Betaine Inhibits NLRP3 Inflammasome Hyperactivation and Regulates Microglial M1/M2 Phenotypic Differentiation, Thereby Attenuating Lipopolysaccharide-Induced Depression-Like Behavior

Microglial NLRP3 inflammasome-mediated neuroinflammation and therapeutic strategies in depression

Previous studies have demonstrated a bidirectional relationship between inflammation and depression. Activation of the nucleotide-binding oligomerization domain, leucine-rich repeat, and NLR family pyrin domain-containing 3 (NLRP3) inflammasomes is closely related to the pathogenesis of various neurological diseases. In patients with major depressive disorder, NLRP3 inflammasome levels are significantly elevated. Understanding the role that NLRP3 inflammasome-mediated neuroinflammation plays in the pathogenesis of depression may be beneficial for future therapeutic strategies. In this review, we aimed to elucidate the mechanisms that lead to the activation of the NLRP3 inflammasome in depression as well as to provide insight into therapeutic strategies that target the NLRP3 inflammasome. Moreover, we outlined various therapeutic strategies that target the NLRP3 inflammasome, including NLRP3 inflammatory pathway inhibitors, natural compounds, and other therapeutic compounds that have been shown to be effective in treating depression. Additionally, we summarized the application of NLRP3 inflammasome inhibitors in clinical trials related to depression. Currently, there is a scarcity of clinical trials dedicated to investigating the applications of NLRP3 inflammasome inhibitors in depression treatment. The modulation of NLRP3 inflammasomes in microglia holds promise for the management of depression. Further investigations are necessary to ascertain the efficacy and safety of these therapeutic approaches as potential novel antidepressant treatments.

The role of TrkB signaling-mediated synaptic plasticity in the antidepressant properties of catalpol, the main active compound of Rehmannia glutinosa Libosch

ETHNOPHARMACOLOGICAL RELEVANCE

Rehmannia glutinosa Libosch. (RGL) is a famous ethnic medicine contained in antidepressant Chinese Medicine formulas and is traditionally clinically used for depression. We have recently confirmed that RGL enhanced synaptic plasticity in a mouse model of Chinese medical syndrome and that catalpol may be the representatively pharmacological component responsible for its improvement in synaptic plasticity and treatment of depression. Impaired synaptic plasticity is closely linked to major depression. Tyrosine kinase receptor B (TrkB) signaling has recently been discovered as a key pathway for synaptic plasticity improvement and antidepressant discovery. However, to date, it is unknown whether the target of catalpol to improve synaptic plasticity involves TrkB and whether its antidepressant mechanism involves synaptic plasticity mediated by TrkB signaling.

AIM OF STUDY

This study aims to uncover the antidepressant targets and mechanisms of catalpol, the main active compound of RGL, based on TrkB signaling-mediated synaptic plasticity.

MATERIALS AND METHODS

We have recently predicted through molecular networking strategy (including network pharmacology, molecular docking, and molecular dynamics simulation) that catalpol may exert its antidepressant effects by regulating TrkB signaling and thus modulating essential synaptic plasticity proteins. Then, this study used classic behavioral tests, targeted diagnostic reagents, Nissl and Golgi staining, immunohistochemical analysis, immunofluorescence analysis, western blotting, enzyme-linked immunosorbent assay, and quantitative PCR to confirm the target and signaling of catalpol to improve synaptic plasticity for the treatment of depression.

RESULTS

The data showed that catalpol could improve synaptic plasticity and depressive behaviors, and its action pathway was predicted to involve TrkB signaling. Subsequently, the blockade of TrkB abolished the improvement of synaptic plasticity by catalpol and its antidepressant properties, which validated that TrkB signaling was the key pathway for catalpol to improve synaptic plasticity and exert antidepressant properties. Inhibition of COX-2 was likely to be a necessary facilitator for the antidepressant efficacy of catalpol via the TrkB target and TrkB-mediated synaptic plasticity.

CONCLUSION

TrkB signaling-mediated synaptic plasticity plays a key role in the antidepressant properties of catalpol. This study provides critical information for the development of new and targeted antidepressant therapies or treatment strategies by catalpol. However, considering the existence of sex differences in depression (female depression is 2-3 times than that of males) and not exploring the antidepressant sex specificity of catalpol is a limitation, we will investigate the sex specificity of the antidepressant effects and molecular mechanisms of catalpol on sex-specific animals in the future, to provide a preclinical basis for more accurate and targeted medication of catalpol.

Engeletin alleviates depressive-like behaviours by modulating microglial polarization via the LCN2/CXCL10 signalling pathway

Microglial polarization and associated inflammatory activity are the key mediators of depression pathogenesis. The natural Smilax glabra rhizomilax derivative engeletin has been reported to exhibit robust anti-inflammatory activity, but no studies to date have examined the mechanisms through which it can treat depressive symptoms. We showed that treatment for 21 days with engeletin significantly alleviated depressive-like behaviours in chronic stress social defeat stress (CSDS) model mice. T1-weighted imaging (T1WI), T2-weighted imaging (T2WI) imaging revealed no significant differences between groups, but the bilateral prefrontal cortex of CSDS mice exhibited significant increases in apparent diffusion coefficient and T2 values relative to normal control mice, with a corresponding reduction in fractional anisotropy, while engeletin reversed all of these changes. CSDS resulted in higher levels of IL-1β, IL-6, and TNF-a production, enhanced microglial activation, and greater M1 polarization with a concomitant decrease in M2 polarization in the mPFC, whereas engeletin treatment effectively abrogated these CSDS-related pathological changes. Engeletin was further found to suppress the LCN2/C-X-C motif chemokine ligand 10 (CXCL10) signalling axis such that adeno-associated virus-induced LCN2 overexpression ablated the antidepressant effects of engeletin and reversed its beneficial effects on the M1/M2 polarization of microglia. In conclusion, engeletin can alleviate CSDS-induced depressive-like behaviours by regulating the LCN2/CXCL10 pathway and thereby altering the polarization of microglia. These data suggest that the antidepressant effects of engeletin are correlated with the polarization of microglia, highlighting a potential avenue for future design of antidepressant strategies that specifically target the microglia.

Arginine Methylation of β-Catenin Induced by PRMT2 Aggravates LPS-Induced Cognitive Dysfunction and Depression-Like Behaviors by Promoting Ferroptosis

Depression is a prevalent and debilitating psychiatric disorder, imposing substantial societal and individual burdens. This study aims to investigate the involvement of ferroptosis and microglial polarization in the pathogenesis of depression, as well as the underlying mechanism. Increased protein arginine methyltransferase 2 (PRMT2) expression was observed in BV2 cells and the hippocampus following lipopolysaccharide (LPS) stimulation. Mechanistically, alkylation repair homolog protein 5 (ALKBH5)-mediated m6A modification enhanced the stability of PRMT2 mRNA. PRMT2 promoted arginine methylation of β-catenin and induced proteasomal degradation of β-catenin proteins, resulting in transcriptional inhibition of glutathione peroxidase 4 (GPX4). The upregulation of PRMT2 further accelerated microglia polarization by activating ferroptosis through the β-catenin-GPX4 axis. Depletion of PRMT2 improved LPS-induced depressive- and anxiety-like behaviors as well as cognitive impairment by inhibiting ferroptosis and M1 polarization of microglia. Our findings underscore the crucial involvement of the ALKBH5-PRMT2-β-catenin-GPX4 axis in ferroptosis and M1 polarization of microglia, thereby offering novel insights into the pathogenesis interventions for depression.

Betaine eliminates CFA-induced depressive-like behaviour in mice may be through inhibition of microglia and astrocyte activation and polarization

Chronic pain can induce not only nociceptive but also depressive emotions. A previous study demonstrated that betaine, a commonly used nutrient supplement, has an anti-nociceptive effect, but whether betaine can alleviate chronic pain-induced depressive emotion is elusive. Our current study found that betaine administration significantly eliminated complete Freund's adjuvant (CFA)-induced pain-related depressive-like behaviour. Mechanistically, betaine treatment inhibited microglia and astrocyte activation. Furthermore, betaine significantly promoted the transition of microglia from the M1 to the M2 phenotype, as well as the transition of astrocytes from the A1 to the A2 phenotype. Additionally, the release of pro-inflammatory factors such as IL-18, IL-1β and IL-6 and anti-inflammatory factors such as IL-10 in the hippocampus induced by CFA were also reversed by betaine administration. Overall, betaine has therapeutic effects on pain-related depressive-like phenotypes caused by CFA, possibly through altering the polarization of microglia and astrocytes to reduce neuroinflammation.

Natural products for the treatment of depression: Insights into signal pathways influencing the hypothalamic-pituitary-adrenal axis

Depression, a prevalent psychiatric malady, afflicts a substantial global demographic, engendering considerable disease burden due to its elevated morbidity and mortality rates. Contemporary therapeutic approaches for depression encompass the administration of serotonin reuptake inhibitors, monoamine oxidase inhibitors, and tricyclic antidepressants, albeit these pharmaceuticals potentially induce adverse neurological and gastrointestinal effects. Traditional Chinese Medicine (TCM) natural products proffer the benefits of multi-target, multi-level, and multi-channel depression treatment modalities. In this investigation, we conducted a comprehensive literature review of the past 5 years in PubMed and other databases utilizing the search terms "Depression," "Natural medicines," "Traditional Chinese Medicine," and "hypothalamic-pituitary-adrenal axis." We delineated the 5 most recent and pertinent signaling pathways associated with depression and hypothalamic-pituitary-adrenal (HPA) axis dysregulation: nuclear factor kappa light-chain-enhancer of activated B cell, brain-derived neurotrophic factor, mitogen-activated protein kinase, cyclic AMP/protein kinase A, and phosphoinositide 3-kinase/protein kinase B. Additionally, we deliberated the antidepressant mechanisms of natural medicines comprising alkaloids, flavonoids, polyphenols, saponins, and quinones via diverse pathways. This research endeavor endeavored to encapsulate and synthesize the progression of TCMs in modulating HPA axis-associated signaling pathways to mitigate depression, thereby furnishing robust evidence for ensuing research in this domain.

Making the case for prophylactic use of betaine to promote brain health in young (15-24 year old) athletes at risk for concussion

Betaine supplementation in the context of human nutrition, athletic performance, and clinical therapy demonstrate that the osmolyte and methyl donor, betaine, is cytoprotective and beneficial to human health. These studies also demonstrate that betaine supplementation in healthy humans is straight-forward with no reported adverse effects. Here, we explore betaine uptake in the central nervous system (CNS) and contribute to evidence that betaine may be uniquely protective to the brain. We specifically describe the therapeutic potential of betaine and explore the potential implications of betaine on inhibition mediated by GABA and glycine neurotransmission. The influence of betaine on neurophysiology complement betaine's role as an osmolyte and metabolite and is consistent with clinical evidence of betaine-mediated improvements to cognitive function (reported in elderly populations) and its anti-convulsant properties. Betaine's therapeutic potential in neurological disorders including epilepsy and neurodegenerative diseases combined with benefits of betaine supplementation on athletic performance support the unique application of betaine as a prophylaxis to concussion. As an example, we identify young athletes (15-24 years old), especially females, for prophylactic betaine supplementation to promote brain health and resilience in a cohort at high risk for concussion and for developing Alzheimer's disease.

Involvement of Antioxidant and Prevention of Mitochondrial Dysfunction, Anti-Neuroinflammatory Effect and Anti-Apoptotic Effect: Betaine Ameliorates Haloperidol-Induced Orofacial Dyskinesia in Rats

With its pathophysiological characteristics strongly similar to patients with tardive dyskinesia (TD), haloperidol (HP)-induced neurotoxicity and orofacial dyskinesia (OD) in animal models have long been used to study human TD. This study aimed to explore the potential protective effects of betaine (BT), a vital biochemical compound present in plants, microorganisms, animals, and various dietary sources. The study focused on investigating the impact of BT on haloperidol (HP)-induced orofacial dyskinesia (OD) in rats, as well as the underlying neuroprotective mechanisms. To induce the development of OD, which is characterized by increased vacuous chewing movement (VCM) and tongue protrusion (TP), rats were administered HP (1 mg/kg i.p.) for 21 consecutive days. BT was administered intraperitoneally (i.p.) at doses of 30 and 100 mg/kg, 60 min later, for 21 successive days. On the 21st day, after evaluating OD behavior, the rats were sacrificed, and various measurements were taken to assess the nitrosative and oxidative status, antioxidant capacity, mitochondrial function, neuroinflammation, and apoptotic markers in the striatum. The results demonstrated that (1) HP induced OD development, and (2) BT was found to prevent most of the HP-induced OD; decrease oxidative stress levels; increase anti-oxidation power; prevent mitochondrial dysfunction; and reduce the levels of neuroinflammatory and apoptotic markers in the striatum. Our results demonstrate that the neuroprotective effects of BT against HP-induced OD are credited to its antioxidant prevention of mitochondrial dysfunction, anti-neuroinflammatory effects, and anti-apoptotic effects, suggesting that BT may be a novel therapeutic candidate in delaying or treating human TD in clinical settings. However, further studies will be warranted to extrapolate preclinical findings into clinical studies for a better understanding of the role of BT.