Evaluation of interleukin-6 and serotonin as biomarkers to predict response to fluoxetine

Objective Only 30% of major depressive disorder (MDD) patients achieve complete remission with a serotonergic antidepressant (selective serotonin reuptake inhibitor). We investigated the potential of serotonin (5-HT) and interleukin-6 (IL-6) to serve as functional biomarkers of fluoxetine response. Methods Serum IL-6 and 5-HT were measured in 73 MDD patients (39 responders and 34 non-responders) pre- and 6 weeks post-treatment and in 44 normal controls with ELISA. Fluoxetine and norfluoxetine were measured using LC MS/MS. Results IL-6 levels were significantly higher in MDD patients when compared with controls (p<0.01), and 5-HT levels were significantly lower in non-responders compared with controls (p=0.0131). Pre- and post-treatment levels of both biomarkers individually and in combination did not significantly differ between responders and non-responders. Area under the receiver operating characteristics curve for the biomarkers was 0.5. Significant correlation was seen between the percentage change in IL-6 and percentage change in Hamilton Rating Scale for Depression score in responders. Fluoxetine and norfluoxetine concentrations were not significantly different in responders and non-responders, and there was no correlation between fluoxetine concentrations and percentage reduction in 5-HT from week 0 to 6. Conclusion 5-HT and IL-6 may not serve as useful markers of response to fluoxetine because of inconsistent results across different studies. Copyright (C) 2016 John Wiley & Sons, Ltd.