Livia A. Carvalho

The glucocorticoid receptor: Pivot of depression and of antidepressant treatment?

Hyperactivity of the hypothalamus-pituitary-adrenal (HPA) axis and increased levels of glucocorticoid hormones in patients with depression have mostly been ascribed to impaired feedback regulation of the HPA axis, possibly caused by altered function of the receptor for glucocorticoid hormones, the glucocorticoid receptor (GR). Antidepressants, in turn, ameliorate many of the neurobiological disturbances in depression, including HPA axis hyperactivity, and thereby alleviate depressive symptoms. There is strong evidence for the notion that antidepressants exert these effects by modulating the GR. Such modulations, however, can be manifold and range from regulation of receptor expression to post-translational modifications, which may result in differences in GR nuclear translocation and GR-dependent gene transcription. The idea that the therapeutic action of antidepressants is mediated, at least in part, by restoring GR function, is consistent with studies showing that decreased GR function contributes to HPA axis hyperactivity and to the development of depressive symptoms. Conversely, excessive glucocorticoid signalling, which requires an active GR, is associated with functional impairments in the depressed brain, especially in the hippocampus, where it results in reduced neurogenesis and impaired neuroplasticity. In this review, we will focus on the GR as a key player in the precipitation, development and resolution of depression. We will discuss potential explanations for the apparent controversy between glucocorticoid resistance and the detrimental effects of excessive glucocorticoid signalling. We will review some of the evidence for modulation of the GR by antidepressants and we will provide further insight into how antidepressants may regulate the GR to overcome depressive symptoms.

Glucocorticoids, cytokines and brain abnormalities in depression

Major depression (MD) is a common psychiatric disorder with a complex and multifactor aetiology. Potential mechanisms associated with the pathogenesis of this disorder include monoamine deficits, hypothalamic-pituitary-adrenal (HPA) axis dysfunctions, inflammatory and/or neurodegenerative alterations. An increased secretion and reactivity of cortisol together with an altered feedback inhibition are the most widely observed HPA abnormalities in MD patients. Glucocorticoids, such as cortisol, are vital hormones that are released in response to stress, and regulate metabolism and immunity but also neuronal survival and neurogenesis. Interestingly depression is highly prevalent in infectious, autoimmune and neurodegenerative diseases and at the same time, depressed patients show higher levels of pro-inflammatory cytokines. Since communication occurs between the endocrine, immune and central nervous system, an activation of the inflammatory responses can affect neuroendocrine processes, and vice versa. Therefore, HPA axis hyperactivity and inflammation might be part of the same pathophysiological process: HPA axis hyperactivity is a marker of glucocorticoid resistance, implying ineffective action of glucocorticoid hormones on target tissues, which could lead to immune activation; and, equally, inflammation could stimulate HPA axis activity via both a direct action of cytokines on the brain and by inducing glucocorticoid resistance. In addition, increased levels of pro-inflammatory cytokines also induce the production of neurotoxic end products of the tryptophan-kynurenine pathway. Although the evidence for neurodegeneration in MD is controversial, depression is co-morbid with many other conditions where neurodegeneration is present. Since several systems seem to be involved interacting with each other, we cannot unequivocally accept the simple model that glucocorticoids induce neurodegeneration, but rather that elevated cytokines, in the context of glucocorticoid resistance, are probably the offenders. Chronic inflammatory changes in the presence of glucocorticoid resistance may represent a common feature that could be responsible for the enhanced vulnerability of depressed patients to develop neurodegenerative changes later in life. However, further studies are needed to clarify the relative contribution of glucocorticoids and inflammatory signals to MD and other disorders.

Shorter telomeres with high telomerase activity are associated with raised allostatic load and impoverished psychosocial resources

Significance These findings indicate that the combination of shorter leukocyte telomeres with high telomerase activity is associated with stress-related impairment of function at both the biological and psychological levels. Slow poststress recovery in cardiovascular activity in inflammatory responses and reduced stress responsivity in blood pressure and cortisol are indicative of a state of heightened allostatic load. Older men with the shorter telomere/high telomerase phenotype also show impoverished resources for dealing with stress, including low levels of social support and optimism and higher levels of hostility. The integrated approach taken in this study advances our understanding of the cellular substrate of stress-related processes and documents the dynamic interplay between social environmental exposures and the mechanisms underlying chromosomal integrity. Recent work has linked psychological stress with premature cellular aging as indexed by reduced leukocyte telomere length. The combination of shorter telomeres with high telomerase activity (TA) may be indicative of active cell stress. We hypothesized that older individuals characterized by shorter telomeres with high TA in unstimulated leukocytes would show signs of high allostatic load and low levels of protective psychosocial resources. We studied 333 healthy men and women aged 54–76 y who underwent laboratory testing in which we measured cardiovascular, neuroendocrine, and inflammatory responses to standardized mental stress tasks. The tasks elicited prompt increases in blood pressure (BP), heart rate, cortisol, and mediators of inflammation and reductions in heart rate variability, returning toward baseline levels following stress. However, men having shorter telomeres with high TA showed blunted poststress recovery in systolic BP, heart rate variability, and monocyte chemoattractant protein-1, together with reduced responsivity in diastolic BP, heart rate, and cortisol, in comparison to men with longer telomeres or men with shorter telomeres and low TA. Shorter telomeres with high TA were also associated with reduced social support, lower optimism, higher hostility, and greater early life adversity. These effects were independent of age, socioeconomic status, and body mass index. We did not observe differences among older women. Our findings suggest that active cell stress is associated with impaired physiological stress responses and impoverished psychosocial resources, reflecting an integration of cellular, systemic, and psychological stress processes potentially relevant to health in older men.

Lack of clinical therapeutic benefit of antidepressants is associated overall activation of the inflammatory system

Despite the evidence of an association between depression and increased inflammatory markers, still little is known in relation to the most severe cases of the disorder i.e., those who fail to respond to antidepressants. We have assessed the cytokine profile and cortisol levels in 21 healthy controls (HC) and 19 medicated patients with depression with treatment-resistance (TRD) moderately ill. As an initial exploratory analysis, we have also related cytokine profile to the patients clinical treatment outcome after an inpatient admission. Cytokine profile was measured in the serum by the Cytokine Array I kit (Randox). Plasma cortisol was carried out using a commercially available for the IMMULITE system. When compared to healthy controls, depressed patients had higher levels of cortisol, IL-6, IL-10, but lower levels of IL-4 and VEGF. Our exploratory analysis showed subjects who did not go on to respond to the inpatient admission treatment package had lower levels of MCP-1, and a trend toward lower levels of VEGF. Taking together, these data suggest that lack of clinical therapeutic benefit of antidepressants is associated with overall activation of the inflammatory system.

Insufficient glucocorticoid signaling and elevated inflammation in coronary heart disease patients with comorbid depression

Coronary heart disease (CHD) and depression are very common and often co-existing disorders. In addition to psychological and social morbidity, depression exacerbates adverse cardiac outcomes in CHD patients. Inflammation has been proposed as one of the mechanisms involved in the association between these two debilitating diseases. Therefore, the present study aimed to evaluate inflammatory responses as well as to investigate the pathophysiological mechanisms underlying the putative inflammatory activation in CHD patients with and without depression, by assessing the function of two important biological factors regulating inflammation, the hypothalamus-pituitary-adrenal (HPA) axis and the glucocorticoid receptor (GR). Eighty-three CHD patients with (n=28) and without (n=55) comorbid depression were recruited from primary care services in South London. Depression status was assessed by means of Clinical Interview Schedule Revised for diagnosis of depression, and Beck Depression Inventory for the presence of depressive symptoms. Serum C-reactive protein (CRP), plasma vascular endothelial growth factor (VEGF), and plasma and salivary cortisol were measured using commercially available ELISA kits. Gene expression of GR and interleukin-6 (IL-6) were conducted via qPCR. GR sensitivity was evaluated in vitro in isolated peripheral blood mononuclear cells using the dexamethasone inhibition of lipopolysaccharide-stimulated IL-6 levels. Serum levels of kynurenine pathway metabolites were measured using high performance liquid chromatography. Our results show that CHD patients with depression had higher levels of CRP, IL-6 gene expression, and VEGF compared with CHD non-depressed, as well as lower plasma and saliva cortisol levels. The CHD depressed group also exhibited a reduction in GR expression and sensitivity. Finally, tryptophan levels were significantly lower in patients with depression, who also showed an increased kynurenine/tryptophan ratio. In conclusion, CHD patients with depression had elevated levels of inflammation in the context of HPA axis hypoactivity, GR resistance, and increased activation of the kynurenine pathway. Reduced cortisol bioavailability and attenuated glucocorticoid responsiveness due to decreased expression and sensitivity of GR may lead to insufficient glucocorticoid signaling and thus elevation of inflammation in these patients.

Inflammatory activation is associated with a reduced glucocorticoid receptor alpha/beta expression ratio in monocytes of inpatients with melancholic major depressive disorder

In this study, we used new technology to investigate whether a coherent pattern of enhanced expression of inflammatory and other immune activation genes in circulating monocytes is found in patients with major depression. Since a high inflammatory state of monocytes might be related to glucocorticoid resistance, we also included the genes for the two isoforms of the glucocorticoid receptor. For this study, we aimed at finding a similar coherent pattern of inflammatory and immune activation genes in monocytes of patients with MDD and recruited 47 medication-free melancholic MDD inpatients and 42 healthy controls. A quantitative-polymerase chain reaction (Q-PCR) monocyte gene expression analysis was performed using a panel of inflammatory-related genes previously identified as abnormally regulated in mood disorder patients. Selected serum cytokines/chemokines were assessed using a cytometric bead array. Depressive symptoms were analysed using Hamilton depression scores (HAMD). Thirty-four of the 47 monocyte inflammatory-related genes were significantly upregulated and 2 were significantly downregulated as compared to controls, the latter including the gene for the active GRα in particular in those with a high HAMD score. The reduced GRα expression correlated strongly to the upregulation of the inflammatory genes in monocytes. Serum levels of IL6, IL8, CCL2 and VEGF were significantly increased in patients compared to controls. Our data show the deregulation of two interrelated homoeostatic systems, that is, the immune system and the glucocorticoid system, co-occurring in major depression.

Disruption of multisystem responses to stress in type 2 diabetes: Investigating the dynamics of allostatic load

Significance Our observations provide evidence to link epidemiological studies implicating stress-related processes with biological dysfunction in type 2 diabetes. The patterns of cardiovascular, inflammatory, neuroendocrine, and cholesterol responses exemplify the disturbances of reactivity and recovery predicted by the allostatic load model, including prolonged responses to stress due to delayed shutdown of physiological reactivity, and inadequate (blunted) responses resulting in compensatory hyperactivity in other mediating pathways. Chronic allostatic load may be a mechanism through which stress exposures contribute to diabetes risk, while also being implicated in the adverse health consequences of diabetes such as coronary heart disease and cognitive decline. Psychological stress-related processes are thought to contribute to the development and progression of type 2 diabetes, but the biological mechanisms involved are poorly understood. Here, we tested the notion that people with type 2 diabetes experience chronic allostatic load, manifest as dynamic disturbances in reactivity to and recovery from stress across multiple (cardiovascular, neuroendocrine, inflammatory, metabolic) biological systems, coupled with heightened experience of chronic life stress. We carried out an experimental comparison of 140 men and women aged 50–75 y with type 2 diabetes and 280 nondiabetic individuals matched on age, sex, and income. We monitored blood pressure (BP) and heart rate, salivary cortisol, plasma interleukin (IL)-6, and total cholesterol in response to standardized mental stress, and assessed salivary cortisol over the day. People with type 2 diabetes showed impaired poststress recovery in systolic and diastolic BP, heart rate and cholesterol, and blunted stress reactivity in systolic BP, cortisol, cholesterol, and IL-6. Cortisol and IL-6 concentrations were elevated, and cortisol measured over the day was higher in the type 2 diabetes group. Diabetic persons reported greater depressive and hostile symptoms and greater stress experience than did healthy controls. Type 2 diabetes is characterized by disruption of stress-related processes across multiple biological systems and increased exposure to life stress. Chronic allostatic load provides a unifying perspective with implications for etiology and patient management.

Clomipramine In Vitro Reduces Glucocorticoid Receptor Function in Healthy Subjects but not in Patients with Major Depression

Previously, we have shown that in vitro antidepressants modulate glucocorticoid receptor (GR) function and expression, and have suggested that these effects could be relevant for the mechanism of action of antidepressants. To further clarify the interaction between antidepressants and glucocorticoids, we evaluated the in vitro effect of the tricyclic antidepressant, clomipramine (CMI), on the GR function in 15 treatment-resistant depressed inpatients and 28 healthy controls. Diluted whole-blood cells were incubated for 24 h in the presence or absence of CMI (10 μM). Glucocorticoid function was measured by glucocorticoid inhibition of lypopolysaccharide (LPS)-stimulated interleukin-6 (IL-6) levels. The results show that glucocorticoids (dexamethasone, prednisolone, cortisol and corticosterone) caused a concentration-dependent inhibition of LPS-stimulated IL-6 levels. In healthy controls, CMI decreased glucocorticoid inhibition of LPS-stimulated IL-6 levels, while this effect was not present in depressed patients. Therefore, depressed patients, who were clinically treatment resistant, also showed a lack of effect of the antidepressant in vitro. Upcoming studies shall test whether assessing the effects of antidepressants in vitro on GR function could predict future treatment response in a clinical setting.

Interplay between the pro-oxidant and antioxidant systems and proinflammatory cytokine levels, in relation to iron metabolism and the erythron in depression

As there is strong evidence for inflammation and oxidative stress in depression, the aim of this study was to elucidate the relationship between oxidative imbalance and cellular immune response and to ask whether these processes are linked with iron metabolism in depressed patients. Blood was collected from patients diagnosed with recurrent depressive disorder (n=15) and from healthy controls (n=19). Whole-blood reduced glutathione (GSH), erythrocyte superoxide dismutase (SOD-1), glutathione peroxidase (GPx-1), glutathione reductase, malondialdehyde (MDA), and methemoglobin (MetHb) and plasma H₂O₂ were assayed spectrophotometrically. The serum heme oxygenase 1 (HO-1), cytokine, neopterin, and iron statuses were measured by ELISA. DNA damage was analyzed by comet assay. Serum concentrations of ferritin and soluble transferrin receptor were assayed by ELISA. MetHb saturation was analyzed spectrophotometrically in red blood cell hemolysate. The erythron variables were measured using a hematological analyzer. We observed a significant decrease in GPx-1 and SOD-1 activities and decreased levels of HO-1 and GSH in depressed patients compared to controls. Conversely, compared with controls, we found increased concentrations of MDA and H₂O₂ and more DNA damage in depressed patients. Furthermore, the levels of the proinflammatory cytokine interleukin-6 and of neopterin were increased in depressed patients along with decreased hemoglobin and hematocrit. A strong association between antioxidant defense, cytokine levels, and iron homeostasis was also revealed. These findings show that depression is associated with increased oxidative stress, inflammation, and restrictions on the available iron supply for red blood cell production. Furthermore, decreased antioxidant defense correlates with an increased cellular inflammatory response, whereas both concur with erythron and iron status, the latter explained by significant canonical correlations with the set of free radical scavenging enzymes and proinflammatory enzymes. The strong links between immune function, oxidative stress, and iron homeostasis suggest the presence of a self-sustaining multipathway mechanism that may progressively worsen, i.e., throughout accumulation of oxidative damage, producing the functional and structural consequences associated with depression. Hence, identifying viable therapeutic strategies to tackle oxidative stress and accompanying physiological disturbances, including inflammation and anemia, of chronic disease provides more opportunities for the treatment and, ultimately, prevention of depression.

In vitro modulation of the glucocorticoid receptor by antidepressants

Clinical studies have demonstrated an impairment of glucocorticoid receptor (GR)-mediated negative feedback on the hypothalamus–pituitary–adrenal (HPA) axis in patients with major depression (GR resistance), and its resolution by antidepressant treatment. Accordingly, reduced GR function has also been demonstrated in vitro, in peripheral tissues of depressed patients, as shown by reduced sensitivity to the effects of glucocorticoids on immune and metabolic functions. We and others have shown that antidepressants in vitro are able to modulate GR mRNA expression, GR protein level and GR function. This paper reviews the in vitro studies that have examined the effect of antidepressants on GR expression, number and function in human and animal cell lines, and the possible molecular mechanisms underlying these effects. Antidepressants are shown to both increase and decrease GR function in vitro, based on different experimental conditions. Specifically, increased GR function is likely to be mediated by an increased intracellular concentration of glucocorticoids, while decreased GR function seems to be the consequence of GR downregulation. We suggest that the study of the effects of antidepressants on glucocorticoid function might help clarify the therapeutic action of these drugs.