Bio-marqueurs découverts pour l'Autisme

Découverte de bio-marqueurs pour l'autisme

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Biomarkers for Autism Discovered

 Traduction: G.M. 
 
 ScienceDaily (23 mars 2012) - 
 
Une étape importante vers l'élaboration d'une méthode rapide et  peu coûteuse de diagnostic de l'autisme a été franchie par l'Université d'Uppsala, parmi d'autres universités. Grâce à la spectrométrie de masse de pointe des chercheurs ont réussi à capturer des biomarqueurs prometteurs à partir d'un petit échantillon de sang. L'étude vient d'être publiée dans la revue Nature Translational Psychiatry
 Il n'y a pas de biomarqueurs pour l'autisme reconnu aujourd'hui. 
Des chercheurs de Centre Berzelii et du laboratoire de science de la vie à Uppsala, qui, en collaboration avec des collègues de l'Université Linnaeus en Suède et de la Faculté de médecine de Téhéran, l'Iran, ont découvert certains biomarqueurs prometteurs. 
De nombreuses maladies sont causées par des altérations des protéines à l'intérieur et l'extérieur des cellules de l'organisme. En étudiant des modèles de protéines dans les tissus et fluides corporels , ces modifications peuvent être cartographiées afin de fournir des informations importantes sur les causes sous-jacentes de la maladie. 
Parfois, des modèles protéiques peuvent également être utilisés comme biomarqueurs pour permettre un diagnostic ou comme outil de pronostic pour suivre l'évolution d'une maladie. 
Dans l'étude courante les perturbations du système nerveux étaient en ligne de mire quand les scientifiques ont étudié des modèles de protéine dans le trouble du spectre autistique (TSA). 
Pour identifier des biomarqueurs potentiels (peptides ou protéines), les chercheurs ont effectué une analyse détaillée des protéines du plasma sanguin des enfants atteints de TSA par rapport à un groupe témoin. 
En utilisant des méthodes de spectrométrie de masse de pointe, ils ont réussi à identifier des peptides composés de fragments d'une protéine dont la fonction naturelle est dans le système immunitaire, la protéine C3 du système du complément . -L'étude est basée sur des échantillons de sang provenant d'un groupe relativement restreint d'enfants, mais les résultats indiquent le potentiel de notre stratégie méthodologique. Il y a déjà un lien connu entre cette protéine et  les TSA, ce qui renforce encore les résultats, dit Jonas Bergquist, professeur de chimie analytique et de la neurochimie au Département de chimie - BMC (Centre biomédical) à Uppsala. 
 
L'espoir est que cette nouvelle série de biomarqueurs conduira au bout du compte à un outil de diagnostic fiable fondé sur l'analyse sanguine .
 

 

 ScienceDaily (23 mars 2012) 
Traduction: Gérard Mercuriali
 
 

Original Article

Citation: Translational Psychiatry (2012) 2, e91; doi:10.1038/tp.2012.19
Published online 13 March 2012

A novel blood-based biomarker for detection of autism spectrum disorders

N Momeni1, J Bergquist2, L Brudin3, F Behnia4, B Sivberg5, M T Joghataei6 and B L Persson1

  1. 1School of Natural Sciences, Linnaeus University, Kalmar, Sweden
  2. 2Department of Chemistry—Biomedical Centre, Analytical Chemistry, Uppsala University, Uppsala, Sweden
  3. 3Department of Clinical Physiology, Kalmar County Hospital, Kalmar, Sweden
  4. 4Department of Occupational Therapy, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran
  5. 5Department of Health Sciences, Lund University, Lund, Sweden
  6. 6Cellular and Molecular Research Centre, Tehran Medical University, Tehran, Iran

Correspondence: Professor BL Persson, School of Natural Sciences, Linnaeus University, Norra vagen 49, Kalmar SE-39182, Sweden. E-mail: bengt.persson@lnu.se

Received 3 February 2012; Accepted 4 February 2012

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Abstract

Autism spectrum disorders (ASD) are classified as neurological developmental disorders. Several studies have been carried out to find a candidate biomarker linked to the development of these disorders, but up to date no reliable biomarker is available. Mass spectrometry techniques have been used for protein profiling of blood plasma of children with such disorders in order to identify proteins/peptides that may be used as biomarkers for detection of the disorders. Three differentially expressed peptides with mass–charge (m/z) values of 2020±1, 1864±1 and 1978±1Da in the heparin plasma of children with ASD that were significantly changed as compared with the peptide pattern of the non-ASD control group are reported here. This novel set of biomarkers allows for a reliable blood-based diagnostic tool that may be used in diagnosis and potentially, in prognosis of ASD.

Keywords: 

ASD; autism spectrum disorders; biomarker; blood

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Introduction

Autism spectrum disorders (ASD) are characterized by impairments in social orientation, communication and repetitive or restricted patterns of interests or behaviors appearing during the first 3 years of life with onset from birth or gradually in a regressive process from the end of the first year but mainly during the second year12 and is in Diagnostic and Statistical Manual of Mental Disorders (DSM)-IV classified as a developmental disorder.3 The pathogenesis of ASD is not yet known. Diagnosis is based on DSM-IV criteria and consists of a triad of symptoms, including social impairment, language disturbances and a rigid adherence to sameness.

In children diagnosed with ASD there is a spectrum of severity of these symptoms reflecting a variation in cognitive development ranging from above average to intellectual disability.45 Boys are 4–5 times more likely than girls to have autism.6Although the genetic determinants of ASD are so far largely unknown a recent report describes enrichments in different gene sets known to be linked to ASD.7Pathophysiology of ASD involves affected cellular and neuronal development and function possibly associated with abnormal patterns of proteins/peptides in the blood and the cerebrospinal fluid,8910 increased levels of neurotransmitter serotonin and β-endorphin,111213 low levels of melatonin,14 increased levels of opioid,15 high levels of homocysteine,16 Ca2+ channel deficiency,17 gene–environment interactions,18 altered levels of serine protease prolyl endopeptidase activity,19 low plasma levels of the neuropeptide hormone oxytocin,20 elevated immune response21 and abnormal activation of the complement system.222324Complement-system activation in response to a foreign antigen or a genetic disorder leads to degradation of complement protein C to C3a and C3b protein fragments with molecular masses of about 9kDa and 177kDa, respectively.25Complement factor I-mediated cleavage of the C3b α-chain liberates three protein fragments with molecular masses of 68, 43 and 2kDa,26 of which the last one is known as C3f.2728 The C3f peptide has been shown to have weak spasmogenic and anaphylatoxic functions and enhances vascular permeability as shown in guinea pig skin tests.28 Further degradation of C3f to C3f-desArg mediated by carboxypeptidase N was shown to result in stronger spasmogenic and anaphylatoxic properties.28 Figure 1 illustrates the location of the C3f domain in the crystal structure of the C3 protein.29 Detection of low-molecular-weight peptides by proteomic profiling of blood plasma and cerebrospinal fluid may reveal altered protein/peptide patterns associated with diseases and disorders.303132,33 In a recent study, adults with Asperger's syndrome was shown to exhibit sex-specific expression of serum biomarkers.33 Previous attempts to find a reliable biomarker for ASD by use of proteomics and protein/peptide profiling have led to a set of potential biomarkers. A proteomic study on autopsied autism brains using 2-D gel electrophoresis revealed a single-nucleotide polymorphism in glyoxalase I.34Another proteomic study of serum from children with autism showed differential expression of apolipoproteins and other components of complement proteins.35

Figure 1.
Figure 1 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Crystal structure of complement protein C3 (C3b/A/1) with location of C3f domain. Location of C3f domain (boxed) in structure model from PyMol (DeLano Scientific LLC, San Carlos, CA, USA).

Full figure and legend (194K)
 

In this study, we undertook a proteomic approach using surface-enhanced laser desorption/ionization time-of-flight (SELDI TOF) mass spectrometry to compare peptide profiles of blood plasma from children with ASD and control children (Table 1) with the aim of discovering novel peptide biomarkers with diagnostic utility and to understand the role of these in the pathophysiology of ASD.

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Subjects and methods

Participants

Thirty-two children with ASD and thirty-one healthy control children were initially selected for this study. Children in the ASD group were recruited from the autism rehabilitation centre at the University of Social Welfare and Rehabilitation Sciences in Tehran, Iran. After receiving the informed consent from the parents, blood samples were collected. All children with ASD were examined by clinical experts on autism. A child psychiatrist examined all the children who were also examined by a child neurologist or a child psychiatrist. All consultants agreed on the diagnosis of autism according to the DSM-IV criteria.3 However, diagnostic procedures applied in Europe and USA/Canada using the Autism Diagnostic Observation Schedule36 and the Autism Diagnostic Interview—Revised37 were not used in the diagnostic process applied in Iran. This shortcoming was met by long clinical experience by the child neurologist/child psychiatrist who was aware of the core behaviors in autism stated by the American Academy of Pediatrics in its Embargo from 2007.38 All children in the ASD group were diagnosed as having autistic syndrome (infantile or Kanner autism) with varying degree of mental retardation but no information about other psychiatric disorders like autoimmune disorders was available besides that none of the children were schizophrenic. The control group consisted of healthy and typically developed children with no signs or diagnoses of neurodevelopmental disorders and was recruited from the same area in order to minimize toxic influences from different environments. Children both in the ASD and control groups who had any kind of infection or disease less than 2 weeks before the time of examination were excluded.

Blood samples for one healthy control (female) and four patients (two females and two males) were not possible to analyze owing to the too small sample volume, resulting in 30 controls and 28 children for children with ASD for further studies (For participant details, see Table 1). The ASD group comprised more males and was insignificantly younger.

The study was approved (MT/1247) by the ethics committee of the University of Medical Sciences, Tehran.

Procedure

All blood samples were collected by a pediatric nurse and the children diagnosed with autism were supervised by a pediatric psychiatrist with special training in the field of childhood psychosis. Venous blood was collected into 3-ml Heparin tubes (Vacutainer System; Becton-Dickinson, Plymouth, UK) and plasma was separated immediately by centrifugation at 1300g for 10min at 4°C. Immediately thereafter, an EDTA-free inhibitor cocktail (Halt protease inhibitor; Thermo Scientific Pierce Protein Research Products, Rockford, IL, USA) and Prefablock SC (Pentapharm, Munich, Germany) were added at a concentration of 10μlml−1 plasma and 20μlml−1 plasma, respectively. The produced plasma was aliquoted in small portions and immediately frozen on dry ice and stored at −80°C.

 

Peptide profiling

SELDI-TOF mass spectrometry (MS) was used to profile low-molecular weight peptides, less than 10kDa, in the plasma of children with ASD and the healthy control group, suitable for the subsequent MS/MS analysis (described below) by matrix-assisted laser desorption/ionization (MALDI)-TOF/TOF MS and post source decay fragmentation. Carboxy methyl CM10 protein chip array surfaces (a weak-cation exchanger bearing the COOH functional group) with eight application spots were prepared according to the manufacturer's protocol (BioRad, Hercules, CA, USA). CM10 protein chip arrays were equilibrated twice with 100μl buffer (0.1M sodium acetate, pH 5.0) for 5min at 25°C. Plasma samples diluted 1:50 with sodium phosphate buffer (25mm, pH 7.0) were applied onto the bioprocessor well. After 45min of incubation with shaking at 25°C samples were washed three times with 150μl of dilution buffer, followed by two quick rinses with 150μl of 1mmHEPES buffer, pH 7.0. The chip array was removed from the bioprocessor, air-dried and 0.8μl of saturated (25mg/ml) CHCA (α-cyano-4-hydroxycinnamic acid; BioRad) was added to each spot, allowed to air-dry, and this step was repeated once. The chip array was read on BioRad protein chip reader (PCS 4000) on SELDI system personal edition. Before reading the chip arrays an external calibration was performed by use of ‘all-in-one peptide standard’ (BioRad) containing a mixture of seven different peptides in the molecular range of 1–7kDa.

 

Sequencing of peptides

100μl of plasma samples were diluted with 300μl of 25mm sodium phosphate buffer, pH 7.0, and subjected to ultrafiltration by use of a 10-kDa Microne membrane (Millipore, Bedford, MA, USA). Ultrafiltrate was dried in a Speed Vacuum centrifuge, reconstituted in 10μl of 20mm sodium phosphate buffer, pH 7.0, and desalted on ZipTip C-18 columns (Millipore). Five microliters of the sample was applied on the prepared SELDI chip, incubated, washed and dried (as described above). One microliter of saturated (25mgml−1) CHCA was added to the spots, allowed to air-dry, and this step was repeated once.

The MALDI TOF/TOF MS instrument used for sequence verification of the peptides was an Ultraflex II TOF/TOF (Bruker Daltonics GmbH, Bremen, Germany) equipped with a SmartBeam laser. All spectra were acquired using the reflectron mode. To acquire MS/MS spectra, post source decay TOF/TOF by laser-induced dissociation was performed. The target of choice for the MALDI approach was a SELDI-TOF target (BioRad). The prepared matrix/sample spots were introduced into the Ultraflex II and MS spectra were recorded from each prepared sample spot. The calibration used was an external near-neighbor calibration. The samples used for calibration were a mixture of peptides covering the mass range of 1–5kDa. From the acquired peptide masses (TOF MS), the candidate peptides were selected manually for subsequent experiments. Spectra were annotated with data processing software, FlexAnalysis (Bruker Daltonics GmbH, Bremen, Germany), and finally interpreted by software assisted de novo sequence analysis (BioTools, Bruker Daltonics GmbH). The results from MALDI TOF/TOF MS were confirmed by analysis using high-resolution nano-LC-ESI FTICR MS.

Data analysis and statistics

The peak intensity from the SELDI TOF mass spectra were analyzed in triplicate and mean values were calculated. These were log-normally distributed and the following analyses were, therefore, made using logarithmic values. Group differences of the individual peaks were analyzed using Student's t-test, and for combination of the peaks, two-group discrimination analysis was used.39Discrimination analysis gives a linear combination of three peaks (composite variable) that maximizes the distance between the mean values of the two groups (the so-called general distance) that is calculated as (zAzB/√ variance of zbetween groups, where zA and zB are the mean values for the two groups A and B for a specific set of parameters (ASD index). Because of uncertainties of the impact of hemolysis,40 the analysis was made using non-hemolytic samples only (n=49), but the ASD index was calculated for all subjects (Table 3). Receiver operating characteristic curves41 were then constructed for all 58 subjects and for those 49 without hemolysis (Figure 3). Of all 58 participants comprising 30 control children and 28 children in the ASD group, 11 ‘outliers’, 7 in the control group and 4 in the ASD group, were identified. Of the 49 participant samples without hemolysis (27 control children and 22 ASD group children) five ‘outliers’, four in the control group and one in the ASD group, were observed. Fisher's exact test was used to test differences between sex and age-categories, and age differences were also tested with Mann–Whitney's U-test (Table 1). For receiver operating characteristic analysis the statistical program MedCalc (version 6.10, 2001; Frank Schoonjans, Mariakerke, Belgium) was used and all other statistical analyses were carried out using Statistica (version 8, Statsoft, Tulsa, OK, USA). AP-value of less than 0.05 was considered significant.

 
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Results

The results show significant group differences of the intensity of the three different peaks with mass to charge ratios (m/z) 1864, 1978, and 2020±1Da (Figure 2Table 2) both in univariate (individual peaks; not shown) and in the multivariate (composite peaks) analysis (Table 3Figure 3). The peaks with anm/z of 1864 and 2020±1Da were upregulated and overrepresented in children with ASD, whereas the peptide of 1978±1Da was downregulated in the children with ASD as compared with the healthy control children. The peptides were selected based on their discriminating abilities. In addition, the mass and intensity of the peptides is determining the possibility to subsequently identify and sequence them with MALDI-TOF/TOF MS and ESI-FTICR MS. From the acquired peptide masses (SELDI TOF MS data), the candidate peptides, for example, those with an m/z of 2020±1, were selected (Figure 4) and the amino-acid sequences were determined using tandem MS (MALDI TOF/TOF MS) as shown in Table 2. These sequences were also confirmed by nano-LC-ESI FTICR MS (not shown). The first peptide with an m/z of 2020±1Da consists of 17 amino-acid residues corresponds to the peptide known as C3f (NCBI accession number 1413205A ) of the complement protein C3 (Figure 1). The second peptide with an m/z of 1864±1Da corresponds to a peptide of 16 residues with the same sequence as C3f but lacks the C-terminal arginine and is known as C3f-desArg. The third peptide with an m/z of 1978±1Da that appears at higher concentration in the group of healthy control children has the same sequence as C3f but carries a modified arginine residue, corresponding to ornithine, in the C-terminus.

Figure 2.
Figure 2 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Typical SELDI TOF-derived mass spectra of plasma from children diagnosed with ASD and control children. Non-hemolytic samples were from three children diagnosed with ASD (d-1, d-2, d-3) and from three control children (c-1, c-2, c-3). The analysis was a blind test with the identities of the children unknown. Following analysis the identities of the children were revealed: d-1 (male, age 5), c-1 (female, age 5), d-2 (male, age 6), c-2 (male, age 7), d-3 (female, age 4) and c-3 (female, age 5). The positions of the three peptides, 1864±1, 1978±1, and 2020±1Da, are indicated.

Full figure and legend (109K)
 

Figure 3.
Figure 3 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Receiver operating characteristic curves for all 58 subjects and for those 49 corrected for hemolysis. A composite of data for the peptides 1864±1, 1978±1 and 2020±1 in the group of 58 participants (hatched line) and in the group of 49 non-hemolytic participants (solid line). For the group of non-hemolytic participants, sensitivity and specificity is 95.5 and 85.2, respectively. Criterion value is >4.2068. Differences between curves, 0.923–0.814=0.109, is not statistically significant (P=0.141).

Full figure and legend (48K)
 

Figure 4.
Figure 4 - Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, please contact help@nature.com or the author

Typical MALDI TOF/TOF mass spectrum for sequence analysis. Fragmentation of C3f (2020.1Da) to C3f-des-arginine (1864.2Da) is identified with monoisotopic mass of arginine of 174.8 (M+H+), and to C3f-modified arginine (1978.1Da).

Full figure and legend (84K)
 



The results show a significant difference between the mean of the an m/z values of these peptide intensities from children with ASD and the control group with P-values <0.05 of the selected peptides (Table 2).

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Discussion

Before starting this study, different aspects that might have an impact on the resulting spectra such as collection, handling and processing of samples, including choice of protease inhibitors, temperature, freezing and thawing cycles have been evaluated. We believe that the optimized procedures during the sample handling secure reproducible spectra of good quality. In collection of serum samples, it is not uncommon to have hemolytic events due to rupturing of red blood cells during the processing steps. We noticed that, of the 58 subjects, 9 showed moderate hemolysis and were subjected to separate statistical evaluation. Hemolysis in the samples was evaluated by examination of the mass peaks at 7.6 and 15.1kDa corresponding to the double-charged and single-charged α-subunit of hemoglobin, respectively.40 To avoid interference of the hemoglobin subunits in the proteomic profiling of the multiple serum specimens where the subunits may compete for or alter the binding affinity of other serum proteins to the surface40 samples with values >80 were excluded (see Table 3 and Figure 3). In the ASD group some children with severe autism were on medication with Risperdal to reduce hyperactivity and violent behavior, and a few children were on medication with Ritalin to improve attention (Table 1). It would have been ethically questionable to discontinue the medication with the purpose of controlling the research design. Although we did not see any detectable correlation between medication and the presence of the biomarker peptides in plasma samples of the ASD children it can not be excluded that some differences may be influenced by medications, as previously discussed.35 In a recently published study on complement factor I activity,42 we could not find any clear influences of the medications also used by subjects in this study. Only six of the children in the ASD group had no medication. Of these five were correctly classified in the discrimination analysis and 1 was a sample with hemolysis and was incorrectly classified. Of the three biomarkers, 2020±1, 1978±1 and 1864±1, identified in this proteomic profiling study of children with ASD and control children, the 1978-kDa ornithine-containing peptide identified by tandem MS is interesting as is suggest that the arginine of the 2020-kDa peptide is recognized as a target for enzymatic conversion. As arginase requires a free arginine for conversion to ornithine43 an interesting alternative possibility is that this C-terminal arginine residue is ADP-ribosylated by an arginine-specific ADP-ribosyltransferase (ART) catalyzing the transfer of ADP-ribose from NAD+ (ref. 44) with the possibility of a ‘secondary’ modification of the ADP-ribosylated arginine resulting in replacement of ADP-ribosylarginine by ornithine as shown for HNP-1.45 Lack of ART expression, that is ART2, has previously been correlated with enhanced susceptibility to autoimmune diseases (see Laing et al.44 and references therein). Altered immune function and complement-system deficiency has been reported for children with ASD indicating a recurrent incidence of immunological diseases.4647484950 Other investigations has shown significantly increased levels of inflammatory markers such as TNF-α, IL-6, IL-8, GM-CSF and IFN-γ in the post mortem brain tissue of individuals with autism and immune dysfunction has also been proposed as a potential mechanism for the pathogenesis of ASD.215152

By the proteomic approach used in this study we have identified differentially expressed peptides that correspond to fragments of the C3 complement protein. Although the study was based on a relatively limited group of children it demonstrates the potential of the proteomic approach in which the relevance and potential diagnostic utility of the panel of biomarkers was further strengthened by known associations between the protein or peptides and pathogenesis of ASD. By use of the proteomic approach we have discovered a unique set of biomarkers, which carries the potential for an early detection of ASD with an improved diagnostic accuracy that would enable an early intervention in the development of this disorder.

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Conflict of interest

Naghi Momeni's PhD studentship was supported by Autism Biodiagnostics Sweden AB (ABSAB). ABSAB had no role in the design of the study, the collection or analysis of data. Dr Momeni has no financial holdings in that company, although he may receive some further compensation if his work leads to a commercial product. All the other authors declare no conflict of interest.

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Acknowledgements

We thank Dr Maria Bergström at the Linnaeus University for her help with the experiments and the SELDI TOF MS analysis. Drs Jörg Hanrieder and Konstantin Artemenko at the Uppsala University are acknowledged for their assistance with high-resolution MS, and Dr Mohammad A Karbasian and staff at the Robat Karin Medical Diagnostic Laboratory, Tehran, for their assistance with collection of samples. We also thank all the children and their families who have contributed to this study. The principal funder of this project was Siamak Shahnooshi (Managing Director and company owner of Autism Biodiagnostics Ltd and Asbestos Consultants to the Environment Ltd—ACEPSI). Michael Krause was the financial director and Carl-Gunnar Nyquist was the Managing Director of the Swedish subsidiary company, Autism Biodiagnostics AB. The funder and his directors had no role in the study design, the data collection and analysis, or the preparation of the manuscript. The Swedish Research Council is acknowledged for grant 621-2008-3562 to JB.

 

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivative Works 3.0 Unported License.
To view a copy of this license, visithttp://creativecommons.org/licenses/by-nc-nd/3.0/ 

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