Research report

Serum Brain-derived neurotrophic factor levels inpost-stroke depression

Jie Li a, Yan-Dong Zhao b, Jun-Wei Zeng c, Xiao-Yan Chen a, Ruo-Dan Wang a, Sai-Yu Cheng a,n

a Department of Neurology, Second Affiliated Hospital and Xin Qiao Hospital, Third Military Medical University, Chongqing 400037, Chinab Department of Neurobiology, College of Basic Medical Sciences, Chongqing Key Laboratory of Neurobiology, Third Military Medical University, Chongqing400038, Chinac Department of Physiology, Zunyi Medical College, Zunyi, Guizhou province 563000, China

a r t i c l e i n f o

Article history:Received 1 June 2014Received in revised form6 July 2014Accepted 7 July 2014Available online 18 July 2014

Keywords:Brain-derived neurotrophic factorDepressionAcute ischemic strokeChinese

a b s t r a c t

Background: Depression is a frequent mood disorder that affects around a third of stroke patients andhas been associated with poorer outcome. Our aim was to determine whether there is a relationshipbetween serum Brain-derived neurotrophic factor (BDNF) levels and post-stroke depression (PSD).Methods: Two hundred and sixteen ischemic stroke patients admitted to the hospital within the first24 h after stroke onset were consecutively recruited and followed up for 3 months. Based on thesymptoms, diagnoses of depression were made in accordance with DSM-IV criteria for post-strokedepression at day 90. Enzyme-linked immunosorbent assay (ELISA) was used to measure serum levels ofBDNF at admission. Multivariate analyses were performed using logistic regression models.Results: In our study, 59 patients (27.3%) were diagnosed as having major depression at 3 months.Patients with major depression showed lower levels of serum BDNF [8.1 (5.6–9.4) vs. 13.7 (10.4–16.5)ng/ml, Po0.0001] at admission. In multivariate analyses, serum BDNF was an independent predictor of PSDat 3 months [odds ratio (OR): 0.79(0.72–0.87), P¼0.003]. Serum levels of BDNFr10.2 ng/ml wereindependently associated with post-stroke (OR, 11.5; 95% CI, 5.6–23.4, Po0.0001), after adjustment forpossible variables.Conclusion: The present study demonstrates a strong relationship between serum BDNF levels atadmission and the development of PSD within 3 months. Further studies are necessary to confirm thisassociation, which may open the way to the proposal of new therapeutic options.

& 2014 Elsevier B.V. All rights reserved.

1. Introduction

Depression is particularly prevalent among stroke survivors,affecting approximately a third of individuals (Lindén et al., 2007).Patients with depression experience worse stroke-related outcomesin the form of greater functional disability and higher mortality(Ellis et al., 2010), and, finally, with worse rehabilitation outcome.Early recognition of depression symptoms and introduction ofpharmacological treatment could lead to better functional outcome(Zavoreo et al., 2009), making the prevention and management ofpost-stroke depression an important area of research.

Neurotrophins are an important class of signaling molecules inthe brain responsible for axon targeting, neuron growth, matura-tion of synapses during development, and synaptic plasticity(Autry and Monteggia., 2012). Brain-derived neurotrophic factor(BDNF) is a neurotrophin that has been linked to the viability of

neurons in brain circuits (Molendijk et al., 2011). In addition to itsimportance in learning, studies have revealed BDNF's involvementin cognition as well as mood-related behaviors (Autry andMonteggia., 2012).

One study found that some BDNF gene polymorphisms may becontributing factors in the pathogenesis of bipolar disorder (Searset al., 2011), and several studies reported that blood levels of BDNFwere reduced in patients with schizophrenia (Green et al., 2011).Recent evidence supports ‘the neurotrophin hypothesis of depres-sion’ in its prediction that BDNF is involved in depression (Taliaz etal., 2010). Several works have demonstrated decreased levels indepressed patients and a recovery after antidepressants treatment(Gazal et al., 2012; Zhou et al., 2011).

It was reported that BDNF could cross the blood–brain barrier, andthat BDNF levels in the brain and serum underwent similar changesduring the maturation and aging processes in rats, suggesting thatserum BDNF levels may reflect BDNF levels in the brain (Hashimoto,2010). Pikula et al. (2013) found that lower serum BDNF wereassociated with increased risk of incident stroke/TIA, and higher levelsof BDNF were also associated with less white matter hyperintensity

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Journal of Affective Disorders

http://dx.doi.org/10.1016/j.jad.2014.07.0110165-0327/& 2014 Elsevier B.V. All rights reserved.

n Corresponding author. Tel.: þ86 23 68755613.E-mail address: cqpek1949@163.com (S.-Y. Cheng).

Journal of Affective Disorders 168 (2014) 373–379

and better visual memory. Kim et al. (2008) reported that the BDNFval66met polymorphism may modify the association between strokeand depression. Thus, the role of BDNF in patients with stroke anddepression excited our interest. In a large cohort, Kim et al. (2012)found evidence for serotonin and BDNF polymorphisms as suscept-ibility factors and gene–gene interactions between these systems fordepression at 2 weeks post-stroke. Interestingly, there is rare study onserum BDNF levels in Chinese patients with post-stroke depression(PSD). One study reported that serum concentrations of BDNFdecrease in Chinese PSD patients and BDNF may play an importantrole in the pathogenesis of PSD. However, only 93 patients wereincluded (Zhou et al. 2011). Therefore, our aim was to determinewhether there is a relationship between serum BDNF and PSD in alarge cohort.

2. Methods

2.1. Study population

Two hundred and ninety-five patients with a first episode ofacute ischemic stroke admitted to our hospital within the first 24 hof stroke onset were prospectively included in the study. Patientswith subarachnoid or intracranial hemorrhage, decreased level ofconsciousness, severe aphasia or dysarthria, or psychiatric illness,severe infectious or inflammatory diseases, and life expectancyo3month were excluded. One hundred and sixty out of 295 patients(54.2%) were male, with a mean age of 68.9711.3 years. Seventy-nine patients were not evaluated at 3 month (38 patients died and12 refused to attend the follow-up, 10 patients had difficulty inbeing transported to hospital, and 19 patients were lost to follow-up); the remaining 216 patients were valid for analysis.

Informed consent was obtained after having provided verbaland written information to participants or nearest relatives whenrelevant. Ethics approval was granted by The Ethics Committee forMedical Research at the Xin Qiao Hospital, Third Military MedicalUniversity.

2.2. Clinical variables

At baseline, age, sex, body mass index and history of risk factorswere obtained. Stroke subtype was classified according to TOAST(Trial of ORG 10172 in Acute Stroke Treatment) criteria (Adams etal., 1993). Routine blood and biochemical tests, brain CT/MRI scanwere performed in all patients at admission. MRI with diffusion-weighted imaging (DWI) was available in some patients. Theinfarct volume was calculated by using the formula 0.5� a�b� c(Sims et al., 2009). Stroke severity was evaluated by trainedneurologists using the NIHSS at admission (Brott et al., 1989).Functional outcome was evaluated by the modified Rankin Scale(mRS) at 3 month (Bonita, 1988). A favorable functional outcomewas defined as an mRS score of 0 to 2 points, while an unfavorablefunctional outcome was defined as an mRS score of 3 to 6 points.

2.3. Psychological measurement

Depression assessments were conducted by a neurologist/psychiatrist who was unaware of the type, size and location ofthe index stroke at the time of 3 months after stroke onset.Previous history of psychiatric disease and depression, educationallevel and people living with the patient were recorded at admis-sion. Patients should finish the Hamilton Rating Scale for Depression(HAM-D) at 3 months follow-up (Hamilton., 1960). Clinical depres-sion was diagnosed according to DSM-III-R criteria using algo-rithms based on psychiatric interview and neuropsychiatric

examination. The presence of anhedonia and depressive moodwas essential for the diagnosis.

2.4. Laboratory tests

Fasting venous blood was collected from all participants invacutainer tubes and quickly centrifuged to avoid glycolysis.Serum samples were kept at �80 1C until assay. Biomarkerconcentrations were measured in a central laboratory by investi-gators blinded to the clinical outcome and neuroimaging findings.BDNF serum levels were measured with sandwich-ELISA, using acommercial kit according to the manufacturer instructions(DuoSet ELISA Development, R&D Systems, Inc., USA). The lowerdetection limit was 1.6 ng/ml and the line range was 1.6–50 ng/ml.The intra-assay coefficient of variation [CV] and inter-assayCV were 3.5–6.8% and 4.4%–7.5%, respectively.

2.5. Statistical analyses

The results are expressed as percentages for categorical vari-ables and as mean (standard deviation, S.D.) or median (inter-quartile range, IQR) for the continuous variables depending ontheir normal distribution. Shapiro–Wilk tests were used fornormal distribution test. Proportions were compared using theChi-square test. Two-group comparison of not normally distrib-uted data was performed using Mann–Whitney U test, and a two-tailed Student's unpaired t-test was used for normally distributedcontinuous variables. Spearman's Rank correlation was usedfor bivariate correlations. Associations between the severityof depression evaluated by HAM-D scale and the serum levels ofBDNF were also assessed by using ordered logistic regressionmodels with multivariate adjustment for possible confounders,for instance, age, sex, body mass index, stroke syndrome, strokeetiology, the NIHSS score, infarct volume, vascular risk factors anda history of depression. The influence of serum BDNF levels on PSDwas performed by binary logistic regression analysis, which allowsadjustment for above confounding factors. The results areexpressed as adjusted odds ratios (ORs) with the corresponding95% confidence intervals (CIs). Receiver operating characteristic(ROC) curves were utilized to evaluate the accuracy of serum BDNFto predict PSD. Area under the curve (AUC) was calculated asmeasurements of the accuracy of the test. All statistical analysiswas performed with SPSS for Windows, version 19.0 (SPSS Inc.,Chicago, IL, USA). Statistical significance was defined as Po0.05.

3. Results

3.1. Baseline characteristics of study samples

The study cohort consisted of 295 patients at baseline (strokeadmission). By the time of follow-up at 3 months, leaving 216individuals were included in our study. However, these 216patients were similar in terms of baseline characteristics [age(P¼0.632), gender (P¼0.803), NIHSS (P¼0.654) and weight(P¼0.723)] compared to the overall cohort. In the study popula-tion, 45.8% were females and the average age was 66.5710.2years. The median (quartiles) NIHSS score on admission was 6 (3,12), and the median time from symptom recognition to admissionto hospital was 4.8 h (IQR, 2.4–7.5). The number of tissue plasmi-nogen activator-treated patients was 65 (30.1%).

3.2. Main findings

Ninety-four patients (43.5%) showed depression (major andminor) at 3 months after admission and in 59 patients (27.3%) this

J. Li et al. / Journal of Affective Disorders 168 (2014) 373–379374

depression was classified as major. The baseline characteristics of216 stroke patients presented with depression or not are describedin Table 1. Patients with depression were older and more fre-quently were female, living with offspring, widowhood, higheradmission stroke severity, higher serum levels of Hs-CRP andlower BDNF. No association was found between etiological subtypeor infarct volume and the presence of depression. Similarly, if theminor depression were included, we got the equal conclusion.

The results indicated that the median serum BDNF level was12.4 (IQR, 8.7–15.5) ng/ml. The serum BDNF levels were signifi-cantly decreased in PSD patients at the time of admission ascompared with stroke patients without depression [8.1 (IQR, 5.6–9.4) ng/ml and 13.7 (IQR, 10.4–16.5) ng/ml, respectively;Po0.0001], Fig. 1a. Similarly, if the minor depression wereincluded, we also found that serum BDNF levels were significantlydecreased in PSD patients [9.3 (IQR, 7.2–12.5) ng/ml and 14.5 (IQR,11.2–17.4) ng/ml, respectively; Po0.0001], Fig. 1b. Serum BDNFlevels decreased with increasing severity of stroke as defined bythe NIHSS score. There was a negative correlation between levelsof BDNF and the NIHSS (r¼�0.286, Po0.0001; Fig. 2a.). Similarly,the lower serum BDNF levels at admission corresponded to thehigher HAM-D score at 3 months (r¼�0.361, Po0.0001; Fig. 2b).BDNF was still significantly associated with HAM-D score(β¼�0.304, P¼0.009), after controlling for age, gender, bodymass index, stroke etiology, the NIHSS score, infarct volume,vascular risk factors and a history of depression. In addition, therewas no correlation between level of BDNF and sex (P¼0.211), andage (P¼0.326).

Based on ROC curves, the optimal cutoff value of serum BDNFlevels at admission which predicted the development of depres-sion at 3 months was 10.2 ng/ml, which yielded the highestsensitivity and specificity [80.3% and 81.8%, respectively; areaunder the curve (AUC) ¼0.854, 95% CI: 0.791–0.917; Po0.0001].See Fig. 3a. BDNF levels had a higher prognostic accuracy ascompared to Hs-CRP [AUC 0.58 (0.47–0.65), P¼0.013], HCY [AUC0.69 (0.51–0.82), P¼0.008] and NIHSS score at admission [AUC

0.66 (0.54–0.77), P¼0.007]. In logistic regression analysis, BDNFlevels at admission were independently associated with depres-sion (OR, 0.79; 95% CI, 0.72–0.87, P¼0.003) after adjustment forage, gender, widowhood, living with offspring, NIHSS on admis-sion, serum levels of HS-CRP and HCY. See Table 2. Serum levels ofBDNFr10.2 ng/ml were independently associated with post-stroke (OR, 11.5; 95% CI, 5.6–23.4, Po0.0001), after adjustmentfor above variables.

Again, if the minor depression were included, we have pro-duced similar results. Based on ROC curves, the optimal cutoffvalue of 11.5 ng/ml, which yielded the highest sensitivity andspecificity [73.2% and 70.7%, respectively; area under the curve(AUC) ¼0.780, 95% CI: 0.717–0.843; Po0.0001]. See Fig. 3b. Inlogistic regression analysis, BDNF levels at admission were inde-pendently associated with depression (OR, 0.85; 95% CI, 0.76–0.93,P¼0.006) after adjustment for age, gender, widowhood, livingwith offspring, NIHSS on admission, serum levels of HS-CRP andHCY. See Table 3. Serum levels of BDNFr11.5 ng/ml were inde-pendently associated with post-stroke (OR, 6.93; 95% CI, 3.89–12.31, Po0.0001), after adjustment for above variables.

4. Discussion

Largely in accord with previous findings and with the neurotrophinhypothesis of depression (Autry and Monteggia., 2012; Molendijk etal., 2011; Hashimoto., 2010; Shimizu et al., 2003), our data showed thatserum BDNF levels were low in PSD patients compared with strokepatients without depression. Our results mainly suggested that serumBDNF level was a powerful biological marker of risk of developingpost-stroke major depression at 3 month after adjustment by vari-ables, and serum BDNF levelsr10.2 ng/ml were associated with 11.5-fold increase in risk of post-stroke depression. Similarly, Yang et al.(2011) reported that serum BDNF on day 1 after admission maypredict the risk of subsequent PSD, and serum BDNF o 5.86 ng/mlwas independently associated with incident PSD at the acute stage of

Table 1Basal characteristic of stroke patients with depression and no depression.

Baseline characteristics Depression patients (n¼59) No depression (n¼157) Pa

Age (years), mean(SD) 72.8 (11.2) 63.6 (9.1) 0.024Female sex, % 59.3 40.8 0.015BMI(kg m�2, IQR) 26.5 (22.8–28.5) 27.2 (23.0–29.2) 0.214Hypertension, % 49.2 51.6 0.762Diabetes at baseline, % 32.2 29.3 0.624Days of hospitalization, median (IQR) 14 (7–18) 13 (6–18) 0.627Admission median NIHSS score (IQR) 8 (4–14) 5 (2–8) 0.011mRS at follow-up, median (IQR) 3 (1–3) 2 (1–3) 0.221Infarct volume (ml), mean(SD) 12.5 (1.6) 12.2 (1.5) 0.424Widowhood (%) 40.7 19.7 0.002Living with offspring (%) 32.2 12.1 0.001Family history of depression, % 13.6 5.7 0.085TOAST classification (%) 0.126

a. Large artery 15.3 19.1 –

b. Small artery 16.9 22.3 –

c. Cardioembolism 33.9 38.2 –

d. Other cause 18.6 10.8 –

e. Unknown 15.3 9.6 –

Laboratory findings (Median, IQR)White cell count, �109/L 7.8 (5.9–8.6) 7.6 (5.5–8.4) 0.512Glucose level, mmol/L 5.45 (4.79–6.52) 5.39 (4.85–6.55) 0.242Hs-CRP, mg/dL 0.80 (0.35–1.88) 0.55 (0.26–1.26) 0.013HCY, umol/L 18.2 (14,3–23.4) 14.9 (11.8–17.8) 0.008BDNF, ng/ml 8.1 (5.6–9.4) 13.7 (10.4–16.5) o0.0001

Results are expressed as percentages or as medians (IQR) and means (SD).IQR: interquartile range; SD: standard deviation; Hs-CRP: high-sensitivity C-reactive protein; HCY: homocysteine; BMI: body mass index; BDNF: brain-derived neurotrophicfactor; TOAST: Trial of ORG 10172 in Acute Stroke Treatment; mRS: modified Rankin Scale; NIHSS: National Institutes of Health Stroke Scale.

a Mann–Whitney U test, student's t test or chi-square test were used.

J. Li et al. / Journal of Affective Disorders 168 (2014) 373–379 375

stroke (OR ¼ 28.992; 95% CI, 8.014–104.891; po 0.001 after adjust-ment). Thus, it may open the way to the proposal of new therapeuticoptions in patients with ischemic stroke. In addition, our results alsoindicated a significant negative correlation between HAM-D score, theseverity of depressive symptoms, and serum BDNF levels. Severalstudies showed a negative correlation between BDNF levels andseverity of depressive symptoms (Shimizu et al., 2003).

The prevalence of PSD varies over time with an apparent peak 3–6months after stroke with a range of 9–34% during this time-frame andsubsequently decline reaching about 50% of the initial rates at one year(Whyte and Mulsant., 2002). In our study, we found that 27.3% ofstroke patients were classified as major depression at 3 month, whilethe depression prevalence was reported to be ranging from 17 to 62.2%among Chinese stroke patients (Zhang et al., 2010; Tang et al., 2004;Cheng et al., 2014). In addition, low circulating BDNF concentrationshave been observed in patients with coronary artery disease, type2 diabetes mellitus, metabolic syndrome, stroke and physical inactivity(Autry andMonteggia., 2012; Pikula et al., 2013). Consistent with thoseresults, in our study, we found low serum BDNF levels in strokepatients and depression patients. Depression had been widely docu-mented to reduce the expression of BDNF in both animal and clinicalstudies (Gazal et al., 2012).

One meta-analysis study demonstrated strong evidence thatBDNF levels were lower in depressed subjects than healthy control

subjects (Po6.8�10�8), and that BDNF levels were significantly(P¼0.003) increased after antidepressant treatment (Sen et al.,2008). The other meta-analysis similarly showed that BDNF levelsincreased significantly after antidepressant treatment (effect size:0.62), and that there was a significant (P¼0.02) correlationbetween changes in BDNF level and depression score changes(Brunoni et al., 2008). Several lines of evidence suggest that theexpression of BDNF may be a downstream target of a variety ofantidepressant treatments; BDNF might therefore be an importanttarget for therapeutic recovery from depression, and it mightalso provide protection against stress-induced neuronal damage(Hashimoto., 2010).

The relationship between BDNF and stroke remains not com-pletely understood. There is experimental evidence that neuronsand glial cells act as endogenous sources of BDNF after ischemicand other brain injuries (Sandhofer et al., 2009). Dysfunction ofcerebral vascular BDNF signaling, therefore, may contribute todisruption of the neurovascular unit, hence to an alteration oftissue responses to vascular injury (Guo et al., 2008). A smallmolecule BDNF mimetic (LM22A-4) when administered immedi-ately after an ischemic stroke in adult mice lead to increasedneurogenesis and improved functional motor recovery (Han et al.,2012). Therefore, BDNF could reduce stroke risk through itsneurotrophic or its vascular effect (Pikula et al., 2013).

Fig. 1. Serum BDNF levels in stroke patients with depression and no-depression group. Mann–Whitney U-test. All data are medians and in-terquartile ranges (IQR).(a) Depression patients were defined as major depression; (b) patients with minor depression were also included.

Fig. 2. Correlation between serum BDNF levels and other predictors. (a) Correlation between serum BDNF levels and the National Institutes of Health Stroke Scale (NIHSS)score; (b) Correlation between serum BDNF levels and HAM-D score.

J. Li et al. / Journal of Affective Disorders 168 (2014) 373–379376

Many etiologies of PSD have been proposed but it is unlikelythat any single hypothesis can explain what appears to be hetero-geneous. It is probable that complex interactions between

hormones, neurotransmitters, and environmental factors are involved.In our study, one found that decreased BDNF levels may be importantin the pathophysiology of depression. One hypothesis would be thatreduced BDNF might reflect a genetic vulnerability in patients withdepression. Two studies using mice with a genetic deletion of theBDNF gene have demonstrated that BDNF play a critical role inneuronal differentiation and survival (Ernfors et al., 1994; Jones etal., 1994). Monteggia et al. (2007) showed that conditional BDNFknockout mice also display an increase in depression-like behavior inthe forced-swim and sucrose preference tests, suggesting that lowproduction of BDNF may precipitate depressive disorder. Anotherpossible explanation would be that stress-induced BDNF reductionsmight cause neuronal damage, which would in turn lead to acquiredbiological vulnerability. Stress, which can precipitate and exacerbatedepression, causes neuronal atrophy and death, especially in thehippocampus (Shimizu et al., 2003) proposed that stress-inducedchanges in the hippocampus may be central to the development ofdepression in genetically vulnerable individuals (Rajkowska, 2000).Levels in PSD may reflect the collapse of the stress-adaptation systemand its failure to protect the brain from stress-induced neuronaldegeneration. Third, BDNF has been shown to have antidepressanteffects in animal models of depression (Hashimoto., 2010). It has beenreported that forced swimming decreased BDNF mRNA in particularregions (CA1, CA3, and the dentate gyrus) of the hippocampus, andthat a combination of physical activity and antidepressant treatmentincreased the level of hippocampal BDNF mRNA to well above thebaseline value as well as enhanced swimming time in an animalmodel (Russo-Neustadt et al., 2001). BDNF signaling appears to besufficient for antidepressant effects, as direct infusion of BDNF intomidbrain areas or the hippocampus induces behavioral responsesthat are similar to those produced by antidepressants (Rantamäkiet al., 2006).

This study has a number of limitations. The major limitation ofour study was that we were not able to examine the risk factors fordepressive episodes including lack of social support, poverty,family violence, and increased life stress. In addition, the studysubjects were few and not randomly selected. The study wasconducted in only one clinic. Therefore, our findings may not begeneralizable to other Chinese stroke patients. Further research is

Table 2Adjusted OR of depression for BDNF levels in stroke patients.

Parameter ORa 95% CI P

Age 1.74 1.10–2.79 0.024Females 1.22 1.04–1.55 0.015Widowhood 1.83 1.18–3.09 0.002Living with offspring 1.33 1.09–1.78 0.001NIHSS on admission 1.11 1.04–1.18 0.001Hs-CRP 1.76 1.25–2.89 0.013HCY 1.16 1.03–1.29 0.008BDNF levels at admission 0.79 0.72–0.87 0.003BDNF levels at admission(r10.2 ng/ml) 11.50 5.60–23.40 Po0.0001

OR: odds ratio; CI: confidence interval; NIHSS: National Institutes of Health StrokeScale; mRS: modified Rankin Scale; Hs-CRP: high-sensitivity C-reactive protein;HCY: homocysteine; BDNF: Brain-derived neurotrophic factor.

a The odds ratio corresponds to a unit increase in the explanatory variable.

Table 3Adjusted OR of depression (minor depression were included) for BDNF levels in thestroke patients.

Parameter ORa 95% CI P

Age 1.77 1.08–2.81 0.019Females 1.22 1.05–1.56 0.016Widowhood 1.87 1.15–3.14 0.002Living with offspring 1.37 1.11–1.82 0.001NIHSS on admission 1.13 1.03–1.22 0.001Hs-CRP 1.79 1.23–2.95 0.011HCY 1.18 1.04–1.33 0.007BDNF levels at admission 0.85 0.76–0.93 0.006BDNF levels at admission(r11.5 ng/ml) 6.93 3.89–12.31 Po0.0001

OR: odds ratio; CI: confidence interval; NIHSS: National Institutes of Health StrokeScale; mRS: Modified Rankin Scale; Hs-CRP: high-sensitivity C-reactive protein;HCY: homocysteine; BDNF: Brain-derived neurotrophic factor.

a The odds ratio corresponds to a unit increase in the explanatory variable.

Fig. 3. Receiver operating characteristic (ROC) curves were utilized to evaluate the accuracy of serum BDNF levels to predict PSD. (a) Depression patients were defined asmajor depression; (b) patients with minor depression were also included.

J. Li et al. / Journal of Affective Disorders 168 (2014) 373–379 377

needed. Third, the serum levels of BDNF were only measured atthe acute stage of stroke in the patients and, hence, this studyyielded no data regarding when and how long biomarkers werechanged in these patients. Forth, depression assessment was madeonly once, at the 3-month follow up, whereas the NIHSS was usedonly at the acute stage. In addition, patients who had more severestroke died before the 3-month follow up were not included. Somepatients who died and had depression might be excluded. Lastly,the depressive status might be influenced by the severity of strokeitself. Schäbitz et al. (2007) found that BDNF may have negativeeffects on the course and prognosis of stroke. However, in thisstudy, the stroke severity was not evaluated at 3 months.

In spite of these limitations, the findings of this study remainedimportant and showed that serum BDNF at admission was sig-nificantly reduced and suggested that these alterations mightparticipate in the pathophysiology of depression symptoms instroke patients. Serum BDNF levels at admission could be seen asone powerful biological marker of risk for developing post-strokemajor depression at 3 month. Further studies are necessary toconfirm this association. Brunoni et al. (2008) found that thatBDNF levels increased significantly after antidepressant treatment,and suggested the applicability of BDNF as an efficient and novelanti-depression tool against depression in patients with ischemicstroke. Future clinical trials with BDNF should be driven.

Role of funding sourceThe funding agencies played no role in the design and conduct of the study.

Conflict of interestWe wish to confirm that there are no known conflicts of interest associated

with this publication and there has been no significant financial support for thiswork that could have influenced its outcome.

We confirm that the manuscript has been read and approved by all namedauthors and that there are no other persons who satisfied the criteria for author-ship but are not listed. We further confirm that the order of authors listed in themanuscript has been approved by all of us.

We confirm that we have given due consideration to the protection ofintellectual property associated with this work and that there are no impedimentsto publication, including the timing of publication, with respect to intellectualproperty. In so doing we confirm that we have followed the regulations of ourinstitutions concerning intellectual property.

We further confirm that any aspect of work covered in this manuscript that hasinvolved either experimental animals or human patients has been conducted withthe ethical approval of all relevant bodies and that such approvals are acknowl-edged within the manuscript.

We understand that the corresponding author is the sole contact for theeditorial process (including Editorial Manager and direct communications with theoffice). He/she is responsible for communicating with other authors about progress,submissions of revisions and final approval of proofs. We confirm that we haveprovided a current, correct email address which is accessible by the correspondingauthor and which has been configured to accept emails.

AcknowledgmentThis research was supported by the fundamental and advanced research

projects of Chongqing (No: cstc2013jcyjA10147). We express our gratitude to allthe patients, the nurses and physicians who participated in this study, and therebymade this work possible. Authors also acknowledge the contribution of thereviewers who have helped us to improve the manuscript.

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