Does the association with diabetes say more about schizophrenia and its treatment?--the GLUT hypothesis

Neuroreceptor Inhibition by Clozapine Triggers Mitohormesis and Metabolic Reprogramming in Human Blood Cells

The antipsychotic drug clozapine demonstrates superior efficacy in treatment-resistant schizophrenia, but its intracellular mode of action is not completely understood. Here, we analysed the effects of clozapine (2.5-20 µM) on metabolic fluxes, cell respiration, and intracellular ATP in human HL60 cells. Some results were confirmed in leukocytes of clozapine-treated patients. Neuroreceptor inhibition under clozapine reduced Akt activation with decreased glucose uptake, thereby inducing ER stress and the unfolded protein response (UPR). Metabolic profiling by liquid-chromatography/mass-spectrometry revealed downregulation of glycolysis and the pentose phosphate pathway, thereby saving glucose to keep the electron transport chain working. Mitochondrial respiration was dampened by upregulation of the F0F1-ATPase inhibitory factor 1 (IF1) leading to 30-40% lower oxygen consumption in HL60 cells. Blocking IF1 expression by cotreatment with epigallocatechin-3-gallate (EGCG) increased apoptosis of HL60 cells. Upregulation of the mitochondrial citrate carrier shifted excess citrate to the cytosol for use in lipogenesis and for storage as triacylglycerol in lipid droplets (LDs). Accordingly, clozapine-treated HL60 cells and leukocytes from clozapine-treated patients contain more LDs than untreated cells. Since mitochondrial disturbances are described in the pathophysiology of schizophrenia, clozapine-induced mitohormesis is an excellent way to escape energy deficits and improve cell survival.

Exploring cellular markers of metabolic syndrome in peripheral blood mononuclear cells across the neuropsychiatric spectrum

Recent evidence suggests that comorbidities between neuropsychiatric conditions and metabolic syndrome may precede and even exacerbate long-term side-effects of psychiatric medication, such as a higher risk of type 2 diabetes and cardiovascular disease, which result in increased mortality. In the present study we compare the expression of key metabolic proteins, including the insulin receptor (CD220), glucose transporter 1 (GLUT1) and fatty acid translocase (CD36), on peripheral blood mononuclear cell subtypes from patients across the neuropsychiatric spectrum, including schizophrenia, bipolar disorder, major depression and autism spectrum conditions (n = 25/condition), relative to typical controls (n = 100). This revealed alterations in the expression of these proteins that were specific to schizophrenia. Further characterization of metabolic alterations in an extended cohort of first-onset antipsychotic drug-naïve schizophrenia patients (n = 58) and controls (n = 63) revealed that the relationship between insulin receptor expression in monocytes and physiological insulin sensitivity was disrupted in schizophrenia and that altered expression of the insulin receptor was associated with whole genome polygenic risk scores for schizophrenia. Finally, longitudinal follow-up of the schizophrenia patients over the course of antipsychotic drug treatment revealed that peripheral metabolic markers predicted changes in psychopathology and the principal side effect of weight gain at clinically relevant time points. These findings suggest that peripheral blood cells can provide an accessible surrogate model for metabolic alterations in schizophrenia and have the potential to stratify subgroups of patients with different clinical outcomes or a greater risk of developing metabolic complications following antipsychotic therapy.

Glucose disturbances, cognitive deficits and white matter abnormalities in first-episode drug-naive schizophrenia

Disturbance of glucose metabolism may be implicated in cognitive deficits of schizophrenia in its early phases. Many studies have reported the important role of widespread disruption of white matter (WM) connectivity in pathogenesis, cognitive deficit and psychopathology of schizophrenia. However, no study has investigated their inter-relationships in drug-naive first episode (DNFE) patients with schizophrenia. Glucose metabolism parameters including fasting glucose, insulin and homeostasis model of assessment-insulin resistance (HOMA-IR) index, cognitive performance on the MATRICS Consensus Cognitive Battery (MCCB) and the voxel-wised WM fractional anisotropy (FA) values were examined using DTI in 39 DNFE schizophrenia and 31 control subjects. The Positive and Negative Syndrome Scale was utilized for clinical symptoms. The patients showed significantly greater fasting plasma levels of glucose and insulin and HOMA-IR, and poorer cognitive scores, together with widespread reduced FA values in five brain areas, including left and right corpus callosum, superior longitudinal fasciculus, posterior thalamic radiation, and corona radiata (all p < 0.05). Association analysis showed that glucose level was positively associated with Digital Sequence Test and Continuous Performance Test, but negatively with FA values in posterior thalamic radiation and left corpus callosum in patients (all p < 0.05). Furthermore, multiple regression analysis revealed that the interactions of glucose × FA in left corpus callosum, longitudinal fasciculus and corona radiata were independent contributors to the Brief Visuospatial Memory Test (BVMT) of MCCB, while the interaction of glucose × FA in left corpus callosum, or in longitudinal fasciculus was associated with MCCB mazes and Trail Making A Test, respectively. Therefore, abnormal glucose metabolism, cognitive impairment and widespread disruption of WM structure occur in an early course of schizophrenia onset. An interaction between glucose metabolism abnormality and the WM dysconnectivity may lead to cognitive impairment.

Oxidative-Antioxidant Imbalance and Impaired Glucose Metabolism in Schizophrenia

Schizophrenia is a neurodevelopmental disorder featuring chronic, complex neuropsychiatric features. The etiology and pathogenesis of schizophrenia are not fully understood. Oxidative-antioxidant imbalance is a potential determinant of schizophrenia. Oxidative, nitrosative, or sulfuric damage to enzymes of glycolysis and tricarboxylic acid cycle, as well as calcium transport and ATP biosynthesis might cause impaired bioenergetics function in the brain. This could explain the initial symptoms, such as the first psychotic episode and mild cognitive impairment. Another concept of the etiopathogenesis of schizophrenia is associated with impaired glucose metabolism and insulin resistance with the activation of the mTOR mitochondrial pathway, which may contribute to impaired neuronal development. Consequently, cognitive processes requiring ATP are compromised and dysfunctions in synaptic transmission lead to neuronal death, preceding changes in key brain areas. This review summarizes the role and mutual interactions of oxidative damage and impaired glucose metabolism as key factors affecting metabolic complications in schizophrenia. These observations may be a premise for novel potential therapeutic targets that will delay not only the onset of first symptoms but also the progression of schizophrenia and its complications.

Transcript Analysis of Zebrafish GLUT3 Genes, slc2a3a and slc2a3b, Define Overlapping as Well as Distinct Expression Domains in the Zebrafish (Danio rerio) Central Nervous System

The transport of glucose across the cell plasma membrane is vital to most mammalian cells. The glucose transporter (GLUT; also called SLC2A) family of transmembrane solute carriers is responsible for this function in vivo. GLUT proteins encompass 14 different isoforms in humans with different cell type-specific expression patterns and activities. Central to glucose utilization and delivery in the brain is the neuronally expressed GLUT3. Recent research has shown an involvement of GLUT3 genetic variation or altered expression in several different brain disorders, including Huntington's and Alzheimer's diseases. Furthermore, GLUT3 was identified as a potential risk gene for multiple psychiatric disorders. To study the role of GLUT3 in brain function and disease a more detailed knowledge of its expression in model organisms is needed. Zebrafish (Danio rerio) has in recent years gained popularity as a model organism for brain research and is now well-established for modeling psychiatric disorders. Here, we have analyzed the sequence of GLUT3 orthologs and identified two paralogous genes in the zebrafish, slc2a3a and slc2a3b. Interestingly, the Glut3b protein sequence contains a unique stretch of amino acids, which may be important for functional regulation. The slc2a3a transcript is detectable in the central nervous system including distinct cellular populations in telencephalon, diencephalon, mesencephalon and rhombencephalon at embryonic and larval stages. Conversely, the slc2a3b transcript shows a rather diffuse expression pattern at different embryonic stages and brain regions. Expression of slc2a3a is maintained in the adult brain and is found in the telencephalon, diencephalon, mesencephalon, cerebellum and medulla oblongata. The slc2a3b transcripts are present in overlapping as well as distinct regions compared to slc2a3a. Double in situ hybridizations were used to demonstrate that slc2a3a is expressed by some GABAergic neurons at embryonic stages. This detailed description of zebrafish slc2a3a and slc2a3b expression at developmental and adult stages paves the way for further investigations of normal GLUT3 function and its role in brain disorders.

SLC2A3 single-nucleotide polymorphism and duplication influence cognitive processing and population-specific risk for attention-deficit/hyperactivity disorder

BACKGROUND

Attention-deficit/hyperactivity disorder (ADHD) is a common, highly heritable neurodevelopmental disorder with profound cognitive, behavioral, and psychosocial impairments with persistence across the life cycle. Our initial genome-wide screening approach for copy number variants (CNVs) in ADHD implicated a duplication of SLC2A3, encoding glucose transporter-3 (GLUT3). GLUT3 plays a critical role in cerebral glucose metabolism, providing energy for the activity of neurons, which, in turn, moderates the excitatory-inhibitory balance impacting both brain development and activity-dependent neural plasticity. We therefore aimed to provide additional genetic and functional evidence for GLUT3 dysfunction in ADHD.

METHODS

Case-control association analyses of SLC2A3 single-nucleotide polymorphisms (SNPs) and CNVs were conducted in several European cohorts of patients with childhood and adult ADHD (SNP, n = 1,886 vs. 1,988; CNV, n = 1,692 vs. 1,721). These studies were complemented by SLC2A3 expression analyses in peripheral cells, functional EEG recordings during neurocognitive tasks, and ratings of food energy content.

RESULTS

Meta-analysis of all cohorts detected an association of SNP rs12842 with ADHD. While CNV analysis detected a population-specific enrichment of SLC2A3 duplications only in German ADHD patients, the CNV + rs12842 haplotype influenced ADHD risk in both the German and Spanish cohorts. Duplication carriers displayed elevated SLC2A3 mRNA expression in peripheral blood cells and altered event-related potentials reflecting deficits in working memory and cognitive response control, both endophenotypic traits of ADHD, and an underestimation of energy units of high-caloric food.

CONCLUSIONS

Taken together, our results indicate that both common and rare SLC2A3 variation impacting regulation of neuronal glucose utilization and energy homeostasis may result in neurocognitive deficits known to contribute to ADHD risk.

An Overview of Links Between Obesity and Mental Health

The American Medical Association recently recognized obesity as both an illness and a leading cause of preventable death and chronic disease. This association is not only linked to physical health outcomes, however, as obesity has also been extensively associated with mental illness as well. Both obesity and severe mental illness decrease quality of life and are associated with an increase in disability, morbidity, and mortality, and when they occur together, these adverse health outcomes are magnified. Despite educational campaigns, increased awareness, and improved treatment options, the high prevalence of mental illness and comorbid obesity remains a serious problem. This review examines this overlap, highlighting clinical and biological factors that have been linked to this association in order to improve our understanding and help elucidate potential therapeutic avenues.

Diabetes and cognitive deficits in chronic schizophrenia: a case-control study

Cognitive impairment occurs in both schizophrenia and diabetes. There is currently limited understanding whether schizophrenia with diabetes has more serious cognitive deficits than schizophrenia without diabetes or diabetes only. This study assessed cognitive performance in 190 healthy controls, 106 diabetes only, 127 schizophrenia without diabetes and 55 schizophrenia with diabetes. This study was conducted from January 2008 to December 2010. Compared to healthy controls, all patient groups had significantly decreased total and five index RBANS scores (all p<0.01-p<0.001), except for the visuospatial/constructional index. Schizophrenia with diabetes performed worse than schizophrenia without diabetes in immediate memory (p<0.01) and total RBANS scores (<0.05), and showed a trend for decreased attention (p = 0.052) and visuospatial/constructional capacity (p = 0.063). Schizophrenia with diabetes performed worse than diabetes only in immediate memory (p<0.001) and attention (p<0.05), and showed a trend for decreased total RBANS scores (p = 0.069). Regression analysis showed that the RBANS had modest correlations with schizophrenia' PANSS scores, their duration of current antipsychotic treatment, and diagnosis of diabetes. Schizophrenia with co-morbid diabetes showed more cognitive impairment than schizophrenia without diabetes and diabetes only, especially in immediate memory and attention.

The prevalence of diabetes mellitus is increased in relatives of patients with a non-affective psychotic disorder

Patients with schizophrenia are more likely to develop diabetes mellitus (DM) compared to the general population. In relatives, however, an increased rate of DM has not consistently been reported. In this study, we compared DM rates in 1740 unaffected first- and second-/third-degree relatives of patients with a non-affective psychotic disorder to 1271 control subjects, by administering the Family Interview for Genetic Studies (FIGS). The prevalence of DM (6.1%) was increased in the relatives of patients as compared to the relatives of the healthy subjects (3.6%, OR=1.6, p=0.007). Our findings support the hypothesis of a familial, possibly genetic, link between DM and non-affective psychotic disorders.