The dopaminergic system in peripheral blood lymphocytes: from physiology to pharmacology and potential applications to neuropsychiatric disorders

Changes in gene expression and methylation in the blood of patients with first-episode psychosis

Schizophrenia is a severe mental health disorder with high heritability. The investigation of individuals during their first-episode psychosis (FEP), before the progression of psychotic disorders and especially before treatment with antipsychotic medications, is particularly helpful for understanding this complex disease and for the identification of potential biomarkers. In this study, we compared the expression of genes that are involved in neurotransmission and neurodevelopment of antipsychotic-naive FEP in the peripheral blood of patients (n=51) and healthy controls (n=51). In addition, we investigated the differentially expressed genes with respect to a) DNA methylation, b) the correlation between gene expression and clinical variables (PANSS), and c) gene expression changes after risperidone treatment. Expression levels of 11 genes were quantified with SYBR Green. For methylation analysis, bisulfite sequencing was performed. A significant decrease in GCH1 mRNA levels was observed in FEP patients relative to controls. Also, when we compare the FEP patients after risperidone treatment with controls, this difference remains significant, and no significant differences were observed in GCH1 mRNA levels when comparing patients before and after risperidone treatment. Additionally, although the differences were non-significant after Bonferroni correction, the expression of GCH1 seemed to be correlated with PANSS scores, and the GCH1 promoter region was more methylated in FEP than in controls, thus corroborating the results obtained at the mRNA level. Few studies have been conducted on GCH1, and future studies are needed to clarify its potential role in the progression of schizophrenia.

Evaluation of levodopa and carbidopa antioxidant activity in normal human lymphocytes in vitro: implication for oxidative stress in Parkinson's disease

The main pathochemical hallmark of Parkinson's disease (PD) is the loss of dopamine in the striatum of the brain, and the oral administration of levodopa (L-dopa) is a treatment that partially restores the dopaminergic transmission. In vitro assays have demonstrated both toxic and protective effects of L-dopa on dopaminergic cells, while in vivo studies have not provided any convincing data. The peripheral metabolic pathways significantly decrease the amount of L-dopa reaching the brain; therefore, all of the current commercial formulations require an association with an inhibitor of dopa-decarboxylase, such as carbidopa. However, the dosage and the actual effectiveness of carbidopa have not yet been well defined. PD patients exhibit a reduced efficiency of the endogenous antioxidant system, and peripheral blood lymphocytes (PBLs) represent a dopaminergic system for use as a cellular model to study the pharmacological treatments of neurodegenerative disorders in addition to analysing the systemic oxidative stress. According to our previous studies demonstrating a protective effect of both L-dopa and carbidopa on neuroblastoma cells in vitro, we used the PBLs of healthy donors to evaluate the modulation of DNA damage by different concentrations of L-dopa and carbidopa in the presence of oxidative stress that was exogenously induced by H2O2. We utilised a TAS assay to evaluate the in vitro direct scavenging activity of L-dopa and carbidopa and analysed the expression of genes that were involved in cellular oxidative metabolism. Our data demonstrate the antioxidant capacity of L-dopa and carbidopa and their ability to protect DNA against oxidative-induced damage that derives from different mechanisms of action.

Reduction of rat brain CD8+ T-cells by levodopa/benserazide treatment after experimental stroke

The activation of inflammatory cascades in the ischemic hemisphere impairs mechanisms of tissue reorganization with consequences for recovery of lost neurological function. Recruitment of T-cell populations to the post-ischemic brain occurs and represents a significant part of the inflammatory response. This study was conducted to investigate if treatment with levodopa, potentially acting as an immunomodulator, affects the T-cell accumulation in the post-ischemic brain. Male Sprague-Dawley rats were subjected to transient occlusion of the middle cerebral artery (tMCAO) for 105 min followed by levodopa/benserazide treatment (20 mg/kg/15 mg/kg) for 5 days initiated on day 2 post-stroke. One week after tMCAO, T-cell populations were analysed from brains, and levels of interleukin (IL)-1β, chemokine (C-X-C motif) ligand 1, IL-4, IL-5, interferon gamma and IL-13 were analysed. After levodopa/benserazide treatment, we found a significant reduction of cytotoxic T-cells (CD3+ CD8+ ) in the ischemic hemisphere together with reduced levels of T-cell-associated cytokine IL-5, while other T-cell populations (CD3+, CD3+ CD4+, CD3+ CD4+ CD25+) were unchanged compared with vehicle-treated rats. Moreover, a reduced number of cells was associated with reduced levels of intercellular adhesion molecule 1, expressed in endothelial cells, in the infarct core of levodopa/benserazide-treated animals. Together, we provide the first evidence that dopamine can act as a potential immunomodulator by attenuating inflammation in the post-ischemic brain.

Neuropsychiatric manifestations of latent toxoplasmosis on mothers and their offspring

Toxoplasmosis is one of the most common parasitic diseases worldwide. It is estimated that approximately one-third of the world's population is latently infected. Infection generally occurs via oral the route and maternal transmission. Damage of the central nervous system is one of the most serious consequences of congenital toxoplasmosis. Moreover, recent investigations proposed that acute and sub-acute congenital toxoplasmosis as well as latent toxoplasmosis during pregnancy; play various roles in the etiology of different neuropsychiatric disorders in mothers and their offspring. This paper reviews new findings about the role of latent toxoplasmosis in the etiology of various neuropsychiatric disorders in mothers and their offspring.

Identification of the mRNA expression status of the dopamine D2 receptor and dopamine transporter in peripheral blood lymphocytes of schizophrenia patients

The aim of this study was to detect the mRNA expression levels of the dopamine D2 receptor (DRD2) and dopamine transporter (DAT) in peripheral blood leukocytes (PBLs) of schizophrenia patients and to explore the relationship between the mRNA expression levels and the clinical symptoms of schizophrenia. The research included 25 cases of acute schizophrenia patients, 27 cases of chronic schizophrenia patients, and 30 healthy controls. In every case, we measured the mRNA levels of DRD2 and DAT in PBLs by real-time quantitative reverse transcription-polymerase chain reaction (real-time RT-PCR), and we evaluated the patients' clinical symptoms using the Positive and Negative Syndrome Scale (PANSS). DRD2 mRNA levels in PBLs of acute schizophrenia patients, chronic schizophrenia patients, and healthy controls were 0.32±0.13, 0.37±0.19, and 0.34±0.09, respectively, and the difference was not significant. DAT mRNA levels in PBLs of the abovementioned groups were 0.48±0.24, 0.58±0.21 and 0.39±0.24, respectively (F = 4.330, P = 0.017), and comparisons between every group showed that DAT mRNA levels in PBLs of chronic schizophrenia patients were significantly higher than those in healthy controls (MS interclass = 0.198, p = 0.005). The correlation between DRD2 mRNA levels in PBLs and the positive symptom points of PANSS in acute schizophrenia patients was significant (r = 0.443, p = 0.044). In conclusion, DRD2 mRNA levels in PBLs are correlated with positive symptoms in acute schizophrenia patients, and DAT mRNA levels in PBLs of chronic schizophrenia patients are over-expressed.

Increases in CSF dopamine in HIV patients are due to the dopamine transporter 10/10-repeat allele which is more frequent in HIV-infected individuals

Dysfunction of dopaminergic neurotransmission has been implicated in HIV infection. We showed previously increased dopamine (DA) levels in CSF of therapy-naïve HIV patients and an inverse correlation between CSF DA and CD4 counts in the periphery, suggesting adverse effects of high levels of DA on HIV infection. In the current study including a total of 167 HIV-positive and negative donors from Germany and South Africa (SA), we investigated the mechanistic background for the increase of CSF DA in HIV individuals. Interestingly, we found that the DAT 10/10-repeat allele is present more frequently within HIV individuals than in uninfected subjects. Logistic regression analysis adjusted for gender and ethnicity showed an odds ratio for HIV infection in DAT 10/10 allele carriers of 3.93 (95% CI 1.72-8.96; p = 0.001, Fishers exact test). 42.6% HIV-infected patients harbored the DAT 10/10 allele compared to only 10.5% uninfected DAT 10/10 carriers in SA (odds ratio 6.31), whereas 68.1 versus 40.9%, respectively, in Germany (odds ratio 3.08). Subjects homozygous for the 10-repeat allele had higher amounts of CSF DA and reduced DAT mRNA expression but similar disease severity compared with those carrying other DAT genotypes. These intriguing and novel findings show the mutual interaction between DA and HIV, suggesting caution in the interpretation of CNS DA alterations in HIV infection solely as a secondary phenomenon to the virus and open the door for larger studies investigating consequences of the DAT functional polymorphism on HIV epidemiology and progression of disease.

Elevated dopamine D2 receptor in prefrontal cortex of CUMS rats is associated with downregulated cAMP-independent signaling pathway

Because depression is associated with significant morbidity and functional disability, it is important to reveal the mechanism of action. A variety of studies have suggested the involvement of dopaminergic receptors in the pathophysiological mechanism of non-stress-associated depression-like behavior in rodents. Nevertheless, controversy exists about whether chronic stress acts on dopaminergic receptors in the prefrontal cortex. Thus, we investigated the level of dopamine D2 receptors (DRD2) and the possible mechanisms involved in a chronic unpredictable mild stress (CUMS) rat model of depression. The results showed CUMS-induced, depression-like symptoms in the rat, characterized by reduced sucrose consumption and body mass, and increased duration of immobility in a forced swimming test. Moreover, chronic stress upregulated the expression of DRD2 but downregulated protein kinase A (PKA), transcription factor cAMP response element binding protein (CREB), and phospho-CREB (p-CREB) in the prefrontal cortex, as demonstrated by Western blot. Notably, in the rat model of depression, decreased cyclic adenine monophosphate (cAMP) levels and PKA activity were present at the same time, which is consistent with clinical findings in depressed patients. Our findings suggested that dopaminergic system dysfunction could play a central role in stress-related disorders such as depression.

Deep brain stimulation modulates nonsense-mediated RNA decay in Parkinson's patients leukocytes

BACKGROUND

Nonsense-Mediated decay (NMD) selectively degrades mRNA transcripts that carry premature stop codons. NMD is often triggered by alternative splicing (AS) modifications introducing such codons. NMD plays an important regulatory role in brain neurons, but the in vivo dynamics of AS and NMD changes in neurological diseases and under treatment were scarcely explored.

RESULTS

Here, we report exon arrays analysis of leukocyte mRNA AS events prior to and following Deep Brain Stimulation (DBS) neurosurgery, which efficiently improves the motor symptoms of Parkinson's disease (PD), the leading movement disorder, and is increasingly applied to treat other diseases. We also analyzed publicly available exon array dataset of whole blood cells from mixed early and advanced PD patients. Our in-house exon array dataset of leukocyte transcripts was derived from advanced PD patients' pre- and post-DBS stimulation and matched healthy control volunteers. The mixed cohort exhibited 146 AS changes in 136 transcripts compared to controls, including 9 NMD protein-level assessed events. In comparison, PD patients from our advanced cohort differed from healthy controls by 319 AS events in 280 transcripts, assessed as inducing 27 protein-level NMD events. DBS stimulation induced 254 AS events in 229 genes as compared to the pre-DBS state including 44 NMD inductions. A short, one hour electrical stimulus cessation caused 234 AS changes in 125 genes compared to ON-stimulus state, 22 of these were assessed for NMD. Functional analysis highlighted disease-induced DNA damage and inflammatory control and its reversal under ON and OFF stimulus as well as alternative splicing in all the tested states.

CONCLUSIONS

The study findings indicate a potential role for NMD both in PD and following electrical brain stimulation. Furthermore, our current observations entail future implications for developing therapies for PD, and for interfering with the impaired molecular mechanisms that underlie PD and other neurodegenerative and neurological disorders, as well as DBS-treatable conditions in general.

A dialogue between the immune system and brain, spoken in the language of serotonin

Neuropsychiatric disorders have long been linked to both immune system activation and alterations in serotonin (5-HT) signaling. In the CNS, the contributions of 5-HT modulate a broad range of targets, most notably, hypothalamic, limbic and cortical circuits linked to the control of mood and mood disorders. In the periphery, many are aware of the production and actions of 5-HT in the gut but are unaware that the molecule and its receptors are also present in the immune system where evidence suggests they contribute to the both innate and adaptive responses. In addition, there is clear evidence that the immune system communicates to the brain via both humoral and neuronal mechanisms, and that CNS 5-HT neurons are a direct or indirect target for these actions. Following a brief primer on the immune system, we describe our current understanding of the synthesis, release, and actions of 5-HT in modulating immune function, including the expression of 5-HT biosynthetic enzymes, receptors, and transporters that are typically studied with respect to the roles in the CNS. We then orient our presentation to recent findings that pro-inflammatory cytokines can modulate CNS 5-HT signaling, leading to a conceptualization that among the many roles of 5-HT in the body is an integrated physiological and behavioral response to inflammatory events and pathogens. From this perspective, altered 5-HT/immune conversations are likely to contribute to risk for neurobehavioral disorders historically linked to compromised 5-HT function or ameliorated by 5-HT targeted medications, including depression and anxiety disorders, obsessive-compulsive disorder (OCD), and autism. Our review raises the question as to whether genetic variation impacting 5-HT signaling genes may contribute to maladaptive behavior as much through perturbed immune system modulation as through altered brain mechanisms. Conversely, targeting the immune system for therapeutic development may provide an important opportunity to treat mental illness.