A Glutamate Transporter GLT1, in the Treatment of Bipolar Disorder

Overview

This study examines if Ceftriaxone, an antibiotic, will improve symptoms of depression in Bipolar Disorder. Purpose: This study will examine whether the drug ceftriaxone can help patients with bipolar depression during short-term treatment of symptoms such as depressed mood, psychomotor retardation (slowed down thinking and movements), and problems with sleep. Recent studies suggest that abnormalities in the brain levels of the chemical glutamate may be involved in causing depression. Ceftriaxone increases a protein in the brain called GLT1, which is responsible for regulating brain levels of glutamate. People between 18 and 65 years of age with bipolar disorder who are currently in a depressive episode of at least 4 weeks but no longer than 12 months duration may be eligible for this study. Participants are admitted to the NIH Clinical Center for about 10 weeks. During the first 1 to 2 weeks, they are evaluated and tapered off any antidepressant or mood stabilizers they have been taking. They remain free of all medication for 2 weeks and are then randomly assigned to take either ceftriaxone or placebo for 6 weeks. The study drugs are given intravenously (through a vein) every day. To minimize discomfort, patients are given a PICC line - a tube that is inserted in a vein in the arm and remains there for the duration of drug treatment. This prevents the need for repeated intravenous injections. Patients have a physical examination at the beginning and at the end of the study and two electrocardiograms (ECG) during the study. They are evaluated periodically with a series of psychiatric rating scales to determine the effects of the study drug on mood and thinking and they have periodic blood tests to assess their health status. In addition, patients are asked to undergo a lumbar puncture (spinal tap) twice during the study to collect a sample of cerebrospinal fluid (CSF, the fluid that bathes the brain and spinal cord). The CSF is examined to try to understand how brain chemicals are related to depression and to the effects of ceftriaxone. A local anesthetic is given and a needle is inserted in the space between the bones in the lower back where the CSF circulates below the spinal cord. A small amount of fluid is collected through the needle. This test is optional. At the end of the study patients are offered free treatment for up to 3 months with standard medications for bipolar depression and a referral to a community physician for long-term treatment will be made.

Bipolar affective disorder (BPD, manic-depressive illness) is a common, severe, chronic and often life-threatening illness. Increasingly, it is being recognized that it is the depressive phase of the illness, which contributes much of the morbidity and mortality. To date, only a few of the available somatic treatments have been proven to be effective for the acute phase of bipolar depression. Thus, there is a clear need to develop novel and improved therapeutics for bipolar depression. Recent preclinical studies suggest that antidepressants may exert delayed indirect effects on the glutamatergic system. Clinical data suggests that glutamatergic modulators may have antidepressant effects in humans. We first tested the glutamatergic modulator riluzole, an inhibitor of glutamate release and enhancer of glutamate reuptake in astrocytes and found it to have antidepressant properties in patients with treatment-resistant major depression and bipolar depression. In a recent study, we found that a single intravenous dose of the non-competitive NMDA antagonist ketamine produced a rapid and relatively sustained antidepressant effect in patients with treatment-resistant major depression. A recent report found that the Beta-lactam antibiotic ceftriaxone increased uptake of glutamate via increased GLT1 function (Rothstein et al 2005) and had antidepressant-like effects in animal models (Mineur et al 2006). Together, these data suggest that the glutamatergic system may play a role in the pathophysiology and treatment of depression, and that agents which more directly reduce glutamatergic neurotransmission may represent a novel class of antidepressants. We propose to expand our previous findings on the efficacy of glutamatergic modulators in patients with unipolar and bipolar depression by testing a specific, new mechanism where by we use ceftriaxone to chronically increase the expression of the glutamate transporter GLT1 in order to facilitate the removal of glutamate from the synaptic cleft in an effort to reduce excessive glutamate transmission and as a result produce acute antidepressant effects. The model presented here is a clinical testable one, and one that, if successful, holds the potential to develop a group of novel pharmacological treatments for major depression. Patients, ages 18 to 65, with a diagnosis of bipolar depression (without psychotic features), will be randomized to double-blind treatment to receive either ceftriaxone (1-4 g/day) or placebo intravenously for a period of 6 weeks. Acute efficacy will be determined by demonstrating a greater response rate using specified criteria. Approximately 86 patients with bipolar depression will be enrolled in the study.