p11 Protein Levels in Patients With Major Depressive Disorder Treated With Citalopram

Major depressive disorder (MDD) is a serious, debilitating, life-shortening illness that affects many persons of all ages and backgrounds. While treatments are effective for a significant portion of patients with MDD, progress in developing more effective treatments is lagging. Furthermore, with regards to existing antidepressant medications, there are yet no reliable predictors of the likelihood of remission, response or non-response with an initial trial of an antidepressant medication. Identifying factors that are likely to predict response would have the advantage of personalizing treatment to a particular individual; that is selecting the antidepressant medication that is most likely to give the greatest probability of having a favorable outcome.

The serotonin system has been implicated in the pathophysiology of depression and mechanism of action of existing effective antidepressant treatments. Fourteen different serotonin receptors have been identified to date. One of them, 5-HT1B, plays an important role in regulating serotonin neurotransmission. Recently, p11 (a member of the S100 family of proteins) was found to interact with 5-HT1B receptors (Svenningsson et al 2006; Svenningsson and Greengard 2007). p11 mRNA levels are markedly reduced in the forebrain in helpless H/Rouen mice and the level of p11 mRNA was down-regulated in the anterior cingulate cortex from depressed patients. p11 mRNA is distributed in an anatomical pattern that closely resembled that of 5-HT1B receptor mRNA, including cortex, hippocampus, hypothalamus and raphe nuclei. Chronic administration of the antidepressants imipramine, tranylcypromine, and citalopram significantly increase the level of p11 in cortex. Finally, we have found that chronic treatment with fluoxetine increases p11 in peripheral mononuclear cells in monkeys.

We will now study whether the blood cell levels of p11 differ between healthy individuals and patients suffering from unipolar depression. Moreover, we will study whether the levels of p11 are affected by treatment with the selective serotonin reuptake inhibitor, citalopram. Complementary work will continue at other laboratories to better characterize the role of p11 in the pathophysiology of depression (e.g., animal studies, post-mortem studies).

In addition, we will also acquire a battery of magnetic resonance imaging (MRI) scans in a subset of 45 more homogeneous depressed subjects, and 45 matched healthy controls at baseline and at 8 weeks. There is a growing body of evidence implicating morphometric and physiologic abnormalities, measureable by MRI, in the pathophysiology of major depressive disorder. We will assess both baseline differences between depressed subjects and healthy controls, treatment effects, and search for possible MRI markers predicting treatment response.

This is an open label study which will be performed at the National Institute of Mental Health. In all, 82 adult subjects with major depressive disorder, between the ages of 18 and 65 years, will be recruited from the community. In addition, we will perform p11 measurements in blood cells from 64 healthy control subjects.