Functional polymorphism of the myeloperoxidase gene (G-463A) in depressive patients

Quetiapine effect on depressive-like behaviors, oxidative balance, and inflammation in serum of rats submitted to chronic stress

Major depressive disorder (MDD) etiology is still not completely understood, and many individuals resist the traditional treatments. Chronic exposure to stressful events can contribute to development and progression and be involved in biological changes underlying MDD. Among the biological mechanisms involved, inflammatory changes and oxidative balance are associated with MDD pathophysiology. Quetiapine, a second-generation antipsychotic, induces a better therapeutic response in individuals refractory to traditional treatments. The main objectives of this research were as follows: to evaluate the effect of chronic mild stress (CMS) on depressive-like behaviors, oxidative stress, and inflammation in adult rats; to evaluate the possible antidepressant, antioxidant, and anti-inflammatory effects of quetiapine. The animals were submitted to CMS protocols. At the end of the CMS, the animals were submitted to a chronic treatment for 14 days with the following drugs: quetiapine (20 mg/kg), imipramine (30 mg/kg), and escitalopram (10 mg/kg). At the end of the treatments, the animals were evaluated in the open field tests, anhedonia (splash test), and forced swimming. The animals were euthanized after the behavioral tests, and serum samples were collected. Myeloperoxidase (MPO) activity and interleukin-6 (IL-6) levels were analyzed. CMS induced an increase in depressive-like behaviors, and quetiapine significantly reduced these behaviors. MPO activity and IL-6 levels increased in the serum of animals submitted to CMS. Quetiapine significantly reduced MPO activity and IL-6 levels. These results corroborate other evidence, indicating that chronic stress is a relevant phenomenon in the etiology of depression and suggesting that quetiapine induces an antidepressant effect because it reduces oxidative and inflammatory mechanisms.

Myeloperoxidase as a Potential Biomarker of Acute-Myocardial-Infarction-Induced Depression and Suppression of the Innate Immune System

While myeloperoxidase (MPO) serves as an indicator of both neutrophil and innate-immune-system function, the potential suppression of the innate immune system in patients with acute myocardial infarction (AMI)-induced depression might be evidenced by a decrease in MPO serum levels. The aim of this prospective study was to (1) determine whether serum concentrations of MPO vary immediately and 6 months after AMI and (2) to investigate whether MPO concentrations at the time of the AMI are significant predictors of AMI-induced depression and the depression-associated suppression of the innate immune system. A total of 109 AMI patients were assessed with the Hamilton Depression Scale (HAMD-17) immediately after admission to the hospital and 6 months later. The MPO status was assessed with serum samples, which were also collected immediately and 6 months after AMI. The depressive patients showed significantly lower MPO blood levels immediately and 6 months after the AMI compared to the patients without depression (ANCOVA: MPO (depression) F = 4.764, df = 1, p = 0.031). The baseline MPO was observed as a significant predictor (p = 0.027) of AMI-induced depression 6 months after AMI. MPO is a potential biomarker for AMI-induced depression, indicating a depression-associated suppression of the innate immune system.

Myeloperoxidase and Neurological Disorder: A Crosstalk

Myeloperoxidase (MPO) is a protein present in azurophilic granules, macrophages, and neutrophils that are released into extracellular fluid (ECF) during inflammation. MPO releases hypochlorous acid (HOCl) and other chlorinated species. It is derived from hydrogen peroxide (H₂O₂) showing response during inflammatory conditions and plays a role in the immune defense against pathogens. MPO may show unwanted effects by indirectly increasing the formation of reactive nitrogen species (RNS), reactive oxygen species (ROS), and tumor necrosis factor alpha (TNF-α) leading to inflammation and oxidative stress. As neuroinflammation is one of the inevitable biological components among most of neurological disorders, MPO and its receptor may be explored as candidates for future clinical interventions. The purpose of this review is to provide an overview of the pathophysiological characteristics of MPO and further explore the possibilities to target it for clinical use. Targeting MPO is promising and may open an avenue to act as a biomarker for diagnosis with defined risk stratification in patients with various neurological disorders.

Acute and chronic treatment with quetiapine induces antidepressant-like behavior and exerts antioxidant effects in the rat brain

Many studies note that changes in oxidative balance are involved in the pathogenesis of major depressive disorder (MDD) and in the success of some antidepressants. Quetiapine exerts a therapeutic response and induces changes in physiological mechanisms that appear to underlie MDD. The objective of this study was to evaluate the antidepressant and antioxidant effects of quetiapine (20 mg /kg) in adult animals. Sixty minutes after an acute treatment or the last administration of chronic treatment (14 days) with quetiapine, animals were subjected to the forced swimming test (FST) to evaluate mobility parameters. Then, the hippocampus, prefrontal cortex (CPF), amygdala and nucleus accumbens (NAc) were removed for the assessment of oxidative stress parameters. Both acute and chronic treatments exerted antidepressant-like effects. Myeloperoxidase (MPO) activity was reduced in the amygdala after acute treatment and in the hippocampus, PFC and amygdala after chronic treatment. In addition, after chronic treatment, the levels of thiobarbituric reactive species (TBARS) were reduced in the amygdala and NAc, and the protein carbonyl content was reduced in the CPF. Superoxide dismutase (SOD) activity increased in the NAc after acute and chronic treatments. Catalase (CAT) activity increased in the PFC after acute treatment and in the NAc after acute and chronic treatments. The concentration of nitrite/nitrate was lower in the CPF after chronic treatment. These results corroborate the antidepressant effect of quetiapine and indicate that quetiapine exhibits an antioxidant profile, a physiological mechanism that appears be involved in the therapeutic function of quetiapine in individuals resistant to classical antidepressant treatments.

Genetic Contributions of Inflammation to Depression

This paper describes the effects of immune genes genetic variants and mRNA expression on depression's risk, severity, and response to antidepressant treatment, through a systematic review on all papers published between 2000 and 2016. Our results, based largely on case-control studies, suggest that common genetic variants and gene-expression pathways are involved in both immune activation and depression. The most replicated and relevant genetic variants include polymorphisms in the genes for interleukin (IL)-1β, IL-6, IL-10, monocyte chemoattractant protein-1, tumor necrosis factor-alpha, C-reactive protein, and phospholipase A2. Moreover, increased blood cytokines mRNA expression (especially of IL-1β) identifies patients that are less likely to respond to conventional antidepressants. However, even for the most replicated findings there are inconsistent results, not only between studies, but also between the immune effects of the genetic variants and the resulting effects on depression. We find evidence that these discrepant findings may be explained, at least in part, by the heterogeneity of the depression immunophenotype, by environmental influences and gene × environment interactions, and by the complex interfacing of genetic variants with gene expression. Indeed, some of the most robust findings have been obtained in patients developing depression in the context of treatment with interferon-alpha, a widely used model to mimic depression in the context of inflammation. Further 'omics' approaches, through GWAS and transcriptomics, will finally shed light on the interaction between immune genes, their expression, and the influence of the environment, in the pathogenesis of depression.

Mechanisms underlying neurocognitive dysfunctions in recurrent major depression

Recent work shows that depression is intimately associated with changes in cognitive functioning, including memory, attention, verbal fluency, and other aspects of higher-order cognitive processing. Changes in cognitive functioning are more likely to occur when depressive episodes are recurrent and to abate to some degree during periods of remission. However, with accumulating frequency and duration of depressive episodes, cognitive deficits can become enduring, being evident even when mood improves. Such changes in cognitive functioning give depression links to mild cognitive impairment and thereby with neurodegenerative conditions, including Alzheimer’s disease, Parkinson’s disease, schizophrenia, and multiple sclerosis. Depression may then be conceptualized on a dimension of depression – mild cognitive impairment – dementia. The biological underpinnings of depression have substantial overlaps with those of neurodegenerative conditions, including reduced neurogenesis, increased apoptosis, reactive oxygen species, tryptophan catabolites, autoimmunity, and immune-inflammatory processes, as well as decreased antioxidant defenses. These evolving changes over the course of depressive episodes drive the association of depression with neurodegenerative conditions. As such, the changes in cognitive functioning in depression have important consequences for the treatment of depression and in reconceptualizing the role of depression in wider neuroprogressive conditions. Here we review the data on changes in cognitive functioning in recurrent major depression and their association with other central conditions.

Oxidant/antioxidant imbalance is an inherent feature of depression

BACKGROUND

50% to 60% of the people who have recovered from the first episode of depression experience a relapse. The immune system of the people suffering from depression is in a permanent state of pathological pro-inflammatory readiness. There are some reports that depressive episodes cause sensitization of immune-inflammatory pathways and that staing of depression (e.g. number of depressive episodes) is correlated with immune-inflammatory markers. The main objective of the study was to delineate whether recurrent major depression (rDD) is characterized by alterations in selected immune-inflammatory biomarkers as compared with first episode of depression (ED-I), i.e. expression of mRNA and enzymatic activity of manganese superoxide dismutase (MnSOD, SOD-2), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS, NOS-2), and cyclooxygenase-2 (COX-2).

METHODS

The study was carried out in a group of 131 patients: ED-I group - 42 patients, rDD group - 89 patients. Depression severity was assessed with the 17-item Hamilton Depression Rating Scale (HDRS). The number of depression episodes and the disease duration periods were recorded in each patient. For the patients, HDRS was administered at admission during the symptomatic phase, which would generally be either before or shortly after modification of the previous antidepressant drug regimen. Reassessment of the mental condition was conducted after 8 weeks of the pharmacological treatment also with the use of the HDRS scale.

RESULTS

No significant statistical differences were found between the analysed groups as regards the intensity of depressive disorders. No differences in the expression of MnSOD, MPO, COX-2 and i-NOS genes on the level of both mRNA and protein were observed between both groups. No significant interrelation was noticed between the number of depression episodes experienced and the expression of selected genes on the mRNA level and protein level.

CONCLUSIONS

There is no significant difference in MnSOD, MPO, COX-2 and i-NOS between patients with recurrent depressive disorders and those in a first episode of depression. These findings suggest that these enzymes are trait markers of depression and are not related to staging of depression.

Myeloperoxidase gene expression and cognitive functions in depression

PURPOSE

Most researchers agree that there are multiple factors influencing the development of recurrent depressive disorder (rDD). Previous studies have found that myeloperoxidase (MPO) may be a key inflammatory enzyme involved in this disorder. The purpose of this study was to determine the mRNA and protein levels of MPO in patients with rDD and to define the relationship between serum MPO levels and cognitive performance.

MATERIAL/METHODS

The study comprised 236 subjects: patients with rDD (n=131) and healthy subjects (n=105, HS). Assessment of cognitive function was based on performance on the Trail Making Test, the Stroop Test, the Verbal Fluency Test (VFT) and the Auditory-Verbal Learning Test (AVLT).

RESULTS

MPO gene expression at mRNA level and at protein level was significantly higher in the rDD group when compared to the HS (p<0.01). There were no significant correlations for each group separately, but in the entire group, statistically significant correlations occurred between both mRNA and protein levels and following test: TMT part A and part B (positive correlations), part RCNb and part NCWd of the Stroop Test (positive correlation), the Verbal Fluency Test (negative correlation) and the AVLT (negative correlation).

CONCLUSIONS

Our study provides evidence that the MPO enzyme coding gene and MPO expression are important for the regulation of cognitive functioning.

Impact of oxidative/nitrosative stress and inflammation on cognitive functions in patients with recurrent depressive disorders

Data show that up to 38.2% of the European population have a mental disorder and that recurrent depressive disorder (rDD) is among the most commonly diagnosed disabling diseases. Over the last few years, neurocognitive impairments in rDD have become a new research front focusing on the role of cognitive decline during the course of rDD and in relation to its clinical presentation and prognosis. Both immune-inflammatory and oxidative and nitrosative stress (O&NS) processes potentially play a role in development of cognitive dysfunction in rDD. New evidence shows that chronic inflammatory and O&NS reactions occur in the brains of patients with neurodegenerative disorders and those with rDD. This narrative review presents the current state of knowledge on the possible impact of selected inflammatory and O&NS enzymes on cognitive functioning in patients with rDD. We focus on manganese superoxide dismutase (MnSOD), inducible nitric oxide synthase (iNOS), and myeloperoxidase (MPO).

Increased autoimmune responses against auto-epitopes modified by oxidative and nitrosative damage in depression: implications for the pathways to chronic depression and neuroprogression

OBJECTIVE

There is evidence that major depression is characterized by oxidative and nitrosative stress (O&NS). The aim of this study is to examine IgM-mediated autoimmune responses against a variety of modified neo-epitopes formed by O&NS damage to self-epitopes in chronic depression.

METHODS

Serum IgM antibodies directed against conjugated oleic and azelaic acid, malondialdehyde (MDA), phosphatidyl inositol (Pi), and conjugated nitric-oxide (NO) adducts, i.e., NO-tryptophan, NO-tyrosine, NO-arginine, and NO-cysteinyl, were determined in 33 healthy controls and 74 depressed patients subdivided into 28 patients with chronic (duration >2 year) and 46 without chronic depression.

RESULTS

Serum IgM levels against all neoepitopes were significantly higher in depressed patients than in healthy controls. Moreover, the IgM levels were significantly higher, except Pi, in chronically depressed patients than in non-chronically depressed patients.

CONCLUSIONS

Depression is characterized by IgM-related autoimmune responses directed against neo-epitopes that are normally hidden from the immune system but that became immunogenic secondary to damage by O&NS. The results show that the generation of neoantigenic determinants that lead to (auto)immune responses is strongly associated with chronic depression.

DISCUSSION

The damage caused by O&NS to auto-epitopes and the consequent formation of O&NS modified neoantigenic determinants may increase the risk to develop depression and in particular chronic depression through transition to autoimmune reactions. This has implications for understanding the immuno-inflammatory and oxidative-autoimmune pathways that lead to chronic depression and neuroprogression in that illness.

The role of immune genes in the association between depression and inflammation: a review of recent clinical studies

The role for dysregulation of the immune system in the pathogenesis of depressive disorder is well established, and emerging research suggests the role of an underlying genetic vulnerability. The purpose of this review is to summarize the existing literature on the genetic variants involved in neurobiological pathways associated with both immune activation and depression. Using PubMed, Scopus, The Cochrane Library, Embase, Ovid of Medline, PsycINFO and ISI web of Knowledge, we selected 52 papers which are relevant for this literature review. Findings across the literature suggest that functional allelic variants of genes for interleukin-1beta (IL)-1β, tumor necrosis factor-alpha (TNF-α) and C-reactive protein (CRP), as well as genetic variations affecting T-cell function, may increase the risk for depression. Moreover, single nucleotide polymorphisms (SNPs) in the IL-1β, IL-6 and IL-11 genes, and in those regulating T-cell function may be associated with reduced responsiveness to antidepressant therapy. There is also some evidence indicative of a role of genetic variants of the enzymes, Cyclo-oxygenase2 (COX-2) and Phospholipase2 (PLA2), in the aetiology of depression. Finally, SNPs in genes related to the serotonin pathway may play a fundamental role in the shared genetic liability to both immune activation and depressive symptoms. Our review confirms that genetic variants influence the biological mechanisms by which the innate immune system contributes to the development of depression. However, future studies are necessary to identify the molecular mechanisms underlying these associations.

Vascular endothelial growth factor receptor 2 gene (KDR) polymorphisms and expression levels in depressive disorder

Recent research findings suggest that vascular endothelial growth factor (VEGF) participates in the development of depressive disorder. VEGF is involved in neurogenesis and neuroprotection processes, mediated by vascular endothelial growth factor receptor 2 (VEGFR2). VEGFR2 also plays a role in angiogenesis, a process related to neurogenesis and other biological processes. We examined VEGFR2 (KDR) gene polymorphism, mRNA expression levels, as well as VEGFR2 protein levels in 268 patients diagnosed with a recurrent depressive disorder (rDD) using the ICD-10 criteria, and in 200 healthy controls. Genotyping and gene expression level analysis was performed using polymerase chain reaction (PCR)-based methods. An Enzyme-Linked Immunosorbent Assay (ELISA) was used for measurement of KDR protein levels. Our study found that distribution of KDR polymorphism +1416T/A differs significantly in patients with rDD when compared to healthy subjects, while A allele and AA genotype are risk factors for rDD. KDR mRNA and protein expression are higher in patients with rDD. We also observed a significant association between the -271A/G variant and gene and protein levels. Our study is the first to demonstrate that the KDR gene may serve as a novel genetic marker that could participate in the etiology of rDD. This new pathway may play a role in the inflammatory pathophysiology of depression.

The expression of genes encoding for COX-2, MPO, iNOS, and sPLA2-IIA in patients with recurrent depressive disorder

BACKGROUND

There is evidence that inflammation, oxidative and nitrosative stress (IO&NS) play a role in the pathophysiology of depression. There are also data indicating altered inflammatory gene expression in depressive disorder and that genetic variants of IO&NS genes are associated with increased risk of the disease in question. The aim of this study was to explore mRNA expression of four IO&NS genes PTGS2, MPO, NOS2A, and PLA2G2A coding respectively: cyclooxygenase-2 (COX-2), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) and secretory phospholipase A2 type IIA (sPLA2-IIA).

METHOD

Expression of the mRNA was determined using quantitative real-time PCR, in peripheral blood cells of patients with recurrent depressive disorder (rDD) and normal controls.

RESULTS

The mRNA expressions of the genes encoding for COX-2, MPO, iNOS and sPLA2-IIA were significantly increased in the peripheral blood cells of depressed patients versus controls.

LIMITATIONS

Patients were treated with antidepressants.

CONCLUSION

Our results indicate and may confirm the role of peripheral IO&NS pathways in the pathophysiology of depression. The results represent a promising way to investigate biological markers of depression.

A review on the oxidative and nitrosative stress (O&NS) pathways in major depression and their possible contribution to the (neuro)degenerative processes in that illness

This paper reviews the body of evidence that major depression is accompanied by a decreased antioxidant status and by induction of oxidative and nitrosative (IO&NS) pathways. Major depression is characterized by significantly lower plasma concentrations of a number of key antioxidants, such as vitamin E, zinc and coenzyme Q10, and a lowered total antioxidant status. Lowered antioxidant enzyme activity, e.g. glutathione peroxidase (GPX), is another hallmark of depression. The abovementioned lowered antioxidant capacity may impair protection against reactive oxygen species (ROS), causing damage to fatty acids, proteins and DNA by oxidative and nitrosative stress (O&NS). Increased ROS in depression is demonstrated by increased levels of plasma peroxides and xanthine oxidase. Damage caused by O&NS is shown by increased levels of malondialdehyde (MDA), a by-product of polyunsaturated fatty acid peroxidation and arachidonic acid; and increased 8-hydroxy-2-deoxyguanosine, indicating oxidative DNA damage. There is also evidence in major depression, that O&NS may have changed inactive autoepitopes to neoantigens, which have acquired immunogenicity and serve as triggers to bypass immunological tolerance, causing (auto)immune responses. Thus, depression is accompanied by increased levels of plasma IgG antibodies against oxidized LDL; and increased IgM-mediated immune responses against membrane fatty acids, like phosphatidyl inositol (Pi); oleic, palmitic, and myristic acid; and NO modified amino-acids, e.g. NO-tyrosine, NO-tryptophan and NO-arginine; and NO-albumin. There is a significant association between depression and polymorphisms in O&NS genes, like manganese superoxide dismutase, catalase, and myeloperoxidase. Animal models of depression very consistently show lowered antioxidant defences and activated O&NS pathways in the peripheral blood and the brain. In animal models of depression, antidepressants consistently increase lowered antioxidant levels and normalize the damage caused by O&NS processes. Antioxidants, such as N-acetyl-cysteine, compounds that mimic GPX activity, and zinc exhibit antidepressive effects. This paper reviews the pathways by which lowered antioxidants and O&NS may contribute to depression, and the (neuro)degenerative processes that accompany that illness. It is concluded that aberrations in O&NS pathways are--together with the inflammatory processes--key components of depression. All in all, the results suggest that depression belongs to the spectrum of (neuro)degenerative disorders.

Recent advances in psychoneuroimmunology: Inflammation in psychiatric disorders

Psychiatric disorders are common and complex and their precise biological underpinnings remain elusive. Multiple epidemiological, molecular, genetic and gene expression studies suggest that immune system dysfunction may contribute to the risk for developing psychiatric disorders including schizophrenia, bipolar disorder, and major depressive disorder. However, the precise mechanisms by which inflammation-related events confer such risk are unclear. In this review, we examine the peripheral and central evidence for inflammation in psychiatric disorders and the potential molecular mechanisms implicated including inhibition of neurogenesis, apoptosis, the HPA-axis, the role of brain-derived neurotrophic factor and the interplay between the glutamatergic, dopaminergic and serotonergic neurotransmitter systems.