Search for viral nucleic acid sequences in the post mortem brains of patients with schizophrenia and individuals who have committed suicide

No Increased Detection of Nucleic Acids of CNS-related Viruses in the Brains of Patients with Schizophrenia, Bipolar Disorder, and Autism Spectrum Disorder

BACKGROUND AND HYPOTHESIS

Viral infections are increasingly recognized in the etiology of psychiatric disorders based on epidemiological and serological studies. Few studies have analyzed viruses directly within the brain and no comprehensive investigation of viral infection within diseased brains has been completed. This study aims to determine whether viral infection in brain tissues is a risk factor for 3 major psychiatric disorders, including schizophrenia, bipolar disorder, and autism spectrum disorder.

STUDY DESIGN

This study directly evaluated the presence of viral DNA or RNA in 1569 brains of patients and controls using whole-genome sequencing and RNA sequencing data with 4 independent cohorts. The PathSeq tool was used to identify known human viruses in the genome and transcriptome of patients and controls.

STUDY RESULTS

A variety of DNA and RNA viruses related to the central nervous system were detected in the brains of patients with major psychiatric disorders, including viruses belonging to Herpesviridae, Polyomaviridae, Retroviridae, Flaviviridae, Parvoviridae, and Adenoviridae. However, no consistent significant differences were found between patients and controls in terms of types and amount of virus detected at both DNA and RNA levels.

CONCLUSIONS

The findings of this study do not suggest an association between viral infection in postmortem brains and major psychiatric disorders.

Effect of Cytomegalovirus Infection on the Central Nervous System: Implications for Psychiatric Disorders

Cytomegalovirus (CMV) is a common herpesvirus that establishes lifelong latent infections and interacts extensively with the host immune system, potentially contributing to immune activation and inflammation. Given its proclivity for infecting the brain and its reactivation by inflammatory stimuli, CMV is well known for causing central nervous system complications in the immune-naïve (e.g., in utero) and in the immunocompromised (e.g., in neonates, individuals receiving transplants or cancer chemotherapy, or people living with HIV). However, its potentially pathogenic role in diseases that are characterized by more subtle immune dysregulation and inflammation such as psychiatric disorders is still a matter of debate. In this chapter, we briefly summarize the pathogenic role of CMV in immune-naïve and immunocompromised populations and then review the evidence (i.e., epidemiological studies, serological studies, postmortem studies, and recent neuroimaging studies) for a link between CMV infection and psychiatric disorders with a focus on mood disorders and schizophrenia. Finally, we discuss the potential mechanisms through which CMV may cause CNS dysfunction in the context of mental disorders and conclude with a summary of the current state of play as well as potential future research directions in this area.

Lifetime pathogen burden, inflammatory markers, and depression in community-dwelling older adults

The link between pathogen exposure and mental health has long been hypothesized, but evidence remains limited. We investigated the association of seropositivity to common pathogens and total pathogen burden with depression and mental health and explored the role of mediating inflammatory cytokines. We profiled in 884 participants in the Singapore Longitudinal Ageing Studies, mean (SD) age: 67.9 (8.1) years, their seropositivities for 11 pathogens (CMV, HSV 1, HSV 2, HHV-6, EBV, VZV, RSV, Dengue, Chikungunya, H. Pylori and Plasmodium) and pathogen burden, Geriatric Depression Scale (GDS) score at baseline and 3-4 and 6-8 years follow-up, and baseline Mental Component Score (MCS) of 12-Item Short Form Survey (SF-12). Inflammatory markers included CRP, TNF-α, IL-6, MIP-1α, sgp130, sTNF-RI, sTNF-RII, C3a, and MCP-2. Controlling for age, sex, ethnicity, education, marital status, living alone, and smoking status, high pathogen burden (7 + cumulative infections) compared to low pathogen burden (1-5 cumulative infections) was significantly associated with period prevalence (the highest GDS score from baseline and follow-up measurements) of depressive symptoms (OR = 2.36, 95% CI = 1.05-5.33) and impaired mental health (OR = 2.25, 95% CI = 1.18-4.30). CMV seropositivity and HSV1 seropositivity, which are highly prevalent and most widely studied, were associated with estimated 2-fold increased odds of depression, but only HSV1 seropositivity was significantly associated with depression after adjusting for confounders. Notably, adjusted for confounders, RSV, H. pylori and Plasmodium seropositivity were significantly associated with increased odds, and Dengue seropositivity was associated with unexpectedly deceased odds of depressive symptoms and impaired mental health. The association of pathogen exposure with depression and mental health were at least in parts explained by inflammatory markers. Adding certain inflammatory markers to the models attenuated or weakened the association. Bootstrap method showed that MIP-1α significantly mediated the association between pathogen burden and mental health. In conclusion, lifelong pathogen burden and specific infections are associated with depression and impaired mental health in older adults.

Different presence of Chlamydia pneumoniae, herpes simplex virus type 1, human herpes virus 6, and Toxoplasma gondii in schizophrenia: meta-analysis and analytical study

In the present study we have performed both a meta-analysis and an analytical study exploring the presence of Chlamydia pneumoniae, herpes simplex virus type 1, human herpes virus 6, and Toxoplasma gondii antibodies in a sample of 143 schizophrenic patients and 143 control subjects. The meta-analysis was performed on papers published up to April 2014. The presence of serum immunoglobulin G and immunoglobulin A was performed by enzyme-linked immunosorbent assay test. The detection of microbial DNA in total peripheral blood was performed by nested polymerase chain reaction. The meta-analysis showed that: 1) C. pneumoniae DNA in blood and brain are more common in schizophrenic patients; 2) there is association with parasitism by T. gondii, despite the existence of publication bias; and 3) herpes viruses were not more common in schizophrenic patients. In our sample only anti-Toxoplasma immunoglobulin G was more prevalent and may be a risk factor related to schizophrenia, with potential value for prevention.

Meta-analysis of infectious agents and depression

Depression is a debilitating psychiatric disorder and a growing global public health issue. However, the relationships between microbial infections and depression remains uncertain. A computerized literature search of Medline, ISI Web of Knowledge, PsycINFO, and the Cochrane Library was conducted up to May 2013, and 6362 studies were initially identified for screening. Case-control studies detected biomarker of microorganism were included. Based on inclusion and exclusion criteria, 28 studies were finally included to compare the detection of 16 infectious agents in unipolar depressed patients and healthy controls with a positive incident being defined as a positive biochemical marker of microbial infection. A customized form was used for data extraction. Pooled analysis revealed that the majority of the 16 infectious agents were not significantly associated with depression. However, there were statistically significant associations between depression and infection with Borna disease virus, herpes simplex virus-1, varicella zoster virus, Epstein-Barr virus, and Chlamydophila trachomatis.

Infectious agents associated with schizophrenia: a meta-analysis

Schizophrenia is a highly disabling and limiting disorder for patients and the possibility that infections by some microorganisms may be associated to its development may allow prevention and recovery. In the current study we have done a meta-analysis of studies that have assessed the possible association between detection of different infectious agents and schizophrenia. We report results that support the idea that there is a statistically significant association between schizophrenia and infection by Human Herpesvirus 2 (OR=1.34; CI 95%: 1.09-1.70; p=0.05), Borna Disease Virus (OR=2.03; CI 95%: 1.35-3.06; p<0.01), Human Endogenous Retrovirus W (OR=19.31; CI 95%: 6.74-55.29; p<0.001), Chlamydophila pneumoniae (OR=6.34; CI 95%: 2.83-14.19; p<0.001), Chlamydophila psittaci (OR=29.05; CI 95%: 8.91-94.70; p<0.001) and Toxoplasma gondii (OR=2.70; CI 95%: 1.34-4.42; p=0.005). The implications of these findings are discussed and further research options are also explicated.

Herpesviruses and Toxoplasma gondii in orbital frontal cortex of psychiatric patients

Herpes simplex virus (HSV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), and human herpesvirus-6 (HHV-6) are viruses capable of establishing latency. All of these infect the CNS and have been detected in human postmortem brains. Toxoplasma gondii is a protozoan organism which can reactivate in the brains of previously infected immunocompromised individuals. To screen for the presence of herpesviruses and T. gondii in postmortem orbital frontal brain samples from patients with schizophrenia, affective disorders, and controls, we used nested-polymerase chain reaction (n-PCR)/sequencing. We identified HHV-6B sequences in 2/51 postmortem brain samples but no sequences from other herpesviruses. We did not detect sequences of T. gondii in the postmortem brains. Additional studies including ones directed at the sensitive detection of viral nucleic acids in multiple brain regions should be directed at confirming or excluding a role for viruses and protozoa in the etiology of these disorders.

Prefrontal cortex dysfunction in Borna disease virus (BDV)--infected rats

Viruses have been proposed to play a role in the pathogenesis of schizophrenia; however, the mechanisms by which infection could cause the affective, cognitive, and movement disorders of schizophrenia are not understood. The neurotropic RNA virus, Borna disease (BD) virus, linked to schizophrenia by serologic studies, causes movement and behavior disorders in a wide variety of mammalian and bird hosts. BD rats have hyperactivity and stereotyped behaviors similar to those that follow neurotoxic or electrolytic lesions in frontal cortex or its catecholamine afferents in rats. BD rats have high levels of viral nucleic acid in the prefrontal cortex (PFC), abnormal mesocortical dopamine activity (elevated levels of DOPAC in PFC), yet no alteration in specific binding of D1 or D2 receptor radioligands in PFC. Since frontal lobe dysfunction is frequently reported in schizophrenia, the BD rat model may provide insights into pathogenesis and management of this debilitating psychiatric disease.

Polymerase chain reaction (PCR) search for viral nucleic acid sequences in schizophrenia

BACKGROUND

Previous studies looking for evidence of viral infection in schizophrenics have yielded conflicting results. We searched for viral nucleic acids to test the hypothesis of the viral aetiology of schizophrenia.

METHOD

We used the polymerase chain reaction (PCR) to search for cytomegalovirus (CMV), human immunodeficiency virus (HIV), influenza A, Borna disease virus (BDV), and bovine viral diarrhoea virus (BVDV) in: hippocampus from three schizophrenic and three non-schizophrenic subjects; cerebrospinal fluid (CSF) from 48 schizophrenic patients; CSF and peripheral blood mononuclear cells (PBMC) from nine sets of identical twins discordant for schizophrenia; and SK-N-SHEP cells co-cultured with schizophrenic and non-schizophrenic brain homogenates. All patients met DSM-III-R criteria.

RESULTS

Virus-specific nucleic acids were not found in any of the samples tested.

CONCLUSIONS

The absence of viral nucleic acids in the samples tested suggest that, in these patients, schizophrenia is not associated with a persistent or latent infection due to these viruses.

Viruses, schizophrenia, and bipolar disorder

The hypothesis that viruses or other infectious agents may cause schizophrenia or bipolar disorder dates to the 19th century but has recently been revived. It could explain many clinical, genetic, and epidemiologic aspects of these diseases, including the winter-spring birth seasonality, regional differences, urban birth, household crowding, having an older sibling, and prenatal exposure to influenza as risk factors. It could also explain observed immunological changes such as abnormalities of lymphocytes, proteins, autoantibodies, and cytokines. However, direct studies of viral infections in individuals with these psychiatric diseases have been predominantly negative. Most studies have examined antibodies in blood or cerebrospinal fluid, and relatively few studies have been done on viral antigens, genomes, cytopathic effect on cell culture, and animal transmission experiments. Viral research on schizophrenia and bipolar disorder is thus comparable to viral research on multiple sclerosis and Parkinson's disease: an attractive hypothesis with scattered interesting findings but no clear proof. The application of molecular biological techniques may allow the identification of novel infectious agents and the associations of these novel agents with serious mental diseases.

Viruses and schizophrenia

A viral hypothesis for the pathogenesis of schizophrenia has been under serious consideration for more than 70 years. To date, attempts have failed to identify a specific virus which contributes to the aetiology of the disorder. There has, however, been a recent resurgence of interest in a possible relationship between viral illness and schizophrenia. This renewed attention is the result of epidemiological evidence suggesting an excess of winter births in patients with schizophrenia, indications of foetal insults in persons who develop schizophrenia and an association between foetal exposure to the influenza virus and the subsequent development of schizophrenia. Advances in our understanding of the pathophysiology of viral diseases and the development of sophisticated techniques to study them have resulted in more complex viral hypotheses of schizophrenic aetiology, such as viral disruption of normal neurodevelopment, viral induced autoimmunity and retroviral integration. These hypotheses are now beginning to be tested experimentally.

Dopamine D4 receptors elevated in schizophrenia

Although the biological basis of schizophrenia is not known, possible causes include genetic defects, viruses, amines, brain structure and metabolism, neuroreceptors, and G proteins. The hypothesis of dopamine overactivity in schizophrenia is based on the fact that neuroleptics block dopamine D2 receptors in direct relation to their clinical antipsychotic potencies. Moreover, dopamine D2 or D2-like receptors are elevated in postmortem schizophrenia brain tissue. This elevation, however, is only found in vivo using [11C]methylspiperone but not [11C]raclopride. The dopamine D4 receptor gene has not yet been excluded in schizophrenia because the 21 gene variants of D4 have not yet been tested. Because the link between D1 and D2 receptors is reduced in schizophrenia tissue, we tested whether one component of this link was sensitive to guanine nucleotide. We report here that the binding of [3H]raclopride to D2 receptors in schizophrenia was not sensitive to guanine nucleotide. This finding permitted analysis of data on the binding of [3H]emonapride to the D2, D3 and D4 receptors. We conclude that the combined density of D2 and D3 receptors (labelled by [3H]raclopride) is increased by only 10% in schizophrenia brain, as found by Farde et al., but that it is the density of dopamine D4 receptors which is sixfold elevated in schizophrenia. These findings resolve the apparent discrepancy, mentioned above, wherein the density of [11C]methylspiperone-labelled sites (D2, D3 and D4), but not that of [11C]raclopride-labelled sites (D2 and D3), was found elevated in the schizophrenia striatum.

JC virus DNA is present in many human brain samples from patients without progressive multifocal leukoencephalopathy

Sections of normal and diseased brain and kidney tissues were screened for the presence of JC virus (JCV) DNA by using the polymerase chain reaction. As expected, all samples obtained from patients with progressive multifocal leukoencephalopathy (PML) tested positive when multiple JCV-specific primer and probe combinations were used. Unexpectedly, more than 50% of non-PML-affected brains were also found to harbor low levels of JCV DNA. To confirm that the positive signals seen in the tissue sections were not the result of contamination, amplified DNA was cloned and sequenced and in some cases was shown to represent strains of JCV not identified previously. Two predominant regulatory region configurations of JCV have been detected in the human host: archetype JCV, which is excreted in the urine of normal and immunocompromised individuals, and "PML-type" JCV found in diseased brains. This latter group of variants appears to derive from archetype JCV by the deletion and duplication of sequences within the promoter-enhancer region. In the present study, the archetype strain of JCV was identified only in normal kidney samples; JCV DNA found in non-PML-affected brain specimens and in kidney tissue from patients with PML resembled that of strains isolated from PML-affected brain tissue. Our findings indicate that JCV reaches the brain more frequently than previously thought and may persist at this site without causing demyelinating disease. A subsequent episode of prolonged immunodeficiency or a direct interaction with an immunocompromising agent (e.g., human immunodeficiency virus type 1) might activate the latent JCV infection and lead to the development of PML.