The Nrf2 Pathway in Depressive Disorders: A Systematic Review of Animal and Human Studies

Emerging role of Nrf2 in Parkinson's disease therapy: a critical reassessment

Parkinson's disease (PD) is the neurodegenerative disorder characterized by the progressive degeneration of nigrostriatal dopaminergic neurons, leading to the range of motor and non-motor symptoms. There is mounting evidence suggesting that oxidative stress, neuroinflammation and mitochondrial dysfunction play pivotal roles in the pathogenesis of PD. Current therapies only alleviate perturbed motor symptoms. Therefore, it is essential to find out new therapies that allow us to improve not only motor symptoms, but non-motor symptoms like cognitive impairment and modulate disease progression. Nuclear factor erythroid 2-related factor 2 (Nrf2) is transcription factor that regulates the expression of numerous anti-oxidants and cytoprotective genes can counteract oxidative stress, neuroinflammation and mitochondrial dysfunction, thereby potentially ameliorating PD-associated pathology. The current review discusses about the Nrf2 structure and function with special emphasis on various molecular signalling pathways involved in positive and negative modulation of Nrf2, namely Glycogen synthase kinase-3β, Phosphoinositide-3-kinase, AMP-activated protein kinase, Mitogen activated protein kinase, nuclear factor-κB and P62. Furthermore, this review highlights the various Nrf2 activators as promising therapeutic agents for slowing down the progression of PD.

Model organisms for investigating the functional involvement of NRF2 in non-communicable diseases

Non-communicable chronic diseases (NCDs) are most commonly characterized by age-related loss of homeostasis and/or by cumulative exposures to environmental factors, which lead to low-grade sustained generation of reactive oxygen species (ROS), chronic inflammation and metabolic imbalance. Nuclear factor erythroid 2-like 2 (NRF2) is a basic leucine-zipper transcription factor that regulates the cellular redox homeostasis. NRF2 controls the expression of more than 250 human genes that share in their regulatory regions a cis-acting enhancer termed the antioxidant response element (ARE). The products of these genes participate in numerous functions including biotransformation and redox homeostasis, lipid and iron metabolism, inflammation, proteostasis, as well as mitochondrial dynamics and energetics. Thus, it is possible that a single pharmacological NRF2 modulator might mitigate the effect of the main hallmarks of NCDs, including oxidative, proteostatic, inflammatory and/or metabolic stress. Research on model organisms has provided tremendous knowledge of the molecular mechanisms by which NRF2 affects NCDs pathogenesis. This review is a comprehensive summary of the most commonly used model organisms of NCDs in which NRF2 has been genetically or pharmacologically modulated, paving the way for drug development to combat NCDs. We discuss the validity and use of these models and identify future challenges.

Inhalation of Curcumae Rhizoma volatile oil attenuates depression-like behaviours via activating the Nrf2 pathway to alleviate oxidative stress and improve mitochondrial dysfunction

OBJECTIVES

Curcumae Rhizoma (CR) is a traditional Chinese medicine used frequently in clinics, which contains volatile components that exhibit various active effects. This study explores the effect of Curcumae Rhizoma volatile oil (CRVO) on depressive mice and its possible mechanism of action.

METHODS

Chemical composition of CRVO was analysed by GC-MS. DPPH and ABTS free radical scavenging assays were used to evaluate the in vitro antioxidant capacity of CRVO. A chronic unpredictable mild stress (CUMS) model was used to evaluate the antidepressant effect of CRVO. The effects of CRVO on oxidative stress in vivo were investigated using Nissl staining, ELISA and transmission electron microscopy. The Nrf2/HO-1/NQO1 signalling pathway was detected by western blotting and immunofluorescence. ML385, a Nrf2 inhibitor was used to validate the effect of Nrf2 on CUMS mice with CRVO treatment.

KEY FINDINGS

Phytochemical analysis showed that CRVO is rich in its characteristic components, including curzerene (31.1%), curdione (30.56%), and germacrone (12.44%). In vivo, the administration of CRVO significantly ameliorated CUMS-induced depressive-like behaviours. In addition, inhalation of CRVO significantly alleviated the oxidative stress caused by CUMS and improved neuronal damage and mitochondrial dysfunction. The results of mechanistic studies showed that the mechanism of action is related to the Nrf2/HO-1/NQO1 pathway and the antioxidant and antidepressant effects of CRVO were weakened when ML385 was used.

CONCLUSIONS

In summary, by regulating the Nrf2 pathway, inhalation of CRVO can reduce oxidative stress in depressed mice, thereby reducing neuronal damage and mitochondrial dysfunction to alleviate depression-like behaviours. Our study offers a prospective research foundation to meet the diversity of clinical medication.

The Interplay of Carveol and All-Trans Retinoic Acid (ATRA) in Experimental Parkinson's Disease: Role of Inflammasome-Mediated Pyroptosis and Nrf2

Parkinson's disease (PD) is a debilitating and the second most common neurodegenerative disorder with a high prevalence. PD has a multifaceted etiology characterized by an altered redox state and an excessive inflammatory response. Extensive research has consistently demonstrated the role of the nuclear factor E2-related factor (Nrf2) and inflammasomes, notably NLRP3 in neurodegenerative diseases. In this study, our focus was on exploring the potential neuroprotective properties of carveol in Parkinson's disease. Our findings suggest that carveol may exhibit these effects through Nrf2 and by suppressing pyroptosis. Male albino mice were treated with carveol, and the animal PD model was induced through a single intranigral dose of 2 µg/2µl lipopolysaccharide (LPS). To further demonstrate the essential role of the Nrf2 pathway, we utilized all-trans retinoic acid (ATRA) to inhibit the Nrf2. Our finding showed the induction of pyroptosis as evidenced by increased levels of NLRP3 and other inflammatory mediators, including IL-1β, iNOS, p-NFKB, and apoptotic cell death indicated by positive fluoro Jade B (FJB) staining. Moreover, increased levels of lipid peroxides and reactive oxygen species indicated a significant rise in oxidative stress due to LPS. The administration of carveol mitigates oxidative stress and suppresses inflammatory pathways through the augmentation of intrinsic antioxidant defenses, primarily via the activation of the Nrf2. Conversely, ATRA reversed carveol protective effects by increasing FJB-positive cells, inflammatory and oxidative biomarkers. Taken together, our findings suggest that carveol mitigated LPS-induced Parkinson-like symptoms, partially through the activation of the Nrf2 and downregulation of pyroptosis notably NLRP3.

Repeated Sulforaphane Treatment Reverses Depressive-like Behavior and Exerts Antioxidant Effects in the Olfactory Bulbectomy Model in Mice

Growing evidence suggests that activators of nuclear factor erythroid-derived 2-like 2 (Nrf2), such as sulforaphane, may represent promising novel pharmacological targets for conditions related to oxidative stress, including depressive disorder. Therefore, we conducted a study to explore the behavioral and biochemical effects of repeated (14 days) sulforaphane (SFN) treatment in the olfactory bulbectomy (OB) animal model of depression. An open field test (OFT), splash test (ST), and spontaneous locomotor activity test (LA) were used to assess changes in depressive-like behavior and the potential antidepressant-like activity of SFN. The OB model induced hyperactivity in mice during the OFT and LA as well as a temporary loss of self-care and motivation in the ST. The repeated administration of SFN (10 mg/kg) effectively reversed these behavioral changes in OB mice across all tests. Additionally, a biochemical analysis revealed that SFN (10 mg/kg) increased the total antioxidant capacity in the frontal cortex and serum of the OB model. Furthermore, SFN (10 mg/kg) significantly enhanced superoxide dismutase activity in the serum of OB mice. Overall, the present study is the first to demonstrate the antidepressant-like effects of repeated SFN (10 mg/kg) treatment in the OB model and indicates that these benefits may be linked to improved oxidative status.

RUTIN, a widely consumed flavonoid, that commonly induces hormetic effects

Rutin is a flavonoid present in numerous fruits and vegetables and therefore widely consumed by humans. It is also a popular dietary supplement of 250-500 mg/day. There is considerable consumer interest in rutin due to numerous reports in the biomedical literature of its multi-system chemo-preventive properties. The present paper provides the first assessment of rutin-induced hormetic concentration/dose responses, their quantitative features and mechanistic basis, along with their biological, biomedical, clinical, and public health implications. The findings indicate that rutin-induced hormetic dose responses are widespread, being reported in numerous biological models and cell types for a wide range of endpoints. Of critical importance is that the optimal hormetic findings shown in in vitro systems are currently not achievable for human populations due to low gastrointestinal tract bioavailability. These findings have the potential to strengthen future experimental studies with rutin, particularly concerning study design parameters.

NLRX1 Inhibits LPS-Induced Microglial Death via Inducing p62-Dependent HO-1 Expression, Inhibiting MLKL and Activating PARP-1

The activation of microglia and the production of cytokines are key factors contributing to progressive neurodegeneration. Despite the well-recognized neuronal programmed cell death regulated by microglial activation, the death of microglia themselves is less investigated. Nucleotide-binding oligomerization domain, leucine-rich repeat-containing X1 (NLRX1) functions as a scaffolding protein and is involved in various central nervous system diseases. In this study, we used the SM826 microglial cells to understand the role of NLRX1 in lipopolysaccharide (LPS)-induced cell death. We found LPS-induced cell death is blocked by necrostatin-1 and zVAD. Meanwhile, LPS can activate poly (ADP-ribose) polymerase-1 (PARP-1) to reduce DNA damage and induce heme oxygenase (HO)-1 expression to counteract cell death. NLRX1 silencing and PARP-1 inhibition by olaparib enhance LPS-induced SM826 microglial cell death in an additive manner. Less PARylation and higher DNA damage are observed in NLRX1-silencing cells. Moreover, LPS-induced HO-1 gene and protein expression through the p62-Keap1-Nrf2 axis are attenuated by NLRX1 silencing. In addition, the Nrf2-mediated positive feedback regulation of p62 is accordingly reduced by NLRX1 silencing. Of note, NLRX1 silencing does not affect LPS-induced cellular reactive oxygen species (ROS) production but increases mixed lineage kinase domain-like pseudokinase (MLKL) activation and cell necroptosis. In addition, NLRX1 silencing blocks bafilomycin A1-induced PARP-1 activation. Taken together, for the first time, we demonstrate the role of NLRX1 in protecting microglia from LPS-induced cell death. The underlying protective mechanisms of NLRX1 include upregulating LPS-induced HO-1 expression via Nrf2-dependent p62 expression and downstream Keap1-Nrf2 axis, mediating PARP-1 activation for DNA repair via ROS- and autophagy-independent pathway, and reducing MLKL activation.

Unraveling the potential of vitamins C and D as adjuvants in depression treatment with escitalopram in an LPS animal model

Depression is linked with oxidative stress and inflammation, where key players include nitric oxide (NO), nuclear factor erythroid 2-related factor 2 (Nrf2), Brain-Derived Neurotrophic Factor (BDNF), and Heme Oxidase-1 (HO-1). Augmenting the efficacy of antidepressants represents a compelling avenue of exploration. We explored the potential of vitamins C and D as adjuncts to escitalopram (Esc) in a lipopolysaccharide (LPS)-induced depression model focusing on the aforementioned biomarkers. Male Swiss albino mice were stratified into distinct groups: control, LPS, LPS + Esc, LPS + Esc + Vit C, LPS + Esc + Vit D, and LPS + Esc + Vit C + Vit D. After a 7-day treatment period, a single LPS dose (2 mg/kg), was administered, followed by comprehensive assessments of behavior and biochemical parameters. Notably, a statistically significant (p < 0.05) alleviation of depressive symptoms was discerned in the Esc + Vit C + Vit D group versus the LPS group, albeit with concomitant pronounced sedation evident in all LPS-treated groups (p < 0.05). Within the cortex, LPS reduced (p < 0.05) the expression levels of NOx, Nrf2, BDNF, and HO-1, with only HO-1 being reinstated to baseline in the LPS + Esc + Vit D and the LPS + Esc + Vit C + Vit D groups. Conversely, the hippocampal NOx, Nrf2, and HO-1 levels remained unaltered following LPS administration. Notably, the combination of Esc, Vit C, and Vit D effectively restored hippocampal BDNF levels, which had been diminished by Esc alone. In conclusion, vitamins C and D enhance the therapeutic effects of escitalopram through a mechanism independent of Nrf2. These findings underscore the imperative need for in-depth investigations.

New pharmacotherapies to tackle the unmet needs in bipolar disorder: a focus on acute suicidality

INTRODUCTION

Suicidal behavior is relatively frequent in patients with bipolar disorder (BD) and constitutes their most frequent cause of death. Suicide rates remain high in patients with BD despite adherence to guidelines recommending lithium as first line, and/or antidepressants, antipsychotics, psychotherapy, psychosocial interventions, and electroconvulsive therapy. Hence the need to identify more effective and rapid anti-suicide interventions.

AREAS COVERED

To tackle the unmet needs of pharmacotherapy, we investigated the PubMed database on 24-25 January 2024 using strategies like ('acute suicid*'[ti] OR 'suicide crisis syndrome' OR 'acute suicidal affective disturbance') AND (lithium[ti] OR clozapine[ti]), which obtained 3 results, and ('acute suicid*'[ti] OR 'suicide crisis syndrome' OR 'acute suicidal affective disturbance') AND (ketamine[ti] OR esketamine[ti] OR NMDA[ti] OR glutamat*[ti]), which yielded 14 results. We explored glutamatergic abnormalities in BD and suicide and found alterations in both. The noncompetitive NMDS antagonist ketamine and its S-enantiomer esketamine reportedly decrease acute suicidality.

EXPERT OPINION

Intranasal esketamine or subcutaneous ketamine, single-bolus or intravenous, and possibly other glutamate receptor modulators may improve suicidal behavior in patients with unipolar and bipolar depression. This may be achieved through prompt remodulation of glutamate activity. The correct use of glutamatergic modulators could reduce acute suicidality and mortality in patients with BD.

α-Pyrrolidinononanophenone derivatives induce differentiated SH-SY5Y neuroblastoma cell apoptosis via reduction of antioxidant capacity: Involvement of NO depletion and inactivation of Nrf2/HO1 signaling pathway

α-Pyrrolidinononanophenone (α-PNP) derivatives are known to be one of the hazardous new psychoactive substances due to the most extended hydrocarbon chains of any pyrrolidinophenones on the illicit drug market. Our previous report showed that 4'-iodo-α-PNP (I-α-PNP) is the most potent cytotoxic compound among α-PNP derivatives and induces apoptosis due to mitochondrial dysfunction and suppression of nitric oxide (NO) production in differentiated human neuronal SH-SY5Y cells. In this study, to clarify the detailed action mechanisms by I-α-PNP, we investigated the mechanism of reactive oxygen species (ROS) -dependent apoptosis by I-α-PNP in differentiated SH-SY5Y with a focus on the antioxidant activities. Treatment with I-α-PNP elicits overproduction of ROS such as H2O2, hydroxyl radical, and 4-hydroxy-2-nonenal, and pretreatment with antioxidant N-acetyl-L-cysteine is attenuated the SH-SY5Y cells apoptosis by I-α-PNP. These results suggested that the overproduction of ROS is related to SH-SY5Y cell apoptosis by I-α-PNP. In addition, I-α-PNP markedly decreased antioxidant capacity in differentiated cells than in undifferentiated cells and inhibited the upregulation of hemeoxygenase 1 (HO1) and glutathione peroxidase 4 (GPX4) expression caused by induction of differentiation. Furthermore, the treatment with I-α-PNP increased the nuclear expression level of BTB Domain And CNC Homolog 1 (Bach1), a transcriptional repressor of Nrf2, only in differentiated cells, suggesting that the marked decrease in antioxidant capacity in differentiated cells was due to suppression of Nrf2/HO1 signaling by Bach1. Additionally, pretreatment with an NO donor suppresses the I-α-PNP-evoked ROS overproduction, HO1 down-regulation, increased nuclear Bach1 expression and reduced antioxidant activity in the differentiated cells. These findings suggest that the ROS-dependent apoptosis by I-α-PNP in differentiated cells is attributed to the inactivation of the Nrf2/HO1 signaling pathway triggered by NO depletion.

Interplay of G-proteins and Serotonin in the Neuroimmunoinflammatory Model of Chronic Stress and Depression: A Narrative Review

INTRODUCTION

This narrative review addresses the clinical challenges in stress-related disorders such as depression, focusing on the interplay between neuron-specific and pro-inflammatory mechanisms at the cellular, cerebral, and systemic levels.

OBJECTIVE

We aim to elucidate the molecular mechanisms linking chronic psychological stress with low-grade neuroinflammation in key brain regions, particularly focusing on the roles of G proteins and serotonin (5-HT) receptors.

METHODS

This comprehensive review of the literature employs systematic, narrative, and scoping review methodologies, combined with systemic approaches to general pathology. It synthesizes current research on shared signaling pathways involved in stress responses and neuroinflammation, including calcium-dependent mechanisms, mitogen-activated protein kinases, and key transcription factors like NF-κB and p53. The review also focuses on the role of G protein-coupled neurotransmitter receptors (GPCRs) in immune and pro-inflammatory responses, with a detailed analysis of how 13 of 14 types of human 5-HT receptors contribute to depression and neuroinflammation.

RESULTS

The review reveals a complex interaction between neurotransmitter signals and immunoinflammatory responses in stress-related pathologies. It highlights the role of GPCRs and canonical inflammatory mediators in influencing both pathological and physiological processes in nervous tissue.

CONCLUSION

The proposed Neuroimmunoinflammatory Stress Model (NIIS Model) suggests that proinflammatory signaling pathways, mediated by metabotropic and ionotropic neurotransmitter receptors, are crucial for maintaining neuronal homeostasis. Chronic mental stress can disrupt this balance, leading to increased pro-inflammatory states in the brain and contributing to neuropsychiatric and psychosomatic disorders, including depression. This model integrates traditional theories on depression pathogenesis, offering a comprehensive understanding of the multifaceted nature of the condition.

Meloxicam Targets COX-2/NOX1/NOX4/Nrf2 Axis to Ameliorate the Depression-like Neuropathology Induced by Chronic Restraint Stress in Rats

Meloxicam has shown significant neuroprotection in experimental models of stroke, Alzheimer's disease, and Parkinson's disease. However, the potential of meloxicam to treat depression-like neuropathology in a chronic restraint stress (CRS) model and the associated molecular changes has been insufficiently explored. The current work aimed to explore the potential neuroprotective actions of meloxicam against CRS-evoked depression in rats. In the current experiments, animals received meloxicam (10 mg/kg/day; i.p.) for 21 days, and CRS was instigated by restraining the animals for 6 h/day during the same period. The sucrose preference test and the forced swimming test were used to explore the depression-linked anhedonia/despair, whereas the open-field test examined the animals' locomotor activity. The current findings revealed that CRS elicited typical depression behavioral anomalies in the animals, including anhedonia, despair, and diminished locomotor activity; these findings were reinforced with Z-normalization scores. These observations were corroborated by brain histopathological changes and increased damage scores. In CRS-exposed animals, serum corticosterone spiked, and the hippocampi revealed decreased monoamine neurotransmitter levels (norepinephrine, serotonin, and dopamine). Mechanistically, neuroinflammation was evident in stressed animals, as shown by elevated hippocampal TNF-α and IL-1β cytokines. Moreover, the hippocampal COX-2/PGE₂ axis was activated in the rats, confirming the escalation of neuroinflammatory events. In tandem, the pro-oxidant milieu was augmented, as seen by increased hippocampal 8-hydroxy-2'-deoxyguanosine alongside increased protein expression of the pro-oxidants NOX1 and NOX4 in the hippocampi of stressed animals. In addition, the antioxidant/cytoprotective Nrf2/HO-1 cascade was dampened, as evidenced by the lowered hippocampal protein expression of Nrf2 and HO-1 signals. Interestingly, meloxicam administration mitigated depression manifestations and brain histopathological anomalies in the rats. These beneficial effects were elicited by meloxicam's ability to counteract the corticosterone spike and hippocampal neurotransmitter decrease while also inhibiting COX-2/NOX1/NOX4 axis and stimulating Nrf2/HO-1 antioxidant pathway. Together, the present findings prove the neuroprotective/antidepressant actions of meloxicam in CRS-induced depression by ameliorating hippocampal neuroinflammation and pro-oxidant changes, likely by modulating COX-2/NOX1/NOX4/Nrf2 axis.