Zinc deficiency induces enhanced depression-like behaviour and altered limbic activation reversed by antidepressant treatment in mice

Investigating the role of GPR39 in treatment of stress-induced depression and anxiety

RATIONALE

Chronic stress is one of the leading causes of depression. Yet, knowledge of the pathomechanism of this process still eludes us. Chronic unpredictable mild stress (CUMS) model of depression enables researchers to look for a root cause of the disease in mice by mimicking a stressful human environment.

OBJECTIVE

Since zinc has already been shown to impact the treatment of depression, in our study we aimed to shed light on the role of the zinc receptor GPR39 in stress-induced depression. We also aimed to highlight the role of GPR39 activation in monoamine-based antidepressant treatment.

METHODS

Using large battery of behavioural tests, we provided a detailed description of CUMS-induced phenotype in both - CD-1 and GPR39 knock-out mice.

RESULTS

Our experiments showed that combined treatment with TC-G 1008 (GPR39 agonist) and antidepressants produces stronger antidepressant-like effect of classic antidepressants. We also demonstrated the inter-strain differences in stress response and the greater stress susceptibility of GPR39 knock-out mice. The lack of GPR39 expression also either diminished or completely abolished the response to treatment with different antidepressants combined with TC-G 1008.

CONCLUSIONS

The results show that GPR39 KO mice are more susceptible to chronic stress and that they are non-responsive to SSRI treatment. Utilizing various behavioural tests gave us much broader understanding not only of the role of GPR39 in depression treatment, but also of the importance of detailed behavioural description in a proper interpretation of the results. Further research with known selective agonists and antagonists of GPR39 will be necessary to understand the full potential of this receptor as a pharmacological target.

Proteomics analysis in rats reveals convergent mechanisms between major depressive disorder and dietary zinc deficiency

BACKGROUND

Preclinical and clinical studies have shown that dietary zinc deficiency can lead to symptoms similar to those observed in major depressive disorder (MDD). However, the underlying molecular mechanisms remain unclear. To investigate these mechanisms, we examined proteomic changes in the prefrontal cortex (PFC) and hippocampus (HP) of rats, two critical brain regions implicated in the pathophysiology of depression.

METHODS

Rats were fed diets either adequate in zinc (ZnA, 50 mg Zn/kg) or deficient in zinc (ZnD, <3 mg/kg) for four weeks. High-throughput proteomic analysis was used to detect changes in protein expression, supplemented by enzyme activity assay for mitochondrial complexes I and IV, examining their functional impacts.

RESULTS

ZnD led to significant alterations in protein expression related to zinc transport and mitochondrial function. Proteomic analysis revealed changes in zinc transporter family members such as Slc30a1 (6.64 log2FC), Slc30a3 (-2.32 log2FC), Slc30a4 (2.87 log2FC), Slc30a5 (5.90 log2FC), Slc30a6 (1.50 log2FC), and Slc30a7 (2.17 log2FC) in the PFC, and Slc30a3 (-1.02 log2FC), Slc30a5 (-1.04 log2FC), and Slc30a7 (1.08 log2FC) in the HP of rats subjected to ZnD. Furthermore, ZnD significantly affected essential mitochondrial activity proteins, including Atp5pb (3.25 log2FC), Cox2 (2.28 log2FC), Atp5me (2.04 log2FC), Cyc1 (2.30 log2FC), Cox4i1 (1.23 log2FC), Cox7c (1.63 log2FC), and Cisd1 (1.55 log2FC), with a pronounced decrease in complex I activity in the PFC.

CONCLUSIONS

Our study demonstrates that ZnD leads to significant proteomic changes in the PFC and HP of rats. Specifically, ZnD alters the expression of zinc transporter proteins and proteins critical for mitochondrial function. The significant decrease in complex I activity in the PFC further underscores the impact of ZnD on mitochondrial function. These results highlight the molecular mechanisms by which ZnD can influence brain function and contribute to symptoms similar to those observed in depression.

Dietary Zinc Restriction and Chronic Restraint Stress Affect Mice Physiology, Immune Organ Morphology, and Liver Function

BACKGROUND

Preclinical and clinical studies suggest that zinc deficiency and chronic stress contribute to depressive symptoms. Our study explores the intricate relationship between these factors by examining their physiological and biochemical effects across various organs in C57Bl/6J mice.

METHODS

The mice were divided into four groups: control, chronic restraint stress for 3 weeks, a zinc-restricted diet (<3 mg/kg) for 4 weeks, and a combination of stress and zinc restriction. Mice spleen and thymus weights were measured, and hematoxylin-eosin staining was conducted for liver and intestinal morphometry. Moreover, metallothionein (MT-1, MT-2, and MT-3), zinc transporter (ZnT-1), oxidative stress markers (TBARS, SOD, and GSH-Px), and zinc, iron, and copper concentrations in the liver were evaluated. Immunohistochemical analysis of the jejunum for ZIP1 and ZIP4 was also performed.

CONCLUSIONS

Our findings reveal that dietary zinc restriction and chronic stress induce structural changes in the intestines and immune organs and impact metallothionein expression, oxidative stress, and liver iron and copper homeostasis.

Association between drinking water quality and mental health and the modifying role of diet: a prospective cohort study

BACKGROUND

Environmental factors play an important role in developing mental disorders. This study aimed to investigate the associations of metal and nonmetal elements in drinking water with the risk of depression and anxiety and to assess whether diets modulate these associations.

METHODS

We conducted a prospective cohort study including 24,285 participants free from depression and anxiety from the Yinzhou Cohort study in the 2016-2021 period. The exposures were measured by multiplying metal and nonmetal element concentrations in local pipeline terminal tap water samples and total daily drinking water intakes. Cox regression models adjusted for multi-level covariates were used to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (95%CIs).

RESULTS

During an average follow-up period of 4.72 and 4.68 years, 773 and 1334 cases of depression and anxiety were identified, respectively. A 1 standard deviation (SD) increase in manganese exposure reduced the incidence of depression by 8% (HR 0.92, 95%CI 0.88 to 0.97). In contrast, with a 1 SD increase in copper and cadmium exposure, the incidence of depression increased by 6% (HR 1.06, 95%CI 1.01 to 1.11) and 8% (HR 1.08, 95%CI 1.00 to 1.17), respectively. The incidence of anxiety increased by 39% (HR 1.39, 95%CI 1.20 to 1.62), 33% (HR 1.33, 95%CI 1.03 to 1.71), and 14% (HR 1.14, 95%CI 1.03 to 1.25) respectively for a 1 SD increase in manganese, iron, and selenium exposure. Diets have a moderating effect on the associations of metal and nonmetal elements with the risk of anxiety. Stronger associations were observed in older, low-income groups and low-education groups.

CONCLUSIONS

We found significant associations between exposure to metal and nonmetal elements and depression and anxiety. Diets regulated the associations to some extent.

Neurodevelopmental Consequences of Dietary Zinc Deficiency: A Status Report

Zinc is a tightly regulated trace mineral element playing critical roles in growth, immunity, neurodevelopment, and synaptic and hormonal signaling. Although severe dietary zinc deficiency is relatively uncommon in the United States, dietary zinc deficiency is a substantial public health concern in low- and middle-income countries. Zinc status may be a key determinant of neurodevelopmental processes. Indeed, limited cohort studies have shown that serum zinc is lower in people diagnosed with autism spectrum disorder (ASD), attention-deficit/hyperactivity disorder (ADHD), and depression. These observations have sparked multiple studies investigating the mechanisms underlying zinc status and neurodevelopmental outcomes. Animal models of perinatal and adult dietary zinc restriction yield distinct behavioral phenotypes reminiscent of features of ASD, ADHD, and depression, including increased anxiety and immobility, repetitive behaviors, and altered social behaviors. At the cellular and molecular level, zinc has demonstrated roles in neurogenesis, regulation of cellular redox status, transcription factor trafficking, synaptogenesis, and the regulation of synaptic architecture via the Shank family of scaffolding proteins. Although mechanistic questions remain, the current evidence suggests that zinc status is important for adequate neuronal development and may be a yet overlooked factor in the pathogenesis of several psychiatric conditions. This review aims to summarize current knowledge of the role of zinc in the neurophysiology of the perinatal period, the many cellular targets of zinc in the developing brain, and the potential consequences of alterations in zinc homeostasis in early life.

The antidepressant effect of short- and long-term zinc exposition is partly mediated by P2X7 receptors in male mice

Background: As a member of the purinergic receptor family, divalent cation-regulated ionotropic P2X7 (P2rx7) plays a role in the pathophysiology of psychiatric disorders. This study aimed to investigate whether the effects of acute zinc administration and long-term zinc deprivation on depression-like behaviors in mice are mediated by P2X7 receptors. Methods: The antidepressant-like effect of elevated zinc level was studied using a single acute intraperitoneal injection in C57BL6/J wild-type and P2rx7 gene-deficient (P2rx7 -/-) young adult and elderly animals in the tail suspension test (TST) and the forced swim test (FST). In the long-term experiments, depression-like behavior caused by zinc deficiency was investigated with the continuous administration of zinc-reduced and control diets for 8 weeks, followed by the same behavioral tests. The actual change in zinc levels owing to the treatments was examined by assaying serum zinc levels. Changes in monoamine and brain-derived neurotrophic factor (BDNF) levels were measured from the hippocampus and prefrontal cortex brain areas by enzyme-linked immunosorbent assay and high-performance liquid chromatography, respectively. Results: A single acute zinc treatment increased the serum zinc level evoked antidepressant-like effect in both genotypes and age groups, except TST in elderly P2rx7 -/- animals, where no significant effect was detected. Likewise, the pro-depressant effect of zinc deprivation was observed in young adult mice in the FST and TST, which was alleviated in the case of the TST in the absence of functional P2X7 receptors. Among elderly mice, no pro-depressant effect was observed in P2rx7 -/- mice in either tests. Treatment and genotype changes in monoamine and BDNF levels were also detected in the hippocampi. Conclusion: Changes in zinc intake were associated with age-related changes in behavior in the TST and FST. The antidepressant-like effect of zinc is partially mediated by the P2X7 receptor.

Appropriate Macronutrients or Mineral Elements Are Beneficial to Improve Depression and Reduce the Risk of Depression

Depression is a common mental disorder that seriously affects the quality of life and leads to an increasing global suicide rate. Macro, micro, and trace elements are the main components that maintain normal physiological functions of the brain. Depression is manifested in abnormal brain functions, which are considered to be tightly related to the imbalance of elements. Elements associated with depression include glucose, fatty acids, amino acids, and mineral elements such as lithium, zinc, magnesium, copper, iron, and selenium. To explore the relationship between these elements and depression, the main literature in the last decade was mainly searched and summarized on PubMed, Google Scholar, Scopus, Web of Science, and other electronic databases with the keywords "depression, sugar, fat, protein, lithium, zinc, magnesium, copper, iron, and selenium". These elements aggravate or alleviate depression by regulating a series of physiological processes, including the transmission of neural signals, inflammation, oxidative stress, neurogenesis, and synaptic plasticity, which thus affect the expression or activity of physiological components such as neurotransmitters, neurotrophic factors, receptors, cytokines, and ion-binding proteins in the body. For example, excessive fat intake can lead to depression, with possible mechanisms including inflammation, increased oxidative stress, reduced synaptic plasticity, and decreased expression of 5-Hydroxytryptamine (5-HT), Brain Derived Neurotrophic Factor (BDNF), Postsynaptic density protein 95(PSD-95), etc. Supplementing mineral elements, such as selenium, zinc, magnesium, or lithium as a psychotropic medication is mostly used as an auxiliary method to improve depression with other antidepressants. In general, appropriate nutritional elements are essential to treat depression and prevent the risk of depression.

Extracellular zinc regulates contextual fear memory formation in male rats through MMP-BDNF-TrkB pathway in dorsal hippocampus and basolateral amygdala

Large amount of zinc (100 µM even up to 300 µM) is released from the nerve terminals in response to high frequency neuronal stimulation in certain brain regions including hippocampus and amygdala. However, its precise pharmacological effect is poorly understood. Here, we investigated the role of extracellular zinc (endogenous zinc) and exogenous zinc in memory formation using contextual fear conditioning (CFC) model. Male Sprague Dawley rats were trained for fear conditioning followed by in vivo microdialysis for collection of microdialysate samples from CA1 and CA3 regions of hippocampus and basolateral amygdala (BLA). Extracellular zinc chelator CaEDTA, BDNF scavenger TrkB-Fc, exogenous 7,8-DHF and matrix metalloproteinases (MMP) inhibitor were infused into the CA1 and CA3 regions of hippocampus and BLA after CFC. Different doses of exogenous zinc hydroaspartate were administered intraperitoneally immediately after CFC. We found that CFC increased the level of extracellular zinc in the hippocampus and BLA. Infusing the CaEDTA, TrkB-Fc and MMP inhibitor into the CA1 and CA3 regions of hippocampus and BLA disrupted the fear memory formation. Furthermore, administration of TrKB agonist 7,8-DHF reversed the inhibitory effect of CaEDTA on fear memory formation, suggesting that extracellular zinc may regulate fear memory formation via the BDNF-TrKB pathway. We also found that high dose of exogenous zinc hydroaspartate supplementation increased extracellular zinc levels in brain and enhanced fear memory formation. Altogether, these findings indicate that extracellular zinc may participate in formation of contextual fear memory through MMP-BDNF-TrkB pathway in the hippocampus and BLA.

The Important Role of Zinc in Neurological Diseases

Zinc is one of the most abundant metal ions in the central nervous system (CNS), where it plays a crucial role in both physiological and pathological brain functions. Zinc promotes antioxidant effects, neurogenesis, and immune system responses. From neonatal brain development to the preservation and control of adult brain function, zinc is a vital homeostatic component of the CNS. Molecularly, zinc regulates gene expression with transcription factors and activates dozens of enzymes involved in neuronal metabolism. During development and in adulthood, zinc acts as a regulator of synaptic activity and neuronal plasticity at the cellular level. There are several neurological diseases that may be affected by changes in zinc status, and these include stroke, neurodegenerative diseases, traumatic brain injuries, and depression. Accordingly, zinc deficiency may result in declines in cognition and learning and an increase in oxidative stress, while zinc accumulation may lead to neurotoxicity and neuronal cell death. In this review, we explore the mechanisms of brain zinc balance, the role of zinc in neurological diseases, and strategies affecting zinc for the prevention and treatment of these diseases.

Combined hyperforin and lanicemine treatment instead of ketamine or imipramine restores behavioral deficits induced by chronic restraint stress and dietary zinc restriction in mice

Clinical and preclinical studies show evidence that chronic stress or nutritional deficits in dietary zinc (Zn) intake may be risk factors for developing major depressive disorder (MDD). Furthermore, there may be possible links between low serum Zn levels and development of treatment-resistant depression. In the present work, we combined chronic restraint stress (CRS) and a low-zinc diet (ZnD) in mice and carried out a set of behavioral and biochemical studies. The mice were treated with four different antidepressant compounds, namely, ketamine, Ro 25–6981 (Ro), hyperforin and lanicemine (Hyp + Lan), and imipramine (IMI). We show that CRS or ZnD alone or a combination of CRS and ZnD (CRS + ZnD) induces anhedonia observed in the sucrose preference test (SPT). The behavioral effects of CRS were restored by ketamine or IMI. However, only Hyp + Lan restored the deficits in behavioral phenotype in mice subjected to CRS + ZnD. We also showed that the antidepressant-like effects observed in Hyp + Lan-treated CRS + ZnD mice were associated with changes in the morphology of the dendritic spines (restored physiological level) in the hippocampus (Hp). Finally, we studied the metabolism of ketamine and its brain absorption in CRS and CRS + ZnD mice. Our results suggest that CRS + ZnD does not alter the metabolism of ketamine to (2R,6R;2S,6S)-HNK; however, CRS + ZnD can induce altered bioavailability and distribution of ketamine in the Hp and frontal cortex (FC) in CRS + ZnD animals compared to the control and CRS groups.

Zinc Deficiency Blunts the Effectiveness of Antidepressants in the Olfactory Bulbectomy Model of Depression in Rats

Currently used antidepressants do not always provide the desired results, and many patients suffer from treatment-resistant depression. Clinical studies suggest that zinc deficiency (ZnD) may be an important risk factor for depression and might blunt the effect of antidepressants. This study aimed to examine whether ZnD might blunt the effectiveness of antidepressants in the olfactory bulbectomy model (OB) of depression in rats. For this purpose, rats were subjected to the OB model, fed a zinc-deficient diet (3 mg Zn/kg) for 3 weeks, and finally treated with escitalopram (Esc), venlafaxine (Ven) 10 mg/kg, i.p., or combined Esc/Ven (1 mg/kg, i.p.) with zinc (5 mg/kg) for another 3 weeks. Open field (OFT), forced swim (FST), and sucrose intake (SIT) tests were used to evaluate depressive-like behavioral changes. In addition, serum, intracellular, and synaptic Zn concentrations and the level of zinc transporter (ZnT) proteins were analyzed. The OB + ZnD model induced hyperactivity in rats in the OFT, increased immobility time in the FST, and anhedonia in the SIT. Chronic treatment with Esc reduced immobility time in the FST in the OB + ZnD model. Esc/Ven +Zn increased sucrose intake in rats from the OB + ZnD group. The OB + ZnD decreased serum zinc levels and intracellular and synaptic Zn concentration in the prefrontal cortex (PFC) and cerebellum. These changes were normalized by chronic administration of Esc/Ven +Zn. Moreover, OB + ZnD decreased levels of the ZnT1 protein in the PFC and Hp and ZnT3 in Hp. Chronic administration of antidepressants did not alter the levels of ZnT proteins. The OB + ZnD model induces more depressive-like effects than either model alone. Our results show that ZnD may induce drug resistance in rats. Normalizing serum or brain zinc concentration is insufficient to reverse behavioral abnormalities caused by the OB + ZnD model. However, zinc supplementation might improve the effectiveness of antidepressants in reversing particular depression symptoms.

Impact of Zinc Transport Mechanisms on Embryonic and Brain Development

The trace element zinc (Zn) binds to over ten percent of proteins in eukaryotic cells. Zn flexible chemistry allows it to regulate the activity of hundreds of enzymes and influence scores of metabolic processes in cells throughout the body. Deficiency of Zn in humans has a profound effect on development and in adults later in life, particularly in the brain, where Zn deficiency is linked to several neurological disorders. In this review, we will summarize the importance of Zn during development through a description of the outcomes of both genetic and early dietary Zn deficiency, focusing on the pathological consequences on the whole body and brain. The epidemiology and the symptomology of Zn deficiency in humans will be described, including the most studied inherited Zn deficiency disease, Acrodermatitis enteropathica. In addition, we will give an overview of the different forms and animal models of Zn deficiency, as well as the 24 Zn transporters, distributed into two families: the ZIPs and the ZnTs, which control the balance of Zn throughout the body. Lastly, we will describe the TRPM7 ion channel, which was recently shown to contribute to intestinal Zn absorption and has its own significant impact on early embryonic development.

RNA-seq analysis of gene expression profiles in posttraumatic stress disorder, Parkinson's disease and schizophrenia identifies roles for common and distinct biological pathways

Evidence suggests that shared pathophysiological mechanisms in neuropsychiatric disorders (NPDs) may contribute to risk and resilience. We used single-gene and network-level transcriptomic approaches to investigate shared and disorder-specific processes underlying posttraumatic stress disorder (PTSD), Parkinson's disease (PD) and schizophrenia in a South African sample. RNA-seq was performed on blood obtained from cases and controls from each cohort. Gene expression and weighted gene correlation network analyses (WGCNA) were performed using DESeq2 and CEMiTool, respectively. Significant differences in gene expression were limited to the PTSD cohort. However, WGCNA implicated, amongst others, ribosomal expression, inflammation and ubiquitination as key players in the NPDs under investigation. Differential expression in ribosomal-related pathways was observed in the PTSD and PD cohorts, and focal adhesion and extracellular matrix pathways were implicated in PD and schizophrenia. We propose that, despite different phenotypic presentations, core transdiagnostic mechanisms may play important roles in the molecular aetiology of NPDs.

Zinc Intakes and Health Outcomes: An Umbrella Review

It is widely accepted that the zinc element is crucial in human beings. Zinc has gained more attention during the COVID-19 pandemic due to its utilization for the treatment and prevention of respiratory tract infections. However, some studies also pointed out that zinc intake might cause unwanted side effects and even be dangerous when overdosed. To reveal the relationship between zinc intake and health outcomes, we performed an umbrella review from human studies. In total, the umbrella review included 43 articles and identified 11 outcomes for dietary zinc intake and 86 outcomes for supplementary zinc intake. Dietary zinc intake in the highest dose would decrease the risk of overall and specific digestive tract cancers, depression, and type 2 diabetes mellitus (T2DM) in adults. Supplementary zinc consumption in adults was linked to an improvement of depression, antioxidant capacity and sperm quality, higher serum zinc concentration, and lower concentration of inflammatory markers. Zinc supplementation in children would reduce the incidence of diarrhea and pneumonia, improve zinc deficiency and boost growth. However, zinc might not decrease all-cause mortality in adults or the in-hospital mortality of COVID-19. And better maternal and neonatal outcomes may not derive from pregnant women who consumed higher or lower doses of zinc supplementation (&gt;20 mg/day and &lt;20 mg/day, respectively). Dose-response analyses revealed that a daily 5 mg increment of zinc would lower the risk of colorectal and esophageal cancer, whereas a large dose of zinc supplementation (daily 100 mg) showed no benefit in reducing prostate cancer risk.

Neuronal correlates underlying the role of the zinc sensing receptor (GPR39) in passive-coping behaviour

The Zn²⁺ receptor GPR39 is proposed to be involved in the pathophysiology of depression. GPR39 knockout (KO) animals show depressive- and anxiety-like behaviour, and resistance to conventional monoamine-based antidepressants. However, it is unclear as to which brain regions are involved in the pro-depressive phenotype of GPR39KO mice and the resistance to monoamine-targeting antidepressant treatment. Our current study confirmed previous results, showing that mice lacking GPR39 display enhanced passive coping-like behaviour compared with their wild-type controls. Furthermore, this study shows for the first time that GPR39KO displayed aberrant challenge-induced neuronal activity in key brain regions associated with passive coping behaviour. Imipramine induced only a marginal reduction in the enhanced passive coping behaviour in GPR39KO mice, which was associated with attenuation of the hyperactive prefrontal cortex. Similarly, the aberrant activity within the amygdalar subregions was normalized following imipramine treatment in the GPR39KO mice, indicating that imipramine mediates these effects independently of GPR39 in the prefrontal cortex and amygdala. However, imipramine failed to modulate the aberrant brain activity in other brain regions, such as the anterior CA3 and the dentate gyrus, in GPR39KO mice. Normalization of aberrant activity in these areas has been shown previously to accompany successful behavioural effects of antidepressants. Taken together, our data suggest that monoamine-based antidepressants such as imipramine exert their action via GPR39-dependent and -independent pathways. Failure to modulate passive-coping related aberrant activity in important brain areas of the depression circuitry is proposed to mediate/contribute to the greatly reduced antidepressant action of monoamine-based antidepressants in GPR39KO mice.

The effect of zinc supplementation on brain derived neurotrophic factor: A meta-analysis

BACKGROUND

Zinc in one of the most abundant trace minerals in human body which is involved in numerous biological pathways and has variety of roles in the nervous system. It has been assumed that zinc exerts its role in nervous system through increasing brain derived neurotrophic factor (BDNF) concentrations.

OBJECTIVES

Present meta-analysis was aimed to review the effect of zinc supplementation on serum concentrations of BDNF.

METHODS AND MATERIALS

Four electronic databases (Pubmed, Scopus, Web of Science, Embase) were searched for identifying studies that examined BDNF levels prior and after zinc supplementation up to May 2020. According to the Cochrane guideline, a meta-analysis was performed to pool the effect size estimate (Hedges' test) of serum BDNF across studies. Risk of publication bias was assessed using a funnel plot and Egger's test.

RESULTS

Five studies were eligible and 238 participants were included. These studies enrolled subjects with premenstrual syndrome, diabetic retinopathy, major depression disorder, overweight/obese and obese with mild to moderate depressive disorders. Zinc supplementation failed to increase blood BDNF concentrations with effect size of 0.30 (95 % CI: -0.08, 0.67, P = 0.119). Funnel plot did not suggest publication bias.

CONCLUSION

Zinc supplementation may not significantly increase BDNF levels. However, the small number of included articles and significant heterogeneity between them can increase the risk of a false negative result; therefore, the results should be interpreted with caution.

Pyroluria: Fact or Fiction?

Objective: The term "Mauve factor" (pyrroluria) dates back to 1958 when Dr. Abram Hoffer defined the condition as elevated levels of pyrroles in the urine, currently called hydroxyhemepyrrolin-2-one (HPL). It was suggested that the raised pyrrole levels lead to depletions in zinc and vitamin B₆, which, in turn, were hypothesized to result in a range of psychiatric disorders, such as schizophrenia, anxiety, and depression. Treatment implications are supplementation with zinc and B₆. This article aimed to review the scientific literature associating pyrroluria with psychiatric symptoms, explore the validity of HPL testing, explore the role of nutrients as treatment options for pyrroluria, and discuss future research directions. Methods: A PRISMA review was conducted using search results from electronic databases PubMed, MEDLINE, PsycINFO, EMBASE from inception to February 2020 using the following keywords: hydroxyhemepyryrrolin (HPL), kryptopyrrole (KP), mauve factor, pyroluria, pyrroluria, monopyrroles. Article reference lists were also scanned and included where relevant. Results: Seventy-three articles were identified of which only three studies identified significantly higher HPL levels in a psychiatric population compared with controls, and there were no placebo-controlled treatment trials directed at pyrroluria. The other 13 clinical studies either showed no association or did not provide adequate data to show group differences in HPL levels. Despite an extensive history of practitioners diagnosing and treating a wide variety of mental health conditions associated with pyrroluria as well as clinical observations of elevated HPL being associated with psychiatric disorders, there was no clear research that showed the following: (1) elevated HPL is robustly associated with increased mental health symptoms, (2) elevated HPL in urine is associated with increased urine excretion of zinc and B₆, and (3) high-dose zinc and B₆ are an efficacious treatment for mental health problems associated with elevated HPL. Conclusions: Elevated HPL is a clinically observed, but poorly researched biomarker with unclear associations with mental disorders. Based on current evidence, HPL testing is not recommended as a screening or treatment tool. Further research is required in the following areas: establishment of which specific clinical populations exhibit elevated HPL, validation of the chemistry and validity of testing, and controlled trials to establish efficacy of high-dose zinc and B₆ as treatment of elevated pyrroles.

The Interaction of Selective A1 and A2A Adenosine Receptor Antagonists with Magnesium and Zinc Ions in Mice: Behavioural, Biochemical and Molecular Studies

The purpose of the study was to investigate whether the co-administration of Mg²⁺ and Zn²⁺ with selective A1 and A2A receptor antagonists might be an interesting antidepressant strategy. Forced swim, tail suspension, and spontaneous locomotor motility tests in mice were performed. Further, biochemical and molecular studies were conducted. The obtained results indicate the interaction of DPCPX and istradefylline with Mg²⁺ and Zn²⁺ manifested in an antidepressant-like effect. The reduction of the BDNF serum level after co-administration of DPCPX and istradefylline with Mg²⁺ and Zn²⁺ was noted. Additionally, Mg²⁺ or Zn²⁺, both alone and in combination with DPCPX or istradefylline, causes changes in Adora1 expression, DPCPX or istradefylline co-administered with Zn²⁺ increases Slc6a15 expression as compared to a single-drug treatment, co-administration of tested agents does not have a more favourable effect on Comt expression. Moreover, the changes obtained in Ogg1, MsrA, Nrf2 expression show that DPCPX-Mg²⁺, DPCPX-Zn²⁺, istradefylline-Mg²⁺ and istradefylline-Zn²⁺ co-treatment may have greater antioxidant capacity benefits than administration of DPCPX and istradefylline alone. It seems plausible that a combination of selective A1 as well as an A2A receptor antagonist and magnesium or zinc may be a new antidepressant therapeutic strategy.

Interaction between zinc, the GPR39 zinc receptor and the serotonergic system in depression

Zinc signalling has a crucial impact on the proper functioning of the brain. Disturbances within the zincergic system may lead to neuropsychological disorders, including major depression. Studying this disease and designing effective treatment is hampered by its heterogeneous etiology and the diversified nature of the symptoms. Over the years, studies have shown that zinc deficiency and disturbances in the expression profile of the zinc receptor - GPR39 - might be a useful neurobiological indicator of a pathological state. Zinc levels and the zinc receptor are altered by classic antidepressant treatment, which indicates possible reciprocity between the monoaminergic system and zinc signalling. Disruptions in this specific interplay might be a cause of a pathological depressive state, and restoring balance and cooperation between those systems might be key to a successful form of pharmacotherapy. In this review, we aim to describe interactions between the serotonergic and zincergic systems and to highlight their significance in the pathophysiology and treatment of depression.

Ketamine and Ro 25-6981 Reverse Behavioral Abnormalities in Rats Subjected to Dietary Zinc Restriction

Clinical and preclinical studies indicate that zinc (Zn) is an essential factor in the development and treatment of major depressive disorder (MDD). Conventional monoamine-based antidepressants mobilize zinc in the blood and brain of depressed patients as well as rodents. N-methyl-D-aspartate acid receptor (NMDAR) antagonists exhibit antidepressant-like activity. However, not much is known about the antidepressant efficacy of NMDAR antagonists in zinc-deficient (ZnD) animals. We evaluated the antidepressant-like activity of two NMDAR antagonists (ketamine; global NMDAR antagonist and Ro 25-6981 (Ro); selective antagonist of the GluN2B NMDAR subunit) in ZnD rats using the forced swim test (FST) and sucrose intake test (SIT). A single dose of either Ro 25-6981 or ketamine normalized depressive-like behaviors in ZnD rats; however, Ro was effective in both tests, while ketamine was only effective in the FST. Additionally, we investigated the mechanism of antidepressant action of Ro at the molecular (analysis of protein expression by Western blotting) and anatomical (density of dendritic spines by Golgi Cox-staining) levels. ZnD rats exhibited decreased phosphorylation of the p70S6K protein, and enhanced density of dendritic spines in the prefrontal cortex (PFC) compared to control rats. The antidepressant-like activity of Ro was associated with the increased phosphorylation of p70S6K and ERK in the PFC. In summary, single doses of the NMDAR antagonists ketamine and Ro exhibited antidepressant-like activity in the ZnD animal model of depression. Animals were only deprived of Zn for 4 weeks and the biochemical effects of Zn deprivation and Ro were investigated in the PFC and hippocampus. The shorter duration of dietary Zn restriction may be a limitation of the study. However, future studies with longer durations of dietary Zn restriction, as well as the investigation of multiple brain structures, are encouraged as a supplement to this study.

The association between antioxidant intake, dietary pattern and depressive symptoms in older Australian men: the Concord Health and Ageing in Men Project

PURPOSE

The objectives of the study were to evaluate the associations between antioxidant intake, dietary patterns and depressive symptoms among older men.

METHOD

794 men participated in a detailed diet history interview at the Concord Health and Ageing in Men Project 3rd wave (considered baseline nutrition) and 781 men participated at the 4th wave (considered 3-year follow-up). Depressive symptoms were measured using the Geriatric Depression Scale (GDS ≥ 5). Dietary adequacy of antioxidant intake was assessed by comparing participants' median intake of vitamin A, E, C and zinc to the Nutrient Reference Values for Australia. Attainment of NRVs of antioxidant was categorised into a dichotomised variable 'poor' (meeting ≤ 2) or 'good' (meeting ≥ 3). Individual antioxidant nutrient was categorised into quartiles. The Australian and Mediterranean diet scores were assessed as predictor variables.

RESULTS

The prevalence of GDS ≥ 5 was 12.8% at baseline nutrition and 13.2% of men developed GDS ≥ 5 at a 3-year follow-up. There was a significant cross-sectional association between poor antioxidant intake and GDS ≥ 5 in adjusted analyses [OR: 1.95 (95% CI 1.03, 3.70)]. Poor antioxidant intake at baseline nutrition remained prospectively associated with incident GDS ≥ 5 [OR: 2.46 (95% CI 1.24, 4.88)] in adjusted analyses. This association was also found for the lowest quartile of zinc [OR 2.72 (95% CI 1.37, 5.42)] and vitamin E intake [OR 2.18 (95% CI 1.05, 4.51)]. None of the other antioxidants and dietary patterns had a significant association with incident depressive symptoms.

CONCLUSION

Inadequacy of antioxidant intake, particularly zinc and vitamin E, is associated with increased risk of clinically significant depressive symptoms in older men.

Serum copper and zinc levels correlate with biochemical metabolite ratios in the prefrontal cortex and lentiform nucleus of patients with major depressive disorder

BACKGROUND

Previous studies have demonstrated that copper and zinc metabolism are associated with the development of major depressive disorder (MDD). Abnormal copper and zinc levels may be related to neurotransmission and biochemical metabolism in the brains of MDD patients, especially in the prefrontal cortex (PFC) and lentiform nucleus (LN). However, the mechanism of how copper and zinc levels contribute to neural metabolism in MDD patients remains to be deciphered. This study aimed to correlate copper and zinc levels with biochemical metabolite ratios in the PFC and LN of MDD patients.

METHOD

Twenty-nine MDD patients and thirty-two healthy control (HC) volunteers were enrolled in this study. Proton magnetic resonance spectroscopy (¹H-MRS) was used to determine the levels of the N-acetylaspartate (NAA), choline (Cho) and creatine (Cr) in the brain, and specifically in the PFC and LN regions. Serum copper and zinc levels were measured using atomic emission spectrometry (AES). Afterwards, copper and zinc levels were correlated with biochemical metabolite ratios in the PFC and LN regions of the brain.

RESULTS

Higher serum copper and lower serum zinc levels with higher copper/zinc ratios were observed in MDD patients. NAA/Cr ratios in the PFC of MDD patients were lower compared to HC volunteers. In MDD patients, serum copper levels were negatively correlated with NAA/Cr ratios in the right PFC and right LN, while copper/zinc ratios were negatively correlated with NAA/Cr ratios in the right LN. No significant differences in serum copper and zinc levels with NAA/Cr ratios in the left PFC and left LN were observed in MDD patients.

CONCLUSION

Our findings suggest that higher serum copper and lower serum zinc levels may contribute to neuronal impairment by affecting neuronal biochemical metabolite ratios in the right PFC and right LN of MDD patients. Abnormal copper and zinc levels may play an important role in the pathophysiology of MDD.

Antidepressant, Anxiolytic and Neuroprotective Activities of Two Zinc Compounds in Diabetic Rats

Behavioral disorders affect most diabetic patients and Zinc (Zn) has been used among adjuvant therapies for involvement in the etiology of depression and anxiety, however, the results are still controversial. The objective of this study was to compare the antidepressant, anxiolytic and neuroprotective activity of the supplementation of two Zn compounds in an animal model of Diabetes Mellitus type 1 (DM1). Thirty-eight (38) adult rats were randomized into four groups: Control (C; n = 8); Diabetic (D; n = 10); Diabetic Zn Sulfate Supplement (DSZ; n = 10) and Diabetic Zn Gluconate Supplement (DGZ; n = 10). The DSZ group received Zn sulfate supplementation and the DGZ group received Zn gluconate supplementation at a dose of 15 mg/kg for 4 weeks. Data (mean ±SEM) were analyzed by the Mann-Whitney test with a significance level of p < 0.05. The results indicate that Zn gluconate supplementation in diabetic animals presented an antidepressant effect demonstrated through the results obtained in the Forced Swim Test, and neuroprotective effect by attenuating alterations in the cerebral cortex; while Zn sulfate supplementation in diabetic animals showed an anxiolytic effect demonstrated by the results obtained in the open field test and the elevated plus maze test. Considering the set of results, supplementation with both zinc compounds showed neurobehavioral benefits in diabetic animals with different effects depending on the type of anion associated with Zn.

Zinc Deficiency During Pregnancy Leads to Altered Microbiome and Elevated Inflammatory Markers in Mice

Zinc is an essential trace metal for bacteria of the intestinal flora. Approximately 20% of dietary zinc – intake is used by intestinal bacteria. The microbiome has recently been described as an important factor for healthy brain function via so-called gut-brain interactions. Similarly, zinc deficiency has been associated with neurological problems such as depression, mental lethargy and cognitive impairments in humans and animal models. However, the underlying pathomechanisms are currently not well understood and a link between zinc deficiency and altered microbiota composition has not been studied. Especially during pregnancy, women may be prone to low zinc status. Thus, here, we investigate whether zinc deficiency alters gut-brain interaction in pregnant mice by triggering changes in the microbiome. To that end, pregnant mice were fed different diets being zinc-adequate, deficient in zinc, or adequate in zinc but high in zinc uptake antagonists for 8 weeks. Our results show that acute zinc-deficient pregnant mice and pregnant mice on a diet high in zinc uptake antagonists have an altered composition of gastro-intestinal (GI) microbiota. These changes were accompanied by alterations in markers for GI permeability. Within the brain, we found signs of neuroinflammation. Interestingly, microbiota composition, gut pathology, and inflammatory cytokine levels were partially rescued upon supplementation of mice with zinc amino-acid conjugates (ZnAA). We conclude that zinc deficiency may contribute to abnormal gut-brain signaling by altering gut physiology, microbiota composition and triggering an increase of inflammatory markers.

Elimination of vesicular zinc alters the behavioural and neuroanatomical effects of social defeat stress in mice

Chronic stress can have deleterious effects on mental health, increasing the risk of developing depression or anxiety. But not all individuals are equally affected by stress; some are susceptible while others are more resilient. Understanding the mechanisms that lead to these differing outcomes has been a focus of considerable research. One unexplored mechanism is vesicular zinc – zinc that is released by neurons as a neuromodulator. We examined how chronic stress, induced by repeated social defeat, affects mice that lack vesicular zinc due to genetic deletion of zinc transporter 3 (ZnT3). These mice, unlike wild type mice, did not become socially avoidant of a novel conspecific, suggesting resilience to stress. However, they showed enhanced sensitivity to the potentiating effect of stress on cued fear memory. Thus, the contribution of vesicular zinc to stress susceptibility is not straightforward. Stress also increased anxiety-like behaviour but produced no deficits in a spatial Y-maze test. We found no evidence that microglial activation or hippocampal neurogenesis accounted for the differences in behavioural outcome. Volumetric analysis revealed that ZnT3 KO mice have larger corpus callosum and parietal cortex volumes, and that corpus callosum volume was decreased by stress in ZnT3 KO, but not wild type, mice.

Zinc as a therapy in a rat model of autism prenatally induced by valproic acid

Autism is characterized by numerous behavioral impairments, such as in communication, socialization and cognition. Recent studies have suggested that valproic acid (VPA), an anti-epileptic drug with teratogenic activity, is related to autism. In rodents, VPA exposure during pregnancy induces autistic-like effects. Exposure to VPA may alter zinc metabolism resulting in a transient deficiency of zinc. Therefore, we selected zinc as a prenatal treatment to prevent VPA-induced impairments in a rat model of autism. Wistar female rats received either saline solution or VPA (400 mg/kg, i.p) on gestational day (GD) 12.5. To test the zinc supplementation effect, after 1 h of treatment with saline or VPA, a dose of zinc (2 mg/kg, s.c.) was injected. The offspring were tested for abnormal communication behaviors with an ultrasound vocalization task on postnatal day (PND) 11, repetitive behaviors and cognitive ability with a T-maze task on PND 29, and social interaction with a play behavior task on PND 30. Tyrosine hydroxylase protein (TH) expression was evaluated in the striatum. Prenatal VPA decreased ultrasonic vocalization, induced repetitive/restricted behaviors and cognitive inflexibility, impaired socialization, and reduced striatal TH levels compared with control group. Zinc treatment reduced VPA-induced autistic-like behaviors. However, we found no evidence of an effect of zinc on the VPA-induced reduction in TH expression. The persistence of low TH expression in the VPA-Zn group suggests that Zn-induced behavioral improvement in autistic rats may not depend on TH activity.

Zinc, Magnesium, Selenium and Depression: A Review of the Evidence, Potential Mechanisms and Implications

Micronutrient deficiency and depression are major global health problems. Here, we first review recent empirical evidence of the association between several micronutrients—zinc, magnesium, selenium—and depression. We then present potential mechanisms of action and discuss the clinical implications for each micronutrient. Collectively, empirical evidence most strongly supports a positive association between zinc deficiency and the risk of depression and an inverse association between zinc supplementation and depressive symptoms. Less evidence is available regarding the relationship between magnesium and selenium deficiency and depression, and studies have been inconclusive. Potential mechanisms of action involve the HPA axis, glutamate homeostasis and inflammatory pathways. Findings support the importance of adequate consumption of micronutrients in the promotion of mental health, and the most common dietary sources for zinc and other micronutrients are provided. Future research is needed to prospectively investigate the association between micronutrient levels and depression as well as the safety and efficacy of micronutrient supplementation as an adjunct treatment for depression.

Association of Serum Trace Elements with Schizophrenia and Effects of Antipsychotic Treatment

Variation of serum trace elements was previously reported in schizophrenia (SZ) patients; however, whether such variation is resulted from the antipsychotic treatment remains obscure. A case control study consist of 165 SZ inpatients and 614 healthy controls measured serum magnesium (Mg), Copper (Cu), calcium (Ca), phosphorus (Phos), iron (Fe), and zinc (Zn) to investigate the relationship of trace elements and SZ. The SZ patients were further followed up (average 3.8 weeks) to evaluate the effects of antipsychotic treatment on the trace element concentrations using repeated measures ANOVA analysis. The results showed that higher concentrations of Mg and Phos and lower concentrations of Ca, Fe, and Zn were significant in SZ patients than that of controls (P < 0.01). The age was positively correlated with Fe and Cu, and negatively correlated with Ca, Phos, and Zn in controls (P < 0.05). Fe in male SZ patients was significantly higher than in female (P < 0.001), as well as in paranoid SZ and acute SZ (P < 0.05). Phos significantly increased after risperidone, clozapine, and aripiprazole treatment (P < 0.05), while Cu was decreased after clozapine and aripiprazole treatment. Zn significantly decreased particularly in mixed type SZ, acute SZ, and schizotypal SZ after antipsychotic treatment. These results suggested that higher concentration of Phos and lower concentration of Fe and Zn have important implications for the risk of SZ and the antipsychotic treatment is likely to result in the decreased Fe and increased Phos in the clinical subtypes of SZ.

Distinctive hippocampal zinc distribution patterns following stress exposure in an animal model of PTSD

Emerging evidence suggests that zinc (Zn) deficiency is associated with depression and anxiety in both human and animal studies. The present study sought to assess whether there is an association between the magnitude of behavioral responses to stress and patterns of Zn distribution. The work has focused on one case study, the association between an animal model of posttraumatic stress disorder (PTSD) and the Zn distribution in the rat hippocampus. Behaviors were assessed with the elevated plus-maze and acoustic startle response tests 7 days later. Preset cut-off criteria classified exposed animals according to their individual behavioral responses. To further characterize the distribution of Zn that occurs in the hippocampus 8 days after the exposure, laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) imaging was used. It has been found that Zn distribution in the dentate gyrus (DG) sub-region in the hippocampus is clearly more widely spread for rats that belong to the extreme behavioral response (EBR) group as compared to the control group. Comparison of the Zn concentration changes in the cornu ammonis 1 (CA1) and the DG sub-regions of the hippocampus shows that the concentration changes are statistically significantly higher in the EBR rats compared to the rats in the control and minimal behavioral response (MBR) groups. In order to understand the mechanism of stress-induced hippocampal Zn dyshomeostasis, relative quantitative analyses of metallothionein (MT), B-cell lymphoma 2 (Bcl-2) and caspase 3 immunoreactivity were performed. Significant differences in the number of caspase-ir and Bcl-2 cells were found in the hippocampal DG sub-region between the EBR group and the control and MBR groups. The results of this study demonstrate a statistically significant association between the degree of behavioral disruption resulting from stress exposure and the patterns of Zn distribution and concentration changes in the various hippocampal regions. Taken together, these findings indicate that Zn distribution patterns play an active role in the neurobiological response to predator scent stress.

Zinc in the Monoaminergic Theory of Depression: Its Relationship to Neural Plasticity

Preclinical and clinical studies have demonstrated that zinc possesses antidepressant properties and that it may augment the therapy with conventional, that is, monoamine-based, antidepressants. In this review we aim to discuss the role of zinc in the pathophysiology and treatment of depression with regard to the monoamine hypothesis of the disease. Particular attention will be paid to the recently described zinc-sensing GPR39 receptor as well as aspects of zinc deficiency. Furthermore, an attempt will be made to give a possible explanation of the mechanisms by which zinc interacts with the monoamine system in the context of depression and neural plasticity.

The level of the zinc homeostasis regulating proteins in the brain of rats subjected to olfactory bulbectomy model of depression

BACKGROUND

Zinc transporters (ZnTs) and metallothioneins (MT) are important in maintaining Zn homeostasis in the brain. The present study was designed to find out whether alterations in ZnTs and MTs are associated with the pathophysiology of depression and the mechanism of antidepressant action.

METHODS

Messenger RNA and proteins of ZnT1, ZnT3, ZnT4, ZnT5, ZnT6 and MT1/2 were measured in the prefrontal cortex (PFC) and hippocampus (Hp) of rats subjected to olfactory bulbectomy (OB) (a model of depression) and chronic amitriptyline (AMI) treatment by Real Time PCR and Western Blot/Immunohistochemistry (IHP).

RESULTS

Results in the OB rats showed: increases in the protein levels of ZnT1 in the PFC and Hp and MT1/2 in the PFC; a decrease in ZnT3 protein level in the PFC; no changes in ZnT4, ZnT5 and ZnT6 in the PFC and Hp. IHP labeling revealed increases in the optical densities of ZnT1-IR in the PFC and Hp and decreases in ZnT3 and ZnT4-IR in the PFC of OB rats. Although OB had no effects on gene expression of ZnTs, mRNAs for MT1/2 were increased. Chronic AMI treatment did not influence protein levels of ZnTs and MT1/2 in Sham and OB rats; however decreased mRNA levels of ZnT4 and ZnT5 in PFC and ZnT1, ZnT3, ZnT4 and ZnT6 in Hp of Sham rats and normalized OB induced increase in MT1/2 gene expression.

CONCLUSIONS

Changes in ZnTs and MT1/2 suggest altered cortical distribution of Zn in the OB model which further supports the hypothesis that Zn dyshomeostasis may be involved in the pathophysiology of depression.

Zinc transporters protein level in postmortem brain of depressed subjects and suicide victims

BACKGROUND

Major depressive disorder (MDD) is a serious psychiatric illness, associated with an increasing rate of suicide. The pathogenesis of depression may be associated with the disruption of zinc (Zn) homeostasis. In the brain, several proteins that regulate Zn homeostasis are present, including Zn transporters (ZnTs) which remove Zn from the cytosol. The present study was designed to investigate whether depression and suicide are associated with alterations in the expression of the ZnTs protein.

METHODS

Protein levels of ZnT1, ZnT3, ZnT4, ZnT5 and ZnT6 were measured in postmortem brain tissue from two different cohorts. Cohort A contained 10 subjects diagnosed with MDD (7 were suicide victims) and 10 psychiatrically-normal control subjects and cohort B contained 11 non-diagnosed suicide victims and 8 sudden-death control subjects. Moreover, in cohort A we measured protein level of NMDA (GluN2A subunit), AMPA (GluA1 subunit) and 5-HT1A receptors and PSD-95. Proteins were measured in the prefrontal cortex (PFC) using Western blotting. In addition, Zn concentration was measured using a voltammetric method.

RESULTS

There was a significant increase in protein levels of ZnT1, ZnT4, ZnT5 in the PFC in MDD, relative to control subjects, while ZnT3 protein level was decreased in MDD. There was no significant difference in the Zn concentration in the PFC between control and MDD subjects. Similarly, in the PFC of suicide victims (non-diagnosed), an increase in protein levels of ZnT1, ZnT4, ZnT5 and ZnT6 was observed. Conversely, protein levels of ZnT3 were decreased in both suicide victims and subjects with MDD, in comparison with control subjects. There was also a significant decrease in the protein level of GluA1, GluN2A, PSD-95 and 5-HT1A in MDD.

CONCLUSIONS

Our studies suggest that alterations in Zn transport proteins are associated with the pathophysiology of MDD and suicide.

The Role of Elements in Anxiety

Elements (bioelements) are necessary factors required for the physiological function of organisms. They are critically involved in fundamental processes of life. Extra- and intracellular message and metabolic pathway factors as well as structural components include one or many elements in their functional structure. Recent years have seen an intensification in terms of knowledge gained about the roles of elements in anxiety disorders. In this chapter we present a review of the most important current data concerning the involvement of zinc, magnesium, copper, lithium, iron, and manganese, and their deficiency, in the pathophysiology and treatment of anxiety.

Potential antidepressant-like properties of the TC G-1008, a GPR39 (zinc receptor) agonist

Some forms of depression appear to be more related to the glutamatergic system. G-coupled protein receptor 39 (GPR39) is the metabotropic zinc receptor, which may be involved in the pathophysiology of depression and in the antidepressant response. Its deficiency abolishes the antidepressant response, which means that GPR39 is required to obtain a therapeutic effect in depression. This raises the possibility that agonists of the zinc receptor may have a role in antidepressant treatment. To explore this possibility we investigated animal behaviour in the forced swim test, the tail suspension test (to assess antidepressant-like properties), the light/dark test and the elevated plus maze test (to assess anxiolytic-like properties), following acute administration of a GPR39 agonist (TC G-1008). We found an antidepressant response (as measured by the forced swim test but not by the tail suspension test) in mice following the GPR39 agonist treatment. Additionally, we observed the opposite results in the light/dark box (decreased overall distance; increased time spent in the lit compartment; decreased time spent in the dark compartment; increased freezing time) and elevated plus maze (no significant changes), which may be a consequence of the sedative effect of TC G-1008. We also found hippocampal GPR39 and brain-derived neurotrophic factor (BDNF) up-regulation following administration of the GPR39 agonist, which may be undiscovered so far as a possible novel agent in the treatment of mood disorders.

Zinc in the Glutamatergic Theory of Depression

Depression is a serious psychiatric illness that affects millions of people worldwide. Weeks of antidepressant therapy are required to relieve depressive symptoms, and new drugs are still being extensively researched. The latest studies have shown that in depression, there is an imbalance between the main excitatory (glutamatergic) and inhibitory (GABAergic) systems. Administration of antagonists of the glutamatergic system, including zinc, has shown an antidepressant effect in preclinical as well as clinical studies. Zinc inhibits the NMDA receptor via its binding site located on one of its subunits. This is thought to be the main mechanism explaining the antidepressant properties of zinc. In the present review, a link between zinc and the glutamatergic system is discussed in the context of depressive disorder.

Influence of Long-Term Zinc Administration on Spatial Learning and Exploratory Activity in Rats

Animal brain contains a significant amount of zinc, which is a cofactor for more than 300 enzymes. Moreover, it provides the basis for functioning of more than 2000 transcription factors, and it is necessary for memory formation and learning processes in the brain. The aim of this study was to investigate the effect of zinc supplementation on behavior in 3-month-old rats. For this purpose, the Morris water maze paradigm, hole-board, and T-maze were used. Wistar rats received a solution of ZnSO4 in drinking water at the doses of 16 mg/kg (Zn16 group) and 32 mg/kg (Zn32 group). In rats pretreated with the lower dose of zinc, the improvement of the mean escape latency was observed in comparison to the control group and Zn32 group. During memory task, both ZnSO4-supplemented groups showed an increase in crossings over the previous platform position. Furthermore, the exploratory activity in Zn16 group was improved in comparison to Zn32 and control group. In the brains of zinc-supplemented rats, we observed the higher content of zinc, both in the hippocampus and the prefrontal cortex. Hippocampal zinc level correlated positively with the mean annulus crossings of the Zn16 group during the probe trial. These findings show that the long-term administration of ZnS04 can improve learning, spatial memory, and exploratory activity in rats. Graphical Abstract Improvement of spatial learning, memory, and exploratory behavior.

Behavioral Abnormality Induced by Enhanced Hypothalamo-Pituitary-Adrenocortical Axis Activity under Dietary Zinc Deficiency and Its Usefulness as a Model

Dietary zinc deficiency increases glucocorticoid secretion from the adrenal cortex via enhanced hypothalamo-pituitary-adrenocortical (HPA) axis activity and induces neuropsychological symptoms, i.e., behavioral abnormality. Behavioral abnormality is due to the increase in glucocorticoid secretion rather than disturbance of brain zinc homeostasis, which occurs after the increase in glucocorticoid secretion. A major target of glucocorticoids is the hippocampus and their actions are often associated with disturbance of glutamatergic neurotransmission, which may be linked to behavioral abnormality, such as depressive symptoms and aggressive behavior under zinc deficiency. Glucocorticoid-mediated disturbance of glutamatergic neurotransmission in the hippocampus is also involved in the pathophysiology of, not only psychiatric disorders, such as depression, but also neurodegenerative disorders, e.g., Alzheimer’s disease. The evidence suggests that zinc-deficient animals are models for behavioral and psychological symptoms of dementia (BPSD), as well as depression. To understand validity to apply zinc-deficient animals as a behavioral abnormality model, this paper deals with the effect of antidepressive drugs and herbal medicines on hippocampal dysfunctions and behavioral abnormality, which are induced by enhanced HPA axis activity under dietary zinc deficiency.

Alterations of Bio-elements, Oxidative, and Inflammatory Status in the Zinc Deficiency Model in Rats

Our previous study showed that dietary zinc restriction induces depression-like behavior with concomitant up-regulation of the N-methyl-D-aspartate receptor (NMDAR). Because metal ions, oxidative stress, and inflammation are involved in depression/NMDAR function, in the present study, bio-elements (zinc, copper, iron, magnesium, and calcium), oxidative (thiobarbituric acid-reactive substances; protein carbonyl content), and inflammatory (IL-1α, IL-1β) factors were measured in serum, hippocampus (Hp), and prefrontal cortex (PFC) of male Sprague-Dawley rats subjected to a zinc-adequate (ZnA) (50 mg Zn/kg) or a zinc-deficient (ZnD) (3 mg Zn/kg) diet for 4 or 6 weeks. Both periods of dietary zinc restriction reduced serum zinc and increased serum iron levels. At 4 weeks, lowered zinc level in the PFC and Hp as well as lowered iron level in the PFC of the ZnD rats was observed. At 6 weeks, however, iron level was increased in the PFC of these rats. Although at 6 weeks zinc level in the PFC did not differ between the ZnA and ZnD rats, extracellular zinc concentration after 100 mM KCl stimulation was reduced in the PFC of the ZnD rats and was accompanied by increased extracellular iron and glutamate levels (as measured by the in vivo microdialysis). The examined oxidative and inflammatory parameters were generally enhanced in the tissue of the ZnD animals. The obtained data suggest dynamic redistribution of bio-elements and enhancement of oxidative/inflammatory parameters after dietary zinc restriction, which may have a link with depression-like behavior/NMDAR function/neurodegeneration.

Immune malfunction in the GPR39 zinc receptor of knockout mice: Its relationship to depressive disorder

Depression is a serious psychiatric disorder affecting not only the monaminergic, glutamatergic, and GABAergic neurosystems, but also the immune system. Patients suffering from depression show disturbance in the immune parameters as well as increased susceptibility to infections. Zinc is well known as an anti-inflammatory agent, and its link with depression has been proved, zinc deficiency causing depression- and anxiety-like behavior with immune malfunction. It has been discovered that trace-element zinc acts as a neurotransmitter in the central nervous system via zinc receptor GPR39. In this study we investigated whether GPR39 knockout would cause depressive-like behavior as measured by the forced swim test, and whether these changes would coexist with immune malfunction. In GPR39 knockout mice versus a wild-type control we found: i) depressive-like behavior; ii) significantly reduced thymus weight; (iii) reduced cell viability of splenocytes; iv) reduced proliferative response of splenocytes; and v) increased IL-6 production of splenocytes after ConA stimulation and decreased IL-1b and IL-6 release after LPS stimulation. The results indicate depressive-like behavior in GPR39 KO animals with an immune response similar to that observed in depressive disorder. Here for the first time we show immunological changes under GPR39-deficient conditions.

The role of glutamatergic, GABA-ergic, and cholinergic receptors in depression and antidepressant-like effect

Depression is one of the most common mental disorders and social issue worldwide. Although there are many antidepressants available, the effectiveness of the therapy is still a serious issue. Moreover, there are many limitations of currently used antidepressants, including slow onset of action, numerous side effects, or the fact that many patients do not respond adequately to the treatment. Therefore, scientists are searching for new compounds with different mechanisms of action. Numerous data indicate the important role of glutamatergic, GABA-ergic, and cholinergic receptors in the pathomechanism of major depressive disorder. This review presents the role of glutamatergic, GABA-ergic, and cholinergic receptors in depression and antidepressant-like effect.

Activation of mTOR dependent signaling pathway is a necessary mechanism of antidepressant-like activity of zinc

The rapid antidepressant response to the N-methyl-D-aspartate (NMDA) receptor antagonists is mediated by activation of the mammalian target of the rapamycin (mTOR) signaling pathway, an increase in the synthesis of synaptic proteins and formation of new synapses in the prefrontal cortex (PFC) of rats. Zinc (Zn), which is a potent NMDA receptor antagonist, exerts antidepressant-like effects in screening tests and models of depression. We focused these studies in investigating whether activation of the mTOR signaling pathway is also a necessary mechanism of the antidepressant-like activity of Zn. We observed that a single injection of Zn (5 mg/kg) induced an increase in the phosphorylation of mTOR and p70S6K 30 min and 3 h after Zn treatment at time points when Zn produced also an antidepressant-like effect in the forced swim test (FST). Furthermore, Zn administered 3 h before the decapitation increased the level of brain derived neurotrophic factor (BDNF), GluA1 and synapsin I. An elevated level of GluA1 and synapsin I was still observed 24 h after the Zn treatment, although Zn did not produce any effects in the FST at that time point. We also observed that pretreatment with rapamycin (mTORC1 inhibitor), LY294002 (PI3K inhibitor), H-89 (PKA inhibitor) and GF109203X (PKC inhibitor) blocked the antidepressant-like effect of Zn in FST in rats and blocks Zn-induced activation of mTOR signaling proteins (analyzed 30 min after Zn administration). These studies indicated that the antidepressant-like activity of Zn depends on the activation of mTOR signaling and other signaling pathways related to neuroplasticity, which can indirectly modulate mTOR function.

Antidepressant-like effect of zinc is dependent on signaling pathways implicated in BDNF modulation

Considering that intracellular signaling pathways that modulate brain BDNF are implicated in antidepressant responses, this study investigated whether signaling pathway inhibitors upstream to BDNF might influence the antidepressant-like effect of zinc, a metal that has been shown to display antidepressant properties. To this end, the influence of i.c.v. administration of H-89 (1μg/site, PKA inhibitor), KN-62 (1μg/site, CAMKII inhibitor), chelerythrine (1μg/site, PKC inhibitor), PD98059 (5μg/site, MEK1/2 inhibitor), U0126 (5μg/site, MEK1/2 inhibitor), LY294002 (10nmol/site, PI3K inhibitor) on the reduction of immobility time in the tail suspension test (TST) elicited by ZnCl2 (10mg/kg, p.o.) was investigated. Moreover, the effect of the combination of sub-effective doses of ZnCl2 (1mg/kg, p.o.) and AR-A014418 (0.001μg/site, GSK-3β inhibitor) was evaluated. The occurrence of changes in CREB phosphorylation and BDNF immunocontent in the hippocampus and prefrontal cortex of mice following ZnCl2 treatment was also investigated. The anti-immobility effect of ZnCl2 in the TST was prevented by treatment with PKA, PKC, CAMKII, MEK1/2 or PI3K inhibitors. Furthermore, ZnCl2 in combination with AR-A014418 caused a synergistic anti-immobility effect in the TST. None of the treatments altered locomotor activity of mice. ZnCl2 treatment caused no alteration in CREB phosphorylation and BDNF immunocontent. The results extend literature data regarding the mechanisms underlying the antidepressant-like action of zinc by indicating that its antidepressant-like effect may be dependent on the activation of PKA, CAMKII, PKC, ERK, and PI3K/GSK-3β pathways. However, zinc is not able to acutely increase BDNF in the hippocampus and prefrontal cortex.

Investigation of the GPR39 zinc receptor following inhibition of monoaminergic neurotransmission and potentialization of glutamatergic neurotransmission

Zinc can regulate neural function in the brain via the GPR39 receptor. In the present study we investigated whether inhibition of serotonin, noradrenaline and dopamine synthesis and potentialization of glutamate, via administration of p-chlorophenylalanine (pCPA), α-methyl-p-tyrosine (αMT) and N-methyl-D-aspartatic acid (NMDA), respectively, would cause changes in GPR39 levels. Western blot analysis showed GPR39 up-regulation following 3-day administration of αMT and NMDA in the frontal cortex, and GPR39 down-regulation following 10-day administration of pCPA, αMT, and NMDA in the hippocampus of CD-1 mice. There were no changes in serum zinc levels. Additionally, we investigated tryptophan, tyrosine and glutamate concentrations in the hippocampus and frontal cortex of GPR39 knockout (GPR39 KO) mice. Liquid chromatography-mass spectrometry (LC-MS) showed a significant decrease in tryptophan and tyrosine, but not in glutamate concentrations in the hippocampus of GPR39 KO mice. There were no changes in the frontal cortex between GPR39 KO and wild type. These results indicate a possible role of the GPR39 receptor in monoaminergic and glutamatergic neurotransmission, which plays an important role in the pathophysiology of depression.

Up-regulation of the GPR39 Zn2+-sensing receptor and CREB/BDNF/TrkB pathway after chronic but not acute antidepressant treatment in the frontal cortex of zinc-deficient mice

BACKGROUND

The GPR39-Zn(2+)-sensing receptor seems to be involved in the pathophysiology of depression. GPR39 knockout animals show depressive- and anxiety-like behavior. Chronic treatment with selective antidepressants (ADs) up-regulates GPR39.

OBJECTIVE AND METHODS

In the present study we investigated whether acute or chronic treatment with imipramine, escitalopram, reboxetine and bupropion would cause changes in CREB, BDNF, TrkB and GPR39-Zn(2+) receptor proteins (measured by Western Blot) in the frontal cortex of mice fed with a low-zinc diet.

RESULTS

The administration of acute antidepressants induced diverse effects in the proteins that were examined (namely, GPR39 down-regulation and a reduction in CREB protein after administration of all ADs; a decrease in BDNF after administration of imipramine and escitalopram; an increase in BDNF after administration of reboxetine; no change in BDNF following administration of bupropion; and a decrease in TrkB following the administration of all ADs except bupropion). On the other hand, chronic treatment (which is required for depression relief) with all antidepressants increased the levels of all these proteins.

CONCLUSIONS

The present study for the first time demonstrates the up-regulation of GPR39 (and CREB, BDNF, and TrkB) protein when induced by chronic treatment with antidepressants (with different pharmacological profiles) in a zinc-deficiency model in mice. These data further indicate that the GPR39 receptor may be an important target in the antidepressant response.

Antidepressant activity of fluoxetine in the zinc deficiency model in rats involves the NMDA receptor complex

The zinc deficiency animal model of depression has been proposed; however, it has not been validated in a detailed manner. We have recently shown that depression-like behavior induced by dietary zinc restriction is associated with up-regulation of hippocampal N-methyl-d-aspartate receptor (NMDAR). Here we examined the effects of chronic administration of a selective serotonin reuptake inhibitor, fluoxetine (FLX), on behavioral and biochemical alterations (within NMDAR signaling pathway) induced by zinc deficiency. Male Sprague Dawley rats were fed a zinc adequate diet (ZnA, 50mg Zn/kg) or a zinc deficient diet (ZnD, 3mg Zn/kg) for 4 weeks. Then, FLX treatment (10mg/kg, i.p.) begun. Following 2 weeks of FLX administration the behavior of the rats was examined in the forced swim test (FST) and the spontaneous locomotor activity test. Twenty four hours later tissue was harvested. The proteins of NMDAR (GluN1, GluN2A and GluN2B) or AMPAR (GluA1) subunits, p-CREB and BDNF in the hippocampus (Western blot) and serum zinc level (TXRF) were examined. Depression-like behavior induced by ZnD in the FST was sensitive to chronic treatment with FLX. ZnD increased levels of GluN1, GluN2A, GluN2B and decreased pS485-GluA1, p-CREB and BDNF proteins. Administration of FLX counteracted the zinc restriction-induced changes in serum zinc level and hippocampal GluN1, GluN2A, GluN2B and p-CREB but not BDNF or pS845-GluA1 protein levels. This finding adds new evidence to the predictive validity of the proposed zinc deficiency model of depression. Antidepressant-like activity of FLX in the zinc deficiency model is associated with NMDAR complex.

GPR39 Zn(2+)-sensing receptor: a new target in antidepressant development?

Zinc is a trace element released from glutamatergic terminals, and modulates the pre- and postsynaptic areas, giving a diverse biological response. Zinc is a natural ligand that inhibits the N-methyl-d-aspartate (NMDA) receptor and regulates the excessive release of glutamate. Moreover, zinc exhibits an antidepressant-like profile, as demonstrated in both preclinical and clinical studies. Recent reports indicate that the GPR39 Zn(2+)-sensing receptor is an important target for zinc "transmission" (its activation modulates/induces diverse biochemical pathways involved in neuroprotection). Preclinical studies provide evidence that zinc deficiency leads to depressive-like behavior related to down-regulation of the GPR39 Zn(2+)-sensing receptor. Zinc binds to the GPR39 and triggers signals, leading to CRE-dependent gene transcription, resulting in increases in proteins such as brain-derived neurotrophic factor (BDNF), that plays a pivotal role in antidepressant action. Chronic administration of many antidepressants induces GPR39 up-regulation, which suggests that the Zn(2+)-sensing receptor may be considered as a new target for drug development in the field of depression.