Microbiota-gut-brain axis: Natural antidepressants molecular mechanism

BACKGROUND

Major depressive disorder (MDD) is a severe mental health condition characterized by persistent depression, impaired cognition, and reduced activity. Increasing evidence suggests that gut microbiota (GM) imbalance is closely linked to the emergence and advancement of MDD, highlighting the potential significance of regulating the "Microbiota-Gut-Brain" (MGB) axis to impact the development of MDD. Natural products (NPs), characterized by broad biological activities, low toxicity, and multi-target characteristics, offer unique advantages in antidepressant treatment by regulating MGB axis.

PURPOSE

This review was aimed to explore the intricate relationship between the GM and the brain, as well as host responses, and investigated the mechanisms underlying the MGB axis in MDD development. It also explored the pharmacological mechanisms by which NPs modulate MGB axis to exert antidepressant effects and addressed current research limitations. Additionally, it proposed new strategies for future preclinical and clinical applications in the MDD domain.

METHODS

To study the effects and mechanism by which NPs exert antidepressant effects through mediating the MGB axis, data were collected from Web of Science, PubMed, ScienceDirect from initial establishment to March 2024. NPs were classified and summarized by their mechanisms of action.

RESULTS

NPs, such as flavonoids,alkaloids,polysaccharides,saponins, terpenoids, can treat MDD by regulating the MGB axis. Its mechanism includes balancing GM, regulating metabolites and neurotransmitters such as SCAFs, 5-HT, BDNF, inhibiting neuroinflammation, improving neural plasticity, and increasing neurogenesis.

CONCLUSIONS

NPs display good antidepressant effects, and have potential value for clinical application in the prevention and treatment of MDD by regulating the MGB axis. However, in-depth study of the mechanisms by which antidepressant medications affect MGB axis will also require considerable effort in clinical and preclinical research, which is essential for the development of effective antidepressant treatments.

The therapeutic potential of traditional Chinese medicine in depression: focused on the modulation of neuroplasticity

Depression, a mood disorder characterized by a persistent low mood and lack of enjoyment, is considered the leading cause of non-fatal health losses worldwide. Neuroplasticity refers to the brain's ability to adapt to external or internal stimuli, resulting in functional and structural changes. This process plays a crucial role in the development of depression. Traditional Chinese Medicine (TCM) shows significant potential as a complementary and alternative therapy for neurological diseases, including depression. However, there has been no systematic summary of the role of neuroplasticity in the pathological development of depression and TCM Interventions currently. This review systematically summarized recent literature on changes in neuroplasticity in depression and analyzed the regulatory mechanisms of active metabolites in TCM and TCM formulas on neuroplasticity in antidepressant treatment. Additionally, this review discussed the limitations of current research and the application prospects of TCM in regulating neuroplasticity in antidepressant research.

Comparing the effect of fluoxetine, escitalopram, and sertraline, on the level of BDNF and depression in preclinical and clinical studies: a systematic review

Brain-derived neurotrophic factor (BDNF) dysfunction is one of the most important mechanisms underlying depression. It seems that selective serotonin reuptake inhibitors (SSRIs) improve depression via affecting BDNF level. In this systematic review, for the first time, we aimed to review the effect of three SSRIs including fluoxetine, escitalopram, and sertraline, on both depression and BDNF level in preclinical and clinical studies. PubMed electronic database was searched, and 193 articles were included in this study. After reviewing all manuscripts, only one important difference was found: subjects. We found that SSRIs induce different effects in animals vs. humans. Preclinical studies showed many controversial effects, while human studies showed only two effects: improvement of depression, with or without the improvement of BDNF. However, most studies used chronic SSRIs treatment, while acute SSRIs were not effectively used and evaluated. In conclusion, it seems that SSRIs are reliable antidepressants, and the improvement effect of SSRIs on depression is not dependent to BDNF level (at least in human studies).

Role of estrogen in treatment of female depression

Depression is a neurological disorder that profoundly affects human physical and mental health, resulting in various changes in the central nervous system. Despite several prominent hypotheses, such as the monoaminergic theory, hypothalamic-pituitary-adrenal (HPA) axis theory, neuroinflammation, and neuroplasticity, the current understanding of depression's pathogenesis remains incomplete. Importantly, depression is a gender-dimorphic disorder, with women exhibiting higher incidence rates than men. Given estrogen's pivotal role in the menstrual cycle, it is reasonable to postulate that its fluctuating levels could contribute to the pathogenesis of depression. Estrogen acts by binding to a diversity of receptors, which are widely distributed in the central nervous system. An abundance of research has established that estrogen and its receptors play a crucial role in depression, spanning pathogenesis and treatment. In this comprehensive review, we provide an in-depth analysis of the fundamental role of estrogen and its receptors in depression, with a focus on neuroinflammation, neuroendocrinology, and neuroplasticity. Furthermore, we discuss potential mechanisms underlying the therapeutic effects of estrogen in the treatment of depression, which may pave the way for new antidepressant drug development and alternative treatment options.

Antidepressant-like Effects of Representative Types of Food and Their Possible Mechanisms

Depression is a mental disorder characterized by low mood, lack of motivation, negative cognitive outlook, and sleep problems. Suicide may occur in severe cases, although suicidal thoughts are not seen in all cases. Globally, an estimated 350 million individuals grapple with depression, as reported by the World Health Organization. At present, drug and psychological treatments are the main treatments, but they produce insufficient responses in many patients and fail to work at all in many others. Consequently, treating depression has long been an important topic in society. Given the escalating prevalence of depression, a comprehensive strategy for managing its symptoms and impacts has garnered significant attention. In this context, nutritional psychiatry emerges as a promising avenue. Extensive research has underscored the potential benefits of a well-rounded diet rich in fruits, vegetables, fish, and meat in alleviating depressive symptoms. However, the intricate mechanisms linking dietary interventions to brain function alterations remain largely unexplored. This review delves into the intricate relationship between dietary patterns and depression, while exploring the plausible mechanisms underlying the impact of dietary interventions on depression management. As we endeavor to unveil the pathways through which nutrition influences mental well-being, a holistic perspective that encompasses multidisciplinary strategies gains prominence, potentially reshaping how we approach and address depression.

Neural plasticity and depression treatment

Depression is one of the most common mental disorders, which can lead to a variety of emotional problems and even suicide at its worst. As this neuropsychiatric disorder causes the patients to suffer a lot and function poorly in everyday life, it is imposing a heavy burden on the affected families and the whole society. Several hypotheses have been proposed to elucidate the pathogenesis of depression, such as the genetic mutations, the monoamine hypothesis, the hypothalamic-pituitary-adrenal (HPA) axis hyperactivation, the inflammation and the neural plasticity changes. Among these models, neural plasticity can occur at multiple levels from brain regions, cells to synapses structurally and functionally during development and in adulthood. In this review, we summarize the recent progresses (especially in the last five years) on the neural plasticity changes in depression under different organizational levels and elaborate different treatments for depression by changing the neural plasticity. We hope that this review would shed light on the etiological studies for depression and on the development of novel treatments.

Polyphenols as novel interventions for depression: exploring the efficacy, mechanisms of action, and implications for future research

Numerous animal and human studies have assessed the relationship between polyphenols and outcomes related to depression. However, no comprehensive synthesis of the main findings has been conducted. The aim of this manuscript was to systematically review the available evidence from animal and human studies on the association and the effects of dietary polyphenols on depression and provide recommendations for future research. We based our review on 163 preclinical animal, 16 observational and 44 intervention articles assessing the relationship between polyphenols and outcomes related to depression. Most animal studies demonstrated that exposure to polyphenols alleviated behaviours reported to be associated with depression. However, human studies are less clear, with some studies reporting and inverse relationship between the intake of some polyphenols, and polyphenol rich foods and depression risk and symptoms, while others reporting no association or effect. Hence, while there has been extensive research conducted in animals and there is some supporting evidence in humans, further human studies are required, particularly in younger and clinical populations.

Multiple mechanisms of curcumin targeting spinal cord injury

Spinal cord injury (SCI) is an irreversible disease process with a high disability and mortality rate. After primary spinal cord injury, the secondary injury may occur in sequence, which is composed of ischemia and hypoxia, excitotoxicity, calcium overload, oxidative stress and inflammation, resulting in massive death of parenchymal cells in the injured area, followed by the formation of syringomyelia. Effectively curbing the process of secondary injury can promote nerve repair and improve functional prognosis. As the main active ingredient in turmeric, curcumin can play an important role in reducing inflammation and oxidation, protecting the neurons, and ultimately reducing spinal cord injury. This article reviews the effects of curcumin on the repair of nerve injury, with emphasis on the various mechanisms by which curcumin promotes the treatment of spinal cord injury.

The effect of glucagon like peptide-1 receptor agonist on behavioral despair and anxiety-like behavior in ovariectomized rats: Modulation of BDNF/CREB, Nrf2 and lipocalin 2

Ovariectomized (OVX) rodents show behavioral despair and anxiety-like behaviors. Glucagon-like peptide-1 receptor agonists (GLP-1RA) possess neuroprotective effects by reducing oxidative stress and neuroinflammation, thereby preventing synaptic loss. The objective of the present study is to evaluate the effect of GLP-1RA, namely liraglutide, on emotional behaviors, and to identify the level of oxidative stress, neuroinflammation, and BDNF signaling in the hippocampus of OVX rats. Forty female young Wistar rats were divided into 5 groups: Control, Control+liraglutide treated, OVX, OVX+fluoxetine, and OVX+liraglutide (150 µg/kg for 15 days, sc). Open field test and elevated plus-maze test were used to evaluate behaviors that are suggestive of anxiety. A forced swimming test was used to evaluate behavioral despair. At the end of the experiments, blood glucose level and body weight gain were measured. The levels of BDNF, CREB, Nrf2, and lipocalin 2 in the hippocampal tissue were measured by ELISA. Malondialdehyde (MDA) and glutathione levels were also evaluated. Statistical analysis was conducted through ANOVA and Bonferroni tests. Seven weeks post-OVX rats exhibited high anxiety related behavior and behavioral despair in comparison with the control groups. These behavioral changes were associated with increased lipocalin 2 and MDA levels in rats. Moreover, BDNF, CREB, and Nrf2 levels decreased significantly in the hippocampus of OVX rats. Liraglutide treatment limited the reduction of BDNF and Nrf2 levels in the hippocampus, maintaining them at the control levels. Liraglutide treatment also prevented the symptoms of behavioral despair and anxiety related behavior. As the main finding of the study GLP-1RA reduced behavioral despair and anxiety level and this may be related to the preservation of BDNF/Nrf2 levels and the decrease in oxidative stress and lipocalin 2 levels in the hippocampus.

An Update on the Exploratory Use of Curcumin in Neuropsychiatric Disorders

Curcumin is a polyphenol extracted from the rhizome of the turmeric plant. Beyond its common use as a culinary spice in Eastern Asia, curcumin has been proposed as a therapeutic compound due to its antioxidant, anti-inflammatory and neuroprotective properties. Thus, its efficacy has been evaluated in various inflammatory-based psychiatric disorders, such as schizophrenia, depression, or autism. Our aim is to review those preclinical and clinical studies carried out in psychiatric disorders whose therapeutic approach has involved the use of curcumin and, therefore, to discern the possible positive effect of curcumin in these disorders. Preclinical studies and completed clinical trials of curcumin for psychiatric disorders published from January 2005 to October 2021 were identified through searching relevant databases until 31st October 2021. Sixty-five preclinical studies and 15 clinical trials and open-label studies were selected. Results showed a bias toward studies in depression and, to a lesser extent, schizophrenia. In all disorders, the results were positive in reducing psychiatric deficits. Despite the considerable number of beneficial outcomes reported, the small number of trials and the heterogeneity of protocols make it difficult to draw solid conclusions about the real potency of curcumin in psychiatric disorders.

Potential Role of Curcumin for the Treatment of Major Depressive Disorder

Curcumin is the major biologically active polyphenolic constituent in the turmeric plant (Curcuma longa) that has been shown to have antioxidant, anti-inflammatory, neuroprotective, anticancer, antimicrobial, and cardioprotective effects. Interest in curcumin as a treatment for mental health conditions has increased and there is an expanding body of preclinical and clinical research examining its antidepressant and anxiolytic effects. In this narrative review, human trials investigating the effects of curcumin for the treatment of depression or depressive symptoms are summarised. Using findings from in vitro, animal, and human trials, possible biological mechanisms associated with the antidepressant effects of curcumin are also explored. To increase the understanding of curcumin for the treatment of depression, directions for future research are proposed.

Anti-Inflammatory Effects of Curcumin in the Inflammatory Diseases: Status, Limitations and Countermeasures

Curcumin is a natural compound with great potential for disease treatment. A large number of studies have proved that curcumin has a variety of biological activities, among which anti-inflammatory effect is a significant feature of it. Inflammation is a complex and pervasive physiological and pathological process. The physiological and pathological mechanisms of inflammatory bowel disease, psoriasis, atherosclerosis, COVID-19 and other research focus diseases are not clear yet, and they are considered to be related to inflammation. The anti-inflammatory effect of curcumin can effectively improve the symptoms of these diseases and is expected to be a candidate drug for the treatment of related diseases. This paper mainly reviews the anti-inflammatory effect of curcumin, the inflammatory pathological mechanism of related diseases, the regulatory effect of curcumin on these, and the latest research results on the improvement of curcumin pharmacokinetics. It is beneficial to the further study of curcumin and provides new ideas and insights for the development of curcumin anti-inflammatory preparations.

In vitro model of perimenopausal depression implicates steroid metabolic and proinflammatory genes

The estimated 20-30% of women who develop perimenopausal depression (PMD) are at an increased risk of cardiovascular and all-cause mortality. The therapeutic benefits of estradiol (E2) and symptom-provoking effects of E2-withdrawal (E2-WD) suggest that a greater sensitivity to changes in E2 at the cellular level contribute to PMD. We developed an in vitro model of PMD with lymphoblastoid cell lines (LCLs) derived from participants of a prior E2-WD clinical study. LCLs from women with past PMD (n = 8) or control women (n = 9) were cultured in three experimental conditions: at vehicle baseline, during E2 treatment, and following E2-WD. Transcriptome analysis revealed significant differences in transcript expression in PMD in all experimental conditions, and significant overlap in genes that were changed in PMD regardless of experimental condition. Of these, chemokine CXCL10, previously linked to cardiovascular disease, was upregulated in women with PMD, but most so after E2-WD (p < 1.55 × 10-5). CYP7B1, an enzyme intrinsic to DHEA metabolism, was upregulated in PMD across experimental conditions (F(1,45) = 19.93, p < 0.0001). These transcripts were further validated via qRT-PCR. Gene networks dysregulated in PMD included inflammatory response, early/late E2-response, and cholesterol homeostasis. Our results provide evidence that differential behavioral responsivity to E2-WD in PMD reflects intrinsic differences in cellular gene expression. Genes such as CXCL10, CYP7B1, and corresponding proinflammatory and steroid biosynthetic gene networks, may represent biomarkers and molecular targets for intervention in PMD. Finally, this in vitro model allows for future investigations into the mechanisms of genes and gene networks involved in the vulnerability to, and consequences of, PMD.

A systematic review of the antidepressant effects of curcumin: Beyond monoamines theory

BACKGROUND

Depression is a severe, chronic, and recurring mental health disorder, which prevalence and morbimortality have increased in recent years. Several theories are proposed to elucidate the mechanisms of depression, such as the involvement of inflammation and the release of cytokines. Alternative treatments have been developed to improve outcomes of the commonly used drugs, and the use of Curcuma longa stands out. Its primary compound is named curcumin that exhibits antioxidant and anti-inflammatory effects.

AIMS

Several studies have shown that curcumin may play antidepressant actions and, therefore, this study aimed to perform a systematic review of the antidepressant effects of curcumin to evaluate the impact of this compound in the treatment of this condition.

METHODS

This systematic review has included studies available in MEDLINE-PubMed, EMBASE, and Cochrane databases, and the final selection included 10 randomized clinical trials.

CONCLUSION

Curcumin improves depressant and anxiety behavior in humans. It can increase monoamines and brain-derived neurotrophic factor levels and may inhibit the production of pro-inflammatory cytokines and neuronal apoptosis in the brain. Systemically, curcumin enhanced insulin sensitivity, reduced cortisol levels, and reversed metabolic abnormalities. Studies with larger samples and standardized dose and formulation are required to demonstrate the benefits of curcumin in depression treatment since there are many variations in this compound's use.

Neuromodulatory effect of curcumin on catecholamine systems and inflammatory cytokines in ovariectomized female rats

Anti-inflammatory products may represent the future for depressive disorder therapies. Curcumin (CUR) is a polyphenol and an active component of the turmeric plant Curcuma longa. The aim of this study was to investigate the impact of CUR, as a natural anti-inflammatory agent, on neuro-inflammation related to depression and compare it with the effects of fluoxetine (FLX) and estradiol (E2 ) in ovariectomized (OVX) rats. The experimental animals were divided into the following five treatment groups (n = 10): sham-operated, OVX, OVX-E2 (100 μg/kg, im, every other day), OVX-FLX (20 mg/kg, ip, daily), and OVX-CUR (100 mg/kg, po, daily). The results indicated that CUR improved the animals' performances in the open field test and modulated dopamine (DA) and norepinephrine levels in several brain regions compared with the OVX group. CUR resulted in the down-regulation of monoamine oxidase b and up-regulation of tyrosine hydroxylase, as well asDA receptor mRNA in the limbic region. In addition, CUR significantly attenuated the production of serum corticosterone hormone, tumour necrosis factor-alpha, interleukin-β1, interleukin-6, and nitric oxide in the limbic system. Furthermore, CUR normalized malondialdehyde levels and led to a significant upsurge in total antioxidant capacity, compared with the OVX group. Consequently, CUR, besides being harmless, was efficient against inflammation and oxidative-nitrosative stress, showing a greater effect on DA receptor expression than FLX and E2 in OVX rats.

Efficacy of a curcumin extract (Curcugen™) on gastrointestinal symptoms and intestinal microbiota in adults with self-reported digestive complaints: a randomised, double-blind, placebo-controlled study

BACKGROUND

There is preliminary evidence to suggest curcumin can alleviate digestive symptoms in adults with self-reported digestive complaints and irritable bowel syndrome. However, in all these trials, curcumin was used as a component of a multi-herbal combination and there were consistent concerns associated with risk of bias in most studies. The goal of this study was to investigate the effects of a curcumin extract (Curcugen™) on gastrointestinal symptoms, mood, and overall quality of life in adults presenting with self-reported digestive complaints. Moreover, to determine the potential therapeutic mechanisms of action associated with curcumin, its effects on intestinal microbiota and small intestinal bowel overgrowth (SIBO) were examined.

METHODS

In this 8-week, parallel-group, double-blind, randomised controlled trial, 79 adults with self-reported digestive complaints were recruited and randomised to receive either a placebo or 500 mg of the curcumin extract, Curcugen™. Outcome measures included the Gastrointestinal Symptom Rating Scale (GSRS), intestinal microbial profile (16S rRNA), Depression, Anxiety, and Stress Scale - 21 (DASS-21), Short Form-36 (SF-36), and SIBO breath test.

RESULTS

Based on self-report data collected from 77 participants, curcumin was associated with a significantly greater reduction in the GSRS total score compared to the placebo. There was also a greater reduction in the DASS-21 anxiety score. No other significant between-group changes in self-report data were identified. An examination of changes in the intestinal microbial profile and SIBO test revealed curcumin had no significant effect on these parameters. Curcumin was well-tolerated with no significant adverse events.

CONCLUSIONS

The curcumin extract, Curcugen™, administered for 8 weeks at a dose of 500 mg once daily was associated with greater improvements in digestive complaints and anxiety levels in adults with self-reported digestive complaints. Compared to the placebo, there were no significant changes in intestinal microbiota or SIBO; however, further research using larger samples and testing methods that allow more detailed microbial analyses will be important. An investigation into other potential mechanisms associated with curcumin's gastrointestinal-relieving effects will also be important such as examining its influence on the intestinal barrier function, inflammation, neurotransmitter activity, and visceral sensitivity.

TRIAL REGISTRATION

Australian New Zealand Clinical Trials Registry, Trial ID. ACTRN12619001236189 . Registered 6 September 2019.

Adaptogenic effects of curcumin on depression induced by moderate and unpredictable chronic stress in mice

Curcumin has been investigated for the prevention and treatment of diseases due to its anti-oxidant, anti-inflammatory, immunomodulatory, and neuroprotective actions. This current study evaluated the adaptogenic effects of a subchronic oral administration of curcumin to Swiss mice that were submitted to a chronic unpredictable mild stress (CUMS) model of depression. Four groups of mice (vehicle control, CO; curcumin control, COC; CUMS + vehicle, CUMS; CUMS + curcumin, CUMSC) were evaluated for the biochemical parameters. The CUMS model caused depressive-like and anxiety-like behavior in the animals when they were viewed in the Forced Swimming Test and in the Elevated Plus Maze Test. The treatments with curcumin prevented the depressive-like behavior in the Forced Swimming Test and they had anxiolytic effects on the non-stressed animals. This was confirmed by the Elevated Plus Maze Test. Curcumin showed antioxidant effects (IC₅₀ of 38.86 ± 1.78 μg/mL) in the in vitro DPPH (2,2-diphenyl-1-picryl-hydrozole) test. The compound also showed antioxidant effects in vivo, increasing the catalase (CAT) levels in the brains of the stressed animals. The biochemical analyses did not reveal potential renal and hepatic damage. Together, these results have demonstrated the antidepressant and antioxidant effects of curcumin, highlighting in this mice model, the compound's novel adaptogenic potential.

Curcumin in Depression: Potential Mechanisms of Action and Current Evidence-A Narrative Review

Major depressive disorder (MDD) is one of the most prevalent and debilitating disorders. Current available treatments are somehow limited, so alternative therapeutic approaches targeting different biological pathways are being investigated to improve treatment outcomes. Curcumin is the main active component in the spice turmeric that has been used for centuries in Ayurvedic medicine to treat a variety of conditions, including anxiety and depressive disorders. In the past decades, curcumin has drawn researchers' attention and displays a broad range of properties that seem relevant to depression pathophysiology. In this review, we break down the potential mechanisms of action of curcumin with emphasis on the diverse systems that can be disrupted in MDD. Curcumin has displayed, in a number of studies, a potency in modulating neurotransmitter concentrations, inflammatory pathways, excitotoxicity, neuroplasticity, hypothalamic-pituitary-adrenal disturbances, insulin resistance, oxidative and nitrosative stress, and endocannabinoid system, all of which can be involved in MDD pathophysiology. To date, a handful of clinical trials have been published and suggest a benefit of curcumin in MDD. With evidence that is progressively growing, curcumin appears as a promising alternative option in the management of MDD.