RT-PCR of nucleic acids from transformed cultures demonstrated plasmid replication and gene expression. A previous report indicated that one or more plasmid-encoded product govern(s) transcription of the glycogen synthase gene (glgA) in standard strains. In L2(25667R) the gene is not expressed, but transformants of that strain given the cloned chlamydial plasmid increase glgA expression, as does L2(434). The cloned plasmid is retained, replicated, and expressed in transformants over at least 5 passages, and GFP is expressed when transformed into growing L2(25667R). This transformation system will allow study of chlamydial gene function in pathogenesis.

Dendrimer-enabled DNA delivery and transformation of Chlamydia pneumoniae

The chlamydiae are important human pathogens. Lack of a genetic manipulation system has impeded understanding of the molecular bases of virulence for these bacteria. We developed a dendrimer-enabled system for transformation of chlamydiae and used it to characterize the effects of inserting the C. trachomatis plasmid into C. pneumoniae, which lacks any plasmids. The plasmid was cloned into modified yeast vector pEG(KG) and the clone complexed to polyamidoamine dendrimers, producing 50-100 nm spherical particles. HEp-2 cell cultures were infected with C. pneumoniae strain AR-39. Twenty-four hours later, medium was replaced for 3 hours with dendrimer-plasmid complexes, then removed and the medium replaced. Cultures were harvested at various times post-transformation. Real-time PCR and RT-PCR of nucleic acids from transformed cultures demonstrated plasmid replication and gene expression. The cloned plasmid was replicated and expressed in transformants over 5 passages. This system will allow study of chlamydial gene function, allowing development of novel dendrimer-based therapies.

FROM THE CLINICAL EDITOR

This team of investigators developed a dendrimer-enabled system for transformation of chlamydiae and successfully utilized it to characterize the effects of inserting the C. trachomatis plasmid into C. pneumonia. This system will allow study of chlamydial gene function, allowing development of novel dendrimer-based therapies.

Can infections cause Alzheimer's disease?

Late-onset Alzheimer's disease (AD) is the most prevalent cause of dementia among older adults, yet more than a century of research has not determined why this disease develops. One prevailing hypothesis is that late-onset AD is caused by infectious pathogens, an idea widely studied in both humans and experimental animal models. This review examines the infectious AD etiology hypothesis and summarizes existing evidence associating infectious agents with AD in humans. The various mechanisms through which different clinical and subclinical infections could cause or promote the progression of AD are considered, as is the concordance between putative infectious agents and the epidemiology of AD. We searched the PubMed, Web of Science, and EBSCO databases for research articles pertaining to infections and AD and systematically reviewed the evidence linking specific infectious pathogens to AD. The evidence compiled from the literature linking AD to an infectious cause is inconclusive, but the amount of evidence suggestive of an association is too substantial to ignore. Epidemiologic, clinical, and basic science studies that could improve on current understanding of the associations between AD and infections and possibly uncover ways to control this highly prevalent and debilitating disease are suggested.

Chlamydia pneumoniae: modern insights into an ancient pathogen

Chlamydia pneumoniae is an enigmatic human and animal pathogen. Originally discovered in association with acute human respiratory disease, it is now associated with a remarkably wide range of chronic diseases as well as having a cosmopolitan distribution within the animal kingdom. Molecular typing studies suggest that animal strains are ancestral to human strains and that C. pneumoniae crossed from animals to humans as the result of at least one relatively recent zoonotic event. Whole genome analyses appear to support this concept - the human strains are highly conserved whereas the single animal strain that has been fully sequenced has a larger genome with several notable differences. When compared to the other, better known chlamydial species that is implicated in human infection, Chlamydia trachomatis, C. pneumoniae demonstrates pertinent differences in its cell biology, development, and genome structure. Here, we examine the characteristic facets of C. pneumoniae biology, offering insights into the diversity and evolution of this silent and ancient pathogen.

Chlamydia infection status, genotype, and age-related macular degeneration

PURPOSE

To evaluate whether Chlamydia (C.) infections are associated with age-related macular degeneration (AMD) and to assess if this association is influenced by the complement factor H (CFH) Y402H or the high temperature requirement A serine peptidase 1 (HTRA1) rs11200638 risk genotypes.

METHODS

One hundred ninety-nine AMD patients with early and late forms of the disease and 100 unaffected controls, at least 50 years old were included in the study. Patients in the AMD and control groups were selected based on known CFH Y402H variant genotype status (one third homozygous CC, one third heterozygous CT, and one third wild-type TT). Plasma from all patients and controls was tested for C. pneumoniae, C. trachomatis, and C. psittaci IgG seropositivity using a micro-immunofluorescent assay to establish previous infection status. Assays were conducted blind to risk genotypes and the results analyzed using univariate and multivariate (logistic regression) analysis.

RESULTS

IgG seropositivity to C. pneumoniae was most prevalent (69.2%, n=207), followed by C. trachomatis (7.4%, n=22) and C. psittaci (3.3%, n=10). No association was found between each of the three Chlamydia species IgG seropositivity and AMD status or severity (early/late). There was also no significant association between Chlamydia species IgG seropositivity and AMD status or severity, in patients carrying at least one CFH Y402H risk allele (C) or HTRA1 rs11200638 risk allele (A), with univariate or logistic regression analysis.

CONCLUSIONS

Chlamydia infection status does not appear to be associated with AMD status or severity. The presence of CFH Y402H and HTRA1 rs11200638 risk genotypes does not alter this negative association.

Towards the prevention of potential aluminum toxic effects and an effective treatment for Alzheimer's disease

In 1991, treatment with low dose intramuscular desferrioxamine (DFO), a trivalent chelator that can remove excessive iron and/or aluminum from the body, was reported to slow the progression of Alzheimer's disease (AD) by a factor of two. Twenty years later this promising trial has not been followed up and why this treatment worked still is not clear. In this critical interdisciplinary review, we provide an overview of the complexities of AD and involvement of metal ions, and revisit the neglected DFO trial. We discuss research done by us and others that is helping to explain involvement of metal ion catalyzed production of reactive oxygen species in the pathogenesis of AD, and emerging strategies for inhibition of metal-ion toxicity. Highlighted are insights to be considered in the quests to prevent potentially toxic effects of aluminum toxicity and prevention and intervention in AD.

Emerging roles of pathogens in Alzheimer disease

Chronic spirochetal infection can cause slowly progressive dementia, cortical atrophy and amyloid deposition in the atrophic form of general paresis. There is a significant association between Alzheimer disease (AD) and various types of spirochete (including the periodontal pathogen Treponemas and Borrelia burgdorferi), and other pathogens such as Chlamydophyla pneumoniae and herpes simplex virus type-1 (HSV-1). Exposure of mammalian neuronal and glial cells and organotypic cultures to spirochetes reproduces the biological and pathological hallmarks of AD. Senile-plaque-like beta amyloid (Aβ) deposits are also observed in mice following inhalation of C. pneumoniae in vivo, and Aβ accumulation and phosphorylation of tau is induced in neurons by HSV-1 in vitro and in vivo. Specific bacterial ligands, and bacterial and viral DNA and RNA all increase the expression of proinflammatory molecules, which activates the innate and adaptive immune systems. Evasion of pathogens from destruction by the host immune reactions leads to persistent infection, chronic inflammation, neuronal destruction and Aβ deposition. Aβ has been shown to be a pore-forming antimicrobial peptide, indicating that Aβ accumulation might be a response to infection. Global attention and action is needed to support this emerging field of research because dementia might be prevented by combined antibiotic, antiviral and anti-inflammatory therapy.

Immunohistological detection of Chlamydia pneumoniae in the Alzheimer's disease brain

Background

Sporadic late-onset Alzheimer's disease (AD) appears to evolve from an interplay between genetic and environmental factors. One environmental factor that continues to be of great interest is that of Chlamydia pneumoniae infection and its association with late-onset disease. Detection of this organism in clinical and autopsy samples has proved challenging using a variety of molecular and histological techniques. Our current investigation utilized immunohistochemistry with a battery of commercially available anti-C. pneumoniae antibodies to determine whether C. pneumoniae was present in areas typically associated with AD neuropathology from 5 AD and 5 non-AD control brains.

Results

Immunoreactivity for C. pneumoniae antigens was observed both intracellularly in neurons, neuroglia, endothelial cells, and peri-endothelial cells, and extracellularly in the frontal and temporal cortices of the AD brain with multiple C. pneumoniae-specific antibodies. This immunoreactivity was seen in regions of amyloid deposition as revealed by immunolabeling with two different anti-beta amyloid antibodies. Thioflavin S staining, overlaid with C. pneumoniae immunolabeling, demonstrated no direct co-localization of the organism and amyloid plaques. Further, the specificity of C. pneumoniae labeling of AD brain sections was demonstrated using C. pneumoniae antibodies pre-absorbed against amyloid β 1-40 and 1-42 peptides.

Conclusions

Anti-C. pneumoniae antibodies, obtained commercially, identified both typical intracellular and atypical extracellular C. pneumoniae antigens in frontal and temporal cortices of the AD brain. C. pneumoniae, amyloid deposits, and neurofibrillary tangles were present in the same regions of the brain in apposition to one another. Although additional studies are required to conclusively characterize the nature of Chlamydial immunoreactivity in the AD brain, these results further implicate C. pneumoniae infection with the pathogenesis of Alzheimer's disease.

Chlamydia pneumoniae-specific intrathecal oligoclonal antibody response is predominantly detected in a subset of multiple sclerosis patients with progressive forms

The purpose of this study was to verify the actual involvement of Chlamydia pneumoniae in multiple sclerosis (MS) by the evaluation of its specific intrathecal humoral immune response in MS. We measured by enzyme-linked immunosorbent assay (ELISA) technique cerebrospinal fluid (CSF) and serum levels of anti-C. pneumoniae immunoglobulin G (IgG) in 27 relapsing-remitting (RR), 9 secondary progressive (SP), and 5 primary progressive (PP) MS patients, grouped according to clinical and magnetic resonance imaging (MRI) evidence of disease activity. Twenty-one patients with other inflammatory neurological disorders (OIND) and 21 with noninflammatory neurological disorders (NIND) were used as controls. Quantitative intrathecal synthesis of anti-C. pneumoniae IgG was determined by antibody-specific index (ASI), whereas the presence of C. pneumoniae-specific CSF oligoclonal IgG bands was assessed by antigen-specific immunoblotting. ASI values indicative of C. pneumoniae-specific intrathecal IgG synthesis were present in a small proportion of MS (29.3%), OIND (33.3%), and NIND (4.8%) patients and were significantly more frequent (P < .05) in total MS and in OIND than in NIND and in SP (P < .01) and PP MS (P < .05) than in RR MS. C. pneumoniae-specific CSF-restricted OCB were detected only in three SP, one PP, and one RR MS patients. These findings suggest that an intrathecal production of anti-C. pneumoniae IgG is part of humoral polyreactivity driven by MS chronic brain inflammation. However, an intrathecal release of C. pneumoniae-specific oligoclonal IgG can occur in a subset of patients with MS progressive forms in whom a C. pneumoniae-persistent brain infection may play a pathogenetic role.

Chlamydia pneumoniae is genetically diverse in animals and appears to have crossed the host barrier to humans on (at least) two occasions

Chlamydia pneumoniae is a common human and animal pathogen associated with a wide range of diseases. Since the first isolation of C. pneumoniae TWAR in 1965, all human isolates have been essentially clonal, providing little evolutionary insight. To address this gap, we investigated the genetic diversity of 30 isolates from diverse geographical locations, from both human and animal origin (amphibian, reptilian, equine and marsupial). Based on the level of variation that we observed at 23 discreet gene loci, it was clearly evident that the animal isolates were more diverse than the isolates of human origin. Furthermore, we show that C. pneumoniae isolates could be grouped into five major genotypes, A-E, with A, B, D and E genotypes linked by geographical location, whereas genotype C was found across multiple continents. Our evidence strongly supports two separate animal-to-human cross species transfer events in the evolutionary history of this pathogen. The C. pneumoniae human genotype identified in the USA, Canada, Taiwan, Iran, Japan, Korea and Australia (non-Indigenous) most likely originated from a single amphibian or reptilian lineage, which appears to have been previously geographically widespread. We identified a separate human lineage present in two Australian Indigenous isolates (independent geographical locations). This lineage is distinct and is present in Australian amphibians as well as a range of Australian marsupials.

Chlamydia pneumoniae is an intracellular bacterial pathogen with an extremely diverse host range (humans, amphibians, reptiles and marsupials). We selected 23 target genes in order to investigate genetic diversity: seven of these had been lost or gained by C. pneumoniae, a further six were conserved, four were polymorphic (defined by greater than 20 SNPs per 1 kbp; in this study), and six were truncated or length polymorphic in one strain or the other. Our research highlights that C. pneumoniae animal isolates are much more genetically diverse than C. pneumoniae human isolates, and have crossed the host barrier to humans on at least two occasions. Our study provides new insights into the evolution of this complex pathogen.

Chlamydia pneumoniae infection and Alzheimer's disease: a connection to remember?

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, whereby it is customary to distinguish between early familial FAD and late-onset AD (LOAD). The development of LOAD, the most prevalent form of AD, is believed to be a multifactorial process that may also involve infections with bacterial or viral pathogens. After the first report on the presence of Chlamydia pneumoniae (Cpn) in brains of patients with AD appeared in 1998, this bacterium has most often been implicated in AD pathogenesis. However, while some studies demonstrate a clear association between Cpn infection and AD, others have failed to confirm these findings. This might be due to heterogeneity of the specimens analyzed and lack of standardized detection methods. Additionally, non-availability of suitable chlamydial infection models severely hampers research in the field. In this review, we will critically discuss the possible role of Cpn in the pathogenesis of LOAD in light of the available data. We will also present three mutually non-exclusive hypotheses how Cpn might contribute to the pathogenesis of AD.

Chlamydophila pneumoniae Infection and Its Role in Neurological Disorders

Chlamydophila pneumoniae is an intracellular pathogen responsible for a number of different acute and chronic infections. The recent deepening of knowledge on the biology and the use of increasingly more sensitive and specific molecular techniques has allowed demonstration of C. pneumoniae in a large number of persons suffering from different diseases including cardiovascular (atherosclerosis and stroke) and central nervous system (CNS) disorders. Despite this, many important issues remain unanswered with regard to the role that C. pneumoniae may play in initiating atheroma or in the progression of the disease. A growing body of evidence concerns the involvement of this pathogen in chronic neurological disorders and particularly in Alzheimer's disease (AD) and Multiple Sclerosis (MS). Monocytes may traffic C. pneumoniae across the blood-brain-barrier, shed the organism in the CNS and induce neuroinflammation. The demonstration of C. pneumoniae by histopathological, molecular and culture techniques in the late-onset AD dementia has suggested a relationship between CNS infection with C. pneumoniae and the AD neuropathogenesis. In particular subsets of MS patients, C. pneumoniae could induce a chronic persistent brain infection acting as a cofactor in the development of the disease. The role of Chlamydia in the pathogenesis of mental or neurobehavioral disorders including schizophrenia and autism is uncertain and fragmentary and will require further confirmation.