Antidepressants enhance glucocorticoid receptor function in vitro by modulating the membrane steroid transporters

Abstract

Previous data demonstrate that the tricyclic antidepressant, desipramine, induces glucocorticoid receptor (GR) translocation from the cytoplasm to the nucleus in L929 cells and increases dexamethasone‐induced GR‐mediated gene transcription in L929 cells stably transfected with the mouse mammary tumour virus‐chloramphenicol acetyltransferase (MMTV‐CAT) reporter gene (LMCAT cells) (Pariante et al., 1997). To extend these findings, the present study has investigated the effects of 24 h coincubation of LMCAT cells with dexamethasone and amitriptyline, clomipramine, paroxetine, citalopram or fluoxetine. All antidepressants, except fluoxetine, enhanced GR‐mediated gene transcription, with clomipramine having the greatest effect (10 fold increase). Twenty‐four hours coincubation of cells with desipramine, clomipramine or paroxetine, also enhanced GR function in the presence of cortisol, but not of corticosterone. It is proposed that these effects are due to the antidepressants inhibiting the L929 membrane steroid transporter, which actively extrudes dexamethasone and cortisol from the cell, but not corticosterone. This is further confirmed by the fact that clomipramine failed to enhance GR‐mediated gene transcription in the presence of dexamethasone when the membrane steroid transporter was blocked by verapamil. The membrane steroid transporters that regulate access of glucocorticoids to the brain in vivo, like the multiple drug resistance p‐glycoprotein, could be a fundamental target for antidepressant action. British Journal of Pharmacology (2001) 134, 1335–1343; doi:

The Antidepressant Desipramine Requires the ABCB1 (Mdr1)-Type p-Glycoprotein to Upregulate the Glucocorticoid Receptor in Mice

“…These findings are remarkably consistent with previous work in cell lines, by us and others, showing that antidepressants are unable to potentiate GR-mediated gene transcription in the presence of an MDR PGP inhibitor or of a glucocorticoid that is not transported by MDR PGP (Pariante et al, 1997(Pariante et al, , 2001(Pariante et al, , 2003a(Pariante et al, , b, 2004bBudziszewska et al, 2000;Miller et al, 2002;Herr et al, 2003). Moreover, we find that desipramine reduces MDR PGP (Mdr1a) expression in the hippocampus of FVB/N control controls, again consistent with previous work in cell lines (Varga et al, 1996;Szabo et al, 1999;Weiss et al, 2003;Pariante et al, 2003b;Weber et al, 2005).…”

“…This confirms the notion that MDR PGP is indeed a barrier to corticosterone access to the brain, and that its absence leads to more corticosterone entering the brain, and thus to an increased negative feedback on the HPA axis. Taken together with previous in vitro work, the present study strongly supports our proposed model that one mechanism through which antidepressants regulate the HPA axis is by reducing the action of glucocorticoid transporters like MDR PGP on the endothelial cells of the BBB (and possibly in neurons), thus leading to enhanced entry of glucocorticoids into the brain and so to facilitated negative feedback (Pariante et al, 2001(Pariante et al, , 2003a(Pariante et al, , b, 2004bPariante, 2006). It is interesting that, in FVB/N controls, there were no effects of desipramine on GR expression in the cortex, and there was a tendency (although not significant) for a GR downregulation in the amygdala.…”

“…We have found that antidepressants enhance GR function in mouse fibroblast cells by inhibiting the MDR PGP, and thus increasing intracellular concentrations of glucocorticoids (Pariante et al, 2001(Pariante et al, , 2003a; a similar effect is also present in rat cortical neurones (Pariante et al, 2003a). Consistent with this finding, pretreatment of cells with an MDR PGP inhibitor, or coincubation with a glucocorticoid that is not transported by MDR PGP in vitro, prevents these effects of antidepressants (Pariante et al, 1997(Pariante et al, , 2001(Pariante et al, , 2003a. Although other researchers have independently replicated these in vitro findings (Budziszewska et al, 2000;Miller et al, 2002;Herr et al, 2003), this model has never been directly tested in animals.…”

“…Recently, we have described in cell cultures that antidepressants control GR function by increasing the intracellular concentration of glucocorticoids (Pariante et al, 2001(Pariante et al, , 2003a(Pariante et al, , b, 2004b. Glucocorticoids are excreted from fibroblasts, leukocytes, and epithelial cells by the ABCB1-type multiple drug resistance (MDR) p-glycoprotein (PGP) present in two isoforms in rodents (abcb1a and abcb1b) and one isoform only in humans (ABCB1).…”

“…Interestingly, the MDR PGP is also localized at the luminal membrane of the endothelial cells of the blood-brain barrier (BBB), and limits the access of endogenous glucocorticoids to the mouse and human brain Meijer et al, 1998;Karssen et al, 2001Karssen et al, , 2002Uhr et al, 2002;Muller et al, 2003). We have found that antidepressants enhance GR function in mouse fibroblast cells by inhibiting the MDR PGP, and thus increasing intracellular concentrations of glucocorticoids (Pariante et al, 2001(Pariante et al, , 2003a; a similar effect is also present in rat cortical neurones (Pariante et al, 2003a). Consistent with this finding, pretreatment of cells with an MDR PGP inhibitor, or coincubation with a glucocorticoid that is not transported by MDR PGP in vitro, prevents these effects of antidepressants (Pariante et al, 1997(Pariante et al, , 2001(Pariante et al, , 2003a.…”