Amyloid-β pathology is attenuated by tauroursodeoxycholic acid treatment in APP/PS1 mice after disease onset

Liver as a new target organ in Alzheimer's disease: insight from cholesterol metabolism and its role in amyloid-beta clearance

Alzheimer's disease, the primary cause of dementia, is characterized by neuropathologies, such as amyloid plaques, synaptic and neuronal degeneration, and neurofibrillary tangles. Although amyloid plaques are the primary characteristic of Alzheimer's disease in the central nervous system and peripheral organs, targeting amyloid-beta clearance in the central nervous system has shown limited clinical efficacy in Alzheimer's disease treatment. Metabolic abnormalities are commonly observed in patients with Alzheimer's disease. The liver is the primary peripheral organ involved in amyloid-beta metabolism, playing a crucial role in the pathophysiology of Alzheimer's disease. Notably, impaired cholesterol metabolism in the liver may exacerbate the development of Alzheimer's disease. In this review, we explore the underlying causes of Alzheimer's disease and elucidate the role of the liver in amyloid-beta clearance and cholesterol metabolism. Furthermore, we propose that restoring normal cholesterol metabolism in the liver could represent a promising therapeutic strategy for addressing Alzheimer's disease.

Probiotics and the microbiota-gut-brain axis in neurodegeneration: Beneficial effects and mechanistic insights

Neurodegenerative diseases (NDs) are a group of heterogeneous disorders with a high socioeconomic burden. Although pharmacotherapy is currently the principal therapeutic approach for the management of NDs, mounting evidence supports the notion that the protracted application of available drugs would abate their dopaminergic outcomes in the long run. The therapeutic application of microbiome-based modalities has received escalating attention in biomedical works. In-depth investigations of the bidirectional communication between the microbiome in the gut and the brain offer a multitude of targets for the treatment of NDs or maximizing the patient's quality of life. Probiotic administration is a well-known microbial-oriented approach to modulate the gut microbiota and potentially influence the process of neurodegeneration. Of note, there is a strong need for further investigation to map out the mechanistic prospects for the gut-brain axis and the clinical efficacy of probiotics. In this review, we discuss the importance of microbiome modulation and hemostasis via probiotics, prebiotics, postbiotics and synbiotics in ameliorating pathological neurodegenerative events. Also, we meticulously describe the underlying mechanism of action of probiotics and their metabolites on the gut-brain axis in different NDs. We suppose that the present work will provide a functional direction for the use of probiotic-based modalities in promoting current practical treatments for the management of neurodegenerative-related diseases.

The role of AMPKα subunit in Alzheimer's disease: In-depth analysis and future prospects

The AMP-activated protein kinase α (AMPKα) subunit is the catalytic subunit in the AMPK complex, playing a crucial role in AMPK activation. It has two isoforms: AMPKα1 and AMPKα2. Emerging evidence suggests that the AMPKα subunit exhibits subtype-specific effects in Alzheimer's disease (AD). This review discusses the role of the AMPKα subunit in the pathogenesis of AD, including its impact on β-amyloid (Aβ) pathology, Tau pathology, metabolic disorders, inflammation, mitochondrial dysfunction, inflammasome and pyroptosis. Additionally, it reviews the distinct roles of its isoforms, AMPKα1 and AMPKα2, in AD, which may provide more precise targets for future drug development in AD.

Alteration of serum bile acids in amyotrophic lateral sclerosis

Hydrophilic endogenous bile acids ursodeoxycholic acid (UDCA), tauroursodeoxycholic acid (TUDCA), and glucourosodeoxycholic acid (GUDCA) have suggested neuroprotective effects. We performed a case-control study to examine the association between ALS diagnosis and serum levels of bile acids. Sporadic and familial ALS patients, age- and sex-matched healthy controls, and presymptomatic gene carriers who donated blood samples were included. Non-fasted serum samples stored at -80°C were used for the analysis. Serum bile acid levels were measured by liquid chromatography-mass spectrometry (LC-MS). Concentrations of 15 bile acids were obtained, 5 non-conjugated and 10 conjugated, and compared between ALS versus control groups (presymptomatic gene carriers + healthy controls) using the Wilcoxon-Rank-Sum test. In total, 80 participants were included: 31 ALS (17 sporadic and 14 familial ALS); 49 controls (22 gene carriers, 27 healthy controls). The mean age was 50 years old and 50% were male. In the ALS group, 45% had familial disease with a pathogenic variant in C9orf72 (29%), TARDBP (10%), FUS (3%), and CHCHD10 (3%) genes. In the control group, 43% carried pathogenic variants: C9orf72 (27%), SOD1 (10%), and FUS (6%). The serum levels of UDCA, TUDCA, and GUDCA trended higher in the ALS group compared to controls (median 27 vs. 7 nM, 4 vs. 3 nM, 110 vs. 47 nM, p-values 0.04, 0.06, 0.04, respectively). No significant group differences were found in other bile acids serum levels. In conclusion, the serum level of UDCA, TUDCA, GUDCA trended higher in ALS patients compared to controls, and no evidence of deficiencies was found.

Diet-induced metabolic and immune impairments are sex-specifically modulated by soluble TNF signaling in the 5xFAD mouse model of Alzheimer's disease

Emerging evidence indicates that high-fat, high carbohydrate diet (HFHC) impacts central pathological features of Alzheimer's disease (AD) across both human incidences and animal models. However, the mechanisms underlying this association are poorly understood. Here, we identify compartment-specific metabolic and inflammatory dysregulations that are induced by HFHC diet in the 5xFAD mouse model of AD pathology. We observe that both male and female 5xFAD mice display exacerbated adiposity, cholesterolemia, and dysregulated insulin signaling. Independent of biological sex, HFHC diet also resulted in altered inflammatory cytokine profiles across the gastrointestinal, circulating, and central nervous systems (CNS) compartments demonstrating region-specific impacts of metabolic inflammation. Interestingly, inhibiting the inflammatory cytokine, soluble tumor necrosis factor (TNF) with the brain-permeant soluble TNF inhibitor XPro1595 was able to restore aspects of HFHC-induced metabolic inflammation, but only in male mice. Targeted transcriptomics of CNS regions revealed that inhibition of soluble TNF was sufficient to alter expression of hippocampal and cortical genes associated with beneficial immune and metabolic responses. Collectively, these results suggest that HFHC diet impairs metabolic and inflammatory pathways in an AD-relevant genotype and that soluble TNF has sex-dependent roles in modulating these pathways across anatomical compartments. Modulation of energy homeostasis and inflammation may provide new therapeutic avenues for AD.

Gut microbiota-host lipid crosstalk in Alzheimer's disease: implications for disease progression and therapeutics

Trillions of intestinal bacteria in the human body undergo dynamic transformations in response to physiological and pathological changes. Alterations in their composition and metabolites collectively contribute to the progression of Alzheimer's disease. The role of gut microbiota in Alzheimer's disease is diverse and complex, evidence suggests lipid metabolism may be one of the potential pathways. However, the mechanisms that gut microbiota mediate lipid metabolism in Alzheimer's disease pathology remain unclear, necessitating further investigation for clarification. This review highlights the current understanding of how gut microbiota disrupts lipid metabolism and discusses the implications of these discoveries in guiding strategies for the prevention or treatment of Alzheimer's disease based on existing data.

Effect of age on metabolomic changes in a model of paclitaxel-induced peripheral neurotoxicity

BACKGROUND AND AIMS

Chemotherapy-induced peripheral neurotoxicity (CIPN) is one of the most common dose-limiting side effects of paclitaxel (PTX) treatment. Many age-related changes have been hypothesized to underlie susceptibility to damage or impaired regeneration/repair after nerve injury. The results of these studies, however, are inconclusive and other potential biomarkers of nerve impairment need to be investigated.

METHODS

Twenty-four young (2 months) and 24 adult (9 months) Wistar male rats were randomized to either PTX treatment (10 mg/kg i.v. once/week for 4 weeks) or vehicle administration. Neurophysiological and behavioral tests were performed at baseline, after 4 weeks of treatment and 2-week follow-up. Skin biopsies and nerve specimens collected from sacrificed animals were examined for intraepidermal nerve fiber (IENF) density assessment and nerve morphology/morphometry. Blood and liver samples were collected for targeted metabolomics analysis.

RESULTS

At the end of treatment, the neurophysiological studies revealed a reduction in sensory nerve action potential amplitude (p < .05) in the caudal nerve of young PTX-animals, and in both the digital and caudal nerve of adult PTX-animals (p < .05). A significant decrease in the mechanical threshold was observed only in young PTX-animals (p < .001), but not in adult PTX-ones. Nevertheless, both young and adult PTX-rats had reduced IENF density (p < .0001), which persisted at the end of follow-up period. Targeted metabolomics analysis showed significant differences in the plasma metabolite profiles between PTX-animals developing peripheral neuropathy and age-matched controls, with triglycerides, diglycerides, acylcarnitines, carnosine, long chain ceramides, sphingolipids, and bile acids playing a major role in the response to PTX administration.

INTERPRETATION

Our study identifies for the first time multiple related metabolic axes involved in PTX-induced peripheral neurotoxicity, and suggests age-related differences in CIPN manifestations and in the metabolic profile.

Glucocorticoid receptor-dependent therapeutic efficacy of tauroursodeoxycholic acid in preclinical models of spinocerebellar ataxia type 3

Spinocerebellar ataxia type 3 (SCA3) is an adult-onset neurodegenerative disease caused by a polyglutamine expansion in the ataxin-3 (ATXN3) gene. No effective treatment is available for this disorder, other than symptom-directed approaches. Bile acids have shown therapeutic efficacy in neurodegenerative disease models. Here, we pinpointed tauroursodeoxycholic acid (TUDCA) as an efficient therapeutic, improving the motor and neuropathological phenotype of SCA3 nematode and mouse models. Surprisingly, transcriptomic and functional in vivo data showed that TUDCA acts in neuronal tissue through the glucocorticoid receptor (GR), but independently of its canonical receptor, the farnesoid X receptor (FXR). TUDCA was predicted to bind to the GR, in a similar fashion to corticosteroid molecules. GR levels were decreased in disease-affected brain regions, likely due to increased protein degradation as a consequence of ATXN3 dysfunction being restored by TUDCA treatment. Analysis of a SCA3 clinical cohort showed intriguing correlations between the peripheral expression of GR and the predicted age at disease onset in presymptomatic subjects and FKBP5 expression with disease progression, suggesting this pathway as a potential source of biomarkers for future study. We have established a novel in vivo mechanism for the neuroprotective effects of TUDCA in SCA3 and propose this readily available drug for clinical trials in SCA3 patients.

The microbiota-gut-brain axis in Huntington's disease: pathogenic mechanisms and therapeutic targets

Huntington's disease (HD) is a currently incurable neurogenerative disorder and is typically characterized by progressive movement disorder (including chorea), cognitive deficits (culminating in dementia), psychiatric abnormalities (the most common of which is depression), and peripheral symptoms (including gastrointestinal dysfunction). There are currently no approved disease-modifying therapies available for HD, with death usually occurring approximately 10-25 years after onset, but some therapies hold promising potential. HD subjects are often burdened by chronic diarrhea, constipation, esophageal and gastric inflammation, and a susceptibility to diabetes. Our understanding of the microbiota-gut-brain axis in HD is in its infancy and growing evidence from preclinical and clinical studies suggests a role of gut microbial population imbalance (gut dysbiosis) in HD pathophysiology. The gut and the brain can communicate through the enteric nervous system, immune system, vagus nerve, and microbiota-derived-metabolites including short-chain fatty acids, bile acids, and branched-chain amino acids. This review summarizes supporting evidence demonstrating the alterations in bacterial and fungal composition that may be associated with HD. We focus on mechanisms through which gut dysbiosis may compromise brain and gut health, thus triggering neuroinflammatory responses, and further highlight outcomes of attempts to modulate the gut microbiota as promising therapeutic strategies for HD. Ultimately, we discuss the dearth of data and the need for more longitudinal and translational studies in this nascent field. We suggest future directions to improve our understanding of the association between gut microbes and the pathogenesis of HD, and other 'brain and body disorders'.

Diet-induced metabolic and immune impairments are sex-specifically modulated by soluble TNF signaling in the 5xFAD mouse model of Alzheimer's disease

Emerging evidence indicates that high-fat, high carbohydrate diet (HFHC) impacts central pathological features of Alzheimer's disease (AD) across both human incidences and animal models. However, the mechanisms underlying this association are poorly understood. Here, we identify compartment-specific metabolic and inflammatory dysregulations that are induced by HFHC diet in the 5xFAD mouse model of AD pathology. We observe that both male and female 5xFAD mice display exacerbated adiposity, cholesterolemia, and dysregulated insulin signaling. Independent of biological sex, HFHC diet also resulted in altered inflammatory cytokine profiles across the gastrointestinal, circulating, and central nervous systems (CNS) compartments demonstrating region-specific impacts of metabolic inflammation. In male mice, we note that HFHC triggered increases in amyloid beta, an observation not seen in female mice. Interestingly, inhibiting the inflammatory cytokine, soluble tumor necrosis factor (TNF) with the brain-permeant soluble TNF inhibitor XPro1595 was able to restore aspects of HFHC-induced metabolic inflammation, but only in male mice. Targeted transcriptomics of CNS regions revealed that inhibition of soluble TNF was sufficient to alter expression of hippocampal and cortical genes associated with beneficial immune and metabolic responses. Collectively, these results suggest that HFHC diet impairs metabolic and inflammatory pathways in an AD-relevant genotype and that soluble TNF has sex-dependent roles in modulating these pathways across anatomical compartments. Modulation of energy homeostasis and inflammation may provide new therapeutic avenues for AD.

Stimulating VAPB-PTPIP51 ER-mitochondria tethering corrects FTD/ALS mutant TDP43 linked Ca2+ and synaptic defects

Frontotemporal dementia (FTD) and amyotrophic lateral sclerosis (ALS) are clinically linked major neurodegenerative diseases. Notably, TAR DNA-binding protein-43 (TDP43) accumulations are hallmark pathologies of FTD/ALS and mutations in the gene encoding TDP43 cause familial FTD/ALS. There are no cures for FTD/ALS. FTD/ALS display damage to a broad range of physiological functions, many of which are regulated by signaling between the endoplasmic reticulum (ER) and mitochondria. This signaling is mediated by the VAPB-PTPIP51 tethering proteins that serve to recruit regions of ER to the mitochondrial surface so as to facilitate inter-organelle communications. Several studies have now shown that disrupted ER-mitochondria signaling including breaking of the VAPB-PTPIP51 tethers are features of FTD/ALS and that for TDP43 and other familial genetic FTD/ALS insults, this involves activation of glycogen kinase-3β (GSK3β). Such findings have prompted suggestions that correcting damage to ER-mitochondria signaling and the VAPB-PTPIP51 interaction may be broadly therapeutic. Here we provide evidence to support this notion. We show that overexpression of VAPB or PTPIP51 to enhance ER-mitochondria signaling corrects mutant TDP43 induced damage to inositol 1,4,5-trisphosphate (IP3) receptor delivery of Ca2+ to mitochondria which is a primary function of the VAPB-PTPIP51 tethers, and to synaptic function. Moreover, we show that ursodeoxycholic acid (UDCA), an FDA approved drug linked to FTD/ALS and other neurodegenerative diseases therapy and whose precise therapeutic target is unclear, corrects TDP43 linked damage to the VAPB-PTPIP51 interaction. We also show that this effect involves inhibition of TDP43 mediated activation of GSK3β. Thus, correcting damage to the VAPB-PTPIP51 tethers may have therapeutic value for FTD/ALS and other age-related neurodegenerative diseases.

Tauroursodeoxycholic acid: a bile acid that may be used for the prevention and treatment of Alzheimer's disease

Alzheimer's disease (AD) is a prevalent neurodegenerative disease that has become one of the main factors affecting human health. It has serious impacts on individuals, families, and society. With the development of population aging, the incidence of AD will further increase worldwide. Emerging evidence suggests that many physiological metabolic processes, such as lipid metabolism, are implicated in the pathogenesis of AD. Bile acids, as the main undertakers of lipid metabolism, play an important role in the occurrence and development of Alzheimer's disease. Tauroursodeoxycholic acid, an endogenous bile acid, has been proven to possess therapeutic effects in different neurodegenerative diseases, including Alzheimer's disease. This review tries to find the relationship between bile acid metabolism and AD, as well as explore the therapeutic potential of bile acid taurocursodeoxycholic acid for this disease. The potential mechanisms of taurocursodeoxycholic acid may include reducing the deposition of Amyloid-β protein, regulating apoptotic pathways, preventing tau hyperphosphorylation and aggregation, protecting neuronal synapses, exhibiting anti-inflammatory properties, and improving metabolic disorders. The objective of this study is to shed light on the use of tauroursodeoxycholic acid preparations in the prevention and treatment of AD, with the aim of identifying effective treatment targets and clarifying various treatment mechanisms involved in this disease.

Microbiota-gut-brain axis and its therapeutic applications in neurodegenerative diseases

The human gastrointestinal tract is populated with a diverse microbial community. The vast genetic and metabolic potential of the gut microbiome underpins its ubiquity in nearly every aspect of human biology, including health maintenance, development, aging, and disease. The advent of new sequencing technologies and culture-independent methods has allowed researchers to move beyond correlative studies toward mechanistic explorations to shed light on microbiome-host interactions. Evidence has unveiled the bidirectional communication between the gut microbiome and the central nervous system, referred to as the "microbiota-gut-brain axis". The microbiota-gut-brain axis represents an important regulator of glial functions, making it an actionable target to ameliorate the development and progression of neurodegenerative diseases. In this review, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases. As the gut microbiome provides essential cues to microglia, astrocytes, and oligodendrocytes, we examine the communications between gut microbiota and these glial cells during healthy states and neurodegenerative diseases. Subsequently, we discuss the mechanisms of the microbiota-gut-brain axis in neurodegenerative diseases using a metabolite-centric approach, while also examining the role of gut microbiota-related neurotransmitters and gut hormones. Next, we examine the potential of targeting the intestinal barrier, blood-brain barrier, meninges, and peripheral immune system to counteract glial dysfunction in neurodegeneration. Finally, we conclude by assessing the pre-clinical and clinical evidence of probiotics, prebiotics, and fecal microbiota transplantation in neurodegenerative diseases. A thorough comprehension of the microbiota-gut-brain axis will foster the development of effective therapeutic interventions for the management of neurodegenerative diseases.

Amyotrophic Lateral Sclerosis in Long-COVID Scenario and the Therapeutic Potential of the Purinergic System in Neuromodulation

Amyotrophic lateral sclerosis (ALS) involves the degeneration of motor neurons and debilitating and possibly fatal symptoms. The COVID-19 pandemic directly affected the quality of life of this group, and the SARS-CoV-2 infection accelerated the present neuroinflammatory process. Furthermore, studies indicate that the infection may have led to the development of the pathology. Thus, the scenario after this pandemic presents "long-lasting COVID" as a disease that affects people who have been infected. From this perspective, studying the pathophysiology behind ALS associated with SARS-CoV-2 infection and possible supporting therapies becomes necessary when we understand the impact on the quality of life of these patients. Thus, the purinergic system was trained to demonstrate how its modulation can add to the treatment, reduce disease progression, and result in better prognoses. From our studies, we highlight the P2X7, P2X4, and A2AR receptors and how their activity can directly influence the ALS pathway.

Novel insight into the etiology of ischemic stroke gained by integrative multiome-wide association study

Stroke, characterized by sudden neurological deficits, is the second leading cause of death worldwide. Although genome-wide association studies (GWAS) have successfully identified many genomic regions associated with ischemic stroke (IS), the genes underlying risk and their regulatory mechanisms remain elusive. Here, we integrate a large-scale GWAS (N = 1 296 908) for IS together with molecular QTLs data, including mRNA, splicing, enhancer RNA (eRNA), and protein expression data from up to 50 tissues (total N = 11 588). We identify 136 genes/eRNA/proteins associated with IS risk across 60 independent genomic regions and find IS risk is most enriched for eQTLs in arterial and brain-related tissues. Focusing on IS-relevant tissues, we prioritize 9 genes/proteins using probabilistic fine-mapping TWAS analyses. In addition, we discover that blood cell traits, particularly reticulocyte cells, have shared genetic contributions with IS using TWAS-based pheWAS and genetic correlation analysis. Lastly, we integrate our findings with a large-scale pharmacological database and identify a secondary bile acid, deoxycholic acid, as a potential therapeutic component. Our work highlights IS risk genes/splicing-sites/enhancer activity/proteins with their phenotypic consequences using relevant tissues as well as identify potential therapeutic candidates for IS.

Neuroprotective Effect of Tauroursodeoxycholic Acid (TUDCA) on In Vitro and In Vivo Models of Retinal Disorders: A Systematic Review

BACKGROUND

Tauroursodeoxycholic acid (TUDCA) is a naturally produced hydrophilic bile acid that has been used for centuries in Chinese medicine. Numerous recent in vitro and in vivo studies have shown that TUDCA has neuroprotective action in various models of retinal disorders.

OBJECTIVE

To systematically review the scientific literature and provide a comprehensive summary on the neuroprotective action and the mechanisms involved in the cytoprotective effects of TUDCA.

METHODS

A systematic review was conducted in accordance with the PRISMA (The Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines. Systematic literature search of United States National Library of Medicine (PubMed), Web of Science, Embase, Scopus and Cochrane Library was performed, which covered all original articles published up to July 2022. The terms, "TUDCA" in combination with "retina", "retinal protection", "neuroprotection" were searched. Possible biases were identified with the adopted SYRCLE's tool.

RESULTS

Of the 423 initially gathered studies, 24 articles met inclusion/exclusion criteria for full-text review. Six of them were in vitro experiments, 17 studies reported in vivo data and one study described both in vitro and in vivo data. The results revealed the effect of TUDCA on different retinal diseases, such as retinitis pigmentosa (RP), diabetic retinopathy (DR), retinal degeneration (RD), retinal ganglion cell (RGC) injury, Leber's hereditary optic neuropathy (LHON), choroidal neovascularization (CNV), and retinal detachment (RDT). The quality scores of the in vivo studies were ranged from 5 to 7 points (total 10 points), according to SYRCLE's risk of bias tool. Both in vitro and in vivo data suggested that TUDCA could effectively delay degeneration and apoptosis of retinal neurons, preserve retinal structure and function, and its mechanism of actions might be related with inhibiting apoptosis, decreasing inflammation, attenuating oxidative stress, suppressing endoplasmic reticulum (ER) stress, and reducing angiogenesis.

CONCLUSION

This systematic review demonstrated that TUDCA has neuroprotective effect on in vivo and in vitro models of retinal disorders, reinforcing the currently available evidence that TUDCA could be a promising therapeutic agent in retinal diseases treatment. However, well designed clinical trials are necessary to appraise the efficacy of TUDCA in clinical setting.

Roles of bile acids signaling in neuromodulation under physiological and pathological conditions

Bile acids (BA) are important physiological molecules not only mediating nutrients absorption and metabolism in peripheral tissues, but exerting neuromodulation effect in the central nerve system (CNS). The catabolism of cholesterol to BA occurs predominantly in the liver by the classical and alternative pathways, or in the brain initiated by the neuronal-specific enzyme CYP46A1 mediated pathway. Circulating BA could cross the blood brain barrier (BBB) and reach the CNS through passive diffusion or BA transporters. Brain BA might trigger direct signal through activating membrane and nucleus receptors or affecting activation of neurotransmitter receptors. Peripheral BA may also provide the indirect signal to the CNS via farnesoid X receptor (FXR) dependent fibroblast growth factor 15/19 (FGF15/19) pathway or takeda G protein coupled receptor 5 (TGR5) dependent glucagon-like peptide-1 (GLP-1) pathway. Under pathological conditions, alterations in BA metabolites have been discovered as potential pathogenic contributors in multiple neurological disorders. Attractively, hydrophilic ursodeoxycholic acid (UDCA), especially tauroursodeoxycholic acid (TUDCA) can exert neuroprotective roles by attenuating neuroinflammation, apoptosis, oxidative or endoplasmic reticulum stress, which provides promising therapeutic effects for treatment of neurological diseases. This review summarizes recent findings highlighting the metabolism, crosstalk between brain and periphery, and neurological functions of BA to elucidate the important role of BA signaling in the brain under both physiological and pathological conditions.

Current State and Future Directions in the Therapy of ALS

Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disorder affecting upper and lower motor neurons, with death resulting mainly from respiratory failure three to five years after symptom onset. As the exact underlying causative pathological pathway is unclear and potentially diverse, finding a suitable therapy to slow down or possibly stop disease progression remains challenging. Varying by country Riluzole, Edaravone, and Sodium phenylbutyrate/Taurursodiol are the only drugs currently approved in ALS treatment for their moderate effect on disease progression. Even though curative treatment options, able to prevent or stop disease progression, are still unknown, recent breakthroughs, especially in the field of targeting genetic disease forms, raise hope for improved care and therapy for ALS patients. In this review, we aim to summarize the current state of ALS therapy, including medication as well as supportive therapy, and discuss the ongoing developments and prospects in the field. Furthermore, we highlight the rationale behind the intense research on biomarkers and genetic testing as a feasible way to improve the classification of ALS patients towards personalized medicine.

Connecting the Gut Microbiota and Neurodegenerative Diseases: the Role of Bile Acids

With the acceleration of global population aging, neurodegenerative diseases (NDs) will become the second leading cause of death in the world, which seriously threatens human life and health. Alzheimer's disease and Parkinson's disease are the most common and typical NDs. The exact mechanisms of the NDs occurrence and development remain unclear, which may be related to immune, oxidative stress, and abnormal aggregation of pathogenic proteins. Studies have suggested that gut microbiota (GM) influences brain function and plays an important role in regulating emotional and cognitive function. Recently, bile acids (BAs) have become the "star molecule" in the microbiota-gut-brain (MGB) axis research. BAs have been reported to exert anti-inflammatory, antioxidant, and neuroprotective activities in NDs. However, the role of BAs in the connection between GM and the central nervous system (CNS) is still unclear. In this review, we will review the possible mechanisms of BAs between GM and NDs and explore the function of BAs to provide ideas for the prevention and treatment of NDs in the future.

Novel insight into the etiology of ischemic stroke gained by integrative transcriptome-wide association study

Stroke, characterized by sudden neurological deficits, is the second leading cause of death worldwide. Although genome-wide association studies (GWAS) have successfully identified many genomic regions associated with ischemic stroke (IS), the genes underlying risk and their regulatory mechanisms remain elusive. Here, we integrate a large-scale GWAS (N=1,296,908) for IS together with mRNA, splicing, enhancer RNA (eRNA) and protein expression data (N=11,588) from 50 tissues. We identify 136 genes/eRNA/proteins associated with IS risk across 54 independent genomic regions and find IS risk is most enriched for eQTLs in arterial and brain-related tissues. Focusing on IS-relevant tissues, we prioritize 9 genes/proteins using probabilistic fine-mapping TWAS analyses. In addition, we discover that blood cell traits, particularly reticulocyte cells, have shared genetic contributions with IS using TWAS-based pheWAS and genetic correlation analysis. Lastly, we integrate our findings with a large-scale pharmacological database and identify a secondary bile acid, deoxycholic acid, as a potential therapeutic component. Our work highlights IS risk genes/splicing-sites/enhancer activity/proteins with their phenotypic consequences using relevant tissues as well as identify potential therapeutic candidates for IS.

Dietary Responses of Dementia-Related Genes Encoding Metabolic Enzymes

The age-related loss of the cognitive function is a growing concern for global populations. Many factors that determine cognitive resilience or dementia also have metabolic functions. However, this duality is not universally appreciated when the action of that factor occurs in tissues external to the brain. Thus, we examined a set of genes involved in dementia, i.e., those related to vascular dementia, Alzheimer's disease, Parkinson's disease, and the human metabolism for activity in 12 metabolically active tissues. Mining the Genotype-Tissue Expression (GTEx) data showed that most of these metabolism-dementia (MD) genes (62 of 93, 67%) exhibit a higher median expression in any of the metabolically active tissues than in the brain. After identifying that several MD genes served as blood-based biomarkers of longevity in other studies, we examined the impact of the intake of food, nutrients, and other dietary factors on the expression of MD genes in whole blood in the Framingham Offspring Study (n = 2134). We observed positive correlations between flavonoids and HMOX1, taurine and UQCRC1, broccoli and SLC10A2, and myricetin and SLC9A8 (p < 2.09 × 10^-4). In contrast, dairy protein, palmitic acid, and pie were negatively correlated, respectively, with the expression of IGF1R, CSF1R, and SLC9A8, among others (p < 2.92 × 10^-4). The results of this investigation underscore the potential contributions of metabolic enzyme activity in non-brain tissues to the risk of dementia. Specific epidemiological or intervention studies could be designed using specific foods and nutrients or even dietary patterns focused on these foods and nutrients that influence the expression of some MD genes to verify the findings presented here.

Alterations in Peripheral Metabolites as Key Actors in Alzheimer's Disease

Growing evidence supports that Alzheimer's disease (AD) could be regarded as a metabolic disease, accompanying central and peripheral metabolic disturbance. Nowadays, exploring novel and potentially alternative hallmarks for AD is needed. Peripheral metabolites based on blood and gut may provide new biochemical insights about disease mechanisms. These metabolites can influence brain energy homeostasis, maintain gut mucosal integrity, and regulate the host immune system, which may further play a key role in modulating the cognitive function and behavior of AD. Recently, metabolomics has been used to identify key AD-related metabolic changes and define metabolic changes during AD disease trajectory. This review aims to summarize the key blood- and microbial-derived metabolites that are altered in AD and identify the potential metabolic biomarkers of AD, which will provide future targets for precision therapeutic modulation.

Well-Defined Bifunctional Dendrimer Bearing 54 Nitric Oxide-Releasing Moieties and 54 Ursodeoxycholic Acid Groups Presenting High Anti-Inflammatory Activity

Nitric oxide (NO) and ursodeoxycholic acid (UDCA) are endogenous molecules involved in physiological processes associated with inflammation. Since inflammatory processes are present in the mechanisms of many diseases, these molecules are important for the development of new drugs. Herein, we describe the synthesis of a well-defined bifunctional dendrimer with 108 termini bearing 54 NO-releasing groups and 54 UDCA units (Dendri-(NO/UDCA)₅₄). For comparison, a lower-generation dendrimer bearing 18 NO-releasing groups and 18 UDCA units (Dendri-(NO/UDCA)₁₈) was also synthesized. The anti-inflammatory activity of these dendrimers was evaluated, showing that the bifunctional dendrimers have an inverse correlation between concentration and anti-inflammatory activity, with an effect dramatically pronounced for Dendri-(NO/UDCA)₅₄ 20, which at just 0.25 nM inhibited 76.1% of IL-8 secretion. Data suggest that nanomolar concentrations of these dendrimers aid in releasing NO in a safe and controlled way. This bifunctional dendrimer has great potential as a drug against multifactorial diseases associated with inflammatory processes.

Linking Nonalcoholic Fatty Liver Disease and Brain Disease: Focusing on Bile Acid Signaling

A metabolic illness known as non-alcoholic fatty liver disease (NAFLD), affects more than one-quarter of the world's population. Bile acids (BAs), as detergents involved in lipid digestion, show an abnormal metabolism in patients with NAFLD. However, BAs can affect other organs as well, such as the brain, where it has a neuroprotective effect. According to a series of studies, brain disorders may be extrahepatic manifestations of NAFLD, such as depression, changes to the cerebrovascular system, and worsening cognitive ability. Consequently, we propose that NAFLD affects the development of brain disease, through the bile acid signaling pathway. Through direct or indirect channels, BAs can send messages to the brain. Some BAs may operate directly on the central Farnesoid X receptor (FXR) and the G protein bile acid-activated receptor 1 (GPBAR1) by overcoming the blood-brain barrier (BBB). Furthermore, glucagon-like peptide-1 (GLP-1) and the fibroblast growth factor (FGF) 19 are released from the intestine FXR and GPBAR1 receptors, upon activation, both of which send signals to the brain. Inflammatory, systemic metabolic disorders in the liver and brain are regulated by the bile acid-activated receptors FXR and GPBAR1, which are potential therapeutic targets. From a bile acid viewpoint, we examine the bile acid signaling changes in NAFLD and brain disease. We also recommend the development of dual GPBAR1/FXR ligands to reduce side effects and manage NAFLD and brain disease efficiently.

The role of hypothalamic endoplasmic reticulum stress in schizophrenia and antipsychotic-induced weight gain: A narrative review

Schizophrenia (SCZ) is a serious mental illness that affects 1% of people worldwide. SCZ is associated with a higher risk of developing metabolic disorders such as obesity. Antipsychotics are the main treatment for SCZ, but their side effects include significant weight gain/obesity. Despite extensive research, the underlying mechanisms by which SCZ and antipsychotic treatment induce weight gain/obesity remain unclear. Hypothalamic endoplasmic reticulum (ER) stress is one of the most important pathways that modulates inflammation, neuronal function, and energy balance. This review aimed to investigate the role of hypothalamic ER stress in SCZ and antipsychotic-induced weight gain/obesity. Preliminary evidence indicates that SCZ is associated with reduced dopamine D2 receptor (DRD2) signaling, which significantly regulates the ER stress pathway, suggesting the importance of ER stress in SCZ and its related metabolic disorders. Antipsychotics such as olanzapine activate ER stress in hypothalamic neurons. These effects may induce decreased proopiomelanocortin (POMC) processing, increased neuropeptide Y (NPY) and agouti-related protein (AgRP) expression, autophagy, and leptin and insulin resistance, resulting in hyperphagia, decreased energy expenditure, and central inflammation, thereby causing weight gain. By activating ER stress, antipsychotics such as olanzapine activate hypothalamic astrocytes and Toll-like receptor 4 signaling, thereby causing inflammation and weight gain/obesity. Moreover, evidence suggests that antipsychotic-induced ER stress may be related to their antagonistic effects on neurotransmitter receptors such as DRD2 and the histamine H1 receptor. Taken together, ER stress inhibitors could be a potential effective intervention against SCZ and antipsychotic-induced weight gain and inflammation.

N-3 PUFA Ameliorates the Gut Microbiota, Bile Acid Profiles, and Neuropsychiatric Behaviours in a Rat Model of Geriatric Depression

The brain−gut−microbiome (BGM) axis affects host bioinformation. N-3 polyunsaturated fatty acids (PUFAs) alleviate cognitive impairment and depression in older adults. This study investigated altered microbiota−bile acid signalling as a potential mechanism linking fish oil-induced gut changes in microbiota to alleviate psychological symptoms. Sprague Dawley rats were fed a fish oil diet and administered D-galactose combined with chronic unpredictable mild stress (CUMS) to simulate geriatric depression. The cognitive function, psychological symptoms, microbiota compositions, and faecal bile acid profiles of the rats were assessed thereafter. A correlation analysis was conducted to determine whether the fish oil-induced alteration of the rats’ microbiota and bile acid profiles affected the rats’ behaviour. D-galactose and CUMS resulted in lower concentrations of Firmicutes, significantly altered bile acid profiles, and abnormal neurobehaviours. Fish oil intake alleviated the rats’ emotional symptoms and increased the abundance of Bacteroidetes, Prevotellaceae, Marinifilaceae, and Bacteroidesuniformis. It also elevated the concentrations of primary bile acids and taurine-conjugated bile acids in the rats’ faeces. The rats’ taurine-conjugated bile acid levels were significantly correlated with their behavioural outcomes. In short, fish oil intake may alleviate psychological symptoms by altering the microbial metabolites involved in the BGM axis, especially in the conjugation of bile acids.

Microbial-derived metabolites as a risk factor of age-related cognitive decline and dementia

A consequence of our progressively ageing global population is the increasing prevalence of worldwide age-related cognitive decline and dementia. In the absence of effective therapeutic interventions, identifying risk factors associated with cognitive decline becomes increasingly vital. Novel perspectives suggest that a dynamic bidirectional communication system between the gut, its microbiome, and the central nervous system, commonly referred to as the microbiota-gut-brain axis, may be a contributing factor for cognitive health and disease. However, the exact mechanisms remain undefined. Microbial-derived metabolites produced in the gut can cross the intestinal epithelial barrier, enter systemic circulation and trigger physiological responses both directly and indirectly affecting the central nervous system and its functions. Dysregulation of this system (i.e., dysbiosis) can modulate cytotoxic metabolite production, promote neuroinflammation and negatively impact cognition. In this review, we explore critical connections between microbial-derived metabolites (secondary bile acids, trimethylamine-N-oxide (TMAO), tryptophan derivatives and others) and their influence upon cognitive function and neurodegenerative disorders, with a particular interest in their less-explored role as risk factors of cognitive decline.

Tauroursodeoxycholic acid: a potential therapeutic tool in neurodegenerative diseases

Most neurodegenerative disorders are diseases of protein homeostasis, with misfolded aggregates accumulating. The neurodegenerative process is mediated by numerous metabolic pathways, most of which lead to apoptosis. In recent years, hydrophilic bile acids, particularly tauroursodeoxycholic acid (TUDCA), have shown important anti-apoptotic and neuroprotective activities, with numerous experimental and clinical evidence suggesting their possible therapeutic use as disease-modifiers in neurodegenerative diseases. Experimental evidence on the mechanisms underlying TUDCA's neuroprotective action derives from animal models of Alzheimer's disease, Parkinson's disease, Huntington's diseases, amyotrophic lateral sclerosis (ALS) and cerebral ischemia. Preclinical studies indicate that TUDCA exerts its effects not only by regulating and inhibiting the apoptotic cascade, but also by reducing oxidative stress, protecting the mitochondria, producing an anti-neuroinflammatory action, and acting as a chemical chaperone to maintain the stability and correct folding of proteins. Furthermore, data from phase II clinical trials have shown TUDCA to be safe and a potential disease-modifier in ALS. ALS is the first neurodegenerative disease being treated with hydrophilic bile acids. While further clinical evidence is being accumulated for the other diseases, TUDCA stands as a promising treatment for neurodegenerative diseases.

Natural bear bile powder suppresses neuroinflammation in lipopolysaccharide-treated mice via regulating TGR5/AKT/NF-κB signaling pathway

ETHNOPHARMACOLOGICAL RELEVANCE

According to the Tang Dynasty classics Dietetic Material Medica and the Ming Dynasty classics Compendium of Materia Medica records, bear bile powder (BBP) has been used to treat a variety of diseases, such as febrile seizures, the pathogenesis of which is associated to neuroinflammation. However, the mechanism of BBP on alleviating neuroinflammation remains unclear.

AIMS OF THE STUDY

Microglia can be activated by peripheral lipopolysaccharide (LPS) and play an important role in the pathogenesis of neuroinflammation. The purpose of this study is to investigate the effects and mechanism of BBP in inhibiting LPS-induced microglia inflammation in vitro and in vivo.

MATERIALS AND METHODS

The anti-microglia inflammatory effects and mechanism of BBP were assessed in LPS-treated BV2 microglial cells and in LPS-treated mice. The mRNA expression levels of the inflammatory factor and the protein expressions of cyclooxygenase-2 (COX2), inducible nitric oxide synthase (iNOS), takeda G-protein coupled receptor 5 (TGR5), nuclear factor-κB (NF-κB), inhibitor of NF-κB (IκBɑ), protein kinase B (AKT) in BV2 cells, mouse hippocampus and cortex were detected. The NF-κB transcription activity and NF-κB nuclear translocation were observed.

RESULTS

Our findings showed that BBP reduces branched process retraction and NO in LPS-treated BV2 cells, inhibits the protein expression of ionized calcium binding adaptor molecule 1 in the hippocampus of LPS-treated mice. Moreover, we observed that BBP decreases tumor necrosis factor α, interleukin (IL)-6 and IL-1β mRNA levels, deceases iNOS and COX-2 protein levels, increases TGR5 protein levels, suppresses the phosphorylation of AKT, NF-κB and IκBɑ protein in microglia both in vitro and in vivo. Further, we found that triamterene, the inhibitor of TGR5, abolishes the effects of BBP in LPS- treated BV2 cells.

CONCLUSION

BBP inhibits LPS-induced microglia activation, and the mechanism of its action is partly through TGR5/AKT/NF-κB signaling pathway.

Multi-Omics Characterization of Type 2 Diabetes Mellitus-Induced Cognitive Impairment in the db/db Mouse Model

Type 2 diabetes mellitus (T2DM) is a complex metabolic disorder frequently accompanied by cognitive impairment. Contributing factors such as modern lifestyle, genetic predisposition, and gene environmental interactions have been postulated, but the pathogenesis remains unclear. In this study, we attempt to investigate the potential mechanisms and interventions underlying T2DM-induced cognitive deficits from the brain–gut axis perspective. A combined analysis of the brain transcriptome, plasma metabolome, and gut microbiota in db/db mice with cognitive decline was conducted. Transcriptome analysis identified 222 upregulated gene sets and 85 downregulated gene sets, mainly related to mitochondrial respiratory, glycolytic, and inflammation. In metabolomic analysis, a total of 75 significantly altered metabolites were identified, correlated with disturbances of glucose, lipid, bile acid, and steroid metabolism under disease state. Gut microbiota analysis suggested that the species abundance and diversity of db/db mice were significantly increased, with 23 significantly altered genus detected. Using the multi-omics integration, significant correlations among key genes (n = 33), metabolites (n = 41), and bacterial genera (n = 21) were identified. Our findings suggest that disturbed circulation and brain energy metabolism, especially mitochondrial-related disturbances, may contribute to cognitive impairment in db/db mice. This study provides novel insights into the functional interactions among the brain, circulating metabolites, and gut microbiota.

Energy homeostasis deregulation is attenuated by TUDCA treatment in streptozotocin-induced Alzheimer's disease mice model

Alzheimer’s disease (AD) is a progressive neurodegenerative disorder and the most common cause of dementia. While cognitive deficits remain the major manifestation of AD, metabolic and non-cognitive abnormalities, such as alterations in food intake, body weight and energy balance are also present, both in AD patients and animal models. In this sense, the tauroursodeoxycholic acid (TUDCA) has shown beneficial effects both in reducing the central and cognitive markers of AD, as well as in attenuating the metabolic disorders associated with it. We previously demonstrated that TUDCA improves glucose homeostasis and decreases the main AD neuromarkers in the streptozotocin-induced AD mouse model (Stz). Besides that, TUDCA-treated Stz mice showed lower body weight and adiposity. Here, we investigated the actions of TUDCA involved in the regulation of body weight and adiposity in Stz mice, since the effects of TUDCA in hypothalamic appetite control and energy homeostasis have not yet been explored in an AD mice model. The TUDCA-treated mice (Stz + TUDCA) displayed lower food intake, higher energy expenditure (EE) and respiratory quotient. In addition, we observed in the hypothalamus of the Stz + TUDCA mice reduced fluorescence and gene expression of inflammatory markers, as well as normalization of the orexigenic neuropeptides AgRP and NPY expression. Moreover, leptin-induced p-JAK2 and p-STAT3 signaling in the hypothalamus of Stz + TUDCA mice was improved, accompanied by reduced acute food intake after leptin stimulation. Taken together, we demonstrate that TUDCA treatment restores energy metabolism in Stz mice, a phenomenon that is associated with reduced food intake, increased EE and improved hypothalamic leptin signaling. These findings suggest treatment with TUDCA as a promising therapeutic intervention for the control of energy homeostasis in AD individuals.

Inflammatory pathways in Alzheimer's disease mediated by gut microbiota

In the past decade, numerous studies have demonstrated the close relationship between gut microbiota and the occurrence and development of Alzheimer's disease (AD). However, the specific mechanism is still unclear. Both the neuroinflammation and systemic inflammation serve as the key hubs to accelerate the process of AD by promoting pathology and damaging neuron. What's more, the gut microbiota is also crucial for the regulation of inflammation. Therefore, this review focused on the role of gut microbiota in AD through inflammatory pathways. Firstly, this review summarized the relationship and interaction among gut microbiota, inflammation, and AD. Secondly, the direct and indirect regulatory effects of gut microbiota on AD through inflammatory pathways were described. These effects were mainly mediated by the component of the gut microbiota (lipopolysaccharides (LPS) and amyloid peptides), the metabolites of bacteria (short-chain fatty acids, branched amino acids, and neurotransmitters) and functional by-products (bile acids). In addition, potential treatments (fecal microbiota transplantation, antibiotics, probiotics, prebiotics, and dietary interventions) for AD were also discussed through these mechanisms. Finally, according to the current research status, the key problems to be solved in the future studies were proposed.

Co-delivery of glial cell-derived neurotrophic factor (GDNF) and tauroursodeoxycholic acid (TUDCA) from PLGA microspheres: potential combination therapy for retinal diseases

Retinitis pigmentosa (RP) is a group of genetically diverse inherited disorders characterised by the progressive photoreceptors and pigment epithelial cell dysfunction leading to central vision impairment. Although important advances in the understanding of the pathophysiologic pathways involved in RP have been made, drug delivery for the treatment of ocular disorders affecting the posterior segment of the eye is still an unmet clinical need. In the present study, we describe the development of multi-loaded PLGA-microspheres (MSs) incorporating two neuroprotectants agents (glial cell-line-derived neurotrophic factor-GDNF and Tauroursodeoxycholic acid-TUDCA) as a potential therapeutic tool for the treatment of RP. A solid-in-oil-in-water (S/O/W) emulsion solvent extraction-evaporation technique was employed for MS preparation. A combination of PLGA and vitamin E was used to create the microcarriers. The morphology, particle size, encapsulation efficiency and in vitro release profile of the MSs were studied. Encapsulation efficiencies of GDNF and TUDCA for the initial multiloaded MSs, prepared with methylene chloride (MC) as organic solvent and polyvinyl alcohol (PVA) solution in the external phase, were 28.53±0.36% and 45.65±8.01% respectively. Different technological parameters to optimise the formulation such as the incorporation of a water-soluble co-solvent ethanol (EtOH) in the internal organic phase, as well as NaCl concentration, and viscosity using a viscosizing agent (hydroxypropyl methylcellulose-HPMC) in the external aqueous phase were considered. EtOH incorporation and external phase viscosity of the emulsion were critical attributes for improving drug loading of both compounds. In such a way, when using a methylene chloride/EtOH ratio 75:25 into the inner organic phase and the viscosity agent HPMC (1% w/v) in the external aqueous phase, GDNF and TUDCA payloads resulted 48.86±1.49% and 78.58±10.40% respectively, and a decrease in the initial release of GDNF was observed (22.03±1.41% compared with 40.86±6.66% of the initial multi-loaded formulation). These optimised microparticles exhibited sustained in vitro releases over 91 days. These results suggest that the microencapsulation procedure optimised in this work presents a promising technological strategy for the development of multi-loaded intraocular drug delivery systems (IODDS).

The bile acid TUDCA and neurodegenerative disorders: An overview

Bear bile has been used in Traditional Chinese Medicine for thousands of years due to its therapeutic potential and clinical applications. The tauroursodeoxycholic acid (TUDCA), one of the acids found in bear bile, is a hydrophilic bile acid and naturally produced in the liver by conjugation of taurine to ursodeoxycholic acid (UDCA). Several studies have shown that TUDCA has neuroprotective action in several models of neurodegenerative disorders (ND), including Alzheimer's disease, Parkinson's disease, and Huntington's disease, based on its potent ability to inhibit apoptosis, attenuate oxidative stress, and reduce endoplasmic reticulum stress in different experimental models of these illnesses. Our research extends the knowledge of the bile acid TUDCA actions in ND and the mechanisms and pathways involved in its cytoprotective effects on the brain, providing a novel perspective and opportunities for treatment of these diseases.

A novel 7α-hydroxysteroid dehydrogenase: Magnesium ion significantly enhances its activity and thermostability

7α-Hydroxysteroid dehydrogenase (7α-HSDH) plays an important role in the efficient biotransformation of taurochenodeoxycholic acid (TCDCA) to tauroursodeoxycholic acid (TUDCA). In this paper, a novel NADP(H)-dependent 7α-HSDH (named J-1-1) was discovered, heterologously expressed in Escherichia coli and biochemically characterized. J-1-1 exhibited high enzymatic activities. The specific activities of J-1-1 toward TCDCA, glycochenodeoxycholic acid (GCDCA) and ethyl benzoylacetate (EBA) were 188.3 ± 0.2, 217.6 ± 0.4, and 20.0 ± 0.2 U·mg^-1, respectively, in 50 mM Glycine-NaOH, pH 10.5. Simultaneously, J-1-1 showed high thermostability; 73% of its activity maintained after heat treatment at 40 °C for 100 h. Particularly noteworthy is that magnesium ion could stabilize the structure of J-1-1, resulting in the enhancement of its enzymatic activity and thermostability. The enzymatic activity of J-1-1 increased 40-fold in the presence of 50 mM Mg²⁺, and T_0.5 increased by approximately 6 °C. Furthermore, after heat treatment at 40 °C for 20 min, the control group only retained 52% of the residual enzyme activity, while the residual enzyme activity of the experimental group was still 77% of the J-1-1 enzyme activity with Mg²⁺ and without heat treatment. These properties of 7α-HSDH would be expected to contribute to more extensive applications in the biotransformation of related substrates.

The bile acid TUDCA improves glucose metabolism in streptozotocin-induced Alzheimer's disease mice model

Alzheimer's disease (AD) is a neurodegenerative disorder and the major cause of dementia. According to predictions of the World Health Organization, more than 150 million people worldwide will suffer from dementia by 2050. An increasing number of studies have associated AD with type 2 diabetes mellitus (T2DM), since most of the features found in T2DM are also observed in AD, such as insulin resistance and glucose intolerance. In this sense, some bile acids have emerged as new therapeutic targets to treat AD and metabolic disorders. The taurine conjugated bile acid, tauroursodeoxycholic (TUDCA), reduces amyloid oligomer accumulation and improves cognition in APP/PS1 mice model of AD, and also improves glucose-insulin homeostasis in obese and type 2 diabetic mice. Herein, we investigated the effect of TUDCA upon glucose metabolism in streptozotocin-induced AD mice model (Stz). The Stz mice that received 300 mg/kg TUDCA during 10 days (Stz + TUDCA), showed improvement in glucose tolerance and insulin sensitivity, reduced fasted and fed glycemia, increased islet mass and β-cell area, as well as increased glucose-stimulated insulin secretion, compared with Stz mice that received only PBS. Stz + TUDCA mice also displayed lower neuroinflammation, reduced protein content of amyloid oligomer in the hippocampus, improved memory test and increased protein content of insulin receptor β-subunit in the hippocampus. In conclusion, TUDCA treatment enhanced glucose homeostasis in the streptozotocin-induced Alzheimer's disease mice model, pointing this bile acid as a good strategy to counteract glucose homeostasis disturbance in AD pathology.

Regulation of neuronal bioenergetics as a therapeutic strategy in neurodegenerative diseases

Neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, Huntington's disease, and amyotrophic lateral sclerosis are a heterogeneous group of debilitating disorders with multifactorial etiologies and pathogeneses that manifest distinct molecular mechanisms and clinical manifestations with abnormal protein dynamics and impaired bioenergetics. Mitochondrial dysfunction is emerging as an important feature in the etiopathogenesis of these age-related neurodegenerative diseases. The prevalence and incidence of these diseases is on the rise with the increasing global population and average lifespan. Although many therapeutic approaches have been tested, there are currently no effective treatment routes for the prevention or cure of these diseases. We present the current status of our knowledge and understanding of the involvement of mitochondrial dysfunction in these diseases and highlight recent advances in novel therapeutic strategies targeting neuronal bioenergetics as potential approach for treating these diseases.

Bile Acids as Key Modulators of the Brain-Gut-Microbiota Axis in Alzheimer's Disease

Recently, the concept of the brain-gut-microbiota (BGM) axis disturbances in the pathogenesis of Alzheimer's disease (AD) has been receiving growing attention. At the same time, accumulating data revealing complex interplay between bile acids (BAs), gut microbiota, and host metabolism have shed new light on a potential impact of BAs on the BGM axis. The crosstalk between BAs and gut microbiota is based on reciprocal interactions since microbiota determines BA metabolism, while BAs affect gut microbiota composition. Secondary BAs as microbe-derived neuroactive molecules may affect each of three main routes through which interactions within the BGM axis occur including neural, immune, and neuroendocrine pathways. BAs participate in the regulation of multiple gut-derived molecule release since their receptors are expressed on various cells. The presence of BAs and their receptors in the brain implies a direct effect of BAs on the regulation of neurological functions. Experimental and clinical data confirm that disturbances in BA signaling are present in the course of AD. Disturbed ratio of primary to secondary BAs as well as alterations in BA concertation in serum and brain samples have been reported. An age-related shift in the gut microbiota composition associated with its decreased diversity and stability observed in AD patients may significantly affect BA metabolism and signaling. Given recent evidence on BA neuroprotective and anti-inflammatory effects, new therapeutic targets have been explored including gut microbiota modulation by probiotics and dietary interventions, ursodeoxycholic acid supplementation, and use of BA receptor agonists.

Long-term survival of participants in the CENTAUR trial of sodium phenylbutyrate-taurursodiol in amyotrophic lateral sclerosis

An orally administered, fixed‐dose coformulation of sodium phenylbutyrate‐taurursodiol (PB‐TURSO) significantly slowed functional decline in a randomized, placebo‐controlled, phase 2 trial in ALS (CENTAUR). Herein we report results of a long‐term survival analysis of participants in CENTAUR. In CENTAUR, adults with ALS were randomized 2:1 to PB‐TURSO or placebo. Participants completing the 6‐month (24‐week) randomized phase were eligible to receive PB‐TURSO in the open‐label extension. An all‐cause mortality analysis (35‐month maximum follow‐up post‐randomization) incorporated all randomized participants. Participants and site investigators were blinded to treatment assignments through the duration of follow‐up of this analysis. Vital status was obtained for 135 of 137 participants originally randomized in CENTAUR. Median overall survival was 25.0 months among participants originally randomized to PB‐TURSO and 18.5 months among those originally randomized to placebo (hazard ratio, 0.56; 95% confidence interval, 0.34‐0.92; P = .023). Initiation of PB‐TURSO treatment at baseline resulted in a 6.5‐month longer median survival as compared with placebo. Combined with results from CENTAUR, these results suggest that PB‐TURSO has both functional and survival benefits in ALS.

Bile Acids: A Communication Channel in the Gut-Brain Axis

Bile acids are signalling hormones involved in the regulation of several metabolic pathways. The ability of bile acids to bind and signal through their receptors is modulated by the gut microbiome, since the microbiome contributes to the regulation and synthesis of bile acids as well to their physiochemical properties. From the gut, bacteria have been shown to send signals to the central nervous system via their metabolites, thus affecting the behaviour and brain function of the host organism. In the last years it has become increasingly evident that bile acids affect brain function, during normal physiological and pathological conditions. Although bile acids may be synthesized locally in the brain, the majority of brain bile acids are taken up from the systemic circulation. Since the composition of the brain bile acid pool may be regulated by the action of intestinal bacteria, it is possible that bile acids function as a communication bridge between the gut microbiome and the brain. However, little is known about the molecular mechanisms and the physiological roles of bile acids in the central nervous system. The possibility that bile acids may be a direct link between the intestinal microbiome and the brain is also an understudied subject. Here we review the influence of gut bacteria on the bile acid pool composition and properties, as well as striking evidence showing the role of bile acids as neuroactive molecules.

Trial of Sodium Phenylbutyrate-Taurursodiol for Amyotrophic Lateral Sclerosis

BACKGROUND

Sodium phenylbutyrate and taurursodiol have been found to reduce neuronal death in experimental models. The efficacy and safety of a combination of the two compounds in persons with amyotrophic lateral sclerosis (ALS) are not known.

METHODS

In this multicenter, randomized, double-blind trial, we enrolled participants with definite ALS who had had an onset of symptoms within the previous 18 months. Participants were randomly assigned in a 2:1 ratio to receive sodium phenylbutyrate-taurursodiol (3 g of sodium phenylbutyrate and 1 g of taurursodiol, administered once a day for 3 weeks and then twice a day) or placebo. The primary outcome was the rate of decline in the total score on the Amyotrophic Lateral Sclerosis Functional Rating Scale-Revised (ALSFRS-R; range, 0 to 48, with higher scores indicating better function) through 24 weeks. Secondary outcomes were the rates of decline in isometric muscle strength, plasma phosphorylated axonal neurofilament H subunit levels, and the slow vital capacity; the time to death, tracheostomy, or permanent ventilation; and the time to death, tracheostomy, permanent ventilation, or hospitalization.

RESULTS

A total of 177 persons with ALS were screened for eligibility, and 137 were randomly assigned to receive sodium phenylbutyrate-taurursodiol (89 participants) or placebo (48 participants). In a modified intention-to-treat analysis, the mean rate of change in the ALSFRS-R score was -1.24 points per month with the active drug and -1.66 points per month with placebo (difference, 0.42 points per month; 95% confidence interval, 0.03 to 0.81; P = 0.03). Secondary outcomes did not differ significantly between the two groups. Adverse events with the active drug were mainly gastrointestinal.

CONCLUSIONS

Sodium phenylbutyrate-taurursodiol resulted in slower functional decline than placebo as measured by the ALSFRS-R score over a period of 24 weeks. Secondary outcomes were not significantly different between the two groups. Longer and larger trials are necessary to evaluate the efficacy and safety of sodium phenylbutyrate-taurursodiol in persons with ALS. (Funded by Amylyx Pharmaceuticals and others; CENTAUR ClinicalTrials.gov number, NCT03127514.).

Discontinued disease-modifying therapies for Alzheimer's disease: status and future perspectives

INTRODUCTION

Alzheimer's disease (AD) is the main cause of dementia and represents a huge burden for patients, carers, and healthcare systems. Extensive efforts for over 20 years have failed to find effective disease-modifying drugs. Although amyloid-β (Aβ) accumulation in the brain predicts cognitive decline, effective reduction of plaque load by numerous drug candidates has not yielded significant clinical benefits. A similar pattern is now emerging for drugs which target hyperphosphorylated tau, and trials with anti-inflammatory drugs have been negative despite neuroinflammation appearing to have a crucial role in AD pathogenesis.

AREAS COVERED

This article reviews key drugs that have been discontinued while in development for AD and delineates the future landscape for present and alternative approaches.

EXPERT OPINION

Anti-Aβ drugs have failed to validate the Aβ cascade hypothesis of AD. Early findings suggest that the same is happening with therapeutics targeting tau and focussing future research solely on anti-tau drugs is inappropriate. Alternative targets should be pursued, including apolipoprotein E, immunomodulation, plasma exchange, protein autophagy and clearance, mitochondrial dysfunction, abnormal glucose metabolism, neurovascular unit support, epigenetic dysregulation, synaptic loss and dysfunction, microbiota dysbiosis, and combination therapies. Meanwhile, repurposing of drugs approved for other indications is justified where scientific rationale and robust preclinical evidence exist.

Should drug discovery scientists still embrace the amyloid hypothesis for Alzheimer's disease or should they be looking elsewhere?

INTRODUCTION

Alzheimer's Disease (AD) represents a large and growing challenge to patients, carers and healthcare systems, yet extensive efforts to develop therapeutics to modify its course have been met with repeated failure in recent decades. Although the evident presence of accumulated β-amyloid (Aβ) in AD brains has singled it out as an obvious therapeutic target, the effective reduction of plaque load or soluble Aβ by numerous drug candidates has not produced commensurate clinical benefits - calling into question the Aβ cascade hypothesis of AD. A similar path is now unfolding in the pursuit of therapeutics targeting hyperphosphorylated tau-comprised neurofibrillary tangles.

AREAS COVERED

This perspective reviews the basis of the Aβ cascade hypothesis of AD and how clinical trials of anti-Aβ drugs have failed to support it, and reflects upon the early findings suggesting that a similar path is being followed with therapeutics targeting tau. Other potential approaches to identifying therapeutics for AD are explored herein.

EXPERT OPINION

The relevance of the Aβ cascade hypothesis to the development of therapeutics for AD appears disproven. Drugs targeting tau appear to be suffering the same fate but may yet produce better results. Alternative approaches are being pursued, some of them with initial small-scale, but promising, results.

Structural and biochemical investigation of MARK4 inhibitory potential of cholic acid: Towards therapeutic implications in neurodegenerative diseases

Microtubule affinity regulating kinase (MARK4) is considered as a potential drug target for diabetes, cancer, and neurodegenerative diseases. Since the role of MARK4 in the phosphorylation of tau protein and subsequently Alzheimer's disease has been established, therefore, we have investigated the binding affinity and MARK4 inhibitory potential of cholic acid (CHA) using both computational and spectroscopic methods. Molecular docking suggested a strong binding of CHA to the functionally important residues of MARK4. We further performed 500 ns molecular dynamics simulation which suggested the MARK4-CHA system was quite stable throughout the simulation trajectory. CHA potential binds to the MARK4 with a binding constant (K) of 10⁷ M^-1 at 288 K. Further, MARK4 activity was inhibited by CHA with an IC₅₀ = 5.5 μM. Further insights into the thermodynamic parameters suggested that MARK4-CHA complex formation is driven by both electrostatic and van der Waals interactions. Overall study provides a rationale to use CHA in the drug development via MARK4 inhibition, towards possible therapeutic implications in neurodegenerative diseases.

Comparison of the Protective Effects of Ginsenosides Rb1 and Rg1 on Improving Cognitive Deficits in SAMP8 Mice Based on Anti-Neuroinflammation Mechanism

This present study was designed to investigate the different effects of ginsenosides Rb1 and Rg1 on improving cognitive deficits in 4-month-old SAMP8 mice. Mice were divided into six groups, including the SAMP8 group, the SAMP8 + Donepezil (1.6 mg/kg) group, the SAMP8 + Rb1 (30 and 60 µmol/kg), and SAMP8 + Rg1 (30 and 60 µmol/kg) groups. SAMR1 mice of the same age were used as the control group. Ginsenosides and donepezil were administrated orally to animals for 8 weeks, then the learning and memory ability of mice were measured by using Morris water maze (MWM) test, object recognition test and passive avoidance experiments. The possible mechanisms were studied including the anti-glial inflammation of Rb1 and Rg1 using HE staining, immunohistochemistry and western blot experiments. Results revealed that Rb1 and Rg1 treatment significantly improved the discrimination index of SAMP8 mice in the object recognition test. Rb1 (60 µmol/kg) and Rg1 (30, 60 µmol/kg) could significantly shorten the escape latency in the acquisition test of the MWM test in SAMP8 mice. Furthermore, Rb1 and Rg1 treatments effectively reduced the number of errors in the passive avoidance task in SAMP8 mice. Western blot experiments revealed that Rb1 showed higher effect than Rg1 in decreasing protein expression levels of ASC, caspase-1 and Aβ in the hippocampus of SAMP8 mice, while Rg1 was more effective than Rb1 in decreasing the protein levels of iNOS. In addition, although Rb1 and Rg1 treatments showed significant protective effects in repairing neuronal cells loss and inhibiting the activation of astrocyte and microglia in hippocampus of SAMP8 mice, Rb1 was more effective than Rg1. These results suggest that Rb1 and Rg1 could improve the cognitive impairment in SAMP8 mice, and they have different mechanisms for the treatment of Alzheimer's disease.

Probiotics ameliorate intestinal pathophysiology in a mouse model of Alzheimer's disease

Evidence suggests that changes in intestinal microbiota may affect the central nervous system. However, it is unclear whether alteration of intestinal microbiota affects progression of Alzheimer's disease (AD). To understand this, wild-type control (C57BL/6) mice were compared with the App^NL-G-F model of disease. We used probiotic supplementation to manipulate the gut microbiota. Fecal samples were collected for microbiota profiling. To study brain and intestinal inflammation, biochemical and histological analyses were performed. Altered metabolic pathways were examined by quantifying eicosanoid and bile acid profiles in the brain and serum using ultraperformance liquid chromatography-tandem mass spectrometry. We observed that brain pathology was associated with intestinal dysbiosis and increased intestinal inflammation and leakiness in App^NL-G-F mice. Probiotic supplementation significantly decreased intestinal inflammation and gut permeability with minimal effect on amyloid-β, cytokine, or gliosis levels in the brain. Concentrations of several bile acids and prostaglandins were altered in the serum and brain because of AD or probiotic supplementation. Our study characterizes intestinal dysfunction in an AD mouse model and the potential of probiotic intervention to ameliorate this condition.

GSK3: A Kinase Balancing Promotion and Resolution of Inflammation

GSK3 has been implicated for years in the regulation of inflammation and addressed in a plethora of scientific reports using a variety of experimental (disease) models and approaches. However, the specific role of GSK3 in the inflammatory process is still not fully understood and controversially discussed. Following a detailed overview of structure, function, and various regulatory levels, this review focusses on the immunoregulatory functions of GSK3, including the current knowledge obtained from animal models. Its impact on pro-inflammatory cytokine/chemokine profiles, bacterial/viral infections, and the modulation of associated pro-inflammatory transcriptional and signaling pathways is discussed. Moreover, GSK3 contributes to the resolution of inflammation on multiple levels, e.g., via the regulation of pro-resolving mediators, the clearance of apoptotic immune cells, and tissue repair processes. The influence of GSK3 on the development of different forms of stimulation tolerance is also addressed. Collectively, the role of GSK3 as a kinase balancing the initiation/perpetuation and the amelioration/resolution of inflammation is highlighted.

Non-polyphenolic natural inhibitors of amyloid aggregation

Protein misfolding diseases (PMDs) are chronic and progressive, with no effective therapy so far. Aggregation and misfolding of amyloidogenic proteins are closely associated with the onset and progression of PMDs, such as amyloid-β (Aβ) in Alzheimer's disease, α-Synuclein (α-Syn) in Parkinson's disease and human islet amyloid polypeptide (hIAPP) in type 2 diabetes. Inhibiting toxic aggregation of amyloidogenic proteins is regarded as a promising therapeutic approach in PMDs. The past decade has witnessed the rapid progresses of this field, dozens of inhibitors have been screened and verified in vitro and in vivo, demonstrating inhibitory effects against the aggregation and misfolding of amyloidogenic proteins, together with beneficial effects. Natural products are major sources of small molecule amyloid inhibitors, a number of natural derived compounds have been identified with great bioactivities and translational prospects. Here, we review the non-polyphenolic natural inhibitors that potentially applicable for PMDs treatment, along with their working mechanisms. Future directions are proposed for the development and clinical applications of these inhibitors.

Alzheimer's disease: The derailed repair hypothesis

A lot of research has been done on Alzheimer's disease, especially focused on factors like amyloid beta, ApoE and tau-protein. However, a complete theory on the disease mechanism of AD, including and connecting all known pathological elements of AD in a conceivable context and order of occurrence, is still lacking. In this article I describe a hypothesis on the entire pathophysiology of Alzheimer's disease, based on the most wellknown pathological elements in AD, filling the gaps with hypothetical mechanisms. This proposed mechanism of derailed repair starts with an insufficiently increased level of injury signalling in the axon by ApoE, DLK, APP, BACE-1, Aβ and iPLA2β, followed by an excessive repair response induced by opening of the mitochondrial permeability transition pore, release of mitochondrial CoA and activation of palmitoylation and massive endocytosis. Excessive compounds, associated with injury signalling and repair, start to accumulate, adding to axonal injury. This increased activation of the repair mechanism causes exhaustion of the repair response by lack of mitochondrial CoA. A vicious circle of increased injury signalling and insufficient repair ensues. Based on this hypothesis, I propose possible markers for early diagnosis and disease-modifying treatments for Alzheimer's disease.