Schizophrenia: Basic and Clinical

The association of SOD and HsCRP with the efficacy of sulforaphane in schizophrenia patients with residual negative symptoms

OBJECTIVES

Emerging evidence indicates a connection between oxidative stress, immune-inflammatory processes, and the negative symptoms of schizophrenia. In addition to possessing potent antioxidant and anti-inflammatory properties, sulforaphane (SFN) has shown promise in enhancing cognitive function among individuals with schizophrenia. This study aims to investigate the efficacy of combined treatment with SFN in patients with schizophrenia who experience negative symptoms and its effect on the levels of superoxide dismutase (SOD) and the inflammatory marker, high-sensitivity C-reactive protein (HsCRP).

DESIGN

Forty-five patients with schizophrenia were recruited, who mainly experienced negative symptoms during a stable period. In addition to the original treatments, the patients received SFN tablets at a daily dose of 90 mg for 24 weeks. At baseline, 12 weeks, and 24 weeks, the participants were interviewed and evaluated. The reduction rate of the Positive and Negative Syndrome Scale (PANSS) was used to assess each participant. The side effects scale of Treatment Emergent Symptom Scale (TESS) was applied to assess the adverse reactions. Additionally, the levels of the SOD, HsCRP, and other indicators were examined.

RESULTS

The study findings revealed a significant decrease in PANSS negative subscale scores (P < 0.001). Furthermore, there was a significant increase in SOD activity and HsCRP levels (P < 0.001 and P < 0.05). Notably, the group of participants who exhibited a reduction in PANSS negative subscale scores demonstrated a significant improvement in HsCRP levels (P < 0.05).

CONCLUSIONS

Our study suggests that SFN may potentially serve as a safe adjunctive intervention to improve the negative symptoms of schizophrenia. The potential mechanism by which SFN improves negative symptoms in schizophrenia patients may involve its anti-inflammatory properties, specifically its ability to reduce HsCRP levels. Trial registration ClinicalTrial.gov (ID: NCT03451734).

Advances in the study of phencyclidine-induced schizophrenia-like animal models and the underlying neural mechanisms

Schizophrenia (SZ) is a chronic, severe mental disorder with heterogeneous clinical manifestations and unknown etiology. Research on SZ has long been limited by the low reliability of and ambiguous pathogenesis in schizophrenia animal models. Phencyclidine (PCP), a noncompetitive N-methyl-D-aspartate receptor (NMDAR) antagonist, rapidly induces both positive and negative symptoms of SZ as well as stable SZ-related cognitive impairment in rodents. However, the neural mechanism underlying PCP-induced SZ-like symptoms is not fully understood. Nondopaminergic pathophysiology, particularly excessive glutamate release induced by NMDAR hypofunction in the prefrontal cortex (PFC), may play a key role in the development of PCP-induced SZ-like symptoms. In this review, we summarize studies on the behavioral and metabolic effects of PCP and the cellular and circuitary targets of PCP in the PFC and hippocampus (HIP). PCP is thought to target the ventral HIP-PFC pathway more strongly than the PFC-VTA pathway and thalamocortical pathway. Systemic PCP administration might preferentially inhibit gamma-aminobutyric acid (GABA) neurons in the vHIP and in turn lead to hippocampal pyramidal cell disinhibition. Excitatory inputs from the HIP may trigger sustained, excessive and pathological PFC pyramidal neuron activation to mediate various SZ-like symptoms. In addition, astrocyte and microglial activation and oxidative stress in the cerebral cortex or hippocampus have been observed in PCP-induced models of SZ. These findings perfect the hypoglutamatergic hypothesis of schizophrenia. However, whether these effects direct the consequences of PCP administration and how about the relationships between these changes induced by PCP remain further elucidation through rigorous, causal and direct experimental evidence.

Detection and analysis of chiral molecules as disease biomarkers

The chirality of small metabolic molecules is important in controlling physiological processes and indicating the health status of humans. Abnormal enantiomeric ratios of chiral molecules in biofluids and tissues occur in many diseases, including cancers and kidney and brain diseases. Thus, chiral small molecules are promising biomarkers for disease diagnosis, prognosis, adverse drug-effect monitoring, pharmacodynamic studies and personalized medicine. However, it remains difficult to achieve cost-effective and reliable analysis of small chiral molecules in clinical procedures, in part owing to their large variety and low concentration. In this Review, we describe current and emerging techniques that detect and quantify small-molecule enantiomers and their biological importance.

A consideration of the increased risk of schizophrenia due to prenatal maternal stress, and the possible role of microglia

Schizophrenia is caused by interaction of a combination of genetic and environmental factors. Of the latter, prenatal exposure to maternal stress is reportedly associated with elevated disease risk. The main orchestrators of inflammatory processes within the brain are microglia, and aberrant microglial activation/function has been proposed to contribute to the aetiology of schizophrenia. Here, we evaluate the epidemiological and preclinical evidence connecting prenatal stress to schizophrenia risk, and consider the possible mediating role of microglia in the prenatal stress-schizophrenia relationship. Epidemiological findings are rather consistent in supporting the association, albeit they are mitigated by effects of sex and gestational timing, while the evidence for microglial activation is more variable. Rodent models of prenatal stress generally report lasting effects on offspring neurobiology. However, many uncertainties remain as to the mechanisms underlying the influence of maternal stress on the developing foetal brain. Future studies should aim to characterise the exact processes mediating this aspect of schizophrenia risk, as well as focussing on how prenatal stress may interact with other risk factors.

Amygdala signal abnormality and cognitive impairment in drug-naïve schizophrenia

BACKGROUND

Recently studies had showed that the amygdala may take part in the cognitive impairment in schizophrenia (SC). However, the mechanism is still unclear, so we explored the relationship between the amygdala resting state magnetic resonance imaging (rsMRI) signal and cognitive function, to provide a reference for the follow-up study.

METHODS

We collected 59 drug-naïve SCs and 46 healthy controls (HCs) from the Third People's Hospital of Foshan. The rsMRI technique and automatic segmentation tool were used to extract the volume and functional indicators of the SC's amygdala. The Positive and Negative Syndrome Scale (PANSS) was used to assess the severity of the disease, and the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) was used to assess cognitive function. Pearson correlation analysis was used to compare the relationship between the structural and functional indicators of the amygdala and PANSS and RBANS.

RESULTS

(1) There was no significant difference between SC and HC in age, gender and years of education. Compared with HC, the PANSS score of SC increased and the RBANS score decreased significantly. Meanwhile, the left amygdala volume decreased (t=-3.675, p < 0.001), and the Fractional amplitude of low-frequency fluctuations (FALFF) values of bilateral amygdala increased (t_L=3.916, p < 0.001; t_R=3.131, p = 0.002). (2) The volumes of the left amygdala were negatively correlated with the PANSS score (r_L=-0.243, p = 0.039). While the FALFF values of the bilateral amygdala were positively correlated with the PANSS score (r_L=0.257, p = 0.026; r_R=0.259, p = 0.026). Bilateral amygdala volumes and FALFF values were positively correlated (r_L=0.445, p < 0.001; r_R=0.326, p = 0.006) and negatively correlated with RBANS score (r_L=-0.284, p = 0.014; r_R=-0.272, p = 0.020), respectively.

CONCLUSION

The abnormal volume and function of the amygdala play important roles in the disease process of SC, and are closely related to cognitive impairment.

The interplay of dopamine metabolism abnormalities and mitochondrial defects in the pathogenesis of schizophrenia

Dopamine (DA) is a major monoamine neurotransmitter in the brain and has essential roles in higher functions of the brain. Malfunctions of dopaminergic signaling have been implicated in various mental disorders such as addiction, attention deficit/hyperactivity disorder, Huntington's disease, Parkinson's disease (PD), and schizophrenia. The pathogenesis of PD and schizophrenia involves the interplay of mitochondrial defect and DA metabolism abnormalities. This article focuses on this issue in schizophrenia. It started with the introduction of metabolism, behavioral action, and physiology of DA, followed by reviewing evidence for malfunctions of dopaminergic signaling in patients with schizophrenia. Then it provided an overview of multiple facets of mitochondrial physiology before summarizing mitochondrial defects reported in clinical studies with schizophrenia patients. Finally, it discussed the interplay between DA metabolism abnormalities and mitochondrial defects and outlined some clinical studies showing effects of combination therapy of antipsychotics and antioxidants in treating patients with schizophrenia. The update and integration of these lines of information may advance our understanding of the etiology, pathogenesis, phenomenology, and treatment of schizophrenia.

Polymorphism of rs12294045 in EAAT2 gene is potentially associated with schizophrenia in Chinese Han population

BACKGROUND

Recent studies have shown that the excitatory amino acid transporters (EAATs) are associated with schizophrenia. The aim of this study was to investigate the relationship between the polymorphism of EAAT1 and EAAT2 genes and schizophrenia in Chinese Han population.

METHODS

A total of 233 patients with schizophrenia and 342 healthy controls were enrolled. Two SNPs in EAAT1 gene (rs2269272, rs2731880) and four SNPs in EAAT2 gene (rs12360706, rs3088168, rs12294045, rs10836387) were genotyped by SNaPshot. Clinical features were collected using a self-made questionnaire. Psychotic symptoms of patients were measured by the Positive and Negative Syndrome Scale (PANSS), and patients' cognitive function was assessed by Matrics Consensus Cognitive Battery (MCCB).

RESULTS

Significant difference in allelic distributions between cases and controls was confirmed at locus rs12294045 (Ρ = 0.004) of EAAT2 gene. Different genotypes of rs12294045 were associated with family history (P = 0.046), in which patients with CT genotype had higher proportion of family history of psychosis. The polymorphism of rs12294045 was related to working operational memory (LNS: P = 0.016) and verbal learning function (HVLT-R: P = 0.042) in patients in which CT genotype had lower scores. However, these differences were no longer significant after Bonferroni correction.

CONCLUSIONS

Our study showed that the polymorphism of rs12294045 in EAAT2 gene may be associated with schizophrenia in Chinese Han population. CT genotype may be one of the risk factors for family history and cognitive deficits of patients.

Drug Design Targeting the Muscarinic Receptors and the Implications in Central Nervous System Disorders

There is substantial evidence that cholinergic system function impairment plays a significant role in many central nervous system (CNS) disorders. During the past three decades, muscarinic receptors (mAChRs) have been implicated in various pathologies and have been prominent targets of drug-design efforts. However, due to the high sequence homology of the orthosteric binding site, many drug candidates resulted in limited clinical success. Although several advances in treating peripheral pathologies have been achieved, targeting CNS pathologies remains challenging for researchers. Nevertheless, significant progress has been made in recent years to develop functionally selective orthosteric and allosteric ligands targeting the mAChRs with limited side effect profiles. This review highlights past efforts and focuses on recent advances in drug design targeting these receptors for Alzheimer’s disease (AD), schizophrenia (SZ), and depression.

The diverse and complex modes of action of anti-NMDA receptor autoantibodies

NMDA receptors are ligand-gated ion channels that are found throughout the brain and are required for both brain development and many higher order functions. A variety of human patients with diverse clinical phenotypes have been identified that carry autoantibodies directed against NMDA receptor subunits. Here we focus on two general classes of autoantibodies, anti-GluN1 antibodies associated with anti-NMDA receptor encephalitis and anti-GluN2 antibodies associated with systemic lupus erythematosus (SLE). These two general classes of anti-NMDA receptor autoantibodies display a wide range of pathophysiological mechanisms from altering synaptic composition to gating of NMDARs. While we have made progress in understanding how these autoantibodies work at the molecular and cellular level, many unanswered questions remain including their long-term actions on brain function, the significance of clonal variations, and their effects on different NMDA receptor-expressing cell types in local circuits. This information will be needed to define fully the transition from anti-NMDA receptor autoantibodies to a clinical phenotype.

Behavioral Deficits in Mice with Postnatal Disruption of Ndel1 in Forebrain Excitatory Neurons: Implications for Epilepsy and Neuropsychiatric Disorders

Dysfunction of nuclear distribution element-like 1 (Ndel1) is associated with schizophrenia, a neuropsychiatric disorder characterized by cognitive impairment and with seizures as comorbidity. The levels of Ndel1 are also altered in human and models with epilepsy, a chronic condition whose hallmark feature is the occurrence of spontaneous recurrent seizures and is typically associated with comorbid conditions including learning and memory deficits, anxiety, and depression. In this study, we analyzed the behaviors of mice postnatally deficient for Ndel1 in forebrain excitatory neurons (Ndel1 CKO) that exhibit spatial learning and memory deficits, seizures, and shortened lifespan. Ndel1 CKO mice underperformed in species-specific tasks, that is, the nest building, open field, Y maze, forced swim, and dry cylinder tasks. We surveyed the expression and/or activity of a dozen molecules related to Ndel1 functions and found changes that may contribute to the abnormal behaviors. Finally, we tested the impact of Reelin glycoprotein that shows protective effects in the hippocampus of Ndel1 CKO, on the performance of the mutant animals in the nest building task. Our study highlights the importance of Ndel1 in the manifestation of species-specific animal behaviors that may be relevant to our understanding of the clinical conditions shared between neuropsychiatric disorders and epilepsy.

Beyond the looking glass: recent advances in understanding the impact of environmental exposures on neuropsychiatric disease

The etiologic pathways leading to neuropsychiatric diseases remain poorly defined. As genomic technologies have advanced over the past several decades, considerable progress has been made linking neuropsychiatric disorders to genetic underpinnings. Interest and consideration of nongenetic risk factors (e.g., lead exposure and schizophrenia) have, in contrast, lagged behind heritable frameworks of explanation. Thus, the association of neuropsychiatric illness to environmental chemical exposure, and their potential interactions with genetic susceptibility, are largely unexplored. In this review, we describe emerging approaches for considering the impact of chemical risk factors acting alone and in concert with genetic risk, and point to the potential role of epigenetics in mediating exposure effects on transcription of genes implicated in mental disorders. We highlight recent examples of research in nongenetic risk factors in psychiatric disorders that point to potential shared biological mechanisms-synaptic dysfunction, immune alterations, and gut-brain interactions. We outline new tools and resources that can be harnessed for the study of environmental factors in psychiatric disorders. These tools, combined with emerging experimental evidence, suggest that there is a need to broadly incorporate environmental exposures in psychiatric research, with the ultimate goal of identifying modifiable risk factors and informing new treatment strategies for neuropsychiatric disease.

Cognition and Reward Circuits in Schizophrenia: Synergistic, Not Separate

Schizophrenia has been studied from the perspective of cognitive or reward-related impairments, yet it cannot be wholly related to one or the other process and their corresponding neural circuits. We posit a comprehensive circuit-based model proposing that dysfunctional interactions between the brain's cognitive and reward circuits underlie schizophrenia. The model is underpinned by how the relationship between glutamatergic and dopaminergic dysfunction in schizophrenia drives interactions between cognition and reward circuits. We argue that this interaction is synergistic: that is, deficits of cognition and reward processing interact, and this interaction is a core feature of schizophrenia. In adopting this position, we undertake a focused review of animal physiology and human clinical data, and in proposing this synergistic model, we highlight dopaminergic afferents from the ventral tegmental area to nucleus accumbens (mesolimbic circuit) and frontal cortex (mesocortical circuit). We then expand on the role of glutamatergic inputs to these dopamine circuits and dopaminergic modulation of critical excitatory pathways with attention given to the role of glutamatergic hippocampal outputs onto nucleus accumbens. Finally, we present evidence for how in schizophrenia, dysfunction in the mesolimbic and mesocortical circuits and their corresponding glutamatergic inputs gives rise to clinical and cognitive phenotypes and is associated with positive and negative symptom dimensions. The synthesis attempted here provides an impetus for a conceptual shift that links cognitive and motivational aspects of schizophrenia and that can lead to treatment approaches that seek to harmonize network interactions between the brain's cognition and reward circuits with ameliorative effects in each behavioral domain.

Phencyclidine-induced cognitive deficits in mice are ameliorated by subsequent repeated intermittent administration of (R)-ketamine, but not (S)-ketamine: Role of BDNF-TrkB signaling

The N-methyl-d-aspartate receptor (NMDAR) antagonists including phencyclidine (PCP) and ketamine produce cognitive deficits in rodents and humans. We previously reported that (R)-ketamine produced the beneficial effects compared to (S)-ketamine in several animal models including depression. Here we compared the effects of two enantiomers of ketamine on cognitive deficits in mice after repeated administration of PCP. PCP (10 mg/kg/day for 10 days)-induced cognitive deficits were ameliorated by subsequent repeated intermittent administration of (R)-ketamine (10 mg/kg/day, twice weekly for 2-weeks), but not (S)-ketamine. Western blot analysis showed decreased levels of brain-derived neurotrophic factor (BDNF) and decreased ratio of phosphorylated-TrkB (p-TrkB) to TrkB in the prefrontal cortex (PFC) and hippocampus of PCP-treated mice. Furthermore, PCP-induced reduction of BDNF and p-TrkB/TrkB ratio in the PFC and hippocampus of PCP-treated mice was ameliorated by subsequent intermittent administration of (R)-ketamine. Interestingly, the beneficial effects of (R)-ketamine were blocked by pretreatment with TrkB inhibitor ANA-12. These findings suggest that (R)-ketamine could ameliorate PCP-induced cognitive deficits via activation of BDNF-TrkB signaling in the brain. Therefore, (R)-ketamine could be a potential therapeutic drug for cognitive impairment in patients with schizophrenia.

Association between polymorphism of the NEDD4 gene and cognitive dysfunction of schizophrenia patients in Chinese Han population

BACKGROUND

Schizophrenia is a complex psychiatric disorder with unknown etiology. A number of recent studies have shown that the polymorphism of the neural precursor cell expressed developmentally down-regulated 4 (NEDD4) gene is associated with a variety of neuropsychiatric disorders, such as schizophrenia, and may also be associated with cognitive dysfunction in these diseases.

METHODS

A case-control study was carried out, the alleles and genotypes distributions of five loci (rs3088077, rs2303579, rs7162435, rs11550869, rs62043855) of the NEDD4 gene from 296 schizophrenia patients and 320 healthy controls were detected by using Taqman single-nucleotide polymorphism (SNP) genotyping technology. The clinical data of case and control group members were collected by self-made questionnaire and the psychotic symptoms of case group members were assessed by the Positive and Negative Syndrome Scale (PANSS). The Matrics Consensus Cognitive Battery (MCCB) was used to test the cognitive function of case group members.

RESULTS

The alleles and genotypes frequency of two loci (rs3088077, rs2303579) between case and control group showed significant differences (P <  0.05). There was no significant difference in MCCB scores of patients with different genotypes at rs3088077, rs11550869 and rs7162435 loci in case group. The study of rs2303579 locus showed that, patients' scores with CT genotype were significantly lower than those with CC and TT genotypes (P <  0.05) in the test of Wechsler Memory Scale-Third Edition (WMS-III): Spatial Span, the scores of patients with TT genotype were significantly higher than those with CT genotype (P < 0.05) in the test of Hopkins Verbal Learning Test-Revised (HVLT-R). The study of rs62043855 locus showed that patients with TG genotype had significantly lower scores than those with GG genotype (P < 0.05) in the test of Neuropsychological Assessment Battery (NAB): Mazes.

CONCLUSIONS

Our study showed that in schizophrenia patients of Chinese Han population, the polymorphisms of rs3088077 and rs2303579 loci were related to the pathogenesis of schizophrenia, while the polymorphisms of rs2303579 and rs62043855 loci were associated with cognitive dysfunction.

Loss of dysbindin-1 affects GABAergic transmission in the PFC

It has been shown that dystrobrevin-binding protein 1 gene that encodes the protein dysbindin-1 is associated with risk for cognitive deficits, and studies have shown decreases in glutamate and correlated decreases in dysbindin-1 protein in the prefrontal cortex (PFC) and hippocampus of post-mortem tissue from schizophrenia patients. The PFC and the hippocampus have been shown to play a fundamental role in cognition, and studies in dysbindin-1 null mice have shown alterations in NMDAR located in pyramidal neurons as well as perturbation in LTP and cognitive deficits. The balance between excitatory and inhibitory transmission is crucial for normal cognitive functions; however, there is a dearth of information regarding the effects of loss of dysbindin-1 in GABAergic transmission. Using in vitro whole-cell clamp recordings, Western blots, and immunohistochemistry, we report here that dysbindin-1-deficient mice exhibit a significant decrease in the frequency of sIPSCs and in the amplitude of mIPSCs and significant decreases in PV staining and protein level. These results suggest that loss of dysbindin-1 affects GABAergic transmission at pre- and postsynaptic level and decreases parvalbumin markers.

Comparative psychopharmacology of autism and psychotic-affective disorders suggests new targets for treatment

The first treatments showing effectiveness for some psychiatric disorders, such as lithium for bipolar disorder and chlorpromazine for schizophrenia, were discovered by accident. Currently, psychiatric drug design is seen as a scientific enterprise, limited though it remains by the complexity of brain development and function. Relatively few novel and effective drugs have, however, been developed for many years. The purpose of this article is to demonstrate how evolutionary biology can provide a useful framework for psychiatric drug development. The framework is based on a diametrical nature of autism, compared with psychotic-affective disorders (mainly schizophrenia, bipolar disorder and depression). This paradigm follows from two inferences: (i) risks and phenotypes of human psychiatric disorders derive from phenotypes that have evolved along the human lineage and (ii) biological variation is bidirectional (e.g. higher vs lower, faster vs slower, etc.), such that dysregulation of psychological traits varies in two opposite ways. In this context, the author review the evidence salient to the hypothesis that autism and psychotic-affective disorders represent diametrical disorders in terms of current, proposed and potential psychopharmacological treatments. Studies of brain-derived neurotrophic factor, the PI3K pathway, the NMDA receptor, kynurenic acid metabolism, agmatine metabolism, levels of the endocannabinoid anandamide, antidepressants, anticonvulsants, antipsychotics, and other treatments, demonstrate evidence of diametric effects in autism spectrum disorders and phenotypes compared with psychotic-affective disorders and phenotypes. These findings yield insights into treatment mechanisms and the development of new pharmacological therapies, as well as providing an explanation for the longstanding puzzle of antagonism between epilepsy and psychosis. Lay Summary: Consideration of autism and schizophrenia as caused by opposite alterations to brain development and function leads to novel suggestions for pharmacological treatments.

Recent Advances in the Early Intervention in Schizophrenia: Future Direction from Preclinical Findings

PURPOSE OF REVIEW

In the past decade, there has been increasing interest in the potential benefit of early intervention in schizophrenia. Patients with schizophrenia show cognitive impairment for several years preceding the onset of psychosis. The author discusses the recent topics on prevention of schizophrenia.

RECENT FINDINGS

Preclinical findings suggest that maternal immune activation (MIA) produces cognitive deficits as a prodromal symptom in juvenile offspring in rodents. Treatment with anti-inflammatory compounds, such as D-serine, 7,8-dihydroxyflavone (a TrkB agonist), sulforaphane (or its precursor glucoraphanin), and TPPU (1-trifluoromethoxyphenyl-3-(1-propionylpiperidin-4-yl) urea: a soluble epoxide hydrolase inhibitor), during adolescence might prevent the onset of behavioral abnormalities and parvalbumin immunoreactivity in the medial prefrontal cortex of adult offspring after MIA. Based on the role of inflammation and cognitive impairment in the prodromal state, early intervention using anti-inflammatory compounds (i.e., D-serine, sodium benzoate, TrkB agonist, Nrf2 agonist, soluble epoxide hydrolase inhibitor) may reduce the risk of subsequent transition to schizophrenia.

Holistic Management of Schizophrenia Symptoms Using Pharmacological and Non-pharmacological Treatment

Individuals with schizophrenia lead a poor quality of life, due to poor medical attention, homelessness, unemployment, financial constraints, lack of education, and poor social skills. Thus, a review of factors associated with the holistic management of schizophrenia is of paramount importance. The objective of this review is to improve the quality of life of individuals with schizophrenia, by addressing the factors related to the needs of the patients and present them in a unified manner. Although medications play a role, other factors that lead to a successful holistic management of schizophrenia include addressing the following: financial management, independent community living, independent living skill, relationship, friendship, entertainment, regular exercise for weight gained due to medication administration, co-morbid health issues, and day-care programmes for independent living. This review discusses the relationship between different symptoms and problems individuals with schizophrenia face (e.g., homelessness and unemployment), and how these can be managed using pharmacological and non-pharmacological methods. Thus, the target of this review is the carers of individuals with schizophrenia, public health managers, counselors, case workers, psychiatrists, and clinical psychologists aiming to enhance the quality of life of individuals with schizophrenia.

Distinctive Roles of D-Amino Acids in the Homochiral World: Chirality of Amino Acids Modulates Mammalian Physiology and Pathology

Living organisms enantioselectively employ L-amino acids as the molecular architecture of protein synthesized in the ribosome. Although L-amino acids are dominantly utilized in most biological processes, accumulating evidence points to the distinctive roles of D-amino acids in non-ribosomal physiology. Among the three domains of life, bacteria have the greatest capacity to produce a wide variety of D-amino acids. In contrast, archaea and eukaryotes are thought generally to synthesize only two kinds of D-amino acids: D-serine and D-aspartate. In mammals, D-serine is critical for neurotransmission as an endogenous coagonist of N-methyl D-aspartate receptors. Additionally, D-aspartate is associated with neurogenesis and endocrine systems. Furthermore, recognition of D-amino acids originating in bacteria is linked to systemic and mucosal innate immunity. Among the roles played by D-amino acids in human pathology, the dysfunction of neurotransmission mediated by D-serine is implicated in psychiatric and neurological disorders. Non-enzymatic conversion of L-aspartate or L-serine residues to their D-configurations is involved in age-associated protein degeneration. Moreover, the measurement of plasma or urinary D-/L-serine or D-/L-aspartate levels may have diagnostic or prognostic value in the treatment of kidney diseases. This review aims to summarize current understanding of D-amino-acid-associated biology with a major focus on mammalian physiology and pathology.

Translational Significance of Selective Estrogen Receptor Modulators in Psychiatric Disorders

Accumulating data from various clinical trial studies suggests that adjuvant therapy with ovarian hormones (estrogens) could be effective in reducing cognitive deficit and psychopathological symptoms in women with psychiatric disorders. However, estrogen therapy poses serious limitations and health issues including feminization in men and increased risks of thromboembolism, hot flashes, breast hyperplasia, and endometrium hyperplasia when used for longer duration in older women (aged ≥ 60 years) or in women who have genetic predispositions. On the other hand, selective estrogen receptor modulators (SERMs), which may (or may not) carry some risks of hot flashes, thromboembolism, breast hyperplasia, and endometrial hyperplasia, are generally devoid of feminization effect. In clinical trial studies, adjuvant therapy with tamoxifen, a triphenylethylene class of SERM, has been found to reduce the frequency of manic episodes in patients with bipolar disorder, whereas addition of raloxifene, a benzothiophene class of SERM, to regular doses of antipsychotic drugs has been found to reduce cognitive deficit and psychological symptoms in men and women with schizophrenia, including women with treatment refractory psychosis. These outcomes together with potent neurocognitive, neuroprotective, and cardiometabolic properties suggest that SERMs could be the potential targets for designing effective and safer therapies for psychiatric disorders.

Dysbindin-1 Involvement in the Etiology of Schizophrenia

Schizophrenia is a major psychiatric disorder that afflicts about 1% of the world’s population, falling into the top 10 medical disorders causing disability. Existing therapeutic strategies have had limited success on cognitive impairment and long-term disability and are burdened by side effects. Although new antipsychotic medications have been launched in the past decades, there has been a general lack of significant innovation. This lack of significant progress in the pharmacotherapy of schizophrenia is a reflection of the complexity and heterogeneity of the disease. To date, many susceptibility genes have been identified to be associated with schizophrenia. DTNBP1 gene, which encodes dysbindin-1, has been linked to schizophrenia in multiple populations. Studies on genetic variations show that DTNBP1 modulate prefrontal brain functions and psychiatric phenotypes. Dysbindin-1 is enriched in the dorsolateral prefrontal cortex and hippocampus, while postmortem brain studies of individuals with schizophrenia show decreased levels of dysbindin-1 mRNA and protein in these brain regions. These studies proposed a strong connection between dysbindin-1 function and the pathogenesis of disease. Dysbindin-1 protein was localized at both pre- and post-synaptic sites, where it regulates neurotransmitter release and receptors signaling. Moreover, dysbindin-1 has also been found to be involved in neuronal development. Reduced expression levels of dysbindin-1 mRNA and protein appear to be common in dysfunctional brain areas of schizophrenic patients. The present review addresses our current knowledge of dysbindin-1 with emphasis on its potential role in the schizophrenia pathology. We propose that dysbindin-1 and its signaling pathways may constitute potential therapeutic targets in the therapy of schizophrenia.