The impact of neuroimmune dysregulation on neuroprotection and neurotoxicity in psychiatric disorders - relation to drug treatment

An inflammatory pathogenesis has been postulated for schizophrenia and major depression (MD). In schizophrenia and depression, opposing patterns oftype-1 vs type-2 immune response seem to be associated with differences in the activation of the enzyme indoleamine 2,3-dioxygenase and in the tryptophan-kynurenine metabolism, resulting in increased production of kynurenic acid in schizophrenia and decreased production of kynurenic acid in depression. These differences are associated with an imbalance in the glutamatergic neurotransmission, which may contribute to an excessive agonist action of N-methyl-D-aspartate (NMDA) in depression and of NMDA antagonism in schizophrenia. Regarding the neuroprotective function of kynurenic acid and the neurotoxic effects of quinolinic acid (QUIN), different patterns of immune activation may also lead to an imbalance between the neuroprotective and the neurotoxic effects of the tryptophanlkynurenine metabolism. The differential activation of microglia cells and astrocytes may be an additional mechanism contributing to this imbalance. The immunological imbalance results in an inflammatory state combined with increased prostaglandin E2 production and increased cyclo-oxygenase-2 (COX-2) expression. The immunological effects of many existing antipsychotics and antidepressants, however, partly correct the immune imbalance and the excess production of the neurotoxic QUIN, COX-2 inhibitors have been tested in animal models of depression and in preliminary clinical trials, pointing to favorable effects in schizophrenia and in MD.     

Depression in late life: psychiatric-medical comorbidity

The links between late-life depression and the medical comorbidities that are often associated with it can be divided into two paths. The path from medical illness to depression reflects general mechanisms related to stress, disability, and loss, as well as more specific physiological mechanisms, including those related to subclinical cerebrovascular disease, adverse drug effects, and endocrine/metabolic effects. Similarly the path from depression to medical illness includes general mechanisms related to self-neglect, decreased adherence to medical treatments, maladaptive health-related behaviors, and, possibly, more specific physiological mechanisms including those related to altered endocrine and autonomic functions, in the clinical context, these two paths can interact to constitute a vicious cycle. With further research, it should be possible to translate current understanding in these areas into advances in both basic knowledge and treatments that could initiate virtuous cycles with beneficial effects for both menial and physical health.     

Research on serotonin and suicidal behavior: neuroendocrine and molecular approaches

We carried out two studies to test the hypothesis that altered central serotonergic function, as assessed by lower prolactin (PRL) response to fenfluramine (D-FEN), is more closely associated with suicidal behavior than a particular psychiatric diagnosis. A D-FEN test was performed in 85 major depressed inpatients, 33 schizophrenic inpatients, and 18 healthy controls. We showed that PRL response to D-FEN is a marker of suicidality, regardless of psychiatric disorder. We then examined the association en the serotonin (5-hydroxytryptamine) receptor 5-HT(2A) gene polymorphism (T102C) and suicide in a sample of Brazilian psychiatric inpatients (95 with schizophrenia, 78 with major depression) and 52 healthy controls. No differences were found in genotypic frequencies across patients and controls. Overall, no differences were found between patients with (n=66) and without (n=107) a history of suicide attempt. We also compared patients with a history of severe suicide attempts (lethality>3; n=32) and patients without such a history (n=107), but they did not exhibit different genotypic frequencies either. These results show thai the 5-HT(2A) gene polymorphism (T102C) may not be involved in the genetic susceptibility to suicidal behavior.     

Partial remission,residual symptoms,and relapse in depression

Partial remission from depression, with residual symptoms, is an important problem in depression. This paper reviews the frequency and features of this outcome, and its association with relapse. Residual symptoms occur in many depressed patients after acute treatment. They span the typical symptoms of depression, except those characteristic of severe disorders. Other persistent abnormalities include social dysfunction, dysfunctional attitudes, hypothalamic-pituitary-adrenal axis overactivity, shortened REM sleep latency, and mood lowering after tryptophan depletion. Associations of some of these with residual symptoms are not clear. There is growing evidence for similar residual symptoms in bipolar disorder, particularly bipolar depression. The most important consequence of residual symptoms is a much-increased risk of relapse, particularly in the first year. Residual symptoms are a strong indication for vigorous and longer than usual continuation of antidepressant treatment, in order to prevent relapse. There is good evidence for the use of cognitive therapy as an adjunct.     

The effectiveness of anticonvulsants in psychiatric disorders

Anticonvulsant drugs are widely used in psychiatric indications. These include mainly alcohol and benzodiazepine withdrawal syndromes, panic and anxiety disorders, dementia, schizophrenia, affective disorders, bipolar affective disorders in particular, and, to some extent, personality disorders. A further area in which neurology and psychiatry overlap is pain conditions, in which some anticonvulsants, and also typical psychiatric medications such as antidepressants, are helpful. From the beginning of their psychiatric use, anticonvulsants have also been used to ameliorate specific symptoms of psychiatric disorders independently of their causality and underlying illness, eg, aggression, and, more recently, cognitive impairment, as seen in affective disorders and schizophrenia. With new anticonvulsants currently under development, it is likely that their use in psychiatry will further increase, and that psychiatrists need to learn about their differential efficacy and safety profiles to the same extent as do neurologists.     

Depression and associated physical diseases and symptoms

Depression can occur in association with virtually all the other psychiatric and physical diagnoses. Physical illness increases the risk of developing severe depressive illness. There are two broadly different mechanisms. The most obvious has a psychological or cognitive mechanism. Thus, the illness may provide the life event or chronic difficulty that triggers a depressive episode in a vulnerable individual. Secondly, more specific associations appear to exist between depression and particular physical disorders. These may turn out to be of particular etiological interest. The best examples are probably stroke and cardiovascular disease. Finally, major depression, but especially minor depression, dysthymia, and depressive symptoms merge with other manifestations of human distress with which patients present to their doctors. Such somatic presentations test the conventional distinction between physical and mental disorder and are a perennial source of controversy.     

Sleep disorders as core symptoms of depression

Links between sleep and depression are strong. About three quarters of depressed patients have insomnia symptoms, and hypersomnia is present in about 40% of young depressed adults and 10% of older patients, with a preponderance in females. The symptoms cause huge distress, have a major impact on quality of life, and are a strong risk factor for suicide. As well as the subjective experience of sleep symptoms, there are well-documented changes in objective sleep architecture in depression. Mechanisms of sleep regulation and how they might be disturbed in depression are discussed. The sleep symptoms are often unresolved by treatment, and confer a greater risk of relapse and recurrence. Epidemiological studies have pointed out that insomnia in nondepressed subjects is a risk factor for later development of depression. There is therefore a need for more successful management of sleep disturbance in depression, in order to improve quality of life in these patients and reduce an important factor in depressive relapse and recurrence.     

New directions for drug discovery in psychiatric disease

Although many new potential drug targets have been discovered subsequent to the cloning of the human genome and the discovery of most of the relevant receptors, the role of these receptors in psychiatric disease is still not clear. We argue that research into the disease process leading to new animal models that can be transposed to man is critical to drug discovery, and present an example of an animal model for schizophrenia using electroencephalography.     

Electroconvulsive therapy and its different indications

In spite of recent developments in the pharmacotherapy of depressive disorders, the delay until clinical improvement can be achieved, and the considerable rate of nonresponse and nonremission, are major problems which remain unresolved. Electroconvulsive therapy (ECT) is a nonpharmacologic biological treatment which has been proven to be a highly effective treatment option, predominantly for depression, but also for schizophrenia and other indications. Though there is a lack of controlled investigations on long-term treatments, ECT can also be used for relapse prevention during maintenance therapies. The safety and tolerability of electroconvulsive treatment have been enhanced by the use of modified stimulation techniques and by progress in modern anesthesia. Thus, today a safe treatment can also be offered to patients with higher somatic risks. ECT still represents an important option, especially in the therapy of treatment-resistant psychiatric disorders after medication treatment failures. Earlier consideration of ECT may reduce the rate of chronic and difficult-to-treat psychiatric disorders.     

Diagnostic classification of psychiatric disorders and familial-genetic research

The validity of diagnostic definitions in psychiatry is directly related to the extent to which their etiology can be specified. However, since detailed knowledge of causal or susceptibility factors is lacking for most psychiatric disorders with a known or suspected familial-genetic origin, the current widely accepted classification systems largely fail to achieve this ideal. To illustrate this problem, this paper looks at the difficulties posed by the criteria for schizophrenia as laid down in the International Classification of Diseases, 10th revision (ICD-10) and the Diagnostic and Statistical Manual of Mental Disorders, Third Edition, Revised (DSM-III-R), and highlights the discrepancies between the majority of diagnostic boundaries and the various phenotype aggregation patterns observed in family studies. Progress in our understanding of psychiatric disorders requires to be firmly based on the findings of epidemiological studies as well as on a clear appreciation of the limitations of classification tools.     

Genetic bases for endophenotypes in psychiatric disorders

This article reviews the concept of an endophenotype, with particular reference to heritability as well as diagnostic specificity. An endophenotype need not be heritable, for example, the possible influence of in utero viral infections for schizophrenia. However, heritability is a useful characteristic for a potential endophenotype, as it can be studied in relation to a plausible candidate gene. It should be noted that the traditional methods of demonstrating heritability, eg, twin studies, can be supplemented with DNA sequence studies, suggesting heritability. Endophenotypes need not be specific to a given nosological class of psychiatric disorders, as these classes do not reflect biological categories. Evidence for two useful schizophrenia endophenotypes, the P50 abnormalities and cognitive deficits, is summarized.     

Various forms of depression

The current subtyping of depression is based on the Diagnostic and Statistical Manual of Mental Disorders, 4th ed, Text Revision (DSM-IV-TR) categorical division of bipolar and depressive disorders. Current evidence, however, supports a dimensional approach to depression, as a continuum/spectrum of overlapping disorders, ranging from bipolar I depression to major depressive disorder. Types of depression which have recently been the focus of most research will be reviewed: bipolar II depression, mixed depression, agitated depression, atypical depression, melancholic depression, recurrent brief depression, minor depressive disorder, seasonal depression, and dysthymic disorder. Most research has focused on bipolar II depression, mixed depression (defined by depression and superimposed manic/hypomanic symptoms), and atypical depression. Mixed depression, by its combination of opposite polarity symptoms, has been found to be common by systematic probing for co-occurring manic/hypomanic symptoms. Mixed depression is a treatment challenge for clinicians, because antidepressants alone (ie, not protected by mood-stabilizing agents) may worsen its manic/hypomanic symptoms, such as irritability and psychomotor agitation, which the Food and Drug Administration (FDA) has listed as possible precursors to suicidality.     

Incomplete remission in depression: role of psychiatric and somatic comorbidity

Depression is one of the most pressing public health issues, because of its high lifetime prevalence and because it is associated with substantial disability. In depressed patients, psychiatric and medical comorbidity is the rule rather than the exception. About 60% to 70% of depressed patients have at least one, while 30% to 40% have two or more, concurrent psychiatric disorders. Among these, anxiety disorders and substance use disorders are the most common axis I comorbidities. Furthermore, two thirds of depressed patients have at least one comorbid medical illness. Among depressed patients, those with a current comorbid psychiatric condition (in particular an anxiety or substance use disorder) or medical illness seem to have an impaired response and remission rate during treatment compared with those patients without comorbidity. However, in depressed patients who all have the same comorbid condition, the relative benefit of an antidepressant compared with placebo appears to be equal to those effects achieved in depressed patients without comorbidity. These findings raise important research and treatment issues regarding the generalizability from randomized controlled trials that tend to exclude patients with comorbidity.     

Subtyping of psychiatric disorders: implications for drug development

Psychiatric diagnosis suffers from being based on phenomenology and not on pathophysiology. Data are presented showing that psychiatric patients reveal consistent quantitative electroencephalographic abnormalities, such that they can be separated from normals and from each other. Clustering these pathophysiological groupings reveals an underlying variability, which permits useful subtyping. Data are presented relating subtyping to pharmacological treatment.     

The intersection of pharmacology,imaging, and genetics in the development of personalized medicine

We currently rely on large randomized trials and meta-analyses to make clinical decisions; this places us at a risk of discarding subgroup or individually specific treatment options owing to their failure to prove efficacious across entire populations. There is a new era emerging in personalized medicine that will focus on individual differences that are not evident phenomenologically. Much research is directed towards identifying genes, endophenotypes, and biomarkers of disease that will facilitate diagnosis and predict treatment outcome. We are at the threshold of being able to predict treatment response, primarily through genetics and neuroimaging. In this review we discuss the most promising markers of treatment response and adverse effects emerging from the areas of pharmacogenetics and neuroimaging in depression and schizophrenia.     

Use of proton magnetic resonance spectroscopy in the treatment of psychiatric disorders: a critical update

Because of the wide availability of hardware as well as of standardized analytic quantification tools, proton magnetic resonance spectroscopy (¹H-MRS) has become widely used to study psychiatric disorders. ¹H-MRS allows measurement of brain concentrations of more traditional singlet neurometabolites like N-acetylaspartate, choline, and creatine. More recently, quantification of the more complex multiplet spectra for glutamate, glutamine, inositol, and γ-aminobutyric acid have also been implemented. Here we review applications of ¹H-MRS in terms of informing treatment options in schizophrenia, bipolar disorder, and major depressive disorders. We first discuss recent meta-analytic studies reporting the most reliable findings. Then we evaluate the more sparse literature focused on 1H-MRS-detected neurometabolic effects of various treatment approaches in psychiatric populations. Finally we speculate on future developments that may result in translation of these tools to improve the treatment of psychiatric disorders.     

Proteomics,metabolomics, and protein interactomics in the characterization of the molecular features of major depressive disorder

Omics technologies emerged as complementary strategies to genomics in the attempt to understand human illnesses. In general, proteomics technologies emerged earlier than those of metabolomics for major depressive disorder (MDD) research, but both are driven by the identification of proteins and/or metabolites that can delineate a comprehensive characterization of MDD''s molecular mechanisms, as well as lead to the identification of biomarker candidates of all types—prognosis, diagnosis, treatment, and patient stratification. Also, one can explore protein and metabolite interactomes in order to pinpoint additional molecules associated with the disease that had not been picked up initially. Here, results and methodological aspects of MDD research using proteomics, metabolomics, and protein interactomics are reviewed, focusing on human samples.