The Beneficial Role of Natural Endocrine Disruptors: Phytoestrogens in Alzheimer's Disease

Secoisolariciresinol diglucoside attenuates neuroinflammation and cognitive impairment in female Alzheimer's disease mice via modulating gut microbiota metabolism and GPER/CREB/BDNF pathway

BACKGROUND

Gender is a significant risk factor for late-onset Alzheimer's disease (AD), often attributed to the decline of estrogen. The plant estrogen secoisolariciresinol diglucoside (SDG) has demonstrated anti-inflammatory and neuroprotective effects. However, the protective effects and mechanisms of SDG in female AD remain unclear.

METHODS

Ten-month-old female APPswe/PSEN1dE9 (APP/PS1) transgenic mice were treated with SDG to assess its potential ameliorative effects on cognitive impairments in a female AD model through a series of behavioral and biochemical experiments. Serum levels of gut microbial metabolites enterodiol (END) and enterolactone (ENL) were quantified using HPLC-MS. Correlation analysis and broad-spectrum antibiotic cocktail (ABx) treatment were employed to demonstrate the involvement of END and ENL in SDG's cognitive improvement effects in female APP/PS1 mice. Additionally, an acute neuroinflammation model was constructed in three-month-old C57BL/6J mice treated with lipopolysaccharide (LPS) and subjected to i.c.v. injection of G15, an inhibitor of G protein-coupled estrogen receptor (GPER), to investigate the mediating role of the estrogen receptor GPER in the cognitive benefits conferred by SDG.

RESULTS

SDG administration resulted in significant improvements in spatial, recognition, and working memory in female APP/PS1 mice. Neuroprotective effects were observed, including enhanced expression of CREB/BDNF and PSD-95, reduced β-amyloid (Aβ) deposition, and decreased levels of TNF-α, IL-6, and IL-10. SDG also altered gut microbiota composition, increasing serum levels of END and ENL. Correlation analysis indicated significant associations between END, ENL, cognitive performance, hippocampal Aβ-related protein mRNA expression, and cortical neuroinflammatory cytokine levels. The removal of gut microbiota inhibited END and ENL production and eliminated the neuroprotective effects of SDG. Furthermore, GPER was found to mediate the inhibitory effects of SDG on neuroinflammatory responses.

CONCLUSION

These findings suggest that SDG promotes the production of gut microbial metabolites END and ENL, which inhibit cerebral β-amyloid deposition, activate GPER to enhance CREB/BDNF signaling pathways, and suppress neuroinflammatory responses. Consequently, SDG exerts neuroprotective effects and ameliorates cognitive impairments associated with AD in female mice.

Unveiling the neuroprotective properties of isoflavones: current evidence, molecular mechanisms and future perspectives

Neurodegenerative diseases encompass a wide range of debilitating and incurable brain disorders characterized by the progressive deterioration of the nervous system's structure and function. Isoflavones, which are naturally occurring polyphenolic phytochemicals, have been found to regulate various cellular signaling pathways associated with the nervous system. The main objective of this comprehensive review is to explore the neuroprotective effects of isoflavones, elucidate the underlying mechanisms, and assess their potential for treating neurodegenerative disorders. Relevant data regarding isoflavones and their impact on neurodegenerative diseases were gathered from multiple library databases and electronic sources, including PubMed, Google Scholar, Web of Science, and Science Direct. Numerous isoflavones, including genistein, daidzein, biochanin A, and formononetin, have exhibited potent neuroprotective properties against various neurodegenerative diseases. These compounds have been found to modulate neurotransmitters, which in turn contributes to their ability to protect against neurodegeneration. Both in vitro and in vivo experimental studies have provided evidence of their neuroprotection mechanisms, which involve interactions with estrogenic receptors, antioxidant effects, anti-inflammatory properties, anti-apoptotic activity, and modulation of neural plasticity. This review aims to provide current insights into the neuroprotective characteristics of isoflavones and shed light on their potential therapeutic applications in future clinical scenarios.

The Caenorhabditis elegans neuroendocrine system and their modulators: An overview

In this review we seek to systematically bring what has been published in the literature about the nervous system, endocrine system, neuroendocrine relationships, neuroendocrine modulations and endocrine disruptors in the alternative model Caenorhabditis elegans. The serotonergic, dopaminergic, GABAergic and glutamatergic neurotransmitters are related to the modulation of the neuroendocrine axis, leading to the activation or inhibition of several processes that occur in the worm through distinct and interconnected pathways. Furthermore, this review addresses the gut-neuronal axis as it has been revealed in recent years that gut microbiota impacts on neuronal functions. This review also approaches xenobiotics that can positively or negatively impact the neuroendocrine system in C. elegans as in mammals, which allows the application of this nematode to screen new drugs and to identify toxicants that are endocrine disruptors.

Endocrine Disruptors and Estrogens in Human Prostatic Tissue

Endocrine disruptors (EDs) are ubiquitous substances both in the environment and everyday products that interfere with the hormonal system. Growing evidence demonstrates their adverse effects on the organism, including the reproductive system and the prostate, owing to their (anti)estrogenic or antiandrogenic effects. Since EDs can interact with steroid hormone actions on-site, understanding the levels of intraprostatic EDs in conjunction with steroids may hold particular significance. The aim of this study was to develop and validate a method for determining estrogens, various groups of EDs (bisphenols, parabens, oxybenzone and nonylphenol) and phytoestrogens in their unconjugated and conjugated forms in prostate tissue by liquid chromatography-tandem mass spectrometry, and subsequently analyze 20 human prostate tissue samples. The method enabled 20 compounds to be analyzed: estrogens (estrone, estradiol, estriol), bisphenols (bisphenol A- BPA, BPS, BPF, BPAF, BPAP, BPZ, BPP), parabens (methyl-, ethyl-, propyl-, butyl-, benzyl- paraben), oxybenzone, nonylphenol and phytoestrogens (daidzein, genistein, equol) with LLOQs between 0.017-2.86 pg/mg of tissue. The most frequently detected EDs in prostate tissues were propylparaben (conjugated and unconjugated forms in 100 % of tissues), methylparaben (unconjugated in 45 % and conjugated in 100 %), ethylparaben (unconjugated in 25 % and conjugated in 100 % BPA (unconjugated in 35 % and conjugated in 60 % and oxybenzone (both forms in 45 % To the best of our knowledge, this is the first study detecting EDs, phytoestrogens and estriol conjugate (E3C) in the prostate. E3C was the most abundant estrogen in prostatic tissue. This highlights the need for further explorations into estrogen metabolism within the prostate.