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A Serum Analysis before and after Antidepressant Treatment in Major Depression: A Pilot Study

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Treatment in Major Depression: A Pilot Study

Murielle Girard, Karine Vuilliers-Devillers, Emilie Pinault, Barbara Bessette, Brigitte Plansont, Dominique Malauzat

To cite this version:

Murielle Girard, Karine Vuilliers-Devillers, Emilie Pinault, Barbara Bessette, Brigitte Plansont, et al..

A Serum Analysis before and after Antidepressant Treatment in Major Depression: A Pilot Study.

Clinical Medicine Insights: Psychiatry, 2015, 6, pp.6 - 7. �10.4137/CMPsy.S20765�. �hal-01829760�

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A Serum Analysis Before and After Antidepressant Treatment in Major Depression: A Pilot Study

Murielle girard

1

, Karine Vuilliers-devillers

2

, emilie Pinault

2

, Barbara Bessette

3

, Brigitte Plansont

1

and dominique Malauzat

1

1Département Recherche et Développement, Centre Hospitalier Esquirol, Limoges, France. 2FR 3503 GEIST, Service Commun de Recherche et d’Analyse de Biomolécules de Limoges (SCRABL), Faculté des Sciences et Techniques, Limoges, France. 3EA 3842 Homéostasie Cellulaire et Pathologies, Faculté de Médecine, Limoges, France.

ABSTRACT: We investigated the serum protein profiles of subjects with major depressive disorder (MDD), with (n = 4) and without clinical improvement (n = 4), at the initiation of antidepressant treatment (venlafaxine) (T0) and 4 weeks later (T28), by difference gel electrophoresis in two dimensions (2D-DIGE) and mass spectrometry. The nine proteins displaying differences in composition between the two time points in the group with clinical improvement between T0 and T28 included gelsolin, clusterin, and the activated fragment of complement C3 (C3a). We then analyzed serum samples from MDD subjects receiving different antidepressants between T0 and T28. Subjects were classified into two groups, with (n = 17) or without (n = 14) clinical improvement (50% decrease in baseline Hamilton Depression Rating Scale score), at T28. Clusterin levels did not differ between groups at either time point. Gelsolin and C3a levels differed between T0 and T28 only in the group presenting clini- cal improvement. A comparison with serum samples from controls suggested that the levels of these two proteins changed during MDD and were potentially modified after successful antidepressant treatment. Despite the small sample size, the results of this pilot study suggest that several changes in the expression of some serum proteins occur in association with the clinical relevance of the treatment, and indicate changes to general pathways requiring further study.

KEYWORDS: proteome, major depressive disorder, C3, gelsolin, clusterin, antidepressant

CITATION: girard et al. a serum analysis Before and after antidepressant treatment in Major depression: a Pilot study. Clinical Medicine Insights: Psychiatry 2015:6 1–12 doi:10.4137/CMPsy.s20765.

RECEIVED: October 2, 2014. RESUBMITTED: February 26, 2015. ACCEPTED FOR PUBLICATION: March 17, 2015.

ACADEMIC EDITOR: Jaswinder Kaur ghuman, editor in Chief TYPE: Original research

FUNDING: authors disclose no funding sources.

COMPETING INTERESTS: Authors disclose no potential conflicts of interest.

COPYRIGHT: © the authors, publisher and licensee libertas academica limited.

this is an open-access article distributed under the terms of the Creative Commons CC-By-nC 3.0 license.

CORRESPONDENCE: murielle.girard@ch-esquirol-limoges.fr

Paper subject to independent expert blind peer review by minimum of two reviewers.

all editorial decisions made by independent academic editor. Upon submission manuscript was subject to anti-plagiarism scanning. Prior to publication all authors have given signed confirmation of agreement to article publication and compliance with all applicable ethical and legal requirements, including the accuracy of author and contributor information, disclosure of competing interests and funding sources, compliance with ethical requirements relating to human and animal study participants, and compliance with any copyright requirements of third parties. this journal is a member of the Committee on Publication ethics (COPe).

Published by libertas academica. learn more about this journal.

Introduction

Proteomic analysis provides an inventory and a means of identifying the proteins involved in specific and well- characterized clinical states, opening up new opportunities for the identification of novel disease biomarkers. This approach has already been explored in mental disorders such as schizo- phrenia,

1

bipolar disorder, Alzheimer’s disease,

2

substance abuse,

3,4

and neurodegenerative diseases.

5,6

Most such studies in humans are based on postmortem analysis or cerebrospinal fluid examination, but blood-based candidate biomarkers of mental diseases are required to facilitate noninvasive test proce- dures on blood samples. Changes to peripheral protein profiles (metabolome, cytokines, proteins) have been observed in several psychiatric diseases,

2

including schizophrenia,

7,8

Alzheimer’s disease,

9

and alcohol dependence.

10,11

These changes result in modifications to the cholesterol system, immunological state, or metabolic pathways.

12

The occurrence of changes to serum protein profiles during major depressive disorder (MDD) has not been studied in detail. MDD is a widespread public health problem, but there are still no reliable biological markers for diagnosis and treatment monitoring, and our understanding of

the pathogenesis of this condition and of the mechanisms of action of antidepressants remains incomplete.

13–16

Studies have essentially focused on the mechanisms occurring in the central nervous system, providing evidence of changes to neurogenesis and synaptic plasticity.

17

The levels of some molecules accessible in plasma or serum are known to vary during major depression, and peripheral bio- chemical variations are known to occur during antidepressant treatment.

18

These changes concern several regulatory path- ways that are probably involved in MDD pathogenesis or its consequences

16,19

: energy homeostasis and metabolic disorder molecules, such as leptin and ghrelin;

20

immunity molecules, such as cytokines

21–23

and steroids; neuromediators, such as homovallinic acid

24

and hydroxyindolacetic acid;

25,26

mole- cules involved in neurogenesis or neurotropism, such as brain- derived neurotrophic factor, glial-derived neurotrophic factor, nerve growth factor,

27–30

TrkB,

31

neopterin,

32

nesfatin,

33

and vascular endothelial growth factor.

34

However, these factors have been assessed separately, are difficult to use in practice, particularly due to their lack of specificity, and are involved in pathways that are affected differently in different clinical

Year: 2015 Volume: 6

Running head verso: Girard et al

Running head recto: Serum proteomic analysis in major depression

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contexts. However, serum is a complex biological fluid and its composition is not well known and difficult to determine.

Nevertheless, serum analysis can provide a broad range of information about a subject and a disease. Little is currently known about the occurrence of modifications to serum pro- tein profiles during MDD and antidepressant treatment in humans.

We hypothesized that peripheral molecular modifica- tions occur in relation to symptoms and clinical changes on antidepressant treatment. We therefore investigated the serum protein profiles of subjects with MDD, at the initiation of antidepressant treatment (venlafaxine) (T0) and 4 weeks later (T28), as a function of clinical improvement, and assessed them on the Hamilton Depression Rating Scale (HDRS).

Difference gel electrophoresis in two dimensions (2D-DIGE) and mass spectrometry were used to screen for modifications to the broadest possible spectrum of proteins in the serum.

Several variant proteins of interest were identified and studied further by enzyme-linked immunosorbent assay (ELISA) in controls and in other subjects with MDD treated with various antidepressants and grouped according to clinical improve- ment after treatment.

Methods Population.

Patients with major depression. All subjects admitted to our hospital (Centre Hospitalier Esquirol, Limoges, France) with a major depressive episode, diagnosed on the basis of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) criteria and beginning a new course of anti- depressant treatment, were asked to participate in this study.

All participants were between the ages of 18 and 60 years, had health insurance coverage, and gave written informed con- sent for participation in the study. The referring psychiatrists checked that their patients did not meet the exclusion criteria:

an inability to understand the tests or the French language, an HDRS score  24, the presence of any psychiatric or somatic comorbid condition that might modify serum protein profiles (eg, acute inflammatory disorders, schizophrenia), the use of treatments with potential side effects including the induction of a major depressive episode or the aggravation of its clinical symptoms (antiviral drugs), and menopause or pregnancy in the case of women. The study was approved by the local eth- ics committee (Persons’ Protection Committee from France South-West and Oversea IV). This research complied with the principles of the Declaration of Helsinki.

Depression intensity was evaluated with the HDRS.

35,36

Patients were considered to have responded to treatment if the HDRS score after treatment, at 28 days, was 50% that at baseline or lower.

37

In total, 63 patients were recruited for the study, 24 of whom were excluded due to a revised diagno- sis (7), not following the antidepressant treatment correctly (3), an HDRS score  24 (4), non-attendance of the T28 visit (7), or other reasons (3 patients; eg, incorrect sampling). The

remaining patients, for whom follow-up at 28 days, with the collection of complete data, was possible, were treated with venlafaxine (n = 16), mirtazapine (n = 8), escitalopram (n = 5), citalopram (n = 4), paroxetine (n = 3), fluoxetine (n = 1), sertra- line (n = 1), or duloxetine (n = 1).

Analyses were carried out with serum samples from sub- jects treated with venlafaxine, the most frequently prescribed antidepressant. Five subjects presented a clinical improvement (HDRS T0/HDRS T28 = 2.2 ± 0.58), and six did not (HDRS T0/HDRS T28  = 1.45  ± 0.24). We aimed to carry out the analysis with the participants with the most pronounced pro- files in each clinical subgroup. We therefore retained, for the analysis, the four participants in the group without clinical improvement with the HDRS ratio values closest to 1, and the four participants from the group with clinical improvement with the highest HDRS ratios (  2).

Controls. Control serum samples were obtained from blood donors between the ages of 18 and 60 with no chronic or psychiatric disease, with no medical treatment. The controls agreed to supply a blood sample for research purposes. Whole blood (5 mL) was collected just before the blood donation and was immediately centrifuged. The only data collected for this group were age and sex. An agreement was signed with the French blood transfusion agency for the testing of the blood samples from donors for pathogens and pathological condi- tions after the centrifuging of the samples. Twenty-four con- trols (9 men and 14 women) were matched with the members of the two MDD groups for age and sex. The mean age of the controls was 37.5 ± 9.4 years.

Two-dimensional fluorescence difference gel electro- phoresis (2-D-DIGE) analysis.

Serum preparation. Blood samples were collected from fasting MDD patients. These samples were collected into tubes without additives on the day immediately after admis- sion (T0), corresponding to the start of a new course of antidepressant treatment, and 28 days later (T28). Samples were allowed to clot at room temperature for a minimum of 120 minutes. Serum was then obtained by centrifugation at 900 g for five minutes at room temperature. Aliquots of the serum (0.5 mL) were taken and stored at -40°C until use. The time from collection to freezing did not exceed four hours.

Inhibitors of serine, cysteine, and calpain proteases (10 µL/mL;

GE Healthcare) were added to the serum samples, and ali- quots of 40 µL of serum were then depleted of albumin and G immunoglobulins according to the kit manufacturer’s instructions (Vivapure anti HSA/IgG kit for human albu- min and IgG depletion, Vivascience), subjected to precipi- tation, and desalted (ReadyPrep 2-D Cleanup kit, Bio-Rad Laboratories). Pellets were redissolved in the solubilization buffer (8 M urea/2 M thiourea/4% w/v CHAPS). Protein content was determined with the PlusOne 2D Quant Kit (GE Healthcare).

2-DE and image analysis. The experimental strategy for

2-D DIGE was based on minimal labeling with dye swapping.

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We labeled 50 µg of serum collected on T0 or T28 with Cy3 or Cy5. The internal standard, which was prepared by mixing equal amounts of all samples, was labeled with Cy2. Label- ing reactions were carried out according to the manufactur- er’s instructions. Each sample was labeled with 400 pmol of CyDye (GE Healthcare) by incubation on ice for 30 minutes in the dark, and reactions were stopped by adding 1 µL of 10 mM lysine. The CyDye-labeled samples (sera collected at T0 and T28, and internal standard) were mixed and added to an equal volume of the solubilization buffer (containing 130 mM DTT, 1% v/v IPG buffer, and a trace of bromophenol blue).

Analytical 2-DE was performed as follows: the CyDye- labeled protein samples were focused in the first dimension on IPG 18 cm pH 4–7 gels. The gels were rehydrated at room temperature for 12 hours in a reswelling tray (GE Healthcare), and isoelectric focusing (IEF) was carried out for 89 kVh in the dark. The gel strips were then equilibrated by incubation in 5 mL of equilibration buffer A (50 mM Tris-HCl pH 8.8, 6 M urea, 30% v/v glycerol, 2% w/v SDS, 50 mM DTT) for 15 minutes, with gentle shaking, followed by 5 mL of equili- bration buffer B (50 mM Tris-HCl pH 8.8, 6 M urea, 30% v/v glycerol, 2% w/v SDS, 2.5% w/v iodoacetamide, with a trace of bromophenol blue). The equilibrated strips were loaded on to the top of a 10% polyacrylamide SDS-PAGE gel (24 × 20 cm), which was then sealed with 1% w/v agarose. Separation in the second dimension was carried out in Tris-glycine buffer.

38

After 2-DE, the gels were scanned with a Typhoon TRIO scanner (GE Healthcare), using appropriate filters for the excitation and emission wavelengths of each dye. We obtained sufficient quantities of the proteins from the individual spots for identification by running 450 µg T0 serum and 450 µg of T28 serum separately on 2-DE gels and staining them by a colloidal CBB G-250 procedure.

39

Preparative gels were run in the same electrophoresis conditions and scanned with an Image Scanner II (GE Healthcare).

The images were scanned and the Nonlinear Dynamics Progenesis Samespots software was used for differential gel analysis.

We compared the 2-D images of T0 serum samples with those of T28 serum samples, using the internal standard sample for the group displaying clinical improvement. The final values for the expression ratio of specific protein spots between T0 and T28 serum samples were determined for dif- ferences of ±1.2-fold.

The statistical significance of differences in protein lev- els between the two time points was calculated by applying ANOVA to the log ratio, with an alpha risk of 5% (P    0.05).

Mass spectrometry analysis.

Protein digestion. Protein spots were excised from 2-DE gels stained with Colloidal blue G-250. The excised spots were destained by washing in milliQ distilled water, then dehydrated by incubation in 50 µL of acetonitrile (ACN), and rehydrated by incubation in 50  µL of 100 mM ammonium bicarbonate for 15 minutes at 37°C. An equal volume of ACN

was then added to the mixture, which was incubated for an additional 15 minutes at 37 ° C. Samples were then dried in a Speed Vac. Sequencing-grade modified trypsin was prepared from a 0.1  µ g/ µ L stock solution, by dilution in 25 mM ammo- nium bicarbonate to give a final concentration of 10 ng/µL.

Dehydrated spots were incubated overnight at 37 ° C in 25  µ L of 10 ng/µL trypsin solution (a total of 250 ng per spot). The supernatant was then collected in a 0.5-mL microfuge tube and the digested peptides were extracted sequentially in 50 µL of 40% ACN/1% FA, followed by 10  µ L of 25% ACN/1% FA and, finally, 25  µL of 60% ACN. All the samples were then dried in a Speed Vac.

Mass spectrometry. After trypsin digestion and evapora- tion, the peptides were resolubilized in 6  µ L of Switchos sol- vent (2% ACN, 0.05% TFA) for analysis by nano-LC MS/

MS with a Packings liquid nano-chromatography system (Dionex) coupled to a QTRAP mass spectrometer (Applied Biosystems). We injected 5  µ L of each sample onto a precol- umn (C18 Pepmap 300  µm ID × 5 mm) with the Switchos unit. The precolumn was desalted for three minutes with the Switchos solvent, the precolumn was switched online with the analytical column (C18 Pepmap 75  µ m ID × 150 mm) pre-equilibrated with 100% solvent A (ACN 2%/FA 0.1%).

Peptides were eluted from the precolumn onto the analytical column and then onto the mass spectrometer, with a linear gradient of 0% to 50% of solvent B (90% ACN, 0.1% FA) over 65 minutes, at a flow rate of 300 nL/min.

Data were acquired with the IDA (Information- Dependent Acquisition) software of Analyst 1.4.2 (Applied Biosystems). MS and MS/MS data were recorded continu- ously, with a cycle duration of three seconds. For each MS scan, two precursors were selected for fragmentation on the basis of their intensity (greater than 20,000 cps), their charge state (2 + , 3 + ), and whether the molecule concerned had already been selected for fragmentation (dynamic exclu- sion). The collision energies were adjusted automatically as a function of the charge state and ionic mass of the selected precursors.

Peptide identification. For protein identification, the results of the nano-LC MS/MS analysis were used to search the SwissProt database with Mascot software (version 2.2, Matrix Science) using the following criteria: species Homo sapi- ens (database version 2011_04 containing 20233 sequences), 0.5  Da tolerance for peptide and peptide fragment mass, a single missed cleavage site allowed during trypsin digestion and carbamidomethylation of cysteine residues (due to the alkylation of -SH groups by iodoacetamide), and methionine oxidation as variable modifications. Protein identification was validated if at least two peptides had a score greater than 25, or if one peptide had a score greater than 50 at a confidence level of at least 95%.

Western blotting. For confirmation of the 2D-DIGE

results and of the production of the proteins identified as

differentially expressed, we carried out western blotting for

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three target proteins. We used depleted serum from all eight patients for whom 2D-DIGE analysis was carried out.

The proteins present in serum samples depleted of IgG and albumin were quantified with the Bradford Quick Start Protein Assay (Bio-Rad), by measuring absorbance at 595 nm, with bovine serum albumin (BSA) as the protein standard.

The protein (5 µg) diluted 1/10 in Laemmli buffer (Bio-Rad) or a standard protein mix (Precision Plus Protein Standards, Bio-Rad) was loaded onto a polyacrylamide gel with a 4%

acrylamide stacking gel (Criterion TGX Stain-Free, Any kD, Bio-Rad) and subjected to electrophoresis at 120 V in a Mini Protean 3 electrophoresis system (Bio-Rad) in the presence of Tris/glycine buffer (25 mM Tris, 192 mM glycine, pH 8.3;

Bio-Rad).

The separated proteins were transferred onto poly (vinylidene difluoride) (PVDF) membranes (Bio-Rad) by blot- ting in 25 mM Tris, 192 mM glycine, and 20% (v/v) methanol.

Protein transfer was carried out at 20 V, for 90 minutes, with a Bio-Rad Transblot SD cell (Bio-Rad). Transfer efficiency was evaluated by staining the membranes in Ponceau-S-Red and then destaining in PBS (50 mM sodium phosphate, 0.9% w/v NaCl, pH 7.4). Membranes were blocked by incubation for one hour in 5% w/v fat-free milk powder in PBS containing 0.5% v/v Tween 20, and then incubated overnight at 4°C with the primary antibody diluted in the same buffer: mouse anti- activated C3 1/500, mouse anti-clusterin 1/200, mouse anti- gelsolin 1/200 (Santa Cruz Biotechnology). Membranes were washed with 0.5% (v/v) Tween 20 in PBS, and incubated with a goat peroxidase-conjugated anti-mouse IgG antibody at a dilution of 1/5000 and Precision Protein StrepTactin-HRP conjugate (dilution of 1/20,000) for the lane containing the protein standards, for one hour at room temperature, in 0.5%

(v/v) Tween 20 and 5% (w/v) fat-free milk powder in PBS.

The membrane was washed at least six times in 0.5% (v/v) Tween 20 in PBS, and immunostaining was detected by che- miluminescence (Immun-Star WesternC chemiluminescence kit, Bio-Rad). The membranes were scanned with a GS-800 densitometer (Bio-Rad). Quantification was performed with Image J software (NIH), and immunodetection was carried out twice in each case.

Enzyme-linked immunosorbent assay. ELISA-based validation experiments were carried out with serum samples from the original pilot cohort and from an independent

serum series. The crude nondepleted sera were diluted 1/2000 for clusterin (Quantikine, R&D Systems), 1/1000 for gelsolin and 1/100 for activated complement component 3a (Uscn, Life Science Inc.), each tested twice, in duplicate. All assays were carried out according to the kit manufacturer’s instructions.

Statistical analysis. Quantitative variables are expressed as medians and interquartile ranges because of their non- normal distribution. Qualitative variables are presented as frequencies and percentages. Analyses were performed with Systat software version 11.0 for Windows. Nonparametric Mann–Whitney tests were used to compare protein levels, age, and HDRS scores between groups (clinical improve- ment vs no clinical improvement). The significance of differ- ences between T0 and T28 for each group was determined by carrying out nonparametric Wilcoxon’s signed rank tests.

Spearman’s correlation tests were carried out to assess the cor- relation between HDRS scores and the protein level deter- mined by ELISA.

A P-value of less than 0.05 was considered statistically significant.

Results

Subjects. The mean age of the participants retained for the 2D analysis (7 women and 1 man) was 41.4 ± 5 years and there was no significant difference between the groups (Table 1).

HDRS scores for the group with clinical improvement and the group without clinical improvement were similar at T0 (P = 0.235), whereas these scores differed significantly between these two groups at T28 (P = 0.004) (Table 1).

2D-DIGE analysis of the immunodepleted serum proteome. Differences in the serum protein profiles between T0 and T28 were analyzed in the groups with and without clinical improvement.

We checked the integrity of the serum profiles after depletion, and all serum samples presented the same protein profiles after one-dimensional electrophoresis and colloidal blue staining.

We initially detected 1452 protein spots for both groups.

Image analysis revealed no evidence of differential expression, for any of the proteins, in the group without clinical improve- ment between T0 and T28. By contrast, in the group with clinical improvement, 147 protein spots were considered to

Table 1. age and hdrs scores characteristics of the subjects retained for 2d-dige analysis (n = 8) in a group with clinical improvement (n = 4) and a group without clinical improvement (n = 4).

ALL WITH CLINICAL IMPROVEMENT WITHOUT CLINICAL IMPROVEMENT

age 38.5 [30.1, 44.6] 38.5 [34, 45.5] 36.5 [15.7, 54.3]

hdrs score at t0 25 [26.4, 24.1] 25 [27.6, 22.4] 25.5 [23.4, 27.6]

hdrs score t28 15 [10.8, 20.1] 11 [14.9, 6.6] 20.5 [16.3, 24.2]

Mean % decrease

(hdrs t0/hdrs t28) 41.3 [20.7, 56.8] 56.6 [40.5, 73.5] 16.3 [5.5, 35.5]

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display differential expression. Protein abundance changed by a factor of more than 1.2 between T0 and T28, as shown by Student’s t-tests, for which values of P    0.05, considered sig- nificant, were obtained for 11 spots. Only nine spots were of sufficient intensity to be picked and subjected to MS (Fig. 1).

Identification of the spots identified as differentially expressed by 2D-DIGE. The nine spots of potential interest were picked and analyzed by MS. The identities of these spots are listed in Table 2.

We attributed the presence of the Ig alpha-1 chain C region and haptoglobin to contamination arising from the deple- tion process or from blood collection (possible unnoticed mild hemolysis, for example). The C3 component of complement was found in five of the nine spots. A comparison of the sequence covered by the identified peptides and molecule processing (Fig. 2A) identified these five spots as one of the complement C3 chains obtained after cleavage. These assignments were confirmed by comparing the experimental isoelectric points and molecular weights with the theoretical parameters of the complement C3 component fragments (Fig. 2B). The sequence coverage percentages of the assigned fragments were related to the theoretical C3 fragment sequences rather than the entire protein sequence, providing support for our hypothesis and an explanation of the origin of these experimental fragments.

40

We checked the localization of the other proteins iden- tified on the Swiss-2DPAGE plasma reference gel (http://

world-2dpage.expasy.org/).

The proteins found to be more abundant in T28 sera than in T0 sera (T28/T0 ratio  1.2) were the complement C3 component (C alpha) and gelsolin. The other compounds

identified had a negative ratio (  -1.2): clusterin, other C3 fragments corresponding to cleaved activated C3 (Calpha’ F1 and Calpha’ F2), zinc alpha-2-glycoprotein (Table 2). The C3 alpha subcomponent was more abundant at T28 than at T0, whereas C3c alpha’ F2, C3dg, C3c alpha’ F1, C3dg (all obtained from C3 alpha subcomponent processing) proteins were less abundant at T28 than at T0. All these observations suggest that processing of the complement C3 component, particularly that of the C3 alpha chain, decreased between T0 and T28.

These findings provided some indication of the functional relevance of these proteins. Literature searches revealed that most of the proteins found to display differential expression between T0 and T28 had previously been associated with apoptosis and inflammation processes. On this basis, we selected three proteins of interest for further validation: gelso- lin, clusterin, and the activated fragment of complement C3, as representative of the activation of the C3 component pathway.

Confirmation of protein production. We carried out western blotting on depleted serum samples to check whether the proteins were present. The proteins were separated electro- phoretically and transferred to membranes, which were then probed with antibodies. The results confirmed that all three proteins were present in all serum samples (Fig. 3).

We then carried out ELISA to evaluate protein levels more accurately for DIGE analysis. The changes in protein levels differed between individuals, for all three proteins, in both groups. Serum clusterin concentrations did not change between T0 and T28 in the group with clinical improvement (343 [289; 403] µg/mL to 337 [204; 504] µg/mL), or in that without clinical improvement (508 [223; 920] µg/mL to 440 [327; 521] µg/mL). However, serum clusterin concentration decreased in two of the four subjects in each group (Fig. 4).

Gelsolin levels followed a similar pattern in both groups: from 95 [58; 135] µg/mL to 81 [55; 11] µg/mL for the group without improvement versus 74 [34; 125] µg/mL to 74 [52; 95] µg/mL for the group with improvement. Three subjects with clinical improvement displayed a tendency toward a decrease in C3a levels (60 [41; 78] ng/mL to 55 [20;

89] ng/mL), whereas such a tendency was observed in only one subject in the group without clinical improvement (58 [15;

101] ng/mL at T0 to 62 [21; 106] ng/mL at T28) (Fig. 4).

Protein quantification and clinical improvement.

Analyses were carried out on serum samples not subjected to 2D-DIGE analysis, from subjects treated with various antide- pressants, and classified according to clinical outcome at T28.

Seventeen showed clinical improvement, whereas 14 did not (Table 3).

No differences were found between the clinical groups in terms of age (P = 0.308), sex (P = 0.293), and the type of antidepressant (P = 0.096). HDRS scores were similar in the two groups at T0 (P = 0.131), but they were significantly dif- ferent at T28 (P    0.001) (Table 3), consistent with the clini- cal significance of the group definitions.

Figure 1. representative 2d-dige image of internal standard master labeled with Cy2. Indicated numbers correspond to identified spots (refer to Table 2). 2-DE was performed using a pH range 4–7 in the first dimension and sds-Page (10%) in the second.

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Table 2. List of overlap proteins that were identified using mass spectrometry. SPOTaRATIObEXP pI/MWcACCESS NUMBERdPROTEIN DESCRIPTIONdSCOREeMATCHED PEPTIDESfSEQUENCE COVERAGETHEOR pI/MASSg 1-1.55.51/65920

CO3_hUManComplement C3 Os= homo sapiens gn= C3 Pe= 1 sV= 2(C3cα’ chain fragment 1 + C3dg fragment)7342344%5.45/62477 igha1_hUManig alpha-1 chain C region Os= homo sapiens gn= igha1 Pe= 1 sV = 2297514%6.08/37631 2-1.54.80/41240CO3_hUManComplement C3 Os= homo sapiens gn= C3 Pe= 1 sV= 2(C3dg fragment)372931%5/38905 ClUs_hUManClusterin Os= homo sapiens gn= ClU Pe= 1 sV = 1164510%5.89/52461 3-1.55.45/132880igha1_hUManig alpha-1 chain C region Os= homo sapiens gn= igha1 Pe= 1 sV = 29027%6.08/37631 41.26.08/91620gels_hUMangelsolin Os= homo sapiens gn= gsn Pe= 1 sV = 15921825%5.90/85644 51.45.79/118280CO3_hUManComplement C3 Os= homo sapiens gn= C3 Pe= 1 sV= 2(C3α chain)21086464%5.55/113028 61.26.14/91620gels_hUMangelsolin Os= homo sapiens gn= gsn Pe= 1 sV = 121169%5.9/85644 71.35.39/33050Not identified 8-1.44.67/43180

CO3_hUManComplement C3 Os= homo sapiens gn= C3 Pe= 1 sV= 2(C3cα’ chain fragment 2)5571946%4.79/38488 Za2g_hUManZinc-alpha-2-glycoprotein Os= homo sapiens gn= aZgP1 Pe= 1 sV = 2149529%5.71/34237 ClUs_hUManClusterin Os = homo sapiens gn = ClU Pe = 1 sV = 1147311%5.89/52461 9–1.54.67/44910

CO3_hUManComplement C3 Os= homo sapiens gn = C3 Pe = 1 sV = 2(C3cα’ chain fragment 2)8923161%4.79/39488 Za2g_hUManZinc-alpha-2-glycoprotein Os = homo sapiens gn = aZgP1 Pe = 1 sV = 23451242%5.71/34237 hPt_hUManhaptoglobin Os = homo sapiens gn = hP Pe = 1 sV = 1123414%6.13/45177 Notes:aspot number refers to numbering in Figure 1. bratio refers to the ratio of normalized spot intensities of t0 and t28 sera. a positive ratio indicates overexpression in t28 sera, whereas a negative ratio indicates a reduced expression in t28 sera. cexperimental isoelectric point and molecular weight (da). daccession numbers of proteins and protein description from swiss-Prot databases. eMascot score for the identified proteins based on the peptide ion score with a confidence level of at least 95% (http://www.matrixscience.com). fnumber of peptides that match with the protein sequence. gtheoretical isoelectric point and molecular weight obtained from swiss-Prot and the exPasy databases (http://www.expasy.org).

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Complement C3 processing Positions pI MW (kDa)

C3 23–1663 6.00 184.9

C3 β chain 23–667 6.82 71.3

C3 α chain 672–1663 5.55 113

C3a anaphylatoxin 672–748 9.69 9.1

C3b α’ chain 749–1663 5.18 103.9

C3f fragment 1304–1320 10.83 2.0

C3c α’ chain fragment 1 749–954 6.79 39.5

C3dg fragment 955–1303 5.00 38.9

C3c α’F1 + C3dg 749–1303 5.45 62.5

C3c α’ chain fragment 2 1321–1663 6.89 23.6

B

Figure 2. (A) Cascade of human complement component C3 cleavages and the resulting chains and fragments. The disulfide bridges are indicated between chains. (B) isoelectric point (pi) and molecular weight (MW) associated to the complement C3 processing.

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Figure 3. immunodetection by chemiluminescence of depleted sera with (A) anti-clusterin antibodies, (B) anti-gelsolin antibodies, and (C) anti-activated C3 antibodies.

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A

2 1

1 2

2 1

B

C

1000 900 800 700

140 120 100 80 60 40 20 0

140 120 100 80 60 40 20 0 120 100 80 60 40 20 0 600

500 400 300 200 100

T0 T28 T0 T28

T0 T28 T0 T28

T0 T28 T0 T28

0

1000 900 800 700 600 500 400 300 200 100 0

1000 900 800 700 600 500 400 300 200 100 0

Figure 4. levels of (A) clusterin, (B) gelsolin, and (C) C3a at t0 and t28 in each sera of venlafaxine-treated Mdd subjects submitted to 2d-dige analysis. 1. subjects without clinical improvement (n = 4). 2. subjects with clinical improvement (n = 4).

No change between T0 and T28 was observed for serum concentrations of clusterin, gelsolin, or C3a in the whole MDD group or in the group without clinical improvement.

In the group with clinical improvement, a very slight trend toward a change in these concentrations was observed for gel- solin, but not for clusterin. Only C3a levels differed between T0 and T28 in this group (Table 4).

There were no differences between the two groups of MDD subjects in terms of serum C3a, gelsolin, or clus- terin concentrations either at T0 (P  =  0.905, 0.311, and 0.552, respectively) or at T28 (P  =  0.105, 0.868, and 0.430, respectively).

The T28/T0 concentration ratio did not differ between groups (P  = 0.868 for clusterin, P  = 0.183 for gelsolin, and =  0.212 for C3a).

The number of participants with a T28/T0 ratio 

 1.2  did not differ, according to the presence or absence of clin- ical improvement, for clusterin (P = 0.818), C3a (P = 0.431), or gelsolin, despite a slight trend (P  =  0.063). However, the T28/

T0 ratio differed from 1, indicating a change between T0 and T28 for C3a (P  =  0.025) and gelsolin (P  =  0.003), only in the group with clinical improvement.

The controls and the group without clinical improvement

tended to have different C3a levels at T0 (P = 0.061), but not at

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Table 3. Characteristics of the controls, the whole Md group, and the subgroups with or without clinical improvement (median [interquartile ranges]).

CONTROLS (n = 24) ALL (n = 31) MD SUBJECTS WITHOUT CLINICAL

IMPROVEMENT (n = 14) WITH CLINICAL IMPROVEMENT (n = 17)

age (years) 38 [35.3; 43.1] 43.5 [37.9; 45.6] 43.5 [36.8; 44.8] 43 [35.9; 49.3]

sex ratio (male/female) 10/14 12/19 4/10 8/9

hdrs score

t0 – 25 [23.2; 26.5] 24 [19.8; 25.9] 25 [24.8; 28.2]

t28 – 15 [13.6; 16.7] 18 [17.1; 20.5] 12 [10.3; 13.5]

t28/t0 – 0.6 [0.537; 0.720] 0.407 [0.272; 0.515] 0.6 [0.496; 0.871]

Table 4. Median serum concentrations and interquartile ranges at t0 and t28 for C3a, gelsolin, and clusterin, in controls, the whole group of Mdd subjects, and the groups of patients with and without clinical improvement after 28 days of antidepressant treatment.

T0 T28 T28/T0 NUMBER WITH T28/T0 │1.2│ P*

Controls (n = 24)

Clusterin 304 [295; 391] – – –

gelsolin 50 [44; 65] – – –

C3a 44 [38; 50] – – –

Md subjects (n = 31) all

Clusterin 309 [290; 366] 296 [286; 362] 1.020 [0.927; 1.120] 7 0.644

gelsolin 38 [29; 55] 43 [37; 59] 1.155 [0.980; 2.145] 14 0.271

C3a 60 [53; 73] 71 [61; 86] 1.120 [1.006; 1.487] 13 0.199

Without clinical improvement (n = 14)

Clusterin 311 [264; 353] 290 [261; 335] 1.013 [0.875; 1.127] 3 0.975

gelsolin 41 [23; 78] 45 [30; 61] 0.900 [0.741; 1.461] 4 0.73

C3a 58 [45; 86] 56 [46; 81] 1.002 [0.837; 1.286] 5 0.778

With clinical improvement (n = 17)

Clusterin 309 [282; 406] 310 [280; 412] 1.020 [0.886; 1.200] 4 0.535

gelsolin 27 [25; 44] 40 [34; 68] 1.369 [0.902; 3.032] 10 0.098

C3a 61 [51; 71] 79 [63; 101] 1.243 [0.993; 1.825] 8 0.049

Note: *Probability for a difference between t0 and t28.

T28 (P = 0.109). Their gelsolin concentrations differed at T0 (P = 0.046) and at T28 (P = 0.049).

The controls and the group with clinical improvement had different C3a levels at T0 (P = 0.004) and T28 (P    0.001), suggesting a trend toward a decrease in these levels during MDD, potentially due to modifications on successful antide- pressant treatment. These two groups had different gelsolin concentrations at T0 (P = 0.005), but not at T28 (P = 0.269), indicating a trend toward a decrease in gelsolin levels in MDD subjects, with these concentrations approaching those of the controls after successful antidepressant treatment (Table 4).

No correlation was observed between HDRS score and the concentration of any of the compounds considered at either T0 or T28.

Discussion

In this pilot study, we used 2D-DIGE to investigate differ- ences in the protein profiles of sera from MDD subjects before and after 28 days of antidepressant treatment, and confirmed some of the results with ELISA. Our observations suggest that several changes in serum concentrations were associated with the clinical relevance of the treatment rather than the precise type of antidepressant prescribed.

The use of 2D-DIGE for comparisons of the proteome

before and after antidepressant treatment revealed a number

of proteins for which changes in levels during treatment dif-

fered between the two groups (those with and without clini-

cal improvement). The changes in serum protein profiles were

analyzed further by mass spectrometry identification of the

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protein spots for which changes in intensity were observed during treatment. The nine compounds identified suggested the involvement of molecular and cellular pathways related to general homeostasis in MDD. The immunoglobulin alpha 1 chain is involved in immune function, constituting the major class of immunoglobulins in bodily secretions. It is involved in the primary immune response. Haptoglobin was also identified as a variant spot. Both these spots were thought to be associated with possible sample contamination.

The function of zinc alpha 2 glycoprotein is not well charac- terized. This protein has been implicated in cancer mecha- nisms and lipid mobilization, and it may also be involved in the immune system.

41

Clusterin has been implicated in several physiological processes, such as the inhibition of plasma protein aggregation, cellular proteasome-based detoxification, apoptosis, and age- related processes and diseases

42

including neurodegeneration in Alzheimer’s disease

43,44

and Parkinson’s disease.

45

It has been suggested that the role of this molecule depends on the isoform expressed and that its subcellular distribution may reflect the level of oxidative stress in the organism.

42

Gelsolin is an essential regulator of cell structure and metabolism involved in immune functions, apoptosis mecha- nisms, and aging. Blood gelsolin concentrations decrease in various clinical conditions, including acute respiratory dis- tress syndrome, sepsis, major trauma, prolonged hyperoxia, malaria, and liver injury.

46

The identification of several compounds associated with the C3 activation pathway provided support for the involvement of this pathway in the changes occurring between T0 and T28 in the group displaying clinical improvement.

The direction of change in the concentrations of the various C3 compounds was consistent with the positions of these mol- ecules on either side of the C3 component cleavage cascade.

Our results suggested a decrease in C3 activation, which plays a key role in inflammation.

47

C3 plays a key role in comple- ment system activation, with C3 activation required for both the classical and alternative complement activation pathways.

The activation of different complement proteins would induce the production of C3 convertase, catalyzing the splitting of C3 into C3a (in the blood) and C3b. This enzyme binds to the membrane of the cell to be lysed, forming the C5 convertase complex. Each cleavage in the complement cascade releases small fragments (C4a, C3a, and C2b) acting on inflamma- tory cells. The C3 pathway has been associated with MDD in murine models of depression,

48,49

and its activation has already been reported in subjects with MDD.

50,51

The demonstration of changes in the concentrations of these proteins with clinical improvement in patients on anti- depressant treatment is consistent with several hypotheses concerning the role of the immune system,

52,53

apopto- sis, and oxidative stress in the pathogenesis of MDD.

54–56

Similarly, 2D-DIGE and mass spectrometry analyses of the hippocampus in the rat model of depression demonstrated

changes in the levels of proteins associated with neurogenesis, cellular localization and transport, cytoskeleton organization, and apoptosis.

57,58

Serum proteomic analysis also led to the identification of peripheral proteins involved in inflamma- tion and transport proteins as associated with stress and the response to antidepressants in rats.

49,57

A key finding of this study was the association of the change in protein levels with clinical improvement and symp- toms rather than with the type of antidepressant treatment, as previously reported for the change in cytokine profiles during electroconvulsive therapy.

59

Further validation of our results with ELISA confirmed the 2D-DIGE observations and the trends observed for the C3a component. The differences in protein levels between T0 and T28 were not confirmed with a larger sample of serum samples from MDD subjects on antidepressant treatment. The 2D-DIGE analysis detected changes only in the group with clinical improve- ment: an increase in gelsolin synthesis and a decrease in the syn- thesis of clusterin. However, this technique is based on the use of antibodies recognizing specific epitopes, not necessarily corre- sponding to those carried by the isoform identified in 2D-DIGE analysis. Indeed, several proteins may have isoforms that cannot be differentiated in 2D-DIGE analysis and are differentially rec- ognized by the antibodies used in ELISA. This may be a crucial issue for clusterin, as this protein has several isoforms with very different roles.

60

The use of specific antibodies in ELISA, not necessarily recognizing the various potential isoforms of the pro- teins in 2D-DIGE, may account for the discrepant observations for gelsolin and clusterin. For C3a, we chose to focus on a single compound from the C3 activation pathway, thereby decreasing the potential risk of not using the most appropriate antibody for detection. Furthermore, the range of concentrations of this com- pound made it easier to detect and follow.

ELISA yielded interesting results for comparisons of serum samples from MDD patients with those of controls.

Gelsolin levels in MDD patients differed from those in con- trols before antidepressant treatment, whether or not clinical improvement subsequently occurred. Differences between MDD patients and controls after treatment were restricted to the group of participants displaying no clinical improve- ment. This suggests that the clinical normalization associ- ated with the improvement in MDD is accompanied by a similar normalization of gelsolin concentration. The profile of change in C3a concentration suggests that the C3 path- way is altered during MDD but tends to be influenced by antidepressant treatment, particularly in cases of clinical improvement.

The absence of a correlation between the levels of the

biological compounds and MDD intensity, as evaluated with

the HDRS, suggests only that there is no direct quantitative

link between the variables. The relationship between changes

in symptoms and concomitant biological changes may involve

other intermediate molecules, or a shift in time, depending on

the time of data collection.

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This study is subject to several limitations. The number of samples studied was small, but we believe that this limitation is offset by the similarity of clinical characteristics between the groups at T0, the similarity of characteristics within groups at T28, and the difference in clinical characteristics between groups at T28. This made it possible to identify changes occurring between T0 and T28, which were com- mon to the patients in one group but not those in the other group. However, replication of these results is required. The 2D-DIGE results must be interpreted with caution because they were obtained with only a small number of serum samples and specific electrophoretic parameters. Proteomic analyses on serum samples are difficult, because 98% of the total mass of protein in the serum corresponds to only about 15 proteins. Even after depletion of the most abundant serum proteins (albumin, immunoglobulins), analysis and identifica- tion of the remaining 2% of proteins of interest remain chal- lenging. The electrical and biochemical conditions used here for protein separation (pH range for isoelectric separation, molecular weight range for gel electrophoresis, etc) are spe- cific to our study, and the observed changes in serum protein levels may not be limited to the proteins identified here. The use of other technical characteristics for protein isolation and preanalytic serum preparation might well lead to the defini- tion of other protein profiles.

In the study design used here, clinical improvement was evaluated at 4 weeks, because we aimed to identify early mark- ers of clinical improvement. However, antidepressant treatment is usually considered effective at 6 weeks, and there is therefore a risk that our sample evaluation was carried out too early to detect clinical improvement in some cases. This may have led to misclassification errors, decreasing the efficacy of marker identification. It was for this reason that we chose to study the subjects presenting the most extreme changes in HDRS score in 2D-DIGE experiment, to maximize the probability of detecting the presence or absence of clinical improvement with a high degree of confidence. However, further exploration at 6 weeks of treatment or after other durations of treatment would be of interest for further validation and exploration.

MDD subjects and controls should also be compared on the basis of samples obtained from different groups in the same conditions. The pattern of intraindividual variation in gelsolin, clusterin, and C3a concentrations is not well known, and diurnal variations are therefore possible. The exclusion of any subject presenting a somatic disorder decreases the like- lihood of serum level variations independent of the param- eters studied here. However, a comparison with control serum concentrations over a 28-day period would provide a more reliable reference.

Despite these limitations and the difficulties involved in determining the superiority of the results obtained with the various protein analysis techniques used here, we consider the results obtained here to implicate gelsolin and the C3 path- way directly or indirectly in MDD. These results therefore

help improve our understanding of the pathophysiological mechanisms underlying MDD. However, given their lack of specificity, the reliability of these results and their true contribution to our understanding of MDD pathology and treatment outcome remain to be confirmed, and further inves- tigations are required with other technical approaches, larger samples, and different clinical designs.

1,2

Conclusion

This study generated contrasting results, which must there- fore be interpreted with caution. However, several key points can be made. First, our findings suggest that protein levels in the serum of subjects with MDD change if clinical improve- ment occurs during antidepressant treatment, suggesting that peripheral modifications may reflect clinical changes rather than being associated purely with treatment. Second, the nature of the proteins displaying a change in abundance identified here may be relevant, indicating changes to general pathways worthy of further study and potentially serving as targets for future therapeutic approaches.

Author Contributions

Conceived and designed the experiments: MG. Analyzed the data: MG. Wrote the first draft of the manuscript: MG. Con- tributed to the writing of the manuscript: KV, EP, DM. Agree with manuscript results and conclusions: MG, DM, KV, EP, BB, BP. Jointly developed the structure and arguments for the paper: MG, DM. Made critical revisions and approved final version: MG, KVD, EP, BB, DM. All authors reviewed and approved of the final manuscript.

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