Effects of Sodium Benzoate, a D-Amino Acid Oxidase Inhibitor, on Perceived Stress and Cognitive Function Among Patients With Late-Life Depression: A Randomized, Double-Blind, Sertraline- and Placebo-Controlled Trial

The clinical perspective on late-onset depression in European real-world treatment settings

The clinical phenotype of the so-called late-onset depression (LOD) affecting up to 30% of older adults and yielding heterogeneous manifestations concerning symptoms, severity and course has not been fully elucidated yet. This European, cross-sectional, non-interventional, naturalistic multicenter study systematically investigated socio-demographic and clinical correlates of early-onset depression (EOD) and LOD (age of onset ≥ 50 years) in 1410 adult in- and outpatients of both sexes receiving adequate psychopharmacotherapy. In a total of 1329 patients (94.3%) with known age of disease onset, LOD was identified in 23.2% and was associated with unemployment, an ongoing relationship, single major depressive episodes, lower current suicidal risk and higher occurrence of comorbid hypertension. In contrast, EOD was related to higher rates of comorbid migraine and additional psychotherapy. Although the applied study design does not allow to draw any causal conclusions, the present results reflect broad clinical settings and emphasize easily obtainable features which might be characteristic for EOD and LOD. A thoughtful consideration of age of onset might, hence, contribute to optimized diagnostic and therapeutic processes in terms of the globally intended precision medicine, ideally enabling early and adequate treatment allocations and implementation of respective prevention programs.

Effects of selective serotonin reuptake inhibitors (SSRIs) on suicide: A network meta-analysis of double-blind randomized trials

The relationship between the use of selective serotonin reuptake inhibitors (SSRIs) and suicide risk in patients with mental disorders remains controversial. We conducted a network meta-analysis to examine the effects of SSRIs on suicide risk in patients with mental disorders. A comprehensive search was conducted across PubMed, Web of Science, PsycINFO, CENTRAL, Wanfang Database, and China National Knowledge Infrastructure for articles published until December 19, 2023. The main outcomes were suicidal ideation and instances of suicidal behavior. We included 29 double-blind randomized trials in our analysis. The findings suggest that SSRIs primarily offer short-term protection against suicidal ideation. By week 2, paroxetine, fluoxetine, escitalopram, and non-SSRI treatments were linked to a decreased suicide risk compared with a placebo, with the exception of sertraline. This protective effect was diminished by week 8. In contrast, studies on instances of suicidal behavior from weeks 1 to 10 found no significant difference in efficacy between SSRIs, non-SSRIs, and placebo. These results indicate that SSRIs may offer short-term protection against suicidal ideation. However, their long-term effectiveness in mitigating suicidal ideation and preventing suicidal behaviors is limited.

Herbal Cannabis and Depression: A Review of Findings Published over the Last Three Years

Public perception contrasts scientific findings on the depression-related effects of cannabis. However, earlier studies were performed when cannabis was predominantly illegal, its production was mostly uncontrolled, and the idea of medical cannabis was incipient only. We hypothesized that recent changes in attitudes and legislations may have favorably affected research. In addition, publication bias against cannabis may have also decreased. To investigate this hypothesis, we conducted a review of research studies published over the last three years. We found 156 relevant research articles. In most cross-sectional studies, depression was higher in those who consumed cannabis than in those who did not. An increase in cannabis consumption was typically followed by an increase in depression, whereas withdrawal from cannabis ameliorated depression in most cases. Although medical cannabis reduced depression in most studies, none of these were placebo-controlled. In clinical studies published in the same period, the placebo also ameliorated depression and, in addition, the average effect size of the placebo was larger than the average effect size of medical cannabis. We also investigated the plausibility of the antidepressant effects of cannabis by reviewing molecular and pharmacological studies. Taken together, the reviewed findings do not support the antidepressant effects of herbal cannabis.

Antidepressants available in Japan for older people with major depressive disorder: A systematic review and meta-analysis

AIM

To update the major depressive disorder (MDD) treatment guidelines of the Japanese Society of Mood Disorders, we conducted a systematic review and pairwise meta-analysis of double-blind, randomized, placebo-controlled trials of available antidepressants in Japan for older adults with MDD.

METHODS

Outcome measures included response rate (primary), improvement in depressive symptom scale score, remission rate, all-cause discontinuation, discontinuation due to adverse events, and at least one adverse event. A random-effects model was used to calculate the risk ratio (RR) and standardized mean difference (SMD) with a 95% confidence interval (95% CI).

RESULTS

Nine double-blind, randomized, placebo-controlled trials (n = 2145) were identified. No study has been conducted in Japan. Our meta-analysis included the following antidepressants: duloxetine, escitalopram, imipramine, sertraline, venlafaxine, and vortioxetine. Antidepressants have significantly higher response rates than placebo (RR [95% CI] = 1.38 [1.04, 1.83], p = 0.02). Antidepressants outperformed placebo in terms of improving depressive symptom scale score (SMD [95% CI] = -0.62 [-0.92, -0.33], p < 0.0001). However, antidepressants were associated with a higher discontinuation rate due to adverse events (RR [95% CI] = 1.94 [1.30, 2.88], p = 0.001) and a higher incidence of at least one adverse event (RR [95% CI] = 1.11 [1.02, 1.21], p = 0.02) compared to placebo. The groups did not differ significantly in terms of remission rate or all-cause discontinuation.

CONCLUSIONS

Our meta-analysis concluded that treatment with antidepressants available in Japan is only weakly recommended for moderate to severe MDD in older adults.

d-Amino acids: new clinical pathways for brain diseases

Free d-amino acids (d-AAs) are emerging as a novel and important class of signaling molecules in many organs, including the brain and endocrine systems. There has been considerable progress in our understanding of the fundamental roles of these atypical messengers, with increasingly recognized implications in a wide range of neuropathologies, including schizophrenia (SCZ), epilepsy, Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), substance abuse, and chronic pain, among others. Research has enabled the discovery that d-serine, d-aspartate and more recently d-cysteine are essential for the healthy development and function of the central nervous system (CNS). We discuss recent progress that has profoundly transformed our vision of numerous physiological processes but has also shown how d-AAs are now offering therapeutic promise in clinical settings for several human diseases.

The Effect of Sodium Benzoate on Host Health: Insight into Physiological Indexes and Gut Microbiota

Sodium benzoate (SB) is a common food preservative widely used in the food industry. However, the effects of SB intake on host health at different stages were still unclear. Hence, we investigated the impact of SB with three concentrations (150 mg/kg, 500 mg/kg and 1000 mg/kg) and at three stages (intake for 5-weeks, intake for 10-weeks and removal for 5 weeks) on host health in normal mice. The results showed that SB intake for 5 weeks slightly changed gut microbiota composition, but it significantly increased TG (only 150 mg/kg and 1000 mg/kg) and blood glucose levels (only 500 mg/kg) and promoted the secretion of interleukin (IL)-1β and IL-6 (p < 0.01). However, SB intake for 10 weeks mostly maintained normal glucolipid metabolism; although, IL-1β (p < 0.01) and IL-6 (p < 0.05) levels were also significantly increased and positively regulated the gut microbiota by significantly increasing the relative abundance of Lactobacillus and significantly decreasing the relative abundance of Ileibacterium. Meanwhile, the safety of SB for host metabolism and gut microbiota was also confirmed via a fecal microbiota transplantation experiment. In addition, we found that SB removal after 10 weeks of intake significantly increased the levels of blood glucose, insulin and HOMA-IR index, which might be attributed to gut microbiota dysbiosis. Mechanistically, these positive effects and negative effects had no close relationship with the concentration of short-chain fatty acids in the gut, which might be associated with metabolites of SB or special bacterial strains. In short, this work provided positive evidence for the safety of SB consumption within the recommended range.

Adjunctive transcranial direct current stimulation (tDCS) plus sodium benzoate for the treatment of early-phase Alzheimer's disease: A randomized, double-blind, placebo-controlled trial

Previous studies found that an NMDA receptor (NMDAR) enhancer, sodium benzoate, improved cognitive function of patients with early-phase Alzheimer's disease (AD). Transcranial direct current stimulation (tDCS) induces NMDAR-dependent synaptic plasticity and strengthens cognitive function of AD patients. This study aimed to evaluate efficacy and safety of tDCS plus benzoate in early-phase dementia. In this 24-week randomized, double-blind, placebo-controlled trial, 97 patients with early-phase AD received 10-session tDCS during the first 2 weeks. They then took benzoate or placebo for 24 weeks. We assessed the patients using Alzheimer's disease assessment scale - cognitive subscale (ADAS-cog), Clinician's Interview-Based Impression of Change plus Caregiver Input, Mini Mental Status Examination, Alzheimer's disease Cooperative Study scale for ADL in MCI, and a battery of additional cognitive tests. Forty-seven patients received sodium benzoate, and the other 50 placebo. The two treatment groups didn't differ significantly in ADAS-cog or other measures. Addition of benzoate to tDCS didn't get extra benefit or side effect in this study. For more thoroughly studying the potential of combining tDCS with benzoate in the AD treatment, future research should use other study designs, such as longer-term benzoate treatment, adding benzoate in the middle of tDCS trial sessions, or administering benzoate then tDCS.

Selection of the optimal dose of sertraline for depression: A dose-response meta-analysis of randomized controlled trials

Sertraline has been shown to be effective in the treatment of depression. However, the relationship between the dosage of sertraline and its efficacy and safety are unclear. We identified RCTs that compared sertraline with placebo for the treatment of depression, conducted conventional meta-analyses on the efficacy and safety of sertraline, and assessed the nonlinear dose-response relationship between sertraline dosage and the changes in HAM-D and CGI-S scores, dropout from care for any reason or due to adverse effects, and the rate of adverse effects, using a 1-stage restricted cubic spline regression model. Twenty-one RCTs involving 4,235 patients were included. The pooled mean differences (MD) in the change in HAM-D total score [MD=-2.34, 95% confidence interval (CI) -2.93, -1.76], CGI-S score and MADRS score, but also the dropout rate for adverse effects, and rate of adverse effects were higher in sertraline group. The therapeutic response of sertraline for treating depression increased with the dosage. Meanwhile, the risk of total adverse reactions slightly decreased between 50 and 150 mg, and increased at doses above 150 mg. The dose-dependence of both efficacy and safety need to be considered when choosing the optimal dosage of sertraline.

An integrated strategy to study the combination mechanisms of Bupleurum chinense DC and Paeonia lactiflora Pall for treating depression based on correlation analysis between serum chemical components profiles and endogenous metabolites profiles

ETHNOPHARMACOLOGICAL RELEVANCE

Bupleurum chinense DC-Paeonia lactiflora Pall (BCD-PLP) is a common clinical herb pair in traditional Chinese medicine (TCM) prescriptions commonly used to treat depression. However, its combination mechanisms with its anti-depressive effects remain highly unclear.

AIM OF THE STUDY

Here, an effective strategy has been developed to study the combination mechanisms of Bupleurum chinense DC (BCD) and Paeonia lactiflora Pall (PLP) by integrating serum pharmacochemistry analysis, metabolomics technology, and molecular docking technology.

MATERIALS AND METHODS

First, the depression model rats were replicated by the chronic unpredictable mild stress (CUMS) procedure, and the difference in the chemical composition in vivo before and after the combination of BCD and PLP was analyzed by integrating background subtraction and multivariate statistical analysis techniques. Then, UPLC/HRMS-based serum metabolomics was performed to analyze the synergistic effect on metabolite regulation before and after the combination of BCD and PLP. Further, the correlation analysis between the differential exogenous chemical components and the differential endogenous metabolites before and after the combination was employed to dissect the combination mechanisms from a global perspective of combining metabolomics and serum pharmacochemistry. Finally, the molecular docking between the differential chemical components and the key metabolic enzymes was applied to verify the regulatory effect of the differential exogenous chemical components on the differential endogenous metabolites.

RESULTS

The serum pharmacochemistry analysis results demonstrated that the combination of BCD and PLP could significantly affect the content of 10 components in BCD (including 5 prototype components were significantly decreased and 5 metabolites were significantly increased) and 8 components in PLP (including 4 prototype components and 3 metabolites were significantly increased, 1 metabolite was significantly decreased), which indicated that the combination could enhance BCD prototype components' metabolism and the absorption of the PLP prototype components. Besides, metabolomics results indicated that the BCD-PLP herb pair group significantly reversed more metabolites (8) than BCD and PLP single herb group (5 & 4) and has a stronger regulatory effect on metabolite disorders caused by CUMS. Furthermore, the correlation analysis results suggested that saikogenin F and saikogenin G were significantly positively correlated with the endogenous metabolite itaconate, an endogenous anti-inflammatory metabolite; and benzoic acid was significantly positively correlated with D-serine, an endogenous metabolite with an antidepressant effect. Finally, the molecular docking results further confirmed that the combination of BCD and PLP could affect the activities of cis-aconitic acid decarboxylase and D-amino acid oxidase by increasing the in vivo concentration of saikogenin F and benzoic acid, which further enhances its anti-inflammatory activity and anti-depressive effect.

CONCLUSIONS

In this study, an effective strategy has been developed to study the combination mechanisms of BCD and PLP by integrating serum pharmacochemistry analysis, multivariate statistical analysis, metabolomics technology, and molecular docking technology. Based on this strategy, the present study indicated that the combination of BCD and PLP could affect the activities of cis-aconitic acid decarboxylase and D-amino acid oxidase by increasing the concentration of saikogenin F and benzoic acid in vivo, which further enhances its anti-depressive effect. In short, this strategy will provide a reliable method for elucidating the herb-herb compatibility mechanism of TCM.

Determination of D-serine and D-alanine Tissue Levels in the Prefrontal Cortex and Hippocampus of Rats After a Single Dose of Sodium Benzoate, a D-Amino Acid Oxidase Inhibitor, with Potential Antipsychotic and Antidepressant Properties

The effects of the N-methyl-D-aspartate receptor activators D-serine, D-alanine, and sarcosine against schizophrenia and depression are promising. Nevertheless, high doses of D-serine and sarcosine are associated with undesirable nephrotoxicity or worsened prostatic cancer. Thus, alternatives are needed. DAAO inhibition can increase D-serine as well as D-alanine and protect against D-serine-induced nephrotoxicity. Although several DAAO inhibitors improve the symptoms of schizophrenia and depression, they can increase the plasma levels but not brain levels of D-serine. The mechanism of action of DAAO inhibitors remains unclear. We investigated the effects of the DAAO inhibitor sodium benzoate on the prefrontal cortex and hippocampal level of D-alanine as known another substrate with antipsychotic and antidepressant properties and other NMDAR-related amino acids, such as, L-alanine, D-serine, L-serine, D-glutamate, L-glutamate, and glycine levels. Our results indicate that sodium benzoate exerts antipsychotic and antidepressant-like effects without changing the D-serine levels in the brain prefrontal cortex (PFC) and hippocampus. Moreover, D-alanine levels in the PFC and hippocampus did not change. Despite these negative findings regarding the effects of D-amino acids in the PFC and hippocampus, sodium benzoate exhibited antipsychotic and antidepressant-like effects. Thus, the therapeutic effects of sodium benzoate are independent of D-serine or D-alanine levels. In conclusion, sodium benzoate may be effective among patients with schizophrenia or depression; however, the mechanisms of actions remain to be elucidated.

Ketamine, benzoate, and sarcosine for treating depression

Studies have demonstrated the beneficial therapeutic effects of sarcosine, benzoate, and ketamine (including esketamine and arketamine) on depression. These drugs mainly act by modulating N-methyl-d-aspartate glutamate receptors (NMDARs) and reducing inflammation in the brain. Although ketamine, benzoate, and sarcosine act differently as the antagonists or coagonists of NMDARs, they all have demonstrated efficacy in animal models or human trials. In vitro and in vivo studies have indicated that sarcosine, benzoate, and ketamine exert their anti-inflammatory effects by inhibiting microglial activity. This review summarizes and compares the efficacy of the possible therapeutic mechanisms of sarcosine, benzoate, ketamine, esketamine, and arketamine. These compounds act as both NMDAR modulators and anti-inflammatory drugs and thus can be effective in the treatment of depression.

Endogenous antioxidants predicted outcome and increased after treatment: A benzoate dose-finding, randomized, double-blind, placebo-controlled trial for Alzheimer's disease

AIM

Previous pilot studies suggest that sodium benzoate may be a potential cognitive enhancer for patients with Alzheimer's disease (AD), schizophrenia, or late-life depression. Especially for AD treatment, a confirmatory trial with predictive biomarkers is urgently needed. This study aimed to confirm benzoate as a novel treatment for AD and to discover its optimal dose and biomarkers.

METHODS

A 24-week, dose-finding, randomized, double-blind, placebo-controlled trial, with clinical measurements at weeks 0, 8, 16, and 24, was conducted in three major medical centers in Taiwan. Among 154 patients screened for AD, 149 were eligible and randomized to one of the four treatments: (i) benzoate 500 group (fixed 500 mg/day); (ii) benzoate 750 (500 mg/day for the first 4 weeks, 750 mg/day from the 5th week); (iii) benzoate 1000 (500 mg/day for the first 4 weeks, 1000 mg/day from the 5th week); and (iv) placebo. The primary outcome measure was AD assessment scale-cognitive subscale (ADAS-cog).

RESULTS

The benzoate 1000 group performed best in improving ADAS-cog (P = 0.026 at week 24), with female advantage. Higher plasma catalase at baseline predicted better outcome. Benzoate receivers tended to have higher catalase and glutathione than placebo recipients after treatment. The four intervention groups showed similar safety profiles.

CONCLUSIONS

By enhancing two vital endogenous antioxidants, catalase and glutathione, sodium benzoate therapy improved cognition of patients with AD, with higher baseline catalase predicting better response. Supporting the oxidative stress theory, the results show promise for benzoate as a novel treatment for AD.

Mapping of Fatty Aldehydes in the Diabetic Rat Brain Using On-Tissue Chemical Derivatization and Air-Flow-Assisted Desorption Electrospray Ionization-Mass Spectrometry Imaging

Fatty aldehydes (FALs) are involved in various biological processes, and their abnormal metabolism is related to the occurrence and development of neurological diseases. Because of their low ionization efficiency, methods for in situ detection and mass spectrometry imaging (MSI) analysis of FALs remain underreported. On-tissue chemical tagging of hardly ionizable target analytes with easily ionized moieties can improve ionization efficiency and detection sensitivity in MSI experiments. In this study, an on-tissue chemical derivatization-air-flow-assisted desorption electrospray ionization-MSI method was developed to visualize FALs in the rat brain. The method showed high sensitivity and specificity, allowing the use of in situ high-resolution MS³ to identify FALs. The methodology was applied to investigate the region-specific distribution of FALs in the brains of control and diabetic encephalopathy (DE) rats. In DE rats, FALs were found to be significantly enriched in various brain regions, especially in the cerebral cortex, hippocampus, and amygdala. Thus, increased FAL levels and oxidative stress occurred in a region-dependent manner, which may contribute to cognitive function deficits in DE. In summary, we provide a novel method for the in situ detection of FALs in biological tissues as well as new insights into the potential pathogenesis of DE.

Late-life depression: Epidemiology, phenotype, pathogenesis and treatment before and during the COVID-19 pandemic

Late-life depression (LLD) is one of the most common mental disorders among the older adults. Population aging, social stress, and the COVID-19 pandemic have significantly affected the emotional health of older adults, resulting in a worldwide prevalence of LLD. The clinical phenotypes between LLD and adult depression differ in terms of symptoms, comorbid physical diseases, and coexisting cognitive impairments. Many pathological factors such as the imbalance of neurotransmitters, a decrease in neurotrophic factors, an increase in β-amyloid production, dysregulation of the hypothalamic-pituitary-adrenal axis, and changes in the gut microbiota, are allegedly associated with the onset of LLD. However, the exact pathogenic mechanism underlying LLD remains unclear. Traditional selective serotonin reuptake inhibitor therapy results in poor responsiveness and side effects during LLD treatment. Neuromodulation therapies and complementary and integrative therapies have been proven safe and effective for the treatment of LLD. Importantly, during the COVID-19 pandemic, modern digital health intervention technologies, including socially assistive robots and app-based interventions, have proven to be advantageous in providing personal services to patients with LLD.

Targeting D-Amino Acid Oxidase (DAAO) for the Treatment of Schizophrenia: Rationale and Current Status of Research

In the brain, D-amino acid oxidase (DAAO) is a peroxisomal flavoenzyme. Through oxidative deamination by DAAO, D-serine, the main coagonist of synaptic N-methyl-D-aspartate receptors (NMDARs), is degraded into α-keto acids and ammonia; flavin adenine dinucleotide (FAD) is simultaneously reduced to dihydroflavine-adenine dinucleotide (FADH2), which is subsequently reoxidized to FAD, with hydrogen peroxide produced as a byproduct. NMDAR hypofunction is implicated in the pathogenesis of schizophrenia. In previous studies, compared with control subjects, patients with schizophrenia had lower D-serine levels in peripheral blood and cerebrospinal fluid but higher DAAO expression and activity in the brain. Inhibiting DAAO activity and slowing D-serine degradation by using DAAO inhibitors to enhance NMDAR function may be a new strategy for use in the treatment of schizophrenia. The aim of this leading article is to review the current research in DAAO inhibitors.

Pharmacokinetics and Safety of Sodium Benzoate, a d-Amino Acid Oxidase (DAAO) Inhibitor, in Healthy Subjects: A Phase I, Open-Label Study

PURPOSE

N-methyl-d-aspartate receptor (NMDAR)-mediated neurotransmission plays a critical role in cognition and memory, and d-serine is a co-agonist of the receptor. d-serine is metabolized by d-amino acid oxidase (DAAO). Sodium benzoate is a DAAO inhibitor that leads to the elevation of d-serine levels and enhances NMDAR functions as a therapeutic for wide-spectrum central nervous system (CNS) disorders, including schizophrenia and dementia. For therapeutic application of sodium benzoate in CNS disorders, we conducted a Phase I study to evaluate its safety, tolerability, and pharmacokinetic profile after single-dose oral administration in healthy volunteers. In contrast to the accumulation in the CNS, sodium benzoate has a rapid pharmacokinetic profile when measured peripherally.

METHODS

In this Phase I study, subjects were randomized into 4 different dose groups after a single oral administration. The pharmacokinetic parameters of sodium benzoate were assessed after exposure to 250, 500, 1000, and 2000 mg of sodium benzoate. All adverse events were investigated and recorded.

FINDINGS

The C_max and AUC of sodium benzoate exhibited a higher than dose-proportional increase within the dose range from 250 to 2000 mg under fasting conditions. The slopes were 1.78 and 2.61 and the 90% CIs were 1.41 to 2.15 and 2.20 to 3.03 for C_max and AUC, respectively. Sodium benzoate was absorbed and converted to benzoic acid rapidly, reaching C_max after ∼0.5 hour and elimination t_1/2 after ∼0.3 hour. No subjects reported adverse events that were sodium benzoate related.

IMPLICATIONS

The nonlinear pharmacokinetic response was observed within the dose range up to 2000 mg. Sodium benzoate treatment exhibited a favorable safety profile and was well tolerated at all dose levels. The study results serve as a foundation that should be useful for investigating efficacy and safety in the drug's subsequent clinical development.

TRIAL REGISTRATION

TFDA-103607047.

Remodeling of microbiota gut-brain axis using psychobiotics in depression

Depression is a multifaceted psychiatric disorder mainly orchestrated by dysfunction of neuroendocrine, neurochemical, immune, and metabolic systems. The interconnection of gut microbiota perturbation with the central nervous system disorders has been well documented in recent times. Indeed, alteration of commensal intestinal microflora is noted in several psychiatric disorders such as anxiety and depression, which are presumed to be routed through the enteric nervous system, autonomic nervous system, endocrine, and immune system. This review summarises the new mechanisms underlying the crosstalk between gut microbiota and brain involved in the management of depression. Depression-induced changes in the commensal intestinal microbiota are majorly linked with the disruption of gut integrity, hyperinflammation, and modulation of short-chain fatty acids, neurotransmitters, kynurenine metabolites, endocannabinoids, brain-derived neurotropic factors, hypothalamic-pituitary-adrenal axis, and gut peptides. The restoration of gut microbiota with prebiotics, probiotics, postbiotics, synbiotics, and fermented foods (psychobiotics) has gained a considerable attention for the management of depression. Recent evidence also propose the role of gut microbiota in the process of treatment-resistant depression. Thus, remodeling of the microbiota-gut-brain axis using psychobiotics appears to be a promising therapeutic approach for the reversal of psychiatric disorders, and it is imperative to decipher the underlying mechanisms for gut-brain crosstalk.

Catalpol Exerts Antidepressant-Like Effects by Enhancing Anti-oxidation and Neurotrophy and Inhibiting Neuroinflammation via Activation of HO-1

Catalpol is an iridoid glycoside with rich content, rich nutrition, and numerous biological activities in Rehmanniae Radix contained in classic antidepressant prescriptions in Chinese clinical medicine. Catalpol has been confirmed previously its exact antidepressant-like effect involved heme oxygenase (HO)-1, but its antidepressant molecular targets and mechanism are still unclear. Here, catalpol's antidepressant-like molecular target was diagnosed and confirmed by ZnPP intervention [the antagonist of HO-1, (10 μg/rat), intracerebroventricular] for the first time, and its molecule mechanism network was determined through HO-1 related pathway and molecules in the hippocampus. Results showed that ZnPP significantly abolished catalpol's (10 mg/kg) reversal on depressive-like behaviors of chronic unpredictable mild stress rats, abolished catalpol's up-regulation on the phosphorylation level of extracellular regulated protein kinases (ERK)1/2 and brain-derived neurotrophic factor (BDNF)'s receptor tropomyosin-related kinase B (TrkB), the nuclear expression level of nuclear factor E 2-related factor 2 (Nrf2), the levels of anti-oxidant factors (such as HO-1, SOD, GPX, GST, GSH) and BDNF, and abolished catalpol's down-regulation on the levels of peroxide and neuroinflammation factors [cyclooxygenase-2 (COX-2), induced nitrogen monoxide synthase (iNOS), nitric oxide (NO)]. Thus, HO-1 could serve as an important potential molecular target for catalpol's antidepressant-like process, and the antidepressant-like mechanism of catalpol could at least involve the activation of HO-1 triggering the up-regulation of the ERK1/2/Nrf2/HO-1 pathway-related factors to enhance the anti-oxidant defense, triggering the down-regulation of the COX-2/iNOS/NO pathway-related factors to inhibit neuroinflammation, and triggering the up-regulation of the BDNF/TrkB pathway to enhance neurotrophy.

Glutamatergic System in Depression and Its Role in Neuromodulatory Techniques Optimization

Depressive disorders are among the most common psychiatric conditions and contribute to significant morbidity. Even though the use of antidepressants revolutionized the management of depression and had a tremendous positive impact on the patient's outcome, a significant proportion of patients with major depressive disorder (MDD) show no or partial or response even with adequate treatment. Given the limitations of the prevailing monoamine hypothesis-based pharmacotherapy, glutamate and glutamatergic related pathways may offer an alternative and a complementary option for designing novel intervention strategies. Over the past few decades, there has been a growing interest in understanding the neurobiological underpinnings of glutamatergic dysfunctions in the pathogenesis of depressive disorders and the development of new pharmacological and non-pharmacological treatment options. There is a growing body of evidence for the efficacy of neuromodulation techniques, including transcranial magnetic stimulation, transcutaneous direct current stimulation, transcranial alternating current stimulation, and photo-biomodulation on improving connectivity and neuroplasticity associated with depression. This review attempts to revisit the role of glutamatergic neurotransmission in the etiopathogenesis of depressive disorders and review the current neuroimaging, neurophysiological and clinical evidence of these neuromodulation techniques in the pathophysiology and treatment of depression.