Taming neuroinflammation in Alzheimer's disease: The protective role of phytochemicals through the gut-brain axis

The Role of Antioxidant Compounds from Citrus Waste in Modulating Neuroinflammation: A Sustainable Solution

In normal conditions, neuroinflammation induces microglia and astrocyte activation to maintain brain homeostasis. However, excessive or prolonged neuroinflammation can inflict harmful damage on brain tissue. Numerous factors can trigger chronic neuroinflammation, ultimately leading to neurodegeneration. In this context, considering the pressing need for novel, natural approaches to mitigate neuroinflammatory damage, attention has turned to unconventional sources such as agricultural by-products. Citrus fruits are widely consumed globally, producing substantial waste, including peels, seeds, and pulp. Traditionally regarded as agricultural waste, these by-products are now recognized as valuable reservoirs of bioactive compounds, including flavonoids, carotenoids, terpenoids, and limonoids. Among these, citrus polyphenols-particularly flavanones like hesperidin, naringenin, and eriocitrin-have emerged as potent modulators of neuroinflammatory pathways through their multifaceted interactions with cellular antioxidant systems, pro-inflammatory signaling cascades, neurovascular integrity, and gut-brain axis dynamics. This review aims to characterize the key molecules present in citrus waste and synthesizes preclinical and clinical evidence to elucidate the biochemical mechanisms underlying neuroinflammation in neurodegenerative disorders.

The effect of curcumin supplementation on cognitive function: an updated systematic review and meta-analysis

Background

Previous randomized controlled trials (RCTs) did not draw a consistent conclusion about the effect of curcumin on cognitive function.

Methods

We searched Web of Science, PubMed, Cochrane Library and Embase, and 9 RCTs (including 12 independent comparisons) with 501 subjects were included in the present meta-analysis.

Results

Compared with placebo, supplementation of curcumin significantly improved global cognitive function (SMD, 0.82; 95% CI, 0.19 to 1.45; p = 0.010). A curvilinear dose-response effect was observed, and the optimal dose is 0.8 g/day. Subgroup analysis indicated that the beneficial effect of curcumin on cognition was significant only if duration ≥24 weeks (SMD, 1.15; 95% CI, 0.13 to 2.18; p = 0.027), age of participants ≥60 years (SMD, 1.12; 95% CI, 0.03 to 2.21; p = 0.044), or participants from Asian countries (SMD, 0.96; 95% CI, 0.08 to 1.83; p = 0.032). Otherwise, this effect became non-significant (p > 0.05). Sensitivity analysis by excluding each study one by one or excluding all studies with high risk of bias did not obviously influence the final results. No significant publication bias was observed (P for Begg's Test and Egger's test = 0.150 and 0.493, respectively).

Conclusion

Supplementation of curcumin can effectively improve global cognitive function, and the optimal dose and duration is 0.8 g/day and ≥24 weeks. The beneficial effect of curcumin on cognition is more potent in older and Asian participants than younger and Western ones.

Flavonoids in the regulation of microglial-mediated neuroinflammation; focus on fisetin, rutin, and quercetin

Neuroinflammation is a critical mechanism in central nervous system (CNS) inflammatory disorders, encompassing conditions such as Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), multiple sclerosis (MS), traumatic brain injury (TBI), encephalitis, spinal cord injury (SCI), and cerebral stroke. Neuroinflammation is characterized by increased blood vessel permeability, leukocyte infiltration, glial cell activation, and elevated production of inflammatory mediators, such as chemokines and cytokines. Microglia act as the resident macrophages of the central nervous system, serving as the principal defense mechanism in brain tissue. After CNS injury, microglia modify their morphology and downregulate genes that promote homeostatic functions. Despite comprehensive transcriptome analyses revealing specific gene modifications in "pathological" microglia, microglia's precise protective or harmful functions in neurological disorders remain insufficiently comprehended. Accumulating data suggests that the polarization of microglia into the M1 proinflammatory phenotype or the M2 antiinflammatory phenotype may serve as a sensible therapeutic strategy for neuroinflammation. Flavonoids, including rutin, fisetin, and quercetin, function as crucial chemical reservoirs with unique structures and diverse actions and are extensively used to modulate microglial polarization in treating neuroinflammation. This paper highlights the detrimental effects of neuroinflammation seen in neurological disorders such as stroke. Furthermore, we investigate their therapeutic benefits in alleviating neuroinflammation via the modulation of macrophage polarization.

Understanding of Alzheimer's disease pathophysiology for therapeutic implications of natural products as neuroprotective agents

Alzheimer's disease (AD) is a leading cause of dementia, affecting more than 24.3 million people worldwide in 2024. Sporadic AD (SAD) is more common and occurs in the geriatric population, while familial AD (FAD) is rare and appears before the age of 65 years. Due to progressive cholinergic neuronal loss and modulation in the PKC/MAPK pathway, β-secretase gets upregulated, leading to Aβ aggregation, which further activates tau kinases that form neurofibrillary tangles (NFT). Simultaneously, antioxidant enzymes are also upregulated, increasing oxidative stress (OS) and reactive species by impairing mitochondrial function, leading to DNA damage and cell death. This review discusses the classifications and components of several natural products (NPs) that target these signaling pathways for AD treatment. NPs, including alkaloids, polyphenols, flavonoids, polysaccharides, steroids, fatty acids, tannins, and polypeptides derived from plants, microbes, marine animals, venoms, insects, and mushrooms, are explored in detail. A synergistic combination of plant metabolites, together with prebiotics and probiotics has been shown to decrease Aβ aggregates by increasing the production of bioactive compounds. Toxins derived from venomous organisms have demonstrated effectiveness in modulating signaling pathways and reducing OS. Marine metabolites have also shown neuroprotective and anti-inflammatory properties. The cholera toxin B subunit and an Aβ15 fragment have been combined to create a possible oral AD vaccine, that showed enhancement of cognitive function in mice. Insect tea is also a reliable source of antioxidants. A functional edible mushroom snack bar showed an increment in cognitive markers. Future directions and therapeutic approaches for the treatment of AD can be improved by focusing more on NPs derived from these sources.

The regulatory mechanism of intermittent fasting and probiotics on cognitive function by the microbiota-gut-brain axis

Intermittent fasting (IF) is an eating pattern that promotes health and cognitive improvement through periodic fasting and eating. It has been shown to enhance neuroplasticity and reduce oxidative stress and inflammation. Recent studies have demonstrated that probiotic supplementation enhances cognitive performance by modulating gut microbiota composition and increasing short-chain fatty acid production, which in turn promotes neurogenesis and synaptic plasticity. The microbiota-gut-brain axis (MGBA) is the communication bridge between gut microbiota and the brain, influencing cognitive function through the immune, endocrine, and nervous systems. The combination of probiotics and IF may exert complementary effects on cognitive function, with IF enhancing gut microbial diversity and metabolic efficiency, while probiotics further modulate gut barrier integrity and neurotransmitter synthesis. This review critically examines the interplay between probiotics and IF on cognitive function via the MGBA, identifying key mechanisms and potential therapeutic strategies that remain underexplored in current research.

Dietary Phytochemicals in Health and Disease: Mechanisms, Clinical Evidence, and Applications-A Comprehensive Review

Phytochemicals are bioactive compounds found in plants that play a key role in promoting health and preventing diseases. Present in fruits, vegetables, grains, and seed oils, these compounds are considered safe for consumption due to the co-evolution and adaptation between mammals and plants. Due to their wide-ranging biological effects, they have attracted considerable research interest. This comprehensive review explores the mechanisms of action, health benefits, and applications of dietary phytochemicals, with a particular focus on key groups such as polyphenols, flavonoids, and carotenoids. Research shows that dietary phytochemicals interact with nuclear and membrane receptors, influence metabolic pathways, and affect epigenetic modifications. Our review highlights the broad range of biological activities of these compounds, including antioxidant, antibacterial, anti-inflammatory, anti-diabetic, and anticancer effects, all of which contribute to their health-promoting properties. Clinical evidence supports their role in the prevention and management of diseases such as cardiovascular disorders, metabolic conditions, and cancer, with diets rich in phytochemicals being linked to a lower risk of disease. Phytochemicals are also at the cutting edge of applications in food preservation, dietary supplements, and emerging medical treatments. Additionally, we identified advancements in extraction and identification techniques, particularly in metabolomics, which further enhance their applications in these areas. Despite their promising benefits, challenges such as bioavailability, regulatory barriers, and the need for robust clinical trials persist. However, innovative delivery systems like nanoparticles, liposomes, and encapsulation offer potential solutions to enhance bioavailability by improving absorption and stability. The review concludes by emphasizing the potential of personalized nutrition and combination therapies to enhance the health benefits of dietary phytochemicals while stressing the need for advancements in extraction methods, clinical trials, and bioavailability.

Therapeutic Mechanisms of Medicine Food Homology Plants in Alzheimer's Disease: Insights from Network Pharmacology, Machine Learning, and Molecular Docking

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by a gradual decline in cognitive function. Currently, there are no effective treatments for this condition. Medicine food homology plants have gained increasing attention as potential natural treatments for AD because of their nutritional value and therapeutic benefits. In this work, we aimed to provide a deeper understanding of how medicine food homology plants may help alleviate or potentially treat AD by identifying key targets, pathways, and small molecule compounds from 10 medicine food homology plants that play an important role in this process. Using network pharmacology, we identified 623 common targets between AD and the compounds from the selected 10 plants, including crucial proteins such as STAT3, IL6, TNF, and IL1B. Additionally, the small molecules from the selected plants were grouped into four clusters using hierarchical clustering. The ConPlex algorithm was then applied to predict the binding capabilities of these small molecules to the key protein targets. Cluster 3 showed superior predicted binding capabilities to STAT3, TNF, and IL1B, which was further validated by molecular docking. Scaffold analysis of small molecules in Cluster 3 revealed that those with a steroid-like core-comprising three fused six-membered rings and one five-membered ring with a carbon-carbon double bond-exhibited better predicted binding affinities and were potential triple-target inhibitors. Among them, MOL005439, MOL000953, and MOL005438 were identified as the top-performing compounds. This study highlights the potential of medicine food homology plants as a source of active compounds that could be developed into new drugs for AD treatment. However, further pharmacokinetic studies are essential to assess their efficacy and minimize side effects.

Gut microbiota in Alzheimer's disease: Understanding molecular pathways and potential therapeutic perspectives

Accumulating evidence suggests that gut microbiota (GM) plays a crucial role in Alzheimer's disease (AD) pathogenesis and progression. This narrative review explores the complex interplay between GM, the immune system, and the central nervous system in AD. We discuss mechanisms through which GM dysbiosis can compromise intestinal barrier integrity, enabling pro-inflammatory molecules and metabolites to enter systemic circulation and the brain, potentially contributing to AD hallmarks. Additionally, we examine other pathophysiological mechanisms by which GM may influence AD risk, including the production of short-chain fatty acids, secondary bile acids, and tryptophan metabolites. The role of the vagus nerve in gut-brain communication is also addressed. We highlight potential therapeutic implications of targeting GM in AD, focusing on antibiotics, probiotics, prebiotics, postbiotics, phytochemicals, and fecal microbiota transplantation. While preclinical studies showed promise, clinical evidence remains limited and inconsistent. We critically assess clinical trials, emphasizing challenges in translating GM-based therapies to AD patients. The reviewed evidence underscores the need for further research to elucidate precise molecular mechanisms linking GM to AD and determine whether GM dysbiosis is a contributing factor or consequence of AD pathology. Future studies should focus on large-scale clinical trials to validate GM-based interventions' efficacy and safety in AD.

Recent Insights on the Role of Nuclear Receptors in Alzheimer's Disease: Mechanisms and Therapeutic Application

Nuclear receptors (NRs) are ligand-activated transcription factors that regulate a broad array of biological processes, including inflammation, lipid metabolism, cell proliferation, and apoptosis. Among the diverse family of NRs, peroxisome proliferator-activated receptors (PPARs), estrogen receptor (ER), liver X receptor (LXR), farnesoid X receptor (FXR), retinoid X receptor (RXR), and aryl hydrocarbon receptor (AhR) have garnered significant attention for their roles in neurodegenerative diseases, particularly Alzheimer's disease (AD). NRs influence the pathophysiology of AD through mechanisms such as modulation of amyloid-beta (Aβ) deposition, regulation of inflammatory pathways, and improvement of neuronal function. However, the dual role of NRs in AD progression, where some receptors may exacerbate the disease while others offer therapeutic potential, presents a critical challenge for their application in AD treatment. This review explores the functional diversity of NRs, highlighting their involvement in AD-related processes and discussing the therapeutic prospects of NR-targeting strategies. Furthermore, the key challenges, including the necessity for the precise identification of beneficial NRs, detailed structural analysis through molecular dynamics simulations, and further investigation of NR mechanisms in AD, such as tau pathology and autophagy, are also discussed. Collectively, continued research is essential to clarify the role of NRs in AD, ultimately facilitating their potential use in the diagnosis, prevention, and treatment of AD.

Molecular Mechanisms Underlying Neuroinflammation Intervention with Medicinal Plants: A Critical and Narrative Review of the Current Literature

Neuroinflammation is a key factor in the progression of neurodegenerative diseases, driven by the dysregulation of molecular pathways and activation of the brain's immune system, resulting in the release of pro-inflammatory and oxidative molecules. This chronic inflammation is exacerbated by peripheral leukocyte infiltration into the central nervous system. Medicinal plants, with their historical use in traditional medicine, have emerged as promising candidates to mitigate neuroinflammation and offer a sustainable alternative for addressing neurodegenerative conditions in a green healthcare framework. This review evaluates the effects of medicinal plants on neuroinflammation, emphasizing their mechanisms of action, effective dosages, and clinical implications, based on a systematic search of databases such as PubMed, SCOPUS, and Web of Science. The key findings highlight that plants like Cleistocalyx nervosum var. paniala, Curcuma longa, Cannabis sativa, and Dioscorea nipponica reduce pro-inflammatory cytokines (TNF-α, IL-6, and IL-1β), inhibit enzymes (COX-2 and iNOS), and activate antioxidant pathways, particularly Nrf2. NF-κB emerged as the primary pro-inflammatory pathway inhibited across studies. While the anti-inflammatory potential of these plants is significant, the variability in dosages and phytochemical compositions limits clinical translation. Here, we highlight that medicinal plants are effective modulators of neuroinflammation, underscoring their therapeutic potential. Future research should focus on animal models, standardized protocols, and safety assessments, integrating advanced methodologies, such as genetic studies and nanotechnology, to enhance their applicability in neurodegenerative disease management.

Novelties on Neuroinflammation in Alzheimer's Disease-Focus on Gut and Oral Microbiota Involvement

Recent studies underscore the role of gut and oral microbiota in influencing neuroinflammation through the microbiota-gut-brain axis, including in Alzheimer's disease (AD). This review aims to provide a comprehensive synthesis of recent findings on the involvement of gut and oral microbiota in the neuroinflammatory processes associated with AD, emphasizing novel insights and therapeutic implications. This review reveals that dysbiosis in AD patients' gut and oral microbiota is linked to heightened peripheral and central inflammatory responses. Specific bacterial taxa, such as Bacteroides and Firmicutes in the gut, as well as Porphyromonas gingivalis in the oral cavity, are notably altered in AD, leading to significant changes in microglial activation and cytokine production. Gut microbiota alterations are associated with increased intestinal permeability, facilitating the translocation of endotoxins like lipopolysaccharides (LPS) into the bloodstream and exacerbating neuroinflammation by activating the brain's toll-like receptor 4 (TLR4) pathways. Furthermore, microbiota-derived metabolites, including short-chain fatty acids (SCFAs) and amyloid peptides, can cross the blood-brain barrier and modulate neuroinflammatory responses. While microbial amyloids may contribute to amyloid-beta aggregation in the brain, certain SCFAs like butyrate exhibit anti-inflammatory properties, suggesting a potential therapeutic avenue to mitigate neuroinflammation. This review not only highlights the critical role of microbiota in AD pathology but also offers a ray of hope by suggesting that modulating gut and oral microbiota could represent a novel therapeutic strategy for reducing neuroinflammation and slowing disease progression.

Curcumin: A Golden Approach to Healthy Aging: A Systematic Review of the Evidence

Aging-related disorders pose significant challenges due to their complex interplay of physiological and metabolic factors, including inflammation, oxidative stress, and mitochondrial dysfunction. Curcumin, a natural compound with potent antioxidant and anti-inflammatory properties, has emerged as a promising candidate for mitigating these age-related processes. However, gaps in understanding the precise mechanisms of curcumin's effects and the optimal dosages for different conditions necessitate further investigation. This systematic review synthesizes current evidence on curcumin's potential in addressing age-related disorders, emphasizing its impact on cognitive function, neurodegeneration, and muscle health in older adults. By evaluating the safety, efficacy, and mechanisms of action of curcumin supplementation, this review aims to provide insights into its therapeutic potential for promoting healthy aging. A systematic search across three databases using specific keywords yielded 2256 documents, leading to the selection of 15 clinical trials for synthesis. Here, we highlight the promising potential of curcumin as a multifaceted therapeutic agent in combating age-related disorders. The findings of this review suggest that curcumin could offer a natural and effective approach to enhancing the quality of life of aging individuals. Further research and well-designed clinical trials are essential to validate these findings and optimize the use of curcumin in personalized medicine approaches for age-related conditions.