Analysis methods for the gut microbiome in neuropsychiatric and neurodegenerative disorders

Deciphering the microbial map and its implications in the therapeutics of neurodegenerative disorder

Every facet of biological anthropology, including development, ageing, diseases, and even health maintenance, is influenced by gut microbiota's significant genetic and metabolic capabilities. With current advancements in sequencing technology and with new culture-independent approaches, researchers can surpass older correlative studies and develop mechanism-based studies on microbiome-host interactions. The microbiota-gut-brain axis (MGBA) regulates glial functioning, making it a possible target for the improvement of development and advancement of treatments for neurodegenerative diseases (NDDs). The gut-brain axis (GBA) is accountable for the reciprocal communication between the gastrointestinal and central nervous system, which plays an essential role in the regulation of physiological processes like controlling hunger, metabolism, and various gastrointestinal functions. Lately, studies have discovered the function of the gut microbiome for brain health-different microbiota through different pathways such as immunological, neurological and metabolic pathways. Additionally, we review the involvement of the neurotransmitters and the gut hormones related to gut microbiota. We also explore the MGBA in neurodegenerative disorders by focusing on metabolites. Further, targeting the blood-brain barrier (BBB), intestinal barrier, meninges, and peripheral immune system is investigated. Lastly, we discuss the therapeutics approach and evaluate the pre-clinical and clinical trial data regarding using prebiotics, probiotics, paraprobiotics, fecal microbiota transplantation, personalised medicine, and natural food bioactive in NDDs. A comprehensive study of the GBA will felicitate the creation of efficient therapeutic approaches for treating different NDDs.

Adolescent male rats show altered gut microbiota composition associated with depressive-like behavior after chronic unpredictable mild stress: Differences from adult rats

Accumulating evidence reveals the metabolism and neurotransmitter systems are different in major depressive disorder (MDD) between adolescent and adult patients; however, much is still unknown from the gut microbiome perspective. To minimize confounding factors such as geographical location, ethnicity, diet, and drugs, we investigated the gut microbial differences between adolescent and adult male Sprague-Dawley rats. We exposed the adolescent rats to chronic unpredictable mild stress (CUMS) for 3 weeks and assessed their behavior using the sucrose preference test (SPT), open field test (OFT), and forced swimming test (FST). We collected and sequenced fecal samples after the behavioral tests and compared them with our previous data on adult rats. Both adolescent and adult CUMS rats exhibited reduced sucrose preference in SPT, reduced total distance in OFT, and increased immobility time in FST. Moreover, compared to their respective controls, the adolescent CUMS rats had distinct amplicon sequence variants (ASVs) mainly in the Muribaculaceae family, Bacteroidetes phylum, while the adult CUMS rats had those in the Lachnospiraceae family, Firmicutes phylum. In the adolescent group, the Muribaculaceae negatively correlated with FST and positively correlated with SPT and OFT. In the adult group, the different genera in the Lachnospiraceae showed opposite correlations with FST. Furthermore, the adolescent CUMS rats showed disrupted microbial functions, such as "Xenobiotics biodegradation and metabolism" and "Immune system", while the adult CUMS rats did not. These results confirmed the gut microbiota differences between adolescent and adult rats after CUMS modeling and provided new insight into the age-related influence on depression models.

Long-Term Implicit Epigenetic Stress Information in the Enteric Nervous System and its Contribution to Developing and Perpetuating IBS

Psychiatric and mood disorders may play an important role in the development and persistence of irritable bowel syndrome (IBS). Previously, we hypothesized that stress-induced implicit memories may persist throughout life via epigenetic processes in the enteric nervous system (ENS), independent of the central nervous system (CNS). These epigenetic memories in the ENS may contribute to developing and perpetuating IBS. Here, we further elaborate on our earlier hypothesis. That is, during pregnancy, maternal prenatal stresses perturb the HPA axis and increase circulating cortisol levels, which can affect the maternal gut microbiota. Maternal cortisol can cross the placental barrier and increase cortisol-circulating levels in the fetus. This leads to dysregulation of the HPA axis, affecting the gut microbiota, microbial metabolites, and intestinal permeability in the fetus. Microbial metabolites, such as short-chain fatty acids (which also regulate the development of fetal ENS), can modulate a range of diseases by inducing epigenetic changes. These mentioned processes suggest that stress-related, implicit, long-term epigenetic memories may be programmed into the fetal ENS during pregnancy. Subsequently, this implicit epigenetic stress information from the fetal ENS could be conveyed to the CNS through the bidirectional microbiota-gut-brain axis (MGBA), leading to perturbed functional connectivity among various brain networks and the dysregulation of affective and pain processes.

Gut microbiota and autism spectrum disorders: where do we stand?

BACKGROUND

Children with autism spectrum disorder (ASD) often have digestive problems and microbial imbalances in their guts, suggesting that these conditions may play a role in the development of the disorder. Scopus-based research on the gut microbiota and ASD was examined in this bibliometric analysis to shed light on the current state of research and identify potential hotspots for future work in this area.

METHODS

We searched documents from the Scopus database and reference citation analysis to collect published data on the gut microbiota and ASD from 2003 to 2022. The downloaded document records were exported to VOSviewer v.1.6.19 to examine and visualize the collaboration between countries and determine the research hotspots.

RESULTS

The search yielded 958 articles specifically dedicated to gut microbiota and ASD. The number of publications in this field increased rapidly after 2013, with a peak in 2022. The United States (n = 267; 27.87%) was the most active country, followed by China (n = 171; 17.85%) and Italy (n = 96; 10.02). International collaboration was observed, with the USA playing a central role. University College Cork, Ireland, was the most productive institution (n = 24; 2.51%). The National Natural Science Foundation of China was the most active funding agency (n = 76; 7.93%). Nutrients journal had the highest number of publications (n = 28; 2.92%). The articles related to gut microbiota and ASD were highly cited, with an h-index of 108. The research themes identified focused on the modulation of gut microbiota as a potential therapy for children with ASD and gut-brain axis dysfunction in ASD.

CONCLUSIONS

In recent years, the study of gut microbiota and its association with ASD has garnered considerable interest as an emergent field of study. The results of this study substantially enhance our current understanding of the knowledge landscape in this field and illuminate potential avenues for future research. It is essential to emphasize the significance of devoting more resources to the newest and most promising research areas, such as investigating the potential therapeutic benefits of modulating the intestinal microbiota in children with ASD. This research has enormous potential and merits intensified focus and investigation.

Neutrophils as a potential therapeutic target in Alzheimer's disease

Alzheimer's disease (AD) is the leading cause of dementia in the United States. Sporadic or late-onset AD remains incompletely understood, with age as the current greatest risk factor. Inflammation in general and neutrophils, a potent mediator of inflammation, have been shown to exacerbate AD associated dementia. This review explores the latest research on neutrophils in AD mouse models and in human cohort studies and discusses current gaps in research and needs for future studies. AD mouse models have shown neutrophil chemotactic migration towards amyloid beta plaques in the brain. Capillary blood flow stalling decreases blood perfusion to associated brain regions and mouse studies have demonstrated that anti-Ly6G antibodies lead to a decrease in capillary blood flow stalling and memory improvement. Several recent transcriptomic studies of blood and brain tissue from persons with AD have shown an upregulation in neutrophil-related genes, and studies have demonstrated neutrophil involvement in brain capillary adhesion, blood brain barrier breaching, myeloperoxidase release, and the propensity for neutrophil extracellular trap release in AD. Neutrophil-derived inflammation and regulation are a potential potent novel therapeutic target for AD progression. Future studies should further investigate neutrophil functionality in AD. In addition, other aspects of AD that may impact neutrophils including the microbiome and the APOE4 allele should be studied.

Does the Gut Microbial Metabolome Really Matter? The Connection between GUT Metabolome and Neurological Disorders

Herein we gathered updated knowledge regarding the alterations of gut microbiota (dysbiosis) and its correlation with human neurodegenerative and brain-related diseases, e.g., Alzheimer’s and Parkinson’s. This review underlines the importance of gut-derived metabolites and gut metabolic status as the main players in gut-brain crosstalk and their implications on the severity of neural conditions. Scientific evidence indicates that the administration of probiotic bacteria exerts beneficial and protective effects as reduced systemic inflammation, neuroinflammation, and inhibited neurodegeneration. The experimental results performed on animals, but also human clinical trials, show the importance of designing a novel microbiota-based probiotic dietary supplementation with the aim to prevent or ease the symptoms of Alzheimer’s and Parkinson’s diseases or other forms of dementia or neurodegeneration.

Gut microbiome in multiple sclerosis-related cognitive impairment

Cognition is one of the most evaluated neurologic subjects with which the gut microbiome is supposed to be associated. Cognitive impairment is a prevalent finding in patients with multiple sclerosis (MS). Here, we are about to study the current evidence on the effect of gut microbiota on cognition and MS. Although no direct evidence is in hand, putting all indirect research together, one could think of the hypothetical benefit of brain-gut axis interventions (possibly diet changes, probiotic administration, microbiota transplant) to solve the drastic problem of cognitive impairment in MS. Hence, researchers are encouraged to scan this horizon in order to fill the knowledge gaps in the field.