A distinct serum protein pattern in patients with paranoid schizophrenia

Introduction: Schizophrenia is a chronic mental illness, whose aetiology is still unclear; therefore, information about differences in serum protein patterns may improve the understanding of the pathophysiology of schizophrenia. The goal of this study was to use the proteomic approach to identify altered protein levels in the serum samples from patients with schizophrenia. Methods: Blood was collected from 10 patients with paranoid schizophrenia and 10 healthy volunteers matched by sex and age. Serum proteins were isolated by 2D gel electrophoresis. Proteins with altered levels were identified by matrix-assisted laser desorption ionisation time-of-flight mass spectrometry. Results: We uncovered major changes in the expression of such proteins as apolipoproteins of classes A4 and C3, transthyretin (TTR) and serum amyloid A1. An increase in expression was found only for apolipoprotein A4, whereas the expression of apolipoprotein C3, TTR and serum amyloid A1 was decreased. The observed differences in the expression of serum proteins (TTR and serum amyloid) are in good agreement with the results obtained by other research groups during analyses of cerebrospinal fluid or post-mortem brain tissues by other methods. Conclusion: Such alterations of the expression of these proteins may indicate problems with regulation, for example, in the synthesis. On the other hand, the altered protein expression may simply reflect the pathophysiological status of patients, where these proteins could be candidates for biomarkers. Further research is needed to confirm the significance of the altered levels of these proteins in the pathogenesis of schizophrenia and to determine their suitability as biomarkers of schizophrenia. D ow nl oa de d fr om p pj . p hy ph a. ir at 0 :1 7 + 04 30 o n W ed ne sd ay A ug us t 1 9t h 20 20 305 | Physiol Pharmacol 21 (2017) 304-311 Alekseeva et al. Schizophrenia (Sch) is a chronic mental illness, whose aetiology is still unclear. Schizophrenia is characterised by hallucinations, delusions (positive psychotic symptoms), affective problems (negative psychotic symptoms) and cognitive dysfunction (van Os and Kapur, 2009). A number of hypotheses have been proposed about the pathogenesis of Sch, for example, aberrations in the pathways of transmission of neurotransmitters dopamine and serotonin (Geyer and Vollenweider, 2008; Moore et al., 1999) or pathological changes in embryonic neurogenesis owing to variations in gene neuregulin-1 (Bramon et al., 2008), as well as oxidative-stress-mediated cell damage due to lowered levels of antioxidant defence enzymes in patients with schizophrenia (Ranjekar et al., 2003). Such pathogenesis may be caused by a dysfunction of some enzymes (proteins) as well as changes of their quantity in the blood of these patients. At the same time, there is no full information about differences in serum protein patterns that can be used for typing of psychopathologies among individuals at risk of developing psychiatric disorders (Ivanova et al., 2013). Diagnosis and nosology rely on symptoms and accumulated clinical observations, and thus far, have been based mostly on interviews with patients and on patients’ subjective complaints (Turck et al., 2005). Moreover, current medications still have substantial adverse effects and/or require weeks for therapeutic effects to manifest themselves; not all patients respond to current pharmacotherapy (Bystritsky, 2006). In sum, an insufficient understanding of psychiatric disorders at the molecular level and the lack of disease-specific changes in serum protein patterns prevent optimisation of diagnosis and treatment of such complex psychiatric disorders as Sch. The proteomic approach, namely, the combination of 2D gel electrophoresis and matrix-assisted laser desorption ionisation time-of-flight mass spectrometry (MALDI-TOF MS), allows researchers to reliably identify proteins isolated from human bodily fluids (Davalieva et al., 2016; Guest et al., 2016). Our exploratory study (Alekseeva et al., 2013) showed that 2D gel electrophoresis is suitable for isolation of proteins from blood of patients with mental disorders. Therefore, in the present work, clinical blood samples from patients with a diagnosis of Sch were tested to identify quantitative differences in the proteomic profile of serum. Materials and methods Chemicals We used urea, SDS, glycerol, acetonitrile from Panreac (Spain), 3-[(3-chloramidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS) from AppliChem (Germany), Bio-Lytes ampholytes from Bio-Rad (USA), dithiothreitol (DTT), HCOOH, NH4HCO3 from Sigma–Aldrich (USA), Tris-HCl, and bromophenol blue from Helicon (Russia), Coomassi Brilliant Blue G250 from Serva (Germany). Subjects The study was conducted according to The Code of Ethics of the World Medical Association (Declaration of Helsinki revised in Fortaleza, Brazil, 2013) regarding experiments on human subjects. The patients in this study were recruited from the clinics of the Mental Health Research Institute (Tomsk, Russia). Written informed consent was obtained from each subject after we obtained approval of the study protocol from the Local Bioethics Committee of the Mental Health Research Institute. The inclusion criteria were a clinical diagnosis of Sch (according to International classification of diseases, 10th revision [ICD-10]: F20.0). Groups of patients with paranoid schizophrenia and healthy volunteers were comparable by sex and age and did not differ statistically. Blood was collected from 10 subjects with Sch (six males and four females) and 10 control subjects (three males and seven females). All subjects were Caucasian inhabitants of the Tomsk region. The age of the patients was from 24 to 57 years (35 ± 13 years). The age of healthy group was from 26 to 56 years (39 ± 11 years). Blood sampling was carried out at the time of patient's admission to hospital, before prescribing psychotropic therapy. At the time of admission to the clinic, patients with Sch (7 from 10) were under the influence of maintenance therapy by Risperidone (4-6 mg/daily) or Haloperidol (10 mg/daily). Sample preparation Venous blood (5 ml) was collected into a BD vacutainer anticoagulant (EDTA) tube between 07:00 and 08:00 am to avoid circadian fluctuation of the measured parameters. The blood was centrifuged D ow nl oa de d fr om p pj . p hy ph a. ir at 0 :1 7 + 04 30 o n W ed ne sd ay A ug us t 1 9t h 20 20 Proteomics of schizophrenia Physiol Pharmacol 21 (2017) 304-311 | 306 immediately after the sampling. After centrifugation (3000 rpm, 10 min, Eppendorf AG 22331), serum was separated and stored at 70 °C prior to proteomic