A multi-etiology model of systemic degeneration in schizophrenia

Main interactions of dopamine and risperidone with the dopamine D2 receptor

Psychosis is one of the psychiatric disorders that is controlled by dopaminergic drugs such as antipsychotics that have affinity for the dopamine D2 receptor (DRD2). In this investigation we perform quantum chemical calculations of two molecules [dopamine and risperidone] within a large cavity of DRD2 that represents the binding site of the receptor. Dopamine is an endogenous neurotransmitter and risperidone is a second-generation antipsychotic. Non-covalent interactions of dopamine and risperidone with DRD2 are analyzed using the Quantum Theory of Atoms in Molecules (QTAIM) and the Non-Covalent Interaction index (NCI). The QTAIM results show that these molecules strongly interact with the receptor. There are 22 non-covalent interactions for dopamine and 54 for risperidone. The electron density evaluated at each critical binding point is small in both systems but it is higher for dopamine than for risperidone, indicating that the interactions of DRD2 with the first are stronger than with the second molecule. However, the binding energy is higher for risperidone (-72.6 kcal mol-1) than for dopamine (-22.8 kcal mol-1). Thus, the strength of the binding energy is due to the number of contacts rather than the strength of the interactions themselves. This could be related to the ability of risperidone to block DRD2 and may explain the efficacy of this drug for controlling the symptoms of schizophrenia, but likewise its secondary effects.

New information of dopaminergic agents based on quantum chemistry calculations

Dopamine is an important neurotransmitter that plays a key role in a wide range of both locomotive and cognitive functions in humans. Disturbances on the dopaminergic system cause, among others, psychosis, Parkinson's disease and Huntington's disease. Antipsychotics are drugs that interact primarily with the dopamine receptors and are thus important for the control of psychosis and related disorders. These drugs function as agonists or antagonists and are classified as such in the literature. However, there is still much to learn about the underlying mechanism of action of these drugs. The goal of this investigation is to analyze the intrinsic chemical reactivity, more specifically, the electron donor-acceptor capacity of 217 molecules used as dopaminergic substances, particularly focusing on drugs used to treat psychosis. We analyzed 86 molecules categorized as agonists and 131 molecules classified as antagonists, applying Density Functional Theory calculations. Results show that most of the agonists are electron donors, as is dopamine, whereas most of the antagonists are electron acceptors. Therefore, a new characterization based on the electron transfer capacity is proposed in this study. This new classification can guide the clinical decision-making process based on the physiopathological knowledge of the dopaminergic diseases.

A quantum chemical approach representing a new perspective concerning agonist and antagonist drugs in the context of schizophrenia and Parkinson's disease

Schizophrenia and Parkinson’s disease can be controlled with dopamine antagonists and agonists. In order to improve the understanding of the reaction mechanism of these drugs, in this investigation we present a quantum chemical study of 20 antagonists and 10 agonists. Electron donor acceptor capacity and global hardness are analyzed using Density Functional Theory calculations. Following this theoretical approach, we provide new insights into the intrinsic response of these chemical species. In summary, antagonists generally prove to be better electron acceptors and worse electron donors than dopamine, whereas agonists present an electron donor-acceptor capacity similar to that of dopamine. The chemical hardness is a descriptor that captures the resistance of a chemical compound to change its number of electrons. Within this model, harder molecules are less polarizable and more stable systems. Our results show that the global hardness is similar for dopamine and agonists whilst antagonists present smaller values. Following the Hard and Soft Acid and Bases principle, it is possible to conclude that dopamine and agonists are hard bases while antagonists are soft acids, and this can be related to their activity. From the electronic point of view, we have evolved a new perspective for the classification of agonist and antagonist, which may help to analyze future results of chemical interactions triggered by these drugs.

A mathematical model of reward and executive circuitry in obsessive compulsive disorder

The neuronal circuit that controls obsessive and compulsive behaviors involves a complex network of brain regions (some with known involvement in reward processing). Among these are cortical regions, the striatum and the thalamus (which compose the CSTC pathway), limbic areas such as the amygdala and the hippocampus, as well as dopamine pathways. Abnormal dynamic behavior in this brain network is a hallmark feature of patients with increased anxiety and motor activity, like the ones affected by OCD. There is currently no clear understanding of precisely what mechanisms generate these behaviors. We attempt to investigate a collection of connectivity hypotheses of OCD by means of a computational model of the brain circuitry that governs reward and motion execution. Mathematically, we use methods from ordinary differential equations and continuous time dynamical systems. We use classical analytical methods as well as computational approaches to study phenomena in the phase plane (e.g., behavior of the system's solutions when given certain initial conditions) and in the parameter space (e.g., sensitive dependence of initial conditions). We find that different obsessive-compulsive subtypes may correspond to different abnormalities in the network connectivity profiles. We suggest that it is a combination of parameters (connectivity strengths between regions), rather than the value of any one parameter taken independently, that provide the best basis for predicting behavior, and for understanding the heterogeneity of the illness.

Dopamine Targeting Drugs for the Treatment of Schizophrenia: Past, Present and Future

Schizophrenia is a chronic and debilitating neuropsychiatric disorder affecting approximately 1% of the world's population. This disease is associated with considerable morbidity placing a major financial burden on society. Antipsychotics have been the mainstay of the pharmacological treatment of schizophrenia for decades. The traditional typical and atypical antipsychotics demonstrate clinical efficacy in treating positive symptoms, such as hallucinations and delusions, while are largely ineffective and may worsen negative symptoms, such as blunted affect and social withdrawal, as well as cognitive function. The inability to treat these latter symptoms may contribute to social function impairment associated with schizophrenia. The dysfunction of multiple neurotransmitter systems in schizophrenia suggests that drugs selectively targeting one neurotransmission pathway are unlikely to meet all the therapeutic needs of this heterogeneous disorder. Often, however, the unintentional engagement of multiple pharmacological targets or even the excessive engagement of intended pharmacological targets can lead to undesired consequences and poor tolerability. In this article, we will review marketed typical and atypical antipsychotics and new therapeutic agents targeting dopamine receptors and other neurotransmitters for the treatment of schizophrenia. Representative typical and atypical antipsychotic drugs and new investigational drug candidates will be systematically reviewed and compared by reviewing structure-activity relationships, pharmacokinetic properties, drug metabolism and safety, pharmacological properties, preclinical data in animal models, clinical outcomes and associated side effects.

Role of C-reactive protein in schizophrenia: an overview

Over the years, schizophrenia is speculated to be associated with immune or inflammatory reactions mediated by cytokines. It is proposed that chronic inflammation might damage the micro-vascular system of brain and hamper cerebral blood flow. Scientific evidence suggests that an increase of stress hormone like norepinephrine may activate the inflammatory arm of the immune system and trigger the expression of genes that cause chronic, low-grade inflammation. Thus, studies were conducted to decipher the potentiality of CRP as a marker for inflammation in schizophrenia. This article reviews the findings of CRP in schizophrenia, and the limitations of the previous studies have been discussed. The importance of simultaneous study of CRP modulating cytokines and CRP gene polymorphism in the study of serum or plasma level of CRP has been emphasized.

Network connectivity modulates power spectrum scale invariance

Measures of complexity are sensitive in detecting disease, which has made them attractive candidates for diagnostic biomarkers; one complexity measure that has shown promise in fMRI is power spectrum scale invariance (PSSI). Even if scale-free features of neuroimaging turn out to be diagnostically useful, however, their underlying neurobiological basis is poorly understood. Using modeling and simulations of a schematic prefrontal-limbic meso-circuit, with excitatory and inhibitory networks of nodes, we present here a framework for how network density within a control system can affect the complexity of signal outputs. Our model demonstrates that scale-free behavior, similar to that observed in fMRI PSSI data, can be obtained for sufficiently large networks in a context as simple as a linear stochastic system of differential equations, although the scale-free range improves when introducing more realistic, nonlinear behavior in the system. PSSI values (reflective of complexity) vary as a function of both input type (excitatory, inhibitory) and input density (mean number of long-range connections, or strength), independent of their node-specific geometric distribution. Signals show pink noise (1/f) behavior when excitatory and inhibitory influences are balanced. As excitatory inputs are increased and decreased, signals shift towards white and brown noise, respectively. As inhibitory inputs are increased and decreased, signals shift towards brown and white noise, respectively. The results hold qualitatively at the hemodynamic scale, which we modeled by introducing a neurovascular component. Comparing hemodynamic simulation results to fMRI PSSI results from 96 individuals across a wide spectrum of anxiety-levels, we show how our model can generate concrete and testable hypotheses for understanding how connectivity affects regulation of meso-circuits in the brain.

Schizophrenia and the immune system: pathophysiology, prevention, and treatment

PURPOSE

Published evidence on established and theoretical connections between immune system dysfunction and schizophrenia is reviewed, with a discussion of developments in the search for immunologically-targeted treatments.

SUMMARY

A growing body of evidence indicates that immunologic influences may play an important role in the etiology and course of schizophrenia. A literature search identified more than 100 articles pertaining to suspected immunologic influences on schizophrenia published over the past 15 years. Schizophrenia researchers have explored a wide range of potential immune system-related causal or contributory factors, including neurobiological and neuroanatomical disorders, genetic abnormalities, and environmental influences such as maternal perinatal infection. Efforts to establish an immunologic basis for schizophrenia and identify reliable immune markers continue to be hindered by sampling challenges and methodological problems. In aggregate, the available evidence indicates that at least some cases of schizophrenia have an immunologic component, suggesting that immune-focused prevention strategies (e.g., counseling of pregnant women to avoid immune stressors) and close monitoring of at-risk children are appropriate. While antipsychotics remain the standard treatments for schizophrenia, a variety of drugs with immunologic effects have been investigated as adjunctive therapies, with variable and sometimes conflicting results; these include the cyclooxygenase-2 inhibitor celecoxib, immune-modulating agents (e.g., azathioprine and various anticytokine agents such as atlizumab, anakinra, and tumor necrosis factor-α blockers), and an investigational anti-interferon-γ agent.

CONCLUSION

The published evidence indicates that immune system dysfunction related to genetic, environmental, and neurobiological influences may play a role in the etiology of schizophrenia in a subset of patients.

Integrative etiopathogenetic models of psychotic disorders: methods, evidence and concepts

Integrative models of the etiopathogesnesis of psychotic disorders are needed since a wealth of information from such diverse fields as neurobiology, psychology, and the social sciences is currently changing the concepts of mental disorders. Several approaches to integrate these streams of information into coherent concepts of psychosis are feasible and will need to be assessed in future experimental studies. Common to these concepts are the notion of psychotic disorders as brain disorders and a polythetic approach in that it is increasingly realized that a multitude of interindividually partially different pathogenetic factors interact in individual persons in a complex fashion resulting in the clinical symptoms of psychosis.

Neurodegeneration in schizophrenia

The neurodegenerative aspect of schizophrenia presupposes gene-environmental interactions involving chromosomal abnormalities and obstetric/perinatal complications that culminate in predispositions that impart a particular vulnerability for drastic and unpredictable precipitating factors, such as stress or chemical agents. The notion of a neurodevelopmental progression to the disease state implies that early developmental insults, with neurodegenerative proclivities, evolve into structural brain abnormalities involving specific regional circuits and neurohumoral agents. This neurophysiological orchestration is expressed in the dysfunctionality observed in premorbid signs and symptoms arising in the eventual diagnosis, as well as the neurobehavioral deficits reported from animal models of the disorder. The relative contributions of perinatal insults, neonatal ventral hippocampus lesion, prenatal methylazoxymethanol acetate and early traumatic experience, as well as epigenetic contributions, are discussed from a neurodegenerative view of the essential neuropathology. It is implied that these considerations of factors that exert disruptive influences upon brain development, or normal aging, operationalize the central hub of developmental neuropathology around which the disease process may gain momentum. Nonetheless, the status of neurodegeneration in schizophrenia is somewhat tenuous and it is possible that brain imaging studies on animal models of the disorder, which may describe progressive alterations to cortical, limbic and ventricular structures similar to those of schizophrenic patients, are necessary to resolve the issue.

Neuronal-immune interactions in mediating stress effects in the etiology and course of schizophrenia: role of the amygdala in developmental co-ordination

Stress, in its many forms, is long associated with the etiology and course of schizophrenia. The mechanisms mediating the impacts of stress are not fully elucidated. Here it is proposed that stress induced cortisol alters kynurenic acid (KA) and quinolinic acid (QA) in the cortex and amygdala/striatum, respectively. These effects are significantly modulated by BAG-1 (bcl-2 associated anthanogene) and involve ROS, IL-18, and the induction of IDO (indoleamine 2,3-dioxygenase). The kynurenine pathway (KP) products response to stress seems to mediate both prenatal etiology and symptom course in adulthood. It is suggested that the effects of cortisol and quinolinic acid in the amygdala, coupled to an increase in dopamine efflux, mediate amygdala driven developmental changes in the cortex and VTA/N.Accumbens junction. This change in patterned brain activity co-ordinates alterations in motivated behaviour and thought outputs. Such developmental alterations determine changes in sensory-amygdala interactions, readily allowing developmental links to changes in lateral inhibition and pre-pulse inhibition. Decreases in vitamin D3 and melatonin further potentiate such stress induced changes. The likely involvement of glia in mediating increases in the KP products suggests that adaptation to stress is driven by neuronal activity as a form of glia to glia communication.

Genetic variants of the inflammatory C-reactive protein and schizophrenia in Armenian population: a pilot study

C-reactive protein (CRP) is an inflammation marker implicated in the pathogenesis of schizophrenia. To investigate association of the CRP rs1417938, rs1800947, rs1205 variants with susceptibility to schizophrenia 208 unrelated Armenians (103 patients and 105 healthy controls) were genotyped. In this pilot study, none of studied variants was associated with schizophrenia.