Antidepressants, but not antipsychotics, modulate GR function in human whole blood: An insight into molecular mechanisms
Introduction
Major depression is often associated with alterations in hypothalamic–pituitary–adrenal (HPA) regulation, including increased plasma cortisol levels, and enlarged anterior pituitary and adrenals (Carvalho et al., 2009, Gold et al., 1988; Pariante et al. 2008). A dysregulation of the HPA axis in patients with major depression is seen after the dexamethasone suppression test (DST) (Pariante 2004) and the DEX/corticotrophin releasing hormone (CRH) (Holsboer, 2000, Nemeroff, 1996) test, indicating in depressed patients a relative impairment of glucocorticoid receptor (GR)-mediated negative feedback (glucocorticoid resistance). In further support to the notion of relative glucocorticoid resistance in depressed patients is the fact that the increased cortisol levels are not accompanied by physical signs of Cushing's Syndrome (Holsboer et al., 1992, Murphy, 1991). Glucocorticoid resistance has also been described in the peripheral blood immune cells from depressed patients (Holsboer, 2000, Pariante et al., 2001). Peripheral glucocorticoid resistance might lead to the decreased immunosuppressive effect of glucocorticoids and the increased levels of inflammation seen in these patients (Carvalho et al., 2008, Dantzer et al., 2008, Pariante et al., 2001). Interestingly, some studies indicate effective antidepressant treatment is associated with resolution of the HPA axis negative feedback disturbance (Linkowski et al. 1987) (Aihara et al., 2007, Binder et al., 2004, Hennings et al., 2009, Ising et al., 2005). In accordance, we have shown that citalopram increases HPA axis negative feedback by glucocorticoids (measured as cortisol suppression by prednisolone) after as little as four days of administration in healthy subjects (Pariante et al. 2004).
Recent studies show that antidepressants may reverse glucocorticoid receptor changes in depression by direct effects on the GR (Holsboer 2000). In laboratory animals, antidepressants increase GR receptor expression and increase negative feedback on the HPA axis (Carvalho and Pariante, 2008). Our own work over the last few years, in cellular and animal models, has contributed to elucidate the mechanisms by which antidepressants directly influence GR function. First, we demonstrated that antidepressants increase GR translocation in fibroblasts (Pariante et al. 1997), a finding later replicated by Funato et al. (2006), Heiske et al. (2003) and Okuyama-Tamura et al. (2003). Second, we showed that this GR translocation is associated with GR downregulation (Pariante et al. 2003a). Third, we described that antidepressants increase the intracellular concentrations of some glucocorticoids by inhibiting membrane transporters that actively expel glucocorticoid from cells, indirectly compensating for the GR downregulation and ultimately increasing GR function in cells where these transporters are present (Pariante et al., 2001, Pariante et al., 2003a, Mason and Pariante, 2006). In contrast, in the absence of functional membrane transporters, or in the presence of glucocorticoids that are not substrates for these transporters, the antidepressants-induced GR activation and downregulation leads to a reduced GR function (Carvalho et al., 2008, Mason and Pariante, 2006, Pariante et al., 1997, Pariante et al., 2001). Again, these findings have been later replicated by Augustyn et al. (2005), Budziszewska (2002) and Budziszewska et al. (2005). Fourth, we have recently found that the antidepressant clomipramine decreases GR function in human peripheral blood cells — that is, in cells that do not express functional glucocorticoid transporters (Park et al., 2003). These findings are consistent with the notion that antidepressants induce GR translocation, GR downregulation, and hence reduce GR function in cells that do not express membrane transporters. Finally, we have recently found that the ability of clomipramine to decrease GR function in peripheral blood cells is impaired in patients with major depression who are clinically resistant to treatment, thus suggesting that the ability of antidepressants to regulate GR function is related to their therapeutic action (Carvalho et al., 2008). These patients also had reduced GR function in peripheral blood cells (Carvalho et al. 2009) and increased levels of interleukin-6 possibly reflecting a pro-inflammatory state of monocytes (Carvalho et al., 2008). Taking together we hypothesize antidepressants correct the glucocorticoid resistance and pro-inflammatory state of monocytes in major depressive disorders. Clinical non-responsiveness to antidepressants is possibly reflected by an inability of antidepressants to exert these corrective functions.
As mentioned above, we have used clomipramine in our previous work in human peripheral blood cells, a tricyclic antidepressant with predominantly serotonergic, but also noradrenergic, reuptake inhibition ability (Carvalho et al., 2008). To further understand the effect of antidepressants on GR function in humans, we have evaluated the effect of other antidepressants with different mechanisms of action on GR function in peripheral whole blood cells of healthy volunteers, and compared to those of clomipramine. Moreover, we have investigated whether the GR regulation is specific to antidepressants by comparing them to antipsychotics. Finally, we have examined a possible molecular mechanisms underlying these effects, with particular reference to a pathway that has been described as relevant for GR regulation by antidepressants and by inflammation, cAMP (Chen and Rasenick, 1995a, Chen and Rasenick, 1995b, Nestler et al., 1989, Nibuya et al., 1996).
Section snippets
Experimental procedures
The study protocol was approved by the Research Ethics Committee of the Institute of Psychiatry, King's College London and Maudsley Hospital (London). All subjects gave their written and informed consent.
Results
In the absence of LPS (unstimulated), cells showed IL-6 levels values in the lower limit of detection or undetectable. As expected, LPS stimulated a large increase of IL-6 production (around 2500 fold-induction). Tricyclics antidepressants like clomipramine and amitryptiline inhibited LPS-stimulated IL-6 levels when compared to vehicle-treated cells in the absence of glucocorticoids (Fig. 1). On the other hand, this effect was not shown in the presence of sertraline, venlafaxine or paroxetine (F
Discussion
In this study, we show that antidepressants of different mechanisms of action all inhibit glucocorticoid receptor function in whole blood cells of healthy subjects. This effect appears to be specific to antidepressants, as antipsychotics did not have the same effect. Furthermore, we have shown that increasing cAMP by the inhibition of phosphodiesterase with rolipram exert a similar effect as that of antidepressants — that of inhibiting GR function — and together rolipram and clomipramine lead
Role of the funding source
This research has been funded by the UK Medical Research Council, the NARSAD, the South London and Maudsley NHS Foundation Trust & Institute of Psychiatry NIHR Biomedical Research Centre for Mental Health, and the Commission of European Communities 7th Framework Programme Collaborative Project Grant Agreement no. 22963 (Mood Inflame). Dr. Livia A Carvalho is also funded by the NARSAD Young Investigator Award.
Contributors
Carvalho LA planned and conducted the experiments, analyzed the data and wrote the paper. Garner conducted the experiments and analyzed the data on antipsychotics. Dew conducted all the IL-6 ELISA measurements. Fazakerley conducted the experiments on paroxetine and antipsychotics. Pariante revised the paper before submission.
Conflict of interest
The authors have no relevant financial interest to disclose.
Acknowledgments
This research has been funded by the UK Medical Research Council, the NARSAD, the South London and Maudsley NHS Foundation Trust & Institute of Psychiatry NIHR Biomedical Research Centre for Mental Health, and the Commission of European Communities 7th Framework Programme Collaborative Project Grant Agreement no. 22963 (Mood Inflame). Dr. Livia A Carvalho is funded by the NARSAD Young Investigator Award 2009. The authors have no relevant financial interest to disclose.
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