measured on the Hamilton Rating Scale for Depression. Secondary outcomes were rumination at post-treatment and depressive symptoms at 6 months follow-up (Trial registered: NCT02278224).

**Results:** RFCBT significantly improved observer-rated depressive symptoms (Cohen's d 0.38; 95% CI 0.03–0.73) relative to group CBT at post-treatment on the primary outcome. No post-treatment differences were found in rumination or in depressive symptoms at 6 months follow-up, although these secondary analyses may have been underpowered.

**Conclusions:** This is the first randomized controlled trial providing evidence of benefits of RFCBT in major depression compared with CBT. Group RFCBT may be a beneficial alternative to group CBT for major depression.

**Conflict of interest:** No

**Keywords:** Psychiatry; Dépression; Rumination; CBT

## O0156

### Kynurenine pathway abnormalities in MDD and their relation to the characteristic inflammatory state of patients

G. Arteaga-Henriquez¹*, B. Burger¹,², E. Weidinger², L. Grosse², N. Moll², G. Schuetze², M. Schwarz², A. Wijkhuijs³, M. Versnel³, V. Arolt², N. Müller² and H. Drexhage³

¹Spain; ²Germany and ³Netherlands

**Introduction:** An activated inflammatory state in major depressive disorder (MDD) has been hypothesized to induce indoleamine 2, 3-dioxygenase 1 (IDO-1) expression, resulting in a preferential breakdown of tryptophan (TRP) to kynurenine (KYN) along the kynurenine pathway. This would explain the decreased TRP and serotonin levels that have been repeatedly found in MDD.

**Objectives:** The aim of the present study was to investigate the concept of a pro-inflammatory state in MDD as an inducer of a preferential breakdown of TRP along the kynurenine pathway.

**Methods:** In N = 281 MDD patients and N = 206 healthy controls, we determined the serum levels of TRP, 5-hydroxytryptophan (5-HTrp) and KYN using high performance liquid chromatography and/or liquid chromatography with mass spectrometry. Additionally, we analyzed potential relations between these metabolites and the expression levels of key inflammatory and kynurenine pathway enzyme genes using standard Q-PCR.

**Results:** TRP serum levels were decreased, KYN serum levels were not raised in patients with MDD. Patient's monocytes showed a significant higher inflammatory gene expression, while IDO-1 gene expression was not upregulated in the circulating monocytes of patients. Interestingly, the expression of key inflammatory genes

negatively correlated to IDO-1 gene expression in the circulating monocytes of patients.

**Conclusions:** Our observations reject the hypothesis of a preferential breakdown of systemic TRP along the kynurenine pathway in patients with MDD linked to their characteristic systemic pro-inflammatory monocyte state.

**Conflict of interest:** No

**Keywords:** Tryptophan; major depressive disorder; Inflammation; kynurenine pathway

## O0159

### Does dynamic thiol/disulfide balance predict mixed symptoms of depression?

Ç. Açar Yıldızoğlu*, H.İ. Taş and E. Yıldızoğlu

Turkey

**Introduction:** Plasma thiol/disulfide levels are thought to be valuable and reliable markers of oxidative stress and antioxidant defense mechanisms. Achieving this balance plays a critical role in the pathogenesis of many diseases such as depression.

**Objectives:** The aim of this study was to evaluate the scores of oxidative stress in patients with unipolar depression (UD) and in patients with mixed type of unipolar depression (mxUD) and to compare these scores with healthy subjects in terms of dynamic thiol/disulfide balance parameters.

**Methods:** 97 patients with the diagnosis of UD and 97 healthy individuals were included in the study. Hamilton Depression Rating Scale (HAM-D) and Modified Hypomania Checklist (M-HCL) were used respectively to determine depressive symptoms, manic symptoms and the severity of the disease. Oxidative stress parameters were measured by evaluating fasting blood samples taken from all participants.

**Results:** In the UD group, the levels of disulfide, total thiol, oxidation-reduction ratio and oxidized thiol were found statistically higher in the depression group than the control group in favor of oxidation (p<0.05). Reduced thiol levels which are favorable for the antioxidant system, were statistically lower in the depression group than the control group (p<0.05). There was no significant difference between the mxUD and non-mixed featured UD in thiol-disulfide balance.

**Conclusions:** This findings showed that, the balance deteriorated in favor of oxidation or antioxidation in depression may not be a significant biomarker for mixed symptoms of depression.

**Conflict of interest:** No

**Keywords:** Dépression; thiol disulfide balance; mixed features