CHAPTER 1
Decreased plasma levels of Brain-derived Neurotrophic Factor (BDNF) during mixed episodes of bipolar disorder (Journal of Affective Disorders 2015; 171:167–170)
Authors: Piccinni A, Veltri A, Costanzo D, Vanelli F, Franceschini C, Moroni I, Domenici L, Origlia N, Marazziti D, Hakiskal HS, Dell’Osso L.
ABSTRACT
Background: Brain-derived Neurotrophic Factor (BDNF) is a neurotrophin involved in neurogenesis and neuroplasticity. Decreased blood levels of BDNF have been found during acute manic and depressive states. BDNF has been proposed as biomarker in illness phases of mood disorders. No information is available regarding BDNF levels during the mixed states of bipolar disorder (BD). The aim of this study was to evaluate BDNF levels during mixed episodes of BD patients and compare them with those of healthy subjects and depressed patients. Methods: Plasma BDNF levels were measured by an ELISA assay in 18 patients with major depressive episode (MDE), 19 patients with mixed episode (ME) and 15 healthy subjects (HS). Results: BDNF levels were significantly higher in HS, as compared with patients’ samples (HS vs. MDE patients: p<.001; HS vs. ME patients: p=.022). No significant differences were found between BDNF levels of ME and MDE patients. The severity of illness as assessed by CGI-S was significantly higher in ME than in MDE patients (p=.01). Limitations: The small sample size may have weakened the power of statistical analyses. All patients received a mood-stabilizing and antidepressant treatment which has been reported to influence peripheral BDNF levels. Conclusions: Our results are consistent with previous studies showing reduced BDNF during both manic and depressive episodes. This finding support the role of BDNF as a state-marker of mood episodes, and may represent a contribution to a unitary approach model between unipolar and BDs as well as to the manic-depressive spectrum model.
BACKGROUND
According to the neurotrophic hypothesis, stress and depression are likely to be associated with a neurotrophins deficit leading to neuronal atrophy and cell loss in key limbic areas and in prefrontal cortex. Antidepressant treatments can block or reverse these effects (Sapolsky, 2001; Sheline et al., 2003; Banasr et al., 2011).
A particular attention has been dedicated to Brain-Derived Neurotrophic Factor (BDNF), a neurotrophin involved in differentiation and survival of neurons, as well as in modulation of synaptic plasticity (Sermasi et al., 2000; Poo, 2001; Popoli et al., 2002). Although the exact relationship between central and peripheral BDNF pools is still unclear, the permeability of the blood-brain barrier to BDNF was demonstrated (Pan et al., 1998); in addition, Karege et al. (2002) reported the twin-course of central and peripheral BDNF levels during the central nervous system (CNS) development in rats. Several recent works analyzed peripheral (serum and/or plasma) BDNF levels in samples of psychiatric patients, with the aim to assess their potential role as a biomarker for mood disorders. Peripheral BDNF levels resulted significantly decreased in patients suffering from major depressive disorder (MDD), compared with healthy subjects. Conversely, BDNF levels returned to the control levels after effective treatments and symptom remission (Piccinni et al., 2008a, 2009; Sen et al., 2008). Moreover, low BDNF levels where shown to be related to both recurrence and severity of depressive episodes (Dell'Osso et al., 2010).
Recent meta-analysis of clinical data suggest that peripheral BDNF levels are significantly reduced during manic and depressive, but not in euthymic phases of bipolar disorder (BD) (Lin, 2009; Fernandes et al., 2011). In particular, BDNF levels increased after treatments leading to clinical recovery of acute mania or depression. In addition, Fernandes et al. (2011) found that the differences between euthymic and non-euthymic states in BD become less evident with aging and duration of illness. These data suggest peripheral BDNF levels as potential biomarkers of mood (depressive and manic) episodes, as well as predictors of antidepressant effectiveness and evaluation of disease progression.
However, the current literature is lacking regarding BDNF levels during the mixed episode of BD patients. The aim of the present study was, therefore, to assess BDNF plasma levels in a sample of patients with mixed episode; and compare them with the values of depressed patients and healthy subjects.
METHODS Subjects
Eighteen inpatients (9 men and 9 women, mean age ± SD: 44.9±17 years) who met the DSM-IV-TR (APA, 2000) criteria for current major depressive episode (MDE) with or without psychotic features (16 with BD, 2 MDD) and 19 in-patients (10 men and 9 women, mean age ± SD: 38.2±9.96 years) who met the DSM-IV-TR criteria for current Mixed Episode (ME) with
Department of Clinical and Experimental Medicine, University of Pisa. Exclusion criteria for patients were: age lower than 18 years, presence of a major neurological or medical illness, diagnoses of substance abuse in the last 6 months, pregnancy, inability to sign informed consent or presence of neurological disorders. Both MDE and ME patients were maintained on the same drug treatment for at least four weeks before the blood collection to avoid a potential effect of drug treatment changes on central and peripheral BDNF levels.
Fifteen healthy subjects (HS, 3 men and 12 women, mean age ± SD: 36.9 ± 9.2 years) were recruited as the control group. Exclusion criteria for healthy subjects were: age lower than 18 years, history of past or current major medical or mental disorders, heavy cigarette smoking, regular medication and drug abuse.
Written informed consent was obtained from each subject to participate in the study. The study was approved by the Ethics Committee of the University of Pisa in accordance with the Declaration of Helsinki (1996).
Clinical assessment
Clinical diagnosis was confirmed by means of the Mini International Neuropsychiatric Interview (MINI) (Sheehan et al., 1998).
The severity of depressive symptoms was assessed by means of the 21-item Hamilton Rating Scale for Depression (HRSD-21) (Hamilton, 1960). The severity of manic symptoms was assessed by means of the Young Mania Rating Scale (YMRS) (Young et al., 1978). Moreover, Clinical Global Impressions — Severity of Illness scale (CGI-S) (Guy, 1976) was administered. Co-morbid diagnoses of anxiety disorders were assessed by means of the MINI. Scale administration was performed by trained raters.
BDNF assay
To avoid a potential bias due to the presence of a diurnal rhythm of plasma BDNF levels (Piccinni et al., 2008b) venous blood samples were drawn in the morning (between 8:00 and 10:00 a.m.). Blood was collected into EDTA-coated tubes that were kept on ice, centrifuged at 2,000 x g for 10 minutes at 4 °C and refrigerated at -20 °C. (Lommatzsch et al., 2005; Begliuomini et al., 2007).
According to the manufacturer’s instructions, acidification and subsequent neutralization of the samples were performed before carrying out the ELISA assay (BDNF Emax Immunoassay system, Promega, Madison, WI, USA).
96-well plates were coated with anti-BDNF monoclonal antibody and incubated at 4 °C for 18 h.
The plates were incubated in a blocking buffer for 1 h at room temperature before samples were added. The samples and BDNF standards were maintained at room temperature under shaking for 2 h, followed by washing with the appropriate buffer.
The plates were then incubated with anti-human BDNF polyclonal antibody at room temperature for 2 h, washed and incubated with anti-IgG antibody conjugated to horseradish peroxidase for 1 h at room temperature. The plates were then incubated in peroxidase substrate and tetramethylbenzidine solution to produce a color reaction. The reaction was stopped with 1 M HCl. The absorbance at 450 nm was measured with a microplate reader (Model 550, Bio Rad Laboratories) to determine BDNF values that are expressed as ng/ml.
Statistical analysis
Data were recorded into a digital database and elaborated by using SPSS software, 17th version. Since BDNF levels and rating scales scores were normally distributed, parametric tests were performed. In particular, the one-way ANOVA, followed by the Bonferroni post-hoc test, was used to compare the mean BDNF plasma levels amongst the three groups (controls, MDE patients and ME patients). ANOVA was also used to test the homogeneity of the independent variable age amongst the same groups. Rating scales scores, number of episodes and the onset age amongst the patients’ groups were compared by means of the t-test for independent samples. The distribution of categorical variables (gender, co-morbidities) was analyzed by means of 2x2 cross tables and the chi-squared test. A p-value < .05 was judged as statistically significant.
RESULTS
The three groups of subjects (HS, MDE and ME patients) resulted homogeneous for age [F(2, 51)=1.98, p=.149] and gender (χ2=4.324, p=.115).
The severity of illness, as assessed by the CGI-S, was significantly higher in ME patients, compared with MDE ones (6.05 vs. 5.56, t=-2.853, p=.01), while no significant differences for the number of episodes and onset age emerged between the two patients groups.
The variance test (ANOVA) showed that the mean plasma BDNF values were significantly different between the three groups [F(2, 51)=9.847, p<.001]. According to the Bonferroni post-hoc test, BDNF levels were significantly higher in HS, as compared with both patients’
lower BDNF levels than ME patients, but the difference was not statistically significant (p=.257).
No significant differences in psychiatric comorbid disorders rate resulted between MDE and ME patients, excepting for social anxiety disorder (SAD) which was diagnosed only amongst MDE patients (χ2=9.113, p=.003) (see Figure 1 and Table 1 for the summary of results).
DISCUSSION, LIMITATIONS AND CONCLUSIONS
The main finding of the present work is that the plasma BDNF levels were significantly decreased in the course of mixed episodes of BD. This is consistent with previous studies showing lower plasma BDNF concentrations in both depressed and manic patients, and further support the consistency of BDNF as a state-dependent marker of mood episodes (Sen et al., 2009; Fernandez et al., 2011; Lin et al., 2009).
Moreover, comparable BDNF levels in manic, depressive and mixed states suggest a shared biological trait strengthening the hypothesis of a unitary model for mood disorders, as for the Kraepelinian description of a continuous manic-depressive spectrum (Cassano et al., 2004; Fiedorowicz et al., 2011; Swann et al., 2009; Zimmermann et al., 2009). In particular, in Dell'Osso et al. (1991), the authors identified the mixed states as a distinct longitudinal pattern of manic-depressive illness, with late onset and tendency to recur with the same characteristics
hyperthymic temperament, and family history of depressive rather than bipolar disorder. Recently, this issue has fostered notable nosological developments. The DSM-IV-TR definition of ME (meeting full manic and depressive criteria), that we used in patients recruitment for the present work, has been removed in the updated DSM-5 version. Overlapping symptoms of opposite polarity are now recognized as independent dimension, codified by the “with mixed features” specifier that can be applied to manic, hypomanic or major depressive episodes (APA, 2013).
Neurobiological and neuroanatomical studies highlighted several brain abnormalities in either unipolar or BD patients, such as hippocampus and prefrontal cortex volume reduction, suggesting an impaired neuroplasticity (Post et al., 2011). These structural changes are associated with BDNF reduction and inflammatory marker increase in the brain, and seem to be directly correlated with a longer duration of illness, higher number of mood episodes and with more severe and rapidly progressive course of the disease in patients with mood disorders (Strakowski et al., 2005; Moorhead et al., 2007; Kauer-Sant’Anna et al., 2009).
Our findings showed that the severity of illness, as assessed by CGI-S, was significantly higher in ME than in MDE patients. This result was not surprising as patients with ME showed more severe and prolonged episodes, while suffering from worse functional impairment (Rosa et al., 2009; Goldberg et al., 2009).
The SAD rate resulted higher in MDE patients, compared to ME. SAD is a frequent comorbid manifestation in both unipolar and BD patients during the depressive episodes, but this rate tends to be higher amongst the unipolar depressed patients, as compared with BD ones (Scott et al., 2013). No information is available on the prevalence of SAD in BD patients during the ME, and also on the difference in SAD comorbidity between BD patients with depressive and manic episodes. On the basis of our clinical experience we would suggest that SAD might be considered as a depressive correlate which tends to vane during the hypomanic or manic phases. However, further investigation on larger samples of BD patients in different phases of illness are needed to confirm this hypothesis (Freeman et al., 2002).
Several limitations affected the present study. Firstly, the small sample size may have weakened the power of the statistical analyses. Secondly, all recruited patients received a mood-stabilizing and antidepressant treatment which has been reported to influence the peripheral BDNF levels (Fernandes et al., 2011). However, the same medication was maintained for at least four weeks before blood collection.
Further research on the neurotrophic factors involvement in mood disorders should be carried out on a wider sample of patients in order to confirm the present data, while taking into
account the recent nosological broadening of the “mixed states” concept. Lastly, we suggest that the relationship between the neurotrophin dysregulation and the neuro-anatomical changes in the brains of the patients with mood disorders may be one of the most intriguing aspect in psychiatric research, that is worth to be investigated more thoroughly in the future .
REFERENCES
American Psychiatric Association Diagnostic and statistical manual for mental disorders, 4th ed. DSM-IV-TR. Washington, D.C., 2000.
American Psychiatric Association Diagnostic and statistical manual for mental disorders, 5th ed. DSM-5. Washington, D.C., 2013.
Banasr M, Dwyer JM, Duman RS. Cell atrophy and loss in depression: reversal by antidepressant treatment. Curr Opin Cell Biol 2011; 23(6):730-737.
Begliuomini S, Casarosa E, Pluchino N et al. Influence of endogenous and exogenous sex hormones on plasma brain-derived neurotrophic factor. Hum Reprod 2007; 22:995–1002. Cassano GB, Rucci P, Frank E et al. The mood spectrum in unipolar and bipolar disorder: arguments for a unitary approach. Am J Psychiatry 2004; 161:1264–1269.
Dell’Osso L, Del Debbio A, Veltri A et al. Associations between Brain-Derived Neurotrophic Factor plasma levels and severity of the illness, recurrence and symptoms in depressed patients. Neuropsychobiology 2010; 62(4):207-212.
Dell'Osso L, Placidi GF, Nassi R et al. The manic depressive mixed state: familial, temperamental, and psychopathologic characteristics in 108 female inpatients. Eur Arch Psychiatry Clin Neurosci 1991; 240 (4-5):234-9
Fernandes BS, Gama CS, Ceresér KM. Brain-derived neurotrophic factor as a state-marker of mood episodes in bipolar disorders: a systematic review and meta-regression analysis. J Psychiatr Res 2011; 45(8):995-1004.
Fiedorowicz JG, Endicott J, Leon AC et al. Subthreshold hypomanic symptoms in progression from unipolar major depression to bipolar disorder. Am J Psychiatry 2011; 168:40–48.
Freeman MP, Freeman SA, McElroy SL. The comorbidity of bipolar and anxiety disorders: prevalence, psychobiology, and treatment issues. J Affect Disord 2002; 68:1-23.
Goldberg JF, Perlis RH, Bowden CL et al. Manic symptoms during depressive episodes in 1380 patients with bipolar disorder: findings from the STEP-BD. Am J Psychiatry 2009; 166: 173–181.
Guy W. ECDEU assessment manual for psychopharmacology. Rev. Rockville, MD: U.S. National Institute of Health, Psychopharmacology Research Branch, 1976.
Karege F, Schwaldt M, Cisse M. Postnatal developmental profile of brain-derived neurotrophic factor in rat brain and platelets. Neurosci Lett 2002; 328:261-264.
Kauer-Sant'Anna M, Bonda DJ, Lamb RW, Yathamc LN. Functional outcomes in first-episode patients with bipolar disorder: a prospective study from the Systematic Treatment Optimization Program for Early Mania project. Compr Psychiatry 2009; 50:1–8.
Lin PY. State-dependent decrease in levels of brain derived neurotrophic factor in bipolar disorder: A metaanalytic study. Neurosci Lett 2009; 466:139-143.
Lommatzsch M, Zingler D, Schuhbaeck K et al. The impact of age, weight and gender on BDNF levels in human platelets and plasma. Neurobiol Aging 2005; 26:115–123.
Moorhead TW, McKirdy J, Sussmann JE et al. Progressive gray-matter loss in patients with bipolar disorder. Biol Psychiatry 2007; 62:894–900.
Pan W, Banks WA, Fasold MB et al. Transport of BDNF across the blood-brain barrier. Neuropharmacology 1998; 37:1553-1561.
Piccinni A, Marazziti D, Catena M et al. Plasma and serum brain-derived neurotrophic factor (BDNF) in depressed patients during 1 year of antidepressant treatments. J Affect Disord 2008a; 105:279–283.
Piccinni A, Marazziti D, Del Debbio A et al. Diurnal variation of plasma brain-derived neurotrophic factor (BDNF) in humans: an analysis of sex differences. Chronobiol Int 2008b; 25(5):819-26.
Piccinni A, Del Debbio A, Medda P et al. Plasma Brain-Derived Neurotrophic Factor in
treatment-resistant depressed patients receiving electroconvulsive therapy. Eur
Neuropsychopharmacol 2009; 19(5):349-55.
Poo MM. Neurotrophins as synaptic modulators. Nat Rev Neuroscience 2001; 2:24-32.
Popoli M, Gennarelli M, Racagni G. Modulation of synaptic plasticity by stress and antidepressants. Bipolar Disord 2002; 4:166-182.
Post RM, Kauer-Sant'Anna M, 2010. In: Yatham LN. An introduction to the neurobiology of bipolar illness onset, recurrence, and progression. Bipolar Disorder: Clinical and neurobiological foundations, pp. 96-109.
Rosa AR, Reinares M, Franco C et al. Clinical predictors of functional outcome of bipolar patients in remission. Bipolar Disorders 2009; 11:401–409.
Sapolsky RM. Depression, antidepressants, and the shrinking hippocampus. Proc Natl Acad Sci USA 2001; 98:12320-12322.
Scott EM, Hermens DF, Naismith SL et al. Distinguishing young people with emerging bipolar disorders from those with unipolar depression. J Affect Disord 2013; 144(3):208-215. Sen S, Duman R, Sanacora G. Serum brain-derived neurotrophic factor, depression, and antidepressant medications: Meta-analyses and implications. Biol Psychiatry 2008; 64:527-532.
Sermasi E, Margotti E, Cattaneo A, Domenici L. Trk B signalling controls LTP but not LTD expression in the developing rat visual cortex. Eur J Neurosci 2000; 12(4):1411-9.
Sheehan DV, Lecrubier Y, Sheehan KH et al. The Mini- International Neuropsychiatric Interview (M.I.N.I.): the development and validation of a structured diagnostic psychiatric interview for DSM-IV and ICD-10. J Clin Psychiatry 1998; 59 (Suppl. 20):22–33.
Sheline YI, Gado MH, Kraemer HC. Untreated depression and hippocampal volume loss. Am J Psychiatry 2003; 160(8):1516-1518.
Strakowski SM, Delbello MP, Adler CM. The functional neuroanatomy of bipolar disorder: a review of neuroimaging findings. Mol Psychiatry 2005; 10:105–116.
Swann AC, Steinberg JL, Lijffijt M, Moeller GF. Continuum of depressive and manic mixed states in patients with bipolar disorder: quantitative measurement and clinical features. World Psychiatry 2009; 8:166–172.
Young RC, Biggs JT, Ziegler VE, Meyer DA. A rating scale for mania: reliability, validity and sensitivity. Br J Psychiatry 1978; 133:429-435.
Zimmermann P, Bruckl T, Nocon A et al. Heterogeneity of DSM-IV major depressive disorder as a consequence of subthreshold bipolarity. Arch Gen Psychiatry 2009; 66:1341–1352.
