Effects of plant cannabinoids on glucocorticoid- driven gene transcription; a possible anti-depressant mechanism

Maha ElBatsh, Charles Marsden, David Kendall

School of Biomedical Sciences and Institute of Neuroscience,University of Nottingham, Nottingham, UK

Excessive activation of the hypothalamic-pituitary-adrenal (HPA) axis is implicated in major depression. Hyperactivity is thought to be related to impaired feedback inhibition by endogenous glucocorticoids (GC) acting via nuclear glucocorticoid receptors (GR) which control the activity of large families of genes. There is evidence from cell, animal and human-based studies that antidepressant treatment is associated with resolution of this impairment by increasing GR expression and function.

One of the mechanisms by which antidepressants are suggested to increase GR function is by inhibiting the action of membrane steroid transporters that expel glucocorticoids from target cells and, therefore, increase the intracellular levels and transcriptional activity of the steroids (Pariante et al., 2003). Pre-clinical and clinical studies suggest that plant cannabinoids may have antidepressant effects and inhibitory effects on steroid transport (Hollandet al., 2006).

The aim of the present study was to investigate, in a model cell system, whether short term exposure to plant cannabinoids could have antidepressant-like effects on glucocorticoid-driven gene transduction.

The LMCAT cell line is derived from mouse fibroblast (L929) cells stably transfected with the mouse mammary tumour virus-chloramphenicol acetyltransferase (MMTV-CAT), a GC-sensitive reporter gene. Exposure of these cells to GC receptor agonists leads to an increase in CAT activity. LMCAT cells were grown to confluency then incubated for 24hrs with Δ9-tetrahydrocannabinol (THC, 2uM), cannabidiol (CBD, 3uM) or the tricyclic antidepressant clomipramine (CLOM, 10uM), with or without dexamethasone (DEX, 20nM). Colorimetric enzyme-linked immunoassay was used to measure CAT activity and Western immuno-blotting was used to measure GC receptor expression. For measuring the intracellular accumulation of GC the LMCAT cells were incubated for 1.5 hrs with [3H]-DEX in the presence of THC, CBD or ClOM.. Data were analysed by one-way ANOVA and Dunnett’s post -hoc test.

Incubating cells for 24hrs with THC, CBD or CLOM significantly increased CAT activity only in the presence of DEX (to 1166 ±198.5 %; 1737 ± 129.3 %; 2384± 267.3 %, respectively; p < 0.05 compared with both control and DEX; n=3). CBD and CLOM, but not THC, significantly reduced the GC receptor expression in the absence of DEX (to 80.0 ± 8.5 %; 77.7 ± 5.8% respectively, p< 0.01; n=4). In the presence of DEX, THC, CBD and CLOM significantly reduced GC receptor expression (to 62.89 ± 4.10%; 51.95± 8.93%; 55.11 ± 9.72 % respectively, p< 0.01; n=4). CLOM significantly enhanced the intracellular accumulation of [3H]-DEX (to 260.3 ± 19.7 %, p< 0.01; n=3). Similarly CBD significantly increased intracellular [3H]-DEX accumulation (to 167.5± 29.0 %, p< 0.05; n=3) indicating a blockade of steroid export.

In conclusion, CBD and the antidepressant CLOM produced similar enhancements of glucocorticoid function while THC directly increased GC-driven gene transcription without any effect on GC receptor expression. These data raise the possibility that the glucocorticoid signalling pathway is a potential antidepressant target for cannabinoids.

This work was supported by a scholarship from the Egyptian Government to ME-B.

Holland,M.L. et al. (2006) Biochemical pharmacology, 71,1146-1154.

Pariante, C.M., et al. (2003) Br J Pharmacol,139, 1111-1118.