Ketamine has rapid and sustained antidepressant effects in patients with treatment resistant depression (TRD). However, the underlying mechanisms of action are not well understood. There is increasing evidence that TRD is associated with a pro-inflammatory state and that ketamine may inhibit inflammatory cytokine production. We investigated whole blood transcriptional profiles related to TRD and gene expression changes associated with treatment response to ketamine. Whole blood was collected at baseline (21 healthy controls [HC], 26 patients with TRD) and then again in patients with TRD 24 hours following a single intravenous infusion of ketamine (0.5 mg/kg). We performed RNA-sequencing and compared a) baseline transcriptional profiles between patients with TRD and HC, b) responders vs. non-responders before ketamine treatment, and c) gene expression signatures associated with clinical improvement. At baseline, patients with TRD compared to HC were characterized by a gene expression signature indicative of interferon signaling pathway activation. Prior to ketamine administration, the metabotropic glutamate receptor gene GRM2 and the ionotropic glutamate receptor gene GRIN2D were upregulated in responders compared to non-responders. Ketamine response was associated with the downregulation of multiple genes coding for pro-inflammatory cytokines, the predicted inhibition of several interferon signaling associated upstream regulators and the downregulation of Indoleamine 2,3-Dioxygenase 1 (IDO1). The current study indicates that response to ketamine may be associated with up-regulation of glutamate receptors at baseline, and linked to transcriptional changes indicative of an anti-inflammatory response following ketamine. One specific anti-inflammatory mechanism might be the downregulation of IDO1 via inhibition of the interferon pathway.

IRF7, IF16, IF135, SOCS1, RSAD2, OAS1, OAS2, OASL, HLA-A, HLA-B, BST2, ISG15