Blue-green algae or cyanobacteria in the intestinal micro-flora may produce neurotoxins such as Beta-N-Methylamino-L-Alanine (BMAA) which may be related to development of amyotrophic lateral sclerosis, Alzheimer's disease and Parkinson-Dementia-Complex in humans and Equine Motor Neuron Disease in horses

The connection between gut microbiota and its metabolites with neurodegenerative diseases in humans

The aging of populations is a global phenomenon that follows a possible increase in the incidence of neurodegenerative diseases. Alzheimer's, Parkinson's, Multiple Sclerosis, Amyotrophic Lateral Sclerosis, and Huntington's diseases are some neurodegenerative disorders that aging could initiate or aggravate. Recent research has indicated that intestinal microbiota dysbiosis can trigger metabolism and brain functioning, contributing to the etiopathogenesis of those neurodegenerative diseases. The intestinal microbiota and its metabolites show significant functions in various aspects, such as the immune system modulation (development and maturation), the maintenance of the intestinal barrier integrity, the modulation of neuromuscular functions in the intestine, and the facilitation of essential metabolic processes for both the microbiota and humans. The primary evidence supporting the connection between intestinal microbiota and its metabolites with neurodegenerative diseases are epidemiological observations and animal models experimentation. This paper reviews up-to-date evidence on the correlation between the microbiota-gut-brain axis and neurodegenerative diseases, with a specially focus on gut metabolites. Dysbiosis can increase inflammatory cytokines and bacterial metabolites, altering intestinal and blood-brain barrier permeability and causing neuroinflammation, thus facilitating the pathogenesis of neurodegenerative diseases. Clinical data supporting this evidence still needs to be improved. Most of the works found are descriptive and associated with the presence of phyla or species of bacteria with neurodegenerative diseases. Despite the limitations of recent research, the potential for elucidating clinical questions that have thus far eluded clarification within prevailing pathophysiological frameworks of health and disease is promising through investigation of the interplay between the host and microbiota.

Blue Green Algae

Blue green algae cyanotoxins have become increasingly more prevalent due to environmental, industrial, and agricultural changes that promote their growth into harmful algal blooms. Animals are usually exposed via water used for drinking or bathing, though specific cases related to equines are very limited. The toxic dose for horses has not been determined, and currently only experimental data in other animals can be relied upon to aid in case interpretation and treatment. Treatment is mostly limited to supportive care, and preventative control methods to limit exposures are more likely to aid in animal health until more research has been performed.

Gut Symptoms, Gut Dysbiosis and Gut-Derived Toxins in ALS

Many pathogenetic mechanisms have been proposed for amyotrophic lateral sclerosis (ALS). Recently, there have been emerging suggestions of a possible role for the gut microbiota. Gut microbiota have a range of functions and could influence ALS by several mechanisms. Here, we review the possible role of gut-derived neurotoxins/excitotoxins. We review the evidence of gut symptoms and gut dysbiosis in ALS. We then examine a possible role for gut-derived toxins by reviewing the evidence that these molecules are toxic to the central nervous system, evidence of their association with ALS, the existence of biochemical pathways by which these molecules could be produced by the gut microbiota and existence of mechanisms of transport from the gut to the blood and brain. We then present evidence that there are increased levels of these toxins in the blood of some ALS patients. We review the effects of therapies that attempt to alter the gut microbiota or ameliorate the biochemical effects of gut toxins. It is possible that gut dysbiosis contributes to elevated levels of toxins and that these could potentially contribute to ALS pathogenesis, but more work is required.

Alzheimer's Disease: Models and Molecular Mechanisms Informing Disease and Treatments

Alzheimer's Disease (AD) is a complex neurodegenerative disease resulting in progressive loss of memory, language and motor abilities caused by cortical and hippocampal degeneration. This review captures the landscape of understanding of AD pathology, diagnostics, and current therapies. Two major mechanisms direct AD pathology: (1) accumulation of amyloid β (Aβ) plaque and (2) tau-derived neurofibrillary tangles (NFT). The most common variants in the Aβ pathway in APP, PSEN1, and PSEN2 are largely responsible for early-onset AD (EOAD), while MAPT, APOE, TREM2 and ABCA7 have a modifying effect on late-onset AD (LOAD). More recent studies implicate chaperone proteins and Aβ degrading proteins in AD. Several tests, such as cognitive function, brain imaging, and cerebral spinal fluid (CSF) and blood tests, are used for AD diagnosis. Additionally, several biomarkers seem to have a unique AD specific combination of expression and could potentially be used in improved, less invasive diagnostics. In addition to genetic perturbations, environmental influences, such as altered gut microbiome signatures, affect AD. Effective AD treatments have been challenging to develop. Currently, there are several FDA approved drugs (cholinesterase inhibitors, Aß-targeting antibodies and an NMDA antagonist) that could mitigate AD rate of decline and symptoms of distress.

Understanding the Gut-Brain Axis and Its Therapeutic Implications for Neurodegenerative Disorders

The gut-brain axis (GBA) is a complex bidirectional communication network connecting the gut and brain. It involves neural, immune, and endocrine communication pathways between the gastrointestinal (GI) tract and the central nervous system (CNS). Perturbations of the GBA have been reported in many neurodegenerative disorders (NDDs), such as Alzheimer's disease (AD), Parkinson's disease (PD), and amyotrophic lateral sclerosis (ALS), among others, suggesting a possible role in disease pathogenesis. The gut microbiota is a pivotal component of the GBA, and alterations in its composition, known as gut dysbiosis, have been associated with GBA dysfunction and neurodegeneration. The gut microbiota might influence the homeostasis of the CNS by modulating the immune system and, more directly, regulating the production of molecules and metabolites that influence the nervous and endocrine systems, making it a potential therapeutic target. Preclinical trials manipulating microbial composition through dietary intervention, probiotic and prebiotic supplementation, and fecal microbial transplantation (FMT) have provided promising outcomes. However, its clear mechanism is not well understood, and the results are not always consistent. Here, we provide an overview of the major components and communication pathways of the GBA, as well as therapeutic approaches targeting the GBA to ameliorate NDDs.

Lewy bodies, iron, inflammation and neuromelanin: pathological aspects underlying Parkinson's disease

Since the description of some peculiar symptoms by James Parkinson in 1817, attempts have been made to define its cause or at least to enlighten the pathology of "Parkinson's disease (PD)." The vast majority of PD subtypes and most cases of sporadic PD share Lewy bodies (LBs) as a characteristic pathological hallmark. However, the processes underlying LBs generation and its causal triggers are still unknown. ɑ-Synuclein (ɑ-syn, encoded by the SNCA gene) is a major component of LBs, and SNCA missense mutations or duplications/triplications are causal for rare hereditary forms of PD. Thus, it is imperative to study ɑ-syn protein and its pathology, including oligomerization, fibril formation, aggregation, and spreading mechanisms. Furthermore, there are synergistic effects in the underlying pathogenic mechanisms of PD, and multiple factors-contributing with different ratios-appear to be causal pathological triggers and progression factors. For example, oxidative stress, reduced antioxidative capacity, mitochondrial dysfunction, and proteasomal disturbances have each been suggested to be causal for ɑ-syn fibril formation and aggregation and to contribute to neuroinflammation and neural cell death. Aging is also a major risk factor for PD. Iron, as well as neuromelanin (NM), show age-dependent increases, and iron is significantly increased in the Parkinsonian substantia nigra (SN). Iron-induced pathological mechanisms include changes of the molecular structure of ɑ-syn. However, more recent PD research demonstrates that (i) LBs are detected not only in dopaminergic neurons and glia but in various neurotransmitter systems, (ii) sympathetic nerve fibres degenerate first, and (iii) at least in "brain-first" cases dopaminergic deficiency is evident before pathology induced by iron and NM. These recent findings support that the ɑ-syn/LBs pathology as well as iron- and NM-induced pathology in "brain-first" cases are important facts of PD pathology and via their interaction potentiate the disease process in the SN. As such, multifactorial toxic processes posted on a personal genetic risk are assumed to be causal for the neurodegenerative processes underlying PD. Differences in ratios of multiple factors and their spatiotemporal development, and the fact that common triggers of PD are hard to identify, imply the existence of several phenotypical subtypes, which is supported by arguments from both the "bottom-up/dual-hit" and "brain-first" models. Therapeutic strategies are necessary to avoid single initiation triggers leading to PD.

Short Term Effect of Ivermectin on the Bacterial Microbiota from Fecal Samples in Chinchillas (Chinchilla lanigera)

The gastrointestinal microbiota plays an important role in health of the host animals and the detrimental influence of pharmaceutical treatment on the fecal microbiota receives an increasing concern. The clinical use of ivermectin on chinchillas has not yet been evaluated. The purpose of our study was to assess the influence of ivermectin injection on the fecal bacterial microbiota of chinchillas. A with-in subject, before and after study was performed on 10 clinically healthy chinchillas during a 14-day period, all chinchillas received the same ivermectin treatment, and the microbiota from their fecal samples before and after administration were compared as two experimental groups. Fecal samples were collected on day 0 (before ivermectin administration) and day 14 (post ivermectin administration). Fecal bacterial microbiota was analyzed by bacterial 16S rRNA gene sequencing. No clinical abnormalities were observed post subcutaneous administration of ivermectin. No significant alteration was found in the abundance and diversity of fecal bacterial microbiota after treatment, but the dominant position of some bacterial species changed. In conclusion, ivermectin administration was associated with minimal alternations of the fecal bacterial microbiota in healthy chinchillas, and these changes had no observed negative effect on general health of chinchillas in short term.

Application of High-Throughput Sequencing (HTS) to Enhance the Well-Being of an Endangered Species (Malayan Tapir): Characterization of Gut Microbiome Using MG-RAST

The Tapirus indicus, also known as Malayan tapir, has been listed as a rapidly declining animal species in the past decades, along with being declared and categorized as an endangered species by the International Union for Conservation of Nature (IUCN) 2016. This tapir species is geographically distributed across several countries in Southeast Asia such as Peninsular Malaysia, Indonesia (Sumatra), South Thailand, and Myanmar. Amongst these countries, the Peninsula Malaysia forest is recorded to contain the highest number of Malayan tapir population. Unfortunately, in the past decades, the population of Malayan tapirs has declined swiftly due to serious deforestation, habitat fragmentation, and heavy vehicle accidents during road crossings at forest routes. Concerned by this predicament, the Department of Wildlife and National Parks (DWNP) Peninsular Malaysia collaborated with a few local universities to conduct various studies aimed at increasing the population number of tapirs in Malaysia. Several studies were conducted with the aim of enhancing the well-being of tapirs in captivity. Veterinarians face problems when it comes to selecting healthy and suitable tapirs for breeding programs at conservation centers. Conventional molecular methods using high-throughput sequencing provides a solution in determining the health condition of Malayan tapirs using the Next-Generation Sequencing (NGS) technology. Unaware by most, gut microbiome plays an important role in determining the health condition of an organism by various aspects: (1) digestion control; (2) benefiting the immune system; and (3) playing a role as a "second brain." Commensal gut bacterial communities (microbiomes) are predicted to influence organism health and disease. Imbalance of unhealthy and healthy microbes in the gut may contribute to weight gain, high blood sugar, high cholesterol, and other disorders. In infancy, neonatal gut microbiomes are colonized with maternal and environmental flora, and mature toward a stable composition in two to three years. Interactions between the microorganism communities and the host allow for the establishment of microbiological roles. Identifying the core microbiome(s) are essential in the prediction of diseases and changes in environmental behavior of microorganisms. The dataset of 16S rRNA amplicon sequencing of Malayan tapir was deposited in the MG-RAST portal. Parameters such as quality control, taxonomic prediction (unknown and predicted), diversity (rarefaction), and diversity (alpha) were analyzed using sequencing approaches (Amplicon sequencing). Comparisons of parameters, according to the type of sequencing, showed significant differences, except for the prediction variable. In the Amplicon sequencing datasets, the parameters Rarefaction and Unknown had the highest correlation, while Alpha and Predicted had the lowest. Firmicutes, Bacteroidetes, Proteobacteria, Bacilli, and Bacteroidia were the most representative genera in Malayan tapir amplicon sequences, which indicated that most of the tapirs were healthy. However, continuous assessment to maintain the well-being of tapir for long term is still required. This chapter focuses on the introduction of 16S rRNA amplicon metagenomics in analyzing Malayan tapir gut microbiome dataset.

The Role of Gut Microbiota in the Pathogenesis of Alzheimer’s Disease

As a degenerative disease of the central nervous system, Alzheimer’s disease (AD) is featured by mental and behavioral dysfunction, and progressive memory loss, which is the most common type of dementia. The incidence of AD is increasing as life expectancy is prolonged, but the pathogenesis of AD remains largely unknown. Recently, the role of gut microbiota in the pathogenesis of AD has drawn increasing attention. The composition of gut microbiota varies across age groups, and the changes in the microbiota metabolites may influence the central nervous system via the brain-gut axis. So far, it has been confirmed that gut bacteria are involved in various pathogenic mechanisms of AD, including amyloid β-protein deposition, Tau protein hyperphosphorylation, neuroinflammation, oxidative stress injury, increased blood-brain barrier permeability, neurotransmitter imbalance, reduced generation of brain-derived neurotrophic factor, and insulin resistance. An important direction of research is to investigate the regulation of gut microbiota for the prevention and treatment of AD.

Non-Proteinogenic Amino Acid β-N-Methylamino-L-Alanine (BMAA): Bioactivity and Ecological Significance

Research interest in a non-protein amino acid β-N-methylamino-L-alanine (BMAA) arose due to the discovery of a connection between exposure to BMAA and the occurrence of neurodegenerative diseases. Previous reviews on this topic either considered BMAA as a risk factor for neurodegenerative diseases or focused on the problems of detecting BMAA in various environmental samples. Our review is devoted to a wide range of fundamental biological problems related to BMAA, including the molecular mechanisms of biological activity of BMAA and the complex relationships between producers of BMAA and the environment in various natural ecosystems. At the beginning, we briefly recall the most important facts about the producers of BMAA (cyanobacteria, microalgae, and bacteria), the pathways of BMAA biosynthesis, and reliable methods of identification of BMAA. The main distinctive feature of our review is a detailed examination of the molecular mechanisms underlying the toxicity of BMAA to living cells. A brand new aspect, not previously discussed in any reviews, is the effect of BMAA on cyanobacterial cells. These recent studies, conducted using transcriptomics and proteomics, revealed potent regulatory effects of BMAA on the basic metabolism and cell development of these ancient photoautotrophic prokaryotes. Exogenous BMAA strongly influences cell differentiation and primary metabolic processes in cyanobacteria, such as nitrogen fixation, photosynthesis, carbon fixation, and various biosynthetic processes involving 2-oxoglutarate and glutamate. Cyanobacteria were found to be more sensitive to exogenous BMAA under nitrogen-limited growth conditions. We suggest a hypothesis that this toxic diaminoacid can be used by phytoplankton organisms as a possible allelopathic tool for controlling the population of cyanobacterial cells during a period of intense competition for nitrogen and other resources in various ecosystems.

The Role of Nutritional Factors in the Modulation of the Composition of the Gut Microbiota in People with Autoimmune Diabetes

Type 1 diabetes mellitus (T1DM) is a disease marked by oxidative stress, chronic inflammation, and the presence of autoantibodies. The gut microbiota has been shown to be involved in the alleviation of oxidative stress and inflammation as well as strengthening immunity, thus its' possible involvement in the pathogenesis of T1DM has been highlighted. The goal of the present study is to analyze information on the relationship between the structure of the intestinal microbiome and the occurrence of T1DM. The modification of the intestinal microbiota can increase the proportion of SCFA-producing bacteria, which could in turn be effective in the prevention and/or treatment of T1DM. The increased daily intake of soluble and non-soluble fibers, as well as the inclusion of pro-biotics, prebiotics, herbs, spices, and teas that are sources of phytobiotics, in the diet, could be important in improving the composition and activity of the microbiota and thus in the prevention of metabolic disorders. Understanding how the microbiota interacts with immune cells to create immune tolerance could enable the development of new therapeutic strategies for T1DM and improve the quality of life of people with T1DM.

Non-Photosynthetic Melainabacteria (Cyanobacteria) in Human Gut: Characteristics and Association with Health

Gut microorganisms are comprised of thousands of species and play an important role in the host’s metabolism, overall health status, and risk of disease. Recently, the discovery of non-photosynthetic cyanobacteria (class “Melainabacteria”) in the human and animal gut triggered a broad interest in studying cyanobacteria’s evolution, physiology, and ecological relevance of the Melainabacteria members. In the present paper, we review the general characteristics of Melainabacteria, their phylogeny, distribution, and ecology. The potential link between these microorganisms and human health is also discussed based on available human-microbiome studies. Their abundance tends to increase in patients with selected neurodegenerative, gastrointestinal, hepatic, metabolic, and respiratory diseases. However, the available evidence is correlative and requires further longitudinal studies. Although the research on Melainabacteria in the human gut is still in its infancy, elucidation of their role appears important in better understanding microbiome–human health interactions. Further studies aiming to identify particular gut cyanobacteria species, culture them in vitro, and characterize them on the molecular, biochemical, and physiological levels are encouraged.

[The role of the gut microbiota in Parkinson's disease]

ABTRACT

Recently, an important role in the development of Parkinson's disease (PD) is assigned to the gastrointestinal tract and the enteral nervous system. In particular, the pathological process of PD begins in the gastrointestinal tract decades before progressing to the central nervous system. The microbiota-gut-brain axis is a two-way connecting system between the central nervous system and the gastrointestinal tract. The pathogenesis of PD can be caused or aggravated by changes in the gastrointestinal microbiota composition. It is shown that patients with PD have changes in the intestinal microbiota. A better understanding of gut-brain interactions and the role of the gut microbiota in regulation the immune response can both bring new knowledge about the pathological progression of PD, and contribute to the development of new diagnostic and therapeutic approaches.

The Prevailing Role of Topoisomerase 2 Beta and its Associated Genes in Neurons

Topoisomerase 2 beta (TOP2β) is an enzyme that alters the topological states of DNA by making a transient double-strand break during the transcription process. The direct interaction of TOP2β with DNA strand results in transcriptional regulation of certain genes and some studies have suggested that a particular set of genes are regulated by TOP2β, which have a prominent role in various stages of neuron from development to degeneration. In this review, we discuss the role of TOP2β in various phases of the neuron's life. Based on the existing reports, we have compiled the list of genes, which are directly regulated by the enzyme, from different studies and performed their functional classification. We discuss the role of these genes in neurogenesis, neuron migration, fate determination, differentiation and maturation, generation of neural circuits, and senescence.

The Microbiota-Gut-Brain Axis as a Key to Neuropsychiatric Disorders: A Mini Review

The central nervous system (CNS) is closely related to the gastrointestinal tract, mainly through regulating its function and homeostasis. Simultaneously, the gut flora affects the CNS and plays an essential role in the pathogenesis of neurologic and neuropsychological disorders such as Parkinson’s and Alzheimer’s disease, multiple sclerosis, amyotrophic lateral sclerosis or autism spectrum disorder. The population of gut microorganisms contains more than one billion bacteria. The most common are six phyla: Proteobacteria, Actinomyces, Verucomicrobia, Fusobacteria, and dominant Bacteroides with Firmicutes. The microbiota–gut–brain axis is a bidirectional nervous, endocrine, and immune communication between these two organs. They are connected through a variety of pathways, including the vagus nerve, the immune system, microbial metabolites such as short-chain fatty acids (SCFAs), the enteric nervous system, and hormones. Age, diet, antibiotics influence the balance of gut microorganisms and probably lead to the development of neurodegenerative disorders. In this article, a review is presented and discussed, with a specific focus on the changes of gut microbiota, gut–brain axis, related disorders, and the factors that influence gut imbalance.

Analysis of mouse faecal dysbiosis, during the development of cachexia, induced by transplantation with Lewis lung carcinoma cells

Cachexia (CC) is a complex wasting syndrome that significantly affects life quality and life expectancy among cancer patients. Original studies, in which CC was induced in mouse models through inoculation with BaF and C26 tumour cells, demonstrated that CC development correlates with bacterial gut dysbiosis in these animals. In both cases, a common microbial signature was observed, based on the expansion of Enterobacteriaceae in the gut of CC animals. However, these two types of tumours induce unique microbial profiles, suggesting that different CC induction mechanisms significantly impact the outcome of gut dysbiosis. The present study sought to expand the scope of such analyses by characterizing the CC-associated dysbiosis that develops when mice are inoculated with Lewis lung carcinoma (LLC) cells, which constitutes one of the most widely employed mechanisms for CC induction. Interestingly, Enterobacteriaceae expansion is also observed in LLC-induced CC. However, the dysbiosis identified herein displays a more complex pattern, involving representatives from seven different bacterial phyla, which were consistently identified across successive levels of taxonomic hierarchy. These results are supported by a predictive analysis of gene content, which identified a series of functional/structural changes that potentially occur in the gut bacterial population of these animals, providing a complementary and alternative approach to microbiome analyses based solely on taxonomic classification.

Gut dysbiosis, defective autophagy and altered immune responses in neurodegenerative diseases: Tales of a vicious cycle

The human microbiota comprises trillions of symbiotic microorganisms and is involved in regulating gastrointestinal (GI), immune, nervous system and metabolic homeostasis. Recent observations suggest a bidirectional communication between the gut microbiota and the brain via immune, circulatory and neural pathways, termed the Gut-Brain Axis (GBA). Alterations in gut microbiota composition, such as seen with an increased number of pathobionts and a decreased number of symbionts, termed gut dysbiosis or microbial intestinal dysbiosis, plays a prominent role in the pathogenesis of central nervous system (CNS)-related disorders. Clinical reports confirm that GI symptoms often precede neurological symptoms several years before the development of neurodegenerative diseases (NDDs). Pathologically, gut dysbiosis disrupts the integrity of the intestinal barrier leading to ingress of pathobionts and toxic metabolites into the systemic circulation causing GBA dysregulation. Subsequently, chronic neuroinflammation via dysregulated immune activation triggers the accumulation of neurotoxic misfolded proteins in and around CNS cells resulting in neuronal death. Emerging evidence links gut dysbiosis to the aggravation and/or spread of proteinopathies from the peripheral nervous system to the CNS and defective autophagy-mediated proteinopathies. This review summarizes the current understanding of the role of gut microbiota in NDDs, and highlights a vicious cycle of gut dysbiosis, immune-mediated chronic neuroinflammation, impaired autophagy and proteinopathies, which contributes to the development of neurodegeneration in Alzheimer's disease, Parkinson's disease, Huntington's disease, multiple sclerosis, amyotrophic lateral sclerosis and frontotemporal lobar degeneration. We also discuss novel therapeutic strategies targeting the modulation of gut dysbiosis through prebiotics, probiotics, synbiotics or dietary interventions, and faecal microbial transplantation (FMT) in the management of NDDs.

Interrelationship between the 5-lipoxygenase pathway and microbial dysbiosis in the progression of Alzheimer's disease

Alzheimer's disease (AD) is an age-related neurodegenerative disorder involving neurofibrillary tangles and amyloid plaques. The tau phosphorylation responsible for neurofibrillary tangles and amyloid deposition which causes plaques are both accelerated through the activity of 5-lipoxygenase (5-LO). In addition to these pathological pathways, 5-LO has also been linked to the neuro-inflammation associated with disease progression as well as to dysbiosis in the gut. Interestingly, gut dysbiosis itself has been correlated to AD development. Not only do gut metabolites have direct effects on the brain, but pro-inflammatory mediators such as LPS, BMAA and bacterial amyloids produced in the gut due to dysbiosis reach the brain causing increased neuro-inflammation. While microbial dysbiosis and 5-LO exert detrimental effects in the brain, the cause/effect relationship between these factors remain unknown. These issues may be addressed using mouse models of AD in the context of different knockout mice in the 5-LO pathway in specific pathogen-free, germ-free as well as gnotobiotic conditions.

Cyanobacteria, Cyanotoxins, and Neurodegenerative Diseases: Dangerous Liaisons

The prevalence of neurodegenerative disease (ND) is increasing, partly owing to extensions in lifespan, with a larger percentage of members living to an older age, but the ND aetiology and pathogenesis are not fully understood, and effective treatments are still lacking. Neurodegenerative diseases such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis are generally thought to progress as a consequence of genetic susceptibility and environmental influences. Up to now, several environmental triggers have been associated with NDs, and recent studies suggest that some cyanotoxins, produced by cyanobacteria and acting through a variety of molecular mechanisms, are highly neurotoxic, although their roles in neuropathy and particularly in NDs are still controversial. In this review, we summarize the most relevant and recent evidence that points at cyanotoxins as environmental triggers in NDs development.

Gut Microbiota and Alzheimer's Disease: Pathophysiology and Therapeutic Perspectives

Alzheimer's disease (AD) is the most common cause of dementia in the elderly and is characterized by a progressive decline in cognitive function. Amyloid-β protein accumulation is believed to be the key pathological hallmark of AD. Increasing evidence has shown that the gut microbiota has a role in brain function and host behaviors. The gut microbiota regulates the bidirectional interactions between the gut and brain through neural, endocrine, and immune pathways. With increasing age, the gut microbiota diversity decreases, and the dominant bacteria change, which is closely related to systemic inflammation and health status. Dysbiosis of the gut microbiota is related to cognitive impairment and neurodegenerative diseases. The purpose of this review is to discuss the impacts of the gut microbiota on brain function and the development of AD. It is a feasible target for therapeutic invention. Modulating the composition of the gut microbiota through diet, physical activity or probiotic/prebiotic supplements can provide new prevention and treatment options for AD.

Linking Oxidative Stress and Proteinopathy in Alzheimer's Disease

Proteinopathy and excessive production of reactive oxygen species (ROS), which are the principal features observed in the Alzheimer’s disease (AD) brain, contribute to neuronal toxicity. β-amyloid and tau are the primary proteins responsible for the proteinopathy (amyloidopathy and tauopathy, respectively) in AD, which depends on ROS production; these aggregates can also generate ROS. These mechanisms work in concert and reinforce each other to drive the pathology observed in the aging brain, which primarily involves oxidative stress (OS). This, in turn, triggers neurodegeneration due to the subsequent loss of synapses and neurons. Understanding these interactions may thus aid in the identification of potential neuroprotective therapies that could be clinically useful. Here, we review the role of β-amyloid and tau in the activation of ROS production. We then further discuss how free radicals can influence structural changes in key toxic intermediates and describe the putative mechanisms by which OS and oligomers cause neuronal death.

Altered Blood Levels of Anti-Gal Antibodies in Alzheimer's Disease: A New Clue to Pathogenesis?

Alzheimer's disease is a neurodegenerative disorder whose pathological mechanisms, despite recent advances, are not fully understood. However, the deposition of beta amyloid -peptide and neuroinflammation, which is probably aggravated by dysbiotic microbiota, seem to play a key role. Anti-Gal are the most abundant xenoreactive natural antibodies. They are supposed to stem from immunization against the gut microbiota and have been implicated in the pathogenesis of several diseases, including multiple sclerosis. These antibodies target the alpha-Gal epitope, expressed on the terminal sugar units of glycoprotein or glycolipid of all mammals except apes, Old World monkeys and humans. The alpha-Gal is constitutively expressed in several bacteria constituting the brain microbiota, and alpha-Gal-like epitopes have been detected in gray matter, amyloid plaque, neurofibrillary tangles and corpora amylacea of the human brain, suggesting a potential link between anti-Gal and Alzheimer's disease etiopathogenesis. For the first time, our study searched for possible alterations of anti-Gal immunoglobulin levels in Alzheimer's disease patients. IgG and IgM blood levels were significantly lower, and IgA significantly higher in patients than in healthy subjects. These results suggest that such immunoglobulins might be implicated in Alzheimer's disease pathogenesis and open new scenarios in the research for new biomarkers and therapeutic strategies.

Gauging the role and impact of drug interactions and repurposing in neurodegenerative disorders

Neurodegenerative diseases (ND) are of vast origin which are characterized by gradual progressive loss of neurons in the brain region. ND can be classified according to the clinical symptoms present (e.g. Cognitive decline, hyperkinetic, and hypokinetic movements disorder) or by the pathological protein deposited (e.g., Amyloid, tau, Alpha-synuclein, TDP-43). Alzheimer's disease preceded by Parkinson's is the most prevalent form of ND world-wide. Multiple factors like aging, genetic mutations, environmental factors, gut microbiota, blood-brain barrier microvascular complication, etc. may increase the predisposition towards ND. Genetic mutation is a major contributor in increasing the susceptibility towards ND, the concept of one disease-one gene is obsolete and now multiple genes are considered to be involved in causing one particular disease. Also, the involvement of multiple pathological mechanisms like oxidative stress, neuroinflammation, mitochondrial dysfunction, etc. contributes to the complexity and makes them difficult to be treated by traditional mono-targeted ligands. In this aspect, the Poly-pharmacological drug approach which targets multiple pathological pathways at the same time provides the best way to treat such complex networked CNS diseases. In this review, we have provided an overview of ND and their pathological origin, along with a brief description of various genes associated with multiple diseases like Alzheimer's, Parkinson's, Multiple sclerosis (MS), Amyotrophic Lateral Sclerosis (ALS), Huntington's and a comprehensive detail about the Poly-pharmacology approach (MTDLs and Fixed-dose combinations) along with their merits over the traditional single-targeted drug is provided. This review also provides insights into current repurposing strategies along with its regulatory considerations.

Health benefits of edible mushroom polysaccharides and associated gut microbiota regulation

Edible mushrooms have been an important part of the human diet for thousands of years, and over 100 varieties have been cultivated for their potential human health benefits. In recent years, edible mushroom polysaccharides (EMPs) have been studied for their activities against obesity, inflammatory bowel disease (IBD), and cancer. Particularly, accumulating evidence on the exact causality between these health risks and specific gut microbiota species has been revealed and characterized, and most of the beneficial health effects of EMPs have been associated with its reversal impacts on gut microbiota dysbiosis. This demonstrates the key role of EMPs in decreasing health risks through gut microbiota modulation effects. This review article compiles and summarizes the latest studies that focus on the health benefits and underlying functional mechanisms of gut microbiota regulation via EMPs. We conclude that EMPs can be considered a dietary source for the improvement and prevention of several health risks, and this review provides the theoretical basis and technical guidance for the development of novel functional foods with the utilization of edible mushrooms.

Role of the gut microbiome in Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of individuals each year and this number is expected to significantly increase. The complicated microorganisms residing in human gut are closely associated with our health. Emerging evidence has suggested possible involvement of human gut microbiome in AD. Symbiotic gut microbiomes are known to maintain brain health by modulating host's barriers integrity, metabolic system, immune system, nervous system and endocrine system. However, in the event of gut dysbiosis and barriers disruption, gut pathobionts disrupt homeostasis of the metabolic system, immune system, nervous system, and endocrine system, resulting in deterioration of neurological functions and subsequently promoting development of AD. Multiple therapeutic approaches, such as fecal microbiome transplant, antibiotics, prebiotics, probiotics, symbiotic, and diet are discussed as potential treatment options for AD by manipulating the gut microbiome to reverse pathological alteration in the systems above.

The Mitochondrial Ribosome: A World of Opportunities for Mitochondrial Dysfunction Toward Parkinson's Disease

Significance: Mitochondrial ribosomes (mitoribosomes) are organelles that translate mitochondrial messenger RNA in the matrix and, in mammals, have evolved to translate 13 polypeptides of the pathway that performs oxidative phosphorylation (OXPHOS). Although a number of devastating diseases result from defects in this mitochondrial translation apparatus, most are associated with genetic mutations and little is known about allelopathic defects caused by antibiotics, toxins, or nonproteinogenic amino acids. Recent Advances: The levels of mitochondrial ribosomal subunits 12S and 16S ribosomal RNA (rRNA) in cells/tissues from patients carrying mutations in these genes have been associated with alterations in mitochondrial translation efficiency and with impaired OXPHOS activities, as well as with the severity of clinical phenotypes. In recent decades, important studies revealed a prominent role of mitochondrial dysfunction in Parkinson's disease (PD); however, the involvement of mitoribosomes remains largely unknown. Critical Issues: Considering that mitoribosomal structure and function can determine the efficiency of OXPHOS and that an impaired mitochondrial respiratory chain is a common finding in PD, we argue that the mitoribosome may be key to disease onset and progression. With this review, we comprehensively integrate the available knowledge on the composition, assembly, and role of the mitoribosome in mitochondrial efficiency, reflecting on its possible involvement in the etiopathogenesis of this epidemic disease as an appealing research avenue. Future Directions: If a direct correlation between mitoribosome failure and PD pathology is demonstrated, these mitochondrial organelles will provide valuable early clinical markers and potentially attractive targets for the development of innovative PD-directed therapeutic agents.

Improving Alzheimer's disease by altering gut microbiota in tree shrews with ginsenoside Rg1

Ginsenoside Rg1 (GRg1) has neuroprotective effects on Alzheimer's disease (AD). The occurrence and progression of AD are closely related to gut microbiota. Few studies have learned the direct relationship between GRg1 and gut microbiota. In this study, we found an original way to research this relationship by using GRg1 in the AD model of tree shrews. Morris water maze and immunohistochemistry were performed to test the cognition repairing function of GRg1 by tree shrews and 16S ribosomal RNA sequencing was used to explore the composition and abundance of gut microbiota. After GRg1 treatment, the result of Morris water maze showed an improvement in cognitive function, and immunohistochemistry revealed a decrease in tau protein. Moreover, 16SrRNA sequencing results showed the abundances of Proteobacteria and Verrucomicrobia were significantly different, and Lactobacillaceae was significantly increased in the GRg1 treatment group. It also showed that the gut microbiome with middle and high doses of GRg1 was close to the normal group. In conclusion, this study suggests that GRg1 at middle and high doses may change the abundance of gut microbiota to improve AD, and thatProteobacteria and Verrucomicrobia are key microbiota. This is the first report that has ever studied the relationship between GRg1 and gut microbiota in tree shrews.

APOE-ε4 Carrier Status and Gut Microbiota Dysbiosis in Patients With Alzheimer Disease

BACKGROUND

Alternations in gut microbiota and a number of genes have been implicated as risk factors for the development of Alzheimer disease (AD). However, the interactions between the altered bacteria and risk genetic variants remain unclear.

OBJECTIVE

We aimed to explore associations of the risk genetic variants with altered gut bacteria in the onset of AD.

METHODS

We collected baseline data and stool and blood samples from 30 AD patients and 47 healthy controls in a case-control study. The rs42358/rs4512 (ApoE), rs3851179 (PICALM), rs744373 (BIN1), rs9331888 (CLU), rs670139 (MS4A4E), rs3764650 (ABCA7), rs3865444 (CD33), rs9349407 (CD2AP), rs11771145 (EPHA1), and rs3818361/rs6656401 (CR1) were sequenced, and microbiota composition was characterized using 16S rRNA gene sequencing. The associations of the altered gut bacteria with the risk genetics were analyzed.

RESULTS

Apolipoprotein ε4 allele and rs744373 were risk loci for the AD among 12 genetic variants. Phylum Proteobacteria; orders Enterobacteriales, Deltaproteobacteria, and Desulfovibrionales; families Enterobacteriaceae and Desulfovibrionaceae; and genera Escherichia-Shigella, Ruminococcaceae_UCG_002, Shuttleworthia, Anaerofustis, Morganelia, Finegoldia, and Anaerotruncus were increased in AD subjects, whereas family Enterococcaceae and genera Megamonas, Enterococcus, and Anaerostipes were more abundant in controls (P < 0.05). Among the altered microbiota, APOE ε4 allele was positively associated with pathogens: Proteobacteria.

CONCLUSION

The interaction of APOE ε4 gene and the AD-promoting pathogens might be an important factor requiring for the promotion of AD. Targeting to microbiota might be an effective therapeutic strategy for AD susceptible to APOE ε4 allele. This needs further investigation.

Preliminary evidence for an influence of exposure to polycyclic aromatic hydrocarbons on the composition of the gut microbiota and neurodevelopment in three-year-old healthy children

Background

During the second and third year after birth the gut microbiota (GM) is subjected to important development. The polycyclic aromatic hydrocarbon (PAH) exposure could influence the GM in animal and early postnatal exposure is associated with neurodevelopment disorder in children. This study was designed to explore the possible influence of the polycyclic aromatic hydrocarbons (PAHs) on the composition of the gut microbiota (GM) and neurodevelopment in a sample of 38 healthy children at the age of 3 years.

Methods

A brief development (Gesell Development Inventory, GDI) and behavior test (Child Behavior Checklist, CBCL) were completed on 3-yr-olds and stool samples were collected for 16S rRNA V4-V5 sequencing. The PAH-DNA adduct in the umbilical cord blood and the urinary hydroxyl PAHs (OH-PAHs) at the age of 12 months were measured as pre- and postnatal PAH exposure, respectively.

Results

The most abundant two phyla were Bacteroidetes (68.6%) and Firmicutes (24.2%). The phyla Firmicutes, Actinobacteria, Proteobacteria, Tenericutes, and Lentisphaerae were positively correlated with most domain behaviors of the GDI, whereas the Bacteroidetes, Cyanobacteria, and Fusobacteria were negatively correlated. Correspondingly, the phyla Bacteroidetes, Actinobacteria, and Fusobacteria showed positive correlations with most CBCL core and broadband syndromes, whereas the Firmicutes, Verrucomicrobia, Synergistetes, Proteobacteria and Tenericules were negatively correlated. The OH-PAH levels were not significantly associated with the Firmicutes phylum whereas the Bacteroidetes, Bacteroidia, and Bacteroidales all showed significant negative association with the OH-PAH levels.

Conclusion

The current findings suggest that composition of the GM is associated with neurodevelopment of the child. PAHs seem to change the relative abundance of some taxa (some deleted and some recruited) to counteract the negative effects of the PAHs.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12887-021-02539-w.

Comparison of Effects and Brain-Gut Regulatory Mechanisms of Acupuncture and Flunarizine for Migraine: Study Protocol for a Randomized Controlled Trial

Background

As a central nervous system disease, migraine often coexists with gastrointestinal disorders, which suggests a disruption of brain-gut regulation. Clinical studies have confirmed that acupuncture and flunarizine not only alleviate migraine attacks but also substantially inhibit accompanying gastrointestinal symptoms. However, it is still not clear how acupuncture and flunarizine regulate the interactions of brain, gut, and microbiome. Therefore, this study will combine neuroimaging technology and gut microbiota detection technology to explore and compare the effects and brain-gut modulating mechanisms of acupuncture and flunarizine for migraine.

Methods

This randomized clinical trial will recruit 66 patients with migraine without aura. Participants will be randomly assigned in a 1 : 1 ratio to an acupuncture group or a control group. The acupuncture treatment strategy is based on experience from our previous study and consensus meetings with clinical experts. Patients will receive 12 sessions of manual acupuncture treatment (once every other day to a total of three times per week, followed by a 2-day break). Flunarizine will be administered at a dose of 5 mg daily in the control group. Participants in both groups will receive treatment for a period of 4 weeks. The primary outcome is the change in frequency of migraine attacks, and the secondary outcomes include the changes in migraine days (days on which migraine attacks occurred), average migraine severity, gastrointestinal symptoms, psychiatric symptoms, and quality of life. Fresh stool samples will be collected, and 16S ribosomal RNA gene sequencing analysis will be used for gut microbiota. Magnetic resonance imaging will be applied to detect between-group changes in brain function. The abovementioned indicators will be collected at baseline, after a 4-week intervention, and at the 12-week follow-up. Discussions. From the perspective of brain-gut regulatory mechanisms, we will combine brain neuroimaging and gut microbiological data to partially reveal the similarities and differences of acupuncture and flunarizine on the treatment of migraine. The trial is registered with ChiCTR2000034417.

Metabolomics analysis of microbiota-gut-brain axis in neurodegenerative and psychiatric diseases

Gut microbiota represents a complex physiological ecosystem that influences the host health. Alterations in the microbiome metabolism affect the body homeostasis and they have been associated with the development of different human neurodegenerative and neuropsychiatric disorders, such as Alzheimer's disease, autism spectrum disorder, bipolar disorder, depression, Huntington's disease, Parkinson's disease, posttraumatic stress disorder and schizophrenia. The development of these complex diseases is influenced by various factors, including genetic predisposition and environmental triggers. Gut microbiota has recently emerged as an important actor in their physiopathology that has been shown to play a role in inflammation, oxidative stress, and gut permeability. Therefore, targeting the metabolites that are produced by or associated with the gut microbiota may help us understand how imbalance in the gut-brain axis affects human health. This review offers a comprehensive overview of the literature on this matter, offering the readers an insight in the state-of-art metabolic measurements of the gut-brain axis in various brain-related diseases.

Biological Functions of Prokaryotic Amyloids in Interspecies Interactions: Facts and Assumptions

Amyloids are fibrillar protein aggregates with an ordered spatial structure called "cross-β". While some amyloids are associated with development of approximately 50 incurable diseases of humans and animals, the others perform various crucial physiological functions. The greatest diversity of amyloids functions is identified within prokaryotic species where they, being the components of the biofilm matrix, function as adhesins, regulate the activity of toxins and virulence factors, and compose extracellular protein layers. Amyloid state is widely used by different pathogenic bacterial species in their interactions with eukaryotic organisms. These amyloids, being functional for bacteria that produce them, are associated with various bacterial infections in humans and animals. Thus, the repertoire of the disease-associated amyloids includes not only dozens of pathological amyloids of mammalian origin but also numerous microbial amyloids. Although the ability of symbiotic microorganisms to produce amyloids has recently been demonstrated, functional roles of prokaryotic amyloids in host-symbiont interactions as well as in the interspecies interactions within the prokaryotic communities remain poorly studied. Here, we summarize the current findings in the field of prokaryotic amyloids, classify different interspecies interactions where these amyloids are involved, and hypothesize about their real occurrence in nature as well as their roles in pathogenesis and symbiosis.

Gut Microbiota and Metabolome Alterations Associated with Parkinson's Disease

To our knowledge, this is one of the few studies thus far that correlates the composition of the gut microbiota with the direct analysis of fecal metabolites in patients with Parkinson’s disease. Overall, our data highlight microbiota modifications correlated with numerous fecal metabolites. This suggests that Parkinson’s disease is associated with gut dysregulation that involves a synergistic relationship between gut microbes and several bacterial metabolites favoring altered homeostasis. Interestingly, a reduction of short-chain fatty acid (SCFA)-producing bacteria influenced the shape of the metabolomics profile, affecting several metabolites with potential protective effects in the Parkinson group. On the other hand, the extensive impact that intestinal dysbiosis has at the level of numerous metabolic pathways could encourage the identification of specific biomarkers for the diagnosis and treatment of Parkinson’s disease, also in light of the effect that specific drugs have on the composition of the intestinal microbiota.

Parkinson’s disease is a neurodegenerative disorder characterized by the accumulation of intracellular aggregates of misfolded alpha-synuclein along the cerebral axis. Several studies report the association between intestinal dysbiosis and Parkinson’s disease, although a cause-effect relationship remains to be established. Herein, the gut microbiota composition of 64 Italian patients with Parkinson’s disease and 51 controls was determined using a next-generation sequencing approach. A real metagenomics shape based on gas chromatography-mass spectrometry was also investigated. The most significant changes within the Parkinson’s disease group highlighted a reduction in bacterial taxa, which are linked to anti-inflammatory/neuroprotective effects, particularly in the Lachnospiraceae family and key members, such as Butyrivibrio, Pseudobutyrivibrio, Coprococcus, and Blautia. The direct evaluation of fecal metabolites revealed changes in several classes of metabolites. Changes were seen in lipids (linoleic acid, oleic acid, succinic acid, and sebacic acid), vitamins (pantothenic acid and nicotinic acid), amino acids (isoleucine, leucine, phenylalanine, glutamic acid, and pyroglutamic acid) and other organic compounds (cadaverine, ethanolamine, and hydroxy propionic acid). Most modified metabolites strongly correlated with the abundance of members belonging to the Lachnospiraceae family, suggesting that these gut bacteria correlate with altered metabolism rates in Parkinson’s disease.

IMPORTANCE To our knowledge, this is one of the few studies thus far that correlates the composition of the gut microbiota with the direct analysis of fecal metabolites in patients with Parkinson’s disease. Overall, our data highlight microbiota modifications correlated with numerous fecal metabolites. This suggests that Parkinson’s disease is associated with gut dysregulation that involves a synergistic relationship between gut microbes and several bacterial metabolites favoring altered homeostasis. Interestingly, a reduction of short-chain fatty acid (SCFA)-producing bacteria influenced the shape of the metabolomics profile, affecting several metabolites with potential protective effects in the Parkinson group. On the other hand, the extensive impact that intestinal dysbiosis has at the level of numerous metabolic pathways could encourage the identification of specific biomarkers for the diagnosis and treatment of Parkinson’s disease, also in light of the effect that specific drugs have on the composition of the intestinal microbiota.

Exercise combined with a probiotics treatment alters the microbiome, but moderately affects signalling pathways in the liver of male APP/PS1 transgenic mice

It has been demonstrated that physical exercise and probiotic supplementation delay the progress of Alzheimer's Disease (AD) in male APP/PS1^TG mice. However, it has also been suggested that both exercise and AD have systemic effects. We have studied the effects of exercise training and probiotic treatment on microbiome and biochemical signalling proteins in the liver. The results suggest that liver is under oxidative stress, since SOD2 levels of APP/PS1 mice were decreased when compared to a wild type of mice. Exercise training prevented this decrease. We did not find significant changes in COX4, SIRT3, PGC-1a or GLUT4 levels, while the changes in pAMPK/AMPK, pmTOR/mTOR, pS6/S6 and NRF2 levels were randomly modulated. The data suggest that exercise and probiotics-induced changes in microbiome do not strongly affect mitochondrial density or protein synthesis-related AMPK/mTOR/S6 pathways in the liver of these animals.

Molecular and cellular mechanisms underlying the pathogenesis of Alzheimer's disease

Alzheimer’s disease (AD) is the most common neurodegenerative disorder seen in age-dependent dementia. There is currently no effective treatment for AD, which may be attributed in part to lack of a clear underlying mechanism. Studies within the last few decades provide growing evidence for a central role of amyloid β (Aβ) and tau, as well as glial contributions to various molecular and cellular pathways in AD pathogenesis. Herein, we review recent progress with respect to Aβ- and tau-associated mechanisms, and discuss glial dysfunction in AD with emphasis on neuronal and glial receptors that mediate Aβ-induced toxicity. We also discuss other critical factors that may affect AD pathogenesis, including genetics, aging, variables related to environment, lifestyle habits, and describe the potential role of apolipoprotein E (APOE), viral and bacterial infection, sleep, and microbiota. Although we have gained much towards understanding various aspects underlying this devastating neurodegenerative disorder, greater commitment towards research in molecular mechanism, diagnostics and treatment will be needed in future AD research.

Human Gut-Microbiota Interaction in Neurodegenerative Disorders and Current Engineered Tools for Its Modeling

The steady increase in life-expectancy of world population, coupled to many genetic and environmental factors (for instance, pre- and post-natal exposures to environmental neurotoxins), predispose to the onset of neurodegenerative diseases, whose prevalence is expected to increase dramatically in the next years. Recent studies have proposed links between the gut microbiota and neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Human body is a complex structure where bacterial and human cells are almost equal in numbers, and most microbes are metabolically active in the gut, where they potentially influence other target organs, including the brain. The role of gut microbiota in the development and pathophysiology of the human brain is an area of growing interest for the scientific community. Several microbial-derived neurochemicals involved in the gut-microbiota-brain crosstalk seem implicated in the biological and physiological basis of neurodevelopment and neurodegeneration. Evidence supporting these connections has come from model systems, but there are still unsolved issues due to several limitations of available research tools. New technologies are recently born to help understanding the causative role of gut microbes in neurodegeneration. This review aims to make an overview of recent advances in the study of the microbiota-gut-brain axis in the field of neurodegenerative disorders by: (a) identifying specific microbial pathological signaling pathways; (b) characterizing new, advanced engineered tools to study the interactions between human cells and gut bacteria.

New mechanism of neuroinflammation in Alzheimer's disease: The activation of NLRP3 inflammasome mediated by gut microbiota

Alzheimer's disease (AD) is a central degenerative disease characterized by cognitive impairment. Polymerization of β-amyloid has been reported to cause the entanglement of nerve cells, leading to the progressive loss of nerve cells. Accumulative studies have confirmed the important roles of neuroinflammation in the development of AD. In this study, the gut microbiota from AD patients were transplanted into APP/PS1 double transgenic mice. As a result, the expression of NLRP3 was increased in the intestinal tract of mice, and the expression levels of inflammatory factors in peripheral blood were also increased. Consistently, the cognitive impairment was more severe in mice receiving gut microbiota from AD patients than those did not, with activation of microglia in the central hippocampus of mice, and increased expression of neuroinflammatory factors. In APP/PS1 mice transplanted with gut microbiota from AD patients, transplantation of healthy human gut microbiota or oral administration of minocycline was further used to improve the composition of gut microbiota. Consequently, the intestinal expression of NLRP3 was down-regulated, the cognitive ability of mice was improved, the activation of microglia in central hippocampus was suppressed and the expression of neuroinflammatory factors was also down-regulated. After transplantation of gut microbiota from AD patients in C57BL/6 mice, the intestinal expression of NLRP3 was up-regulated. Although the cognitive ability of mice was not significantly changed, the microglia in the hippocampus of mice were still activated and the expression of inflammatory factors was up-regulated. In this study, we found that gut microbiota in AD patients could induce the activation of NLRP3 inflammasome in the intestinal tract of mice, subsequently causing the release of inflammatory factors. The absorption and circulation of inflammatory factors through the intestinal tract could further aggravate the inflammation in the nervous tissues and the activation of microglia. Therefore, improving the composition of gut microbiota in AD patients can further attenuate neuroinflammation, which is considered as a novel idea for AD treatment.

Microbial BMAA and the Pathway for Parkinson's Disease Neurodegeneration

The neurotoxin β-N-methylamino-L-alanine (BMAA) is a natural non-proteinogenic diamino acid produced by several species of both prokaryotic (cyanobacteria) and eukaryotic (diatoms and dinoflagellates) microorganisms. BMAA has been shown to biomagnify through the food chain in some ecosystems, accumulating for example in seafood such as shellfish and fish, common dietary sources of BMAA whose ingestion may have possible neuronal consequences. In addition to its excitotoxic potential, BMAA has been implicated in protein misfolding and aggregation, inhibition of specific enzymes and neuroinflammation, all hallmark features of neurodegenerative diseases. However, the exact molecular mechanisms of neurotoxicity remain to be elucidated in detail. Although BMAA is commonly detected in its free form, complex BMAA-containing molecules have also been identified such as the paenilamicins, produced by an insect gut bacterial pathogen. On the other hand, production of BMAA or BMAA-containing molecules by members of the human gut microbiota, for example by non-photosynthetic cyanobacteria, the Melainabacteria, remains only hypothetical. In any case, should BMAA reach the gut it may interact with cells of the mucosal immune system and neurons of the enteric nervous system (ENS) and possibly target the mitochondria. Here, we review the available evidence and hint on possible mechanisms by which chronic exposure to dietary sources of this microbial neurotoxin may drive protein misfolding and mitochondrial dysfunction with concomitant activation of innate immune responses, chronic low-grade gut inflammation, and ultimately the neurodegenerative features observed across the gut-brain axis in Parkinson's disease (PD).

Organ-On-A-Chip in vitro Models of the Brain and the Blood-Brain Barrier and Their Value to Study the Microbiota-Gut-Brain Axis in Neurodegeneration

We are accumulating evidence that intestinal microflora, collectively named gut microbiota, can alter brain pathophysiology, but researchers have just begun to discover the mechanisms of this bidirectional connection (often referred to as microbiota-gut-brain axis, MGBA). The most noticeable hypothesis for a pathological action of gut microbiota on the brain is based on microbial release of soluble neurotransmitters, hormones, immune molecules and neuroactive metabolites, but this complex scenario requires reliable and controllable tools for its causal demonstration. Thanks to three-dimensional (3D) cultures and microfluidics, engineered in vitro models could improve the scientific knowledge in this field, also from a therapeutic perspective. This review briefly retraces the main discoveries linking the activity of gut microbiota to prevalent brain neurodegenerative disorders, and then provides a deep insight into the state-of-the-art for in vitro modeling of the brain and the blood-brain barrier (BBB), two key players of the MGBA. Several brain and BBB microfluidic devices have already been developed to implement organ-on-a-chip solutions, but some limitations still exist. Future developments of organ-on-a-chip tools to model the MGBA will require an interdisciplinary approach and the synergy with cutting-edge technologies (for instance, bioprinting) to achieve multi-organ platforms and support basic research, also for the development of new therapies against neurodegenerative diseases.

Alzheimer's disease and symbiotic microbiota: an evolutionary medicine perspective

Microorganisms resident in our bodies participate in a variety of regulatory and pathogenic processes. Here, we describe how etiological pathways implicated in Alzheimer's disease (AD) may be regulated or disturbed by symbiotic microbial activity. Furthermore, the composition of symbiotic microbes has changed dramatically across human history alongside the rise of agriculturalism, industrialization, and globalization. We postulate that each of these lifestyle transitions engendered progressive depletion of microbial diversity and enhancement of virulence, thereby enhancing AD risk pathways. It is likely that the human life span extended into the eighth decade tens of thousands of years ago, yet little is known about premodern geriatric epidemiology. We propose that microbiota of the gut, oral cavity, nasal cavity, and brain may modulate AD pathogenesis, and that changes in the microbial composition of these body regions across history suggest escalation of AD risk. Dysbiosis may promote immunoregulatory dysfunction due to inadequate education of the immune system, chronic inflammation, and epithelial barrier permeability. Subsequently, proinflammatory agents-and occasionally microbes-may infiltrate the brain and promote AD pathogenic processes. APOE genotypes appear to moderate the effect of dysbiosis on AD risk. Elucidating the effect of symbiotic microbiota on AD pathogenesis could contribute to basic and translational research.

Gut microbiota in ALS: possible role in pathogenesis?

Introduction: The gut microbiota has important roles in maintaining human health. The microbiota and its metabolic byproducts could play a role in the pathogenesis of neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS). Areas covered: The authors evaluate the methods of assessing the gut microbiota, and also review how the gut microbiota affects the various physiological functions of the gut. The authors then consider how gut dysbiosis could theoretically affect the pathogenesis of ALS. They present the current evidence regarding the composition of the gut microbiota in ALS and in rodent models of ALS. Finally, the authors review therapies that could improve gut dysbiosis in the context of ALS. Expert opinion: Currently reported studies suggest some instances of gut dysbiosis in ALS patients and mouse models; however, these studies are limited, and more information with well-controlled larger datasets is required to make a definitive judgment about the role of the gut microbiota in ALS pathogenesis. Overall this is an emerging field that is worthy of further investigation. The authors advocate for larger studies using modern metagenomic techniques to address the current knowledge gaps.

Tuna Oil Alleviates d-Galactose Induced Aging in Mice Accompanied by Modulating Gut Microbiota and Brain Protein Expression

To discern whether tuna oil modulates the expression of brain proteins and the gut microbiota structure during aging induced by d-galactose, we generated an aging mouse model with d-galactose treatment, and the mice showed aging and memory deterioration symptoms according to physiological and biochemical indices. Treatment with different doses of tuna oil alleviated the symptoms; the high dose showed a better effect. Subsequently, brain proteomic analysis showed the differentially expressed proteins were involved in damaged synaptic system repairment and signal transduction system enhancement. In addition, tuna oil treatment restored the diversity of gut microbiota, 27 key operational taxonomic units, which were identified using a redundancy analysis and were significantly correlated with at least one physiological index and three proteins or genes. These findings suggest that the combination of proteomics and gut microbiota is an effective strategy to gain novel insights regarding the effect of tuna oil treatment on the microbiota-gut-brain axis.

Microbiota and neurodegenerative diseases

PURPOSE OF REVIEW

Despite the extensive research carried out in the past decades, the current pathophysiological notions of neurodegenerative disease as well as effective treatments to reduce their progression are largely unknown. Alterations of the human microbiota, the plethora of different microscopic organisms that our body hosts, have been linked to neurodegenerative disease risk, onset and progression. This review summarizes the current knowledge on the possible role of microbiota in neurodegenerative disorders and briefly discusses strategies to restore microbiota homeostasis.

RECENT FINDINGS

Preclinical evidences and human cross-sectional studies posit the gut microbiota as a key actor in the Parkinson's disease onset and progression, reporting the presence of a specific gut microbiota profile in association with the modulation of disease and symptoms. Gut microbiota alterations have been correlated with brain disease and peripheral inflammation also in Alzheimer's patients.

SUMMARY

The interaction between the microbiota and the host is promising to answer clinical questions that have so far escaped clarification with the current pathophysiological notions of health and disease. However, human longitudinal studies starting in the earlier disease phases are needed to understand the causative relation between microbiota and the hallmarks of these neurodegenerative disorders and to develop innovative treatments aimed at preventing or slowing brain damages.